JPS6244837B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to - group compound semiconductor devices, particularly
This article relates to the structure of electrodes in light emitting diodes (hereinafter abbreviated as LEDs) using single crystal Ga compound semiconductors such as GaP, GaAs, and GaAs _1-x Px.

Conventionally, LEDs emit visible light using GaP.
Alternatively, devices using GaAs _1-x Px crystals have been put into practical use and are generally widely used in various pilot lamps and numeric display elements. In addition, devices using GaAs crystal for the purpose of emitting infrared light are used for remote control, solid,
Used in state relays, etc. like this
GaPLEDs (capable of emitting light of various colors from red to green), which account for a large portion of Ga compound semiconductor LEDs, will be explained below.

The conventional manufacturing method of this GaPLED will be explained using FIG.

Next, the manufacturing process will be explained in order.

On the n-type GaP wafer 1 obtained by the LEC method, an n-type GaP layer 2 is formed by the liquid phase epitaxial method.
and crystal growth of the P-type GaP layer 3...FIG. 1a.

Next, the crystal growth surface (P-type layer surface) and the n-type wafer surface (back surface) are mechanically polished to give the wafer a predetermined thickness.

Then, Au and Be are used as the electrode 4 on the P-type growth layer side.
alloy (hereinafter abbreviated as Au-Be) or Au and Zn
(hereinafter abbreviated as Au-Zn), and an alloy of Au and Si (hereinafter abbreviated as Au-Zn) as the electrode 5 on the n-type substrate side.
(abbreviated as Au-Si) or an alloy of Au and Ge (hereinafter referred to as
Au-Ge (abbreviated as Au-Ge) is vacuum deposited...Figure 1b.

After that, each electrode is processed into a predetermined shape using a photo-etching method, and then
Heat treatment at 500°C to 600°C to form ohmic contacts of the electrodes...Figure 1c.

Then, the wafer is processed into chips of a predetermined size by a dicing method or a scribing method...FIG. 1d.

After fixing the LED chip thus obtained on the stem 7 with Au paste (or Ag paste) 6, as shown in Figure 1e,
Connect the P-side electrode 4 and the stem post 8 with a thin gold wire 9.
They are bonded by thermocompression bonding. The LED lamp is then completed by covering the top of this stem with epoxy resin.

By the way, a wire made of such a thin gold wire 9
Whether or not bonding can be performed well depends on the P side electrode 4.
Although good ohmic contact can be obtained when using conventional Au-based alloy electrodes, it is affected by metals added to Au such as Zn and Be, and due to the heat treatment process. Due to the influence of diffusion of Ga in the semiconductor substrate into the electrode layer, which is thought to occur in the process, the thin gold wire could not be properly thermocompressed onto the electrode surface, making it difficult to obtain good wire bonding properties. Therefore, conventionally
The yield of wire bonding process in LED production was not satisfactory.

On the other hand, Al, which is used as a wiring material for semiconductor devices using Si substrates, has good wire bonding properties as is well known, but -
Contrary to the above-mentioned Au-based alloys, it is difficult to obtain ohmic contact with group compound semiconductors, especially semiconductor crystals with low impurity concentrations such as GaP and GaAs crystals grown by liquid phase epitaxial method. and
It has been impossible to use Al as an ohmic electrode in such semiconductor crystals.

On the other hand, in Japanese Patent Application No. 53-149263 (Japanese Unexamined Patent Publication No. 55-75276), the same applicant proposed that the first layer is an alloy layer mainly composed of Ag, Ti, Mo, W, or
We proposed an electrode structure in which the second layer is a high-melting point metal made of Ti, Mo, W, and other alloys (which acts as a barrier layer), and the third layer is an Al layer. With the above electrode structure,
For the time being, good wire bonding properties were obtained with Al.

However, when an alloy containing Ag as the main component was used for the first layer, the contact resistance was high and the forward voltage varied widely on the somewhat high side.

The present invention has been made in view of the above conventional drawbacks, and by forming an electrode with a multilayer structure containing an Au-based alloy as the P-side electrode of a - group compound semiconductor, the contact resistance with the crystal substrate is low. It is an object of the present invention to provide a semiconductor device having an electrode having good ohmic contact and good wire bonding properties.

That is, an Au-Be or Au-Zn layer is provided as an electrode to form ohmic contact with the crystal substrate, and an Al layer is provided as a surface layer of the electrode to obtain better wire bonding properties. Furthermore, the above object is achieved by providing two layers of titanium nitride (TiN) and titanium (Ti) between the two as a barrier layer to prevent mutual diffusion of the two.

An embodiment of the present invention will be described below.

Example Regarding an example in which the present invention is applied to GaPLED,
The explanation will be given with reference to FIG.

On the n-type GaP substrate 10 obtained by the LEC method, n-type GaP 11 and p
A type GaP 12 is grown to form a pn junction 13. Next, after processing both sides of this GaP wafer to a predetermined thickness by wrapping and polishing,
Au--Si 18 is vacuum-deposited on the back surface as an n-side electrode. Then, by photo-etching, this n
The side electrodes are etched into a predetermined shape and heat treated at 500 to 600°C in a nitrogen atmosphere to form ohmic contact. Next, the P layer surface of this GaP wafer was coated with 0.2% by weight by vacuum evaporation method.
Au-Be film 14 containing ~1.0% Be with a thickness of 500 to 5000 Å
Deposits to a film thickness of . Furthermore, by sputtering, TiN film 15, Ti film 16 and Al film 17 are
are deposited sequentially. The film thickness is 500 to 2000 for TiN film.
Å, the Ti film is 1000 to 4000 Å, and the Al film is 0.8 to 2.0 μm. Here, the TiN film 15 is obtained by reactive sputtering of a Ti target in a nitrogen gas atmosphere, so one Ti target can be sputtered with nitrogen gas and argon gas.
TiN and Ti can be deposited sequentially.

Next, the four-layer film laminated in this way was photographed.
It is processed into a predetermined shape using an etching method. At this time, the Al film is etched with phosphoric acid (H ₃ PO ₄ ) heated to 80-90°C, and the TiN film and Ti film are etched with aqueous ammonia (NH ₄ OH). The Au-Be film can be easily etched with a mixture of hydrogen oxide (H ₂ O ₂ ), and the Au-Be film can be etched with a mixture of iodine (I ₂ ) and ammonium iodide (NH ₄ I).

Next, this GaP wafer was heated at 420°C in a nitrogen atmosphere.
Ohmic contact is formed by heat treatment at 500℃.

The GaP wafer thus obtained is processed into a predetermined size by dicing or scribing in the same way as the conventional GaP wafer shown in FIG.
It is mounted on a stem and becomes an LED lamp. The wire bonding process in the GaPLED manufacturing process described above has been dramatically improved compared to the conventional Au-Be electrode.
The yield of the bonding process has been greatly improved. In addition, the contact resistance with the GaP substrate was as good as that of conventional electrodes using Au-Be, and it was stable even when energized for a long time. The reason why the above electrode exhibits such excellent properties is that the TiN film and Ti film provided as the intermediate layer are free from Au, Be, and GaP substrates that are generated during heat treatment to obtain ohmic contact.
GaP acts as a barrier to prevent Ga from diffusing to the electrode surface, prevents impurities from entering the Al film on the surface, and is necessary to obtain good ohmic contact.
This is because alloying with Au-Be is performed stably. Note that when TiN or Ti is used alone as a barrier layer, its function is insufficient;
After heat treatment to obtain ohmic contact, Au−Be and
A reaction with Al can be seen.

That is, when using an Au-based alloy, it is necessary to perform heat treatment at at least 420° C. or higher in order to obtain good ohmic adhesion. However, Ti
Single high-melting point metals such as Ti tend to react with Au-based alloys; for example, Ti tends to react with Au-based alloys.
A reaction occurs at temperatures above 370-380°C, destroying its barrier properties and causing the Au-based alloy to react with Al. In other words, at a temperature at which good ohmic contact can be obtained with the Au-based alloy, Al diffuses into the Au-based alloy, and as a result, good ohmic contact cannot be obtained.

The patent application No. 53-149263, which was previously proposed by the same applicant, focused on the special characteristics of Ag-based alloys and high-melting point metals. Even at high temperatures, it does not react with a single high-melting point metal such as Ti, and even a single layer works effectively as a barrier layer. However, as described above, this electrode structure has a high forward voltage and large variations.

On the other hand, TiN is an electrically conductive and chemically very stable compound. This TiN can withstand temperatures at which good ohmic contact is achieved with Au-based alloys and can act as a barrier layer. However,
In order for a single TiN film to function effectively as a barrier layer, the film must be extremely thick, at 4000 to 5000 Å or more. However, experiments have shown that increasing the film thickness reduces the mechanical adhesion strength between the Au-based alloy and the TiN film, causing the electrode to peel off during wire bonding, making it unsuitable for use as a barrier layer. Nakatsuta. In addition, when forming a TiN film by the reactive sputtering method, the formation rate is slow, and the TiN
It has been extremely difficult to obtain a film thickness sufficient to provide sufficient barrier properties as a single layer.

The reason why a Ti film (for example, 1000 to 4000 Å) was layered on top of a TiN film (for example, 500 to 2000 Å) was based on the above points. A stable layer was obtained.

Note that when a Ti film is formed as the second layer and a TiN film is formed as the third layer, a reaction occurs between the Ti film and the Au-based alloy, and since the thickness of the TiN film on top of the Ti film is thin, the Au-based alloy eventually Al diffuses inside and good ohmic contact cannot be obtained.

Figure 3 shows the electrode structure according to the present invention and the patent application filed in 1983.
A comparison of the characteristics of the electrode structure according to No. 149263 is shown below. The horizontal axis is the forward voltage, and the vertical axis is the number. In the present invention, it is clear that the contact resistance is small and has little variation, so that a low forward voltage can be stably obtained without variation.

In the above examples, Au-Be was deposited by vacuum evaporation, but this may also be done by sputtering, etc. In this example, TiN, Ti, and Al were deposited by
Although it was deposited by sputtering, it may also be deposited by vacuum evaporation.

Note that the electrode structure in the above embodiments is applicable not only to GaP but also to other metals such as GaAs, GaAsP, and GaAlAs.
It can also be applied as an electrode structure for group compound semiconductors.

As explained above, according to the semiconductor device of the present invention, the electrode has good wire bonding properties and can have ohmic contact with the substrate.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the manufacturing process of a conventional GaPLED, and FIG. 2 is a side sectional view of a GaPLED according to the present invention. Moreover, FIG. 3 is a characteristic comparison diagram. In the figure, 1... n-type GaP substrate, 2... n-type GaP
Layer 3...P-type GaP layer, 4...Au-Be or Au
-Zn, 5...Au-Si or Au-Ge, 6...Au
Paste or Ag paste, 7...Stem, 8
...Stem post, 9...Gold wire, 10...n
type GaP substrate, 11...n type GaP layer, 12...p type
GaP layer, 13...p-n junction, 14...Au-Be
layer, 15...TiN layer, 16...Ti layer, 17...Al
Layer, 18...Au-Si layer.

Claims (1)

[Claims] 1 A first layer is an alloy layer mainly composed of gold, which makes ohmic contact with a P-type compound semiconductor, a second layer is a titanium nitride layer, a third layer is a titanium layer, and a fourth layer is an aluminum layer. - group compound semiconductor device, characterized in that a - group compound semiconductor device is used as an electrode.