JPH07153822A - Plasma process equipment - Google Patents

Abstract

PURPOSE:To eliminate the potential difference between a wafer surface and a wafer mounting electrode during plasma irradiation, and prevent the deterioration of withstand voltage. CONSTITUTION:A clamp ring 21 is mainly constituted of conductive material. The electric potential of the clamp ring 21 is made equal to that of an electrode on which a wafer 3 is mounted. More practically, aluminum 23 is used as the core material of the clamp ring 21, and the surface of the core material is formed of alumina 25. At least in the contact part 21a with the wafer mounting electrode 1 and the contact part 21b with the wafer surface, the aluminum 23 is exposed and electric contact is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma processing apparatus used for manufacturing a semiconductor device, and more particularly to an improvement of a clamp device for fixing a wafer.

[0002]

2. Description of the Related Art A plasma processing apparatus (plasma etching apparatus) used for manufacturing a semiconductor device is, for example, CF ₄
The gas of the system is ionized by a high frequency (RF) electric field, the wafer surface is removed by the reaction with the generated radicals, and a fine flat plate pattern is processed. FIG. 4 is a side view of a wafer mounting portion of a conventional plasma etching apparatus. A silicon wafer 3 is placed on the lower electrode 1, and the end of the wafer 3 is pressed to the lower electrode 1 side by a clamp ring 5. The lower electrode 1 is provided with a pipe 7 opening to the upper surface, and the pipe 7 introduces He gas between the lower electrode 1 and the wafer 3 to enhance the cooling effect of the wafer 3. When the lower electrode 1 is grounded and the RF power is applied from the RF power supply 11 to the upper electrode 9 in the plasma etching apparatus having the wafer mounting portion thus configured, plasma is formed between the electrodes. become. In such a situation, the clamp ring 5 presses the wafer 3 to prevent the wafer 3 from sliding off the lower electrode 1 due to the introduction of He gas. And this clamp ring 5
In order to prevent the contamination of the wafer 3, the wafer 3 is made of a material that is covered with Teflon or the like that is an insulating film, or that is made of a ceramic material that is an insulator.

[0003]

However, since the clamp ring 5 made of an insulating material such as a ceramic material covers the lower electrode 1 in the wafer mounting portion of the conventional apparatus, the wafer surface and the lower electrode 1 are exposed to each other during plasma irradiation. A potential difference is generated between the gate electrodes, and as a result, when etching a gate electrode in a MOS transistor, for example, a potential difference is generated between the gate electrode and the wafer substrate, which may deteriorate the breakdown voltage of the gate insulating film. was there. The present invention has been made in view of the above circumstances, and provides a plasma processing apparatus capable of eliminating a potential difference between a wafer surface and a wafer mounting electrode during plasma irradiation caused by covering the wafer mounting electrode, Therefore, the purpose is to prevent deterioration of breakdown voltage of the gate insulating film.

[0004]

The structure of a plasma processing apparatus according to the present invention for achieving the above object is to eliminate the potential difference between the wafer mounting electrode and the wafer surface during plasma irradiation. A conductive material such as aluminum is used as the material for the clamp ring that fixes the wafer.When the wafer is clamped, the clamp ring and the wafer mounting electrode make electrical contact so that they have the same potential, while they are exposed to plasma. The surface of the clamp ring is covered with alumina to prevent the contamination of the wafer.

[0005]

With the above-described structure, the potential of the clamp ring and the potential of the wafer mounting electrode during plasma irradiation become the same, and the potential of the wafer surface and the potential of the clamp ring become substantially the same. The potential difference between the potential of the gate electrode and the wafer mounting electrode is almost eliminated, and the breakdown voltage of the gate insulating film is prevented from being degraded.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the plasma processing apparatus according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a side view of the plasma processing apparatus of the present invention. Silicon wafer 3
A pipe 7 is provided on the lower electrode 1 which is an electrode on which the wafer 3 is mounted, and the pipe 7 introduces He gas between the lower electrode 1 and the wafer 3 to enhance the cooling effect of the wafer 3. The wafer 3 is pressed to the lower electrode 1 side by the clamp ring 21,
Sliding down from the lower electrode 1 due to introduction of He gas is prevented.

The clamp ring 21 is formed in a ring shape having an inverted L-shaped cross section, and has aluminum 23 which is a conductive material as a core material. The outer side of the clamp ring 21 is covered with alumina 25, which is a material having high plasma resistance, so that it is difficult to be etched by plasma irradiation.
Therefore, the contamination of the wafer 3 due to the corrosion of the clamp ring 21 during the plasma irradiation is prevented. The alumina 25 is formed with a film thickness of, for example, about 50 μm. The aluminum 23 is exposed at least on the surface 21a of the clamp ring 21 that contacts the lower electrode 1 and the surface 21b that contacts the wafer 3. That is, the clamp ring 21 and the lower electrode 1 are in electrical contact with each other at this portion. In this wafer mounting portion, the lower electrode 1 on which the wafer 3 is mounted and the clamp ring 21 have substantially the same potential, and the clamp ring 21 and the wafer surface have substantially the same potential.

In the plasma processing apparatus (plasma etching apparatus) configured as described above, the measurement result of charge-up when the gate electrode is etched is shown in FIG.
It will be described with reference to FIG. This chargeup measurement is
This was done using a MNOS capacitor. This capacitor has a SiO ₂ film of 2n on a 6-inch P-type silicon substrate.
m, Si ₃ N ₄ film with a thickness of 50 nm and a phosphorus-doped polysilicon film with a thickness of 300 nm were formed thereon, a resist pattern was formed by a photolithography process, and the polysilicon was etched by the plasma etching apparatus to form a pattern. The gate electrode area is 0.27 mm ² . 2 and 3 show the flat band voltage distributions of the 116 MNOS capacitors formed on the wafer in this way. FIG. 2 shows an embodiment of the present invention and FIG. A case where a clamp ring made of ceramics is used is shown. The horizontal axis is the flat band voltage,
The vertical axis shows the frequency ratio. Further, Table 1 shows the results of the average value and standard deviation of the flat band voltage when the clamp ring of the present invention is used and when the clamp ring of the conventional example is used.

[Table 1]

From these results, considering that the flat band voltage of the MNOS capacitor when the polysilicon electrode is etched by wet etching without any problem of charge-up is about -1.3 V, the conventional example. Flat band voltage is -0.04 on average
Since it is V (see Table 1), it shifts in the positive direction by about 1.3 V on average, and the variation is large, whereas in the embodiment according to the present invention, the flat band voltage is −1 on average. .31 (see Table 1), there is almost no shift. That is, the fact that the flat band voltage does not shift indicates that no electric field is applied to the gate insulating film.

[0010]

As described above in detail, according to the plasma processing apparatus of the present invention, the clamp ring used for fixing the wafer is made of a conductive material, and the wafer mounting electrode and the wafer surface are electrically connected. Since they are brought into contact with each other to have the same potential, the potential difference between the wafer surface and the wafer mounting electrode is eliminated, and the breakdown voltage of the gate insulating film can be prevented from deteriorating. Moreover, since the surface of the clamp ring is covered with alumina, it is possible to prevent the problem that the surface of the clamp ring is etched by the plasma irradiation to contaminate the wafer.

[Brief description of drawings]

FIG. 1 is a side view of a plasma processing apparatus of the present invention.

FIG. 2 is a diagram showing measurement results of the present invention.

FIG. 3 is a diagram showing measurement results of a conventional example.

FIG. 4 is a side view of a wafer mounting portion of a conventional plasma etching apparatus.

[Explanation of symbols]

 1 Lower Electrode (Electrode on which Wafer is Placed) 3 Wafer 21 Clamp Rings 21a, 21b Contact Part 23 Aluminum (Conductive Material) 25 Alumina

Claims (2)

[Claims] 1. A plasma processing apparatus characterized in that a clamp ring for fixing a wafer is composed mainly of a conductive material, and the potential of the clamp ring and the potential of an electrode on which the wafer is placed are made to be the same. . 2. A dual structure in which the core material of the clamp ring is made of aluminum and the surface of the core material is made of alumina, and at least a contact portion with an electrode on which the wafer is mounted and a contact with the wafer surface. The plasma processing apparatus according to claim 1, wherein the part is formed by exposing aluminum.