Angle Measurement and Control in High Current Ion Implantation

Abstract

Precise beam‐to‐wafer angle control continues to become more important for critical high current implants where gate stack shadowing variations lead to parametric shifts. This paper examines contributors to variations in beam‐to‐wafer angle from a beamline, process chamber, and control system standpoint. Wafer positioning, beam steering, and beam angular spread are discussed, along with techniques to precisely measure and control them.Direct, in‐situ techniques are used to measure beam angular offset and spread in a ‘spot beam’ high current implanter. The relationships between position and angle, both on average and within the beam, are detailed. In a 2‐D mechanical scan system, angle uniformity (the local angle variation at different points on the wafer) is influenced by how each point on the wafer samples the angles within the beam. Angle uniformity is shown to be less sensitive than dose uniformity to scan spacing. Furthermore, conditions which result in better dose uniformity also tend to give better angle uniformity.