INFICON SQC-310 Thin Film Deposition Controller User Manual

Page 38

2 - 14

N 07

SQC-310 Operating Manual

NOTE: Control loop tuning is a trial and error process and there is no "best"

procedure to accomplish this task. The procedure described here works
best for fast sources.

Set System Parameters: A Period of 0.25 seconds is a good starting point. Set
Tooling parameters to 100% for now. Initially set the Rate Filter to 1.00 (no filter) to
see the noise of the system. Simulate should be OFF. Keep in mind that Simulate
mode is a tool for testing process layers. It is not likely to match the control
response of your vacuum system.

Create a One-Layer Test Process: Create a new film with all default values and
select the material you will be depositing. Create a process that has the new film
as its only layer, and edit that layer. Set Init Rate to your desired rate and Final
Thickness to a large value to avoid the layer stopping during the tests. Select the
proper Sensor(s) and Source. Leave the other layer and film parameters at their
default values.

Test the Setup: Press Next Menu until the Sensor Info button is displayed, and
press Sensor Info. Verify that the Sensor Status is ON and a stable frequency is
displayed. Exit to the main screen and press Next Menu until the Auto/Manual
button is displayed. Press Auto/Manual to enter Manual mode, then press Start
Layer.

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 near
your desired setpoint is achieved. Again, verify that the power supply output agrees
with the SQC-310 Power (%) reading. If the readings don’t agree, check your wiring
and verify that the System Menu, Source setup Voltage Scale agrees with your
power supply’s input specifications.

With the power set to your desired rate (Init Rate in the Quick Edit menu), push
Next Menu then Next Graph until the Rate Deviation graph is displayed, and
observe the noise. If the system has significant short term noise at fixed power
(maybe >10%), the control loop will be very difficult to adjust, especially at low
rates. It is better to eliminate the source of the noise before attempting to set the
PID values.

Select a Filter Alpha: On the Quick Edit menu, slowly decrease the filter Alpha
from 1 to a lower value until the rate display noise is minimized. If you set Alpha too
low, the display will lag the true system response and may hide significant
problems. A value of 0.5 equally weights the current reading and the previous
filtered readings.

Determine Open Loop Gain: Record the Power reading at the desired rate as
PWR

. Slowly lower the power until the Rate (

/s) reading is just at (or near)

zero. Record the zero rate Power reading as PWR

Determine Open Loop Response Time: Calculate 1/3 of your desired rate
(RATE

1/3

), and 2/3 of the desired rate (RATE

2/3

) for this layer. Slowly increase the

power until Rate (

/s) matches RATE

1/3

. Get ready to record the loop’s response