Abstract: The radiation beam of discrete light source such as LEDs is shaped by a cylindrical lens and a spherical lens to form two perpendicular narrow lines to illuminate a surface. The first line is projected onto a sample surface to improve illumination efficiency, and the second line is projected onto a pupil plane of an imaging lens to improve illumination uniformity. The layout of the LED chip is optimized to match the aspect ratio of the imaging detector. Multiple LEDs at different wavelengths are combined to improve sensitivity. The full surface of the sample is inspected through the relative motion between the sample and the optics.

Abstract: Techniques for inspecting a substrate with improved defect sensitivity are disclosed. High sensitivity is achieved by reducing the noise due by using multiple laser beams for illumination, in which each beam is nearly collimated and illuminates uniformly a field of view. The images generated respectively by the laser beams are added incoherently by means of delivering the illumination beams incoherently in either time domain or space domain. According to one embodiment, all the illumination beams may not be interact with each other coherently so that the images generated by each laser beams can be summed together incoherently to average out possible excessive noise.