JPH02114569A - Manufacture of nonvolatile semiconductor storage device - Google Patents

Abstract

PURPOSE:To reduce the number of processes and to obtain a gate insulating film of a uniform film thickness by a method wherein an oxinitride film which has been formed by oxidizing a silicon nitride film formed in a prescribed position on an silicon substrate is used as a tunneling insulating film. CONSTITUTION:A thermal silicon nitride film 2 is formed on a silicon substrate 1 and is patterned; the thermal silicon nitride film 2 is left only in a part where a tunneling insulating film is formed. Then, this assembly is oxidized thermally in an atmosphere of a vapor until the thermal silicon nitride film 2 is transformed completely into an oxinitride; an oxinitride film 4 to be used as the tunneling insulating film is formed. During this process, since an oxidation velocity of silicon nitride is slower than that of silicon, a thermal silicon oxide film 3 is formed simultaneously in a part where the silicon substrate is exposed. Thereby, it is possible to sharply reduce the number of processes and to sharply enhance uniformity and reproducibility of a film thickness of the thermal silicon oxide film 3 around the tunneling insulating film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a nonvolatile semiconductor memory device composed of nonvolatile memory transistors having an MIO8 structure or a floating gate structure.

(Prior art) Conventionally, electrically rewritable non-volatile memories have been known, such as those with an MIO8 structure and those with a floating gate structure. It is used to rewrite information.

A conventional method for manufacturing a nonvolatile semiconductor memory device will be described below.

FIG. 2 is a process-order cross-sectional view for explaining an example of a conventional method for manufacturing a nonvolatile semiconductor memory device, in which 1 is a silicon substrate, 5, 7, 8.9 are thermally oxidized silicon films, and 6 is a silicon nitride film. It is. Manufacturing R+ below.

Explain.

First, a thermal oxidation silicon film 5 for protection and a silicon nitride film 6 as a mask for thermal oxidation are formed on a silicon substrate 1 by LP.
It is formed by the CVD method and removed leaving only the part where the tunnel insulating film will be formed (FIG. 2(a)). This is then thermally oxidized to form a relatively thick thermally oxidized silicon around the part where the tunnel insulating film is to be formed. After forming a film 7 (as shown in FIG. 2(b)), the thermally oxidized silicon film 8 on the silicon nitride film 6, the silicon nitride film 6, and the thermally oxidized silicon film 5 for protection are removed by wet etching. Next, a thermally oxidized silicon film 9 which will become a tunnel insulating film is formed (FIG. 2(d)). After this, in order to obtain the MIO8 structure, an insulating film with a high dielectric constant such as a silicon nitride film is formed, and then polysilicon or the like which becomes a gate electrode is formed. At this time, a relatively thick thermally oxidized silicon film 7 is formed on both ends of the gate so as to have a thickness I4, and has the function of improving the withstand voltage of the drain and source of the memory transistor. Further, in order to obtain a floating gate structure, it is sufficient to directly form a polysilicon film that will serve as a floating gate, and then to form a polysilicon film that will serve as a control gate via an insulating film thereon. In this case, the thermally oxidized silicon film 7 becomes the gate insulating film of the memory transistor.

(Problem M to be solved by the invention) However, in the conventional manufacturing method as described above, in order to obtain a structure having a relatively thick silicon oxide film around the tunnel insulating film, three thermal oxidation steps and three At the same time, the process is complicated, including two wet etching steps and one LPG VD step.

When the thermally oxidized silicon film 5 for protection is wet-etched, the thermally oxidized silicon film 7 that becomes the gate insulating film is also etched to some extent at the same time, and due to the nature of wet etching, the thickness of the thermally oxidized silicon film 7 after etching is uneven. It had the problem of becoming

SUMMARY OF THE INVENTION The present invention solves the above conventional problems, and aims to provide a method for manufacturing a nonvolatile semiconductor memory device that can reduce the number of steps and obtain a gate insulating film with a uniform thickness.

(Means for Solving the Problems) In order to achieve this object, the method for manufacturing a non-volatile semiconductor memory device of the present invention uses oxynitrite formed by oxidizing a silicon nitride film formed at a predetermined position on a semiconductor substrate. This method is characterized in that a Ride film is used as a tunnel insulating film.

(Function) According to the manufacturing method of the present invention, the formation of the tunnel insulating film and its surroundings can be achieved by only three steps: forming a silicon nitride film, partially removing the silicon nitride film, and oxidizing the silicon nitride film and silicon substrate. Since a relatively thick silicon oxide film can be formed at the same time and there is no wet etching process, the silicon oxide film around the tunnel insulating film can be formed with good uniformity and reproducibility.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a step-by-step sectional view illustrating a method of manufacturing a nonvolatile semiconductor memory device according to an embodiment of the present invention. In FIG. 1, 1 is a silicon substrate, 2 is a thermal silicon nitride film,
3 is a thermally oxidized silicon film, and 4 is an oxynitride film. The manufacturing steps of the method for manufacturing the nonvolatile semiconductor memory device of this embodiment will be described below.

First, as shown in FIG. 1(a), a t
Approximately 20 thermal silicon nitride films 2 are formed in an ammonia atmosphere at 00°C, and then the thermal silicon nitride film 2 is patterned using a known photoetching technique, and thermal silicon nitride is applied only to the portion where the tunnel insulating film is to be formed. Leave membrane 2 behind. Next, as shown in FIG. 1(b), thermal oxidation is performed in a steam atmosphere at 1000°C until the thermal silicon nitride film 2 is completely converted to oxynitride, thereby forming an oxynitride film 4 that will become a tunnel insulating film. do.

At this time, since the oxidation rate of silicon nitride is much slower than that of silicon, a thermally oxidized silicon film 3 on the exposed portion of the silicon substrate or on the order of 500 layers is simultaneously formed.

As described above, according to this embodiment, by using the oxynitride film 4 formed by oxidizing the thermal silicon nitride film 2 formed at a predetermined position on the silicon substrate 1 as the tunnel insulating film, the number of steps is reduced. It is possible to significantly reduce the amount of noise, and to significantly improve the uniformity and reproducibility of the thickness of the thermally oxidized silicon film 3 around the tunnel insulating film.

In this example, the silicon nitride film was formed by thermal nitriding of the silicon substrate, but it may also be formed by the LPCVD method. In addition, 20 people made 1000 silicon nitride films.
℃ in a steam atmosphere, but by appropriately selecting the thickness of this silicon nitride film and the oxidation conditions, the thickness of the tunnel insulating film and the thickness of the thermally oxidized silicon film around it can be controlled within a certain range. Needless to say, it can be set arbitrarily.

(Effects of the Invention) The present invention uses an oxynitride film formed by oxidizing a silicon nitride film formed at a predetermined position on a silicon substrate as a tunnel insulating film. The uniformity of the film thickness of the silicon oxide film around the insulating film or the tunnel insulating film used as a part thereof and the embeddability can be significantly improved. In addition, by using an oxynitride film as the 1-channel insulating film, which has much higher dielectric breakdown strength than the normally used silicon oxide film, it is possible to increase the number of rewrites allowed for nonvolatile memory transistors by more than an order of magnitude. . Furthermore, by forming a silicon nitride film directly on a silicon substrate and oxidizing it, we can obtain a number of excellent effects such as greatly suppressing bird's beak and making it possible to miniaturize nonvolatile memory transistors. The present invention provides a method for manufacturing a nonvolatile semiconductor memory device that allows for the following.

[Brief explanation of drawings]

FIG. 1 is a step-by-step cross-sectional view showing a method for manufacturing a non-volatile semiconductor memory device according to an embodiment of the present invention, and FIG. 2 is a step-by-step cross-sectional view showing a conventional method for manufacturing a non-volatile semiconductor memory device. 1...Silicon substrate, 2...Thermal silicon nitride film, 3, 5, 7, 8.9...Thermal oxidation silicon film,
4... Oxynitride film, 6... Silicon nitride film. Patent applicant Matsushita Electronics Co., Ltd. Figure 2

Claims (1)

[Claims] An oxynitride film formed by oxidizing a silicon nitride film formed at a predetermined position on a silicon substrate is used as a tunnel insulating film in a nonvolatile semiconductor memory device that performs rewriting using tunnel current in the insulating film. A method for manufacturing a non-volatile semiconductor memory device.