Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1997-09-22
1999-04-27
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
25055927, 250225, 356369, G01N 2100
Patent
active
058981810
ABSTRACT:
A method and apparatus for inspecting a reflective surface, or material on such surface, such as lubricant and planarizing layers on a substrate surface. A beam of controlled polarization impinges obliquely at a spot in the plane of the substrate. A collector such as an integrating sphere is spaced away from the substrate and has an opening oriented to catch the oblique specular reflectance from the surface. Preferably the opening is substantially larger than the beam, so that substrate run out does not send the beam astray or defeat its measurement, and the oblique beam is aimed at an angle lying between the Brewster angle of the lubricant and that of the adjacent layer. A temperature-controlled laser diode with constant-current driver provides a beam that is free of wavelength hops and amplitude changes, making beam aiming repeatable and allowing point-by-point comparisons of the detected reflectance. The substrate spins at high speeds on an encoded shaft, and the assembly is radially stepped to allow inspection of the substrate at radial and angular positions while a microprocessor synchronized with the spinning substrate collects light data to compile a map of surface reflectance. The polarization may be controlled to enhance image quality for different coatings and improve signal discrimination. Simple logic applied to point-by-point inequalities identifies the nature of physical changes responsible for observed effects. Polarization contrast and time difference contrast images allow visualization of defects and changes in substantially transparent layers well under a quarter wave thickness.
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HDI Instrumentation
Pyo Kevin
Westin Edward P.
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