MONITORING OF HEAVY-METAL CONTAMINATION DURING CHEMICAL CLEANING WITHSURFACE PHOTOVOLTAGE

This paper presents surface photovoltage (SPV) applications for the mo nitoring of chemical cleaning and purity of chemicals through mapping of minority carrier diffusion length, Fe concentration in the bulk, an d surface contamination (surface charge and surface recombination). Th e noncontact, wafer-scale character of the new SPV approach and refine d apparatus make this technique uniquely suited for heavy metal monito ring. This method was used to monitor Cu contamination in BHF by measu rement of its effect on surface recombination and Fe contamination thr ough it effect on bulk recombination after the rapid thermal annealing step used to drive Fe deposited at the surface during cleaning into t he bulk. Fe surface contamination was measured down to the 1 x 10(9) c m-2 level while the detection limit of this approach is 2 x 10(8) cm-2 . Different Fe contamination levels (1 to 13 ppb) present in differen t grades of H2O2 were easily distinguished. This procedure should allo w one to monitor Fe contamination in H2O2 at the 1 ppt level. Cleanlin ess of incoming chemicals is not always a limiting factor and often is not related to the cleanliness of chemicals at the point of use (in t he cleaning station).