1. A method for reducing errors in locating particles on a semiconductor wafer, the method comprising the steps of: (a) scanning a semiconductor wafer in a scanning device to produce a first set of coordinate data values pertaining to the positions and sizes of contaminant particles on the wafer; (b) scanning the wafer a second time, to produce a second set of coordinate data values pertaining to the particles on the wafer; (c) transforming at least one of the first and second sets of coordinate data values, to produce two consistent sets of coordinate data values based on a common coordinate system, whereby the first and second sets of coordinate data values will not, in general, be identical because of physical uncertainties associated with the scanning steps; (d) averaging coordinate data values, from the two consistent sets, pertaining to identical particles, to obtain a more accurate estimate of the positions of the particles on the wafer; (e) selecting at least two reference particles that are relatively recognizable because of their size and shape; (f) moving the semiconductor wafer to a high-magnification imaging device; (g) using the more accurate estimate of the positions of the reference particles, obtained in step (d), to facilitate location of the reference particles in the high-magnification imaging device.