Nonlinear optical characterization of silicon wafers: in-situ detection of stacking faults and external stress

Femtosecond second harmonic generation from the surface of as-grown 6-inch silicon wafers is used as a tool for in-situ characterization. Czochralski-grown crystal are not homogeneous over their cross section. A central zone of vacancy-rich and as outer zone of interstitial-rich crystal are separated by a ring of stacking faults. Gate oxide layers grown on such substrate show different quality in their dielectric properties, making it desirable to locate these zones before producing different devices. Exploiting the symmetry sensitivity of surface SHG, we use a particular two-pulse arrangement, similar to a conventional pump-probe setup, to obtain a non-destructive, in-situ information about the location of the three different crystal zones. Further, we demonstrate the potential of surface SHG to monitor external stress, exerted on the sample for instance by improper mounting, providing a tool for on-line optimization of process parameters. Finally, the applicability of the technique for on-line analysis and control during the growth of different types of gate dielectrics is discussed.