Optical alignment apparatus having multiple parallel alignment marks

A method of aligning first and second relatively movable plates, the first plate including a first alignment mark comprising a first pair of linear grating patterns having a first set of spatial periods and a second pair of linear grating patterns having a second set of spatial periods, and the second plate including a second alignment mark comprising a third pair of linear grating patterns having a third set of spatial periods different from said first set of spatial periods and a fourth pair of linear grating patterns having a fourth set of spatial periods different from said second set of spatial periods, said method comprising:

• illuminating the first and third pairs of grating patterns to form at least a first interference pattern therebetween having a first spatial phase;
• illuminating the second and fourth pairs of grating patterns to form at least a second interference pattern therebetween having a second spatial phase;
• and
• adjusting the relative position of said first and second plates until said first spatial phase and said second spatial phase assume a predetermined spatial phase difference.

An alignment apparatus for aligning first and second relatively movable plates, comprising:

• on a face of each of said first and second plates, first and second alignment marks, respectively, each including a first set of linear gratings of parallel lines of uniform spatial period, the spatial periods of selected linear gratings on each plate being different from each other to form first and second pairs of linear grating patterns, respectively;
• on said face of each said first and second plates, each of said first and second alignment marks including at least a second set of linear gratings of parallel lines of uniform spatial period, selected spatial periods being different from each other to form third and fourth pairs of linear grating patterns, respectively, said third and fourth pairs of linear grating patterns being disposed parallel to said first and second pairs of linear grating patterns;
• a light source for illuminating said first, second, third and fourth pairs of linear gratings to produce first, second, third and fourth interference patterns, respectively, having first, second, third and fourth spatial phases, respectively;
• a detector configured to detect when said first and second spatial phases assume a first predetermined difference in phase values, and to detect when said third and fourth spatial phases assume a second predetermined difference in phase values;
• and
• a position adjuster for adjusting the relative position of said first and second plates until said detector detects the first and second predetermined differences in phase values.

An alignment apparatus for aligning first and second relatively movable plates, comprising:

• on a face of each of said first and second plates, first and second alignment marks, respectively, each including a linear grating of parallel lines of uniform spatial period, the spatial periods being different from each other to form first and second linear grating patterns, respectively;
• on said face of each said first and second plates, at least third and fourth linear gratings of parallel lines of uniform spatial period associated with said first and second alignment marks, respectively, the spatial periods of said third and fourth linear gratings being different from each other to form third and fourth linear grating patterns, respectively;
• indicia on one of said first and second plates forming a periodic reference pattern having a reference spatial phase;
• a light source for illuminating said linear gratings to produce at least first and second interference patterns having first and second spatial phases, respectively;
• a detector configured to detect when said first and second spatial phases assume a predetermined difference in phase values, said detector configured to detect when the spatial phase of said first interference pattern and the spatial phase of said second interference pattern differ from said reference spatial phase by a predetermined value;
• and
• a position adjuster for adjusting the relative position of said first and second plates until said detector detects the predetermined difference in phase values.

An alignment apparatus for aligning first and second relatively movable plates, comprising:

• on a face of each of said first and second plates, first and second alignment marks, respectively, each including a linear grating of parallel lines of uniform spatial period, the spatial periods being different from each other to form first and second linear grating patterns, respectively;
• on said face of each said first and second plates, at least third and fourth linear gratings of parallel lines of uniform spatial period associated with said first and second alignment marks, respectively, the spatial periods of said third and fourth linear gratings being different from each other to form third and fourth linear grating patterns, respectively;
• indicia on one of said first and second plates forming a periodic reference linear grating pattern;
• a light source for illuminating said linear gratings to produce at least first and second interference patterns having first and second spatial phases, respectively;
• a detector configured to detect when said first and second spatial phases assume a predetermined difference in phase values;
• and
• a position adjuster for adjusting the relative position of said first and second plates until said detector detects the predetermined difference in phase values, wherein
• said first linear grating pattern has a spatial period p.sub.1, said second linear grating pattern has a spatial period p.sub.2, and said reference linear grating pattern lies adjacent to one of said first and second linear grating patterns and comprises a grating pattern of spatial period p.sub.3 being equal to p.sub.1 .times.p.sub.2 /.vertline.p.sub.1 -p.sub.2 .vertline..

An alignment apparatus for aligning first and second relatively movable plates, comprising:

• on a face of each of said first and second plates, first and second alignment marks, respectively, each including a linear grating of parallel lines of uniform spatial period, the spatial periods being different from each other to form at least first and second linear grating patterns, respectively;
• a light source for illuminating said linear gratings to produce at least first and second interference patterns having first and second spatial phases, respectively;
• a detector configured to detect when said first and second spatial phases assume a predetermined difference in phase values, said detector including an imaging sensor and controlled spatial filtering for inhibiting the transmission of unwanted light energy to said imaging sensor;
• and
• a position adjuster for adjusting the relative position of said first and second plates until said detector detects the predetermined difference in phase values.

An alignment apparatus for aligning first and second relatively movable plates, comprising:

• on a face of each of said first and second plates, first and second alignment marks, respectively, each including first and second linear gratings of parallel lines of uniform spatial period, the spatial periods being different from each other to form first and second linear grating patterns, respectively;
• light source for illuminating said linear gratings to produce at least first and second interference patterns having first and second spatial phases, respectively;
• a detector configured to detect when said first and second spatial phases assume a predetermined difference in phase values;
• and
• a position adjuster for adjusting the relative position of said first and second plates until said detector detects the predetermined difference in phase values, wherein
• selected gratings are formed with spaces in their lines to form a secondary grating with period p.sub.s to cause a secondary diffraction in a plane perpendicular to the primary diffraction to define light paths between the light source and detector at angles different from the normal to said plates so that the exposure area between said plates is free of optics.