JPS5830171A - Compound semiconductor element and forming method of its electrode - Google Patents

Abstract

PURPOSE:To obtain the electrode with good reproducibility, when the electrode is provided in the semiconductor including Al, by forming the three layer structure of the electrode comprising a Ti layer which is provided on the substrate, a layer including Sn and an ohmic contacting metal, and an Au layer. CONSTITUTION:On the P type GaAlAs substrate 1, a P type GaAlAs region 2 and an N type GaAlAs region 3 are laminated and grown by a liquid phase epitaxial method. At first, the Ti layer 7, which is to become a protecting film at the time of etching is deposited on the region 3. Then the metal layer 8 comprising Sn, Ge, and Ni which can obtain the excellent ohmic contact with respect to the region 3, and the Au layer 9 which is readily bonded are laminated and deposited on the Ti layer 7. Thereafter, a light sensitive film 10 having a fine precise pattern is provided on the layer 9. The exposed part of the layer 9 and the layer 8 are etched away by using a mixed liquid of KI-I2. Then the layer 7 is etched by using an HF series solution, the film 10 is removed, and the three layer structure comprising the layers 7, 8, and 9 is obtained. Thereafter, an electrode 5 such as Au-Zn is deposited on the back surface of the substrate 1, and the heat treatment is performed for the entire element.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compound semiconductor device containing aluminum and a method for forming an electrode of the device, and particularly relates to a method for forming an electrode in a selective region of a compound semiconductor device containing kt.
It is something to do.

As is well known, elements such as light emitting diodes, transistors, lasers, and photodetectors are made of GaAs, GaAjAs, etc.
, GaAsPs, GaP, Cd8, Zn8, and other compound semiconductor materials are currently being used, and the field of application of these semiconductor materials is currently expanding.

Compared to single-element semiconductor materials such as 81, the physical properties of these compound semiconductor materials change in a complicated manner during the device manufacturing process, so the device manufacturing process, including the method of electrode formation, is not simple and requires sophisticated techniques. Technical skills are often required, especially G.
Compound semiconductor materials containing more than Kl, such as aAtA-, have many problems, such as the semiconductor surface being unstable and easily condensing during heat treatment and chemical treatment during the manufacturing process, making it difficult to form electrodes for ohmic contact. It had drawbacks. Therefore, as is the case with other compound semiconductors,
In particular, various materials, techniques, and methods have been developed for forming nine-element electrodes using compound semiconductor materials containing At. However, the current situation is that the process is complicated, and many problems remain in terms of performance, yield, etc. The disadvantages and problems of this conventional method of forming electrodes will be specifically explained using a method of forming electrodes of a GaAtA-light emitting diode as an example.

FIG. 1(a) shows an example of the cross-sectional structure of a conventional GaAtAs light emitting diode. In this figure, the diode consists of a pliGaAtAs region 2 obtained by liquid phase growth on a pli GaAjAs crystal substrate 1, an n-type GaAt
It is a png combination in which the As layer 6 is stacked. As electrodes of the element, ohmic electrodes 5 are formed on the entire back surface, and ohmic electrodes 4 are selectively formed on the front surface by opening windows with predetermined shapes and sizes in an insulating film 6 such as StO.

Such electrode structures are usually obtained by aqueous methods. That is, a pn junction is formed on the entire surface of the nine substrates.
The insulating film 6 such as O, etc. is coated with CVD (chemical
Adhesive coating is performed using the vapor d@position method or the like.

Thereafter, a photoresist film is applied to the insulating film 6, and a window for forming an electrode having a predetermined shape and size is formed by a conventional photolithography method. Thereafter, electrode metal is deposited on the entire surface by vacuum evaporation or the like, and the electrode area 4 is masked again by photoresist coating, photolithography, and chemical etching to obtain the cross-sectional structure shown in FIG. 1(a). Since the ohmic electrode on the back surface is formed on the entire surface, the above steps are not necessary.

These include the adhesion of the electrode to the GaAtAs crystal, stability,
An O heat treatment step is usually added to improve the contact with the oak.

The following four drawbacks and problems in the conventional electrode forming method are listed below.

b) Since the insulating film 6 such as 81 (h) is formed by thermal overloading such as CVD method, thermal strain and stress strain due to the slight difference in physical properties from the crystal may occur at the boundary with the crystal. Crystals occur on the surface, especially around the window.
When the insulator and the ohmic electrode metal come into contact with each other, multiple strains occur. These unnecessary strains adversely affect the characteristics of devices made of compound semiconductor crystals, which are particularly sensitive to strain, leading to a decline in yield and reliability.

Opening of the insulating film for selective ohmic electrode formation is done by chemical treatment using chemicals. Even if the chemical dissolves the insulating film but does not dissolve the crystal, in the case of a crystal containing At, the surface of the crystal inside the window that comes into contact with the chemical is likely to be activated and easily oxidized.
Even if a later ohmic electrode is deposited and formed, the contact resistance tends to increase or vary, and it is difficult to make good ohmic contact.

c) If this compound semiconductor element is a light emitting diode, the upper part becomes the light extraction surface. Therefore, since the ratio of the electrode area to the light emitting area affects the light emitting characteristics of the diode such as efficiency, the electrode area is required to be as small as possible and to have good precision in shape and size. In other words, the region protruding from the window of the electrode 4 and covering the insulating film 6 is not unnecessary but rather a problematic region. If chemical etching is performed using a mask butter that minimizes this protruding part by photo-etching, the accuracy and misalignment of the mask alignment, side etching phenomenon, etching quality, etc. will be affected (the turn may be misaligned and the etching liquid may leak onto the window). There were cases in which the crystals were often reached at the edges. Compound semiconductors containing the chemical etching solution FiAt, such as electrodes (for example, gold), were also subjected to JIK etching, which often resulted in a decrease in device characteristics and yield. Ta.

2) Despite the various drawbacks and problems mentioned above, the number of steps required to form electrodes on the upper part of the device is relatively large, leading to an increase in the cost of the device.

As another method, there is a method book for forming electrodes of a light emitting diode using a simple method as shown below.

FIG. 1(b) is an example of the cross-sectional structure of a nine-light emitting diode obtained by this method. Each area 1, 2, 5.4 is shown in Figure 1 (a
) is the same as each area 1 to 4 in . Considering only the shape, the structure shown in FIG. 1(b) has no insulating film and is a convenient structure for a light emitting diode. In order to obtain this, the electrode metal is deposited on the entire surface of the upper surface and the electrode 4 is left by photolithography or chemical etching, but as mentioned above, the etching solution for the electrode metal also etches the compound semiconductor containing At. It is not used because it is stored away, so a metal mask is used. That is, a hole of a predetermined shape is made in a thin metal plate such as Mo, and the mask is used as a mask, and with this in close contact with the semiconductor substrate, electrode metal is deposited from above using a method such as vacuum evaporation to form a wire. fb) This method is simple in principle, but it has the following drawbacks.

There is a limit to the processing of holes in a metal plate mask, and holes with minute shapes and sizes cannot be made, so it is not possible to obtain electrodes with the precise shapes and sizes that are possible with photolithographic methods. Furthermore, even though the mask is brought into close contact with the semiconductor substrate, since it is overlapped, a certain amount of gap inevitably occurs, and furthermore, thermal expansion of the mask during vapor deposition,
Due to vibrations and the like, shifts and blurring tend to occur at the ends of the 4 deposited electrode regions, resulting in poor reproducibility of the shape and size of the electrodes.

Moreover, there are various problems with conventional electrode formation methods.
This has been a major hindrance to performance, precision, yield, and reproducibility in device manufacturing.

The present invention aims to solve or avoid the above-mentioned drawbacks and problems by providing a compound semiconductor device containing HT and a method for selectively forming electrodes on this semiconductor device with precision and good reproducibility. Hereinafter, one embodiment of the present invention will be described with reference to FIG. 2.

FIGS. 2(a) to (f) show GmAIAa according to the present invention.
This is an example of a process for forming electrodes of a light emitting diode.

(1) In FIG. 2 (1), p! Is!
A compound semiconductor substrate is shown having a pm junction in which a GaAtAs region 2 and a nill GaAtA-region 3 are formed.

(b) This semiconductor substrate 0nfliG*kLkmIA
A metal that will become an electrode is deposited on the entire surface of area 6 by a method such as vacuum evaporation or snok vine ring (see Fig. 2(b)).
)reference). This electrode is formed in the following structure. That is, first of all, the deposited n fjIGaAtA-region 6
The metal of the first layer 7 that will be in contact with is T1.

This Ti layer is used as a protective film during the first selective chemical etching described later, and it suppresses the occurrence of strain at the interface and exhibits the effect of ohmic formation by the metal of the next second layer 8. In order to make the AU thinner, it is desirable to make the AU thinner. Very good results were obtained when the thickness of the web was several hundred, and it was found that a thickness of several hundred λ to several thousand 1 was sufficient, but it became a problem at a thickness of 1 am or more.

On this first layer 7, a metal layer of 8 m% G and N1 is deposited as a second layer 8 over the entire surface. The metal layer forming the second layer 8 contains G.,8m which can make an ohic contact with the R-type Gam tAs region 3. 7 and n-type GmAtAs to form a good Ozuc contact. If the metal can achieve this purpose, G
・It may be made of another metal instead of SR. Like the T1 layer, Bn is also a protective film for the first selective chemical etching described later, and has four other functions for the next selective chemical etching, so it is a necessary metal in the present invention. .

This second layer 8 may be a mixed metal layer of 8ws, G@sNl, but it has a two-layer structure in which the preparatory layer for the T1 layer Kll is the 811 layer, and the KG and N1 layers are formed thereon. Even better if so.

The thickness of this second layer 8 is also desirably 4 thin for the reasons mentioned above, and the thickness for obtaining good results is several hundred amps and several thousand λ.
(It is possible, but it becomes a problem if the thickness is 1 or more.

Finally, the metal used for the third layer 9' to be formed is
It is. The reason why Au is used is to facilitate lead wire removal after lead wire bonding and the like. This A+
It is sufficient for the thickness of the a-layer to be several pm.

As described above, in the present invention, the electrode metal has a structure in which three thin metal layers each having a different function and effect are laminated. However, because each of the three layers is a thin film and is heat-treated later, it is considered that the boundaries between the three layers are not clearly defined. These three layers can be obtained in the same container and in the same process by using a method such as using a vapor deposition source or using a sputtering discharge electrode.

(cl) A photoresist film' is applied to the substrate on which these three layers of metal are attached.
frI! ! Then, a photoresist film with a predetermined shape and size is left behind using conventional photolithography. The photoresist film 1 has an extremely fine and precise pattern because it uses a photographic etching method that is different from metal masks.
0 is formed (see FIG. 2 (@)).

(d) Next, the substrate that has undergone the above steps is immersed in a chemical etching solution such as a K1-1 layer mixture. In this first selective chemical etching, etching proceeds while leaving a certain portion of the photoresist film 10. This mixed solution contains ^U, G, and Nl.
It is also etched, but s 8n.

Since Tl ti cannot be etched, the etching will stop when it reaches the first layer 7t or its vicinity.

In this way, the first selective chemical etching
Since it is sufficient that the etching liquid 9 stops in the vicinity thereof, it is not necessary to use the above-mentioned mixed liquid as long as the etching liquid has 4 such effects.

(@) After the above process is completed, 9 ft of photoresist film 10 is left.
Perform the next selective etching using the etching solution T.
A HF system is used for etching a film, or a mixed solution is prepared by adding NH4F to the HF system. As a result of the experiment, 8m is not included (
(or not coated with Bm) When a layer of only Tt is formed, the above mixed solution etches T1 as well, but the GaAtAs crystal is also etched at a high rate. Therefore, it is difficult to control the etching to stop at the GaktAs surface, but when a T1 layer containing 8m (or covered with fim) is formed, this 0 layer can be quickly removed by changing the composition of the above mixed solution. Although it is etched, it is found that the G1 layer is hardly etched. This result shows that if a substrate with a 1% layer with the surface condition described in (d) is etched with the above mixed solution, the etching will be GaAtAs.
It is possible to reach the surface and stop etching, and this control is impressive. Therefore T
When one layer is removed, the 4 GaAtAs surface is hardly eroded, the lock surface is maintained, the light emitting characteristics as a light emitting diode are not deteriorated, and fine shapes and sizes can be obtained with good precision and reproducibility (see Figure 2). ·)reference).

(f) After printing, remove the photoresist film 10 and remove the p-type Qa on the back side.
A4A @ Ohmic electrode metal on crystal substrate 1 (for example, A
(u-Zn, etc.) is deposited on the entire surface, and the i! Heat treated at 30°F. Through this heat treatment, both n-type and p-type Ga
4 has a strong adhesion force to the AtAs crystal, and good ohmic contact can be stably obtained with good reproducibility (second
(See figure (f)).

The present invention has been described above using a method for forming electrodes of a GaAtA light emitting diode as an example. According to the present invention, on a compound semiconductor substrate containing At, such as a GaAtAs crystal, a T1 layer is disposed in contact with the compound semiconductor crystal, and this T layer and A
Contains a metal that enables ohmink contact with the u layer 8
The first selective chemical etching was carried out on 8n-Ti@ by a method of forming an electrode film with a three-layer structure in which the m layer was sandwiched in a sandwich pattern, and a method of using chemical etching using photolithography in two steps. Stop this chemical kt
Avoid contact with compound semiconductors containing 8n-'
rs@ was removed by the following chemical etching and GaAtA-
It is possible to selectively form electrodes with extremely fine shapes and sizes without eroding the crystals with high accuracy and reproducibility.In addition, according to the present invention, as described in the explanation of FIG. 1(a), This eliminates the need to form an insulating film, which simplifies the manufacturing process, eliminates the need to apply stress and strain to the semiconductor element due to thermal strain and differences in physical properties during the formation of the insulator, and further facilitates the formation of electrodes. Since a method is used that does not allow chemicals to come into contact with the IN-finished compound semiconductor surface, activation and oxidation of the GaAtAs crystal surface is avoided, resulting in better ohmic contact and improved reproducibility in the electrode formation process. .

The above example is GaAJ! , the book uses AI crystal as a substrate, but if At is included in the compound semiconductor,
As mentioned above, the crystal surface properties are sensitive to chemicals, so the present invention is fully effective for compound semiconductors containing Mut.

The present invention is not limited to the light emitting diode of the embodiment,
It is of course possible to use other semiconductor elements such as a semiconductor laser, and it is also possible to change or add steps without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of a GaAt layer 1 light-emitting diode according to a conventional method. FIGS. 2(a) to 2(f) show Gajlkt according to the present invention.
A-A diagram showing one method of forming electrodes of a light emitting diode. j-p 21I GaAtA-crystal substrate; 2-p
1lGaAtAs region; 6... mJllGaAtm region near... first layer; 8... second layer; 9... third layer; 10... photoresist film. Figure 2

Claims (1)

[Claims] 1) As a metal layer of an electrode of a compound semiconductor containing kl, is a T layer in contact with the compound semiconductor? and the Ti
1. A compound semiconductor device containing kt, characterized in that it has a substantially three-layer structure consisting of an Au layer, a layer containing Srs and a metal that enables ohmic contact, and an Au layer. 2) As a metal layer of the electrode of the compound semiconductor containing kt, a T1 layer is formed on the side facing the compound semiconductor Km, and then a layer containing 8n and a metal that enables ohmic contact is formed, and then a KA11 layer is formed; Thus, a three-layer structure is obtained, and the electrode is processed into a predetermined shape by chemical etching using a chemical that does not substantially corrode 8n and TI, and chemical etching using a chemical containing glHF. A compound semiconductor electrode formation method that takes this into account.