Formation of Epitaxial Heavy-doped Silicon Films by PECVD Method

Abstract

Plasma-enhanced CVD (PECVD) epitaxy at 200 °C was used to deposit heavy doped n-type silicon films. Post-annealing by rapid thermal processing was applied to improve the properties of the epitaxial layer. By analyzing the Raman spectra and the imaginary part of the dielectric constant spectra of the samples, it was found that high-quality heavy-doped epitaxial n-type silicon layer can be obtained by optimizing the parameters of the PECVD depositing process. Reducing the electrodes distance of the PECVD had a great effect on the crystallzation of the epitaxialed n-type silicon films. Sillicon films with high-crystallization were obtained with the electrodes distance of 18 mm. Post-annealing process can improve the crystallization and reduce the resistance of the epitaxial films. In our research, it was found that the sheet resistance (R _□) of the post-annealed films with thickness of about 50 nm has a simple relationship with R _PH3/SiH4 (ratio of the flow rate of PH₃ and SiH₄) of the PECVD processing: R _□=-184-125 lg(RPH₃/SiH₄). In the end, high-quality epitaxial n-type silicon film was obtained with R _□ of 15 Ω/□ and thickness of ~50 nm.

Keywords

heavy-doped n-type silicon / epitaxial deposition / PECVD

References

[1] Shieh M, Lee C, Yew T. The Kinetics of Very Low Temperature (about 300 °C) Silicon Epitaxial Growth by Confined Plasma Enhanced Chemical Vapor Deposition[J]. J. Electrochem. Soc., 1994, 141: 3584-3587.

[2] Fujiwara H, Kondo M. Interface Structure in a-Si:H/c-Si Heterojunction Solar Cells Characterized by Optical Diagnosis Technique[ C]. Proceedings of the IEEE 4th World Conference on Photovoltaic Energy Conversion, 2006 1443-1448.

[3] Fujiwara H, Kondo M. Impact of Epitaxial Growth at the Heterointerface of a-Si:H/c-Si Solar Cells[J]. Appl. Phys. Lett., 2007, 90: 013.

[4] Vázquez C, Alonso J, Vázquez M A, et al. Efficiency of Commercial Cz-Si Solar Cell with a Shallow Emitter[J]. Mater. Sci. Eng. B, 2010, 172: 43-49.

[5] Mai Y, Klein S, Geng X, et al. Differences in the Structure Composition of Microcrystalline Silicon Solar Cells Deposited by HWCVD and PECVD: Influence on Open Circuit Voltage[J]. Thin Solid Films, 2006, 501: 272-275.

[6] Aspnes D E, Studna A A, Kinsbron E. Dielectric Properties of Heavily Doped Crystalline and Amorphous Silicon from 1.5 to 6.0 eV[J]. Phys. Rev. B, 1984, 29: 768-779.

[7] Levi D, Iwaniczko E, Page M, et al. Silicon Heterojunction Solar Cell Characterization and Optimization Using In Situ and Ex Situ Spectroscopic Ellipsometry[C]. Proceedings of the IEEE 4th World Conference on Photovoltaic Energy Conversion, 2006 1740-1743.

[8] Wolf I D. Micro-raman Spectroscopy to Study Local Mechanical Stress in Silicon Integrated Circuit[J]. Semicond. Sci. Technol., 1996, 11: 139-154.