Creating ion energy distribution functions (IEDF)
Systems and methods for creating arbitrarily-shaped ion energy distribution functions using shaped-pulse-bias. In an embodiment, a method includes applying a positive jump voltage to an electrode of a process chamber to neutralize a wafer surface, applying a negative jump voltage to the electrode to set a wafer voltage, and modulating the amplitude of the wafer voltage to produce a predetermined number of pulses to determine an ion energy distribution function. In another embodiment a method includes applying a positive jump voltage to an electrode of a process chamber to neutralize a wafer surface, applying a negative jump voltage to the electrode to set a wafer voltage, and applying a ramp voltage to the electrode that overcompensates for ion current on the wafer or applying a ramp voltage to the electrode that undercompensates for ion current on the wafer.
1. A method, comprising:
applying a negative jump voltage to an electrode of a process chamber to set a wafer voltage for a wafer;
modulating the wafer voltage at different amplitudes;
producing a relative number of pulses at each of the different amplitudes; and
determining a relative ion fraction at an ion energy corresponding to at least one of the different amplitudes based on a number of pulses produced at the at least one of the different amplitudes.
2. The method of claim 1 , comprising:
applying a positive jump voltage to the electrode of the process chamber to neutralize a surface of the wafer.
3. The method of claim 2 , wherein the positive jump voltage is applied to the electrode of the process chamber prior to applying the negative jump voltage.
4. The method of claim 1 , wherein the modulation of the amplitude of the wafer voltage controls a feature profile of a resulting ion energy distribution function.
5. The method of claim 1 , wherein the amplitude of the wafer voltage is modulated to create a desired ion energy distribution function.
6. The method of claim 5 , wherein the desired ion energy distribution function is created to induce a specific bias voltage waveform on the wafer.
7. The method of claim 1 , comprising:
modulating the wafer voltage at different points in time to create an ion energy distribution function having more than one energy peak.
8. The method of claim 7 , wherein an ion fraction for each of the energy peaks is determined by a number of pulses produced during a respective modulation of the wafer voltage at the different points in time.
9. A method comprising:
applying a positive jump voltage to an electrode of a process chamber to neutralize a surface of a wafer;
applying a negative jump voltage to the electrode to set a wafer voltage for the wafer; and
applying a voltage ramp to the electrode that has a more negative slope than is required to maintain a constant voltage on the wafer.
10. The method of claim 9 , wherein a minimum voltage and a maximum voltage of a current induced on the wafer determine a width of a resulting ion energy distribution function.
11. The method of claim 9 , comprising:
adjusting a slope of the ramp voltage to create a desired ion energy distribution function.
12. The method of claim 11 , wherein the desired ion energy distribution function is created to induce a specific bias voltage waveform on the wafer.
13. A method comprising:
applying a positive jump voltage to an electrode of a process chamber to neutralize a surface of a wafer;
applying a negative jump voltage to the electrode to set a wafer voltage for the wafer; and
applying a ramp voltage to the electrode that has a less negative slope than is required to maintain a constant voltage on the wafer.
14. The method of claim 13 , wherein a minimum voltage and a maximum voltage of a current induced on the wafer determine a width of a resulting ion energy distribution function.
15. The method of claim 13 , comprising:
adjusting a slope of the ramp voltage to create a desired ion energy distribution function.
16. The method of claim 15 , wherein the desired ion energy distribution function is created to induce a specific bias voltage wave form on the wafer.