JPH03225823A - Compound semiconductor device - Google Patents

Abstract

PURPOSE:To make it possible to manufacture an electrode provided with a desired electric characteristic at a good yield by configuring the electrode so that it includes a first metallic film being in contact with a semiconductor substrate and a second metallic film formed through laminating it on a part of the top face of the first metal lic film. CONSTITUTION:An SiO2 film 11 is provided on the surface of an n-type active region 101 being on the top face side of a GaAs substrate 100, and in the opening part 11a thereof, an electrode is formed by configuring it in the following manner. That is, the electrode is made to comprise an AuGe layer 13 a first metallic layer which is formed, being close to the periphery of the opening part 11a, on the n-type active region 101 exposed in the opening part 11a the SiO2 film, and a small areal Pt layer 14 of a second metallic layer which is formed on the AuGe layer 13, being apart from the periphery thereof. Therefore, since no metallic layer being from the second layer on is contacted with the surface of GaAs, the electric characteristic of the field- effect transistor of gallium arsenide is determined only by the first metallic layer 13 being in contact with the surface of GaAs, and the faultiness of the characteristic caused by contacting the semiconductor with the two or more kinds of metals 13, 14 in the one electrode is prevented. Thereby, no deterioration of the characteristic is caused and the yield at which the electrode is manufactured is improved.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an electrode for a compound semiconductor device, and particularly provides an electrode structure suitable for an ohmic electrode or a Schottky electrode in a compound semiconductor device. It is something.

(#: Current Technology) The structure of an electrode in a compound semiconductor device, particularly a gallium arsenide field effect transistor (hereinafter abbreviated as GaAsFET), generally often uses a multilayer structure made of a plurality of metals. For example, as an ohmic electrode for a GaAsFET, it is common to deposit a metal film on GaAs in the order of AuGe and then PT, and then perform heat treatment to alloy GaAs and AuGe to obtain ohmic characteristics. The reason for laminating PT on AuGe here is to prevent the morphology of the electrode surface from deteriorating due to heat treatment.

In addition, the Schottky electrode of GaAsFET is also made of Au.
/Ti is often used in a multilayer structure. In this case, the reason for using multiple layers is that Ti is used as the metal to form a stable Schottky junction with n-type GaAs, and Au, which has a lower resistivity than Ti, is layered to lower the electrical resistance of the electrode. .

The structure of an ohmic electrode in a GaAsFET is shown in a cross-sectional view in FIG. 3, and the method for forming the same will be explained with reference to FIGS. 4(a) and 4(b), which show cross-sectional views in the order of steps. First, a 5in2 film 102 and a photoresist 103 are placed in this order on a GaAs substrate 100 on which a lot of n-type active regions are formed on the surface by, for example, ion implantation, and then an opening 102a is formed in an area where an electrode is to be formed using photolithography. to expose the n-type active region 101.

At this time, in order to facilitate the subsequent lift-off,
By over-etching the O□ film 102, SiO□
The opening in the membrane is made wider than the opening in the photoresist;
Create an overhang-like structure (Figure 4(a)). Next, evaporation is performed in the order of 10 AuGe layers and 04 layers 105 (FIG. 4(b)). Thereafter, lift-off is performed, and then heat treatment is performed to alloy the 04As substrate on the 10 AuGe layers to form an ohmic electrode (FIG. 3).

(Problem to be Solved by the Invention) In the diagonal formation method, 04
Ideally, the PT layers 105 of the second layer should be formed so as to overlap each other accurately as shown in FIG.
The t-layer 115 often wraps around the top layer 04 of the first AuGe layer 10 and comes into contact with the n-type active region 101 on the GaAs substrate 100 (FIG. 5). The problem here is metal.
The electrical properties of compound semiconductor junctions vary depending on the type of metal used. Specifically, AuGe-n type GaAs exhibits ohmic characteristics through heat treatment, while Pt-n type GaAs exhibits Schottky characteristics both before and after heat treatment. Therefore, a part of the electrode that should originally be an ohmic junction becomes a Schottky junction, and electrons in the n-type GaAs in contact with the PT become depleted, effectively pinching off the channel through which current flows. happens. That is.

Not only can only a smaller current be obtained than the current value that should originally flow through the channel, but the value of the current flowing through the channel varies depending on the polarity of the bias, showing electrical characteristics that are undesirable for an ohmic electrode (Figure 6). . GaAsFETs equipped with such electrodes have disadvantages in that desired high frequency characteristics cannot be obtained, current values vary significantly, and manufacturing yields are significantly reduced.

Similarly, in a Schottky electrode with a multilayer structure, the height of the Schottky barrier varies depending on the type of metal, and depending on the metal used, it may not be possible to form a stable Schottky junction. There was a problem in that the desired Schottky characteristics could not be obtained when it came into contact with the substrate.

An object of the present invention is to provide a novel electrode structure that eliminates the above-mentioned problems.

[Structure of the invention]

(Means for Solving the Problems) A compound semiconductor device according to the present invention includes an electrode made of a metal film sequentially laminated on at least an active region of a compound semiconductor substrate, a first metal film in contact with the semiconductor substrate, and a first metal film in contact with the semiconductor substrate; It is characterized in that it includes at least a second metal film that is laminated on a portion of the upper surface of one metal film and is spaced apart from the periphery of the second metal film.

This provides a structure in which the second and subsequent metal films do not contact the semiconductor substrate.

(Function) As described above, in the structure of the electrode according to the present invention, since the second and subsequent metal layers do not come into contact with the GaAs surface, the GaAsF
The electrical characteristics of the ET are determined only by the first metal layer in contact with the GaAs surface, and it is possible to prevent characteristic defects due to contact between the semiconductor and two or more metals at one electrode.

(Example) The electrode structure of a GaAsFET according to an example of the present invention is shown in a cross-sectional view in FIG. 1, and the method for forming the same is shown in cross-sectional views in FIGS. .

- As shown in FIG. 1, the structure of the electrode in the example GaAsFET is that a 5in2 film 11 is provided on the surface of the n-type active region 101 on the upper surface side of the GaAs substrate 100, and the electrode is placed in the opening 11a of the 5in2 film 11. It is formed in the structure of

That is, the n exposed in the opening 11a of the SiO□ film
A first metal layer of AuGe 113 is formed on the mold active region 101 close to the periphery of the opening 11a, and this AuGe layer 13
It consists of a PT layer 14 which is a metal layer on the layer surface 3.

Next, the manufacturing process for the GaAsFET electrode of one embodiment will be explained with reference to FIGS. 2(a) to 2(C). A GaAs substrate 100 with an n-type active region 101 formed on its surface is prepared, and a 5in2 film 11 and a photoresist layer 12 are formed on this surface in this order, and then an opening 11a is formed in the area where an electrode is to be formed using the photoresist layer. , n-type active region 10
1 is exposed. At this time, in order to facilitate lift-off, the opening 11a of the SiO□ film is made wider than the opening of the photoresist to form an overhang-like structure. (Second m(a)). Next, an AuGe layer 13 is deposited as a first metal layer to a thickness of 1300 angstroms over the entire surface of the semiconductor substrate. At this time, a substrate holder, such as an umbrella-shaped jig that rotates and revolves around the evaporation source, a so-called auto-revolution type planetary holder, in which the evaporated metal particles are incident on the substrate surface in an oblique direction, is used to form the AuGe layer 13. The main 13 is made to penetrate into the bottom of the photoresist layer 12 in the form of a bar hang. As a result, the AuGe layer 13 main 13
It is formed to be larger than the opening in the resist layer.

(Fig. 2(b)) Next, a PT layer 14 is formed as a second metal layer.
is deposited to a layer thickness of 300 angstroms. At this time, a flat plate type substrate holder is used so that the deposited metal is incident perpendicularly to the substrate. As a result, P of the second metal layer
Since the T layer 14 does not penetrate under the photoresist layer, the surface area of the Pt layer 14 is the same size as the opening in the photoresist layer, and is smaller around the main AuGe layer 13 of the first metal layer (Fig. 2). (C)). Next, the photoresist and unnecessary metal layer are removed by a lift-off method, and then heat treatment is performed to obtain an ohmic electrode (FIG. 1).

Although this embodiment has been described using an ohmic electrode of a GaAsFET as an example, the present invention is not limited thereto, and can be similarly applied to any electrode that utilizes the electrical characteristics of a metal-semiconductor junction. For example, GaAs
It is also possible to apply the present invention to a Schottky electrode made of multiple metal layers such as Au/Ti in FET,
In this case, good Schottky characteristics are exhibited between Ti and GaAs, which are the first metals, and the use of multiple layers does not cause deterioration of the characteristics.

Furthermore, although GaAs has been described as an example of a compound semiconductor, the present invention can of course be applied to other compound semiconductors.

In this embodiment, the electrode is formed of two metal layers, but if three or more metal layers are used, the third and subsequent metal layers may be formed to have the same size as the second metal layer.

〔Effect of the invention〕

As described above, according to the present invention, the second
Since the subsequent metal layers do not come into contact with the semiconductor substrate, the electrical characteristics of the junction are determined only by the first metal layer that is in contact with the semiconductor substrate, and good results can be obtained. Therefore, it becomes possible to manufacture electrodes with desired electrical characteristics with high yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the electrode structure of a GaAsFET according to an embodiment of the present invention, and FIGS. 2(a) to (c) are cross-sectional views showing the manufacturing process of a GaAsFET according to an embodiment of the present invention. , FIG. 3 is a cross-sectional view showing the structure of the electrode of a conventional GaAsFET, FIG. 4 is a cross-sectional view showing the manufacturing process of a conventional GaAsFET, and FIG. 5 is a cross-sectional view showing the structure of the electrode of a conventional GaAsFET. A cross-sectional view showing a state in contact with a semiconductor substrate,
FIG. 6 is a diagram showing the ohmic characteristics of a GaAsFET. A in FIG. 1 shows good characteristics due to the electrode of the present invention, and B shows poor characteristics due to the electrode of the conventional structure. 100...GaAs substrate, 101...n-type active region, 11.102-5in□ film, 12.103.7 photoresist 11a, 102a-opening, 13,104-AuG
e layer, 14.105, 115...pt layer. layer,

Claims (1)

[Claims] An electrode made of metal films sequentially laminated on at least an active region of a compound semiconductor substrate is formed by laminating a first metal film in contact with the semiconductor substrate and a part of the upper surface of the first metal film and is spaced from the periphery thereof. A compound semiconductor device comprising at least a molten second metal film.