An Electron Beam Exciter device has been developed to perform as a controllable optical emission spectroscopy diagnostic system.1 In this design, a small to moderate amount of current extraction (0-5 mA) is necessary to achieve the desired emission signal to produce reliable optical measurements utilized in etch process monitoring and control. Current extraction from this downstream plasma system is achieved in a Non-ambipolar Flow regime.2 Non-ambipolar flow occurs when all electron thermal flux, from the exciter plasma system, exits through a uniform electron sheath formed about the perimeter of a Nozzle Aperture (area Ae) while the ions are lost to the Exciter ICP grounded wall (area Ai). Electron extraction from the exciter ICP is maximized when the ratio of the ion loss collection area (Ai) to the electron loss collection area (Ae) is proportionally equal to the square root of the ratio of the ion mass to the electron mass, and the ion sheath potential drop to the Exciter ICP grounded wall is much larger than Te/e.2,3 To investigate the degree of Non-ambipolar Electron flow in our device, we have tested a set of manufactured Nozzle extractors with different geometrical dimensions so as to discern the influence of Ai/Ae on the electron extraction process in low pressure (5-35 mTorr) Ar discharges. Strong agreement is observed between the measured plasma parameters at the ICP extraction region and the total amount of extracted current, Ie. In addition there is a measurable energy dependent response in the ratio of Ii(E)/Ie(E) indicative of electron-atom/molecule collision cross section for ionization. We have measured this ratio response in Ar and O2atmospheres. This project is funded by NSF-Grant (CBET - 0922962) and Verity Instruments.

 

1P. L. Stephan Thamban; J. Hosch; M. J. Goeckner. Rev. Sci. Instrum,2010, 81, 013502

2B. Longmier; S. D. Baalrud; N. Hershkowitz. Review of Scientific Instruments, 2006, 77, 113504 (1-8)

3S. D. Baalrud; N. Hershkowitz; B. Longmier. Physics of Plasmas, 2007, 14, 042109 (1-6)