Plasma chambers need preventive maintenance (PM) at regular intervals due to:
Installing refurbished or new chamber parts result in process changes.

Wafer number
The number of wafers needed for conditioning is mostly determined empirically, and often too many wafers and time are used for the process. The tool is not able to detect the conditioning status. however, the collision rate is very sensitive to the chemistry at the chamber wall and can be used as a status indicator when conditioning is complete.
Wafer type
Complex layer systems and processes require a series of conditioning wafers such as:
  • Blank
  • Resist
  • Oxide
  • Structured conditioning wafers
Using incorrect wafer types (e.g., blamk Silicon) can reserve the conditioning process. These de-conditioning effects can not be detected by tool parameters. It requires a chemical indicator such as the electron collision rate. 

Insufficient conditioning can lead to process instabilities and yield loss.
Using the electron collision rate and electron density optimizes the conditioning procedure, and increases tool uptime and OEE (Overall Equipment Effectiveness). Once the plasma parameters are stable, chamber conditioning is complete. This enables dynamic conditioning. 
The electron collision rate and electron density can also used to determine the sucess of other maintenance procedures.