Abstract

Detection and identification of submicrometer contaminant particles in processing liquids is of critical importance in semiconductor manufacturing. Typical particle detection instruments sense scattered intensity and offer no means to determine particle composition. By detecting both the magnitude and phase of the forward scattered light from a particle, refractive index information can be obtained in addition to size. The size is also computed more accurately since the refractive index is determined, rather than assumed. This measurement is analogous to the use of ellipsometry to determine the thickness and refractive index of thin films. A laser inter­ferometer using Nomarski optics is used to detect the phase shift and extinction in one beam relative to the other as a particle traverses both beams. These measurements are corrected for particle trajectory (off-axis and defocus) by judicious alignment of the beam shear direction and are then used to compute the forward scattered phase and magnitude from the particle. This instrument has been used to accurately size and bin particles into four composition classes: low dielectrics, medium dielectrics, metals, and bubbles.

© 1992 Optical Society of America