Mathematical image assembly in a scanning-type microscope

1. A method of accumulating an image of a specimen using a scanning-type microscope, comprising the following steps:

providing a beam of radiation that is directed from a source through an illuminator so as to irradiate the specimen;

providing a detector for detecting a flux of radiation emanating from the specimen in response to said irradiation;

causing said beam to undergo scanning motion relative to a surface of the specimen, and recording an output of the detector as a function of scan position,

in a first sampling session S 1 , gathering detector data from a first collection P 1 of sampling points distributed sparsely across the specimen, the collection P 1 comprising fewer than all the sampling points in a sampling grid;

repeating this the procedure of gathering detector data from subsequent collections of sampling points so as to accumulate a set {P n } of such collections, gathered during an associated set {S n } of sampling sessions, each set with a cardinality N>1;

assembling an image of the specimen by using the set {P n } as input to an integrative mathematical reconstruction procedure,

wherein, as part of said assembly process, a mathematical registration correction is made to compensate for drift mismatches between different members of the set {P n }.

2. A method according to claim 1 , wherein:

each member P n of the set {P n } is used to mathematically reconstruct a corresponding sub-image I n ;

said mathematical registration correction is used to align the members of the sub-image set {I n };

a combined image is mathematically composed from said aligned sub-image set.

3. A method according to claim 1 , wherein:

prior to reconstruction, said mathematical registration correction is used to align the members of the collection set {P n };

a composite image is mathematically reconstructed from said aligned collection set.

4. A method according to claim 1 , wherein different members of the set {P n } have different associated sparse distributions of sampling points across the specimen.

5. A method according claim 1 , wherein at least one member P n of the set {P n } comprises a sparse distribution of sampling points that is not arranged on a regular grid.

6. A method according to claim 1 , wherein correction is made for lower-order drift mismatches selected from the group consisting of displacement, rotation, and combinations hereof.

7. A method according to claim 1 , wherein correction is made for higher-order drift mismatches selected from the group consisting of skew, shear, scaling, and combinations hereof.

8. A method according to claim 1 , wherein the positions of sampling points in at least one given collection P n are at least partially elected on the basis of an analysis of at least some scan information obtained from at least one previous sampling sessions S n .

9. A method according to claim 8 , wherein;

in a given sampling session S n , sampling points in the associated collection P n . are visited sequentially while scanning out a line-by-line pattern on the specimen;

along a given line L j in said line-by-line pattern, the positions of sampling points are elected using detection results obtained in scanning a previous line L i in said line-by-line pattern.

10. A method according to claim 1 , wherein, in at least one sampling session S n , at least some of the sampling points in the associated collection P n are located below said surface of the specimen.

11. A method according to claim 1 , wherein the set {P n } is accumulated using a plurality of beams of radiation.

12. A method according to claim 1 , wherein said radiation comprises charged particles and said microscope comprises a charged-particle microscope.

13. A method according to claim 12 , wherein said charged-particle microscope is selected from the group consisting of a Scanning Electron Microscope and a Scanning Transmission Electron Microscope.

14. A method according to claim 1 , wherein said radiation comprises photons and said microscope comprises a confocal microscope.

15. A scanning-type microscope, comprising:

a specimen holder, for holding a specimen;

a source, for producing a beam of radiation;

an illuminator, for directing said beam so as to irradiate said specimen;

a detector, for detecting a flux of radiation emanating from the specimen in response to said irradiation;

beam deflectors, for causing said beam to undergo scanning motion relative to a surface of the specimen;

a controller, for recording an output of said detector as a function of scan position, wherein the controller stores instructions which can be invoked to execute the following steps:

in a first sampling session S 1 , gathering detector data from a first collection P 1 of sampling points distributed sparsely across the specimen, the collection P 1 comprising fewer than all the sampling points in a sampling grid;

repeating the procedure of gathering detector data from subsequent collections of sampling points so as to accumulate a set {P n } of such collections, gathered during an associated set {S n } of sampling sessions, each set with a cardinality N>1;

assembling an image of the specimen by using the set {P n } as input to an integrative mathematical reconstruction procedure; and

as part of said assembly process, making a mathematical registration correction to compensate for drift mismatches between different members of the set {P n }.

16. The scanning-type microscope of claim 15 wherein the stored instructions include instructions for correction of lower-order drift mismatches selected from the group consisting of displacement, rotation, and combinations hereof.

17. The scanning-type microscope of claim 15 wherein the stored instructions include instructions for correction of higher-order drift mismatches selected from the group consisting of skew, shear, scaling, and combinations hereof.

18. The scanning-type microscope of claim 15 , wherein said radiation comprises charged particles and said microscope comprises a charged-particle microscope.

19. The scanning-type microscope of claim 15 , wherein said radiation comprises photons and said microscope comprises a confocal microscope.

20. The scanning-type microscope of claim 15 wherein the stored instructions include instructions for, in at least one sampling session S n , at least some of the sampling points in the associated collection P n are located below said surface of the specimen.