SYSTEM, METHOD, AND APPARATUS FOR ION CURRENT COMPENSATION
Systems, methods and apparatus for regulating ion energies in a plasma chamber and chucking a substrate to a substrate support are disclosed. An exemplary method includes placing a substrate in a plasma chamber, forming a plasma in the plasma chamber, controllably switching power to the substrate so as to apply a periodic voltage function (or a modified periodic voltage function) to the substrate, and modulating, over multiple cycles of the periodic voltage function, the periodic voltage function responsive to a defined distribution of energies of ions at the surface of the substrate so as to effectuate the defined distribution of ion energies on a time-averaged basis.
1 . A system comprising:
a power supply configured to provide a periodic voltage function to an output configured to couple to a substrate support, the periodic voltage function having pulses and a portion between the pulses;
an ion current compensation component configured to provide compensation current, I C , to modify a slope, dV 0 /dt, of the portion between the pulses to form a modified periodic voltage function, which is provided to the output; and
a controller in communication with the power supply and the ion current compensation component wherein the controller is configured to adjust a magnitude of the compensation current, I C , applied to the substrate support so I C <C 1 dVo/dt, where dV 0 /dt, is a slope of the portion between pulses and effective internal capacitance, C 1 , of a plasma processing chamber.
2 . The system of claim 1 , wherein the ion current compensation component is configured to provide zero compensation current, I C .
3 . The system of claim 1 , wherein the controller is configured to:
access a memory to obtain the effective internal capacitance, C 1 , of a plasma processing chamber; and
determine the slope, dV 0 /dt, of the portion between pulses to calculate ion current
I
i
=
C
1
dVo
dt
.
4 . The system of claim 1 , wherein the compensation current, I C , is initially adjusted so
I
C
=
C
1
dVo
dt
,
and then the magnitude of the compensation current is further adjusted that
I
C
=
C
1
dVo
dt
to widen an ion energy distribution function of ions reaching a surface of the substrate.
5 . The system of claim 1 , wherein the power supply is configured to be DC-coupled to the plasma processing chamber without a blocking capacitor.
6 . The system of claim 1 , wherein the ion current compensation component comprises a controllable DC voltage source coupled to the output via a series inductor.
7 . The system of claim 1 , wherein the ion current compensation component comprises a controllable current source coupled to the output.
8 . A method, comprising:
providing a periodic voltage function to a substrate support, the periodic voltage function having pulses comprising a negative voltage step, ΔV, and a portion between the pulses to set a sheath voltage for a wafer on the substrate support; and
modulating the negative voltage step, ΔV, at different amplitudes to create an ion energy distribution function having a desired number of energy peaks with different amplitudes, wherein a relative number of pulses with the negative voltage step, ΔV, at a specific amplitude determines a relative ion fraction at an ion energy corresponding to the specific amplitude;
wherein a ramp voltage between the pulses occurs in response to ion current on the wafer.
9 . The method of claim 8 , comprising controlling the ramp voltage to undercompensate for ion current on the wafer.
10 . The method of claim 8 , comprising controlling the ramp voltage to overcompensate for ion current on the wafer.
11 . The method of claim 8 , wherein the ramp voltage is not controlled.
12 . A system comprising:
a plasma processing chamber;
a plasma source to produce a plasma in the plasma processing chamber;
a substrate support within the plasma processing chamber to support a substrate; and
a switch mode power supply configured to provide a periodic voltage function to the substrate support to effectuate a voltage on a surface of the substrate that is capable of attracting ions in a plasma in the plasma processing chamber to collide with the substrate, the periodic voltage function having pulses and a portion between the pulses;
wherein a ramp voltage between the pulses occurs in response to the ion current on the substrate.
13 . The system of claim 12 , wherein the switch mode power supply is configured to provide no compensation current to the substrate support when the ramp voltage is occurring.
14 . The system of claim 12 , wherein the power supply is configured to be DC-coupled to the plasma processing chamber without a blocking capacitor.
15 . A method for applying a periodic voltage waveform to a substrate support in a plasma processing chamber, the method comprising:
connecting a first voltage to the substrate support and then disconnecting the first voltage from the substrate support to produce a first portion of the periodic voltage waveform at the substrate support that increases to a second portion of the periodic voltage waveform;
connecting, after the first voltage is disconnected from the substrate support, a second voltage to the substrate support and then disconnecting the second voltage from the substrate support to produce a third portion of the periodic voltage waveform that decreases from the second portion of the periodic voltage waveform; and
wherein a fourth portion of the periodic voltage waveform is produced between the third portion and the first portion of the periodic voltage waveform, the fourth portion varies based upon ion current in the plasma processing chamber while the first voltage and the second voltage are disconnected from substrate support.
16 . The method of claim 15 , wherein the fourth portion increases in a ramp-like manner from the third portion of the periodic voltage waveform to the first portion of the periodic voltage waveform.
17 . The method of claim 15 , wherein no compensation current is provided to the substrate support.
18 . The method of claim 17 , wherein no compensation current is provided to the substrate support during the fourth portion of the periodic voltage waveform.