Charge exchange effects in production high energy implanter dosimetry

Electrical charge neutralization effects are well known as an important factor in dosimetry of high current implanters. Extending this to energies of 1 MeV and beyond requires an understanding and a numerically efficient model for the effects of charge stripping as well as neutralization. This stripping effect generates ions of a higher charge state and may cause the measured electronic current from a faraday cup to overestimate the true particle current. We have developed an analysis based on the concept of an effective charge state for an ion beam to develop a more general formalism that can cover the stripping effect as well as neutralization effect. This patent pending formulation requires only two adjustable parameters: an apparent cross section of interaction and the ratio of the final steady charge state to the initial charge state. We present experimental measurements of the observed electrical currents and show that this new numerical model Is a sufficiently accurate representation of the observations to allow excellent dose uniformity and reproducibility.