Beam Current Improvements on the Axcelis Optima HD Imax Implanter

The ability to use large molecular species such as octadecaborane (B18H22) has been investigated at semiconductor device manufacturers as a way to significantly increase wafer throughput relative to standard high current ion implanters. Over the past two years, improvements in the machine design to support the use of B18H22 have led to beam current increases of 50% from 30pmA to 45pmA of boron at an equivalent boron energy of 4keV. This boron energy is required by p+ doping of dual poly gate (DPG) structures in DRAM. Beam current has also been significantly improved at the low equivalent boron energies anticipated to be required by 32nm processes for PMOS source/drain extensions (SDE). For example, at 250eV equivalent beam energy, a 100% increase in cluster boron beam current has been attained. This paper describes the techniques by which these beam current improvements were accomplished, primarily through the refinement of ion beam optics. Other techniques for increasing overall tool productivity are also described, such as beam utilization and overall operational improvements. Wafer throughputs are presented for critical p+ implant processes such as dual poly gate (DPG), source/drain (S/D), source drain extension (SDE) and S/D contact. The higher throughputs resulting from these changes are translated into a cost per wafer (CPW) model and it is demonstrated that an increase in average beam current is the largest contributor to a reduction in CPW.