Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
2002-03-06
2003-07-01
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111210, C315S502000, C315S307000, C250S291000, C250S285000, C250S300000, C219S121570
Reexamination Certificate
active
06586887
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a high-frequency power supply apparatus for a plasma generation apparatus, and particularly to a high-frequency power supply apparatus for a plasma generation apparatus in which the output of the power supply apparatus can be made intermittent so as to make the average output of the power supply under control.
First, a background art will be described on a plasma processing apparatus called an ECR (Electronic Cyclotron Resonance) system by way of example.
In the plasma processing apparatus of the ECR system, a microwave is introduced into a vacuum vessel to which a magnetic field is applied from the outside so as to generate plasma. Electrons make cyclotron motion due to the magnetic field. If the frequency of the cyclotron motion and the frequency of the microwave are made resonant with each other, it is possible to generate plasma efficiently. In order to accelerate ions entering a sample (or wafer), a high-frequency voltage is applied to the sample. As a gas for generating plasma, a halogen gas such as chlorine or fluorine is used.
In such a plasma processing apparatus, the output of the high-frequency power supply apparatus to be applied to the sample (wafer) is subject to ON/OFF control so that the output of the high-frequency power supply apparatus is controlled for the purpose of improvement in accuracy of finishing. By such control, the selection ratio of silicon (Si) which is a substance to be etched to a foundation oxidation film can be made high and the aspect-ratio dependence can be reduced.
Further, the output of the high-frequency power supply apparatus to be applied to a wafer is subject to ON/OFF control so that it becomes possible to reduce ablation of a sample table without lowering the wafer processing speed. Accordingly, the frequency of maintenance for sample table exchange can be reduced and the throughput of the apparatus can be improved.
FIG. 6
is a drawing for explaining the relation between the average output and the peak output value. In
FIG. 6
, the output of the high-frequency power supply apparatus has a waveform
141
. Further, the high-frequency power supply apparatus has an ON-time
144
and an OFF-time
145
for a pulse output, and has a peak output value
142
and an average output
143
. For example, when polysilicon is subject to etching, the electric power ranging from 10 W to 100 W is supplied as an average output.
Further, the duty ratio (ON-time ratio), which is a typical one for use in the ON-OFF control, is about 20%, and the average output of the high-frequency power supply apparatus is about 40 W when the peak output value of the high-frequency power supply apparatus is 200 W.
FIG. 7
is a diagram showing a high-frequency power supply apparatus for a plasma generation apparatus in the background art. In
FIG. 7
, there are provided: a controller microcomputer
1
for operating the high-frequency power supply apparatus; a high-frequency power supply apparatus (hereinafter simply referred to as “high-frequency power supply”)
20
for a plasma generation apparatus; a peak value setting signal
21
for setting a peak value of the output of the high-frequency power supply; a repetition frequency setting signal
36
for setting the repetition frequency of ON-OFF control; an ON-time interval setting signal
37
for setting the ON-time interval when ON-OFF control is carried out; an output controller
22
for generating an operation signal
23
for operating the output peak on the basis of the peak value setting signal
21
and a fed-back peak value detection signal
30
; a modulator
24
for generating a high-frequency output
25
which is made intermittent on the basis of the operation signal
23
and a modulation reference signal
31
which will be described later; a peak value detector
29
for detecting the above-mentioned intermittent high-frequency output at the timing of a pulse reference signal
38
; and a pulse generator
35
for generating the modulation reference signal
31
and the pulse reference signal
38
on the basis of a repetition frequency setting signal and the ON-time interval setting signal
37
supplied from the controller microcomputer
1
. The pulse generator
35
generates a rectangular wave, with a predetermined duty ratio, on the basis of the signals indicating the above-mentioned repetition frequency and the ON-time interval. The pulse generator
35
outputs the rectangular wave as the pulse reference signal
38
, and further outputs, as the modulation reference signal
31
, a signal obtained by multiplying the pulse reference signal
38
by a high-frequency reference signal (output of an oscillator).
First, the peak value setting signal
21
is set by the controller microcomputer
1
. On the basis of the peak value setting signal
21
and the peak value signal
30
detected by the peak value detector
29
, the output controller
22
outputs the operation signal
23
for controlling the peak value of the output of the high-frequency power supply
20
. The modulator
24
generates intermittent high-frequency output
25
on the basis of the operation signal
23
and the modulation reference signal
31
generated in the pulse generator
35
. The peak value detector
29
detects the high-frequency output which is intermittent at the timing at which the pulse reference signal
38
is supplied. By this arrangement, the detector
29
can detect the peak value of the high-frequency output (the peak output value in the ON-period of the intermittent high-frequency output). The pulse generator
35
generates a rectangular wave, with a predetermined duty ratio, on the basis of the signal
36
indicating the repetition frequency and the signal
37
indicating the ON-time interval. The rectangular wave is supplied, as the pulse reference signal
38
, to the peak value detector
29
so as to be used as timing information for detecting the peak value. Further, the pulse generator
35
generates, as the modulation reference signal
31
, a signal which is intermittent at the same timing as the pulse reference signal
38
, and supplies this signal
31
to the modulator
24
. On the basis of the peak value operation signal
23
and the modulation reference signal
31
, the modulator
24
generates the high-frequency output
25
having a peak value indicated by the peak value operation signal and having duty ratio and the repetition frequency indicated by the modulation reference signal.
SUMMARY OF THE INVENTION
The average value of the above-mentioned intermittent high-frequency output can be calculated by multiplying the peak value detected by the peak value detector by the duty ratio (ON-period/ON-period+OFF-period). That is, if the peak value detected by the peak value detector, the repetition frequency setting signal and the ON-period setting signal are monitored, a high-frequency output at a desired average value can be supplied to the load.
However, the real output waveform (pulse waveform) of the high-frequency output subjected to intermittent control may generate distortion in the rectangular wave.
FIGS. 8A and 8B
are views showing the waveforms of the intermittent high-frequency outputs. Particularly,
FIG. 8A
shows the intermittent waveform of the high-frequency output, and
FIG. 8B
is an enlarged view of a part of FIG.
8
A. As shown in
FIGS. 8A and 8B
, the waveform of the output power may fluctuate in the leading/trailing edge due to individual differences in the response property of the above-mentioned modulator, or due to individual differences between the parts. Accordingly, if the control is performed only through monitoring of the above-mentioned peak value, it is impossible to accurately calculate the real output value (the average value) in the above-mentioned method.
Incidentally, the fluctuation in the average output which is supplied to the load may give a large influence to the etching property given to wafers in the semiconductor finishing process. Further, even in the case where another high-frequency power supply with the same spe
Kanekiyo Tadamitsu
Oogoshi Yasuo
Takahashi Youji
Umemoto Tsuyoshi
Antonelli Terry Stout & Kraus LLP
Hitachi High-Technologies Corporation
Vo Tuyet T.
Wong Don
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