Noncontact acoustic wave metrology of SOI substrates

Summary form only given. Accurate counting and reduction of silicon defects in SIMOX substrates has been an intense focus of materials research since the initiation of the technology. Recently, a photoacoustic method, impulsive stimulated thermal scattering (ISTS), has been developed for noncontact evaluation of thin film properties (Rogers and Nelson, J. Appl. Phys. vol. 75, p. 1534, 1994). The method involves crossed laser pulses which are used to generate acoustic waves that propagate within the plane of the film. A CW probe beam is used to monitor the acoustic waves, providing accurate measurement of acoustic frequencies and damping rates. Significantly for SOI applications, delamination of films from substrates (such as HF undercut etch pits or possibly lattice disruption resulting from an unetched dislocation) may be detected. In this research, unetched and etched pairs of SIMOX substrates within the same lot, annealed and unannealed substrates within the same lot, and etched/unetched substrate pairs from a dose matrix were examined by the ISTS method and analyzed. Bare Si (annealed and unannealed) substrates were evaluated as a baseline.