<title>Fiber optic low-coherence reflectometry for silicon sheet growth monitoring during the growth process</title>

Abstract

The accurate measurement of growth parameters is essential for the development of automated, low cost silicon growth technology. The ideal growth parameter sensor for these applications is accurate, non-invasive, immune to electromagnetic interference (especially if induction heaters are used), and able to function at high temperatures. Fiber optics sensors exhibit characteristics which can meet these requirements. In this paper we report on the first use of optical low-coherence reflectometry (OLCR) for on-line, non-invasive characterization of edge-defined film-fed growth (EFG) solar silicon sheets during the actual silicon growth process. This OLCR sensor system has been used to measure vertical profiles of the thickness and flatness of one side of an EfG grown silicon octagon to an accuracy of +/- 5 micrometers . Since thickness and flatness are two important growth parameters for sheet grown silicon, the use of this non-invasive sensor for on-line silicon sheet growth monitoring may lead to improvements in solar cell manufacturing processes. In addition, this technique shows promise for providing non-invasive dimensional monitoring for a variety of other crystal types during the crystal growth process.