JP2739593B2 - Semiconductor device manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a high-performance and high-reliability semiconductor device, for example, a semiconductor nonvolatile memory having a polysilicon two-layer structure, a polysilicon stack type dynamic random access memory, and the like. The present invention relates to a method for forming an insulating film on a substrate or a polysilicon electrode having a pattern.

[Summary of the Invention]

In the present invention, rapid thermal oxidation (RTO) is performed on a silicon substrate or a polysilicon electrode.
n)) silicon oxide film (hereinafter referred to as RTO (Rapid Therma
l Oxide) film, and a CVD silicon nitride film was deposited on the RTO film by a chemical vapor deposition (CVD) method. The CVD silicon nitride film was thermally oxidized to form a thermally oxidized silicon nitride film on the surface of the film.
Through the above series of steps, a multilayer insulating film on a silicon substrate or polysilicon was formed.

[Conventional technology]

A conventional technique will be described with reference to the drawings. Fig. 2 (a)-
(C) is a cross-sectional view showing a step of forming a multilayer insulating film on a polysilicon electrode formed using a conventional technique. First, a thin gate insulating film 2 is formed on the surface of a semiconductor substrate 1, and a first polysilicon electrode 3 is formed on the gate insulating film 2 by CV.
It is deposited by the D method (FIG. 2 (a)). Next, the first-layer polysilicon electrode 3 is thermally oxidized to form a polysilicon thermal oxide film 8. Thereafter, a CVD silicon nitride film 5 is deposited on the polysilicon thermal oxide film 8 by a CVD method (FIG. 2B). Further, the CVD silicon nitride film 5 is thermally oxidized to form a thermal silicon oxide nitride film 6 on the film surface. Finally, a second-layer polysilicon electrode 7 is deposited by the CVD method (FIG. 2C).

[Problems to be solved by the invention]

However, the conventional formation process has the following two problems. First, in the case of performing polysilicon oxidation of a first-layer polysilicon electrode doped with a high phosphorus concentration, the oxidation rate is high because of phosphorus, which is a doped impurity. It is difficult to obtain uniformity. Secondly, when oxidizing polysilicon in a high-temperature atmosphere of 1000 ° C. or higher to obtain good film quality, a long-time high-temperature heat treatment after depositing the first-layer polysilicon electrode may result in 100%.
The result that the film quality of the thin gate insulating film of Å or less is significantly deteriorated is obtained.

[Means for solving the problem]

In order to solve the above problems, in the present invention, an RTO film that can be formed in a shorter high-temperature heat treatment time is used instead of a polysilicon thermal oxide film in a normal oxidation furnace on a polysilicon electrode.

[Action]

Since the above RTO film is a heat treatment method of high temperature and short time, it is not affected by the concentration of phosphorus impurities as much as thermal oxidation in an ordinary oxidation furnace. Further, the silicon oxide film of the same thickness can be formed in a time (about two to three minutes) much shorter than the thermal oxidation time of polysilicon in an ordinary oxidation furnace.

As described above, the RTO film is most suitable as the base oxide film of the multilayer insulating film of the present invention.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 (a) to 1 (c) are cross-sectional views showing steps of forming a multilayer insulating film on a polysilicon electrode formed by using the technique of the present invention. First, a thin gate insulating film is formed on the surface of a semiconductor substrate 1, and a first-layer polysilicon electrode 3 is deposited thereon by a CVD method (FIG. 1A). Next, R is formed on the polysilicon electrode 3 by the RTO method.
The TO film 4 is formed. Then, a thin CVD silicon nitride film 5 is deposited thereon (FIG. 1 (b)). Furthermore, this CVD
The silicon nitride film 5 is thermally oxidized to form a thermally oxidized silicon nitride film 6 on the film surface. Finally, a second-layer polysilicon electrode 7 was deposited by a CVD method (FIG. 1C). When a multilayer insulating film is formed on a polysilicon electrode as described above, since the RTO film is a rapid heat treatment, even in a large-diameter silicon wafer, the in-plane film thickness uniformity is good regardless of the phosphorus impurity concentration. Furthermore, the formation of the RTO film is much faster than the thermal oxidation of polysilicon in a normal oxidation furnace (1- 1).
(Approximately 2 minutes), so that even if the temperature is higher than that of an ordinary oxidation furnace, it is possible to prevent the thin gate insulating film having a thickness of 100 ° or less from significantly degrading the film quality. Further, since the RTO film is processed in a short time, there is an advantage that asperity of polysilicon is not generated.

〔The invention's effect〕

As described above, the present invention uses the RTO film in place of the polysilicon thermal oxide film of the multilayer insulating film, thereby having excellent film thickness uniformity and film quality of itself, and further, is formed in a previous step. It is possible to provide an excellent feature that there is almost no adverse effect on a thin gate insulating film.

[Brief description of the drawings]

1 (a) to 1 (c) are cross-sectional views in the order of forming a multilayer insulating film on a polysilicon electrode according to the present invention. 2 (a) to 2 (c) are cross-sectional views in the order of steps of forming a multilayer insulating film on a conventional polysilicon electrode. DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2 ... Gate insulating film 3 ... First layer polysilicon electrode 4 ... RTO film 5 ... CVD nitride film 6 ... Thermal silicon oxide nitride film 7 ... Second layer polysilicon electrode

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 29/788/29/792 (56) References JP-A-63-224367 (JP, A) JP-A-61-147576 (JP, A) JP-A-1-117332 (JP, A) JP-A-64-15985 (JP, A)

Claims (3)

(57) [Claims] 1. A step of forming a thin gate insulating film having a thickness of not more than 100 ° on a silicon substrate, and depositing polysilicon as a gate electrode on the thin gate insulating film by a chemical vapor deposition (CVD) method. Forming a silicon oxide film on the polysilicon by a rapid ramp thermal oxidation (RTO) method; and depositing a silicon nitride film on the silicon oxide film by a chemical vapor deposition (CVD) method. Forming a thin thermal oxide silicon nitride film on the silicon nitride film; and depositing polysilicon on the thermal silicon oxide nitride film by chemical vapor deposition (CVD). Manufacturing method. 2. The method according to claim 1, wherein the step of forming the silicon oxide film by the RTO method is performed with a lamp heating time of 2 minutes or less. 3. The step of forming a silicon oxide film by the RTO method, wherein a lamp heating temperature is 1000 ° C. or higher.
The manufacturing method of the semiconductor device described in the above.