INFICON SQM-242 Thin Film Deposition Controller Card Software Operating Manual - Manual (Page 83)

6 - 1
IP
N 07
4-
55
1-
P1
A
SQS-242 Operating Manual
Chapter 6
Loop Tuning
This section will help you adjust your control loop PID parameters to achieve a
stable deposition process. Keep in mind that there is no "best" way to determine
PID parameters, and no one set of settings that are "best."
1 Setup System Parameters: Be sure that the output Full Scale voltage and
crystal Min/Max Frequency parameters are accurate for your system. All
Tooling parameters are best set to 100% for now. A Period of .25 seconds is
also a good starting point. Simulate should be OFF.
2 Create a One-Layer Test Process: Create a new process that has a single
film as its only layer, and select it as the current process. Set the film's Initial
Rate to your desired rate and Final Thickness to a large value, say 10X your
desired Final Thickness. Select the proper Sensor(s), Output, and Material. Set
Max Power to 100% and Slew rate to 100%. Disable all errors except Crystal
Fail. Set On Error to Stop Layer.
3 Test the Setup: Press Auto/Manual to start the layer in Manual mode. Slowly
turn the control knob to a power of 10%, and verify that your power supply
output is about 10% of full scale. Continue to turn the control knob until a
Rate(Å/s) above 0 is shown. Again, verify that the power supply output agrees
with the SQS-242 Power(%) reading. If the readings don't agree, check your
wiring and process setup. In particular, verify that the System, Outputs, Full
Scale voltage agrees with your power supply input specifications.
4 Determine Open Loop Gain: Slowly adjust the control knob until the Rate(Å/s)
reading approximately matches your Initial Rate setting. Record the Power(%)
reading as PWRDR (power @ desired rate). Slowly lower the power until the
Rate(Å/s) reading is just at (or near) zero. Record the zero rate Power(%)
reading as PWR0R.
5 Determine Open Loop Response Time: Calculate 1/3 of your desired rate
(RATE1/3), and 2/3 of the desired rate (RATE2/3) for this layer. Slowly increase
the power until Rate(A/s) matches RATE1/3. Get ready to record the loop's
response to an input change. Quickly adjust Power(%) to PWRDR. Measure
the time for the Rate (A/s) reading to reach RATE2/3. You may want to do this
several times to get an average response time reading. Displaying the Rate
graph will also help. Twice the measured time is the step response time,
TIMESR. TIMESR is typically 0.7 to 1.5 seconds for E-Beam evaporation, 5 to
20 seconds for thermal evaporation.
Press Abort Process, then Manual/Auto to return to Auto mode. Follow these steps
to set the loop PID parameters: