GB2173945A

GB2173945A - Scanning electron beam apparatus

Info

Publication number: GB2173945A
Application number: GB08530697A
Authority: GB
Inventors: Hirotami Koike
Original assignee: INTERNATIONAL PRECISION Inc
Current assignee: INTERNATIONAL PRECISION Inc
Priority date: 1982-03-19
Filing date: 1985-12-13
Publication date: 1986-10-22
Also published as: JPS58161235A; GB8530697D0; GB2118361A; GB2173945B; GB8307619D0; GB2118361B

Abstract

A scanning electron beam apparatus such as electron microscope comprises an electron gun 3, condenser lenses 5,6, deflection coils 7,8 for scanning two- dimensionally a specimen 15 with an electron beam, a secondary electron detector 13 and an objective lens 9 which consists of a lens body 20. A specimen holder 11 of a greater area than the end face of the pole piece of the objective lens is swingably mounted within the space below the lens body 20. The specimen 15 of a large size e.g. 10-12.5 cm such as IC wafer can be observed at a low accelerating voltage eg 1 Kv, with high resolution at various angular dispositions of the specimen. <IMAGE>

Description

1 GB2173945A 1

SPECIFICATION

Scanning electron beam apparatus The present invention relates in general to a scanning electron beam apparatus such as a scanning electron microscope and in particular to a scanning electron beam apparatus which is improved with respect to the structure of an objective lens.

For having a better understanding of the in vention, description will first be made in some detail of a scanning electron beam apparatus.

As a typical one of the scanning electron beam apparatus, there is heretofore known a 80 scanning electron microscope of the structure shown in Fig. 1 of the accompanying draw ings. Referring to the figure, the scanning elec tron microscope is composed of a microscope main body or column which includes an elec- 85 tron gun 3, first and second condenser lenses and 6, first and second deflection coils 7 and 8 disposed below the condenser lenses 5 and 6 and an objective lens 9, and a speci men chamber portion 2 which is disposed fix- 90 edly to and below the microscope column 1 and defines an inner hollow chamber 14. A specimen stage 10 is disposed vertically mo vably below the objective lens 9 within the chamber 14, in which there are further dis posed a movable aperture 12 for the objective lens 9 and a secondary electron collector or detector 13 at a fixed position. The objective lens 9 is composed of an upper pole piece 9a and a lower pole piece 9b which is disposed 100 below the former with a predetermined dis tance thereto. A manipulator for the movable aperture member 12 is inserted between the magnetic pole pieces 9a and 9b. The speci- men stage 10 severs to support a specimen 105 holder 11 and a specimen 15 at a position below the objective lens 9. In Fig. 1, a refer ence numeral 4 denotes an evacuating conduit connected to a vacuum system.

The scanning electron microscope of the structure described above is certainly advan tageous in that the specimen 15 of a con siderably large size can be inserted by increas ing the distance between the specimen stage 10 and the objective lens 9 by displacing the 115 former downwardly by virtue of such arrange ment that the specimen 15 is disposed exter nally of the objective lens 9. However, disad vantage is seen in the fact that high resolution can not be attained unless the accelerating voltage of the objective lens 9 is correspon dingly increased, when the distance between the center of the objective lens 9 and the specimen 15 which distance is referred to as the working distance is increased, because then aberrations of the objective lens 9 will become significant.

Relationship between the resolving power of the objective lens 9 and the working distance is generally such as illustrated graphically in 130 Fig. 2 in which the resolving power of the objective lens 9 at the accelerating voltage of 25 kV is represented in terms of a disc of minimum confusion (i.e. spreading of the elec- tron beam on the surface of the specimen) as a function of the working distance, with the disc of minimum confusion being taken along the ordinate, while the working distance is taken along the abscissa. It is safe to say that the shorter the working distance is, the less significant the aberrations of the objective lens 9 become, assuring the higher resolving power of the latter. As can be seen from the graph shown in Fig. 2, aberrations cannot be so reduced as to allow high resolution unless the working distance is selected short, in the conventional scanning electron microscope. In other words, the working distance should be as short as possible in order to obtain a specimen image of high resolution.

Under the circumstances, an attempt has been made to place the specimem 15 in the magnetic field of the objective lens 9 so that observation may be carried out in the state in which aberrations of the objective lens 9 are suppressed to a minimum. A structure of the scanning electron microscope resulted from the above attempt is schematically shown in Fig. 3 of the accompanying drawings. Referring to the figure, arrangement is made such that the specimen can be positioned between the upper objective pole piece 9a and the lower objective pole piece 9b so as to be irradiated with a scanning electron beam deflected by the deflection coils 7 and 8, wherein secondary electrons emitted by the specimen 15 are trapped in a magnetic field of high intensity to be collected by a secondary electron detector 13 disposed above the objective lens 9. To detect also X-rays emitted by the specimen, an X-ray detector 16 is disposed above the objective lens. Further, a fluorescent screen 18 is rotatably mounted on the microscope column 1 by means of hinges

19 below the objective lens 9, while a detector 17 for detecting electrons transmitted through the specimen 15 is provided to make it possible to obtain a transmission electron image as well.

The electron microscope of the structure shown in Fig. 3 however suffers a problem that limitation is imposed to the size of the specimen which can be inserted between the pole pieces 9a and 9b of the objective lens 9 because the gap available between the pole pieces 9a and 9b is very small in the objective lens of the known struture. In reality, the size of the specimen 15 allowable to be positioned in the inter-pole gap of the conventional objective lens 9 is up to only 1 cm in diameter at the largest. Accordingly, it is common in practice that a specimen of a diameter greater than 1 cm is observed by resorting to the electron microscope of the structure shown in Fig. 1 with relatively low resolution 2 GB2173945A 2 of the order of 60 A (angstrom) at the expence of desired high resolution.

By the way, there exists at present in the field of integrated circuit (IC) technology a great demand for the possibility of abservation of a large size wafer having a diameter in a range of 4 to 5 inches (10 to 12.5 cm) with the aid of an electron beam apparatus. In this connection, it is known that integrated circuits realized in the wafer may undergo injuries upon irradiation with the beam of electrons accelerated at a high voltage (which is one of the conditions required for attaining high resolution), eventually being rendered useless. To evade such trouble, observation has to be conducted at a low accelerating voltage of the order of 1 kV. In the case of the scanning electron microscope, the low accelerating voltage however involves degradation of resolu- tion. For example, at the accelerating voltage of 1 kV, the attainable resolution is impracticably as low as about 1000 A, giving rise to a problem, as can be seen from Fig. 4 in which the resolving power of the objective lens 9 is represented in terms of the disc of minimum confusion as a function of the accelerating voltage with various aberrations being taken as parameters and in which the disc of minimum confusion is taken along the ordinate while the accelerating voltage is taken along the abscissa. More specifically, a single-dot broken curve F in Fig. 4 represents variation of the resolution with chromatic aberration being taken as a parameter, a double-dot broken curve G reopresents variation of the resolution with quantity of electron incident to the specimen being taken as a parameter, a broken line H represents variation of the resolution with spherical aberration being taken as a para- meter, and a broken line 1 represents variation of the resolution with aberration due to diffraction being taken as a parameter. Finally, a solid line curve E is depicted with all the parameters being synthetically taken into account.

As will be appreciated from the foregoing description, the wafer should preferably be in serted between the upper and lower objective pole pieces in order to observe it with high resolution at a low accelerating voltage. It is however impossible in the scanning electron microscope of the hitherto known structure to assure a space for allowing the wafer to be accommodated between the objective pole pieces for the reason mentioned hereinbefore.

Accordingly, when a wafer has to be ob served at a high resolution at any rate, the wafer must be fragmented into small pieces so that observation may be performed piece by piece. However, such fragmentation means nothing but the uselessness of the wafer as a product and can not be tolerated at all.

It will now be understood that a great diffi culty has been encountered in observing a wafer of large size in a range of 4 to 5 inches in diameter with high resolution by using an 130 accelerating voltage of the order of 1 kV.

It is therefore an object of the present invention to enable by means of a scanning electron microscope observation of a wafer or the like of a large size in a range of 4 to 6 inches in diameter with an improved resolution at a low accelerating voltage of the order of 1 kV without any need for fragmentation of the specimen.

According to this invention we propose scanning electron beam apparatus as set forth in the appendent claims. More particularly we propose, a scanning electron microscope in which a magnetic pole of an objective lens is divided into two magnetic pole halves which are disposed vertically apart from each other to thereby define a specimen accommodating space or specimen chamber between the divided magnetic poles, which space extends perpendicularly to and transversely of the vertical direction or the optical axis of the microscope to such an extent that a specimen holder of a greater area than that of the divided magnetic poles can be disposed within the specimen chamber. In a preferred embodiment of the invention, the specimen holder is supported rotatably or swingably around an axis extending perpendicularly to the optical axis so that angular position or inclination of the specimen holder can be varied by means of a manipulating mechanism. In another preferred embodiment of the invention, each of the objective lens halves is realised substantially in the form of a frustum flaring progressively from the top toward the base to assure a maximum rotation or inclination of the specimem holder. With the structure of the objective lens according to the invention, it is possible to dispose a large size specimen such as an IC wafer between the objective pole halves so far as the specimen can be disposed on the specimen holder. Further, the specimen can be observed in a desired inclined state by correspondingly manipulating the holder. The description makes reference to the accompanying drawings wherein:;

Figure 1 is a vertical sectional view showing a structure of a hitherto known scanning electron microscope; Figure 2 is a view for graphically illustrating a relation between a working distance and resolution of a scanning electron microscope; Figure 3 is a fragmental sectional view showing schematically a structure of an objec- tive lens of a hitherto known scanning electron microscope in which the objective lens is so configured that a specimen may be disposed between the objective pole pieces; Figure 4 is a view for graphically illustrating relationships between the accelerating voltage and resolution of a scanning electron microscope with various aberrations being taken into account as parameters; Figure 5 shows in a vertical sectional view a scanning electron microscope according to a 3 GB2173945A 3 first embodiment of the present invention; Figure 6 shows in a similar view a second embodiment of the scanning electron micro scope according to the invention; Figure 7 shows in a perspective view a spe- 70 cimen supporting portion of the microscope shown in Fig. 6; Figure 8 shows in a vertical sectional view a scanning electron microscope according to a third embodiment of the invention; Figure 9 shows in a perspective view a spe cimen holder portion of the microscope shown in Fig. 8; Figure 10 is a vertical sectional view show ing a scanning electron microscope according to a fourth embodiment of the invention; and Figure 11 is a fragmental sectional view showing a structure of an objective lens in which an objective lens half is adjustable in position.

Now, the invention will be described in de tail by referring to Figs. 5 et seq Fig. 5 shows in a vertical sectional view a scanning electron microscope according to a first embodiment of the present invention. The illustrated microscope comprises a column 1 which includes condenser lenses 5 and 6 and deflection coils 7 and 8, and a specimen chamber enclosure 2 disposed below the microscope column 1 and defining therein a specimen accommodating chamber 28. It is important to note that an objective lens 9 mounted within the specimen accommodating chamber 28 is divided into a pair of an upper objective lens half 20 and a lower objective lens half 21 which are disposed in alignment with the optical axis 30 of the microscope with a predetermied distance between the lens halves 20 and 21 so that a space extending perpendicularly to and transversely of the opti cal axis 30 is defined between the upper and lower lens halves 20 and 21.

More particularly, the upper objective lens half 20 is composed of a magnetic pole piece 22 located substantially at a center of an up per wall of the specimen chamber enclosure 2 and depending downwardly therefrom and an eletromagnetic coil 24 wound around the pole piece 22 which may be formed integrally with the top wall 2a of the enclosure 2 or prepared separately and fixedly mounted thereon by suitable means. The upper pole piece 22 is of substantially cylindrical form having a flat end face and has a bore 29 formed therein which extends coaxially with the optical axis 30. An opening 26 is formed in the bottom end face of the depending upper magnetic pole piece 22. On the other hand, the lower objective lens half 21 is also composed of a lower magnetic pole piece 23 disposed substantially at the center of a bottom wall 2b of the spe cimen chamber enclosure 2 and projecting up wardly in opposition to the upper magnetic pole piece 22 and an electromagnetic coil 25 wound around the lower magnetic pole piece 23, which may be formed integrally with the bottom wall 2b of the specimen chamber enclosure 2 or alternatively prepared separately and secured to the bottom wall 2b by suitable means. The lower magnetic pole piece 23 is also of a substantially cylindrical form having a flat top face. A bore 31 is formed in the lower magnetic pole piece 23 and extends coaxially with the optical axis. An opening 27 is formed in the flat top end face of the lower magnetic pole piece 23. A space or gap 23 of a predetermined dimension is thus defined between the opposite end faces of the upper and lower pole pieces 22 and 23.

There is disposed within the specimen chamber 28 a specimen holder 11 in such an orientation as to traverse the gap 32 between the pole pieces 22 and 23. The specimen hol der 11 is composed of a plate-like specimen supporting member 33 having one end (lefthand end as viewed in Fig. 5) provided with an integral reinforcing portion 34 and a reinforcing member 35 of a structure similar to that of the reinforcing portion 34 secured to the specimen supporting member 33 at the other end (righthand end) by means of screws 36. A specimen 15 such as an IC wafer is disposed on the top surface of the specimen supporting member 33. In consideration of the fact that the upper and the lower objective lens halves 20 and 21 are of cylindrical configuration, the specimen holder may be fixedly disposed within the specimen chamber 28 or alternatively pivotally supported so as to be angularly displaced between the horizontal position A indicated by solid line and a gently inclined position B indicated by a phantom line B. Further, the specimen holder may be so supported as to be movable in the horizontal plane. A reference numeral 13 denotes a secondary electron detector mounted in the microscope column 1 at a position above the objective lens.

In the scanning electron microscope of the structure described above, there is available between the upper and the lower objective lens halves 20 and 21 of the objective lens 9 a larger space extending perpendicularly to and transversely of the optical axis 30 as compared with the corresponding space of the hitherto known scanning electron microscope. Accordingly, the area of the specimen holder 11 can be made far greater than that of the pole piece of the objective lens, whereby a specimen 15 such as an IC wafer having a diameter in the range of 4 to 6 inches can be placed on the specimen holder 11 without any difficulty. As the specimen 15 supported on the specimen holder 11 is scanned by an electron beam emitted by the electron gun 3, secondary electrons are produced by the specimen. The secondary electrons thus emitted flow into the bore 29 through the opening 26 formed in the pole face of the upper objective lens half 20 to be detected by the secondary 4 GB2173945A 4 electron detector 13. During observation of the specimen 15, the electron beam accelerat ing voltage can be set at a relatively low level of the order of 1 W. Nevetheless, the work ing distance mentioned hereinbefore can be set at a small value which assures high resolu tion, by virtue of the arrangement in which the specimen 15 is disposed between the upper and the lower magnetic pole piece 22 and 23 of the objective lens 9.

Figs 6 and 7 show a scanning electron microscope according to a second embodi ment of the present invention which differs primarily from the one shown in Fig. 5 in that the magnetic pole pieces of the upper and lower objective lens halves 20 and 21 consti tuting the objective lens 9 are beveled or chamfered at the end portions facing toward each other. More specifically, each of the magnetic pole pieces 22 and 23 has a drum like (cylindrical) base portion and a frusturn portion tapering progressively from the base portion toward the pole end defining the gap 32. The angle of chamfer may be selected on the order of 60', by way of example. Further, a coil holder 40 is mounted within the bore 29 of the pole piece 22 of the upper objective lens half 20, wherein first and second scann ing coils 7 and 8 are fixedly mounted on the coil holder 40. A mounting hole is formed in the cylindrical portion of the upper magnetic pole piece 22 for allowing the secondary elec tron detector 13 to be fixedly mounted and exposed to the bore 29, as is shown in Fig.

6. A symbol D indicates the area of the pole 100 piece of the objective lens 9.

The specimen holder 11 is disposed in such a positional relationship and 23 of the upper and lower objective lens halves 21 and 22 as is shown in Fig. 7. A magnetic field is formed in the gap defined by the pole pieces 22 and 23 between which the specimen holder 11 is inserted. Observation of the specimen 15 may be effected either in the horizontal disposition of the specimen holder 110 11 or in an inclined position thereof. In this connection, it should be noted that the angle at which the specimen holder 11 can be inclined within the specimen chamber 28 from the horizontal position A to the maximum in- 115 clination C is greater than the angle allowable in the case of the first embodiment shown in Fig. 5. In other words, the specimen 15 can be inclined at an angle of 60' or more, whereby inspection of a finished IC wafer or a 120 product on the way of manufacture can be carried out in a very satisfactory manner. Fur ther, because of the structure in which the scanning deflection coils 7 and 8 are incorpor ated in the objective lens 9, the distance be- 125 tween the deflection coil assembly (7, 8) and the opening 26 can be made shorter to thereby enlarge the scanning range (or stroke) of the electron beam. The secondary electrons emitted from the specimen upon irradiation of to the pole pieces 22 the electron beam are detected by the secondary electron detector 13. Although the first and second deflection coils 7 and 8 incorporated in the objective lens 9 are disposed above the secondary electron detector 13 in the case of the microscope illustrated in Fig. 6, the invention is not restricted to such struture. For example, the second deflection coil 8 or both of the first and second deflection coil 7 and 8 may be located below the secondary electron detector 13 without departing from the scope of the invention.

Figs. 8 and 9 show a scanning electron microscope according to a third embodiment of the present invention, in which the upper and lower objective lenses include the respective magnetic pole pieces 22 and 23 chamfered in the same manner as in the case of the microscope shown in Figs. 6 and 7. The third embodiment however differs from the second embodiment in respect that only the upper magnetic pole piece 22 is wound with the electromagnetic coil 24 for excitation of the objective lens 9. Further, the first and sec- ond scanning deflection coils 7 and 8 are mounted within the microscope column 1 with the secondary electron detector 13 also being fixedly located in the column 1 below the scanning coil assembly (7, 8), while a third deflection coil 42 is fixedly mounted on a coil holder 41 within the bore 29 of the magnetic pole piece 22 of the upper objective lens half 20. For observation of a specimen, arbitrarily selected two of the deflection coils 7, 8 and 42 are excited for deflecting the electron beam. The specimen holder 11 is constituted by a specimen supporting plate 33 having a reinforcing structure integrally formed only at one end and supported within the specimen chamber 28 in a cantilever-like manner. The specimen 15 is disposed on the specimen supporting plate 33, as is shown in Fig. 9.

Although the lower objective lens half 21 of the objective 9 is not provided with the electromagnetic coil in the case of the third embodiment as described above, it is possible with such structure of the objective lens to produce a relatively low accelerating voltage of the order of 1 kV, by way of example. By providing the deflection coils 7, 8 and 42 for the electron beam scanning in the arrangement described above, aberrations of image under observation can be significantly reduced. More particularly, so far as the electron beam deflection is concerned, operation of the hitherto known scanning electron microscope corresponds to that of the inventive microscope shown in Fig. 8 which takes place when the deflection coils 7 and 8 are energized. On these conditions. it is assumed that a point P on the specimen 15 is to be irradiated. The electron beam emitted by the electron gun 3 undergoes first deflection at a point C under the influence of the deflection coil 7, which is followed by a second deflection at a point R by the action of the second deflection coil 8 to impinge on the specimen 15 at the point P. In contrast, when the deflection coils 7 and 42 of the microscope shown in Fig. 8 are excited, the electron beam emitted by the electron gun 3 and undergone the deflecting action of the first deflection coil 7 at the point Q is subsequently deflected at a point S by the third deflection coil 42 to impinge on the specimen at the point P. It will be readily appreciated that the path Q-S- P followed by the electron beam upon excitation of the first and third deflection coils 7 and 42 is positioned closer to the optical path 30 than the electron beam path Q-R-P attained through excitation of the deflection coils 7 and 8 which corresponds to the operation of the hitherto known microscope. Thus, the off-axis aberrations due to the electron beam path can be reduced according to the third embodiment of the invention, whereby the image can be observed with an enhanced sharpness or contrast.

As a modification of the third embodiment, the magnetic pole 22 of the lower objective lens half 21 may be spared. Such modification is shown in Fig. 10 as a fourth embodiment of the invention. In the structure of the scanning electron microscope shown in Fig. 10, the lower objective lens half 21 may be regarded as being located at a point at infinity relative to the upper objective lens half 20, wherein excitation of the objective lens is effected only for the upper objective half 20. In this case, the working distance is defined as the one between the bottom end of the pole piece 22 and the specimen 15. With this structure, the specimen chamber 28 of a significantly increased volume is available for mounting various detectors in addition to the secondary electron detector 13 and/or facilitating installation of the manipulating mechanism for the specimen holder 11, to further advantage.

As another modification common to the first to fourth embodiments of the invention de- scribed above, the pole piece for one or both 110 of the upper and lower objective lens half may be realized in such a structure as shown in Fig. 11. More specifically, the pole piece shown in Fig. 11 is composed of an outer sleeve having an axially extending bore 58 formed therein and having an offset portion at the upper end and an inner sleeve 51 slideably inserted into the bore 58 of the outer sleeve 50. The inner sleeve 51 is rotatably supported at the upper offset end of the bore 58 by means of a crown gear 52 which is operatively connected to a manipulating rod supported rotatably on the specimen chamber enclosure 2 by means of a bearing 59. The outer periphery of the inner sleeve 51 is toothed at 54, while teeth 55 are formed in the inner periphery of the crown gear 52 so as to mesh with the teeth 54. A gear 56 is integrally formed with the crown gear 52 at a lateral surface and adapted to mesh with a GB2173945A 5 gear 56 formed at the free end portion of the manipulating rod 53. By rotating the manipulating rod 53 with a knob 60 in one or the other direction, the crown gear 52 is rotated in a corresponding direction within a horizontal plane, resulting in that the inner sleeve 51 is moved upward or downward through the feeding action taking place between the crown gear 52 and the inner sleeve 51. Needless to say, the crown gear 52 is supported by suitable means (not shown) so as not to fall within the bore 58, while the inner sleeve 51 is prevented from being rotated together with the crown gear. With the structure of the pole piece for the lower and/or upper objective lens half described above, the working distance can be varied. For example, the working distance may be shortened with the specimen being held horizontally to attain high resolu- tion, or the working distance may be increased to allow the specimen to be inclined at a greater angle in dependence on observations as desired. In this way, utility of the scanning electron microscope can be en- hanced according to the invention.

As will be appreciated from the foregoing description, the scanning electron beam apparatus inclusive of the scanning electron beam microscope in which the objective lens is div- ided into a pair of an upper objective half and a lower objective half to form a specimen chamber extending transversely through a gap defined between the upper and the lower objective halves in the direction perpendicular to the optical axis of the microscope, wherein a specimen holder of a larger area than that of the pole face is disposed in the gap between the upper and the lower objective lens halves according to the teaching of the invention al- lows observation of the specimen of a larger size with high resolution at a low accelerating voltage even at inclined states of the specimen. By chamfering the opposite end portions of the upper and lower objective lens halves, inclination of the specimen holder at a large angle relative to the horizontal is facilitated. Furthermore, in the structure in which the deflection coil is incorporated in the upper objective lens half, not only the stroke over which the specimen is scanned with the electron beam can be increased, but also the electron beam path can be positioned closer to the optical axis to thereby reduce the aberrations to lesser degree. When the upper or the lower magnetic pole piece is realized to be movable along the optical axis, the working distance can be varied as desired for attaining high resolution, while the specimen can be in clined at a greater angle.

In the foregoing, the present invention has been described in conjunction with the exem plary embodiments illustrated in the drawing.

It will however be appreciated that the inven tion is never restricted tothese embodiments, but numerous modifications and variations will 6 GB2173945A 6 readily occur to those skilled in the art without departing from the spirit and scope of the invention. By the way, although the lower objective half of the objective lens is omitted in the scanning electron microscope shown in Fig. 10, it goes without saying that structure is covered by the concept of the present invention, the since the lower objective half may be considered as being located at infinity.

Claims

1. A scanning electron beam apparatus, comprising an electron gun, condenser lenses, deflection coils for scanning two-dimensionally a specimen with an electron beam, an objective lens, and a secondary electron detector wherein said objective lens is divided into a pair of an upper objective lens half and a lower objective lens half to define a specimen accommodating space between said objective lens halves, said specimen accommodating space extending transversely of a direction in which said objective lens halves are disposed in opposition to each other, and a specimen holder having a larger area than the pole face of said objectives lens halves is disposed is a gap defined between said upper and lower objective lens halves.

2. A scanning electron beam apparatus ac- cording to claim 1, wherein said specimen hol- der is swingably supported so as to be in clined relative to a line extending perpendicu larly to the optical axis of said apparatus at a variable angle.

3. A scanning electron beam apparatus ac cording to claim 2, wherein said pieces of said upper and lower objective lens halves disposed in opposition to each other substan tially in alignment with the optical axis of said apparatus are formed in a frustum-like configu ration at respective opposing end portions, so that said specimen holder can be inclined at a greater angle relative to said line.

4. A scanning electron beam apparatus ac cording to one of preceding claims 1 to 3, further including a specimen chamber enclo sure confining said specimen accommodating space, wherein the pole pieces of said upper and lower objective halves are mounted, re spectively, on an inner top wall and an inner bottom wall of said enclosure in opposition to each other substantially in alignment with the optical axis of said apparatus with said gap defined between the opposing ends of said pole pieces and are wound with respective 120 electromagnetic coils.

5. A scanning electron beam apparatus ac cording to claim 4, wherein only one of said magnetic poles is wound with the electromag netic coil.

6. A scanning electron beam apparatus ac cording to one of preceding claims 1 to 5, wherein said deflection coils are incorporated in said upper magnetic lens half.

7. A scanning electron beam apparatus ac- cording to one of preceding claims 1 to 5, wherein said deflection coils are mounted in a column at locations above said upper objective lens half, further including an additional deflection coil incorporated in said upper lens half.

8. A scanning electron beam apparatus according to one of preceding claims 1 to 7, wherein said lower objective lens half is posi- tioned at infinity relative to said upper objective lens half.

9. A scanning electron beam apparatus comprising an electron gun, deflection coils for scanning two-dimensionally a specimen with an electron beam, an objective lens being located on one side of a holder for a specimen larger in area than the pole face of the objective lens pole piece, and a secondary electron detector.

10. Scanning electron beam apparatus constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 60

11. Scanning electron beam microscope comprising apparatus according to any one of claims 1 to 10.

Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8818935, 1986, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

9. A scanning electron beam apparatus according to one of preceding claims 1 to 8, wherein at least one of said magnetic poles of said objective lens halves is constituted by an outer sleeve mounted fixedly on said specimen chamber enclosure and an inner sleeve slideably fitted in said outer sleeve so that said inner sleeve can be axially moved relative to said outer sleeve by means of a manipulating mechanism.

10. A scanning electron beam apparatus according to claim 9, wherein said manipulating mechanism includes a rod rotatably mounted in said specimen chamber enclosure and extending outwardly therefrom, and transmission gear means provided between said inner sleeve and an inner end of said rod for translating rotation of said rod in one di- rection into an axial movement of said inner sleeve in a corresponding direction.

11. Scanning electron beam apparatus constructed and arranged substantially as herein described with reference to and as illustrated in Figs. 5 to 11 of the accompanying drawings.

12. A scanning electron beam apparatus comprising an electron gun, deflection coils for scanning two-dimensionally a speciment with an electron beam, an objective lens of which one objective lens pole piece is located on one side of a holder for a specimen larger in area than the pole face of the said one objective lens pole piece and a second optional pole piece is disposed on the ojther side of the specimen holder, and detector.

13. Scanning electron beam microscope comprising apparatus according to any one of claims 1 to

12.

a secondary electron CLAIMS Amendments to the claims have been filed, and have the following effect- New or textually amended claims have been filed as follows- 1. A scanning electron beam apparatus comprising an electron gun; condenser lenses; deflection coils for scanning two-dimensionally a specimen with an electron beam; and an objective lens disposed in a specimen chamber and comprising a magnetic pole piece provided on an upper wall of the specimen chamber and defining below the magnetic pole piece, a wide specimen accomodating space 7 GB2173945A 7 extending from one side of the specimen chamber to the other perpendicular to an optical axis of the apparatus, and from an end face of the magnetic pole piece of the specimen chamber to the wall opposite thereto.

2. Apparatus according to claim 1, wherein the magnetic pole piece is integral with or mounted on an upper wall of the specimen chamber enclosure substantially at a centre thereof, and depending downwardly therefrom.

3. Apparatus according to claim 1 or claim 2 wherein and electro-magnetic coil is wound around the magnetic pole piece.

4. Apparatus according to any one of claims 1 to 3 wherein the end portion of the magnetic pole piece has a frustum-like configuration, so that a specimen holder having an area considerably larger than that of the pole piece and disposed in the vicinity of the pole piece can be inclined at a greater angle relative to the optical axis of the electron beam apparatus.

5. Apparatus acording to any one of claims 1 to 4 wherein the deflection coil is incorporated in the objective lens.

6. Apparatus according to claim 1 wherein the deflection coils are mounted in an electron beam column at locations above the objective lens, further including an additional deflection coil incorporated in the objective lens.

7. Apparatus according to any one of claims 1 to 6 wherein the magnetic pole piece comprises an outer sleeve fixed on the upper wall of the specimen chamber enclosure, and an inner sleeve slidably fitted in the outer sleeve so that the inner sleeve can be axially moved relative to the outer sleeve by means of a manipulating mechanism.

8. Apparatus according to claim 7 wherein the manipulating mechanism includes a rod rotatably mounted in the specimen chamber enclosure and extending outwardly therefrom, and transmission gear means provided between the inner sleeve and an inner end of the rod translating rotation of the rod in one direction into an axial movement of the inner sleeve in a corresponding direction.