Direct Laser Doping of Poly-Silicon Thin Films Via Laser Chemical Processing

Laser chemical processing (LCP) is an attractive doping technique for thin films due to its process simplicity, high achievable doping concentrations, and relatively shallow doping depths. During LCP processing, an infinite supply of dopants is available from the pressurized doping medium. In this paper, LCP is employed for n-type doping of poly-silicon thin films on glass. We achieved a peak doping concentration of 6 × 10¹⁸ to 1 × 10¹⁹ cm^-3 and a junction depth up to 350 nm, as determined by electrochemical capacitance-voltage profiling and secondary ion mass spectrometry. We evaluate the structural quality of the LCP-doped layers with cross-sectional transmission electron microscopy (XTEM), as well as ultraviolet reflectance measurements. The LCP-doped regions are of suitable material quality for device fabrication. The resulting sheet resistance and doping levels are promising for a back surface field for poly-silicon thin-film solar cells on glass (e.g., an n⁺/ n^-/ p⁺/glass layer structure in superstrate configuration).