Methods and apparatus for measuring height on a semiconductor wafer

1. A system for determining height of a semiconductor structure, comprising:

an illumination module for directing one or more source lines or points towards a specimen having a plurality of surfaces at different relative heights;

a collection module for detecting light reflected from the surfaces, wherein the collection module contains at least two detectors that are positioned to receive light reflected from a one of the surfaces, wherein a first one of the detectors receives more reflected light from a position before a focal point and a second one of the detectors receives more reflected light from a position after the focal point so that the first and second detector receive light having different intensity values unless such one of the surfaces is at an optimum focus for which such first and second detector receive light having a same intensity; and

a processor system for determining a height value based on converting the detected light, which is received by each of the at least two detectors from two of the surfaces at different relative heights, into the height value for one of the two surfaces relative to the other of the two surfaces, wherein the height value is determined via a function or model based on a difference or ratio of light detected by the first and second detectors from the two surfaces.

2. The system of claim 1 , wherein:

the illumination module comprises a pinhole for receiving illumination light and directing a source point of the illumination light onto the specimen; and

the collection module further comprises:

a first pinhole positioned before the focal point through which a portion of the reflected light is passed to the first detector; and

a second pinhole positioned after the focal point through which a portion of the reflected light is passed to the second detector, wherein the first and second detectors are photodiode detectors.

3. The system of claim 1 , wherein:

the illumination module comprises a slit for receiving illumination light and directing a source line of the illumination light onto the specimen; and

the collection module further comprises:

a first slit positioned before the focal point through which a portion of the reflected light is passed to the first detector; and

a second slit positioned after the focal point through which a portion of the reflected light is passed to the second detector, wherein the first and second detectors are photodiode arrays.

4. The system of claim 1 , wherein the collection module further comprises a pair of pinholes or slits that are positioned such that the focal point reflected from an expected range of heights for the surfaces at different relative heights is received between or on one of such pinholes or slits with respect to image space.

5. The system of claim 4 , wherein the pair of pinholes or slits are positioned so as to receive different amounts of light when one of the surfaces is de-focused and equal amounts of light when such surface is in focus.

6. The system of claim 5 , wherein the pair of pinholes or slits are positioned so that only one of the first and second detectors receive a maximum intensity from a particular one of the surfaces when it is de-focused by a particular amount.

7. The system of claim 1 , wherein:

the illumination module comprises a slit for receiving illumination light and directing a source line of the illumination onto the specimen,

wherein the first detector is positioned before the focal point, and

wherein the second detector is positioned after the focal point.

8. The system of claim 1 , wherein:

the illumination module comprises a plurality of slits or pinholes for receiving illumination light and directing a plurality of source lines or points of the illumination onto the specimen, and

the at least two detectors are two dimensional image sensors.

9. The system of claim 1 , wherein the collection module comprises three or more detectors and the function or model further relates detected light received by the three or more detectors to a position of a surface and a longitudinal magnification factor, M.

10. The system of claim 1 , wherein the collection module further comprises a pair of pinholes or slits that are positioned relative to the first and second detectors so that the first detector receives a maximum amount of light for a maximum expected under-focus value and the second detector receives a maximum amount of light for a maximum expected over-focus value.

11. A method of determining height, comprising:

directing one or more source lines or points towards a specimen having a plurality of surfaces at different relative heights;

detecting light reflected from the surfaces, wherein the reflected light is detected by at least two detectors that are positioned to receive light reflected from a one of the surfaces, wherein a first one of the detectors receives more reflected light from a position before an optimum focal point and a second one of the detectors receives more reflected light from a position after the optimum focal point so that the first and second detector receive light having different intensity values unless such one of the surfaces is at an optimum focus for which such first and second detector receive light having a same intensity; and

determining a height value based on converting the detected light, which is received by each of the at least two detectors from two of the surfaces at different relative heights, into the height value for one of the two surfaces relative to the other of the two surfaces, wherein the height value is determined via a function or model based on a difference or ratio of light detected by the first and second detectors from the two surfaces.

12. The method of claim 11 , further comprising receiving illumination light and directing a source point of the illumination light via a source pinhole onto the specimen, wherein a first pinhole is positioned before the optimum focal point through which a portion of the reflected light is passed to the first detector and a second pinhole is positioned after the optimum focal point through which a portion of the reflected light is passed to the second detector, wherein the first and second detectors are photodiode detectors.

13. The method of claim 11 , further comprising receiving illumination light and directing a source line of the illumination light via a source slit onto the specimen, wherein a first slit is positioned before the optimum focal point through which a portion of the reflected light is passed to the first detector and a second slit is positioned after the optimum focal point through which a portion of the reflected light is passed to the second detector, wherein the first and second detectors are photodiode arrays.

14. The method of claim 11 , further comprising receiving illumination light and directing a source line of the illumination light via a source slit onto the specimen, wherein the first detector is positioned before the optimum focal point and the second detector is positioned after the optimum focal point, and wherein the first and second detectors are photodiode arrays.

15. The method of claim 11 , further comprising receiving illumination light and directing a plurality of source lines or points of the illumination light via a plurality of source pinholes or slits onto the specimen and receiving the reflected light from the surfaces at a pair of pinholes or slits that are positioned such that the focal point reflected from an expected range of heights for the surfaces at different relative heights is received between or on one of such pinholes or slits with respect to image space, and wherein the at least two detectors are two dimensional image sensors.

16. The method of claim 11 , wherein the reflected light is detected by three or more detectors, and the function or model further relates detected light received by the three or more detectors to a position of a surface and a longitudinal magnification factor, M.

17. The method of claim 11 , further comprising receiving and directing a source point or slit of the illumination light via a source pinhole or slit onto the specimen, wherein a pair of pinholes or slits are positioned relative to the first and second detectors so that the first detector receives a maximum amount of light for a maximum expected under-focus value and the second detector receives a maximum amount of light for a maximum expected over-focus value.