SURFACE-ROUGHNESS OF SILICON-WAFERS ON DIFFERENT LATERAL LENGTH SCALES

We measured the surface roughness of three unpatterned Si wafers by fo ur different instruments: atomic force microscope, wafer inspection st ation (based on light scattering), Nomarski optical microscope, and in terferometric profiler. The root-mean-square surface roughness (R(rms) ) values vary between 1.2 angstrom as measured by an atomic force micr oscope over a 1 x 1 mum area to 19.4 angstrom as measured by an interf erometric profiler over a 1.32 mm path length. To explain the observat ion that samples showing high roughness values when measured with one technique but low when measured with another technique, we discuss the lateral (within the surface plane) characteristics of the different m ethods and show that the experimental results are not contradictory. W e suggest that a parameter describing the lateral properties of a surf ace roughness measurement technique should be included when reporting surface roughness data.