Emission features of a conventional radio frequency glow discharge source and a magnetically enhanced source

Abstract

A side-on-viewed source was developed in order to determine spatial emission features of a radio frequency (rf)-powered glow discharge. The discharge was formed inside a stainless steel T-shaped cell, which acted as the grounded anode. The cathode assembly was inserted into the leg of the T with the cathode situated near the T intersection. The resulting plasma was formed in the long arm of the T and was viewed through a window at one end of the T. Spatial profiles of Ar emission at 420 nm, Cu emission at 324 nm, and OH band emission at 309 nm were collected with an imaging spectrometer. The source was operated over a pressure range of 0.1–1.0 torr at rf power levels between 20 and 50 W. A power supply was employed at frequencies of 3.5, 6.78, and 13.56 MHz in order to determine the effect of driving frequency. The source was then modified by the placement of two magnets (either cobalt-samarium or ceramic) on its exterior. The magnets were placed on opposite sides of the T next to the cathode in order to create a transverse magnetic field in the region of the discharge above the cathode surface. The effect of the applied magnetic field on the voltage characteristics, sputtering rate, and spatial emission features of the source were then explored. Detection limits of the magnetically modified source for Monel 400 samples (Ni/Cu alloy) were also determined (10–50 ppm) using a high-resolution photodiode-array spectrometer.