Alignment sensor and height sensor
One embodiment relates to a device that senses alignment and height of a work piece. The device may include both an alignment sensor and a height sensor. The alignment sensor generates a first illumination beam that illuminates an alignment mark on the work piece so as to create a first reflected beam, and determines the alignment of the work piece using the first reflected beam. The height sensor generates a second illumination beam that is directed to a surface of the work piece at an oblique angle so as to form a second illumination spot and images the second illumination spot to determine the height of the work piece. Other embodiments, aspects and features are also disclosed.
1. A device that senses alignment and height of a work piece, the device comprising:
an alignment sensor that generates a first illumination beam that forms a first illumination spot having a long axis of illumination and a short axis of illumination which illuminates an alignment mark on the work piece so as to create a first reflected beam, and detects the first reflected beam using a detector that generates a signal indicating alignment of the first illumination beam relative to the alignment mark, wherein the alignment sensor includes a mechanism for controllably rotating the first illumination spot by ninety degrees; and
a height sensor that generates a second illumination beam that is directed to a surface of the work piece at an oblique angle so as to form a second illumination spot and uses a detector that locates a center of the second illumination spot to determine the height of the work piece.
2. The device of claim 1 , wherein the alignment sensor and the height sensor have a same optical axis.
3. The device of claim 1 , wherein the alignment mark on the work piece comprises a long dimension and a short dimension, and wherein the first illumination spot is rotated using the mechanism so that the long axis of illumination is parallel to the long dimension of the alignment mark and the short axis of illumination is parallel to the short dimension of the alignment mark.
4. The device of claim 3 , wherein the shape of the first illumination spot is one of a group of shapes consisting of an ellipse and a rectangle.
5. The device of claim 3 , wherein the alignment sensor comprises a cylindrical lens that shapes the first illumination beam so as to form the shape of the first illumination spot, and wherein the mechanism rotates the cylindrical lens.
6. The device of claim 3 , wherein the alignment sensor comprises an illumination aperture in an image plane that shapes the first illumination beam so as to form the shape of the first illumination spot, and wherein the mechanism rotates the illumination aperture.
7. The device of claim 3 , wherein the alignment sensor comprises an illumination source that is shaped so as to form the shape of the first illumination spot, and wherein the mechanism rotates the illumination source.
8. The device of claim 1 , wherein the height sensor generates a derivative signal of the second illumination spot.
9. The device of claim 8 , wherein the height sensor applies a threshold to the derivative signal to construct a spot outline and finds a center of the spot outline to determine a center of the second illumination spot.
10. The device of claim 1 further comprising:
a polarizing filter that polarizes the second illumination beam.
11. A method of determining an alignment and height of a work piece, the method comprising:
generating a first illumination beam using a first illumination source;
shaping the first illumination beam using an illumination lens to form a first illumination spot on the work piece, the first illumination spot having a shape comprising a long axis of illumination and a short axis of illumination;
rotating the first illumination spot by rotating an optical element so that the long axis of illumination is parallel to a long dimension of a rectangular alignment mark on the work piece and the short axis of illumination that is parallel to a short dimension of the rectangular alignment mark;
obtaining a first reflected beam from the first illumination spot using an objective lens;
determining the alignment using the first reflected beam by diffracting the first reflected beam using a grating to generate a diffracted beam and detecting the diffracted beam using a first detector so as to determine the alignment;
generating a second illumination beam using a second illumination source that is directed to a surface of the work piece at an oblique angle such that a second illumination spot is formed on the surface of the work piece; and
imaging the second illumination spot using a second detector so as to determine a height of the surface.
12. The method of claim 11 further comprising:
generating a derivative signal of the second illumination spot;
applying a threshold to the derivative signal to construct a spot outline; and
locating a center of the spot outline to determine a center of the second illumination spot.