JPS60176231A - Electrode forming process of compound semiconductor element - Google Patents

Abstract

PURPOSE:To form an electrode with high reliability by a method wherein a Ti/ Pt evaporated film formed for forming an electrode is heat-treated to form an alloy layer and then further evaporates Ti/Au to form multilayered metallic film. CONSTITUTION:A surface protective insulating film 2 is formed on the surface of a compound semiconductor 1 while photoresist 3 in a specific region on the film 2 is removed by coating, exposing and developing processes and then the insulating film below the removed region 3 is further removed by etching process to expose the surface of semiconductor 1. Firstly after evaporating Ti/Pt 5, a Ti4/ Pt5 film is selectively formed on a specific region by peeling off the photoresist 3. Then Ti, a semiconductor and an alloy layer are formed to obtain electrode ohmic. Later another surface protective insulating film 6 is formed again and another photoresist 7 in a specific region located on the Ti/Pt is removed by coating, exposing and developing processes. Secondly the insulating film 6 is selectively removed to evaporate Ti8/Au9. Finally the photoresist 7 is peeled off to form the bonding pad Ti8/Au9 selectively on the specific region.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing electrodes of a compound semiconductor device. Compound semiconductors have been widely used in optical communication devices, high-speed devices, and the like, but these devices are sometimes used under harsh conditions and in situations where maintenance is difficult.

Therefore, these devices are required to have excellent characteristics and high reliability depending on the environment in which they are used. One of the factors that most affects reliability is electrode deterioration that progresses due to the reaction between the electrode and the semiconductor.

Semiconductor devices have conventionally contained small amounts of doping impurities (Zn,
Ohmic electrodes having a structure in which Au containing Ge, etc.) are brought into direct contact with a semiconductor have been widely used. However, in this structure, Au reacts with the semiconductor at about 200'C, which significantly deteriorates the device. In order to improve this, an electrode with a multilayer structure of Ti/(Pd, Pt, W)lAu in which high-melting point metals such as Ti, Pd, Pt, and W are sandwiched has attracted attention. 'l' i/P I lA
The u-electrode has a three-layer structure in which Ti is used as the alloy layer, Au is used as the bonding pad, and Pt, which is a high-melting point metal, is sandwiched between these two layers. It is a typical type of structured electrode and is attracting strong interest.

However, it is difficult to say that the intermetallic reactivity due to mutual diffusion between Au and via metal is sufficiently small at high temperatures. Therefore, during the heat treatment after forming the T i /P t /A u vapor deposited film, I
/cPt%Ti Au atoms that reach the interface with the semiconductor may react with the semiconductor to generate alloy spikes and cause deterioration of device characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional drawbacks and provide a highly reliable method for forming electrodes of compound semiconductor devices.

This invention KJ: First, Ti/Pt is used for electrode formation.
A method for forming electrodes of a compound semiconductor device is obtained, which includes a step of forming a vapor-deposited film and then heat-treating it to obtain an alloy layer, and further forming a multilayer metal film by performing T r /Au vapor deposition thereon.

This invention will be explained in detail below using the drawings. lol
Figure c1 represents a cross-sectional view of a conventional Ti/Pt/Au pole.

In the structure shown in FIG. 1(a), there are gaps between the insulating film 2 of the surface protector 6 and the electrodes 3, 4, and 5. For this reason, Ti
3. Pt4. During heat treatment after continuous deposition of Au5,
In addition to the deterioration caused by the high reactivity of Au5 mentioned above,
Since the surface of the semiconductor 1 is exposed in the gap region,
The problem of deterioration of the semiconductor surface is that the surface state is easily changed due to contamination from the atmosphere.

In the structure shown in FIG. 1(b) K, the electrode metal 3.4.5 covers the end portion of the insulating film 2, so that the semiconductor surface is not exposed.

However, since the coefficient of thermal expansion of the insulating film 2 is too small compared to the metals 3, 4.5 and the semiconductor 1, stress is easily applied to the end portions of the insulating film 2 during heat treatment, causing deterioration.

In addition, when the metal coating on the side surface of the insulating film step is not suitable, Au5 collapses on the interface between the metal 3 and the insulating film 2 and penetrates to the semiconductor surface, causing reaction deterioration (a1
Compared to the structure shown in the figure, alloy spikes are more likely to occur.

FIGS. 2(a) to 2(h) show schematic diagrams of the method for forming Ti/Pt/Ti/Au electrodes using the button of the present invention.

According to the present invention, first, as shown in FIG. 2(a), a surface protection insulating film 2 is formed on the surface of the compound semiconductor 10, and then a photoresist 3 is coated on the insulating film. The photoresist in a specific area is removed by exposure and development. Next, the insulating film in the specific region is removed by etching Vc1 to expose the semiconductor surface. ((b) in the same figure) Ti4/Pt5 is deposited (((b) in the same figure)
c)) After that, remove the photoresist.
A Ti4/Pt5 film is selectively formed only in a specific region.

((d) in the same figure) Heat treatment is performed in this state to form an alloy layer of Ti and semiconductor to obtain ohmic properties of the electrode. After that, as shown in the same figure (el), the surface protection insulating film 6 is formed again, and the photoresist 7 is further applied.
) Remove the photoresist in specific areas located on the Tilpt. Next, the insulating film is selectively removed (see figure (f)).
), and T i 8/Au 9 is deposited ((g) in the same figure).

Finally, by peeling off the photoresist 7, bonding pads T i 8/Au 9 are selectively formed in specific areas (FIG. 4(h)).

According to the present invention, during heat treatment, Au passes through the barrier metal due to interdiffusion, reaches the interface with the semiconductor, causes a reaction, and does not cause deterioration of device characteristics due to the formation of spikes. Furthermore, since the electrode metal and the insulating film are not in contact with each other during heat treatment, stress due to the difference in thermal expansion coefficients is not applied.

- By leaving the first insulating film formed under a clean surface condition before electrode formation, the interface between the insulating film and the semiconductor can be kept stable. Furthermore, the final result is that the insulating film has no step breaks (it has a structure that covers all the way to the edges of the Ti/Pt, so no part of the semiconductor surface is exposed to the atmosphere, preventing surface deterioration. By pressing down, the adhesion of the stain electrode will also increase.

As explained above, according to the present invention, a highly reliable electrode for a compound semiconductor device can be obtained.

[Brief explanation of the drawing]

Figure 1 + al, (bl is a structural schematic diagram of a compound semiconductor device having an electrode with a Ti/Pt/Au three-layer structure, Figure 2 [
(a) y(b) p (cl p (ct) , (
e), (r) p (gl, (h)) are schematic diagrams of the manufacturing process of a highly reliable electrode of a compound semiconductor device having a Ti/Pt/Ti/Au four-layer structure electrode according to an embodiment of the present invention. be. In the figure, 1 is Au%, 2 is Pt, 3 is Ti,
4 is an insulating film, 5 is a compound semiconductor, and 6 is a photoresist.

Claims (1)

[Claims] A first multilayer metal film made of Ti/Pt is deposited on the region where the compound semiconductor is selectively exposed by the first insulating film so as not to be in contact with the insulating film, and a semiconductor crystal on which the metal film is formed is formed. and then forming a second insulating film, selectively removing a specific region on the first multilayer metal film in the second insulating film, and removing the surface of the first multilayer metal film. A method for forming an electrode of a compound semiconductor device, comprising the step of depositing a second multilayer metal film consisting of an exposed region ICT i lA u.