JPH0265112A - Manufacture of semiconductor capacitor and dopant solution used therefor - Google Patents

Abstract

PURPOSE:To obtain capacitor bodies having large electrostatic capacity and large insulating resistance and to make the products uniform, by jetting only a needed amount of dopant solution uniformly with an ink jet printer on a semiconductor surface in a way like dripping. CONSTITUTION:When a pressure-molded substance 1 of BaTiO3, SrTiO3 high- permittivity porcelain material is reduction-burned, it becomes to have the property of semiconductors. On the surface of a semiconductor obtained by doing like this, only a needed amount of dopant solution is uniformly jetted in a state of dripping with an ink jet printer forming an applied layer 2 of the dopant solution. The ink jet printer jets independent small drops one by one arranging, and the size of the small drops is uniform, too. Accordingly, the variance of the thickness of the layer 2 becomes small, and high-precision applying becomes possible. After that, the whole is heat-treated. Through this heat treatment, metallic components contained in the dopant solution are diffused in the grain boundary of the semiconductor particles 3, and dielectrics 4 are formed around the particles 3. And, the dielectrics 4 accumulate static electricity and form a semiconductor capacitor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention involves reducing and firing a ceramic/Ix material to obtain a semiconductor, adding a metal component to this semiconductor, and oxidizing and firing it. The present invention relates to a method for manufacturing a grain boundary insulated semiconductor capacitor in which a dielectric is formed at the grain boundaries of each particle of a semiconductor, and a dopant liquid used therein.

[Conventional technology]

Conventionally, when manufacturing this kind of grain boundary insulation type semiconductor capacitor, ceramic material powder is first formed into a molded body by pressure molding, extrusion molding, doctor blade molding, etc., and the molded body is reduced and fired. By doing this, a semiconductor (capacitor body) made of ceramic material is obtained. Then, a dopant dispersion liquid (a solid containing a metal component to form a dielectric material at the grain boundaries of semiconductor particles) is applied to the surface of this semiconductor by a screen printing method, a dropper dropping method, a spray coating method, a submerged immersion method, etc. oxide dispersion) is attached. After that, the moisture is volatilized by drying, and the whole is oxidized and fired. By this oxidation firing, the metal component of the dopant dispersion liquid adhering to the surface of the semiconductor element can be diffused into the grain boundaries of the semiconductor element, thereby making the grain boundary layer an insulator. Therefore, a semiconductor capacitor having an apparently large dielectric constant as a whole is manufactured.

(Problems to be Solved by the Invention) However, in any of the conventional manufacturing methods described above, the amount of the dopant dispersion applied to the surface of the semiconductor of the ceramic material is non-uniform. Therefore, the amount of dopant that diffuses to the grain boundaries inside the semiconductor tends to be non-uniform. This non-uniformity of the adhered dopant dispersion liquid causes variations in the electrical properties of the dielectric formed on the circumferential surface of each semiconductor particle, which has the drawback of causing variations in the capacitance accumulated in this dielectric. Furthermore, if the amount of dopant Nu is too large, the insulating layer at the grain boundaries becomes too thick, resulting in a decrease in the overall dielectric constant.

This is clear from the fact that the capacitance C of this type of grain boundary insulated semiconductor capacitor is expressed by C=εX (S/T). However, ε is the dielectric constant, S is the area of the dielectric, and T is the thickness of the dielectric. On the other hand, if the amount of dopant 1 is too small, the overall insulation resistance decreases, resulting in a loss of function as a capacitor.

In short, in the production of this type of semiconductor capacitor, it is extremely important to add just the right amount of dopant to the semiconductor element. All of these methods tend to have non-uniformity in the amount of dopant, which has the disadvantage of sacrificing electrical characteristics.

In addition, in the screen printing method, the dopant dispersion is applied in the form of a paste, but making it into a paste requires a lot of impurities such as organic binders, is expensive in terms of equipment, and in principle does not change over time. This is difficult to avoid, and as a result, it becomes difficult to adjust the amount of dopant applied, resulting in a drawback that the thickness of the dielectric material tends to vary. In addition, dopant dispersions used for sub-washing, spray coating, beneficial insect immersion, etc. other than conventional screen-printing methods tend to cause the gold mud component as a dopant to precipitate in liquids such as water or alcohol over time. However, as a result, there is a drawback that the amount of dopant varies.

[Means to solve the problem]

The present invention improves and eliminates the above-mentioned conventional problems by uniformly applying a dopant liquid to the surface of a ceramic semiconductor, and then applying a heat treatment process to uniformly coat the circumferential surface of each semiconductor particle. A method for manufacturing a semiconductor capacitor that forms a thick dielectric material, has a large capacitance, and has little variation in capacitance between products, and has a method for producing a semiconductor capacitor that has a small amount of unnecessary components such as an organic binder and does not cause phenomena such as precipitation. The aim is to provide a dopant solution free of oxidation.

Therefore, the manufacturing method adopted by the present invention in order to solve the above problem is to obtain a semiconductor by reducing and firing a molded body of BaTiOa, SrTiO3-based high rust electromagnetic material, and then applying a dopant liquid to the surface of the semiconductor. The dopant liquid is sprayed uniformly in the required amount using an inkjet printer in a drip state to adhere the dopant liquid to the semiconductor surface, and then the whole is heat-treated to diffuse the dopant liquid at the grain boundaries of the semiconductor particles to form a dielectric. In this way, a grain boundary insulated capacitor is obtained.

Further, the dopant liquid employed in the present invention is a liquid in which an ionizable salt of a metal is dissolved in a soluble medium.

[For production]

A semiconductor can be produced by reducing and firing a molded body of a ceramic material such as BaT103 or SrTiO3. Then, when the dopant liquid is applied to the surface of the semiconductor in the form of droplets using an inkjet printer and is injected onto the semiconductor, individual droplets are arranged and deposited one by one. The droplets are uniform in size. In addition, inkjet printers can electrically control the ejection density and ejection direction of small droplets with high precision, and are therefore excellent in making the amount of dopant aqueous solution applied to the semiconductor surface uniform.

Therefore, by heat-treating it, it is possible to control the dielectric layer formed on the circumferential surface of each semiconductor particle by grain boundary diffusion into the inside of the semiconductor with extremely high precision, resulting in a large capacitance and insulation resistance. It is possible to obtain a large semiconductor capacitor element body.

This also reduces variations in capacitance between products (and makes products more uniform).

On the other hand, the dopant solution is made by dissolving ionizable metal salts in a soluble medium, and since it is ionized, it does not precipitate over time.

〔Example〕

The manufacturing method of the present invention will be described below based on embodiments shown in the drawings.

1 to 3 show manufacturing steps according to an embodiment of the present invention. First, as shown in FIG. 1, barium carbonate, titanium oxide, etc.
2) +1/2DyzO3(0,2) +SiO
The ceramic materials mixed at a ratio of 2 (1, 6) are pulverized, and a press molded body 1 of a predetermined shape is obtained using a mold. The pressurization method may be dry press molding (or wet extrusion molding may be used. Various other ceramic materials are also known. Next, the press molded body 1 is fired for 2 hours at a temperature of about 1450° C. As a result, the ceramic material of the press-molded body 1 becomes oxygen-deficient and has semiconductor properties.

After obtaining a semiconductor in this way, a dopant liquid used in manufacturing a grain boundary insulated capacitor is supplied into an ink tank of an on-demand inkjet printer. The dopant liquid is a liquid obtained by dissolving metal ionizable salts in a soluble medium to form a dielectric on the peripheral surface of semiconductor particles, and examples of its components are as follows. That is, <Component example 1> (NO3) 3 Cu (NO3) z Ethanolconc-HNOa Component example 2> BiCl3...2.5g CuC1z --2,5g ・6Hz O...・2.5g ・3■20 ・・・・・・2.5g ・・・・・・90ml ・・・・・・10ml 11zO--90ml <Component example 3> Bi (N0a) 3 ・5I-120・・・・・・
2.5gCu (N0a) 2 ・3 )-120-
--2.5g ethanol ・・・90m
111NOa...-10 ml This component example 3 was mixed in a beaker and melted at room temperature, and then an experiment was conducted over a long period to determine the occurrence of precipitation. As a result, no precipitation occurred and the mixture was stable. This dopant solution had a pH≦2.

Component example 4> Bi (N0a) 3 ・5H20...6.
68gCu (N0a)z ・31-120 ・・
・－・−3,32g citric acid ・・・・・・
・15g11NOa ・"-10m
1 ethanol...70ml
This Component Example 4 was mixed in a beaker and left at room temperature for a day and night, and then aqueous ammonia was added to carry out a neutralization reaction until the pH reached about 7. At this time, the ammonia water is 2
It took just over 0m1. In the case of Component Example 4, no precipitation was observed even after about one month, and the solution was stable.

Next, a dopant solution prepared by dissolving the ionizable salts of metals shown in component examples 1 to 4 above in a soluble medium is injected onto the surface of the semiconductor in a drip form from a jet nozzle, as shown in FIG. As shown, a coating layer 2 of dopant liquid is formed. Inkjet printers eject individual droplets in an array, and the droplets are uniform in size. Therefore, there is little variation in the thickness of the coating layer 2 of the dopant liquid adhered to the semiconductor surface, and uniform coating with high precision is possible.

Incidentally, the amount of the dopant liquid to be applied is so small that approximately 1 g of the metal component (in terms of Bi203/CuO) is applied per 0.2 g of the semiconductor particles (capacitor body). In such a small amount of application,
Even a slight variation in the amount of coating can greatly affect the performance of the final product, so extremely strict control of the amount of coating is required. For reference, Table 1 below shows the results of an experiment on coating variations using a conventional dopant dispersion using the inkjet printer coating method according to the present invention and the conventional dropper dropping method. A comparative example of the components of the conventional dopant dispersion liquid used in the experiment is as follows. That is, <Component Comparison Example 1 (Conventional case)> Bi2Q3--1g CuO...1g Ethanol...100a+1 As is clear from this Table 1, the conventional dropper dropping method, Both the spray method and the immersion method have large variations in the amount of coating applied. In the method according to the present invention, the variation is about 1/4 compared to the most excellent conventional method, the immersion method.
Compared to the conventional dropper dropping method, which has a large variation in the amount, the variation is less than 1/7, and can be said to be an extremely excellent coating method.

The dopant in the coating layer 2 thus formed is diffused into the semiconductor ceramic material by heat treatment.
It comes to adhere uniformly to the circumferential surface of each semiconductor particle. After that, the whole is fired in the air at a temperature of 900° C. for 2 hours. As a result of this heat treatment, the metal components Bi and Cu contained in the dopant solutions such as component examples 1 to 4 are diffused into the grain boundaries of the semiconductor particles, and as shown in FIG.
A dielectric 4 is formed around the . This dielectric 4 accumulates capacitance and forms a so-called grain boundary insulation type semiconductor capacitor.

As mentioned above, in such semiconductor capacitors, the dopant liquid is a liquid in which ionizable salts of metals are dissolved in its soluble medium, and phenomena such as precipitation do not occur, so the dopant liquid itself causes variations in the dopant 1. There is no such thing.

Furthermore, the formation of the coating layer 2 of the dopant liquid can be performed extremely accurately and uniformly using an inkjet printer.These two factors make it possible to obtain a large capacitance as a final product function. A uniform capacitance with little variation can be obtained.

In addition, the following Table 2 shows the above-mentioned ingredient example 3 (dopane).
A case where a semiconductor capacitor with a diameter of 8 mm and a thickness of 0.7+u was actually manufactured using the method of the present invention described above by changing only the coating amount, and a dropper using a dopant liquid of component example 3> The electrical characteristics were measured and compared with the case where a semiconductor capacitor with a diameter of 8 mm and a thickness of 0.7 mm was actually manufactured using the dripping method.

(The following margins continue on the next page) Table 2 It is clear from the above Table 2 that the semiconductor capacitors manufactured by the method of the present invention and the semiconductor capacitors manufactured by the conventional dropper dropping method have different electrical characteristics. The semiconductor capacitor according to the present invention is also superior to the conventional method in terms of variations in dielectric constant, variations in dielectric m loss, and variations in insulation resistance.

In addition, Table 3 below shows that Component Examples 3 and 4 of the dopant liquid according to the present invention and Component Comparative Example 1, which is a conventional dopant liquid, were applied by the dropper dropping method and the diameter was Semiconductor capacitors of 8 ml and 0.7 mm in thickness were manufactured and their electrical characteristics were compared.

(The following is a blank space, continued on the next page) Table 3 What is clear from this Table 3 is the component example 3 according to the present invention.
When the dopant liquids No. 4 and 4 are applied, there is no significant difference in electrical characteristics even if the p■ is different. Moreover, when Component Comparative Example 1, which is a conventional dopant dispersion liquid, is applied, the resistance value becomes too low and the function as a semiconductor capacitor is lost.

By the way, the present invention is not limited to the embodiments described above, and for example, the type of ceramic material and the type of dopant liquid for producing the capacitor body can be changed as appropriate. Furthermore, various types of in-jet printers are applicable.

(Effects of the Invention) As explained above, in the manufacturing method of the present invention, in principle, the addition of dopant can be controlled by computer in units of Im, so for example, when applying aooo drops, 1/3
This means that control can be performed at a ratio of 0.0000 = 0.000033, making it possible to control more precisely by several orders of magnitude than was possible with conventional methods, and its industrial value is enormous. In addition, the nozzle of an inkjet printer is small and consumes little power during coating, making it extremely flexible and convenient in terms of equipment. Furthermore, since the required amount of dopant is applied in the form of droplets, there is no need to apply the dopant to anything other than the target object, and there is no need for liquid recovery equipment or anti-scattering equipment, making it easier to apply than conventional application methods. This is extremely advantageous in terms of cost.

On the other hand, the dopant liquid according to the present invention is an ionizable salt of gold mud, and when applied to the surface of a semiconductor and diffused inside by heat treatment, the dopant liquid according to the present invention has a higher diffusion rate than a conventional dispersion liquid in which solid particles are dispersed. is extremely easy. In addition, since the dopant liquid is completely dissolved in the ionic state, there are no problems such as clogging in the equipment due to precipitation that occurs with conventional dispersion liquids, and there is little variation in the amount of dopant added, making it easier to manage. Extremely advantageous. Furthermore, if the solution is ionized and the solution itself is highly corrosive, its p
l+ can be changed to neutral, and even in that case, the electrical characteristics will not be affected.

[Brief explanation of the drawing]

The drawings are all related to embodiments of the present invention, and the first
The figure is a vertical cross-sectional view showing a press-molded body of ceramic material.
The figure is a longitudinal cross-sectional view of the pressure-molded body on which a coating layer of a dopant aqueous solution is formed, and FIG. 3 is a partially enlarged cross-sectional view of the semiconductor capacitor. 1... Pressure-molded body 2... Dopant liquid coating layer 3... Semiconductor particles 4... Dielectric patent applicant
Toshihiko Uchida, Patent Attorney, Inax Co., Ltd.

Claims (2)

[Claims] 1. A semiconductor is obtained by reducing and firing a molded body of BaTiO_3, SrTiO_3-based high dielectric ceramic material, and the dopant liquid is dripped onto the surface of the semiconductor using an inkjet printer and sprayed uniformly in the required amount, and the dopant liquid is applied to the semiconductor. A semiconductor capacitor characterized in that the dopant is deposited on the surface and then heat-treated as a whole to diffuse the dopant into the grain boundaries of the semiconductor particles to form a dielectric, thereby obtaining a grain boundary insulated capacitor. Production method. 2. A dopant liquid used in the production of a semiconductor capacitor, characterized in that an ionizable salt of a metal is dissolved in a soluble medium.