JPH02296343A - Field effect transistor - Google Patents

Abstract

PURPOSE:To prevent the direct contact of a gate electrode and a semiconductor substrate, restrain leak current in this region, and prevent side gate effect turning to the cause of circuit malfunction in the case where an element approaches, by selectively forming an insulating film under a gate electrode in a region except a channel layer. CONSTITUTION:In a necessary region of the surface of a semiinsulative GaAs substrate 1, a channel layer 3 is formed, on which a gate electrode 4 is formed by using metal constituting a Schottky junction. This gate electrode 4 with a specified gate length is formed all over the width direction of the channel layer 3; a part of the electrode is formed in a large area in the adjacent region of the channel layer 3, and used as a connection electrode with other elements. In a region except the channel layer 3 and under the gate electrode 4, a silicon nitride film 2 is selectively formed between the GaAs substrate 1 and the gate electrode 4, and direct contact of the gate electrode 4 and the GaAs substrate 1 is prevented in said region. Thereby the leak current between the gate electrode 4 and the GaAs substrate 1 can be restrained in the region except the channel layer 3, so that circuit malfunction is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a metal Schottky junction field effect transistor (MESFET), and particularly to a field effect transistor with reduced leakage current.

[Prior Art] In general, a Schottky junction type field effect I transistor has a channel layer (active layer) formed on the surface of a semiconductor substrate, and a metal serving as a gate electrode forming a Schottky junction in this channel layer is made of a semiconductor. The structure is formed on a substrate.

In this case, the planar width of the gate electrode is usually formed to be larger than the planar width of the channel layer so that the gate electrode extends on the channel layer, and a part of the gate electrode is connected to wiring or electrodes. In order to configure it as a channel, the structure is such that it is formed over a large area in a region other than the channel.

[Problems to be Solved by the Invention] In the conventional field effect transistor described above, the following problems occur because the gate electrode is in direct contact with the semiconductor substrate even in areas other than the channel layer.

For example, when forming a GaAs semiconductor integrated circuit, a leakage current flows from the electrodes of other elements in the vicinity of the formed field effect transistor to the electrodes 1 to 1. When this leakage current is large enough, it injects electrons or holes into the trap level at the bottom of the channel layer of the field effect transistor, thereby modulating the thickness of the channel layer and, as a result, changing the threshold voltage of the field effect transistor. This causes a phenomenon called the Seidgate effect.

In this GaAs semiconductor, electron traps are the main feature, and the channel is narrowed by injection of electrons due to an external negative potential, thereby reducing the threshold voltage.

In order to prevent this, it is possible to reduce the area where the gate electrode is in direct contact with the semiconductor substrate other than the channel layer, but in order to connect the field effect transistor to other elements, the area must be larger than necessary. However, there is a problem in that it is difficult to suppress the leakage current described above.

An object of the present invention is to provide a field effect transistor in which the leakage current described above is suppressed.

[Means to solve the problem]

The field effect transistor of the present invention is a field effect transistor in which a gate electrode of a Schottky junction is provided on a channel layer provided on a semiconductor substrate, in which insulation is provided between the semiconductor substrate surface and the D1-electrode in a region other than the channel layer. The film is selectively formed.

[Function] With this configuration, the gate electrode can be prevented from coming into direct contact with the semiconductor substrate in a region other than the channel layer, and leakage current between the gate electrode and the semiconductor substrate in this region can be suppressed.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which FIG. 1(a) is a plan view and FIG. 1(b) is an enlarged sectional view taken along line 8-A. In the figure, a channel layer 3 is formed in a required area on the surface of a semi-insulating GaAs substrate 1, and a gate electrode 4 is formed thereon from a metal constituting a Schottky junction. This gate electrode 4 is formed on the channel layer 3 with a predetermined gate length over the entire width direction of the channel layer 3, and a part thereof is formed in a large area in an area adjacent to the channel layer 3, and the other part is formed in a large area in an area adjacent to the channel layer 3. It is configured as an electrode for connection with an element. Then, in a region other than the channel layer 3 and below the gate electrode 4, a silicon nitride film 2 is selectively formed between it and the surface of the GaAsJJ plate 1,
Direct contact between the gate electrode 4 and the GaAs substrate 1 is prevented in this region.

Figure 2 is Figure 1(b) showing a part of the manufacturing method.
It is a sectional view similar to.

First, silicon nitride If! is applied to a semi-insulating GaAs substrate 1. J
After depositing 300 layers of C.2, a channel layer pattern was formed by lithography using FoI resist 5, and C.
The silicon nitride film 2 at the opening is removed by reactive ion etching using a mixed gas of F and H2, and Si' ions are implanted by ion implantation to form a channel layer 3. After that, it is treated with diluted hydrofluoric acid, and the silicon nitride film 2 is coated with a photoresist 5 to a thickness of 0.2 to 0.5 μm.
Etching.

Next, the film 1 to the resist 5 are removed, tungsten silicide 4 is deposited on the entire surface, a gate pattern is formed by lithography using another film 1 and the resist, and a reactive layer is formed using a mixed gas of CF 4 and SF. Form electrodes 1 to 4 by ion etching.

Therefore, according to the field effect transistor having this configuration, in the channel layer 3, the gate electrode 4 is made of GaAs5.
A Schottky junction is formed by direct contact with the plate 1, but direct contact between the gate electrode 4 and the GaAs substrate 1 is prevented by the silicon nitride film 2 in regions other than the channel layer 3. This makes it possible to suppress the leakage current between the gate electrode 4 and the GaAs substrate in the region other than the channel layer 3, thereby reducing the FI! ! Prevent malfunction.

In the above embodiment, the data 1-electrode 5 and the GaAs substrate 1
Although a silicon nitride film was used for insulating isolation from the
V may also be used. Further, the present invention can be applied not only to C'aAs substrates but also to all metal Schottky junction field effect transistors made of Si or other compounds.

〔Effect of the invention〕

As explained above, in the present invention, an insulating film is selectively formed under the gate electrode in a region other than the channel layer to prevent direct contact between the gate electrode and the semiconductor substrate.
This area has the effect of suppressing leakage current between the electrode and the semiconductor substrate and preventing the xytoge effect that causes circuit malfunctions even when elements are brought close together in an integrated circuit. .

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, in which (a) is a plan view, (b) is an enlarged sectional view taken along line 8-Δ,
FIG. 2 is a sectional view similar to FIG. 1(b) showing a part of the manufacturing method. DESCRIPTION OF SYMBOLS 1... Semi-insulating GaAs substrate, 2... Silicon nitride film, 3... Channel layer, 4... Kate electrode, 5...
...Fol~Resist. ! −Issho

Claims (1)

[Claims] 1. In a field effect transistor in which a Schottky junction gate electrode is provided on a channel layer provided on a semiconductor substrate, an insulating film is selectively formed between the semiconductor substrate surface and the gate electrode in a region other than the channel layer. A field effect transistor characterized by: