JP2009041921A - Fine shape measuring device - Google Patents

Abstract

An optical system is simplified, and disturbances such as thermal expansion, vibration, and movement of a mechanism are removed, thereby realizing highly reliable and accurate measurement of a fine shape.
Splitting means for splitting monochromatic light into measurement light that travels in the direction of a measurement surface and reference light that travels in a direction orthogonal to the measurement light, and the reference light as measurement light. Reflecting means 17 that reflects in a parallel direction, measuring light 15 reflected by the dividing means 7 in the direction opposite to the reference light 9 after being reflected by the measuring surface, and reflected by the measuring surface A fine shape measuring apparatus based on a Michelson interferometer provided with a synthesizing means 16 for synthesizing the reference light 19 returned in a direction parallel to the measuring light 14, wherein the measuring surface 13 is a right-angle trihedral mirror. The mirror surface portions M ₁ , M ₂ , and M ₃ corresponding to the right-angled three-way mirror are arranged in the optical path of the reference light 18 reflected by the reflecting means 17 so as to correspond to the corner point O.
[Selection] Figure 9

Description

  The present invention relates to a fine shape measuring apparatus, and more particularly to a fine shape measuring apparatus suitable for application to the measurement of the surface roughness of processed parts and the fine shapes of a lattice, scale, microlens, and the like.

  As a conventional fine shape measuring device, a heterodyne laser interferometer directly measures the coordinates of the fine shape in the horizontal direction (X axis) and the vertical direction (Z axis or height direction) numerically. 1 and 2.

  FIG. 1 shows an outline of this fine shape measuring apparatus, and the amount of movement in the horizontal direction of an X-axis stage on which a measurement object is placed is measured by an X-axis interferometer. The Z-axis interferometer 100 is fixed to a top plate 102 supported by a side plate 101 constituting the apparatus frame, and reflected light when a laser is projected onto a measurement object via the objective lens by the interferometer. The height or depth of the fine surface shape is measured based on the above. A microscope that moves integrally therewith is attached to the back of the Z-axis interferometer. This is used to select a sample measurement location in advance before the start of measurement, and can be switched by sliding alternately with a Z-axis interferometer.

  Further, as another fine shape measuring apparatus, Patent Document 1 describes an atomic force microscope using a heterodyne interferometer shown in FIG.

The output from the linearly polarized laser oscillator 50 is converted to S-polarized light by the optical isolator 52 and branched into measurement light and reference light by the beam splitter 54. The reference light subtracted by the acousto-optic modulator 56 (80.0 MHz) and the acousto-optic modulator 58 (80.1 MHz) and modulated by 100 kHz, and the measurement light converted to P-polarized light by the half-wave plate 60 are: The beams are combined again by the polarization beam splitter 62. If the frequency of the measurement light is fp and the frequency of the reference light is fs, the interference frequency fB of these two lasers transmitted through the beam splitter 64 and interfered by the polarizing plate 65 and detected by the photoelectric converter 66 is
fB = | fp−fs | (= 100 kHz)
It is expressed.

  On the other hand, the light reflected by the beam splitter 64 passes through the beam expander 68 and the mirror 70 and enters the bifocal lens 72, and is again divided into measurement light and reference light.

  As shown in FIG. 3, the bifocal lens 72 is a triplet lens in which calcite 80, which is a uniaxial birefringent crystal material, is sandwiched between optical glasses 82, and the focal length varies depending on the polarization direction of incident light. The focal length with respect to the ordinary ray 84 is almost infinite, the focal length with respect to the extraordinary ray 86 is finite, and it is designed to match the position 88 of the front focal point of the objective lens 74.

  Of the incident light rays, rotate the bifocal lens 72 around the optical axis so that the P-polarized component (measurement light) corresponds to ordinary light and the S-polarized component (reference light) corresponds to extraordinary light. Separate light and reference light. The reference light emitted from the objective lens 74 is irradiated on the surface of the sample 75 as a parallel light beam, and the measurement light is focused on the surface of the cantilever 76.

  The reflected light of the measurement light from the cantilever 76 and the reflected light of the reference light from the surface of the sample 75 change as follows under the influence of the surface roughness and disturbance.

Measuring light: fp + Δfp + Δfd
Reference beam: fs + Δfd

  Here, Δfp is a frequency change component due to the deflection of the cantilever 76, that is, the surface roughness of the sample 75, and Δfd is a frequency change component due to disturbance. The two reflected lights pass through the objective lens 74, the bifocal lens 72, the mirror 70, the beam expander 68, and the beam splitter 64, are interfered by the polarizing plate 77, and are beat signals (frequency fD) by the measurement photoelectric converter 78. ) Is detected. The detected frequency fD is canceled by the frequency change component Δfd caused by the disturbance common to both, and becomes fD = | fp−fs + Δfp |, and this and the reference frequency fB detected by the reference photoelectric converter 66. Thus, a frequency change component Δfp due to only pure surface roughness is obtained. The displacement Zs is expressed by the following equation.

Zs = (λ / 2) ∫Δfpdt
Δfp is counted as a phase difference between the reference light and the measurement light.

JP-A-7-83608 Tanimura, Toyota: Non-contact fine shape measuring device using laser interferometer, precision machine, 50, 10 (1984) 87/91. Y. Tanimura, K.M. Toyoda: Micro-Shapes and Their Edge Signals Measured by Laser Interferometer, Proceeding of the ISMQC, (Tokyo 1984) 158/163. Tanimura, Yamamoto: Laser interference lead screw lead measuring instrument, precision machine, 37, 9 (1971) 31/37. Y. Tanimura, A.M. Yamamoto: Lead Measuring Machine for Leadscrews with Laser Interferometer, Bull. of JSPE, 6, 2 (1972) 45/50.

  However, the fine shape measuring devices described in Non-Patent Documents 1 and 2 have the following problems.

  1) In the structure of the fine shape measuring apparatus shown in FIG. 1, the frame top plate 102, the side plate 101, etc. are affected by thermal expansion, and the distance from the interferometer body 100 to the surface of the measurement object changes slowly with time. Therefore, measurement with high reliability cannot be performed.

  2) With the arrangement of the interferometer main body 100 of the fine shape measuring apparatus shown in FIG. 1, no matter how strong the apparatus frame is made, if the force is applied to the frame top plate 102, the whole is deformed. Since the distance to the surface of the measurement object changes slightly, high-precision measurement cannot be performed.

  3) When the motor is driven and the X stage is moved or stopped, vibrations from the motor and fluctuations in torque transmission affect the movement of the X stage, causing a phenomenon of floating or sinking. FIG. 4 shows an example of the measurement result of the step sample (measurement object) in which the influence appears, and it can be seen that the shape measurement is adversely affected. For reference, FIG. 5 shows an example of measurement results when those adverse effects do not appear.

  Further, the atomic force microscope described in Patent Document 1 has the following problems.

  1) Since a special optical system designed exclusively for use as shown in FIGS. 2 and 3 is employed, the optical system is complicated as a whole, and costs increase.

  2) The use of a Fizeau interferometer has the advantage that the reference light and the measurement light pass through almost the same optical path and are optically stable. However, in general, in the case of measurement of a processed surface having irregularities, the reference light incident as parallel light on the surface of the object to be measured is reflected and used again as reference light, so that the wavefront is disturbed by the irregularities on the surface. For this reason, the S / N ratio of the interference signal is lowered, the surface roughness of the measurement object is limited, and the measurement is limited to measurement of minute unevenness on the surface close to the mirror surface.

  3) The stray light of the measurement light reflected on the cantilever type stylus mirror is mixed in the reference light. In addition, the intensity of the reference light is reduced only in the portion blocked by the cantilever.

  The present invention was made to solve the above-mentioned conventional problems, and after simplifying the optical system, it eliminates (reduces) the influence of disturbances such as thermal expansion, vibration, and fluctuations in the motion performance of the mechanism, It is an object of the present invention to provide a highly reliable and highly accurate fine shape measuring apparatus.

  The present invention provides a splitting unit that divides monochromatic light into measurement light traveling in the direction of the measurement surface and reference light traveling in a direction orthogonal to the measurement light, and reflects the reference light in a direction parallel to the measurement light. And reflecting light reflected by the measurement surface and then reflected by the dividing means in a direction opposite to the reference light and returned in a direction parallel to the measurement light reflected by the measurement surface. A fine shape measuring apparatus based on a Michelson interferometer, comprising: a combining means for combining the reference light, wherein the measuring surface is made to correspond to a corner point of a right-angled trihedral mirror and reflected by the reflecting means. By disposing each mirror surface portion corresponding to the right-angled trihedral mirror in the optical path of the reference light, the above-mentioned problem is solved.

  In the present invention, when one side of the equilateral triangular section of the right-angled trihedral mirror is a, the objective is applied to a circular space having a diameter smaller than a / 3 centered on the corner point on the incident side of the measurement light from the corner point. A lens may be arranged. In this case, a stylus sensor having a stylus provided with a reflecting mirror on the back surface is disposed corresponding to a corner point with the reflecting mirror as the measurement surface, and the focal point of the objective lens is the measurement point. You may make it correspond to a surface.

  In the present invention, the dividing unit, the reflecting unit, and the combining unit may be fixed to a frame top plate supported by a frame side plate fixed on the base.

  According to the present invention, each of the mirror surface portions is fixed to each of three orthogonally laminated plates included in a right-angled three-sided frame integrally formed, and the outer side of the side wall of the right-sided three-sided frame has an upper end on the frame top plate. The fixed support plate may be supported by leaf springs, respectively. In this case, the lower end of the right-angled three-sided frame is slidable on a stage that can move horizontally on the base. It may be supported by.

  Here, the principle of the present invention will be described first.

The greatest point in the present invention is as follows. That is, as described in Non-Patent Documents 3 and 4,
(1) In the optical path of the right-angled trihedral mirror 1 whose image is shown in FIG. 6, the right-angled three surfaces (AOB, AOC, BOC) that are orthogonal to each other are rotated around the corner point O that is the intersection of the three planes. be reflected three times by the right-angle triple mirror 1 from the base point M ₀ of the incident light, the sum of the optical path length traveling is reflected in a direction parallel to the incident light again, from the base point O ₂ of the incident direction corresponding to M ₀ Equal to the round trip optical path to corner point O. That is,
M ₀ M ₁ + M ₁ M ₂ + M ₂ M ₃ + M ₃ M ₄ = 2OO ₂
It has the unique property of being.

On the other hand, M ₀ M ₁ = O ₁ O ₂ = M ₃ M ₄ . Therefore,
M ₁ M ₂ + M ₂ M ₃ = 2OO ₁
The point that uses the geometrical optical property.

(2) On the other hand, when the right-angled trihedral mirror 1 in FIG. 6 is viewed from the direction (front) where the laser is incident, the cut (end) surface of the right-angled trihedral mirror 1 has a side length of a as shown in FIG. An equilateral triangle ABC is formed. FIG. 8 is a side view thereof. In FIG. 7, there is a circular (cylindrical) space having a diameter a / 3 around the corner point O that does not obstruct the optical paths M ₁ M ₂ and M ₂ M ₃ . Non-Patent Documents 3 and 4 describe that a long screw measuring device is realized using this principle.

In the present invention, using these two geometric optical properties of the right-angle trihedral mirror 1 described above, the reference light in the Michelson interferometer is placed in the optical path of M ₁ M ₂ + M ₂ M ₃ , and the measurement light is placed in 2OO ₁ . By adopting a structure in which an objective lens having a diameter smaller than a / 3 is arranged in a space centered on a corner point O which corresponds to the optical path and does not obstruct the optical paths M ₁ M ₂ and M ₂ M ₃ , a laser interferometer The right-angled trihedral mirror 1 is used as a reflector for measuring the length of the beam, and its optical path and its geometrical optical properties are used skillfully to realize a “fine shape measuring device robust against disturbance”.

  According to the present invention, the right-angled three-plane that “the sum of the optical path lengths that repeat the incidence and reflection three times with the right-angled trihedral mirror is equal to the round-trip distance of the optical path length from the base point at the same position as the first incident point to the corner point” By utilizing the geometric optical properties of the mirror 1 and making the respective optical path lengths correspond to the reference light and the measurement light of the Michelson interferometer, it is possible to provide a fine shape measurement device that is robust against disturbance.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  9 is a front view of the fine shape measuring apparatus according to the embodiment of the present invention as viewed in the optical axis section, FIG. 10 is a side view of the measuring apparatus in FIG. 9 as viewed in section AA ′, and FIG. It is the top view which saw through the measuring apparatus of No. 9 centering on the optical path below from a BB 'section. FIG. 12 is a right-angle three-plane frame canopy when the measuring apparatus of FIG.

  For convenience, the description will be made from the right-angle three-plane frame canopy 2 shown in FIG.

  The canopy 2 is a plate member that covers a part of the cross-section corresponding to the equilateral triangle ABC of the right-angled trihedral mirror shown in FIG. 7, and the first hole 3 into which the laser is incident and the laser is reflected and emerges. The second hole 4 and a fixing screw 5 for fixing an objective lens to be described later are penetrated.

  Next, the configuration of the optical system will be described.

The entire optical system forms a Michelson interferometer. In FIG. 9, the linearly polarized light 6 emitted from the laser light source and set at an angle of 45 ° is a P-polarized light component having a vibration plane parallel to the paper surface at point O ₂ of the polarizing beam splitter (splitting means) 7. It is separated (divided) into two parts, that is, a measurement light (8) and an S-polarized component (reference light) 9 having a vibration plane perpendicular to (perpendicular to) the paper surface.

  After passing through the polarization beam splitter 7, the P-polarized component 8 is converted to circularly polarized light 11 by the λ / 4 plate 10. The laser of the circularly polarized light 11 is focused to the point O on the measurement target surface (measurement surface) 13 by the objective lens 12 fixed to the right-angled three-plane frame canopy 2. The O point is also in a spatial position that corresponds geometrically to the O point of the corner point of a right-angled trihedral mirror. In the following description, the measurement target surface 13 means not only the upper surface to be measured but also the object itself.

The laser of the circularly polarized light 14 reflected from the measurement target surface 13 corresponds to measurement light in the optical system of the Michelson interferometer, and when it passes through the λ / 4 plate 10 again, this time becomes the S-polarized light component 15, and the polarization beam splitter 7 The light is reflected at the point O _{2 and the} point M _{4 of the} polarization beam splitter 16 and travels in the P direction.

On the other hand, the S-polarized light component 9 reflected in the direction orthogonal to the P-polarized light component 8 at the O ₂ point of the polarizing beam splitter 7 is reflected in the direction parallel to the P-polarized light component 8 at the M ₀ point of the right-angle prism (reflecting means) 17. Similarly, the light passes through the λ / 4 plate 10 to become circularly polarized light 18 and is sequentially reflected by the _three plane mirrors (mirror surface portions) M ₁ , M ₂ , and M ₃ forming the right-angled trihedral mirror 1. The light passes again and becomes the P-polarized light component 19 and passes through the point M _{4 of the} polarizing beam splitter (combining means) 16. The overlapping components 15 and 19 pass through the polarizing plate 20 and generate interference fringes in Q.

  Next, the structure of the mechanism system will be described.

9, the three plane mirrors forming a right-angle triple mirror _{1 M 1, M 2, M} 3 is attached fixed to each other at right angles (perpendicular) plate surface of the three-clad plate 21, 22, 23. The adhesive plates 21, 22, and 23 form an integral right-angled three-plane frame 24, and the side plates 24A and 24A on both sides thereof are firmly attached to the support plates 27 and 28 via parallel leaf springs 25 and 26 that are paired on the left and right. It is fixed. The upper ends of the support plates 27 and 28 are fixed to the frame top plate 29 and supported. Accordingly, the right and left trihedral frame 24 is restrained from moving in the left-right direction by the parallel leaf springs 25 and 26, and is coupled and held in a state with some degree of freedom in the vertical direction.

  Legs 30 and 31 having hemispherical steel balls at the tip (lower end) are attached to the left and right below the bottom 24B of the right-angled three-plane frame 24, and are equidistant from each other with respect to the corner point O. The ends of the left and right steel balls respectively contact the reference planes 32 and 33 in a mirror state with a light force and are supported so as to be slidable. A light contact force is provided by two pairs of parallel leaf springs 25 and 26. The reference planes 32 and 33 are almost the same height as the measurement target surface 13. The reference planes 32 and 33 also mean the member itself in addition to the reference upper surface.

  The motor 34 moves the stage 36 on which the measurement target surface 13 and the left and right reference planes 32 and 33 are placed to the left and right via a coupling 35. The motor 34 is fixed on the base, and the stage 36 is placed so as to be movable in the horizontal direction on the same base. Therefore, when the motor 34 is driven and the stage 36 is moved left and right, the fine shape of the measurement target surface 13 is scanned and measured in a non-contact state. However, the unevenness of the measurable measurement target surface 13 depends on the magnification of the objective lens 12 as is clarified in Non-Patent Documents 1 and 2, and the amplitude of the objective lens having a magnification of 60 to 10 times It is limited to a range of 50 μm or less and an inclination of ± 5 ° or less.

  Although it is sufficient that the measurable range of the measurement target surface 13 is 50 μm in amplitude, the limitation on the inclination must be solved.

  Therefore, like the roughness measuring apparatus described in Patent Document 1, the stylus sensor 37 of FIG. 13 is appropriately attached to the lens barrel of the objective lens 12 fixed at the center of FIG. . The circular frame 38 of the stylus sensor 37 can be removed from the objective lens 12, and the measurement target surface 13 can be traced with the stylus 40 by being fixed to the lens barrel with a screw 39.

  A small reflecting mirror 41 is attached to the back surface of the stylus 40, and the position of the reflecting mirror is made to correspond to the corner point O, and the same position and the focal point of the objective lens 12 are made to correspond (match) to move the measurement target surface 13 up and down. (Unevenness) is measured. By this method, the limitation on the inclination of the fine shape of the measurement target surface 13 can be removed. The stylus 40 is supported by a leaf spring 42 joined to one end of the circular frame 38 so as to be movable up and down.

  With respect to the fine shape measuring apparatus of the present embodiment having the above-described optical system and mechanism system, the effects can be obtained with reference to the side view of FIG. 10 and the plan view of FIG. explain.

(1) Removal of disturbance (vertical movement, fine vibration, tilt) of the measurement object When the motor 34 is driven and the stage 36 is moved via the coupling 35, the stage 36 is moved up and down or slightly from outside. The vibration moves up and down in the reference planes 32 and 33, and moves the right-angle three-plane frame 24 up and down. The vertical movement of the right-angled three-plane frame 24 is mechanically absorbed by the flexibility of the parallel leaf springs 25 and 26.

On the other hand, since the measurement target surface 13 moves up and down by the same amount at the same time, as a result, the optical path length of the reference light: M ₀ M ₁ + M ₁ M ₂ + M ₂ M ₃ + M ₃ M ₄ and the optical path length of the measurement light: 2OO ₂ There is no relative change. Therefore, there is no influence on the measurement of the fine shape of the measurement target surface 13. Note that the fact that the optical path length in the space of M ₁ M ₂ + M ₂ M ₃ in FIG. 9 is equal to the optical path length of 2OO ₁ has already been described with reference to FIG. Yes.

  Further, even if the stage 36 moves while causing a slight change in inclination during movement, the corner point O of the measurement target surface 13 is located at the center of the left and right reference planes 32 and 33, so that the left and right reference points depend on the inclination. Even if there are different vertical displacements on the planes 32 and 33, the average value will have an effect, and the optical path lengths of the reference light and the measurement light will also change by the same amount, and will have no effect on the measurement of the fine shape of the measurement target surface 13. Not give.

(2) Removal of thermal expansion in the vertical direction of the frame side plate The influence of the left and right frame side plates 43 and 44, which support and fix the frame top plate 29 on the base, expands and contracts up and down due to temperature changes will be described.

First, for the sake of simplicity, the base point of expansion and contraction is set at a corner point O located on the measurement target surface 13. It is assumed that the frame side plates 43 and 44 are extended upward by ΔL due to thermal expansion. At this time, the O ₂ point of the polarization beam splitter 7 fixed to the frame top plate 29 is displaced upward by ΔL. Similarly, the M ₀ point of the right-angle prism 17 fixed to the frame top plate 29 and the M ₄ point of the polarization beam splitter 16 are also displaced upward by ΔL.

Therefore, the sum of the optical path lengths of O ₂ M ₀ + (M ₀ M ₁ + ΔL) + M ₁ M ₂ + M ₂ M ₃ + (M ₃ M ₄ + ΔL) corresponding to the reference light of the Michelson interferometer, and Since the optical path lengths of 2 (OO ₂ + ΔL) + O ₂ M ₄ corresponding to the measurement light are equal, there is no influence on the fine shape measurement of the measurement target surface 13.

  Strictly speaking, there is thermal expansion of the support plates 27 and 28, but the amount of thermal expansion can be represented by the frame side plates 43 and 44, assuming that they are made of the same material as the frame. Even if the materials are different from each other, it is considered to be an influence of the relative thermal expansion amount, so it is not necessary to consider the difference in materials.

(3) Removal of thermal expansion in the left-right direction of the frame top plate The effect of the frame top plate 29 expanding and contracting to the left and right due to temperature changes will be described. For simplicity, the expansion / contraction base point is set to a point O ₂ of the polarization beam splitter 7. As the temperature rises, the frame top plate 29 extends by an equal amount ΔL to the left and right. At this time, the sum of the optical path lengths corresponding to the reference light of the Michelson interferometer is O ₂ M ₀ + M ₀ M ₁ + M ₁ M ₂ + M ₂ M ₃ + M ₃ M ₄ + ΔL, and the optical path length corresponding to the measurement light The sum of 2OO ₂ + O ₂ M ₄ + ΔL changes equally.

  This is difficult to understand in the optical path of the right-angled trihedral mirror 1 in which the laser travels while reflecting in the three-dimensional space. Therefore, the right-angled mirror 45 in FIG. The change in the optical path length will be explained using a right-angled prism. In order to facilitate understanding of the correspondence, in FIG. 14, the optical components and positions that are considered to correspond to FIG. 9 are represented by the same reference numerals.

In FIG. 14, the optical path length of the reference light O ₂ M ₀ + M ₀ M ₁ + M ₁ M ₃ + M ₃ M ₄ before thermal expansion
= Optical path length of measuring light 2O ₂ O + O ₂ M ₄
It is.

If the frame top plate 29 extends ΔL to the left and right after thermal expansion, the optical path length of the reference light is O ₂ M ₀ ′ + M ₀ ′ M ₁ ′ + M ₁ ′ M ₃ ′ + M ₃ ′ M ₄ ′. The optical path length of is changed to 2O ₂ O + O ₂ M ₄ ′. Here, O ₂ M ₀ ′ = O ₂ M ₀ + ΔL, M ₀ ′ M ₁ ′ = M ₀ M ₁ −ΔL, M ₁ ′ M ₃ ′ = M ₁ M ₃ + 2ΔL, M ₃ ′ M ₄ ′ = M _It can be easily understood from FIG. 14 that ₃ M ₄ −ΔL and O ₂ M ₄ ′ = O ₂ M ₄ + ΔL.

After all, even after thermal expansion,
Optical path length of reference light O ₂ M ₀ '+ M ₀ ' M ₁ '+ M ₁ ' M ₃ '+ M ₃ ' M ₄ '
= Optical path length of measuring light 2O ₂ O + O ₂ M ₄ '
Thus, the measurement of the fine shape of the measurement target surface 13 is not affected by the thermal expansion of the frame top plate 29 in the left-right direction.

  However, if the right-angled mirror 45 in FIG. 14 has a thermal expansion amount to the left and right, the optical path length of the reference light is affected. Therefore, the right-angle three-plane frame canopy 2 and the adhesive plate 21 shown in FIGS. , 22, 23, and the right-angled three-plane frame 24 are effectively made of a low thermal expansion material such as invar.

  As mentioned above, according to this embodiment explained in full detail, the following effects can be acquired.

  (1) The sum of the optical path lengths that repeats incidence and reflection three times with a right-angle trihedral mirror is equal to the round-trip distance of the optical path length from the base point at the same position as the first incident point to the corner point. By utilizing the geometrical optical properties and making the respective optical path lengths correspond to the reference light and the measuring light of the Michelson interferometer, it is possible to provide a fine shape measuring device that is robust against disturbance.

  (2) When one side of the equilateral triangle of the cross section of the right-angled trihedral mirror 1 is a, the objective lens 12 having a diameter smaller than a / 3 is arranged in the geometric optical space centered on the corner point, thereby It is possible to prevent the optical path of the laser traveling forward by repeating the incidence / reflection three times with the mirror 1.

  (3) As shown in FIG. 13, the small reflecting mirror 41 attached to the back surface of the stylus 40 is made to correspond to the corner point O, and the focal point of the objective lens 12 coincides with the reflecting mirror 41. By attaching the stylus type sensor 37, the measurement point (corner point O of the right angled three-way mirror 1) and the measurement object (measurement target surface 13) more strictly than Abbe's principle. The measurement point O ′ can be completely aligned at one point in space. According to the Abbe principle known in the past, the scale and the measurement object are arranged in a straight line, so that each measurement point is always arranged at a position separated in space, so that it is easily affected by disturbance. Become.

(4) Measurement with reference light until linearly polarized laser beam (P-polarized component 8 and S-polarized component 9) divided into _two at O ₂ point of polarizing beam splitter 7 overlaps again at M ₄ point of polarizing beam splitter 16 Since the optical path lengths in the light space are exactly the same, it is possible to provide a Michelson interferometer optical system with a sufficiently improved visibility (visibility) when generating interference fringes.

  (5) When there is vertical movement due to ups and downs of the stage 36 on which the measurement object is mounted, fine vibrations from the outside, etc., the vertical movement of the right-angled three-plane frame 24 is mechanically absorbed by the two pairs of parallel leaf springs 25 and 26. The The measurement target surface 13 also moves up and down at the same time as the right-angled three-surface frame 24. That is, since the optical path lengths of the reference light and the measurement light of the right-angled trihedral mirror 1 are changed by equal amounts, it is possible to exhibit the characteristic that no influence is exerted on the fine shape measurement of the measurement target surface 13.

  (6) Even if the entire frame constituting the measuring apparatus is vertically expanded and contracted by thermal expansion with the position of the measurement target surface 13 as a base point, the frame top plate 29 is expanded and contracted by the thermal expansion and contraction with the polarizing beam splitter 7 as a base point. However, the reference optical path and the measurement optical path of the right-angled trihedral mirror 1 constituting the Michelson interferometer change in equal amounts. Therefore, there is a feature that the measurement of the fine shape of the measurement target surface 13 has no influence.

  (7) Even when the frame top plate 29 is deformed by applying an upper and lower external force, the optical path lengths of the reference light and the measurement light constituting the Michelson interferometer change equally. It has the characteristic that it does not have any influence.

Front view showing a fine shape measuring apparatus described in Non-Patent Document 1. The perspective view which shows the principal part of the atomic microscope described in patent document 1 Sectional drawing which expands and shows a part of FIG. Diagram showing the measurement result of the step sample when affected by disturbance by the fine shape measuring apparatus described in Non-Patent Documents 1 and 2 A diagram showing the measurement results of a step sample when there is almost no influence of disturbance by the fine shape measuring apparatus described in Non-Patent Documents 1 and 2. Image diagram showing a bird's-eye optical path of a right-angled trihedral mirror Front view from the incident direction showing the theoretical dimensions and optical path length of a right-angle trihedral mirror Side view showing the theoretical dimensions and optical path length of a right angled mirror The front view which shows typically the structure of the fine shape measuring apparatus of one Embodiment which concerns on this invention The side view which shows typically the structure of the fine shape measuring apparatus of one Embodiment which concerns on this invention The top view which shows typically the structure of the fine shape measuring apparatus of one Embodiment which concerns on this invention Plan view showing right-angle three-sided frame canopy Front view schematically showing a stylus sensor attached to an objective lens Diagram showing optical path change of right-angled mirror when frame top plate receives thermal expansion from side to side

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Right-angled trihedral mirror 2 ... Right-angled three-plane frame canopy 3 ... Hole which a laser injects 4 ... Hole which a laser reflects and exits 5 ... Screw for fixing an objective lens 6 ... Linearly polarized light set inclining at 45 degrees 7 ... Polarization beam splitter 8 ... P polarization component 9 ... S polarization component 10 ... λ / 4 plate 11 ... Circular polarization 12 ... Objective lens 13 ... Measurement surface 14 ... Circular polarization 15 ... S polarization component 16 ... Polarization beam splitter 17 ... Right angle prism DESCRIPTION OF SYMBOLS 18 ... Circularly polarized light 19 ... P-polarized light component 20 ... Polarizing plate 21, 22, 23 ... Pasting plate 24 ... Right angle three-plane frame 25, 26 ... Parallel leaf spring 27, 28 ... Support plate 29 ... Frame top plate 30, 31 ... Leg 32 , 33 ... reference plane 34 ... motor 35 ... coupling 36 ... stage 37 ... stylus type sensor 38 ... circular frame 39 ... screw 40 ... stylus 41 ... small reflector 42 ... leaf springs 43, 44 ... Frame side plate 45 ... Right-angled mirror

Claims (6)

Splitting means for splitting monochromatic light into measurement light traveling in the direction of the measurement surface and reference light traveling in a direction orthogonal to the measurement light;
Reflection means for reflecting the reference light in a direction parallel to the measurement light;
After being reflected on the measurement surface, the measurement light reflected in the direction opposite to the reference light by the dividing unit, and the reference light returned in a direction parallel to the measurement light reflected on the measurement surface; A fine shape measuring apparatus based on a Michelson interferometer, comprising:
The measurement surface corresponds to the corner point of a right-angled trihedral mirror,
A fine shape measuring apparatus, wherein each mirror surface portion corresponding to the right-angled trihedral mirror is arranged in the optical path of the reference light reflected by the reflecting means.   When one side of the equilateral triangular section of the right-angled trihedral mirror is a, the objective lens is arranged in a circular space smaller than the diameter a / 3 centered on the corner point on the incident side of the measurement light from the corner point. The fine shape measuring apparatus according to claim 1, wherein   A stylus-type sensor having a stylus with a reflecting mirror on the back is arranged corresponding to the corner point with the reflecting mirror as the measurement surface, and the focal point of the objective lens coincides with the measurement surface The fine shape measuring apparatus according to claim 2, wherein   The fine shape measuring apparatus according to claim 1, wherein the dividing unit, the reflecting unit, and the combining unit are fixed to a frame top plate supported by a frame side plate fixed on the base.   Each of the mirror surface portions is fixed to each of three orthogonally attached sticking plates included in an integrally formed right-angled three-sided frame, and the outer side walls of the right-sided three-sided frame are fixed to a support plate whose upper end is fixed to the frame top plate. The fine shape measuring device according to claim 1, wherein the fine shape measuring device is supported via a leaf spring.   6. The fine shape measuring apparatus according to claim 5, wherein a lower end of the right-angled three-plane frame is slidably supported on a stage movable in the horizontal direction on the base.

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