Browse Prior Art Database

Improved Witness Plate Collection

IP.com Disclosure Number: IPCOM000061168D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Williams, RR: AUTHOR

Abstract

The contribution of electrostatic attraction to particle fallout in a semiconductor clean room is often overlooked as being a significant factor. Typical test surfaces, or witness plates, use blank silicon wafers as the collection medium. Semiconductor wafers are not highly conductive and consequently are susceptible to high electrostatic charges on the surface. Once a wafer has developed a surface charge, its attraction for small particles that also carry electrostatic charges is enhanced.

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Improved Witness Plate Collection

The contribution of electrostatic attraction to particle fallout in a semiconductor clean room is often overlooked as being a significant factor. Typical test surfaces, or witness plates, use blank silicon wafers as the collection medium. Semiconductor wafers are not highly conductive and consequently are susceptible to high electrostatic charges on the surface. Once a wafer has developed a surface charge, its attraction for small particles that also carry electrostatic charges is enhanced.

If the surface of the wafer is conductive, this charge can be discharged quickly once the surface becomes grounded. A silicon wafer can be made into a highly conductive witness plate by implanting a large concentration of a dopant, such as arsenic, into the wafer. Alternatively, the wafer can have a conductive metallic surface deposited on it using any of the conventional deposition methods. The wafer surface must remain highly reflective so that measurements can still be obtained using typical light-scattering wafer surface inspection systems.

Once the particle fallout without electrostatic attraction is measured, and the contribution of electrostatic attraction to particle fallout is determined, a better correla between airborne and settled particulate contamination levels can be obtained.

Anonymous.

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