JPH0547977B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a thermal oxide film (SiO ₂
The present invention relates to a dry etching method for a PSG film (phosphorus silica glass film) and a PSG film (phosphorus silica glass film).

(Conventional technology) Conventionally, oxide films (thermal oxide films and
The etching method for PSG film is HF
There was a wet etching method using a buffer solution of (hydrofluoric acid). When a thermal oxide film and a PSG film are etched by this wet method, the etching rate ratio is 1 for the thermal oxide film and 7 to 8 times that for the PSG film after vapor phase growth.
5 after annealing the PSG film after vapor phase growth.
It was ~6 times as hot.

However, with the wet method, etching progresses isotropically and the adhesion between the photoresist and PSG film is poor, resulting in a very large undercut under the photoresist film, resulting in poor dimensional accuracy. It was hot.

Instead of such a wet method, a dry etching method has come to be used for etching the above-mentioned thermal oxide film and PSG film. The dry etching method is a method in which etching is performed using gas plasma without using a solution. A typical example of the dry etching method is to deposit a semiconductor substrate (thermal oxide film and
A Freon-based gas (CF ₄ , C ₂ F _{6 ,} etc.) is passed through the electrodes, and a high-frequency voltage is applied between the electrodes.

However, such a dry etching method has two drawbacks: etching proceeds isotropically and the amount of etching varies widely. The reason for this is that the electric field inside the inner electrode is almost zero, and etching is performed only by plasma without being affected by the electric field, so etching progresses isotropically. Since the flow is perpendicular to the opposite direction, it becomes a turbulent flow, which is thought to increase the variation in etching.

In recent years, a parallel plate type etching apparatus has been developed. Along with this, dry etching methods using parallel plate type etching equipment have come to be applied to the etching of thermal oxide films and PSG films.

When dry etching a thermal oxide film or PSG film using a parallel plate type etching device,
Etching progresses anisotropically (fast in the vertical direction of the semiconductor substrate and slow in the horizontal direction),
Compared to the wet method described above, this method has the advantage of less undercutting, higher dimensional accuracy, and less variation. The reason for this is thought to be related to the fact that an electric field is applied perpendicularly to the semiconductor substrate and that the gas flow is laminar.

Because of these advantages and the recent trend toward finer patterns, the dry etching method using the above-mentioned parallel plate type etching apparatus is frequently used as a dry etching method for thermal oxide films and PSG films. ing.

(Problems to be Solved by the Invention) However, when a thermal oxide film and a PSG film are etched using this dry etching method,
Etching progresses not only due to chemical factors but also physical factors such as the application of an electric field, so the etching rate of the thermal oxide film and the etching rate of the PSG film are relatively close to each other, and the etching rate increases. As a ratio, the thermal oxide film is 1, while the PSG
The drawback was that even after the film was grown in a vapor phase, a value that was only 2 to 3 times greater could be obtained at most. This drawback is
In selective etching of the PSG film, in which only the PSG film portion of a composite film consisting of a PSG film and a thermal oxide film is etched away according to a predetermined pattern, if the PSG film is over-etched, the thermal oxide film is etched. occurs.

This invention was made in view of the above points, and it is possible to increase the ratio of the etching speed of the PSG film to the etching speed of the thermal oxide film to 10 or more while maintaining the etching anisotropy in which the etching speed is high in the vertical direction of the semiconductor substrate. It is an object of the present invention to provide a dry etching method that allows for a sufficiently large size.

(Means for Solving the Problems) In the present invention, a semiconductor substrate having a thermal oxide film (SiO ₂ film) and a PSG film is placed on one of two parallel plate electrodes of a parallel plate etching apparatus, and the semiconductor substrate is 0.8torr of mixed gas _{of C2F6} and _CHF3 on the surface
While flowing at the above pressure, a high frequency voltage is applied between the two parallel plate electrodes to perform dry etching.

(Function) In the present invention, the etching rate ratio of the PSG film to the thermal oxide film is 10 or more while maintaining etching anisotropy.

(Example) A parallel plate type etching apparatus used in the dry etching method of the present invention is shown in FIG. This device has parallel plate electrodes 2 and 3 facing each other in a closed container 1, and the parallel plate electrodes 2 and 3 are
The configuration is such that a high frequency voltage is applied from a high frequency power supply 4 between the two. Here, parallel plate electrodes 2 and 3
The interval is set to 1 cm or more and 5 cm or less. Also,
The gas flows through the laminate as shown by the arrow and exits through the exhaust port 5.
More exhaust.

An embodiment of the present invention will be described in detail below. In one embodiment, a semiconductor substrate (having a thermal oxide film and a PSG film) is placed on a lower parallel plate electrode 3 using a parallel plate type etching apparatus shown in _{FIG. 6} gas and CHF ₃ gas are used. Further, using this mixed gas, the flow rate is kept constant, and the etching pressure is set to 0.8 torr or more.
In this state, a high frequency voltage is applied from the high frequency power source 4 between the pair of parallel plate electrodes 2 and 3 to perform etching.

FIG. 1 shows the etching pressure-PSG/SiO ₂ etching speed ratio when the etching pressure was gradually increased from 0.2 torr in the above etching using the above mixed gas. Up to about 0.7torr,
Although the etching rate ratio of the PSG film to the thermal oxide film is not a very large value, it rapidly increases when the etching rate exceeds 0.8 torr, and it is recognized that the etching rate ratio becomes 10 or more. Under the same etching conditions, PSG
Figure 2 shows the pressure dependence of the etching rate of the film and the thermal SiO ₂ film. In addition, since this etching uses a parallel plate type etching device, it maintains anisotropy (etching anisotropy in which the etching rate is fast in the direction perpendicular to the semiconductor substrate).
Therefore, there was little undercutting at the interface between the photoresist and the film to be etched, a sharp etched cross section was obtained, the dimensional accuracy was very good, and it was possible to process fine patterns. In addition, the etching uniformity is good, with 3% within a wafer and 5% between wafers.
The value is obtained.

(Effects of the Invention) As described above, the dry etching method of the present invention uses a parallel plate type etching apparatus to perform C ₂
By flowing a mixed gas of F ₆ and CHF ₃ at a pressure of 0.8 torr or higher, etching anisotropy with a high etching rate in the vertical direction of the semiconductor substrate is maintained.
The ratio of the etching rate of the PSG film to the etching rate of the thermal oxide film can be sufficiently increased to 10 or more. Therefore, after forming a multilayer film of a thermal oxide film and a PSG film on a semiconductor substrate (silicon substrate) and forming a desired pattern with photoresist,
Etching only the PSG film and leaving the thermal oxide film,
Moreover, it can be used for ion implantation. That is, in the manufacture of semiconductor devices, a thermal oxide film of approximately 1000 Å is formed on a silicon substrate to prevent damage from ion implantation, and then
After depositing a PSG film of approximately 5,000 to 10,000 Å and patterning using photoresist, etching is first performed under conditions where the etching rate ratio of the PSG film to the thermal oxide film is high to remove the PSG film, and then ion implantation is performed to remove impurities. This method can be applied to processes such as diffusing etchants into a silicon substrate and finally etching a thermal oxide film formed as a protection during ion implantation.

[Brief explanation of the drawing]

Figure 1 shows the PSG/
The characteristic diagram showing the SiO ₂ etching speed ratio, Figure 2, is
FIG. 3, which is a pressure dependence characteristic diagram of the etching rate of PSG and SiO ₂ , is a sectional view showing a parallel plate type etching apparatus used in the dry etching method of the present invention. 1... Sealed container, 2, 3... Parallel plate electrode, 4
...High frequency power supply, 5...Exhaust port.

Claims (1)

[Claims] 1. A step of preparing a semiconductor substrate having a phosphorous silica glass (PSG) film formed on the surface of a thermal oxide film (SiO ₂ film); a step of placing a gas mixture of C ₂ F ₆ and CHF ₃ on the surface of the semiconductor substrate at a pressure of 0.8 torr or more; A dry etching method comprising the step of etching the thermal oxide film and the PSG film at an etching rate ratio of 10 or more by applying a voltage.