JPS5935168B2 - Manufacturing method of tantalum oxide film capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing tantalum oxide film capacitors.

Capacitors using tantalum oxide films as dielectrics are well known.

It is also known that when a tantalum oxide film suitably doped with phosphorus is used as a dielectric, the characteristics are theoretically better than when a tantalum oxide film is simply used. By the way, as a means of doping phosphorus into a tantalum oxide film, conventionally, a tantalum layer that does not contain phosphorus is anodized in an electrolyte solution using phosphorus oxygen acid and its salt as an electrolyte, or in a molten salt containing these electrolytes. This is done by applying the following.

However, the manufacturing method involving the above-mentioned doping means has the following problems.

That is, the tantalum oxide film obtained by the conventional method is a so-called composite film in which the inner side of the film is a tantalum oxide layer that does not contain phosphorus, and the row side is a tantalum oxide layer that contains phosphorus. For this reason, the properties of the tantalum oxide layer containing an appropriate amount of phosphorus, such as high dielectric constant, low loss coefficient, low leakage current not only at low voltage but also at high voltage, high breakdown voltage, etc. There are some problems that prevent it from fully utilizing its superior advantages. That is, a tantalum oxide layer that does not contain phosphorus has electrical properties such as a relatively low dielectric constant, a relatively large loss coefficient, a large leakage current at high voltage, and a low breakdown voltage. On the other hand, a tantalum oxide layer containing a high concentration of phosphorus has electrical properties such as a very low dielectric constant, a very large loss coefficient, and a very large leakage current at low and high voltages. Therefore, the properties of the above two layers act to cancel out the characteristics caused by the inclusion of phosphorus, and the effect of the inclusion of phosphorus is not exhibited as expected, making it impossible to obtain a capacitor with superior characteristics. Nakatsuta. The present invention was made in view of these circumstances, and its purpose is to easily and uniformly contain phosphorus throughout the entire tantalum oxide layer provided as a dielectric, thereby maximizing the phosphorus-containing effect. An object of the present invention is to provide a method for manufacturing a tantalum oxide film capacitor that can produce a large amount of capacitors that can exhibit high performance. The inventors conducted various experimental studies to achieve the above object and found the following fact. That is, if tantalum is reactively sputtered onto the surface of a substrate in a gas atmosphere containing at least one of phosphorus, phosphine, and diphosphine, a phosphorus-containing tantalum film (
Consists of partially phosphoroused tantalum. ) was formed, and it was found that if this phosphorous-containing tantalum film was anodized in an electrolyte solution or solid electrolyte molten salt, a phosphorous-containing tantalum film in which phosphorus was uniformly distributed could be obtained. The basic conditions for such a manufacturing method are listed below.

[A] Sputtering conditions (1) Substrate gold, copper, silicon, tantalum, iron-nickel-chromium alloy,
So-called metals including alloys such as brass, so-called glasses such as quartz glass and borosilicate glass, or so-called sapphire, ruby, aluminum phosphide, gallium arsenide,
Compound single crystals such as cadmium sulfide or ceramics such as silicon carbide, aluminum nitride, and magnesium oxide can be used.

(2) Atmosphere A phosphorus-containing gas consisting of at least one gas selected from phosphorus, phosphine, and diphosphine has a partial pressure of 10-0
~10-3t0rr1 preferably 10-6 to 10-4t
An atmosphere containing 0rr is used.

It is very effective to include a noble gas such as argon, helium, neon, xenon, etc. in an amount of 10-8 to 10-1 t0rr, preferably 10-5 to 10-2 t0rr, in this atmosphere to obtain a preferable phosphorus-containing tantalum film. Also,
The atmosphere may contain one or more gases such as oxygen, nitrogen, water vapor, ammonia, nitrogen monoxide, nitrous oxide, and sulfur dioxide at a partial pressure of 10-0 to 10-6 t0rr. When diluting a phosphorus-containing gas with a noble gas, it is necessary to adjust the partial pressure of the phosphorus-containing gas to about 1/400 to 1/70 of the partial pressure of the noble gas in order to obtain a good phosphorus-containing tantalum film. . (3) Cathode voltage It is preferable to apply a voltage in the range of -7000 to -2000V, particularly in the range of -6000 to -3000V.

(4) Anode voltage It is preferable to apply a voltage in the range of -500 to 300V, particularly in the range of -200 to 200V.

(5) Cathode current density is affected by the type of substrate, surface condition of the substrate, etc., but is it 0.01 to 50 nV? range, especially 0.1
It is preferable to select the distance between 1.0 m and 4 d.

(6) Substrate temperature Although it is affected by the type of substrate and the surface condition of the substrate, it is generally 200 to 1000℃, especially 300 to 60℃.
Preferably, the temperature is maintained within the range of 0°C.

(7) Annealing at 400-600℃ after sputtering
Annealing the sputtered film for 0 to 200 minutes can improve the electronic and electrochemical properties of the final dielectric film.

[B] Anodizing treatment conditions (1) Contains one or more polar liquids such as chemical liquid water, ethylene glycol, dimethylformamide, adiponitrile, dimethyl sulfoxide, γ-butyrolactone, N-methyl-2-pinodone, and glacial acetic acid. Solvents include inorganic acids such as sulfuric acid, nitric acid, and phosphoric acid; organic acids such as acetic acid, citric acid, picric acid, and benzenesulfonic acid; inorganic bases such as lithium hydroxide and ammonium hydroxide; ethylenediamine, guanidine,
Organic bases such as pyridine, inorganic salts such as sodium sulfate, potassium fluoride, ammonium pentaborate, calcium hydrogen carbonate, barium chromate, aluminum nitrate, cobalt hydrogen sulfate, ammonium acetate, disodium tartrate, φ-toluenesulfone one or more minerals selected from organic salts such as potassium acid, tetraethylene ammonium benzoate, trimethylammonium cyanurate, aluminum sulfosalicylate, barium hexaethyl phosphate, dipiperidine biscatecholate zincate, etc. In the resulting electrolyte solution or in a molten salt solution such as ammonium formate, lithium hydrogen sulfate, sodium nitrate, or tetraethylammonium benzoate, a phosphorus-containing tantalum film is formed along with a counter electrode made of platinum, tantalum, iron, graphite, etc. The phosphorus-containing tantalum film is used as an anode and the counter electrode is used as a cathode to perform chemical conversion.

(2) Chemical current density 100 μA to 500 mA/Cdl preferably 500 μA
It is desirable to perform chemical formation with a constant current in the range of ~10m4Ti.

Note that constant current chemical formation is performed with the initial current density set within the above range. A method may be adopted in which the current density is attenuated over time. (3) Temperature of electrolyte liquid and co-fused salt -100~300℃, especially 50~120℃
A range of 0.degree. C. is preferred.

(4) Aging treatment time The temperature of the electrolyte is 50 to 120
℃, the aging voltage V is calculated as V - formation voltage x (0.7
~1.0) for 30 to 400 minutes, preferably 100 minutes
Requires aging treatment for ~200 minutes.

The phosphorous tantalum film obtained in this way has zero
．． It contains 4-1.5% by weight of phosphorus in a uniform distribution. This tantalum oxide film was heated at 200 to 350℃ for 10
In an oxygen atmosphere of 0 to 800 t0rr or 350 to 55
1 in an air atmosphere of 0°C and 100 to 800 t0rr
The electronic properties can be further improved by annealing for 0 to 100 minutes. Therefore, aluminum, copper,
Metal counter electrodes such as chromium, nickel, tin, zinc, nichrome, brass, and nickel silver, or manganese oxide, nickel sesquioxide, tin monoxide, cadmium sulfide, aluminum phosphide, tantalum mononitride, gallium arsenide, graphite, silicon, etc. A semiconducting counter electrode is adhesively bonded by vapor deposition, sputtering, electrolytic plating, chemical plating, or other chemical reaction to form a capacitor.

Note that when attaching the counter electrode, it is effective to increase the operating voltage of the capacitor if the semiconductor is selected and attached so that a Pn junction is formed at the interface between the tantalum oxide film and the semiconductor counter electrode. Furthermore, a nonpolar capacitor can be formed by depositing a metal such as tantalum on the tantalum oxide film and using this as a counter electrode. Alternatively, a counter electrode coated with a conductive paint in which metal powder or semiconductor powder is dispersed together with a resin can also be used. Next, more specific examples and comparative examples will be described.

Example 1 Aluminoborosilicate glass was used as a substrate. After leaving 0.5 d of the surface of the slide of this substrate and covering the other parts with resist, it was placed in a sputtering device, and the inside of the device was replaced with an argon atmosphere. A trace amount of white phosphorus was injected to maintain the partial pressure of phosphorus gas at 1×10 −6 t0rr and the partial pressure of argon gas at 1×10 −3 t0rr.

Next, tantalum was reactively sputtered under the sputtering conditions of cathode voltage - 6000 V, anode voltage - 200 V, cathode current density 0.1 m, 4 d, 1 substrate temperature of 300°C to form a phosphorus-containing tantalum film with a thickness of 3000 V on the substrate surface. Ta. Subsequently, the atmosphere was changed to an argon atmosphere of 1×10 4 t0rr, and the substrate temperature was raised to 400° C. and held for 200 minutes to anneal the phosphorus-containing tantalum film. Next, the substrate was slowly cooled, taken out from the apparatus, and immersed in an aqueous sodium hydroxide solution at room temperature to melt and remove the resist. Subsequently, the substrate was immersed in a 1×10 −2 M citric acid aqueous solution at 50° C., and direct current was applied at a constant current density of 500 μVcd with the tantalum film as the anode and the counter electrode (platinum) as the cathode.
Anodization was performed until the potential difference between the two electrodes reached 100V. After the potential difference reaches 100V, increase the potential difference by 1 to 100V.
The tantalum oxide film was aged for 0.00 minutes.
The thickness of the tantalum oxide layer was 1950 mm. Next, the substrate was transferred to a vapor deposition apparatus, and the nichrome alloy, which was preheated to 200°C in an argon atmosphere of 5×10-4 tons and evaporated at 1350°C, was vapor-deposited on the tantalum oxide film to form a 2000-layer thick nichrome alloy layer. This nichrome alloy layer was used as a cathode, and the tantalum metal layer under the tantalum oxide film was used as an anode, and lead wires were attached to each to form a capacitor. Comparative Example 1 Using the same substrate as that used in Example 1 described above, tantalum was sputtered under the same sputtering conditions as Example 1 in an argon atmosphere of 1 x 10-3 t0rr without phosphorus gas to produce phosphorus-free tantalum. After forming the film, a tantalum oxide film was formed on the surface of the tantalum film by immersing it in 3X10-3M phosphoric acid at 50°C under the same chemical formation conditions and the same aging conditions as in Example 1, and then a nichrome electrode was formed in the same manner. I attached it and made it into a capacitor.

As a result of analyzing the two types of capacitors obtained in Example 1 and Comparative Example 1 in this way, it was found that each of the dielectric layers contained 0.4% by weight of phosphorus.

Further, the electrical characteristics of each were as shown in the attached table. Example 2 A silicon single crystal wafer measuring 0.7 cm long, 0.7 cm wide, and 0.5 gourd thick was placed as a substrate in a sputtering device, and after degassing, it was made into a phosphine atmosphere of 1 x 10-4 t0rr, and then a cathode voltage of -3000 was applied. , anode voltage 200V1
Cathode current density 0.5mA/Cril substrate temperature 600℃
A phosphorus-containing tantalum film was formed on the silicon surface by reactive sputtering under the following sputtering conditions, and then the substrate temperature was maintained at 600°C for 20
The tantalum film was annealed for minutes.

Next, the parts of the substrate not covered with the tantalum film were insulated with a resist, and then immersed in a 1X10-1M5 ammonium borate solution in ethylene glycol and heated to 90°C. ) as a cathode and apply direct current at a constant current density of 10 m/4 d.
Anodization was performed until the potential difference between the two electrodes reached 60V. After the potential difference reaches 60V, reduce the potential difference to 50V,
The tantalum oxide film was aged by holding this state for 200 minutes. The thickness of the formed tantalum oxide film is 100
There were 0 people. Next, the substrate was immersed in 0.2M perchloric acid containing 0.02M leadous perchlorate dissolved at 30°C, and a DC current of 50°C was applied using the tantalum metal as the anode and the counter electrode (gold) as the cathode.
An initial current density of 4 J was applied, and the current was passed for 100 minutes to form an α-type lead dioxide layer with a thickness of 2,000 J on the tantalum oxide layer. Next, the resist was removed and a colloidal solution of graphite was sprayed onto the lead dioxide layer.
C. for 20 minutes to form a 5000 λ thick graphite layer, which was used as a cathode, the substrate was used as an anode, lead wires were attached to each, and then an insulating resin was coated to complete the capacitor. Comparative Example 2 Using the same substrate as that used in Example 2 above,
A 2000λ thick tantalum film containing no phosphorus was formed by sputtering under the same sputtering conditions in a neon atmosphere of 1×10−3 t0rr, and then immersed in an ethylene glycol solution of 2M ammonium dihydrogen cyclotripolyphosphate at 90°C. Anodization and aging were performed under the same conditions as in Example 2 to form a 1000 layer tantalum oxide layer.

Next, lead dioxide was electrodeposited and graphite was baked in the same manner to sequentially form a lead dioxide layer and a graphite layer on the tantalum oxide layer, and then a capacitor was completed. As a result of analyzing the two types of capacitors obtained in Example 2 and Comparative Example 2 in this way, it was found that each of the dielectric layers contained 1.5% by weight of phosphorus.

Further, the electrical characteristics of each were as shown in the attached table. Example 8 Using silicon carbide ceramic as a substrate, its surface was
．． 5 cr! After leaving i and covering the other parts with resist,
The phosphorus gas is charged into a sputtering device, and the partial pressure of phosphorus gas in the device is set to 5.
×10-6t0rr5 phosphine gas partial pressure 1.5×10
It was filled with a mixed gas atmosphere consisting of -6 t0rr1 nitrogen partial pressure 2 0-4 t0rr1 nitrogen monoxide gas partial pressure 4 x 10-7 TOrr.

Next, cathode voltage - 5000V1 anode voltage 0, cathode current density 1.0m~? , Tantalum was reactively sputtered under sputtering conditions with a substrate temperature of 450°C to form a 3500°C coating on the substrate surface.
After forming a tantalum film containing phosphorus, nitrogen, oxygen, and hydrogen to a human thickness, the substrate was slowly cooled, taken out of the apparatus, and the resist was removed at room temperature. Next, the substrate is immersed in molten ammonium formate salt, the tantalum film is used as an anode, and the counter electrode (platinum) is used as a cathode. Direct current is applied at a constant current density of 2 mA/Cd, and the potential difference between the two electrodes increases to 120 V. Anodization was applied up to the point. After the potential difference reached 120 V, the potential difference was reduced to 80 V, and then aging was performed by holding at a constant voltage for 120 minutes in molten salt at 120°C. Next, after washing with water and drying, the substrate was transferred to an air atmosphere of 550° C. and 800 t0rr and annealed for 30 minutes. The thickness of the tantalum oxide layer thus formed was 2500λ. Next, after slowly cooling to room temperature, the substrate was transferred to a steam apparatus and heated to 100°C in a phosphorus atmosphere of 5 x 10-6 tons, and then the aluminum was heated to 700°C to evaporate, and the vapor was removed. It was deposited by condensation on top of the tantalum oxide layer. This aluminum layer was used as a cathode, and the tantalum layer below the tantalum oxide layer was used as an anode, and lead wires were attached to complete the capacitor. Comparative Example 3 Using the same substrate as that used in Example 3 above,
Nitrogen partial pressure 2×10-4t0rr1 Nitrogen monoxide partial pressure 4×1
After reactively sputtering tantalum under the same sputtering conditions as in Example 3 in a mixed gas atmosphere of 0-7 TOrrl to form a tantalum film containing nitrogen and oxygen with a thickness of 3,500 mm on the surface of the substrate, this substrate was 4. at 120°C.
Ammonium dihydrogen phosphate at a concentration of 5X10-1M?
The sample was immersed in molten ammonium formate, which was present, and anodized under the same formation conditions as in Example 3, and then annealed under the same annealing conditions to form a tantalum oxide layer with a thickness of 2500 mm.

Thereafter, a capacitor was completed by vapor depositing aluminum on the tantalum oxide layer in the same manner as above. As a result of analyzing the two types of capacitors obtained in Example 3 and Comparative Example 3 in this way, it was found that the dielectric layer, that is, the tantalum oxide layer, each contained 0.8% by weight of phosphorus.

Further, each electrical characteristic was as shown in the attached table. Example
4 A sapphire single crystal wafer was used as a substrate, and the surface of this substrate except for 0.5 cd was covered with a resist.

The substrate is placed in a sputtering device, and the atmosphere is set to a diphosphine partial pressure of 4×10-5t0rr1, and a neon partial pressure of 1×10-2t.
After ventilating to 0rr, tantalum was sputtered under sputtering conditions with a cathode voltage of -4000 V, an anode voltage of 100 V, and a cathode current density of 0.7 mA/Cdl and a substrate temperature of 500°C to form a phosphorus-containing tantalum layer on the substrate surface with a thickness of 2500 mm. Ta. Next, while keeping the substrate temperature at 500℃, 1X
After annealing the tantalum layer in a neon atmosphere of 10-2 Torr, it was immersed in a 2 x 10-3 M sodium sulfate aqueous solution at 60°C, and the tantalum layer was used as an anode and a counter electrode (SUS
27 stainless steel) was used as a cathode, a DC current of 30°C was applied between the two electrodes, and constant voltage chemical conversion was performed for 150 minutes to form a tantalum oxide layer with a thickness of 550mm. Next, the substrate was transferred to a sputtering device and heated in a neon atmosphere of 500°C and 1 x 10-2 t0rr for 30 minutes.
Tantalum was sputtered under the sputtering conditions of a V1 anode voltage of -50 and a cathode current density of 3 mVcrA to form a tantalum layer with a thickness of 2000 mm on the tantalum oxide layer. Then 500℃
, 20 in a neon atmosphere of 1 x 10-2 t0rr
After annealing for 0 minutes, the resist was removed, and lead wires were attached to the internal tantalum layer and the surface tantalum layer to create a non-polar capacitor. Comparative Example 4 The same substrate as used in Example 4 was used, and after being coated with resist in the same manner, tantalum was sputtered onto the surface of the substrate in a neon atmosphere of 1 x 10-2 t0rr under the same sputtering conditions as Example 4. After forming a tantalum layer with a thickness of 2,500 people, it was immersed in an aqueous solution containing sodium sulfate at a concentration of 2 x 10-3M and sodium phosphate (trisodium phosphate) at the same concentration at 60°C. A non-polar capacitor was similarly made by sputtering tantalum onto a tantalum oxide layer under the same sputtering conditions.

In this way, the 2 obtained in Example 4 and Comparative Example 4
When we investigated the electrical characteristics of various types of capacitors, we obtained the results shown in the following table.

As is clear from the table above, the capacitors manufactured by the method of the present invention (Examples 1, 2, 3, 4) are different from the capacitors manufactured by the conventional method (Comparative Examples 1, 2, 3, 4).
The capacity is 1.24 to 1.45 times that of
It has been significantly improved by 6 to 1/3 times, CR loss by 1/10 to 1/5 times, and equivalent resistance by 1/12 to 1/3 times.

The reason for this is that in the method of the present invention, tantalum is sputtered onto the substrate surface in a gas atmosphere containing phosphorus, so phosphorus can be uniformly distributed in the tantalum film formed on the substrate surface. This is because the phosphorus-containing effect due to this uniform distribution is effectively exhibited. Note that the amount of phosphorus contained in the dielectric is preferably in the range of 0.4 to 1.5% by weight, and if it is outside this range, the phosphorus-containing effect will not be effectively exhibited. 1 and 2 show two examples of cross sections of capacitors made by the method of the present invention, 1 is a nichrome alloy or aluminum layer (cathode), 2 is a phosphorus-containing tantalum layer (dielectric layer), 3 is a phosphorus-containing tantalum metal layer (anode), 4 is a silicon metal layer, 5 is
6 indicates a graphite layer (cathode), and 6 indicates a lead dioxide layer (semiconductor layer).

As described in detail above, according to the present invention, it is possible to provide a method for manufacturing a tantalum oxide film capacitor that can dope the tantalum layer with phosphorus so as to maximize the phosphorus-containing effect and is easy to manufacture.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of different capacitors made by the method of the invention, respectively. 2...Phosphate-containing tantalum layer.

Claims (1)

[Claims] 1. A phosphorus-containing tantalum layer is formed by reactively sputtering tantalum on the substrate surface in a gas atmosphere containing at least one gas selected from phosphorus, phosphine, and diphosphine, and the phosphorus-containing tantalum layer is subjected to an oxidation treatment. A method for manufacturing a tantalum oxide film capacitor, characterized in that a dielectric layer is formed from the obtained tantalum oxide layer.