OBSERVATION DEVICE

Abstract

An observation device capable of observing a subject plane. The observation device includes a light receiving surface and an imaging optical system for forming an image of light from the subject plane onto the light receiving surface. The imaging optical system includes a concave primary mirror, a secondary mirror, and a flat extraction mirror. The beam of the light from the subject plane is reflected at the concave primary mirror, the convex secondary mirror, and the concave primary mirror in the named order, after which an image of the beam is formed on the light receiving surface via the flat extraction mirror. The observation device changes an angle and an angle .

Claims

1. An observation device comprising: a light receiving surface that receives light from a subject plane; and an imaging optical system that forms an image of the light from the subject plane on the light receiving surface, wherein the imaging optical system comprises an equimagnification reflective imaging optical system that includes a concave primary mirror, a convex secondary mirror, and a flat extraction mirror, and the imaging optical system reflects a beam of the light from the subject plane at the concave primary mirror, the convex secondary mirror, and the concave primary mirror in that order, and then forms the image on the light receiving surface via the flat extraction mirror; first tilting means that changes an angle defined between first optical axis of light directed toward the concave primary mirror from the subject plane and a perpendicular line to the subject plane; and second tilting means that changes an angle defined between second optical axis of light directed toward the light receiving surface from the flat extraction mirror and a perpendicular line to the light receiving surface.

2. The observation device according to claim 1, comprising: control means that controls the first tilting means and the second tilting means, the control means controlling the first tilting means and the second tilting means so that the angle and the angle are equal to each other.

3. The observation device according to claim 1, wherein the first tilting means changes the angle within a range of 0 to 70, and the second tilting means changes the angle within a range of 0 to 70.

4. The observation device according to claim 1, wherein the observation device is a microscope, a spectroscopic ellipsometer, a defect detection device, or a reflectance measurement device.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 provides a front view, a top view, and a side view of an observation device with an X axis as a rotation axis;

[0025] FIG. 2 provides a front view, a top view, and a side view of the observation device with a Y axis as a rotation axis;

[0026] FIG. 3 is a top view of the observation device rotated by 0 about the X axis;

[0027] FIG. 4 is a side view of the observation device rotated by 0 about the X axis;

[0028] FIG. 5 is a front view of the observation device rotated by 0 about the X axis;

[0029] FIG. 6 is a front view of the observation device rotated by 30 about the X axis;

[0030] FIG. 7 is a front view of the observation device rotated by 60 about the X axis;

[0031] FIG. 8 is a front view of the observation device rotated by 60 about the X axis;

[0032] FIG. 9 is a top view of the observation device rotated by 0 about the Y axis;

[0033] FIG. 10 is a side view of the observation device rotated by 0 about the Y axis;

[0034] FIG. 11 is a front view of the observation device rotated by 0 about the Y axis;

[0035] FIG. 12 is a front view of the observation device rotated by 30 about the Y axis;

[0036] FIG. 13 is a front view of the observation device rotated by 60 about the Y axis;

[0037] FIG. 14 is a front view of the observation device rotated by 30 about the Y axis;

[0038] FIG. 15 is a front view showing the more specific appearance of the observation device;

[0039] FIG. 16 is a front view of the observation device rotated by 45 about the Y axis;

[0040] FIG. 17 is a side view of the observation device;

[0041] FIG. 18 shows the result of calculating the resolution (MTF) for the observation device rotated by 0 about the X axis;

[0042] FIG. 19 shows the result of calculating the resolution (MTF) for the observation device rotated by +30 about the X axis;

[0043] FIG. 20 shows the result of calculating the resolution (MTF) for the observation device rotated by 60 about the X axis;

[0044] FIG. 21 shows the result of calculating the resolution (MTF) for the observation device rotated by 0 about the Y axis;

[0045] FIG. 22 shows the result of calculating the resolution (MTF) for the observation device rotated by 30 about the Y axis; and

[0046] FIG. 23 shows the result of calculating the resolution (MTF) for the observation device rotated by +60 about the Y axis.

DETAILED DESCRIPTION

[0047] The following describes embodiments of the invention in detail with reference to the drawings.

[0048] FIG. 1 provides a front view, a top view, and a side view of an observation device with an X axis as a rotation axis. FIG. 2 provides a front view, a top view, and a side view of the observation device with a Y axis as a rotation axis.

[0049] As shown in FIGS. 1 and 2, an observation device 10 of one or more embodiments includes a light receiving surface 20 for receiving light from a subject plane S, and an imaging optical system 30 for forming an image of light from the subject plane S on the light receiving surface 20.

[0050] In the observation device 10 of one or more embodiments, the imaging optical system 30 is constituted by an Ofner optical system which is one of the equimagnification reflection type imaging optical systems. The imaging optical system 30 is constituted by a telecentric optical system.

[0051] The observation device 10 of one or more embodiments may include an illumination optical system (not shown) for irradiating the subject plane S with light. The illumination optical system may include a telecentric optical system in accordance with the imaging optical system 30. For example, the Kohler illumination system disclosed in Japanese Patent Application Laid-open No. 2013-174844 is available as the illumination optical system.

[0052] As shown in FIGS. 1 and 2, the imaging optical system 30 constituted by the Ofner optical system is provided with a primary mirror 32 constituted by a concave mirror, a secondary mirror 34 constituted by a convex mirror, and a flat extraction mirror 36 there. A beam of light from the subject plane S is reflected at the primary mirror 32, the secondary mirror 34, the primary mirror 32, and the extraction plane mirror 36 in the named order, and is then focused on the light receiving surface 20.

[0053] The subject plane S and the light receiving plane 20 are in a conjugate relationship of equimagnification in the Ofner optical system.

[0054] The subject plane S is the surface of a subject to be observed, for example, the surface of a printed circuit board.

[0055] The light receiving surface 20 is a surface on which light from the subject plane S forms an image, and is, for example, the light receiving surface of an image pickup device such as a two-dimensional CCD.

[0056] The secondary mirror 34 serves as the pupil of the optical system.

[0057] In addition, a commonly used CCD incorporates a condenser lens called a micro lens, and a color filter having a thickness on the front face of each element in order to increase the light receiving efficiency. Since the luminous flux having a large inclination does not reach the light receiving surface of the CCD, however, it is difficult for the micro lens to condense light.

[0058] Therefore, it may be that the two-dimensional CCD to be used for the light receiving surface 20 is of a type that does not incorporate micro lenses or thick color filters.

[0059] As shown in FIGS. 1 and 2, the beam of light directed from the subject plane S toward the concave primary mirror 32 is telecentric. The light reflected by the primary mirror 32 is reflected at the convex secondary mirror 34 serving also as a diaphragm. The light reflected at the secondary mirror 34 is again reflected at the concave primary mirror 32 to be telecentric.

[0060] The light that is reflected at the primary mirror 32 to be telecentric is reflected at the flat extraction mirror 36 to form an image on the light receiving surface 20 by an equimagnification.

[0061] The field of view of the subject plane S is, for example, 24.624.6 mm with NA=0.04.

[0062] The field of view of the light receiving surface 20 on which the image of the light from the subject plane S is formed by an equimagnification is, for example, 24.624.6 mm with NA=0.04.

[0063] FIG. 3 is a top view of the observation device 10 rotated by 0 about the X axis. FIG. 4 is a side view of the observation device 10 rotated by 0 about the X axis. FIG. 5 is a front view of the observation device 10 rotated by 0 about the X axis.

[0064] As shown in FIG. 5, with the observation device 10 rotated by 0 about the X axis, a perpendicular line N1 to the subject plane S in the YZ plane is tilted by 0 with respect to an optical axis L1 of light traveling from the subject plane S toward the primary mirror 32 (=0). A perpendicular line N2 to the light receiving surface 20 is tilted by 0 with respect to an optical axis L2 of light traveling from the flat extraction mirror 36 toward the light receiving surface 20 (=0).

[0065] FIG. 6 is a front view of the observation device 10 rotated by 30 about the X axis.

[0066] As shown in FIG. 6, with the observation device 10 rotated by 30 about the X axis, the perpendicular line N1 to the subject plane S in the YZ plane is tilted by 30 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=30). The perpendicular line N2 to the light receiving surface 20 is tilted by 30 with respect to the optical axis L2 of the light traveling from the extraction plane mirror 36 toward the light receiving surface 20 (=30).

[0067] FIG. 7 is a front view of the observation device 10 rotated by 60 about the X axis.

[0068] As shown in FIG. 7, with the observation device 10 rotated by 60 about the X axis, the perpendicular line N1 to the subject plane S in the YZ plane is tilted by 60 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=60). The perpendicular line N2 to the light receiving surface 20 is tilted by 60 with respect to the optical axis L2 of the light traveling from the flat extraction mirror 36 toward the light receiving surface 20 (P=60).

[0069] FIG. 8 is a front view of the observation device 10 rotated by 60 about the X axis.

[0070] As shown in FIG. 8, with the observation device 10 rotated by 60 about the X axis, the perpendicular line N1 to the subject plane S in the YZ plane is tilted by 60 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=60). The perpendicular line N2 to the light receiving surface 20 is tilted by 60 with respect to the optical axis L2 of the light traveling from the flat extraction mirror 36 toward the light receiving surface 20 (=60).

[0071] FIG. 9 is a top view of the observation device 10 rotated by 0 about the Y axis. FIG. 10 is a side view of the observation device 10 rotated by 0 about the Y axis. FIG. 11 is a front view of the observation device 10 rotated by 0 about the Y axis.

[0072] As shown in FIG. 11, with the observation device 10 rotated by 0 about the Y axis, the perpendicular line N1 to the subject plane S in the XZ plane is tilted by 0 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=0). The perpendicular line N2 to the light receiving surface 20 is tilted by 0 with respect to the optical axis L2 of the light traveling from the flat extraction mirror 36 toward the light receiving surface 20 (=0).

[0073] FIG. 12 is a front view of the observation device 10 rotated by 30 about the Y axis.

[0074] As shown in FIG. 12, with the observation device 10 rotated by 30 about the Y axis, the perpendicular line N1 to the subject plane S in the XZ plane is tilted by 30 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=30). The perpendicular line N2 to the light receiving surface 20 is tilted by 30 with respect to the optical axis L2 of the light traveling from the extraction plane mirror 36 toward the light receiving surface 20 (=30).

[0075] FIG. 13 is a front view of the observation device 10 rotated by 60 about the Y axis.

[0076] As shown in FIG. 13, with the observation device 10 rotated by 60 about the Y axis, the perpendicular line N1 to the subject plane S in the XZ plane is tilted by 60 with respect to the optical axis L1 of the light traveling from the subject plane S toward the primary mirror 32 (=60). The perpendicular line N2 to the light receiving surface 20 is tilted by 60 with respect to the optical axis L2 of the light traveling from the flat extraction mirror 36 toward the light receiving surface 20 (=60).

[0077] FIG. 14 is a front view of the observation device 10 rotated by 30 about the Y axis.

[0078] As shown in FIG. 14, with the observation device 10 rotated by 30 about the Y axis, the perpendicular line N1 to the subject plane S in the XZ plane is tilted by 30 with respect to the optical axis L1 (=30) of the light traveling from the subject plane S toward the primary mirror 32. The perpendicular line N2 to the light receiving surface 20 is tilted by 30 with respect to the optical axis L2 of the light traveling from the flat extraction mirror 36 to the light receiving surface 20 (P=30).

[0079] As described above, the observation device 10 of one or more embodiments can rotate about both the X axis and the Y axis. That is, when the subject plane S to be observed is positioned in the two-dimensional XY plane, the lens barrel body for accommodating the primary mirror 32, the secondary mirror 34, and the extraction plane mirror 36 can be rotated about both the X axis and the Y axis. Further, it is possible to freely rotate the light receiving surface 20 including, for example, a CCD image pickup device according to the rotation angle of the lens barrel body. Accordingly, it is possible to rotate the barrel main body of the observation device 10 and the light receiving surface 20 so that the subject plane S and the light receiving surface 20 satisfy the Scheimpflug conditions. As a result, it is possible to focus on the entire subject plane S even when the subject plane S is observed obliquely.

[0080] FIG. 15 is a front view showing the more specific appearance of the observation device 10. FIG. 17 is a side view of the observation device 10. FIG. 16 is a front view of the observation device 10 rotated by 45 about the Y axis.

[0081] As shown in FIGS. 15 to 17, the observation device 10 includes a lens barrel body 12 that integrally accommodates the primary mirror 32, the secondary mirror 34, and the flat extraction mirror 36 therein. In addition, the observation device 10 is provided with means for rotating the lens barrel body 12 about the X axis and the Y axis. This driving means is constituted by, for example, a stepping motor or a servo motor. The means for rotating the barrel main body 12 is not particularly limited, and may be other than the stepping motor or the servo motor. The means for rotating the barrel main body 12 corresponds to the first tilting means of one or more embodiments of the invention.

[0082] The observation device 10 includes means for rotating the light receiving surface 20 constituted by, for example, a CCD image pickup device. This driving means is constituted by, for example, a stepping motor or a servomotor. The means for rotating the light receiving surface 20 is not particularly limited, and may be other than the stepping motor or the servo motor. The means for rotating the light receiving surface 20 corresponds to the second tilting means of one or more embodiments of the invention.

[0083] Further, the observation device 10 includes control means for controlling the means (first tilting means) for rotating the lens barrel body 12 and the means (second tilting means) for rotating the light receiving surface 20, respectively. The control means can control the rotation angle of the lens barrel body 12 and the light receiving surface 20 by controlling the first tilting means and the second tilting means, respectively. This control means is constituted by, for example, a personal computer. The first tilting means and the control means are electrically connected together. The second tilting means and the control means are electrically connected together. Software for controlling the first tilting means and the second control means may be installed in the control means.

[0084] By rotating the lens barrel body 12, the first tilting means can change the angle defined by the optical axis L1 of light traveling from the subject plane S toward the concave primary mirror 32 and the perpendicular line N1 to the subject plane S. The first tilting means may be capable of changing the angle in the range of 0 to 70.

[0085] By rotating the light receiving surface 20, the second tilting means can change the angle defined by the optical axis L2 of the light traveling from the extraction plane mirror 36 toward the light receiving surface 20 and the perpendicular line N2 to the light receiving surface 20. The second tilting means may be capable of changing the angle in the range of 0 to 70.

[0086] The control means can individually control the first tilting means and the second tilting means so that the angle and the angle are equal to each other. In other words, the tilt angle of the subject plane S and the light receiving surface 20 with respect to the optical axis can be controlled so that the subject plane S and the light receiving surface 20 satisfy the Scheimpflug conditions. This makes it possible to focus on the entire subject plane S even when the subject plane S is observed from a direction tilted by, for example, 60.

[0087] As described above, the imaging optical system for forming an image of light from the subject plane S on the light receiving surface 20 is constituted by an Ofner optical system which is one of the equimagnification reflective imaging optical systems. Such a reflective optical system has an advantage over a refractive lens such that the wavelength of light to be used to observe the subject plane S is not limited. Therefore, the observation device 10 of one or more embodiments may be applied to various fields such as semiconductor field and bio field since the wavelength of light used for observation is not limited.

[0088] The observation device 10 of one or more embodiments can be applied to, for example, a microscope for observing a subject plane.

[0089] The observation device 10 of one or more embodiments may be applied to, for example, a spectroscopic ellipsometer, a defect detection device, or a reflectance measurement device.

[0090] In addition to those devices, the observation device of one or more embodiments is potentially applicable to general optical observation devices.

[0091] FIG. 18 shows the result of calculating the resolution (MTF) for the observation device of one or more embodiments rotated by 0 about the X axis. FIG. 19 shows the result of calculating the resolution (MTF) for the observation device of one or more embodiments rotated by 30 about the X axis. FIG. 20 shows the result of calculating the resolution (MTF) for the observation device of one or more embodiments rotated by 60 about the X axis. FIG. 21 shows the result of calculating the resolution (MTF) for the observation device of one or more embodiments rotated by 0 about the Y axis. FIG. 22 shows the result of calculating the resolution (MTF) for the observation device of one or more embodiments rotated by 30 about the Y axis. FIG. 23 shows the result of calculating the resolution (MTF) for the observation device according to one or more embodiments rotated by 60 about the Y axis. The resolution (MTF) was calculated in the wavelength range from 250 nm (Weight 1.0) to 800 nm (Weight 1.0) with the dominant wavelength being 550 nm (Weight 1.0). In addition, the resolution (MTF) was calculated up to 100 LP/mm (5 m L&S).

[0092] When the observation device is perpendicular to the XY plane (the rotation angles about the X axis and the Y axis=0), the subject plane and the light receiving plane are symmetrical (axisymmetric) with respect to the Y axis within the XY projection plane, and are asymmetric with respect to the X axis. In this case, as shown in FIGS. 18 and 21, the MTFs at the center of the light receiving surface and the four corners substantially match the theoretical values.

[0093] When the observation device is rotated by 30 and 60 about the X axis, the subject plane and the light receiving plane are symmetric (line symmetric) with respect to the Y axis within the XY projection plane, and are asymmetric with respect to the X axis. In this case, as shown in FIGS. 19 and 20, the MTFs in the X direction of the light receiving surface are hardly changed from the case of the rotation angle=0. The MTFs in the Y direction of the light receiving surface are lower by cos 30=0.866 for the rotation angle of 30 and by cos 60=0.5 for the rotation angle of 60, and substantially match the theoretical values.

[0094] When the observation device is rotated by 30 and 60 about the Y axis, the subject plane and the light receiving plane are asymmetric with respect to both the X axis and the Y axis in the XY projection plane. In this case, as shown in FIGS. 22 and 23, the MTFs in the X direction of the light receiving surface are hardly changed from the case of the rotation angle=0. The MTFs in the Y direction of the light receiving surface are lower by cos 30=0.866 for the rotation angle of 30 and by cos 60=0.5 for the rotation angle of 60, and substantially match the theoretical values.

[0095] As shown in FIG. 1, when the observation device is rotated about the X axis within the YZ plane, the observation device of one or more embodiments may substantially achieve the theoretical resolution. Further, as shown in FIG. 2, even when the observation device is rotated about the Y axis in the XZ plane, the observation device of one or more embodiments may substantially achieve the theoretical resolution.

[0096] There may be a case where with the subject plane being placed on the XY plane, the observation device shown in FIG. 1 placed in the Z-axial direction perpendicular to the subject plane can be tilted in the X-axial direction.

[0097] There may also be a case where with the subject plane being placed on the XY plane, the observation device shown in FIG. 2 placed in the Z-axial direction perpendicular to the subject plane can be tilted in the Y-axial direction.

[0098] The observation device of one or more embodiments may observe the subject plane from substantially all the directions.

[0099] The observation device of one or more embodiments may substantially achieve the theoretical resolution even when the subject plane is observed from an oblique direction.

[0100] Generally, the subject plane of a microscope on which a sample is placed moves in the X and Y directions. The objective lens that needs focusing moves in the Z-axial direction perpendicular to the subject plane. That is, the microscope has three drive shafts.

[0101] The observation device according to one or more embodiments further includes a drive shaft for rotating the observation device about the X axis and a drive shaft for rotating the observation device about the Y axis. That is, the observation device of one or more embodiments may have five drive shafts. In this case, the observation device of one or more embodiments may be implemented by incorporating a 5-axis robot.

[0102] Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.

DESCRIPTION OF REFERENCE NUMERALS

[0103] 10 Observation device [0104] 12 Lens barrel body [0105] 20 Light receiving surface [0106] 30 Image forming optical system [0107] 32 Primary mirror [0108] 34 Secondary mirror [0109] 36 Flat extraction mirror [0110] L1, L2 Optical axis [0111] N1, N2 Perpendicular line [0112] S Subject plane