Hiding in Plain Sight


a preventive maintenance strategy to improve gas purity and reduce wafer defects

Often overlooked as a source of wafer contamination, a gas filter used beyond its useful lifetime can be the culprit. Contamination can be introduced from several areas:

  • Air
  • Equipment
  • Cleanroom personnel
  • Process water
  • Process chemicals
  • Process gases
Accurate identification of the contaminant source is required to best identify mitigation strategies that involve filtration. While installing a filter can reduce defectivity, this strategy alone will not protect a gas stream from contamination indefinitely.

The gas type and process conditions will determine the useful lifetime of the filter. Two case studies highlight the challenges and impact
varying lifetimes have on wafer contamination levels:

  • HMDS (hexamethyldisilane) used in photolithography
  • SiH4 (tetrahydride) and B2H6 (diborane) used in deposition

Filters are often chosen when equipment is first installed.  However, that equipment may be used for many different process nodes that can change filtration requirements. The filter chosen for one process node is often not the most efficient option for another node, and change-out during preventive maintenance activities is frequently overlooked. Incorporating gas filter lifetime validation into a preventive maintenance program contributes to reducing wafer contamination levels.