Detection of 30–40-nm Particles on Bulk-Silicon and SOI Wafers Using Deep UV Laser Scattering

As semiconductor devices continue to get smaller, and thus the size of yield-limiting particles decreases, a need has arisen for detecting smaller particles on silicon surfaces. The current minimum detectable diameter of wafer-surface particle-detection systems employing 488-nm wavelength Ar⁺ gas lasers widely used in semiconductor production lines is, under optimized conditions, 50-60 nm on bulk-silicon surfaces. The sensitivity for SOI wafers, however, is considerably lower than this level due not only to the additional optical reflections from Si/SiO₂/Si interfaces within the SOI stack but also to the undesirable light scattering at the rough interfaces. The challenges in meeting the requirement to detect smaller particles specified in the ITRS will be presented. Using a 266-nm solid-state laser, we have developed for semiconductor manufacturing a high sensitivity system capable of detecting particles as small as 30 and 40 nm on unpatterned bulk-silicon wafers and SOI wafers, respectively. Our technique of single-wafer spin cleaning with repetitive use of ozonated water and dilute HF cleaning of silicon wafers can reduce surface microroughness, thus reducing background noise in this system, and providing higher particle-detection sensitivity than conventional RCA cleaning. Defect classification using this system integrated with a review scanning electron microscope will also be discussed