Ion Beam Purity and Wafer Contamination

Many factors related to the design, construction materials, and operation of beamline and plasma systems can compromise the expected precision and cleanliness of the ion implantation process. The list of commonly used ions and target materials has widely expanded beyond the classic set of Si dopants and Si wafers, greatly increasing the complications for beam purity. Among the issues to be discussed are: (1) “mass overlaps” resulting from various molecular ion breakup and charge exchange events resulting from collisions with residual gases, (2) transport of energetic and vapor phase dopants and metals, (3) wetting of device structures by contaminant-containing atmospheric water vapor during load lock pump down and following cryo-implants, (4) organic materials contamination from vacuum oils, o-rings and related sources, (5) particle transport, adhesion and ion blocking effects. Specific metrology methods, effects on IC devices and operational counter-measures will be discussed for each contamination issue.