JP2001085396A - Plasma treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly monitor and control the increase or decrease of a wafer- by-wafer etching rate by using a the high-frequency bias voltage. SOLUTION: The impedance of an electrostatic attraction electrode 15 is regulated so that it is equal to the impedance of plasma 12 or smaller, allowing the increase or decrease of an etching rate to match with the increase or decrease of the highfrequency bias voltage. By controlling the impedance of the electrostatic attraction electrode to be that of the plasma impedance or smaller, the increase or decrease in the wafer-by-wafer etching rate can be monitored correctly and controlled by the changes in the high-frequency bias voltage.

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 for performing processing such as etching while applying high-frequency bias power to an electrostatic chucking electrode to control the energy of ions incident from a plasma onto a wafer.

[0002]

2. Description of the Related Art The prior art is disclosed in Japanese Patent Laid-Open No. 8-1993.
As described in No. 78, the output of the high-frequency power supply is controlled so that the peak-to-peak voltage Vpp of the high-frequency bias voltage applied to the sample table on which the wafer to be processed is mounted matches a preset value, and the etching rate and the like are controlled. A method for improving the reproducibility of the process characteristics is described.

[0003]

The above-mentioned prior art does not consider the influence of the impedance of the electrostatic chucking electrode, and is applied to a plasma processing apparatus using an electrostatic chucking electrode for holding a wafer during processing. Considering the above, there were the following problems.

When the impedance of the electrostatic attraction electrode is larger than the plasma impedance, the high frequency bias voltage Vpp applied to the sample stage changes depending on the impedance of the electrostatic attraction electrode, and therefore, the etching rate and the high frequency bias voltage Vpp change. Indicates a tendency to stop responding.

Therefore, it has been difficult to monitor and control a change in plasma impedance which affects characteristics such as an etching rate by using a high-frequency bias voltage applied to a sample stage.

An object of the present invention is to provide a plasma processing apparatus suitable for obtaining reproducibility of etching characteristics in consideration of the influence of the impedance of an electrostatic chucking electrode on plasma impedance.

[0007]

A feature of the present invention is a means for generating plasma, an electrostatic chuck electrode for holding a wafer to be processed, and a high-frequency power supply for applying a high-frequency bias power to the electrostatic chuck electrode. Means, in a plasma processing apparatus provided with a ground electrode paired with the electrostatic adsorption electrode,
The impedance of the electrostatic attraction electrode is set to a plasma impedance or less.

In general, the high-frequency bias voltage Vpp is expressed by the following equation, and it can be seen that under the condition that the high-frequency power is constant, it depends on the sum of the electrostatic adsorption electrode and the plasma impedance determined by the process conditions.

Vpp = (W (Z _D + Z _P ) ^1/2 W: High frequency power (W) Z _D : Inductance (Ω) of the electrostatic attraction electrode Z _P : Flat-main inductance (Ω) Actually using microwave discharge As a result of measuring the high frequency bias voltage while changing the plasma impedance,
In a region where the plasma impedance is equal to or lower than the impedance of the electrostatic attraction electrode, a phenomenon occurs in which the high frequency bias voltage sharply increases, and it has been clarified that this behavior does not tend to coincide with the increase or decrease in the etching rate.

Therefore, the above object of the present invention is achieved by reducing the impedance of the electrostatic attraction electrode to the plasma impedance or less.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a configuration of a so-called magnetic field microwave etching apparatus to which an embodiment of the present invention is applied.
Shown in A method for etching the wafer 2 using the magnetic field microwave etching apparatus 1 will be described. First,
After the inside of the discharge tube 5 made of a material that transmits the microwave 4 such as quartz is reduced to a predetermined pressure by the evacuation device 3, Ar, Cl ₂ , SF _6, etc. as the process gas 6 are flow-controlled by the mass flow controller. While introducing the discharge tube 5
The variable valve 7 is adjusted so that the internal pressure becomes a predetermined processing pressure. Next, 2.45 GHz from the microwave oscillator 8
Microwave 4 is radiated into the discharge tube 5 via the waveguide 9 and the auto tuner 10 and the upper, middle and lower 3
A direct current is applied to the step solenoid coil 11 to form a magnetic field in the discharge tube 5, and a plasma 12 is formed by the interaction between the electric field generated by the microwave 4 and the magnetic field generated by the solenoid coil 11. Then, by applying a high frequency bias voltage between the electrostatic chucking electrode 15 holding the wafer 2 and the ground electrode 16 via the matching unit 14 by the high frequency power supply 13, the ions in the plasma 12 enter the wafer 2. The wafer 2 is etched while controlling the energy.

The electrostatic attraction electrode 15 is made of a material that is a conductor and has a high thermal conductivity, in this case, an electrode 17 formed of Al.
It is configured by joining an insulating film 18 made of Al ₂ O ₃ with a brazing material, and a DC power supply 20 is connected via a low-pass filter 19 made up of a coil and a capacitor. When the wafer 2 is sucked at the start of the etching process, the switch 21 is connected to the terminal 22 in a state where the plasma 12 is generated.
When the wafer 2 is released after the etching process, a switch 21 is connected to the terminal 23 while the plasma 12 is generated, and the electrostatic chucking electrode 15 is connected to the resistor 2.
After grounding via the wafer 4, the wafer 2 is lifted by the wafer lifting device 25, and the wafer 2 is transferred to the next processing chamber by the pick-and-press type transfer device.

On the other hand, the wafer 2 to be etched is cooled while the wafer 2 is detected by the pressure gauge 26 while the wafer 2 is held on the electrostatic attraction electrode 15 by the method described above.
The mass flow controller 27 controls the flow rate of the He gas 28 so that the pressure on the back surface becomes a constant value. Further, the temperature of the electrostatic adsorption electrode 15 is controlled by circulating a refrigerant whose temperature is controlled by the circulator 29 through the refrigerant line 30 inside the electrode 17.

Next, a description will be given of the result of an experimental study on the correlation between the high frequency bias voltage and the etching rate of the SiO ₂ film. The etching was performed under the condition that the pressure of the wafer with the surface SiO ₂ film was adjusted to 2.5 Pa while introducing Cl ₂ gas 6 into the discharge tube 5 with a flow rate of 900 to 900 to 900 Pa.
Apply a current of 19/19 / 6A to the upper, middle, and lower stages of the solenoid coil 11 in the range of 1000 W, respectively, and apply high-frequency power (frequency 800 KH
z) was applied at 50 W for processing.

Under these conditions, the impedance of the plasma 12 is about 20 Ω, and the impedance of the electrostatic attraction electrode 15 changes depending on the film thickness.
FIG. 3 shows the case of about 20Ω.

First, a case where the impedance of the electrostatic attraction electrode 15 is about 50Ω, which is higher than the impedance of the plasma 12, will be described with reference to FIG. The etching rate of the SiO ₂ film shows a tendency to decrease as the output of the microwave 4 increases, whereas the high frequency bias voltage Vpp monitored once shows a tendency to decrease and then increase, It can be seen that it does not correspond to the increase or decrease in the etching rate. This is because the impedance of the electrostatic attraction electrode 15 is larger than the impedance of the plasma 12.

FIG. 3 shows a case where the impedance of the electrostatic attraction electrode 15 is set to about 20Ω which is almost equal to the impedance of the plasma 12. The high-frequency bias voltage shows a tendency to decrease with an increase in the output of the microwave 4 similarly to the etching rate, and it is understood that the change in the etching rate can be accurately monitored by the high-frequency bias voltage.

According to the results of this experiment, the high frequency bias voltage generally used as a monitor of the etching rate is affected by the impedance of the electrostatic attraction electrode 15, and its value is set to be equal to or less than the impedance of the plasma 12.
It became clear that the increase and decrease of the etching rate for each wafer can be accurately monitored and controlled.

In the present embodiment, the plasma 12 is generated by the microwave 4, but the same effect can be obtained by generating the plasma 12 by RF power like other ICP, TCP and RF parallel plates.

The frequency of the high frequency power supply 13 is also
Not only 800KHz but also 13.56MHz, 2MHz, 40 commonly used
Similar effects can be obtained in the case of 0 KHz.

[0021]

According to the present invention, it is possible to accurately monitor and control the increase / decrease of the etching rate for each wafer by changing the high frequency bias voltage by setting the impedance of the electrostatic chucking electrode to be equal to or lower than the plasma impedance. It is.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an etching apparatus to which an embodiment of the present invention is applied.

FIG. 2 is a diagram showing measurement results of an SiO ₂ film etch rate with respect to Vpp when the impedance of an electrostatic chucking electrode is higher than the impedance of plasma.

FIG. 3 is a diagram showing a measurement result of an SiO ₂ film etch rate with respect to Vpp when the impedance of the electrostatic chucking electrode is equal to or less than the impedance of plasma.

[Explanation of symbols]

12-Plasma 13-High frequency power supply 15-Electrostatic chuck electrode 16-Earth electrode 18-Insulating film

Claims (4)

[Claims] 1. A means for generating plasma, an electrostatic attraction electrode for holding a wafer to be processed, a high frequency power supply means for applying a high frequency bias power to the electrostatic attraction electrode, and a pair with the electrostatic attraction electrode. In the plasma processing apparatus provided with the ground electrode, the impedance of the electrostatic attraction electrode is set to be equal to or less than the plasma impedance. 2. The plasma processing apparatus according to claim 1, wherein a microwave is used as the means for generating the plasma. 3. The plasma processing apparatus according to claim 1, wherein high-frequency power is used for said means for generating plasma. 4. The frequency of said high frequency power supply means is 13.5
2. The frequency range of 6 MHz to 400 KHz.
The plasma processing apparatus as described in the above.