Monitoring of Heavy Metal Contamination during Chemical Cleaning with Surface Photovoltage

Abstract

This paper presents surface photovoltage (SPV) applications for the monitoring of chemical cleaning and purity of chemicals through mapping of minority carrier diffusion length, Fe concentration in the bulk, and surface contamination (surface charge and surface recombination). The noncontact, wafer‐scale character of the new SPV approach and refined apparatus make this technique uniquely suited for heavy metal monitoring. This method was used to monitor Cu contamination in BHF by measurement of its effect on surface recombination and Fe contamination through it effect on bulk recombination after the rapid thermal annealing step used to drive Fe deposited at the surface during cleaning into the bulk. Fe surface contamination was measured down to the level while the detection limit of this approach is. Different Fe contamination levels (1 to 13 ppb) present in different grades of were easily distinguished. This procedure should allow one to monitor Fe contamination in at the 1 ppt level. Cleanliness 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 the cleaning station).