Paper MS-ThM9
Analysis of Ion Implantation Damage in Silicon Wafers

Thursday, October 18, 2007, 10:40 am, Room 615

Ion implantation has become the standard method for building high-density, microelectronic devices. Rapid thermal annealing (RTA) is required to activate the implanted donor and acceptor species. Also, RTA is required to heal the lattice damage created by heavy ion implants such as boron, BF2, phosphorous and arsenic. The RTA process is required to maintain the structural integrity of the semiconductor used for submicron-integrated circuits, as dopant diffusion will destroy the implantation pattern using a long-duration heat treatment. There is a trade-off between the maintenance of the implantation pattern and the elimination of radiation damage. A quick, efficient, and contactless diagnostic of the implantation damage is highly desirable in both research and production environments. The resonant-coupled photoconductive decay (RCPCD) technique uses a deeply penetrating, low-microwave-frequency probe in conjunction with pulses from a tunable laser source. The recombination lifetime of the implanted region decreases many orders of magnitude as a result of implantation. The implanted region has electrical transport characteristics that are similar to those of amorphous silicon. For example, the recombination lifetime of the implanted regions becomes sub nanosecond, and similar to that of amorphous silicon. I have found the doubled YAG laser frequency of 532 nm to be especially useful for sensitivity to implantation damage. RTA restores the crystalline structure, and the degree of restoration depends on the RTA process. The implantation damage is manifested in a sharp decrease in the recombination lifetime when using strongly absorbed light, that is primarily absorbed in the implanted region. In addition, the as-implanted layer acts as a "sink" for minority carriers that are generated in the undamaged crystalline regions. The lifetime increases with various annealing processes, and one can correlate the lifetime changes with the specific annealing protocol. I will also show data for the sheet resistance, which is correlated with the increase of lifetime in the implanted volume. In summary, I will present a method for quickly evaluating the damage elimination of various implantation-annealing processes.