JPH0799745B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for 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.

[Problems to be solved by the invention]

Although the above-described conventional method for forming an insulating layer involves a small number of steps, it is very difficult to obtain an insulating layer having a uniform film thickness. Particularly, the edge of the lower conductive layer which is provided on the insulating film and processed into a predetermined shape is processed. The film thickness of the insulating film becomes thin on the side wall of the portion, and the insulating property is deteriorated because the film quality of the insulating film is not uniform at the boundary portion in contact with the underlying insulating film. In order to obtain a sufficient insulating property, in order to increase the film thickness of the insulating film, it is necessary to increase the film thickness of the lower conductive layer before thermal oxidation, resulting in poor flatness. Further, the surface of the formed insulating film has more irregularities than the surface of the lower conductive layer before thermal oxidation, which makes it difficult to process in the subsequent process.

[Means for solving problems]

A method for manufacturing a semiconductor device according to the present invention is a multilayer film in which a first conductive film is provided in a predetermined region of one main surface of a semiconductor substrate having an insulating film, and a first oxide film and an oxidation prevention film are alternately stacked on the first conductive film. Forming a polycrystalline silicon film on the entire surface, converting the polycrystalline silicon film into a silicon oxide film in an oxidizing atmosphere, and removing the silicon oxide film in the oxidizing atmosphere. And then oxidizing the first conductive film to form a second oxide film at the interface between the first conductive film and the silicon oxide film, and removing the silicon oxide film by isotropic etching. And exposing the insulating film, and forming a second conductive film electrically insulated from the first conductive film through the second oxide film.

〔Example〕

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

1A to 1F are longitudinal cross-sectional views in order of the processes of one embodiment of the present invention. Silicon substrate 1 having silicon oxide film 2
After depositing the polysilicon film 3 by vapor deposition, an impurity such as phosphorus (P) is added to the polysilicon film 3 to form a good 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 nitride film 5 is further formed thereon by a vapor phase growth method. Here, the silicon oxide film 2 insulates between the silicon substrate 1 and the polysilicon film 3 (FIG. 1 (a)). Next, a region other than the desired region of the three-layer film composed of the silicon nitride film 5, the silicon oxide film 4 and the polysilicon film 3 is removed by etching by photolithography (FIG. 1 (b)), and then the entire surface is removed. A polysilicon film 6 is deposited (FIG. 1 (c)). Next, the polysilicon film 6 is entirely changed to the silicon oxide film 7 by the thermal oxidation method, and the thermal oxidation is further continued to oxidize the side surface of the polysilicon film 3. The polysilicon film 3 is oxidized faster than the silicon substrate 1 due to the acceleration effect of the contained phosphorus, but this oxidation is limited to the side surface of the polysilicon film 3 and is not formed on the upper surface where the oxidation is blocked by the silicon nitride film 5. It does not reach (Fig. 1 (d)). Next, the entire surface is removed by etching with an isotropic wet etching solution to completely remove the silicon oxide films 2 and 7 in contact with the silicon substrate 1, leaving the silicon oxide film 7 on the surface of the polysilicon film 3. Stop with (Fig. 1 (e)). Finally, a silicon oxide film 8 having a desired thickness is formed on the exposed surface of the silicon substrate 1 by a thermal oxidation method, and then a polysilicon film 9 is deposited as an upper conductive layer by a vapor phase growth method to contain phosphorus. At most, a good conductive film is formed, and the region other than the desired region is removed by etching by photolithography (FIG. 1 (f)).

According to this embodiment, the film thickness of the oxide film formed on the side surface of the polysilicon film 3 is not particularly uneven, and the film quality is uniform. This is because the initial stage of lateral oxidation is improved. That is, in the present embodiment, first, the oxidizing agent is supplied to the side surface of the polysilicon film 3 through the silicon oxide film having almost the same film thickness. Therefore, the supply of the oxidizing agent to the side surface of the polysilicon film is performed substantially uniformly over the entire side surface of the polysilicon film 3. Secondly, since the side surface of the polysilicon film 3 is oxidized through the silicon oxide film, the film growth is diffusion-controlled, so that the rapid film growth is suppressed. Moreover, since the polysilicon film 3 is not oxidized so much, the film pressure of the silicon oxide film 7 can be reduced. Therefore, these two
Due to the two synergistic effects, a film having a uniform film pressure and good film quality grows on the side surface of the polysilicon film 3 in the initial stage of side surface oxidation. Then, by prolonging the oxidation time, such an oxide film having a good film quality can be formed sufficiently thick. Further, as described above, the film quality of the oxide film formed on the side surface of the polysilicon film 3 is uniform, and the film quality of the silicon oxide film formed by the oxidation of the polysilicon film 6 is uniform. In the subsequent isotropic etching process, a highly uniform shape is preserved. In addition, the polysilicon film 6 is thermally oxidized so that the polysilicon film 3 is
There are no sharp edges or corners left. Therefore, the insulation between the polysilicon film 3 and the polysilicon film 9 can be made sufficiently high.

2A to 2E are longitudinal cross-sectional views in order of the processes of another embodiment of the present invention. Silicon nitride film on the silicon oxide film 2
A polysilicon film 3, a silicon oxide film 4, and a silicon nitride film 5 are formed on the silicon substrate 1 having an insulating film in which 10 are laminated in the same manner as in the above-mentioned embodiment, and further, a silicon film is formed on the silicon nitride film 5. An oxide film 12 and a silicon nitride film 13 are sequentially deposited by a vapor phase epitaxy method, and this five-layer film is processed into a predetermined shape. At this time, the silicon nitride film 13, the silicon oxide film 12, the silicon nitride film 5 and the silicon oxide film 4 are first subjected to isotropic plasma etching for selectively removing the silicon oxide film and the nitride film with respect to the polysilicon film 3. After sequentially removing the respective films, the polysilicon film 3 is removed by anisotropic plasma etching. Next, a polysilicon film 6 is deposited on the entire surface (FIG. 2 (a)). Next, the polysilicon film 6 is thermally oxidized to be entirely converted into the silicon oxide film 7 (FIG. 2B), and subsequently, the silicon oxide film 7 on the silicon nitride film 10 and the silicon nitride film 13 is changed.
Is removed by isotropic wet etching to leave the silicon oxide film 7 only on the side surface of the polysilicon film 3 (FIG. 2C). Next, the silicon nitride films 10 and 13 exposed on the surface and the The silicon oxide films 2 and 12 immediately below are sequentially removed by etching (FIG. 2 (d)), and then the silicon oxide film 8 is formed on the surface of the silicon substrate by the thermal oxidation method.
A polysilicon film 9 having a predetermined shape is formed (FIG. 2 (e)).

In this embodiment, since the surface of the silicon substrate is covered with the silicon nitride film 10, it is not oxidized unlike the above embodiment. Further, when the silicon nitride film 10 is removed by etching, since the upper surface of the polysilicon film 3 has two layers of silicon nitride films, the insulating film on the upper surface of the polysilicon film may be excessively removed due to overetching during etching. There is an advantage that can be prevented.

〔The invention's effect〕

As described above, according to the present invention, the polysilicon film which contacts the side surface of the lower conductive film pattern and covers the entire surface of the substrate is entirely changed to the silicon oxide film, and the lower conductive film is formed at the interface between the side surface of the lower conductive film pattern and the silicon oxide film. Forming an oxide film,
All of the silicon oxide film is removed to form an upper conductive film that is electrically insulated from the lower conductive film through the oxide film of the lower conductive film. This makes it possible to form an insulating film having excellent insulating properties and suitable for flattening and miniaturizing the element.

[Brief description of drawings]

1 (a) to 1 (f) are longitudinal cross-sectional views in order of steps of one embodiment of the present invention, and FIGS. 2 (a) to 2 (e) are longitudinal cross-sectional views in order of steps of other embodiments 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.

Claims (1)

[Claims] 1. A step of forming a first conductive film and a multi-layered film in which a first oxide film and an oxidation prevention film are alternately laminated on a predetermined region of a main surface of a semiconductor substrate having an insulating film. A step of forming a polycrystalline silicon film on the entire surface, converting the polycrystalline silicon film into a silicon oxide film in an oxidizing atmosphere, and forming the first silicon oxide film through the silicon oxide film in the oxidizing atmosphere. By oxidizing the conductive film, the first
Forming a second oxide film on the interface between the conductive film and the silicon oxide film, exposing the insulating film by isotropically removing the silicon oxide film, and removing the second oxide film from the second oxide film. A method of manufacturing a semiconductor device, comprising the step of forming a second conductive film electrically insulated from the first conductive film through the above.