JPS5950215B2 - Method for forming ohmic electrodes on N-type gallium arsenide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an ohmic electrode on N-type gallium arsenide (GaAs).

Conventionally, as an ohmic electrode formed on N-type GaAs, A
Au-based electrode materials such as u (gold)-Ge (germanium) alloy and Au-Sn (tin) alloy have been used.

When bonding wires such as Au wires to this ohmic electrode, thermocompression bonding or ultrasonic bonding is usually used, but since such Au-based electrode materials are alloys, they have a very high hardness, so these methods cannot be used. There was a problem that it was difficult to achieve stable bonding. If pure Au is used as the ohmic electrode, it can be firmly crimped to the Au wire and is good, but pure Au does not become an ohmic electrode for N-type GaAs and is therefore difficult to use. Furthermore, in order to form the alloy of the ohmic electrode into N-type GaAs, ohmic contact cannot be obtained simply by bonding, and it is necessary to perform appropriate heat treatment after bonding.

This heat treatment causes a mutual reaction between the two bonding surfaces, resulting in ohmic contact. However, during heat treatment, the electrode becomes a complex alloy, which makes bonding even more difficult. It was hot. When wire-bonding Au wires to such conventional ohmic electrodes by thermocompression bonding or ultrasonic compression bonding, the bonder strength was measured using a tension meter and found that the bonder strength was quite weak at 2 g or less.

Further, even if bonding was initially performed with a predetermined strength, the Au wire often peeled off from the electrode due to thermal stress such as temperature cycling. For this reason, the conventional method has disadvantages in that wire bonding work for Au wires is difficult, and sufficient bonding strength cannot be obtained, resulting in poor manufacturing yield and low reliability.

This invention was made in order to eliminate the above-mentioned drawbacks of the conventional technology.The purpose of this invention is to provide an ohm to N-type GaAs so that wire bonding can be easily and firmly performed, and the manufacturing cost can be reduced. An object of the present invention is to provide a method for forming a sex electrode.

In order to achieve such an object, the present invention forms an ohmic electrode made of Ge, Ni (nickel), and Al (aluminum) through the following steps. First, a GaAs substrate containing an N-type layer is placed in a vacuum evaporation apparatus, and after sufficiently exhausting the air inside, the substrate is heated to a temperature of 450°C to
Heat to a temperature of 550°C.

Next, Ge is deposited on the surface of the N-type layer of the heated substrate by vacuum evaporation.
form a layer. Next, a Ni layer is subsequently formed on the Ge layer by vacuum evaporation. and the above 450℃~55
The temperature of 0° C. is maintained for a predetermined time. After that, the board is
After cooling to below 0°C, A was deposited on the Ni layer by vacuum evaporation.
Form l layer. Here, the substrate temperature was set at 450°C to 550°C when forming the Ge and Ni layers by vacuum evaporation, as will be described in detail later, in order to keep the contact resistance low, and also to keep the Al layer low. The reason why the substrate temperature was set to 400°C or less when forming by vacuum evaporation is that if the temperature is higher than this, Ge
- This is because the Ni layer and Al react. Next, an embodiment in which the present invention is applied to a GaAs infrared light emitting diode will be described in detail based on the drawings.

In the figure, an N-type GaAs layer 2 is formed by liquid phase epitaxial growth on one surface of an N-type GaAs substrate 1 doped with Si (silicon) as an impurity, and an N-type GaAs layer 2 is further formed on one surface of an N-type GaAs substrate 1 doped with Si (silicon) as an impurity.
P is also deposited on the s layer 2 by liquid phase epitaxial growth.
A shaped GaAs layer 3 is formed.

Note that 4 is a PN junction. In this case, in the liquid phase epitaxial growth, Si used as an impurity acts as an amphoteric, so the growth process changes from N-type GaAs to P.
This PN junction 4 is formed by inverting it to GaAs type. Next, the P-type Ga of the wafer thus obtained is
An ohmic P-type electrode 5 is formed on the surface of the As layer 3 using a suitable material.

Thereafter, the other surface 1a of the N-type GaAs substrate 1 is polished to a predetermined thickness. Finish to a mirror finish. This side 1a
An ohmic N-type electrode 6 is formed above by the method characterizing the invention. That is, the wafer is placed in a vacuum evaporation apparatus, and while the N-type GaAs substrate 1 is heated to a temperature of 450° C. to 550° C., Ge and Ni are vacuum evaporated to form a Ge-Ni layer 6a on the surface 1a. be done.

Next, the Al layer 6b is formed by vacuum evaporating Al onto the Ge-Ni layer 6a while keeping the N-type GaAs substrate 1 at a temperature of 400° C. or lower. Since the temperature at the time of forming this Al layer 6b is below 400°C, Al is Ge-Ni.
The pure form of Al is exposed on the surface without any reaction. Note that the ohmic N-type electrode 6 is formed on a part of the surface 1a, but in order to form it in this way, the vapor deposition is performed selectively on a predetermined location using a mask, or the ohmic N-type electrode 6 is formed on a part of the surface 1a. A well-known method is used, such as forming an electrode by vapor deposition and then removing unnecessary portions by photolithography. The wafer on which the ohmic P-type electrode 5 and the ohmic N-type electrode 6 are formed is separated into, for example, 400×400 μm squares, and pellets of GaAs infrared light emitting diodes as shown in the figure are completed.

After such a pellet is mounted on a suitable metal plate or the like in such a way that the ohmic P-type electrode 5 is in contact with it,
An Au wire is wire-bonded to the surface of the Al layer 6b of the ohmic N-type electrode 6 by thermocompression bonding. A light emitting diode is assembled in this way. A forward current of 50 mA was applied to the light emitting diode of this example, and the forward current at that time was measured, and a value of 1.25V was obtained.

Au-Ge (Ge: 12 wt%) was vacuum deposited to 430
Since a conventional light emitting diode having an ohmic N-type electrode obtained by jitter at a temperature of .degree. C. has a forward voltage value of 1.25 V, the same value was obtained. This conventional light-emitting diode has a contact resistance of about 10-'Ω·-, but the light-emitting diode according to this embodiment also has a contact resistance as low as that. Note that the heating temperature of the N-type GaAs substrate 1 during vacuum evaporation of Ge and Ni was set to 4.
When the temperature was lower than 50°C or higher than 550°C, the forward voltage value of the light emitting diode was 1.3V or more, and in some cases was 1.5V or more. Therefore, it is necessary to limit the heating temperature to 450°C to 550°C. Next, regarding wire bonding, since wire bonding of Au wire is performed on a pure Al surface by thermocompression bonding, it is extremely easy to wire bond, just like wire bonding to an Al electrode on ordinary Si. Strong and stable bonding can be achieved.

There were no bonding defects that were observed in conventional Au-based alloy electrodes. When the bonding strength of 100 samples of the light emitting diode of the above example was measured using a tension meter, all of them were 5 g.
It had the above strength, and when it was pulled even stronger, the Au wire was cut in the middle, and there was no separation between the electrode and the Au wire. Furthermore, a reliability test was conducted on this light emitting diode by preparing 40 pieces for each of the following test items.

(1) Temperature cycle test: -50°C to 100°C 50 cycles.

(2) Heat shock test: 0°C $100°C 5 cycles.

(3) Continuous current test: 100mA for 1000 hours. (4)
Intermittent current test: Junction temperature 40'C: 100°C 2500
0 citals. (5) Humidity test: temperature 60℃, relative humidity 9
5% 1000 hours.

(6) Drop test: Dropped onto a wooden board from a height of 75 cm, 3
times.

As a result of the above tests, it was possible to obtain a very reliable light emitting diode without any defects.

In the above embodiments, an example of a GaAs infrared light emitting diode has been described, but it goes without saying that the present invention can be applied to various semiconductor devices using GaAs.

As described above, according to the method for forming an ohmic electrode on N-type GaAs according to the present invention, an ohmic electrode can be formed with low contact resistance, and wire bonding of an Au wire to the ohmic electrode can be easily and firmly performed. , manufacturing yield can be improved, cost can be reduced, and reliability can also be greatly improved. Furthermore, since expensive Au is not used as an electrode material, the material cost is also reduced, and there are many other excellent effects.

[Brief explanation of the drawing]

The figure is a cross-sectional structural diagram of a GaAs infrared light emitting diode pellet according to an embodiment of the present invention. 1... N-type GaAs substrate, 2... N-type GaAs layer, 3... P-type GaAs layer, 4...
...P-N junction, 5...Ohmic P-type electrode,
6...Ohmic N-type electrode, 6a...G
e-Ni layer, 6b...Al layer.

Claims (1)

[Claims] 1 heating a gallium arsenide substrate having an N-type layer to a temperature of 450°C to 550°C in a sufficiently evacuated room;
Ge is deposited on the surface of the N-type layer of this heated substrate by vacuum evaporation.
a step of forming a layer, a step of further forming a Ni layer on this Ge layer by vacuum evaporation, and a step of
A method for forming an ohmic electrode on N-type gallium arsenide, comprising the steps of cooling to a temperature of 00° C. or lower, and further forming an Al layer on the Ni layer by vacuum evaporation after cooling. .