Overlay target and overlay method
An overlay target includes a plurality of working zones, a plurality of holes in each of the working zones, and a first layer filling in the plurality of holes. The plurality of holes are not filled up by the first layer, and a plurality of spaces are reserved in the plurality of holes.
1. An overlay method, used to determine an overlay error of a device structure formed in a semiconductor manufacturing process, comprising:
forming a first overlay target, comprising:
providing a plurality of working zones;
forming a plurality of holes in a first sub-zone of each of the working zones; and
forming a first layer in the holes, wherein the holes are not filled up by the first layer, and a plurality of spaces are reserved, the spaces have a plurality of first diameters and a plurality of second diameters greater than the first diameters;
taking a plurality of midpoints of the second diameters of the spaces as a plurality of calibration center points;
forming a second overlay target, comprising forming a plurality of line segments in a second sub-zone of each of the working zones; and
determining the overlay error of the device structure by using the calibration center points and a plurality of centers of the line segments.
2. The overlay method according to claim 1 , wherein the first layer is an opaque layer.
3. The overlay method according to claim 1 , wherein the opaque layer comprises a metal layer.
4. The overlay method according to claim 1 , wherein the first layer is a deposition layer formed on a second layer and filled in a plurality of openings of the second layer.
5. The overlay method according to claim 4 , further comprising that the spaces are asymmetric.
6. The overlay method according to claim 1 , wherein a maximum thickness of the first layer in the holes is less than a radius of the holes.
7. The overlay method according to claim 1 , wherein a thickness of the first layer in the holes is not uniform.
8. The overlay method according to claim 1 , wherein shapes of the spaces are different from shapes of the holes.
9. The overlay method according to claim 8 , wherein the holes are circular and the spaces are off-axis football-shaped.