Electron beam apparatus and a device manufacturing method using the same apparatus Number:7,385,197 from the United States Patent and Trademark Office (PTO) owispatent

Title: Electron beam apparatus and a device manufacturing method using the same apparatus

Abstract: Disclosed is an electron beam apparatus, in which a plurality of electron beams is formed from electrons emitted from an electron gun 21 and used to irradiate a sample surface via an objective lens 28, said apparatus comprising: a beam separator 27 for separating a secondary electron beams emanating from respective scanned regions on the sample from the primary electron beams; a magnifying electron lens 31 for extending a beam space between adjacent beams in the separated plurality of secondary electron beams; a fiber optical plate 32 for converting the magnified plurality of secondary electron beams to optical signals by a scintillator and for transmitting the signals; a photoelectric conversion device 35 for converting the optical signal to an electric signal; an optical zoom lens 33 for focusing the optical signal from the scintillator into an image on the photoelectric conversion device; and a rotation mechanism 36 for rotating the photoelectric conversion device 35 around the optical axis.

Patent Number: 7,385,197 Issued on 06/10/2008 to Nakasuji,   et al.

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Inventors:	Nakasuji; Mamoru (Yokohama, JP), Noji; Nobuharu (Zushi, JP), Satake; Tohru (Chigasaki, JP), Murakami; Takeshi (Tokyo, JP), Sobukawa; Hirosi (Isehara, JP), Kaga; Toru (Hachioji, JP), Hatakayama; Masahiro (Fujisawa, JP)
Assignee:	Ebara Corporation (Tokyo, JP)
Appl. No.:	11/175,390
Filed:	July 7, 2005

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Foreign Application Priority Data

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Jul 08, 2004 [JP]			2004-201736
Jul 21, 2004 [JP]			2004-213083
Aug 26, 2004 [JP]			2004-246468

Current U.S. Class:	250/310 ; 250/306; 250/307; 250/492.1; 250/492.2; 250/492.3
Field of Search:	250/310

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References Cited [Referenced By]

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U.S. Patent Documents

3961190	June 1976	Lukianoff et al.
4983834	January 1991	Lindmayer et al.
5097127	March 1992	Hildenbrand et al.
5153434	October 1992	Yajima et al.
5444256	August 1995	Nagai et al.
5670782	September 1997	Sato
6140644	October 2000	Kawanami et al.
6172363	January 2001	Shinada et al.
6274876	August 2001	Kawanami et al.
6291823	September 2001	Doyle et al.
6608308	August 2003	Takagi et al.
6787772	September 2004	Ose et al.
6855929	February 2005	Kimba et al.
6855938	February 2005	Preikszas et al.
6909930	June 2005	Shishido et al.
7138629	November 2006	Noji et al.
7157703	January 2007	Nakasuji et al.
7241993	July 2007	Nakasuji et al.
2004/0000858	January 2004	Hwang et al.
2004/0084629	May 2004	Preikszas et al.
2005/0194917	September 2005	Yoshinaga
2006/0016989	January 2006	Nakasuji et al.
2007/0228922	October 2007	Nakasuji

Primary Examiner: Vanore; David
Assistant Examiner: Souw; Bernard
Attorney, Agent or Firm: Westerman, Hattori, Daniels & Adrian, LLP.

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Claims

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What is claimed is:

1. An electron beam apparatus comprising: an electron irradiation optics for irradiating a plurality of primary electron beams onto a sample surface; a scanning deflector for performing a scanning operation with said plurality of primary electron beams across the sample surface; a beam separator for separating secondary electron beams emanating from respective scanned regions on the sample from said primary electron beam; a magnifying electron lens for magnifying a distance between any two beams of the plurality of secondary electron beams that have been separated by said beam separator; an optical output converter for converting the plurality of magnified secondary electron beams to optical signals; a photoelectric conversion device for converting said optical signal to an electric signal; an optical magnifying lens for magnifying said optical signal from said optical output converter into an image on said photoelectric conversion device; and a multi-aperture plate disposed in front of said photoelectric conversion device and having a plurality of apertures formed therethrough, said aperture having an aperture area that is large in a peripheral region.

2. An electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beams onto a sample surface via an objective lens; an image projection optical system including at least two-stage of deflectors, an magnifying lens and an aperture for detecting secondary electrons emanating from the sample; a wobbler application circuit for applying a wobbler to an exciting or an excitation voltage of said magnifying lens subject to axial alignment; an image formation system for forming an image separated by the wobbler in synchronization with the x- and y-directional scanning according to a signal from the electron beam transmitted through said aperture, while carrying out the x- and y-directional scanning by at least one of the deflectors in the at least two-stage of deflectors; and a deflector controller operable to control the other one of said at least two-stage of deflectors to minimize the separation of the image for the purpose of adjusting the optical axis so that a principal ray having exited from said objective lens is directed through a central region of said magnifying lens and through said aperture.

3. An electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beam onto a sample surface via an objective lens; an image projection optical system for focusing secondary electrons emanating from the sample into an image on a detection surface, said image projection optical system having at least two-stage of deflectors, a magnifying lens and an aperture; an optical output converter for converting the secondary electron image formed by said image projection optical system to an optical signal; an optical member for extracting said optical signal into an atmosphere side, in which a plane disposed in a vacuum side of said optical member defines an optical output converter and an output surface of the optical signal disposed in the atmosphere side defines a curved surface; a wobbler application circuit for applying a wobbler to an exciting or an excitation voltage of said magnifying lens subject to axial alignment; an image formation system for forming an image separated by the wobbler in synchronization with the x- and y-directional scanning according to a signal from the electron beam transmitted through said aperture, while carrying out the x- and y-directional scanning by at least one of the deflectors in the at least two-stage of deflectors; and a deflector controller operable to control the other one of said at least two-stage of deflectors to minimize the separation of the image for the purpose of adjusting the optical axis so that a principal ray having exited from said objective lens is directed through a central region of said magnifying lens and through said aperture.

4. An electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beam onto a sample surface via an objective lens; an image projection optical system for focusing secondary electrons emanating from the sample into an image on a detection surface; an optical output converter for converting the secondary electron image formed by said image projection optical system to an optical signal; an optical member for extracting said optical signal into an atmosphere side, in which a plane disposed in a vacuum side of said optical member defines an optical output converter and an output surface of the optical signal disposed in the atmosphere side defines a curved surface; wherein said objective lens comprises: a magnetic lens including an inner magnetic pole and an outer magnetic pole with a magnetic gap produced by said inner and said outer magnetic poles defined in the sample side; a pipe made of ferrite and disposed inside said inner magnetic pole; and a deflector disposed inside said pipe made of ferrite.

5. An objective lens for focusing an electron beam onto a sample surface, comprising: a magnetic lens including an inner magnetic pole and an outer magnetic pole with a magnetic gap produced by said inner and said outer magnetic poles defined in the sample side; a substantially cylindrical pipe made of ferrite and disposed inside said inner magnetic pole; and a deflector disposed inside said pipe made of ferrite.

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Description

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BACKGROUND OF THE INVENTION

The present invention relates to an electron beam apparatus for making an inspection of a sample, such as a wafer, a mask, a reticle or a liquid crystal, for example, having a pattern with a minimum line width equal to or smaller than 0.1 .mu.m formed thereon, with high throughput and high precision by irradiating an electron beam onto the sample, and also to a device manufacturing method using the same electron beam apparatus.

There has been well known such an electron beam apparatus that uses an electron beam in order to detect a defect on a sample, such as a semiconductor wafer or a mask, in a manner that a primary electron beam emitted from an electron gun is focused via an optical system into an image on the sample, secondary electrons emanating from the sample are detected to provide a secondary electron image, and finally the sample is evaluated based on thus obtained secondary electron image.

The method for irradiating the primary electron beam onto the sample in such an electron beam apparatus may include one method in which a multi-beam of primary electrons is formed and focused into an reduced image on the sample, while deflecting the multi-beam for scanning the sample surface or while providing the irradiation of the multi-beam across a relatively large area on the sample at once. The method for detecting the secondary electrons emanating from the scanned region or the irradiated region on the sample as the result of the electron beam irradiation includes one method using an image projection optical system which can provide a magnified projection image of the secondary electrons covering a relatively large area onto a detection surface so as to carry out the detection of the secondary electrons. In that detection method, for example, the secondary electrons are focused into an image in an entrance of a MCP or the like and converted to an optical signal by a scintillator or the like, and then an image of resultantly multiplied secondary electrons from the MCP is converted to an optical signal by the scintillator and guided onto a detector, such as a CCD, via a FOP (Filter Optic Plate), where the optical signal is converted to an electric signal to provide the secondary electron image.

The conventional electron beam apparatus as described above is, however, suffered from the following problems.

(1) When employing one type of optical system operable for converging both of the primary electron beam and the secondary electron beam simultaneously in an uniform magnetic field, there is a fear from the reason of a narrow beam spacing in the multi-beam used for the scanning operation that all of the secondary electrons forming a single secondary electron beam are not received in a single beam detector arranged for the detection of said secondary electron beam but a part of signal from said secondary electron beam could be get mixed onto any adjacent beam detectors.

(2) Although an electromagnetic lens of said image projection optical system normally produces a small magnitude of aberration along an optical axis, if the primary electron beam is deflected for the scanning over the sample, it could occasionally enter the lens at an angle in a position off from the optical axis, adversely enhancing the aberration. Further, the image projection optical system, if attempting to enlarge the field of view, could resultantly reduce transmission of the secondary electron and again adversely enhance the aberration. Further disadvantageously, the image projection optical system is likely to suffer from a problem of distortion that could be induced in association with a magnifying lens placed in a second and subsequent steps.

(3) Although some type of CCD implementing a surface detector may include an element having an exposure time as short as 5 .mu.s, it is typically time-consuming when extracting data.

(4) From the fact that the spacing between the MCP and the scintillator may produce a blured beam on the order of 30 .mu.m, it is required that a pixel on the sample should be enlarged sufficiently over said blur of 30 .mu.m. To address this, it is required to employ an image projection optical system having an optical path as long as 1000 mm, but unfortunately the space charge effect from such a long optical path could adversely enhance the blur of the beam and the same image projection optical system is expensive, as well.

(5) The arrangement of the FOP and the CCD that have been optically adhered to each other makes the maintenance difficult.

(6) As for the irradiation optical system serving for irradiating an electron beam onto the sample, which is required to determine two different focal conditions, one for a crossover image and the other for a shaping aperture image, the system must have the optical path as long as 500 mm and ends up in an expensive system.

(7) For the case employing an immersion-type magnetic lens characterized by a reduced axial chromatic aberration as an objective lens, there has been no optical axis adjusting method developed for controlling a primary optical beam emitted from the field away from the optical axis so as to pass through an NA aperture. Therefore, it is difficult to reduce the aberration in the image projection optical system satisfactorily.

(8) There has been no method established for designing an objective lens comprising a deflection coil to satisfy the MOL (Moving Objective Lens) condition by using the immersion-type magnetic lens.

The present invention has been made in the light of the above lined-up current situations, and an object thereof is to provide an electron beam apparatus that can overcome the above problems.

Another object of the present invention is to provide a device manufacturing method directed to improve an inspection precision and throughput by using the above-designated electron beam apparatus to inspect a semiconductor device in the course of its manufacturing or as a finished product.

SUMMARY OF THE INVENTION

In Order to solve the above problems, according to an aspect of the present invention, there is provided an electron beam apparatus comprising: an electron source for irradiating a plurality of primary electron beams onto a sample surface; a scanning deflector for performing a scanning operation with the plurality of primary electron beams across the sample surface; an electron lens operable to converge the plurality of primary electron beams onto the sample surface, and also to converge secondary electrons emanating from respective scanned regions on the sample surface onto a detection surface, respectively; an electric field generation controller for generating an electric field between the electron source and the detection surface; an optical output converter for converting a plurality of secondary electron images that have been converged onto the detection surface to optical signals; and a photoelectric conversion device for converting the optical signal to an electric signal. Preferably, the electric field generator generates an electric field in a direction approximately at a right angle relative to a field generated by the electron lens.

According to the present aspect, since the electric field is applied between the electron source and the detection surface, it becomes possible to arrange the electron source and the detection surface with a longer distance therebetween, which facilitates the detection of the secondary electrons.

According to another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation optics for irradiating a plurality of primary electron beams onto a sample surface; a scanning deflector for performing a scanning operation with the plurality of primary electron beams across the sample surface; an electron lens operable to converge secondary electrons emanating from respective scanned regions on the sample surface onto a detection surface, respectively; an optical output converter for converting a plurality of secondary electron images that have been converged onto the detection surface to optical signals, respectively; and a photoelectric conversion device having a plurality of light-sensitive surfaces, each of the light-sensitive surfaces arranged in a geometry and a position so as to make it possible to optically receive each of the optical signals from the plurality of secondary electron images distributed corresponding to the extent of scanning with the plurality of primary electron beams.

According to the present aspect, the secondary electron beams travels across the detection surface by the scanning operation with a plurality of primary electron beams. Typically, the travel extent of the secondary electron beam is wider than the scanning width of the primary electron beam. In conjunction with this traveling, the optical signals that have been converted from the secondary electron beams by the optical output converter are also distributed over the corresponding extent. Since each of the light-sensitive surfaces of the photoelectric converter is arranged in the geometry and the position that allows for the optical acceptance of each of thus distributed optical signals, the overlapping of detection areas could be avoided. In other words, the primary electron beam is allowed to make the scanning operation over the extended range. The geometry of the light-sensitive surface may include a rectangular shape extending in the direction corresponding to the scanning direction, for example. Further, making an adjustment to the position of each light-sensitive surface can achieve the optimal positioning of the light-sensitive surface by taking an effect from the rotation of the secondary electron beam due to the magnetic field into account.

According to yet another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation optics for irradiating a plurality of primary electron beams onto a sample surface; a scanning deflector for performing a scanning operation with the plurality of primary electron beams across the sample surface; an electron lens operable to converge secondary electrons emanating from respective scanned regions on the sample surface onto a detection surface, respectively; an optical output converter for converting a plurality of secondary electron images that have been converged onto the detection surface to optical signals; a photoelectric conversion device for converting the optical signal to an electric signal; and a photoconduction path for guiding the optical signal output from the optical output converter to the photoelectric conversion device, said photoconduction path having light-sensitive areas, each configured in a geometry capable of optically receiving the optical signals distributed corresponding to the extent of scanning with the plurality of primary electron beams, respectively.

According to the present aspect, the electron beam apparatus employs the photoconduction path for guiding the optical signal output from the optical output converter to the photoelectric conversion device. Since the photoconduction path has the light-sensitive areas, each configured in such a geometry that is capable of optically receiving the optical signals distributed corresponding to the extent of scanning with the plurality of primary electron beams, respectively, the apparatus can accommodate the travel of the optical signals by the a plurality of primary electron beams and thus the overlapping of the detection areas is avoided, as is the case with the previously-discussed aspect. The geometry of the light-sensitive surface may includes a rectangular shape extending in the direction corresponding to the direction of scanning, for example.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation optics for irradiating a primary electron beam onto a sample surface; a scanning deflector for performing a scanning operation with the primary electron beam across the sample surface; an beam separator for separating a secondary electron beam emanating from a scanned region on the sample from the primary electron beam; a magnifying electron lens for magnifying the secondary electron beam that has been separated by the beam separator; an optical output converter for converting the magnified secondary electron beam to an optical signal; a photoelectric conversion device for converting the optical signal to an electric signal; and an optical zoom lens for focusing the optical signal from the optical output converter into an image on the photoelectric conversion device.

According to the present aspect, even through the pitch between secondary electron beams and thus the pitch between the optical signals are different from the design values, the adjustment by using the optical zoom lens, if applied to the magnification scale, can set the optical signals to be in consistency with the pitch between the photoelectric conversion devices. This can help prevent the overlapping and/or the missing of the detection areas.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising; an electron irradiation optics for irradiating a primary electron beam onto a sample surface; a scanning deflector for performing a scanning operation with the primary electron beam across the sample surface; a beam separator for separating a secondary electron beam emanating from each scanned region on the sample from the primary electron beam; a magnifying electron lens for magnifying the secondary electron beam that has been separated by the beam separator; an optical output converter for converting the magnified secondary electron beam to an optical signal; a photoelectric conversion device for converting the optical signal to an electric signal; and a rotation mechanism for rotating the photoelectric conversion device around an optical axis.

According to the present aspect, even through the rotational amount of the used electromagnetic lens is different from its design value and thus the orientation of the secondary electron images does not match the orientation of the photoelectric conversion device, the adjustment by using the rotation mechanism, if applied to the rotational position of the photoelectric conversion devices, can achieve the orientation alignment easily.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation optics for irradiating a plurality of primary electron beams onto a sample surface; a scanning deflector for performing a scanning operation with the plurality of primary electron beams across the sample surface; a beam separator for separating secondary electron beams emanating from respective scanned regions on the sample from the primary electron beam; a magnifying electron lens for magnifying a distance between any two beams of the plurality of secondary electron beams that have been separated by the beam separator; an optical output converter for converting the plurality of magnified secondary electron beams to optical signals; a photoelectric conversion device for converting the optical signal to an electric signal; an optical magnifying lens for magnifying the optical signal from the optical output converter into an image on the photoelectric conversion device; and a multi-aperture plate disposed in front of the photoelectric conversion device and having a plurality of apertures formed therethrough, said aperture having an aperture area that is small in the vicinity of an optical axis but is large in a peripheral region.

According to the present aspect, since the multi-aperture plate is disposed in front of the photoelectric conversion device, which has a plurality of apertures, each having the aperture area that is small in the vicinity of the optical axis but is large in the peripheral region, it can help compensate for the deteriorated secondary electron signal intensity due to the deteriorated off-axis intensity of the electron irradiation optics and/or the deteriorated signal of the secondary electron enlarged image due to the aberration from the secondary optical system.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation optics for irradiating a primary electron beam onto a sample surface; a scanning deflector for performing a scanning operation with the primary electron beam across the sample surface; an optical system including an at least one-stage of lens for converging the primary electron beam onto the sample surface and for converging secondary electrons emanating from the scanned region on the sample surface onto a detection surface; and an MOL motion deflector for driving a lens of the optical system positioned proximally to the sample to perform the MOL motion in synchronization with the scanning operation by the scanning deflector.

According to the present aspect, owing to the MOL motion, or the motion in which the optical axis of the lens positioned proximal to the sample, preferably that of the objective lens, that may be positioned most proximal to the sample, can be driven electro-magnetically to perform the MOL motion in synchronization with the scanning operation, such an aberration that could be induced by the primary electron beam or the secondary electron beam entering the location off from the optical axis during the scanning operation can be reduced, and consequently the higher resolution of the primary electron beam and thus the highly efficient detection of the secondary electron beams can be provided.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an electron irradiation system for irradiating a primary electron beam onto a sample surface; an magnification projection optical system for projecting secondary electrons emanating from the sample onto a detection surface in a magnified scale; an optical output converter for converting the electron image projected on the detection surface to an optical signal; and a detection device having a plurality of light-sensitive surfaces which is exposed to the optical signal from the optical output converter, wherein during at least one of the light-sensitive surfaces is being exposed to the optical signal, image data is transferred sequentially from other light-sensitive surfaces that have been exposed to the optical signal. Preferably, the electron beam apparatus further comprises a deflector for deflecting the secondary electrons so that the secondary electrons are sequentially projected in respective areas on the detection surface in a magnified scale, each of the areas corresponding to each one of the plurality of light-sensitive surfaces.

According to the present aspect, since the detection device having a plurality of light-sensitive surfaces to be exposed to the light signal is provided so that the image data may be transferred sequentially from each of the light-sensitive surfaces that has been exposed to the light signal, therefore the total time required to extract the image data from the detector can be reduced. This may help improve the throughput of the electron beam apparatus.

According to still another aspect of the present invention, there is provided an electron beam apparatus in which a field of view on the sample subject to irradiation of an electron beam is segmented into a plurality of sub-fields, and an electron image is obtained by each of the sub-fields so as to provide the final evaluation by an entire field on the sample, said apparatus comprising: an irradiation optical system for focusing an electron beam into an image by each of the sub-fields on the sample surface; an image projection optical system for focusing secondary electrons emanating from the sample into an image by each of the sub-fields on a detection surface; and an exposure controller for controlling an exposure time for each of the sub-fields to the detection surface in dependence on a distance from an optical axis of the image projection optical system to the each sub-field.

According to the present aspect, the exposure time per each sub-field to the detection surface can be controlled to be variable in dependence on the distance from the optical axis of the image projection optical system to the sub-field. For example, the control may be carried out in such a manner that the exposure time may be set longer for the sub-field distant from the optical axis, which has typically a smaller amount of light, but the exposure time may be set shorter for the sub-field close to the optical axis, which has typically a larger amount of light. This variable control can achieve the uniform S/N ratio of the secondary electron image over the entire field.

According to still another aspect of the present invention, there is provided an electron beam apparatus in which a field of view on the sample subject to irradiation of an electron beam is segmented into a plurality of sub-fields, and an electron image is obtained by each of the sub-fields so as to provide the final evaluation by an entire field on the sample, said apparatus comprising: an irradiation optical system for focusing an electron beam into an image by each of the sub-fields on the sample surface via an objective lens, wherein the electron beam is irradiated onto the sample surface at an angle relative to a normal line of the sample surface in the sub-field distant from an optical axis of the irradiation optical system, so that secondary electrons emanating from the sub-field can enter the objective lens in the vicinity of the optical axis thereof; and an image projection optical system for focusing the secondary electrons into an image on a detection surface.

In the present aspect, since the secondary electrons are incident in the objective lens in the vicinity of the optical axis thereof, the aberration from the optical system can be reduced.

According to still another aspect of the present invention, there is provided an electron beam apparatus in which a field of view on the sample subject to irradiation of an electron beam is segmented into a plurality of sub-fields, and an electron image is obtained by each of the sub-fields so as to provide the final evaluation by an entire field on the sample, said apparatus comprising: an irradiation optical system for focusing an electron beam into an image by each of the sub-fields on the sample surface; and an image projection optical system for focusing secondary electrons emanating from the sample into an image by each of the sub-fields on a detection surface, in which an auxiliary lens is disposed in front of a lens in the last-stage of the image projection optical system so that an image of crossover produced by a lens system positioned upstream to the auxiliary lens can be formed in the proximity to a principal plane of the lens in the last-stage.

According to the present aspect, since the image of crossover produced by the lens positioned upstream to the auxiliary lens can be formed in the proximity to the principal plane of the lens in the last-stage, the distortion and the transverse chromatic aberration and/or rotation in the image projection optical system can be reduced.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beam into an image on a sample surface via an objective lens; an image projection optical system for focusing secondary electrons emanating from the sample into an image on a detection surface; an optical output converter for converting the secondary electron image formed by the image projection optical system to an optical signal; and an optical member for extracting the optical signal into an atmosphere side, in which a plane disposed in a vacuum side of the optical member defines an optical output converter and an output surface of the optical signal disposed in the atmosphere side defines a curved surface. Preferably, the optical output converter is a scintillator and the curved surface of the optical member may be convexly curved in a semi-spherical shape, a paraboloid of revolution or a hyperboloid of revolution in order to obtain the magnified image.

According to the present aspect, if the optical system has been configured to magnify the secondary electron image, the optical path could be made longer without the need for the MCP or the FOP. This facilitates a maintenance of the image projection optical system, and allows to fabricate the system with low cost.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beam into an image on a sample surface via an objective lens; an image projection optical system for focusing secondary electrons emanating from the sample into an image on a detection surface; and at least one deflector cooperating with the objective lens to focus the secondary electrons emanating from a field distant from an optical axis into an image on the optical axis.

According to the present aspect, it has become possible to control the principal ray emitted from the field distant from the optical axis to be directed through the NA aperture.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an irradiation optical system for shaping and focusing an electron beam emitted from an electron gun into an image on a sample surface via an objective lens, said irradiation optical system including at least two-stage of lenses for focusing a light source image of the electron gun into an image on a principal plane of the objective lens, while focusing the shaped electrons image into an image on the sample; and an image projection optical system for focusing secondary electrons emanating from the sample or electrons transmitted through the sample into an image on a detection surface.

According to the present aspect, the image would not be formed between at least two-stage of lenses but the image of the shaping aperture is formed on the sample surface while satisfying the Koehler illumination condition. Therefore, it is no more necessary to intensify the excitation or magnetic excitation of each lens, which favorably helps reduce the size of the lens and the optical path length of the irradiation optical system.

According to still another aspect of the present invention, there is provided an electron beam apparatus comprising: an irradiation optical system for focusing a primary electron beams into an image on a sample surface via an objective lens; an image projection optical system including at least two-stage of deflectors, an magnifying lens and an NA aperture for detecting secondary electrons emanating from the sample; a wobbler application circuit for applying a wobbler to an exciting or an excitation voltage of the magnifying lens subject to an axial alignment; an image formation system for forming an image separated by the wobbler in synchronization with the x- and y-directional scanning according to a signal from the electron beam transmitted through the NA aperture, while carrying out the x- and y-directional scanning by at least one of the deflectors in the at least two-stage of deflectors; and a deflector controller operable to control the other of said at least two-stage of deflectors to minimize the separation of the image for the purpose of adjusting the optical axis so that a principal ray having exited from the objective lens is directed through a central region of the magnifying lens and through the NA aperture.

According to the present aspect, by minimizing the separation of the image produced by the image formation system, it becomes possible to provide the adjustment to the optical axis so that the principal ray having exited from the objective lens can be directed through the center of the magnifying lens and through the NA aperture. It is also contemplated that the wobbler application circuit, the image formation system and the deflector controller of the present aspect may be incorporated at least either one of the above-disclosed other aspects of the present invention in its allowable range.

At least either one of the objective lens defined in the above-disclosed respective aspects is the objective lens comprises: a magnetic lens including an inner magnetic pole and an outer magnetic pole with a magnetic gap produced by said inner and said outer magnetic poles defined in the sample side; a pipe made of ferrite and disposed inside the inner magnetic pole; and a deflector disposed inside the pipe made of ferrite.

According to the above aspect, such an objective lens could be provided by using an immersion-type magnetic lens that comprises a deflection coil to satisfy the MOL condition. If the deflector activates the MOL motion, or moves the optical axis of the objective lens magnetically in synchronization with the scanning operation, the aberration resultant from the primary or secondary electron beam entering the region off from the optical axis during the scanning operation could be reduced, so that the higher resolution of the primary electron beam and the highly efficient detection of the secondary electron beam could be achieved.

The aspect of the present invention for enabling the MOL motion can be applied not only to the electron beam apparatus but also to a general apparatus employing a charged particle beam, in this aspect, provided is an apparatus for evaluating a sample, in which a surface of the sample is scanned with a primary charged particle beam and secondary charged particles emanating from or transmitted through the sample are projected by an at least one-stage of lens onto a detection surface so as to provide the evaluation of the sample based on a detection image, wherein a lens positioned proximal to the sample is driven to make the MOL motion to reduce an aberration from the primary charged particle beam or an aberration from the secondary charged particle beam.

An electron beam apparatus according to any one of the above-disclosed aspects of the present invention may be used in a device manufacturing method for providing an evaluation of a sample represented by a wafer in the course of manufacturing or as a finished product.

Those and other advantages and effects of the present invention would be further apparent from the detailed description of the invention with reference to the attached drawings, as will be described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing depicting a configuration of an electron beam apparatus according to a first to a third embodiment of the present invention, wherein FIGS. 1(a), (b), (c) and (d) are side elevational views of the electron beam apparatus looking from four different directions, respectively and FIG. 1(e) is a schematic diagram showing a detection section of the electron beam apparatus according to a second embodiment:

FIG. 2 is a schematic drawing depicting a configuration of an electron beam apparatus according to a fourth to an eighth embodiment of the present invention;

FIG. 3(a) shows a detailed configuration of an objective lens of the electron beam apparatus of FIG. 2 (the eighth embodiment), and FIG. 3(b) is a graphical representation indicating an axial magnetic field distribution for the objective lens of FIG. 3(a);

FIG. 4 is a schematic drawing depicting a configuration of an electron beam apparatus according to a ninth embodiment of the present invention;

FIG. 5 is an enlarged plan view of an aperture plate used in the electron beam apparatus of FIG. 4;

FIG. 6 is a schematic drawing depicting a configuration of an electron beam apparatus according to a tenth embodiment of the present invention;

FIG. 7 is an illustration showing schematically an electron beam transfer unit using an optical system of an electron beam apparatus according to an eleventh embodiment of the present invention;

FIG. 8 shows how the optical member illustrated in FIG. 7 operates to project a scintillator image in a magnified scale on a CCD detector;

FIG. 9 is a flow chart showing a semiconductor device manufacturing process; and

FIG. 10 is a flow chart showing a lithography process included in the semiconductor device manufacturing process of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

First to Third Embodiment

FIGS. 1(a), (b), (c) and (d) are side elevational views of the electron beam apparatus according to a first embodiment of the present invention, looking from four different directions, respectively. The electron beam apparatus comprises a multi-emitter 8 serving as an electron source for emitting primary electrons, a multi-aperture plate 2 having a plurality of small apertures, a lens configured so as to generate a magnetic field of uniform intensity in the z direction (along the optical axis) between the multi-aperture plate 2 and a sample 4, an electrostatic deflector that is not shown but operable to apply a deflecting electric field within the x-y plane for driving an irradiation spot of the primary electron beam that has been focused into an image by said lens on the sample 4 and thereby to scan the sample surface, a FOP (Fiber Optical Plate) 6 comprising a scintillator applied to a front surface thereof for converting electrons to light and a bundle of optical fibers capable of transmitting the converted light, and a photo multiplier (referred to PMT in abbreviation) 7 for detecting the intensity of the light that has been transmitted from the FOP.

The multi-emitter 1 is constructed in the FS-shape in a central location of the control electrode 8. The respective apertures of the multi-aperture plate 2 are spaced equally by a distance on the order of 200 .mu.m along the x direction. Only the beams among the electron beams emitted from the respective emitters that have passed through the small apertures of the multi-aperture plate 2 can enter said lens. Specifically, the multi-beam can be formed from the primary electrons. The same lens converges the multi-beam along the trajectories 3 onto the wafer 4. The electron beam apparatus carries out the evaluation of the sample by detecting the secondary electrons with the PMT 7 while moving the sample table with the sample 4 loaded thereon continuously in the y direction.

The front view of FIG. 1(a) shows an electric field E being applied in the direct current from the front surface to the back surface of the sheet, which serves to direct the secondary electron beam toward the FOP 6 is. Simultaneously with this, a deflecting electric field .DELTA.E serving for providing the x-directional scanning with the primary electron beam is applied in the x direction. It is to be noted in this regard that taking the rotation induced by the magnetic field into account, the deflecting electric field .DELTA.E is applied in the direction slightly rotated in the x direction.

To understand clearly an effect of the electric field E, looking at the electron beam apparatus of the present embodiment from the side, it can be recognized that the primary electron beam is deflected slightly toward the right due to the electric field E and converged onto the wafer 4, as shown in FIG. 1(b). Further, the secondary electrons emanating from the wafer 4 once form a crossover, as its trajectories are indicated by 5, and are focused into an image on the scintillator applied over the FOP (Fiber Optical Plate) 6 in its side facing to the vacuum side. In this connection, the rightward deflection of the secondary electrons by the electric field E permits the secondary electrons to be collected onto the scintillator surface distant from the electron source. An electron signal in the focused image is converted by the scintillator to an optical signal and transmitted via the FOP to the atmosphere, where it is detected by the PMT 7 and converted to an electric signal.

Looking at the electron beam apparatus of the present embodiment from the PMT side, it can been seen that in association with the deflection of the primary electron beam caused by the deflecting voltage .DELTA.E, the trajectories of the corresponding secondary electron beam varies as from the trajectories 5 to the trajectories 6a, as shown in FIG. 1(c).

The PMT 7 has a structure including a light-sensitive surface in a rectangular shape, as shown in FIG. 1(d). Although the secondary electrons travels over a wider extent than the scanning width 9 of the primary beam, the detection should follow the direction at a certain angle from the x-axis as indicated by 7 in FIG. 1(d) because of the rotation induced by the magnetic field. Owing to this effect, the scanning can be carried out over an extensive range by the primary electron beams without overlapping of detection areas by respective beams.

It is also contemplated that instead of the PMT in itself including the rectangular light-sensitive surface, a light-sensitive surface 10 configured in a rectangular shape can be connected to an output surface 11 configured in a circular or other shapes and located in the PMT 12 side via a bundle of optical fibers provided as a photoconduction path, as shown in FIG. 1(e) (a second embodiment). Further, in case where the space between electron sources 1 is small and a large number of electron sources are to be arranged, the space between incident planes for the secondary electrons is also small and it would be occasionally difficult to arrange the optical fibers 10, 11 in place. In such a situation, the space between respective optical signals may be expanded by the optical lens and the optical fibers should be arranged on the light-sensitive surface, as shown by 10, 11, and thereafter the PMT 12 should be provided (a third embodiment).

Fourth to Eighth Embodiment

FIG. 2 shows schematically a configuration of an electron beam apparatus according to a fourth to an eighth embodiment of the present invention.

As shown in FIG. 2, the electron beam apparatus comprises an electron gun 21 of LaB.sub.6 cathode for emitting a primary electron beam and a condenser lens 22 for converging the primary electron beam into a crossover in the vicinity of an NA aperture plate 24. A multi-aperture plate 23 having a plurality of apertures in the array of 8-row times 8-column is disposed below the condenser lens 22. The primary electron beam emitted from the electron gun 21 passes through the multi-aperture to be formed into a plurality of primary electron beams or the multi-beam. An reduction lens 25 and an objective lens 28 are disposed below the NA aperture plate 24. Respective beams of the multi-beam are reduced by two stages, one stage by the reduction lens 25 and the other stage by the objective lens 28, into individually narrowly converged irradiation spots on a sample 30, such as a wafer.

The electron beam apparatus further comprises a deflector 26 for making axial alignment and a beam separator 27. The beam separator comprises an electrostatic deflector and an electromagnetic deflector, which will be described later in detail, and they are set such that a force exerting from a magnetic field B on the primary electron beam should be as two times strong as the force exerting from an electric field E thereon so as to deflect the primary electron beam incident on the beam separator at a certain angle to be irradiated on the sample 30 substantially at a right angle, as will also be described later in more detail. On the other hand, the beam separator 27 is operable to deflect the secondary electrons incident on the beam separator from the sample side to the predetermined direction with respect to an optical axis thereof and thereby to separate the secondary electrons from the primary electron beam.

In this connection, the optical axis defined from the electron gun 21 to the deflector 26 and the optical axis of the objective lens 28 and of the beam separator 27 are offset from each other in the x y directions by about 20 mm (a fourth embodiment). A chromatic aberration from the deflection can be eliminated almost completely by setting the deflection by the electromagnetic deflector of the beam separator 27 as approximately two times strong as the deflection by the electrostatic deflector of the beam separator 27 (the term "approximately" is used herein in consideration of the contribution from the axial aligning deflector 26). As a result, there should be no problem from the viewpoint of the aberration, even if the beam separator is not disposed on a conjugate plane with the sample 30. Only a magnetic deflector is also useful for the beam separator.

Further, to meet the condition where the sample 30 are scanned with a multiple of irradiation spots on the surface thereof, a deflector is provided, which is operable to vary a deflection voltage so as to deflect the primary multi-beam in the x direction. Such a deflector usable for the scanning control may include, for example, the axial aligning deflector 26 and the electrostatic deflector of the beam separator, which may also serve as the scanning deflector.

Along the direction of the secondary electron beam deflected by the beam separator 27, disposed are, respectively, a magnifying lens 31, a FOP 32 comprising a bundle of optical fibers with a scintillator applied on the front surface thereof for converting an electron beam to light, an optical zoom lens 33, a multi-aperture plate 34 including a plurality of apertures in the array of 8-row times 8-column formed therethrough, a PMT array 35 for detecting intensity of the light transmitted through each aperture of the multi-aperture, and a rotation mechanism capable of adjusting a rotational position of the PMT array around the optical axis.

Further, the multi-aperture plate 34 is configured such as shown in the lower section of FIG. 2 that the apertures located closet to the optical axis 30 (e.g., aperture 37) have the aperture areas that are smaller than those of the apertures located farther from the optical axis (e.g., aperture 38). A deflector (not shown) for deflecting the secondary electron beam in synchronization with the deflecting motion of the multi-beam of the primary electrons is operatively arranged in the step subsequent to the magnifying lens 31 so as to direct each beam of the multi-beam of the secondary electrons through each corresponding aperture of the multi-aperture plate 34 even under the scanning that is carried on over the sample with the irradiation spots.

The PMT array 35 is connected with an image processing unit, though not shown, via an A/D converter. The image processing unit forms and outputs an image of the sample 30 based on the light intensity distribution that has been detected by the PMT array 35. Further, the output image signals are sent to a CPU (not shown) serving for controlling and managing respective components of the electron beam apparatus, where an evaluation including a defect detection of the sample 30 based on the image may be carried out. It is to be noted that the sample 30 has been placed on a stage, though not shown. The stage is controlled in accordance with instructions from the CPU so that the stage may be moved continuously in the y direction at a right angle relative to the x-direction or the direction of scanning, and that the stage may be moved in a step-by-step manner upon changing scanning stripes.

An operation of the first embodiment will now be described.

The primary electron beam emitted from the electron gun 21 is converged by the condenser lens 22 and passed through the plurality of apertures of the multi-aperture plate 23 to be shaped into the multi-beam in the array of 8.times.8 and to form the crossover in the vicinity of the NA aperture 24. The multi-beam of the primary electrons is reduced by the reduction lens 25 and deflected by the axial aligning deflector 26 to pass through the axially offset beam separator 27, and the multi-beam after exiting from the beam separator 27 is again reduced by the objective lens 28 into the image on the sample 30. Simultaneously, the multi-beam is deflected so that the scanning can be carried out with the spots moving over the sample in a certain direction (e.g., in the x direction). Those secondary electrons emanating from the scanned points are deflected toward the right on the drawing sheet, when transmitted through the beam separator 27, to enter the magnifying lens 31, where the space between respective groups of secondary electrons in the form of multi-beam is extended, and the secondary electrons activate the scintillator applied on the front surface of the FOP 32 to emit light. Since the FOP 32 is made of optical fibers, each having a self-focusing function, or material having a high refractive index in the central region and a low refractive index in the peripheral region, therefore the optical signals entered at different incident angles are to come out with their angles relative to the optical axis having been reduced at the exit of the FOP 32. Accordingly, even with a larger F number of the optical zoom lens 33 in the subsequent step, the light having exited from the FOP 32 can enter the lens 33 efficiently. Owing to the configuration that the lens 33 is implemented as the zoom lens, even if the space between respective beams of the multi-beam of secondary electrons dependent on the resultant magnification scale from the objective lens 28, the magnifying lens 31 and others is different from the design value, simply changing the magnification scale (focal distance) of the zoom lens 33 can provide the match between the beam space and the pitch of the PMT array 35 easily (a fifth embodiment). In addition to the above advantage, to modify the beam space in the primary multi-beam in order to change a pixel size, as well, simply changing the magnification of the zoom lens 33 can provide the match between the beam space and the pitch of the PMT array 35 easily. Still advantageously, even if the orientation of the array of the secondary electron images is offset from the orientation of the PMT array 35 due to the different rotational amount of the electromagnetic lens 31 from the design value, the rotation mechanism 36 (a sixth embodiment) can help adjust the rotational position of the PTM array to thereby achieve the match in orientation easily. It is to be noted that the fifth and the sixth embodiments are applicable not only to the electron beam apparatus performing the scanning operation with the multi-beam but also that with a single beam.

Further, since the multi-aperture plate 34 including the aperture 37 having a smaller area adjacent to the optical axis 39 and the aperture 38 having a larger area distant from the optical axis is disposed in front of the PMT array 35, it can help compensate for the deteriorated secondary electron signal intensity in conjunction with the deteriorated off-axis intensity of the electron gun 21 and/or the deteriorated signal of the secondary electron enlarged image due to the aberration from the secondary optical system (a seventh embodiment). It is also useful that only peripheral apertures have rectangular shapes with a larger side.

FIG. 3(a) shows a detailed configuration of the objective lens 28 of the electron beam apparatus of FIG. 2 as an eighth embodiment. As shown in FIG. 3(a), the objective lens 28 has a structure including a magnetic excitation coil 40 inside an inner magnetic pole 43 and an outer magnetic pole 42 with lens gap defined in the sample 30 side. An electromagnetic deflector 29 comprising two pairs of electromagnetic deflection coils 47, 46 is disposed between the lens and the sample 30. The coil current from those pairs of coils is taken out through the hermetic seal 49 into the atmosphere side. The exciting coil 40 is isolated from the vacuum zoon by a seal cylinder 50 sealed with an O-ring 48. The beam separator 27 comprises an electrostatic deflector 45 and an electromagnetic deflector 44, whose core is shared with an inner surface of the inner magnetic pole 43.

An axial magnetic field distribution of the objective lens 28 is indicated in a graphical representation of FIG. 3(b). Further, the differentiation of the magnetic field B with respect to the optical direction, z, is indicated by D.sub.B. The MOL (Moving Objective Lens) motion can be generated by bringing the z-dependency of the deflecting field by the electromagnetic deflector 29 close to the distribution of D.sub.B. The z-dependency of the deflecting magnetic field by the electromagnetic deflector 29 can be brought close to the D.sub.B by making the coil 47 and the coil 46 produce their magnetic fields in opposite directions from each other and by adjusting the relative intensity thereof to each other. It is to be noted that a bobbin for the coil may be made of cera