A review of analytical techniques for process control of contaminants introduced during ion implantation

During the ion implantation process wafers may be contaminated by transition metals, mobile ions, carbon, and organics. These contaminants may arise from (i) deposition onto the surface of the silicon wafer or, (ii) co-implantation to depths of several hundreds of angstroms. A number of analytical tools can be used to characterize these contaminants. The choice of the technique depends on whether a contaminant was introduced non-energetically (contaminant that is located on the surface of the wafer) or energetically (a contaminant that has penetrated into the wafer to some depth). The key parameter to consider when choosing the appropriate analytical tool is its analytical depth of information, Common analytical tools used today to characterize non-energetic contaminants include total reflection X-ray fluorescence (TXRF), SurfaceSIMS, vapor phase decomposition (VPD) with TXRF, time-of-flight SIMS (TOF-SIMS), and minority carrier lifetime (MCLT). In this paper, some of the advantages and shortfalls of using these techniques as a process control tool for ion implantation are discussed.