Systems and methods for monitoring faults, anomalies, and other characteristics of a switched mode ion energy distribution system
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 for monitoring a plasma processing chamber, the system comprising:
an electrical node to couple to a substrate support of the plasma processing chamber;
a bias supply configured to provide a modified periodic voltage function to the electrical node, wherein each cycle of the modified periodic voltage function includes four portions: a first portion with a voltage that increases to a second portion that has a positive voltage relative to an onset of the voltage of the first portion, a third portion starting at an end of the second portion with a voltage drop, ΔV, and a fourth portion,
dV
0
dT
,
that includes a negative voltage ramp from an end of the third portion;
a controller coupled to the electrical node, the controller is configured to monitor the modified periodic voltage function over multiple cycles to monitor a relationship
dV
0
dt
-
I
c
C
1
=
D
to represent a status of a plasma process or the plasma processing chamber, where I c represents a controllable ion compensation current, D is a unitless value, and C 1 is an effective capacitance including, at least, a capacitance of a substrate support.
2. The system of claim 1 , wherein the controller is configured to calculate ion current by:
determining a first slope, dV 01 /dt for the negative voltage ramp over one or more cycles of the modified periodic voltage function, for a first ion current compensation, I C1 ;
determining a second slope, dV 02 /dt for the negative voltage ramp over one or more other cycles of the modified periodic voltage function, for a second ion current compensation, I C2 ; and
calculating ion current, I I , as a function of the effective capacitance, C 1 , the first slope, dV 01 /dt, the second slope, dV 02 /dt, the first ion current compensation, I C1 , and the second ion current compensation, I C2 .
3. The system of claim 2 , wherein the controller is configured to monitor the ion current, I I , in the plasma for cyclical changes in the plasma density to detect instabilities in a plasma source.
4. The system of claim 2 , wherein the controller is configured to monitor the ion current, I I , in the plasma for non-cyclical changes in the plasma density to detect plasma instabilities.
5. The system of claim 1 , wherein the controller is configured to:
measure a standard deviation of sampled voltages along the fourth portion of each cycle of the modified periodic voltage function;
monitor the standard deviation of several cycles over time; and
determine there may be variation in the plasma processing chamber causing the standard deviation increasing over time.
6. The system of claim 1 , wherein the controller is configured to monitor the fourth portion by:
obtaining a reference modified periodic voltage function; and
comparing the fourth portion of the modified periodic voltage function to the fourth portion of the reference modified periodic voltage function to detect changes in the fourth portion indicating a variation in the plasma processing chamber.
7. The system of claim 6 , wherein the controller is configured to compare the fourth portion of the modified periodic voltage function to the fourth portion of the reference modified periodic voltage function by comparing a slope of the fourth portion of the modified periodic voltage function to a slope of the fourth portion of the reference modified periodic voltage function.
8. A system for monitoring a plasma processing chamber, the system comprising:
an electrical node to couple to a substrate support of the plasma processing chamber;
a bias supply coupled, without a blocking capacitor, to the electrical node, the bias supply configured to provide a modified periodic voltage function to the electrical node;
a controller coupled to the electrical node, the controller including non-transitory, tangible computer readable storage medium storing a representation of a reference modified periodic voltage function, and the tangible computer readable storage medium is encoded with processor readable instructions for monitoring an ion current of a plasma in the plasma processing chamber, the instructions including instructions to:
control the bias supply so the bias supply applies a currently-monitored modified periodic voltage function to the electrical node wherein each cycle of the modified periodic voltage function includes four portions: a first portion with a voltage that increases to a second portion that has a positive voltage relative to an onset of the voltage of the first portion, a third portion starting at an end of the second portion with a voltage drop, AV, and a fourth portion that includes a negative voltage ramp from an end of the third portion; and
compare the reference modified periodic voltage function and the currently-monitored modified periodic voltage function to characterize the plasma processing chamber.
9. The system of claim 8 , wherein the non-transitory, tangible computer readable storage medium includes instructions to:
determine a first slope, dV01/dt for the negative voltage ramp over one or more cycles of the modified periodic voltage function, for a first ion current compensation, IC1;
determine a second slope, dV02/dt for the negative voltage ramp over one or more other cycles of the modified periodic voltage function, for a second ion current compensation, IC2; and
calculate the ion current, II, as a function of an effective capacitance, C1, that includes, at least, a capacitance of a substrate support, the first slope, dV01/dt, the second slope, dV02/dt, the first ion current compensation, IC1, and the second ion current compensation, IC2.
10. The system of claim 8 , wherein the non-transitory, tangible computer readable storage medium includes instructions to monitor the ion current, I I , in the plasma for non-cyclical changes in plasma density to detect plasma instabilities.
11. The system of claim 8 , wherein the non-transitory, tangible computer readable storage medium includes instructions to:
measure a standard deviation of sampled voltages along the fourth portion of each cycle of the modified periodic voltage function;
monitor the standard deviation of several cycles over time; and
determine there may be variation in the plasma processing chamber causing the standard deviation increasing over time.
12. The system of claim 8 , wherein the non-transitory, tangible computer readable storage medium includes instructions to:
obtain a reference modified periodic voltage function; and
compare the fourth portion of the modified periodic voltage function to the fourth portion of the reference modified periodic voltage function to detect changes in the fourth portion indicating a variation in the plasma processing chamber.
13. The system of claim 12 , wherein the non-transitory, tangible computer readable storage medium includes instructions to compare the fourth portion of the modified periodic voltage function to the fourth portion of the reference modified periodic voltage function by comparing a slope of the fourth portion of the modified periodic voltage function to a slope of the fourth portion of the reference modified periodic voltage function.
14. The system of claim 1 , wherein the controller is configured to monitor the modified periodic voltage function without a plasma in the plasma processing chamber.
15. The system of claim 1 , wherein the controller is configured to monitor the modified periodic voltage function with a plasma in the plasma processing chamber.
16. The system of claim 1 , wherein the controller is configured to determine a value of Ic that will result in a defined ion energy distribution function based on a desired value of D.
17. The system of claim 1 , wherein the controller is configured to store values of of I c and compare the stored values to upper and lower limits for I c .
18. The system of claim 1 , wherein the controller is configured to store values of of D and compare the stored values of D to upper and lower limits for D.
19. The system of claim 1 , wherein the controller is configured to:
calculate ion current, I i , as
I
i
=
I
c
*
C
1
C
1
+
C
stray
where C stray is a stray capacitance; and
compare a calculated value of I i to upper and lower limits for I i.
20. The system of claim 1 , wherein the controller is configured to detect changes in C 1 by detecting changes in D.
21. The system of claim 1 , wherein the controller is configured to monitor D for an indication of a change in the modified periodic voltage function.
22. The system of claim 1 , wherein the controller is configured to monitor the modified periodic voltage function without monitoring a voltage across a blocking capacitor.