JPS6258141B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a semiconductor device in which a cinnamic acid photoresist is used as a photoresist material and a sloped surface is formed in the cross section of a silicon oxide film during etching of the silicon oxide film by using appropriate conditions. Conventionally, in the photoetching method for opening windows in silicon oxide films, the organic polymer thin film material used is generally a rubber-based photoresist whose main component is isoprene. The cross section 3 of the silicon oxide film 2 photoetched using the material 1 is approximately perpendicular to the surface of the silicon 4 at an angle of 70 to 90 degrees. For this reason, as shown in FIG. 2, for example, when aluminum is deposited, the thickness of the aluminum evaporated film becomes thinner at the vertical silicon oxide film cross section 5, and the aluminum film 6 becomes easier to cut at the cross section. In addition, in the spin-on diffusion method,
As shown in FIG. 3, when a diffusion source is applied to a silicon wafer, the film thickness of the diffusion source 8 becomes thicker on the inside 7 of the vertical silicon oxide film cross section of the window, and the silicon is attacked around the diffusion region. be done. Furthermore, as shown in FIG. 4, even when an organic polymer material is coated on a silicon oxide film to form an organic polymer thin film 9, the thickness of the thin film may be cut or tends to be uneven. The following taper etching method has been proposed in order to avoid such a nearly vertical cut in the silicon oxide film and provide a gently sloped surface. That is, a substance having a faster etching rate than the silicon oxide film is formed on the silicon oxide film, and silicon oxide films with different densities are vapor-phase grown or coated on the silicon oxide film by a method that takes advantage of the difference in etching rate. There is also a method of forming a phosphor glass layer and performing taper etching by utilizing the difference in etching speed of a silicon oxide film with a mixture of fluoric acid or ammonium fluoride aqueous solution. However, this method has drawbacks such as poor reproducibility during mass production, complicated processing and a large number of processing steps, contamination of the silicon or silicon oxide film surface, and failure to obtain an appropriate tilt angle. In addition, unless water molecules, etc. are chemically adsorbed on the surface of a commercially available rubber photoresist thermal oxide film, a photoresist film is formed on the silicon oxide film surface, and a hydrofluoric acid 1 In the mixed system of 6 volumes of the ammonium fluoride aqueous solution, undercuts (a phenomenon in which the silicon oxide film beneath the silicon film is etched in the lateral direction) and gentle inclinations in the cross section of the silicon oxide film do not occur. The cinnamic acid photoresist typified by KPR (trade name of Kodak Co., Ltd.) according to the present invention has a smaller bonding force to the silicon thermal oxide film than the rubber photoresist, and taper etching can be performed using appropriate conditions. It is possible to do so. Examples thereof will be described below. Negative (photo-insolubilized) photoresist whose main component is polyvinyl cinnamate, etc. has a viscosity of 15 centipoise, and when applied onto a silicon oxide film at a rotation speed of 800 rpm, a photoresist film with a thickness of approximately 0.5μ is formed. Thickness can be obtained. As shown in FIG. 5, a silicon wafer 10 is thermally oxidized in a steam atmosphere to form a silicon oxide film 11 with a thickness of about 1.0 to 1.2 μm, and immediately a photoresist is applied under the above conditions. Next 60~
Heat treatment is performed at 90°C, preferably 70°C, in a nitrogen atmosphere for 10 minutes or less. Next, the photoresist film is irradiated with ultraviolet rays through a photomask, and in the areas not irradiated with ultraviolet rays, the photoresist is partially polymerized, so it is dissolved in a mixed system of xylene and ethyl cellosolve acetate and isopropyl alcohol, and the photoresist in the partially polymerized areas is removed. . Next, in order to increase the bonding strength between the photoresist film 12 and the silicon oxide film,
Heat treatment at 150-180℃ in nitrogen atmosphere for 30~
Do it for 60 minutes. Next, the silicon oxide film not masked with photoresist was etched at a temperature of 20°C.
This is carried out for about 15 minutes in a mixed system of hydrofluoric acid and ammonium fluoride aqueous solution (1 volume to 6 volumes) at ~25°C. The silicon oxide film etching rate is approximately 1000 Å per minute, so for a silicon oxide film of 1.2μ, approximately 3
This results in excessive etching. In this manner, the cross section 13 of the silicon oxide film can have a gentle slope as shown in FIG. Here, as shown in FIG. 7, if the thickness of the silicon oxide film is tμ, the amount of taper in the cross section of the silicon oxide film viewed from the top of the wafer is dμ, and the angle of inclination due to taper etching is θ°, then tanθ=t /d. Comparing the above method with the photoetching method using rubber resist,

[Table] Therefore, taper etching is possible using a cinnamic acid photoresist such as polyvinyl cinnamate. Furthermore, the formation of inclined surfaces using a cinnamic acid-based photoresist such as polyvinyl cinnamate is reproducible. The effect of the present invention is that by having the above-mentioned structure, the etched cross section of the silicon oxide film can be made into a sloped surface, and a stable sloped surface and process can be achieved without implementing a complicated manufacturing method to form the sloped surface. Can be secured. Further, as shown in FIG. 8, the aluminum film 14
The spin-on diffusion source can be uniformly applied, and the organic polymer thin film can be uniformly applied.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a silicon oxide film etched when a rubber-based photoresist is used, and Figure 2 is a cross-sectional view of a silicon oxide film and an aluminum film when an aluminum film is formed on a conventional vertical silicon oxide film cross-section. , Figure 3 is a cross-sectional view of a diffusion region when a spin-on diffusion source is applied to a cross-section of a conventional silicon oxide film, and Figure 4 is a cross-sectional view of a silicon oxide film when an organic polymer thin film is formed on a cross-section of a conventional silicon oxide film. 5 is a cross-sectional view of a cinnamic acid photoresist film formed on a silicon oxide film, and FIG. 6 is a slanted surface of a silicon oxide film formed according to the present invention. Figure 7 is a cross-sectional view showing the measurement points used in the experiment, and Figure 8 is a cross-sectional view showing the effectiveness of the tapered etching method in preventing cutting of the aluminum film using the sloped surface of the silicon oxide film. be. 1...Rubber photoresist film, 2...Silicon oxide film, 3...Cross section of silicon oxide film, 4...
Silicon surface, 5...Silicon oxide film cross section, 6...
...aluminum film, 7...inner side of silicon oxide film cross section,
8...Applied diffusion source, 9...Organic polymer thin film,
10...Silicon wafer, 11...Silicon oxide film, 12...KPR film, 13...Silicon oxide film cross section with an inclined surface, 14...Aluminum film.

Claims (1)

[Claims] 1. A step of applying a cinnamic acid photoresist to the surface of the silicon oxide film, and a step of heat treatment at a temperature of 60 to 90°C in a nitrogen atmosphere for 10 minutes or less,
A step of exposing using a photomask, a step of developing using a mixed liquid system of xylene and ethyl cellosolve acetate and isopropyl alcohol, and a step of developing at a temperature of 150 to 180°C in a nitrogen atmosphere for 30 to 30 minutes in a nitrogen atmosphere.
It includes a step of heat treatment for 60 minutes and a step of etching the silicon oxide film with a hydrofluoric acid-based etching solution, and through these steps, the silicon oxide film is etched with a taper angle of 10° to 20°. A method for manufacturing a featured semiconductor device.