JPS5848402A - Method of forming electrode for oxide semiconductor element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for forming ohmic electrodes on oxide semiconductor devices, and relates to a method for forming electrodes with excellent adhesion, voltage resistance, and heat resistance. - Conventionally, methods for attaching ohmic electrodes to oxide semiconductor devices include attaching In-Ga alloy, attaching Ml by electroless plating, and attaching Ou and Mu1tznll by vacuum evaporation or metal spraying. Method,
Six methods have been used to bake the oh-mink Ag paste. However, although In-Ga alloy and gold can provide good ohmic contact, the melting point of the alloy is low and there are problems with heat resistance.1. It was unsuitable for practical use. In addition, the M1 electrode formed by electroless plating requires heat treatment at several hundred degrees Celsius in order to obtain ohmic contact, and since it is a wet method, M1 electrodes may be formed by microcracks in the oxide semiconductor element.
In addition to penetrating the material and lowering its voltage resistance, residual ions that adhered to and penetrated into the substrate due to chemical processing were a factor in deteriorating life characteristics. Furthermore, when performing N1 electroless plating, careful management of the processing solution and plating solution was required, and strict pollution treatment was required when disposing of the processing solution, plating solution, and cleaning water. . In addition, electrodes made of O, Al, Zn, etc. formed by vacuum evaporation or metal spraying have a practical problem because of their weak adhesion to oxide semiconductor elements. Furthermore, electrodes formed by baking an ohmink Ag paste have a practical problem because migration of mug occurs during use.

The present invention solves the above-mentioned conventional drawbacks and provides a method for forming an ohmic □ electrode that has excellent ohmic properties, strong adhesion, and excellent voltage resistance and heat resistance. It is something.

That is, the gist of the present invention is to produce Ou, Al, Ni, Zn, and ann in a plasma discharge of a reduced pressure inert gas by the ion blating method.

A method for forming an electrode of an oxide semiconductor device, characterized in that Or or an alloy thereof is evaporated and the metal vapor is attached to the surface of the oxide semiconductor device.

In particular, when the present invention is applied to a barium titanate semiconductor, which is a positive characteristic ceramic semiconductor, the withstand voltage discharge can be greatly improved, and the effect is remarkable.

Next, the present invention will be explained in detail.

FIGS. 1(a) and 1(b) show an example of an ion blating apparatus used in the present invention. Figure 1(a) is a basic schematic diagram of a DC bipolar discharge gripping ion brating device.
Figure (b) is a basic schematic diagram of a high frequency ion brating device. In FIG. 1, 1 is a vacuum container, 2 is an evacuation pipe, 3 is an inert gas supply pipe 14, which is an evaporation source made of an electrode material, 5 is a heating power source for an evaporation heater, and 6 is an oxidation object, which is an object to be processed. 6a is a holding stand for the object to be processed, 7 is a DC power source, 8 is a high frequency power source, 9 is a matching box, and 1'0 is a high frequency antenna.

The basic operating procedure is to first evacuate the inside of the vacuum container 1 to a high vacuum of about io Torr through the vacuum exhaust pipe 2, then introduce an inert gas such as Ar through the inert gas supply pipe 6, and then supply a predetermined amount of gas. Adjust to the pressure. Next, in the case of DC bipolar discharge type ion brating, plasma discharge is generated by applying a high voltage to the DC power source 7, while in the case of high frequency ion brating, the high frequency antenna 10 is generated by the high frequency power source 8. A high frequency is applied through the tube to generate plasma discharge. In the case of DC bipolar discharge type ion brating, the DC power supply 7 is a plastic
This is a high-voltage power supply for accelerating positive ions in the plasma at the same time as generating pragmas. The main purpose is to accelerate the positive ions that exist inside, and each has a different purpose.

Next, the heating power source 5 heats the evaporation source 4 to evaporate the electrode material. In addition to this resistance heating method, heating methods include an electron beam heating method, a high frequency heating method, and the like, and it is possible to use any of them. The particles evaporated from the evaporation source are ionized in the plasma, and the particles are ionized in the plasma.
It has an energy of V, which is the oxide semiconductor element 6
It collides with the surface, loses its energy, and adheres to the surface to form a film.

It is said that the adhesion of the formed film to the element surface depends on the energy of the ions, and the adhesion of species with higher energy becomes stronger.

Generally, in the case of vacuum evaporation, the energy of particles is i o
”V or less, the sputtering temperature is about 1O-eV,
In the case of ion blating, it depends on the conditions, but as mentioned above, it is said that there are several tens to several @Y". Therefore, when using the ion blating method, the The adhesion force to the element surface becomes very strong.Also, when using the ion blating method, the evaporated particles have high energy as mentioned above, so the formed film is dense, and therefore the electrode When used as
The density of the current flowing through the electrode becomes uniform, increasing stability. ◇Also, since the ion blating method is a dry method, residual ions from chemical treatment will adhere, unlike in the case of wet methods such as electroless plating. There is no danger and there is no penetration of electrode material through micro-cracks.
It is stable as an electrode with no loss of voltage resistance. Furthermore, as in the case of N1 made by electroless plating, there is no need for heat treatment to make it ohmic1, and since it is non-polluting, there is no need for pollution treatment equipment, and the process of attaching the electrodes is extremely simple. Can be simplified. When performing ion plating, regarding the pressure of the inert gas, as the gas pressure increases, the mean free path of the evaporated particles becomes shorter, and therefore more energy is lost before the particles adhere to the oxide semiconductor element. Adhesive force is reduced,
Further, since it becomes difficult to maintain plasma discharge if the gas pressure becomes extremely low, it is desirable that the pressure of the non-2-5 active gas is 10 to 10 T6rr.

The device shown in Figures 1(a) and (b) is a basic ion blating device, and in order to increase the ionization efficiency, multiple auxiliary electrodes are provided between the evaporation source and the substrate. , there is no harm in applying a direct current or high-frequency electric field to this. It is also possible to attach a heater to heat the oxide semiconductor element, and
It is also possible to use a barrel or the like in place of the holding stand that holds the oxide semiconductor element.

Au, Pt, Ag, Ou', Mul,
Ni, Zn.

It is also possible to form a two-layer electrode structure by forming a film of 9n, Or, etc. By having a two-layer electrode structure, it is possible to reduce the in-plane resistance of the electrode and allow a large current to flow, while also improving the tactility and solderability. is possible. FIG. 2 shows a schematic diagram of a two-layer electrode structure.

In FIG. 2, 11 is an oxide semiconductor element, 12 is an ohmic electrode, and 18 is a second layer electrode.

The second layer electrode can be formed by screen printing, metal spraying, electroplating, electroless plating 1, vacuum deposition, ion blating, or the like.

The reason why various methods can be used to form the second layer electrode is because a dense and strongly adhesive ohmic electrode is already formed on the surface of the oxide semiconductor element by the ion blating method. Regarding the second layer electrode film, even if wet plating is used, the adverse effects of residual ions can be ignored, and the adhesion between the ohmic electrode and the second layer electrode film is due to metal-to-metal adhesion. Therefore, the difference in thermal expansion coefficient is small, so a large adhesion force is not required.

As described above, Ou, silica, and Ni are formed on an oxide semiconductor element by the ion blating method.

Films made of Zn, 8n, Or, or their alloys exhibit good ohmic contact as electrodes, and have strong adhesion to oxide semiconductor elements, so they do not cause peeling of ornaments or large currents during hot water temperature cycle tests. There is no peeling damage to the electrode that occurs when ion is applied, and the properties are sufficiently satisfied as an ohmic electrode for an oxide semiconductor device.
Since the electrode formation method is also dramatically simplified, its industrial value is extremely high.

EXAMPLES Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. 4 Example 1 A barium titanate semiconductor having a diameter of 20 cm and a thickness of 2 was used as an oxide semiconductor, and each metal and alloy were deposited by the ion booting method. First, a drop of titanate (lium-based semiconductor) is held in a container, and
After evacuation to a high vacuum of 4 Torr, the gas pressure was adjusted to the pressure shown in Table 1 using Ar as an inert gas. In the case of a terrible DC bipolar discharge, the I
Apply KV. Generated plasma discharge. On the other hand, in the case of the high frequency method, a high frequency of 300 W was applied from a high frequency power source to generate plasma discharge. In the case of the high frequency method, a DC voltage of 600 V was applied as the ion acceleration DC voltage, and then various metals or alloys listed in Table 1 were evaporated from the source using the electron beam heating method. Oxide semiconductor device - It was attached to both sides to form electrodes. In order to confirm the ohmic properties of each sample, the DC voltage was varied between 0.1' and 2 V and the voltage-current characteristics were measured. As a result, good ohmic properties were confirmed for all samples. Table 1 also shows the resistance values R at 25° C. of the obtained samples. Sample numbers 1 to 14 show examples of the present invention. Sample No. 15 is a comparative example in which an electrode is formed by rubbing a n-Ga alloy onto the surface of a barium titanate semiconductor element, and sample No. 16 is an N1 electrode formed by electroless plating on a barium titanate semiconductor element. A comparative example will be shown in which a film was formed and heat treated at 400°C.

As is clear from Table 1, the electrodes according to the present invention and the third embodiment have very high adhesion strength and are excellent as ohmic electrodes for oxide semiconductor devices. Mug paste was applied to the sample of this example as a second layer electrode by screen printing method, and baked at 60'0''C to form a two-layer electrode structure.An AC voltage was applied at 1-minute intervals to instantaneously A current was passed through the electrode 200,000 times.As a result, there was no damage to the electrodes, and there was almost no change in resistance value, indicating extremely stable characteristics.

Table 1 11F: High frequency ion, embrating DO:, direct fi
When the two-electrode discharge type was turned on and the firing was repeated 10 times, there was no separation or damage to the electrode. J-based semiconductor device I is the original product! Characteristics when electrodes are formed by electroless plating of -G and N1 when +6 electric current is formed on i, -G and N1 electrodes have higher voltage resistance and reliability compared to the comparative example. It can be seen that it is very good in terms of both sides. Recently, using positive characteristic electrodes,
Although only a barium titanate-based semiconductor that conducts electroless → energized N , i%, N~It can be similarly used for oxide semiconductors such as voltage nonlinear resistors such as the Noah 8203 series. In the case of a voltage nonlinear resistor, if the material itself has nonlinearity, it is desirable that the electrode be an ohmic resistor6, and an electrode with excellent pulse resistance is desired. Conventionally, as ohmic electrodes for voltage nonlinear resistors, electrodes made by baking ohmic Ag, spraying ZN, etc. have been used;
In the case of g, migration becomes a problem, and in the case of thermal spraying, peeling becomes a problem because the adhesion force is only about 197 cd, and damage to the electrode becomes a problem when a high surge pulse is applied. When one electrode according to the method of the present invention is used as a voltage nonlinear resistor, there is no need to worry about migration.Also, since the adhesive force is strong and the electrode is dense, it can withstand high surge pulses. Its industrial value is extremely high.

4. Brief explanation of the drawings Figure (a) is a basic schematic diagram of a DC two-electrode discharge type ion brating device, and Figure 1 (b) is a high-frequency one.
A basic schematic diagram of the on-plating device is shown.

FIG. 2 shows a schematic diagram of a device with a two-layer electrode structure. Figure 3 shows the voltage-current characteristics due to alternating current, which is the static characteristic of a thermistor of a barium titanate-based semiconductor element. 11. (A) shows the characteristics when the electrode is formed by the present invention, and the square shows the characteristics when the electrode is formed by electroless plating of N1.

1... Vacuum container 2... Vacuum exhaust pipe 6.
...Inert gas supply pipe 4...Evaporation source made of electrode material 5...Heating power supply for evaporation heater 6
...Oxide semiconductor element as the object to be processed 7...DC power source 8...High frequency power source 9...Matching box 10...High frequency antenna 11.
...Oxide semiconductor cord 12...Ohmic electrode
13...Second layer mtm diagram 2

Claims (2)

[Claims] (1) Ou, Mu1. Ni. A method for forming an electrode for an oxide semiconductor device, which comprises vaporizing Zn, Sn, Or, or an alloy thereof, and depositing the metal vapor on the surface of the oxide semiconductor device. (2) The method according to claim 1, wherein the oxide semiconductor element is made of a barium titanate-based semiconductor.