Generation and Deposition of Nanoscale Particles for Reference Wafers

In the semiconductor industry, standard reference wafers are needed for calibrating wafer surface scanners. Scanners are currently available for detecting particles down to a lower size limit of approximately 100 nm (0.1 um). Advanced wafer scanners capable of detecting particles to 60 nm will be needed for future generation of devices such as the 1 Gbit DRAMs (dynamic random access memory) expected by the year 2002. This proposal is concerned with developing advanced concepts for generating and depositing PSL spheres to 30 nm. In the Phase I proposal, the lower size limit of the current PSL generation methods will first be established experimentally. Various atomizer concepts will then be explored to identify those capable of producing fine droplets with a maximum droplet diameters in the 0.1-0.5 um range in order to reduce the residue particles to the < 10 nm diameter range. The residue particles are formed when empty water droplets containing dissolved impurities are evaporated. Since they are generated and deposited simultaneously with the PSL spheres, they must be of a considerably smaller size than the PSL in order to avoid interfering with the PSL in producing light scattering signals for wafer scanner calibration.