Measurement of Silicon Particles by Laser Surface Scanning and Angle‐Resolved Light Scattering

Distinguishing false counts caused by surface microroughness and haze when measuring particles below 0.1 μm has become a significant concern for ultralarge scale integrated (ULSI) product yield. Initial results are presented from an industry-wide, cross-functional, SEMATECH task force exploring this issue by investigating both measurement capability and alternative detector strategies for laser surface scanners. Polystyrene latex (PSL) spheres and real-world particles deposited under controlled conditions on 150 mm polished silicon wafers are used. Particle counting measurements taken at several facilities using the same model of laser surface scanner and the same instrument parameter settings are compared. Silicon particles are consistently sized incorrectly when the laser surface scanner is calibrated using standardized procedures utilizing PSL spheres. Measurements from similarly prepared samples using angle-resolved scattering (ARS) to obtain scattering cross section as a function of angle are favorably compared to a numerical light scattering model. Modeling allows the comparison of data from instruments which measure ARS from individual particles as well as those which measure ARS from multiple identical particles. The improved signal-to-noise ratio of the multiple particle technique allows study of particle scattering at sizes below typical commercial equipment detection limits. A novel haze surface is described which can be used to verify the modeling of both research and commercial light scattering instruments.