Apparatus for correlating an optical image and a SEM image and method of use thereof

• US 20030025087A1
• Filed: 08/01/2002
• Published: 02/06/2003
• Est. Priority Date: 08/01/2001
• Status: Active Grant

• Current Assignee: FEI Company (Thermo Fisher Scientific Incorporated)
• Original Assignee: Aspex Limited
• Inventors: Ritchie, Nicholas, Beek, Cornelis Van, Schamber, Frederick
• Granted Patent: US 6,683,316 B2
• Time in Patent Office: Days
• US Class Current: 250/491.1
• CPC Class Codes: G01N 23/2251 using incident electron beams, e.g. scanning electron microscopy [SEM]
• CPC Class Codes: H01J 2237/2826 Calibration for object processing apparatus H01J2237/30433
• CPC Class Codes: H01J 37/226 Optical arrangements for illuminating the object; optical arrangements for collecting light from the object
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: Y10S 977/86 Scanning probe structure
• CPC Class Codes: Y10S 977/869 Optical microscope
• CPC Class Codes: Y10S 977/881 Microscopy or spectroscopy, e.g. sem, tem

Abstract

An instrument system is controlled to acquire an optical image of an object, with the optical image defining a first coordinate system The object is positioned in a second coordinate system and a point in the optical image is selected. The object is repositioned so that a point on the object corresponding to the selected point in the optical image is positioned at a predetermined point in the second coordinate system. Alternatively, movement of the object causes an indicia on the optical image to move to a point thereon corresponding to the point on the object that is positioned at the predetermined point in the second coordinate system.

Claims

1. An instrument system comprising:

a camera for acquiring an optical image of an object, the optical image defining a first coordinate system;

means for positioning the object in a second coordinate system;

means for adjusting the position of the object in the second coordinate system; and

a computer operative for storing the optical image, for defining a relationship between the first and second coordinate systems and for at least one of;

(i) causing the adjusting means to move the object in response to selection of a point in the first coordinate system corresponding to a point on the optical image so that the point on the object corresponding to the point on the optical image is located at a point in the second coordinate system related to the selected point in the first coordinate system; and

(ii) causing an indicia superimposed on the optical image to move to a point in the first coordinate system corresponding to the point in the second coordinate system in response to moving the object in the second coordinate system.

2. The system as set forth in claim 1, wherein the computer includes a processor and memory means.

3. The system as set forth in claim 1, further including a monitor operatively connected to the computer.

4. The system as set forth in claim 1, further including means for positioning the digital camera and the object relative to each other in a predictable spatial manner during acquisition of the optical image.

5. The system as set forth in claim 1, wherein the computer is further operative for at least one of (i) correcting for optical distortion between the optical image and the object, (ii) correcting for a scale difference between optical image and the object, and (iii) correcting for an offset difference between a point in the optical image and a corresponding point on the object.

6. The system as set forth in claim 5, wherein, to correct for optical distortion, the computer is operative for acquiring an image of a target object having a plurality of concentric circles of known spacing, for determining a distance between each pair of concentric circles in the optical image, for determining a relationship between the distance between each pair of concentric circles in the optical image and the actual distance between each pair of concentric circles of the target object and for causing the adjusting means to position the object as a function of the determined relationship.

7. The system as set forth in claim 5, wherein, to correct for the scale difference, the computer is operative for acquiring a first optical image of an object, for recording a first location in the first optical image where a reference point is located, for recording a first position of the adjusting means related to the first location in the first optical image, for causing the adjusting means to displace the object, for acquiring a second optical image of the object, for recording a second location in the second optical image where the reference point is located, for recording a second position of the adjusting means related to the second location in the second optical image, for determining a ratio between the first and second locations and the first and second positions and for causing the adjusting means to position the object as a function of the thus determined ratio.

8. The system as set forth in claim 5, wherein, to correct for the scale difference, the computer is operative for acquiring an optical image and a first virtual test image of an object, for recording a first position of the adjusting means related to a location of a first feature in the first virtual test image, for recording a first location in the optical image where the first feature is located, for causing the adjusting means to displace the object, for acquiring a second virtual test image of the object, for recording a second position of the adjusting means related to a location of a second feature in the second virtual test image, for recording a second location in the optical image where the second feature is located, for determining a ratio between the first and second locations and the first and second positions and for causing the adjusting means to position the object as a function of the thus determined ratio.

9. The system as set forth in claim 5, further including a detector for detecting the response of the object to an electron beam and for supplying an indication of the detected response to the computer, wherein, to correct for the offset difference, the computer is operative for constructing a virtual image of the object from the indication of the detected response, for displaying the virtual image, for receiving the selection of a reference point in the virtual image, for determining a position in the virtual image corresponding to the selected reference point therein, for displaying the optical image, for receiving the selection of a corresponding reference point in the optical image, for determining a position in the optical image corresponding to the selected reference point therein, for determining a difference between the positions in the virtual and optical images and for causing the adjusting means to position the object as a function of the thus determined difference.

10. A computer-assisted method of controlling an instrument system comprising the steps of:

acquiring an optical image of an object, the optical image defining a first coordinate system;

positioning the object in a second coordinate system having a predetermined relation to the first coordinate system; and

at least one of;

in response to selecting a point in the first coordinate system, repositioning the object whereupon a point on the object corresponding to the selected point is located at a point in the second coordinate system related to the selected point in the first coordinate system; and

in response to repositioning the object, moving an indicia superimposed on the optical image to a point thereon corresponding to a point on the object that is located at the predetermined point in the second coordinate system.

11. The method as set forth in claim 10, further comprising at least one of the steps of:

correcting for optical distortion between points in the optical image and corresponding points of the object;

correcting for a scale difference in the distance between two points in the optical image and two corresponding points of the object; and

correcting for an offset difference between a point in the optical image and a corresponding point of the object.

12. The method as set forth in claim 11, wherein the step of correcting for optical distortion includes the steps of:

acquiring an image of a target object having a plurality of concentric circles of known spacing;

determining a distance between each pair of concentric circles in the optical image;

determining a relationship between the distance between each pair of concentric circles in the optical image and the actual distance between each pair of concentric circles of the target object; and

positioning the object as a function of the thus determined relationship.

13. The method as set forth in claim 11, wherein the step of correcting for the scale difference includes the steps of:

selecting a first reference point in a first optical image;

recording a first location in the first optical image where the first reference point is located;

recording a first position of the adjusting means related to the first location of the first reference point;

adjusting the position of the object;

selecting a second reference point in a second optical image;

recording a second location in the second optical image where the second reference point is located;

recording a second position of the adjusting means related to the second location of the second reference point;

determining a ratio between the first and second positions and the first and second locations; and

positioning the object as a function of the thus determined ratio.

14. The method as set forth in claim 11, wherein the step of correcting for the scale difference includes the steps of:

acquiring an optical image and a first virtual image of an object;

recording a first position of the adjusting means related to a location of a first feature in the first virtual image;

recording a first location in the optical image where the first feature is located;

moving the object;

acquiring a second virtual image of the object;

recording a second position of the adjusting means related to a location of a second feature in the second virtual image;

recording a second location in the optical image where the second feature is located;

determining a ratio between the first and second locations and the first and second positions; and

causing the adjusting means to position the object as a function of the thus determined ratio.

15. The method as set forth in claim 11, wherein the step of correcting for the offset difference includes the steps of:

detecting the response of the object to an electron beam;

constructing a scanning electron microscope (virtual) image of the object from the detected response;

selecting a reference point in the virtual image;

determining a position in the virtual image corresponding to the selected reference point therein;

selecting a reference point in the optical image corresponding to the reference point selected in the virtual image;

determining a position in the optical image corresponding to the selected reference point therein;

determining a difference between the positions in the virtual and optical images; and

positioning the object as a function of the thus determined difference.

16. An instrument apparatus comprising:

means for acquiring an optical image of an object, the optical image defining a first coordinate system;

means for positioning the object in a second coordinate system related to the first coordinate system; and

at least one of;

(i) means responsive to the selection of a point in the optical image for causing the positioning means to position the object whereupon a point on the object corresponding to the selected point in the optical image is located at a predetermined point in the second coordinate system; and

(ii) means responsive to the positioning means moving the object in the second coordinate system whereupon an indicia on the optical image moves to a point thereon corresponding to the point on the object that is located at the predetermined point in the second coordinate system.

17. The apparatus as set forth in claim 16, further including means for constructing a virtual image of the object.

18. The apparatus as set forth in claim 17, wherein the constructing means includes:

means responsive to interaction between the object and an electron beam at the second location for outputting an indication thereof; and

means responsive to the output indication for constructing the virtual image of the object.