JPH0766184A - Emission intensity observation port for lep etching system - Google Patents

Abstract

PURPOSE:To provide an LEP dry etching system in which a uniform plasma can be generated under low pressure while preventing follow effect at the observation port and the end of etching can be confirmed. CONSTITUTION:A transparent body 8 for blocking an observation port is arranged such that the inner end thereof is substantially in flush with the inner wall of a chamber 1. Since the observation port has no excess space, high density plasma is not generated locally thus realizing highly uniform etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emission intensity observation port used in a low pressure plasma generator.

[0002]

2. Description of the Related Art A plasma generating method using a high frequency discharge is used in various fields such as dry etching for fine processing, sputtering for forming a thin film, plasma CVD, and an ion implantation apparatus. Plasma generation in a higher vacuum is required in order to miniaturize the processing size and control the film quality with high accuracy.

Hereinafter, as an application example of the plasma generation method,
Dry etching suitable for fine processing will be described.
Advances in modern high-density semiconductor integrated circuits are bringing about changes comparable to the industrial revolution. Higher density of semiconductor integrated circuits has been realized by miniaturization of element size, improvement of devices, and increase in chip size. The miniaturization of element dimensions has advanced to about the wavelength of light. Photolithography is approaching the limit where it is no longer compatible with g-line and i-line of a high-pressure mercury lamp. Excimer lasers and X-rays are promising for future lithography. Along with lithography, dry etching plays an important role in realizing a fine pattern.

Dry etching is a processing technique for removing an unnecessary portion of a thin film or a substrate by utilizing a chemical or physical reaction between a gas phase and a solid phase surface caused by radicals and ions existing in plasma. At present, the most widely used dry etching technique is reactive ion etching (RIE). This is to remove an unnecessary portion of the sample surface by exposing the sample to the high frequency discharge plasma of a suitable gas having a high chemical reactivity to cause an etching reaction. The necessary part, that is, the part that is not removed,
It is usually protected by the photoresist pattern used as a mask.

In order to miniaturize the pattern, it is necessary to align the directionality of ions. A parallel ion beam must be applied to the wafer. To this end, it is essential to reduce the scattering of ions in the plasma. In order to make the directionalities of the ions uniform, it is effective to increase the vacuum degree of the plasma generator to increase the mean free path of the ions. This is because if the degree of vacuum is high, scattering is reduced and parallel ion beams are likely to occur. However, on the other hand,
There is a problem that high-frequency discharge is less likely to occur when the degree of vacuum in the plasma chamber is increased. If no discharge occurs, the gas cannot be turned into plasma. High vacuum and electric discharge have opposite properties.

Therefore, as a countermeasure against this, a method of applying a magnetic field to the plasma chamber to facilitate the generation of discharge has been invented. For example, magnetron RIE or ECR dry etching techniques have been developed.

However, when a magnetic field is used, electrons are biased in the plasma captured by the magnetic field, resulting in nonuniform etching species and a local potential difference. For this reason, a plasma process using a magnetic field is applied to MOSLSI.
When applied to the process, there is a problem that the gate oxide film is deteriorated.

In order to solve these problems, a method of generating a uniform plasma using a rotating electric field has been studied by the present applicant. Since it is generated by a rotating electric field, it may be called a Lissajous etching device. There are an upper electrode and a lower electrode, and the upper electrode is adapted to apply high-frequency power whose phases are different by a certain angle so as to form a rotating electric field. Another high frequency power is also applied to the lower electrode. This was first proposed in Japanese Patent Application No. 2-402319. Furthermore, Japanese Patent Application No. 4
No. 215820 suggests that the improvement of plasma uniformity can be realized by improving the electrode arrangement method.

1 and 2 are a horizontal sectional view and a vertical sectional view of a plasma generator using a rotating electric field. In FIG. 2, 1
Is a chamber whose inner wall is covered with an insulating material such as ceramics, Teflon, or quartz. It can be evacuated. The chamber 1 is grounded. Reference numerals 2, 3, and 4 are lateral electrodes (also referred to as upper electrodes and LEP electrodes) to which high-frequency power is applied. The number of upper electrodes is not limited to 3, 4,
5, 6, ... Are optional. The side electrodes 2, 3, 4 are circumferentially arranged at equal intervals above the inside of the chamber 1 so as to face each other. The discharge power applied to each electrode is the same, but the phase of the power is different by about 120 °. That is, the phase of the side electrode 3 is advanced by 120 ° with respect to the side electrode 2, and that of the side electrode 4 is 120 °.
It is configured to be delayed. The lower electrode 5 is an electrode to which another high frequency power is applied. The fourth electrode,
It is installed horizontally. It serves as a sample table for fixing the semiconductor wafer 6. Since the chamber 1 is grounded, it is insulated from these electrodes 2, 3, 4, and 5. An observation port 7 is provided on the side of the chamber 1. The wall surface has a cylindrical flange. A transparent body 8 (quartz window, glass window) is attached to the open end of this.

Etching gas is introduced into the chamber 1 from the inlet 16 via a mass flow controller (not shown). The chamber 1 is evacuated by a vacuum pump. The chamber internal pressure is controlled to about 0.1 Pa to 10 Pa by, for example, a turbo pump (not shown). High frequency power of 50 MHz is supplied to the side electrodes 2, 3 and 4 through a matching circuit (not shown), and a phase difference of 120 ° is given by a phase shifter (not shown).

In order to independently control the ion energy and plasma density, a frequency of 5 is applied to the three side electrodes 2, 3, 4.
High frequency power of 4.24 MHz is applied. A high frequency power having a frequency of 13.56 MHz is applied to the lower electrode 5 which is also the sample stage. The inner wall of the chamber is ceramic,
It is covered with an insulator such as Teflon or quartz. this is,
This is because the inner wall of the chamber is charged more negatively than the plasma potential. This minimizes plasma loss,
It is possible to realize efficient plasma generation under high vacuum.

With the above structure, a rotating electric field can be formed by N side electrodes. The electrons contained in the gas cause a motion of drawing a Lissajous figure such as a circle or a cycloid due to the rotating electric field. Therefore, high ionization efficiency can be obtained even in a high vacuum. The plasma density in the chamber is increased. Unlike magnetron discharge and ECR discharge, it is a plasma generation method that does not use a magnetic field. The movement of the charged particles is restricted by the magnetic field, and the uniformity of plasma is not deteriorated. Furthermore, the wafer char
Almost no jiup occurs. The deterioration of the device due to charge-up is extremely small. Further, since the magnetic field generator is unnecessary, it is easy to downsize the device. Since a bulky magnetic field generator is not required, it is possible to easily cope with an increase in wafer diameter.

[0013]

The dry etching apparatus has an observation port for detecting the end point of etching. There is a cylindrical protrusion on the wall surface of the chamber 1, and a transparent body 8 such as glass or quartz is fixed to the open end. The state of plasma and the state of etching of the wafer can be observed from the outside through the transparent body and looking inside. Such a viewing window is provided in any vacuum device. However, a low-pressure dry etching apparatus causes a new problem.

The LEP dry etching device skillfully generates high density plasma under a low pressure of several Pa. The electric field in the chamber is a rotating electric field, and the electric field distribution is also symmetrical.
However, the space itself is not rotationally symmetric due to the observation port. Therefore, the plasma distribution is not uniform. High density plasma is localized inside the observation port 7 due to the hollow effect. This is shown in FIGS. FIG. 3 is a perspective view showing a high density plasma A near the observation port 7.
Is present. The existence of the observation port greatly deteriorates the plasma uniformity in the chamber. The high density plasma near the observation port also extends to the periphery of the wafer. The etching rate depends on the plasma density. Therefore, the edge portion B of the wafer near the observation port is more strongly etched. Therefore, the etching depth is not uniform on the wafer surface.

FIG. 8 is a sectional view of a conventional observation port. Since the transparent body 8 is attached to the end surface of the observation port, the internal space 9 of the observation port is long. This has a volume obtained by multiplying the cross-sectional area by the distance Z between the inner surface of the transparent body and the inner wall surface of the chamber. A hollow effect is generated in this space.

In the apparatus having the observation port shown in FIGS.
The i-wafer was tested for etching. The sample is n ⁺ Po
It is ly-Si. The etching condition is Cl ₂ flow rate of 80.
sccm, power input to lower electrode 5 100 W (frequency 1
3.56 MHz), input power to the side electrodes 2, 3, 4 1
It was 00 W (frequency 50 MHz). Etching rate
And non-uniformity were 350 nm / min and 8%, respectively. The non-uniformity is the maximum depth minus the minimum depth divided by the average. The larger the value, the more uneven. With such a large non-uniformity, it is difficult to guarantee a uniform shape.

The present invention generates a high density plasma under a low pressure, has a fine processing property, and has a discharge etching port for enhancing plasma uniformity in a dry etching apparatus with little damage to devices. The purpose is to provide.

[0018]

In order to solve the above-mentioned problems, the observation port makes the inner surface of the transparent body and the inner wall of the chamber substantially flush with each other. That is, the inner surface of the transparent body and the inner wall of the chamber are arranged on the same plane. Even if they are not on the same plane, the difference Z between the inner surface of the transparent body and the inner wall of the chamber should be 10 mm or less. That is, the difference Z between the transparent inner surface and the chamber inner wall surface is set to 0 to 10 mm. This is done by shortening the observation port and making the transparent body a little thicker. Alternatively, it can also be realized by making the transparent body extremely thick while leaving the observation port as it is.

[0019]

Since the transparent body extends close to the inner wall of the chamber, the spatial symmetry in the chamber is improved. 5 and 6 show examples of the present invention. In FIG. 5, the length of the observation port 7 is left unchanged, and the transparent body such as glass or quartz is lengthened. The long transparent body occupies most of the inside of the observation port. No space remains inside the observation port. Since the transparent body is long, the difference Z between the inner end of the transparent body and the inner wall of the chamber is extremely narrow. Z is 0 to 10 mm. The one shown in FIG. 6 has a shorter observation port. The transparent body 8 such as glass or quartz is also slightly thickened so as to completely fill the space of the observation port. Plasma cannot exist here because the inside of the observation port is filled with a transparent material. The hollow effect disappears at the observation port.

In this way, the space inside the chamber becomes rotationally symmetrical. Since the electric field is a rotating electric field and the electric field distribution is also rotationally symmetrical, the plasma density is also spatially rotationally symmetrical. Since there is no high-density plasma in the vicinity of the observation port, the wafer etching rate does not become non-uniform. That is, highly uniform etching becomes possible. The present invention enables high-quality etching by filling the observation port with a transparent material, eliminating the hollow effect, and enhancing the uniformity of plasma.

[0021]

FIG. 5, FIG. 6 and FIG. 7 show an embodiment of the present invention.
The structure other than the observation port is the same as that shown in FIGS. For simplicity, the side electrodes and the lower electrode are not shown.
In the figure, 1 is a cylindrical chamber made of aluminum whose inner wall is sprayed with alumina. It is grounded. An observation port 7 is located at one location in the chamber. Internal space 9 of this
Is filled with the transparent body 8. In FIG. 5, a relatively long observation port 7 is used. This remains the conventional chamber. In this case, a long transparent body 8 is used so that the observation port 7 is almost closed. The transparent body is glass, quartz, or the like. The one in FIG. 6 is especially for observation.
The inner surface of the transparent body 8 is flush with the inner wall of the chamber. FIG. 7 is an enlarged sectional view. The flange 12 of the observation port has a slight annular ridge, and the groove 10 is cut in the end surface of the flange. The O-ring 11 is fitted into the groove 10. The convex transparent body 8 is inserted into the opening. The transparent body 8 is fixed to the chamber wall by a bolt (not shown) held by a holding plate (not shown). The O-ring and the transparent body are in close contact,
A vacuum can be maintained. FIG. 8 shows an observation port according to the conventional example, but the length Z of the space is large. With such a long length, high-density plasma is localized here. However, as shown in FIG. 7, when there is almost no space, plasma does not exist.

Therefore, the uniformity of the plasma density in the rotating direction is improved. There is a strong correlation between plasma density and etching rate. If the plasma density is uniform, the etching rate will also be uniform. The uniformity of the etching depth on the wafer surface can be improved. The etching performance of n ⁺ Poly-Si using this observation port was investigated. The etching conditions are the same as in the conventional example, with a Cl ₂ flow rate of 80 sccc.
m, power input to the lower electrode 5 100 W (frequency 13.5
6MHz), input power 100W to side power 2, 3, 4
(Frequency 54.24 MHz). Etching rate
And non-uniformity were 350 nm / min and 3%, respectively.

There is almost no difference in etching rate.
However, the non-uniformity is significantly reduced from the conventional 8% to 3%. That is, the uniformity of etching is greatly improved. This is a result of the fact that there is no space for generating the hollow effect and no local high-density plasma part is generated. By using the observation port, it is possible to detect the etching end point by observing the light emission while obtaining a uniform plasma at a low pressure.

[0024]

According to the present invention, an observation port is used in which the inner end of the transparent body is arranged substantially flush with the inner wall of the chamber. There is no space in the observation port, and the hollow effect does not occur in the observation port section. High density plasma is not unevenly distributed in the vicinity of the observation port. Therefore, highly uniform plasma can be generated in the rotation direction. Therefore, highly uniform etching is possible. Since there is such an observation port, it is possible to generate uniform plasma under a low pressure and confirm the etching end point.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional plan view of an etching apparatus that uses a LEP electrode to generate a rotating electric field to generate plasma.

FIG. 2 is a vertical sectional view of the same thing.

FIG. 3 is a perspective view showing that a high density plasma is generated in the vicinity of an observation port and a wafer is etched deeper in the vicinity of an observation port in a conventional LEP dry etching apparatus.

FIG. 4 is a cross-sectional plan view of the same.

FIG. 5 is a cross-sectional plan view in which electrodes inside the LEP dry etching apparatus according to the embodiment of the present invention are omitted.

FIG. 6 is a cross-sectional plan view in which electrodes inside a LEP dry etching apparatus according to another embodiment of the present invention are omitted.

FIG. 7 is an enlarged cross-sectional view of only the vicinity of the observation port of FIG.

FIG. 8 is an enlarged cross-sectional view in the vicinity of an observation port of a LEP dry etching apparatus of a conventional example.

[Explanation of symbols]

 1 Chamber 2 Side Electrode 3 Side Electrode 4 Side Electrode 5 Lower Electrode 6 Wafer 7 Observation Port 8 Transparent Body 9 Observation Port Inner Space 10 Groove 11 O Ring 12 Flange Z Chamber Inner Wall Surface and Transparent Body Edge distance

Front page continuation (72) Inventor Tokuhiko Tamaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Mitsuhiro Oguni, 1006 Kadoma, Kadoma City, Osaka Prefecture (72) ) Inventor Ichiro Nakayama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Masafumi Kubota 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 1006 Kadoma, Kadoma-shi, Fuchu Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A cylindrical chamber capable of evacuating the interior thereof, N LEP electrodes provided at rotationally symmetrical positions in the upper portion of the chamber so as to face each other, and etching provided at the bottom of the chamber. An observation port having a lower electrode on which a semiconductor wafer to be placed is placed, a gas inlet for introducing an etching gas into the chamber, a gas outlet for discharging the chamber, and a window provided with a transparent body for looking inside the chamber. -, A first high-frequency power source that generates high-frequency power to be applied to the LEP electrode, a phaser that causes the power of the first high-frequency power source to differ in phase by 2π / N, and a high-frequency wave on the lower electrode. A second high frequency power source to be applied, and by applying high frequencies having different phases to the LEP electrodes, a rotating electric field is generated in the chamber, and the gas is plasma-generated by the rotating electric field. Then, in the LEP dry etching apparatus for etching the wafer, the distance Z between the inner surface of the transparent body of the observation port and the inner surface of the chamber is 0 mm to 10 mm. Strength observation port.