Application of Quantum Mechanics for Computing the Vibrational Spectra of Nitrogen Complexes in Silicon Nanomaterials

Abstract

Nitrogen is a key dopant in silicon for modern electronics including nanoscale devices and third generation solar cells. Even at concentration levels as low as 1015 cm-3 nitrogen doping can change drastically the physical properties of silicon wafers. For instance, large Czochralski silicon (CZ Si) wafers, as well as float zone silicon (FZ Si) wafers for photovoltaic applications benefit from nitrogen in silicon by increasing wafer toughness. An exceptional hardening due to nitrogen doping enabled the growth of wider silicon crystals, in excess of 300 mm in diameter. Nitrogen doped silicon appeared tougher than its oxygen doped counterpart, which enabled thinner and lighter wafers, thus easier to handle. The hardness is induced by dislocation locking effect (Sumino et al., 1983; Chiou et al., 1984; Abe et al., 1884; Murphy et al., 2006), and an increase of the density of asgrown precipitates which originates from nitrogen-oxygen clusters (Karoui et al., 2004; Karoui & Rozgonyi, 2004; Nakai et al., 2001; Karoui et. al., 2002). Nitrogen interacts with point defects such as Si vacancy (V) or Si self-interstitial (I), as well as light impurities affecting the formation of micro-defects, thereby significantly reducing swirl defects as well as vacancy related defects known as D-defects, COPs and voids, and improving the gate oxide integrity (GOI) (von Ammon et al., 1996; Tamatsuka et al., 1999; Ikari et al., 1999). Nitrogen also dramatically enhances oxygen precipitation by interacting with oxygen, achieving strong gettering of metallic impurities in the bulk (Ikari et al., 1999; von Ammon et al., 2001; Shimura & Hockett, 1986; Sun et al., 1992; Aihara et al., 2000). Fourier Transform Infrared Spectroscopy (FTIR) has been extensively used to identify the atomic structure of N-related defects and to determine nitrogen concentration in nitrogen doped FZ (N-FZ) and CZ (N-CZ) Si wafers (Stein, 1983, 1986; Wagner, 1988; Qi et al., 1991; Yang et al., 1998; Qi et al., 1992). FTIR measurements on N-FZ Si wafers shows that 80% of nitrogen atoms are paired (N-pairs) and bonded to silicon at concentration much larger than the solid solubility limit (Stein, 1983). Most nitrogen atoms are coupled by pair and