Detection of interstitial oxygen contents in Czochralski grown silicon crystals using internal calibration in laser-induced breakdown spectroscopy (LIBS).

We use an internal calibration approach in laser-induced breakdown spectroscopy (LIBS) for quantitative detection of dead load interstitial oxygen contents (O) in industrial-grade silicon (Si) crystal ingots. Si crystal samples were grown via Czochralski technique and supplied by SunEdison Semiconductor Ltd. with known O contents measured via gas fusion analysis (GFA) and Fourier transform infrared (FTIR) spectroscopy. The LIBS analyses reported here use and compare a direct approach based on the known oxygen atomic emission line at 777. 19 nm and an indirect approach based on an internal calibration technique using an emission line at 781 nm associated to Si I. Unlike the first direct approach, the latter exhibited much higher sensitivity, reliability and less error. In this approach, an internal calibration uses systematic variations in the 781 nm emission line in conjunction with observed changes in plasma excitation temperatures as a quantitative measure of changes in plasma conditions and laser-matter interactions due to varying O contents in the analyte matrix. Using this technique, we establish the detection limit of LIBS in measuring O in Si crystal ingots down to 8 ± 1 ppma level. The approach assists to overcome the limitations of common industrial techniques such as FTIR that cannot provide accurate quantitative measurements for heavily doped Si crystals and GFA that is significantly cumbersome to be an online technique. Our results establish LIBS at the forefront of alternative industrial analytical tools heretofore not considered for rapid, potential on-line monitoring of dead loads in commercial grade Si wafers during their growth processes.