CONDITIONING: DRY CLEAN

• to back-etch films on the chamber wall caused by the deposition process, or byproducts and resist mask fragments.
  • Keep the film thickness as thin as possible to aviod flaking and particles!
  • Deposition chambers need frequent dry cleans due to the higher deposition rate.
  • Whereas a clean wafer is used for deposition chambers, newer etch chambers often apply a WAC (Waferless Auto Clean).

• to avoid the first wafer effect caused by
  • the chamber wall temperature (e.g. liner) below process level or
  • inappropriate surface layer at chamber wall through idle time or process mix.

Every dry clean increases the total process time and decreases the wafer throughput and tool productivity (OEE).
The optimization of a dry clean is not only a question of process stability but also MTBC.
When the dry clean is too short, process stability (first wafers) is affected and more wet cleans can be necessary!

REASON	DESCRIPTION
Dry clean in etch chamber	Typically, etch processes mostly are very complex because various materials are etched. Therefore, the chamber gets covered with a mix of several byproducts, plasma polymers, and parts of the mask sputtered during the process.
Example: Parameter drift after dry clean shown by the electron collision rate.
Dry clean at Novellus SPEED	Due to the use of insulating material for deposition chamber wall parts,the grounded electrode is smaller than the RF driven electrode. This means the energy of the ions going to the grounded chamber wall is higher than the ion energy at the RF driven electrode.Therefore the sputter rate in the back etch step at the grounded wall is high and leads to a removal of the films deposited during the deposition. Hence the deposition rate at the wall is much lower than at the wafer and the ceramic dome. At the Novellus Speed the bias voltage is usually positve (normal case = negative)