Comparison of sensitivity and precision of instruments used for monitoring low dose Si+ implant uniformity

A newly developed optical densitometer (Process Diagnostics, Inc. Model OMS 3000), a thermal wave (Therms Wave Model TP-400), an eddy current sheet resistance probe (Lehighton Electronics, Inc. Model 1310), and a four-point probe for GaAs wafers (Four Dimensions Model 880) were used to measure low dose Si⁺ ion implants. The four systems were evaluated for their ability to detect implant dose uniformity, their sensitivity to low doses, and their repeatability for multiple measurements on a single wafer, and on several wafers implanted with the same dose. The OMS 3000 probe was found to be highly sensitive (S=0.5-0.6) to low doses (Si⁺, 100 keV, 0.75-5E12 cm^-2 ). The Therma Wave probe was found to be relatively insensitive (S= 0.1-0.15) in the same low dose region (Si⁺, 100 keV, 2E12-4E12) and moderately sensitive (S=0.40) at higher doses (Si⁺ , 150 keV, 6.755E13-8.25E13). The Lehighton probe was found to be about four times more precise as the Four Dimensions probe. Providing precise information about low Si⁺ dose uniformity, all four techniques can be applied to yield improvement of GaAs devices made with ion implantation