JPS61220381A - Manufacture of metal-semiconductor-metal photodiode - Google Patents

Abstract

PURPOSE:To reduce the number of mask alignment, and to obtain a MSM photodiode, in which field concentration is not generated and which has excellent coupling efficiency, through self-alignment by forming irregularities to a substrate and shaping an electrode. CONSTITUTION:Recessed sections 12 are formed onto a GaAs substrate 11, and removed successively through chemical etching when the surfaces of the recessed sections 12 are damaged through dry etching. An electrode-forming metal such as Al is evaporated onto the whole surface in film thickness, but Al in approximately the same film thickness is also deposited on the side walls of the recessed sections because the evaporation is conducted through a self- revolution system. A resist is applied onto the whole surface, and the surface of a resist film 14 is also flattened approximately. The resist film 14 is etched until the surface of the substrate is exposed from the surface of the resist film 14 through etching employing ion beams, and the resist remaining in the recessed sections 12 is removed. Accordingly, an Al electrode 13 does not shield a light- receiving surface in the substrate, thus improving coupling efficiency, then resulting in no electric concentration at the edge of the Al electrode.

Description

[Detailed Description of the Invention] [Summary] A metal/semiconductor/metal (MSN) photodiode in which an electrode is formed by providing irregularities on the substrate in order to prevent electric field concentration from occurring at the metal edge. This is a method of manufacturing an MSM photodiode using a self-line method, which eliminates the above-mentioned electric field concentration and has improved coupling efficiency.

[Industrial application field]

The present invention relates to a method for manufacturing an MSM photodiode. More specifically, the present invention relates to a method for manufacturing an MSM photodiode, and more specifically, by forming irregularities on a gallium arsenide (GaAs) substrate and then forming electrodes in the recesses by self-alignment, electric field concentration is eliminated. , relates to a method of manufacturing an MSM photodiode with improved coupling efficiency.

When forming an MSM photodiode, the comb-shaped electrodes are
It is known that it can be formed by depositing metal on a semiconductor using prenal vapor deposition. FIG. 3 is a cross-sectional view of such an MSM photodiode, in which 31 is a Ga
As substrate, 32 indicates ^l electrode, Af electrode 3
2 have a width of 3 μm, for example, and are arranged at intervals of 3 μm. Such MSN diodes have lower F than PIN diodes and APDs (avalanche photodiodes).
It has the advantage of being easy to integrate with ET, and is used in optoelectronic integrated circuits (OBICs).

[Conventional technology]

However, in the MSM photodiode shown in FIG. 3, a problem was found in which electric field concentration occurred at the edge of the i-electrode 22. Therefore, the present inventor developed an MSM photodiode shown in the cross-sectional view of FIG. Furthermore, the third
In the figure, 31 is a GaAs substrate, 32 is an Al electrode, 3
3 indicates a recess formed in the GaAs substrate 31. As shown in FIG. In such an MSM photodiode, the problem of electric field concentration has been improved, and a recess 33 is formed by drilling the semiconductor to a depth approximately equal to the reciprocal of the light absorption coefficient α, and a Schittky electrode (A
By forming the β electrode 33), it is possible to increase the electric field strength at a depth that is the reciprocal of the absorption coefficient, and it is possible to accelerate photoexcited carriers at high speed, thereby providing a photodetector with high speed response. It became.

[Problem that the invention seeks to solve]

In manufacturing the MSM photodiode shown in FIG. 4, mask alignment is required to form the Alt electrode 32, and if the mask alignment is not performed correctly, there is a problem that the β electrode will not be formed as shown. Furthermore, since the Af electrode is formed by blocking a part of the light-receiving surface of the GaAs substrate, the area that receives light irradiation is reduced to the area shown by the arrow in the figure, resulting in a problem of poor coupling efficiency. Furthermore, according to experiments conducted by the present inventor, it was found that the electric field concentration at the edge of the β electrode was not completely eliminated.

The present invention was created in view of these points, and provides a method for manufacturing an MSM photodiode that does not cause electric field concentration at the edge of the electrode and has improved coupling efficiency, using a simpler process than conventional methods. The purpose is to provide

[Means for solving problems]

FIGS. 1A to 1C are cross-sectional views of essential parts of an MSN photodiode in the process of carrying out the method of the present invention.

First, a recess 12 is formed in a GaAs substrate 11.

Next, Al is deposited on the entire surface to form an All film 13,
Subsequently, a resist is applied to the entire surface to form a resist film 14 having a flat surface.

Resist until the surface of the GaAs substrate is exposed by ion beam etching! 11114 and A1[113 are etched, and then the resist remaining in the recess 12 is removed.

In this way, an MSM photodiode can be manufactured in fewer steps than in the conventional example, without using a mask (by forming an Al electrode).

[Effect]

In the above method, mask alignment is necessary only in patterning a resist film (not shown) for forming recesses 12 in GaAs substrate 11, and the A1 electrode 13 shown in FIG. 1(C) is used for mask alignment. It is formed with Selfa Line without any problems. Further, the AI electrode 13 is made of Ga
Since the light receiving portion on the surface of the As substrate 11 is not blocked, the coupling efficiency is improved.

〔Example〕

Referring again to FIG. 1, a film of photoresist (hereinafter referred to as resist) (not shown) is formed on a GaAs substrate 11, exposed and developed, and recesses 12 are formed by, for example, chemical etching or ion beam etching. The recess 12 has a depth and width of 3 μm.

Also, the spacing is formed to be 3μ steel. If the surface of the recess 12 is damaged by the dry etching described above, chemical etching is subsequently performed to remove the damage. Mask alignment is required in the exposure of the resist film described above, but in implementing the method of the present invention, mask alignment is performed only in this step.

Next, as shown in Fig. 1, an electrode-forming metal such as Al is vapor-deposited to a thickness of 3000 mm over the entire surface.

Since this vapor deposition is performed in a rotation-revolution manner, Al is deposited with approximately the same thickness on the side walls of the recess. Subsequently, a resist (for example, a resist with the trade name Az) is applied to the entire surface so that the film thickness on the substrate surface is about 3 μm. Since the resist is applied by a spin cord method, not only the inside of the recess 12 is filled with the resist, but also the surface of the resist film 14 is made substantially flat.

Next, etching is performed using an ion beam until the surface of the substrate is exposed from the surface of the resist film 14. The ion beam conditions for this etching are appropriately set in consideration of the resist, the type of electrode metal, etc.

Next, the resist remaining in the recesses 12 is removed using, for example, an acetone-based solution, resulting in the structure shown in FIG. 1(C).

At this company, it has been confirmed through experiments that the coupling efficiency is improved because the AI electrode 13 does not block the light-receiving surface of the substrate, and there is no electric field concentration at the edge of the Al electrode.

An application example of the present invention is shown in the cross-sectional view of FIG. 2, in which 21 is a semi-insulating GaAs substrate, 22 is a buffer layer, 23 is an MSM photodiode formed by the method of the present invention, and 24 is an active FET. The layers 25, 26, 2, 7 represent the source, gate, and drain electrodes, respectively, and in the device shown, FET integration is possible by using the buffer layer of the FIST as the active layer of the MSM photodiode.

〔Effect of the invention〕

As described above, according to the present invention, an MSM photodiode with no electric field concentration and improved coupling efficiency can be manufactured using a self-line with a reduced number of mask combinations compared to the conventional method, and it is possible to manufacture an MSM photodiode with improved coupling efficiency by reducing the number of mask combinations compared to the conventional method. It is extremely effective for

[Brief explanation of drawings]

FIGS. 1(a) to 4(c) are cross-sectional views of essential parts of an MSM photodiode in the process of carrying out the method of the present invention, FIG. 2 is a cross-sectional view of an application example of the present invention, and FIGS. The figure is a cross-sectional view of a conventional MSM photodiode. In FIGS. 1 and 2, 11 is a GaAs substrate, 12 is a recess, 13 is an Al electrode, 14 is a resist film, 21 is a semi-insulating GaAs substrate, and 22 is a single layer of breadlayer. , 23 is an MSM photodiode according to the present invention, 24 is an F
In the ET active layer, 25, 26, and 27 are source, gate, and drain electrodes. 1st! i! i7

Claims (1)

[Claims] Step of forming recesses (12) with predetermined dimensions and intervals on the substrate (11) that will become the active layer of the photodiode, electrode (13)
A metal film for formation is deposited on the entire surface, and a photoresist (
14), etching the photoresist (14) and the metal film (13) until the substrate surface is exposed, and then removing the photoresist remaining in the recesses. Method of manufacturing semiconductor/metal photodiodes.