Abstract Number: 393 Working Group: Instrumentation and Methods
Abstract National Institute of Advanced Industrial Science and Technology (AIST), Japan developed a technique to make a reference material for calibrating the counting efficiencies wafer surface scanner (WSS). It is a silicon-wafers which has known number of polystyrene latex (PSL) spheres on its surface. The number of PSL particles on the wafer can be controlled, and the uncertainty of the particle number is well characterized. In our approach, aerosolized PSL particles are deposited onto a wafer by inertial impaction. In order to deposit PSL particles in submicrometer-range and below, we enlarge the particle size up to micrometer range by condensing working fluid vapor on the particle sphere. We currently use water-based growth tube (GT) developed by Aerosol Dynamics Inc. The particle number concentration fed into the GT is measured by an optical particle counter that is placed in parallel with the GT. In order to specify the particle number on a standard wafer the efficiency of particle deposition and its uncertainty need to be evaluated. The actual particle number on the wafer was determined by taking scanning electron microscope images over the deposited area and by subsequently counting the PSL particles in the images. Then the actual particle number was divided by the total particle number fed to the GT to calculate deposition efficiencies. The average value and standard uncertainty of the deposition efficiency were 0.922 and 0.068, respectively. Examples of particle-number-standard wafer are presented. The standard wafers were made using PSL spheres whose diameter was 0.8 um. The particle number were varied from 1000 to 4000, and the wafer was used to evaluate the counting efficiencies of a WSS.