New Technique to Determine Gettering Efficiency of Heavy Metals and Its Application to Carbon-Ion-Implanted Si Epitaxial Wafers

Using a newly developed method to evaluate the gettering efficiency of Si wafers, we found that C-ion implantation prior to epitaxial growth greatly improves the gettering efficiency of heavy metals in epitaxial Si wafers. The gettering efficiency was evaluated through direct observation by total X-ray reflection fluorescence (TXRF) by counting the number of heavy metal atoms that diffused from the back to the front surface of wafers. Heavy metals were deposited on the backside surface of Si wafers from metal-dissolved aqua solution. Two-step annealing was carried out after the deposition. The first step caused metal diffusion and the second produced precipitation from the front surface of the wafers. The effectiveness of the method was confirmed by comparing the results obtained from as-received and intrinsic (or internal) gettering (IG)-processed Czochralski-grown Si wafers. The method was applied to C-ion-implanted epitaxial Si wafers to confirm the improvement in gettering efficiency in accordance with the implanted C dose. The effectiveness of the C-ion implantation was also confirmed by evaluating the electrical characteristics of the oxide grown on the Si wafers.