Advances in cross-contamination control using single-wafer, high-current implantation

The Varian VIISta 80 is a single-wafer high-current implanter, which uses a ribbon beam and a single-direction mechanical scan for implantation. The placement of the wafers on an electrostatic platen, and the absence of end station parts in the vicinity of the wafer during implant, translate into an expected advantage in implanter memory over batch tools. This paper focuses on P-in-As cross-contamination and compares the performance of the VIISta 80 to a representative of the batch family of high-current tools-the Varian VIISion 80. The results of experiments designed to understand the mechanisms of phosphorus build-up in machine parts exposed to the P/sup +/ beam, as well as their cleanup by a variety of subsequent ion beams, are discussed in detail. Phosphorus levels in arsenic-implanted wafers are assessed using secondary ion mass spectrometry (SIMS) and four-point probe sheet resistance measurements. Typical cross-contamination performance is presented and recommendations on further reduction of the memory effects are made. Additionally, data on P-in-B, B-in-As, and B-in-P cross-contamination modes are reported.