JPS5935167B2 - Capacitor manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a capacitor using at least a tantalum oxynitride film as a dielectric.

This type of tantalum oxynitride film has conventionally been used as shown below (1) to (3).
) was formed as shown. (1) Heat nitriding the tantalum material in nitrogen or an atmosphere containing nitrogen to form a nitride film on the tantalum surface, and then chemically or electrochemically oxidize the nitride film to transform it into an oxynitride film. .

(2) The tantalum material is heated in air or a mixed atmosphere of oxygen and nitrogen to form an oxynitride film on the tantalum surface.

(3) Metal, glass, in nitrogen or an atmosphere containing nitrogen,
A tantalum nitride film is formed by reactive sputtering of tantalum on the surface of a ceramic or the like, and then the nitride film is chemically or electrochemically oxidized to change into an oxynitride film.

However, since the nitride film obtained by the method (1) above is a film with a low degree of nitridation that is mainly composed of tantalum mononitride, it will have a large leakage current when oxidized.
This results in an oxynitride film that has the drawbacks of increasing R loss and decreasing withstand voltage.

In addition, the oxynitride film obtained by the method (2) above has a non-uniform composition and many structural defects, so it is undeniable that the leakage current increases, and as a result, as in (c) above, the CR loss is large and the withstand voltage is low. In addition to having the disadvantage of being low, the loss coefficient (t
anδ) is large. In addition, since the nitride film obtained by the method (3) above is a film with a low degree of nitridation containing tantalum mononitride and tantalum mononitride as the main components, an oxynitride film obtained by oxidizing this nitride film has the same drawbacks as the oxynitride film obtained by the method (1) above. The present invention maintains a wide ohm range or a wide operating voltage range in leakage current/voltage characteristics, which are the characteristics of tantalum oxynitride films, as well as a small tan δ, etc., and reduces CR loss by reducing leakage current. Provided is a method for manufacturing a capacitor that can obtain a dielectric with increased coefficient. The present invention is characterized in that a tantalum material is anodized in a liquid ammonia electrolyte solution to form a tantalum nitride film on the surface of the tantalum, and then nitrided in a nonaqueous electrolyte solution, an aqueous electrolyte solution, or a mixed solution of both. A part of the tantalum material is anodized together with the tantalum film or the tantalum nitride film to obtain a tantalum oxynitride film or a composite film consisting of a tantalum oxynitride layer and a tantalum oxide layer, which serves as a dielectric.

In order to obtain the tantalum nitride film, the tantalum nitride film is prepared in an ammonia solution maintained at -33°C or lower, preferably -80 to -33°C, and in which an electrolyte (described later) that does not contain oxygen atoms is dissolved. , a tantalum material formed in the form of powder sinter, film, etc. is immersed as an anode, and gold, platinum, tantalum,
It is necessary to perform anodization while applying a DC voltage between the counter electrode (cathode) made of graphite, copper, or the like.

The current density at this time is 500 μA-14d, preferably 10 to 300 mA/Cd. However, the electrolytes to be dissolved in the ammonia solution include (1) alkali metal amides such as sodium amide, (2) alkaline earth metal amides such as barium amide, and (3) alkali metals such as potassium monomethylamide and lithium diethylamide. monoorganamides and diorganamides, (4
) monoorganamides and diorganamides of alkaline earth metals such as strontium mono-n-propylamide and calcium di-n-butylamide; (5) tetrahydroborates of alkali metals and alkaline earth metals such as potassium tetrahydroborate and strontium tetrahydroborate; , (6) Tetraorganoborates of alkali metals and alkaline earth metals such as lithium tetra n-butylborate, barium tetraethylborate, (7
) Tetrahydroborates and tetraorganoborates of 0 to quaternary aluminum such as tetraethylammonium tetrahydroborate and ammonium tetraphenylborate, (8) sodium tetrafluoroborate,
Tetrafluoroborates of alkali metals or alkaline earth metals or 0- to quaternary ammonium such as barium tetrafluoroborate, trimethylammonium tetrafluoroborate, (9) lithium tetrahydroaluminate, calcium tetraethyl aluminate, di-n-butylammonium tetra Alkali metal or alkaline earth metal such as iodoaluminate, tetrahydroaluminate or tetraorganoaluminate of quaternary or lower ammonium (including ammonium ion), lithium iodide, magnesium iodide, Iodides of alkali metals or alkaline earth metals or quaternary or lower ammonium such as triisobutylammonium iodide, a1) rubidium thiocyanate, strontium thiocyanate,
There are alkali metals or alkaline earth metals such as tetraphenylammonium thiocyanate, or tanned products of quaternary or lower γ ammonium, and at least one of these is selected and used.

In addition, during anode formation, water, oxygen,
Organic compounds containing oxygen such as carbon dioxide, methyl alcohol, and ether, metal alcoholades, metal hydroxides and oxides, salts of oxygen acids (salts of acids containing oxygen), chlorine, hydrogen chloride, chlorides, and chlorine. Care must be taken to ensure that substances that inhibit the production and growth of the tantalum nitride film, such as acid salts, are not included.Also, the produced tantalum nitride film contains hydrogen in the form of -NH or -NH2. When the current density applied during anodization is increased, the hydrogen content in the film decreases, and at the same time, the degree of nitridation of the film tends to increase.

Generally, the tantalum nitride film obtained by the above-mentioned nitriding method is mostly composed of amorphous tantalum nitride, and the average degree of nitridation is in the range of 1 to 2. The degree of nitridation is larger than that of tantalum nitride films obtained by reactive sputtering.

For the anodization of tantalum after nitriding, the anodization method conventionally used for valve metals such as tantalum, niobium, titanium, and aluminum is applied. Therefore, an aqueous electrolyte solution, a non-aqueous electrolyte solution, or a mixed solution of water and a non-aqueous electrolyte is used. If non-aqueous milky liquid is used here, alcohols, ketones, ethers, lactones, lactams, acid amides, sulfoxides, sulfones, etc., which are oxygen ion sources, have oxygen atoms in their molecules? Of course, a solute of a salt of an oxyacid containing a medium or an oxygen atom may be used.
Naturally, a fused salt of an oxyacid salt can also be used as the electrolyte. However, during this anodic oxidation, is it necessary to prevent the tantalum oxynitride film from dissolving? It is necessary to maintain the pH of the liquid between 5.0 and 8.5, preferably between 6.0 and 8.0.

Furthermore, if the current density is high, the nitrogen concentration in the oxynitride film tends to decrease, so it is desirable to regulate the current density to 50 m/4 d or less. The thus obtained tantalum oxynitride film can be used as a dielectric to which a metal or conductor counter electrode is directly bonded, or a metal or conductor counter electrode can be attached to the semiconductor through a Pn junction, or alternatively, a metal or conductor counter electrode can be attached to it as a dielectric. Alternatively, a capacitor is formed by attaching the opposite electrode of a conductor via a solid electrolyte.

Examples will be explained below.

Example 1 Length 7.0wm 1 width 7.0r! High-purity tantalum foil with a Tml thickness of 10 μm was annealed at 1850°C and 1×10-5 t0rr for 15 minutes, and then the surface was polished using a chemical polishing solution consisting of nitric acid, sulfuric acid, and hydrofluoric acid, washed with water, and dried. did.

(Pre-treatment) This tantalum foil was immersed in an ammonia solution of 0.1N sodium amide as an anode, and heated to -80℃ for 5 minutes.
Constant current chemical formation was performed by applying a direct current with a current density of 00 ttA/Cd between gold (Au) counter electrodes.

When the voltage increase became slow and stagnant, the power was turned off, and the sample was cleaned with liquid ammonia and dried. Next, it was immersed in a 0.1N nitric acid aqueous solution as an anode, and constant current chemical formation was performed by applying a direct current between it and a gold (Au) cathode under the chemical formation conditions of 20° C. and 500 μm for 4 days.

When the voltage reached 50V, the chemical formation conditions were changed to a constant voltage of 50V and aging was performed for 3 hours, followed by washing with water and drying. The tantalum foil 1 on which the tantalum oxynitride film 3 was formed as shown in FIG.
A nichrome layer 4 was formed on the surface of the tantalum oxynitride film 3 by depositing a mixed vapor of nickel and chromium evaporated at 1400°C, and then under 1×10 −6 t0rr.
Aluminum evaporated at 1000° C. was deposited on the nichrome layer 4 to form an aluminum layer 5.

This aluminum layer 5 was used as a cathode, and the tantalum metal part 1 was used as an anode, leads 6 and 1 were attached to each, with a part of the leads protruding, and the whole was covered with an insulator 8, thereby completing a capacitor. Note that 2 is a tantalum oxide layer. Reference example 1
After pre-treating tantalum foil having the same shape as in Example 1,
4 at 1200℃ in a nitrogen atmosphere of 1X10-1t0rr
A tantalum nitride film was formed by reacting for 5 minutes.

After slowly cooling, it was immersed in a 0.1N nitric acid aqueous solution and anodized in the same manner as in Example 1, and then finished into a capacitor of the same shape.

The performance of each capacitor obtained by the methods of Example 1 and Reference Example 1 will be compared and studied based on actual measurement results.

FIG. 2 shows the change in leakage current with respect to applied voltage.

As is clear from the figure, the leakage current in the DC voltage range of 5 to 30 V was reduced to 1/50 to 1/80 in the capacitor according to Example 1 compared to the capacitor according to Reference Example 1.
Regarding the width of the ohm region of leakage current, the capacitor according to Example 1 was 6.5 to 44 V, while the capacitor according to Reference Example 1 was 8 to 26 V. It has an ohmic range 2.1 times that of a capacitor. Furthermore, the rate of change in leakage current with respect to applied voltage in the ohmic region is 2.0X10-120hn-1·m-2 in Example 1, and 5.3X10-110hm-1●Cm-2 in Reference Example 1.
/27. This means that not only the leakage current is an extremely small value, but also the amount of change in response to voltage fluctuations is extremely small. Figure 3 shows C for AC frequency.
It shows the change in R loss, 3~1X104Hz
It is shown that the CR loss of the capacitor according to Example 1 is 1/40 to 1/45 of the CR loss according to Reference Example 1 in the AC frequency region of .

The table below shows the results of measuring the capacitance of the capacitors according to Example 1 and Reference Example 1 for each AC frequency.

As is clear from the above table, the capacitance of the capacitor according to Example 1 was 1.2 to 1.3 times that of the capacitor according to Reference Example 1 in the AC frequency range of 10 to 104 Hz.

Example 2 Tantalum was deposited vertically on a silicon substrate in an argon atmosphere of 5×10 −5 tons under the following conditions: substrate temperature 450° C., anode voltage −100 V, cathode voltage −4000, and cathode current density 400 μ.

0r1r1n1 sideways 7.0 fight division.

This was immersed in an ammonia solution of 0.001N ammonium iodide as an anode, and a direct current with a current density of 4 m/4 d was applied between it and a platinum (Pt) counter electrode at -35°C to perform constant current chemical formation. . When the voltage increase became slow and stagnant, the power was turned off, and the tantalum nitride film formed on the tantalum surface was washed with liquid ammonia and dried. then 0.0
It was immersed in a dimethyl sulfoxide solution of 3N tetramethylammonium tetrafluoroborate, the tantalum nitride layer was used as an anode, and a direct current with a current density of 200 μm/8 Zml was applied between it and a platinum (Pt) counter electrode at 50°C. Conducted electric current conversion.

When the voltage reached 100V, the chemical formation was stopped and aging was performed for 2 hours under a constant voltage of 100V, and then washed with water and dried. Next, it was placed in a nitrogen atmosphere furnace at 500° C. and 760 t0rr and annealed for 20 minutes.

After that, it was immersed in the above electrolyte solution again and heated to 100°C at 20°C.
The sample was aged for 3 hours by applying a direct current of . After aging, rinse with water and heat in a nitrogen atmosphere at 200°C and 760t0rr for 5 minutes.
A 0% by weight aqueous solution of manganese nitrate was sprayed onto the surface of the oxynitride film in the form of a mist and thermally decomposed to form a β-type manganese dioxide layer on the surface of the oxynitride film.

Thereafter, it was transferred to a vapor deposition apparatus and an aluminum layer was formed on the manganese dioxide layer in the same manner as in Example 1 to form the capacitor shown in FIG. 4. In FIG. 4, 1 is a tantalum metal layer, 2 is a tantalum oxide layer, 3 is a tantalum oxynitride layer, 5 is an aluminum layer, 6 and 1 are leads, 8 is an insulator,
9 is a β-type manganese dioxide layer. Reference example 2 On a silicon substrate in a nitrogen atmosphere of 5X104t0rr, substrate temperature 400°C, anode voltage 50, cathode voltage -5000
V1 cathode current density 200μv? tantalum vertically under the conditions of
．． A tantalum nitride film was formed by reactive sputtering on a 7.0 rm horizontal section, and then immersed in a dimethyl sulfoxide solution of 0.03N tetramethylammonium tetrafluoroborate.

Thereafter, a capacitor was formed in the same manner as in Example 2. The performance of each capacitor manufactured by the methods of Example 2 and Reference Example 2 will be compared and studied based on actual measurement results.

FIG. 5 shows the change in leakage current with respect to applied voltage.

As is clear from the figure, the leakage current in the DC voltage range of 5 to 73 V was able to be reduced by 3/10 to 1/10 in the capacitor according to Example 2 compared to the capacitor according to Reference Example 2.
Regarding the width of the ohm range of leakage current, the capacitor according to Example 2 was 13 to 81 V, while it was 6 to 43 V in Reference Example 2. It has an ohmic area 1.8 times that of the conventional one. Furthermore, the ratio of change in leakage current to applied voltage in the ohmic region is 6 in Example 2.
．． 3X10-130hm-m-2, and 5 of Reference Example 2
, 0x10-120hm-1 .m-2. As described above, the method of Example 2 produces a capacitor with extremely low leakage current and very little change in leakage current with respect to voltage fluctuations, as well as a wide voltage range that changes according to Ohm's law, compared to Reference Example 2. Can be manufactured. Figure 6 shows the change in CR loss with respect to AC frequency,
It is shown that the CR loss of the capacitor according to Example 2 is 1/20 to 1/27 of the CR loss of the capacitor according to Reference Example 2 in the frequency range of 3 to 1×10 4 Hz.

Note that the same effects as in Examples 1 and 2 are obtained when linear or powdered sintered tantalum materials are used, and the results are particularly remarkable in terms of leakage current and CR loss compared to the conventional technology. was gotten.

Also, when an electrolytic capacitor was manufactured, the above-mentioned good characteristics were observed. However, a capacitor using only a tantalum oxynitride film as a dielectric has a drawback that leakage current and CR loss are larger than other capacitors, and the capacitance is smaller than a capacitor using a tantalum oxide film as a dielectric.

Regarding this point, as shown in Examples 1 and 2, after forming the tantalum nitride layer (not by anodizing only the tantalum nitride layer, but by anodizing a part of the tantalum material together with the tantalum nitride layer). Capacity can be increased by forming a composite film consisting of a tantalum oxynitride layer and a tantalum oxide layer and forming a capacitor using this composite film as a dielectric.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a normal polar capacitor formed according to Example 1, FIG. 2 is a diagram showing changes in leakage current with respect to applied voltage in each capacitor according to Example 1 and Reference Example 1, and FIG. A diagram showing changes in CR loss with respect to frequency in each of the above capacitors, FIG. 4 is a longitudinal cross-sectional view of a junction capacitor formed according to Example 2, and FIG. 5 is an applied voltage in each capacitor according to Example 2 and Reference Example 2. FIG. 6 is a diagram showing changes in CR loss with respect to frequency in each of the above capacitors. 1...Tantalum metal layer, 2...Tantalum oxide layer, 3...Tantalum oxynitride layer, 4...
... Nichrome alloy layer, 5 ... Aluminum metal layer, 6 ... Cathode lead, r ... Anode lead, 8 ... Insulator, 9.・・・・・・β-type manganese dioxide layer.

Claims (1)

[Claims] 1. A tantalum material is anodized in a liquid ammonia electrolyte solution to form a tantalum nitride film on the tantalum surface, and then the tantalum nitride film or the tantalum nitride film is anodized in a non-aqueous electrolyte solution, an aqueous electrolyte solution, or a mixed solution of both. A method for manufacturing a capacitor, comprising the step of anodizing a portion of the tantalum material to form a tantalum oxynitride film or a composite film consisting of a tantalum oxynitride layer and a tantalum oxide layer, which serves as a dielectric.