JPS5931212B2 - Method for manufacturing compound semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing compound semiconductor devices such as light emitting diodes, and in particular to manufacturing an electrode that makes low resistance contact with a P-type crystal of a light emitting diode using an I-V compound semiconductor such as GaAs or CaP. Regarding the method.

Gold (Au)-Zn is used as an ohmic electrode material for P-type crystals such as red and green light-emitting diodes using GaP and infrared light-emitting diodes that form a P-N junction in a single growth using the amphoteric impurity properties of Si. , Au-Zn-Ni
, Au-Zn-indium (In) Au-helium (B
Gold-based ohmic electrode materials such as e) are widely used. The optimal impurity concentration in the P-type crystal of the GaP light emitting diode is approximately 1017°-3, and it is difficult to obtain ohmic contact because GaP itself has a large band width and there are many residual impurities for impurity compensation. GaAs light emitting diodes form a P-N junction by taking advantage of the fact that the ratio of Ga lattice points and As lattice points in Si changes with temperature, so P-type crystals compensate for impurities. Because of this, it is difficult to obtain ohmic contact. In order to form ohmic electrodes on crystals where ohmic contact is difficult to obtain, a method of increasing the impurity concentration on the surface by diffusion or ion implantation is commonly used.
Also for the 4-xAS light emitting diode, zinc is diffused to increase the surface concentration and then the gold-based electrode material is added to form an ohmic electrode. In a light emitting diode using GaAs1-xPx, which is a mixed crystal of GaAs and GaP, aluminum alone becomes a good ohmic electrode, diffuses to form a P-N junction, and deposits Al on the diffusion surface.
A heat treatment method is used. Al is GaAsxP
Although it is good as a P-type electrode for 1-x, GaAs, Ga
It is difficult to obtain ohmic contact for P, GaxA -xAs because the work functions do not match.

The gold-based ohmic electrode material widely used in GaAs and GaP light-emitting diodes has the advantage of being chemically stable, but the etching material that can be used is expensive and selective etching using photoresistor technology is difficult. The disadvantage is that the liquid and the processes involved are limited.

Furthermore, since light emitting diodes are required to be low in cost, it is necessary to automate the assembly of pellets.

A normal light emitting diode is assembled by using a pellet made of eutectic metal material, mounting the N-type crystal side on a stem, and bonding a gold wire onto the P-type electrode.
When bonding a gold wire to an electrode using the above-mentioned gold-based electrode material, there is a drawback that bonding is difficult to achieve.Especially when using automatic bonding equipment, it is necessary to raise the temperature at which the pellet is heated and the bonding load to be applied compared to manual bonding equipment. This would result in damage to the beret during bonding, significantly reducing the characteristics and reliability of the device. The present invention provides a method for manufacturing a compound semiconductor device that eliminates the above-mentioned drawbacks, uses low-cost materials, reduces deterioration in device characteristics and reliability, and enables automation of bonding.

That is, according to the present invention, 5
Nickel layer with a thickness of 0 A or more and 1000 Å or less, 500
A compound semiconductor characterized in that a resistive contact to the P-type-V compound semiconductor is formed by successively forming a zinc layer with a thickness of Å or more and 2000λ or less and an aluminum layer thicker than these and performing heat treatment. A method for manufacturing the device is obtained.

In the method of the present invention, since the electrode material is mainly made of Al, it is easy to adhere to the gold wire, and bonding can be performed at a lower temperature and with a lower bonding load compared to gold-based electrode materials, making it easier to automate bonding. be able to.

Next, embodiments of the present invention will be described with reference to the drawings.

Implementation 1 FIG. 1 is a cross-sectional view of a CaP light emitting diode wafer used in an example of the present invention, in which an N-type epitaxial layer 11 and a P-type epitaxial layer 12 are formed on an N-type GaP substrate 10 by liquid phase epitaxy. It is formed by natural growth.

The impurity of the substrate is sulfur, 5~10X1017cTr
This is the impurity concentration of L-3. In the wafer for red light emitting diodes, the n-type epitaxial layer 11 is made of tellurium (Te).
, the P-type epitaxial layer 12 contains zinc (Zn) and oxygen (
In the wafer for a green special light diode, the N-type epitaxial layer 11 is doped with sulfur (S), nitrogen (N),
The P-type epitaxial layer is doped with Zn and N. P
The surface impurity concentration of the type epitaxial layer is 1 to 3 x 10170rtL-3 for both red and green. The above GaP
Several wafers were mixed with zinc 1007r9 and GaP powder 200
Add soybean powder and vacuum seal in a quartz tube. The quartz tube containing the GaP wafer is inserted into the uniform distribution furnace and a diffusion knob is performed at 750° C. for 60 minutes.

One end of the quartz tube is rapidly cooled to precipitate the evaporated zinc and stop diffusion. The diffused GaP wafer is immersed in a mixture of nitric acid and hydrochloric acid to remove dirt from the surface, then a metal mask is placed on the wafer and the wafer is placed in a vacuum deposition apparatus to deposit Ni, Zn, and Al. The thickness of the deposited metal film was measured using an interference microscope at the boundary between a portion of glass placed near the GaP wafer to which the deposited film was attached and a portion not attached.

The film thickness of Ni and Zn, which have a small amount of evaporation, was estimated on the assumption that the amount of evaporation and the film thickness are proportional. Z without evaporating Ni at all
An attempt was made to form a low resistance electrode by depositing only n and Al. Ni
Ohmic contact was obtained even without vapor deposition, but the disadvantages are that the electrodes tend to peel off if there is cloudiness or other contamination on the surface of the GaP wafer that occurs during diffusion, and that the electrodes tend to condense during heat treatment, resulting in a smaller electrode area. It was hot. In order to prevent these drawbacks, Ni needs to be at least 50A. On the other hand, if a Ni film is deposited by about 2,000 people, 550
A low resistance contact could not be obtained by heat treatment at ℃ for 5 minutes. In order to obtain a desired low resistance contact, the Ni thickness is preferably 1,000 Å or less. Figure 2 shows the results when the amount of Ni evaporated was fixed at 30η, the thickness of A2 was fixed at 1.5μ, and the amount of Zn evaporated was changed.
The figure shows the change in contact resistance Ra [Ω] when a current of 10 mA is applied to an electrode with an area of 2×10 −4 c7 n −3 , and the heat treatment conditions were set at 550° C. for 5 minutes. Zn
The amount of evaporation is 100T! If (the Zn film thickness on the electrode is 2.0
00λ), the bonding strength of the gold wire decreases, so the amount of Zn evaporated is less than 100W, that is, 2
,000λ or less. In addition, in order to make the contact resistance sufficiently small, Zn should be 25η, that is, 500
A or higher is desirable. Figure 3 shows the amount of Ni evaporation at 30Tf1.
9. It shows the change in contact resistance Rc [Ω] of the above electrode when the heat treatment temperature T [°C] is changed with the Zn evaporation amount fixed at 80 and the Al film thickness 1.5μ, and the heat treatment time was fixed at 5 minutes.

The contact resistance became extremely small when the heat treatment temperature was 450 to 600°C. FIG. 4 shows the change in the contact resistance Rc [Ω] of the electrode when vapor deposition was performed under the same vapor deposition conditions as in FIG. 3, the heat treatment temperature was fixed at 550° C., and the heat treatment time [Mil] was changed. As a result, it can be seen that a heat treatment time of 3 minutes or more is required. Based on the above experimental results, the back side of the GaP wafer on which the P-type electrode was formed was polished to a total thickness of 180 μm, and Au+SiI::. Au
were sequentially deposited and heat treated at 500° C. for 5 minutes to form a back electrode.

This wafer was divided into 0.4 m x 11 pellets using a diamond point scriber to produce light emitting diode pellets. As a result of assembling these pellets using an automatic bonding device, it is possible to bond at a lower temperature and with less stress than with gold-based ohmic electrodes, reducing the number of defects due to increased reverse current after assembly to approximately 20%. I was able to do that.

Example 2 FIG. 5 is a cross-sectional view of a silicon (Si)-doped GaAs wafer used in this example. An N-type epitaxial layer 21 and a P-type epitaxial layer 22 are formed in the same growth process.

The GaAs wafer shown in Figure 5 was etched with a normal etching solution.
After 2μ etching, ZnlOO immediately, arsenic (As) 10
0~ is added, sealed in a quartz tube, and diffused at 730°C for 1 hour.

Example 1 by placing a metal mask on the above diffused wafer
Ni, Zn, and A2 were vapor-deposited in the same manner as in 470°C.
A heat treatment was performed for 5 minutes to obtain a low resistance contact. The contact resistance of the electrode according to the present invention is 0.1Ω, which is sufficient for practical use as an electrode for light emitting diodes and the like.

Example 3 Zinc (Zn), indium (
In) and aluminum (Al) were used.

One conical heater containing 60W1f7 zinc and about 5 weight of indium? Two conical heaters containing 29% of aluminum containing aluminum were installed in a vapor deposition apparatus, and zinc was first vapor-deposited at a predetermined degree of vacuum, and then aluminum containing indium was vapor-deposited.

The total thickness is approximately 1μ. The wafer with the metal film added above was placed in a jitter furnace with nitrogen flowing at 51/min for 500 min.
A heat treatment was performed at ℃ for 5 minutes.

When a probe was placed between the electrodes and the relationship between current and voltage was examined using a curve tracer, it was found to be almost linear, and the resistance value Rc [Ω] when 10 mA was applied was the same as the value obtained with the metal material in Example 2. A value of about 0.1Ω was obtained.

The back side of this wafer has a total thickness of 160 μm.
A commonly used Au+Ge-based automic electrode was formed by polishing the electrode until it became opaque. It was scribed in the cleavage direction with a diamond point scriber and divided into pellets. As a result of using this pellet in an NTC-type automatic bonding device, it was found that bonding was easier than with conventional gold-based ohmic electrodes (compared to conventional gold-based ohmic electrodes), and bonding wires were formed due to changes in the resin during temperature cycles that occurred with conventional gold-based electrodes. Peeling between the electrodes could be prevented.Also, the forward voltage of the GaAs infrared light emitting diode produced by the above method was within the standard of 1.2 to 1.4 at 50 mA.

In this example as well, In is used as A/
! It is desirable that the amount is 1 to 20% by weight. Although the embodiments of the present invention have been described using GaP light emitting diodes and Si-doped GaAs light emitting diodes as examples, the method of the present invention
It goes without saying that this method can also be applied as an electrode formation method for P-type crystals of GaAs light emitting diodes other than doped ones.
In addition, although the example shows an example in which diffusion is performed to increase the impurity concentration on the surface of a P-type crystal, it can also be applied to wafers in which the surface concentration is increased by doping impurities during ion implantation or epitaxial growth. It is possible. As described above in detail, according to the method of the present invention, when using low-cost electrode materials and applying it to an automatic bonding apparatus, it is possible to form a practical electrode that can reduce the number of defects.

[Brief explanation of the drawing]

1 and 5 are cross-sectional views of wafers used in embodiments of the present invention. FIG. 2 shows the relationship between the amount of Zn evaporated and the contact resistance of the electrode, FIG. 3 shows the relationship between the heat treatment temperature and the contact resistance of the electrode, and FIG. 4 shows the relationship between the heat treatment time and the contact resistance of the electrode. 10, 20...
... N type substrate crystal, 11, 21... N type epitaxial layer, 12, 22... P type epitaxial layer.

Claims (1)

[Claims] 1 50 Å or more, 100 Å on P-type III-V compound semiconductor
Nickel layer with thickness less than 0 Å, more than 500 Å, 2000 Å
By sequentially forming a zinc layer with a thickness of Å or less and an aluminum layer thicker than these, and performing heat treatment, the P-type I
A method of manufacturing a compound semiconductor device comprising forming a low resistance contact to a II-V compound semiconductor.