Nonmelt Laser Annealing of 1 Kev Boron Implanted Silicon
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NONMELT LASER ANNEALING OF 1 KEV BORON IMPLANTED SILICON Susan Earles1, Mark Law1, Kevin Jones1, Somit Talwar2, and Sean Corcoran3 1 SWAMP Center, University of Florida, Gainesville USA 2 Verdant, San Jose, CA USA 3 Intel Corp, Portland OR USA ABSTRACT Heavily-doped, ultra-shallow junctions in boron implanted silicon using pulsed laser annealing have been created. Laser energy in the nonmelt regime has been supplied to the silicon surface at a ramp rate greater than 1010oC/sec. This rapid ramp rate will help decrease dopant diffusion while supplying enough energy to the surface to produce dopant activation. High-dose, non-amorphizing 1 keV, 1e15 ions/cm2 boron is used. Four-point probe measurements (FPP) show a drop in sheet resistance with nonmelt laser annealing (NLA) alone. Transmission electron microscopy (TEM) shows the NLA dramatically affects the defect nucleation resulting in fewer defects with post annealing. Hall mobility and secondary ion mass spectroscopy (SIMS) results are also shown. INTRODUCTION One of the key issues involved in scaling PMOS transistors is reducing the depth of the p-type source/drain extensions. Junction depths less than 30 nm are required for 70 nm gate lengths [1]. The simplest method of producing p-type junctions is to implant boron, a p-type dopant. After the implant, the wafer is rapid thermally annealed (RTA) in an effort to activate the boron and remove damage created by the implant. Upon annealing, the heating of the lattice and the damage from the implant results in boron diffusion, boron clustering, and defect evolution [2, 3, 4]. This produces deeper junctions, lower boron activation, and reduced mobility. Variations in the implant energy and thermal annealing techniques are thus required to produce shallower junctions. Previous studies have investigated the use of high power pulsed lasers to melt the implanted layers to achieve high activation and abrupt junctions [5, 6]. Complications arising from melting and regrowth however limit the use of this technique [7, 8, 6]. Experiments show increasing the ramp up rate during thermal processing has been shown to decrease the TED of boron in silicon [9, 10, 11]. Plots of the ramp up rate versus diffusion length show that the ramp up rate would need to be around 1010 oC /sec to result in a diffusion length of zero, and hence no TED [12]. Unfortunately, conventional RTA systems have peak ramp up rates of 200-400 oC. However, using a laser for thermal processing results in a ramp up ramp which approaches the 1010 oC /sec that current data suggests is needed for zero TED. The ramp down or cooling rate is also dramatically higher for the laser annealed sample since only a small surface region of the wafer is heated during the NLA thermal conductivity dominates the cooling down of the wafer instead of radiation. In a continued effort to reduce TED while achieving high dopant activation, the following study investigates the effects of nonmelt laser annealing on silicon heavily-doped with 1 keV boron. J4.1.1
EXPERIMENTAL RESULTS A 1 k
