Advanced Lithography Measurements:
Production Process Control begins with advanced lithography measurements of the existing process of record (POR) for compliance with performance specifications. This advanced litho measurement should be as close to actual process control conditions as possible, with minimal time offline for testing, and easy to use.
Advanced Lithography Monitor:
The advanced lithography measurements are monitored and tracked versus the process control specifications. When the lithography monitoring metric is within specification, the process passes. When the lithography monitoring metric goes out of the lithography process control limits, the process is down and needs to be diagnosed for root cause and corrective action. SPC charts are commonly used to monitor lithography processes for control.
Fault Detection & Classification:
When the monitoring method determines the lithography 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 lithography process control conditions and typically much finer detail than monitoring.
If the root cause analysis points to the lithography processing control tool settings, the lithography processing control tool will be recalibrated and the process brought back into monitoring control. Calibration should be traceable so the original process is not lost.
Getting the lithography 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 process regime to truly understand what is happening. Process capability must be enhanced to keep pace with Moore’s Law.