There are three major types of contamination risks commonly encountered at SNF. For an excellent overview about contamination in an IC lab, click <here> for Prof. Krishna Saraswat's excellent presentation [pdf file format].) In brief:

1. Heavy metal and alkali metal ions. Sodium, potassium, gold, and other non-standard metals and alkaline metals are highly mobile ions in silicon, and thus pose serious device issues with respect to breakdown, oxide quality, carrier mobility, and threshold shifts. Extremely minute quantities will affect device performance. Please control contact of your wafers with any potentially contaminating sources (equipment, tweezers, skin) by following the Materials and General lab policies at SNF.

2. Photoresist. Photoresist poses some extreme contamination risks, particularly for high temperature processing tools such as furnaces. Resist is primarily organic materials, which will turn to ash and carbon. Even after extensive hard-baking, resist will still contain significant levels of solvent and other volatiles, which can outgas and thus contaminate some high vacuum systems. Residual photoresist, from incomplete cleaning, also poses contamination risks. Recommended clean procedures will vary, depending on the processing the wafer has undergone (for example, high energy processes such as implantation or plasma etching, will harden photoresist). Please be scrupulously careful about wafer cleaning and ensuring the process flow does not expose sensitive equipment to photoresist.

3. Particulate. Particles introduce not only chemical contamination risks, but also physically interfere with pattern definition at any point in the process (eg., micromasking, incomplete etch, bad film deposition.) Please be conscientious in your personal cleanroom habits by following the SNF policies.