Plasma doping implant depth profile calculation based on ion energy distribution measurements

Abstract

In traditional beamline implantation, the incident ion mass and energy are well known parameters and simulation programs are available to predict the implant profiles. In plasma based ion implantation, all ionized species present in the plasma are extracted and implanted by applying negative voltage pulses to the wafer. Therefore, prediction of implant profile is more complicated since it requires the knowledge of relative abundance of each ion species as well as their energy distribution prior to entering the wafer surface. This information is not readily available using conventional plasma characterization techniques because most of them measure plasma bulk properties. In order to collect the information needed for predicting plasma implant profiles, an ion mass and energy spectrometer is installed at the wafer level to allow in situ measurement of ion mass and energy distribution. In this paper, BF3 plasma in the pressure range from 30to250mTorr is studied. The relative flux and energy distribution of B+, BF+, BF2+, and BF3+ ions striking the wafer surface with energies up to 1keV are measured. As expected, no energy contamination was observed during a plasma doping implantation and the maximum energy of the ions is defined by the cathode voltage. Based on the spectrometer data, a series of simulations was performed to calculate the boron and fluorine dopant depth profiles. The calculated profiles were in good agreement with secondary ion mass spectrometry (SIMS) results and give some additional explanations of the unique surface-peaked SIMS profile of plasma doping implantation.