The transfer of metallic contamination via contact between solid objects

The transfer of metallic contamination via solid contact is an almost non documented topic in the literature when compared to the spread through liquids which is has been intensively investigated for cleaning studies.This paper presents the transfer mechanisms of metallic aggregates from substrate to substrate though contact with tools used during wafer processing. In addition we propose models which agree with the experimental observations. The influence of several parameters on the transfer coefficients has been investigated, including the type of contamination (deposited films, particles…), the size or shape of the particle, the composition of the particle (metallic or dielectric), the substrate and the roughness and flatness of the plates used to hold the wafers during processing as well as the substrate surface composition (bare Si, oxidized…).The transfer of metals via the contact between solid objects only occurs from particular mechanisms. Not considering electrical forces, the first order parameter on the transfer is the particle size. Global transfer by contact occurs mainly in the 0.5–5 μm range and can be as high as 10%. For the second order, the parameters mentioned previously can affect the transfer of the particles, for example, an increase of the particle roughness induces an increase of the separation distance between particle and substrate which consequently decreases the Van der Waals interactions.