Defect detection and counting have been used to qualify silicon wafers for use in device production for several years. Defect sizing is attempted by comparing scatter signals, used for detection, to signals produced from spherical polystyrene latex spheres of known diameter. Real particles are neither spherical nor made of plastic, and scatter differently. This paper addresses the issue of spherical particle material identification through the measurement of scatter signals into several directions. The basic idea is that the average diameter and material constants comprising the complex index amount to three unknowns. The question is whether they can be estimated from three independent measurements. The results presented here are quite positive. The issue of particle shape is left for another paper.
Laser particle scanners are traditionally calibrated with polystyrene latex spheres, and these spheres are used to create a sizing scale in light scatter equivalents. Particle scatter signals can vary strongly with particle materials, thus concealing the true particle size. As previously reported, particle material identification in a laser scanner will allow true sizing of spherical particles through the application of accurate scatter models. This paper reports extending that work to non-spherical particles through the use of modeling scatter from ellipsoidal particles.
This paper briefly reviews the use of a verified model to investigate light scatter metrology to detect the presence of defects in semiconductor circuit vias. Three types of defects are examined. Although defects can be detected, there are practical problems associated with separating defects from acceptable changes in dielectric film thickness.
The paper reviews techniques to calculate differential scattering cross-section of sub-micron surface bound particles from scatter measurement. It discusses both the multiple and single particle measurement approaches to obtaining scatter data and the associated problems with each method. Measured results are compared to a scatter model based on the discrete source method. For spherical particles the model has very close agreement with the measured scatter. For non-spherical particles the agreement is close only for particle diameters smaller than about one fifth wavelength.
Computer simulations of scatter from various surface features are very important for addressing the design issues associated with producing scanners to meet evolving industry needs. This paper deals with mathematical modeling of light scattering by small pits of arbitrary shape on the surface of silicon wafers. The code based on method of moments applied to the volume integral equation, has been developed, and the numerically modeled differential scattering cross- section is presented for various types of pits. Pit shape and orientation are investigated.
The paper reviews the process for comparing PSD's generated by profile measurements and scatter measurements. Rayleigh scatter as a noise source is reviewed and a new polarization based measurement is presented for discrimination between roughness scatter and particulate scatter. AFM results are compared for both a molybdenum mirror and a silicon wafer. The mirror compares well but 2D detrending technique used impacts the results for the wafer.
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