Raman Scattering Characterization of the Microscopic Structure of Semi-Insulating Polycrystalline Si Thin Films

Raman scattering experiments were carried out to study the microscopic structure of semi-insulating polycrystalline Si (SIPOS) thin films prepared by low-pressure chemical vapor deposition. The samples contain 18, 25, and 30 at. % of oxygen and after growth they were annealed at 900 and 1000°C for 30 min. The Raman spectra show in the vibrational region of the optical frequencies of Si two bands, which arise from scattering in crystalline grains and disordered forms of Si. The behavior of these bands as a function of oxygen content and annealing temperatures was established in detail. The crystallinelike band peaks below the transverse optical frequency of Si at zone center and is broadened with respect to the Raman line of a Si wafer. From the broadenings, estimates of grain sizes are obtained. The band due to the disordered form of Si appears at frequencies above those of an extended network of amorphous Si. A model for the SIPOS microscopic structure is proposed in which the disordered Si corresponds to the surface layers of the crystalline grains. The latter are embedded in an amorphous SiO2 matrix. Quantitative estimates of the contributions of the ordered and disordered phases of Si to the SIPOS structure are attempted. The Raman results provide additional experimental evidence that the crystallization temperature of Si increases under the presence of oxygen

Strains in Si-onSiO\u3csub\u3e2\u3c/sub\u3e Structures Formed By Oxygen Implantation: Raman Scattering Characterization

Low-temperature Raman scattering measurements were carried out to characterize Si-on-SiO2 structures formed by oxygen implantation and subsequent furnace or lamp annealing. The experiments were conducted with 413.1 nm laser light to probe only the thin Si layers at the top of the structures. The Raman spectra of the furnace-annealed samples are red shifted and broadened when compared with a virgin Si surface. The shifts and broadenings decrease with increasing annealing temperatures but they are still present in samples annealed above 1250°C for 3 h. No shifts or broadenings affect the Raman peaks of the layers, which were lamp annealed at 1405°C for half an hour. The red shifts indicate that the recrystallized Si layers are under tensile strains, whose origin is attributed to oxide precipitates. Quantitative estimates of the strains and associated stresses are obtained from the measured Raman shifts