JPH03238829A - Manufacture of field effect transistor - Google Patents

Abstract

PURPOSE:To enable adhesion property between a pad an a semiconductor substrate to be improved and the pad without any increase in leak current to be formed by forming a pad to be connected to a source electrode, a drain electrode, and a gate electrode on a ground pad by performing heat treatment. CONSTITUTION:After forming a metal which makes an ohmic contact at an operation layer region on a semiconductor substrate 101, Ti is formed as a first metal layer 14 which becomes a Schottky junction as a ground pad and for example Pt is formed as a second metal layer 15 which becomes a barrier metal on it at a region which does not overlap the metal which makes an ohmic contact except the operation layer. Then, heat treatment is performed to enable an ohmic electrode (source/drain electrode) to be formed and at the same time the first metal layer 14 is allowed to strike through the semiconductor. After that, a pad 17 which is connected to an ohmic electrode and a Schottky electrode is formed on the second metal layer 15, thus enabling adhesion between the pad and the semiconductor substrate to be improved and a pad 17 without any increase in leak current to be formed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a field effect transistor, and particularly to a method for manufacturing a field effect transistor in which a method for forming pads of a field effect transistor is improved. Regarding the method.

(Prior Art) In recent years, a Schottky field effect transistor has been proposed as a semiconductor device used in an ultra-high frequency band, and has reached the practical stage. A typical Schottky type GaAs field effect transistor will be described with reference to FIGS. 3 and 4, which are cross-sectional views.

After forming an ohmic metal 103 for a source electrode and a drain electrode in an active layer region 102 selectively formed on the upper surface of a GaAs semi-insulating substrate (hereinafter referred to as substrate) 1o1 by ion implantation or epitaxial growth,
Ohmic electrodes (source, drain electrodes) are formed by heat treatment.
After forming the gate electrode 106, for example, Ti, P is deposited on the substrate 101 from the gate electrode, source electrode, and drain electrode to facilitate connection with bonding wires.
A pad 107 made of Au is formed.

The GaAs field effect transistor having the above structure has the following problems.

Next, another commonly used method is to form an ohmic metal under the pad to form an ohmic electrode, improve adhesion by alloying it with the substrate, and then form a pad on top of it. There is a method of increasing the adhesion between the semiconductor substrate and the pad by doing so. An example of the manufacturing method will be described below with reference to the drawings.

As shown in the cross-sectional view in FIG.
3 is patterned by a lift-off method, and then heat treated to form an alloy layer of the GaAs substrate and the ohmic metal layer. Thereafter, as shown in the cross-sectional view of FIG. 4(b), after forming a gate electrode 106, a pad 107 is formed on the alloy layer by a lift-off method. As a result, board 1
The adhesion between the pad layer 107 and the pad layer 107 is improved.

(Problems to be Solved by the Invention) In the GaAs field effect transistor having the conventional structure explained with reference to FIG. 3 above, pad separation may occur due to insufficient adhesion between the semiconductor substrate and the pad. One method for solving this problem is to improve adhesion by forming a pad in the structure shown in FIG. 3 and then sintering it so that Ti, which is the pad metal, bites into GaAs. In order to obtain sufficient adhesion with this method, sintering at 400° C. or higher is desirable. However, due to this sintering, the ohmic metal and pad metal may diffuse into each other, resulting in deterioration of the ohmic characteristics.FET characteristics (saturation current, etc.) may also fluctuate due to the high temperature sintering performed after forming the gate electrode. Generally, this is not done because it affects the characteristics of the transistor itself.

In the field effect transistor having the conventional structure explained with reference to FIG. There is a problem in that if the bonding properties of the substrate are not sufficient, leakage current between pads increases.

The purpose of this invention was made in view of the above-mentioned conventional problems.The purpose of this invention is to improve the adhesion between the semiconductor substrate and the pad without affecting the ohmic characteristics and the Schottky characteristics, to prevent electrode peeling from occurring, and to reduce leakage current. An object of the present invention is to provide a method for manufacturing a field effect transistor having a highly reliable pad that does not increase the number of pads.

[Structure of the invention]

(Means for Solving the Problems) A method for manufacturing a field effect transistor according to the present invention includes forming a metal that makes ohmic contact with an active layer region on a semiconductor substrate when forming a pad electrode on a semiconductor substrate. After that, in a region other than the active layer that does not overlap with the metal that will make ohmic contact, a first metal layer of, for example, Ti, which will become a Schottky junction as a base pad, and a second metal layer, such as PT, which will become a barrier metal, will be formed on top of it.
is formed, and then heat-treated to form ohmic electrodes (source/drain electrodes). At the same time, the first metal layer digs into the semiconductor to improve adhesion with the semiconductor substrate, and then ohmic electrodes and Schottky electrodes are formed. The method is characterized in that a pad connected to the electrode is formed on the second metal layer.

(Function) The FET manufacturing method according to the present invention improves the adhesion between the pad and the semiconductor substrate without affecting the Schottky characteristics and ohmic characteristics, and forms a pad that does not increase leakage current.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1(a) and 1(b) are cross-sectional views showing the manufacturing method of one embodiment in the order of steps, and in each step, the same parts as in the conventional method are denoted by the same reference numerals as in the conventional method, and the explanation thereof will be omitted. Further, FIG. 2 shows the main parts of the MESFET according to the embodiment from the top, and FIG. 1 shows a cross section taken along the line A--A in FIG.

First, resist patterning for ohmic electrodes (source/drain electrodes) is performed by photolithography on the active layer region 102 selectively formed on the substrate 101 by, for example, ion implantation.
: After depositing the Ni layer, lift-off is performed to pattern the ohmic metal layer 13. Subsequently, resist patterning of a base pad is performed by photolithography in a region other than the active layer region that does not overlap with the ohmic metal layer, and as the first metal layer 14, for example, a Ti layer is formed to a layer thickness of 500A, and then a second layer is formed. As the metal layer 15, for example, a PT layer is deposited to a thickness of 500 Å, and then a base pad is formed by a lift-off method. Next, heat treatment is performed at 450° C. to form ohmic electrodes (source/drain electrodes) in the active layer region. At this time, the first metal layer 14 of the base pad digs into the GaAs substrate 1 without forming ohmic contact, so that the adhesion is increased without increasing leakage current. Also, at this time, the ohmic metal layer 13 and the first metal layer 14. Since it is separated from the second metal layer 15, the heat treatment will not cause a reaction with each other and deteriorate the ohmic characteristics (FIG. 1(a)).

Next, after forming the gate metal, resist patterning for pads connected to the source/drain electrode 103 and the gate electrode 106 is performed by photolithography so as to overlap with the base pad, and as a pad, for example, a Ti layer is formed with a layer thickness of too much. A PT layer with a thickness of 1,000 Å and an Au layer with a thickness of 8,000 Å are sequentially deposited on a substrate, followed by lift-off to form a pad 17 (FIG. 1(b)).

〔Effect of the invention〕

As described above, according to the present invention, the adhesion between the pad and the semiconductor substrate can be improved without affecting the Schottky characteristics and ohmic characteristics. It is possible to provide a method for forming a pad without increasing the amount of water.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) show M according to an embodiment of the present invention.
Cross-sectional views showing the manufacturing process of ESFET in order of process,
FIG. 2 is a top view for explaining the MESFET according to the embodiment, FIG. 3 is a sectional view of the MESFET of the conventional example, and FIG.
Figures (a) and (b) are both cross-sectional views showing the manufacturing process of a conventional MESFET in order of process. 13... Ohmic metal layer, 14... Ti layer (first metal layer), 15... pt
layer (second metal layer), 17... pad, 101...
- Semi-insulating GaAs substrate, 102...active layer region, 1
06... Schottky gate electrode. 15:PtJ!

Claims (1)

[Claims] In manufacturing a field effect transistor having a source electrode, a drain electrode, and a gate electrode on the surface of a high-resistance semiconductor substrate on which an active layer of one conductivity type is selectively formed, a metal layer is formed to form an ohmic contact on the active layer. a first metal layer that serves as a Schottky junction as a base pad and a second metal layer that is laminated thereon to serve as a barrier metal so as not to overlap the metal layer in a region other than the active layer on the semiconductor substrate; A field effect transistor comprising the steps of forming each layer to a desired thickness, performing heat treatment, and forming pads connected to a source electrode, a drain electrode, and a gate electrode on the base pad. Production method.