Measuring and controlling wafer potential in pulsed RF bias processing

• US 8,303,763 B2
• Filed: 04/25/2012
• Issued: 11/06/2012
• Est. Priority Date: 09/20/2006
• Status: Active Grant

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Kuthi, Andras, Hwang, Stephen, Vetter, James C., Eilenstine, Greg, Wang, Rongping, Ngo, Tuan
• Primary Examiner(s): Kackar, Ram N.
• Application Number:
  US13/456,122
• Publication Number:
  US 20120206127A1
• Time in Patent Office: 195 Days
• Field of Search: 156/345.28, 156/345.24, 156/345.25, 156/345.26, 118/712, 118/723.E
• US Class Current: 156/345.28
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32174 Circuits specially adapted for controlling the RF discharge
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge
• CPC Class Codes: H01L 22/26 Acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection, in-situ thickness measurement endpoint detection arrangements in CMP apparatus B24B37/013, in discharge apparatus H01J37/32

Abstract

Apparatus and methods are provided for monitoring a pulsed RF bias signal applied to a chuck in a processing chamber. One method includes operations for detecting voltage values of individual pulses of the pulsed RF bias voltage, and for determining the time for sampling the value of each individual detected pulse. At the sampling time for each pulse, a particular voltage value of the respective individual detected pulse is sampled and the particular voltage value is held. Each particular voltage value represents a characteristic peak-to-peak voltage value of each individual detected pulse. A feedback signal representing the characteristic peak-to-peak voltage value for a voltage envelope of one of the individual detected pulses is generated, and the voltage of the pulsed RF bias voltage signal applied to the chuck is adjusted according to a difference between the feedback signal and a desired voltage value of the pulsed RF bias voltage signal.

Claims

1. A method for monitoring and adjusting a pulsed RF bias voltage signal to be applied to a chuck in a plasma chamber for processing a semiconductor wafer, the chuck being configured to mount the semiconductor wafer for processing, the method comprising:

detecting voltage values of individual pulses of the pulsed RF bias voltage applied to the chuck;

determining a sampling time at which to sample a voltage value of each of the individual detected pulses;

at the sampling time for each of the individual detected pulses, sampling a particular voltage value of the respective individual detected pulse and holding the particular voltage value, each particular voltage value representing a characteristic peak-to-peak voltage value of each respective individual detected pulse, wherein the sampling time corresponds to a time when a characteristic peak-to-peak voltage value occurs in each individual detected pulse, the characteristic peak-to-peak voltage representing a maximum peak-to-peak voltage of an envelope of each individual detected pulse;

generating a feedback signal representing the characteristic peak-to-peak voltage value for a voltage envelope of one of the individual detected pulses; and

adjusting the voltage of the pulsed RF bias voltage signal applied to the chuck according to a difference between the feedback signal and a desired voltage value of the pulsed RF bias voltage signal to hold electrical characteristics of the plasma steady during processing to compensate for a variation of an impedance presented to the chuck.

2. The method as recited in claim 1, wherein the detecting operation provides the voltage envelope representing peak-to-peak voltage values of each individual pulse of the respective pulses of the pulsed RF bias voltage signal.

3. The method as recited in claim 1, wherein the determining operation identifies the sampling time or multiple sampling times temporally spaced from a rising edge of each of the detected individual pulses so that each sampled particular voltage value of a respective individual detected pulse or a characteristic function that is an average of multiple samples within an individual detected pulse represents a characteristic peak-to-peak voltage value of the respective individual detected pulse.

4. The method as recited in claim 1, wherein averaging is performed for two or more peak peak-to-peak voltage values of the respective individual detected pulses.

5. The method as recited in claim 1, wherein adjusting the voltage of the pulsed RF bias further includes:

holding electrical characteristics of the plasma steady during processing to compensate for a variation of an impedance presented to the chuck.

6. A method for determining a peak-to-peak voltage value of a pulsed RF bias signal applied to an RF bias electrode supporting a substrate in a processing chamber, the applied signal consisting of a pair of ON mode pulses separated by an OFF mode, the method comprising:

identifying a first ON mode pulse of the pulsed RF bias signal, the first ON mode pulse being characterized by amplitudes of cycles that vary with respect to time;

defining an envelope representing peak-to-peak voltage values of the amplitudes of the cycles of the identified first ON mode pulse as a function of time during the first ON mode pulse; and

sampling the envelope at a sampling time when a characteristic peak-to-peak voltage value occurs in the envelope to generate an output signal representing the characteristic peak-to-peak voltage value of the pulsed RF bias signal, the characteristic peak-to-peak voltage representing a maximum peak-to-peak voltage of the envelope, the output signal being used for holding electrical characteristics of the plasma steady during processing to compensate for a variation of an impedance presented to the electrode.

7. The method as recited in claim 6 further comprising:

generating a feedback signal for controlling the voltage value of the pulsed RF bias signal, the feedback signal being based on the characteristic peak-to-peak voltage value of the output signal and on a desired peak-to-peak voltage value of the pulsed RF bias signal.

8. The method as recited in claim 6 further comprising:

repeating the identifying, defining, and sampling operations with respect to successive ON modes pulses of a series of pulses to update the output signal based on the envelopes representing peak-to-peak voltage values of the amplitudes of the cycles of the successive ON mode pulses.

9. The method as recited in claim 6, wherein the sampling time corresponds to a time when a characteristic peak-to-peak voltage value occurs in each ON mode pulse.

10. The method as recited in claim 6, further including:

holding electrical characteristics of a plasma steady during processing to compensate for a variation of an impedance presented to the RF bias electrode.