Displacement detector

Abstract

To provide a displacement detector with high versatility while having high measuring accuracy.SOLUTION: A displacement detector 1 includes: a light source 111; a first birefringent part 114 configured to separate light into first light L1 and second light L2 having a phase difference from the first light; a second birefringent part 121 configured to deflect the first light and the second light; a third birefringent part 123 configured to condense the first light and the second light; a fourth birefringent part 131 configured to overlap the first light with the second light; and a displacement detection part 13 configured to detect a displacement in a measurement direction of a target T according to a change in the phase difference between the first light and the second light. The second birefringent part 121 and the third birefringent part 123 is configured to change the phase difference between the first light L1 and the second light L2, along a movement of the target T in the measurement direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a displacement detection device that uses light to measure the displacement of a measurement target member in a measurement direction in a non-contact manner. [Background technology]

[0002] Optical displacement detection devices are known as devices that measure the displacement of a measurement target in a specific direction without contact, and are used to measure the displacement of, for example, a semiconductor wafer or a photomask in a specific direction.

[0003] Patent Document 1 discloses a displacement detection device that uses optical interference. This displacement detection device includes a light source that emits light, a beam splitter, a diffraction grating, a reflector, a beam combiner, a light receiving unit, and a relative position information output means. In this device, one of the beams split by the beam splitter is used as a reference beam, and the other is used as an object beam and is irradiated onto the measurement surface of the measurement object. The reference beam and object beam are each diffracted by a diffraction grating inside the displacement detection device and then superimposed again by the beam combiner. This causes the reference beam and object beam to interfere with each other. The light receiving unit receives this interference beam. The relative position information output means outputs displacement information in the height direction of the measurement surface based on the intensity of the received interference beam.

[0004] Patent Document 2 discloses a displacement detection device that utilizes changes in polarization. In this displacement detection device, a birefringent prism is attached to the member to be measured. When light is irradiated onto the birefringent prism, the light is split into two beams of light with different phases due to the difference in refractive index. When the member to be measured moves laterally from this state, the optical path length of the light passing through the birefringent prism changes. This also changes the phase difference between the two beams of light. The displacement detection device measures the lateral movement of the birefringent prism, i.e., the lateral displacement of the member to be measured, based on the change in the phase difference between the two beams of light. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-152205 [Patent Document 2] Japanese Patent Publication No. 2020-046273 Summary of the Invention [Problem to be solved by the invention]

[0006] The displacement detection device of Patent Document 1 is configured so that when the measurement surface is displaced in the height direction, the position of the object light incident on the diffraction grating is displaced twice in the height direction. This displacement detection device also causes interference between the reference light and the object light, and measures displacement from the interference signal. When the measurement surface moves in the height direction by one period of the diffraction grating, the interference signal moves by two periods. Therefore, this interference-based displacement detection device can measure the displacement in the height direction of the measurement surface with extremely high resolution. Furthermore, this displacement detection device allows the object light to be incident obliquely on the measurement surface. Therefore, this displacement detection device can directly measure the displacement in the height direction of the wafer or photomask while avoiding a semiconductor wafer exposure device or a photomask direct imaging device located above the measurement surface.

[0007] In semiconductor wafer exposure devices and photomask direct imaging devices, the wafer or photomask may be tilted slightly (for example, by a few mrad), which requires a displacement detection device that can widen the tolerance range for changes in the posture of the measurement surface and measure displacement in the height direction with high accuracy.

[0008] In the displacement detection device of Patent Document 1, the interference intensity is likely to decrease when the orientation of the measurement surface changes, due to the principle of interfering between object light and reference light. Therefore, in an interferometric displacement detection device, the tolerance range for orientation change of the measurement surface is small (for example, several mrad), and it is not very versatile.

[0009] On the other hand, the displacement detection device of Patent Document 2 directly measures the birefringent prism and detects the lateral displacement of the birefringent prism, making it difficult to directly measure the vertical displacement of the wafer or photomask.

[0010] Furthermore, when splitting light from a light source into two beams using a birefringent prism as disclosed in Patent Document 2, the refractive index of each beam differs depending on the polarization direction. Therefore, in the displacement detection device of Patent Document 2, a correction prism is provided in the optical path to align the inclination of the wavefronts of the two beams. However, if the refractive indices of the two beams passing through the birefringent prism are different, the two beams will travel away from each other. In the displacement detection device of Patent Document 2, the displacement detection unit receives the two beams and detects the displacement of the birefringent prism based on the phase difference between the two beams. Therefore, it is assumed that the displacement detection unit receives both beams, making it difficult to ensure a large distance between the birefringent prism and the displacement detection unit. In other words, the amount of polarization change caused by the birefringent prism (detection resolution) and the distance between the birefringent prism and the displacement detection unit are in a tradeoff relationship. For example, for a displacement detection device to achieve nm-level resolution, the distance between the birefringent prism and the displacement detection unit must be within several tens of millimeters. Light is incident obliquely on the exposure position of a semiconductor wafer or photomask, and to directly measure the displacement of the wafer or photomask in the height direction, it may be necessary to set the distance between the birefringent prism and the displacement detection unit to 500 mm or more. With the displacement detection device of Patent Document 2, it is difficult to obtain nm measurement resolution while maintaining a large distance between the birefringent prism and the displacement detection unit, and the device is not very versatile.

[0011] The present invention provides a displacement detection device that detects the displacement of a measurement object in the height direction, and that has high measurement accuracy and is highly versatile. [Means for solving the problem]

[0012] The displacement detection device of the present invention is a displacement detection device that detects a displacement of a target in a measurement direction, a light source that emits light; a first birefringent unit that is provided on an optical path from the light source to a target onto which the light is irradiated, and that splits the light into a first light and a second light having a phase difference with respect to the first light; a second birefringent portion that is provided on an optical path of the first light and the second light reflected by the target and that refracts the first light and the second light; a third birefringent section that is provided on an optical path of the first light and the second light that have passed through the second birefringent section and that condenses the first light and the second light; a fourth birefringent section that is provided on optical paths of the first light and the second light that have passed through the third birefringent section and that superimposes the first light and the second light; a displacement detection unit that detects a displacement of the target in the measurement direction based on a change in a phase difference between the first light and the second light that have passed through the fourth birefringent unit, The second birefringent section and the third birefringent section are configured to change the phase difference between the first light and the second light as the target moves in the measurement direction. [Effects of the Invention]

[0013] In the displacement detection device of the present invention, the first light and the second light separated by the first birefringent section are superimposed by passing through the second birefringent section, the third birefringent section, and the fourth birefringent section. Because the first light and the second light are prevented from separating, the displacement detection section can receive both the first light and the second light even if the optical path length from the light source to the displacement detection section is long. As a result, the displacement detection device can measure the displacement of the target in the measurement direction from various positions, making it highly versatile. Furthermore, in the displacement detection device, both the first light and the second light that pass through the first birefringent section are reflected by the same target. Therefore, the relative angular change between the first light and the second light is suppressed between the time they leave the first birefringent section and the time they enter the second birefringent section. Therefore, even if the target is tilted, the displacement of the target in the measurement direction can be measured without being affected by the tilt. Therefore, the displacement detection device can achieve high measurement accuracy and high versatility. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram showing an example of an application of the displacement detection device of the first embodiment. [Figure 2] FIG. 1 is a front view showing the configuration of a displacement detection device according to a first embodiment. [Figure 3] FIG. 2 is a side view showing the configuration of an illumination unit and a light reflecting unit of the first embodiment. [Figure 4] 3 is a side view showing the configuration of a light reflecting section and a displacement detecting section according to the first embodiment. FIG. [Figure 5] FIG. 3 is a diagram showing the configurations of first to fourth birefringent portions of the first embodiment. [Figure 6] 4A and 4B are diagrams illustrating changes in the optical axis of light passing through a first birefringent portion and a second birefringent portion. [Figure 7] 10 is a diagram showing a change in the optical axis of light passing through a third birefringent portion and a fourth birefringent portion. FIG. [Figure 8] 10A and 10B are diagrams for explaining a phase change of light passing through a second birefringent portion when a target is displaced in a measurement direction. [Figure 9] 10A and 10B are diagrams for explaining a phase change of light passing through a third birefringent portion when a target is displaced in a measurement direction. [Figure 10] FIG. 2 is a functional block diagram of a displacement information output unit in the displacement detection device of the first embodiment. [Figure 11] FIG. 10 is a diagram showing the configurations of first to fourth birefringent sections according to a modified example of the first embodiment. [Figure 12] FIG. 10 is a diagram showing a change in the optical axis of light passing through a first birefringent portion and a second birefringent portion according to a modified example of the first embodiment. [Figure 13] FIG. 10 is a diagram showing a change in the optical axis of light passing through a third birefringent portion and a fourth birefringent portion according to a modified example of the first embodiment. [Figure 14] FIG. 4 is a schematic diagram showing another example of application of the displacement detection device of the first embodiment. [Figure 15] 10A and 10B are diagrams illustrating an example of the configuration of a scale in another application example of the displacement detection device according to the first embodiment. [Figure 16] 10A and 10B are diagrams illustrating another example of the configuration of the scale in another example of application of the displacement detection device according to the first embodiment. [Figure 17] FIG. 10 is a front view showing the configuration of a displacement detection device according to a second embodiment. [Figure 18] FIG. 10 is a front view showing the configuration of a displacement detection device according to a third embodiment. [Figure 19] FIG. 10 is a front view showing the configuration of a displacement detection device according to a fourth embodiment. [Figure 20] FIG. 11 is a front view showing the configuration of a displacement detection device according to a modified example of the fourth embodiment. [Figure 21] FIG. 10 is a front view showing the configuration of a displacement detection device according to a fifth embodiment. [Figure 22] FIG. 10 is a diagram showing a change in the optical path when the target is tilted around the Y axis. [Figure 23] FIG. 10 is a front view showing the configuration of a displacement detection device according to a sixth embodiment. [Figure 24] FIG. 23 is a front view showing the configuration of a displacement detection device according to a second modification of the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Specific embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are merely examples. The present invention should not be construed as being limited in any way by the embodiments described below.

[0016] First Embodiment First, the configuration of the displacement detection device of the first embodiment will be explained briefly.

[0017] FIG. 1 is a schematic diagram showing an example of an application of the displacement detection device of the first embodiment. The displacement detection device 1 measures the displacement of a target T in the Z direction (measurement direction). In this embodiment, the object to be measured is the surface of a semiconductor wafer. The target T is a part of the surface of the semiconductor wafer. The target T is defined by the range of the object to be measured that is irradiated with light. The semiconductor wafer is placed on a stage A. A circuit pattern is formed on the surface of the semiconductor wafer. The circuit pattern is formed on the surface of the semiconductor wafer by light (e.g., ultraviolet light) irradiated by a projection optical device 100.

[0018] The surface of the semiconductor wafer placed on stage A is not necessarily flat. Furthermore, when the semiconductor wafer is attached to stage A, its position in the height direction (Z direction) may fluctuate, or it may be attached at an angle. In such cases, the distance between the projection optical device 100 and target T will fluctuate. As a result, when the semiconductor wafer is exposed, the image may become blurred, or the magnification or exposure position may shift. For this reason, the displacement of target T in the Z direction is measured by displacement detection device 1.

[0019] More specifically, in the case of manufacturing a semiconductor wafer, a photosensitive resist is first applied to the surface of the semiconductor wafer. Then, an exposure light source 101 of the projection optical device 100 irradiates light. A mask 102 on which a circuit pattern is formed is provided on the optical path of the light from the exposure light source 101. The light from the exposure light source 101 passes through the mask 102 and exposes the object to be measured. In this way, the surface of the semiconductor wafer is exposed by the exposure light source 101, and the circuit pattern is transferred. Although not shown, the projection optical device 100 is provided with various components such as lenses. The lenses adjust the focus so that the image to be transferred (circuit pattern) is aligned with the surface of the semiconductor wafer.

[0020] When exposing a semiconductor wafer, it is necessary to maintain a constant distance between the projection optical apparatus 100 and the semiconductor wafer in order to adjust the focus. Therefore, it is necessary to know the height of the exposure position on the surface of the semiconductor wafer. Furthermore, when transferring a multi-layer circuit pattern onto the surface of the semiconductor wafer, the surface of the semiconductor wafer may warp. Therefore, it is necessary to adjust the focus to match the warpage of the semiconductor wafer surface, that is, to match the exposure position. Therefore, after measuring the height of the semiconductor wafer using the displacement detection device 1 of this embodiment, the projection optical apparatus 100 exposes the surface of the semiconductor wafer.

[0021] The displacement detection device 1 includes an illumination unit 11, a light reflecting unit 12, a displacement detection unit 13, and a displacement information output unit 14. The illumination unit 11 emits light. The light emitted from the illumination unit 11 is reflected by the target T and reaches the light reflecting unit 12. The light reflecting unit 12 reflects the received light. The light reflected by the light reflecting unit 12 is reflected again by the target T and reaches the displacement detection unit 13. The displacement detection unit 13 measures the displacement of the target T in the Z direction using the received light. Because a projection optical device 100 is provided above the target T, the illumination unit 11, the light reflecting unit 12, the displacement detection unit 13, and the displacement information output unit 14 are provided diagonally above the target T. The light emitted from the illumination unit 11 is incident on the target T at an angle.

[0022] It is preferable that the illumination unit 11, the light reflecting unit 12, the displacement detection unit 13, and the displacement information output unit 14 are fixed in a single housing. Alternatively, the illumination unit 11, the displacement detection unit 13, and the displacement information output unit 14 may all be configured as an integrated member. The illumination unit 11, the displacement detection unit 13, and the displacement information output unit 14 may each be separate units, or some of them may be separate units. The displacement information output unit 14 is configured from an arithmetic processing circuit such as a CPU. The displacement information output unit 14 executes a computer program stored in a recording medium to realize various processes described below.

[0023] In this specification, the Z direction is parallel to the vertical direction, with the upward direction being the +Z direction and the downward direction being the -Z direction. The X direction is a direction perpendicular to the Z direction in a plane including the Z direction and the optical axis of the light emitted from the illumination unit 11. The Y direction is a direction perpendicular to the Z direction and the X direction.

[0024] 2 is a front view showing the configuration of the displacement detection device of the first embodiment. The front view corresponds to a top view of the displacement detection device 1. The illumination unit 11 is configured to irradiate light onto the target T. Specifically, the illumination unit 11 includes a light source 111, a collimator lens 112, a polarizer 113, and a first birefringent unit 114.

[0025] The light source 111 emits light. The light source 111 is, for example, a semiconductor laser, an LED (Light Emitting Diode), an SLD (Super Luminescent Diode), a gas laser, a solid-state laser, or the like. The type of the light source 111 is not particularly limited. The light source 111 may emit coherent light. The light source 111 may be any light source as long as it can emit light whose polarization state changes due to a birefringent portion.

[0026] The collimator lens 112 is provided on the optical path of the light emitted from the light source 111. The collimator lens 112 converts the light emitted from the light source 111 into a plane wave. However, the collimator lens 112 does not need to create a strict plane wave. The collimator lens 112 may have an accuracy of, for example, about the wavelength λ of the light within the effective diameter of the light. In this embodiment, a configuration in which the illumination unit 11 includes the collimator lens 112 will be described, but the illumination unit 11 does not need to include the collimator lens 112. For example, a beam emitted from a gun such as a HeNe laser has a high wavefront accuracy. In such a case, the collimator lens 112 may not be provided.

[0027] The polarizer 113 is provided on the optical path of the light that has passed through the collimator lens 112. The polarizer 113 receives the light that has passed through the collimator lens 112. The polarizer 113 changes the polarization state of the received light. The polarizer 113 converts the received light into light having a specific polarization direction. The polarizer 113 is, for example, a polarizing plate. In this embodiment, a configuration in which the illumination unit 11 includes the polarizer 113 will be described, but the polarizer 113 may not be provided.

[0028] The first birefringent section 114 is provided on the optical path from the light source 111 to the target T. The first birefringent section 114 receives light that has passed through the polarizer 113. The first birefringent section 114 birefrings the received light. The first birefringent section 114 is, for example, a quartz plate. However, the first birefringent section 114 is not particularly limited as long as it has the function of birefringing the received light. The first birefringent section 114 may be a thin film or the like.

[0029] The light reflecting unit 12 receives light emitted from the illumination unit 11 and reflected by the target T. The light reflecting unit 12 reflects the received light. The light reflecting unit 12 reflects the received light so that it is irradiated onto the target T again. Specifically, the light reflecting unit 12 includes a second birefringent unit 121, a reflecting member 122, and a third birefringent unit 123.

[0030] The second birefringent section 121 is provided on the optical path of the light reflected by the target T. The second birefringent section 121 receives the light reflected by the target T. The second birefringent section 121 birefringes the received light. The second birefringent section 121 is, for example, a quartz plate. However, the second birefringent section 121 is not particularly limited as long as it has the function of birefringing the received light. The second birefringent section 121 may be a thin film or the like.

[0031] The reflecting member 122 is provided in the optical path between the second birefringent section 121 and the third birefringent section 123. The reflecting member 122 receives light that has passed through the second birefringent section 121. The reflecting member 122 reflects the received light. The reflecting member 122 reflects the received light so as to fold it back. The reflecting member 122 is configured to make the received light incident on the third birefringent section 123. The reflecting member 122 is not particularly limited. The reflecting member 122 is, for example, a corner cube mirror.

[0032] The third birefringent section 123 is provided on the optical path from the reflecting member 122 to the target T. That is, the third birefringent section 123 is provided on the optical path of light that has passed through the second birefringent section 121. The third birefringent section 123 receives light reflected by the reflecting member 122. The third birefringent section 123 birefrings the received light. The third birefringent section 123 is, for example, a quartz plate. However, the third birefringent section 123 is not particularly limited as long as it has the function of birefringing the received light. The third birefringent section 123 may be a thin film or the like.

[0033] The displacement detection unit 13 includes a fourth birefringent unit 131. In addition, the displacement detection unit 13 has a plurality of functional units for measuring the displacement of the target T in the Z direction based on the received light, which will be described later.

[0034] The fourth birefringent section 131 is provided on the optical path of the light that has passed through the third birefringent section 123. The fourth birefringent section 131 receives the light that has passed through the third birefringent section 123 and been reflected by the target T. The fourth birefringent section 131 birefringes the received light. The fourth birefringent section 131 is, for example, a quartz plate. However, the fourth birefringent section 131 is not particularly limited as long as it has the function of birefringing the received light. The fourth birefringent section 131 may be a thin film or the like.

[0035] FIG. 3 is a side view showing the configuration of the illumination unit and the light reflector of the first embodiment. The side view corresponds to a view of the displacement detection device 1 as seen from the side (Y direction). This figure shows the optical path of light emitted from the light source 111 until it reaches the reflecting member 122, i.e., the outward path of the light. The light from the illumination unit 11 is incident on the target T at an angle with respect to the measurement direction (Z direction). The incident angle θ1 on the target T is, for example, 85 degrees. However, the incident angle θ1 is not limited to 85 degrees and may be set appropriately. The incident angle θ1 is greater than 0 degrees. The incident angle θ1 is less than 90 degrees. For example, when a projection optical device 100, which is an exposure device, is provided above the target T, the distance between the projection lens of the projection optical device and the target is short. In such a case, the incident angle θ1 is set to, for example, 85 degrees or more. The incident angle θ1 is set within a range in which the displacement detection device 1 can measure the displacement of the target in the Z direction with the projection optical device 100 provided above the target. Light from the illumination unit 11 is reflected by the target T and travels toward the light reflecting unit 12. The reflection angle θ2 of the light from the illumination unit 11 is the same as the incident angle θ1. In other words, θ1=θ2.

[0036] 4 is a side view showing the configuration of the light reflecting unit and displacement detecting unit of the first embodiment. This figure shows the optical path of light reflected by the reflecting member 122 until it reaches the displacement detecting unit 13, i.e., the return path of the light. The light reflected by the light reflecting unit 12 is incident on the target T again at an angle with respect to the Z direction. The angle of incidence on the target T is θ1. In other words, the light reflecting unit 12 is arranged so that the angle of incidence on the target T is equal on the outward and return paths of the light. The light reflected by the light reflecting unit 12 is reflected on the target T at a reflection angle θ2 (= θ1) and travels toward the displacement detecting unit 13.

[0037] Next, the displacement detection device of the first embodiment will be described in detail.

[0038] 5(A) is a diagram showing the configuration of the first birefringent section 114. The first birefringent section 114 is made up of two birefringent sections 114A and 114B. The birefringent section 114A is provided so that light from the light source 111 is incident on it. The birefringent section 114A is provided at a position on the optical path closer to the light source 111 than the birefringent section 114B.

[0039] The birefringent portion 114A has a triangular shape in the ZX plane. In this embodiment, the birefringent portion 114A is a quartz crystal plate cut at an angle a1. The birefringent portion 114A is configured so that its thickness varies depending on the position in the plane of the plane wave of the incident light. The birefringent portion 114A is configured so that its thickness varies along a direction perpendicular to the optical axis in the ZX plane. The thickness preferably varies linearly. Note that the thickness is the length of the birefringent portion 114A in the direction along the optical axis. The same applies to the other birefringent portions. The birefringent portion 114A has a crystal axis. The refractive index of the birefringent portion 114A in the crystal axis direction is n1. The refractive index of the birefringent portion 114A in the axis direction perpendicular to the crystal axis is n2. The refractive index n2 is different from the refractive index n1.

[0040] The birefringent portion 114B is provided so that light that has passed through the birefringent portion 114A is incident thereon. The birefringent portion 114B has a triangular shape in the ZX plane. The birefringent portion 114B has a shape that is symmetrical to the birefringent portion 114A. The birefringent portion 114B has a shape that is point-symmetrical to the birefringent portion 114A in the ZX plane. The birefringent portion 114B is a quartz crystal plate cut at an angle b1. In this embodiment, the angle b1 is the same as the angle a1, but they may be different.

[0041] The birefringent portion 114B is bonded to the birefringent portion 114A. The bonding method is not particularly limited. For example, the birefringent portion 114B is bonded to the birefringent portion 114A with an optical adhesive. The optical adhesive preferably has high light transmittance. The optical adhesive is preferably made of a material that does not change the polarization state of light passing through it. The birefringent portion 114B is configured so that its thickness changes depending on the position in the plane of the plane wave of the incident light. The birefringent portion 114B is configured so that its thickness changes along the direction perpendicular to the optical axis in the ZX plane. The thickness preferably changes linearly. However, the change in thickness of the birefringent portion 114B is opposite to the change in thickness of the birefringent portion 114A.

[0042] The birefringent portion 114B has a crystal axis. The crystal axis direction of the birefringent portion 114B is different from the crystal axis direction of the birefringent portion 114A. The crystal axis of the birefringent portion 114B is perpendicular to the crystal axis of the birefringent portion 114A in the YZ plane. In this embodiment, the birefringent portion 114B is made of the same material as the birefringent portion 114A, but may be made of a different material. The refractive index of the birefringent portion 114B in the crystal axis direction is n1. The refractive index of the birefringent portion 114B in the axis direction perpendicular to the crystal axis is n2.

[0043] 5(B) is a diagram showing the configuration of the second birefringent section. The second birefringent section 121 is configured to have an optical axis that is perpendicular to the optical axis of the first birefringent section 114. In this embodiment, the second birefringent section 121 is configured to be symmetrical with respect to the YZ plane with respect to the first birefringent section 114. The second birefringent section 121 is preferably made of the same material as the first birefringent section 114.

[0044] The second birefringent portion 121 is composed of two birefringent portions 121A and 121B having optical axes perpendicular to each other. The birefringent portion 121A is provided so that light reflected by the target T is incident on the birefringent portion 121A. The birefringent portion 121A is provided at a position on the optical path closer to the target T than the birefringent portion 121B.

[0045] The birefringent portion 121A has a triangular shape in the ZX plane. In this embodiment, the birefringent portion 121A is a quartz crystal plate cut at an angle a2. The angle a2 is preferably the same as the angle a1. The birefringent portion 121A is configured so that its thickness varies depending on the position in the plane of the plane wave of the incident light. The birefringent portion 121A is configured so that its thickness varies along a direction perpendicular to the optical axis in the ZX plane. The thickness preferably varies linearly. The birefringent portion 121A has a crystal axis. The refractive index of the birefringent portion 121A in the crystal axis direction is n1. The refractive index of the birefringent portion 121A in the axis direction perpendicular to the crystal axis is n2.

[0046] The birefringent portion 121A is configured symmetrically to the birefringent portion 114A in the first birefringent portion 114. The birefringent portion 121A has a crystal axis that is perpendicular to the crystal axis of the birefringent portion 114A in the first birefringent portion 114 in the YZ plane.

[0047] The birefringent portion 121B is provided so that light that has passed through the birefringent portion 121A is incident thereon. The birefringent portion 121B has a triangular shape in the ZX plane. The birefringent portion 121B has a shape that is point-symmetric with respect to the birefringent portion 121A in the ZX plane. In this embodiment, the birefringent portion 121B is a quartz crystal plate cut at angle b2. In this embodiment, angle b2 is the same as angle a2, but may be different. The birefringent portion 121B is bonded to the birefringent portion 121A. The birefringent portion 121B is configured so that its thickness changes depending on the position in the plane of the plane wave of the incident light. The birefringent portion 121B is configured so that its thickness changes along a direction perpendicular to the optical axis in the ZX plane. It is preferable that the thickness change linearly. However, the change in thickness of the birefringent portion 121B is opposite to the change in thickness of the birefringent portion 121A. The birefringent portion 121B has a crystal axis. The crystal axis direction of the birefringent portion 121B is different from the crystal axis direction of the birefringent portion 121A. The crystal axis of the birefringent portion 121B is perpendicular to the crystal axis of the birefringent portion 121A in the YZ plane. The birefringent portion 121B is preferably made of the same material as the birefringent portion 121A. That is, the refractive index of the birefringent portion 121B in the crystal axis direction is n1. The refractive index of the birefringent portion 121B in the axis direction perpendicular to the crystal axis is n2.

[0048] In this way, the first birefringent portion 114 and the second birefringent portion 121 are configured to form an optical pair.

[0049] FIG. 5(C) is a diagram showing the configuration of a third birefringent section, and FIG. 5(D) is a diagram showing the configuration of a fourth birefringent section. The third birefringent section 123 and the fourth birefringent section 131 are configured to form an optical pair, similar to the first birefringent section 114 and the second birefringent section 121. The third birefringent section 123 has a configuration in which a birefringent section 123A cut at an angle a3 and a birefringent section 123B cut at an angle b3 are joined together. The fourth birefringent section 131 has a configuration in which a birefringent section 131A cut at an angle a4 and a birefringent section 131B cut at an angle b4 are joined together. In this embodiment, the angles a1, a2, a3, a4, b1, b2, b3, and b4 are the same, but may be different from each other. Other configurations of the third birefringent section 123 are omitted because they are similar to those of the second birefringent section 121. Other configurations of the fourth birefringent section 131 are omitted because they are similar to those of the first birefringent section 114.

[0050] 6 is a diagram showing the change in the optical axis of light passing through the first birefringent section and the second birefringent section. The first birefringent section 114 splits the light emitted from the light source 111 into a first light L1 and a second light L2 having a different polarization state from the first light L1. In the first birefringent section 114, the refractive index differs between the polarization axis in the Z direction and the polarization axis in the Y direction. Due to this difference in refractive index, the light emitted from the light source 111 is split into the first light L1 and the second light L2, which is refracted at an angle different from that of the first light L1. Here, the refractive index and phase difference in birefringence are expressed by the following equation (1): Phase difference=2 pi d (n2-n1) / λ (1) where pi is the ratio of the circumference of a circle to its diameter, d is the thickness of the birefringent portion through which light passes (apparent optical path length), (n2-n1) is the difference in refractive index, and λ is the wavelength of the light. As described above, due to the difference in refractive index between the different polarization axes, the second light L2 has a phase difference with respect to the first light L1. The first light L1 that has passed through the first birefringent portion 114 has an optical axis that is tilted at an angle c1 with respect to the optical axis of the incident light. The second light L2 that has passed through the first birefringent portion 114 has an optical axis that is tilted at an angle c2 with respect to the optical axis of the incident light. The second light L2 is refracted in the opposite direction to the first light L1 across the optical axis of the incident light.

[0051] The first light L1 and the second light L2 that pass through the first birefringent section 114 are reflected by a target (not shown) and enter the second birefringent section 121. The refractive index of the second birefringent section 121 is the same as that of the first birefringent section 114. Therefore, in the second birefringent section 121, the first light L1 is refracted by an angle c1, and the second light L2 is refracted by an angle c2. However, as described above, the second birefringent section 121 has an optical axis that is perpendicular to the optical axis of the first birefringent section 114. In other words, the second birefringent section 121 is configured to refract the optical axes of the first light L1 and the second light L2 refracted in the first birefringent section 114 in the direction opposite to that of the first birefringent section 114. The second birefringent section 121 is configured to return the optical axes of the first light L1 and the second light L2 refracted by the first birefringent section 114 to the optical axes before entering the first birefringent section 114. The optical axes of the first light L1 and the second light L2 that have passed through the second birefringent section 121 become parallel to the optical axes before entering the first birefringent section 114. The first light L1 and the second light L2 that have passed through the second birefringent section 121 pass through the reflecting member 122 and enter the third birefringent section 123.

[0052] 7 is a diagram showing the change in the optical axis of light passing through the third birefringent section and the fourth birefringent section. The third birefringent section 123 condenses the first light L1 and the second light L2. The first light L1 that has passed through the third birefringent section 123 has an optical axis tilted at an angle d1 with respect to the optical axis before entering the third birefringent section 123. The first light L1 is refracted in the third birefringent section 123 so as to approach the second light L2. The second light L2 that has passed through the third birefringent section 123 has an optical axis tilted at an angle d2 with respect to the optical axis before entering the third birefringent section 123. The second light L2 is refracted in the third birefringent section 123 so as to approach the first light L1.

[0053] The first light L1 and the second light L2 that pass through the third birefringent section 123 are reflected by a target (not shown) and enter the fourth birefringent section 131. The refractive index of the fourth birefringent section 131 is the same as that of the third birefringent section 123. Therefore, in the fourth birefringent section 131, the first light L1 is refracted by an angle d1, and the second light L2 is refracted by an angle d2. However, as described above, the fourth birefringent section 131 has an optical axis that is perpendicular to the optical axis of the third birefringent section 123. In other words, the fourth birefringent section 131 is configured to refract the optical axes of the first light L1 and the second light L2 refracted in the third birefringent section 123 in the direction opposite to that of the third birefringent section 123. The fourth birefringent section 131 is configured to return the optical axes of the first light L1 and the second light L2 refracted by the third birefringent section 123 to the optical axes before entering the third birefringent section 123. The optical axes of the first light L1 and the second light L2 that have passed through the fourth birefringent section 131 become parallel to the optical axes before entering the third birefringent section 123.

[0054] The fourth birefringent portion 131 overlaps the first light L1 and the second light L2. The fourth birefringent portion 131 is preferably provided so that the first light L1 and the second light L2 enter the fourth birefringent portion 131 at a position where the first light L1 and the second light L2 join together. This configuration makes it easier to overlap the first light L1 and the second light L2.

[0055] As described above, in the displacement detection device 1, the first birefringent section 114 and the second birefringent section 121 form an optical pair, and the third birefringent section 123 and the fourth birefringent section 131 form an optical pair. As a result, the first light L1 and the second light L2 that have passed through the fourth birefringent section 131 become parallel to and are superimposed on the light that enters the first birefringent section 114. The optical axes of the first light L1 and the second light L2 that have passed through the fourth birefringent section 131 coincide or substantially coincide with each other.

[0056] FIG. 8 is a diagram illustrating the phase change of light passing through the second birefringent section when the target is displaced in the measurement direction. The dashed line in the figure indicates the target T in its initial position, and the solid line indicates the target T displaced by D in the Z direction from its initial position. As described above, the angle of incidence θ1 of light passing through the first birefringent section and reflected by the target T is equal to the angle of reflection θ2. When the target T is displaced by D in the Z direction, the position of the light incident on the second birefringent section 121 moves by a movement amount S in a direction perpendicular to the incident light. Here, S is expressed by the following equation (2). For example, if θ1 = 85 degrees and D = 0.5 mm, then the movement amount S = 1 mm. S=2·D·sinθ (2)

[0057] When the target T does not displace, the first light L1 and the second light L2 passing through the second birefringent portion 121 do not move. Therefore, the phase difference between the first light L1 and the second light L2 does not change. On the other hand, when the target T displaces by D in the Z direction, the position at which the first light L1 and the second light L2 pass through the second birefringent portion 121 changes. In this case, when viewed as the second birefringent portion 121 as a whole, the apparent optical path length of the first light L1 and the second light L2 passing through the second birefringent portion 121 does not change. However, the apparent optical path length passing through the birefringent portion 121A changes from DA0 to DA1. Similarly, the apparent optical path length passing through the birefringent portion 121B also changes. In other words, the parameter d in the above equation (1) changes. As a result, when the target T displaces in the Z direction, the phase difference between the first light L1 and the second light L2 changes. In other words, when the target T is displaced by D in the Z direction, the apparent optical path length of the first light L1 and the second light L2 passing through the second birefringent portion 121 does not change when viewed as the whole of the second birefringent portion 121. However, when the target T is displaced by D in the Z direction, the optical path length of the first light L1 and the second light L2 in the second birefringent portion 121 changes. Here, the optical path length is expressed as the product of the apparent optical path length and the refractive index. This changes the phase difference between the first light L1 and the second light L2 that have passed through the first birefringent portion 114.

[0058] 9 is a diagram illustrating the phase change of light passing through the third birefringent section when the target is displaced in the measurement direction. The dashed line in the figure indicates the target T in its initial position, and the solid line indicates the target T displaced by D in the Z direction from its initial position. As explained above, when the target T is displaced by D in the Z direction, the position of the light incident on the third birefringent section 123 moves by a movement amount S in a direction perpendicular to the incident light. The movement amount S is expressed by the above-mentioned formula (1). The first light L1 and the second light L2 that have passed through the third birefringent section are reflected again by the target T at an incident angle θ1 and a reflection angle θ2, and then enter the fourth birefringent section.

[0059] When the target T is displaced by D in the Z direction, the positions at which the first light L1 and the second light L2 pass through the third birefringent section 123 change. The third birefringent section 123 is configured so that the optical path lengths of the first light L1 and the second light L2 within the third birefringent section 123 change as the target T moves in the Z direction (measurement direction). This changes the phase difference between the first light L1 and the second light L2 that have passed through the second birefringent section 121. Furthermore, the phase difference between the first light L1 and the second light L2 changes not only due to the second birefringent section 121 but also due to the third birefringent section 123. In other words, the change in phase difference between the first light L1 and the second light L2 due to passing through the second birefringent section 121 is added to the change in phase difference between the first light L1 and the second light L2 due to passing through the third birefringent section 123.

[0060] Furthermore, the first light L1 and the second light L2 that have passed through the third birefringent section 123 pass through the first birefringent section 114 and are reflected by the target T at the same incident angle θ1 and reflection angle θ2 as the first light L1 and the second light L2 that are reflected by the target T. Therefore, even if the target T is displaced in the Z direction, the first light L1 and the second light L2 that have passed through the third birefringent section 123 and are reflected by the target T travel toward the fourth birefringent section along the same optical path as the optical path when the target T is in the initial position. The first light L1 and the second light L2 that have entered the fourth birefringent section are photoelectrically converted by the displacement detection section, and the displacement of the target T is measured.

[0061] 2, the displacement detection unit 13 includes a phase plate 132, a condenser lens 133, a beam splitter 134, polarizing beam splitters 135 and 136, and light receiving elements 137A, 137B, 137C, and 137D.

[0062] The phase plate 132 receives the first light L1 and the second light L2 that have passed through the fourth birefringent portion 131. The phase plate 132 converts each of the first light L1 and the second light L2 into circularly polarized light. The first light L1 and the second light L2 are lights with polarization axes that are orthogonal to each other. The first light L1 and the second light L2 that have passed through the phase plate 132 become a combined light that is a combination of circularly polarized light whose rotation directions are opposite to each other. The combined light of the first light L1 and the second light L2 becomes linearly polarized light whose angle changes in accordance with the change in the phase of the first light L1 and the second light L2.

[0063] The condenser lens 133 receives the combined light that has passed through the phase plate 132. The condenser lens 133 converts the received combined light into a plane wave. The condenser lens 133 is conveniently provided because it can adjust the optical path. However, the condenser lens 133 may be provided as needed.

[0064] Beam splitter 134 receives the combined light that has passed through condenser lens 133. Beam splitter 134 splits the received combined light into two beams. Beam splitter 134 is a non-polarizing beam splitter that is not polarization dependent.

[0065] Polarizing beam splitter 135 receives one of the beams split by beam splitter 134. Polarizing beam splitter 136 receives the other of the beams split by beam splitter 134. Polarizing beam splitters 135 and 136 each split the received light into two beams. Polarizing beam splitters 135 and 136 each change the polarization state of the received light. For example, polarizing beam splitters 135 and 136 each reflect the S component of the received light and transmit the P component. Polarizing beam splitter 136 is rotated 45 degrees with respect to polarizing beam splitter 135. That is, polarizing beam splitter 136 is arranged so that light receiving element 137C receives light that is 90 degrees out of phase with light receiving element 137A. Polarizing beam splitter 136 is arranged so that light receiving element 137D receives light that is 90 degrees out of phase with light receiving element 137B.

[0066] Light receiving element 137A receives one of the beams split by polarizing beam splitter 135. Light receiving element 137B receives the other beam split by polarizing beam splitter 135. Light receiving elements 137A and 137B each photoelectrically convert the received light. Light receiving elements 137A and 137B are, for example, photodiodes. Light receiving elements 137A and 137B each receive light whose amount varies depending on the angle of linear polarization. Light receiving elements 137A and 137B each output an electrical signal according to the amount of light received.

[0067] Similarly, the light receiving element 137C receives one of the beams split by the polarizing beam splitter 136. The light receiving element 137D receives the other beam split by the polarizing beam splitter 136. The light receiving elements 137C and 137D each photoelectrically convert the received light. The light receiving elements 137C and 137D are, for example, photodiodes. The light receiving elements 137C and 137D each receive light whose amount varies depending on the angle of linear polarization. The light receiving elements 137C and 137D each output an electrical signal corresponding to the amount of light received. The light receiving elements 137A, 137B, 137C, and 137D each transmit the photoelectrically converted electrical signal to the displacement information output unit 14.

[0068] 10 is a functional block diagram of the displacement information output unit in the displacement detection device of Embodiment 1. The displacement information output unit 14 includes differential amplifiers 141 and 142, A / D conversion units 143 and 144, a waveform correction processing unit 145, and an incremental signal generator 146.

[0069] The differential amplifier 141 receives the electrical signals output by the light receiving elements 137A and 137B. Here, the first light L1 and the second light L2 have different phases (a 180-degree difference). Therefore, the differential amplifier 141 outputs a displacement detection signal, which is a differential signal in which the DC component has been canceled and amplified, based on the electrical signals output from the light receiving elements 137A and 137B. The displacement detection signal is output as phase A (first phase). The differential amplifier 141 transmits the displacement detection signal to the A / D conversion unit 143. By canceling the DC component in this way, it is possible to cancel the influence of a DC offset in the electrical signals due to changes in the light intensity of the first light L1 and the second light L2.

[0070] Similarly, the differential amplifier 142 receives the electrical signals output by the light receiving elements 137C and 137D. Based on the electrical signals output from the light receiving elements 137C and 137D, the differential amplifier 142 outputs a displacement detection signal, which is a differential signal in which the DC component has been cancelled and which has been amplified. This displacement detection signal is output as a B phase (second phase). The differential amplifier 142 transmits the displacement detection signal to the A / D conversion unit 144.

[0071] The displacement detection signals output from the differential amplifiers 141 and 142 are analog signals. The A / D converters 143 and 144 convert the displacement detection signals output from the differential amplifiers 141 and 142 into digital signals. In this embodiment, the displacement detection signal output from the differential amplifier 141 is treated as a sine signal, and the displacement detection signal output from the differential amplifier 142 is treated as a cosine signal. By using two displacement detection signals (A-phase and B-phase) with a phase difference of 90 degrees in this way, it is possible to determine whether the B-phase displacement detection signal is ahead or behind the A-phase displacement detection signal. In other words, it is possible to determine whether the target T has displaced in the +Z direction or the −Z direction. The differential amplifiers 141 and 142 each transmit the converted digital signals to the waveform correction processor 145. Note that if direction determination is not required, the phase plate 132 may not be provided. In other words, the displacement of the target may be measured based only on the sine signal.

[0072] The waveform correction processing unit 145 appropriately corrects the DC component, gain, and phase of each received digital signal. The waveform correction processing unit 145 sends the corrected signal to the incremental signal generator 146. The incremental signal generator 146 accumulates the amount of phase change per unit clock from a lookup table of sine and cosine signals, and outputs relative position information. This allows the displacement of the target T in the Z direction to be measured.

[0073] Specifically, the difference between the refractive index of ordinary light and extraordinary light in a quartz plate, that is, n1 and n2 is approximately 0.0091. For example, suppose that the wavelength λ of light emitted by the light source is 655 nm, the angle of incidence θ1 on the target T is 85 degrees, the target T is displaced in the Z direction by D=0.5 mm, and the incidence positions of the first light L1 and the second light L2 on the second birefringent portion 121 are moved by S=1 mm. The angle a at which the quartz plate is cut (= the angles a1=a2=a3=a4=b1=b2=b3=b4 of the birefringent portions) to generate a phase difference between the first light L1 and the second light L2 equal to the wavelength λ of the light source is calculated by the following equation (3), and under the above conditions, it is a=1.03 degrees. a=Atan(λ / 4·S·(n2-n1)) (3) Therefore, when the target T moves D=0.5 mm in the Z direction, the phase of the signal detected by each of the light receiving elements 137A-137D of the displacement detection unit 13 goes around once, resulting in a 0.5 mm period. When one period is 0.5 mm, the displacement detection device of this embodiment can detect the displacement of the target T in the Z direction with a resolution of 7.6 nm.

[0074] As described above, in the displacement detection device 1, the first light L1 and the second light L2, which are separated by the first birefringent section 114 so as to be separated from each other, are superimposed by passing through the second birefringent section 121, the third birefringent section 123, and the fourth birefringent section 131. Because the first light L1 and the second light L2 are prevented from separating from each other, the displacement detection unit 13 can receive both the first light L1 and the second light L2 even if the distance between the displacement detection unit 13 and the target T is long. Even if the projection optical device 100 is provided above the target T, it is possible to measure the displacement of the target T in the Z direction from various positions.

[0075] In general, displacement detection devices using optical interference irradiate a target with a fixed reference beam and an object beam. Therefore, if the target surface is tilted, the object beam reflected by the target and returning is likely to be tilted. In this case, interference fringes are likely to occur in the interference light generated on the light-receiving element surface at a pitch of d = λ / sinθ, where λ is the wavelength of the light source and θ is the angular deviation of the object beam reflected by the target and returning. Meanwhile, because the optical axis of the reference beam is fixed, it does not change even if the target is tilted. In other words, if interference fringes occur at a pitch finer than the effective dimensions of the light-receiving element surface, the light-dark contrast of the photoelectrically converted interference signal decreases, and the signal output is likely to decrease. In contrast, in the displacement detection device 1 of the first embodiment, both the first light L1 and the second light L2 that pass through the first birefringent portion 114 are reflected by the same target T. Therefore, the relative angular change between the first light L1 and the second light L2 is suppressed between the time they exit the first birefringent portion 114 and the time they enter the second birefringent portion 121. Therefore, even if the target T is tilted, the displacement of the target T in the Z direction can be measured without being affected by the tilt. In other words, the problems that arise with displacement detection devices that use optical interference are unlikely to occur. Therefore, the displacement detection device 1 can have high measurement accuracy and can be highly versatile.

[0076] Furthermore, in the displacement detection device 1, the first birefringent section 114 is configured by joining two birefringent sections 114A and 114B. Therefore, compared to when the first birefringent section 114 is configured from a single birefringent section, the phase difference between the first light L1 and the second light L2 imparted by passing through the first birefringent section 114 is likely to be large. This improves the resolution of displacement measurement of the target T.

[0077] Furthermore, in the displacement detection device 1, the first light L1 and the second light L2 that pass through the third birefringent section 123 and are reflected by the target T follow the same optical path regardless of the position of the target T in the Z direction. In other words, the first light L1 and the second light L2 that are reflected by the target T return to their original optical paths. Therefore, the optical axes of the first light L1 and the second light L2 that proceed toward the fourth birefringent section are easily kept constant, independent of the movement of the target T in the Z direction. As a result, there is no need to change the position of the displacement detection section even if the target T moves in the Z direction.

[0078] Furthermore, in the displacement detection device 1, the phenomenon in which the first light and the second light returning to the displacement detection unit become separated due to the influence of the refraction difference in each birefringent section relative to the difference in polarization components can be suppressed. Therefore, to increase the resolution in the displacement detection device 1, it is sufficient to simply increase the cut angle of the quartz plate that constitutes each birefringent section.

[0079] <Modification> 11 is a diagram showing the configuration of first to fourth birefringent sections according to a modified example of the first embodiment. In the above-described embodiment, each of the first to fourth birefringent sections is formed by joining two birefringent sections. However, each of the first to fourth birefringent sections may be formed by a single birefringent section having a triangular shape.

[0080] Referring to FIG. 11(A), the first birefringent section 114 is composed of one birefringent section having an angle a1. The refractive index of the first birefringent section 114 is n1 in the Y direction and n2 in the Z direction. Referring to FIG. 11(B), the second birefringent section 121 is composed of a birefringent section having an angle a2. The second birefringent section 121 has a crystal axis perpendicular to the first birefringent section 114. That is, the refractive index of the second birefringent section 121 is n2 in the Y direction and n1 in the Z direction. Referring to FIG. 11(C), the third birefringent section 123 is composed of a birefringent section having an angle a3. The refractive index of the third birefringent section 123 is n2 in the Y direction and n1 in the Z direction. Referring to FIG. 11(D), the fourth birefringent section 131 is composed of a birefringent section having an angle a4. The fourth birefringent portion 131 has a crystal axis that is perpendicular to the third birefringent portion 123. That is, the refractive index of the fourth birefringent portion 131 is n1 in the Y direction and n2 in the Z direction.

[0081] 12 is a diagram illustrating the change in the optical axis of light passing through a first birefringent section and a second birefringent section according to a modified example of the first embodiment. The first birefringent section 114 splits incident light into a first light L1 and a second light L2. Because the first birefringent section 114 is composed of a single birefringent section, the first light L1 and the second light L2 are refracted toward the same side relative to the optical axis of the incident light. The first light L1 and the second light L2 are reflected by a target (not shown) and enter the second birefringent section 121. The optical axes of the first light L1 and the second light L2 that have passed through the second birefringent section 121 become parallel to the optical axis before entering the first birefringent section 114. The first light L1 and the second light L2 that have passed through the second birefringent section 121 enter the third birefringent section 123 via a reflecting member.

[0082] 13 is a diagram showing changes in the optical axes of light passing through a third birefringent section and a fourth birefringent section according to a modified example of the first embodiment. The third birefringent section 123 condenses the first light L1 and the second light L2. The first light L1 and the second light L2 that have passed through the third birefringent section 123 are reflected by a target (not shown) and enter the fourth birefringent section 131. The optical axes of the first light L1 and the second light L2 that have passed through the fourth birefringent section 131 become parallel to the optical axes before entering the third birefringent section 123 and are superimposed on each other.

[0083] According to the displacement detection device having such a configuration, the number of members constituting the first to fourth birefringent portions can be reduced, the structure can be simplified, and costs can be reduced.

[0084] <Other uses> In the first embodiment and its modified example described above, the displacement detection device measures the displacement in the Z direction of the target T. In addition to this displacement detection device, a scale and an encoder may be added to measure the displacement of the target T in the X and Y directions in addition to the displacement in the Z direction.

[0085] 14 is a schematic diagram showing another application example of the displacement detection device of the first embodiment. The displacement measurement system includes the displacement detection device 1, an encoder 200, and a scale 300. The displacement measurement system is a three-dimensional measurement system that measures the displacements of a target T in the X, Y, and Z directions.

[0086] The displacement detection device 1 is the same as the displacement detection device of the first embodiment described above. However, the displacement detection device 1 may be a displacement detection device according to a modified example of the first embodiment, or a displacement detection device according to another embodiment described later. The displacement detection device 1 measures the displacement in the Z direction of the target T by measuring the displacement in the Z direction of the surface of the scale 300 near the detection position of the encoder 200.

[0087] The encoder 200 is provided above the target T. The encoder 200 may be a one-dimensional linear encoder or a two-dimensional linear encoder. The scale 300 is a planar scale. The scale 300 may be a one-dimensional linear scale or a two-dimensional linear scale. The scale 300 is provided so that at least a portion thereof is located on the surface of the target T.

[0088] 15 is a diagram showing an example of the configuration of a scale in another application example of the displacement detection device of the first embodiment. In the figure, (A-1) and (A-2) indicate one-dimensional scales, (B-1) and (B-2) indicate two-dimensional scales, and (C-1) and (C-2) indicate two-dimensional scales different from (B-1) and (B-2).

[0089] First, we will explain the one-dimensional scale. (A-1) is a front view, i.e., a view seen in the Z direction, and (A-2) is a side view, i.e., a view seen in the Y direction. The one-dimensional scale is a grating scale with a grating vector in one direction (a direction included in the XY plane). Protrusions 301 are provided at a constant pitch on the surface of the grating. Recesses 302 are formed between the protrusions 301. A reflective material is used on the surfaces of the recesses 302 and protrusions 301, i.e., the surface of the grating.

[0090] Next, the two-dimensional scale will be described. (B-1) is a front view, and (B-2) is a side view. The two-dimensional scale is a grating scale with grating vectors in two directions (directions included in the XY plane). On the surface of the grating, convex portions 303 are provided at a constant pitch in two orthogonal directions (vertical and horizontal directions on the paper). The convex portions 303 have a dot shape. Concave portions 304 are formed between the convex portions 303. A reflective material is used on the surface of the grating. Note that the convex portions 303 and the concave portions 304 may be interchanged. A two-dimensional scale with such a configuration is shown in (C-1) and (C-2) in the figure.

[0091] 14, encoder 200 irradiates light onto scale 300 and measures displacement of scale 300 in the X and / or Y directions, i.e., displacement of target T in the X and / or Y directions. When a one-dimensional scale is used, the measurement system is able to detect displacement in two directions, the X and Z directions, and when a two-dimensional scale is used, it is able to detect displacement in three directions, the X, Y, and Z directions. Encoder 200 may be a moiré type that irradiates light onto a grating scale and detects displacement using moiré fringes obtained by the grating scale, or a grating interference type that detects displacement using diffracted light.

[0092] FIG. 16 is a diagram showing another example of the configuration of the scale in another application example of the displacement detection device of the first embodiment. In the diagram, (A) shows a one-dimensional scale, (B) shows a two-dimensional scale, and (C) shows a two-dimensional scale with the concave and convex portions reversed from (B). The scale 300 may have a protective layer 305 on top of the grating scale. The scale 300 may also have a reflective film 306 provided on the surface of the protective layer 305 and reflecting only specific wavelengths. The encoder 200 may irradiate the grating scale with light to measure displacement in the X and / or Y directions, and the displacement detection device 1 may irradiate the reflective film 306 provided on the surface of the protective layer 305 with light to measure the Z direction (the gap between the scale and the displacement detection device). Furthermore, referring to FIG. 14, the illumination unit 11, the displacement detection unit 13, and the light reflecting unit 12 of the displacement detection device 1 may be placed on the stage A, which is a movable unit, to measure the relative gap with a fixed scale or mirror, and the installation locations of the illumination unit 11, the displacement detection unit 13, and the light reflecting unit 12 of the displacement detection device 1 are not limited to those described above.

[0093] Second Embodiment 17 is a front view showing the configuration of a displacement detection device according to the second embodiment. In the displacement detection device according to the first embodiment, light is reflected twice by the target. In contrast, in the displacement detection device according to the second embodiment, light is reflected once by the target.

[0094] The displacement detection device 2 includes an illumination unit 21 and a displacement detection unit 22. Unlike the displacement detection device of the first embodiment, the displacement detection device 2 does not include a light reflecting unit. The illumination unit 21 is the same as that of the displacement detection device of the first embodiment. The displacement detection unit 22 includes a second birefringent unit 221, a third birefringent unit 222, and a fourth birefringent unit 223. The first light and second light that have passed through the first birefringent unit 211 are reflected by the target T and enter the second birefringent unit 221. The first light and second light that have passed through the second birefringent unit 221 enter the third birefringent unit 222 without being reflected by the target T. The first light and second light that have passed through the third birefringent unit 222 also enter the fourth birefringent unit 223 without being reflected by the target T. In short, the first light and second light that pass through the first birefringent portion 211 and are reflected by the target T pass through the third birefringent portion 222 and the fourth birefringent portion 223 without being folded back. The other configurations of the displacement detection device 2 are the same as those of the displacement detection device of the first embodiment.

[0095] As described above, the displacement detection device 2 of the second embodiment measures the displacement of the target T in the Z direction by reflecting light once on the target T. This configuration is effective, for example, when the reflectivity of the target T is low. Furthermore, because light is reflected once on the target T, the displacement of the target T can be measured with pinpoint accuracy. Furthermore, because the first and second lights are reflected only once on the target T, the optical axes of the first and second lights also move as the target moves in the Z direction. As a result, the incident position of the light on the fourth birefringent portion 223 also moves (the optical axes move). Therefore, changes in the phases of the first and second lights due to the movement of the optical axes of the first and second lights in the third birefringent portion 222 and the fourth birefringent portion 223 are canceled out. Therefore, only the change in the phases of the first and second lights due to the movement of the optical axes of the first and second lights in the second birefringent portion 221 is detected as the displacement of the target T in the Z direction. Furthermore, in the displacement detection device 2, although not shown, a condenser lens (see reference numeral 133 in FIG. 2) that condenses the first light and the second light that have passed through the fourth birefringent section 223 works effectively. The condenser lens condenses light onto each of the four light receiving elements. Therefore, even if the movement of the target T in the Z direction causes the optical axes of the first light and the second light that have been superimposed at the fourth birefringent section 223 to shift, the optical axes at the positions of the light receiving elements remain almost unchanged, and each light receiving element can stably output a signal to the displacement information output unit 23.

[0096] In the displacement detecting device 2 of the second embodiment, each birefringent portion may also be made up of one birefringent portion, as described in the modified example of the first embodiment.

[0097] <Third embodiment> 18 is a front view showing the configuration of a displacement detection device of the third embodiment. In the displacement detection device of the first embodiment, the positions at which light is reflected twice on the target are different. In contrast, in the displacement detection device of the third embodiment, the positions at which light is reflected twice on the target are the same, and the outward path and return path of light coincide.

[0098] In the displacement detection device 3, the first birefringent section 31 and the fourth birefringent section 34 are made of the same material. That is, one member functions as the first birefringent section 31 when it splits light emitted from the light source, and functions as the fourth birefringent section 34 when it receives light that has passed through the third birefringent section 33. Similarly, the second birefringent section 32 and the third birefringent section 33 are made of the same material. That is, one member functions as the second birefringent section 32 when it receives light that has passed through the first birefringent section 31, and functions as the third birefringent section 33 when it receives light that has passed through the second birefringent section 32.

[0099] Furthermore, in the displacement detection device 3, a beam splitter 36 and an isolator 37 are provided between the light source 35 and the first birefringent section 31. The beam splitter 36 splits the light on the return path and guides it to the displacement detection section 38. The isolator 37 is provided to prevent a portion of the light on the return path from returning to the light source 35. The output signal of the displacement detection section 38 is sent to a displacement information output section 39.

[0100] According to the displacement detection device 3 of the third embodiment having such a configuration, the positions on the target T where light is irradiated are concentrated at one point. Therefore, it is possible to measure the displacement of the target T with pinpoint accuracy. Note that, in the displacement detection device 3 of the third embodiment as well, each birefringent portion may be configured with one birefringent portion, as described in the modified example of the first embodiment.

[0101] <Fourth embodiment> 19 is a front view showing the configuration of a displacement detection device of a fourth embodiment. In the displacement detection device of the third embodiment, the position at which light is reflected twice from the target is the same, and the outward path and the return path of the light are the same. In contrast, in the displacement detection device of the fourth embodiment, the position at which light is reflected twice from the target is the same, but the outward path and the return path of the light are different.

[0102] In the displacement detection device 4, when viewed in the Z direction, the optical axis A-A' of the light from the first birefringent section 411 to the second birefringent section 412 (optical axis of the outgoing path) and the optical axis B-B' of the light from the third birefringent section 413 to the fourth birefringent section 414 (optical axis of the returning path) intersect at a predetermined angle. In other words, the optical axis A-A' of the outgoing path and the optical axis B-B' of the returning path are not parallel. Furthermore, the optical axis A-A' of the outgoing path and the optical axis B-B' of the returning path intersect on the target T. The angle formed by the optical axis A-A' of the outgoing path and the optical axis B-B' of the returning path is set appropriately by adjusting the reflection angle of the reflecting member 421.

[0103] According to the displacement detection device 4 of the fourth embodiment having such a configuration, the positions where light is irradiated on the target T are concentrated at one point. Therefore, the displacement of the target T can be measured with pinpoint accuracy. Furthermore, since the optical axis A-A' of the outgoing path and the optical axis B-B' of the return path are parallel and do not overlap, the illumination unit 41 and the displacement detection unit 43 can be separated in position. Therefore, there is no need to take measures against light returning to the light source 415, and the isolator 37 described in the third embodiment can be omitted, simplifying the configuration of the displacement detection device and reducing costs. Furthermore, separating the illumination unit 41 and the displacement detection unit 43 in position facilitates the layout and manufacturing of the displacement detection device 4. Note that, in the displacement detection device 4 of the fourth embodiment, each birefringent unit may be composed of a single birefringent unit, as described in the modified example of the first embodiment.

[0104] 19, the illumination unit 41 and the displacement detection unit 43 are each tilted so that the optical axis A-A' of the outgoing path and the optical axis B-B' of the returning path intersect. However, the means for intersecting the optical axis A-A' of the outgoing path and the optical axis B-B' of the returning path is not limited to this.

[0105] Fig. 20 is a front view showing the configuration of a displacement detection device according to a modification of the fourth embodiment. The displacement detection device 4A shown in this example differs from the example shown in Fig. 19 in that the illumination unit 41, the light reflection unit 42, and the displacement detection unit 43 each include tilting means.

[0106] The illumination unit 41 includes tilting means 416 that refracts light emitted from a light source 415. The tilting means 416 is provided ahead of the first birefringent section 411 in the optical path in the illumination unit 41. The tilting means 416 is provided between the first birefringent section 411 and the target T in the optical path.

[0107] The light reflecting unit 42 includes tilting means 422 and tilting means 423. The tilting means 422 refracts light that is reflected by the target T and travels toward the second birefringent unit 412. The tilting means 422 is provided before the second birefringent unit 412 in the optical path in the light reflecting unit 42. The tilting means 422 is provided between the target T and the second birefringent unit 412 in the optical path. The tilting means 423 refracts light that passes through the third birefringent unit 413 and travels toward the target T. The tilting means 423 is provided beyond the third birefringent unit 413 in the optical path in the light reflecting unit 42. The tilting means 423 is provided between the third birefringent unit 413 and the target T in the optical path.

[0108] The displacement detection unit 43 includes tilting means 431 that refracts light that is reflected by the target T and travels toward the fourth birefringent unit 414. The tilting means 431 is provided before the fourth birefringent unit 414 in the optical path in the displacement detection unit 43. The tilting means 431 is provided between the target T and the fourth birefringent unit 414 in the optical path.

[0109] In this way, even if the illumination unit 41 and the displacement detection unit 43 are not tilted and the optical axis A-A' of the outward path and the optical axis B-B' of the return path are parallel, the tilting means 416, 422, 423, and 431 can be provided to make the optical axis A-A' of the outward path and the optical axis B-B' of the return path intersect. According to the displacement detection device 4A of this modified example, the optical path can be designed regardless of the posture of the illumination unit 41, etc., which simplifies the layout and manufacturing of the displacement detection device 4. The tilting means 416, 422, 423, and 431 are realized by optical components such as triangular prisms and mirrors. The tilting means 416, 422, 423, and 431 preferably have the same refractive index (inclination angle of light), but may have different refractive indices. The number of tilting means is not limited to four. The tilting means only needs to be provided so that the optical axis AA' of the outgoing path and the optical axis BB' of the returning path intersect, and the position and number of the tilting means are not limited to the example shown in the figure.

[0110] Fifth Embodiment 21 is a front view showing the configuration of a displacement detection device according to a fifth embodiment. In the displacement detection device according to the first embodiment, one displacement detection device measures the displacement of the target in the Z direction. In contrast, in the displacement detection device according to the fifth embodiment, two displacement detection devices arranged opposite each other measure the displacement of the target in the Z direction. These two displacement detection devices are configured to cancel out displacement errors when the target is tilted around the Y axis.

[0111] The displacement detection device 5 includes a main displacement detection device 51 and a sub-displacement detection device 52. Both the main displacement detection device 51 and the sub-displacement detection device 52 have the same configuration as the displacement detection device 1 of the first embodiment. However, the main displacement detection device 51 and the sub-displacement detection device 52 may have the same configuration as the displacement detection devices of the second to fourth embodiments. The main displacement detection device 51 and the sub-displacement detection device 52 are arranged point-symmetrically around the center of the target T. The main displacement detection device 51 is provided so that light is reflected in an area of ​​the target T that is more in the +Y direction than the center. The sub-displacement detection device 52 is provided so that light is reflected in an area of ​​the target T that is more in the -Y direction than the center.

[0112] FIG. 22 is a diagram showing the change in the optical path when the target is tilted around the Y axis. Assume that the target T, which was originally horizontal as shown by the dashed line in the figure, is tilted around the Y axis as shown by the solid line. In this case, the angle of incidence θ1 and the angle of reflection θ2 of the light irradiated from the illumination unit change. As a result, the position at which the reflected light passes through the second birefringent unit 121 changes, and the phase of the light changes. This may result in the displacement detection device detecting that the target T has been displaced in the Z direction even though the target T has not been displaced in the Z direction, i.e., a measurement error may occur.

[0113] 21 , in the displacement detection device of the fifth embodiment, a secondary displacement detection device 52 is provided to cancel out measurement errors of the primary displacement detection device 51. More specifically, when the target T tilts around the Y axis, the phase of the light irradiated from the primary displacement detection device 51 changes. On the other hand, when the target T tilts around the Y axis, the phase of the light irradiated from the secondary displacement detection device 52 changes in the same way as the primary displacement detection device 51. However, the secondary displacement detection device 52 is provided so as to generate a phase change that is opposite to the phase change of the light irradiated from the primary displacement detection device. Therefore, although the phases of the lights irradiated from the primary displacement detection device 51 and the secondary displacement detection device 52 both change, the phase change can be canceled out by adding up the phase changes of these lights. In other words, the tilt of the target T can be canceled out. In addition, the displacement detection device can detect only the phase change, i.e., the tilt of the target T, by calculating the difference between the phase changes of the lights from the primary displacement detection device 51 and the secondary displacement detection device 52. As described above, according to the displacement detection device 5 of the fifth embodiment, by measuring the displacement of the target T in the Z direction based on the displacement information of the main displacement detection device 51 and the displacement information of the sub-displacement detection device 52, it is possible to suppress measurement errors in the Z direction that may occur when the target T is tilted around the Y axis. Note that, in the displacement detection device 5 of the fifth embodiment as well, each birefringent portion may be composed of a single birefringent portion, as described in the modified example of the first embodiment.

[0114] Sixth Embodiment 23 is a front view showing the configuration of a displacement detection device of the sixth embodiment. The displacement detection device 6 of the sixth embodiment differs from the above-described embodiments in that it includes a scanning mechanism 65 that can change the reflection position of light on the target, and a displacement information output unit 66. The scanning mechanism 65 is applicable to all of the above-described embodiments, but the following description will be given based on the displacement detection device of the third embodiment as an example.

[0115] First, the configuration of the scanning mechanism 65 will be described. The scanning mechanism 65 is included in the illumination unit 61. The scanning mechanism 65 is provided between the light source 611 and the first birefringent unit 614 in the optical path. The scanning mechanism 65 scans the surface of the target T with light from the light source 611. More specifically, the scanning mechanism 65 includes an optical scanning unit 651 and a lens 652.

[0116] The optical scanning unit 651 is provided between the light source 611 and the lens 652 in the optical path. The optical scanning unit 651 includes, for example, a polygon mirror, a driving device for rotating the polygon mirror, and a rotary encoder for detecting the rotation angle of the polygon mirror. Note that the optical scanning unit 651 is not limited to a configuration including a polygon mirror. The optical scanning unit 651 may include a galvanometer mirror, a MEMS mirror (Micro Electro Mechanical Systems Mirror), etc. The lens 652 is provided between the optical scanning unit 651 and the first birefringent unit 614 in the optical path. The lens 652 is, for example, a collimator lens.

[0117] Next, a description will be given of how the scanning mechanism 65 changes the reflection position of light on the target T. Light emitted from the light source 611 passes through the polarizer 612 and the beam splitter 613, and reaches the optical scanning unit 651. The optical scanning unit 651 reflects the light received from the light source 611 in various directions. The optical scanning unit 651 changes the reflection angle of the light received from the light source 611 in various ways. In this example, the light from the light source 611 is irradiated onto a polygon mirror that is rotated by a driving device, and the light is reflected in various directions. The scanning mechanism 65 can move the optical path incident on the lens 652 in the Y direction. The light reflected by the optical scanning unit 651 is incident on the lens 652.

[0118] The lens 652 makes the incident light parallel to the X direction. As a result, even if the incident position on the lens 652 is changed by the light scanning unit 651, the light that has passed through the lens 652 remains parallel to the X direction. The light that has passed through the lens 652 is incident on the first birefringent unit 614. The optical path of the light after it has entered the first birefringent unit 614 is the same as in the third embodiment, and therefore will be briefly described below.

[0119] The light (first light L1 and second light L2) that passes through the first birefringent section 614 is reflected by the target T. The first light L1 and second light L2 reflected by the target T pass through the second birefringent section 621. At this time, if the target T is displaced in the Z direction, the incident positions of the first light L1 and second light L2 reflected by the target T onto the second birefringent section 621 will be different from those before the target T was displaced. The birefringent section changes the phase difference that occurs in each polarization component depending on the incident position. The first light L1 and second light L2 with this phase difference are reflected by the reflecting means 622. The first light L1 and second light L2 reflected by the reflecting means 622 return along the same path as the outward path. The first light L1 and second light L2 are reflected by the beam splitter 613 and reach the displacement detecting section 63. The processing in the displacement detecting section 63 is the same as in the above-described embodiment and will not be described.

[0120] Next, we will explain the displacement information output unit 66. The displacement information output unit 66 links the reflection position of light moved by the scanning mechanism 65 with the calculated displacement of the target T. To achieve this function, the displacement information output unit 66 includes each functional unit described below.

[0121] The displacement information output unit 66 includes a displacement information unit 661 that acquires the displacement of the target in the measurement direction calculated by the displacement detection unit 63. For explanation purposes, consider the optical path indicated by the solid line in the figure. In this case, the reflection position of the first light L1 and the second light L2 on the target T is position P1. The displacement detection unit 63 calculates the displacement of the target T in the Z direction at position P1. The displacement detection unit 63 sends the calculated displacement information of the target T at position P1 to the displacement information unit 661. The displacement information unit 661 sends the acquired displacement information to the output unit 664. In addition, the scanning mechanism 65 sends rotation angle information of the polygon mirror when the first light L1 and the second light L2 follow the optical path indicated by the solid line to the displacement information output unit 66 (angle information unit 662).

[0122] The angle information unit 662 is connected to the rotary encoder of the scanning mechanism 65. The angle information unit 662 acquires the rotation angle of the polygon mirror based on a signal from the rotary encoder. That is, the angle information unit 662 acquires information for identifying the optical path traveled by the scanning mechanism 65. The angle information unit 662 sends the acquired information to the Y-direction position calculation unit 663.

[0123] The Y-direction position calculation unit 663 calculates the Y-direction position information of the light reflection position P1 on the target T based on the information received from the angle information unit 662. The Y-direction position calculation unit 663 sends the calculated position information to the output unit 664.

[0124] The output unit 664 associates the information on the light reflection position P1 acquired from the Y direction position calculation unit 663 with the Z direction displacement information of the target T at position P1 acquired from the displacement information unit 661. The output unit 664 outputs the associated information, i.e., the Z direction displacement information of the target T at position P1.

[0125] The displacement information output unit 66 executes this process each time the light reflection position moves, and as a result, it is possible to obtain displacements in the Z direction (YZ data) at multiple positions on the target T that are shifted in the Y direction.

[0126] <Variation 1> The accuracy of the components that make up the displacement detection device 6, such as the lens and birefringent portion, and the tilt of the stage on which the target T is placed, affect the measurement of the displacement in the Z direction of the target T. To reduce this effect, the displacement detection device 6 may be configured as follows.

[0127] The displacement information output unit 66 may include a memory unit 665 in which calibration data is stored. The calibration data is data for eliminating errors when measuring the displacement of the target T in the Z direction. The calibration data is stored in advance in the memory unit 665. The calibration data can be obtained, for example, as follows.

[0128] First, a reference mirror having a highly accurate reference surface is placed in place of the target T. The reference mirror may be a mirror whose reference surface flatness is known in advance. Next, the displacement detection device 6 measures YZ data for this reference mirror in the same manner as described above. The displacement detection device 6 stores the measurement results (YZ data) of the reference mirror in the memory unit 665 as calibration data.

[0129] Thereafter, target T is placed in place of the reference mirror. The displacement detection device 6 measures the YZ data of target T in the same manner as described above. After obtaining the YZ data of target T, the output unit 664 obtains calibration data from the memory unit 665. The output unit 664 subtracts the calibration data from the YZ data of target T. The calibration data includes information about the reference mirror used and information about the accuracy of each component of the displacement detection device 6, the tilt of the base, and the like. The measured YZ data of target T includes information about the target to be measured in addition to this information. Because the reference mirror has a highly accurate reference surface, its flatness can be substantially ignored. Therefore, by subtracting the calibration data from the YZ data of target T, it is possible to extract only the information about target T to be measured. Therefore, the displacement detection device 6 according to the first modification can measure the displacement of target T in the Z direction with higher accuracy.

[0130] <Variation 2> 24 is a front view showing the configuration of a displacement detection device according to Modification 2 of the sixth embodiment. In the above-mentioned Modification 1, the case where the displacement detection device moves the displacement measurement position on the target T in the Y direction has been described. The displacement detection device according to Modification 2 can move the displacement measurement position in the X direction as well as the Y direction. Below, the configuration of the displacement detection device according to Modification 2 that differs from that of the displacement detection device according to Modification 1 will be described, based on the displacement detection device according to Modification 1.

[0131] The displacement detection device 6 includes a movable stage 67 that moves the target T in the X direction. The movable stage 67 is disposed below the target T. The movable stage 67 supports the target T. The movable stage 67 is configured to be movable in the X direction by a feed mechanism (not shown). The feed mechanism is, for example, a linear slider. A linear encoder is attached to the movable stage 67. With this configuration, the displacement measurement position (light reflection position) on the target T in the Z direction can be moved not only in the Y direction but also in the X direction.

[0132] The displacement information output unit 66 includes an X-direction position calculation unit 666 that acquires information about the X-direction of the light reflection position. The X-direction position calculation unit 666 calculates the X-direction information about the light reflection position based on a signal from a linear encoder attached to the movable stage 67. The X-direction position calculation unit 666 sends the calculated X-direction information to the output unit 664.

[0133] The output unit 664 links the information on the light reflection position P1 acquired from the X-direction position calculation unit 666, the information on the light reflection position P1 acquired from the Y-direction position calculation unit 663, and the Z-direction displacement information of the target T at position P1 acquired from the displacement information unit 661. The output unit 664 outputs the linked information, i.e., the Z-direction displacement information of the target T at position P1. The displacement information output unit 66 executes this processing each time the light reflection position moves. As a result, it is possible to obtain Z-direction displacements (XYZ data) at multiple positions on the target T that are shifted in the X and Y directions.

[0134] The output unit 664 may calibrate the measurement data in the same manner as in Modification 1. The movable stage 67 may also move in the Y direction. In this case, the movable stage 67 may move the reflection position of light in the Y direction instead of the scanning mechanism 65. The movable stage 67 may also rotate the target T. That is, the displacement measurement position in the Z direction may be specified by polar coordinates (r-θ-Z data) instead of XY coordinates.

[0135] The above-described embodiments are illustrative in all respects and are not limiting. Modifications and variations are possible for those skilled in the art. The scope of the present invention is defined not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention includes modifications from the embodiments within the scope of the claims and their equivalents.

[0136] For example, in the above-described embodiment, the case where the measurement object on which the target is set is the surface of a semiconductor wafer has been described. However, the measurement object is not limited to the surface of a semiconductor wafer. For example, the measurement object may be the processed surface of a photomask, the side surface of a photomask, the surface of raw glass, the side surface of raw glass, the surface of a semiconductor wafer coated with resist, the surface of a Si, SiC, or GaN ingot, the surface of a mirror or lens, the surface of a linear scale, the surface of a film, a ground surface, or the like. The target is set on a part of these measurement objects. Furthermore, the target is not limited to the surface of the measurement object itself. The target may be a reflective member that displaces with the displacement of the measurement object. In short, the target may be anything that reflects light.

[0137] For example, in the displacement detection device of each of the above-described embodiments, the first birefringent section may be separate from the fourth birefringent section or may be integrated with it. The second birefringent section may be separate from the third birefringent section or may be integrated with it. Furthermore, in the displacement detection device, the illumination section, displacement detection section, and displacement information output section 14 may be configured to be distributed separately from the light reflecting section 12 or may be configured to be distributed as a single unit.

[0138] For example, in the displacement detection device of each of the above-described embodiments, the displacement direction of the target, i.e., the measurement direction, is the Z direction. However, the measurement direction may be the X direction or the Y direction. When the measurement direction is the X direction or the Y direction, the components of the displacement detection device are appropriately positioned so that the displacement of the target in the X direction or the Y direction can be measured.

[0139] For example, in each of the above-described embodiments, the first light and the second light that pass through the second birefringent section are described as being parallel. However, the first light and the second light that pass through the second birefringent section do not have to be parallel. In short, the displacement detection device only needs to be configured so that the first light and the second light that are separated by the first birefringent section are ultimately superimposed in the fourth birefringent section. The refraction angles of the first light and the second light in the second birefringent section and the third birefringent section can be set in various ways within the range in which the first light and the second light are superimposed in the fourth birefringent section.

[0140] For example, in each of the above-described embodiments, the projection optical device and the displacement detection device are provided as separate devices, but the projection optical device and the displacement detection device may be integrated. [Explanation of symbols]

[0141] 1: Displacement detection device 11: Lighting department 12:Light reflecting part 13: Displacement detection unit 14: Displacement information output section 111: Light source 112: Collimator lens 113: Polarizer 114: First birefringent portion 114A: Birefringent section 114B: Birefringent part 121: Second birefringent portion 121A: Birefringent section 121B: Birefringent part 122: Reflective material 123: Third birefringent section 131: Fourth birefringent section 132: Phase plate 133: Condenser lens 134: Beam splitter 135: Polarizing beam splitter 136: Polarizing beam splitter 137A: Photodetector 137B: Photodetector 137C: Photodetector 137D: Photodetector 141: Differential amplifier 142: Differential amplifier 143: A / D conversion section 144: A / D conversion section 145: Waveform correction processing unit 146: Incremental signal generator L1: 1st light L2 :Second light T: Target

Claims

1. A displacement detection device that detects a displacement of a target in a measurement direction, A light source that emits light; a first birefringent unit that is provided on an optical path from the light source to a target onto which the light is irradiated, and that splits the light into a first light and a second light having a phase difference with respect to the first light; a second birefringent portion that is provided on optical paths of the first light and the second light reflected by the target and that refracts the first light and the second light; a third birefringent section that is provided on an optical path of the first light and the second light that have passed through the second birefringent section and that condenses the first light and the second light; a fourth birefringent section that is provided on optical paths of the first light and the second light that have passed through the third birefringent section and that superimposes the first light and the second light; a displacement detection unit that detects a displacement of the target in the measurement direction based on a change in a phase difference between the first light and the second light that have passed through the fourth birefringent unit, a displacement detection device, wherein the second birefringent section and the third birefringent section are configured to change a phase difference between the first light and the second light in accordance with movement of the target in a measurement direction;

2. The displacement detection device according to claim 1 , the first light and the second light that have passed through the third birefringent portion are reflected again by the target, The fourth birefringent portion a displacement detection device provided on the optical paths of the first light and the second light reflected by the target;

3. The displacement detection device according to claim 1 , At least one of the first birefringent portion, the second birefringent portion, the third birefringent portion, and the fourth birefringent portion is A displacement detection device whose thickness varies depending on the position in the plane of the incident plane wave of light.

4. The displacement detection device according to claim 1 , At least one of the first birefringent portion, the second birefringent portion, the third birefringent portion, and the fourth birefringent portion is A displacement detection device that is composed of two birefringent parts having optical axes that are perpendicular to each other.

5. The displacement detection device according to claim 1, further comprising: a scanning mechanism for changing the positions at which the first light and the second light are irradiated on the target; The displacement detection unit a displacement detection device that detects displacements in the measurement direction at a plurality of positions on the target;

6. The displacement detection device according to claim 1, further comprising: a displacement information output unit that outputs the displacement of the target in the measurement direction detected by the displacement detection unit, The displacement information output unit a displacement detection device that calibrates the displacement of the target in the measurement direction based on preset calibration data, and outputs the calibrated displacement of the target in the measurement direction;

7. A projection optical apparatus that transfers a pattern onto a measurement object including a target, a mask on which a pattern to be transferred to the measurement object is formed; an exposure light source that exposes the measurement object through the mask; a light source that is different from the exposure light source and emits light; a first birefringent unit that is provided on an optical path from the light source to a target onto which the light is irradiated, and that splits the light into a first light and a second light having a phase difference with respect to the first light; a second birefringent portion that is provided on optical paths of the first light and the second light reflected by the target and that refracts the first light and the second light; a third birefringent section that is provided on an optical path of the first light and the second light that have passed through the second birefringent section and that condenses the first light and the second light; a fourth birefringent section that is provided on optical paths of the first light and the second light that have passed through the third birefringent section and that superimposes the first light and the second light; a displacement detection unit that detects a displacement of the target in the measurement direction based on a change in a phase difference between the first light and the second light that have passed through the fourth birefringent unit, a second birefringent section configured to change a phase difference between the first light and the second light in accordance with movement of the target in a measurement direction;

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