Metallic Impurities and Dopant Cross-Contamination Effects in Ion Implanted Surfaces

Abstract

ABSTRACTContamination of implanted surfaces by metals and dopants is a significant limitation to the use of high-dose implantation for semiconductor IC fabrication. RBS, SIMS, SRP, chemical etching and IC device parameter measurements have been used to characterize contaminated surfaces implanted with modern, production-type implanters. Levels of dopant cross -contamination of the order of 10% of the primary dose have been observed. A systematic study of the effects of As, P, B and Sb implanted Si has shown measurable effects on diffusion profiles and junction depths at contamination levels as low as 0.01% of the primary dose. These effects are particularly serious for fast-diffusing contaminants in slow-diffusing primary dopants (such as P contamination in As implants). Evidence has been found for both sputtering and ‘vaporization’ mechanisms for transfer of contaminants from implanter surfaces to the wafer target. The effectiveness of machine design choices and process procedures (such as wafer clamp design, post-implant chemical cleans, and the use of screen oxides) in minimizing the effects of contamination are discussed.