Systems and methods for monitoring faults, anomalies, and other characteristics of a switched mode ion energy distribution system

1. A method for monitoring a plasma processing chamber, the method comprising:

applying, with a bias supply, a modified periodic voltage function to an 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,

d

⁢

V

0

dT

,

 that includes a negative voltage ramp from an end of the third portion; and

monitoring, with the bias supply, at least the fourth portion of the modified periodic voltage function over multiple cycles;

calculating, based upon the monitoring, ion current in the plasma processing chamber; and

utilizing the calculation of ion current to monitor conditions in the plasma processing chamber.

2. The method of claim 1 comprising:

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 the ion current, I I , as a function of an 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 method of claim 2 comprising:

monitoring the ion current, I I , in the plasma for cyclical changes in the plasma density to detect instabilities in a plasma source.

4. The method of claim 2 comprising:

monitoring the ion current, I I , in the plasma for non-cyclical changes in the plasma density to detect plasma instabilities.

5. The method of claim 1 comprising:

measuring a standard deviation of sampled voltages along the fourth portion of each cycle of the modified periodic voltage function;

monitoring the standard deviation of several cycles over time; and

determining there may be variation in the plasma processing chamber causing the standard deviation increasing over time.

6. The method of claim 1 , wherein the monitoring the fourth comprises monitoring 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 method of claim 6 , wherein comparing the fourth portion of the modified periodic voltage function to the fourth portion of the reference modified periodic voltage function comprises 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. The method of claim 1 , wherein the monitoring comprises monitoring the modified periodic voltage function without a plasma in the plasma processing chamber.

9. The method of claim 1 , wherein the monitoring comprises monitoring the modified periodic voltage function with a plasma in the plasma processing chamber.

10. The method of claim 1 , comprising storing values of I c and comparing the stored values to upper and lower limits for I c .

11. The method of claim 1 , comprising:

calculating ion current, I i , as

I

i

=

I

c

*

C

1

C

1

+

C

stray

where C stray is a stray capacitance; and

comparing a calculated value of I i to upper and lower limits for I i .

12. The method of claim 1 , comprising monitoring the modified periodic voltage function without monitoring a voltage across a blocking capacitor.

13. A non-transitory, tangible computer readable storage medium encoded with processor readable instructions for monitoring a plasma processing chamber, the instructions comprising instructions to:

apply, with a bias supply, a modified periodic voltage function to an 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; and

monitor, with the bias supply, at least the fourth portion of the modified periodic voltage function over multiple cycles;

calculating, based upon the monitoring, ion current in the plasma processing chamber; and

utilizing the calculation of ion current to monitor conditions in the plasma processing chamber.

14. The non-transitory, tangible computer readable storage medium of claim 13 , wherein the non-transitory, tangible computer readable storage medium includes instructions to:

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 an 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 .

15. The non-transitory, tangible computer readable storage medium of claim 14 , wherein the non-transitory, tangible computer readable storage medium includes instructions to monitor the ion current, I I , in the plasma for cyclical changes in the plasma density to detect instabilities in a plasma source.

16. The non-transitory, tangible computer readable storage medium of claim 14 , 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.