JPS6350072A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To resolve the discontinuity of the molybdenum silicide film of a second gate electrode, by making the sum of the film thickness of a first gate electrode and that of a second gate insulating film smaller than or nearly equal to the thickness of the molybdenum silicide film. CONSTITUTION:On the surface of a gate oxide film 3 and that of a field oxide film 2, a polycrystalline silicon film is formed, on a specified part of which a resist pattern 9 is formed. This film is subjected to an isotopic plasma etching applying the pattern 9 to a mask, and the remaining film is subjected to an anistropic plasma etching applying the pattern 9 to a mask to form a first gate electrode 40. After the pattern 9 is eliminated, a gate oxide film 50 is formed on the electrode 40, and a polycrystalline silicon film 60 is formed on the surface of the film 50 and that of the film 2. A molybdenum silicide film 70 is formed on the surface of the film 60, and a second electrode is constituted of the films 50 and 70. The sum of the following two is made smaller than or nearly equal to the thickness of the film 70; i.e. the larger one out of step differences 40a and 40b of the edge part of the electrode 40, and the thickness of the film 50.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a semiconductor device and a method for manufacturing the same, and particularly relates to an improvement for continuously forming a molybdenum silicide film of a second gate electrode in a two-layer gate electrode structure. It is something.

[Prior Art] FIGS. 2A and 2B are process cross-sectional views for explaining a method of manufacturing a conventional floating gate nonvolatile MOS memory device.

To explain this manufacturing method, first, a field oxide film 2 is selectively formed on the surface of a silicon substrate 1, and then a first gate oxide film 3 is formed on the surface of the silicon substrate 1 between the field oxide films 2.

Next, a first polycrystalline silicon film having a thickness of about 4000 Å is formed on the surface of the first gate oxide film 3 and the field oxide film 2 by vapor phase growth. Next, a resist pattern is formed on a predetermined portion of this first polycrystalline silicon film, and after this,
Using this resist pattern as a mask, this first polycrystalline silicon film is anisotropically plasma etched using OF4 gas to form a first gate electrode 4 (FIG. 2A). next,
The first gate electrode 4 is thermally oxidized to form a second gate electrode with a thickness of about 60 OA.
A gate oxide film 5 is formed. Next, the second gate oxide film 5
A second polycrystalline silicon film 6 having a thickness of about 3000 Å is formed on the surface and the surface of the field oxide film 2 by vapor phase growth. Next, the surface of the second polycrystalline silicon film 6 is heated to a wafer temperature of 200 to 400°C.

A molybdenum silicide film 7 having a thickness of about 3000 A is formed by sputtering at an argon gas pressure of 10 -2 to 10 -a TOrr. Here, the second polycrystalline silicon film 6 and molybdenum silicide I! lI7 constitutes the second gate electrode. Next, although not shown, a molybdenum silicide film 7°, a second polycrystalline silicon film 6. The second gate oxide film 5. The first gate electrode 4 and the first gate oxide film 3 are etched. Next, an impurity diffusion layer that will become a source/drain, a smooth coat film 8, aluminum wiring, etc. are formed in this order.

[Problems to be Solved by the Invention] The conventional floating gate type nonvolatile MOS memory device is manufactured as described above, but the molybdenum silicide film 7 is formed on the second polycrystalline silicon film 6 by the battering method. At this time, the step difference at the edge portion of the first gate electrode 4 is about 4200 to 4300 Å, which is the sum of the thickness of the first gate electrode 4 and the thickness of the second gate oxide film 5. There was a problem in that the silicide film 7 could not sufficiently cover the step difference in the second polycrystalline silicon w46, resulting in a discontinuous portion like 7a and increasing the wiring resistance of the second gate electrode. In order to improve the discontinuity of the molybdenum silicide film 7, if the molybdenum silicide film 7 is formed thickly to a thickness of about 4000 to 5000 Å, the internal stress of the molybdenum silicide film 7 becomes large, and the molybdenum silicide film 7 Although this eliminates the discontinuity, there are problems such as an increase in the level difference in the film.

This invention was made to solve the above-mentioned problems, and an object thereof is to obtain a semiconductor device and a method for manufacturing the same that can eliminate the discontinuity of the molybdenum silicide film of the second gate electrode. .

Means for Solving Problem L] The semiconductor device according to the present invention has the following features: the thickness of the first gate electrode formed on the surface of the first gate insulating film and the surface of the field insulating film; The sum of the thickness of the second gate insulating film formed on the surface of the field insulating film is approximately the same as the thickness of the molybdenum silicide film of the second gate electrode formed on the surface of the second gate insulating film and the surface of the field insulating film. or less.

A method for manufacturing a semiconductor device according to the present invention includes forming a first conductive film on a surface of a first gate insulating film and a surface of a field insulating film, forming a resist pattern on a predetermined portion of the surface of the first conductive film, and masking the resist pattern. After this isotropic etching, the remaining first conductive film is etched using the same resist pattern as a mask.
forming a first gate electrode by anisotropically etching the conductive film, removing the resist pattern, and forming a second gate insulating film on the first gate electrode surface and the field insulating film surface;
A second conductive film is formed on the surface of the second gate insulating film and the field insulating film, a molybdenum silicide film is formed on the surface of the second conductive film, and a second gate electrode is formed from the second conductive film and the molybdenum silicide film. It's a method.

[Function] In this semiconductor device invention, the sum of the film thickness of the first gate electrode and the film thickness of the second gate insulating film is made to be equal to or less than the film thickness of the molybdenum silicide film.
A molybdenum silicide film can be continuously formed on the surface of the second conductive film.

Therefore, in the case of conventional semiconductor devices, the problem of increased wiring resistance of the second gate electrode caused by discontinuity of the molybdenum silicide film is solved.

In this method of manufacturing a semiconductor device, the first conductive film is first isotropically etched by a predetermined thickness, and then the remaining first conductive film is anisotropically etched, so that the edge portion of the first gate electrode A two-step step is formed. For this reason,
The step formed in the 21F electrical film also has two steps, which makes the step smaller, and the molybdenum silicide film can be continuously formed on the surface of the second conductive film.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

In the description of this embodiment, the description of parts that overlap with the description of the conventional technology will be omitted as appropriate.

FIGS. 1A and 1B are process cross-sectional views for explaining a method of manufacturing a floating gate nonvolatile MOS memory device according to an embodiment of the present invention.

To explain this manufacturing method, first, using a method similar to the conventional manufacturing method, approximately 4,000 ml of
A's ff! A thick first polycrystalline silicon film is formed, and then a resist pattern 9 is formed in a predetermined portion of the first polycrystalline silicon film.

Next, this first polycrystalline silicon film is subjected to isotropic plasma etching using resist pattern 9 as a mask. At this time, this first polycrystalline silicon film is etched to a thickness of 2000 Å. 40a is a step formed by this isotropic etching.

Next, using the same resist pattern 9 as a mask, the remaining first polycrystalline silicon film with a thickness of 2000 Å is anisotropically plasma etched using CF and gas in the same manner as in the prior art to form the first gate electrode 40. . 40b is a step formed by this anisotropic etching (FIG. 1A).

Next, the resist pattern 9 is removed, and then the first gate electrode 40 is thermally oxidized at approximately 600A in the same manner as in the prior art.
A second gate oxide film 50 having a thickness of . Next, the second
A second polycrystalline silicon film 60 is formed on the surface of gate oxide film 50 and field oxide film 2 by vapor phase growth. At this time, the steps 40a, 40 of the first gate electrode 40
A two-step step is formed in the second polycrystalline silicon film 60 corresponding to b, and the step in the second polycrystalline silicon film 60 becomes smaller. Next, a molybdenum silicide film 70 is formed on the surface of the second polycrystalline silicon 1II60 by sputtering.

Here, the second gate oxide film 50 and the molybdenum silicide film 70 constitute a second gate electrode. At this time, the first
The larger of the two steps 40a and 40b at the edge portion of the gate electrode 40 and the second gate oxide film 50
It is necessary to make the sum of the film thicknesses equal to or less than the film thickness of the molybdenum silicide film 70. The thickness of the molybdenum silicide film 70 is, for example, about 2
It is 300A.

In this way, two steps 40a and 40b are formed in the etched portion of the first gate electrode 40, and a predetermined thickness of molybdenum silicide is formed. By forming 1I70 on the surface of the second polycrystalline silicon film 60, it becomes possible to form this molybdenum silicide film 7o continuously, which eliminates the problems that occur due to discontinuity of the molybdenum silicide film 7 in the case of conventional semiconductor devices. The problem of increased wiring resistance of the second gate electrode is solved. In addition, molybdenum silicide [170
Since the film thickness can be made thinner than in the conventional case, its internal stress does not become large.

Next, as in the prior art, an impurity diffusion layer that will become a source/drain, a smooth coat film 8, an aluminum wiring, etc. are sequentially formed.

In the above embodiment, the first gate electrode 40 having two steps 40a and 40b in the etched portion is obtained by etching the first polycrystalline silicon film twice. If the thickness of the crystalline silicon film can be made sufficiently thin, the sum of the thickness of this first polycrystalline silicon film and the thickness of the second gate insulating film should be equal to or smaller than the thickness of the molybdenum silicide film. The following may be used, and in this case as well, the molybdenum silicide film can be continuously formed on the surface of the second polycrystalline silicon film.

Furthermore, although the above embodiments have been described with respect to a floating gate type non-volatile MOS memory device, the present invention is also applicable to other devices in which a polycrystalline silicon film is used for the first gate electrode and a molybdenum silicide film is used for the second gate electrode. The present invention can also be applied to semiconductor devices, and in this case as well, the same effects as in the above embodiments can be achieved.

[Effects of the Invention] As described above, according to the invention of this semiconductor device, the thickness of the first gate electrode formed on the surface of the first gate insulating film and the surface of the field insulating film, and the thickness of the first gate electrode formed on the surface of the first gate insulating film and the field insulating film are The sum of the thickness of the second gate insulating film formed on the film surface is approximately the same as the thickness of the molybdenum silicide film of the second gate electrode formed on the surface of the second gate insulating film and the field insulating film. or less,
A semiconductor device in which a molybdenum silicide film is continuously formed on the surface of the second conductive film can be obtained.

Therefore, in the case of a conventional semiconductor device, the problem of increased wiring resistance of the second gate electrode caused by discontinuity of the molybdenum silicide film is solved, and a semiconductor device with good characteristics can be obtained.

Furthermore, according to the invention of the first method for semiconductor devices, the first
Since the conductive film is first isotropically etched to a predetermined thickness and then the remaining first conductive film is anisotropically etched, a two-step step is formed in the etched portion of the first gate electrode. Therefore, the step difference formed in the second conductive film becomes two steps, and the step difference becomes smaller, thereby obtaining a method for manufacturing a semiconductor device in which a molybdenum silicide film can be continuously formed on the surface of the second conductive film. Can be done.

[Brief explanation of the drawing]

FIGS. 1A and 1B are process cross-sectional views for explaining a method of manufacturing a floating gate nonvolatile MOS memory device according to an embodiment of the present invention. FIGS. 2A and 2B are process cross-sectional views for explaining a method of manufacturing a conventional floating gate type nonvolatile MOS memory device. In the figure, 1 is a silicon substrate, 2 is a field oxide film, 3 is a first gate oxide film, 40 is a first gate electrode, 40
a, 40b are steps, 50 is a second gate oxide film, 60 is a second polycrystalline silicon film, 70 is a molybdenum silicide film,
8 is a smooth coat film, and 9 is a resist pattern. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (8)

[Claims] (1) a silicon substrate, a field insulating film selectively formed on the surface of the silicon substrate for isolating elements, and a first gate insulating film formed on the surface of the silicon substrate between the field insulating films; , a first gate electrode made of a first conductive film formed on the surface of the first gate insulating film and the surface of the field insulating film, and a second gate insulating film formed on the surface of the first gate electrode and the surface of the field insulating film. a second conductive film formed on the surface of the second gate insulating film and the surface of the field insulating film, and a molybdenum silicide film formed on the surface of the second conductive film; What is molybdenum silicide film?
forming a gate electrode, the sum of the film thickness of the first gate electrode and the film thickness of the second gate insulating film being approximately equal to or less than the film thickness of the molybdenum silicide film; Semiconductor equipment. (2) Two steps are formed at the edge portion of the first gate electrode, and the sum of the larger of the two steps and the thickness of the second gate insulating film is: 2. The semiconductor device according to claim 1, wherein the thickness of the molybdenum silicide film is approximately equal to or less than that of the molybdenum silicide film. (3) The semiconductor device according to claim 1 or 2, wherein the first and second conductive films are polycrystalline silicon films. (4) The semiconductor device according to any one of claims 1 to 3, wherein the field insulating film, the first gate insulating film, and the second gate insulating film are oxide films. (5) selectively forming a field insulating film for isolating elements on the surface of the silicon substrate;
forming a gate insulating film; forming a first conductive film on the surface of the first gate insulating film and the field insulating film; and forming a resist pattern on a predetermined portion of the surface of the first conductive film. , isotropically etching the first conductive film by a predetermined thickness using the resist pattern as a mask, and after the isotropic etching, anisotropically etching the remaining first conductive film using the resist pattern as a mask. a step of removing the resist pattern; a step of forming a second gate insulating film on a surface of the first gate electrode and a surface of the field insulating film; forming a second conductive film on a film surface and the field insulating film surface; and forming a molybdenum silicide film on the second conductive film surface; A method for manufacturing a semiconductor device comprising two gate electrodes. (6) The method of manufacturing a semiconductor device according to claim 5, wherein the first and second conductive films are polycrystalline silicon films formed by vapor phase growth. (7) The method of manufacturing a semiconductor device according to claim 5 or 6, wherein the field insulating film, the first gate insulating film, and the second gate insulating film are oxide films. (8) The method of manufacturing a semiconductor device according to claim 7, wherein the second gate insulating film is formed by thermally oxidizing the first gate electrode.