Hamamatsu Systems, Inc.

David L Brewer

Charly D Allemand

Hitoshi Iida

Mario A Maldari

Gary P Green

A monochromatic imaging apparatus comprising a pair of similar diffraction gratings, a pair of focusing lenses, a pair of collimating lenses, an entrance slit, an exit slit and an intermediate slit, and means for concurrently moving the two gratings; wherein a polychromatic source image is placed at the entrance slit, and a collimating lens collimates the light rays from the source image and projects the collimated rays onto the first diffraction grating thereby to disperse the rays. The dispersed rays are then focused by the first focusing lens onto the intermediate slit, and then collimated by the second collimating lens onto the second diffraction grating which thereupon recombines the dispersed light. The recombined rays are then focused by the second focusing lens onto the exit slit. The two gratings may be concurrently moved in opposite or similar directions about an axis in the grating ruling plane and at the centers thereof, and at similar angles, so that the angle of incidence at the first grating is equal to the angle of diffraction at the second grating. In this manner, a monochromatic image of the polychromatic source image will appear at the exit slit and be of a selected band of wavelengths of the visible or other spectrum dependent upon the angular position of the two gratings from zero order of diffraction.

Monochromatic imaging apparatus

A method and apparatus for detecting and measuring the number and sizes of impurities on the surface of a material, such as a semiconductor wafer, wherein high intensity collimated light is directed onto the surface, in the absence of any extraneous light, through a collimating mirror, and employing a point source, whereat the particles will scatter the light, and wherein the surface is viewed by a highly light sensitive TV camera which picks up the scattered light and displays same on a viewing screen. The intensity of scattered light will indicate the size of the particles when compared with a calibrated model. Advantageously, a broad range of light waves is employed and thus enables a range of sizes of particles to be detected by the light scattered thereby. Also, advantageously, with the use of ordinarily available equipment, the system can inspect wafer surfaces for particles having sizes as small as 0.3 microns. The system also enables detection and identification of moving particles as distinguished from stationary particles.

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Stow, MA, United States of America

David L Brewer