Real time profile control for chemical mechanical polishing
A method of controlling processing of a substrate includes generating, based on a signal from an in-situ monitoring system, first and second sequences of characterizing values indicative of a physical property of a reference zone and a control zone, respectively, on a substrate. A reference zone rate and a control zone rate are determined from the first and sequence of characterizing values, respectively. An error value is determined by comparing characterizing values for the reference zone and control zone. An output parameter value for the control zone is generated based on at least the error value and a dynamic nominal control zone value using a proportional-integral-derivative control algorithm, and the dynamic nominal control zone value is generated in a second control loop based on at least the reference zone rate and the control zone rate. The control zone of the substrate is processed according to the output parameter value.
1. A computer program product, tangibly embodied in a non-transitory computer readable media, comprising instructions for causing a processor to:
generate, based on a signal from an in-situ monitoring system, a first sequence of characterizing values indicative of a physical property of a reference zone on a substrate undergoing processing in a processing system and being monitored by the in-situ monitoring system;
generate, based on the signal from the in-situ monitoring system, a second sequence of characterizing values indicative of a physical property of a control zone on the substrate;
determine a reference zone rate from the first sequence of characterizing values;
determine a control zone rate from the second sequence of characterizing values;
determine an error value by comparing a characterizing value for the reference zone to a characterizing value for the control zone;
calculate, using a proportional-integral-derivative control algorithm, an output parameter value for the control zone in a first control loop based on at least i) the error value and ii) a dynamic nominal control zone value;
generate the dynamic nominal control zone value in a second control loop based on at least the reference zone rate and the control zone rate; and
cause the processing system to process the control zone using the output parameter value.
2. The computer program product of claim 1 , wherein the instructions to determine the error value comprise instructions to calculate a difference between the characterizing value for the reference zone and the characterizing value for the control zone.
3. The computer program product of claim 1 , wherein the instructions to determine the reference zone rate comprise instructions to fit a first function to the sequence of values for the reference zone and to determine a first slope of the first function, and wherein the instructions to determine the control zone rate comprise instructions to fit a second function to the sequence of values for the control zone and to determine a second slope of the second function.
4. The computer program product of claim 1 , wherein the instructions to calculate the output parameter value comprise instructions to calculate the parameter value u(t) according to
u
(
t
)
=
u
′
(
0
)
+
K
p
e
(
t
)
+
K
I
∫
0
t
e
(
t
)
dt
+
K
D
de
(
t
)
dt
where u′(0) is the dynamic nominal control zone value, e(t) is the error value, and K P , K I and K D are PID controller parameter constants.
5. The computer program product of claim 1 , wherein the instructions to generate the dynamic nominal control zone value comprise instructions to generate an error rate based on at least the reference zone rate and the control zone rate.
6. The computer program product of claim 5 , wherein the instructions to generate the error rate comprise instructions to calculate a rate set point value based on the reference zone rate.
7. The computer program product of claim 6 , wherein the instructions to calculate the rate set point value comprise instruction to calculate the rate set point value based on the error value, the reference zone rate and the control zone rate.
8. The computer program product of claim 7 , wherein the instructions to calculate a rate set point value comprise instructions to calculate the rate set point value r SP according to
r SP =r R ( t )−DSPW* R MAX
where r R (t) is the reference zone rate, R MAX is a predetermined constant, and DSPW is a dynamic set point weight.
9. The computer program product of claim 8 , comprising instruction to calculate the dynamic set point weight according to
DSPW
=
1
-
e
-
err
*
f
1
+
e
-
err
*
f
where err is the error value e(t) and f is a tuning value.
10. The computer program product of claim 6 , wherein the instructions to calculate the rate set point value comprise instruction to calculate the rate set point value based on the characterizing value for the reference zone, the characterizing value for the control zone, and the reference zone rate, and a target characterizing value.
11. The computer program product of claim 10 , wherein the instructions to calculate the rate set point value comprises instructions to calculate the rate set point value r SP according to the following:
r
SP
=
y
R
-
y
EP
y
c
-
y
EP
*
r
R
(
t
)
where y R and y C are the characterizing values of the reference zone and control zone, respectively, y EP is the target characterizing value, and r R (t) is the reference zone rate.
12. The computer program product of claim 6 , wherein the instructions to generate the error rate comprise instructions to compare the rate set point value to the control zone rate.
13. The computer program product of claim 12 , wherein the instructions to generate the error rate comprise instructions to calculate a difference between the rate set point value and the control zone rate.
14. The computer program product of claim 5 , wherein the instructions to generate the dynamic nominal control zone value comprise instructions to calculate the dynamic nominal control zone value from the error rate and a predetermined control zone nominal pressure.
15. The computer program product of claim 5 , wherein the instructions to generate the dynamic nominal control zone value comprise instructions to calculate the dynamic nominal control zone value u′(0) according to
u ′(0)= u (0)+ K R *r err
where u(0) is a predetermined control zone nominal pressure, K R is a control parameter constant and r err is the error rate.
16. A method of controlling processing of a substrate, comprising:
generating, based on a signal from an in-situ monitoring system, a first sequence of characterizing values indicative of a physical property of a reference zone on a substrate undergoing processing and being monitored by the in-situ monitoring system;
generating, based on the signal from the in-situ monitoring system, a second sequence of characterizing values indicative of a physical property of a control zone on the substrate;
determining a reference zone rate from the first sequence of characterizing values;
determining a control zone rate from the second sequence of characterizing values;
determining an error value by comparing a characterizing value for the reference zone to a characterizing value for the control zone;
calculating, using a proportional-integral-derivative control algorithm, an output parameter value for the control zone in a first control loop based on at least i) the error value and ii) a dynamic nominal control zone value;
generating the dynamic nominal control zone value in a second control loop based on at least the reference zone rate and the control zone rate; and
processing the substrate, including processing the control zone of the substrate according to the output parameter value.
17. The method of claim 16 , comprising processing the reference zone of the substrate according to a reference zone parameter value.
18. The method of claim 16 , wherein processing the substrate comprises polishing the substrate.
19. The method of claim 16 , wherein the in-situ monitoring system comprises an optical monitoring system and/or an eddy current monitoring system.
20. A polishing system, comprising:
a platen to hold a polishing pad;
a carrier to hold a substrate in contact with the polishing pad;
a motor coupled to at least one of the platen and the carrier to create relative motion therebetween;
an in-situ monitoring system configured to generate a signal indicative of a physical property of the substrate during polishing of the substrate; and
a controller to receive the signal and configured to
generate, based on the signal from the in-situ monitoring system, a first sequence of characterizing values indicative of the physical property of a reference zone on the substrate;
generate, based on the signal from the in-situ monitoring system, a second sequence of characterizing values indicative of the physical property of a control zone on the substrate;
determine a reference zone rate from the first sequence of characterizing values;
determine a control zone rate from the second sequence of characterizing values;
determine an error value by comparing a characterizing value for the reference zone to a characterizing value for the control zone;
calculate, using a proportional-integral-derivative control algorithm, an output pressure value for the control zone in a first control loop based on at least i) the error value and ii) a dynamic nominal control zone value;
generate the dynamic nominal control zone value in a second control loop based on at least the reference zone rate and the control zone rate; and
cause the carrier to apply the output pressure value to the control zone of the substrate.