JPS592377B2 - Method for manufacturing semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and in particular, to a method for manufacturing a semiconductor device, in particular, a silicon oxide film having a thickness at least twice the thickness of a silicon oxide film on a single crystal silicon substrate is simultaneously oxidized with a silicon substrate and a polycrystalline silicon film. The present invention relates to a method for manufacturing a semiconductor element formed on the surface of a polycrystalline silicon film.

Generally, the manufacturing method of silicon gate MOS integrated circuits having a polycrystalline silicon film is a self-aligned manufacturing method, and is widely put into practical use as a manufacturing method of high integration density MOS integrated circuits.

Further, as a method for increasing the number of semiconductor elements within a certain area and further improving the integration density, a MOS integrated circuit manufactured using a two-layer polycrystalline silicon film in which a polycrystalline silicon film has a two-layer structure is known. A semiconductor element having such a structure is used as a memory element for dynamic memory. FIG. 1 shows a cross-sectional structure of such a memory element. In the figure, this memory element includes a silicon substrate 1, a silicon oxide film 2 formed by thermal oxidation, a first layer polycrystalline silicon film 3, and a second transistor silicon oxide film 4 on the silicon substrate 1. It is composed of a silicon oxide film 4 for insulating and separating a first layer polycrystalline silicon film 3 and a second layer polycrystalline silicon film 5. In a semiconductor device configured in this way, the silicon oxide film 4 for insulating and separating the first layer polycrystalline silicon film 3 and the second layer polycrystalline silicon film 5 is usually made of first layer polycrystalline silicon film 4. It is produced by thermal oxidation of the film 3, and at the same time, a silicon oxide film 4 of a predetermined thickness is also produced on the silicon substrate 1. Since the thickness of the silicon oxide film 4 is directly related to the threshold voltage that defines the operation of the transistor, it is necessary to keep the thickness within a certain range. On the other hand, due to the characteristics of the silicon oxide film 4, that is, since it is used as an insulating separation film between the first layer polycrystalline silicon film 3 and the second layer polycrystalline silicon film 5, it is preferable that the film is as thick as possible. It is also preferable from the viewpoint of improving overall characteristics. However,
This silicon oxide film 4 is simultaneously generated on the silicon substrate 1 by the oxidation process of the first layer polycrystalline silicon film 3, so in the conventional oxidation method, the silicon oxide film 4 on the silicon substrate 1 and the polycrystalline silicon film 4 are The film thickness ratio of the silicon oxide film 4 grown on the crystalline silicon film 3 is about 1.5 to 1.7, and it is extremely difficult to form a film with this film thickness ratio of twice or more. In particular, when impurities are diffused at a high concentration into the polycrystalline silicon film 3, if this film 3 is oxidized at high temperature for a long period of time, the surface of the polycrystalline silicon film 3 will become extremely rough.
This has been a cause of defects and a decrease in reliability due to a decrease in the withstand voltage characteristics between the layers. Therefore, an object of the present invention has been made to eliminate the above-mentioned drawbacks, and involves implanting impurities in a higher concentration in advance near the surface of a polycrystalline silicon film than in the film, and then placing the film in a high-pressure oxidizing atmosphere. By thermally oxidizing the single-crystal silicon substrate at a relatively low temperature at the same time as the single-crystal silicon substrate, a silicon oxide film that is thicker than the silicon oxide film that grows on the surface of the single-crystal silicon substrate is generated on the surface of the polycrystalline silicon film. An object of the present invention is to provide a method for manufacturing a semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor device according to the present invention will be described in detail below with reference to the drawings. 2A to 2D are cross-sectional process diagrams of essential parts for explaining one embodiment of the method for manufacturing a semiconductor device according to the present invention.

In these figures, first, as shown in figure a, a polycrystalline silicon film 3 having a predetermined thickness is formed on the upper surface of a silicon oxide film 2 of a silicon substrate 1. Contains impurities with a predetermined concentration. In such a structure, impurities of the same type as those contained in the polycrystalline silicon film 3 are implanted in a high concentration near the surface of the polycrystalline silicon film 3 to form a high concentration impurity diffusion layer 6.
form. In this case, for example, ion implantation is used to form the diffusion layer 6. Next, as shown in FIG. 4B, the polycrystalline silicon film 3 and the diffusion layer 6 are turned by a known photolithography technique. In this step, for example, a plasma etching method using gas plasma using carbon tetrafluoride is used. Next, as shown in FIG. 3c, a part of the silicon oxide film 2 on the silicon substrate 1 is removed by wet etching using a hydrofluoric acid solution or selective etching using gas plasma, and a part of the silicon substrate 1 is exposed. let For example, the oxidation temperature of such a structure is 80
A silicon oxide film 7 is formed on the surface 1a of the silicon substrate 1 to a thickness of, for example, 1000 by immersing it in a high-pressure oxidizing atmosphere of 0° C. and H2/02 atmospheric pressure of 4.5 kg/CTil for a predetermined time, as shown in FIG. For example, if the resistivity of the high concentration impurity diffusion layer 6 is about 20Ω/hole, about 3,500 silicon oxide films 7 with about 3.5 times the film thickness will grow on the polycrystalline silicon film 3. is formed. Furthermore, if the specific resistance of the high concentration impurity diffusion layer 6 is about 10 Ω/hole, a silicon oxide film 7 about five times thicker will be formed on the polycrystalline silicon film 3 under the same high-pressure oxidation conditions. be done. In addition, in order to increase the film thickness ratio under acid under the same oxidation pressure, for example 4.5 kg/d, the oxidation temperature must be set to 800°C, for example.
It is sufficient to lower the oxidation temperature from 700℃ to 700℃.
If it is fixed at , the oxidation pressure can be increased. In this way, in high-pressure oxidation, by appropriately combining the oxidation temperature and the impurity concentration of the high-concentration impurity layer on the surface of the polycrystalline silicon film 3, it is easy to form a film on the silicon substrate 1 with a thickness that is more than twice the thickness of the silicon oxide film 7. A silicon oxide film 7 can be formed on the polycrystalline silicon film 3. FIGS. 3a to 3d are cross-sectional process diagrams of essential parts for explaining another embodiment of the method for manufacturing a semiconductor device according to the present invention.

In these figures, first, as shown in figure a, a polycrystalline silicon film 3 having a predetermined thickness is formed on the upper surface of a silicon oxide film 2 of a silicon substrate 1. Contains impurities with a predetermined concentration. Next, as shown in FIG. 3B, the polycrystalline silicon film 3 is patterned using a known photolithography technique. Next, as shown in FIG. 3C, a high concentration impurity diffusion layer 6 is formed on the surface of the patterned polycrystalline silicon film 3 by an impurity implantation method such as an ion implantation method. At this time, impurities are also diffused into the surface layer of the silicon oxide film 2, forming a high concentration impurity diffusion layer 6 on the film surface, as shown in FIG. In this case, a similar high concentration impurity diffusion layer 6 is formed on the etched side surface 3a of the polycrystalline silicon film 3 at the same time as the surface 2a of the silicon oxide film 2. Next, the diffusion layer 6 on the silicon oxide film 2 is removed by the selective etching method described above, as shown in FIG. 4D, to expose a portion of the silicon substrate 1. Although not shown in the figure, such a structure can be obtained by appropriately combining the oxidation temperature, high-pressure oxidation using oxidation pressure, and impurity concentration of the high-concentration impurity layer on the surface of the polycrystalline silicon film 3 as explained in the above embodiment. Figure 2 d
A silicon oxide film 7 having a thickness more than twice the thickness of the silicon oxide film 7 can be formed on the polycrystalline silicon film 3 on the silicon substrate 1 in substantially the same manner as shown in FIG. As explained above, according to the method for manufacturing a semiconductor device according to the present invention, a silicon oxide film having a thickness more than twice the thickness of a silicon oxide film formed on a silicon substrate can be easily formed on a polycrystalline silicon film. , extremely excellent effects can be obtained that can significantly improve various characteristics and reliability of semiconductor devices and integrated circuits.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an example of a conventional semiconductor device, FIGS. Figures a to d are cross-sectional process diagrams of main parts for explaining another embodiment of the method for manufacturing a semiconductor device according to the present invention. 1...Silicon substrate, 1a...Surface, 2
...Silicon oxide film, 2a...Surface,
3...First layer polycrystalline silicon film, 3a...
...Side surface, 4...Silicon oxide film, 5...
. . . second layer polycrystalline silicon film, 6 . . . high concentration impurity diffusion layer, 7 . . . silicon oxide film.

Claims (1)

[Claims] 1. locally forming an impurity diffusion layer with a higher concentration than the impurity concentration in the film by an impurity implantation method within a certain distance of the surface of a polycrystalline silicon film containing a predetermined impurity concentration;
exposing a single crystal silicon substrate surface in the same substrate as a polycrystalline silicon film having a high concentration impurity diffusion layer on the surface portion, and forming a high concentration impurity diffusion layer on the single crystal silicon substrate surface and the surface portion. oxidizing the polycrystalline silicon film in a high-pressure oxidizing atmosphere higher than at least atmospheric pressure to produce a silicon oxide film on the surface of the polycrystalline silicon film that is sufficiently thicker than the silicon oxide film grown on the surface of the single-crystal silicon substrate. A method for manufacturing a semiconductor device, comprising the steps of: