JPH01120073A - Mes transistor - Google Patents

Abstract

PURPOSE:To obtain a MES transistor whose surface is stable and whose high-frequency gain is large by forming the following: a silicon oxide film covering both side-wall parts directly under the overhang of a T-shaped gate electrode; a silicon nitride film which covers the T-shaped gate electrode including the silicon oxide film and the surface of an active layer between drain an source electrodes. CONSTITUTION:The following are contained: a T-shaped gate electrode 5 formed on the surface of an active layer 2 on one main face of a GaAs substrate 1; drain and source electrodes 3, 4 which sandwich the T-shaped gate electrode 5 and are formed on the surface of the active layer 2; a silicon oxide film 6 covering both side- wall parts directly under eaves of the T-shaped gate electrode 5; and a silicon nitride film 7 which covers the T-shaped gate electrode 5 including the silicon oxide film 6 and the surface of the active layer 2 between the drain and the source electrode 3, 4. By this setup, because a side-wall protective film directly under the overhang of the T-shaped gate is composed of the silicon oxide film, its film thickness is made thicker and a capacitance value Cgd between the gate and the drain electrode 3, 4 is reduced; the surface of the gate electrode is made stable due to the silicon nitride film; as a result, a stable MES transistor whose high-frequency gain is large can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an MES transistor, in particular to a GaAs field effect MES transistor.

[Conventional technology]

As transistors become more widespread, demands for improved reliability have also become stronger.

Conventionally, a surface protective film of a gate electrode having a T-shaped cross section (hereinafter referred to as a T-shaped gate electrode) of an MES field effect transistor using GaAs as a substrate has been made of either a silicon oxide film or a silicon nitride film. It was used.

[Problem that the invention seeks to solve]

The above-mentioned conventional MES transistors each have their own advantages and disadvantages when only one type is used as a surface protective film for the T-shaped gate.

In other words, when only a silicon nitride film is used as a protective film, the interface level at the interface between GaAs and silicon nitride film is GaAs.
It has the advantage of being more stable than the interface between s and silicon oxide film.

However, since the dielectric constant of the silicon nitride film is larger than that of the silicon oxide film, the gate-drain electrode capacitance FikCgd due to the sidewall film directly under the eaves of the T-shaped gate is
The problem is that it is thicker than in the case of a silicon oxide film, resulting in a reduction in high frequency gain.

The purpose of the present invention is to provide an ME with a stable surface and a large high frequency gain.
An object of the present invention is to provide an S transistor.

[Means for solving problems]

The MES transistor of the present invention includes a T-shaped gate electrode provided on the surface of an active layer on one main surface of a GaAs substrate, and drain and source electrodes provided on the surface of the active layer with the T-shaped gate electrode sandwiched therebetween. a silicon oxide film covering both side walls directly under the eaves of the T-shaped gate electrode; and a silicon nitride film covering the active layer surface between the T-shaped gate electrode and the drain and source electrodes, including the silicon oxide film. It is composed of a membrane.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention.

The MES transistor has a T-shaped gate electrode f! that includes an eaves portion 5u formed on the surface of an active layer 2 formed on an upper layer of an insulating GaAs substrate 1. 5 and eaves 5.

A silicon oxide film 6 covering the side wall directly below and a silicon oxide film M
A silicon nitride film covers the surface of the active M2 between the T-shaped gate electrode 5 including the gate electrode 6 and the drain and source electrodes 3 and 4.

The surface is stable due to the silicon nitride film 7, and the capacitance Cgd between the gate and drain electrodes is small due to the silicon oxide 1i6.

〔Effect of the invention〕

As explained above, the present invention makes the sidewall protection film directly under the eaves of the T-shaped gate a silicon oxide film to increase the film thickness and reduce the gate-drain electrode interface ICGD, and the gate electrode surface is made of silicon oxide. By stabilizing it with a nitride film, there is an effect that a stable MES transistor with a large high frequency gain can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention. 1... Insulating GaAs substrate, 2... Active layer, 3...
- Drain electrode, 4... Gate electrode, 5... T-shaped gate electrode, 5H... Eaves, 6... Silicon oxide film, 7... Silicon nitride film.

Claims (1)

[Claims] T provided on the surface of the active layer on one main surface of the GaAs substrate
a drain and source electrode provided on the surface of the active layer with the T-shaped gate electrode sandwiched therebetween;
a silicon oxide film covering both side wall portions directly under the eaves of the T-shaped gate electrode; and a silicon nitride film covering the active layer surface between the T-shaped gate electrode and the drain and source electrodes, including the silicon oxide film. An MES transistor characterized by comprising: