JPS6278852A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To obtain an insulating film suitable for flattening and microminiaturization of an element by a method wherein the polysilicon film being in contact with the side surface of the lower conductive film pattern is entirely changed into a silicon oxide film and the upper conductive film insulated from the lower conductive film is provided through the oxide film of the lower conductive film. CONSTITUTION:The region other than the desired region of a three layer film is etched away by a photo etching method and a polysilicon film 6 is deposited on the whole surface. The polysilicon film 6 is entirely changed into a silicon oxide film 7 by a thermal oxidation method, a thermal oxidation is continued and the side surface of a polysilicon film 3 is oxidized. The whole surface being etched away, a silicon oxide film 2 being in contact with silicon substrate 1 and the silicon oxide film 7 are all etched away and the etching is stopped in the state that the silicon oxide film 7 is left on the side surface of the polysilicon film 3. A silicon oxide film 8 is formed on the exposed surface of the substrate 1 in the desired thickness and a polysilicon film 9 is deposited as the upper conductive layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor device, and particularly to a method of forming an insulating film between conductive layers.

[Conventional technology]

Conventionally, in order to form an insulating film between conductive layers, an insulating film is formed on the surface of a lower conductive layer by a thermal oxidation method, and an upper conductive layer is formed thereon.

[Problem that the invention seeks to solve]

Although the conventional method for forming an insulating film described above requires a small number of steps, it is very difficult to obtain an insulating film with a uniform thickness. The thickness of the insulating film becomes thinner on the sidewalls of the area, and the quality of the insulating film is not uniform at the boundary portion where it contacts the underlying insulating film, resulting in deterioration of insulation. In order to increase the thickness of the insulating film in order to obtain sufficient insulation, it is necessary to increase the thickness of the lower conductive layer before thermal oxidation, which deteriorates the flatness. Further, the surface of the insulating film formed has increased irregularities compared to the surface of the underlying conductive layer before thermal oxidation, which makes processing in subsequent steps difficult.

[Means for solving problems]

The method for manufacturing a semiconductor device of the present invention includes forming a multilayer film in which a first conductive film and a first oxide film and an oxidation prevention film are alternately stacked on a predetermined region of one principal surface of a semiconductor substrate having an insulating film. forming a polycrystalline silicon film on the entire surface; and converting all of the polycrystalline silicon film into a silicon oxide film in an oxidizing atmosphere, and forming a polycrystalline silicon film on the interface between the first conductive film and the silicon oxide film. A second conductive film made of an oxide film of the first conductive film.
forming an oxide film, etching away all of the silicon oxide film, and forming a second conductive film electrically insulating from the first conductive film via the second oxide film. It is characterized by including a process.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) to 1(f) are longitudinal cross-sectional views in the order of steps of an embodiment of the present invention. Silicon substrate 1 having silicon oxide film 2
A polysilicon film 3 is deposited thereon by vapor phase growth, and then impurities such as phosphorus (P) are added to the polysilicon film 3 to make it a highly conductive film. A silicon oxide film 4 is formed on the surface of the polysilicon film 3 by a thermal oxidation method, and a silicon 9 oxide film 5 is further formed thereon by a vapor phase growth method. Here, silicon oxide film 2
provides insulation between the silicon substrate 1 and the polysilicon film 3 (FIG. 1(a)). Next, areas other than the desired areas of the three-layer film consisting of silicon nitride film 5, silicon oxide film 4, and polysilicon film 3 are removed by photoetching (Fig. 1(b)), and then the entire surface is etched. A polysilicon film 6 is deposited on the surface (FIG. 1(C)). Next, the entire polysilicon film 6 is changed into a silicon oxide film 7 by thermal oxidation, and the thermal oxidation is continued to oxidize the side surface of the polysilicon film 3. Polysilicon film 3 is oxidized faster than silicon substrate 1 due to the speed-enhancing effect of the phosphorus it contains, but this oxidation is limited to the side surfaces of polysilicon film 3, and oxidation is limited to the top surface where oxidation is prevented by silicon nitride film 5. (Fig. 1(d)). Next, the entire surface is etched away using an isotropic wet etching solution, and all of the silicon oxide films 2 and 7 in contact with the silicon substrate are etched away, leaving the silicon oxide film 7 on the side surface of the polysilicon film 3. (Fig. 1 (e))
. Finally, after forming a silicon oxide film 8 to a desired thickness on the exposed surface of the silicon substrate 1 by thermal oxidation, a polysilicon film 9 is deposited as an upper conductive layer by vapor phase epitaxy. The film is made into a highly conductive film, and the areas other than the desired areas are removed by photolithography (Fig. 1(f)).
).

According to this embodiment, there is no part where the thickness of the silicon oxide film 7 is particularly uneven on the side surface of the polysilicon film 3, the quality of the silicon oxide film is uniform, and the polysilicon film 3 is not oxidized much. Therefore, the thickness of the silicon oxide film 7 can be reduced. Furthermore, thermal oxidation of the polysilicon film 6 leaves no sharp edges or corners on the wrinkled silicon film 3, so that sufficient insulation is ensured.

FIGS. 2(a) to 2(e) are vertical cross-sectional views in the order of steps of another embodiment of the present invention. On a silicon substrate 1 having an insulating film in which a silicon nitride film 10 is laminated on a silicon oxide film 2,
A polysilicon film 3, a silicon oxide film 4, and a silicon nitride film 5 are formed in the same manner as in the previous embodiment, and then a silicon oxide film 12 and a silicon nitride film 13 are sequentially formed on the silicon nitride film 5 by vapor phase growth. This five-layer film is then processed into a predetermined shape. At this time, the silicon nitride film 1 is first etched by isotropic plasma etching that selectively etches the silicon oxide film and nitride film with respect to the polycone film 3.
3. After the six films of silicon oxide film 12, silicon nitride film 5, and silicon oxide film 4 are removed by etching in sequence, polysilicon film 3 is etched away by anisotropic plasma etching. Next, a polysilicon film 6 is deposited on the entire surface (
Figure 2(a)).

Next, the polysilicon film 6 is thermally oxidized to form a silicon oxide film 7.
(Fig. 2)), and then the silicon oxide film 7 on the silicon nitride film 10 and the silicon nitride film 13 is removed by isotropic wet etching, and silicon oxide is formed only on the sides of the polysilicon film 3. The film 7 is left (FIG. 2(C)). Next, the silicon 9 oxide films 10 and 13 exposed on the surface and the silicon oxide films 2 and 12 immediately below them are sequentially etched away (FIG. 2(d)), and then the silicon substrate surface is removed by thermal oxidation. After forming a silicon oxide film 8, a polysilicon film 9 of a predetermined shape is formed (FIG. 2(e)).
.

In this example, the silicon substrate surface is covered with a silicon nitride film 10.
Since it is covered with oxide, it is not oxidized unlike the previous embodiment.

Furthermore, when removing silicon nitride [10] by etching, since there are two layers of silicon nitride films on the top surface of the polysilicon film 3, the insulating film on the top surface of the polysilicon film may be excessively removed due to overetching during etching. There are advantages to preventing this.

〔Effect of the invention〕

As explained above, the present invention replaces the polysilicon film that is in contact with the side surface of the lower conductive film pattern and covers the entire surface of the substrate with a silicon oxide film, and furthermore, the lower conductive film is added to the interface where the side surface of the lower conductive film pattern and the silicon oxide film contact. Forms an oxide film,
The silicon oxide film is completely removed, and an upper conductive film is formed which is electrically insulated from the lower conductive film via the oxide film of the lower conductive film.

This makes it possible to form an insulating film that has superior insulating properties and is suitable for planarization and miniaturization of elements.

[Brief explanation of drawings]

FIGS. 1(a) to (f) are vertical sectional views in the order of steps of one embodiment of the present invention, and FIGS. 2(a) to (e) are longitudinal sectional views in the order of steps of another embodiment of the present invention. . 1...Silicon substrate, 2, 4, 7, 8, 11.
12... Silicon oxide film, 3, 6, 9...
...Polysilicon film, 5.10.13...Silicon nitride film. Agent: Susumu Uchihara, Patent Attorney 7″゛ko・−1.

Claims (1)

[Claims] A step of forming a multilayer film in which a first conductive film and a first oxide film and an oxidation prevention film are alternately stacked on a predetermined region of one main surface of a semiconductor substrate having an insulating film, and polycrystalline silicon is formed on the entire surface. a step of forming a film, converting the polycrystalline silicon film into a silicon oxide film in an oxidizing atmosphere, and converting the polycrystalline silicon film into a silicon oxide film in the first
forming a second oxide film made of an oxide film of the first conductive film at the interface between the conductive film and the silicon oxide film; etching away the silicon oxide film entirely; and removing the second oxide film. A method for manufacturing a semiconductor device, comprising the step of forming a second conductive film that is electrically insulated from the first conductive film through the step of forming a second conductive film.