tailieunhanh - Crystalline Silicon Properties and Uses Part 6

Tham khảo tài liệu 'crystalline silicon properties and uses part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 114 Crystalline Silicon - Properties and Uses Wavelength nm Fig. 10. Ellipsometric spectra of wafers G3 in the infrared range at 75 . Fig. 11. Ellipsometric spectra of wafers G4 in the infrared range at 75 . Infrared Spectroscopic Ellipsometry for Ion-Implanted Silicon Wafers 115 Fig. 12. Ellipsometric spectra of wafers G5 in the infrared range at 75 . For comparison the spectra of a non-annealed reference wafer were shown by the solid lines. In opposition to the results obtained in the visible spectral range as presented in section 3 the IRSE is not a sensitive method for implanted wafers without thermal annealing. The value of ellipsometric parameter T ranged only 2-4 as shown in Fig. 8 Fig. 10 and Fig. 12. The results indicated that ion implantation alone introduced no significant change to the optical properties of damaged crystal structure in the infrared range. However once the implanted wafers were thermally annealed at high temperature the IRSE could effectively distinguish the wafers with different implantation doses especially for wafers implanted with a high dose as presented in Fig. 9. On the other hand the IRSE could not clearly distinguish the wafers implanted with different energies as shown in Fig. 11. In the following the infrared ellipsometric spectra for implanted and annealed wafers were analyzed in details. In the infrared range different absorption processes exist in a silicon wafer such as free carrier absorption impurity absorption and Reststrahlen absorption as shown in Fig. 13. Fig. 13. Absorption coefficient plotted as a function of the photon energy in a silicon wafer illustrating various possible absorption processes 116 Crystalline Silicon - Properties and Uses At room temperature for silicon the impurity absorption is too weak to be observed. The influence of the Reststrahlen absorption process on the optical properties of implanted silicon wafer is at least two orders of magnitude lower than the influence of the free carrier .