Study on Particle Detection for Patterned Wafers by Annular Evanescent Light Illumination (1st Report)

Abstract

This paper presents a new particle detection method using annular evanescent light illumination. In this method, a converging annular light used as a light source is incident to a micro-hemispherical lens. When the converging angle is larger than critical angle, annular evanescent light is generated under the bottom surface of the hemispherical lens. The evanescent light is localized near by the bottom surface and decays exponentially away from the bottom surface, which selectively illuminates the particulate defect existing on the patterned wafer surface. So, the proposed method will be able to evaluate the particulate defect on the patterned wafer surface by detecting the fringe pattern formed by scattered light from particulate defect, which is called “Scattered Evanescent Light Fringe Pattern (SELFP)”.In order to verify the feasibility of the proposed method, fundamental experiments are carried out for the two typical defect samples, namely a tip of AFM probe with nano scale size and a particle on patterned wafer. First, from the circular SELFPs for the tip of AFM probe, it is suggested that the proposed method enables the nano particle detection. Next, for a 220nm particle with almost the same size as 200nm lines and spaces fabricated by FIB (Focused Ion Beam), it is found that the circular SELFP is clearly detected without background scattered noise from patterned wafer surface.