JPH0338345B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an electrode for plasma processing.

(Prior art and its problems) FIG. 1 shows the basic configuration of a conventional plasma etching apparatus using two parallel plate electrodes. Planar electrode 1b connected to high frequency power source 7a
and a counter electrode 1a at ground potential opposite to this.
is installed. It consists of an introduction system 8 for introducing reactive gas and an exhaust system 6 for keeping the pressure inside the etching chamber 9 constant. The electrode 1b connected to the high frequency power source 7a is insulated from the vacuum container 5 by an insulating member 3. Further, cooling water 10 is allowed to flow from the outside into the hollow portion 4 that is in direct contact with the electrode 1b, thereby cooling the electrode 1b. The object to be processed 2 is usually placed on a lower electrode 1b connected to a high frequency power source 7a. This electrode 1b is connected to a high frequency power source 7a via a DC blocking capacitor 7b. A discharge is generated between these opposing electrodes 1a and 1b, but in this case, cathode drop occurs in contact with the electrode surface due to the large difference in mobility between electrons and positive ions. The reactive gas ions accelerated in this cathode descending section are perpendicularly incident on the electrode and the object to be processed 2, and etching progresses in that direction.

It is extremely difficult to maintain the in-plane uniformity of the etching (or deposition) rate of the workpiece 2 on the surface of the workpiece 2 within about ±5% using this type of apparatus. This is the discharge electrode 1a,
1b and the workpiece 2 are selected to be approximately equal in diameter, the so-called end effect occurring at the electrode end or, depending on the atmospheric pressure region, etching may occur near the center of the surface of the workpiece 2. This is because a decline is seen. This is thought to be due to a decrease in current density in these parts or insufficient replenishment of reactive radicals. As a method of compensating for these non-uniformities, a method of providing concentric guard rings on the object 2 to be processed is used. Although we have achieved some success in removing edge effects using guard rings, it is not possible to compensate for non-uniformity caused by causes other than edge effects, and it also increases the size of the discharge vessel, so it is not economically viable. Undesirable. In addition, since there are a wide variety of discharge vessels used, a wide variety of non-uniformities can be seen in areas other than the center of the end effect. A drastic improvement in sexuality is not desired.

(Objective of the Invention) The present invention provides an electrode for parallel plate discharge that can deal with any in-plane non-uniformity that has not been possible with the conventional techniques as described above.

(Principle of the Invention) In order to achieve this object, in the present invention, in order to increase the current density in the part where etching (or deposition) is reduced on the surface of the object to be processed, a recess is formed in the corresponding part on the counter electrode. By providing a hole and concentrating the current in the recess,
This increases the current density on the surface of the workpiece.

Furthermore, since the same electrode has an electrode structure that allows a large current to be obtained with the same power input, it has an electrode structure that can meet the demands for increasing the etching (or deposition) rate without increasing damage to the object to be processed. By increasing the in-plane uniformity of the discharge current density obtained in this way, the in-plane uniformity of the etching (or deposition) rate can be significantly improved (about ±3% or less).

(Structure of the Invention) Examples of the present invention will be described below based on the accompanying drawings.

Example 1 Perforated Electrode FIG. 2 is a diagram of an electrode structure according to an embodiment of this structure, and is drawn with dimensions suitable for a 4-inch wafer. This figure shows a circular electrode, with a structure symmetrical about the center of the circle, and only half of the electrode is shown. In the example shown in this figure, holes with a radius of 7 mm and a depth of 15 mm are drawn, with more holes on the outer periphery of the disk and fewer holes toward the inside. That is, the number of holes is arranged so that the ratio of the area of the hole to the unit surface area on the electrode surface decreases from the outside toward the inside. This example has an electrode structure in which the discharge current density is high at the outer periphery of the electrode, and the current density decreases toward the center. The hole dimensions, i.e. radius and depth, have optimal dimensions depending on the type of gas and the gas pressure used.
It is possible to operate in the area of Since a so-called hollow cathode discharge is generated and used in the hole, it is optimal that twice the thickness of the cathode fall of the cold cathode glow discharge is slightly smaller than the diameter of the hole. Regarding the depth of the hole, if the depth of the hole is about twice or more than the diameter of the hole, stable hollow cathode discharge can be obtained.

The electrode having the structure described above is used as the counter electrode 1a shown in FIG. 1, and the electrode 1 on which the object to be treated 2 is placed
Place it parallel to b. The optimal distance between these electrodes 1a and 1b is approximately several times the mean free path of electrons with respect to the gas used. If the interval is narrower than this, the current distribution on the perforated electrode will directly affect the workpiece 2.
affects the current on the surface, causing small irregularities in the current distribution on the surface. On the other hand, if the spacing is too wide, the effect of the perforated electrodes will be masked.

Example 2 Grooved Electrode This is an electrode structure in which a groove is cut in place of the hole in Example 1 and a hollow cathode discharge is formed within the groove. The example shown in FIG. 3 has a circular electrode with a diameter of 4 inches, with four grooves cut in a circular pattern around the electrode. This is an example in which the width of the groove is 7 mm and the depth is 30 mm.
Stable hollow cathode discharge has been obtained with argon gas at a gas pressure of 0.01 to 0.1 Torr.

The example shown in Figure 4 is an example in which grooves are cut across the entire surface of a circular electrode, and the thickness of the side wall separating the grooves is 1 mm at the periphery and 2 mm at the inner side. In the example shown in FIG. 3, the current density ratio between the peripheral part and the central part is selected to be larger than that in the example shown in FIG.

In the electrode of the present invention, a concave portion is provided on the surface of the flat electrode, and a hollow cathode discharge is generated in the concave portion. This discharge form can be used with direct current or R/F/frequency. Taking advantage of the fact that when a hollow cathode discharge occurs in a recess, the current density increases approximately 10 times compared to a flat electrode, by arbitrarily setting the arrangement of recesses such as holes or grooves, it is possible to The current density distribution at can be set arbitrarily. By using this type of electrode as a counter electrode, the current distribution on the electrode of the object to be processed can be made similar to the current distribution of the electrode.

There is a product of the optimal gap d (diameter in the case of a hole, width of the groove in the case of a groove) and atmospheric pressure p to form a hollow cathode discharge in the recess, and this product pd follows the law of similarity of discharge. . The spatial region dominated by the current density distribution on the electrode surface has a distance from the electrode surface that is within several times the mean free path of electrons with respect to the gas.

(Effects of the Invention) (a) General Effects In the present invention, the current density distribution on the counter electrode is set in order to obtain a high uniformity of the current density distribution on the surface of the object to be processed such as etching or deposition. Thereby, the in-plane uniformity of etching rate and deposition rate can be improved within ±3%.

(b) Effects on specific objectives Conventionally used methods such as using a guard ring cannot compensate for the increased size of the device and the non-uniformity of the complex current density distribution. In contrast, in the case of the present invention, the electrode size is the same as the size of the object to be processed or slightly larger than that, and even in the case of non-uniformity at the electrode end, non-uniformity in the center, or any other non-uniformity, the opposing electrode surface Uniformity can be improved by varying the proportions of the grooves or holes on the top.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram of a conventional plasma etching apparatus, FIG. 2 is a plan view and a sectional view showing an example of the arrangement of holes as an example of the electrode of the present invention, and FIGS. 3 and 4 are the electrodes of the present invention. FIG. 7 is a plan view and a cross-sectional view showing an example of a structure in which grooves are cut as another example. 1a... Counter electrode, 1b... Planar electrode, 2...
Object to be processed, 3...Insulating member, 4...Cavity shaped part, 5
. . . Vacuum container, 6 . . . Exhaust system, 7a . . . High frequency power supply, 7b .

Claims (1)

[Claims] 1. In a parallel plate discharge electrode for a plasma processing device, in order to improve the uniformity of discharge current density between the two electrodes, a unit area of the electrode surface is provided on the surface of one electrode. A parallel plate type discharge electrode characterized in that a large number of holes or concentric grooves are provided with dimensions such that the area ratio of the concave portions in contact decreases from a portion with a low discharge current density to a portion with a high discharge current density.