Identification and sizing of particle defects in semiconductor-wafer processing

An experimental study of the sizing of submicron particles on semiconductor wafers is presented. The objective of the study was to determine the accur acy of a state-of-the-art optical wafer scanner, by comparing its size resp onse with that of two well established techniques, namely, differential mob ility analysis (DMA) and secondary electron microscopy (SEM). Test particle s used include polystyrene-latex spheres and SiO2, Si3N4, W, and Cu particl es of 64, 107, and 202 nm nominal (DMA) sizes. The scanner-indicated sizes using the oblique and normal operational modes were compared to the DMA siz es and to average sizes determined from the SEM images. Results show that t he scanner-indicated size is comparable to the SEM-indicated size. However, both the scanner size and SEM size exhibit large distributions for a given nominal (DMA) size. The discrepancies are due to a combination of factors such as the effects of particle shape and material, and the presence of lar ger, doubly charged particles among those analyzed. A comparison of the nor mal and oblique scanner operational mode results for the scanner further sh ow that the normal mode undersizes particles somewhat. These results collec tively indicate that accurate sizing of complex and unknown submicron sized particles on semiconductor wafers is not an easy task. A thorough understa nding of the scanner response to a variety of process particles is essentia l for the meaningful interpretation of scanning results. (C) 2001 American Vacuum Society.