JPH0122727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for photoetching oxide and silicon on silicon semiconductor wafers.

When introducing impurity atoms at a desired location at a desired concentration to create a semiconductor device or an integrated circuit, the oxide film at the desired location is locally cut out and the exposed silicon portion is etched to create a hole. This may be necessary. Photoetching is used as a means of cutting out this oxide film and drilling holes in the silicon.

Conventionally, photoetching has been performed in the following steps. That is, first, a photosensitive material called a photoresist agent is applied as a mask to the entire surface of the wafer and dried. A glass photomask is placed on top of this, and ultraviolet light is irradiated from above. When this wafer is developed, a wafer having a cross section as shown in FIG. 1 is obtained.

In FIG. 1, an oxide film 3 is formed on the surface of silicon 2 of a silicon wafer 1, and the photoresist 4 coated on top of the oxide film melts only the portions that are not irradiated with ultraviolet rays, forming holes 4a. .

Next, when this wafer 1 is placed in a mixed solution of, for example, ammonium fluoride aqueous solution and hydrofluoric acid for an appropriate time,
As shown in FIG. 2, holes 3 in the oxide film are etched from the removed portion 4a of the photoresist 4.
A is pierced. The silicon 2 is etched by further extending the etching time or by using another etching agent. Finally, by peeling off the photoresist 4, the purpose of photoetching is achieved.

However, when the silicon layer 2 is etched after the oxide film 3 is etched by the above method, the etching naturally spreads not only in the depth direction but also in the lateral direction. The etching rate of the oxide film varies depending on the film formation conditions and the etching agent, but in general, the etching rate of silicon is faster than that of the oxide film, so the oxide film is left behind and spreads laterally, as shown in Figure 3. As shown, an eave-shaped oxide film 3b is formed over the silicon hole 2a.
remains.

Conventional methods like this have the disadvantage that it is difficult to obtain the desired pattern on the wafer, and that the eaves of the oxide film are irregularly damaged during ultrasonic cleaning or subsequent processing, degrading the wafer's characteristics. . In addition, the chipped oxide film is scattered and has a negative effect on subsequent steps.

An object of the present invention is to eliminate the above-mentioned drawbacks by etching the oxide film in an etched area where the oxide film and the silicon layer gradually widen from the contact area of the silicon layer and the oxide film toward the outside of the hole (with a tapered surface). The object of the present invention is to provide a method for etching a silicon layer (cross-sectional shape), and also to provide an etching method that does not leave an oxide film in the shape of an eaves when etching a silicon layer.

This purpose, according to the invention, is to
A silane coupling agent, which is a simple organosilicon, has in its molecule one or more reactive groups that chemically bond with inorganic materials such as silicon oxide films, and one or more reactive groups that chemically bond with organic materials such as various photoresists. a layer of photoresist agent thereon, irradiating the photoresist with ultraviolet rays, followed by a development process, and etching the silane coupling layer and the oxide film simultaneously, followed by etching the silicon layer. can be achieved.

Next, the present invention will be explained with reference to an embodiment shown in FIGS. 4 to 9. First, a silane coupling agent 5 is applied to the entire surface of a silicon wafer 1 in which silicon 2 is covered with an oxide film 3, and baking is performed. This baking process greatly influences the etching result, as will be shown later, and can be controlled.
As the silane coupling agent, it is possible to use, for example, the aminosilane-based coupling agent "Toray Silicone SH6020" (trade name). Apply this coupling agent using a spinner.
It is applied to a thickness of 2 to 3 μm at 2500 rpm and baked at about 200°C in the air. The wafer shown in FIG. 4 is obtained by coating the silane coupling layer 5 of the wafer 1 with a photoresist 4 and prebaking it in the same manner as in the prior art. Next, a photomask having a pattern to be etched is applied to the wafer shown in FIG. 4, and ultraviolet rays are irradiated from above, followed by predetermined development processing and post-baking. In this way, a wafer as shown in FIG. 5 is obtained. After that, the etching process begins.

First, for example, 1 c.c. of fluoric acid and 4 ammonium fluoride.
Etching of the oxide film 3 and the silane coupling layer 5 is performed using a mixture of an aqueous solution prepared by dissolving 1.g in 6 c.c. of water. In this case, the silane coupling layer 5 has a much faster etching rate than a thermally generated silicon oxide film or the like. Therefore, first, the silane coupling layer 5 is etched to expose the top surface of the oxide film 3, and then the top surface and side surfaces of the oxide film 3 are etched. Moreover, since the etching speed of the silane coupling layer 5 is fast, as the etching spreads laterally, the oxide film 3 is gradually etched into a tapered shape as shown in the cross section of FIG. This completes the etching of the oxide film.

Next, for example, 1 c.c. of hydrofluoric acid, 3 c.c. of nitric acid, 2 c.c. of complex acid,
The silicon layer 2 is etched using a mixed solution of cc. In this case, as the etching of the silicon layer progresses, it also spreads laterally, but since the oxide film 3 has already become tapered and its tip is very thin, it is etched and oxidized relatively quickly, as shown by the dotted line in FIG. The eaves portion of the membrane 1 does not remain. Thus, the photoresist layer 4 and the silane coupling layer 5
By removing the wafer, a wafer with the desired pattern as shown in FIG. 8 can be obtained.

FIG. 9A shows the relationship between the baking time and the etching amount after applying the silane coupling agent to the silicon wafer. In Figure 9A, the horizontal axis is baking time (minutes) conducted at 200℃, and the vertical axis is
The taper amount (M) is shown when a 0.7 micron oxide film is etched at 20°C for 15 minutes. This taper amount corresponds to the distance 6 between the inner line of the hole in the photoresist and the etched pre-etched portion of the silane coupling layer, as shown in FIG. 9B.

As explained above, according to the present invention, when photoetching a silicon wafer, by providing a silane coupling layer between the oxide film and the photoresist layer, the oxide film can be etched in a tapered shape. . Furthermore, for this reason, when the silicon layer below the oxide film is etched, the oxide film does not remain in the shape of an eaves, allowing highly accurate etching. Furthermore, the eaves-like portions of the oxide film are not broken irregularly during the process, deteriorating the wafer's characteristics, or scattering fragments, causing no negative effects, making it possible to obtain high-quality integrated circuits and semiconductor devices. .

[Brief explanation of drawings]

1 to 3 are sectional views showing a conventional photoetching process, FIGS. 4 to 8 are sectional views showing a photoetching process according to the present invention, and FIG. 9A
9 is a diagram showing the relationship between the baking time of the silane coupling agent and the taper amount, and FIG. 9B is a cross-sectional view for explaining the term taper amount used in FIG. 9a. 2... Silicon layer, 3... Oxide film, 4... Photo etching layer, 5... Silane coupling layer.

Claims (1)

[Claims] 1. In a method of etching a silicon semiconductor using a silicon oxide film as a mask, a layer of silane coupling agent is provided on the oxide film of the silicon semiconductor wafer, a layer of photoresist is provided on top of the silane coupling agent, and the photoresist is irradiated with ultraviolet rays. Then, after a development process, the silane coupling layer and the oxide film are simultaneously wet-etched to form a tapered silicon oxide film mask. A method for etching a silicon semiconductor wafer, which is characterized in that it is performed without leaving an eaves-like shape.