On the mechanism underlying the elimination of nitrogen-oxygen shallow thermal donors in nitrogen-doped Czochralski silicon at elevated temperatures

Nitrogen-doped Czochralski (NCZ) silicon has been a base material for integrated circuits. The interaction between nitrogen (N) and interstitial oxygen (Oi) atoms in the low temperature regime (300-650 °C), which leads to N-O complexes in the form of NOx (x = 1, 2, or 3), forms a series of shallow thermal donors (denoted as N-O STDs). Such N-O STDs are detrimental to the stability of electrical resistivity of NCZ silicon. In this work, we have experimentally investigated the elimination of N-O STDs in NCZ silicon by means of conventional furnace anneal (CFA) and rapid thermal anneal at elevated temperatures ranging from 900 to 1250 °C, aiming to explore the underlying mechanism. It is found that most of the N-O STDs formed in NCZ silicon can be eliminated by a very short period of anneal at the aforementioned temperatures, providing solid evidence for the viewpoint that the elimination of N-O STDs is ascribed to the decomposition of NOx complexes. Somewhat unexpectedly, the residual N-O STDs are much more after the 1250 °C/2 h CFA than after the 900 °C/2 h or 1000 °C/2 h counterpart, which is found to be due to the fact that more nitrogen pairs [(N2)s] are remaining after the 1250 °C/2 h CFA. It is proposed that most of the (N₂) atoms are involved in the growth of grown-in oxide precipitates during the 900 or 1000 °C/2 h CFA. The first-principles calculations and molecular dynamics simulation indicate that the elimination of N-O STDs is essentially ascribed to the destruction of “NO ring” that is the core of NOx complexes. Furthermore, based on the experimental and theoretical results, we have made a thorough thermodynamic analysis to account for the details of elimination of N-O STDs as revealed in this work. It is believed that our experimental and theoretical studies have gained more insight into the N-O STDs in NCZ silicon.