JPH03185841A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent deterioration of characteristics of an FET after a long time operation by a method wherein, after a gate electrode is formed, a dielectric film is formed, after the electrode surface is subjected to plasma discharge processing or heat treatment. CONSTITUTION:A positive type resist film 5 which is formed on the whole surface of a semiinsulative substrate composed of GaAs semiconductor single crystal and composed of organic polymer is fused and eliminated, and a metal layer 5 except an aperture part 5' is eliminated, thereby forming a gate electrode 7. The upper parts of the gate electrode 7, a source electrode 3 and a drain electrode 4, and the surface of the substrate 1 containing an exposed active layer 2 region between the source electrode 3 and the drain electrode 4 are subjected to plasma processing in oxygen gas or carbon tetrafluoride gas with a parallel plate type plasma equipment. The plasma processing in oxygen gas is performed under gas pressure of 0.48 torr and substrate temperature at 50 deg.C. The plasma processing in the carbon tetrafluoride is performed under gas pressure of 410 torr and substrate at a room temperature. A silicon nitride film 8 is formed on the whole surface of the active layer 2 by plasma CVD for 8 minutes using reaction between silane gas and nitrogen gas while the substrate 1 is heated at 230 deg.C.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a field effect transistor having a gate electrode forming a Schottky junction, and in particular,
The present invention relates to a method of forming a protective dielectric film (passivation film). [Prior art] A field effect transistor (hereinafter referred to as F) is equipped with a gate electrode that forms a Schottky junction on a semiconductor such as GaAs.
(ET) has excellent high-speed operation and is often used as an amplification element in the microwave band. The surface of this FET is coated with silicon oxide to protect the semiconductor surface and electrodes.
It is necessary to form a protective dielectric film made of silicon nitride or the like. Conventionally, the gate electrodes of these FETs are formed by forming a mask (made of a resist film or an insulating film such as silicon oxide) on the semiconductor surface with an opening corresponding to the gate electrode, and then depositing a metal film over the opening and the mask. It is formed by a lift-off method in which the metal film on the mask is removed by forming and then removing the mask, and the metal film is formed only in the opening. The method for forming a protective dielectric film is to form a gate electrode by a lift-off method, then wash the semiconductor surface with an organic solvent or the like, and form a protective dielectric film by a sputtering method or the like. [Problems to be Solved by the Invention] However, when an FET using a protective dielectric film made by the above conventional method is operated for a long time, various characteristics of the FET in high frequency operation and DC operation deteriorate. was known. The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a method for forming a protective dielectric film in which the characteristics of an FET do not deteriorate even after long-term operation. [Means and effects for solving the problem] The present invention is based on the idea that deterioration of FET characteristics can be prevented by performing some treatment on the gate electrode and the front surface of the semiconductor before forming a protective dielectric film. It is something. The present invention provides a method for manufacturing a field effect transistor having a source electrode, a drain electrode, and a gate electrode forming a Schottky junction on a semiconductor, including a first step of forming the gate electrode by a lift-off method; A second step of plasma discharge treatment or heat treatment of the surface of the semiconductor between the drain electrodes, and a third step of forming a dielectric film on the surface are sequentially performed. In the second step, the plasma discharge treatment is performed in an atmosphere of oxygen, a compound gas forming an oxidizing atmosphere, or a carbon compound gas containing fluorine. Further, the heat treatment is performed by heating from about 150° C. to 400° C. in an oxidizing atmosphere. Although the effect of the present invention is not clear, it is thought that since the semiconductor surface and gate electrode surface of the FET change into a stable oxide or fluoride, stable operation will be possible if a dielectric film is subsequently formed. It will be done. [Example 1] Fig. 1 (
This will be explained below using a) to (c). 0 on a substrate l made of semi-insulating GaAs semiconductor single crystal.
．． An active layer 2 is formed of a conductive GaAs epitaxial layer having a thickness of about 3 μm. A source electrode 3 and a drain electrode 4 are formed in ohmic contact with this active layer 2. Next, a positive resist film 5 made of an organic polymer is formed on the entire surface of the substrate 1. An opening 5' having a width of 1 μm is formed between the source electrode 3 and the drain electrode 4 of this resist film 5 by ordinary photolithography. Then, a metal layer 6 is formed on the resist film 5 and on the opening 5' of the active layer 2. (Figure 1(a)
) The resist M5 is dissolved and removed, and the metal layer 6 other than the opening 5' is removed.
By removing the gate electrode 7, a gate electrode 7 corresponding to the area of the opening 5' is formed. (Lift-off method) Next, the surface of the substrate l including the exposed active layer 2 region on the gate electrode 7, source electrode 3, and drain electrode 4 and between the source electrode 3 and drain electrode 4 is heated using a parallel plate plasma device. Perform plasma treatment. The plasma treatment is performed in oxygen gas or carbon tetrafluoride gas. (Figure 1 (
b)) This plasma treatment in oxygen gas is carried out at a gas pressure of 0°4.
This is carried out for 5 minutes at 8 torr and a substrate temperature of 50°C. In addition, plasma processing in carbon tetrafluoride (CF) gas is performed at a gas pressure of 410 torr and a substrate temperature of 1 to 5 torr at room temperature.
Do this for minutes. Note that an oxidizing atmosphere such as oxygen gas or a fluorine-containing carbon compound gas such as CHF can be used as the atmosphere for the plasma treatment. Thereafter, a silicon nitride film 8 (SiN) having a thickness of 1100 nm is formed on the entire surface of the active layer 2 by plasma CVD. This plasma CVD is performed for about 8 minutes by heating the substrate 1 to 230° C. and reacting silane (S i H 4 ) gas with nitrogen gas. Note that as the protective dielectric film, in addition to the silicon nitride film, a dense insulating film such as a silicon oxide film can be used. Silicon nitride film 8 on source electrode 3 and drain electrode 4 is partially removed to form wiring metal 9.9'. (Figure 1 (C)) Time-dependent change in breakdown voltage between the gate and drain electrodes of the FET fabricated through the process of Example 1 above (gate and drain electrodes)
FIG. 2 shows Example 1 in which a constant reverse current (50 mA) was continued to flow between the drain electrodes. Further, a case where the plasma treatment was not performed and the other steps were the same as in Example 1 was described as a comparative example. As can be seen from Figure 2, in the comparative example, the breakdown voltage, which was -16V immediately after fabrication of the FET, was 1800V.
After minutes, the voltage has deteriorated to -10V. However, in Example 1, such deterioration was not observed, and the breakdown voltage was constant at about -16V, indicating that no change occurred over time. Note that in Example 1 above, plasma treatment was performed after forming the gate electrode by beam lift-off, but other examples (
As Example 2), it is also possible to perform heat treatment in an oxygen atmosphere instead of this plasma treatment. This heat treatment in an oxygen atmosphere is performed by maintaining the substrate 1 at a temperature of about 300° C. for about 1 hour using a heater (such as a hot plate) in an air atmosphere. Note that the atmosphere at this time is not limited to the air, but may be any oxidizing atmosphere containing oxygen. FIG. 3 shows the change in breakdown voltage over time when a constant reverse current continues to flow through the FET manufactured according to Example 2. Further, as a comparative example, a case in which heat treatment in an oxygen atmosphere was not performed and other steps were the same as in Example 2 was described as a comparative example. In the comparative example, the same deterioration as shown in Fig. 2 was observed, but in the example 2
It can be seen that the breakdown voltage is constant at about -16V and does not change over time as in Example 1. Note that although the above embodiment uses a lift-off method using a resist film, it is also possible to use an insulating film such as a silicon oxide film instead of the resist film.

【Effect of the invention】

1. As explained above, the present invention provides a method for manufacturing a field effect transistor having a source electrode, a drain electrode, and a gate electrode forming a Schottky junction on a semiconductor. The first step, the second step of plasma discharge treatment or heat treatment of the surface of the semiconductor between the source electrode and the drain electrode, and the third step of forming a dielectric film on the surface are sequentially performed. Therefore, the characteristics of the field effect transistor according to the present invention do not deteriorate even after long-time operation, and stable operating characteristics can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are cross-sectional views for explaining one embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing changes over time in the breakdown voltage of the embodiment and the comparative example. It is. In the figure, l...substrate, 2... active layer, 3... source electrode,
4...Drain electrode, 5...Resist film, 5'...
・Opening portion, 6... Metal layer, 7... Gate electrode, 8.
...Silicon nitride film, 9.9'...Metal for wiring.

Claims (1)

[Claims] In a method for manufacturing a field effect transistor having a source electrode, a drain electrode, and a gate electrode forming a Schottky junction on a semiconductor, a first step of forming the gate electrode by a lift-off method, a step of forming the gate electrode between the source electrode and the drain electrode; A method for manufacturing a semiconductor device, comprising sequentially performing a second step of plasma discharge treatment or heat treatment on the surface of the semiconductor, and a third step of forming a dielectric film on the surface.