Negative ion beam production by a microwave ion source equipped with a magnetically separated double plasma cell system

Abstract

Filamentless negative ion beam production was investigated with a compact microwave ion source (2.45 GHz). One of the key points for negative ion production is the magnetic configuration. A magnetic filter field to lower electron temperature was generated in a negative ion production cell, which was shielded magnetically from a discharge cell with a magnetic field to couple microwave to plasma. Production of H− beam was studied with this source. H− was extracted through a grid slit (2×16 mm2) from plasma and accelerated to 20–40 keV. H− beam current was measured with a Faraday cup after magnetic mass separation. Continuous H− beam current of 73 μA (0.23 mA/cm2) was obtained with a magnetron power of 700 W. H− beam current was increased around 1.4 times by adding Xe gas to the H2 gas. Other negative ion species, which have a potential for applications to industrial ion beam processing with little charge-up problem, were also investigated. Carbon and hydrocarbon negative ion beams were produced using boron alkoxide (B(OCH3)3) and methane. C2H2− beams (22 μA) were obtained with the alkoxide. C2−(1.6 μA), C2H−(2.3 μA), C2H2−(0.6 μA), and H−(6.9 μA) beams were produced with methane. SiF4 and BF3 were used to generate F−, Si−, SiF3− and B− beams. Beam currents of these ion species were 17, 0.25, 1.5, and 0.03 μA, respectively.