L. Jastrzebski et al., MONITORING OF HEAVY-METAL CONTAMINATION DURING CHEMICAL CLEANING WITHSURFACE PHOTOVOLTAGE, Journal of the Electrochemical Society, 140(4), 1993, pp. 1152-1159
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).