Patent ID: 6879391
Filing Date: 2005-04-12
Classification: G01N

Abstract:
1. Apparatus for detecting particles on a surface of a semiconductor wafer, said surface having repetitive patterns, the apparatus comprising: (a) a laser for illuminating an area on said surface with a beam of polarized light, (b) a first camera, (c) a first imaging lens for collecting light scattered from said area, said first imaging lens forming a Fourier diffraction pattern of light scattered from said area illuminated at the back focal plane of said first imaging lens, (d) a Fourier mask for blocking light in said Fourier diffraction pattern where the intensity is above a predetermined level indicative of of background information and leaving in areas where the intensity is below said predetermined level indicative of particle information, the Fourier mask including a spatial light modulator (SLM) which is optically addressable and a polarization discriminator in the form of a polarizing beamsplitter, the polarizing beamsplitter being disposed optically between the first imaging lens and the SLM the SLM including a 100% reflective dielectric mirror and a photoconductive layer, the polarizing beamsplitter receiving light collected by said first imaging lens and splitting said light so collected into a transmitted beam and a reflected beam, the first camera being disposed along the path of the transmitted beam, (e) a second camera disposed along the path of the reflected beams, (f) a second imaging lens for imaging the Fourier diffraction pattern formed by the first imaging lens of light from the reflected beam in the back focal plane of the first imaging lens into the second camera, said second camera converting the image of the Fourier diffraction patterns into a stream of digital electrical signals, (g) light from the polarizing beamsplitter in the transmitted beam striking the 100% reflective dielectric mirror which is disposed in the back focal plane of the first imaging lens, (h) a processor for processing the stream of digital electrical signals formed by the second camera, (i) a liquid crystal display (LCD) for converting the output of the processor into a video image, and (j) a third imaging lens for imaging the video image of the LCD onto the photoconductive layer in the SLM, (k) light reflected back from said 100% reflective dielectric mirror as modified by light striking the photoconductive layer from the LCD is reflected by said polarizing beamsplitter and imaged onto said first camera, said first camera recording the image of the area imaged by said first imaging lens using scattered light not blocked by said Fourier mask.