What is claimed is:
1. An overlay mark for determining the relative position between two or more successive layers of a substrate or between two or more separately generated patterns on a single layer of a substrate, the overlay mark comprising:
a plurality of working zones used to calculate alignment between a first and a second layer of the substrate or between a first and a second pattern on a single layer of the substrate, each of the working zones being positioned within the perimeter of the mark, each of the working zones representing a different area of the mark, the working zones being configured to substantially fill the perimeter of the mark such that the combined area of the working zones is substantially equal to the total area of the mark.
2. The overlay mark as recited in claim 1 wherein the perimeter of the mark corresponds to the optical perimeter of the field of view of the metrology tool used to image the overlay mark, the field of view defining the area available for capturing an image via the metrology tool.
3. The overlay mark as recited in claim 1 wherein the working zones are configured to diminish the impact of non-uniformities across the mark on tool and wafer induced shifts.
4. The overlay mark as recited in claim 1 further including a periodic structure positioned within each of the working zones, each of the periodic structures including a plurality of coarsely segmented elements.
5. The overlay mark as recited in claim 4 wherein the pitch, period and duty cycle of the coarsely segmented elements is configured to balance the resolution of the metrology used to image the overlay mark and the robustness of the process used to form the layers.
6. The overlay mark as recited in claim 4 wherein the coarsely segmented elements are parallel lines.
7. The overlay mark as recited in claim 4 wherein the relative shift between the first and second layers of the wafer is determined by comparing the relative positions of periodic structures on different layers.
8. The overlay mark as recited in claim 4 wherein the plurality of coarsely segmented elements are formed by a plurality of finely segmented elements.
9. The overlay mark as recited in claim 8 wherein finely segmented elements are configured to provide shift information that more closely matches the relative shift between patterns of an integrated circuit formed on each of the two layers of the substrate.
10. The overlay mark as recited in claim 1 wherein the working zones are separated by exclusion zones.
11. The overlay mark as recited in claim 1 wherein the working zones are configured to represent one of a first layer or first pattern or a second layer or second pattern.
12. The overlay mark as recited in claim 11 wherein the working zones represent an equal number of first layers or patterns and second layers or patterns.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An aircraft slat assembly comprising a first slat and a second slat positioned adjacent thereto and aligned therewith, the first and second slats being moveable between extended and retracted positions in which the first and second slats remain aligned,
wherein the slats are connected by a joint, the joint prevents the slats becoming misaligned and the joint being arranged to transfer the shear load generated as the slats are being urged into a misaligned configuration, from one slat to the other slat, such that the shear load may be detected or otherwise used to identify the existence of a condition which could have lead to excess misalignment, before such misalignment actually occurs.
2. An assembly according to claim 1, wherein the slat assembly comprises an actuator system arranged to drive the slats between the extended and retracted positions.
3. An assembly according to claim 2, wherein the actuator system comprises a common drive means arranged to drive both the slats between the extended and retracted positions.
4. An assembly according to claim 2 further comprising a protector system, wherein the protector system is arranged to trip at least part of the actuator system in the event of an excessive load occurring in the actuator system.
5. An assembly according to claim 4 wherein the protector system is arranged to trip the actuator system when the magnitude of the shear load transferred from one slat to the other slat exceeds a threshold magnitude.
6. An assembly according to claim 1 wherein the joint comprises a rigid coupling between the slats, which substantially resists deformation under the shear load.
7. An assembly according to claim 1, wherein the joint is arranged to allow relative movement between the slats in a direction along the longitudinal axis of the slats.
8. An assembly according to claim 1, wherein the joint is arranged to allow relative rotation between the slats.
9. An assembly according to claim 1, wherein each slat comprises a first region proximal to the joint, and a second region distal from the joint, the first region being stiffer than the second region such that deformation of the slat in the first region, under the influence of the shear load, is inhibited.
10. An aircraft slat assembly comprising a first slat and a second slat positioned adjacent thereto and aligned therewith, the first and second slats being moveable between extended and retracted positions in which the first and second slats remain aligned,
wherein the slats are connected by a joint, the joint permitting relative movement between the slats in at least some directions, but the joint prevents relative movement between the slats in the direction of extensionretraction of the slats, the joint thereby prevents the slats becoming misaligned.