Collimator Magnet with Functionally Defined Profile for Ion Implantation

Advanced implantation systems used for semiconductor processing should have high precision of ion beam collimation (⁠$+/−0.1 deg$ and better) and wide beam aperture (400 mm and more). Typical arrangements of ion implantation systems include beam scanning (BSM) and collimator magnets (CM). Standard collimator magnets have limited precision of beam collimation due to magnetic poles that have piecewise circular profile. This study proposes a novel “constant sum angle collimator magnet” (CSACM) with non‐circular magnetic pole profile. Angles of incidence $αi$ and exit $αe$ are defined as angles between ion trajectory and local normal to CM input/output magnetic pole edge. Profile of the CSACM is defined as having constant algebraic sum $αi+αe = const$ for every ion trajectory of the scanned beam, in addition to “usual” beam collimation. An iterative procedure allows improve CSACM taking into account magnetic fringe field effects. Simulation results prove that CSACM assures precise beam collimation in two orthogonal planes. Circular approximations for CSACM magnetic poles are proposed. The model may be further developed for global design of the ion beam line $(BSM+CM)$ and for taking into account space‐charge effects.