2, University of Tennessee, Knoxville, Tennessee, United States
3, ChemTrace, Quantum Global Technologies, LLC Company, Portland, Oregon, United States
4, GlobalWafers Co. Ltd., St. Peters, Missouri, United States
Current largest market share of a continually growing semiconductor manufacturing sector in the US demands rapid and cost-effective quality control and characterizations of Si-based semiconducting materials. To this end, recently we have developed Laser Induced Breakdown Spectroscopy (LIBS) as a facile and effective tool for process-line quantitative analysis of silicon oxide (SiO2) thin-films on industrial-grade Si wafers grown as metal-oxide-semiconductors (MOS).1 Herein, we present a matrix-assisted calibration technique used in LIBS for quantitative detection of dead load interstitial oxygen contents (Oi) in industrial-grade Si crystal ingots. Si crystal samples were grown via Czochralski technique and supplied by SunEdison Semiconductor Ltd. with known Oi contents measured via gas fusion analysis (GFA) and Fourier transform infrared (FTIR) spectroscopy. The LIBS analyses presented here use and compare a direct approach based on known oxygen atomic emission line at 777.19 nm and an indirect approach based on a matrix-assisted calibration technique using a lesser known emission line at 781 nm for the first time.2 Unlike the first direct approach, the latter exhibited much higher sensitivity, reliability and less error. In this approach, a matrix-assisted calibration uses systematic variations in the unique 781 nm 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 Oi contents in the analyte matrix. Using this technique, we establish the detection limit of LIBS in measuring Oi in Si crystal ingots down to ~ 7 ppm level, while overcoming the limitations of common industrial techniques such as FTIR that cannot provide accurate quantitative measurements for highly doped Si crystals or GFA that is too cumbersome to be an online technique. Our results establish LIBS at the forefront of alternative industrial analytical tools heretofore not considered for rapid, on-line monitoring of dead loads in commercial grade Si wafers during their growth processes.
(1) S. A. Davari, S. Hu, R. Pamu, and D. Mukherjee; "Calibration-free quantitative analysis of thin-film oxide layers in semiconductors using laser induced breakdown spectroscopy (LIBS)," Journal of Analytical Atomic Spectrometry, 2017, 32, 1378-1387.
(2) Seyyed Ali Davari, Patrick A. Taylor, Robert W. Standley, and Dibyendu Mukherjee; "Detection of interstitial oxygen contents in Czochralski grown silicon crystals using matrix-assisted calibration in laser-induced breakdown spectroscopy (LIBS)," Analytical Chemistry, 2017, Submitted.