Browse Prior Art Database

Mask Inspection Device

IP.com Disclosure Number: IPCOM000092396D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Mathisen, ES: AUTHOR

Abstract

The electro-optical system is for inspection of transparent objects, such as photo and metal masks, for integrated circuit or semiconductor manufacturing. The principle of operation is based upon spatial filtering, sometimes referred to as optical computation. A point source 1 of monochromatic light is collimated by lens 2. The input function in the form of transparency 3, i.e., photo or metal mask is placed in plane 4 which is located a focal length from lens 6. Due to the phenomenon of diffraction, the light a focal distance from lens 6 on its output side is distributed according to the two-dimensional Fourier Transform of the input function.

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Mask Inspection Device

The electro-optical system is for inspection of transparent objects, such as photo and metal masks, for integrated circuit or semiconductor manufacturing. The principle of operation is based upon spatial filtering, sometimes referred to as optical computation. A point source 1 of monochromatic light is collimated by lens 2. The input function in the form of transparency 3, i.e., photo or metal mask is placed in plane 4 which is located a focal length from lens 6. Due to the phenomenon of diffraction, the light a focal distance from lens 6 on its output side is distributed according to the two-dimensional Fourier Transform of the input function.

Transparency 5, containing the complex transmission function of the reciprocal of the error-free original pattern, is placed at the focal plane of lenses 6 and 7. The Fourier Transform of the mask under inspection containing both the pattern, as well as imperfections in the form noise in the spatial frequency domain, is therefore modified. The spatial frequencies of the pattern are then filtered. Lens 7, a focal distance away from the plane of transparency 5, takes the inverse Fourier Transform of the modified function emanating from transparency 5, and displays it at plane 8 indicating the difference between the two functions of transparencies 3 and 5. The output, which does not resemble the original signal, indicates the location and magnitude, i.e., amount of imperfections, of the input function d...