Radical-controlled plasma processing for nanofabrication

Nanofabrication processes employing reactive plasma, such as etching and deposition, were discussed in this paper on the basis of knowledge of reactive species in the plasma. The processing characteristics were studied based on the absolute density measurements of radicals and ions. In the case of organic low-k film etching employing N-H plasma, H and N radicals have different roles from each other; the H radicals contribute to the chemical etching, while the N radicals form the protection layer. Therefore, the ratio of H and N radical densities is an important factor for determining the etching performance. Furthermore, the radical injection technique, an active way to control the composition of radicals in the reaction field, was successfully applied to grow carbon nanowalls, self-organized, free-standing, layered graphenes. For example, with increasing density ratio of H and fluorocarbon (CF_x) radicals, the density of carbon nanowalls decreases. In addition, according to the carbon nanowalls' growth by the simultaneous irradiation of CF_x radicals, hydrogen atoms and Ar ions, the ion bombardment is crucial for the nucleation and vertical growth of carbon nanowalls. Identification and characterization of radicals and ions in the processing plasma could open the way to the precise controls of nano-scale plasma processing.