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

Abstract

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 asimplanted 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-300® 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.