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 negative jump voltage to an electrode of a process chamber to set a wafer voltage for a wafer, modulating an amplitude of the wafer voltage to produce a train of groups of pulse bursts with different amplitudes, and repeating the modulating of the amplitude of the wafer voltage to repeat the train of the groups of pulse bursts to create an ion energy distribution function having more than one energy peak. In some embodiments, the negative jump voltage can include a single-cycle voltage waveform with a voltage ramp during an ion-current phase, in which the voltage ramp can be positive or negative and a duration of the ion-current phase can comprise more or less than fifty percent of a period of the waveform.
1 . A method, comprising:
applying a negative jump voltage to an electrode of a process chamber to set a wafer voltage for a wafer, wherein the negative jump voltage comprises a repeating single-cycle voltage waveform with a voltage ramp during an ion-current phase;
modulating an amplitude of the wafer voltage to produce a train of groups of pulse bursts with different amplitudes, wherein each group of pulse bursts is composed of pulses having a same amplitude; and
repeating the modulating of the amplitude of the wafer voltage to repeat the train of the groups of pulse bursts to create an ion energy distribution function having one or more energy peaks; and
wherein the relative number of bursts with a given amplitude in a train determines the relative portion of ions at a specific energy corresponding to that amplitude.
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 desired ion energy distribution function is created to induce a specific bias voltage waveform on the wafer.
5 . The method of claim 1 , comprising:
modulating the wafer voltage at different points in time to create the ion energy distribution function having more than one energy peak.
6 . The method of claim 5 , 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.
7 . The method of claim 1 , further comprising:
applying a positive jump voltage to an electrode of a process chamber to neutralize a surface of a wafer; and
applying a ramp voltage to the electrode that at least one of overcompensates or undercompensates for ion current on the wafer.
8 . The method of claim 7 , wherein applying a ramp voltage to the electrode that overcompensates for ion current on the wafer comprises applying a ramp voltage to the electrode that comprises a slope that is more negative than is required to maintain a constant voltage on the wafer.
9 . The method of claim 8 , 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.
10 . The method of claim 7 , wherein applying a ramp voltage to the electrode that undercompensates for ion current on the wafer comprises applying a ramp voltage to the electrode that comprises a slope that is less negative than is required to maintain a constant voltage on the wafer.
11 . The method of claim 10 , 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.
12 . The method of claim 7 , comprising:
adjusting a slope of the ramp voltage to create a desired ion energy distribution function to induce a specific bias voltage waveform on the wafer.
13 . The method of claim 1 , further comprising:
a period in between the groups of pulses where no voltage pulses are provided to the electrode.
14 . The method of claim 1 , wherein the voltage ramp during the ion-current phase comprises a positive voltage ramp.
15 . The method of claim 1 , wherein the voltage ramp during the ion-current phase comprises a negative voltage ramp.
16 . The method of claim 1 , wherein the voltage ramp during the ion-current phase comprises no voltage ramp.
17 . The method of claim 1 , wherein a duration of the ion-current phase comprises less than fifty percent of a period of the waveform.
18 . The method of claim 1 , wherein a duration of the ion-current phase comprises more than fifty percent of a period of the waveform.
19 . The method of claim 1 , wherein the waveform comprises a positive peak voltage.
20 . The method of claim 1 , wherein the waveform comprises a negative peak voltage.