Plasma-Induced Electronic Defects: Generation and Annihilation Kinetics in Hydrogenated Amorphous Silicon

Plasma processing is a key technology for fabrication of state-of-the-art semiconductor devices. The device performance is often limited by electronic defects generated during plasma processing, although most of those defects are annihilated by postannealing. Here we experimentally study the defect kinetics in hydrogenated amorphous silicon (alpha-Si:H) during hydrogen- (H-2-) and argon- (Ar-) plasma treatment, and also consecutive postannealing. The generation and annihilation of electronic defects such as silicon dangling bonds are monitored via in situ measurements of the photocurrent. From the measurements, the following results are found: (i) The defects are generated dominantly by radical species such as H atoms for a H-2 plasma and metastable Ar atoms for an Ar plasma. (ii) The Ar+-ion bombardment creates residual defects, whereas the H-3(+)-ion bombardment does not create such defects. The residual defects are mostly recovered by an additional H-2-plasma and postannealing treatment. (iii) The annihilation of defects exhibits stretched exponential behavior, revealing the dispersive nature of alpha-Si:H. (iv) The activation energy for the annihilation of defects depends on the origins of the defect generation. The activation energy is smaller for defects generated by plasma treatments compared with that for defects induced by photon irradiation. A rate equation for the generation and annihilation of defects is described, and the defect kinetics is discussed in terms of microstructural changes associated with hydrogen diffusion.