JPH06120170A - Plasma etching treating method - Google Patents

Abstract

PURPOSE:To provide a plasma etching treating method in which good selectivity and required anisotropy is obtained even if a low-deposition etching gas is used. CONSTITUTION:A Cl2 gas is respectively supplied into a plasma generating chamber 1 set to a required degree of vacuum and a sample chamber 3, and a magnetic field is formed by a primary exciting coil 14, and further a microwave is introduced into the plasma generating chamber 1 and a plasma is generated from the Cl2 gas. Then, the plasma is guided to the surface of a sample S at a distance of 250mm or more from an ECR point P by a divergence magnetic field generated through the primary exciting coil 14, and a magnetic flux density of the surface of the sample S is regulated to 50 gausses or less by a secondary exciting coil 15 carrying a current opposite to the primary exciting coil 14 and an etching is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching treatment method in a semiconductor manufacturing process, and more particularly to a method of subjecting a sample surface to etching treatment using plasma generated by utilizing electron cyclotron resonance.

[0002]

2. Description of the Related Art FIG. 3 (a) is a schematic diagram showing the configuration of a conventional plasma etching apparatus utilizing electron cyclotron resonance (hereinafter referred to as ECR) using microwaves disclosed in Japanese Patent Laid-Open No. 57-133636. FIG. In the figure, 31 is a plasma generation chamber that generates plasma for etching. The plasma generating chamber 31 has a microwave introduction window 31a of a quartz glass plate that seals it in the center of the upper wall, and a circular plasma extraction window 31b at the position opposite to the microwave introduction window 31a in the center of the lower wall. Each has.

One end of a waveguide 32, the other end of which is connected to a high-frequency oscillator (not shown), is connected to the microwave introduction window 31a, and a sample chamber 33 is provided so as to face the plasma extraction window 31b. ing. An exciting coil 34 is concentrically arranged around the plasma generating chamber 31 and one end of a waveguide 32 connected thereto so as to surround them. On the other hand, a mounting table 37 is provided in the sample chamber 33, and a sample S such as a disk-shaped wafer is directly placed on the mounting table 37.
Alternatively, it is detachably mounted by means such as electrostatic adsorption.

The method of etching with such an apparatus is as follows. A source gas is supplied into each of the plasma generation chamber 31 and the sample chamber 33, which are set to a required degree of vacuum.
Then, while forming a magnetic field by the exciting coil 34, a microwave is introduced into the plasma generation chamber 31, and the source gas supplied as a cavity resonator in the plasma generation chamber 31 is ECR excited to generate plasma. The generated plasma is generated by the exciting coil 34, and the divergent magnetic field whose magnetic flux density decreases toward the sample chamber 33 side causes the sample S on the mounting table 37 in the sample chamber 33 to move.
The surface of the sample S is etched by leading to the periphery.

FIG. 3 (b) is a graph showing the magnetic flux density gradient of the divergent magnetic field described above. The magnetic flux density of the divergent magnetic field becomes maximum near the center of the exciting coil 34, and when the microwave frequency that causes plasma generation is 2.45 GHz, the magnetic flux density is 875 Gauss, the so-called electron cyclotron resonance point (hereinafter also referred to as ECR point). It gradually decreases from P to the sample S. The magnetic flux density on the surface of the sample S is 100-200.
It is Gaussian, and the distance from the ECR point P to the surface of the sample S is approximately 200 mm.

[0006]

By the way, when attempting to etch polycrystalline silicon by such a conventional method, a high selection ratio with respect to a resist film and a base film (generally a SiO ₂ film) and a required anisotropic shape are obtained. In order to obtain it, a protective film is formed on the side wall of the pattern to be etched using an etching gas such as HBr, SiCl ₄ , C ₂ H ₂ F _4, etc., and etching is performed while protecting the side wall against etching. However, such a method has a problem that deposits are formed on the inner wall surface of the sample chamber during etching, which causes particles and reduces the manufacturing yield of semiconductor devices.

On the other hand, for example, when Cl ₂ gas is used as an etching gas, the deposits are not formed, but it becomes difficult to form a protective film on the side wall, and in order to obtain a desired anisotropic shape, a high frequency wave is applied to the sample. Then, by increasing the energy of the ions in the plasma incident on the sample, the sputtering effect on the resist film is enhanced, and the carbon supplied from the resist forms the side wall protective film to perform etching. However, such a method has a problem that the selection ratio with respect to the resist film and the base film is significantly lowered.

The present invention has been made in view of such circumstances, and an object thereof is to have a high selection ratio with respect to a resist film and a base film even if Cl ₂ gas is used,
Another object of the present invention is to provide a plasma etching treatment method capable of obtaining a required anisotropic shape.

[0009]

In the plasma etching method according to the present invention, a gas plasma mainly generated at an electron cyclotron resonance point is guided to a sample by a magnetic field to etch the sample, The magnetic flux density of the magnetic field on the sample surface is 50 Gauss or less, and the distance between the electron cyclotron resonance point and the sample surface is 250 mm or more.

[0010]

In the plasma etching method of the present invention, since the magnetic flux density on the sample surface is 50 gauss or less, the magnetic flux density gradient increases and the energy of ions in the plasma increases to the energy for anisotropic etching. Further, since the distance between the electron cyclotron resonance point and the sample surface is 250 mm or more, the incident angle of the ions becomes an angle capable of etching into the required anisotropic shape over the entire region of the sample surface.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. FIG. 1 shows an ECR plasma etching apparatus configured so that the magnetic flux density gradient of a divergent magnetic field can be adjusted. In the figure, 1 is a plasma generation chamber. The plasma generation chamber 1 is provided with a microwave introduction window 1a that seals the upper wall center thereof and a circular plasma extraction window 1b at a position facing the microwave introduction window 1a at the lower wall center thereof. . One end of a waveguide 2 whose other end is connected to a high-frequency oscillator (not shown) is connected to the microwave introduction window 1a, and the sample chamber 3 is exposed to the plasma extraction window 1b.
Are connected via shoulders 4.

On the other hand, the periphery of the plasma generation chamber 1 and the waveguide 2
The main excitation coil 14 is provided around one end of
A device for reducing the magnetic flux density on the surface of the sample from the upper part of the sample chamber 3 to the lower part of the shoulder part 4, for example, a sub-excitation coil adapted to pass a current in the direction opposite to that of the main excitation coil 14.
There are 15 around. In the sample chamber 3, a mounting table 7 on which the sample S is removably mounted is installed from the ECR point P to the sample S.
It is arranged so that the distance to the surface is 250 mm or more.

Next, a method of performing ECR plasma etching processing using such an apparatus will be described. A raw material gas having a low deposit forming ability, for example, Cl ₂ gas is supplied into the plasma generation chamber 1 and the sample chamber 3 which are set to a required degree of vacuum.
Then, while forming a magnetic field by the main excitation coil 14, microwaves are introduced into the plasma generation chamber 1 to excite Cl ₂ gas by ECR and generate plasma. The generated plasma is guided to the periphery of the sample S by a divergent magnetic field to etch the surface of the sample S.
At this time, the magnetic flux density on the surface of the sample S is 50 gauss or less as shown in FIG. 1 (b) by flowing a current in the sub-excitation coil 15 in the direction opposite to that of the main excitation coil 14 to form a magnetic field. The etching is performed after adjustment.

As described above, the distance from the ECR point P to the surface of the sample S (hereinafter referred to as P-S distance) is 250 m.
The reason why the magnetic flux density is m or more and the surface of the sample S is 50 gauss or less will be described with reference to Tables 1 and 2 and FIG. Table 1 shows P- in the conventional example, the comparative example and the example of the present invention.
The relationship between the S distance, the magnetic flux density on the surface of the sample S, and the current between the main exciting coil 14 and the sub exciting coil 15 is shown. The minus sign "-" in the table indicates that the direction of the current is opposite. ing. In addition, in the conventional example, since the sub-excitation coil 15 is not provided, it is set to “none”.

[0015]

[Table 1]

As is clear from Table 1, in the conventional example, PS
Distance is 200mm, current of exciting coil 34 (see Fig.3) is 20
In the case of A, the magnetic flux density on the surface of the sample is 100 gauss, and in the comparative example, the P-S distance and the current of the main exciting coil 14 are the same as those of the conventional example, and the current of the sub exciting coil 15 is the same as the main exciting coil.
The magnetic flux density on the surface of the sample is set to 50 gauss by flowing 15 A in the opposite direction to 14. In the example of the present invention, the P-S distance is 25
It is 0 mm, and the current of the main excitation coil 14 is 20 A, and the current of 10 A in the opposite direction is passed through the sub excitation coil 15 to make the magnetic flux density on the surface of the sample 50 Gauss.

FIG. 2 shows the three examples in Table 1 with the diameter of 8 inches.
A sample in which a SiO ₂ film 22, a polycrystalline silicon film 23, and a resist film 24 were deposited in this order on a Si substrate 21 was Cl ₂ : 20 sccm, O ₂ :
It is a typical sectional view showing the etching shape of the sample after etching with 2 sccm, pressure: 1 mTorr, and microwave power: 1 kW. Table 2 shows the uniformity W of the etching rate when etching is performed as described above.

[0018]

[Table 2]

As is clear from FIG. 2 and Table 2, when Cl ₂ gas was used as the etching gas, the sidewall of the polycrystalline silicon film 23 was etched at any point in the circumferential direction from the sample center in the conventional example. No anisotropic shape is obtained, and the etching rate uniformity W is low.

In the case of the comparative example in which the magnetic flux density on the surface of the sample is 50 gauss, the required anisotropic shape is obtained in the polycrystalline silicon film 23 up to about 70 mm from the center of the sample, and the uniformity W of the etching rate is also a little. Improved, but 90mm from sample center
In the vicinity, the side wall is etched. By the way, in the above-mentioned device, the electrons in the plasma are accelerated from the one with a strong magnetic flux density to the one with a weak magnetic flux density, and the ions in the plasma are accelerated due to the potential gradient (ambipolar electric field) in which the voltage of the weak magnetic flux density decreases. However, as described above, it is possible to obtain an anisotropic shape by increasing the potential gradient by lowering the magnetic flux density on the sample surface to 50 Gauss and further increasing the ion energy.

However, when the P-S distance is 200 mm as in the above-mentioned comparative example, the side wall is etched at the outer peripheral portion of the sample, and particularly the sample center side is excessively etched as compared to the sample outer side wall. This is because when the P-S distance is 200 mm, the incidence of the ions on the sample is almost vertical (approximately
The angle of incidence is less than 70 ° near 90 mm from the center of the sample. Therefore, if the sample is a small mouth type, the required anisotropic shape can be obtained in the entire region, but in the large mouth type sample as in this embodiment, the required anisotropic shape cannot be obtained in the outer peripheral portion.

Therefore, when the magnetic flux density on the sample surface is 50 gauss and the P-S distance is 250 mm as in the case of the present invention, the energy of the ions increases and the incident angle of the ions becomes about 75 ° at the outer edge of the sample. Therefore, the required anisotropic shape can be obtained even in the outer peripheral portion, and the uniformity of the etching rate can be further improved. It can be carried out. If the incident angle of the ions is 70 ° or more, a desired anisotropic shape can be obtained.

[0023]

As described in detail above, in the plasma etching method of the present invention, since the magnetic flux density of the sample surface is 50 Gauss or less, the etching gas is Cl ₂ gas which has a low deposit forming ability. Can be performed, the generation of particles is suppressed, and the manufacturing yield of semiconductor devices is improved. Further, since the P-S distance is 250 mm or more, the present invention has excellent effects such that even in a sample having a large mouth shape, anisotropic etching can be uniformly performed over the entire area of the sample surface.

[Brief description of drawings]

FIG. 1 is a schematic view showing a plasma etching apparatus configured so that a magnetic flux density gradient of a divergent magnetic field can be adjusted.

FIG. 2 is a schematic diagram showing a comparison of etching shapes.

FIG. 3 is a schematic diagram showing a conventional plasma etching apparatus.

[Explanation of symbols]

 1 Plasma generation chamber 2 Waveguide 3 Sample chamber 14 Main excitation coil 15 Sub excitation coil S Sample P ECR point

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirokazu Arai 4-53-3 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] 1. A method for guiding a gas plasma mainly generated at an electron cyclotron resonance point to a sample by a magnetic field to etch the sample, wherein a magnetic flux density of the magnetic field on the surface of the sample is 50 gauss or less, and The plasma etching method is characterized in that the distance between the electron cyclotron resonance point and the sample surface is 250 mm or more.