JPH0693443B2 - Method for forming electrode of semiconductor device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for forming an ohmic electrode of a semiconductor device, and more particularly to improvement of a method for forming an ohmic electrode in a III-V compound semiconductor device.

[Technical background of the invention]

In III-V group compound semiconductor devices, gold or gold alloy electrode metals are often used as internal terminals formed on the chip surface for bonding external lead wires to semiconductor chips.

In this case, although the gold-based electrode has good bonding performance in a state where it is attached to the main surface of the lead wire lead-out area of the semiconductor chip, it is subjected to heat treatment to bring the electrode into ohmic contact with the semiconductor layer. It is known that when applied, the bonding efficiency decreases. It is considered that this is because the constituent component of the semiconductor crystal or the ohmic component in the gold alloy is diffused to the surface of the electrode film by heat treatment to form a thin oxide film on the surface layer.

As one measure against this problem, a “gold overcoat method” is used in which a gold alloy layer is deposited and heat treatment for ohmic contact is performed in the same manner as described above, and then a gold layer is further deposited thereon. A method has been proposed. By this method, the bonding efficiency is dramatically improved.
% Bonding success rate improved to 99.99%. In any of the examples applied to other semiconductor crystals, the result that the bonding efficiency can be improved compared to the conventional method is obtained in any case.

In the following description, the electrode first deposited by the "gold overcoat method" will be referred to as an ohmic electrode, and the electrode laminated and deposited thereon will be referred to as a bonding electrode.

[Problems of background technology]

However, when the above “gold overcoat method” is also applied to a semiconductor having low bonding properties, for example, GaAlAs red light emitting element, the bonding success rate, which was 40 to 70% in the past, is significantly improved to 85 to 95%. However, this number is not always satisfactory in comparison with the case where it is applied to other semiconductor devices. Also in this case, the bonding success rate can be further improved by increasing the thickness of the bonding electrode layer, but the cost increases and the substrate temperature rises during the vacuum deposition of the electrode metal. , Ga, etc. may diffuse on the gold layer of the bonding electrode and accumulate on the surface, which may deteriorate the bondability.

By the way, in the case of GaAlAs red light-emitting diode, the reason why the bonding efficiency remains low even when the “gold overcoat method” is applied is estimated from the results of surface physical analysis such as ion microanalysis as follows. can do.

That is, in the “gold overcoat method”, after forming the ohmic electrode, for example, when forming the bonding electrode by vacuum deposition, in order to improve the adhesion between the ohmic electrode and the bonding electrode, the semiconductor on which the ohmic electrode layer is deposited is formed. Gold is evaporated and deposited while heating the substrate to about 200 ° C. At this time, the semiconductor components and the like that have already been deposited on the surface of the ohmic electrode diffuse in the bonding gold layer during vapor deposition, and are deposited on the surface in large amounts. It is considered that the bonding efficiency is lowered as a result of the precipitation component being subsequently oxidized by moisture or the like.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and improves the above-mentioned "gold overcoat method", and particularly applies to a semiconductor element having a low bonding efficiency even in the "gold overcoat method" such as GaAlAs red light emitting diode. Thus, the present invention provides a method for forming an electrode of a semiconductor device, which can significantly improve the bonding efficiency.

[Outline of Invention]

The method for forming an electrode of a semiconductor device according to the present invention comprises depositing a metal layer capable of forming an ohmic electrode on the surface of a semiconductor single crystal, and then performing heat treatment to form an ohmic electrode layer in ohmic contact with the surface of the semiconductor single crystal. And the step of stacking on the ohmic electrode layer to deposit the first metal layer for the bonding electrode, and then cooling the metal layer for the first bonding electrode without taking it out of the deposition apparatus. And a step of re-depositing the second metal layer for the bonding electrode after the temperature becomes lower than the deposition start temperature.

By forming the metal layer for the bonding electrode in two or more steps as described above, it is possible to prevent large amounts of semiconductor components, etc. deposited on the surface of the ohmic electrode from depositing on the surface of the gold layer for the bonding electrode. it can. That is, since the lower bonding electrode metal layer is deposited and then the upper bonding electrode metal layer is deposited by cooling, the upper electrode metal layer such as the semiconductor components deposited on the lower electrode layer surface is deposited. The diffusion inside will be suppressed.

Example of Invention

An embodiment of the present invention will be described below with reference to the accompanying drawings.

First, the P-type GaAlAs layer 2 and the N-type GaAl are formed on the P-type GaAs substrate 1.
The As layer 3 is sequentially epitaxially grown to form a PN junction which becomes a light emitting region of the red light emitting diode. Then P-type Ga
An AuBe alloy layer 4 and an AuGe alloy layer 5 are vacuum-deposited on the back surface of the As substrate 1 and the surface of the N-type GaAlAs layer 3, respectively. Then N ₂
Alloy layer by heat treatment in gas at 520 ℃ for 5 minutes
Ohmic contacts are applied to 4,5 to form ohmic electrodes.

In addition, it has been clarified by Auger analysis that the oxides of Ge and Ga are present in the surface layers of the ohmic electrodes 4 and 5 thus formed, respectively.

Next, as a metal layer for the bonding electrode on the AuGe electrode surface
Vacuum deposit Au. At that time, first, as in the case of the usual “gold overcoat method”, the first Au layer 6 is formed by heating to about 150 ° C. and then starting vapor deposition. Thus, the temperature rises further during the deposition of the first Au layer 6. Therefore,
When the first Au layer 6 is formed with a predetermined film thickness, the vapor deposition is once stopped, and after cooling to a temperature of about 120 ° C., the vapor deposition of Au is started again and the second Au layer 7 is deposited. After forming the metal layer for the bonding electrode consisting of the Au laminated film in this way, the wafer is taken out of the vacuum evaporation apparatus, and then the Au laminated film is patterned into a predetermined electrode shape by the photo-etching method to form the bonding electrode. .

In the bonding electrode formed by the method of the above embodiment,
It was revealed that the amount of Ga, Ge, etc. deposited on the surface was about an order of magnitude smaller than that in the case of the conventional "gold overcoat method". This is because once the first Au layer 6 is vapor-deposited, it is cooled once, so that Ga, Ge, etc. deposited on the surface of the Au layer 6 can be removed from the second A layer 6.
It is shown that diffusion into the u layer 7 could be suppressed.

As a result, deposition of semiconductor components on the surface of the bonding electrode is avoided, and as a result, the bondability can be greatly improved. In order to verify this effect, the following three types of GaAl
A bonding test was conducted on the As red light emitting diode device.

Example product GaAlAs red light emitting diode chip on which an electrode is formed by the method of the above example.

Conventional product A AuGe GaAlAs red light emitting diode chip with only ohmic electrode 5 formed.

Conventional product B GaAlAs red light emitting diode chip with bonding electrodes formed by the conventional "gold overcoat method".

Comparing the bonding success rates in the above bonding tests, the results are shown in Table 1 below.

From the results shown in Table 1, according to the above-mentioned examples, even for the GaAlAs element which was required to have sufficient bonding performance even by the "gold overcoat method", the bonding performance was remarkably improved, and in the case of other elements, It is clear that a bonding success rate similar to that can be obtained.

Although the bonding electrode is formed in two steps in the above embodiment, it may be formed in three or more steps.

The present invention can also be applied to the case where a semiconductor chip other than GaAlAs or an electrode material other than Au is used.

〔The invention's effect〕

As described above in detail, by using the electrode forming method according to the present invention, it is possible to significantly improve the bonding efficiency even for a semiconductor element having a low bonding efficiency even in the “gold overcoat method” such as the GaAlAs red light emitting diode. A remarkable effect can be obtained.

[Brief description of drawings]

The accompanying drawings are cross-sectional views for explaining an embodiment in which the present invention is applied to electrode formation of a GaAlAs red light emitting diode element. 1 ... P-type GaAs substrate, 2 ... P-type GaAlAs layer, 3 ... N-type
GaAlAs layer, 4 ... AuBe ohmic electrode, 5 ... AuGe ohmic electrode, 6 ... first Au bonding electrode layer, 7 ...
… Second Au bonding electrode layer.

Claims (3)

[Claims] 1. A step of forming an ohmic electrode layer in ohmic contact with the surface of the semiconductor single crystal by depositing a metal layer capable of forming an ohmic electrode on the surface of the semiconductor single crystal and then performing heat treatment. Stacking on the ohmic electrode layer, depositing the first bonding electrode metal layer, and without removing the semiconductor single crystal from the deposition apparatus,
The method further comprises a step of cooling to below the deposition start temperature of the first bonding electrode metal layer, and a step of depositing a second bonding electrode metal layer again after the cooling step. Method for forming electrode of semiconductor device. 2. The semiconductor single crystal is GaAlAs, the ohmic electrode layer is an AuGe alloy layer, and the first and second bonding electrode metal layers are Au layers. Item 7. A method for forming an electrode of a semiconductor device according to item. 3. The deposition temperature of the first metal layer for a bonding electrode is about 150 ° C., and the temperature achieved in the cooling step is about 120 ° C. A method for forming an electrode of a semiconductor device as described above.