Abstract:
A dark field inspection system that minimizes the speckle noise due to sample surface roughness can include a plurality of beam shaping paths for generating a composite, focused illumination line on a wafer. Each beam shaping path can illuminate the wafer at an oblique angle. The plurality of beam shaping paths can form a ring illumination. This ring illumination can reduce the speckle effect, thereby improving SNR. An objective lens can capture scattered light from the wafer and an imaging sensor can receive an output of the objective lens. Because the wafer illumination occurs at oblique angles, the objective lens can have a high NA, thereby improving optical resolution of the imaging sensor, and the resulting signal level.
Abstract:
A curved mirrored surface (78) is used to collect radiation scattered by a sample surface (76a) and originating from a normal illumination beam (70) and an oblique illumination beam (90). The collected radiation is focused to a detector (80). Scattered radiation originating from the normal and oblique illumination beams may be distinguished by employing radiation at two different wavelengths, by intentionally introducing an offset between the spots illuminated by the two beams or by switching the normal and oblique illumination beams (70, 90) on and off alternately. Beam position error caused by change in sample height may be corrected by detecting specular reflection of an oblique illumination beam and changing the direction of illumination in response thereto. Butterfly-shaped spatial filters may be used in conjunction with curved mirror radiation collectors (78) to restrict detection to certain azimuthal angles.
Abstract:
Systems and methods for inspecting a wafer are provided. One system includes an illumination subsystem configured to illuminate the wafer; a collection subsystem configured to collect light scattered from the wafer and to preserve the polarization of the scattered light; an optical element configured to separate the scattered light collected in different segments of the collection numerical aperture of the collection subsystem, where the optical element is positioned at a Fourier plane or a conjugate of the Fourier plane of the collection subsystem; a polarizing element configured to separate the scattered light in one of the different segments into different portions of the scattered light based on polarization; and a detector configured to detect one of the different portions of the scattered light and to generate output responsive to the detected light, which is used to detect defects on the wafer.