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Plasma-induced damages become more fatal, especially in sub-50nm ULSI devices. This makes a neutral beam source one of the most promising candidates for the next generation processing tool. Various types of neutral beam sources for etching process have been proposed and they show superior performance in improvement of semiconductor devices. However, they have some issues in patterning and there are few studies about neutral beam process itself. In this study, research work on process optimization of Si trench etching with low-angle forward-reflected neutral beam source (LAR-NBS) will be presented. In this source, ions extracted from an ion source are reflected and neutralized on a flat conductor surface, called reflector, with low angle below 10° to produce near-parallel and energetic neutral beam flux. The low-angle reflection leads to highly effective neutralization, little losses of energy and directionality, and negligible damage to IC devices. Bare Si wafer with line-patterned SiN hardmask was etched with Cl2 at a fixed rate for trench etching. Various kinds of reflector with different material and surface roughness were prepared to investigate the effects of neutralization process on trench profile. In the case of SUS reflector, profile shows rough sidewall with positive slope. However, vertical and smooth sidewall is obtained in the case of graphite reflector. From XPS analysis, it was confirmed that chloride produced by reaction of chlorine radicals from plasma and reflector material is deposited on Si sidewall. Metal chloride deposited on sidewall is difficult to be removed because its boiling point is very high and little energetic neutrals impinge on sidewall. Sidewall passivation by deposited metal chloride layer leads to positively-sloped trench profile and rough sidewall. On the contrary, carbon chloride from graphite reflector is easy to be removed even by small amounts of energetic neutrals impinging on sidewall due to its low boiling point and this leads to vertical profile. From this study, it was confirmed that reflector properties are critical to etch profile and graphite reflector is the best choice for trench etching in LAR-NBS. In addition, effects of reflector surface roughness on trench profile are discussed in the conference. |