Characterization of neutral beam source using dc cold cathode discharge and its application processes

Abstract

Fast atom beam (FAB) sources using dc cold cathode discharge, comprising parallel plate electrodes and thick carbon plate cathodes with multiple beam extracting apertures, were developed to generate parallel and straight energetic neutral beams for precise etching of three-dimensional microstructures consisting of insulating materials. Conventional FAB sources and their applications are briefly reviewed, and the advantages of newly developed FAB sources and new applications are introduced. By using SF6 gas, a precise etching of quartz glass with an etch rate of 30 nm min−1, a uniformity of within 4% (P–V) in Ø76 mm, vertical etch profile, smooth etch surface and long-term etch rate stability over 250 min were realized. The neutralization coefficient and the beam current density were also measured using a secondary electron method and a pulse-counting method, making it possible to measure the neutralization coefficient without referring to databases for secondary electron yields. A neutralization coefficient of 98% was obtained at maximum, although, under practical etching conditions, the neutralization coefficient is less than 70%. By comparing the results of the simple model calculation with the experimental data, it was determined that the neutralization mechanism was dominated by charge transfer. The importance of neutralization in a process chamber is also discussed.

Modeling and Simulation of Fast Neutral Beam Sources for Materials Processing

“…Ions extracted from a plasma source (for example gridded ion source) can be neutralized in a charge‐exchange cell (volume neutralization) or by impingement on a neutralizer plate (surface neutralization). Kuwano and Shimokawa,9 as well as Ichiki and Hatakeyama10 produced fast neutral beams by neutralizing ions in charge exchange cells. Ions produced in McIlraith DC cold cathode discharges, were extracted through holes in a graphite cathode plate, and neutralized by charge exchange with the gas downstream of that plate (Figure 1).…”

“… Neutral beam source based on volume neutralization of ions 10. A McIlairth DC cold‐cathode discharge produces ions that are extracted through holes in the (lower) cathode plate.…”

“…The charge exchange cell pressure [or more precisely the product of background neutral density and cell length, NL , see Equation (4) below] should be high enough to achieve substantial neutralization but not too high to minimize beam scattering, that reduces the beam flux and directionality. Several researchers have reported on neutral beam sources based on volume neutralization of ions 10, 19, 20…”