Laser Thermal Processing of Alternate Dopants in Silicon

Abstract

AbstractTraditionally, the choice of dopant has been limited to those species with the highest solid-solubility, however, Laser Thermal Processing (LTP) is not fundamentally limited by solid-solubility. Therefore, it is of interest to evaluate alternate dopants that have previously been excluded due to low solid-solubility. To this end, alternate dopants of 14N, 121Sb (n-type), 27Al, 70Ga, and 115In (p-type) are compared to conventional dopants of As and B respectively, after LTP and post-LTP thermal processing. Dopants were implanted into <100> silicon wafers of opposite background doping type that had previously been amorphized to a depth of approximately 300 angstroms by a 15 keV 28Si+ implant of 1x1015/cm2 dose. An implant energy of 5 keV was sufficiently low to confine the implanted ions to the amorphous layer, with the exception of B, which required an energy of 2 keV. All species were implanted at doses of 1x1014, 5x1014 and 1.5x1015/cm2. Samples were LTP utilizing a 308 nm, 18 ns laser pulse with a fluence of 0.680 J/cm2. Post-LTP thermal processing of the samples consisted of a 900 °C rapid thermal anneal (RTA) in a nitrogen ambient for a duration ranging from spike to 300 seconds. Measurements of the sheet resistance, mobility and carrier concentration were taken after both LTP, and the post-LTP thermal processing. Experimental results show that LTP of alternate dopants increases the electrically active carrier concentration of Ga, Al and Sb above solid-solubility. Additionally, the amount of deactivation upon post- LTP thermal processing depends on the alternate dopant species.