Electrical and Structural Characterization of Boron Implanted Silicon Following Laser Thermal Processing
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Electrical and Structural Characterization of Boron Implanted Silicon Following Laser Thermal Processing K. A. Gable1¤, K. S. Jones1, M. E. Law2, L. S. Robertson3, S. Talwar4 1 Materials Science and Engineering, University of Florida, Gainesville, FL 32611 2 Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611 3 Texas Instruments, Dallas, TX 75265 4 Verdant Technologies, San Jose, CA 95134 ¤
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ABSTRACT One alternative to conventional rapid thermal annealing (RTA) of implants for ultra-shallow junction formation is that of laser annealing. Laser thermal processing (LTP) incorporates an excimer pulsed laser capable of melting the near surface region of the silicon (Si) substrate. The melt depth is dependent upon the energy density supplied by the irradiation source and the melting temperature of the substrate surface. A process window associated with this technique is able to produce similar junction depths over a range of energy densities due to the melting temperature depression established with pre-amorphization of the substrate surface prior to dopant incorporation. The process window of germanium (Ge) preamorphized, boron (B) doped Si was investigated. 200 mm (100) n-type Si wafers were preamorphized via 18 keV Ge+ implantation to 1x1015/cm2 and subsequently implanted with 1 keV B+ to doses of 1x1015/cm2, 3x1015/cm2, 6x1015/cm2, and 9x1015/cm2. The wafers were laser annealed from 0.50 J/cm2 to 0.88 J/cm2 using a 308 nm XeCl excimer irradiation source. Transmission electron microscopy (TEM) was used to determine the process window for each implant condition, and correlations between process window translation and impurity concentration were made. Four-point probe quantified dopant activation and subsequent deactivation upon post-LTP furnace annealing. INTRODUCTION Silicon (Si) technology is approaching a transition period for which novel front end processing techniques must be developed and implicitly understood in order to maintain the aggressive scaling trend outlined by the International Technology Roadmap for Semiconductors (ITRS).1 Currently, ion implantation and rapid thermal annealing (RTA) are the methods by which dopants are introduced into the substrate and subsequently activated, respectively. While advances in RTA have extended its use, its isothermal nature introduces limits associated with the annealing parameters that cause anomalous diffusion2 and electrical saturation3 of the dopant during the thermal process. As a result, RTA is unable to produce junctions with the performance characteristics required for critical scale integration (CSI) and the need for investigating alternate annealing techniques becomes apparent. One potential alternative to conventional thermal annealing is that of laser annealing. Laser thermal processing (LTP) incorporates an excimer pulsed laser capable of melting the near surface region of the crystalline Si (c-Si) substrate.4 An issue with LTP is the fact that the melt depth displays a linear dependence with energy density,
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