JPS6224940B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a compound semiconductor device, and more particularly to a method for manufacturing a compound semiconductor device by improving an electrode to an n-type compound semiconductor such as n-type gallium phosphide (GaP).

Generally, devices using compound semiconductors include microwave elements such as light emitting diodes, semiconductor lasers, and Gunn diodes. Among these, GaP single crystal, which is being used most recently,
Alternatively, there are light emitting diodes using GaAsP single crystals, which are used for displays in automobiles, industrial measuring instruments, watches, etc.

By the way, a single crystal alone cannot perform any effective function; an electrode film must be formed on a certain surface of the single crystal, and energy must be applied to the single crystal through the electrode before it can operate as a compound semiconductor device.

For example, in the case of a GaP light emitting diode, an n-type layer is epitaxially grown on an n-type GaP single crystal substrate, followed by a p-type layer to form a p-n junction, and the p-type layer surface and the back surface (n-type surface) of the substrate are , it is customary to form an electrode film on each electrode film and apply a voltage to the electrode film to cause light to be emitted at the pn junction surface.

By the way, the material of the electrode film mentioned above has the following limitations. That is, ohmic contact with the semiconductor surface,
These include bonding properties, chemical resistance, heat resistance, microprocessability, mass productivity, and reliability. and
For the electrode film of a GaP light emitting diode, a film material that almost satisfies these conditions is used for the n-side electrode film.
Si-Au alloy film containing 2% by weight (2wt%) of Si and 98% by weight (98wt%) of Au (hereinafter referred to as Si (2%)-Au (98%) alloy film for convenience of explanation), p side A Be(1%)-Au(99%) alloy film is known as an electrode film. However, the formation of these films in a mass production process involves many problems, which actually results in a decrease in yield, and cannot be said to be an excellent film. The main reason for this is the non-uniformity of ohmic contact,
The cause of this problem is the variation in alloy composition ratio that occurs during the formation of an alloy film by vacuum evaporation.
This is especially noticeable in the n-side electrode film, but this is due to the Si and
This is unavoidable in vapor deposition methods due to the difference in the evaporation temperature of Au. In addition to the combination of Si and Au, a Ge (12%)-Au (88%) film is said to be effective for GaAs substrates, but heat treatment above 450°C deforms the film and makes it smaller. It has the disadvantage of forming lumps, and to improve this, it is necessary to
It has been reported that heat treatment can be performed by laminating a Ni film or the like. This is detailed in Special Publication No. 42-24852. However, during mass production, the complexity of film formation and the difficulty of microfabrication become a problem, causing an increase in costs.

After forming the alloy film, the step of heat treatment in an inert gas is absolutely necessary in order to bring the film into ohmic contact with the compound semiconductor surface. The heat treatment temperature varies depending on the combination of the compound semiconductor material and the film material, but is around 450 to 550°C for the electrode film using Au as the base material. When heat treatment is performed at this temperature, interdiffusion occurs at the interface between the semiconductor and the electrode film, which should result in ohmic contact, but as mentioned above, the electrode film deforms into small lumps, which prevents ohmic contact. There are many.

By the way, among the above electrode films, the Ge-Au alloy film is
Since the deposition temperatures of Ge and Au are almost the same, they can be formed more easily and stably in vacuum deposition than the combination of Si and Au.

Therefore, the present inventors carried out experiments to determine whether it was possible to obtain ohmic contact with a Ge-Au alloy electrode film on a compound semiconductor, particularly an n-type compound semiconductor, with good yield without the need for a metal film such as a Ni film. It was found that by selecting appropriate weight percentages (wt%) of Au and Au, good ohmic contact could be obtained without the need for a metal film such as a Ni film.

That is, the present invention was made based on the above-mentioned experimental facts.
-The weight percent of Ge to Au in the Au alloy is at the above concentration, and the gas flow rate or vacuum level is 1×10 ^-5 Torr to the extent that gas turbulence does not occur in an inert atmosphere.
The present invention provides a method for manufacturing a compound semiconductor device that enables the formation of an ohmic electrode film with good yield by performing the following heat treatment in a vacuum.

Next, an embodiment in which the present invention is applied to a GaP light emitting diode will be described in detail with reference to the drawings. First, FIG. 1 is a cross-sectional view schematically showing the structure of a GaP light emitting diode.

The GaP light emitting diode shown in FIG. 1 is manufactured as follows. That is, an n-type GaP layer 12 is formed on an n-type GaP crystal 11 by liquid phase epitaxial growth or the like to obtain an n-type GaP substrate 11 .
11 by liquid phase epitaxial growth etc.
A p-type GaP layer 14 is formed to form an n-junction 13 to obtain a GaP light emitting diode body 15 . Then, on the p-type GaP layer 14, a Zn--Au alloy layer 14a and an Au
The layer 14b is formed by vacuum evaporation, and the layer 14b is formed on an n-type GaP substrate.
Ga (0.5%)-Au (99.5%) alloy layer 11a in 11
is formed by vacuum evaporation. After that, put it in a heating furnace and bring it to a temperature of 500°C and apply Ar gas at 3ml/minute per minute.
cm ² for 10 minutes to obtain the ohmic contact between the metal and the semiconductor described above. In this way, a good electrode film can be obtained, and a GaP light emitting diode with high luminous efficiency and high yield can be manufactured.

Note that in this GaP light emitting diode, p-type
If Zn and O are placed in the GaP layer 14, red light will be emitted.
If nitrogen N is placed in the type GaP layer 12, green light emission can be obtained.

The experimental facts conducted by the present inventors will be explained below. First, in Fig. 2, a Ge-Au alloy film with a different weight percentage of Ge to Au is formed on an n-type GaP substrate 11, and this is placed in a heating furnace at a temperature of 500°C and Ar gas is injected at 3 ml per minute. ² is a curve diagram showing the relationship between the weight percent of Ge and the contact resistance value when heat treated by flowing at a rate of /cm 2 for 10 minutes. FIG. As is clear from this figure 2, Ge relative to Au at room temperature
Au at the eutectic temperature from the solid solubility limit concentration (0.07wt%) of
It can be seen that when the concentration of Ge is within the solid solubility limit (1.2 wt%), the contact resistance value is 7×10 ^-5 Ω or less and good ohmic contact is achieved. For example, Ge
(0.5%) - Au (9.95%) alloy film at 3 times per minute
When the contact resistance value was measured when the heat treatment temperature was changed at an Ar gas flow rate of ml/cm ² , it was found that the contact resistance value was as shown in FIG. 3. As is clear from FIG. 3, if heat treatment is performed at a temperature of 475° C. or higher, the contact resistance value is 7×10 ⁻⁵ Ω or less and good ohmic contact can be obtained. However, if the heat treatment temperature is set to 600°C or higher, for example 700°C, ohmic contact with a small contact resistance value can be obtained, but the element body deteriorates and the light emitting efficiency of the light emitting diode is reduced.

Also, Ge (0.5%), which is the Ohmic contact mentioned above.
Au (99.5%) alloy film at 100ml/ ^cm2 per minute.
When we measured the contact value when the heat treatment temperature was changed in the Ar gas flow rate, we found that the contact resistance value was small around 490℃ to 500℃, and the ohmic contact was good.
When the temperature was below 475°C or above 510°C, the contact resistance value became large. The film heat-treated at temperatures above 510°C was deformed into small lumps.

As is clear from the above explanation, n-type
To obtain good ohmic contact with n-type semiconductors such as GaP crystals, the weight percent of Ge to Au in the Ge-Au alloy must be adjusted from the solid solubility limit of Ge at room temperature to the solid solubility limit concentration of Ge at the eutectic temperature. The gas atmosphere during the heat treatment was set at 475°C to 475°C at a gas flow rate (10 ml/cm ² or less per minute) that was inert to the Au-Ge alloy film and did not cause gas turbulence.
It is heat treated at a temperature of 600℃. This relationship is shown in FIG. In FIG. 4, the dotted line area is the area where ohmic contact is obtained, and the hatched area within the dotted line area is the area where the best ohmic contact is obtained.

Therefore, we will speculate on the reason why the Ge-Au alloy film is deformed into small lumps and does not form ohmic contact due to the weight percentage and manufacturing conditions of the Ge-Au alloy film mentioned above. First, it is thought that the conditions under which a Ge-Au alloy film deforms into small lumps depend only on heat treatment for films with 1.2% Ge% or more, and depend on the gas flow rate during heat treatment for films with 1.2% Ge or less.

For example, looking at the alloy phase diagram of a Ge-Au alloy film,
At 1.2% Ge or more, it becomes a eutectic structure at 356℃. and
In a Ge-Au film of 1.2 Ge% or more on a GaP crystal, interdiffusion of Au and Ge occurs due to the eutectic reaction during heat treatment.
It is thought that this occurs at a faster rate than the diffusion to the area, resulting in localized small lumps. In addition, the cause of dependence on the gas flow rate in a film with 1.2 Ge% or less is thought to be high temperature due to an increase in the flow rate or turbulent flow of the gas. The former is not the main factor, as it has been measured to only increase the temperature by 20 to 30 degrees Celsius at most. Regarding the latter, we conducted experiments by placing various obstacles around the substrate to create a state of turbulent flow, and it was found that the film surface deformed into small lumps at the locations where turbulent flow occurred. did. Therefore, even if the film is 1.2% Ge or less, the interdiffusion of Au and Ge during heating will result in a soft film that looks like it has melted, and if turbulence occurs on the surface, the film will deform and form into small lumps during cooling. It seems like it will solidify.

Furthermore, the % of Ge in contact with Omics is 0.07 to 1.2
I found that it is in the range of %, but this is also Ge
- According to the alloy phase diagram of the Au alloy film, 1.2% is the maximum solid solubility limit at the eutectic temperature, 0.07% is the maximum solid solubility limit at room temperature, and after heat treatment, 100% is 0.07% with a small amount of Ge mixed in.
It is a solid solution of Ge and does not have a eutectic structure.
It seems that 100% Ge without this eutectic structure works effectively because the mixed state becomes ohmic contact.

Based on the above experimental results and inferences, by limiting the amount of Ge and the flow rate of inert gas during heat treatment,
It has become possible to form an electrode film using a single layer of Ge-Au alloy film. As a result, the conventional process of laminating films such as Ni is eliminated, special vapor deposition equipment is not required, and microfabrication is facilitated, making it possible to dramatically improve the efficiency of the film format and mass productivity. Also, conventional
The film formation method is easy compared to Au-Si film.
The mass production method is also extremely superior.

Furthermore, the higher the luminous efficiency of a light emitting diode, the brighter the display can be obtained, and the lower the driving energy. Luminous efficiency is determined by the characteristics of the pn junction, but if the facing surface of the electrode film closest to the luminescent center is black, light absorption occurs there, reducing the overall luminous efficiency. mentioned above
The AuSi film is blackened by Si, and the AuGe film does not turn black but maintains its golden color. For this reason, it is more desirable to use an AuGe film than AuSi for light emitting diodes.

In addition, in the explanation of the above embodiment, a light emitting diode using a GaP crystal was explained, but a light emitting diode using a GaAs crystal or a GeAsP crystal instead of a GaP crystal, a microwave element using a GaAs crystal, a GaAs crystal, etc. can also be used. It can also be used for semiconductor lasers.

Furthermore, in the explanation of the above embodiment, the gas atmosphere is Ar.
However, the same is true even in an N ₂ gas atmosphere, and Ne
Or it may be He, and the degree of vacuum is 1×
It may be in a vacuum of 10 Torr or less.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining a method for manufacturing a GaP light emitting diode, which is an embodiment of the method of the present invention.
FIG. 2 is for explaining an embodiment of the method of the present invention.
FIG. 3 is a diagram showing the relationship between the weight percentage of Ge relative to Au and the contact resistance value. FIG. 3 is a diagram showing the relationship between the heat treatment temperature and the contact resistance value to explain an embodiment of the method of the present invention. FIG. FIG. 3 is a diagram showing the relationship between heat treatment temperature and gas flow rate to explain the region where the best ohmic contact can be obtained in one embodiment of the method of the present invention. 11...n-type GaP substrate, 13...p-n junction,
14... p-type GaP layer, 15... GaP light emitting diode body, 11a... Ge (0.5%) - Au (99.5%)
Alloy layer, 14a...Zn-Au alloy layer, 14b...
Au layer.

Claims (1)

[Claims] 1. When manufacturing a compound semiconductor device by forming a gold-germanium alloy film on an n-type compound semiconductor,
The weight percentage of germanium to gold in the gold-germanium alloy film is in the range from the weight percent of the solid solubility limit concentration of germanium at room temperature to the weight percent of the solid solubility limit concentration of germanium at the eutectic temperature. forming the gold-germanium alloy film, and performing heat treatment in a gas atmosphere that is inert to the gold-germanium alloy film at a gas flow rate that does not cause gas turbulence or in a vacuum with a degree of vacuum of 1 × 10 ^-5 Torr or less. A method for manufacturing a compound semiconductor device characterized by: 2. The method for manufacturing a compound semiconductor device according to claim 1, characterized in that the gas atmosphere inert to the gold-germanium alloy film is argon or nitrogen. 3. The method for manufacturing a compound semiconductor device according to claim 1, characterized in that the flow rate of a gas that is inert to the gold-germanium alloy film is 10 ml/cm ² or less per minute. 4. The method for manufacturing a compound semiconductor device according to claim 1, wherein the heat treatment temperature is performed within a range of 475°C to 600°C.