Development of a Negative Helium Ion Source with Non-Metallic Charge Exchange

Synopsis

Negative Helium ion beams are required for tandem accelerators used at research centers and at implanter facilities. The common production method of such He⁻ beams involve the interaction of a positive Helium ion beam with a low pressure alkali metal vapour. This results in a small portion of He⁺ undergoing two charge exchanges to create the desired He⁻, on the order of a few percent. However, utilizing alkali metal vapour is problematic: leaving interior surfaces prone to flammability, contributing to sparking near electrostatic devices, and, for implanter facilities, negatively impacting silicon wafer production due to metallic contamination. Additionally, the use of a vapour for charge exchange requires a specialized vacuum system and considerable expense to limit the dispersion of the vapour. In efforts to address or remove these issues, a possible alternative creation method for He⁻ is being explored at SFU, which uses a non-metallic foil as the charge exchange medium.

In this presentation we shall outline the need for He⁻ beams, how they are commonly created and used, and the issues with this method. We shall also describe efforts at SFU to investigate an alternative method, namely, using the He⁺ beam generated by SFU’s helium ion microscope (HIM) to measure the conversion rate to He⁻ using non-metallic foils. Efforts and results to date will be presented, as well as a discussion of obstacles and future plans.