Capacitance measurement without disconnecting from high power circuit
Methods and apparatus for measuring capacitance are disclosed.
1. A method of plasma-assisted semiconductor processing in multiple stations in a process chamber, the method comprising:
providing a substrate to each of the multiple stations;
distributing RF power including a first target frequency to multiple stations to thereby generate a plasma in the multiple stations using a circuit configured to distribute the RF power; and
for a first station of the multiple stations:
measuring a capacitance of a capacitor in the circuit without disconnecting the capacitor from the circuit while distributing the RF power; and
adjusting, according to at least the measured capacitance, the capacitance of the capacitor.
2. The method of claim 1 , further comprising determining a RF power parameter configured to reduce station-to-station variation.
3. The method of claim 2 , further comprising performing a semiconductor processing operation on the substrate at each of the multiple stations based on the RF power parameter being within an acceptable range.
4. The method of claim 3 , wherein the semiconductor processing operation is one of: depositing, etching, stripping, or cleaning a thin film.
5. The method of claim 3 , further comprising determining that the RF power parameter is within the acceptable range, the determining comprising:
determining a difference based on a comparison between the RF power parameter and a set point associated with each of the multiple station; and
determining that the difference does not exceed a threshold.
6. The method of claim 2 , further comprising determining an adjustment to a characteristic of at least one of the multiple stations based on a difference determined based on a comparison between the RF power parameter and a set point associated with each of the multiple station exceeding a threshold.
7. The method of claim 1 , wherein measuring the capacitance of the capacitor comprises:
generating a first signal including a first frequency above the first target frequency in the RF power being distributed;
filtering a signal at the capacitor, the signal at the capacitor being generated in response to at least the first signal and the RF power being distributed;
measuring the filtered signal; and
converting the measured filtered signal to a measured capacitance value for the capacitor.
8. The method of claim 7 , wherein the filtering includes a passband centered at greater than a 10th harmonic frequency of the first target frequency, and the filtering includes a stopband including the first target frequency in the RF power being distributed.
9. The method of claim 7 , wherein:
generating the first signal includes generating an alternating voltage (Vin) as the first signal using a fixed frequency oscillator configured at the first frequency (ω), an output of the fixed frequency oscillator being coupled to a resistance (R) that is in series with the capacitor; and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal (Vout) to the measured capacitance value (C) based in part on the resistance (R), the first frequency (ω), and the alternating voltage (Vin), where Vout/Vin=1/(1+jωRC).
10. The method of claim 7 , wherein:
generating the first signal includes generating an alternating voltage (Vin) as the first signal using a variable frequency oscillator, an output of the variable frequency oscillator being coupled to an inductance (L) that is in series with the capacitor, the variable frequency oscillator being configured to scan a frequency range including a resonant frequency (fo=ωo/2π) of the capacitor and the inductance;
measuring the filtered signal includes using the measured filtered signal to determine the resonant frequency; and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal to the measured capacitance value (C) based in part on the resonant frequency (fo=ωo/2π) and the inductance (L), where fo=ωo/2 π=1/2π sqrt(LC).
11. The method of claim 7 , wherein:
generating the first signal includes generating an alternating voltage (Vin) as the first signal at the first frequency (ω) using an oscillator, an output of the oscillator being coupled to a first terminal of the capacitor through at least a first impedance (z1) and a second impedance (z2) that are each in series with the capacitor, the output of the oscillator also being coupled to a second terminal of the capacitor through at least a third impedance (z3) that is in series with the capacitor;
measuring the filtered signal includes measuring as the measured filtered signal a current or voltage at a node coupling the first impedance (z1), the second impedance (z2), and the third impedance (z3), wherein the measured filtered signal represents an imbalance between a first impedance combination comprising the first impedance (z1) and the second impedance (z2), and a second impedance combination comprising the third impedance (z3) and an impedance of the capacitor (zC); and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal to the measured capacitance value (C) based in part on a ratio z1/z2=z3/zC, where zC=1/jωk.
12. The method of claim 7 , wherein:
generating the first signal includes generating an alternating voltage (Vin) as the first signal at the first frequency (ω) using an oscillator, an output of the oscillator being coupled to a reference capacitor (Cref), and connecting the reference capacitor to be electrically parallel with the capacitor when the alternating voltage charges the reference capacitor to a reference voltage (Vref);
measuring the filtered signal includes measuring as the measured filtered signal a voltage corresponding to a charge in the electrically parallel combination of the reference capacitor and the capacitor at the first frequency (ω); and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal to the measured capacitance value (C) based in part on C=Cref (Vref/Vout−1).
13. The method of claim 7 , wherein:
generating the first signal includes generating an alternating current (Iin) as the first signal at the first frequency (ω) at a first terminal of the capacitor using a current source, an output of the current source being coupled to a voltage measurement interface for measuring a voltage (V);
measuring the filtered signal includes measuring as the measured filtered signal a filtered current (I) corresponding to a current at a second terminal of the capacitor; and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal to the measured capacitance value (C) based in part on the filtered current (I) and a rate of change of the measured voltage at the voltage measurement interface (dV/dt), where I=C dV/dt.
14. The method of claim 7 , wherein:
generating the first signal includes generating a timer signal using a timer circuit where a timer frequency (f) is configured using a first resistance (R1), a second resistance (R2), and the capacitance (C) of the capacitor;
measuring the filtered signal includes measuring as the measured filtered signal a timer pulse count within a time period for determining the timer frequency (f); and
converting the measured filtered signal to the measured capacitance value includes converting the measured filtered signal to the measured capacitance value (C) based in part on the determined timer frequency, where f=1/(C×(R1+2×R2)×ln2).
15. The method of claim 7 , further comprising using an inductance (L), capacitance (C), and resistance (R) meter (LCR meter) to measure the capacitance of the capacitor at the first frequency (ω), or using a vector network analyzer to measure an impedance of the capacitor at the first frequency (ω).
16. The method of claim 1 , wherein the first target frequency in the RF power being distributed is about 13.56, 27, 40, 60 or 100 MHz, or about 100 or 400 kHz.
17. An apparatus for plasma-assisted semiconductor processing, the apparatus comprising:
multiple stations within a process chamber, each station configured to receive at least one substrate;
a capacitance sensor; and
one or more controllers, wherein the one or more controllers and the capacitance sensor are communicatively connected, and the controller is configured to:
provide a substrate to each of the multiple stations;
distribute RF power including a first target frequency to multiple stations to thereby generate a plasma in the multiple stations using a circuit configured to distribute the RF power;
for a first station of the multiple stations:
measure, using the capacitance sensor, a capacitance of a capacitor in the circuit without disconnecting the capacitor from the circuit while distributing the RF power; and
adjust, according to at least the measured capacitance, a capacitance of the capacitor.
18. The apparatus of claim 17 , wherein the controller is further configured to determine a RF power parameter configured to reduce station-to-station variation.
19. The apparatus of claim 18 , wherein the controller is further configured to perform a semiconductor processing operation on the substrate at each of the multiple stations based on the RF power parameter being within an acceptable range;
wherein the semiconductor processing operation is one of: depositing, etching, stripping, or cleaning a thin film.
20. The apparatus of claim 18 , wherein the controller is further configured to determine an adjustment to a characteristic of at least one of the multiple stations based on a difference determined based on a comparison between the RF power parameter and a set point associated with each of the multiple station exceeding a threshold.
21. The apparatus of claim 17 , wherein, to measure the capacitance of the capacitor, the capacitance sensor is configured to:
generate a first signal including a first frequency above the first target frequency in the RF power being distributed;
filter a signal at the capacitor by a filter, the signal at the capacitor being generated in response to at least the first signal and the RF power being distributed;
measure the filtered signal; and
convert the measured filtered signal to a measured capacitance value for the capacitor.
22. The apparatus of claim 21 , further comprising an oscilloscope configured to measure a voltage drop across the capacitor at the first frequency (ω).