JPS602948A - Etching method - Google Patents

Abstract

PURPOSE:To control easily the angle of a taper only by a change in the thickness of a photosensitive resin without changing etching conditions by taperingly etching a substrate by making use of the thermal deformation of the photosensitive resin as an etching mask. CONSTITUTION:A thermally oxidized film 12 is grown on a silicon single crystal substrate 11. The film 12 is coated with a photoresist 13, and a photoresist pattern 13' is formed in a conventional photolithographic stage. The film 12 is etched through the pattern 13' as a mask to form a pattern 12' having the same shape as the pattern 13'. The substrate 11 is then etched through the patterns 12', 13' as a mask. During the etching, the photoresist undergoes thermal deformation and flows toward the side wall of the etched part. The substrate 11 is taperingly grooved 14 by continuing the etching while covering the side wall of the etched part with the flowing photoresist.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an etching method for performing taper etching on a single crystal silicon substrate.

(Prior Art) The most common device active region separation method will be explained with reference to FIG.

First, a silicon oxide film 2 is formed on a single-crystal silicon substrate 1, and then subjected to a normal photolithography process (FIG. 1(a)).

Next, using the patterned silicon oxide film 2 as an etching mask, the silicon substrate 1 is etched vertically.
A groove 3 is formed (side 1 figure (b)).

Next, after growing a silicon oxide film 4 on the inner wall of the ff'j: 3, polycrystalline silicon 5 is buried in the groove 3.

Further, a silicon oxide film 6 is formed on the surface of the polycrystalline silicon 5 by thermal oxidation. (FIG. 1(C)) Thereafter, only the silicon oxide film 2 is removed by utilizing the difference in thickness between the silicon oxide films 2 and 6 (FIG. 1(d)). By removing this silicon oxide film 2, the silicon substrate portion exposed is a separation region between 5 (consisting of silicon oxide film 6 and polycrystalline silicon 5).
The device active regions 7 are separated from each other.

However, in such a separation method, in the step of thermally oxidizing polycrystalline silicon 5, silicon substrate IK stress is generated due to the volume expansion of polycrystalline silicon due to oxidation, so crystal defects are generated in the element active region 7. Therefore, there is a problem that transistor characteristics are deteriorated.

In order to solve this problem, it is necessary to make #3 into which the polycrystalline silicon 5 is embedded into a tapered shape so that the stress caused by the volumetric expansion pressure can be alleviated by its slope.

To do this, it is necessary to taper-etch the silicon substrate 1, which involves changing the type of gas and the gas flow in the etching process.
1. It is necessary to change conditions such as pressure and RF power, but changing these conditions also changes etching speed, uniformity 1 selectivity, etc. When etching angle) is required, it is extremely difficult to select etching conditions.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an etching method in which the taper angle can be controlled using the same etching apparatus without changing the etching conditions.

(Example) An embodiment of the present invention will be described below with reference to FIG.

In FIG. 2(a), 11 is a single crystal silicon substrate with a (100) surface.First, about 15
A thermal oxide film 12 is grown to a thickness of 00X.

Furthermore, on the thermal oxide film 12, a photoresist (for example, Microposit 1400-17) 1 is applied to a thickness of about 1.5 μm.
Apply 3. (FIG. 2(a)) After that, the photoresist 13 is applied to the photoresist pattern (
) and turn) of the sensitive resin layer 13'. Next, the thermal oxide film 12 is etched using the photoresist pattern 13' as a mask, thereby forming the thermal oxide film 12 into the same thermal oxide film pattern 2' as the photoresist pattern 13'. (FIG. 20)) Next, the single crystal silicon substrate 11 is etched by about 1 μm using the thermal oxide film/lean 12' and the photoresist pattern 13' as an etching mask or turn.

Here, etching was performed using a parallel plate type dry etching apparatus using carbon tetrachloride gas of 50 SCCM*pressure of 0.
The test was conducted under the conditions of ITorr, high frequency power supply frequency of 1400 KHz, and high frequency current of 3 A. Then, during etching, the photoresist of the photoresist pattern 13' is thermally deformed and flows out onto the side wall of the etched area, which becomes an etching mask. In this way, by proceeding with etching while covering the side wall of the etched area with the flowed out photoresist, in this case, as shown in FIG. shaped groove 1
4 is formed on the substrate 11.

After that, a mixed solution of hydrogen peroxide and sulfuric acid (mixing ratio HJ
04'H20t=4:1) for 30 minutes to remove the photoresist pattern 13'. According to the above, the element active area is covered with a thermal oxide film (thermal oxide film pattern 12).
'), and a structure is formed in which the element isolation region is tapered etched. (FIG. 2(d)) As described above, in one embodiment, tapered etching was performed using thermal deformation of the photoresist. That is, carbon tetrachloride gas 5 was
08CCM, pressure 0. ITorr, high frequency current3. OA
In etching under these conditions, if the etching mask is only a thermal oxide film, the single crystal is etched vertically (taper angle 90°), but by placing photoresist on the thermal oxide film as an etching mask, a tapered Etching can be performed. And this taper angle is the third
As shown in the figure, changing the photorenost film thickness can be easily controlled, and there is no need to change gas extraction, gas flow rate, gas pressure, or high-frequency power, so one device can process various devices and each This is very useful when the device requires grooves with different taper angles.

(Effects of the Invention) As detailed above, according to the etching method of the present invention, since the substrate is chip-etched using thermal deformation of the sensitive resin as an etching mask, it is possible to change the etching conditions. The tenor angle can be easily controlled by simply changing the thickness of the sensitive resin.

[Brief explanation of the drawing]

FIG. 1 is a sectional view for explaining a general device active region separation method, FIG. 2 is a sectional view for explaining an embodiment of the etching method of the present invention, and FIG. 3 is a photorenost film. A characteristic diagram showing the relationship between thickness and taper angle. 11... Single crystal silicon substrate, 12^... Thermal oxide film. 12'...Thermal oxide film pattern, 13...Photoresist. 13'... Photoresist pattern, 14... Groove. Patent applicant: Oki Electric Industry Co., Ltd.

Claims (1)

[Claims] The method comprises a step of forming an etching mask arm turn including a photosensitive resin layer on a single crystal silicon substrate, and a step of taper etching the substrate while thermally deforming the photosensitive resin using the turn or turn as an etching mask. An etching method.