JP7784717B2 - Film Thickness Measurement Device - Google Patents

Description

The present invention relates to a film thickness measurement device and method for quantitatively analyzing surface oxide films that form on the surface of silicon wafers and the like, organic thin films on the copper foil surface of printed circuit boards, surface oxide films, and surface oxide films formed by soldering. It also relates to a film removal device and film removal method that easily removes surface organic thin films and surface oxide films. It also relates to a head for electrodes and the like used in electrochemical reduction.

During the IC manufacturing process, semiconductor wafers are manufactured using special heat treatments tailored to the purpose. Oxygen in the atmosphere can cause surface oxide films to form on the copper foil of printed circuit boards, and oxidation and contamination can cause inorganic and organic films to adhere to the copper foil surface. Surface oxide films, etc., form on the copper foil surface during soldering. Surface oxide films, etc., affect corrosion resistance, solder adhesion, and device reliability, and pose challenges. Therefore, evaluating their composition and film thickness is important in manufacturing.

To prevent defects such as non-fusion during board mounting and flip-chip connection of BGA packages, it is necessary to quantitatively measure the oxide film on the bump surface during reflow and take appropriate measures. Therefore, it is important to analyze the condition of the oxide film on the solder bump surface and evaluate its thickness and material composition.

The composition of surface oxide films is complex, as it is affected by the heat treatment temperature, atmosphere, and chemical components of the metal material. The thickness of surface oxide films ranges from a few nanometers at very thin locations to several tens of micrometers at thicker locations.

Patent Document 1 describes a method for quantitatively analyzing metal surface oxide films, in which a glow discharge is performed to measure the ratio of the emission intensities of the target element and the matrix element, and the concentration of the target element is determined using a calibration curve.

The thickness of thin films has been evaluated using so-called surface analysis methods such as secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS), which evaluate the composition of the oxide film along with the compositional changes in the depth direction from the surface. However, these methods have been rarely used due to their shortcomings in terms of speed and the broad analytical range required to obtain average information about the metal surface.

JP 9-273992

Secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) have been rarely used because they lack the breadth of analytical range required.

Glow discharge optical emission spectroscopy (hereinafter referred to as GDS) has the problem that fluctuations in the spectrometer system and vacuum exhaust system can cause the emission intensity to become unstable, reducing quantitative accuracy.

In the film thickness measurement device of the present invention, a counter electrode 112 and a reference electrode 111 are formed on a solid electrolyte 171. A contact area is arranged around the solid electrolyte 171 and the thin film 123 to be measured. The inside of the contact area is filled with a charged liquid 124. The tip of the solid electrolyte 171 is permeated with or filled with the charged liquid 124.

A voltage is applied to the electrode 110, reference electrode 111, and counter electrode 112 by the potentiostat 119, causing electrochemical reduction of the thin film 123. Incident light 114a2 from the light generator 108 is irradiated onto the thin film 123, and reflected light 114b is received by the light receiver 117 to measure the spectral reflectance. The composition and film thickness of the thin film 123 are determined from the plateau potential due to electrochemical reduction, the time over which the plateau potential changes, and the film thickness simulation results based on the spectral reflectance.

By using spectroscopic film thickness measurement and electrochemical reduction, the composition, structure, and film thickness of the thin film material being measured can be measured with high accuracy.

The cleaning solution can easily remove protective films and other materials from the thin film, exposing the thin film to be measured, making it easy to measure the film thickness of the oxide thin film material being measured.

The head section, which performs electrochemical reduction, is made of solid electrolyte 171. This allows the head section to be small and space-saving. Furthermore, the electrolyte solution 124 is permeated into a sponge-like material at the tip of the head. This prevents the electrolyte solution 124 from leaking out and allows the electrolyte solution 124 to adhere tightly to the thin film 123.

1 is a block diagram and an explanatory diagram of a film thickness measuring device according to the present invention; 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. FIG. 2 is an explanatory diagram of a film thickness measurement method according to the present invention. FIG. 2 is an explanatory diagram of a film thickness measurement method according to the present invention. FIG. 2 is an explanatory diagram of a film thickness measurement method according to the present invention. FIG. 2 is an explanatory diagram of a film thickness measurement method according to the present invention. 1 is an explanatory diagram of a film thickness measurement device and a film thickness measurement method according to the present invention. FIG. 1 is a flowchart of a film thickness measurement method according to the present invention. 1A and 1B are diagrams illustrating a configuration of a film thickness measurement device and a film thickness measurement method according to the present invention. 1A and 1B are a configuration diagram and an explanatory diagram of a head portion of a film thickness measuring device according to the present invention; 1A and 1B are a configuration diagram and an explanatory diagram of a head portion of a film thickness measuring device according to the present invention; 1A and 1B are a configuration diagram and an explanatory diagram of a head portion of a film thickness measuring device according to the present invention; 1A and 1B are a configuration diagram and an explanatory diagram of a head portion of a film thickness measuring device according to the present invention;

The following describes the configuration of a film thickness measurement device and a film thickness measurement method according to an embodiment of the present invention, with reference to the attached drawings. The present invention is not limited to film thickness measurement devices and film thickness measurement methods, but also relates to surface processing or treatment methods for steel materials, solder, plated sheets, bumps such as ICs, copper foil, printed circuit boards, semiconductor-related products such as silicon wafers, steel materials, electronic devices, electrical devices, mechanical devices, precision devices, structures, coating materials, and the like.

In the drawings for explaining the embodiments of the invention, elements having the same function or similarity are given the same reference numerals, and matters not necessary for the explanation are omitted from the drawings.
For ease of explanation, drawings may be simplified or schematic. Explanations may also be omitted in the specification.

The embodiments of the present invention can be combined in part or in whole with the respective embodiments described in this specification and drawings. They can also be combined or implemented with partial changes or modifications.

Figure 1 is a block diagram of the film thickness measurement device and an explanatory diagram of the film thickness measurement method of the present invention. The film thickness measurement device of the present invention not only measures the film thickness of the target film, but also has the function of removing surface oxide films, organic films, organic solderability preservatives (OSPs), etc.

The cleaning liquid LA used to remove organic films and organic protective films (OSP) is filled into the liquid tank 104a. The amount of cleaning liquid LA filled into the liquid tank 104a is constantly measured or monitored, and a constant amount is filled or allowed to penetrate. One example of the cleaning liquid LA is a solvent. The cleaning liquid LA is also replaced with a rinse liquid as appropriate.

If the OSP is water-soluble, the cleaning solution LA, etc., is based on the same water-soluble solvent. For example, HO-(CH ₂ ) ₂ -OH (ethylene glycol) is freely miscible with water. HO-(CH ₂ ) ₂ -O(CH ₂ ) ₃ CH ₃ (ethylene glycol, monobutyl ether) is soluble in water. HO-(CH ₂ ) ₂ -O(CH ₂ ) ₅ CH ₃ (ethylene glycol, monohexyl ether) is slightly soluble in water.

Regarding the relationship between the cleaning liquid LA and the rinse liquid, if the cleaning liquid LA is methyl alcohol, examples of the rinse liquid include acetone, ethanol-based, and isopropyl alcohol (IPA). If the cleaning liquid LA is ethanol, examples of the rinse liquid include acetone, ethanol-based, and isopropyl alcohol (IPA). If the cleaning liquid LA is propylene alcohol, an example of the rinse liquid is acetone.

When the cleaning liquid LA is 1-butanol, examples of the rinse liquid include acetone, an ethanol base, and isopropyl alcohol (IPA).When the cleaning liquid LA is ethylene glycol, examples of the rinse liquid include isopropyl alcohol (IPA).
The liquid tank 104b is filled with the electrolyte LB 124. The amount of the electrolyte LB 124 filled in the liquid tank 104b is constantly measured or grasped, and a constant amount is filled.

Examples of the electrolyte 124 include potassium chloride (KCl), sodium chloride (NaCl), hydrochloric acid solution, sodium hydroxide, boric acid solution, sodium tetraborate solution, etc.

The electrolytic solution 124 may be a solid electrolyte material or a gel electrolytic solution. The electrolytic solution 124 may be impregnated in a sponge or the like. The electrolytic solution 124 may be filled between the container 105 and the permeable membrane 172.
When the electrolyte material is a solid electrolyte material or a gel electrolyte solution, the defoamer 103b and the solution reservoir 162b are not necessary, and there is no need to circulate the liquid inside the container 105.

An example of the solid electrolyte is stabilized zirconia. Examples of stabilized zirconia include zirconia (zirconium dioxide ZrO ₂ ) to which a few percent of magnesium oxide MgO, calcium oxide CaO, or rare earth oxide has been added. Another example is yttria-stabilized zirconium (ZrO ₂ —Y ₂ O ₃ ). The solid electrolyte material will be described as solid electrolyte 171 or solid electrolyte 171 part.

When oxides such as yttrium oxide (Y ₂ O ₃ ), calcium oxide (CaO), cerium oxide (CeO ₂ ), and magnesium oxide (MgO) are added to zirconia, the cubic crystals can be stable even at room temperature. Zirconia whose cubic crystals are stable at room temperature is called stabilized zirconia or partially stabilized zirconia, and is used as the solid electrolyte 171 in the present invention.

There are two main methods for producing the zirconia used in the head of this invention: wet refining and dry refining. Both use zirconium ores such as zircon and hadelite as raw materials. In the wet refining method, selected ores are melted with caustic soda, then decomposed and concentrated with hydrochloric acid. After further processes such as washing and filtration, the resulting zirconium hydroxide is fired and pulverized to produce zirconia powder.

In the dry refining method, pure zirconia is produced by crushing the ore to remove impurities and then repeatedly filtering it. In the present invention, the counter electrode 112 and reference electrode 110 are formed on zirconia produced by the wet refining method or the dry refining method using plating technology. Alternatively, the counter electrode 112 and reference electrode 110 are formed by sintering.

In this specification, drawings, etc., it is described that the electrochemical reduction reaction is carried out by filling the container 105 with the electrolyte 124, but the electrolyte 124 may be a solid electrolyte material or a gel electrolyte. The electrolyte 124 or electrolytic material 124 is not limited to liquids. It also includes solid electrolyte materials and gel electrolyte materials.

In the present invention, the container 105 is configured such that the substrate 109 or the like serves as a lid, and the space between the lid (printed circuit board or the like) and the container 105 is filled with the electrolyte 124, but this is not limited to this. For example, the electrolyte 124 may be used in a state where it is impregnated into or mixed with glass wool, fiber, organic matter such as agar, etc.

A material containing or permeating the electrolyte 124, such as agar, or a permeable structure (permeable membrane 172) may be placed or installed at the location where the electrolyte 124, etc., comes into contact with or comes into contact with the thin film 123, etc. An electrochemical reduction action is achieved by bringing the agar or other material containing the electrolyte, etc., into contact with or comes into contact with the thin film 123, etc.

To prevent leakage of the electrolyte 124, it is preferable to form or arrange a permeable membrane 172, as shown in Figures 2, 15, etc. Examples of the permeable membrane 172 include cellophane, a precipitated membrane of copper ferrocyanide, a collodion membrane, or a bladder membrane. Other examples include porous membranes made of regenerated cellulose (cellophane), acetyl cellulose, polyacrylonitrile, Teflon (registered trademark), polyester polymer alloy, or polysulfone.

The electrolyte 124 may contain or be mixed with polyacrylate. By impregnating glass wool, rayon, polyester, polypropylene, polyethylene, agar, etc. with the electrolyte 124, leakage or elution of the electrolyte 124 can be prevented.

Due to the action of the permeable membrane 172, the electrolyte 124 does not leak out even when it comes into contact with the thin film 123. Furthermore, the electrolyte 124 can come into contact with, be immersed in, or be filled into the thin film 123, etc., via the permeable membrane 172, thereby electrochemically reducing the thin film 123, etc.

The defoamer 103 is a defoaming device that removes gas from the solution. Examples of defoamers include those that use vacuum (reduced pressure) or centrifugal force. Other defoaming devices that use ultrasonic waves or a gas-permeable membrane may also be used.
By removing air bubbles from the liquid, the strength, properties, and surface characteristics of the product can be made uniform, improving yield and quality.

A vacuum degassing device uses a vacuum pump to reduce the pressure in the solution, causing bubbles contained in the liquid to expand. The expanded bubbles rise to the liquid surface due to buoyancy, and over time, the liquid film on the surface breaks down, causing the bubbles to be expelled into the decompressed air.
A centrifugal degassing device uses the principle that liquid and gas, which have different densities, are separated by centrifugal force when a container containing a solution rotates and revolves around its axis.

The cleaning liquid (rinse liquid) LA degassed by the degasser 103a is stored in the solution reservoir 162a. The liquid volume in the solution reservoir 162a is detected by the level detector 161a and controlled by the liquid volume control unit 120 so that it does not exceed a predetermined liquid volume.

The electrolyte solution LB defoamed by the defoamer 103b is stored in the solution reservoir 162b. The amount of liquid in the solution reservoir 162b is detected by a level detector 161b and controlled by a liquid amount control unit 120 so that the amount does not exceed a predetermined amount or does not fall below a predetermined amount.
The amounts of the cleaning liquid (rinse liquid) LA and the electrolyte LB poured into the liquid tanks are controlled by a liquid volume control unit 120 so that the liquid volumes do not exceed a certain value.

Solenoid valve 101a controls whether cleaning liquid (rinse liquid) LA is supplied to pump 102a or cut off. Solenoid valve 101b controls whether electrolyte LB is supplied to pump 102a or cut off.

A flow meter (not shown) is attached to pump 102. Pump 102a controls the amount of cleaning liquid (rinse liquid) LA or electrolyte solution LB injected into container 105 by means of its torque and rotation speed.

The cleaning liquid (rinse liquid) LA or the electrolyte solution LB124 is injected into the container 105 via a liquid injection pipe 106 connected to the container 105. The cleaning liquid (rinse liquid) LA or the electrolyte solution LB124 is discharged from the container 105 via a liquid drain pipe 107.

A circulation fan 122 is placed inside the container 105 to agitate the injected cleaning solution (rinse solution) LA or electrolyte solution LB. The circulation fan 122 rotates as needed to agitate or circulate the solution inside the container 105. When discharging the solution, the fan rotates in the direction that sends the solution to the drain pipe 107.

The cleaning solution LA or the electrolyte solution LB is injected into the area in contact with the thin film 123, etc. through the liquid injection tube 106. The cleaning solution LA or the electrolyte solution LB is drained from the area in contact with the thin film 123, etc. through the liquid drainage tube 107.

In the embodiments of the present invention, for ease of understanding and explanation, the explanation will be given assuming that an electrode 110 is formed on a printed circuit board 109, and that an oxide film 123, an organic film 126, etc. are formed on the electrode 110.

The film thickness measurement device of the present invention is configured so that solution 124 is filled into container 105, which uses substrate 109 as a lid. Solution 124 is electrolyte solution LB or cleaning solution LA. The tip of container 105 may be sealed with a material such as agar that allows electrolyte solution LB or cleaning solution LA to penetrate. Cleaning and electrochemical reduction are performed by bringing agar or the like or a permeation membrane 172 into contact with thin film 123.

An electrode 110 is disposed inside the container 105. The electrode 110 is part of a wiring pattern formed on the substrate 109, and functions as a working electrode (WE) when a predetermined potential is applied to the wiring pattern. In addition, a counter electrode (CE) and a reference electrode (RE) are disposed in the solid electrolyte 171.

It functions as a working electrode (WE). Furthermore, by applying a constant current between the counter electrode (CE) and the working electrode (WE) of the solid electrolyte 171 and controlling the potential with the reference electrode (RE), the materials forming the thin film 123 of the working electrode (WE) are electrochemically reduced.

Electrodes are classified into polarizable electrodes and non-polarizable electrodes. A polarizable electrode is an electrode whose potential can be changed without passing a current. This electrode is used as the working electrode 110 or counter electrode 112. A non-polarizable electrode is an electrode 111 through which a current flows when an attempt is made to change the potential, and is usually used as a reference electrode (RE) 111.
Examples of polarizable electrodes used as the counter electrode (CE) 112 include platinum, gold, carbon, and mercury. Platinum is preferred because of its high physical and chemical stability.

When using in aqueous systems, care must be taken as hydrogen molecules are generated in the reduction direction. In the oxidation region, oxidation of the electrode surface occurs and a corresponding reduction current flows. Similar surface redox couples are found on most solid metal electrodes.

In systems containing high concentrations of chloride ions, if the oxidation potential is increased, they may dissolve as chloroplatinate ions. Gold is often referred to as platinum. Because its overpotential for the generation of hydrogen molecules is greater than that of platinum, the potential window in the reduction region is wide. A large amount of chloride ions is contained, deepening the oxidation potential.

There are many types of carbon electrodes. The most commonly used is glassy carbon. Microscopically, it is graphite, but macroscopically, as the name suggests, it has an amorphous structure. Graphite is a layered structure of two-dimensional planes formed by the condensation of benzene rings. There is anisotropy due to the orientation of the planes (basal planes and edge planes).

The reference electrode (RE) 111 is non-polarizable. If an attempt is made to change the potential, a surface reaction occurs on the electrode itself, causing a sudden increase in current. It is preferable to use the reference electrode (RE) 111 without passing current in order to maintain a constant potential. The standard is a hydrogen electrode. When standard state hydrogen molecules and hydrogen ions are in equilibrium on the platinum surface, the potential shown by the platinum electrode is defined as zero.

A calomel electrode replaces Ag with mercury (Hg). A saturated calomel electrode (SCE) has an internal solution of saturated KCl aqueous solution, which is at +0.242 V relative to the hydrogen electrode. For non-aqueous solutions, a silver wire is placed in a solution of silver nitrate or silver perchlorate (which provide silver ions) dissolved in a non-aqueous solvent together with a supporting electrolyte (silver ion electrode).

1, 2, 15, etc., the reference electrode (RE) 111 and the counter electrode (CE) 112 are formed on or arranged in contact with the solid electrolyte 171. Alternatively, the reference electrode (RE) 111 and the counter electrode (CE) 112 are formed or arranged inside the solid electrolyte 171.
FIG. 4 is a diagram showing the arrangement and configuration of electrodes (working electrode (WE) 110, counter electrode (CE) 112, and reference electrode (RE) 111) according to an embodiment of the present invention.
4A is a diagram showing the arrangement of electrodes with the liquid injection tube 106 at the center, and FIG. 4B is a cross-sectional view taken along line AA' in FIG. 4A.

A contact portion 125 is located at the tip of the solid electrolyte 171. The contact portion 125 can be easily detached from the solid electrolyte 171, allowing the head portion to be replaced. Various head sizes are available, allowing selection to correspond to the size of the electrode used for reduction, etc.

The solid electrolyte 171 is cylindrical or cubic. The reference electrode 111 and counter electrode 112 are formed or arranged on the side or at predetermined locations of the solid electrolyte 171. The solid electrolyte 171 and the electrolyte solution 124 are arranged so that they are in contact with or face each other.

The contact portion 125 that contacts the solid electrolyte 171 is filled with the electrolyte 124 or the like. The electrolyte 124 or the like is permeated into glass wool, rayon, polyester, polypropylene, polyethylene, agar, or the like as needed. Preferably, a permeation membrane 172 is disposed or formed on the surface (location) that contacts the thin film 123 or the like that undergoes electrochemical reduction. By disposing the permeation membrane 172, the electrolyte 124 does not leak out.

In Figure 4, the counter electrode (CE) 112 and reference electrode (RE) 111 are formed or arranged around the solid electrolyte 171. The counter electrode (CE) 112 and reference electrode (RE) 111 are formed by plating nickel, copper, zinc, etc.

The working electrode (WE) 110 is, for example, one electrode of the printed circuit board 109. The working electrode (WE) 110 is connected to a wiring pattern. By connecting the WE terminal of the potentiostat 119 to the wiring pattern, the working electrode (WE) 110 functions as a reduction electrode.
15 is an explanatory diagram of the film thickness measurement device and film thickness measurement method of the present invention, particularly showing the electrode arrangement of the solid electrolyte 171.

The following embodiment is an example of a method for manufacturing the solid electrolyte 171. The solid electrolyte 171 has a reference electrode 111 and a counter electrode 112 formed therein. The reference electrode 111 is formed inside the solid electrolyte 171.

Zirconia powder is mixed with various solvents and crushed to form a muddy paste. This is then formed into a sheet. A metal paste that will become the reference electrode 111 or counter electrode 112 is applied to the zirconia sheet. It is preferable to use Ni for the electrode. In this case, Ni paste is applied to the sheet.

A zirconia sheet that has not been coated with metal paste is placed on top of a zirconia sheet that has been coated with metal paste. The stacked pieces are then pressed together to form a single piece. This process is carried out in a clean room to prevent the inclusion of foreign matter.
The integrally molded zirconia block is cut to the desired size. After cutting, it is sintered. Sintering allows the zirconia and internal electrodes to be integrated.

After firing, the zirconia block is coated with a metal paste that will serve as an electrode to electrically connect it to the potentiostat 119. In the case of Ni internal electrodes, Cu paste is applied, and then baked at a temperature of around 800°C.

After the electrodes are baked, a two-layer plating of Ni and Sn is applied to the surface. Electrolytic plating is typically used, with Ni plating improving reliability and Sn plating making soldering easier.

The counter electrode 112 is formed on the side of the solid electrolyte 171. The surface of the counter electrode 112 is Sn-plated, so a lead terminal is soldered to it and connected to the CE terminal of the potentiostat 119.

The reference electrode 111 is formed on the upper surface of the solid electrolyte 171. The surface of the reference electrode 111 is Sn-plated, and a lead terminal is soldered to the surface, and the reference electrode 111 is connected to the RE terminal of the potentiostat 119.
The positions of the counter electrode 112 and the reference electrode 111 may be interchanged.

The solid electrolyte 171 is in contact with the electrolytic solution 124. If necessary, a permeation membrane 172 is formed or placed at the location where the electrolytic solution 124 comes into contact with the thin film 123 or the like where electrochemical reduction occurs. The electrolytic solution 124 is also used by permeating agar, glass wool, or the like. The area in contact with the permeation membrane 172 comes into contact with the electrolytic solution 124, where electrochemical reduction occurs.

Figures 16, 17, 18, and 19 are explanatory diagrams of the configuration or structure of the solid electrolyte 171 of the present invention. However, they are illustrated schematically to facilitate understanding. Figures 16, 17, 18, and 19 are schematic diagrams of the state viewed from direction C in Figure 4 (the state of the solid electrolyte 171 viewed from above).

In Figures 16, 17, 18, and 19, the counter electrode 112 and reference electrode 111 are shown individually formed for each solid electrolyte 171, but this is not limited to this. For example, one counter electrode 112 may be formed or placed for multiple solid electrolytes 171. The same applies to the reference electrode 111.

In Figure 18 and other figures, a space (gap) can be maintained around the periphery of the reference electrode 111. The electrolyte solution 124 and cleaning solution LA can be filled into or passed through the space. For example, it can be used to function as the liquid injection tube 106 and the liquid drainage tube 107. Furthermore, as shown in Figures 7 and 8, it can be used as the optical path for incident light 114a2 and reflected light 114b.

In Figures 16, 17, 18, and 19, three or four solid electrolytes 171 are shown, but this is not limited to this. For example, the solid electrolyte 171 may be formed into thin fibers and bundled together to be used, formed, or configured as a head.

Figures 16, 17, 18, and 19 only show the solid electrolyte 171, but the device also includes the components described in Figures 1, 2, 4, etc., such as the electrolyte solution 124 and the contact portion 125.

16 shows a head for electrochemical reduction formed or configured using a plurality of (for example, four) solid electrolytes 171. A reference electrode 111 is formed or disposed around each solid electrolyte 171.
The tip of the head is made of a sponge-like material that is permeated with the electrolyte 124. This allows the electrolyte 124 and the thin film 123 to come into close contact with each other.

The reference electrode 111 is formed (prepared) by applying Cu paste to the area where the reference electrode 111 is to be formed, followed by baking at a temperature of around 800°C. After baking the reference electrode 111, a two-layer plating of Ni and Sn is applied to the surface. Electrolytic plating is usually used, but electroless plating may also be used. Furthermore, if necessary, a gold plating film is formed on the surface.
The reference electrode 111 is soldered and electrically connected to the RE terminal of the potentiostat 119 .

A counter electrode 112 is formed or placed on the upper surface of each solid electrolyte 171. To form (produce) the counter electrode 112, Cu paste is applied to the area where the counter electrode 112 is to be formed, and then the paste is baked at a temperature of around 800°C. After the counter electrode 112 is baked, a two-layer plating of Ni and Sn is applied to the surface. Electrolytic plating is usually used. Electroless plating is also acceptable. If necessary, a gold plating film is formed on the surface. The counter electrode 112 is soldered and electrically connected to the CE terminal of the potentiostat 119.

The reference electrodes 111 (reference electrodes 111a, 111b, 111c, 111d) of each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d) are formed of a conductive material. Therefore, by arranging each solid electrolyte 171 in close contact, the reference electrodes 111 (reference electrodes 111a, 111b, 111c, 111d) are electrically connected.

A counter electrode 112 (counter electrode 112a, counter electrode 112b, counter electrode 112c, counter electrode 112d) is formed on each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d), and each counter electrode 112 is electrically connected.

All of the counter electrodes 112 may be electrically connected, or any one or more of the counter electrodes 112 may be connected to the CE terminal of the potentiostat 119. By changing the position and number of counter electrodes 112 connected to the CE terminal, it is possible to set or change the electrochemical reduction capacity and the reduction position.

The example in Figure 16 is an example in which a reference electrode 111 (reference electrode 111a, reference electrode 111b, reference electrode 111c, reference electrode 111d) is formed on each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d).

Figure 17 shows an example in which a separate reference electrode 111 is used. The reference electrode 111 is made by cutting metal or by processing a metal plate. The reference electrode 111 is placed or attached in close contact with each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d). If necessary, an electrolyte solution 124 (not shown) is filled between the solid electrolyte 171 and the reference electrode 111. Other details are the same as or similar to those in Figure 16, so a description will be omitted.

Figure 18 shows an example of a head configured to perform electrochemical reduction using a cylindrical solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d).

Although the solid electrolyte 171 is illustrated as three or four pieces, the number is not limited to this. For example, the solid electrolyte 171 may be formed into a thin fiber shape and bundled together to form or configure ten or more of these. It may also be thin and angular.
A reference electrode 111 (reference electrode 111a, reference electrode 111b, reference electrode 111c, reference electrode 111d) is formed or arranged around each solid electrolyte 171.

The reference electrodes 111 (reference electrode 111a, reference electrode 111b, reference electrode 111c, reference electrode 111d) are formed (produced) by applying Cu paste to the area where the reference electrodes 111 will be formed, and then baking it at a temperature of around 800°C. They may also be formed using electroless plating technology.

After the reference electrodes 111 (reference electrodes 111a, 111b, 111c, and 111d) are baked, a two-layer plating of Ni and Sn is applied to the surface of the reference electrodes 111. Zn plating may also be applied. If necessary, a gold plating film is applied to the surface.

Reference electrodes 111a, 111b, 111c, and 111d are arranged in close contact with each other, and each reference electrode 111 is electrically connected. A terminal is attached to at least one of the reference electrodes 111 by soldering or crimping. The terminal is electrically connected to the RE terminal of the potentiostat 119.

A counter electrode 112 is formed or placed on the upper surface of each solid electrolyte 171. The counter electrode 112 is formed (produced) by applying Cu paste to the area where the counter electrode 112 is to be formed, and then baking it at a temperature of around 800°C.

After the counter electrode 112 is baked, its surface is plated with a double layer of Ni and Sn. Electrolytic plating is usually used. If necessary, a gold plating film may also be formed on the surface. The counter electrode 112 may also be formed by applying a conductive paste.

The same applies to the reference electrode 111. The same applies to the other embodiments. A terminal is connected to the counter electrode 112 by soldering or crimping, and the terminal is electrically connected to the CE terminal of the potentiostat 119.

The reference electrodes 111 (reference electrodes 111a, 111b, 111c, 111d) of each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d) are formed of a conductive material. Therefore, by arranging each solid electrolyte 171 in close contact, the reference electrodes 111 (reference electrodes 111a, 111b, 111c, 111d) are electrically connected.

Multiple solid electrolytes 171 are stored in a container 105. As shown in Figures 2, 3, and 4, an electrolyte solution 124 and a permeation membrane 172 are attached to the tip of the container. The above points can also be applied to other embodiments of the present invention.

A counter electrode 112 (counter electrode 112a, counter electrode 112b, counter electrode 112c, counter electrode 112d) is formed on each solid electrolyte 171 (solid electrolyte 171a, solid electrolyte 171b, solid electrolyte 171c, solid electrolyte 171d), and each counter electrode 112 is electrically connected. However, all counter electrodes 112 may be electrically connected, or any one or more counter electrodes 112 may be connected to the CE terminal of the potentiostat 119.

By changing the position and number of counter electrodes 112 connected to the CE terminal, it is possible to set or change the electrochemical reduction capacity and the reduction position. For example, if counter electrodes 112a and 112c are connected to the CE terminal, electrochemical reduction is achieved in an oblique position. For example, if counter electrodes 112a and 112b are connected to the CE terminal, electrochemical reduction is achieved in an upward position.

A gap (space) is created between the container 105 and the solid electrolyte 171. The electrolyte solution 124 and cleaning solution LA can be filled into or passed through this space. For example, this can be used to function as the liquid inlet tube 106 and the liquid outlet tube 107. It can also be used as the optical path for incident light 114a2 and reflected light 114b, as shown in Figures 7 and 8.

The embodiment in Figure 18 was configured with a head portion using a cylindrical solid electrolyte 171. The present invention is not limited to this. For example, as shown in Figure 19, the head portion may be configured with a plate-shaped or planar solid electrolyte 171. Other configurations are the same or similar to those in Figure 18, so explanations will be omitted.

FIG. 5 is an explanatory diagram of a potentiostat that drives the working electrode (WE) 110, the reference electrode (RE) 111, and the counter electrode (CE) 112 in the film thickness measuring device of the present invention.
5, the potentiostat is comprised of three operational amplifiers 135 and associated resistors 136. The potentiostat has three basic functions.
(1) The potential of the working electrode (WE) 110 is regulated relative to the reference electrode.
(2) The current flowing through the working electrode (WE) 110 is measured.
(3) No current is passed through the reference electrode (RE) 111.

Current flows between the working electrode (WE) 110 and the counter electrode (CE) 112, and the portion of the potential drop due to solution resistance that is caused by the resistance between the counter electrode (CE) 112 and the reference electrode (RE) can be controlled with a potentiostat. However, the resistance between the reference electrode (RE) 111 and the working electrode (WE) 110 cannot be controlled.

The potentiostat controls the potential by taking into account the potential drop due to the solution resistance between the reference electrode (RE) 111 and the working electrode (WE) 110, so the potential is always lower than the intended value by this drop.
This shows that unless an extra potential is applied to compensate for the voltage drop due to the resistance, the potential at which the peak current is obtained cannot be reached.

In a potentiostat, potential control is performed by subtracting the potential drop caused by the solution resistance between the working electrode (WE) 110 and the reference electrode (RE) 111. Therefore, this amount is added and compensated for using a convenient method called positive feedback.

The solution resistance between the reference electrode (RE) 111 and working electrode (WE) 110 is measured in some way and applied to a set potential. The best way to measure the solution resistance is directly by impedance measurement, but this is somewhat complicated, so a simpler method is used.

The positive feedback of iR compensation is achieved by multiplying the measured current value by a certain percentage and adding it to the set voltage.
A variable resistor Rpf (137) shown in FIG. 5 is used to add a voltage proportional to the current flowing through the working electrode (WE) 110 to the set voltage Eset.

The potentiostat circuit described in Figure 5 corresponds to the potentiostat 119 shown in Figure 3. Container 105 is filled with cleaning solution (rinse solution) LA124 or electrolyte solution LB124, and circulation fan 122 rotates as needed to circulate solution 124, etc.

As an example, the working electrode (WE) 110 is made up of solder, a terminal electrode, or a BGA pad. The surfaces of the working electrode (WE) 110, thin film 123, protective film 126, etc. are permeated with electrolyte 124. The reference electrode 111 and counter electrode 112 are formed on the solid electrolyte 171. The protective film 126 is removed using cleaning solution LA before electrochemical reduction.

The solid electrolyte 171 and the electrolyte solution 124 are in contact. Therefore, when a voltage is applied between the working electrode 110 and the counter electrode 112, the thin film 123 of the working electrode 110 and other components undergo electrochemical reduction. The amount of electrochemical reduction is controlled by the voltage of the reference electrode 111. The electrolyte solution 124 is agitated by a circulation fan 122.

Container 105 is provided with an inlet pipe 106 and a drain pipe 107. Cleaning solution LA or electrolyte solution LB is injected through inlet pipe 106. Cleaning solution LA or electrolyte solution LB is discharged through drain pipe 107. Valves (not shown) are formed or placed in inlet pipe 106 and drain pipe 107 to prevent backflow of the liquid.

The surfaces of the working electrode (WE) 110, thin film 123, etc. are filled with electrolyte 124, and a reduction reaction occurs when a current is passed through the electrode. Since the target substance has a specific reduction potential, the film thickness can be calculated by measuring the time required for reduction.

In Figure 3, the reference electrode (RE) 111 and counter electrode (CE) 112 may be interchanged. The same applies to Figures 4, 15, 16, 17, 18, and 19. Also, in Figure 4 and other figures, the counter electrode 112, reference electrode 111, etc. are shown formed on the surface of the solid electrolyte 171, but this is not limited to this. For example, it goes without saying that the counter electrode 112, reference electrode 111, etc. may be formed inside the solid electrolyte 171, as shown in Figure 15 and other figures.

In Figures 4, 15, 16, 17, 18, 19, etc., the reference electrode 111 is shown as being formed or arranged so as to surround the periphery of the solid electrolyte 171, but the present invention is not limited to this. For example, the counter electrode 112 and reference electrode 111 may be formed as multiple electrodes and arranged discretely or individually around the solid electrolyte 171. Needless to say, the above points also apply when the counter electrode 112 and reference electrode 111 are formed inside the solid electrolyte 171, as in Figure 15.

It goes without saying that a portion of the solid electrolyte 171 may be cut or polished to form a recess or the like, and the counter electrode 112, the reference electrode 111, etc. may be formed in the recess or the like. Alternatively, the counter electrode 112 and the reference electrode 111 may be formed or configured by forming a paste-like material on the solid electrolyte 171 portion and drying or sintering the material.
The above items, contents, and configurations can be applied to other embodiments of the present invention, and some or all of them can be combined.

Figures 2 and 4 are explanatory diagrams of a portion of Figure 1 and are schematic diagrams of the film thickness measurement device of the present invention. As shown in Figure 2, a ring-shaped contact part 125 is attached to the tip of the container 105. The contact part 125 is made of silicone rubber, butyl rubber, polypropylene, nitro rubber, or the like. The contact part 125 is flexible and brings the tip of the container 105 into close contact with the substrate 109. The contact part 125 is filled with an electrolyte solution 124, or the like. If necessary, a permeation membrane 172 is also arranged.

When the film thickness measurement device of the present invention is pressed against an area containing a sample for which film thickness measurement is to be performed, the contact portion 125 deforms. The deformation of the contact portion 125 prevents leakage of the electrolyte 124 and other liquids. Furthermore, the permeation membrane 172 is in close contact with the sample (thin film 123, etc.), ensuring good contact of the electrolyte 124 with the sample surface. Therefore, electrochemical reduction can be effectively achieved.

As shown in Figure 2, the contact part 125 is configured to be movable in direction A (upward) and direction B (downward). The size (diameter, etc.) of the contact part 125 is configured to be detachable so that it can be changed according to the sample to be measured. The solid electrolyte 171 is also configured to be detachable from the main body (not shown) of the film thickness measurement device of the present invention and can be replaced.

The incident light 114a needs to be focused on the object (electrode 110). By moving in direction A (upward) and direction B (downward), the incident light 114a can be focused on the object (electrode 110).

As shown in Figure 4, a reference electrode 111 is disposed in the solid electrolyte 171. A counter electrode 112 is attached to the upper surface of the solid electrolyte 171, facing the working electrode 110.

Incident light 114a and reflected light 114b pass through the area filled with electrolyte solution 124. Incident light 114a is irradiated onto thin film 123 and organic film 126. Incident light 114a is reflected by the surface of electrode 110 and becomes reflected light 114b.

Note that an optical window 127, indicated by a dotted line in Figure 1, is formed or placed in the container 105. Incident light 114a from a light generator 108 placed outside the container 105 is allowed to enter the container 105 through the optical window 127. Reflected light 114b passes through the optical window 127 formed or placed in the container 105 and enters a light receiver 117 placed outside the container 105.

The optical window 127 is preferably made of quartz glass, but may also be made of light lime glass, alkali-free glass, or sodium glass. In particular, if the incident light 114, etc., does not require much spectral transmittance (spectral reflectance) in the ultraviolet wavelength range, the optical window 127 may be made of or composed of a resin material such as polyester, acrylic resin, or polycarbonate resin.

The working electrode (WE) 110 is, for example, one electrode of the printed circuit board 109. Examples include a bump of a BGA, a connection land with an IC, and a through-hole. However, it is not limited to an electrode. For example, it may be any conductive material, such as a silicon wafer, a steel plate, a plated plate, or a carbon substrate. For example, it may be an oxide.
When the solid electrolyte 171 and the electrolytic solution 124 come into contact with each other, ions flow in and out.

The working electrode (WE) 110 is connected to a wiring pattern. By connecting the WE terminal of the potentiostat 119 to the wiring pattern, it functions as a reduction electrode. A current is applied between the working electrode (WE) 110 and the counter electrode 112, and the working electrode (WE) 110, thin film 123, or thin film on the surface undergoes continuous electrochemical reduction.

In the container 105, a cleaning liquid (rinse liquid) LA is replaced with an electrolyte solution LB. First, the cleaning liquid (rinse liquid) LA is poured into the container 105 to remove an organic film, an organic solderability preservative (OSP), and the like on the electrode 110. The cleaning liquid (rinse liquid) LA is discharged by turning on and off the electromagnetic valve 101c, and the liquid is discharged as a liquid LC by the pump 102.
Thereafter, the cleaning liquid (rinse liquid) LA is discharged from the container 105 through the drain pipe 107, and the electrolyte LB 124 is injected into the container 105 through the injection pipe 106.

The injection and discharge of the cleaning solution (rinse solution) LA and electrolyte solution LB is controlled by the liquid volume control unit 120. The electrodes (working electrode (WE), reference electrode (RE), and counter electrode (CE)) are controlled by the potentiostat 119.

The film thickness measurement device of the present invention has an optical controller 118 that measures the film thickness or state of the thin film 123 by irradiating the thin film 123 with light 114a and receiving reflected light 114b.

This is achieved by measuring the spectral reflectance using reflected light 114b. Spectral reflectance is the ratio of the spectral density of the reflected radiant flux or luminous flux to the spectral density of the incident radiation. It is the reflectance for monochromatic radiation and is a function of wavelength.

The optical structure of the thin film, such as its film thickness and refractive index, is calculated (simulated) from the changes in the polarization state of light irradiated onto the thin film 123 on the substrate 109. The optical controller 118 models the dielectric function of the thin film from the measurement results of the polarization state of light, and uses this dielectric function to perform theoretical optical calculations (such as simulations) on the changes in the polarization state of light.

The dielectric function of the thin film is determined by numerically optimizing the fitting parameters in the dielectric function model so that the difference between the calculated and experimental results for the polarization state is as small as possible.

The optical constants (refractive index and extinction coefficient) of the film thickness can be calculated from the obtained dielectric function, and by using a model with optical anisotropy, the anisotropy of the optical constants and orientation parameters can be evaluated.

Since the constituent materials of the thin film 123 are known or have a similar known composition, it is easy to model the dielectric function. Furthermore, changes in the thin film 123 can be continuously monitored using the electrochemical reduction method using a potentiostat 119 or similar.

An electrode 110 made of copper (Cu) is formed on a substrate 109, and a thin film 123 (oxide film) is formed on the electrode 110. The light generator 108 includes a deuterium lamp and a halogen lamp.

Deuterium lamps are used in spectroscopy when a continuous spectrum in the ultraviolet is required. Hydrogen-based plasma "arc" or discharge lamps have high output in the ultraviolet and relatively low output in the visible and infrared. At the same temperature, deuterium-based lamps have a longer life and three to five times the emissivity (intensity) at the far end of the UV range of a typical hydrogen arc lamp.

Halogen lamps are very small compared to silica bulbs, clear bulbs, and compact fluorescent lamps. Because the lamps are small, the light generator 108 can be made small. They have very high brightness and light properties that make them suitable for use as a point light source.
For wavelengths in the ultraviolet region, light emitted from a deuterium lamp is used, and for light in the visible and infrared regions, light emitted from a halogen lamp is used.

6 and other figures, the incident light 114a1 generated by the light generator 108 is incident on the diffraction grating 116. The diffraction grating 116 is an optical element that separates (disperses) light (white light) that is a mixture of various wavelengths into individual wavelengths. The diffraction grating 116 has a structure in which many parallel slits are arranged at equal intervals.
The diffraction grating 116 is not limited to a parallel slit type, but may be a diffraction grating (spectroscope) using a prism.

The diffraction grating 116 is moved to extract incident light 114a2 with wavelengths spaced apart by a predetermined wavelength. The incident light 114a2 is focused by the lens 115a, or the direction of the light is adjusted so that it strikes the electrode 110 surface.

Incident light 114a2 is irradiated onto thin film 123. The constituent material of thin film 123 or electrode 110 reflects or absorbs incident light 114a2, and the reflected light 114b is collected by lens 115b and is converted optically to electricity by photodetector 117.
The reflected light 114b for each wavelength has an intensity relative to the incident light 114a2 for each wavelength. From this intensity for each wavelength, the spectral reflectance can be measured or obtained.

The optical structure, such as the film thickness and refractive index of the thin film 123 on the substrate 109, is calculated inversely from the spectral reflectance. The optical controller 118 models the dielectric function of the thin film from the measurement results of the polarization state of light, etc., and uses this dielectric function to perform theoretical optical calculations on changes in the polarization state of light to determine the film thickness of the thin film 123, etc.

In spectroscopic film thickness measurement, it is necessary to eliminate the effects of reflected light from the back surface of the object being measured. However, in the film thickness measurement device of the present invention, the object being measured is composed of a copper electrode 110, etc., and all of the incident light 114a is reflected or absorbed by the copper electrode 110, etc., so there is little effect from reflected light.

Figure 12 shows an example in which the spectral reflectance of electrode 110 was measured using the spectral film thickness measurement method. Electrode 110 is made of copper (Cu). This is an example in which the spectral reflectance of Cu in electrode 110 was measured using the spectral film thickness measurement method. As shown by the dotted line, Cu has high reflectance in the long wavelength region and good reflectance in the near infrared region of 700 nm.

The solid line shows the spectral reflectance when copper oxide (CuO) is formed as the thin film 123 on the electrode 110. Copper oxide (CuO) has low reflectance in the visible light range and high transmittance in the long wavelength range.

The thickness of copper oxide (CuO) films can be determined by simulation using an optical model of copper oxide (CuO) and spectral reflectance. Therefore, by measuring spectral reflectance (spectral transmittance) using the spectral film thickness measurement method, it is possible to estimate or determine the presence or absence of the material being measured and its film thickness.

The thin film 123 is an oxide film or organic film that is optically transparent. The electrode 110 is a metal film such as copper, and therefore reflects incident light 114a2. The thin film 123 exhibits spectral transmittance (spectral reflectance) according to the refractive index and attenuation coefficient of the material that makes it up.

The cleaning liquid (or rinse liquid) LA or the electrolyte LB has a refractive index close to 1.33, which is the refractive index of water. If the oxide of the thin film 123 is copper dioxide (CuO ₂ ), the refractive index is 2.17. The optical model of copper dioxide is known, and simulation fitting for film thickness calculation is easy.

If the oxide of thin film 123 is copper oxide (CuO), the refractive index is 2.63. The optical model for copper oxide is known, making it easy to fit simulations when calculating film thickness.

By defining an optical model assuming that the components of thin film 123 are copper dioxide and copper oxide, and performing a simulation to calculate the film thickness, the film thickness of thin film 123 can be calculated.

Copper dioxide (CuO ₂ ) and copper oxide (CuO) have a large difference in refractive index from the cleaning solution (rinse solution) LA or the electrolyte solution LB 124, and the reflectance of the copper of the electrode 110 is also relatively high, so the intensity of the reflected light 114 is also large, enabling stable measurement. This optical film thickness measurement method is called a spectroscopic film thickness method.

When the thin film 123 is not filled with the cleaning liquid (rinse liquid) LA or the electrolyte LB (air, nitrogen), the difference between the refractive index of 1.0 and the refractive index of copper dioxide (CuO ₂ ), which is 2.17, or the refractive index of copper oxide (CuO), which is 2.63, is large, allowing for stable measurement.

When thin film 123 is an oxide of silicon (Si) used in semiconductor elements, etc., the refractive index of silicon dioxide (SiO ₂ ) is 1.46, and the refractive index of silicon monoxide (SiO) is 1.90. Although the difference in refractive index with the cleaning liquid (rinse liquid) LA or the electrolyte liquid LB is small, optical models for silicon dioxide (SiO ₂ ) and silicon monoxide (SiO) have been established, and therefore film thickness calculations can be performed with high accuracy.

The spectroscopic film thickness measurement method using reflected light 114b and the electrochemical reduction method using a potentiostat can be performed simultaneously. The film thickness of thin film 123 can be measured or obtained from reflected light 114b, and the film thickness can also be measured or obtained using electrochemical reduction. By combining the two methods, the film thickness and material of thin film 123 can be measured or determined with high accuracy.

The spectroscopic film thickness measurement method can achieve high film thickness accuracy if an optical model of the thin film 123 can be constructed with high accuracy. However, if the thin film 123 is composed of two layers of copper dioxide (Cu ₂ O) and copper oxide (CuO), for example, or is composed or formed of a mixture of copper dioxide (Cu ₂ O) and copper oxide (CuO), it cannot be modeled with a high-accuracy optical model. Therefore, the film thickness accuracy obtained by calculation or simulation decreases.

The electrochemical reduction method is controlled by a potentiostat, a constant current is applied to cause a reduction reaction at the electrode (WE), and the change in potential E (V) over time is recorded or measured. The amount of material forming the thin film 123 can be quantitatively measured or determined from the recorded or measured plateau. However, it is difficult to quantitatively measure or determine the film thickness.

The present invention can quantitatively measure the film thickness of thin film 123 and the like using a spectroscopic film thickness measurement method. Furthermore, the forming materials and amounts of forming materials of thin film 123 and the like can be quantitatively measured using an electrochemical reduction method.

Therefore, the spectroscopic film thickness measurement method can quantitatively measure the film thickness of the thin film 123, etc. The synergistic effect of the spectroscopic film thickness measurement method and the electrochemical reduction method allows the film thickness, amount of forming material, and forming material of the thin film material 123, etc. to be measured quantitatively and with high accuracy.

Because the spectroscopic film thickness measurement method and electrochemical reduction method can be performed simultaneously, the film thickness of the thin film 123, etc. can be measured while measuring the potential (V) of the thin film 123, etc., making it possible to accurately determine the material being reduced and the change points in that material. By constantly or at appropriate times feeding back the determined change points to the optical model of the spectroscopic film thickness measurement method, highly accurate film thickness calculations (film thickness simulations) can be achieved.

Before performing the spectroscopic film thickness measurement method, the container 105 is filled with cleaning liquid LA and the organic film 126 is removed. This allows the electrochemical reduction method to be carried out smoothly. Furthermore, because the film thickness of the organic film 126 can be measured using the spectroscopic film thickness measurement method, the time required to fill the container 105 with cleaning liquid LA can be accurately estimated.

Figure 6 is a diagram and explanatory view of the configuration of a spectroscopic film thickness measurement method for measuring the film thickness of an object (such as thin film 123). In Figure 6, lenses 115 (lenses 115a and 115b) are shown as concave mirrors, but this is not limited to this and they may also be configured with convex lenses, etc. The focusing optical system may also be configured with a combination of concave and convex lenses, etc. Concave mirrors can also be used.

As an example, as shown in Figure 13, an electrode 110 made of copper (Cu) is formed on a substrate 109, and a thin film 123 (such as an oxide film, thin film 123a, thin film 123b) and an organic film 126 are formed on the electrode 110.

The light generator 108 includes a deuterium lamp and a halogen lamp. The deuterium lamp is primarily responsible for generating light in the ultraviolet wavelength range, while the halogen lamp is primarily responsible for generating visible and infrared light.

Incoming light 114a1 generated by light generator 108 is incident on diffraction grating (including prisms, etc.) 116. Diffraction grating (including prisms, etc.) 116 (Gratings) is an optical element that separates light (white light) that is a mixture of various wavelengths into individual wavelengths. Diffraction grating 116 has a structure in which many parallel slits are arranged at equal intervals.

Light 114a1 incident on diffraction grating 116 is split into wavelengths by diffraction grating 116. The split light 114a2 has its direction changed by lens or reflecting mirror 115a and illuminates thin film 123 or the like.
By moving the diffraction grating 116 or by moving the position at which light is incident on the diffraction grating 116, incident light 114a2 having wavelengths spaced apart by a predetermined wavelength is extracted.

The incident light 114a2 does not have to be light that is continuously changed within a predetermined wavelength range. For example, it may be fixed at a constant wavelength of 630 nm, and this wavelength may be irradiated, and the magnitude of the reflected light 114b may be continuously monitored. The change in film thickness can be determined from the magnitude of the reflected light 114b. Therefore, the measurement or acquisition of the spectral reflectance of the film thickness measuring device of the present invention may be performed at a constant wavelength.
The position of the lens 115 or the position of the substrate 109 is changed to adjust the position so that the incident light 114a2 is focused on the target (electrode 110).

Incident light 114a2 is irradiated onto the thin film 123. The thin film 123 or the material of the electrode 110 reflects or absorbs the incident light 114a2, and the reflected light 114b is collected by the lens 115b and subjected to optical-to-electrical conversion by the photodetector 117.

Spectroscopic film thickness measurement requires that a reference base reflectance be measured in advance. Reflectance is measured as a percentage of the base reflectance (100%).

To measure the base reflectance, a reflector having a highly reflective film made of silver, aluminum, or the like is placed at the position of the electrode 110 (placed at the focal position of the incident light 114a), and the reference spectral reflectance is measured. The reflectance of the reflected light 114b is measured relative to the measured reference spectral reflectance. The film thickness of the thin film 123 or the like is calculated using the measured spectral reflectance characteristics and an optical model of the thin film 123 or the like to be measured.
In FIG. 6, the incident light 114a is incident on the thin film 123 etc. from an oblique direction, but the film thickness measuring device of the present invention is not limited to this.
7 and 8 show an optical system in which incident light 114a is incident on a plane of a thin film 123 or the like in a direction perpendicular to the plane, and reflected light 114b is extracted in a direction perpendicular to the plane.

In Figure 7, incident light 114a1 from the light generator 108 is changed in direction by mirror 128, passes through half mirror 151, and strikes the thin film 123 perpendicularly. Incident light 114a2 passes through the center of the injection tube 106.

The incident light 114a2 is reflected by the thin film 123, and the reflected light passes through the center of the liquid injection tube 106 (or the liquid drainage tube 107, etc.) again. The reflected light 114b is reflected by the reflecting surface of the half mirror 151 and enters the light receiver 117.
FIG. 8 shows an embodiment in which a polarizing beam splitter 152 is used in place of the half mirror 151 in FIG.

Incoming light 114a1 from the light generator 108 is changed in direction by the mirror 128 and passes through the light separation surface (polarization surface) 153 of the polarizing beam splitter 152, whereupon the incident light 114a2 becomes polarized and enters the thin film 123 perpendicularly. The incident light 114a2 passes through the center of the injection tube 106.

Incoming light 114a2 is reflected by thin film 123, and the reflected light 114b, with its polarization disturbed, passes through the center of infusion tube 106 again. Reflected light 114b is reflected by the light separation surface (polarization surface) 153 of polarizing beam splitter 152 and enters photodetector 117. Use of polarizing beam splitter 152 allows the light irradiation section of the device to be configured compactly.

In the examples shown in Figures 7 and 8, the incident light 114a2 and reflected light 114b pass through the liquid injection tube 106, but this is not limited to this. The incident light 114a2 may be incident from above the thin film 123, and the reflected light 114b may be configured to pass through a location other than the drain tube 107 and the liquid injection tube 106.

9 is an explanatory diagram of a film thickness measurement method using electrochemical reduction. As an example, a case is shown in which tin-containing solder is formed on an electrode or the like, and a thin film 123 made of tin oxide (tin oxide SnO, tin dioxide SnO ₂ ) is formed (generated) on the solder surface. The solder corresponds to the electrode 110. The solder 110 serves as a working electrode 110, and a current is supplied between the working electrode 110 and a counter electrode 112.

In Figure 9, the horizontal axis represents time. For ease of explanation and understanding, the time is expressed in minutes (min). The vertical axis represents potential (V). The reduction time varies depending on the magnitude of the constant current applied.

When the surface of the solder 110 is filled with electrolyte 124 and a small current is passed through the solder as the electrode 110, a reduction reaction occurs. Since each substance has or changes its own reduction potential (V), the film thickness can be calculated (estimated) by measuring the time required for reduction.

The electrochemical reduction method is controlled by a potentiostat 119, which applies a constant current to the electrode (WE) to cause a reduction reaction, and records the change in potential E (V) over time. The amount of material forming the thin film 123 can be quantitatively measured from the recorded plateau potential.

Figure 9 shows an example of measuring the Sn surface of solder. The vertical axis is potential (E (V)) and the horizontal axis is time (min). The potential on the vertical axis differs between a calomel electrode and a silver (Ag) electrode. It also differs depending on the electrolyte (e.g., AgCl). The potential E (V) can be corrected depending on the type of electrolyte and electrode.
The first plateau of A is estimated to be SnO at a potential of −0.85 to −1.06 V. When the reduction time is 30 sec (0.5 min), the film thickness is 11 Å.

The second plateau at B has a potential of -1.06 to -1.18 V and is presumed to be _SnO2 . When the reduction time is 100 sec, the film thickness is 15 Å. The potential at C is -1.2 V, which is presumed to be the hydrogen evolution potential of Sn.
It is estimated that in the first plateau of A, SnO is converted to Sn, and in the first plateau of B, _SnO2 is converted to Sn.

The electrochemical reduction method used in the film thickness measurement device of the present invention has a short measurement time and is inexpensive. It is also possible to distinguish or discriminate between oxide films with different valences. Examples of metal oxide films that can be measured include oxides of Cu, Ag, Sn, Si, and solder. Examples of metal film thicknesses include Si, Ni, Cu, Ag, Sn, Au, and Ag.

Figure 11 is an explanatory diagram showing the state of electrochemical reduction when the thin film 123 of the present invention is coated with an organic film 126 or the like. The organic film 126 may be an organic film caused by contamination, or an organic solderability preservative (OSP) may be formed on the electrode.

For example, there is the heat-resistant water-soluble preflux (OSP) used in the printed wiring board (PWB) manufacturing process. It has excellent solder wettability for high temperatures and multiple mounting with lead-free solder. Many types of OSP are sold by manufacturers.

Figure 11 shows two types of OSP (OSP1, OSP2) as an example. In Figure 11, Cu1 indicates the potential change of an electrode made of Cu when OSP1 is not present (when OSP1 is removed). Cu2 indicates the potential change of an electrode made of Cu when OSP2 is not present (when OSP2 is removed).

OSP1 in Figure 11 has almost no plateau. OSP2 has a first plateau, but the redox potential remains constant for 70 seconds or more. In the case of Cu alone, there is no plateau with large changes, and the change is gradual. The solid line (Cu2) has a plateau step. The short dotted line (Cu1) also has a plateau step. The solid line (Cu2) and the short dotted line (Cu1) have different times at which the plateau flattens.

The first plateau is presumed to be Cu ₂ O, and the second plateau is presumed to be CuO. For Cu2, the potential becomes constant for 40 seconds or more, which is presumed to be the reduction potential of Cu2. For Cu1, the potential becomes constant for 60 seconds or more, which is presumed to be the reduction potential of Cu1.

As shown in Figure 11, if OSPs (OSP1, OSP2) are formed, it is highly likely that the Cu oxide film underneath the OSPs cannot be measured. Removing OSP1 exposes thin film 123, allowing for accurate measurement of the redox potential. Similarly, removing OSP2 exposes thin film 123, allowing for accurate measurement of the redox potential. Therefore, in order to measure the film thickness of thin film 123, which is made of an oxide film, it is necessary to remove the OSPs.

The film thickness measurement device of the present invention can inject cleaning liquid LA into container 105 to remove organic films 126 such as OSP. Furthermore, spectroscopic film thickness measurement can be used to measure the presence or absence and thickness of organic films (organic protective films OSP) 126.

In the present invention, before pouring the cleaning liquid LA into the container 105, the presence or absence of the organic film 126 and the estimated film thickness of the organic film are measured or obtained using a spectroscopic film thickness measurement method. The estimated film thickness is used when the optical model of the organic film 126 is unclear. When the optical model is known, the film thickness can be determined with high accuracy.

If the organic film 126 is not observed using the spectroscopic film thickness measurement method, the cleaning solution LA is not poured into the container 105, and instead the electrolyte solution LB is poured. Before pouring the electrolyte solution LB, the presence or absence of the thin film 123 and the estimated film thickness of the thin film 123 are measured or obtained.

If an organic film 126 is present (organic film 126 is present), cleaning liquid LA is injected. The change in the film thickness of the organic film 126 (spectral reflectance) is monitored or acquired using a spectroscopic film thickness measurement method. When injecting cleaning liquid LA, the circulation fan 122 is operated as needed to circulate cleaning liquid LA within the container 105. In addition, cleaning liquid LA is injected and drained.

The change in the film thickness (spectral reflectance) of the organic film 126 is monitored or acquired. With the spectral film thickness measurement method, the presence or absence of the organic film 126 and changes in film thickness can be determined from changes in spectral reflectance. The cleaning solution LA does not remove the thin film 123 made of an inorganic material, but can remove the organic film 126 made of an organic material.

In the film thickness measurement device and film thickness measurement method of the present invention, if necessary, the OSP is removed using cleaning solution LA, and then electrochemical reduction is performed. Spectroscopic film thickness measurement is also performed simultaneously or sequentially.

In addition, cleaning performance can be improved by applying ultrasonic waves (cleaning and agitation using ultrasonic vibrations) during cleaning with cleaning solution LA and electrolysis with electrolyte 124. While ultrasonic waves may be applied to the container 105, applying them to the substrate 109 is more effective.

If the OSP is applied thickly, it may interfere with measuring the film thickness of the thin film 123, but stable measurements can be made by using cleaning solution LA and performing spectroscopic film thickness measurement.

FIG. 10 shows an example of an embodiment in which measurement by electrochemical reduction method was performed by using an electrolytic solution (boric acid, sodium tetraborate, potassium chloride) to induce a reduction reaction on the surface of the electrode 110 at a constant current (30 μA/cm ² ) or a predetermined current, and recording the change in potential over time.

The contact part 125 uses a silicone rubber pad with a diameter of 3.5 mm. As shown in Figure 2, the contact part 125 is moved in the direction A or B to adjust the state of contact with the substrate 109 and the focal position in the spectroscopic film thickness measurement method.

The times indicated in Figure 10 indicate the time left in reflow. It is assumed that the longer the time left in reflow, the thicker the oxide film (thickness of thin film 123) formed on electrode 110. As shown in the graph in Figure 10, the plateau time is longest at 30 minutes and shortest at 1 minute.

The film thickness measurement device of the present invention performs spectroscopic film thickness measurement simultaneously with or sequentially after the electrochemical reduction method. The spectroscopic film thickness measurement method can measure the film thickness of the thin film 123. When the thin film 123 is configured or formed by mixing or stacking Cu ₂ O, CuO, and Cu portions, the spectroscopic film thickness measurement method can grasp the state of the stacking or mixture as a difference in spectral transmittance. However, it is difficult to grasp the film thickness of each layer (e.g., Cu ₂ O, CuO).

With the electrochemical reduction method, as shown in the graphs in Figures 9 and 11, the first and second plateaus can be observed and the time for each plateau can be measured, making it possible to determine the composition of the constituent materials of each layer. Knowing the composition of the constituent materials allows for improving or determining the accuracy of the optical model for each layer in the spectroscopic film thickness measurement method, making it possible to separate each layer and determine its film thickness.

For example, if the thin film 123 is composed of a Sn-related layer, in the electrochemical reduction method, the thickness of the SnO is determined from the time required in the potential range of -0.85V to -1.05V (first plateau), and the thickness of the SnO2 is determined from the time required in the potential range of -1.05V to -1.15V (second plateau). When all the oxide film is removed, the final hydrogen evolution potential of Sn is approximately -1.30V.

The first plateau can be understood to be amorphous SnO, and the second plateau to be crystalline _SnO2 or a mixture of SnO and _SnO2 . The thickness of each layer can be determined by spectroscopic film thickness measurement using an optical model of each constituent material.

Figures 13 and 14 are explanatory diagrams of the film thickness measurement method of the present invention. Figure 13 is a structural diagram of the thin film 123, etc., for illustrative purposes. Figure 14 is a flowchart of the film thickness measurement method of the present invention.

As shown in Figure 13, thin films 123a and 123b, for example, made of oxide films, are formed on the electrode 110 on the substrate 109, and an organic film 126 is formed on the thin film 123a.

Spectroscopic film thickness measurement requires that a reference base reflectance be measured in advance. Reflectance is measured as a percentage of the base reflectance (100%).

To measure the reflectance that serves as the base for reflectance using the spectroscopic film thickness measurement method, a reflector having a highly reflective film made of silver (Ag), aluminum (Al), or the like is measured. The reflectance of the reflected light 114b from the thin film 123, etc., is measured using the reflectance of the reflector as a baseline (S01).

To measure the reflectance of the reflector, the position of the contact portion 125 is adjusted so that the focal position of the incident light 114a is adjusted to the object to be measured (such as the thin film 123) (S02).

Next, incident light 114a is irradiated onto the organic film 126, and reflected light 114b is measured. At this time, the cleaning liquid LA is not poured into the container 105. However, this does not apply if the reflected light 114b can be measured by the spectroscopic film thickness measurement method after the cleaning liquid LA is poured and before the organic film 126 is peeled off or the like.
In the spectroscopic film thickness measurement method of the present invention, incident light 114a is irradiated onto the organic film 126, etc., and reflected light 114b from the organic film 126, etc. is measured (S03).

The reflectance of reflected light 114b is measured relative to the measured reference spectral reflectance. The film thickness of organic film 126, thin film 123, etc. is calculated using the measured spectral reflectance characteristics of reflected light 114b and an optical model of the organic film 126, thin film 123, etc. being measured (S04). Step S04 and other steps are not necessary if organic film 126 is not formed. Furthermore, if only the presence or absence of organic film 126 is required, there is no need to calculate the film thickness of organic film 126.

If an organic film 126 is formed, or if there is a contaminant film corresponding to the organic film 126, the organic film 126 is removed. To remove the organic film 126, a cleaning liquid LA is poured into the container 105. After the cleaning liquid LA is poured (S05), the film thickness calculation by the spectroscopic film thickness measurement method is performed by corresponding the refractive index of air (atmospheric refractive index 1.0) to the refractive index of the cleaning liquid LA and correcting the calculation.
By pouring in the cleaning liquid LA (S05), the organic film 126 is dissolved by the cleaning liquid LA or peeled off and removed from the thin film 123.
The state of dissolution or peeling of the organic film 126 can be detected by the spectroscopic film thickness measurement method of the film thickness measurement method of the present invention.

The film thickness measurement method of the present invention is not limited to film thickness measurement; the method of removing the thin film 123 and the organic film 126 (the method of removing the thin film, etc., and the thin film, etc., removal device) also falls within the scope of the technical concept of the present invention.
Since the organic film 126 is not detected by the spectroscopic film thickness measurement method, it can be confirmed that the organic film 126 has been removed from the thin film 123 .

Next, or continuously, incident light 114a is irradiated and reflected light 114b is measured (S06). Because the structure or composition of thin film 123 is estimated using an optical model, it is difficult to accurately simulate it using the spectroscopic film thickness measurement method. Furthermore, it is often unclear how many thin film layers thin film 123 is made up of. In some cases, thin film 123 is made up of a mixture of materials with multiple compositions.

In the example of Figure 13, thin film 123 is described as being formed or composed of thin film 123a and thin film 123b. Film thickness data for thin film 123a and thin film 123b obtained by calculation or simulation are calculated (S07). In addition, the film thickness data for thin film 123a and thin film 123b are recorded.

In the electrochemical reduction method of the present invention, the type, composition, and chemical symbol of the material that makes up thin film 123 can be determined from the plateau potential, the number of plateaus, and the plateau time. An optical model can be determined from the type, composition, and chemical symbol of the material that makes up thin film 123. The optical model and the film thickness calculated using the spectroscopic film thickness measurement method are taken into consideration. Furthermore, by making corrections, the film thickness, composition, etc. of thin films 123a and 123b can be determined with high precision.

Next, the cleaning liquid LA is discharged from the drain pipe 107, and the electrolyte LB is injected into the container 105 from the injection pipe 106 (S08). At this time, the circulation fan 122 rotates so as to discharge the cleaning liquid LA from the drain pipe 107.
In the steps from S08 onwards, both or either of the electrochemical reduction method of the present invention and the spectroscopic film thickness measurement method of the present invention are carried out alternately or simultaneously.
The spectroscopic film thickness measurement method of the present invention is Sa1 to Sa3. The electrochemical reduction method of the present invention is Sb1 to Sb3.

The spectroscopic film thickness measurement method of the present invention irradiates a thin film with incident light 114a and measures reflected light 114b (Sa1). The incident light 114a is focused on a thin film 123. The light reflected by the thin film 123 is incident on a photodetector 117 as reflected light 114b (Sa1). The incident light 114a and reflected light 114b travel through a solution 124 as shown in FIGS. 2 and 13.
In addition, the electrochemical reduction method of the present invention is carried out simultaneously with or at an appropriate time to the spectroscopic film thickness measurement method (Sb1).

The film thicknesses of thin films 123a and 123b are calculated using spectroscopic film thickness measurement (Sa2). Using electrochemical reduction, thin film 123b is detected or obtained from the potential and time of the first plateau (sb2). Next, thin film 123a is detected or obtained from the potential and time of the second plateau (Sb3).

When the first plateau is completed in the electrochemical reduction process, thin film 123b is removed. Therefore, the film thickness measured using the spectroscopic film thickness measurement method of the present invention corresponds to the film thickness of thin film 123a.

When thin film 123b and thin film 123a remain, the spectral reflectance of reflected light 114b due to thin film 123b and thin film 123a is measured (Sa2). When thin film 123b is removed and thin film 123a remains, the spectral reflectance of reflected light 114b due to thin film 123b is measured (sa3).

Therefore, the material composition of thin films 123a and 123b and the remaining state of thin film 123 can be determined from the plateau potential and time state in the electrochemical reduction method. Knowing the material composition of thin films 123a and 123b makes it possible to construct an optical model, enabling accurate film thickness calculations using spectroscopic film thickness measurement methods (sa2, Sa3).

Simply irradiating the thin film 123 with incident light 114a and measuring the reflected light 114b will only estimate the optical model of the structure or composition of the thin film 123. With electrochemical reduction, the composition, structure, and chemical model of each thin film can be determined from the number of plateaus, potential, and time, such as the potential and time of the first plateau and the potential and time of the second plateau. By alternately or simultaneously using both the electrochemical reduction method and the spectroscopic film thickness measurement method of the present invention, or by using either one of them, the film thickness, composition, etc. of each thin film 123 can be accurately determined or obtained. The spectroscopic film thickness measurement method and the spectroscopic film thickness measurement method have a synergistic effect.

The above-described embodiments and the accompanying drawings are examples of preferred embodiments, and the embodiments described in this specification, the drawings, etc. can be combined with each other in part or in whole.
Furthermore, the present invention can be substituted, modified, and changed in various forms within the scope of the technical idea of the present invention described in the claims.

This invention can quantitatively measure oxide films on solder and copper foils on printed circuit boards. Surface oxide films, etc., are factors that affect corrosion resistance, solder adhesion, and device reliability, so their composition and film thickness can be evaluated. This invention contributes to industrial development.

101: Solenoid valve 102: Pump 103: Defoamer 104: Liquid tank 105: Container 106: Liquid inlet pipe 107: Liquid outlet pipe 108: Light generator 109: Substrate 110: Electrode (working electrode (WE))
111 Reference electrode (RE)
112 Counter electrode (CE)
114a Incident light 114b Reflected light 115 Lens 116 Diffraction grating 117 Light receiver 118 Light controller 119 Potentiostat 120 Liquid volume control unit 121 Controller 122 Circulation fan 123 Thin film (organic film, oxide film)
124 Solutions (electrolytes, cleaning solutions)
125 Adhesion part 126 Organic film 127 Optical window 128 Mirror 135 Operational amplifier 136 Resistor 151 Half mirror 152 Polarization beam splitter 153 Light separation surface 161 Level detector 162 Solution reservoir 171 Solid electrolyte 172 Permeation membrane

Claims (10)

A film thickness measuring device for determining the film thickness of a thin film on a conductor,
a counter electrode (CE) and a reference electrode (RE) disposed or formed in the solid electrolyte;
an electrolytic material disposed between the thin film and the solid electrolyte;
A film thickness measuring device characterized in that the conductor is used as a working electrode (WE) and electrochemical reduction is carried out to determine the film thickness of the thin film. A film thickness measuring device for determining the film thickness of a thin film on a conductor,
a counter electrode (CE) and a reference electrode (RE) disposed or formed in the solid electrolyte;
an electrolytic material disposed between the thin film and the solid electrolyte;
a current circuit that applies a constant current between the conductor as a working electrode (WE) and the counter electrode (CE);
A film thickness measuring device comprising a measuring circuit for measuring a reduction potential resulting from electrochemical reduction. A film thickness measuring device for determining the film thickness of a thin film on a conductor,
a counter electrode (CE) and a reference electrode (RE) disposed or formed in the solid electrolyte;
a cleaning device for filling a cleaning liquid between the thin film and the solid electrolyte;
a filler for filling an electrolytic solution between the thin film and the solid electrolyte;
A film thickness measuring device characterized in that the conductor is used as a working electrode (WE) and electrochemical reduction is carried out to determine the film thickness of the thin film. A film thickness measuring device for determining the film thickness of a thin film on a conductor,
a counter electrode (CE) and a reference electrode (RE) disposed or formed in the solid electrolyte;
The solid electrolyte is disposed in contact with a material or a permeable membrane impregnated with an electrolytic solution,
A film thickness measuring device characterized in that the conductor is used as a working electrode (WE), a material or a permeated membrane permeated with the electrolyte is placed in contact with the thin film, and the film thickness of the thin film is determined by performing electrochemical reduction. A film thickness measuring device for determining the film thickness of a thin film on a conductor,
a counter electrode (CE) and a reference electrode (RE) disposed or formed in the solid electrolyte;
an electrolytic material disposed between the thin film and the solid electrolyte;
a light generator that generates incident light to irradiate the thin film;
a light receiver that receives light reflected by the thin film;
A film thickness measuring device characterized in that the conductor is used as a working electrode (WE) and electrochemical reduction is carried out to determine the film thickness of the thin film. 6. The film thickness measuring device according to claim 1, wherein the solid electrolyte is stabilized zirconia. 6. The film thickness measuring device according to claim 1, 2, 3, 4 or 5, wherein the reference electrode (RE) is formed within the solid electrolyte. Further comprising an adhesive portion disposed between the periphery of the thin film and the solid electrolyte,
5. The film thickness measuring device according to claim 3, wherein the electrolyte is disposed or filled in the contact portion. Further comprising an adhesive portion disposed between the periphery of the thin film and the solid electrolyte,
5. The film thickness measuring device according to claim 3, further comprising: an injection pipe for injecting the electrolytic solution into the contact portion; and a drain pipe for discharging the electrolytic solution from the contact portion. 6. The film thickness measuring device according to claim 1, 2, 3, 4, or 5, wherein the solid electrolyte is composed of a plurality of solid electrolyte portions, and the counter electrode (CE) and the reference electrode (RE) are disposed or formed in the solid electrolyte portions.