JPH04192520A - Plasma reactor - Google Patents

Abstract

PURPOSE:To reduce plasma damage to the process subject by disposing an overlapping structure of cylindrical inner electrodes in which a plurality of cylindrical inner electrodes are placed inside a cylindrical reactor so that the small holes of each do not actually overlap. CONSTITUTION:The system consists of a cylindrical reactor container 5 with a gas inlet pipe 1 and exhaust pipe 2 connected to a vacuum system, outer electrodes 3 densely placed on the periphery of the reaction container 5, and cylindrical inner electrodes 4 with many small holes on the inner walls which are placed on the same axis inside the reactor container 5 and at the same spacing as the outer electrodes. Then, a plurality of inner electrodes 4 are placed inside the reactor container 5 in an overlapping structure so that the holes of each do not actually overlap. As a result, the plasma ions which enter the plasma processing region are effectively caught and the ultraviolet rays produced from the glow discharge region are effectively blocked. This enables a reduction in the plasma damage to the process subject.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a plasma reactor, and more specifically, in a plasma reactor having a cylindrical coaxial electrode structure, the cylindrical internal electrode is formed into a specific structure. In particular, the present invention relates to a plasma reactor that has been improved to reduce damage to a processed object (plasma damage) caused by plasma ions (charged particles), electrons, or ultraviolet rays emitted from a glow discharge region.

[Conventional technology]

As is well known, plasma reactors are capable of performing plasma low-temperature etching processing, plasma low-temperature ashing processing, plasma C
This is a reactor used for VD processing, etc., and there are various types depending on the electrode structure, such as a cylindrical coaxial type and a counter electrode type.

A cylindrical coaxial plasma reactor includes a cylindrical reaction vessel equipped with a gas inlet pipe and a gas exhaust pipe connected to a vacuum system.
It mainly consists of an external electrode disposed closely around the outer periphery of the reaction vessel, and a cylindrical internal electrode disposed coaxially with the reaction vessel at a predetermined distance inside the reaction vessel and having a large number of small holes in the side wall. Then, the object to be processed is accommodated inside the cylindrical internal electrode and subjected to plasma processing.

In a cylindrical coaxial type plasma reactor, the plasma generation region is between the inner wall of the cylindrical reaction vessel and the outer wall of the cylindrical internal electrode, and the plasma processing region is inside the cylindrical internal electrode.

In a cylindrical coaxial plasma reactor,
Since the cylindrical internal electrode is grounded and maintained at ground potential, ions in the plasma are captured by the cylindrical internal electrode.

Therefore, in a cylindrical coaxial plasma reactor,
It is said that damage caused by charge-up due to plasma potential is relatively small.

[Problem to be solved by the invention]

However, in the conventional cylindrical coaxial type plasma reactor, although the plasma damage to the processed object is much less than in the facing electrode type plasma reactor,
This is not necessarily sufficient, and further reduction of plasma damage is desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an improved plasma reactor that can further reduce plasma damage to a workpiece.

[Means to solve the problem]

The above object of the present invention is to provide a cylindrical reaction vessel equipped with a gas inlet pipe and a gas exhaust pipe connected to a vacuum system, an external electrode closely disposed around the outer periphery of the reaction vessel, and an external electrode disposed inside the reaction vessel. In a plasma reactor mainly composed of cylindrical internal electrodes arranged coaxially at a predetermined distance from each other and having a large number of small holes in the side wall, a plurality of cylindrical internal electrodes are arranged in a cylindrical reaction vessel with each small hole. This can be easily achieved by a plasma reactor characterized in that the cylindrical internal electrodes are arranged in a multilayer structure so that they do not substantially overlap.

[Effect]

A cylindrical internal electrode with a multi-layered structure is arranged so that the small holes do not substantially overlap in the cylindrical reaction vessel.
Plasma ions flowing into the plasma processing region collide with the wall of the cylindrical internal electrode and are captured, and ultraviolet rays emitted from the glow discharge region are blocked.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings, but the present invention is not limited to the following embodiments unless it exceeds the gist thereof.

FIG. 1 and FIG. 2 are explanatory diagrams schematically showing an example of the plasma reactor of the present invention configured vertically.
The figure is an explanatory overall cross-sectional view taken along the line XX in FIG. 2, and FIG. 2 is an explanatory cross-sectional view of a main part. FIG. 3 is an explanatory diagram schematically showing main parts of another example.

The plasma reactor of the present invention is basically the same as a conventional cylindrical coaxial type plasma reactor, and is a cylindrical type equipped with a gas inlet pipe (1) and a gas exhaust pipe (2°) connected to a vacuum system. a shaped reaction vessel (5), an external electrode (3) disposed in close contact with the outer periphery of the reaction vessel, and an external electrode (3) disposed coaxially with the reaction vessel at a predetermined distance inside the reaction vessel, and having a large number of small holes in the side wall. It mainly consists of a cylindrical internal electrode (4).

The cylindrical reaction vessel (5) is usually made of quartz glass. An external electrode (3) is arranged in close contact around the cylindrical reaction vessel (5), and the external electrode is connected to a high frequency power source (lO).

Inside the cylindrical reaction vessel (5), cylindrical internal electrodes (4) are coaxially arranged at predetermined intervals. The cylindrical internal electrode (5) is made of aluminum or alumite-treated metal, and has a large number of small holes in its side wall. The diameter of the small holes is usually 0.5 to 10 mm, and they are provided at intervals of 0.5 to 20 mm. The cylindrical internal electrode (4) is normally grounded as is.

The gas introduction pipe (1) is arranged externally to the cylindrical reaction vessel (5). The gas introduction pipe (1) is provided with a large number of gas ejection holes (not shown) in the longitudinal direction, and the plasma gas in the cylinder (20) is passed through the piping from the ejection holes into a cylindrical shape. It can be introduced into the reaction vessel (5).

The gas exhaust pipe (2) is arranged externally to the cylindrical reaction vessel (5). The gas exhaust pipe (2) is provided with a large number of gas suction holes (not shown), and the vacuum system (
30), the reaction exhaust gas inside the cylindrical reaction vessel (5) is exhausted to the outside of the system from the suction hole via piping.

The object to be processed, such as a wafer (A), is supported by a wafer support made of, for example, several pillars (40) provided with notched grooves fixed with an appropriate number of rings (50), and a cylindrical internal electrode (4). is housed inside and subjected to plasma treatment. The above-mentioned wafer support is usually made of quartz, and is inserted into the cylindrical reaction vessel (5) from the lower part thereof by releasing the fixture (70) and lowering the pedestal (60). Ru.

In addition, in FIGS. 1 and 2, (6) is a quartz pipe line that is cut off from the internal space of the cylindrical reaction vessel (5),
A rod-shaped heater (7) is inserted into the pipe to constitute an internal heater. An internal heater having such a structure is a preferred embodiment of the heating means proposed by the present inventor.

The greatest feature of the plasma reactor of the present invention is that in the cylindrical coaxial type plasma reactor as described above, each small hole is substantially connected to a plurality of cylindrical internal electrodes (4) in the cylindrical reaction vessel (5). The reason is that they are arranged so that they do not overlap, creating a multilayer structure.

In the example shown in FIGS. 1 and 2, two cylindrical internal electrodes (4) are arranged, but more can be arranged. For example, as shown in FIG. 3, four cylindrical internal electrodes (4) are arranged. It can also be placed.

The distance between the cylindrical internal electrodes (4) is not particularly limited, but is usually in the range of 5 to 50+ nm.

Due to the cylindrical internal electrode having a multilayer structure as described above, plasma ions collide with the wall of the cylindrical internal electrode and are captured.
Entry into the plasma processing area is blocked. Moreover, since the cylindrical internal electrodes with the multilayer structure are arranged so that the small holes do not substantially overlap, ultraviolet rays emitted from the glow discharge region are effectively blocked.

In the present invention, a bias voltage is applied to the plurality of cylindrical internal electrodes (4) in order to more reliably prevent plasma ions from flowing into the plasma processing region and to control the flowing plasma ions. It is preferable to apply

The bias voltage can be applied in various ways by connecting a variable DC power source (80) to the internal electrode (4) through a low-pass filter (90), as shown in FIG.

For example, if the cylindrical internal electrode (4) has a double structure, the first
(The ordinal number of internal electrodes is the outermost one is the first) of the internal electrode is grounded, and a positive or negative bias voltage is applied to the second internal electrode by switching a switch, or
Become electrically floating.

When the bias voltage is positive, an electric field is generated from the second internal electrode to the first internal electrode, and as a result, plasma ions with an energy level below the electric field flow into the second internal electrode against the electric field. I can't. Then, the electrons will move along the above electric field.

On the other hand, if the bias voltage is negative, an electric field in the opposite direction to the above is generated, plasma ions are accelerated by the electric field, and electrons are repelled.

As described above, the application of the bias voltage controls the flow of plasma ions and electrons into the plasma processing region.

In order to reduce damage caused by plasma potential such as charge-up, it is usually sufficient to apply a positive bias voltage to about the plasma potential.

On the other hand, when the second internal electrode is electrically floating,
The second internal electrode itself has a potential because it is charged by plasma ions entering from the first internal electrode. Since this potential depends on the plasma potential, which varies depending on process conditions, the second internal electrode itself has a potential wall, and as a result, damage can be easily reduced without applying a bias voltage. It is possible.

Further, when the cylindrical internal electrode (4) has a triple structure, one of the internal electrodes is grounded, and a positive or negative bias voltage is applied to the other two internal electrodes.

This makes it possible to prevent plasma ions and electrons from flowing into the plasma processing region, unlike the case where the internal electrodes have a double structure.

Furthermore, as shown in FIG. 3, a cylindrical internal electrode (4)
In the case of a quadruple structure, any two internal electrodes are grounded, and a positive or negative bias voltage is applied to the other two internal electrodes. For example, each of the first and fourth internal electrodes (4) is grounded, the second internal electrode (4) is grounded, and the third internal electrode (4) is grounded.
) apply a positive bias voltage to As a result, both plasma ions and electrons are reflected by the internal electrodes (2) and (3) and are prevented from flowing into the plasma processing region.

In normal plasma processing, the double-structure internal electrode is sufficient for the purpose of reducing plasma damage caused by the influence of plasma potential such as charge-up and damage caused by ultraviolet rays generated from the glow discharge region.

Further, in the present invention, it is preferable to add an automatic bias function to the plurality of cylindrical internal electrodes.

The automatic bias function described above is performed by controlling the bias voltage of the cylindrical internal electrode by the space potential inside the cylindrical internal electrode disposed at the innermost position.
This can be done by a circuit as shown in the figure.

FIG. 4 is a conceptual diagram showing an example of the plasma reactor of the present invention in which an automatic bias function is added to the innermost cylindrical internal electrode.

As shown in Figure 4, the Faraday cup (B) is placed at an appropriate position within the wafer support, the DC potential is measured with a voltmeter (8), and this is input into a control device such as a computer (CP). , a bias voltage based on the above measured values is applied by the variable DC power supply (80). The magnitude of the bias voltage varies depending on the energy of the plasma ions to be captured, but is usually between -200 and 200.
The range is V.

In FIG. 4, AMP represents an amplifier, and A/D and D/A represent signal converters.

According to the automatic bias function described above, even if the plasma state changes, the bias voltage applied to the innermost cylindrical internal electrode is automatically changed to maintain a constant flow of plasma ions into the plasma processing area. It can be prevented in the state.

In addition, although the above embodiment is a plasma reactor configured vertically, C in the present invention can also be configured horizontally by appropriately using the wafer support of 4.

The plasma reactor of the present invention is operated and used in the same manner as a conventional plasma reactor.

The degree of vacuum inside the cylindrical reaction vessel (5) is usually 0.
．． The plasma gas is in the range of 1 to 10 Toor, and the plasma gas used depends on the purpose of the treatment, for example, in the case of ashing treatment, oxygen, nitrogen, hydrogen, argon, ammonia, water, etc. are used, and in the case of etching treatment, , fluorine, oxygen, ozone, etc.

〔Effect of the invention〕

According to the plasma reactor of the present invention as described above, the cylindrical internal electrode with a specific structure can effectively capture plasma ions flowing into the plasma processing region, and can also effectively block ultraviolet rays emitted from the glow discharge region. ,
Accordingly, an improved plasma reactor is provided that can further reduce plasma damage to a processed object.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are explanatory diagrams schematically showing an example of the plasma reactor of the present invention configured vertically.
The figure is an explanatory overall cross-sectional view taken along the line XX in FIG. 2, and FIG. 2 is an explanatory cross-sectional view of important parts. FIG. 3 is an explanatory diagram schematically showing main parts of another example. FIG. 4 is a conceptual diagram showing an example of the plasma reactor of the present invention in which an automatic bias function is added to the innermost cylindrical internal electrode. In the figure, (1) is the gas inlet pipe, (2) is the gas discharge pipe, and (3) is the gas inlet pipe.
) represents an external electrode, (4) represents an internal electrode, and (5) represents a cylindrical reaction vessel. Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) A cylindrical reaction vessel equipped with a gas inlet pipe and a gas exhaust pipe connected to a vacuum system, an external electrode closely disposed around the outer periphery of the reaction vessel, and a predetermined space between the external electrode and the external electrode disposed inside the reaction vessel. In a plasma reactor mainly composed of cylindrical internal electrodes arranged coaxially and having a large number of small holes in the side wall, a plurality of cylindrical internal electrodes are arranged in a cylindrical reaction vessel so that each small hole substantially overlaps. 1. A plasma reactor characterized in that the cylindrical internal electrodes are arranged in a multi-layered structure so that they do not overlap. (2) The plasma reactor according to claim 1, wherein a bias voltage is applied to the plurality of cylindrical internal electrodes. (3) The plasma reactor according to claim 2, wherein the bias voltage of the cylindrical internal electrode is controlled by the space potential inside the cylindrical internal electrode disposed at the innermost position.