JPH0487330A - Cooling method of wafer in plasma treatment apparatus - Google Patents

Abstract

PURPOSE:To eliminate an electrostatic breakdown and to enhance the uniformity of a plasma treatment by a method wherein the rear of a wafer is brought into close contact with a dielectric installed at the peripheral part on a wafer-mounting face and a gap formed between the wafer-mounting face and the wafer is filled with a heat-transfer gas. CONSTITUTION:A wafer 70 is placed on a wafer-mounting face 13a including the surface 15a of a dielectric 15; a plasma treatment gas is supplied to the inside of a treatment chamber 12; a part of the gas is evacuated from an evacuation tube 21; the pressure inside the treatment chamber 12 is kept definite. Then, high-frequency electric power is supplied to a wafer electrode 13; a self-bias voltage is generated between the wafer electrode 13 and the wafer 70; static electricity is generated between the wafer electrode 13 and the wafer 70; static electricity is generated at the dielectric 15. Thereby, the peripheral part on the rear 70b of the wafer 70 is brought into close contact with the surface 15a of the dielectric 15. Very small gaps 22 formed between the wafer-mounting face 13a and the rear 70b of the wafer 70 are filled with a heat- transfer gas G via a plurality of opening parts 17a in order to increase heat-transfer property. As a result, the wafer 70 which is being plasma-treated is cooled, and the temperature of the wafer 70 is set to a temperature which is nearly the same as the temperature of the wafer electrode 13.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a wafer cooling method for a plasma processing apparatus that cools a wafer during plasma processing.

<Prior Art> When a wafer is subjected to plasma processing, it is known that the wafer temperature during plasma processing affects the plasma processing characteristics. For this reason, in conventional plasma processing apparatuses, various wafer cooling methods have been proposed in order to keep the wafer temperature constant.

For example, the plasma processing apparatus 31 shown in FIG. 2 has a wafer mounting surface 3 inside the wafer electrode 33.
Heat transfer gas introduction path 3 having an opening 34a in the center of 3a
4 and a constant temperature water circulation path 35 through which constant temperature water is circulated, and a clamp 36 having a claw 37 for pressing the wafer 70 against the wafer placement surface 33a is provided on the side of the wafer electrode 33. .

In this plasma processing apparatus 31, the claw 37 of the clamp 36
The wafer 70 is pressed against the wafer mounting surface 33a. At this time, the wafer 70 is
A minute gap (not shown) is created between the wafer mounting surface 33a and the wafer mounting surface 33a, and this gap is filled with a heat transfer gas having a higher thermal conductivity than the heat transfer gas introduction path 34, such as helium. . Further, the constant temperature water circulation path 35 has constant temperature water (for example, 5°
The wafer electrode 33 is always kept at a predetermined temperature by flowing water (C). Therefore, the heat of the wafer 70 whose temperature has increased due to plasma processing is transferred between the wafer 70 and the wafer mounting surface 3.
The heat is directly conducted at the contact portion with the wafer 70 and the wafer electrode 33 via the heat transfer gas filled in the gap. As a result, wafer 70 is cooled.

Further, another plasma processing apparatus 51 shown in FIG. 3 has a dielectric material 54 provided on the entire upper surface of a wafer electrode 53, and a constant temperature water circulation path 55 through which constant temperature water is circulated inside the wafer electrode 53. It is something.

In this plasma processing apparatus 51, by supplying high frequency power to the wafer electrode 53, the wafer electrode 53 and the dielectric material 54 are connected to each other.
A self-bias voltage is generated between the wafer 70 and the wafer 70 placed above to generate static electricity across the dielectric 54, and this static electricity brings the entire back side of the wafer 70 into close contact with the upper surface of the dielectric 54. In addition, constant temperature water at a predetermined temperature (for example, 5° C.) is flowed through the constant temperature water W1 ring path 55, and the constant temperature water is supplied to the wafer electrode 53.
is maintained at a predetermined temperature. Therefore, the heat of the wafer 70 whose temperature has increased due to the plasma treatment is conducted to the wafer electrode 53 whose temperature is lower than that of the wafer 70 via the dielectric 54. As a result, the temperature of the wafer 70 is lowered by the temperature of the wafer electrode 53.
is cooled to approximately the same temperature as that of

<Problems to be Solved by the Invention> However, in the former case of the above plasma processing apparatus, the opening of the heat transfer gas introduction path for filling the heat transfer gas is formed in the center of the wafer mounting surface. Therefore, the heat transfer gas cannot reach all the gaps created between the wafer and the wafer mounting surface. Therefore, in the portion where the gap is not filled with heat transfer gas, the heat of the wafer is not sufficiently conducted to the wafer electrode, resulting in non-uniform temperature distribution of the wafer. As a result, the uniformity of plasma processing on the wafer is reduced.

Further, since the wafer is pressed against the wafer mounting surface by the claws of the clamp, the wafer surface against which the clamp is pressed is damaged by the clamp, and dust is generated. As a result, the wafer becomes contaminated with dust.

Furthermore, since the threshold voltage of plasma discharge is different between the vicinity of the clamped wafer and the other wafers, uniform plasma processing cannot be performed.

On the other hand, in the latter plasma processing equipment, the entire back side of the wafer is in close contact with the dielectric, so a voltage of several hundred volts is applied to the entire surface of the wafer, and the thin wA of the elements formed on the wafer is
There is an adverse effect that the edge film, such as the gate insulating film, is destroyed by electrostatic discharge.

The present invention was made to solve the above problems, and
It is an object of the present invention to provide a wafer cooling method for a plasma processing apparatus that is free from electrostatic damage and has excellent uniformity of plasma processing.

<Means for Solving the Problems> The present invention has been made to achieve the above objects, and
When performing plasma processing in a plasma processing apparatus, high-frequency power is supplied to the wafer electrode on which the wafer is placed, so that the periphery of the back surface of the wafer is applied to the dielectric material provided around the wafer placement surface of the wafer electrode. The back surface of the wafer, excluding the peripheral portion that is in close contact with the dielectric, is brought into close contact with the wafer mounting surface. Next, wafers! ! This is a wafer cooling method in which a gap created between a wafer mounting surface and a wafer is filled with heat transfer gas through a heat transfer gas introduction path having a plurality of openings on two surfaces.

<Function> In the wafer cooling method of the plasma processing apparatus described above, the wafer is brought into close contact with the dielectric material provided around the wafer mounting surface of the wafer electrode, so that the wafer adhesion due to static electricity is prevented from occurring at the wafer backside around the wafer surface. Therefore, electrostatic damage to the wafer is reduced. In addition, the gap created between the wafer placement surface and the wafer is filled with heat transfer gas through a heat transfer gas introduction path with multiple openings on the wafer placement surface. Most of the gap created between the wafer and the wafer is filled with heat transfer gas, so the heat generated in the wafer during plasma processing is directly conducted from the wafer to the wafer electrode in the area where the wafer is in direct contact with the wafer electrode. In the gap, the heat is conducted to the wafer electrode using a heat transfer gas as a medium. As a result, the wafer is cooled throughout, resulting in uniform plasma processing of the wafer.

<Example> A cross-sectional view of an example of a plasma processing apparatus in which the wafer cooling method of the present invention is implemented is shown in FIG. 1(a) and FIG. 1(+)
) will be explained using an enlarged view of part A.

The plasma processing apparatus 11 shown in the figure is a so-called parallel plate plasma processing apparatus, which is provided with a wafer electrode 13 on which a wafer 70 is placed inside a processing chamber 12, and an electrode 14 opposed in parallel to the wafer electrode 13. It is.

On the periphery of the wafer placement surface 13a of the wafer electrode 13,
A ring-shaped dielectric 15 is provided with an upper surface 15a formed at the same height as the wafer mounting surface 13a. Also, wafer electrode 1
3 has a constant temperature water circulation path 16 and a wafer mounting surface 13.
A heat transfer gas introduction path 17 having a plurality of minute openings 17a is formed in a.

In addition, a blocking capacitor 18 is connected to the wafer electrode 13.
A high frequency power source 19 is connected via.

On the other hand, a processing gas introduction path 20 having an opening on the wafer electrode 13 side is formed inside the electrode 14 .

Next, a wafer cooling method performed by the plasma processing apparatus 11 having the above configuration will be explained.

The zero wafer cooling method is performed during plasma processing.

First, constant temperature water (for example, water at a temperature of 5° C.) is circulated through the constant temperature water circulation path 16 to maintain the wafer electrode 13 at a predetermined temperature.

A wafer mounting surface 13 including the upper surface 15a of the dielectric 15
Place the wafer 70 on top a. After that, the processing gas introduction path 20
A plasma processing gas is supplied into the processing chamber 12 and a part of the supplied plasma processing gas is exhausted from an exhaust pipe 21 provided in the processing chamber 12 to keep the pressure of the plasma processing gas within the processing chamber 12 constant. .

Next, high frequency power is supplied to the wafer electrode 13 from the high frequency power supply 19 in order to generate plasma between the wafer electrode 13 and the electrode 14 . At this time, a self-bias voltage is generated between the wafer electrode 13 and the wafer 70. Static electricity is generated in the dielectric 15 due to this self-bias voltage. This static electricity brings the peripheral portion of the back surface 70b of the wafer 70 into close contact with the upper surface 15a of the dielectric 15. Therefore, the wafer 70
Since only the peripheral portion is affected by the static electricity generated in the dielectric 15, most of the elements formed on the wafer 70 are not damaged by static electricity.

Furthermore, the wafer placement surface 13a of the wafer electrode 13 and the dielectric 1
Since the upper surface 15a of the wafer 70 is formed at the same height as the upper surface 15a of the wafer 70,
b is brought into close contact with the wafer mounting surface 13a.

However, the back surface 70b of the wafer 70 and the wafer mounting surface 13
Since a has minute irregularities due to normal grinding,
A minute gap 22 is created between the wafer placement surface 13a and the back surface 70b of the wafer 7°.

Therefore, in order to improve the heat conductivity of this gap 22, the gap 22 is filled with heat transfer gas G from the heat transfer gas introduction path 17 through the plurality of openings 17a. Helium, which has high thermal conductivity, is used as the heat transfer gas G. Therefore, the heat of the wafer 70 whose temperature has increased due to plasma processing is
In the part where the wafer 7o and the wafer mounting surface 13a are in direct contact, the heat is directly conducted to the wafer electrode 13, and in the part where the heat transfer gas G is filled, the heat is conducted to the wafer electrode 13 using the heat transfer gas G as a medium. Ru. At this time, the filled heat transfer gas G
Since the wafer 70 and the dielectric 15 are in close contact with each other,
There is no leakage into the processing chamber 12.

As a result, the wafer 7o undergoing plasma processing is cooled,
The temperature of the wafer 70 becomes approximately the same as the temperature of the wafer electrode 13.

As described above, the wafer 70 is caused by static electricity to cause the dielectric 15 to
Since it is in close contact with the surface, no dust is generated when it is in close contact with the surface.

Further, since there is nothing on the upper surface of the wafer 70 that disturbs the plasma discharge, the threshold voltage of the plasma discharge is stable, and plasma is generated uniformly between the wafer 7o and the electrode 14.

Although the above embodiment has been explained using a plasma processing apparatus 11 with parallel plate electrodes, it is also possible to use a plasma processing apparatus with a parallel plate electrode structure in which the upper electrode is formed as a wafer electrode, or a plasma processing apparatus with a so-called hexode electrode. The wafer cooling method of the present invention can also be applied to the following.

<Effects of the Invention> As described above, according to the present invention, high-frequency power is supplied to the wafer electrode, and static electricity is generated in the dielectric provided around the wafer mounting surface of the wafer electrode to tightly bond the wafer. As a result, electrostatic damage to the wafer is reduced and the quality of the wafer can be improved. Further, since no dust is generated when the wafer is brought into close contact with the wafer, the cleanliness of the wafer is maintained. Furthermore, most of the gaps between the wafers and the electrodes are filled with heat transfer gas through a heat transfer gas introduction path with multiple openings, so the heat from the wafers can be conducted to the wafer electrodes using the heat transfer gas as a medium. .

Therefore, the cooling effect of the wafer is enhanced, so that the uniformity of plasma processing can be improved.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of the configuration of the plasma processing apparatus.
Figure (b) is an enlarged view of section A in Figure 1 (a), Figure 2 is
3 is a sectional view of another conventional example. 11... Plasma processing apparatus, 12... Processing chamber. 13... Wafer electrode, 13a... Wafer mounting surface. 14... Electrode, 15... Dielectric. 15a... Upper surface of dielectric, 16... Constant temperature water circulation path 17... Heat transfer gas introduction path, 17a... Opening 22... Gap.

Claims (1)

[Claims] When plasma processing is performed in a plasma processing apparatus, by supplying high-frequency power to the wafer electrode, the periphery of the back surface of the wafer is applied to the dielectric provided around the wafer mounting surface of the wafer electrode. a step of bringing the back surface of the wafer, excluding the peripheral portion that is in close contact with the dielectric, into close contact with the wafer placement surface; and a heat transfer gas introduction path provided with a plurality of openings on the wafer placement surface of the wafer electrode. A wafer cooling method for a plasma processing apparatus, comprising the steps of: filling a gap formed between the wafer mounting surface and the wafer with a heat transfer gas.