X-ray characterization of crystal perfection and surface contamination in large-diameter silicon wafers

Abstract

This paper reviews recent development of X-ray techniques, which cover laboratory experiments and synchrotron radiation (SR) applications, to detect crystal imperfections and surface contamination in large-diameter Czochralski-grown silicon (CZ-Si) wafers. While process-induced defects can be easily detected by a large-sized Lang camera, it is difficult to observe grown-in microdefects and slight impurity-inhomogeneity even when the double-crystal method is applied. SR plane-wave X-ray topography has overcome this difficulty, except for observing void defects, with the help of its high strain sensitivity although it cannot be directly applied to large Si wafers because of their warpage. Recently, SR X-ray topography using a 300-mm-wide monochromatic beam has been employed for measuring the warpage of 200- and 300-mm wafers as well as inspecting surface damage caused by various steps of wafer-manufacturing. Although energy-dispersive total-reflection X-ray fluorescence analysis using a rotating-anode X-ray generator is now widely used for detecting traces of metallic impurities on the surface of 300-mm Si wafers, the requirement of a large scale integrated circuit miniaturization has promoted the combination of a vapor-phase decomposition technique and the TXRF for lowering the lower-limit of detection (LLD). SR-TXRF using an ED solid-state detector is effective in nondestructive and low LLD features, while newly developed wavelength-dispersive (WD) SR-TXRF in good energy resolution. The combined use of the laboratory and SR experiments leads to precise information about crystal perfection and surface contamination in large-diameter Si wafers.