JPH0210875A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To eliminate the discontinuity of a molybdenum silicide film by burying beforehand a step of the edge of a polycrystalline silicon film as a floating electrode with a sidewall having a low inclination, and forming a polycrystalline film as a control electrode and a molybdenum silicide film. CONSTITUTION:After a field oxide film 2 and a gate oxide film 3 are formed on a silicon semiconductor substrate 1, a polycrystalline silicon film 4 is deposited, with a resist pattern as a mask the film 4 is selectively removed by etching by an anisotropic plasma etching method, an oxide film 9 is then formed. Then, when the film 9 is removed by an anisotropic etching method, the step of the edge of the film 4 is formed with a sidewall 9a having a low inclination. Thereafter, a gate oxide film 5 is formed on the film 4, a polycrystalline silicon film 6 is deposited, and a molybdenum silicide film 7 is deposited. Subsequently, an impurity diffused layer to become source, drain, a smooth coating film 8, aluminum wirings are formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a semiconductor device, and more specifically, the present invention relates to a method for manufacturing a semiconductor device, and more specifically, it has a two-layer electrode consisting of a floating electrode and a control electrode, and the second layer of the control electrode is This invention relates to an improvement in a method for manufacturing a floating gate type nonvolatile MOS memory device that uses a silicide film of a high melting point metal such as molybdenum silicide.

[Conventional technology]

As a conventional semiconductor device of this type, the main manufacturing steps of a floating gate type nonvolatile MOS memory device are sequentially shown in FIGS. 2(a) and 2(b).

That is, in FIG. 2, the device configuration according to the conventional example is such that first, on one main surface of the silicon semiconductor substrate 1,
Field oxide film 2. After forming the first gate oxide [3], a first polycrystalline silicon film 4, which will become the first gate electrode (floating electrode), is formed using a vapor phase growth method or the like to form a film of about 3,000 yen.
The first polycrystalline silicon film 4 is deposited to the same thickness as a human body, and is selectively etched away using an anisotropic plasma etching method using CF and gas using a resist pattern created by photolithography as a mask. Molding (see figure (
a)).

Next, the first polycrystalline silicon film 4 is thermally oxidized to form a second gate oxide film 5 to a thickness of approximately 500 nm, and then a second polycrystalline silicon film that will become a second gate electrode (control electrode) is formed. A film 6 is deposited to a thickness of about 3,000 layers by vapor phase growth, and a silicide film of a refractory metal, in this case a molybdenum silicide film 7, is deposited to a thickness of about 3,000 layers.
The film was deposited to a thickness of about 0.00 mm at a wafer temperature of about 200 to 400°C and an argon pressure of about 10-2 to 1 O-3 Torr, and the spacing between the source and drain of this floating gate type MOS memory transistor was determined. (not shown), these molybdenum silicide films 7. are formed using a photolithographic resist pattern as a mask. Second polycrystalline silicon film6. Second gate oxide film5. The first polycrystalline silicon film 4 and the first gate oxide film 3 are sequentially selectively etched away using an appropriate etching means, and then shaped.
Furthermore, after that, an impurity diffusion layer (not shown) and a smooth coat film 8 which become a source and a drain are added. Then, aluminum wiring (not shown) is formed on each of them (see figure (a)
)), and in this way the desired floating gate type non-volatile MOS memory device is obtained.

[Problem to be solved by the invention]

However, in the conventional floating gate type non-volatile MOS memory device configured as described above, a silicide film of a high melting point metal, in this case, When the molybdenum silicide film 7 is deposited by sputtering or the like, the thickness of the stepped portion at the edge of the first polycrystalline silicon film 4, which will serve as a floating electrode, is the same as that of the first polycrystalline silicon film 4 and the second gate oxide M5. Since the combined film thickness is about 3,500, the part corresponding to this step is made of molybdenum silicide M7.
When the molybdenum silicide film 7 and the second polycrystalline silicon film 6 are used as a wiring material, the molybdenum silicide film 7 and the second polycrystalline silicon film 6 are used as wiring materials. There is a disadvantage that the electrical resistance value becomes high.

In this case, in order to avoid the discontinuity of the molybdenum silicide 7Ii7 as the silicide film of the above-mentioned high melting point metal, as the thickness of the molybdenum silicide film 7 is increased, the internal stress and the stepped portion become more and more Since the molybdenum silicide film 7 becomes larger, the discontinuity of the molybdenum silicide film 7 cannot be solved by such means of increasing the film thickness.

This invention has been made to solve these conventional problems, and therefore, its purpose is to reduce the height of the step at the edge of the first polycrystalline silicon film that becomes the floating electrode. By eliminating the discontinuity of the melting point metal silicide film, it was possible to obtain an electrode structure consisting of a second polycrystalline silicon film as a control electrode with as low an electrical resistance value as possible and a high melting point metal silicide film. . An object of the present invention is to provide a method for manufacturing a semiconductor device of this type, in particular a method for manufacturing a floating gate type nonvolatile MOS memory device.

[Means to solve the problem]

In order to achieve the above object, the method for manufacturing a semiconductor device according to the present invention includes forming a stepped portion at an edge portion of a first polycrystalline silicon film serving as a floating electrode with a gentle slope of, for example, about 45°. The discontinuity of the molybdenum silicide film is eliminated by filling it with a side wall and then forming a second polycrystalline silicon film as a control electrode and a silicide film of a high melting point metal.

That is, the present invention forms a first polycrystalline silicon film to serve as a floating electrode on the main surface of a semiconductor substrate via a first gate oxide film, and anisotropically etches the first polycrystalline silicon film. Selectively mold it using the method and place it on top of the straw.
A step of forming an oxide film by a vapor phase growth method or the like, and removing the oxide film by an anisotropic etching method to form a step portion at an edge portion of the first polycrystalline silicon film with a gentle gentle slope. A step of leaving a sidewall, and forming a second gate oxide film containing a high melting point metal silicide film by sputtering or the like on the first polycrystalline silicon ridge including the sidewall portion, and forming a second control electrode. A method of manufacturing a semiconductor device, comprising at least a step of forming a polycrystalline silicon film.

[For production]

Therefore, in the method of this invention, the first
After leaving a sidewall with a gentle gentle slope in the stepped portion at the edge portion of the polycrystalline silicon film, on the first polycrystalline silicon film including this sidewall portion,
Since the second polycrystalline silicon film containing a high-melting-point metal silicide film and serving as a control electrode is formed by sputtering or the like through the second gate oxide film, the edges of the first polycrystalline silicon film The silicide film of the high-melting point metal is continuous even in the stepped portion, which makes it possible to significantly reduce the electrical resistance value at the control electrode.

〔Example〕

Hereinafter, an embodiment of the method for manufacturing a semiconductor device according to the present invention will be described in detail with reference to FIG.

1(a) to 1C) are cross-sectional views schematically showing the outline configuration of the main manufacturing process of a floating gate type nonvolatile MOS memory device to which this embodiment method is applied; In the method of the embodiment, the same reference numerals as in the conventional method shown in FIG. 2 represent the same or corresponding parts.

That is, in FIGS. 1A and 1B, the device configuration according to this embodiment first includes a field oxide film 2. After forming the first gate oxide film 3 on each, a first polycrystalline silicon film 4, which will become the first gate electrode (floating electrode), is deposited to a thickness of about 3000 nm by vapor phase growth or the like. Using a photolithographic resist pattern as a mask, this first polycrystalline silicon film 4 is selectively etched away and formed by an anisotropic plasma etching method using CF4 gas, and then, on top of these, Similarly, about 200
An oxide film 9 having a thickness of about 0 to 3,000 layers is formed (FIG. 3(a)).

Next, the oxide film 9 is removed by etching by a dry anisotropic etching method using (JIF, +02 gas), but since this etching is anisotropic, when the etching corresponding to the thickness of the oxide film 9 is completed, In this case, a sidewall 9a having a gentle slope of, for example, about 45 degrees is formed in the stepped portion at the edge of the first polycrystalline silicon film 4 (°(b) in the same figure). )).

Furthermore, after that, the first polycrystalline silicon film 4 including the sidewall 9a portion is thermally oxidized to form a second gate oxide film 5 to a thickness of approximately 500 nm, and the second gate electrode ( A second polycrystalline silicon film 6, which will become a control electrode (control electrode), is deposited to a thickness of about 3,000 layers by vapor phase growth or the like, and a silicide film of a refractory metal, in this case a molybdenum silicide film 7, is sputtered. By law etc.
The thickness of the wafer is approximately 3,000, and the wafer temperature is 200 to 400.
℃, and an argon pressure of about 101 to 10-' Torr, the source and drain spacing of the floating gate type MOS memory transistor shown in parentheses is determined (not shown), and a resist pattern made by photolithography is used as a mask. These molybdenum silicide film 7, second polycrystalline silicon film 6. Second gate oxide film5. The first polycrystalline silicon film 4 and the first gate oxide film 3 are sequentially etched and removed selectively by an appropriate etching method, and then formed.
Subsequently, an impurity diffusion layer (not shown) and a smooth coat film 8 which will become a source and a drain are formed. Aluminum wiring (not shown) and the like are then formed on each of them (Figure (C)). In this way, the desired floating gate type non-volatile MOS memory device having a continuous molybdenum silicide film 7 is obtained. It is.

Therefore, in the method of this embodiment, a sidewall 9a having a gentle gentle slope is left in advance at the step portion at the edge of the first polycrystalline silicon film 4, which will serve as a floating electrode, and this sidewall 9a is A second polycrystalline silicon film 6 including a molybdenum silicide film 7 and serving as a control electrode is formed by sputtering or the like on the first polycrystalline silicon film 4 including the second gate oxide film 5. Therefore, the molybdenum silicide film 7 is continuous even in the stepped portion at the edge portion of the first polycrystalline silicon film 4, and for this reason, the molybdenum silicide film 7 is made up of the second polycrystalline silicon film 6 and the molybdenum silicide film 7. The electrical resistance value at the control electrode can be kept low.

On the other hand, in this type of floating gate type nonvolatile MOS memory device, a capacitor formed by a first polycrystalline silicon film 4 serving as a first gate electrode and a second polycrystalline silicon film 6 serving as a second gate electrode to keep it as large as possible,
In other words, in this S, the second gate oxide, which also serves as an interlayer insulating film,
Although forming the first and second polycrystalline silicon films 4.6 thinly is important for its characteristics,
There is a conflicting demand to maintain a high dielectric strength between the first polycrystalline silicon film 4 and the second polycrystalline silicon film 6. By making the thickness of the second gate oxide film 5 thinner in the portion facing the sidewall, the thickness of the corresponding insulating film on the sidewall portion of the first polycrystalline silicon film 4 is increased by the sidewall 9a. Therefore, while the capacitance formed between each of the first and second polycrystalline silicon films 4 and 6 is kept large, the dielectric breakdown voltage can be effectively improved.

In the above embodiments, the case where the present invention is applied to a floating gate type non-volatile MOS memory device has been described, but it is of course applicable to other semiconductor devices having a similar configuration. In addition, although this article has described the discontinuity of the molybdenum silicide film that occurs at the step portion at the edge of the first polycrystalline silicon film, the discontinuity of the molybdenum silicide film that occurs at the step portion formed by other materials This is also useful for improving discontinuity when another high melting point metal silicide film 1, for example, a tungsten silicide film, is formed thereon.

〔Effect of the invention〕

As detailed above, according to the method of the present invention, the method has a two-layer electrode consisting of a first polycrystalline silicon film serving as a floating electrode and a second polycrystalline silicon film serving as a control electrode, and the second layer control electrode In a floating gate non-volatile MOS memory device in which a second polycrystalline silicon film is combined with a silicide film of a high-melting point metal such as molybdenum silicide, there is a gentle, gentle step at the edge of the first polycrystalline silicon film. With the sloped sidewall remaining, a control electrode is formed on the first polycrystalline silicon crotch, including the sidewall portion, through a second gate oxide film, including a silicide film of a high melting point metal by sputtering or the like. Since the second polycrystalline silicon film is formed, the high melting point metal silicide film is continuous even in the step portion at the edge of the first polycrystalline silicon film. the second of
It has the advantage that the electrical resistance value of the control electrode made of the polycrystalline silicon film and the molybdenum silicide film can be significantly lowered compared to the conventional structure. The capacitance formed by the first and second polycrystalline silicon films can be maintained as large as possible, and the dielectric breakdown voltage between the first and second polycrystalline silicon films can also be maintained high. It has excellent features such as being relatively simple in structure and easy to manufacture.

[Brief explanation of the drawing]

FIGS. 1(a) to 1(c) are cross-sectional views schematically showing the outline structure of the main manufacturing steps of a floating gate nonvolatile MOS memory device to which an embodiment of the method of the present invention is applied; FIGS. 2(a) and 2(b) are cross-sectional views each schematically showing a general configuration of the main manufacturing process of the floating gate type nonvolatile MOS memory device to which the conventional method is applied. ■...Silicon semiconductor substrate, 2...Field oxide film, 3...First gate oxide film, 4...First
Polycrystalline silicon film (floating electrode), 5... second gate oxide film, 6... second polycrystalline silicon film (control electrode)
, 7...Molybdenum silicide film (high melting point metal silicide M), 8...Smooth coat film,...
Oxide film, 9a...side wall.

Claims (1)

[Claims] Forming a first polycrystalline silicon film to serve as a floating electrode on the main surface of the semiconductor substrate via a first gate oxide film, and selectively forming the first polycrystalline silicon film by an anisotropic etching method. Then, there is a step of forming an oxide film on these by a vapor phase growth method or the like, and removing the oxide film by an anisotropic etching method to form a stepped portion at the edge of the first polycrystalline silicon film. , a step of leaving a sidewall with a gentle gentle slope; and a step of forming a high melting point metal silicide film by sputtering or the like on the first polycrystalline silicon film including the sidewall portion via a second gate oxide film. 1. A method of manufacturing a semiconductor device, comprising at least the step of forming a second polycrystalline silicon film to serve as a control electrode.