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 (O-i) atoms in the low temperature regime (300-650 degrees 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 degrees 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 N O x complexes. Somewhat unexpectedly, the residual N-O STDs are much more after the 1250 degrees C/2h CFA than after the 900 degrees C/2h or 1000 degrees C/2h counterpart, which is found to be due to the fact that more nitrogen pairs [(N-2)s] are remaining after the 1250 degrees C/2h CFA. It is proposed that most of the (N-2) atoms are involved in the growth of grown-in oxide precipitates during the 900 or 1000 degrees C/2h 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.