Browse Prior Art Database

Universal Automatic Wafer Fine Alignment and Positioning System

IP.com Disclosure Number: IPCOM000081868D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 5 page(s) / 155K

Publishing Venue

IBM

Related People

Chwalow, ML: AUTHOR [+2]

Abstract

This system is applicable for use with a wide variety of lithographic equipments including but not limited to projection printers, width, length, and (film) thickness measuring equipment, and equipment for the measurement of color, fluorescence, etc., on small specific areas.

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Universal Automatic Wafer Fine Alignment and Positioning System

This system is applicable for use with a wide variety of lithographic equipments including but not limited to projection printers, width, length, and (film) thickness measuring equipment, and equipment for the measurement of color, fluorescence, etc., on small specific areas.

The key problems to be solved in automating wafer positioning at any process level to a specified location are those associated with signal detection in a background of noise composed of returns originating from reflections in the field of view, other than from the positioning target. The origins of the spurious reflections (so-called clutter) may be located adjacent to, over, or underneath the positioning target.

Examples of clutter in the field of view adjacent to the positioning or alignment target may include but are not limited to: pattern * metallurgy (e.g. scattering from aluminum surfaces deposited on hot substrates).

Examples of clutter in the field of view superimposed over or lying under the positioning target may include but are not limited to: film thickness structure causing interferometric return signal cancellation dirt on or presence of defects in alignment or positioning target * striated photo or electro resist changes in target shape or periodicity effectively due to shape and other optical properties of superimposed layers.

The starred items might be listed in both the fields of view adjacent to and occupied by the positioning or alignment target. Practically, the presentation of a positioning or alignment target in an uncluttered "surround" may be difficult or even impossible for anything but the first processing level, when it is realized that the "surround" includes the area occupied by the target, that is, clutter also originates from the material directly above and below the target.

Fig. 1 depicts one embodiment of the Universal Automatic Wafer and Positioning System used to align equipment for the measurement of line width. The positions of all the real images of the alignment target are marked with vertical lines ending in arrowheads and the magnifications associated therewith are referred to the alignment or positioning target on the wafer. The positions of all the diffraction patterns or Fourier transforms of the positioning target are marked F. T. PLANE and a sketch of a diffraction pattern and the magnification associated therewith are referred to the size of the first diffraction pattern, in the case depicted within the objective lens. The lenses shown in Fig. 1 were chosen for one particular application. Both the lenses and the distances shown would, a priori, be different for other applications.

In Fig. 1, the wide spectral band illumination required for alignment regardless of thickness of the film(s) over or underlying the alignment target is supplied through an off-the-shelf microscope modified Kohler vertical illuminator. A small xenon or mercury high-pressu...