JPH06204179A - Plasma processing method - Google Patents

Abstract

PURPOSE:To improve the adhesion between an electrode and the abutting face of a semiconductor wafer so as to improve the electric coupling property and heat conductivity by providing a fixing mechanism. which fixes the semiconductor wafer to the electrode at lowering, freely of ascent and descent above the electrode, and pressing the margin of the semiconductor wafer so as to fix it. CONSTITUTION:In the condition that a wafer push-up pin 35 has gone up, a wafer carrier places a semiconductor wafer 20 on a wafer push-up pin 35. Then, it lowers the wafer push-up pin 35. In this condition, the topside of the wafer susceptor 22a is gently projecting, so gap occurs between itself and the semiconductor wafer along the periphery, but this gap disappears by lowering a clamp spring 9 and pushing the periphery of the semiconductor wafer 20 against the wafer susceptor 22a. Here, the adhesion can be improved by sticking a conductive silicon rubber 33 excellent in elasticity onto the wafer susceptor 22a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing method for processing a semiconductor substrate using plasma.

[0002]

2. Description of the Related Art Recently, plasma C has been used as a semiconductor processing apparatus.
Semiconductor processing devices using plasma, such as VD devices, plasma etching devices, and sputtering devices, have become widespread.

For example, in a plasma etching apparatus, a reactive gas is introduced into an etching tank to excite the reactive gas into a plasma state, and the generated active component reacts with a processing object on a substrate such as a semiconductor wafer to perform an etching process. I do. The plasma etching apparatus will be described below as an example of the plasma processing apparatus.

FIG. 6 shows a plasma etching apparatus having a parallel plate type electrode, and a lower electrode 3 which also serves as a mounting table for a semiconductor wafer 2 in an etching tank 1 for keeping airtightness.
The high frequency electrode 4 is arranged so as to face the lower electrode 3. The high-frequency electrode 4 has a structure that acts as a reaction gas introduction pipe, and a porous member is used for the electrode portion 4a at the lower end thereof.

In such a plasma etching apparatus,
The atmosphere in the etching tank 1 is set to a high vacuum, for example, 10 ⁻⁶ Torr by the vacuum pump 5, and then the reaction gas such as argon gas is supplied from the reaction gas source 6 into the etching tank 1.
Then, the inside of the etching tank 1 is maintained at a degree of vacuum necessary for the etching process, for example, 10 to 10 ^-2 Torr.

Next, a high-frequency power 7 is applied to the high-frequency electrode 4 to turn the reaction gas into plasma, and an etching process is performed with the reaction components of the gas plasma 8.

In the plasma etching apparatus as described above, since the semiconductor wafer 2 directly contacts the lower electrode 3, the semiconductor wafer 2 and the lower electrode 3 are not sufficiently adhered to each other. A gap is formed between the lower electrode 3 and the lower electrode 3, and this gap may cause a decrease in electrical coupling and thermal conductivity.

The decrease in electrical coupling property causes a decrease in processing efficiency, for example, a decrease in etching processing rate (hereinafter referred to as an etching rate) in a plasma etching apparatus and occurrence of processing unevenness, and a decrease in thermal conductivity of a semiconductor wafer. There is a problem in that the temperature rises and the photoresist applied to the wafer is softened and easily peeled off during the etching process.

Therefore, in the conventional plasma etching apparatus, the upper surface of the lower electrode is flattened to improve the adhesion with the semiconductor wafer.

[0010]

However, a slight distortion occurs in the manufacturing process of the semiconductor wafer,
Moreover, since this strain varies depending on the individual semiconductor wafer, there is a problem that even if the upper surface of the lower electrode is flattened, this distortion causes a considerable gap between the semiconductor wafer and the lower electrode, resulting in incomplete contact.

In order to solve this, as shown in FIG. 7, the contact surface 3a of the lower electrode 3 with the semiconductor wafer 2 is formed in a gentle convex shape, and a fixing mechanism for the semiconductor wafer 2 is provided above the lower electrode 3. In parallel with this, a wafer fixing ring body (hereinafter referred to as a clamp ring) 9 having an inner diameter slightly smaller than the diameter of the semiconductor wafer 2 is provided so as to be able to move up and down, and the clamp ring 9 is lowered so that the peripheral edge portion of the semiconductor wafer 2 is lower electrode 3. There is a device provided with a wafer fixing mechanism that presses against to increase the adhesion.

However, the above-described wafer fixing mechanism cannot sufficiently cope with the case where the curvature of the strain of the semiconductor wafer 2 and the curvature of the lower electrode upper surface 3a are greatly different,
Further, since the structure is such that only the peripheral edge of the semiconductor wafer is pressed by the clamp ring 9, the stress from the peripheral edge of the wafer is concentrated in the central portion when the semiconductor wafer is fixed, and the semiconductor wafer 2 is arcuate upward as shown in FIG. Therefore, a void 10 is formed between the central portion of the wafer 2 and the lower electrode 2. As shown in FIG. 9, the semiconductor wafer 2 that has been subjected to the etching process in such a state has a blue central portion 2a and a peripheral portion 2b of the wafer.
Has a green color. This indicates that the central portion 2a of the wafer has a smaller etching rate than the outer peripheral portion 2b of the wafer, and that uniform processing is not performed.

The present invention has been made to solve the above-mentioned problems, and improves the adhesion between the contact surface between the electrode and the semiconductor wafer to improve the electrical coupling property and the thermal conductivity, thereby making it uniform. It is an object of the present invention to provide a plasma processing method that is capable of performing plasma processing with good performance and high processing efficiency.

[0014]

According to the plasma processing method of the present invention, an electrode is placed in an airtight container provided with a plasma generation source, a semiconductor wafer is brought into contact with the electrode surface, and cooling is provided on the electrode. In a plasma processing apparatus configured to cool the semiconductor wafer and perform plasma processing by means, a wafer push-up pin in a state where the semiconductor wafer transferred to the airtight container by the wafer transfer apparatus is lifted above the electrode. A step of placing the semiconductor wafer on a resin film provided on the electrode by lowering the wafer push-up pin, Pressing the peripheral edge of the semiconductor wafer by a fixing mechanism for fixing the wafer to the electrode, and fixing the semiconductor wafer by the cooling means. A step of cooling to a constant temperature, characterized in that said semiconductor wafer comprises a step of plasma processing.

The resin film is preferably a carbon rubber-containing silicon rubber or the like having excellent heat resistance and flexibility, and has a thickness of
A diameter of about 0.2 mm is suitable.

As a means for attaching the electrode and the resin film, it is preferable to use means such as adhesion using a conductive adhesive having elasticity even after curing or thermocompression bonding.

[0017]

In the plasma processing method of the present invention, by providing the resin film on the electrode, the semiconductor wafer can be brought into close contact with the electrode, and the thermal conductivity to the electrode is improved, so that uniform plasma processing can be performed on the semiconductor. It can be done on a wafer.

Further, by forming the electrode surface in a convex shape, abutting the semiconductor wafer, and pressing the peripheral edge of the semiconductor wafer by the substrate pressing ring, the substrate to be processed is curved along the electrode surface, and the degree of adhesion is improved. Is maintained at a high temperature, the thermal conductivity is further improved, and uniform plasma treatment can be performed.

Further, by providing the cooling means in the electrode, it is possible to perform uniform plasma treatment while uniformly cooling the substrate to be treated.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the method of the present invention is applied to plasma etching will be described below with reference to the drawings.

FIGS. 1 and 2 show an etching treatment section, which is installed in an etching tank (not shown) for maintaining airtightness.

The semiconductor wafer 20 as the substrate to be processed is taken out of the wafer cassette by a transfer device (not shown) and transferred to the etching processing part 21, where the disk-shaped lower electrode 2 is formed.
After being placed on the substrate 2 and subjected to the etching process here, it is carried out again by the carrying device.

A hollow disk-shaped high-frequency electrode 23 connected to a high-frequency power source 40 is disposed above the lower electrode 22 so as to oppose thereto, and a reaction gas generated by a reaction gas generator 24 is provided at the center of the upper surface of the high-frequency electrode 23. For example, an introduction pipe 25 for introducing an argon gas into the etching tank 1 is vertically provided.

The lower surface electrode portion 23a of the high frequency electrode 23 is formed of a porous member such as carbon in the form of a mesh, and the reaction gas introduced from the reaction gas introduction pipe 25 passes through this lower surface electrode portion 23a. The structure is such that it reaches the semiconductor wafer 20 mounted on the lower electrode 22.

A reaction gas exhaust pipe 26, which is an annular hollow body having a V-shaped cross section, is disposed below the side surface of the lower electrode 22 so as to be stepped from the upper surface of the lower electrode 22. The holes 27 are concentrically formed at regular intervals.
From a part of the outer periphery of the reactive gas exhaust pipe 26, a large number of exhaust holes 2
A pipe 29 for guiding the used reaction gas introduced from 7 to the vacuum pump 28 is provided.

The lower electrode 2 is used as a semiconductor wafer fixing mechanism.
2. A ring-shaped clamp ring 30 having an inner diameter slightly smaller than the diameter of the semiconductor wafer is disposed above the two semiconductor wafers. The clamp ring 30 includes four clamp rings 30 arranged at equal intervals along the circumference of the lower electrode 22. It is supported by a clamp ring support rod 31. The four clamp ring support rods 31 are connected to an air cylinder 32 which is a drive mechanism for raising and lowering the clamp ring arranged below the lower electrode 22, and the action of the air cylinder 32 enables the clamp ring to move up and down. .

The lower electrode 22 has a diameter of about 200 mm and a thickness of about 10 mm.
It has a disk shape, and the diameter of about 125 m
Wafer mounting table 22a with a disk-shaped convex portion of m and a thickness of about 8 mm
Are formed. The upper surface of the wafer mounting table 22a has a smooth convex shape in order to improve the adhesion with the semiconductor wafer 20. As a material of the lower electrode 22, a metal material having excellent electrical conductivity and thermal conductivity such as aluminum is used.

On the upper surface of the wafer mounting table 22a, a conductive silicon rubber 33 containing a carbon having a diameter of about 0.2 mm and a diameter substantially equal to or larger than that of the wafer mounting table 22a is attached. Conductive silicon rubber 33 and wafer mounting table 2
In this example, as a means for adhering to 2a, thermocompression bonding was performed using a conductive synthetic resin adhesive having elasticity even after curing.

Lattice-shaped shallow grooves 33a are formed on the surface of the conductive silicon rubber 33, and holes 33b for raising and lowering the wafer push-up pins are formed at four locations in the central portion.

This wafer push-up pin lifting hole 33b
Is for elevating a wafer push-up pin 35 that is connected to an air cylinder 34 that is a push-up pin up-and-down drive mechanism penetrating the lower electrode 22. The push-up pin 35 pushes the semiconductor wafer 20 after etching processing from the lower surface. Is pushed up to separate it from the conductive silicon rubber 33.

At a position of the lower electrode 22 facing the back surface of the semiconductor wafer 20, the semiconductor wafer 20 is etched during the etching process.
An annular cooling water circulation pipe 36 for cooling the water is buried, and this cooling water circulation pipe 3 is provided during the etching process.
Cooling water at a low temperature, for example, 15 ° C., is introduced into the inside 6 from the cooling water introducing device 37.

A wafer fixing operation of such a plasma etching apparatus will be described with reference to FIG.

First, in a state where the wafer push-up pin 35 is raised (FIG. 3C), the semiconductor wafer 20 is placed on the wafer push-up pin 35 by a wafer transfer device (not shown), and then the wafer push-up pin 35 is placed. Is lowered (FIG. 3 (a)). In this state, since the upper surface of the wafer mounting table 22a has a gentle convex shape, a gap with the semiconductor wafer is generated in the peripheral edge portion, but the clamp ring 9 descends to press the peripheral portion of the semiconductor wafer 20 against the wafer mounting table 22a. By doing so, this gap disappears (FIG. 3 (b)). At this time, in the conventional wafer fixing mechanism, the semiconductor wafer 2 is subject to distortions peculiar to the semiconductor wafer, problems in processing accuracy of the surface of the wafer mounting table 22a, and stress generated in the central portion of the wafer due to clamping pressure.
0 and a wafer mounting table 22a, a gap is not a little generated, and the gap lowers the electrical coupling property and the thermal conductivity, resulting in uneven etching process and a decrease in process efficiency.
In this example, since the conductive silicon rubber 33 having excellent elasticity is attached to the wafer mounting table 22a, the adhesion is improved,
The occurrence of such a gap is eliminated, and the electrical coupling and thermal conductivity between the semiconductor wafer 20 and the wafer mounting table 22a are very excellent.

After the etching operation is completed, the clamp ring 9 is raised, and then the wafer push-up pin 35 is raised to push the semiconductor wafer 20 from the wafer mounting table 22a (FIG. 3 (c)). Since the etching process is usually performed in a high temperature environment, the semiconductor wafer 20 is heated to a high temperature, for example, about
The temperature may rise to 100 ° C., and the semiconductor wafer 20 and the conductive silicon rubber 33 may be fused to each other, which may make it difficult to separate the semiconductor wafer 20 from the conductive silicon rubber 33. In this example, the conductive silicon rubber 33 is used. Since the lattice-shaped shallow grooves 33a are formed on the −33 surface, such a problem does not occur. It is needless to say that the shallow groove 33a is completely crushed when the semiconductor wafer 20 is fixed as shown in FIG. 3B so that no gap is generated.

An actual experiment was carried out using the plasma etching apparatus having the above-mentioned structure, which will be described below.

The experiment was carried out for two kinds of devices, a device not using the conductive silicon rubber and a device using the carbon-containing conductive silicon rubber of this example. Further, in the experiment, not only the apparatus structure but also the etching treatment conditions such as the member and shape of the electrode used, the kind of reaction gas, the power output value, and the degree of vacuum were the same. As the power supply, a 380 kHz high frequency power supply is used because the etching target was an oxide film. Of course, the optimum power supply frequency differs depending on the etching target.

Experiments were conducted under the experimental conditions shown in Table 1 below, and the results shown in Table 2 were obtained.

[0038]

[Table 1]

[Table 2] The results of this experiment have revealed that when the conductive silicon rubber is used, (1) the etching rate is 469 Å / min (2) Si etching rate is lower than that when the conductive silicon rubber is not used. 154 angstrom / min (3) Si selection ratio 6.3 (4) The temperature of the top surface of the semiconductor wafer was improved by about -20 ° C, clearly showing the effect of the conductive silicon rubber. Further, the temperature distribution on the upper surface of the semiconductor wafer during the etching operation became almost uniform.

From the above experimental results, it can be considered that the adhesion between the semiconductor wafer and the lower electrode is greatly improved by the conductive silicon rubber, resulting in (a) good electrical connection between the semiconductor wafer and the lower electrode. As a result, the electric field strength between the semiconductor wafer and the counter electrode becomes uniform and the processing efficiency is improved.

(B) The thermal conductivity between the semiconductor wafer and the lower electrode is improved, and the cooling effect is improved.

It is In addition, when separating the semiconductor wafer from the conductive silicon rubber after the completion of the etching process, no fusion between the semiconductor wafer and the conductive silicon rubber was observed, and the device does not have the conductive silicon rubber attached. It could be easily separated without any change. This is because the shallow groove formed on the conductive silicon rubber prevents fusion with the semiconductor wafer.

The inventors of the present invention also paid attention to the pressing force of the clamp ring on the semiconductor wafer, and conducted an experiment to find the relationship between the pressing force change of the clamp ring and the etching rate, which will be described below. The experiment was conducted under the experimental conditions shown in Table 3 below using the apparatus of the above-mentioned example. For the measurement, the clamping pressure was 10 kgf (2.5 kgf per clamp ring support rod), 27 kgf (6.75 kgf), 42 kgf (same).
10.5 kgf), and the results are shown in FIG.

[0043]

[Table 3] In FIG. 4, a, b, and c on the X-axis are a point at the peripheral edge of the semiconductor wafer, b is the central portion of the semiconductor wafer,
A point provided on the periphery of the semiconductor wafer on the side opposite to a through b is defined as c, and the etching rate on these lines a → b → c is taken as the Y axis.

The experimental results reveal that (a) the etching rate decreases as the clamping pressure increases.

(B) When the clamping pressure is 27 kgf and 42 kgf, the etching rate at the central portion of the semiconductor wafer is significantly reduced.

(C) The most uniform etching can be performed when the clamping pressure is 10 kgf.

It is

These causes are because when the clamping pressure becomes too large, the semiconductor wafer 20 warps upward in an arc shape and a gap is generated between the central portion of the semiconductor wafer and the conductive silicon rubber 33. Therefore, the thickness of 630 μm
In the case of a 5-inch wafer, it was found that the method of pressing the peripheral edge with 10 kgf was the most efficient.

By the way, the conductive synthetic resin body used in the present invention is preferably superior in flexibility so that the adhesiveness is improved, but stress is applied to the clamp ring pressing portion, that is, the peripheral edge portion of the conductive synthetic resin body when the wafer is fixed. Wrinkles are likely to occur, and the wrinkles may cause voids.

As another embodiment of the present invention, as shown in FIG. 5, a recess 40 having a diameter slightly smaller than that of the semiconductor wafer 20 and a depth substantially the same as that of the conductive synthetic resin film 41 is formed on the wafer mounting table 22a. , The conductive synthetic resin film 4 is formed in the recess 40.
By mounting No. 1 (FIG. 5A), the stress on the outer peripheral portion of the conductive synthetic resin film 41 at the time of fixing the wafer can be absorbed by the wafer mounting table 22a to reduce the occurrence of wrinkles (FIG. b)). The resin film used in the present invention may be any of conductive Teflon, conductive silicone rubber, conductive fluorine-based rubber, etc., as long as it has excellent elasticity, thermal conductivity and electrical conductivity.

Further, the method of the present invention includes plasma CVD, E
The present invention can be applied to any structure such as a CR etching or sputtering device having a structure in which an electrode and a substrate to be processed are in contact with each other and a plasma atmosphere is provided. The plasma atmosphere is not limited to high frequency discharge, and may be formed by microwave discharge or direct current discharge.

[0052]

As described above, according to the plasma processing method of the present invention, the adhesion between the object to be processed and the lower electrode is improved, so that the electrical coupling property and the thermal conductivity are improved, and the uniformity is improved. A good plasma treatment with high treatment efficiency is possible.

[Brief description of drawings]

FIG. 1 is a perspective view showing an etching processing unit of a plasma etching apparatus used in an embodiment of the present invention.

2 is a vertical cross-sectional view of the plasma etching apparatus of FIG.

FIG. 3 is a sectional view showing the operation of the wafer fixing mechanism.

FIG. 4 is a diagram showing a relationship between a clamp pressure and an etching rate.

FIG. 5 is a view showing a wafer fixing mechanism of another embodiment.

FIG. 6 is a sectional view showing a conceptual configuration of a plasma etching apparatus.

FIG. 7 is a sectional view showing a conventional wafer fixing mechanism.

FIG. 8 is a sectional view showing a conventional wafer fixing mechanism.

FIG. 9 is a diagram showing a processing state of a surface of a semiconductor wafer that has been subjected to etching processing by a conventional apparatus.

[Explanation of symbols]

 20 Semiconductor Wafer 21 Etching Processing Section 22 Lower Electrode 22a Wafer Mounting Table 23 Counter Electrode 30 Clamp Ring 31 Clamp Ring Support Rod 33 Conductive Silicon Rubber 35 Wafer Push Pin

Claims (2)

[Claims] 1. An electrode is arranged in an airtight container provided with a plasma generation source, a semiconductor wafer is brought into contact with the electrode surface, and the semiconductor wafer is cooled by a cooling means provided on the electrode for plasma treatment. In the plasma processing apparatus configured to perform, a step of placing a semiconductor wafer transferred to the airtight container by a wafer transfer apparatus on a wafer push-up pin in a state of being raised above the electrode, and the wafer push-up pin. And placing the semiconductor wafer on a resin film provided on the electrodes, and a fixing mechanism that is provided above the electrodes to be movable up and down and fixes the semiconductor wafer to the electrodes when descending. Pressing the peripheral edge of the semiconductor wafer to fix it; cooling the semiconductor wafer to a predetermined temperature by the cooling means; The plasma processing method characterized by comprising the step of plasma processing the Movement. 2. An electrode is arranged in an airtight container equipped with a plasma generation source, a semiconductor wafer is brought into contact with the electrode surface, and the semiconductor wafer is cooled by a cooling means provided on the electrode for plasma treatment. In the plasma processing apparatus configured to perform, after the plasma processing is completed, the step of raising the semiconductor wafer fixing mechanism provided above the electrodes from the position for fixing the semiconductor wafer on the electrodes, And a step of raising the semiconductor wafer to push it up and away from the resin film on the electrode, and a step of taking out the semiconductor wafer from the wafer push-up pin and feeding it to the outside of the airtight container. A plasma processing method characterized by the above.