Non-Contact SPV-based Method for Advanced Ion Implant Process Control

Surface photo voltage (SPV) measurement has become an important semiconductor characterization tool due to the availability of commercial equipment and its non-contact nature. In this study, we discuss the application of the SPV technique for the control and monitoring of ion implanters, specifically for quantifying and qualifying lattice damage and electrically-activated dopants due to ion implantation in p-type CZ silicon. For as- implanted silicon, a measured SPV response includes the implant induced defect density and provides a photo-carrier lifetime; for annealed wafers, SPV measures the surface depletion layer charge of the activated dopants. Using the corona-charging technique and fine-tuning the wavelength and intensity of the probing light allows SPV to be successfully applied to a wide range of implant conditions. In this study, the QC Solutions ICT-300reg system (based on ac-SPV technology) is used for the monitoring and process control of 18 fab implanters. Seven production recipes are monitored daily, allowing process control to be managed within 2 percent accuracy. The theory of small signal ac surface photo voltage and the principles of the technique are briefly discussed. A detailed explanation of the method and how it applies to implanter monitoring is provided. The ICT-300 system is used throughout the study to measure samples and collect presented data. The controlled processes reported are related to critical implant steps, including threshold adjust voltage, P well, and Halo implants. A detailed discussion of the threshold adjust voltage implant characterization and all pertinent aspects of the measurement process are presented.