Plasma processing apparatus and plasma processing method
In a plasma processing apparatus, a radio-frequency power supply adjusts frequencies of radio-frequency power in each bias cycle of electrical bias energy. The radio-frequency power supply uses a reference time series of frequencies of the radio-frequency power in each bias cycle. The radio-frequency power supply repeats using a changed time series of frequencies of the radio-frequency power in each bias cycle to increase a degree of match based on an evaluation value. The changed time series results from shifting the reference time series by a phase shift amount, scaling the reference time series in a frequency direction, or scaling two or more of multiple time zones of the reference time series in a time direction.
1. A plasma processing method, comprising:
providing radio-frequency power from a radio-frequency power supply to generate plasma from a gas in a chamber in a plasma processing apparatus, the plasma processing apparatus including a substrate support in the chamber;
providing electrical bias energy to the substrate support to draw ions toward a substrate on the substrate support, the electrical bias energy having a waveform with repeated cycles each having a time length being an inverse of a bias frequency; and
adjusting frequencies of the radio-frequency power in each of the repeated cycles while the radio-frequency power is being provided and the electrical bias energy is being provided to the substrate support,
wherein the adjusting the frequencies includes
(a) using a predetermined reference time series of frequencies of the radio-frequency power in each of the repeated cycles,
(b) using, after the (a), a changed time series of frequencies of the radio-frequency power in each of the repeated cycles, and
(c) repeating the (b) to increase a degree of match of impedance between the radio-frequency power supply and a load coupled to the radio-frequency power supply based on an evaluation value indicating the degree of match, and
the changed time series used in the (b) is
a time series of frequencies resulting from shifting the reference time series by a phase shift amount for each of the repeated cycles,
a time series of frequencies resulting from scaling up or down the reference time series in a frequency direction, or
a time series of frequencies resulting from scaling up or down two or more of a plurality of time zones of the reference time series in a time direction and including as many frequencies as the reference time series.
2. The plasma processing method according to claim 1 , further comprising:
in the repeating of the (b), changing the phase shift amount.
3. The plasma processing method according to claim 1 , further comprising:
in the repeating of the (b), changing a factor for the scaling up or down using at least one of
a time series of frequencies of the radio-frequency power resulting from scaling up or down the reference time series in the frequency direction while maintaining a minimum frequency in the reference time series,
a time series of frequencies of the radio-frequency power resulting from scaling up or down the reference time series in the frequency direction while maintaining a maximum frequency in the reference time series,
a time series of frequencies of the radio-frequency power resulting from scaling up or down the reference time series in the frequency direction while maintaining frequencies lower than or equal to a specified frequency in the reference time series, or
a time series of frequencies of the radio-frequency power resulting from scaling up or down the reference time series in the frequency direction while maintaining frequencies higher than or equal to the specified frequency in the reference time series.
4. The plasma processing method according to claim 3 , further comprising:
selecting, from a plurality of time series of frequencies of the radio-frequency power used in the repeating of the (b), a first time series causing a greatest increase in the degree of match based on the evaluation value;
further repeating the (b) using a second time series of frequencies resulting from shifting the first time series by a phase shift amount for each of the repeated cycles; and
changing the phase shift amount in further repeating the (b).
5. The plasma processing method according to claim 1 , wherein
in a first repeat of the (b), the method changes the phase shift amount and selects, from a plurality of time series of frequencies of the radio-frequency power used in the first repeat of the (b), a first time series of frequencies causing a greatest increase in the degree of match based on the evaluation value,
in a second repeat of the (b), the method changes a factor for the scaling up or down using at least one of
a time series of frequencies of the radio-frequency power resulting from scaling up or down the first time series in the frequency direction while maintaining a minimum frequency in the first time series,
a time series of frequencies of the radio-frequency power resulting from scaling up or down the first time series in the frequency direction while maintaining a maximum frequency in the first time series,
a time series of frequencies of the radio-frequency power resulting from scaling up or down the first time series in the frequency direction while maintaining frequencies lower than or equal to a specified frequency in the first time series, or
a time series of frequencies of the radio-frequency power resulting from scaling up or down the first time series in the frequency direction while maintaining frequencies higher than or equal to the specified frequency in the first time series, and
the method selects, from a plurality of time series of frequencies of the radio-frequency power used in the second repeat of the (b), a second time series of frequencies causing a greatest increase in the degree of match based on the evaluation value, and
in a third repeat of the (b), the method changes a factor for the scaling up or down in the time direction using a time series of frequencies resulting from scaling up or down each of a plurality of time zones of the second time series in the time direction and including as many frequencies as the second time series, and selects, from a plurality of time series of frequencies of the radio-frequency power used in the third repeat of the (b), a third time series of frequencies causing a greatest increase in the degree of match based on the evaluation value.
6. The plasma processing method according to claim 1 , wherein
the evaluation value is a single representative value in a period longer than or equal to the time length of each of the repeated cycles.
7. The plasma processing apparatus according to claim 6 , wherein
the evaluation value is a representative value of power levels of reflected waves of the radio-frequency power returning to the radio-frequency power supply from the load coupled to the radio-frequency power supply or a representative value of ratios of the power levels of the reflected waves to an output level of the radio-frequency power of the radio-frequency power supply.
8. The plasma processing apparatus according to claim 6 , wherein
the evaluation value is a representative value of phase differences between voltages and currents of the radio-frequency power measured between the radio-frequency power supply and the load coupled to the radio-frequency power supply, a representative value of impedances determined based on the voltages and the currents, or a representative value of resistive components of the impedances.
9. The plasma processing method according to claim 1 , wherein
the electrical bias energy includes radio-frequency bias power or voltage pulses periodically generated at a time interval with a time length being the inverse of the bias frequency.