Plasma processing apparatus
A plasma processing apparatus can efficiently perform a pulse modulation method of switching a high frequency power to be used in a plasma process between a high level and a low level alternately according to a duty ratio of a modulation pulse. In this plasma processing apparatus, when performing a high/low pulse modulation on the high frequency power for plasma generation, if a weighted variable K is set to be 0.5<K<1, a constant reflection wave power PR H is generated on a high frequency transmission line of a plasma generation system even during a pulse-on period T on . Meanwhile, during a pulse-off period T off , a reflection wave power PR L decreases. By adjusting the value of K, a balance between the reflection wave power PR H during the pulse-on period T on and the reflection wave power PR L during the pulse-off period T off can be controlled.
1. A plasma processing apparatus of generating plasma by high frequency discharge of a processing gas within a decompression processing vessel that accommodates therein a processing target object, which is loaded into and unloaded from the processing vessel, and performing a process on the processing target object within the processing vessel with the plasma, the plasma processing apparatus comprising:
a first high frequency power supply configured to output a first high frequency power;
a first high frequency power modulation unit configured to pulse-modulate an output of the first high frequency power supply with a modulation pulse having a regular frequency such that the first high frequency power has a high level during a first period and has a low level lower than the high level during a second period, the first period and the second period being repeated alternately with a preset duty ratio;
a first high frequency transmission line configured to transmit the first high frequency power outputted from the first high frequency power supply to a first electrode provided within or in the vicinity of the processing vessel; and
a first matching device configured to measure a load impedance on the first high frequency transmission line with respect to the first high frequency power supply, and configured to match a weighted average measurement value, which is obtained by weighted-averaging a load impedance measurement value during the first period and a load impedance measurement value during the second period with a preset weighted value, with an output impedance of the first high frequency power supply.
2. The plasma processing apparatus of claim 1 , further comprising:
a second high frequency power supply configured to output a second high frequency power;
a second high frequency transmission line configured to transmit the second high frequency power outputted from the second high frequency power supply to the first electrode or a second electrode provided within or in the vicinity of the processing vessel; and
a second high frequency power modulation unit configured to pulse-modulate an output of the second high frequency power supply with the modulation pulse such that the second high frequency power is turned on or has a high level during the first period and the second high frequency power is turned off or has a low level lower than the high level during the second period.
3. The plasma processing apparatus of claim 2 ,
wherein the second high frequency power has a frequency suitable for attracting ions from the plasma into the processing target object.
4. The plasma processing apparatus of claim 1 ,
wherein the first high frequency power supply comprises:
a first RF power monitor configured to detect, on the first high frequency transmission line, a power of a progressive wave propagating in a forward direction from the first high frequency power supply toward the first electrode and a power of a reflection wave propagating in a backward direction from the first electrode toward the first high frequency power supply, and configured to generate a progressive wave power detection signal and a reflection wave power detection signal indicating the power of the progressive wave and the power of the reflection wave, respectively;
a first load power measurement unit configured to obtain a measurement value of a load power applied to a load including the plasma, based on the progressive wave power detection signal and the reflection wave power detection signal detected from the first RF power monitor; and
a first high frequency output control unit configured to perform a feedback control on the power of the progressive wave during the second period in each cycle of the modulation pulse such that the measurement value of the load power obtained from the first load power measurement unit is equal to or approximate to a load power set value.
5. The plasma processing apparatus of claim 1 ,
wherein the first high frequency power supply comprises:
a first RF power monitor configured to detect, on the first high frequency transmission line, a power of a progressive wave propagating in a forward direction from the first high frequency power supply toward the first electrode and a power of a reflection wave propagating in a backward direction from the first electrode toward the first high frequency power supply, and configured to generate a progressive wave power detection signal and a reflection wave power detection signal indicating the power of the progressive wave and the power of the reflection wave, respectively;
a first load power measurement unit configured to obtain a measurement value of a load power applied to a load including the plasma, based on the progressive wave power detection signal and the reflection wave power detection signal detected from the first RF power monitor; and
a first high frequency output control unit configured to perform a feedback control on the power of the progressive wave during the first period and the second period individually in each cycle of the modulation pulse such that the measurement value of the load power obtained from the first load power measurement unit is equal to or approximate to a first load power set value and a second load power set value applied during the first period and the second period, respectively.
6. The plasma processing apparatus of claim 1 ,
wherein the first high frequency power has a frequency suitable for generating the plasma.
7. The plasma processing apparatus of claim 6 ,
wherein the processing target object is placed on the first electrode.
8. The plasma processing apparatus of claim 2 ,
wherein the second high frequency power during the second period is higher than a minimum power required to maintain a plasma generation state.
9. The plasma processing apparatus of claim 2 , further comprising:
a DC power supply unit configured to apply a negative DC voltage to the second electrode only during the second period in synchronization with the modulation pulse.
10. The plasma processing apparatus of claim 1 , further comprising:
a DC power supply unit configured to apply a negative DC voltage to an electrode facing the processing target object via a plasma generation space within the processing vessel, and set an absolute value of the negative DC voltage during the second period to be higher than an absolute value thereof during the first period in synchronization with the modulation pulse.
11. The plasma processing apparatus of claim 1 ,
wherein a frequency of the modulation pulse is in a range from 2 kHz to 8 kHz, and a duty ratio of the modulation pulse is in a range from 20% to 80%.