Low Temperature Poly-Si Sputtering Deposition Through Metal-induced Crystallization and its Application
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0910-A21-05
Low Temperature Poly-Si Sputtering Deposition Through Metal-induced Crystallization and its Application Hsiu-Wu Guo1, Chen-Luen Shih2, Joe Ketterl3, and Scott Dunham1 1 Electrical Engineering, University of Washington, Seattle, WA 98195 2 Materials Science and Engineering, University of Washington, Seattle, WA 98195 3 MicroConnex, Snoqualmie, Washington, WA 98065
ABSTRACT Growth of Si thin films via metal-induced crystallization (MIC) has been demonstrated by several research groups. This process lowers the crystallization temperature compared to standard solid phase crystallization (SPC). Ni is the metal that is most often adopted for this purpose. In this work, a 20-50nm Ni layer was deposited by DC magnetron sputtering onto a 500nm SiO2 layer grown on silicon wafers, followed by Si deposition at 500°C without breaking vacuum. X-ray diffraction (XRD) results and cross-sectional transmission electron microscopy (XTEM) confirmed the formation of poly-Si in a columnar structure with grain sizes in the 100300nm range. XTEM and XPS show that nickel silicide was formed at the Si-Ni interface. We find that doping type and concentration do not have a significant impact on the grain structure. SIMS reveals no significant loss or redistribution in doping concentration during sputtering. INTRODUCTION The recent development of metal induced-crystallization (MIC) techniques represents a potential breakthrough in Si technology by enabling formation of polycrystalline silicon at relatively low temperatures. Liu et al. [1] found the crystallization temperature of a Si film dropped from 700 to 500°C upon introduction of an ultra thin (10nm) Pd film. This observation was later confirmed by Konno et al. [2] and Radnoczi et al. [3]. Hayzelden et al. [4] studied the enhancement of Si film crystallization by Ni implantation via formation of NiSi2 precipitates which served as nucleation sites for Si crystallization due to the close lattice match (0.4% mismatch: 5.408Å for NiSi2 versus 5.430Å for Si). Kim et al. [5] annealed a low pressure chemical vapor deposited (LPCVD) Si/Ni film at 500oC under hydrogen at 1atm to produce poly-Si. Guliants et al. [6, 7] have successfully demonstrated the growth of poly-Si films from Si sputtered on a Ni layer at 575°C. In this work, we used Ni as a prelayer for the MIC process. Ni and Si were deposited by DC magnetron sputtering without breaking vacuum. Films were characterized by an array of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), crosssectional transmission electron microscopy (XTEM), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). EXPERIMENTS Initial substrates consisted of 0.5µm thermal oxide on 4” (100) silicon wafers. A 20-50nm Ni layer was deposited at 80W with a 2” DC magnetron sputtering gun at room temperature. The base vapor pressure was 5x10-7 Torr with Ar working pressure at 1.5x10-3 Torr. After the temperature was ramped up to ~500°C over two hours, Si was deposited onto the Ni layer with
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