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ProM Approach

A. Does it pose a safety risk?
  • Physical/Chemical hazards
  • Supporting documentation: MSDS, application notes
B. Material properties – some examples:
  • What is the composition?
  • Mechanical properties?
  • What is the oxidation state?
  • How much of it is there?
C. Technology/contamination risks – some examples:
  • Is it a deep-level trap?
  • Is it a fast diffuser (Gold, copper, zinc)?
  • Does it form stable (non-diffusing) silicides?


A. Mechanisms of contamination transfer (during process and in subsequent steps.).
  • Liquid. Contamination can be transferred through a shared chemical bath or shared labware.
  • Mechanical.  Contamination can be transferred through contact with shared tools, such as tweezers, automatic wafer handlers on equipment, or an equipment chuck.
  • Vapor phase.  Contamination can be transferred via redeposition from equipment chamber walls, resputter from equipment cathode.  High temperatures/low pressures can cause materials with high vapor pressure to outgas, distributing the contaminant in the vapor phase.  High temperaures also facilitates diffusion of contaminant that may be present on the surface into the substrate.  Ion bombardment in plasmas might also serve as a transfer mechanism.

B.  Quantity.  The amount of contaminant present and how often it will be processed at a station are important considerations.  For a given material, a very small amount processed infrequently will generally pose much less risk than a large amount processed frequently.

C.  Type.  The nature of the contaminant may pose different risks for different technologies.  For example, gold is a lifetime killer for electronic devices but is the most common biocompatible electrode materials in bioanalytical devices.


After examination of the material, equipment flow, and transfer risks, define the controls to manage these risks.  Examples:

  • Dedicated equipment.  Fully or part-time.
  • Equipment set up.  Precleans, pre-coat with diffusion barrier, hardware changeout.
  • Sample preparation. sample cleans pre-furnace, Decontamination procedures, deposition of diffusion barrier film/capping layer, carrier wafer


Last modified: 27 Oct 2020