JPS5923475B2 - Method for forming electrodes for semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming an electrode for a semiconductor device, which is capable of forming an electrode extending onto an insulating film covering a semiconductor substrate using an electrode forming method using a lift-off method.

When forming electrodes on the base region and emitter region of a semiconductor device, for example, a planar transistor, a photoresist film that serves as a mask for forming electrode formation windows is formed in an insulating film covering these regions, and then a window is formed. An electrode metal film is formed on the entire surface in this state, and then, by removing the photoresist film, the electrode metal film deposited on this is also removed, and the electrode metal film is removed. A so-called lift-off method is known in which an electrode metal film is left only inside the window.

FIGS. 1a to 1c are diagrams for explaining the method of forming an electrode by the lift-off method described above. First, as shown in FIG. A base region 3 and an emitter region 4 are formed by a well-known selective diffusion technique using the silicon dioxide film 2 formed on the surface as a mask for impurity diffusion.

Incidentally, after the above-mentioned diffusion process is completed, the silicon substrate is entirely covered with a silicon dioxide film, but as is clear from the formation of the transistor, the thickness is the thickest on the collector region as shown in the figure; It is thinnest on the emitter region and has an intermediate thickness on the base region. Next, a photoresist film 5 is formed over the entire upper surface of the silicon dioxide film 2, and using this photoresist film as a mask, a window for forming an electrode is formed in the silicon dioxide film. An electrode metal film is formed on the surface. FIG. 1b is a diagram showing the state of the silicon substrate after undergoing such processing, and as shown in the figure, there is electrode metal on the top of the photoresist film 5 and inside the base electrode forming window 6 and the emitter electrode forming window 7. A membrane 8 is applied. After the electrode metal film 8 is deposited in this way, the photoresist film 5 on the silicon substrate is
The electrode metal film 8 on the photoresist film 5 is removed at the same time by melting or incinerating it, and as shown in FIG. A transistor in which only the electrode metal film 8 is formed is obtained. The electrode metal film formed by the conventional electrode forming method described above always exists only inside the window of the silicon dioxide film.

Therefore, this method of forming an electrode is suitable for forming an electrode having a fine and complicated pattern, and also eliminates the need for selective etching of the electrode metal film, making the work for forming the electrode easier. By the way, as a structure for increasing the withstand voltage in a planar semiconductor device, an electrode that contacts a diffusion region formed in a silicon substrate to form a PN junction is made of silicon dioxide that covers the PN junction exposed on the surface of the silicon substrate. A structure in which the breakdown voltage at the end of the PN junction is substantially increased by continuously extending it to the upper surface of the film is already known, for example, from the invention described in Japanese Patent Publication No. 15139/1983.

However, in the electrode formation method described with reference to FIG. 1, the electrode is formed only inside the window, as described above, and therefore the electrode formation as described in the above publication cannot be performed. Therefore, when forming such electrodes, instead of using the lift-off method, which is highly workable, conventional methods have involved, for example, forming an electrode metal film over the entire surface and then selectively etching it. Therefore, a method of forming electrodes had to be adopted. The present invention has been made in view of the problems in the conventional electrode formation methods described above, and it is possible to form an electrode that extends to the upper surface of an insulating film covering a semiconductor substrate by making full use of the lift-off method. A method for forming an electrode is provided. The feature of the electrode forming method of the present invention is, for example, PN
A photoresist film is formed on the insulating film of a semiconductor substrate in which a diffusion region for forming a junction is formed, and an insulating film is formed over the entire surface so that the film is thin on the diffusion region and thick on other parts. Further, a window is bored in this photoresist film to expose the entire electrode forming window bored region of the insulating film covering the diffusion region and a part of the thick insulating film covering the outside of the diffusion region, and then, Regarding the insulating coating exposed in the opening formed in the photoresist film, the insulating coating in the area where the window for electrode formation is formed is completely removed, while the thick insulating coating is not completely removed. A window for forming an electrode is formed by etching over several steps, then an electrode metal film is deposited over the entire area on the semiconductor substrate while leaving the photoresist film, and finally the photoresist film is removed. As a result, the electrode metal film deposited thereon is removed at the same time. The method for forming an electrode for a semiconductor device according to the present invention will be described in detail below with reference to FIG.

In FIG. 2, the same parts as in FIG. 1 are given the same numbers. FIGS. 2a to 2d show electrodes formed in the base region and emitter region of a planar transistor, and
FIG. 6 is a diagram illustrating a method of forming an electrode in which the base electrode extends above the insulating coating covering the collector region.

In FIG. 2a, a base region 3 of an opposite conductivity type and an emitter region 4 of one conductivity type forming a PN junction are formed in a silicon substrate 1 of one conductivity type, and an insulating coating 2 is further formed to cover the surface of the silicon substrate. The state is shown after a photoresist film 5 is formed on the photoresist film 5, and a window 9 for forming a base electrode and a window 10 for forming an emitter electrode are formed in this photoresist film 5. Since the transistor is manufactured in the order of base region 3 and emitter region 4, the insulating coatings on base region 3 and emitter region 4 become thinner in sequence as shown in FIGS. 1a and 2a described above. The present invention effectively utilizes such a structure and makes it possible to simultaneously form electrodes on an insulating film from a semiconductor substrate by a lift-off method. Therefore, in the present invention, when drilling the window 9,
It is important to make the width 12 of the window 9 larger than the width 11 of the window perforation area for base electrode formation, and to establish a relationship such that a part of the insulating film covering the upper part of the silicon substrate 1 is exposed inside the window 9. be. After establishing the above relationship and drilling the window, the insulating film is etched using the photoresist film 5 as a mask.

At this time, the etching time is set to ensure that the insulating coating portion 11 in the region where the window for forming the base electrode is formed is removed, while the window 9
The time is selected to be less than completely removing the insulating coating portion 12 which is thicker than the insulating coating portion 11 covering the upper part of the silicon substrate 1 exposed in the silicon substrate 1 . FIG. 2b shows the state after the insulating film has been etched by an etching process that satisfies the above conditions. By this etching process, the thin insulating coating portion 11 exposed in the window 9 and the insulating coating exposed in the window 10 are all removed, and the base electrode forming window 6 and the emitter electrode forming window 7 are formed. An insulating coating 12 that is not covered with the photoresist film 5 exists outside the electrode forming window. Note that the thickness of this insulating film 12 is smaller than the thickness before etching. Next, as shown in FIG. 2c, an electrode metal film 8 is formed over the entire surface.

Due to the presence of the photoresist film 5, this electrode metal film 8 is divided into the top of the photoresist film 5 and the inside of the window formed in the photoresist film 5, and moreover, the electrode metal film in ohmic contact with the base region 3 is on the insulating coating 12. are formed continuously until Thereafter, by removing the photoresist film, the electrode metal on the photoresist film is simultaneously removed, and a transistor substrate with electrodes formed thereon as shown in FIG. 2d is obtained.

In a transistor with electrodes formed in this way,
As shown in the figure, the base electrode is collector-base PN junction 1.
3, and has a structure that can substantially increase the breakdown voltage at the collector-base junction end.

As is clear from the above explanation, the method for forming an electrode for a semiconductor device of the present invention is performed under manufacturing conditions that make full use of the lift-off method, in which the electrode is formed continuously onto the insulating film adjacent to the electrode forming window. It is capable of forming an electrode metal film, and can greatly improve workability, especially when forming a high-voltage semiconductor device, and greatly contributes to the manufacture of semiconductor devices.

Note that the above description can be applied to the formation of electrodes of planar transistors as well as to the case where electrodes are extended on an insulating film.

[Brief explanation of the drawing]

Figures 1 a-e are diagrams for explaining a conventional method of forming electrodes for semiconductor devices using the lift-off method, and Figures 2 a-d
FIG. 3 is a diagram for explaining a method of forming an electrode for a semiconductor device according to an embodiment of the present invention. 1... Silicon substrate, 2, 11, 12...
...Insulating coating, 3...Base region, 4...
...Emitter region, 5...Photoresist film, 6
... Window for forming base electrode, 7 ... Window for forming emitter electrode, 8 ... Electrode metal film, 9, 1
0... Window drilled in photoresist, 13...
...Collector base PN junction.

Claims (1)

[Claims] 1. Forming a photoresist film on the insulating film of a semiconductor substrate in which a base and a collector diffusion region are formed, and an insulating film is formed over the entire surface such that it is thin on both the diffusion regions and thick on other parts. Step: drilling a window for forming a base electrode and an emitter electrode in the photoresist film formed in the same step, and at least forming a region for forming an electrode forming window in the insulating film covering the base diffusion region within the window for forming the base electrode. and a part of the thick insulating film covering the semiconductor substrate that will become the collector region, and exposing only the area where the window for electrode formation is formed, with respect to the insulating film exposed in the window formed in the photoresist film. A step of applying an etching process that can completely remove the photoresist film, a step of depositing an electrode metal film over the entire area on the semiconductor substrate that has undergone the same process, and a step of removing the photoresist film on the semiconductor substrate and simultaneously removing the electrode metal film deposited on the semiconductor substrate. A method for forming an electrode for a semiconductor device, characterized in that the step of removing the metal film forms a base electrode and an emitter electrode extending onto an insulating film covering a portion of the semiconductor substrate that will become the collector region.