JPS6238850B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a P-type gallium arsenide ohmic electrode that can be contacted with low resistance.

Conventionally, for P-type compound semiconductors,
Au-based ohmic electrode materials such as gold (Au)-zinc (Zn) alloys or Al-based ohmic electrode materials such as aluminum (Al)-zinc (Zn) alloys are widely used. However, these materials
For example, it is used to manufacture infrared light emitting diodes and is applied to relatively low concentration P-type compound semiconductors such as P-type gallium arsenide (GaAs) doped with silicon (Si) formed by liquid phase growth. In this case, it is difficult to obtain ohmic contact simply by vacuum-depositing the electrode material on the surface of the P-type compound semiconductor and subjecting it to heat treatment. For this reason, Zn
The Au-based or Al-based electrode was formed after increasing the surface concentration by performing so-called P ⁺ diffusion using, for example, P + diffusion. However, this P ⁺ diffusion is −
In group compound semiconductors, the sealing diffusion method is usually used. That is, the diffusion source and −
A group compound semiconductor is vacuum sealed in a quartz tube, heat treated at a predetermined temperature for a predetermined time, and then a part of the quartz tube is rapidly cooled to separate out the evaporated diffusion source.
Stop the spread. In order to perform P ⁺ diffusion in this way, quite expensive equipment is required for vacuum sealing and heat treatment, and the semiconductor device manufacturing process takes a long time, which makes the P ⁺ diffusion process itself ^uneconomical . Along with the process, troublesome processes such as buffing are required. In other words, a part of the quartz tube is rapidly cooled when the P ⁺ diffusion is completed, but even if this process is done very skillfully, it is impossible to avoid a part of the diffusion source from depositing on the surface of the P type - group compound semiconductor. . If such deposits remain, serious problems such as peeling of the electrode material or an increase in contact resistance will occur in the subsequent electrode forming process. Therefore, it is necessary to remove the deposits, but since chemical methods such as etching cannot completely remove the deposits without damaging the P-type compound semiconductor, buffing is not necessary. It must be done by mechanical methods such as
This buffing process involves bonding the P-type compound semiconductor to a polishing jig using wax or the like.
It requires a considerable amount of time to remove and clean. Furthermore, crystal cracking is likely to occur during this process, resulting in an increase in subsequent process time and a decrease in yield.

As described above, in the conventional method of forming ohmic electrodes, P ⁺
Diffusion was used to obtain ohmic electrodes with low resistance contact, but with the introduction of the P ⁺ diffusion process, there were problems such as an increase in process time, a decrease in the yield of semiconductor device manufacturing, and an increase in the cost of semiconductor devices. There were many shortcomings.

This invention was made to eliminate the above-mentioned drawbacks, and it is an ohm that makes low-resistance contact with P-type gallium arsenide, which is a relatively low concentration P-type compound semiconductor, without performing P ⁺ diffusion. The present invention seeks to provide a method for forming a sex electrode.

This invention will be explained below.

First, to explain the outline of this invention, Si
A liquid phase epitaxial GaAs wafer with a PN junction formed using the amphoteric nature of the wafer is loaded into a vacuum evaporation apparatus. After sufficiently evacuating the inside of this vacuum evaporation apparatus, the GaAs wafer is heated to a temperature of 100°C to 450°C. Thereafter, zinc (Zn) and nickel (Ni) are deposited on the surface of the P-type layer of the GaAs wafer. in this case,
You can load Zn and Ni into separate filaments and deposit Zn first and then Ni, or you can load Zn and Ni into the same filament and heat the filament to deposit Zn and Ni. good. Even in the latter case, Zn having a high vapor pressure is first deposited on the surface of the P-type layer, and then Ni is deposited to form a Zn--Ni electrode. Next, after cooling the GaAs wafer on which Zn and Ni have been deposited, it is taken out from the vacuum deposition equipment.
Place in a separate inert or reducing atmosphere (such as nitrogen or hydrogen) furnace and heat this to a temperature of 450°C to 550°C. In addition, in the above process, the heating temperature of the GaAs wafer was set at 100℃ to 450℃ during Zn-Ni vapor deposition.
The reason for this is as follows.

First, if the temperature is below 100℃, the deposited Zn−
This is because Ni may peel off, and 450
The reason why the temperature is set to be below 0.degree. C. is because after vapor deposition, heat treatment is performed at a temperature of 450.degree. C. or higher, so there is no need to heat the temperature above 450.degree. C. during vapor deposition. This reduces power consumption in this process. Further, the heat treatment of Zn-Ni was performed in an inert or reducing atmosphere in order to prevent oxidation of the Zn-Ni electrode.

As described above, relatively low concentration P-type GaAs
The fact that electrodes with low contact resistance can be obtained will be explained below.

First, in P-type GaAs doped with Si,
Since Si, which is amphoteric, occupies more As lattice points than Ga lattice points, it is P-type, and since the impurities are compensated as described above, P-type GaAs obtained by diffusing Zn The concentration is considerably lower compared to that of

Now, six such Si-doped liquid phase epitaxial GaAs wafers are prepared, and Zn--Ni is vacuum-deposited on the P-type layer surface of each GaAs wafer as described above. Each GaAs wafer with Zn−Ni deposited was heated for 430 min in an inert or reducing atmosphere.
℃, 450℃, 500℃, 550℃, 600℃ and 650℃. Next, after polishing the N-type GaAs layer so that the GaAs wafer has a predetermined thickness, the surface of the N-type GaAs layer is mirror-finished, and this surface is coated with a gold-germanium (Au-Ge) alloy (Ge content 12%). ) to form an appropriately shaped N-type electrode. A GaAs wafer with P-type and N-type electrodes formed in this way is 400μm×
Separate into 400 μm infrared light emitting diode pellets 6. In Figure 1, 1 is a PN junction formed using the amphoteric nature of Si, 2 is a P-type GaAs layer, and 3 is an N-type layer.
A GaAs layer, 4 a Zn-Ni electrode, and 5 an Au-Ge electrode.

The above infrared light emitting diode pellets 6 are
For each Zn-Ni electrode heat treatment condition, 10 Zn-Ni electrodes were assembled on an appropriate header and the forward voltage was measured at a forward current of 50 mA. The results are shown in FIG. In Figure 2 a to f, the heat treatment temperatures of the Zn-Ni electrode are 430℃, 450℃, 500℃, 550℃, respectively.
This shows the frequency distribution of forward voltage at 600℃ and 650℃. Moreover, the average values shown in each of FIGS. 2a to 2f are the average values of the forward voltages of ten infrared light emitting diode pellets 6. Note that the Au-Ge electrode is 10 ^-6 for N-type GaAs.
Since it has a fairly low contact resistance of [Ω·cm ² ], the magnitude of the forward voltage of the infrared light emitting diode pellet 6 can be considered as one measure of the contact resistance of the electrode to P-type GaAs. Conventionally, when a P-type electrode is formed using an Au-Zn alloy or an Al-Zn alloy by performing P ⁺ diffusion, the forward voltage is
It is about 1.25V. Now, as shown in FIG. 2b, the Zn--Ni electrode heat-treated at 450 DEG C. has a contact resistance comparable to that obtained by conventional P ⁺ diffusion. Heat treatment temperature: 500℃, 550℃
As shown in Figure 2 c and d, the temperature rises to 450℃.
The contact resistance of the Zn-Ni electrode is slightly higher than in the case of , but the variation is small and it is ohmic, and the forward voltage at 50 mA is 1.3 V in both cases.
It is considered that the electrode is suitable for practical use. When the heat treatment temperature is 430℃, the variation in contact resistance increases as shown in Figure 2a.
The forward voltage at 500mA also exceeds 1.3V. Further, as shown in FIGS. 2e and 2f, if the heat treatment temperature is set to 600° C. or higher, the contact resistance value and its dispersion further increase, making it impossible to put it into practical use.

In the above embodiment, an infrared light emitting diode was manufactured using a liquid phase epitaxial GaAs wafer doped with Si. Needless to say, this method can also be applied to low concentration P-type GaAs.

As explained above, this invention uses Zn-Ni as an electrode material and heat-treats it at a temperature of 450°C to 550°C, thereby making an ohmic electrode in low-resistance contact with relatively low concentration P-type GaAs. can be easily obtained. Therefore, in the manufacturing process of GaAs devices, it is possible to form ohmic electrodes with low resistance contact without P ⁺ diffusion, making it possible to form ohmic electrodes with low resistance.
This method has the advantage of being able to solve all of the problems associated with the introduction of the P ⁺ diffusion process, such as increased work time, lower production yields, and increased device costs.

[Brief explanation of the drawing]

Figure 1 is obtained by the manufacturing method of this invention.
The cross-sectional views of the GaAs infrared light emitting diode pellets in FIGS. 2a to 2f are frequency distribution diagrams of the forward voltage of the infrared light emitting diodes subjected to different heat treatment temperatures. In the figure, 1 is a PN junction, 2 is a P-type GaAs layer, and 3 is an N
4 is a Zn-Ni electrode, 5 is an Au-Ge electrode, and 6 is an infrared light emitting diode pellet.

Claims (1)

[Claims] 1 P characterized in that a gallium arsenide substrate is heated, Zn and Ni layers are formed by vacuum evaporation on the P-type layer surface of the heated gallium arsenide substrate, and then heat treated at a temperature of 450°C to 550°C. Method for forming ohmic electrodes of gallium arsenide.