He¯/H¯ High-Current Low-Metal-Contamination Volume-Cusp Ion Source for Semicon Applications

Implanted Helium or Hydrogen ions are used to exfoliate a thin layer of GaAs, which can be bonded to Silicon to create high quality Silicon-On-Insulator wafers having applications in optoelectronics, microwave electronics, and high temperature electronics [1].

The class of ion implanter that utilizes the Tandem acceleration technique, such as the Varian 3000XP, requires a negative ion to be stripped to positive at the midpoint of the accelerator which ultimately results in an accelerating potential that is twice the bias voltage. At present the VARIAN 3000XP utilizes a positive ion source to generate energetic H+ or He+ ions, and to achieve negative charge states H¯ and He¯, the positive ions are focused through a vacuum chamber with a high metallic vapour content (Group 1 or 2 in the Periodic Table) where charge exchange occurs and the energetic negative ions emerge at the downstream exit port of the chamber, and are ready after mass analysis for acceleration by the Tandem technique [2]. This charge exchange technique results in a transmission of only ~1%, and more importantly the metallic vapour tends to work its way downstream in the implanter such that it becomes a contaminant to the semiconductor wafers being implanted. This contamination adversely affects the performance of the wafer.

The goal of this PhD thesis project is to R&D an innovative concatenated volume-cusp ion source arrangement that achieves industry leading beam currents (Direct Production of H¯ > 10 milli-Ampere; and Charge Exchange Production of He¯ > 50 micro-Ampere) at ~30 keV with normalized 4-RMS emittances less than 1 mm.mrad with the elimination of metallic vapour charge exchange for the purpose of reducing metallic contamination of semiconductor wafers by an order of magnitude.