Electron beam apparatus and device fabrication method using the electron beam apparatus

• US 7,244,932 B2
• Filed: 11/02/2001
• Issued: 07/17/2007
• Est. Priority Date: 11/02/2000
• Status: Expired due to Fees

• Current Assignee: Ebara Corporation
• Original Assignee: Ebara Corporation
• Inventors: Kimba, Toshifumi, Yoshikawa, Shoji, Noji, Nobuharu, Sobukawa, Hirosi, Satake, Tohru, Saito, Mutsumi, Nakasuji, Mamoru, Karimata, Tsutomu, Oowada, Shin, Hamashima, Muneki, Kohama, Yoshiaki, Okubo, Yukiharu
• Primary Examiner(s): Wells; Nikita
• Application Number:
  US09/985,323
• Publication Number:
  US 20020148961A1
• Time in Patent Office: 2,083 Days
• Field of Search: 250/306, 250/307, 250/310, 250/442.11, 250/492.3
• US Class Current: 250/306
• CPC Class Codes: G01N 23/225 using electron or ion
• CPC Class Codes: G01N 23/2251 using incident electron beams, e.g. scanning electron microscopy [SEM]
• CPC Class Codes: H01J 2237/082 Electron beam
• CPC Class Codes: H01J 2237/202 Movement
• CPC Class Codes: H01J 2237/20228 Mechanical X-Y scanning
• CPC Class Codes: H01J 2237/204 Means for introducing and/or outputting objects
• CPC Class Codes: H01J 2237/22 Treatment of data
• CPC Class Codes: H01J 2237/24564 Measurements of electric or magnetic variables, e.g. voltage, current, frequency
• CPC Class Codes: H01J 2237/2806 Secondary charged particle
• CPC Class Codes: H01J 2237/2816 Length
• CPC Class Codes: H01J 2237/2817 Pattern inspection
• CPC Class Codes: H01J 37/06 Electron sources; Electron guns
• CPC Class Codes: H01J 37/073 Electron guns using field emission, photo emission, or secondary emission electron sources
• CPC Class Codes: H01J 37/185 Means for transferring objects between different enclosures of different pressure or atmosphere
• CPC Class Codes: H01J 37/20 Means for supporting or positioning the object or the material; Means for adjusting diaphragms or lenses associated with the support
• CPC Class Codes: H01J 37/222 Image processing arrangements associated with the tube
• CPC Class Codes: H01J 37/244 Detectors; Associated components or circuits therefor
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence

Abstract

The purpose of the invention is to provide an improved electron beam apparatus with improvements in throughput, accuracy, etc. One of the characterizing features of the electron beam apparatus of the present invention is that it has a plurality of optical systems, each of which comprises a primary electron optical system for scanning and irradiating a sample with a plurality of primary electron beams; a detector device for detecting a plurality of secondary beams emitted by irradiating the sample with the primary electron beams; and a secondary electron optical system for guiding the secondary electron beams from the sample to the detector device; all configured so that the plurality of optical systems scan different regions of the sample with their primary electron beams, and detect the respective secondary electron beams emitted from each of the respective regions. This is what makes higher throughput possible. To provide high accuracy, the apparatus is configured such that the axes of its optical systems can be aligned, and aberrations corrected, by a variety of methods.

Claims

1. An electron beam apparatus comprising:

an electron optical system comprising a plurality of optical systems, each of which further comprises

a primary electron optical system for collecting, focusing, scanning and irradiating a sample with a plurality of primary electron beams;

a detector device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

a secondary electron optical system for guiding the secondary electron beams from the sample to the detector device;

configured such that the plurality of optical systems scan different regions of the sample with their primary electron beams, and detect the respective secondary electron beams emitted from each of the respective regions;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber,

wherein said secondary electron optical system has an optical axis and at least one lens along said optical axis and multiple detectors.

2. An electron beam apparatus as recited in claim 1, wherein said optical systems are arranged in a two-flow, multi-column array.

3. An electron beam apparatus as recited in claim 1, wherein said plurality of optical systems are arranged in a single row.

4. An electron beam apparatus comprising:

an optical system, further comprising

a primary electron optical system for collecting, focusing, scanning and irradiating a sample with a plurality of primary electron beams;

a detector device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

an E×

B separator device for guiding the plurality of secondary electron beams from the sample to the plurality of detector devices;

arranged such that evaluation regions are scanned by the primary electron beams, and secondary electron beams emitted from these evaluation regions are detected, wherein said E×

B separator device comprises a multiple electrostatic deflector device having at least six poles, and a saddle-type or toroidal-type electromagnetic deflector device placed around the exterior of said electrostatic deflector,

wherein the electron beam apparatus comprises a plurality of said optical systems, each of which transmits primary electron beams therethrough in a straight line perpendicular to a surface of the sample, for irradiating the sample; and

has a deflector device for deflecting, in a prescribed direction with respect to the primary electron beam, secondary electron beams from the surface of the sample, said optical systems are arranged in a two-row, multi-column array, and the secondary electron beams deflected by the deflector device of the optical systems of one of the rows of the two-row, multi-column array are deflected in a direction apart from that in which the secondary electron beams deflected by the deflector device of the optical systems of the other row are deflected, such that the paths of the secondary electron beams deflected by the deflector device do not interfere with each other.

5. An electron beam apparatus as recited in claim 4, having a laser interferometer system comprising, at least,

a laser generator;

a laser-reflecting moving mirror; and

a laser-reflecting stationary mirror attached to the outside of an objective lens;

for accurately measuring the position of said stage.

6. An electron beam apparatus as recited in claim 4, further comprising a secondary-electron-image-forming circuit and a reference standard image memory;

and a device for detecting, and correcting, a positional offset between a secondary electron image and a reference standard image.

7. A device fabrication method comprising:

(a) preparing wafers;

(b) performing a wafer processing process;

(c) inspecting wafers using the electron beam apparatus as recited in claim 4;

(d) repeating above steps (b) and (c); and

(e) assembling devices.

8. An electron beam apparatus comprising:

an optical system, further comprising

a primary electron optical system for collecting, focusing, scanning and irradiating a sample with a plurality of primary electron beams;

a detector device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

an E×

B separator device for guiding the plurality of secondary electron beams from the sample to the plurality of detector device;

arranged such that evaluation regions are scanned by the primary electron beams, and secondary electron beams emitted from these evaluation regions are detected, wherein said E×

B separator device comprises a multiple electrostatic deflector device having at least six poles, and a saddle-type or toroidal-type electromagnetic deflector device placed around the exterior of said electrostatic deflector,

wherein it comprises a plurality of said optical systems, each optical system thereof transmits primary electron beams therethrough to a surface of the sample, for irradiating the sample; and

has a deflector device for deflecting, in a prescribed direction with respect to the primary electron beam, the secondary electron beams from the surface of the sample;

said optical systems are arranged in a single row;

each of said optical systems has a plurality of primary electron beams aligned in the direction of said single row for irradiating the sample; and

each of said deflector devices is configured for deflecting the secondary electron beams in a direction substantially perpendicular to the direction of said single row.

9. An electron beam apparatus comprising an electron optical system further comprising:

an optical system still further comprising

a primary electron optical system for scanning and irradiating a sample with a plurality of primary electron beams;

a detection device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

an E×

B separator device for guiding the secondary electron beams from the sample to the detection device;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein said electron optical system performs axial alignment for minimizing differences between the focusing conditions of at least two of said plurality of electron beams.

10. An electron beam apparatus as recited in claim 9, wherein both of said two electron beams are positioned on a circle, the center of which is at the optical axis.

11. An electron beam apparatus comprising:

an electron optical system further comprising an optical system comprising

a primary electron optical system for scanning and irradiating a sample with a plurality of primary electron beams;

a detection device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

a secondary electron optical system for guiding the secondary electron beams from the sample to the detection device;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein said primary and secondary electron optical system comprises an electron lens, and said electron optical system performs axial alignment of said primary or secondary electron beams with respect to said electron lens, such that when a slight change is made in the excitation of said lens, the amount of positional displacement of at least two electron beams is substantially equal.

12. A device fabrication method comprising:

(a) preparing wafers;

(b) performing a wafer processing process;

(c) inspecting wafers using the electron beam apparatus as recited in claim 11;

(d) repeating above steps (b) and (c); and

(e) assembling devices.

13. An electron beam apparatus comprising:

an electron optical system having an optical system further comprising

a primary electron optical system for collecting, focusing, scanning and irradiating a sample with a plurality of primary electron beams;

a detector device for detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

a secondary electron optical system for guiding the secondary electron beams from the sample to the detector device;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein said primary electron optical system comprises an electron gun; and

an aperture plate having a plurality of apertures for passing therethrough, a plurality of electron beams from the electron gun, for forming said plurality of primary electron beams;

and said aperture plate is mounted on one or more stages reflected from the group consisting of a θ

stage and a Z stage; and

said one or more stages are configured such that the intensities of said plurality of primary electron beams are made substantially equal, or are maximized.

14. An electron beam apparatus alignment method in an electron beam apparatus having an electron optical system comprising:

scanning and irradiating a sample with a plurality of primary electron beams;

guiding the secondary electron beams from the sample to the detection device through a secondary electron optical system;

detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams; and

executing axial alignment of the primary or the secondary electron optical system of said electron beam apparatus by minimizing differences between the focusing conditions of at least two of said plurality of primary or secondary of electron beams.

15. An adjustment method as recited in claim 14, wherein said apparatus has an objective lens, and the objective lens has an electrostatic electrode.

16. An axial alignment method for an electron beam apparatus comprising:

scanning and irradiating a sample with a plurality of primary electron beams;

guiding the secondary electron beams from the sample to the detection device; and

detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams;

wherein the primary are the secondary electron optical system comprises an electron lens;

axial alignment of the primary or secondary electron beam with respect to said electron lens is preformed by making adjustments such that when a slight change is made in the excitation conditions of said lens, the amount of positional displacement of at least two of the electron beams will be substantially equal.

17. An adjustment method as recited in claim 16 wherein the plurality of primary electron beams is obtained by irradiating an aperture plate having a plurality of apertures therein, with the electron beam emitted from the electron source.

18. An optical system adjustment method for an electron beam apparatus, the method comprising:

scanning and irradiating a sample with a plurality of primary electron beams;

guiding by a secondary electron optical system, the secondary electron beams from the sample to the detection device;

detecting a plurality of secondary electron beams emitted by irradiating the sample with the primary electron beams;

wherein said primary optical system comprises an electron gun and an aperture plate having a plurality of apertures for passing therethrough electron beams emitted from the electron gun, for forming said plurality of primary electron beams;

said aperture plate is mounted on one or more stages selected from the group consisting of θ

stage and a Z stage, and

said one or more stages being configured such that the intensities of said plurality of primary electron beams are made substantially equal, or are maximized.

19. An adjustment method as recited in claim 18, wherein said adjustment is performed after axial alignment of the objective lens has been performed.

20. An electron beam apparatus comprising:

a deflector device for scanning electron beams over a sample;

an image-forming circuit for forming an image in synchronization with the scanning of the electron beams;

an electron beam deflector device placed on an optical axis;

a deflection signal generator device; and

a device for changing an output of the deflection signal generator device, and supplying it to said electron beam deflector device;

wherein said electron beam deflector device further comprises

an electron optical system configured to be capable of receiving the changed output from the deflection signal generator device, and deflecting the electron beams;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber; and

wherein said electron optical system is configured such that secondary electron beams emitted from the sample are passed through an objective lens, are separated from a primary beam by an E×

B separator device, are passed through at least one lens stage and an aperture, and are detected by a multiple-detector device; and

comprises a mechanism configured such that the primary electron beams are caused to pass through the center of an aperture stop by changing the output of the deflection signal generator device.

21. An electron beam apparatus as recited in claim 20, wherein the image is formed by the output of at least one of the detector devices of said multiple-detector device.

22. An electron optical system as recited in claim 20, wherein the multibeam beamlets are arranged in straight line.

23. An electron beam apparatus comprising:

a deflector device for scanning an electron beam over a sample;

an image-forming circuit for forming in synchronization with the scanning of the electron beam;

an electron beam deflection device placed on an optical axis;

a deflection signal generator device; and

a device for changing an output of the deflection signal generator device, and supporting it to said electron beam deflection device;

wherein said electron beam deflector device further comprises

an electron optical system configured to be capable of receiving the changed output from the deflection signal generator device, and deflecting the electron beam;

a stage device for supporting the sample;

a working chamber for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein said electron optical system is configured such that a secondary electron beam emitted from the sample is passed through an objective lens, is separated from a primary beam, by an E×

B separator device, and is detected by a detector device; and

comprises a mechanism configured such that the primary electron beam is caused to pass through the center of an aperture stop by changing the output of the deflection signal generator device; and

wherein the aperture stop is provided between the E×

B separator device and a beam source.

24. An electron beam apparatus as recited in claim 23, further comprising an objective lens and an alignment signal for the objective lens alignment, which superimposes a scan signal on the alignment signal, and supplies it to said electron beam deflector device.

25. A device fabrication method comprising:

(a) preparing wafers;

(b) performing a wafer processing process;

(c) inspecting wafers using the electron beam apparatus as recited in claim 23;

(d) repeating above steps (b) and (c); and

(e) assembling devices.

26. An electron beam apparatus axial alignment method in an electron optical system, the method comprising:

emitting an electron beam from a single electron gun;

forming multibeam beamlets by an aperture plate from the beam emitted from the electron gun;

irradiating through a lens and an E×

B separator device, with the multibeam beamlets, a sample to be scanned; and

separating the secondary electrons emitted from the sample through a secondary optical system, guiding them by the E×

B separator device into a detector device for detecting secondary electrons;

changing the electric or magnetic field applied to the E×

B separator device making the magnitudes of the positional displacements of at least two electron beams equidistant from the optical axis of the primary optical system equal.

27. An electron beam apparatus alignment method as recited in claim 26, wherein the multibeam beamlets are arranged in straight line.

28. An electron beam apparatus comprising:

an electron optical system, further comprising

a stage on which a sample can be loaded;

a position measurement mark provided on the stage;

an electron-beam-forming device for forming a plurality of primary electron beams;

a scanning device for scanning the primary electron beams such that the position measurement mark associated therewith are scanned at the same time by the plurality of primary electron beams;

a separator device for separating, from the paths of the plurality of primary electron beams, a plurality of secondary electron beams emitted from the mark by the scanning of the plurality of primary electron beams thereover, by the scanning device;

a detector device for detecting the plurality of secondary electron beams separated by the separator device; and

a measurement device for comparing differences between the plurality of signals, and measuring the positional displacement of irradiated points relative to the position measurement mark, based on differences between the plurality of signals;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein the electron optical system has a correction device or a calibration device for correcting the points irradiated by the plurality of primary electron beams, based on the positional displacement, when said positional displacement is measured by the measurement device.

29. An electron beam apparatus as recited in claim 28, wherein said correction device comprises a lens of at least two stages, placed between the electron-beam-forming device and the sample;

and a two-stage lens control device for operating the two stage lens, for adjusting the distances between the irradiation points and the position measurement mark such as to minimize differences between said plurality of signals.

30. An electron beam apparatus as recited in claim 28 wherein the measurement device determines, based on said positional displacement, whether the plurality of primary electron beams has a positioning error in terms of their rotation about the optical axis;

and provided in the calibration device, between the electron-beam-forming device and the separator device, is a function that is capable of rotating the plurality of primary electron beams and when a rotation error is detected, rotates the beams as required to bring the value of the rotation error within tolerance.

31. An electron beam apparatus as recited in claim 28, wherein a memory device is provided for storing the positions of the position measurement mark, and when the measurement device measures positional displacement, and the plurality of primary electron beam irradiation points is calibrated based on that positional displacement, the positions of the position measurement mark, as stored in the memory device, are updated, based on the calibrated irradiation points of the primary electron beams.

32. An electron beam apparatus comprising:

an electron-beam-forming device for forming a plurality of primary electron beams; and

a position measurement mark formed on said stage, for scanning the plurality of primary electron beams such that the plurality of primary beams and their associated position measurement mark is scanned at the same time;

a plurality of secondary electron beams emitted from the position measurement mark as a result of the scanning of the plurality of primary electron beams by the scanning device;

a detector device, for detecting said plurality of secondary electron beams

a measurement device that compares differences in said plurality of signals, and based on the differences in the plurality of signals, measures positional displacements of said irradiation points relative to the position measurement mark; and

a correction device or calibration device for correcting or calibrating the irradiation points irradiated by the plurality of primary electron beams, based on positional displacements thereof, as measured by the measurement device.

33. An electron beam apparatus as recited in claim 32, wherein said correction device comprises a lens of at least two stages, placed between the electron-beam-forming device and the sample;

and a two-stage lens control device for operating the two stage lens, for adjusting the distances between the irradiation points and the position measurement mark such as to eliminate differences between said plurality of signals.

34. An electron beam apparatus as recited in claim 32, wherein the measurement device determines, based on said positional displacement, whether the plurality of primary electron beams has a positioning error n terms of rotation centered on the optical axis;

and the calibration device is provided between the electron-beam-forming device and the separator device, and is capable of rotating the plurality of primary electron beams; and

when a rotation error is detected, the beams can be rotated to bring the value of the rotation error within tolerance.

35. An electron beam apparatus as recited in claim 32, wherein a memory device is provided for storing the positions of the position measurement marks, and when the measurement device measures positional displacement, and the plurality of primary electron beam irradiation points is calibrated based on that positional displacement, the positions of the position measurement marks, as stored in the memory device, are updated, based on the calibrated irradiation points of the primary electron beams.

36. An electron beam apparatus comprising:

an electron optical system for

directing, onto a sample, a plurality of primary electron beams obtained from an electron beam emitted from an electron beam source having a cathode,

operating a deflection device to separate, from a primary optical system,

a plurality of secondary electron beams emitted from the sample, such that the separation occurs after the secondary electron beams have passed through an objective lens, and before they reach a lens immediately subsequent thereto,

injecting the secondary electron beams into a secondary optical system, and

guiding them to a detector circuit;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

wherein said electron optical system has a function for varying a voltage applied to the cathode of the electron source to adjust for the least movement, on the sample, of the plurality of primary electron beams, in the radial direction, and in rotation centered on the optical axis, in order to adjust the position along the optical axis of a crossover formed near the objective lens by the plurality of primary electron beams.

37. An electron beam apparatus as recited in claim 36, wherein the objective lens has an electrostatic electrode.

38. An electron beam apparatus as recited in claim 36, wherein the plurality of primary electron beams is obtained by irradiating, with the electron beam emitted from the electron source, an aperture plate having a plurality of apertures therein.

39. An electron beam apparatus comprising:

an electron optical system further comprising

a single electron gun for emitting an electron beam;

a condenser lens;

an aperture plate having a plurality of apertures provided therein;

a primary optical system, having an E×

B separator device and an objective lens, for irradiating, with the electron beams from the electron gun, the surface of a sample to be inspected; and

a secondary optical system, for injecting into a secondary electron detector device, secondary electrons that have been emitted from the sample, accelerated by the objective lens, and separated from the primary optical system by the E×

B separator device;

a stage device, for supporting the sample;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber;

configured such that the condenser lens of the electron optical system is placed adjacent to the electron gun, the aperture plate is placed after a crossover formed by the preceding condenser lens, and the aperture plate is irradiated by the electron beam to form a plurality of electron beamlets.

40. An electron beam apparatus as recited in claim 39, wherein the electron gun thereof is operated under space-charge-limited conditions.

41. An electron beam apparatus as recited in claim 40, wherein it is configured such that the position, in the radial direction, of the highest intensity portion of the beam emitted from the electron gun can be aligned with the aperture region of the aperture plate by changing the position of a crossover formed by the condenser lens adjacent to the electron gun.

42. An electron beam apparatus comprising:

a single electron gun for emitting an electron beam;

a condenser lens;

an aperture plate having a plurality of apertures provided therein;

a primary optical system, having an E×

B separator device and an objective lens, for irradiating, with the electron beams from the electron gun, the surface of a sample to be inspected; and

a secondary optical system, for injecting into a secondary electron detector device, secondary electrons that have been emitted from the sample, accelerated by the objective lens, and separated from the primary optical system by the E×

B separator device;

configured such that the condenser lens is placed adjacent to the electron gun, the aperture plate is placed after a crossover formed by the preceding condenser lens, and the aperture plate is irradiated by the electron beam to form a plurality of electron beamlets.

43. An electron beam apparatus comprising:

an electron optical system further comprising

a primary and secondary optical system that constitute a primary optical system for irradiating a sample with a plurality of primary electron beams, and a secondary optical system for guiding secondary electrons from the sample to a detector device, wherein the separation between the primary beams is such that the individual electron beams irradiate locations separated by a distance greater than the distance resolution of the secondary optical system;

a stage device for effecting relative motion between the primary beam irradiation positions of the primary optical system and the sample position;

a working chamber, for containing the stage device within a vacuum atmosphere therein; and

a loader for supplying a sample onto the stage device in the working chamber.

44. An electron beam apparatus as recited in claim 43, further comprising a measurement device for measuring a dose based on the magnitudes of the beam currents of the primary electron beams irradiating the sample and the speed of the relative motion effected by the stage device.

45. An electron beam apparatus as recited in claim 43, further comprising a measurement device for measuring a dose based on the quantity of secondary electrons emitted from the sample.

46. An electron beam apparatus as recited in claim 43, wherein the electron optical system comprises an image acquisition device for acquiring image data on the sample based on secondary electrons emitted therefrom;

and the measurement device measures said dose based on the contrast ratios of the image data acquired by the image acquisition device.

47. An electron beam apparatus comprising:

an electron optical system comprising a plurality of optical systems, each of which further comprising;

an optical system having a primary optical system for irradiating a sample with a primary electron beam, and a secondary electron detector device,

an actuator device for effecting relative motion between the primary electron beam irradiation positions of the primary optical system and the sample position;

a measurement device for measuring the dose of the primary electron beams irradiating the sample during operation of the primary optical system and stage device;

wherein each optical system thereof passes through primary electron beam in a straight line perpendicular to a surface of the sample, for irradiating the sample, and also has a deflector device for deflecting, in a prescribed direction with respect to the primary electron beams, the secondary electron beam, the surface of the sample;

said optical systems are arranged in a two-flow, multi-optical axis array; and

the secondary electron beams deflected by the deflector device of the optical system of one of the rows of the two-rows, the multi-optical axis array are deflected by the deflector devices of the optical system of the other row are deflected, such that the path of the secondary electron beams deflected by the deflection devices do not interfere with each other.

48. An electron beam apparatus as recited in claim 47, wherein the measurement device measures said dose based on the magnitudes of the beam currents of the electron beams irradiating the sample and the speed of the relative motion effected by the actuator.

49. An electron beam apparatus as recited in claim 47, wherein the measurement device measures said dose based on the quantity of secondary electrons emitted from the sample.

50. An electron beam apparatus as recited in claim 47, wherein the measurement device comprises an image acquisition device for acquiring image data on the sample, based on secondary electrons emitted therefrom;

and the measurement device measures said dose based on the contrast ratios of the image data acquired by the image acquisition device.

51. A device fabrication method comprising:

(a) preparing wafers;

(b) performing a wafer processing process;

(c) inspecting wafers using the electron beam apparatus as recited in claim 47;

(d) repeating above steps (b) and (c); and

(e) assembling devices.