JPS6237972A - Metal-electrode forming method - Google Patents

Abstract

PURPOSE:To form a low resistance electrode, whose pattern width is controlled highly accurately, by forming an opening part, whose cross section is of an inverted trapezoidal-shape, in an insulating film on a substrate, forming an etched recess part in the substrate through the opening part, and thereafter depositing and forming an electrode metal in the opening part. CONSTITUTION:An insulating film 9 of SiO2 is grown on a substrate 8 comprising a GaAs active layer. Then a gate pattern is formed with polymethyl methacrylate resist 10. The film 9 is etched with the mixed liquid of HF and NH4F. An opening part, whose cross section is of an inverted trapezoidal-shape, is formed. The width of the lower surface side of the opening is the same as that of the opening pattern of the resist 10. After the opening of the resist 10 is expanded, the substrate 8 undergoes isotropic etching, and an etched recess part is formed. Then, an Al film 11 is evaporated. Finally the resist 10 is removed, and a low gate resistance electrode 12, which is supported by the inverted trapezoidal-shaped opening part, is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming metal electrodes, particularly to a Schottky barrier gate structure field effect transistor (hereinafter referred to as MESFET).
The present invention relates to a method for forming a metal electrode that is effective for forming a low gate resistance electrode.

27. Conventional technology Conventionally, this type of low gate resistance electrode formation method is shown in Fig. 2a.
The structure was as shown in the step-by-step sectional view of -e. That is, to explain the conventional example sequentially, as shown in FIG. 2a, a low-sensitivity positive resist 2 is coated on the GaAs active layer 1, and a high-sensitivity positive resist 3 is applied thereon. The gate pattern is exposed using the electron beam 4 as shown in FIG. As shown in FIG. 2C, a resist opening 5 having a T-shaped cross section is obtained by development. Here, the reason why the pattern width of the upper resist 3 is wider than that of the lower resist 2 is because the upper resist 3 has a high sensitivity and therefore has a higher dissolution rate than the lower resist 2. Next, as shown in FIG. 2d, a metal 6 for the gate electrode is deposited, and finally, as shown in FIG. 2e, the resists 2 and 3 are removed and lifted off to form a T-shaped cross-sectional shape. A low gate resistance electrode 7 is obtained.

Problems to be Solved by the Invention In such a conventional configuration, there is a problem in that it is difficult to control the pattern width of the large-diameter upper surface electrode width and the small-diameter lower surface electrode width of the gate electrode. The reason for this is that it is difficult to combine two types of resists such that the resist opening has a T-shaped cross-sectional shape, and that it is difficult to control exposure and development. moreover,
There was also the problem that lift-off was difficult. Therefore, it was not possible to form a gate electrode with good reproducibility.

Furthermore, since the formed gate electrode has a structure in which the upper surface portion is larger than the lower surface portion, physical strength is insufficient, and there is a problem in that the gate electrode is easily damaged. The present invention solves these problems, and aims to manufacture a low gate resistance electrode with sufficient physical strength, which allows highly accurate pattern width control, and has good reproducibility.

Means for Solving the Problem In order to solve this problem, the present invention provides a step of forming an opening with an inverted trapezoidal cross section in an insulating film on a semiconductor substrate through a resist mask, , forming an etched recess through the opening, forming an electrode metal on the entire surface by vapor deposition, removing the electrode metal together with the resist mask by lift-off, and removing the metal electrode from the four etched portions of the semiconductor substrate. and a method for forming a metal electrode, comprising the step of forming a coating on an opening with an inverted trapezoidal cross section of the insulating film.

Function: With this configuration, it is possible to control the pattern width with high precision, and it is possible to form a low gate resistance electrode with good reproducibility and sufficient physical strength. , MESFET according to an embodiment of the present invention
The method for forming a low gate resistance electrode is shown in Figure 1.
) A resist 1o is applied to a thickness of 5,000 yen by a spin cord method. PMA resist 10 at 170℃
Bake for 5 minutes.

After that, as shown in FIG. 1, a gate pattern is drawn by electron beam exposure at an exposure dose of 64 μc/cni, and a resist gate pattern is obtained by development for 4 minutes with a developer of methyl isobutyl ketone (MIBK). PM
Using the MA resist 10 as a mask, the S102 film 9 is wet-etched with a mixed solution of HF and NH4F as shown in FIG. Make it the same width as the donkey pattern.

As shown in Fig. 1 d, a width slightly smaller than the opening width on the upper surface side of the SiO2 film was exposed at once to ultraviolet light using a mask, and MIBKTPMMAL/cyst 1o was developed again for 4 minutes, as shown in Fig. 1 e. Obtain an expanded resist opening. Next, sulfuric acid: hydrogen peroxide: water - 8:1:1
By isotropically etching the GaAs active layer 8 from the opening with a mixed solution of the above and forming an etched recess in the substrate at the opening, the cross-sectional shape shown in FIG. 1F can be obtained. Thereafter, as shown in FIG. 1q, an aluminum film (Al) 11 as a gate metal is deposited, and finally, the PMMA resist 10 is removed by boiling trichlorethylene, as shown in FIG. The low gate resistance electrode 12 supported in the inverted trapezoidal opening of the SiO2 film 9 can be formed using a lift-off technique.

As described above, according to this embodiment, the pattern width on the lower surface side of the low gate resistance electrode is determined by the opening width on the lower surface side of the insulating film formed first. Further, the pattern width on the upper surface side of the low gate resistance electrode is determined by the second phosphorography process. Therefore, the pattern width on the top side and bottom side can be set independently and accurately.

It can be controlled with good reproducibility. Furthermore, since the low gate resistance electrode is supported by an insulating thin film, it has sufficient physical strength. Furthermore, the insulating thin film that contacts the upper surface of the gate electrode does not directly contact the GaAs active layer due to recess etching of the GaAs active layer. Therefore, the increase in capacity can be kept to a minimum.

Effects of the Invention As described above, according to the present invention, it is possible to control the pattern width with high accuracy, and to form a low gate resistance electrode with good reproducibility and sufficient physical strength.

[Brief explanation of the drawing]

FIG. 1 shows a MESFET according to an embodiment of the present invention.
FIG. 2 is a step-by-step sectional view showing a method for forming a low gate resistance electrode according to a conventional method. 1...G a As active layer, 2...
Low-sensitivity positive resist, 3... High-sensitivity positive resist, 4... Electron beam, 6... T-shaped cross-section resist open pattern, 6... Gate metal, 7... T-shaped gate electrode, 8...
・G a As active layer, 9...SiO2 film,
10. Old... PMMA resist, 11... A1
112・Mountain・・Low gate resistance electrode. Name of agent: Patent attorney Toshio Nakao and one other person

Claims (1)

[Claims] (1) A step of forming an opening with an inverted trapezoidal cross section in an insulating film on a semiconductor substrate through a resist mask, a step of forming an etched recess in the semiconductor substrate through the opening, and a step of forming an etched recess on the entire surface with metal for an electrode. the electrode metal is removed together with the resist mask by lift-off, and the etched recess of the semiconductor substrate and the inverted trapezoid cross-sectional opening of the insulating film are coated with the metal electrode. Metal electrode formation method.