Fabrication of p+/n Ultra Shallow Junctions (USJ) in silicon by excimer laser doping from spin-on glass sources
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Fabrication of p+/n Ultra Shallow Junctions (USJ) in silicon by excimer laser doping from spin-on glass sources. S. Coutanson1, E. Fogarassy1, J. Venturini2 1 CNRS/PHASE, BP 20 – 67037, Strasbourg Cedex 02, France 2 SOPRA-SA, 26, rue Pierre Joigneaux, 92270 Bois-Colombes, France e-mail : [email protected]
ABSTRACT In this work was investigated a simple laser doping method employing doped oxide glass films as dopant source (up to 2.1021 cm-3) which are deposited onto silicon by the spin coating technique. Both short (20 ns) and long (200 ns) pulse duration excimer laser beams were used to deposit a large amount of energy in a short time onto the near-surface region. Under suitable conditions, the irradiation leads to surface melting and dopant incorporation by liquid phase diffusion from the surface. Boron distribution profiles in the two pulses duration regimes were studied as well as their electrical properties, and the junction formation of less than 20 nm in depth was demonstrated.
INTRODUCTION In the last few years, laser processing of semiconductors has been regarded as a promising technique for manufacturing new generations of microelectronic devices in silicon. According to the International Technology Roadmap for Semiconductors (ITRS) [1], the doping technology requirements for the MOSFET source and drain (S/D) regions of the future CMOS generations is a major challenge. A critical point of this evolution is the formation of Ultra Shallow Junctions (USJ) [2]. As an alternative to the Rapid Thermal Processing (RTP) [3], Laser Thermal Processing (LTP) [3] was demonstrated to be suitable for the doping of Si by different ways, including laser annealing of ions implanted dopant [3,4,5] and laser induced diffusion of dopant from gas (GILD) [6,7,8] or solid sources like Spin-On Glass (SOG) [9,10]. This last one presents in particular the advantage to avoid any ion implantation-related defects and not to require any vacuum system. In this work borosilicate (BSG) glass films used as dopant source (dopant concentration: up to 2.1021 cm-3) were deposited onto crystalline silicon (c-Si) wafers by the spin coating technique. Both short (20 ns) and long (200 ns) pulse duration excimer laser beams were used to deposit a large amount of energy in a short time onto the near-surface region. Under suitable conditions, the irradiation leads to surface melting and dopant incorporation by liquid phase diffusion from the surface. The final distribution profiles of the dopants (P and B) in the two pulses duration regimes were studied by Secondary Ion Mass Spectrometry (SIMS) and their electrical activation was deduced by sheet resistance classical technique. Finally, p+/n ultra shallow junctions (< 20 nm in depth) were achieved through an optimization of the laser processing conditions.
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