Method of sampling a sample and displaying obtained information

Abstract

The invention relates to a method of sampling and displaying information comprising scanning a beam over the sample in a series of N overlapping sub-frames, each comprising M.sub.n scan positions, thereby irradiating the sample at N×M.sub.n scan positions, which form the field of view; detecting a signal, sampled for each scan position, emanating from the sample; and displaying the sub-frames having at least N×M.sub.n pixels in such a way, that after the series of N scans each of the pixels displays information derived from the signal from one or more scan positions; in which after the scan of the first sub-frame each of the pixels displays information derived from the scan positions of the first sub-frame; and after the scan of the second sub-frame each of the pixels displays information derived during the scanning of the first, the second, or both sub-frames.

Claims

1. A method of sampling a sample and displaying obtained information on a display, the method comprising: scanning a beam over the sample in a series of N overlapping sub-frames of a frame, one sub-frame at a time, each sub-frame comprising M.sub.n scan positions spanning over an entire image area of the frame, except for at least two peripheral pixel areas, and spread over M.sub.n sub-cells with each sub-cell having a scan position for each sub-frame, the scan positions of each sub-frame not overlapping with the scan positions of other sub-frames, the beam thereby irradiating the sample at N×M.sub.n scan positions, the N×M.sub.n scan positions forming a field of view; using a detector detecting a signal emanating from the sample in response to the irradiation of the sample by said beam, said signal sampled for each of the N×M.sub.n scan positions; and displaying the sub-frames on the display using at least N×M.sub.n pixels in such a way that after the series of N scans, each of the at least N×M.sub.n pixels displays information derived from the signal from one or more of the N×M.sub.n scan positions; in which: after the scan of the first sub-frame each of the at least N×M.sub.n pixels displays information derived from one or more scan positions of the first sub-frame and at least part of the at least N×M.sub.n pixels show interpolated information derived from two or more scan positions of the first sub-frame; and after the scan of the second sub-frame each of the at least N×M.sub.n pixels displays information derived during the scanning of the first sub-frame, the second sub-frame, or both sub-frames.

2. The method of claim 1 in which the number of scan positions and pixels per sub-frame is identical for all sub-frames.

3. The method of claim 1 in which N=(k.sub.x×k.sub.y), with k.sub.x and k.sub.y a positive integer, at least one of k.sub.x and k.sub.y larger than 1, more specifically N=k.sup.2, with k an integer larger than 1.

4. The method of claim 1 in which the beam is a beam from the group of infrared light, visible light or X-rays, or a beam of particles from the group of electrons, ions, charged clusters, charged molecules, atoms or molecules.

5. The method of claim 1 in which for at least one of the series of N sub-frames the position of the sub-frame with respect to one or more of the other sub-frames is corrected for drift and/or vibration and/or displacement of the sample.

6. The method of claim 1 in which a new sequence of sub-frames is started after displacement larger than a predetermined value is detected between the last obtained sub-frame and at least one of earlier obtained sub-frames.

7. The method of claim 1 in which a user can initiate the start of a new sequence of sub-frames, or a new sequence of sub-frames is started after a movement of a sample stage on which the sample is mounted, a change of the field of view, or a change in detector settings.

8. The method of claim 1 in which the detector detects the number and/or energy and/or angular distribution of X-ray photons, light photons, secondary electrons or backscattered electrons emanating from the sample.

9. The method of claim 1 in which a scan time of each sub-frame is identical to a scan time of each other sub-frame.

10. The method of claim 1 wherein, within each sub-cell, the scan positions for each sub-frame are offset from the each other such that no two scan positions are adjacent side-by-side or adjacent top-to-bottom.

11. A charged-particle apparatus comprising: a charged particle source for producing a charged particle beam; a sample holder for holding and positioning a sample; a charged-particle lens system for directing said beam through the sample; a detector for detecting a signal emanating from the sample in response to the irradiation of the sample by the beam; and a system controller including a program memory for storing machine readable instructions for: scanning the beam over the sample in a series of N overlapping sub-frames of a frame, one sub-frame at a time, each sub-frame comprising M.sub.n scan positions spanning over an entire image area of the frame, except for at least two peripheral pixel areas, and spread over M.sub.n sub-cells with each sub-cell having a scan position for each sub-frame, the scan positions of each sub-frame not overlapping with the scan positions of other sub-frames, the beam thereby irradiating the sample at N×M.sub.n scan positions, the N×M.sub.n scan positions forming a field of view; using the detector to detect a signal emanating from the sample in response to the irradiation of the sample by the beam, said signal sampled for each of the N×M.sub.n scan positions; and displaying the sub-frames on the display using at least N×M.sub.n pixels in such a way that after the series of N scans, each of the at least N×M.sub.n pixels displays information derived from the signal from one or more of the N×M.sub.n scan positions; in which: after the scan of the first sub-frame each of the at least N×M.sub.n pixels displays information derived from one or more scan positions of the first sub-frame and at least part of the at least N×M.sub.n pixels show interpolated information derived from two or more scan positions of the first sub-frame; and after the scan of the second sub-frame each of the at least N×M.sub.n pixels displays information derived during the scanning of the first sub-frame, the second sub-frame, or both sub-frames.

12. The charged particle apparatus of claim 11 in which the number of scan positions and pixels per sub-frame is identical for all sub-frames.

13. The charged particle apparatus of claim 11 in which N=(k.sub.x×k.sub.y), with k.sub.x and k.sub.y a positive integer, at least one of k.sub.x and k.sub.y larger than 1, more specifically N=k.sup.2, with k an integer larger than 1.

14. The charged particle apparatus of claim 11 in which the beam is a beam from the group of infrared light, visible light or X-rays, or a beam of particles from the group of electrons, ions, charged clusters, charged molecules, atoms or molecules.

15. The charged particle apparatus of claim 11 in which for at least one of the series of N sub-frames the position of the sub-frame with respect to one or more of the other sub-frames is corrected for drift and/or vibration and/or displacement of the sample.

16. The charged particle apparatus of claim 11 in which a new sequence of sub-frames is started after displacement larger than a predetermined value is detected between the last obtained sub-frame and at least one of earlier obtained sub-frames.

17. The charged particle apparatus of claim 11 in which a user can initiate the start of a new sequence of sub-frames, or a new sequence of sub-frames is started after a movement of a sample stage on which the sample is mounted, a change of the field of view, or a change in detector settings.

18. The charged particle apparatus of claim 11 in which the detector detects the number and/or energy and/or angular distribution of X-ray photons, light photons, secondary electrons or backscattered electrons emanating from the sample.

19. The charged particle apparatus of claim 11 in which a scan time of each sub-frame is identical to a scan time of each other sub-frame.

20. The apparatus of claim 11 wherein, within each sub-cell, the scan positions for each sub-frame are offset from the each other such that no two scan positions are adjacent side-by-side or adjacent top-to-bottom.

Description

(1) The invention is now elucidated using figure, in which identical reference numerals indicate corresponding features. To that end:

(2) FIG. 1 schematically shows the scanning strategy used in MUSE;

(3) FIG. 2 schematically shows a SEM.

(4) FIG. 1 schematically shows the scanning strategy used in MUSE.

(5) In MUSE a frame consists of 4 sub-frames. Each sub-frame is displaced with respect to the other sub-frames. The 1.sup.st sub-frame consists of the scan positions marked “1”, and displays these scan positions on the corresponding positions of a display. Likewise the second sub-frame consists of the scan positions marked “2”, and displays these scan positions on the corresponding positions of a display, etc. Analog to crystallography, several “unit-cells” can be defined, such as unit-cell 10, unit-cell 11 and unit-cell 12. Each of these cells contains one scan position of each of the N sub-frames with a minimum of displacement. Especially the diamond shaped unit cell 12 is suited to use as a cell to fill the complete image of N-sub-frames, although its orientation is such that it is unlikely to fit the image of N*M scan positions, as such images often show straight edges.

(6) The MUSE scan scheme shows many unscanned areas 15. As can be seen in the unit-cells, only half of the area of the sample is scanned, resulting in undersampling (not sampling all the area of the sample). To avoid undersampling a slightly oversized spot 20 can be used to scan the image. This lowers the undersampling, although (depending on the diameter of the spot and the scan raster) it may lead to a slight oversampling, where one sample contains information of other scan positions as well.

(7) FIG. 2 schematically shows a SEM equipped to perform the method according to the invention.

(8) FIG. 2 shows an apparatus 200 with a scanning electron microscope column 241, along with power supply and control unit 245. An electron beam 232 is emitted from a cathode 253 by applying voltage between cathode 253 and an anode 254. Electron beam 232 is focused to a fine spot by means of a condensing lens 256 and an objective lens 258. Electron beam 232 is scanned two-dimensionally on the specimen by means of a deflection coil 260. The deflector coils can deflect the beam along the x-axis and along the y-axis so that the beam can be scanned along a sample surface in a simple or complex pattern, such as a raster scan, serpentine scan, or a Hilbert scan. Deflectors can be magnetic or electrostatic. Operation of condensing lens 256, objective lens 258, and deflection coil 260 is controlled by power supply and control unit 245.

(9) A system controller 233 controls the operations of the various parts of the apparatus 200. The vacuum chamber 210 is evacuated with ion pump 268 and mechanical pumping system 269 under the control of vacuum controller 234.

(10) Electron beam 232 can be focused onto sample 202, which is on a movable X-Y stage 204 within vacuum chamber 210. When the electrons in the electron beam strike sample 202, the sample gives off radiation. Backscattered electrons are detected by backscattered electron detector 242, preferably a segmented silicon drift detector.

(11) Data processor 220 can comprise a computer processor, programmable gate array, or other digital or analog processing means; operator interface means (such as a keyboard or computer mouse); program memory 222 for storing data and executable instructions; interface means for data input and output, executable software instructions embodied in executable computer program code; and display 244 for displaying the results by way of video circuit 292.

(12) Data processor 220 can be a part of a standard laboratory personal computer, and is typically coupled to at least some form of computer-readable media. Computer-readable media, which include both volatile and nonvolatile media, removable and non-removable media, may be any available medium that can be accessed by data processor 220. By way of example and not limitation, computer-readable media comprise computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. For example, computer storage media include RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by processor 220.

(13) Also program memory 222 can include such computer storage media in the form of removable and/or non-removable, volatile and/or nonvolatile memory and can provide storage of computer-readable instructions, data structures, program modules and other data.

(14) By loading the program memory with appropriate instructions, the apparatus is equipped to perform the method according to the invention.

(15) It is noted that, although the apparatus discussed here is an apparatus equipped with an electron microscope column, but also apparatuses equipped with a focused ion beam column, a laser beam column, a charged cluster column, etc., may be used, as well as combinations thereof.

(16) It is further noted that the demand for a long dwell time can vary: it may be the result of the sample (for example fluorescence or phosporescense result in long decay time, necessitating log sample times), or the detector (for example as a result of the deterioration of the signal-to-noise ratio when the sampling time is low, or having a limited bandwidth).

Non-Patent Literature

(17) [-1-] Brochure for the Nova NanoSEM, FEI Company: http://www.fei.com/products/scanning-electron-microscopes/nova-nanosem/nanosembrochure.aspx [-2-] “Interlace and MPEG—Can motion compensation help?”, J. O. Drewery, International Broadcasting Convention 1994 (IBC1994). http://www.bbc.co.uk/rd/pubs/papers/pdffiles/jodibc94.pdf [-3-] “A Fast Super Resolution Algorithm for SEM Image”, L. Hengshu, Proc. of SPIE Vol. 6623 66231Z.