JP3382099B2 - Electrolytic ionic water generation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing electrolytic ionized water, and more particularly to an electrode structure of an electrolytic cell for electrolysis.

[0002]

2. Description of the Related Art Conventionally, ionized water produced by an ionized water producing apparatus has been used in various fields, especially in the production of semiconductor devices and liquid crystals. In the manufacture of semiconductor devices, it is used for cleaning semiconductor substrates such as silicon semiconductors with ionized water obtained by electrolyzing pure water or ultrapure water, and for polishing. Up to now, fluorocarbon solvents such as CFCs have been used for cleaning semiconductor substrates in the manufacture of semiconductor devices, but they have begun to be shunned because they adversely affect the living environment. Instead, pure water or ultrapure water is used instead. Has come to be used as the safest solvent. Pure water is high-purity water having a resistivity of about 5 to 18 MΩcm in which impurities such as ions, fine particles, microorganisms, and organic substances are almost removed. Ultrapure water is extremely high-purity water having a higher purity than that of pure water obtained by removing suspended substances, dissolved substances, and highly efficiently from water by an ultrapure water production apparatus. By electrolyzing these pure water or ultrapure water, ionic water such as highly oxidative anodic ion water (acidic water) and strongly reducing cathodic ion water (alkaline water) is generated.

In the manufacture of semiconductor devices and liquid crystals,
It is also considered to clean the surface of the substrate using pure water or ultrapure water such as anodic ion water or cathodic ion water.
FIG. 10 shows a conventional electrolytic ionized water generator. Electrolyzer 5
Reference numeral 0 includes a cathode chamber 52 and an anode chamber 53, a cathode 541 is disposed in the cathode chamber 52, and an anode 542 is disposed in the anode chamber 53. Then, these electrodes 54 (cathode 54
1 and the anode 542) are both made of platinum or titanium. In order to efficiently separate the cathode ionized water 58 formed in the cathode chamber 52 and the anode ionized water 59 formed in the anode chamber 53, the cathode chamber and the anode chamber are formed of a porous diaphragm 56 such as ceramic or polymer. It is partitioned. Electrolyzer 5
The cathode 541 of 0 is connected to the negative electrode 67 of the DC power supply 66, and the anode 542 is connected to the positive electrode 68 thereof. In the electrolytic cell 50, a power supply voltage from a power source 66 is applied to electrolyze a diluted electrolyte solution 51 obtained by adding a supporting electrolyte such as ammonium chloride to pure water supplied from an ultrapure water supply line 61 of the electrolytic cell 50. To do. The cathode ion water generated on the cathode 541 side as a result of this electrolysis is alkaline water, and the anode ion water generated on the anode 542 side is acidic water.

Cathode ionized water 58 produced in the cathode chamber 52
Is supplied to the outside from the cathode ionized water supply line 62,
The anode ionized water 59 generated in the anode chamber 53 is supplied to the outside from the anode ionized water supply line 63. Since alkaline water is usually generated in the cathode chamber 52, for example, when using a polishing apparatus used for manufacturing a semiconductor device, in order to perform polishing using alkaline water,
The alkaline ionized water supply line 62 connected to the electrolytic bath 50 is used as an ionized water supply line to supply alkaline water to the polishing cloth of the polishing apparatus. In this case, the acidic water generated in the anode chamber 53 is unnecessary and is discarded. Therefore, the anode ionized water supply line 63 is connected to the ionized water discharge line for discharging ionized water. Further, in order to perform polishing using acidic water, the anode ionized water supply line 63 connected to the electrolytic cell 50 serves as an ionized water supply line to supply the acidic water to the polishing cloth. In this case, the alkaline water generated in the cathode chamber 52 is unnecessary and is discarded. Therefore, the cathode ionized water supply line 62 is connected to the ionized water discharge line for discharging ionized water.

As described above, the electrolytic cell 50 is divided into two cells by the diaphragm 56, and each electrode is arranged in each of the separated cells. Therefore, alkaline water or acidic water is supplied from each cell depending on the purpose. Can be taken out. As described above, the ion water includes alkaline water and acidic water, and is diluted in the electrolytic cell, for example, HCl, HNO ₃ , NH ₄
Ionized water having an arbitrary pH is generated by electrolyzing an electrolytic solution such as Cl or NH ₄ F. However, in this method, the metal ions contained in the electrolyte solution and the metal ions generated from the electrodes are also attracted to the electric field generated at the electrodes, and a large amount of metal ions enter the electrolytic cell, especially the alkaline cell (cathode chamber), and the purity of the electrolytic ion water is Had lowered. Recently, there has been an increasing demand for using ionized water for cleaning wafers in the manufacture of semiconductor devices. In such a current situation, in semiconductor devices, minute amounts of metal impurities have a great influence on device characteristics, so that highly purified ionized water is required.

[0006]

When using electrolytic ion water for cleaning semiconductor substrates, it is essential that there be no particles or metal contamination. When a metal electrode is used, the electrode is usually manufactured in a general room, and various metal elements are contained in the electrode. Even if an electrode coated with a noble metal such as Pt, which has high oxidation resistance, is used, various metal elements including Pt elute on the anode side even though the amount is very small, and are contained in the electrolytic ion water produced. Will end up. Such a phenomenon is the same even when an electrode made of a metal oxide is used. It is also known to use carbon for the electrode, but when a carbon electrode is used for an electrolytic cell, oxygen is generated by electrolysis of water, and particularly carbon is generated on the anode side as shown in the following formula (1). Electrodes are significantly consumed by reacting with oxygen. C + O ₂ → CO ₂ ↑ (1) As a result, the electrode surface is attacked and carbon fragments are spilled from the electrode. The carbon pieces cause particles.

In cleaning semiconductor wafers, HF treatment is indispensable for removing metal impurities. Fe, A
Metals such as l and Na can be easily removed from the wafer surface. However, HF is inferior in removal rate to a metal element having a higher redox potential than hydrogen such as Cu as compared with a metal element having a lower redox potential than hydrogen. On the contrary, if these metals are present in HF, these metals will be adsorbed on the wafer surface. Furthermore, even if an attempt was made to carry out electrolysis using HF as a supporting electrolyte, HF could corrode the metal electrode, so that HF could not be used as a supporting electrolyte.
The present invention provides a method for producing electrolytic ion water using an electrolytic ion water producing apparatus having a novel structure, which enables reduction of running cost, pollution of waste water, and improvement of work environment safety.

[0008]

In order to solve the above problems, the present invention performs electrolysis using an electrode solution of pure water or ultrapure water to which HF is added as a supporting electrolyte. . The electrolytic ionized water produced is particularly suitable for cleaning wafers. The HF concentration of the electrolyte solution is 100 to 1
0000 ppm is suitable. As the carbon electrode, a carbon molded body formed by molding crystalline carbon by firing or the like and an amorphous carbon layer on the surface thereof are used in order to reduce loss of carbon pieces. A crystalline carbon electrode such as graphite has many pores, and an uneven surface is formed on the surface. Since the carbon electrode has a large surface area, it is also a desirable material from the viewpoint of enhancing the electrolytic effect. Therefore, after forming the molded body of the electrode, a carbon layer such as an amorphous layer is formed on the surface. Since the carbon layer is deposited even inside the pores on the surface of the molded body, the bonds between the carbon elements are strengthened to make it difficult for the carbon pieces to be lost.
Further, in order to reduce the influence of the lack of carbon pieces from the carbon electrode on the electrolytic ionized water, a filter is introduced. A ceramic filter made of quartz or the like is suitable as the filter. Since carbon particles have a large particle size, it is effective to use a plurality of filters. The first filter enlarges the particle size to remove carbon fragments having a large particle size. further,
The carbon particles are surely removed by using the second filter, the third filter, ...

At least the first filter can be regularly cleaned with pure water or ultrapure water to prolong the life of the filter. However, since HF corrodes the filter, it is advantageous not to place it around the electrodes, but to attach it to the electrolytic ion water supply line that delivers the electrolytic ion water generated from the electrolytic cell. By using a carbon electrode, HF has not been conventionally used for a supporting electrolyte because the electrode is etched by a metal electrode, but in the present invention, the use of a carbon electrode enables an HF supporting electrolyte. The electrolytic ion water generated at the anode can raise the oxidation-reduction potential higher than that of HF water which is usually used for cleaning. It is considered that Cu diffuses in the natural oxide film on the wafer and is directly bonded to Si. However, by increasing the oxidation-reduction potential, Cu that could not be completely removed by the HF water is also removed. Will be possible.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an electrolytic cell of an electrolytic ionized water producing apparatus used in the producing method of the present invention. The electrolytic cell 1 is divided into an anode chamber 2 and a cathode chamber 3, which are separated by an ion exchange membrane 6 arranged at the boundary. A carbon electrode, which is a feature of the present invention, is installed in the electrolytic cell 1. The carbon electrode comprises an anode 4 and a cathode 5, the anode 4 being arranged in the anode chamber 2 and the cathode 5 being arranged in the cathode chamber 3. Both ends of the anode 4 and the cathode 5 are fixed to the upper lid of the electrolytic cell 1. Although not shown, the anode 4 is connected to the positive electrode of the power source, and the cathode 5 is connected to the negative electrode of the power source. Ultrapure water to which a supporting electrolyte has been added or pure water is supplied from the lower portion of the electrolytic cell 1 through electrolyte-added ultrapure water (electrolyte solution) supply lines 8 and 9. A first electrolyte added ultrapure water supply line 8 is connected to the anode chamber 2, and a second electrolyte added ultrapure water (electrolyte solution) supply line 9 is connected to the cathode chamber 3. A DC voltage is applied between the electrodes 4 and 5 to generate electrolyzed ionic water by electrolyzing the ultrapure water added with the supporting electrolyte, that is, the electrolyte solution supplied from the supply lines 8 and 9.

Acid water is produced in the anode chamber 2 with the anode 4, and alkaline water is produced in the cathode chamber 3 with the cathode 5. The anode chamber 2 and the cathode chamber 3 have electrolytic ion water drain lines 10 and 11 (that is, acidic water drain line 10).
And an alkaline water drainage line 11) is formed, from which electrolytic ionized water is discharged. The electrolyte concentration of the electrolyte solution is such that the electrolyte solution on the anode chamber side is HF1000 to 10,000.
About 10 ppm, the electrolyte solution on the cathode chamber side is ammonia 10
It is suitable to make it about 500 ppm. The pH of the electrolyte solution is set to about 8-9. The electrolytic ion water drain lines 10 and 11 are also electrolytic ion water supply lines that supply electrolytic ion water to other devices such as a wafer cleaning device. The electrolytic cell 1 has, for example, 10 × 10 cm to 30 ×.
It is a 30 cm square and has a height of 20 to 50 cm. FIG. 2 is a schematic cross-sectional view of an electrolytic ionized water generator showing the arrangement of filters. As described above, in the electrolytic cell 1, the anode-side electrolyte solution is received in the anode chamber from the anode-side electrolyte solution supply line 8 and electrolyzed there to generate anode ionized water. Anode ionized water generated in the anode chamber is supplied to the outside via the electrolytic ionized water drainage line 10, for example,
It is supplied to a semiconductor manufacturing apparatus such as a wafer cleaning apparatus of the semiconductor manufacturing apparatus. Further, in the electrolytic cell 1, the cathode side electrolyte solution is received from the cathode side electrolyte solution supply line 9 into the cathode chamber where it is electrolyzed to generate cathode ionized water. The cathode ionized water generated in the cathode chamber is supplied to an external wafer cleaning device or the like via the electrolytic ionized water drainage line 11.

Next, for example, the electrolytic ion water drainage line 1
At 0, a plurality of filters 71, 72, 73 for purifying electrolytic ionized water before being supplied to a cleaning device or the like are arranged.
Such a filter is necessary when cathodic ionized water is supplied to other systems. A ceramic filter made of quartz or the like is used as the filter. Since carbon particles have a large particle size, it is effective to use a plurality of filters. The first filter 71 has a large particle size and removes carbon fragments having a large particle size. Further, the carbon particles are surely removed by using the second filter 72, the third filter 73, ... An ultrapure water supply line 74 for supplying pure water or ultrapure water and an ultrapure water drain line 75 for discharging the supplied pure water or ultrapure water are attached to the first filter 71. Then, pure water or ultrapure water is used as the first filter 71 for periodic cleaning. The carbon pieces captured by the first filter 71 can be effectively removed, and the life of the filter can be extended.

FIG. 3 is a perspective view and a partial side view of the electrode (anode). The anode 4 in this embodiment is plate-shaped as shown. The present invention has various possible shapes as other embodiments. In addition to a plate shape, a round bar shape, a polygonal column, or the like can be used. The anode is obtained by molding crystalline carbon such as graphite and firing it with heat of about 1000 ° C. to 1200 ° C. for several hours to several hundred hours. The fired molded body 41 is porous and has irregularities on its surface. The molded body 41 is dipped in an amorphous carbon material and fired to form the carbon layer 42 even in the pores. Since the carbon layer 42 is in close contact with the surface of the molded body 41 along the irregularities, it strengthens the bond between the carbon elements and makes it difficult for the carbon pieces to drop out. In addition to this, as the means for forming the carbon layer 42, a low pressure CVD method, a vacuum vapor deposition method, or the like is used. FIG. 4 is a perspective view of the filter 7 shown in FIG. As a material for the filter 7, for example, there is a ceramic filter obtained by baking and hardening quartz used for a dry filter. The ceramic filter is formed of, for example, three layers of molded bodies 71, 72, 73 having different particle sizes, and impurities can be sufficiently removed.

FIG. 5 is a sectional view of a portion taken along the line AA 'in FIG. As shown in the figure, the electrode composed of the anode 4 and the cathode 5 is composed of a plurality of molded bodies. The carbon fragments that are missing from the electrodes are removed so that the carbon fragments do not enter the electrolytic ion water. Therefore,
Filters 71, 72, 73 made of high-purity ceramic are attached to the electrolytic ion water drainage line 10, and filters 71 ', 72', 73 'are attached to the electrolytic ion water drainage line 11. When electrolyzed ion water is used for cleaning a semiconductor wafer, particles can be suppressed by using a metal-based electrode, but the metal becomes ions and is eluted from the anode. With a carbon electrode alone, the anode should be oxidized (CO
₂ generation) causes the surface to be eroded, resulting in the loss of carbon fragments and the generation of large numbers of particles. In the present invention, the surface of the carbon electrode is covered with a carbon layer of amorphous carbon in order to make it difficult for the carbon electrode itself to be lost, and this serves as an adhesive to strengthen the bond between carbons. In addition, since it is considered that chipping is inevitable as long as a carbon electrode is used, a high-purity filter is installed to collect particles that are generated.
Further, in the above embodiments, the case where there is one electrolysis cell for performing electrolysis has been described, but the present invention is not limited to this case, and as shown in FIG. ″ ・ ・ ・
Can be used in combination.

FIG. 7 is a characteristic diagram for explaining the effect of the present invention. The electrolytic ion water generated at the anode can raise the oxidation-reduction potential higher than that of HF water which is usually used for cleaning. Cu diffuses in the native oxide film on the wafer and Si
Although it is considered that they are directly bonded to Cu, by increasing the redox potential, it becomes possible to remove Cu and the like that could not be completely removed by the HF water. FIG. 7 shows the removal rate of Cu, the vertical axis represents the concentration of metal impurities (atoms / cm ² ), and the horizontal axis represents the pure water or ultrapure water (Ini) before electrolysis (electrolysis). The state, the state of HF water in which HF is dissolved, and the state of pure water or ultrapure water after electrolysis (electrolysis) are shown. Pure water or ultrapure water before electrolysis has a metal impurity concentration of 1 × 10 ¹³ (atoms / cm ² ), whereas pure water or ultrapure water after electrolysis has a metal impurity concentration of 2 × 10 ⁹ ( at
oms / cm ²⁾ to have reduced. The metal impurity concentration of HF water is in the middle of the metal impurity concentration of pure water or ultrapure water before and after electrolysis.

Next, a process of producing electrolytic ion water from ultrapure water will be described with reference to the process diagram of FIG. The supporting electrolyte (2) is added to ultrapure water or pure water (1) to form an electrolyte solution (3). An electrolyte solution of hydrochloric acid (HCl) is supplied to the anode chamber of the electrolytic cell, and an electrolyte solution to which ammonia (NH ₃ ) and, if necessary, hydrochloric acid (HCl) are added is supplied to the cathode chamber. The electrolyte solution is electrolyzed (4) in the electrolytic cell to generate acidic ionized water in the anode chamber and alkaline ionized water in the cathode chamber. The electrolyzed ionized water is sent to a cleaning tank or the like used for manufacturing a semiconductor device and used as cleaning water or the like.

Next, referring to FIG. 9, an electrolytic ionized water producing apparatus having a structure different from that of FIG. 2 will be described. In the apparatus shown in FIGS. 1 and 2, in the electrolytic cell 1, the anode-side electrolyte solution containing HF is received in the anode chamber, where it is electrolyzed to generate anode ion water, and the cathode-side electrolyte solution containing ammonia is stored in the cathode chamber. It was accepted by the company and was electrolyzed here to produce cathodic ionized water. However, in this electrolytic ionized water generator, only the electrolyte solution containing HF is supplied to both the anode chamber 2 and the cathode chamber 3. The ion water that is actually used is the anode ion water, and the cathode ion water is not used for cleaning. The electrolytic ion water drain lines 10 and 11 include a plurality of filters 71 for purifying the electrolytic ion water before being supplied to a cleaning device or the like.
72, 73 and 71 ', 72', 73 'are arranged.

As the filter, a ceramic filter made of quartz or the like is used. Since carbon particles have a large particle size, it is effective to use a plurality of filters. First filter 7
In Nos. 1 and 71 ', the particle size is increased to remove carbon particles having a large particle size. Further, the second filters 72, 72 'and the third filters 73, 73' ...
・ Use to ensure that the carbon fragments are removed.
Ultrapure water supply line 74 for supplying pure water or ultrapure water, intermediate ultrapure water drainage supply line 76, and the supplied pure water or ultrapure water are discharged to first filters 71, 71 '. Attach the ultrapure water drainage line 75. Then, the first filters 71, 71 'are regularly cleaned with pure water or ultrapure water. The carbon fragments captured by the first filters 71, 71 'can be effectively removed and the filter life can be extended.

[0019]

INDUSTRIAL APPLICABILITY As described above, the present invention enables the HF supporting electrolyte by using the carbon electrode. Also,
The electrolytic ionized water generated at the anode can raise the oxidation-reduction potential higher than that of HF water normally used for cleaning, etc., so that it is possible to remove Cu and the like that could not be completely removed by normal HF water. .

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an electrolytic cell used in the electrolytic ionized water production method of the present invention.

FIG. 2 is a schematic sectional view of an electrolytic cell used in the electrolytic ionized water producing method of the present invention.

FIG. 3 is a perspective view and a sectional view of an anode of the present invention.

FIG. 4 is a perspective view of a high-purity filter used in the present invention.

5 is a cross-sectional view of a portion taken along the line AA ′ in FIG.

FIG. 6 is a perspective view of the electrolytic cell of the present invention.

FIG. 7 is a characteristic diagram illustrating effects of the present invention.

FIG. 8 is a process diagram of a method for producing electrolytic ionized water according to the present invention.

FIG. 9 is a schematic sectional view of an electrolytic cell used in the method for producing electrolytic ionized water according to the present invention.

FIG. 10 is a sectional view of a conventional electrolytic cell.

[Explanation of symbols]

1 ... Electrolyzer, 2 ... Anode chamber, 3 ... Cathode chamber, 4 ... Anode, 5 ... Cathode, 6 ...
Ion exchange membrane, 7, 71, 71 ', 72, 72', 7
3, 73 '... High-purity filter, 8, 9 ... Electrolyte-added ultrapure water (electrolyte solution) supply line, 10 ... Acid water drainage line, 11 ... Alkaline water drainage line, 39 ... -Cleaning tank, 40 ... Semiconductor wafer, 41 ... Molded body, 42 ... Carbon layer, 4
5 ... Ultrapure water tank, 48, 43, 49 ... Supporting electrolyte tank, 74, 76 ... Ultrapure water supply line,
75 ... Ultrapure water drainage line.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C02F 1/46 C25B 9/00 C25B 11/12

Claims (6)

(57) [Claims] 1. A step of supplying an electrolytic solution in which HF is added to pure water or ultrapure water as a supporting electrolyte to an electrolytic cell for electrolysis in which an electrode composed of an anode and a cathode is a carbon electrode, and a DC voltage is applied to the electrode. A step of electrolyzing the electrolyte solution by applying to generate electrolytic ionic water , the electrode is formed of a crystalline carbon molded body, on the surface
Is a method for producing electrolytic ionized water, characterized in that an amorphous carbon layer is formed . 2. The HF concentration of the electrolyte solution is 100 p
It is pm-10000ppm, The electrolytic ionized water production method of Claim 1 characterized by the above-mentioned. 3. The electrolytic cell has an electrolytic ion water supply line for supplying the generated electrolytic ion water, and the electrolytic ion water supply line is provided with at least one filter at a predetermined position. Claim 1 or
The method for producing electrolytic ionized water according to claim 2 . 4. The method for producing electrolytic ionized water according to claim 3 , wherein the filter closest to the electrolytic cell is provided with means for cleaning with pure water or ultrapure water. Wherein said filter is electrolytic ion water generating method according to claim 3 or claim 4, characterized in that it consists of a ceramic such as quartz. 6. The method for producing electrolyzed ionized water according to claim 5 , wherein the filter closest to the electrolytic cell has the largest ceramic particle size, and the ceramic further away from the electrolytic cell has a smaller particle size. .