JPS617632A - Plasma etching device - Google Patents

Abstract

PURPOSE:To control the plasma etching process precisely by a method wherein the inner wall of vacuum chamber is formed of multiple materials subject to different secondary electron discharging activity while making the occupying space ratio upon the inner wall variable. CONSTITUTION:Within electrodes engaged with a vacuum chamber main body 1 by means of Teflon rings 4, 5, the lower side of upper electrode 3 is covered with a variable space sheet 20. The variable space sheet 20 is composed of two sectoral carbon sheets 21 alternately coating the electrode 2, two sectoral Teflon sheets 22 and two rotary Teflon sheets 23 concentrically fixed to the tube axle 24 of gas inlet 9. Any etching product is deposited on the inner wall corresponding to etching times to change the secondary electron discharge fluctuating the cathode fall voltage. At this time, the spaces of sheets 21, 22 may be varied to keep the fall voltage constant. Besides, when any specified cathode fall voltage is differentiated in case of etching multilayer film, after etching the first layer, the space ratio may be varied to lower the voltage down to the specified cathode fall voltage of the second layer without stopping the discharge.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a plasma etching apparatus for etching a sample by irradiating plasma within a vacuum container.

[Technical background of the invention and its problems] Plasma etching is used as a microfabrication technology for integrated circuits.
It is an indispensable means for manufacturing ed circuits. The characteristics of this plasma etching are:
The etching rate, its uniformity, processed shape, etc. depend on the pressure, flow rate, mixing ratio of etching gas, high frequency power supplied, etc., and the dependence on these parameters is also complicated.

Among these, the cathode drop voltage VdC is a measure of the state of plasma etching. In other words, positive ions generated in the plasma are accelerated by the cathode drop voltage Vdc and collide with a sample placed on the cathode, such as a wafer.
Etching progresses by promoting the reaction between the active species and the substance to be etched.

Therefore, the energy possessed by positive ions can be controlled to some extent by controlling this cathode drop voltage Vdc.

On the other hand, the parameters that determine the cathode drop voltage Vdc include the etching gas pressure, flow rate, mixing ratio, and high frequency power, and it is known that it also depends on the material of the inner wall of the vacuum chamber.

Among these, the reason that depends on the material of the inner wall of the vacuum chamber is that when ions generated in the plasma are accelerated by the potential difference between the plasma potential and the inner wall of the vacuum chamber and collide with the inner wall of the vacuum chamber, secondary electrons are emitted. This is thought to be because the amount of secondary electrons differs depending on the material. In other words, the emitted secondary electrons promote ionization of the plasma and determine the degree of ionization in the equilibrium state.

Conventionally, the cathode drop voltage MC was controlled by changing the properties of the etching gas (pressure, flow rate, mixing ratio), but even if the properties of the etching gas were slightly changed, the cathode drop voltage V
The amount of change in dc is quite large, making it difficult to precisely control the etching state.

(Object of the invention) The present invention has been made to eliminate the above-mentioned drawbacks.
The object of the present invention is to provide a plasma etching apparatus that enables fine control of etching characteristics.

[Summary of the invention]

In order to achieve this object, the present invention provides a plasma etching apparatus for etching a sample by irradiating plasma within a vacuum container, in which the vacuum container has an inner wall made of two or more materials having different secondary electron emission abilities. It is characterized in that the area ratio occupied by these materials on the inner wall is made variable.

[Embodiments of the invention]

FIG. 1 is a longitudinal sectional view showing the structure of an embodiment of the present invention.

In FIG. 1, a main body 1 of the vacuum vessel is made of cylindrical stainless steel, and Teflon rings 4 and 5 are connected to the axial ends of the main body 1, and a disc-shaped upper electrode 2 and a lower electrode are connected to each other through Teflon rings 4 and 5, respectively. 3 are fitted together to form a vacuum container together with the main body part 1.

Note that the upper electrode 2 and the lower electrode 3 are connected to a Teflon ring 4.
．． The sample to be etched 6 is insulated from the main body 1 by 5 and facing each other.
is placed.

Further, a pipe 7 for water cooling is provided on the upper electrode 2, and a pipe 7 for water cooling is provided on the lower electrode 3.
A water-cooling vibrator 8 is passed through the upper electrode 2, and a gas inlet 9 is provided at the axial center of the upper electrode 2, while an exhaust pipe 10 is connected to the side wall of the main body 1.

Here, the gas inlet 9 is for introducing etching gas, and the exhaust pipe 10 is for exhausting the gas inside the container by means of a rotary pump and an oil diffusion pump (not shown).

On the other hand, a common terminal of a changeover switch 12 is connected to a high frequency power source 11 for generating plasma, and one changeover terminal of this changeover switch 12 is connected to the upper electrode 2 via a matching box 13, and the other changeover terminal is connected to the upper electrode 2 via a matching box 13. are respectively connected to the lower electrode 3 via the matching box 14.

Although the main body 1 of the vacuum container is always installed, the upper electrodes 2 and 3 are equipped with a switch 15 and a switch 15 at one end, respectively, in order to cooperate with the changeover switch 12 and install one of them. The other end of 16 is connected.

Next, the inside of the upper electrode 2, that is, the side facing the lower electrode 3, is covered with a variable area plate 20. This variable area plate 20, as shown in FIG.
The fan-shaped Teflon plates 22 are attached symmetrically to each other with respect to a pipe-shaped shaft 24 passed through the gas inlet 9 so that they overlap concentrically with these members and can rotate in the circumferential direction. It is composed of two fan-shaped Teflon plates 23.

Here, the variable area plate 20 is intended to continuously change the area ratio of carbon to Teflon in the upper electrode, that is, (area of carbon)/(area of Teflon). This area ratio can be continuously changed from 1 to 0 by using a plate divided into approximately four equal parts. On the other hand, if a fan-shaped carbon plate is used instead of the fan-shaped Teflon plate 23 in FIG. 2, this area ratio can be continuously changed from 1 to infinity (OO).

By the way, the effective area of the variable area plate 20, upper electrode 2, and lower electrode 3 having the configuration shown in FIG. 2 is approximately 0.1y [
Trtl, a carbon plate is used as the lower electrode 3, the thickness of the variable area plate 20 is small, and the distance between the upper electrode 2 and the lower electrode 3 is maintained at 60 [am], as shown in the table below. Effective discharge occurred under these conditions.

Next, when the variable area plate 20 was operated under this discharge condition, the percentage of (area of carbon)/(area of Teflon) occupied by the upper electrode 2 and the cathode drop voltage vdC had the relationship shown in FIG. Ta.

That is, if the area of carbon and the surface of Teflon are approximately equal and the area of carbon is gradually reduced until the entire upper electrode surface is finally covered with Teflon, the cathode drop voltage Vdc will be -225 [V]. It changes continuously and linearly from -375 [V].

In this case, although the exact secondary electron emission ability of Teflon and carbon is unknown, insulating materials generally have a higher secondary electron emission ability.

Therefore, if the area of Teflon, which has a large secondary electron emission ability, is increased, the degree of ionization of the plasma will be high, and the cathode drop voltage vd
It is thought that C will also become large.

FIG. 4 is a diagram showing the pressure dependence of the cathode drop voltage Vdc when the area ratio of Teflon and carbon is 1 using the apparatus of this example. The amount of change is quite large, indicating that it is difficult to finely control the cathode drop voltage Vdc by varying the pressure inside the vacuum chamber.

As is clear from FIGS. 3 and 4, according to this embodiment, it is possible to finely control the cathode drop voltage, thereby making it possible to finely control the etching characteristics.

In the above embodiment, the area ratio of Teflon and carbon in the electrode was changed, but the present invention is not limited to this. The same effect as described above can be achieved by using two or more materials having different electron emission capabilities and by making it possible to vary the area ratio of the inner wall occupied by these materials.

Furthermore, although the above embodiments have explained improvement in etching characteristics, the present invention can also be applied to the following cases.

In a normal vacuum container, as the number of treatments increases, etching products adhere and accumulate on the inner wall of the vacuum container, so the secondary electron emission period changes, and the cathode fall voltage changes accordingly.

Conventionally, when the cathode drop voltage has changed to a certain extent, the inner wall of the vacuum container is cleaned to return it to its initial state, but this cleaning takes a long time and is inefficient.

Therefore, by using the apparatus of the present invention, the cathode drop voltage can be maintained at the same value by changing the area ratio of materials having different secondary electron emission abilities depending on the number of treatments.

Further, the present invention is applicable to multilayer film etching, that is, when the desired cathode drop voltage Vdc is different between the first layer film and the second layer film, after the etching of the first layer film is completed, the area of the different materials that emit secondary electrons is By changing the ratio, the cathode drop voltage of the second layer can be lowered to a desired value without stopping the discharge.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the inner wall of the vacuum container is made of two or more materials having different secondary electron emission abilities, and the area ratio occupied by these materials on the inner wall is variable. Therefore, the effect that fine control of etching characteristics becomes possible can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the configuration of an embodiment of the present invention, Fig. 2 is a plan view showing the detailed structure of the main part of the embodiment, and Figs. 3 and 4 show the operation of the embodiment. It is a characteristic diagram for explanation. 1... Main body of vacuum container, 2... Upper electrode, 3...
・Lower electrode, 9... gas inlet, 10... exhaust pipe,
11... High frequency power supply, 20... Variable area plate, 21.
...Fan-shaped carbon plate, 22.23...Fan-shaped Teflon plate. Applicant's agent Kiyoshi Inomata 1st figure 2

Claims (1)

[Claims] 1. A plasma etching apparatus that etches a sample by irradiating plasma in a vacuum container, wherein the vacuum container has an inner wall made of two or more materials having different secondary electron emission abilities, A plasma etching apparatus characterized in that the area ratio occupied by these materials on the inner wall is made variable. 2. The plasma etching apparatus according to claim 1, wherein the vacuum container has a constant total area of the inner wall, and only the area ratio occupied by the materials having different secondary electron emission abilities on the inner wall is variable. 3. The vacuum container is formed into a drum shape, and a plurality of fan-shaped members including those having different secondary electron emission abilities are arranged in parallel on one or both inner walls of the axial end portion, and these fan-shaped members 2. The plasma etching apparatus according to claim 1, further comprising another fan-shaped member which overlaps the member concentrically and is rotatably supported in the circumferential direction.