Depth profile metrology using grazing incidence x-ray fluorescence

Abstract

For small angles that are near critical angle, a primary incident X-ray beam has excellent depth resolution. A series of X-ray fluorescence measurements are performed at varying small angles and analyzed for depth profiling of elements within a substrate. One highly useful application of the X-ray fluorescence measurements is depth profiling of a dopant used in semiconductor manufacturing such as arsenic, phosphorus, and boron. In one example, angles are be varied from 0.01° to 0.20° and measurements made to profile arsenic distribution within a semiconductor wafer. In one embodiment, measurements are acquired using a total reflection X-ray fluorescence (TXRF) type system for both known and unknown profile distribution samples. The fluorescence measurements are denominated in counts/second terms and formed as ratios comparing the known and unknown sample results. The count ratios are compared to ratios of known to unknown samples that are acquired using a control analytical measurement technique. In one example the control technique is secondary ion mass spectroscopy (SIMS) so that the count ratios from the TXRF-type measurements are compared to ratios of integrals of SIMS profiles. In another example, the TXRF-type measurement ratios are compared to simulation profiles of known samples. Integrals of the SIMS profile that vary as a function of depth into the substrate correspond to the grazing incidence angles of the TXRF-like measurement and respective count rates.