Abstract
Silicon wafers are usually polished mechanochemically using a cloth polisher. Their surfaces are not damaged, but their flatness deteriorates with polishing time. To investigate the cause of flatness degradation, the surface shapes generated in silicon wafers with plane, cone-shaped and saucer-shaped polishers were simulated by measuring polisher deformation characteristics and silicon wafer polishing rate. A difference between the simulated and experimental values was seen, and this difference, or flatness degradation, resulted from the fact that: (1) A porous polyurethane cloth polisher has viscoelastic characteristics. (2) The work is inclined by polishing force, which consists of frictional force and squeezing force caused by the work edge. (3) Viscous deformation due to work inclination becomes larger in the center region, as compared with the inner and outer region, of a polisher. (4) As a result, a non-linear average pressure distribution occurs over the work, where the pressure is higher on the outer periphery of the work. A very flat surface could be obtained when the work inclination decreased through making the work plate support point low or when a very slightly inclined cone-shaped polisher was used.
