Interference measuring device

Abstract

An interference measuring device (100) comprises: an optical splitting element (50) that splits light from a light source into measurement light and reference light on a split surface (51) and emits the same; a reference mirror (60) that reflects the reference light (42); and a light-condensing optical system (CS) on which return light of the measurement light (43) irradiated onto a measurement object (W) is incident through the optical splitting element (50). The optical splitting element (50) comprises: a first optical surface (P1) through which passes the measurement light (43) from the split surface (51); and a second optical surface (P2) through which passes the reference light (42) from the split surface (51). The first optical surface (P1) is inclined with respect to a plane (V1) perpendicular to and intersecting an optical axis (I1) of the light-condensing optical system (CS), and the second optical surface (P2) is inclined with respect to a reflecting surface (61) of the reference mirror (60).

Description

Interferometric measurement device

[0001] The present invention relates to an interferometry apparatus and an interferometry method.

[0002] Conventionally, there has been known an interferometric measurement device such as that disclosed in Patent Document 1, which measures the unevenness of an object by separating light from a light source using a beam splitter or the like into light to be irradiated onto the object and a reference light, and observing the interference wave between the two. In such an interferometric measurement device, unintended reflected light and stray light within the beam splitter affect the measurement results.

[0003] U.S. Pat. No. 10,260,867

[0004] The first interference measurement device comprises an optical division element that divides light from a light source at a division surface into measurement light and reference light and emits the light; a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light; and a focusing optical system in which the measurement light emitted from the optical division element and irradiated onto the measurement object is returned from the measurement object and incident via the optical division element as measurement returned light, wherein the measurement returned light and the reference reflected light incident from the reference mirror are incident on the focusing optical system via the optical division element, and the optical division element comprises a first optical surface through which the measurement light from the division surface passes and a second optical surface through which the reference light from the division surface passes, wherein the first optical surface is inclined with respect to a plane that intersects perpendicularly with the optical axis of the focusing optical system, and the second optical surface is inclined with respect to the reflecting surface of the reference mirror.

[0005] The second interference measurement device includes an optical division element that divides light from a light source at a division surface into measurement light and reference light and emits the light; a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light; and a focusing optical system in which the measurement light emitted from the optical division element and irradiated onto the measurement object is returned from the measurement object and enters the optical division element as measurement returned light, via the optical division element. The measurement returned light and the reference reflected light incident from the reference mirror are incident on the focusing optical system, and the optical division element further includes an optical surface that is inclined with respect to the optical axis of the focusing optical system or a plane that intersects perpendicularly with the optical axis of the focusing optical system, and is configured so that the traveling direction of at least one of the measurement return light and the reference reflected light that pass through the optical surface is different from the traveling direction of flare light generated on the optical surface by at least one of the measurement light and the reference light.

[0006] The third interference measurement device is an interference measurement device comprising: an optical division element that splits light from a light source into measurement light and reference light having different polarization directions using a polarization splitting surface and emits the light; and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light. The third interference measurement device comprises a polarizer into which measurement return light, which is return light from the measurement object of the measurement light emitted from the optical division element and irradiated onto the measurement object, and reference reflected light from the reference mirror, are incident via the optical division element; and quarter-wave conversion elements that are respectively arranged between the optical division element and the reference mirror, and between the optical division element and the measurement object, and the polarizer is configured to be rotatable around an axis along a plane perpendicular to the traveling direction of the measurement return light and the reference reflected light from the optical division element.

[0007] The fourth interference measurement device is an interference measurement device comprising an optical division element that splits light from a light source into measurement light and reference light having different polarization directions using a polarization splitting surface and emits the split light, and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light, and further comprising a polarizer onto which light traveling from the light source to the optical division element is incident, and quarter-wave conversion elements that are respectively arranged between the optical division element and the reference mirror and between the optical division element and the object to be measured, and the polarizer is configured to be rotatable around an axis along a plane perpendicular to the direction of travel of the light traveling from the light source to the optical division element.

[0008] The fifth interference measurement device is an interference measurement device that includes an optical splitting element that splits light from a light source into measurement light and reference light having different polarization directions using a polarization splitting surface and emits the light, and a reference mirror that reflects the reference light emitted from the optical splitting element and makes it incident on the optical splitting element as reference reflected light, and includes quarter-wave conversion elements that are respectively placed between the optical splitting element and the reference mirror, and between the optical splitting element and the object to be measured, and that change the polarization state of the light from the light source to change the light intensity ratio between the measurement light and the reference light from the polarization splitting surface.

[0009] A sixth interference measurement device is an interference measurement device comprising an optical division element that divides light from a light source into measurement light and reference light at a division surface and emits the light, and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light, and further comprising an illumination optical system that makes the light from the light source incident on the optical division element, and the illumination optical system comprises a fly's eye optical member having a plurality of optical surfaces arranged along a plane that intersects with the optical axis of the illumination optical system, and a condenser optical system that superimposes light from each of the plurality of optical surfaces of the fly's eye optical member.

[0010] The seventh interference measurement method includes splitting light from a light source into measurement light and reference light at a splitting surface of an optical dividing element and emitting the light; reflecting the reference light from the splitting surface and directing it toward the splitting surface as reference reflected light; causing return light from the measurement object of the measurement light that is emitted from the optical dividing element and irradiated onto the measurement object to be incident on a focusing optical system via the splitting surface as measurement returned light; causing the reference reflected light via the splitting surface to be incident on the focusing optical system; passing the measurement light from the splitting surface through a first optical surface that is inclined with respect to a plane that perpendicularly intersects with the optical axis of the focusing optical system; and passing the reference light from the splitting surface through a second optical surface that is inclined with respect to a reflecting surface of the reference light, wherein the first and second optical surfaces are optical surfaces of the optical dividing element.

[0011] an optical splitter element configured to split light from a light source into a measurement light beam and a reference light beam having different polarization directions, the measurement light beam being incident on a first quarter-wavelength conversion element; reflecting the reference light beam from the first quarter-wavelength conversion element and directing the reflected light as reference reflected light toward the polarization splitter element via the first quarter-wavelength conversion element; making the measurement light beam from the polarization splitter element incident on a second quarter-wavelength conversion element; irradiating a measurement object with the measurement light beam from the second quarter-wavelength conversion element; directing return light from the measurement object, which has been irradiated onto the measurement object, as measurement return light toward the polarization splitter element via the second quarter-wavelength conversion element; making the measurement return light and the reference reflected light from the polarization splitter element incident on a polarizer; and changing the polarization passing direction of the polarizer by rotating the polarizer around an axis along a plane perpendicular to the traveling direction of the measurement return light and the reference reflected light from the polarization splitter element.

[0012] FIG. 1 is a schematic diagram showing the configuration of an interference measurement device according to a first embodiment. FIG. 2 is a partially enlarged view of the schematic diagram showing the configuration of an interference measurement device according to a second embodiment. FIG. 3 is a partially enlarged view of the schematic diagram showing the configuration of an interference measurement device according to a second embodiment. FIG. 4 is a schematic diagram showing the path of a light beam in the interference measurement device according to the first embodiment. FIG. 5 is a side cross-sectional view as an example of the overall configuration of the interference measurement device according to the first embodiment. FIG. 6 is a graph showing experimental results regarding brightness and S / N ratio according to the present invention. FIG. 7 is a schematic diagram showing a processing system as an embodiment of the present invention. FIG. 8 is a schematic configuration outline diagram showing the configuration of a commonly known interference measurement device. FIG. 9 is a graph of an interference signal showing an example of a measurement result related to the interference measurement device of the present invention.

[0013] A preferred embodiment of the present invention will be described below. First, a processing system SYS equipped with an interference measurement device according to this embodiment will be described with reference to FIG. 8. As shown in FIG. 8, this processing system SYS is composed of a processing apparatus 1, a measurement apparatus 2 including an interference measurement apparatus 100 according to the present invention, a stage apparatus 3, and a control device (not shown). Under the control of the control device, the processing apparatus 1 irradiates a processing light EL such as pulsed light or laser light onto an object W placed on the stage apparatus 3 to scan the surface of the object W and perform processing. Under the control of the control device, the measurement apparatus 2 irradiates a measurement light ML onto the object W placed on the stage apparatus 3 to scan the surface and measure the condition of the surface of the object W. Measurement results by the measurement apparatus 2 are output to the control device, and the control device controls and performs processing based on the measurement results.

[0014] The processing apparatus 1 includes a processing head 12 that emits processing light EL, a head drive system 13 that moves the processing head 12, and a processing head position measurement device (not shown) that measures the position of the processing head 12. The processing head 12 is configured to be movable in the X-axis and Y-axis directions (predetermined directions within a horizontal plane) and the Z-axis direction perpendicular to the X-axis and Y-axis (a direction perpendicular to the horizontal plane, i.e., the up-and-down direction of the processing system SYS) by the head drive system 13 and the processing head position measurement device. Furthermore, the processing head 12 may be configured to be movable in the θX direction, θY direction, and θZ direction, which are rotational directions around the X-axis, Y-axis, and Z-axis. The measurement device 2 includes a measurement unit 21 that emits measurement light ML, a measurement drive system 22 that moves the measurement unit 21, and a measurement unit position measurement device (not shown). The measurement unit 21 is configured to be movable in the X-axis and Y-axis directions and the Z-axis direction perpendicular to the X-axis and Y-axis by the measurement drive system 22 and the measurement unit position measurement device. Furthermore, the stage device 3 may be configured to be movable in the θX direction, the θY direction, and the θZ direction, which are rotational directions around the X-axis, the Y-axis, and the Z-axis. The stage device 3 has a stage 32 on which the object W is placed, a stage drive system 33 that moves the stage 32, and a stage position measurement device (not shown) that measures the position of the stage 32. The stage 32 may be configured to be movable in the X-axis and Y-axis directions (predetermined directions in a horizontal plane) by the stage drive system 33 and the stage position measurement device. Instead of a configuration in which the machining head 12 and the measurement unit 21 are movable in the Z-axis direction by the drive systems 12 and 21, the object W may be configured to be movable in the Z-axis direction by the stage 32. The interferometric measurement device 100 according to the present invention corresponds to the measurement device 2, and irradiates the object W with measurement light ML (measurement light 43, 243 in the embodiments) to scan the surface of the object W and measure the surface condition of the object W.

[0015] 8 is a schematic diagram of the processing device 1, the measuring device 2, and the stage device 3, and is not limited to this configuration. The processing device 1, the measuring device 2, and the stage device 3 may or may not be housed in a housing. Furthermore, the processing system SYS may not have a housing.

[0016] Next, the configuration of an interference measurement apparatus 100 of the present invention used as the measurement apparatus 2 constituting such a machining system SYS will be described, but before that, a commonly known interference measurement apparatus 200 will be described with reference to Fig. 9. This interference measurement apparatus 200 includes a light source A, an optical system GL arranged side by side on the optical axis from the light source A and collecting light from the light source A, an optical dividing element P that splits the collected light L, and a reference mirror D that reflects light C that has passed through the optical dividing element P, a measurement object W provided at a position where it receives light B that has been split by the optical dividing element P and is irradiated downward perpendicular to the optical axis from the light source A, and a detection device E provided at a position where it receives light that has been reflected upward from the measurement object W and passed through the optical dividing element P.

[0017] In the interference measurement apparatus 200 configured as described above, as shown in FIG. 9 , light L emitted from light source A and collected by optical system GL enters optical dividing element P. This light L is split by dividing surface Q of optical dividing element P into measurement light B, which is reflected and irradiated onto measurement object W, and reference light C, which passes through and is reflected by reference mirror D. Measurement light B is reflected by measurement object W and returns to optical dividing element P, while reference light C is reflected by reference mirror D and returns to optical dividing element P. Then, the return light of measurement light B, which passes through optical dividing element P and is irradiated upward, and the return light of reference light C, which is reflected by optical dividing element P and is irradiated upward, are combined and reach detection device E along the same optical path. Detection device E measures an interference wave signal of the return light of measurement light B and reference light C. This makes it possible to measure the optical path difference between the return light of measurement light B and the return light of reference light C as an interference signal. In this measurement result, the height at which the amplitude of the interference signal is maximum is the height of the object A. Fig. 10 shows an example of a waveform (interferogram) obtained when the measurement unit 21 is moved in the Z direction to scan the point of interest X on the measurement object W using the configuration shown in Fig. 9 and the intensity of the interference signal between the measurement light B and the reference light C is measured. When the optical path lengths of the measurement light B and the reference light C are equal, the intensity of the interference signal is measured as maximum contrast, and the height H of peak F at which the amplitude in this waveform is maximum corresponds to the height of the point of interest X. In this specification, the term "contrast" refers to the difference in interference intensity when the amplitude of the interference signal is maximum, and "high contrast" is used to indicate a large difference in interference intensity.

[0018] In the interference measurement device 200 configured as described above, a portion of the measurement light B reflected by the dividing surface Q of the optical dividing element P and irradiated onto the measurement object W is reflected by the lower surface P200 of the optical dividing element P, generating flare light F1. Also, a portion of the reference light C passing through the dividing surface Q and proceeding toward the reference mirror D is reflected by the side surface P201 of the optical dividing element P, generating flare light F2. The flare light F1 overlaps with the measurement light B reflected by the measurement object W and returning to the optical dividing element P, and the flare light F2 overlaps with the reference light C reflected by the reference mirror D and returning to the optical dividing element P. This causes a problem in that the flare light F1 and the flare light F2 adversely affect the measurement of the intensity of the interference signal between the measurement light B and the reference light C, reducing the measurement accuracy. The interference measurement devices according to the embodiments described below are intended to solve these problems, and each embodiment will be described in detail below.

[0019] First Embodiment An interference measurement apparatus according to the first embodiment will be described. An interference measurement apparatus 100(1) as an example of an interference measurement apparatus 100 according to the first embodiment will be described with reference to both Fig. 1 and Fig. 2. Fig. 1 is a schematic cross-sectional view of the overall configuration of the interference measurement apparatus 100(1) according to the first embodiment as seen from the side, and Fig. 2 is an enlarged view of a portion thereof.

[0020] The interferometer 100 ( 1 ) includes a light source 40 , an illumination optical system LS, an optical splitting element 50 , a reference mirror 60 , an imaging optical system DS, and a detection device 80 .

[0021] The illumination optical system LS is arranged on the optical axis of the light source 40 and includes a first lens group GL1 that collects light 41 from the light source 40, a fly's-eye optical element FE that homogenizes the collected light 41, a reflecting mirror 90 that receives and reflects the homogenized light 41 from the fly's-eye optical element FE, and a second lens group GL2 that collects the light 41 reflected from the reflecting mirror 90. An optical dividing element 50 is provided at a position that receives the light 41 that has passed through the second lens group GL2. The optical dividing element 50 has a splitting surface 51 that splits the light 41 into a reference light 42 that passes through the splitting surface 51 and a measurement light 43 that is reflected downward. A reference mirror 60 is provided at a position that receives the reference light 42 that has passed through the splitting surface 51, and the reference reflected light 42a reflected by the reference mirror 60 is configured to return toward the optical dividing element 50. Meanwhile, a measurement object W is placed at a position that receives the measurement light 43 that has been reflected downward by the splitting surface 51. The measurement light 43 is irradiated onto the measurement object W, and the measurement return light 43a is reflected and returned to the optical dividing element 50. The optical dividing element 50 has a characteristic configuration in which it is slightly tilted with respect to the optical axis I1 (the optical axis extending from the measurement object W to the detection device 80) that extends vertically, which will be described later.

[0022] In this way, a portion of the reference reflected light 42a reflected by the reference mirror 60 and returning toward the optical dividing element 50 is reflected by the splitting surface 51 and emitted upward, and a portion of the measurement return light 43a reflected by the measurement object W and returning to the optical dividing element 50 passes through the splitting surface 51 and emitted upward. The imaging optical system DS is provided on the optical axis I1 along which the reference reflected light 42a and measurement return light 43a emitted upward extend. The imaging optical system DS is configured to include a third lens group GL3, a diaphragm S, and a fourth lens group GL4, which are arranged in this order from the top surface of the optical dividing element 50 upward. A detection device 80 is provided at a position that receives the combined light of the reference reflected light 42a and measurement return light 43a that have passed through the imaging optical system DS.

[0023] In the interference measurement device 100(1) configured as described above, light 41 from the light source 40 is collected by the first lens group GL1, and the collected light 41 passes through the fly's-eye optical member FE to be homogenized. The homogenized light 41 is reflected by the reflecting mirror 90 and collected by the second lens group GL2. The light 41 that passes through the second lens group GL2 is incident on the optical dividing element 50. A portion of the light 41 that has thus entered the optical dividing element 50 passes directly through the dividing surface 51 to become reference light 42, which is irradiated onto the reference mirror 60. The portion is reflected by the reflecting surface 61 of the reference mirror 60 and returns toward the optical dividing element 50 as reference reflected light 42a. The remainder of the light 41 is reflected downward by the dividing surface 51 to become measurement light 43, which is irradiated onto the measurement object W. The measurement light 43 is irradiated onto the measurement object W, reflected by the measurement surface Wa, and returned as measurement return light 43a, which returns to the optical dividing element 50.

[0024] In this way, a portion of the reference reflected light 42a reflected by the reflecting surface 61 of the reference mirror 60 and returning toward the optical dividing element 50 is reflected by the dividing surface 51 and emitted upward, and a portion of the measurement return light 43a reflected by the measurement surface Wa of the measurement object W and returning to the optical dividing element 50 passes through the dividing surface 51 and emitted upward. In this way, the reference reflected light 42a and measurement return light 43a emitted upward from the optical dividing element 50 are incident on the imaging optical system DS. In the imaging optical system DS, the reference reflected light 42a and measurement return light 43a emitted upward pass together through the third lens group GL3, the diaphragm S, and the fourth lens group GL4 and are incident on the detection device 80. The reference reflected light 42a and measurement return light 43a incident on the detection device 80 are imaged on the detection surface 80a of the detection device 80, and the interference wave or interference signal is measured by the detection unit 80.

[0025] The interference measurement device 100 (1) according to the first embodiment described above has a characteristic configuration in which the optical splitting element 50 is provided at a slight incline with respect to the optical axis I1 (the optical axis extending from the measurement object W to the detection unit 80) that extends vertically, as shown in Fig. 1. As a result, an effect specific to this embodiment is obtained, which will be described in detail below.

[0026] First, the optical dividing element 50 has a dividing surface 51 and is an element that divides incident light into reflected light and transmitted light at the dividing surface 51. The optical dividing element 50 is, for example, a beam splitter. The optical dividing element 50 may be, but is not limited to, a cube-shaped one. A rectangular or oblong cross section is easy to manufacture, and it is easy to control the reflection direction of flare light P1a and P2a generated by the optical dividing element 50 when the entire optical dividing element 50 is tilted. The dividing surface 51 is a surface that extends in the depth direction of the drawing along the diagonal of the rectangle in the cross section of the optical dividing element 50, and is configured so that the slope is inclined toward the incident side. As described above, when the optical dividing element 50 is slightly tilted with respect to the optical axis I1, the transmitted light at the dividing surface 51 of the optical dividing element 50 reaches the reference mirror 60 as the reference light 42, and the reflected light at the dividing surface 51 reaches the measurement object W as the measurement light 43.

[0027] In this configuration, the outer surface of the optical dividing element 50 through which the measurement light 43 passes is referred to as the first optical surface P1, and the outer surface of the optical dividing element 50 through which the reference light 42 passes is referred to as the second optical surface P2. These first optical surface P1 and second optical surface P2 are surfaces of the optical dividing element 50 that come into contact with the outside air, and when the measurement light 43 passes through the first optical surface P1, a portion of the measurement light 43 is reflected by the first optical surface P1, generating flare light P1a. Similarly, when the reference light 42 passes through the second optical surface P2, a portion of the reference light 42 is reflected by the second optical surface P2, generating flare light P2a. Here, because the optical dividing element 50 is disposed at a slight inclination with respect to the vertically extending optical axis I1 (the optical axis extending from the measurement object W to the detection unit 80), the reflection direction of the flare light P1a differs from the reflection direction of the measurement return light 43a reflected from the measurement object W and returning to the optical dividing element 50, and the reflection direction of the flare light P2a differs from the reflection direction of the reference reflected light 42a reflected by the reference mirror 60 and returning toward the optical dividing element 50. Therefore, only the reference reflected light 42a and the measurement return light 43a emitted upward from the optical dividing element 50 enter the imaging optical system DS, and most of the flare light P1a and the flare light P2a do not enter the imaging optical system DS. As a result, the problem of the flare light P1a and the flare light P2a adversely affecting the measurement of the intensity of the interference signal between the measurement light 43 and the reference light 42, resulting in reduced measurement accuracy, can be reduced. In other words, the amount of unintended light (P1a, P2a) reaching the detection device 80 is reduced, improving contrast. The arrangement of the optical splitting element 50 will be described in detail later.

[0028] Alternatively, instead of the above configuration, the transmitted light at the splitting surface 51 of the optical splitting element 50 may reach the measurement object W as measurement light 43, and the reflected light at the splitting surface 51 may reach the reference mirror 60 as reference light 42.

[0029] In the following description, the portion of the imaging optical system DS closer to the light source than the diaphragm S will be referred to as the first light-collecting optical system CS1, and the portion closer to the detection device 80 than the diaphragm S will be referred to as the second light-collecting optical system CS2. The first light-collecting optical system CS1 is composed of a third lens group GL3 and a diaphragm S. The second light-collecting optical system CS2 is composed of a fourth lens group GL4, and is configured so that light incident on the imaging optical system DS is imaged on the detection surface 80a of the detection device 80. It is desirable to place this diaphragm S at or near the back focal position 70 of the first light-collecting optical system CS1.

[0030] With this configuration, the first focusing optical system CS1 is telecentric on the measurement object W side, and the interference signal can be measured without changing the size of the image formed on the detection surface 80a even if the distance between the measurement surface Wa of the measurement object W and the imaging optical system DS changes. In this case, the diaphragm S is an aperture diaphragm, but the location where the diaphragm S is located is not limited to the position of the aperture diaphragm, i.e., the entrance pupil position of the imaging optical system DS. For example, the diaphragm S may be located at the position of the field diaphragm or at another position.

[0031] The first optical surface P1 and the second optical surface P2 may be arranged at an inclination so that the flare light P1a and P2a in the optical splitting element 50 are reflected toward the light-blocking portion 71 of the diaphragm S that blocks the progression of light via the first light-collecting optical system CS1. If the diaphragm S is a field stop, it is desirable to arrange the first optical surface P1 and the second optical surface P2 at an inclination so that the flare light P1a and P2a are reflected toward the outside of the actual field of view. With such a configuration, it is possible to prevent light unnecessary for measurement from reaching the detection device 80.

[0032] Furthermore, it is desirable that the diaphragm S coincide with the entrance pupil position and the exit pupil position of the imaging optical system DS. With this configuration, the imaging optical system DS becomes telecentric on the entrance side and the exit side, and the optical path difference can be measured as an interference signal without being affected by the unevenness of the surface of the measurement object W, and without changing the size of the image formed on the detection surface 80a even if the distance between the measurement surface Wa of the measurement object W and the detection surface 80a changes.

[0033] Next, the arrangement of the optical splitting element 50 will be described. In the optical splitting element 50, the angle at which the first optical surface P1 is inclined relative to the plane V1 perpendicularly intersecting the optical axis I1 is defined as the inclination angle δ. The second optical surface P2 is also inclined relative to the reflecting surface 61 of the reflecting mirror 60. When the cross-sectional shape of the optical splitting element 50 viewed from the side is square, the second optical surface P2 is also inclined by the inclination angle δ relative to the first focusing optical system CS1. FIG. 5 is a schematic diagram showing the path of light reflected by the measurement surface Wa of the measurement object W. In FIG. 5, the dashed line, the one-dot chain line, and the two-dot chain line indicate the path of light rays from positions in the X direction or the Y direction (left-right direction of the device) of the measurement surface, respectively, and the solid line indicates the path of light rays of flare light P1a and P2a at the first optical surface P1 and the second optical surface P2 of the optical splitting element 50. In this case, it is desirable for the optical splitting element 50 to satisfy the following conditional expression (1).

[0034] f1×sin(2δ−θ)>f1×NA(D) (1) where f1: focal length of the first light-collecting optical system CS1 NA(D): numerical aperture of the first light-collecting optical system CS1 on the optical dividing element 50 side NA(L): numerical aperture of the illumination optical system LS on the optical dividing element 50 side θ: θ=sin －１ δ: a value defined by (NA(L)), and δ: an inclination angle of the first optical surface P1 with respect to a plane V1 that perpendicularly intersects with the optical axis I1 of the first light-collecting optical system CS1, or an inclination angle of the second optical surface P2 with respect to the optical axis I1 of the first light-collecting optical system CS1.

[0035] Conditional expression (1) above expresses the magnitude relationship between the height of the light reflected at the obtuse angle of the flare light P1a or P2a relative to the optical axis I1 of the first focusing optical system CS1 at the position of the aperture stop S and the beam radius of the measurement return light 43a or the reference reflected light 42a at the position of the aperture stop S. By satisfying this conditional expression, it is possible to prevent light reflected by the first optical surface P1 and the second optical surface P2 of the optical splitting element 50 from being incident on the detection surface 80a side of the aperture stop S of the first focusing optical system CS1. Conditional expression (1) may be replaced by f1×tan(2δ-θ)>f1×tan θ, or f1×(2δ-θ)>f1×θ. Conditional expression (1) may be replaced by sin(2δ-θ)>NA(D), tan(2δ-θ)>tan θ, or (2δ-θ)>θ.

[0036] The illumination optical system LS, more specifically, the optical axis I2 of the illumination optical system LS may be inclined with respect to a plane V1 that perpendicularly intersects with the optical axis I1 of the first focusing optical system CS1. The inclination angle may be twice the inclination angle δ of the optical splitting element 50 described above.

[0037] With this configuration, it is possible to improve contrast by reducing the effect of flare light on the measurement results at the optical splitting element 50 while keeping the optical axis I1 of the first light-collecting optical system CS1 fixed. The light source 40, first lens group GL1, fly's-eye optical member FE, reflecting mirror 90, and second lens group GL2 that constitute the illumination optical system LS are arranged so as to achieve the tilt angle of the illumination optical system LS described above.

[0038] The illumination optical system LS is an optical system that irradiates the measurement surface Wa of the measurement object W with light 41 from the light source 40 with uniform brightness, and is composed of a first lens group GL1, a fly's-eye optical element FE, a reflecting mirror 90, and a second lens group GL2, which are arranged side by side on the optical axis from the light source 40 as described above. The fly's-eye optical element FE in the illumination optical system LS is an optical element having multiple optical surfaces FEa formed in a direction perpendicular to the optical axis, such as a fly's-eye lens. The second lens group GL2 constitutes a condenser optical system ES that superimposes light from each of the multiple optical surfaces FEa of the fly's-eye optical element FE and emits light of uniform brightness to the measurement object W. In the interferometry device 100(1) according to this embodiment, the illumination optical system LS has the above-mentioned characteristic configuration. This characteristic configuration provides the effect of improving measurement results, which will be explained below.

[0039] 7 shows a graph of experimental results, with illumination brightness plotted on the horizontal axis and the S / N ratio (the measured value of the interference signal including noise divided by the measured value of the noise signal) plotted on the vertical axis. In this graph, the average brightness values ​​indicated by the solid lines indicate that the S / N ratio rapidly deteriorates when the brightness falls below 50%. According to these experimental results, uneven illumination in an interferometer causes brightness fluctuations depending on the position on the measurement surface, leading to a deterioration in the accuracy of the measurement values ​​due to a deterioration in the S / N ratio, as shown in the graph. The configuration of the illumination optical system LS of this embodiment makes it possible to irradiate the measurement object W with light of uniform brightness. This allows for highly accurate measurement results to be obtained.

[0040] In this embodiment, it is desirable to position the measurement object W at the back focal position of the condenser optical system ES. With this configuration, even if the position of the measurement surface Wa relative to the illumination optical system LS changes, it is possible to illuminate the measurement surface Wa of the measurement object W with parallel light of uniform brightness, which is formed by superimposing light from multiple optical surfaces FEa of the fly's eye optical member FE.

[0041] In FIG. 1 , the illumination optical system LS includes a reflector 90 disposed along the optical path. The reflector 90 bends the optical path of the light source 40, preventing the entire device from becoming too large in one direction. It is installed according to the desired shape and size of the device and is not necessarily required. The reflector 90 may be, for example, a mirror or a prism. While the light that passes through the fly's-eye optical element FE is bent by the reflector 90, the opposite arrangement is also possible. That is, the light may be configured to enter the fly's-eye optical element FE after its optical path is bent by the reflector 90. The illumination optical system LS may not include the fly's-eye optical element FE. Even in this case, it is desirable to illuminate the measurement object W with parallel light. Furthermore, it is desirable to employ an optical system that irradiates light with uniform brightness. Such a configuration allows for highly accurate measurement results.

[0042] With the above-described configuration, it is possible to provide an interference measurement apparatus capable of measuring an interference signal with improved contrast. FIG. 6 shows an example of a side cross-sectional view of the overall configuration of the interference measurement apparatus 100(1) according to the first embodiment. As shown in FIG. 6, the interference measurement apparatus 100(1) is configured such that the measurement object W and the imaging optical system DS are aligned straight on the same optical axis I1, and the illumination optical system LS and the optical splitter 50 are slightly tilted as described above. Note that the angle of the reflecting mirror 90 may be set so that the optical axis of the imaging optical system DS and the optical axis of the optical system of the illumination optical system LS that is closer to the light source than the reflecting mirror 90 are parallel to each other.

[0043] Second Embodiment Next, an interferometry apparatus 100(2) according to a second embodiment will be described. The interferometry apparatus 100(2) according to the second embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic cross-sectional side view of the overall configuration of the interferometry apparatus 100(2) according to the second embodiment, and FIG. 4 is a partially enlarged view thereof. The second embodiment uses polarizers 270a and 270b, quarter-wave conversion elements 271a and 271b, and a polarization-type optical splitting element 250, instead of the configuration in the first embodiment in which the illumination optical system LS and the optical splitting element 50 are arranged at a slight angle. The configurations of the illumination optical system LS and the imaging optical system DS are the same as those of the first embodiment. Therefore, the same symbols as those in the first embodiment will be used whenever possible, and redundant explanations will be omitted as much as possible.

[0044] The interference measurement apparatus 100(2) includes a light source 40, an illumination optical system LS, an optical splitting element 250, a reference mirror 60, polarizers 270a and 270b, quarter-wave conversion elements 271a and 271b, an imaging optical system DS, and a detection apparatus 80.

[0045] The illumination optical system LS is arranged side by side on the optical axis from the light source 40 and is composed of a first lens group GL1 that collects light 41 from the light source 40, a fly's eye optical element FE that homogenizes the collected light 41, a reflecting mirror 90 that receives and reflects the homogenized light 41 from the fly's eye optical element FE, and a second lens group GL2 that collects the light 41 reflected from the reflecting mirror 90. A polarizer 270b is arranged at a position where the light 41 that has passed through the second lens group GL2 passes, and passes linearly polarized light of a specific orientation out of the light 41. A polarizing optical splitting element 250 is arranged at a position where the linearly polarized light of a specific orientation that has passed through the polarizer 270b is incident. The optical splitting element 250 has a polarization splitting surface 251 that splits this light 41 into light beams with different polarization directions, and splits the light 41 at the polarization splitting surface 251 into a reference light 242 that travels in the same direction as the incident optical axis I20 and a measurement light 243 that travels in a direction reflected downward and has a polarization direction that differs by 90 degrees from the reference light 242. A quarter-wave conversion element 271a is disposed at a position that receives the reference light 242 that has traveled directly through the polarization splitting surface 251, and a reference mirror 60 is provided in the direction in which the light that has passed through the quarter-wave conversion element 271a travels, so that the reference reflected light 242a reflected by the reference mirror 60 passes through the quarter-wave conversion element 271a again and returns toward the optical splitting element 250. Meanwhile, a quarter-wave conversion element 271b is disposed at a position that receives the measurement light 243 that has been reflected downward on the polarization splitting surface 251, and a measurement object W is placed in the direction in which the light that has passed through the quarter-wave conversion element 271b travels. The measurement light 243 is irradiated onto the measurement object W, and the measurement return light 243a is reflected and returned, and is configured to pass through the quarter wavelength conversion element 271b again and return toward the optical splitting element 250.

[0046] In this way, a portion of the reference reflected light 242a reflected by the reference mirror 60 and returning toward the optical splitting element 250 is reflected by the polarization splitting surface 251 and emitted upward, and a portion of the measurement return light 243a reflected by the measurement object W and returning to the optical splitting element 250 passes through the polarization splitting surface 251 and emitted upward. However, a polarizer 270a installed on the optical axis I1 along which the reference reflected light 242a and measurement return light 243a emitted upward in this manner allows only linearly polarized light of a specific orientation to pass, and an imaging optical system DS is provided in the direction in which the linearly polarized light passes. The imaging optical system DS is configured to include a third lens group GL3, a diaphragm S, and a fourth lens group GL4, which are arranged in this order from the top surface of the optical splitting element 250 upward. A detection device 80 is provided at a position that receives the combined light of the reference reflected light 242a and measurement return light 243a that have passed through the imaging optical system DS.

[0047] The optical dividing element 250 is, for example, a polarizing beam splitter. In this configuration, the outer surface of the optical dividing element 250 through which the measurement light 243 passes is referred to as the first optical surface P10, and the outer surface of the optical dividing element 250 through which the reference light 242 passes is referred to as the second optical surface P20. The first optical surface P10 and the second optical surface P20 do not need to have the inclination angle δ as in the first embodiment. When the cross section of the side surface of the optical dividing element 250 is rectangular, the first optical surface P10 may be parallel to a plane V1 that perpendicularly intersects with the optical axis I1 of the imaging optical system DS, and the second optical surface P20 may be parallel to the optical axis I1 of the imaging optical system DS. As described in the first embodiment, flare light generated at the first optical surface P10 is referred to as flare light P10a, and flare light generated at the second optical surface P20 is referred to as flare light P20a. The polarization direction of this flare light P10a differs from the polarization direction of the measurement return light 243a reflected from the measurement object W and returning to the optical splitting element 250, and the polarization direction of the flare light P20a differs from the polarization direction of the reference reflected light 242a reflected by the reference mirror 60 and returning toward the optical splitting element 250. Therefore, only the reference reflected light 242a and the measurement return light 243a emitted upward from the optical splitting element 250 enter the imaging optical system DS, and most of the flare light P10a and the flare light P20a do not enter the imaging optical system DS. As a result, the problem of the flare light P10a and the flare light P20a adversely affecting the measurement of the intensity of the interference signal between the measurement light 243 and the reference light 242, resulting in a decrease in measurement accuracy, can be reduced. In other words, the amount of unintended light (P10a, P20a) reaching the detection device 80 can be reduced, improving contrast. The cutting of the flare light P10a and P20a by the polarization direction will be described in detail later.

[0048] The illumination optical system LS is configured such that the light source 40, the first lens group GL1, the fly's eye optical element FE, the reflecting mirror 90, and the second lens group GL2 of the illumination optical system LS are arranged so that the direction of travel of the measurement light 243 reflected by the polarization splitting surface 251 is the same as the optical axis I1 of the imaging optical system DS.

[0049] The polarizers 270a and 270b are elements that have the function of passing linearly polarized light of a specific direction among the incident light, and may be either transmissive or reflective. The polarizer 270b causes the linearly polarized light of the incident light of a specific direction to enter the optical splitting element 250, and the polarizer 270a causes the linearly polarized light of a specific direction to exit from the optical splitting element 250 to the imaging optical system DS. By changing the polarization directions that the polarizers 270a and 270b pass and combining these polarization directions, the amount of light that is output to the imaging optical system DS can be changed.

[0050] In the above configuration, this embodiment has a characteristic configuration in which the polarizers 270a and 270b are configured to be rotatable around an axis along a plane perpendicular to the optical axis of the incident light. This configuration provides the unique effect of adjusting the amount of light incident on the imaging optical system DS and changing the light intensity ratio between the measurement light 243 and the reference light 242 by rotating each of the polarizers 270a and 270b and changing their respective polarization orientations. This allows for measurement results with high contrast regardless of the reflectance of the surface of the measurement object W. Alternatively, the configuration may include only the polarizer 270a, which is located on the exit side of the optical splitting element 250 that exits from the optical splitting element 250 to the imaging optical system DS. Even in this case, it is possible to configure the system so that only polarized light of a specific orientation is exited to the imaging optical system DS. Note that the light intensity ratio between the measurement light 243 and the reference light 242 may be changed by rotating only one of the polarizers 270a and 270b. In this case, the other polarizer of the polarizers 270a and 270b does not have to be configured to be rotatable, and may be fixed.

[0051] The quarter-wave conversion elements 271a and 271b are elements that shift the phase difference between orthogonal polarization components of the incident light by a quarter wavelength before emitting the light, and are, for example, quarter-wave plates. The quarter-wave conversion element 271a is disposed between the optical splitting element 250 and the reference mirror 60, and the quarter-wave conversion element 271b is disposed between the optical splitting element 250 and the measurement object W. At least one of the quarter-wave conversion elements 271a and 271b may be disposed tilted with respect to the optical axis I20. In this case, the angle between the normal to the entrance surface or exit surface of at least one of the quarter-wave conversion elements 271a and 271b and the optical axis I20 may be approximately the above-mentioned δ, for example δ±5%. In the above configuration, the polarization direction of the reference reflected light 242a reflected by the reference mirror 60 and returning to the optical dividing element 250 differs from the polarization direction of the reference light 242, and the polarization direction of the measurement reflected light 243a reflected by the measurement object W and returning to the optical dividing element 250 differs from the polarization direction of the measurement light 243. On the other hand, of the light passing through the optical dividing element 250, the flare light P10a and P20a reflected by the optical dividing element 250 maintain the same polarization direction as the measurement light 243 and the reference light 242. Due to the difference in the polarization states of the measurement return light 243a and the flare light P10a, and the reference reflected light 242a and the flare light P20a, the flare light P10a and P20a proceeding to the imaging optical system DS can be cut. This will be described below.

[0052] 4, the measurement light 243 is emitted from the optical splitting element 250, reflected by the measurement object W, and passes through the quarter-wave conversion element 271b twice before returning to the optical splitting element 250. As a result, the polarization direction of the returned measurement light 243a is rotated 90 degrees with respect to the measurement light 243. Furthermore, the reference light 242 is emitted from the optical splitting element 250, reflected by the reference mirror 60, and passes through the quarter-wave conversion element 271a twice before returning to the optical splitting element 250. As a result, the polarization direction of the reflected reference light 242a is rotated 90 degrees with respect to the reference light 242. Meanwhile, the flare light P10a reflected at the first optical surface P10 of the optical splitting element 250 maintains the polarization direction of the incident light, is reflected at the polarization splitting surface 251 toward the polarizer 270b, and does not enter the imaging optical system DS. Furthermore, flare light P20a reflected by the second optical surface P20 of the optical splitting element 250 maintains the polarization orientation of the incident light and passes through the polarizer 270b at the polarization splitting surface 251, without entering the imaging optical system DS. In this manner, measurement return light 243a and reference reflected light 242a, which are each rotated 90 degrees relative to the polarization orientation of the incident light, pass through the first polarizer 270a. In FIG. 4 , the direction in which each light travels is indicated by an arrow, and different symbols are superimposed on the arrows to indicate the differences in polarization orientation. Alternatively, the polarizers 270a and 270b may be rotated to change the polarization orientation of the light passing through, and the reference light 242 and measurement light 243 may be alternately measured, the measurement results may be stored, and an interference signal may be synthesized.

[0053] With the above configuration, it is possible to provide an interference measurement apparatus capable of measuring an interference signal with improved contrast.

[0054] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit and scope of the present invention.

[0055] SYS Machining system 1 Machining device 2 Measuring device 3 Stage device 100(1), 100(2) Interference measurement device 40 Light source 50 Optical splitting element 51 Splitting surface 250 Polarization type optical splitting element 251 Polarization splitting surface 60 Reference mirror 61 Reflecting surface 80 Detection device FE Fly's eye optical member LS Illumination optical system CS1 First light-collecting optical system CS2 Second light-collecting optical system DS Imaging optical system ES Condenser optical system W Measurement object Wa Measurement surface P1, P10, P200 First optical surface P2, P20, P201 Second optical surface 270a, 270b Polarizer 271a, 271b 1 / 4 wavelength conversion element 42, 242 Reference light 43, 243 Measurement light

Claims

1. An interference measurement device comprising: an optical division element that divides light from a light source at a division surface into measurement light and reference light and emits the light; a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light; and a focusing optical system into which the measurement light emitted from the optical division element and irradiated onto a measurement object is returned from the measurement object and enters the focusing optical system as measurement returned light via the optical division element, wherein the measurement returned light and the reference reflected light incident from the reference mirror are incident on the focusing optical system via the optical division element, and the optical division element has a first optical surface through which the measurement light from the division surface passes and a second optical surface through which the reference light from the division surface passes, wherein the first optical surface is inclined with respect to a plane perpendicular to the optical axis of the focusing optical system, and the second optical surface is inclined with respect to the reflecting surface of the reference mirror.

2. An interference measuring device according to claim 1, further comprising a diaphragm member disposed at or near the back focal position of said focusing optical system.

3. An interference measuring device according to claim 2, wherein the light reflected by the first optical surface and the light reflected by the second optical surface reach the light-shielding portion of the diaphragm member via the focusing optical system.

4. An interference measuring apparatus according to claim 2 or 3, further comprising an illumination optical system that illuminates the measurement object with the light from the light source via the optical dividing element.

5. The interference measurement device according to claim 4, which satisfies the following condition: f1×sin(2δ−θ)>f1×NA(D), where f1: focal length of the focusing optical system, NA(D): numerical aperture of the focusing optical system on the optical dividing element side, NA(L): numerical aperture of the illumination optical system on the optical dividing element side, θ: θ=sin －１ δ: a value defined as (NA(L)), where δ is the inclination angle of the first optical surface with respect to a plane perpendicular to the optical axis of the focusing optical system, or the inclination angle of the second optical surface with respect to the optical axis of the focusing optical system.

6. An interference measuring device according to any one of claims 1 to 5, wherein the cross section of said optical dividing element in a plane parallel to the optical axis of said focusing optical system has a rectangular shape.

7. An interference measurement device according to any one of claims 1 to 6, comprising an illumination optical system that causes light from the light source to be incident on the optical splitting element, wherein an illumination tilt angle at which the optical axis of the illumination optical system is tilted with respect to a plane that intersects perpendicularly with the optical axis of the focusing optical system is twice the tilt angle of the first optical surface or the second optical surface through which light of the measurement return light or the reference reflected light that passes through the splitting surface and enters the focusing optical system passes, with respect to the plane that intersects perpendicularly with the optical axis of the focusing optical system.

8. An interference measurement device according to any one of claims 1 to 7, further comprising: a second focusing optical system into which the reference reflected light and measurement reflected light emitted from the first focusing optical system are incident when the focusing optical system is a first focusing optical system; the first focusing optical system and the second focusing optical system constitute an imaging optical system; and a detection unit that detects interference light of the reference reflected light and measurement return light imaged by the imaging optical system.

9. An interference measuring apparatus according to claim 8, wherein said focusing optical system has a diaphragm member, said diaphragm member being disposed at a pupil position of said imaging optical system.

10. An interference measurement device comprising: an optical division element that divides light from a light source at a division surface into measurement light and reference light and emits the light; a reference mirror that reflects the reference light emitted from the optical division element and makes it incident as reference reflected light on the optical division element; and a focusing optical system in which the measurement light emitted from the optical division element and irradiated onto a measurement object is returned from the measurement object and enters the optical division element as measurement returned light, via the optical division element, wherein the measurement returned light and the reference reflected light incident from the reference mirror are incident on the focusing optical system, and the optical division element further comprises an optical surface that is inclined with respect to the optical axis of the focusing optical system or a plane perpendicular to the optical axis of the focusing optical system, and wherein the traveling direction of at least one of the measurement return light and reference reflected light that pass through the optical surface is different from the traveling direction of flare light generated on the optical surface by at least one of the measurement light and the reference light.

11. An interference measurement device comprising: an optical division element that splits light from a light source into measurement light and reference light having different polarization directions using a polarization splitting surface and emits the light; and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light; a polarizer into which measurement return light, which is return light from the measurement object of the measurement light emitted from the optical division element and irradiated onto the measurement object, and reference reflected light from the reference mirror, are incident via the optical division element; and quarter-wave conversion elements that are respectively arranged between the optical division element and the reference mirror, and between the optical division element and the measurement object, wherein the polarizer is configured to be rotatable around an axis along a plane perpendicular to the traveling direction of the measurement return light and the reference reflected light from the optical division element.

12. An interference measuring device according to claim 11, wherein the polarization state of the light from the light source is changed to change the ratio of the amounts of the measurement light and the reference light from the polarization splitting plane.

13. An interference measurement device according to claim 11 or 12, wherein when the polarizer is a first polarizer, the device further comprises a second polarizer that can rotate about an axis along a plane perpendicular to the direction of propagation of the light from the light source toward the optical dividing element.

14. An interference measurement device comprising: an optical division element that splits light from a light source into measurement light and reference light having different polarization directions using a polarization splitting surface and emits the split light; and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light; a polarizer onto which light from the light source toward the optical division element is incident; and quarter-wave conversion elements that are respectively placed between the optical division element and the reference mirror and between the optical division element and the object to be measured; and the polarizer is configured to be rotatable around an axis along a plane perpendicular to the direction of travel of the light from the light source toward the optical division element.

15. An interference measurement device comprising: an optical splitting element that splits light from a light source using a polarization splitting surface into measurement light and reference light having different polarization directions and emits the light; and a reference mirror that reflects the reference light emitted from the optical splitting element and makes it incident on the optical splitting element as reference reflected light, wherein the interference measurement device further comprises quarter-wave conversion elements that are respectively disposed between the optical splitting element and the reference mirror, and between the optical splitting element and the object to be measured, and that changes the polarization state of the light from the light source to change the light intensity ratio between the measurement light and the reference light from the polarization splitting surface.

16. An interference measurement device comprising: an optical division element that divides light from a light source into measurement light and reference light at a division surface and emits the light; and a reference mirror that reflects the reference light emitted from the optical division element and makes it incident on the optical division element as reference reflected light, wherein the interference measurement device further comprises an illumination optical system that makes the light from the light source incident on the optical division element, the illumination optical system comprising: a fly's eye optical element having a plurality of optical surfaces arranged along a plane that intersects with the optical axis of the illumination optical system; and a condenser optical system that superimposes light from each of the plurality of optical surfaces of the fly's eye optical element.

17. The interference measurement device according to claim 16, wherein the back focal position of a condenser optical system is located near the object to be measured.

18. An interference measurement method comprising: splitting light from a light source into measurement light and reference light at a splitting surface of an optical splitting element and emitting the light; reflecting the reference light from the splitting surface and directing it toward the splitting surface as reference reflected light; making the measurement light emitted from the optical splitting element and irradiated onto the measurement object, and returned from the measurement object, incident on a focusing optical system via the splitting surface as measurement returned light; making the reference reflected light via the splitting surface incident on the focusing optical system; passing the measurement light from the splitting surface through a first optical surface provided at an angle with respect to a plane perpendicular to the optical axis of the focusing optical system; and passing the reference light from the splitting surface through a second optical surface provided at an angle with respect to the reflecting surface of the reference light, wherein the first and second optical surfaces are optical surfaces of the optical splitting element.

19. An interference measurement method comprising: splitting light from a light source into measurement light and reference light having different polarization directions by a polarization splitting surface of an optical splitting element and emitting the light; making the reference light from the polarization splitting surface incident on a first quarter-wavelength conversion element; reflecting the reference light from the first quarter-wavelength conversion element and directing it as reference reflected light towards the polarization splitting surface via the first quarter-wavelength conversion element; making the measurement light from the polarization splitting surface incident on a second quarter-wavelength conversion element; irradiating the measurement light from the second quarter-wavelength conversion element onto a measurement object; directing return light from the measurement object of the measurement light irradiated onto the measurement object as measurement return light towards the polarization splitting surface via the second quarter-wavelength conversion element; making the measurement return light and the reference reflected light from the polarization splitting surface incident on a polarizer; and changing the polarization passing direction of the polarizer by rotating around an axis along a plane perpendicular to the traveling direction of the measurement return light and the reference reflected light from the polarization splitting surface.

Images