Wafer Inspection System: Calibration and Measurement
Wafer surface scanners are widely used in semiconductor industries to detect particle contamination on wafers. The performance characteristics of a PMS SAS-3600 wafer surface scanner have been evaluated using ideal polystyrene latex (PSL). It was also used to measure irregularly shaped silicon particles. Three sizes of PSL spheres (0.199μm, 0.3μm, and 0.426μm) were used to study the sizing accuracy and counting efficiency of this wafer scanner. The results show that this scanner sizes 0.199μm and 0.3μm PSL reasonably accurate. But it cannot size 0.426μm PSL very well. The background noise lever was so high that this scanner could not measure particles near its nominal lower detection limit: 0.1μm. It over-counted Si particles by 28%. An electrostatic enhanced wafer deposition chamber was used to prepare the test wafers. Both the theoretical calculations and experimental results show that electrostatic force increases the deposition velocity by 2 orders of magnitudes for particles smaller than 1μm. The sedimentation is the dominant mechanism for particles larger than 1μm.
Experimental study of particle deposition on semiconductor wafers
A sensitive method for detecting particle deposition on semiconductor wafers has been developed. The method consisted of generating a monodisperse fluorescent aerosol, depositing the known-size monodisperse aerosol on a wafer in a laminar flow chamber, and analyzing the deposited particles using a fluorometric technique. For aerosol particles in the size range of 0.1–1.0 μm, the mobility classification-inertial impaction technique developed by Romay-Novas and Pui (1988) was used to generate the monodisperse test aerosols. Above a particle diameter of 1.0 μm, monodisperse uranine-tagged oleic acid aerosols were generated by a vibrating-orifice generator. The test wafer was a 3.8-cm diameter silicon wafer placed horizontally in a vertical laminar flow chamber which was maintained at a free stream velocity of 20 cm/s. A condensation nucleus counter and an optical particle counter were used to obtain the particle concentration profile in the test cross section and to monitor the stability of aerosol concentra...
Particle deposition on wafers: A comparison between two modeling approaches
Abstract The rate of particle deposition on wafers and the particle concentration profile above a wafer surface are calculated and compared using two different model approaches. Both methods deal with the steady-state, two-dimensional flow, temperature and concentration profiles above a flat surface. In the first approach, these governing equations are solved numerically by finite difference techniques. In the second approach, boundary layer theory is utilized to approximate the flow and temperature profiles, a perturbation technique is used to approximate the inertial effects, and the concentration profile is solved numerically via finite difference methods. Comparisons are made for calculations representing both one and two-dimensional geometries for stagnation flow to a wafer. Mechanisms that were considered to effect particle deposition included convection, diffusion, sedimentation, electrical forces and thermophoresis. In the one-dimensional cases, comparisons between model approaches was quite good. In the two dimensional cases, comparisons were acceptable but not as good as those for the one-dimensional cases. Of particular interest was the prediction of particle deposition for the situation in which both electrical forces and thermophoretic forces influenced the particle. It was seen that the “beneficial” effects of thermophoresis (i.e., the formation of a particle-free zone for certain ranges of particle size) were completely negated by quite modest attractive electrical forces.