Studies on defect complexes in Si and SiC

P. Deák, A. Gali & A. Sólyom

Institute of Physics, Technical University of Budapest H-1111 Budafoki ut. 8. Budapest, HUNGARY

Defect engineering is a key part of microelectronic device processing. Tight control of the doping requires detailed knowledge about the incorporation and activation of the dopants as well as about the influence of intrinsic defects and impurities. One of the main concern in implantation doping and subsequent annealing is the formation of complexes. Dopant - dopant or dopant - defect complexes diminish the activation rate while defect-defect complexes may act as traps, again reducing the free carrier concentration. Identification of the most likely complexes might help designing successful annealing strategies to get rid of these effects. An effective way for this is the comparison of calculated spectroscopic properties of a variety of complexes with experimentally observed centers. Such a study is described here for boron interstitial clusters (BIC) in silicon and intrinsic defects in SiC. The large number of self-interstitials created during implantation mediate the fast transient diffusion of the implanted boron, leading to clustering. The BICs are either electrically inactive or the number of holes they can provide per number of boron atoms is significantly less than one. The standard approach for studying the deactivation of boron due to clustering is to try to elucidate defect properties from comparison of SIMS diffusion profiles and spreading resistance profiles. While the formation and dissolution energies of the possible clusters have been obtained earlier as fitting parameters of kinetic models, in recent years attempts have been made to determine these data a priori from theoretical calculations. However, energy calculations alone are not sufficient to establish the key players in the clustering process of boron. The present paper describes a systematic first principles quantum mechanical study of the characteristic vibration frequencies of a large number of possible configurational isomers of BICs containing up to 4 boron atoms. In binary semiconductors, such as SiC, the early stage of postimplantation annealing ought to lead to the "wrong type" of recombination between self-interstitials and vacancies, creating antisite defects or their clusters. The carbon anitisite as well as the carbon self-interstitial are low energy mobile defects. As a result various various clusters are expected which might act as traps for free carriers. Electronic and vibrational properties of several such clusters will be presented based on first principles quantum mechanical caculations.