JPS6342862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for manufacturing a semiconductor device.

Among the conventional manufacturing methods for semiconductor devices, SOS-
Cross-sectional views of the MOS structure up to the step of forming the gate electrode are shown in FIGS. 1a to 1d and e to h. Figure 1 a~
d is a process diagram using spatial separation to separate active regions;
Figures 1e to 1h are process diagrams using the coplanar technology.

First, the steps shown in FIGS. 1A to 1D will be explained. As shown in FIG. 1a, a silicon oxide film, that is, a SiO ₂ film 103, is formed on a silicon single crystal layer 102 on a sapphire substrate 101. As shown in FIG. Next, as shown in FIG. 1B, a portion of the SiO ₂ film 103 outside the active region is patterned, and the silicon single crystal layer 102 is selectively etched using the SiO ₂ film 103 as a mask.
Thereafter, as shown in FIG. 1c, the SiO ₂ film 103 is removed and a gate oxide film 104 is formed. Note that the ion implantation process and the like are omitted here. Next, a gate electrode 105 is formed as shown in FIG. 1d.

In the case obtained by the manufacturing method shown in FIGS. 1a to 1d, the end portion 106 (see FIG. 1d) of the gate oxide film 104 formed in the step shown in FIG. 1c is not sufficiently thick.
There was a drawback that the dielectric breakdown strength between the gate electrode 105 and the silicon single crystal layer 102 was reduced, resulting in a lack of reliability.

1e to 1h show the steps considered to eliminate the above-mentioned defects. As shown in FIG. 1e, the silicon single crystal layer 102 on the sapphire substrate 101 is
Above, SiO ₂ film 107, Si ₃ N ₄ film 108, SiO ₂ film 1
09 are formed one after another. Next, as shown in Figure 1 f
Patterning the outside of the active region of the SiO ₂ film 109,
Using this as a mask, Si ₃ N ₄ film 108, SiO ₂ film 1
07 is selectively etched, and the silicon single crystal layer 102 is further etched to approximately half the thickness. Next, as shown in FIG. 1g, this is selectively oxidized to form an oxide film 110, and the SiO ₂ film 109 is removed. Furthermore, as shown in FIG. 1h, a Si ₃ N ₄ film 10
8. After removing the SiO ₂ film 107, the oxide film 110
A gate oxide film 111 is formed integrally with the gate electrode 112.

The product obtained by the manufacturing method shown in FIGS. 1e to 1h can suppress the reduction in dielectric breakdown strength of the active region, that is, the end portion 106 of the gate oxide film 104, as shown in FIG. 1d. However, performing selective oxidation to oxidize non-active regions requires a large distance between active regions, which has the drawback of hindering high density.

This invention is an attempt to eliminate the above-mentioned drawbacks, and after etching the portion of the silicon single crystal layer that is not covered by the mask layer to expose the sapphire, a silicon thin film is formed over the entire main surface of the wafer. By oxidizing this silicon thin film and converting it into an oxide film, we can improve the reliability of the device and
It is an object of the present invention to provide a method for manufacturing a semiconductor device that can achieve high density.

Hereinafter, a method for manufacturing a semiconductor device according to the present invention will be explained in detail.

FIGS. 2a to 2d are according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of the SOS structure up to the step of forming a gate electrode. In FIGS. 2a to 2d, 201 is a sapphire substrate, 202 is a silicon single crystal layer, and 203 is a sapphire substrate.
204 is a _{polycrystalline} or amorphous silicon thin film, and 205 is an oxide film obtained by oxidizing the silicon thin film.

First, as shown in FIG. 2a, the sapphire substrate 2
SiO ₂ film 2 on silicon single crystal layer 202 on 01
Form 03. Next, as shown in Figure 2b,
Patterning the outside of the active region of the SiO ₂ film 203,
Using this as a mask layer serving as a silicon etching-resistant material, the silicon single crystal layer 202 is selectively etched to expose the sapphire substrate 201. Thereafter, as shown in FIG. 2c, the SiO ₂ film 203 is removed and a silicon thin film 204 is formed over the entire main surface of the wafer including the exposed sapphire substrate 201. In this case, the thickness of the silicon thin film 204 is set to approximately 1/2 or less of the thickness of the gate oxide film to be formed in the next gate oxidation process. Also,
The silicon thin film 204 is made of polycrystalline silicon or amorphous silicon. Next, as shown in FIG. 2d, the silicon single crystal layer 202 is
At the same time as forming a gate oxide film 205 thereon, the silicon thin film 204 is converted into an oxide film 205. Although not shown, the gate oxide film 205
Forming a gate electrode thereon is similar to the conventional method described above.

As explained above, in the manufacturing method according to one embodiment of the present invention, after all the silicon single crystal layer in the inactive region is removed, a silicon thin film is formed on the entire main surface of the wafer, and this is oxidized. , the active region can be sufficiently isolated to overcome the disadvantage caused by conventional fabrication methods of reduced gate breakdown strength. In addition, since a thin silicon film is formed that is so thick that it is completely oxidized during gate oxidation, there is no need to selectively oxidize thick silicon, which is required for coplanar structures, making it possible to integrate elements at a high density. It becomes possible. Furthermore, if the silicon thin film is made to have a thickness approximately half of the planned gate oxide film thickness, the gate oxide film can be formed at the same time as the conversion process to this oxide film. Therefore, the reliability of the SOS structure element can be improved and higher density can be achieved.

In the method of manufacturing a semiconductor device according to the present invention, after selectively etching a silicon single crystal layer, a silicon thin film is formed over the entire main surface, and this is oxidized to convert it into an oxide film, thereby increasing the gate breakdown voltage of the device. , it is possible to achieve high density as well as high reliability.

[Brief explanation of drawings]

FIGS. 1a to 1d and e to h are cross-sectional views showing one example and another example of a conventional semiconductor device manufacturing method in order of process, respectively, and FIGS. 2a to d are sectional views of a semiconductor device manufacturing method according to an embodiment of the present invention. FIG. 201...Sapphire substrate, 202...Silicon single crystal layer, 203...SiO ₂ film, 204...Silicon thin film, 205...Oxide film.

Claims (1)

[Scope of Claims] 1. A step of selectively forming a mask layer made of a silicon etching resistant material on a silicon single crystal layer on a sapphire, and etching the silicon single crystal layer not covered with the mask layer to remove the silicon single crystal layer on the sapphire. and after removing the mask layer,
A method for manufacturing a semiconductor device, comprising the steps of forming a silicon thin film over the entire main surface including the exposed sapphire, and converting the silicon thin film into an oxide film by oxidizing the silicon thin film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the silicon thin film is polycrystalline silicon. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the silicon thin film is amorphous silicon. 4. Claim 1, wherein the silicon thin film is formed to a thickness that is approximately 1/2 or less of the thickness of the intended oxide film,
The method for manufacturing a semiconductor device according to any one of Items 2 and 3.