A 13.56 MHz multicusp ion source for high intensity Ar beam

A 13.56 MHz radio frequency (rf) inductively coupled multicusp ion source h as been developed for producing an intense argon beam with current density in excess of 30 mA cm(-2). The source chamber is a 10 cm diam aluminum cyli nder surrounded by 20 rows of 3.5 kG Sm-Co-5 magnets which form a longitudi nal line-cusp field configuration. The rf antenna coil, placed inside the s ource chamber, is made of a braided wire threaded through a two turn pyrex tube 6 cm in diameter to prevent electrical leakage and ion sputtering. A 1 0:1 turns-ratio matching transformer is used to match the 50 Omega output i mpedance of the rf generator to the impedance of the plasma load. Prelimina ry measurements were carried out with a single- and four-hole aperture extr acting system using argon gas. For single-hole extraction with pressure at 5 mTorr and rf power at 500 W, the ion current density was 27 mA cm(-2). Un der the same operating condition, a four-hole extracting system could achie ve almost the same amount of current density of 25 mA cm(-2). (C) 2000 Amer ican Institute of Physics. [S0034-6748(00)68402-2].