Production Process Control begins with measuring the existing process of record (POR) for compliance with performance specifications. The plasma etch measurement should be as close to actual process conditions as possible, with minimal time offline for testing, and easy to use.
The plasma etch measurements are tracked versus the process control specifications. When the plasma etch monitoring metric is within specification, the process passes. When the metric goes out of control limits, the process is down and needs to be diagnosed for root cause and corrective action. SPC charts are commonly used to monitor processes for control.
Fault Detection & Classification:
When the plasma etch process monitoring method determines the process is out of spec, the root cause(s) should be identified prior to any adjustment or corrective action. Root cause analysis requires deep insight into the process conditions and typically much finer detail than plasma etch process monitoring.
If the root cause analysis points to the processing tool settings, the tool will be recalibrated and the process brought back into monitoring control. Calibration should be traceable so the original plasma etch process is not lost.
Getting the plasma etch process calibrated recovers from the excursion, but to enhance the performance normally takes a detailed understanding of the sources of error, and the ability to automate fixes to these errors. The metrology system must take the engineer inside the plasma etch process regime
to truly understand what is happening. Process capability must be enhanced to keep pace with Moore’s Law.