JPH03194926A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a narrow electrode without being restricted by the line width obtained by transferring a mask pattern of exposure to photoresist, by a method wherein the width of an aperture is made small by forming a first metal film having compressive stress on the photoresist provided with the aperture. CONSTITUTION:The following are contained; a process that photoresist 13 is formed on a substrate 10, a process that an aperture 14 is formed in the photoresist 13, a process that a first metal film 15 having compressive stress is formed on the whole surface and the width of the aperture is narrowed, a process that a second metal film 16 is formed on the whole surface, a process that the photoresist 13 and the first and the second metal films 15, 16 on the photoresist 13 are eliminated, and a process that the left first metal film 15 is etched by using the left second metal film 16 as a mash. For example, the photoresist 13 having the aperture 14 of 0.5mum in width is formed to be 1mum thick, and a W film 15 having compressive stress is formed to be 300Angstrom thick on the whole surface by sputtering method. Hence, by the effect of compressive stress of the W film 15, the width of the aperture 14 becomes smaller than 0.5mum, and the aperture becomes 0.2mum wide.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for forming electrodes and interconnections with fine line widths.

(b) Prior Art Lift-off is a method for selectively forming electrodes and wiring in a semiconductor device. This involves coating a photoresist on a substrate, selectively exposing the photoresist, developing it to open holes in the photoresist, and depositing an electrode material on top of the photoresist to separate the photoresist and the electrode material on the photoresist. By removing the photoresist, electrodes are formed on the substrate using only the openings of the photoresist.

Generally, selective exposure of photoresist is performed using a mask. The minimum realizable line width of an electrode formed using a photoresist with holes opened by exposure to ultraviolet rays or deep ultraviolet rays as a mask is about 0.5 μm. Means for obtaining a line width smaller than this include exposure to X-rays, exposure to excimer laser, or direct writing of the photoresist with an electron beam without using a mask.
However, in the case of X-ray exposure, it is difficult to manufacture an X-ray exposure mask, requiring many steps and the production cost is high, and in the case of excimer laser exposure, the exposure source has a short lifespan. I haven't. Furthermore, direct drawing with an electron beam requires a very long drawing time, which has the drawback of extremely low manufacturing efficiency and making it unsuitable for mass production.

These technologies are 5solid 5tate techno
logy/Japanese version/August 1986 p52-
591 "Microphosphorography technology for high-speed GaAs FETs".

Field-effect transistors (FETs), especially FETs using GaAs using Schottky failure, and HEMTs using highly mobile electrons accumulated at heterojunction interfaces, especially GaAs
HEMTs having an As/AIGaAs heterojunction have high electron mobility and are therefore used as ultra-high frequency devices. In order to improve the microwave characteristics of FETs and HEMTs (particularly to reduce the noise figure), it is necessary to shorten the gate length.

(c) Problems to be Solved by the Invention As mentioned above, although it is necessary to shorten the gate length in order to improve the microwave characteristics of FETs and HEMTs, the line width is limited by the transfer of the mask pattern. The width of the openings in the resulting photoresist was limiting. Furthermore, the techniques for direct writing using X-ray exposure, excimer laser exposure, or electron beams have not been established, or the productivity is poor, making them unsuitable for mass production.

The present invention uses conventional ultraviolet rays or far ultraviolet rays [,
The purpose of this method is to form electrodes with a narrower width without being limited by the line width obtained by transferring a mask pattern to a photoresist.

(D) Means for Solving the Problems The present invention comprises a step of forming a photoresist on a substrate;
a step of forming an opening in the photoresist, a step of forming a first metal film having compressive stress over the entire surface to reduce the width of the opening, and a step of forming a second metal film over the entire surface. a step of removing the photoresist and the first and second metal films on the photoresist; and a step of etching the remaining first metal film using the remaining second metal film as a mask. A method of manufacturing a semiconductor device is characterized in that it includes the steps of:

(e) Production The stress of the metal film is given by the following equation.

a=Es-D"/ (3d・(1-Vs)-4')
・δ Here, σ: stress, ES: Young's modulus, Vs: Poisson's ratio, D = upper and lower substrate thickness, d: film thickness,
δ: displacement, 2: length of the metal film (see Figure 3).

As is clear from the above equation, the larger the stress σ of the metal film, the
The amount of displacement (warpage: δ) of the substrate increases.

Therefore, when the lower substrate is a photoresist with openings, the width of the openings increases or decreases depending on the stress σ of the metal film (see FIGS. 4a and 4b).

The stress in the metal film when the width of the opening increases as shown in Figure 4a is called tensile stress, and the stress in the metal film when the width of the opening decreases as shown in Figure 4a is compressive stress. That's what it means.

As is clear from the above description, by forming a metal film having compressive stress on a photoresist having an opening, the width of the opening becomes smaller.

(f) Example 1 in which the method of the present invention is applied to the production of MESFET
Examples will be described with reference to FIGS. 1a to 1d.

After forming an n-type ion implantation layer 11 by implanting silicon ions into a semi-insulating aAs substrate 10 at an acceleration voltage of 30 kV and a dose of 5 x 10', a tungsten silicide (WSix) film 12 is formed on the entire surface by sputtering. 3
Form 000 people. Thereafter, the n-type ion implantation layer 11 is activated by heat treatment at 800° C. for 20 minutes. Subsequently, a photoresist 13 having an opening 14 with a width of 0.51 m is formed in a thickness of 1pm (FIG. 1a). The openings 14 in the photoresist 13 were formed using deep ultraviolet rays.

A tungsten CW'' film (first metal film) 15 having compressive stress is formed on the entire surface by sputtering (Fig. 1b).Then, the compressive stress of the W film 15 causes the openings 14 to be Width is less than 0.5pm Q,2
pm. The W film 15 having compressive stress can be formed by appropriately adjusting the sputtering conditions, and in this example, the conditions were set to 0.3 kW power and 5 Ar gas pressure.
mmTorr and time was 3 minutes. Note that if the Ar gas pressure is several + mn + Torr, it becomes tensile stress.

A gate electrode material (second
16 (FIG. 1C).

By removing the photoresist 13, the W film 15 and gate electrode material 16 on the photoresist 13 are removed, and carbon tetrafluoride (CF) and oxygen (O3) are mixed using the remaining gate electrode material 16 as a mask. The gate electrode 17 is formed by etching the WSix film 12 and the W film 15 by anisotropic etching using gas. The gate length of this gate electrode 17 corresponds to the width of the opening 14, so it is 0.2
It becomes μm. Finally, a photoresist with an aperture is formed at the location where the ohmic electrode is to be formed, an ohmic electrode material made of Au, Ge/Ni/AU, etc. is formed by electron beam evaporation, and the ohmic electrode 18 is formed by a lift-off method. The MESFET is completed by forming (FIG. 1d).

Note that in this example, in order to obtain good shot characteristics, W
Although the WSix film, which has better heat resistance than the W film, is interposed between the film and the substrate, this WSix film is not necessarily necessary.

Next, a second embodiment in which the present invention is applied to the production of a MESFET with a self-line structure will be described with reference to FIGS. 2a to 2d.

After forming an n-type ion implantation layer 21 by implanting silicon ions into a semi-insulating GaAs substrate 20 at an acceleration voltage of 30 kV and a dose of 5 x 10 "cm-", a photoresist having an opening 23 with a width of 0° FBm is formed. 22 is formed lpm (Fig. 2a).

A W film (first metal film) 24 having compressive stress is formed by 1000 people on the entire surface by sputtering. Then,
Due to the compressive stress of the W film 24, the width of the opening 23 is 0.
5 #m is 0.1 pm, which is smaller than #m. In this example, the above conditions are: power 0.3 kW, Ar gas pressure 5 mm Tor.
r, time was 10 minutes.

Ti 300/Au1 by electron beam evaporation method on the entire surface
Gate electrode material (second metal film) consisting of 700 people 25
(Figure 2b).

By removing the photoresist 22, the W film 24 and gate electrode material 25 on the photoresist 22 are removed, and silicon ions are accelerated using the remaining gate electrode material 25 and W film 24 as masks at a voltage of 100 kV and a dose of 3X10. "cm-1 implantation to form n+ ion implantation layer 2
6 (Figure 2C). In this ion implantation, a shallow n'' ion implantation layer 27 is formed under the W film 24 by the silicon ions that have passed through the W film 24, which is effective in reducing the series resistance.

Then, using the remaining gate electrode material 25 as a mask, C
The gate electrode 28 is formed by etching the W film 24 by anisotropic etching using a mixed gas of F and O8.

The gate length of this gate electrode 28 corresponds to the width of the opening 23, so it is 0.1 pm. Finally, 800℃, 2
By performing heat treatment for 0 minutes, the n-type ion implantation layer 21
After activating the ion-implanted layers 26 and 27, a photoresist with openings is formed at the locations where the ohmic electrodes are to be formed, and Au is deposited by electron beam evaporation.
By forming an ohmic electrode material made of -Ge/Ni/Au, etc., and forming an ohmic electrode 29 by a lift-off method, a ME SFET with a self-line structure is completed (FIG. 2d).

In addition, in each of the above-mentioned examples, a W film was used as the first metal film having compressive stress, but in addition to this, WSiN, W
N, WAl, etc. can be used.

(G) Effects of the Invention As is clear from the above description, the width of the openings is not reduced by forming the first metal film having compressive stress on the photoresist having the openings. In other words, it is possible to obtain a gate electrode with a gate length shorter than the line width that can be achieved with conventional photoetching, and it is possible to
It is possible to significantly improve the characteristics of HEMT.

[Brief explanation of drawings]

FIGS. 1 a to d are process explanatory diagrams for explaining the first embodiment of the present invention, FIGS. 2 a to d are process explanatory diagrams for explaining the second embodiment of the present invention, and FIG. The figure is a diagram for explaining the stress in the metal film, and FIGS. 4a and 4b are diagrams for explaining the change in the opening width of the photoresist. 10.20-...Semi-insulating GaAs substrate, 11.21-
...N-type ion implantation layer, 13.22...Photoresist, 14.23...Open hole, 15.24...W film,]
7.18...Gate electrode. Figure 1

Claims (1)

[Claims] 1. A step of forming a photoresist on a substrate, a step of forming an opening in the photoresist, and a step of forming a first metal film having compressive stress on the entire surface to reduce the width of the opening. and a step of forming a second metal film on the entire surface,
the photoresist and the first photoresist on the photoresist;
A method for manufacturing a semiconductor device, comprising: removing a second metal film; and etching the remaining first metal film using the remaining second metal film as a mask.