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Microcircuit Processing Control by Optical Diffraction

IP.com Disclosure Number: IPCOM000088736D
Original Publication Date: 1977-Jul-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 82K

Publishing Venue

IBM

Related People

Gambino, RJ: AUTHOR [+2]

Abstract

Magnetic bubble circuits such as those in Fig. 1 (shown magnified about 800 times) and charge-coupled storage circuits with bit densities of 1 million bits per square inch have repetitive components which are a few microns or a fraction of a micron in dimension. The quality of the circuits is determined by high power microscope examination (1000x) or scanning electron microscopy (SEM). Both methods have numerous handling steps and a limited field of view, which makes rapid circuit evaluation difficult.

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Microcircuit Processing Control by Optical Diffraction

Magnetic bubble circuits such as those in Fig. 1 (shown magnified about 800 times) and charge-coupled storage circuits with bit densities of 1 million bits per square inch have repetitive components which are a few microns or a fraction of a micron in dimension. The quality of the circuits is determined by high power microscope examination (1000x) or scanning electron microscopy (SEM). Both methods have numerous handling steps and a limited field of view, which makes rapid circuit evaluation difficult.

These circuits 10 (Fig. 2), being periodic in nature and containing only specific sets of components, produce discrete diffraction patterns when illuminated by a source 11 of monochromatic radiation such as a .6328 mu m wavelength helium-neon laser. These patterns, which are the optical transforms of the probed circuits, are uniquely determined by the scattering factors of the individual components and their periodicities, and thus produce the diffraction pattern of Fig. 3. Fig. 3 shows a display upon the screen 15 with a dark spot where the aperture 13 is located. Fig. 3 was photographed by a camera 12 located as indicated generally in Fig. 2.

Elimination of a focusing system makes the diffraction technique particularly attractive for microcircuit quality control under manufacturing conditions.

Listed below are applications: (1) Measurement.

The spacing d of the components is determined by the diffraction angles theta, while the variation in gap spacing between the components shows up as a line broadening in the diffraction pattern using the normal diffraction equation d = n lambda/sin theta, where lambda is the wavelength of light and n is the diffraction order of the diffraction pattern. Component periodicities of 7.5 mu m are determined to an accuracy of 1 1/2% within the p...