High-power fast-atom beam source and its application to dry etching

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Abstract
We have developed a new high-power fast-atom beam (FAB) source by modifying a McIlraith-type ion source. The beam current density emitted from a source with an electromagnet and multiaperture grid is about ten times higher (up to 1 mA/cm2) than that emitted from a conventional source. Silicon dioxide can therefore be etched at 60 nm/min when CF4 gas is used, or about six times faster than by using a conventional source with the same discharge current. The beam neutralization coefficient of the new FAB source is nearly 100%. We have used this FAB source to etch Si, SiO2, GaAs, and other compound materials. We could easily etch an anisotropic profile (nearly vertical with an aspect ratio of more than 10 for a 0.6 μm L&S pattern), etch at a high rate (0.3–0.5 μm/min), and etch with high selectivity (GaAs:resist =30:1). We also fabricated a SiO2 fine pattern in 0.6 μm L&S by using CF4 reactive-fast-atom beam etching. The uniformity of the etch depth is about ±5% over a 4-in. wafer. Surface radiation damage (total oxide charge) caused by FAB bombardment of the SiO2/Si structure is very close to that of reference (not etched) samples. This damage is significantly less than that caused by ion beam bombardment under almost the same radiation conditions.

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