JPH0531819B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to the formation of selective oxide film regions for isolation between elements in the manufacturing process of semiconductor devices, and in particular to reducing the lateral spread of the selective oxide film under the mask. The present invention relates to a method for manufacturing a selective oxide film with fewer steps.

[Conventional technology]

Conventionally, the following method has been used as an element isolation method using this type of selective oxide film.

First, a silicon nitride film is formed on a silicon substrate, and a desired portion of the silicon nitride film is removed by etching using a photoresist film as a mask.

Next, after removing the photoresist film, the silicon substrate is oxidized using the silicon nitride film as a mask to form a selective oxide film to form element isolation regions.

FIGS. 3a to 3c are longitudinal cross-sectional views of selective oxide film regions shown in the order of steps to explain an example of such a conventional method.

As shown in FIG. 3a, first a silicon oxide film 2 is formed on a silicon substrate 1, and then a silicon nitride film 3 is formed. Thereafter, a photoresist is applied, and the photoresist film 4 is patterned using lithography technology.

Next, as shown in FIG. 3B, the silicon nitride film 3 is etched using the photoresist film 4 as a mask. Next, the silicon oxide film 2 is etched with a hydrofluoric acid solution, and the silicon substrate 1 is further dry etched to form a silicon substrate stepped convex portion 5. Therefore, after removing the photoresist film 4, the silicon substrate 1 is oxidized using the silicon nitride film 3 as a mask.

Next, as shown in FIG. 3c, a selective oxide film 8 is formed by oxidizing the silicon substrate 1. It is not sharply separated from the area of membrane 8. That is, at the end of the silicon nitride film 3, the silicon substrate 1 under the silicon nitride film is continuously oxidized starting from the end of the silicon nitride film, although the amount of oxidation gradually decreases, and its lateral dimension is equal to that of the selective oxide film. The thickness is approximately the same.

[Problem that the invention seeks to solve]

In the conventional element isolation method using a selective oxide film using a silicon nitride film as a mask, the volume of the oxide film expands when the oxidized region is oxidized, and the surface of the oxidized region is higher than the surface of the non-oxidized region. There will be a step in between. This difference in level between the oxidized region and the non-oxidized region prevents the pattern from being formed to a desired size when a fine photoresist film pattern is formed in the non-oxidized region near the oxidized region in miniaturization of the device. Therefore, the dimensions of a pattern formed in a region sufficiently distant from the oxidized region are different from the dimensions of a pattern formed in a non-oxidized region near the oxidized region.
There is a problem that leads to a decrease in dimensional accuracy. In addition, the silicon nitride film used as an oxidation mask is oxidized to the bottom of the mask part, and its lateral dimension becomes almost the same as the thickness of the selective oxide film, which has the disadvantage that it cannot be used in future formation of fine element regions.

[Means for solving problems]

The selective oxide film manufacturing method of the present invention involves forming a silicon oxide film and a silicon nitride film on a silicon substrate, and then etching the silicon nitride film and the base silicon oxide film using a photoresist film as a mask and etching the silicon substrate. A process of etching using dry etching technology to form a stepped part on the silicon substrate and forming a convex part on the non-etched part of the silicon substrate, and a process of removing the photoresist film used as a mask and then etching the silicon using a CVD method. There is a step of forming a silicon oxide film on the substrate, a step of applying photoresist to a film thickness approximately equal to the height of the silicon substrate, and a step of removing the photoresist film surface under plasma conditions using oxygen gas or the like to remove the step portion of the silicon substrate. A process of exposing the surface of the silicon oxide film in the convex region, a process of etching the exposed part of the CVD silicon oxide film using the remaining photoresist film as a mask so that the surface of the silicon nitride film is exposed, and after removing the photoresist film. The method includes a step of oxidizing a silicon oxide film and a silicon substrate using a silicon nitride film as a mask to form a selective oxide film, and a step of removing the silicon nitride film used as the mask.

〔Example〕

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

FIGS. 1a to 1h are vertical cross-sectional views of a selective oxide film region shown in the order of steps for explaining a first embodiment of the present invention.

As shown in FIG. 1a, first, a silicon oxide film 2 is formed on a silicon substrate 1 to a thickness of about 300 to 500 Å, and a silicon nitride film 3 is formed on it to a thickness of 1000 to 1500 Å.
It is formed to a thickness of about 100 Å. Thereafter, a photoresist is applied, and a patterned photoresist film 4 is formed using photolithography.

Next, as shown in FIG. 1b, the silicon nitride film 3 is dry-etched using Freon gas or the like using the photoresist film 4 as a mask, and then the underlying silicon oxide film 2 is etched with a hydrofluoric acid aqueous solution using the silicon nitride film 3 as a mask. etching. After that, the silicon substrate 1 is heated to 0.5 to 1.0μ using oleon plasma gas or the like.
A step portion 5 is formed on the silicon substrate 1 by dry etching to a thickness of approximately m. That is, a convex portion is formed in the non-etched portion of the silicon substrate 1. Further, the lateral dimension of the remaining silicon nitride film 3 at this time is about 1 μm to 10 μm.

Next, as shown in FIG. 1c, a silicon oxide film 6 having a thickness of about 0.5 to 0.6 μm is formed on the etched silicon substrate 1 using the CVD method. At this time, the surface of the CVD silicon oxide film 6 is uneven along the steps of the silicon substrate 1.

Next, as shown in Figure 1 d, the viscosity is about 20 cp.
photoresist is coated under high-speed rotation of approximately 6000 to 7000 rpm to obtain a film thickness of 0.5 to 0.6 μm on the CVD silicon oxide film 6 on which no pattern is formed, and to obtain a film thickness of 0.5 to 0.6 μm on the CVD silicon oxide film 6 on the silicon nitride film 3. A film thickness of 0.2 to 0.3 μm is obtained on the surface.

Next, as shown in FIG. 1e, the photoresist film 7 on the surface of the CVD silicon oxide film 6 is removed to a thickness of 0.2 to 0.3 μm on the silicon nitride film 3 using oxygen plasma. At this time, the thickness of the surrounding photoresist film 7 also decreases to about 0.3 μm.

Next, as shown in FIG. 1f, for the photoresist film 7, the opening 10 in the surface of the CVD silicon oxide film 6 on the silicon nitride film 3 is filled with a hydrofluoric acid solution until the surface of the silicon nitride film 3 is exposed. Etching is performed to expose the surface of silicon nitride film 3.

Next, as shown in FIG. 1g, after removing the photoresist film 7, using the silicon nitride film 3 as a mask, a silicon oxide film 6 is grown by vapor phase growth at a level that is not higher than the surface position of the silicon nitride film 3. A selective oxide film 8 is formed by oxidizing at a high temperature of about 1000° C. to obtain a desired film thickness.

Finally, as shown in FIG. The surface of the silicon substrate 1 can be made extremely flat without any steps, and the surface of the silicon substrate 1 can be formed into a fine selective oxide film having a size of 2 to 5 μm.

Therefore, the pattern size on the silicon substrate is 1μ.
It becomes possible to form fine dimensions down to m or less.

FIG. 2 is a longitudinal sectional view of a region including a silicon oxide film for explaining a second embodiment of the present invention.

As shown in FIG. 2, a silicon oxide film 2 is formed on a silicon substrate 1, and a silicon nitride film 3 is formed thereon. After that, similar to the previous example
A CVD oxide film 6 is formed, and then a photoresist film 9 is formed. In this second embodiment, when the pattern size of the silicon nitride film 3 is as large as 10 μm or more, the thickness of the photoresist film 9 on the surface of the CVD silicon oxide film 6 in FIG. Differences between the two become less likely to occur. Therefore, if it is difficult to remove only the resist film from the silicon substrate step convex portion using oxygen plasma, ultraviolet rays are irradiated and exposed only to the silicon substrate step convex portion using photolithography. Thereafter, the resist film 9 on the convex portion of the silicon substrate 1 is developed by forming an opening 10 in the resist.
can be removed, the silicon nitride film 3
A selective oxide film can be formed even on patterns with pattern dimensions of 10 μm or more.

In this way, the second embodiment has the advantage that a selective oxide film can be formed even when the silicon nitride film pattern size in the first embodiment described above is large.

〔Effect of the invention〕

As explained above, the present invention forms a step on a silicon substrate, forms a CVD silicon oxide film and an opening in the photoresist film using the difference in film thickness after coating at the step part, and then applies a photoresist film. Remove the CVD silicon oxide film using the mask,
After that, the desired selective oxide film can be obtained by oxidizing the CVD silicon oxide film using the silicon nitride film as a mask, so that the surface of the selective oxide film and the silicon substrate can be made extremely flat, and the selective oxide film can be prevented from spreading in the lateral direction. There is an effect that can be reduced. Therefore, there is an effect that a selective oxide film can be formed that allows a large pattern size of 1 μm or more on one side of the silicon substrate surface.

[Brief explanation of the drawing]

1A to 1H are vertical sectional views of a selective oxide film region shown in the order of steps for explaining the first embodiment of the present invention, and FIG. 2 is a longitudinal sectional view for explaining the second embodiment of the present invention. 3A to 3C are vertical cross-sectional views of a silicon oxide film region for explaining a conventional example. 1...Silicon substrate, 2...Silicon oxide film,
3...Silicon nitride film, 4,7,9...Photoresist film, 5...Stepped convex portion, 6...CVD silicon oxide film, 8...Selective oxide film, 10...Opening.

Claims (1)

[Claims] 1. Selectively etching the silicon oxide film and silicon nitride film formed on the silicon substrate and dry etching the silicon substrate to form a stepped portion on the silicon substrate, and forming a convex portion on the non-etched portion of the silicon substrate. a step of forming a silicon oxide film by a CVD method on the silicon substrate on which the step portion is formed;
A step of applying a photoresist on the CVD silicon oxide film to form a photoresist film having a thickness approximately equal to the step height of the silicon substrate, and removing the photoresist film on the convex portion of the step portion of the silicon substrate using oxygen plasma; a step of exposing the surface of the CVD silicon oxide film; a step of etching the surface of the exposed part of the CVD silicon oxide film using the remaining photoresist film as a mask until the surface of the silicon nitride film is exposed; and after removing the photoresist film. A selective oxide film comprising the steps of: oxidizing the silicon oxide film and the silicon substrate using the silicon nitride film as a mask to form a selective oxide film; and removing the silicon nitride film used as the mask. manufacturing method.