Microphysical investigations on mechanical structures realized in p + silicon

Secondary Ion Mass Spectroscopy (SIMS) and Microprobe Raman Spectroscopy (MRS) together with optical evaluation of cantilever bending were used for the characterization of micromechanical structures realized in p⁺ silicon. Boron profiles in different steps of the fabrication process were accurately traced by SIMS. SIMS is, however, a destructive method. MRS is a noncontact, nondestructive method with high spatial resolution. It was used to evaluate boron concentration in the near surface region, together with lattice disorder and stresses. Mechanical behavior of p⁺ microstructures was found to be strongly related to the history of boron concentration profile. Parameters of Raman spectra are in direct relation with the level of boron in the near surface region. Such measurements can be used for p⁺ layer monitoring during the fabrication process and for the prediction of mechanical behavior in the final structure. A new explanation is suggested for the observed compressive behavior of oxidized/annealed p⁺ microstructures. It is based on the hysteresis introduced by the plastic deformations in the strain-concentration characteristic of the diffused layer. Detailed investigations in better technological environment could bring an accurate quantitative description of the phenomena with useful connections between Raman frequencies and elastic constants of the p⁺ layer