Raman scattering characterization of the microscopic structure of semi-insulating polycrystalline Si thin films

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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.