JPH06318576A - Dry etching - Google Patents

Abstract

PURPOSE:To dry-etch a polysilicon film having a step with a good accuracy without leaving even a small part of it unetched. CONSTITUTION:This is a method for dry-etching a polysilicon film 12 which is formed in such a shape as to have a step on a semiconductor substrate 10. In a first process, a polysilicon oxide film 13 is formed on the surface of the polysilicon film 12 by anisotropic film formation wherein a film is formed only in the vertical direction on the surface of the semiconductor substrate 10. In a second process, a resist film 14 is formed in a necessary section on an upper surface of the silicon oxide film 13 and an exposed section of the polysilicon film 12 is selectively etched isoropically with the silicon oxide film being used as a mask. In a third process, the silicon oxide film 13 and the polysilicon film 12 are etched anisotropically with the resist film 14 being used as a mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dry etching method, and more particularly to a method of dry etching a polysilicon film having a step in a manufacturing process of a semiconductor device.

[0002]

2. Description of the Related Art In recent years, with the high integration of devices, the device structure has been multi-layered. As a result, the step aspect ratio on the wafer surface tends to become higher and higher. Therefore, in the manufacturing process of a semiconductor device, there is a demand for a technique for accurately forming a pattern of polysilicon or the like on the upper surface of a wafer on which a step having a high aspect ratio is formed.

The dry etching of a polysilicon film having a step on the base will be described below. As shown in FIG. 2, the wafer 2 has an oxide film 21 formed to have a step.
A polysilicon film 22 is formed on the upper surface of the.

When the polysilicon film 22 in the wafer 2 having the above-described structure is dry-etched,
A pattern of the resist film 23 is formed on the upper surface of the polysilicon film 22. Then, the polysilicon film 22 is dry-etched using the patterned resist film 23 as a mask.

When the above dry etching is performed under a condition of strong anisotropy, the polysilicon film 22 under the resist film 23 has a vertical shape which can suppress the dimensional conversion difference as shown in FIG. However, in the above case, since the condition of strong anisotropy is satisfied, the polysilicon film 22 on the sidewall portion of the step is not removed by etching during the normal etching time, and the film residue 22a is generated. Therefore, the film residue 22a is removed by lengthening the etching time.

When the polysilicon film 22 of FIG. 2 is etched isotropically, the polysilicon film 22 on the side wall of the step is completely removed by etching as shown in FIG.

[0007]

However, the above dry etching method has the following problems. That is, when the polysilicon film 22 is dry-etched under a condition of strong anisotropy, the etching time is lengthened to remove the film residue 22a, but this also affects the underlying oxide film 21. And oxide film 21
Will be thin. Alternatively, by lengthening the etching time, the resist film 23 is etched and the target dimension cannot be obtained in the pattern of the polysilicon film 22.

When the polysilicon film 22 is isotropically dry-etched, the polysilicon film 22 below the resist film 23 is etched by side etching, and the pattern dimension of the polysilicon film 22 is changed to the resist film. It becomes smaller than 23. Further, the shape of the polysilicon film 22 due to etching becomes a taper shape, and a good anisotropic shape cannot be obtained.

Therefore, an object of the present invention is to provide a dry etching method that solves the above problems and improve the reliability of a semiconductor device.

[0010]

The dry etching method of the present invention for achieving the above object is a method of dry etching a polysilicon film formed in a shape having a step on the upper surface of a semiconductor substrate. , Follow the procedure below. First, in the first step, a silicon oxide film is formed on the surface of the polysilicon film by anisotropic film formation in which the film is grown only in a direction perpendicular to the surface of the semiconductor substrate. Then, in a second step, a resist film is formed on a necessary portion of the upper surface of the silicon oxide film, and then the exposed portion of the polysilicon film is selectively isotropically etched using the silicon oxide film as a mask. Alternatively, the exposed portion of the polysilicon film is selectively isotropically etched using the silicon oxide film as a mask, and then a resist film is formed on a necessary portion of the upper surface of the silicon oxide film. Then, in the third step, the silicon oxide film and the polysilicon film are anisotropically etched using the resist film as a mask. Further, in the above dry etching method, the anisotropic film formation of the silicon oxide film is characterized by implanting oxygen ions into the polysilicon film. Further, in the above dry etching method, the anisotropic film formation of the silicon oxide film is characterized by performing CVD of oxygen plasma on the polysilicon film.

[0011]

In the first step, the silicon oxide film is formed on the surface of the polysilicon film by the anisotropic film forming technique of growing only in the direction perpendicular to the surface of the semiconductor substrate. For this reason, the silicon oxide film is not formed on the side wall of the step, and the polysilicon film is exposed. Therefore, the second
When the polysilicon film is selectively and anisotropically etched in the step (1), the polysilicon film exposed on the side wall portion is removed by etching using the silicon oxide film as a mask. In the third step, since the silicon oxide film and the polysilicon film are etched by anisotropic etching, the polysilicon film below the resist film has a good anisotropic shape. Further, in the implantation of oxygen ions into the polysilicon film, the implanted ions are irradiated in a fixed direction, so that oxygen ions are implanted only in the irradiation direction and the silicon oxide film grows anisotropically. Further, in the oxygen plasma CVD of the polysilicon film, the oxygen ions existing in the oxygen plasma are irradiated in a certain direction, so that the oxygen ions are implanted only in the irradiation direction and the silicon oxide film becomes anisotropic. grow up.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of essential parts of a wafer for explaining this embodiment. The wafer 1 to be dry-etched has an oxide film 11 formed on the upper surface of a semiconductor substrate 10. A step is formed on the surface of the oxide film 11 by a wiring pattern (not shown) formed on the upper surface of the semiconductor substrate 10. Then, a polysilicon film 12 having a predetermined thickness is formed on the upper surface of the oxide film 11, and the oxide film 11 of the base is formed.
Due to the influence of the step, the polysilicon film 12 also has a stepped shape. Here, the polysilicon film 1
The film thickness of 2 is, for example, 1000Å.

Dry etching of the polysilicon film 12 having steps as described above is performed according to the following procedure. First, on the upper surface of the polysilicon film 12, for example, 200
The Å silicon oxide film 13 is anisotropically formed. The anisotropic film formation of the silicon oxide film 13 is performed by an ion implantation method using an ion implantation device. In this case, oxygen ions are vertically implanted into the surface of the semiconductor substrate 10 to form the silicon oxide film 13 on the surface layer of the polysilicon film 12 in the region where the oxygen ions are implanted.

Next, as shown in FIG. 1B, a resist film 14 is patterned on the upper surface of the silicon oxide film 13, and then the polysilicon film 12 exposed on the surface is masked with the silicon oxide film 13. Is anisotropically etched selectively. The resist film 14 is patterned on a necessary portion on the silicon oxide film 13 by a photolithography process. Further, the selective anisotropic etching of the polysilicon film 12 is performed using a magnetic field microplasma etching apparatus and using SF ₆ as an etching gas.
As an example of etching conditions, etching gas flow rate =
100 SCCM (Standard Cubic CM / Min), chamber gas pressure = 100 mTorr, microwave power =
It sets to 400W and RF power = 0W, and discharges for 10 seconds.

After the above etching, as shown in FIG. 1C, the silicon oxide film 1 is formed using the resist film 14 as a mask.
3 and the polysilicon film 12 are anisotropically etched. Continuing from the above, this anisotropic etching is performed by switching the etching gas to a mixed gas of SF ₆ and CH ₂ F ₂ using a magnetic field microplasma etching apparatus. As an example of etching conditions, SF ₆ gas flow rate = 40 SC
CM, CH ₂ F ₂ gas flow rate = 60 SCCM, chamber gas pressure = 10 mTorr, microwave power = 400
W, RF power = 30 W.

According to the above procedure, dry etching proceeds as follows. First, in the anisotropic film formation of the silicon oxide film 13 on the surface of the polysilicon film 12 shown in FIG. 1A, by implanting oxygen ions perpendicularly to the semiconductor substrate 10, the polysilicon film on the sidewall portion of the step is formed. Oxygen ions are prevented from being implanted into 12.
As a result, the silicon oxide film 13 is formed on the side wall of the step.
Is not formed, and the polysilicon film 12 on the side wall portion is exposed.

The wafer 1 in the above state is subjected to selective isotropic etching of the polysilicon film 12. Here, by using SF ₆ as an etching gas,
The etching selectivity of the polysilicon film 12 with respect to the silicon oxide film 13 is obtained. Further, by performing the etching with the RF power set to 0 W, the irradiation energy of the ions to the wafer 1 is suppressed and the etching isotropic is obtained. As a result, as shown in FIG. 1B, the polysilicon film 12 exposed on the sidewall of the step is removed by etching using the silicon oxide film 13 as a mask.

In the subsequent anisotropic etching of the silicon oxide film 13 and the polysilicon film 12, a mixed gas of SF ₆ and CH ₂ F ₂ is used as an etching gas to remove the silicon oxide film 13 and the polysilicon film 12. To etch. Further, by performing the etching with the RF power set to 30 W, the irradiation energy of the ions to the wafer 1 is increased to obtain the etching anisotropy. As a result, as shown in FIG. 1C, a good anisotropic shape can be obtained in the silicon oxide film 13 and the polysilicon film 12 which are etched using the resist film 14 as a mask.

Next, another embodiment of the present invention will be described with reference to FIG. 1 similar to the above embodiment. In this embodiment, the anisotropic deposition of the silicon oxide film 13 in the above embodiment is carried out by oxygen plasma CVD using a plasma generator.

In the above anisotropic film formation, the discharge condition is O ₂
Gas flow rate = 50 SCCM, chamber gas pressure = 1 mT
orr, microwave power = 500 W, RF power = 5
The silicon oxide film 13 is formed by setting it to 0 W.

After the silicon oxide film 13 is formed as described above, the polysilicon film 12 is formed in the same procedure as in the above embodiment.
Dry etching is performed.

According to the above procedure, in the CVD of oxygen plasma on the polysilicon film 12, the oxygen ions existing in the oxygen plasma enter the semiconductor substrate 10 perpendicularly, so that the side wall of the step is oxidized with silicon oxide. The film 13 is not formed, and the polysilicon film 12 is exposed as in the above embodiment. Since the wafer 1 in this state is dry-etched in the same manner as in the above embodiment,
The polysilicon film 12 on the side wall of the step is removed by etching, and the silicon oxide film 13 and the polysilicon film 12 have a good anisotropic shape using the resist film 14 as a mask.

In the two embodiments described above,
The case where the resist film 14 is formed on the upper surface of the silicon oxide film 13 and then the polysilicon film 12 is selectively isotropically etched using the silicon oxide film 13 as a mask has been described. However, according to the present invention, the resist film 14 is formed on the upper surface of the silicon oxide film 13 after the polysilicon film 12 is selectively isotropically etched using the silicon oxide film 13 as a mask.
May be formed.

The conditions for forming the silicon oxide film 13 are as follows:
The conditions are not limited to those shown in the above two embodiments,
The condition is that the silicon oxide film 13 is anisotropically formed. Furthermore, the etching conditions for the polysilicon film 12 and the silicon oxide film 13 are not limited to the above settings, but may be any conditions that allow anisotropic etching or isotropic etching depending on the process.

[0025]

As described in the above embodiments, according to the present invention, in the dry etching of a polysilicon film having a step, the anisotropically formed silicon oxide film is used as a mask to selectively etch the polysilicon film. Isotropically etched, and then the silicon oxide film and the polysilicon film are anisotropically etched using the resist film as a mask. Therefore, the polysilicon film on the side wall of the step is removed by etching, and a good anisotropic shape is obtained in the pattern of the polysilicon film formed by etching. Therefore, the pattern of the polysilicon film can be accurately formed without any film remaining on the side wall of the step, and the reliability of the semiconductor device is expected to be improved. Moreover, since the silicon oxide film is anisotropically formed on the surface of the polysilicon film by the implantation of oxygen ions, the polysilicon film having a step can be dry-etched into a good anisotropic shape without leaving a film. Furthermore, since the silicon oxide film is anisotropically formed on the surface of the polysilicon film by the CVD of oxygen plasma, the polysilicon film having the step difference can be dry-etched similarly to the above.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example.

FIG. 2 is a diagram illustrating a conventional example.

FIG. 3 is a diagram illustrating a conventional example.

FIG. 4 is a diagram illustrating a conventional example.

[Explanation of symbols]

 10 semiconductor substrate 12 polysilicon film 13 silicon oxide film 14 resist film

Claims (3)

[Claims] 1. A method of dry-etching a polysilicon film formed in a shape having a step on the upper surface of a semiconductor substrate, wherein anisotropic film growth is performed only in a direction perpendicular to the surface of the semiconductor substrate. A first step of forming a silicon oxide film on the surface of the polysilicon film, a resist film is formed on a necessary portion of the upper surface of the silicon oxide film, and then the silicon oxide film is used as a mask to form the polysilicon film. The exposed portion is selectively isotropically etched, or the exposed portion of the polysilicon film is selectively isotropically etched using the silicon oxide film as a mask, and thereafter, a required portion of the upper surface of the silicon oxide film is formed. A second step of forming a resist film, and anisotropically etching the silicon oxide film and the polysilicon film using the resist film as a mask And a third step of etching the polysilicon. 2. The dry etching method according to claim 1, wherein the anisotropic film formation of the silicon oxide film is performed by implanting oxygen ions into the polysilicon film. 3. The dry etching method according to claim 2, wherein the anisotropic deposition of the silicon oxide film is performed by CVD of oxygen plasma on the polysilicon film.