Sub-melt laser annealing followed by low-temperature RTP for minimized diffusion

The combination of sub-melt laser annealing plus low-temperature rapid thermal annealing (the V²LTP Process) has been investigated for the formation of shallow doped regions with minimal thermal diffusion and without melting. In particular, the process can be used to form ultra-shallow, low sheet resistance junctions or deeper regions where thermal diffusion after implant is undesired. In this two-step process an implanted wafer is first laser annealed using a laser energy density that achieves a high wafer temperature (1100-1300°C) but does not melt the silicon (“sub-melt”). This step achieves dopant activation to the desired level. Finally, the wafer is annealed with a low-temperature (650-850°C) rapid thermal anneal. This process repairs crystalline damage from the implant so that devices have good mobilities and low leakage currents. SIMS and sheet resistance data have been measured for a wafer implanted with 1 keV B⁺ ions to a dose of 9×10 ¹⁴ cm^-2, then laser annealed below the melting threshold with 100 laser pulses, and finally rapid annealed at 700°C for 20 sec. The SIMS profiles clearly show that no measurable diffusion has occurred during the V²LTP process, and yet a sheet resistance of 360 Ωsq. was produced