JP2010237183A - Low coherence interferometer and optical microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low coherence interferometer allowing highly accurate measurement regardless of measurement range with suppressing an influence of disturbance (e.g., temperature change, vibration) on measurement precision. <P>SOLUTION: The low coherence interferometer 1, for measuring a three-dimensional shape or a film thickness of a measured object 2 includes: a light source 11 emitting white light; an objective lens 14 which focuses the white light to the measured object and is movable in an optical axis direction, an optical multiplexer demultiplexer 16 which divides the white light into object light 3 irradiating the measured object 2 and reference light 4 irradiating a reference mirror 17 and combines the object light 3 reflected by the measured object and the reference light 4 reflected by the reference mirror 17 to output white interference light, a white light detector 20 detecting the white interference light output from the optical multiplexer demultiplexerr 16, and a movement amount measurement instrument 30 measuring a movement amount of the objective lens in the optical axis direction, in which the movement amount measurement instrument has a laser light source 31 emitting laser light and a reflective film 32 formed on the optical axis and reflecting the laser light. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a low coherence interferometer and an optical microscope. More specifically, the present invention relates to a low-coherence interferometer and an optical microscope that are used for three-dimensional shape measurement or film thickness measurement of a measurement target and precisely measure the interface position in the height direction through measurement of the amount of movement of the objective lens position.

  When measuring the amount of movement of the objective lens from the reference position in the optical axis direction (height direction: Z direction) in measuring the three-dimensional shape or film thickness of the measurement object, the Z-axis stage is moved in the height direction (Z direction). The distance between the objective lens and the objective lens was changed to measure the amount of movement of the objective lens position relative to the measurement object. (A) When using an actuator using a stepping motor as the Z-axis stage (moving range of about several hundred mm), the amount of movement depends on a precision linear scale (for example, a glass scale using a diffraction grating) attached to the actuator. (B) When a piezo actuator (moving range of about several hundred μm) was used as the Z-axis stage, it was measured by a capacitance sensor combined with the piezo actuator.

  When measuring the movement amount of the objective lens with the precision linear scale of (A) above, the movement amount to be measured is the movement amount on the optical axis of the objective lens, but the position where the precision linear scale is installed. Is far from the optical axis of the objective lens, there is a problem that the measurement accuracy is lowered due to the influence of disturbance (for example, temperature change or vibration). Further, when the movement amount of the objective lens is measured by the capacitance sensor (B), the measurement resolution of the capacitance sensor is proportional to the measurement range (generally proportional to about 0.03%). ), A problem that high measurement accuracy cannot be maintained when the measurement range becomes long, and the capacitance sensor is placed close to the optical axis of the objective lens, but is not strictly on the optical axis, so disturbance (for example, temperature change) There is a problem that the measurement accuracy is lowered due to the influence of vibration and vibration.

  Incidentally, a three-dimensional shape measuring apparatus that uses laser light for measuring the amount of movement of the objective lens in the optical axis direction has been proposed (for example, Patent Document 1). In this device, both a white light source (broadband light source) and a laser light source (coherent light source) are incident on the measurement target and the reference mirror, and the object light reflected by the measurement target and the reference light reflected by the reference mirror are combined. Then, white light interference fringes and laser light interference fringes are formed. At this time, the movement amount of the objective lens position with respect to the measurement object is obtained by the interference fringe of the laser light, and the surface position (that is, the surface shape) of the measurement object at each point on the XY plane is obtained by analyzing the interference fringe of the white light. By measuring the amount of movement of the objective lens position with laser light, high accuracy measurement independent of the measurement range can be performed due to the high coherence of the laser light.

  Further, by irradiating the measurement target with laser light in the vicinity of the optical axis, Abbe's principle can be approximately satisfied and the influence of disturbance (for example, temperature change and vibration) on measurement accuracy can be suppressed. Abbe's principle is the principle that the object to be measured and the reference (scale) should be placed on the same axis in order to achieve high measurement accuracy.

Japanese Patent No. 4180084

  However, since the apparatus using the laser beam irradiates the measurement target with the laser beam, the measurement accuracy becomes unstable due to the influence of the surface condition such as the inclination, surface roughness, absorption, etc. on the surface of the measurement target. There was a problem. Furthermore, an ordinary three-dimensional shape measuring device can measure the optical distance between the front and back interfaces of a thin film, but this device measures the amount of movement of the objective lens position with the laser beam reflected by the measurement object. When the object to be measured is a thin film, the measurement accuracy in the amount of movement of the objective lens position relative to the object to be measured decreases due to interference of reflected light at the front and back interfaces, or measurement by interference fringes of reflected light on the back surface of the thin film The result of measuring the amount of movement of the objective lens position relative to the object has a problem that it does not become an accurate value due to variations in the refractive index of the thin film.

The present invention can suppress the influence on the measurement accuracy due to disturbance (for example, temperature change and vibration) in the three-dimensional shape measurement or film thickness measurement of the measurement object, and does not depend on the measurement range and affects the surface condition of the measurement object. An object of the present invention is to provide a low-coherence interferometer that enables highly accurate three-dimensional shape measurement or film thickness measurement that is not received.
Another object of the present invention is to provide an optical microscope capable of measuring the amount of movement of the objective lens with high accuracy.

  In order to solve the above-described problem, a low coherence interferometer 1 according to the first aspect of the present invention is provided with a low coherence provided for three-dimensional shape measurement or film thickness measurement of a measurement object 2 as shown in FIG. A low-coherence light source 11 that emits low-coherence light having a short coherence length, an objective lens 14 that collects the low-coherence light on the measurement object 2 and is movable in the optical axis direction, and an objective lens 14. The object light 3 and the reference mirror 17 which are demultiplexed into the object light 3 which irradiates the measurement object 2 with the low-coherence light before or after the passage and the reference light 4 which irradiates the reference mirror 17 and are reflected by the measurement object 2. The optical demultiplexing / multiplexing unit 16 for combining the reference light 4 reflected by the optical output and outputting the low coherence interfering light, and the low coherence detecting for detecting the low coherence interfering light output from the optical demultiplexing / multiplexing unit 16. With vessel 20 A moving amount measuring device 30 for measuring the moving amount of the objective lens 14 in the optical axis direction is provided. The moving amount measuring device 30 is formed on the optical axis or in the vicinity of the optical axis with a laser light source 31 that emits laser light. And has a reflector 32 for reflecting the laser beam.

  Here, the three-dimensional shape measurement includes not only the measurement of the surface shape, but also the measurement of the film thickness distribution and the distribution of defects (foreign matter, scratches, etc.) in the film when the surface to be measured is a transparent film. included. Also, the short coherence length means that the coherence distance of the superimposed light waves is short, and in the case of natural light, about several wavelengths (about several μm) are common. The optical axis direction refers to the optical axis of the objective lens 14, and coincides with the optical axis of the low-coherence light passing through and the optical axis of the object light 3 demultiplexed from the low-coherence light. Further, the reflector includes a reflective film and a reflecting mirror, and includes a reflector that reflects a part of incident light. Further, being formed on the optical axis means that the reflector intersects the optical axis.

  According to this configuration, in the three-dimensional shape measurement or film thickness measurement of the measurement object 2, since the measurement is performed using the reflected light from the reflector formed on or near the optical axis, disturbance (for example, The influence on the measurement accuracy due to temperature changes and vibrations can be suppressed, and the coherence length of the laser light used for the measurement is as long as about several meters to several tens of kilometers, so that highly accurate measurement independent of the measurement range can be performed. Therefore, for the three-dimensional shape measurement or film thickness measurement of the object to be measured, the low coherence interferometer that can suppress the influence on the measurement accuracy due to disturbance (for example, temperature change and vibration) and enables high-precision measurement independent of the measurement range. Can provide. Moreover, since the amount of movement of the objective lens 14 is measured using the reflected light from the reflector 32 formed on the surface of the objective lens 14, the influence of the surface state (surface roughness, slope, absorption, etc.) of the measurement target surface is affected. I do not receive it.

  Further, the low coherence interferometer 1 according to the second aspect of the present invention is the low coherence interferometer according to the first aspect. For example, as shown in FIG. 3, the reflector is placed on the objective lens 14 on the optical axis. The reflection film 32 is formed.

  When configured in this manner, the reflective film 32 is formed in close contact with the objective lens 14, so that the amount of movement of the objective lens 14 can be measured very precisely by using the laser reflected light from the reflective film 32. . In addition, since it is formed on the optical axis and satisfies Abbe's principle, it is not affected by the measurement accuracy due to disturbance (for example, temperature change or vibration).

  In order to solve the above-described problem, a low coherence interferometer 1A according to the third aspect of the present invention is provided with a low coherence provided for three-dimensional shape measurement or film thickness measurement of a measurement object 2, for example, as shown in FIG. A low-coherence light source 11 that emits low-coherence light having a short coherence length, an objective lens 14 that collects the low-coherence light on the measurement object 2 and is movable in the optical axis direction, and an objective lens 14. The object light 3 and the reference mirror 17 which are demultiplexed into the object light 3 which irradiates the measurement object 2 with the low-coherence light before or after the passage and the reference light 4 which irradiates the reference mirror 17 and are reflected by the measurement object 2. The optical demultiplexing / multiplexing unit 16 for combining the reference light 4 reflected by the optical output and outputting the low coherence interfering light, and the low coherence detecting for detecting the low coherence interfering light output from the optical demultiplexing / multiplexing unit 16. Vessel 20 The moving amount measuring device 30 for measuring the moving amount of the objective lens 14 in the optical axis direction is provided. The moving amount measuring device 30 is provided near the objective lens 14 and a laser light source 31 that emits laser light. A reflector 43 that reflects the laser light that moves integrally with the lens 14 is provided.

  Here, the vicinity of the objective lens 14 means that it is in contact with the housing 40B of the objective lens or is at a position within several mm from the housing 40B. With this configuration, since the reflector 43 is in a fixed positional relationship with the objective lens 14, the amount of movement of the objective lens 14 is precisely determined by using the laser light reflected by the reflector 43. It can be measured. In addition, the reflector 43 is located at a position relatively close to the optical axis and approximately satisfies Abbe's principle, so that the influence on the measurement accuracy due to disturbance (for example, temperature change and vibration) can be suppressed. Therefore, a low-coherence interferometer that can suppress the influence on the measurement accuracy due to disturbances such as temperature changes and vibrations for the three-dimensional shape measurement or film thickness measurement of the measurement target, and enables high-precision measurement independent of the measurement range. Can be provided. In addition, since the amount of movement of the objective lens 14 is measured using the reflected light from the reflector 43 that moves integrally with the objective lens 14, the influence of the surface state (surface roughness, slope, absorption, etc.) of the measurement target surface Not receive.

  Further, the low coherence interferometer according to the fourth aspect of the present invention is the low coherence interferometer according to the third aspect. For example, as shown in FIG. 7, the reflector includes the objective lens 14 and the low coherence interferometer. It is the reflecting mirror 43 formed in the objective lens attachment member 40 for attaching to 1A.

  Here, the objective lens attachment member 40 (40A or 40B) is a member that attaches the objective lens to the low coherence interferometer 1A, and the housing 40B and the housing 40B that hold the objective lens 14 are the low coherence interferometer 1A. Includes a revolver 40A for attachment to the housing. With this configuration, since the reflecting mirror 43 is formed on the objective lens mounting member in the vicinity of the objective lens 14, the Abbe principle is approximately satisfied, and the measurement accuracy due to disturbance (for example, temperature change or vibration) is improved. In addition, the reflector can be easily attached.

  The low coherence interferometer 1 according to the fifth aspect of the present invention is the low coherence interferometer according to any one of the first to fourth aspects. For example, as shown in FIG. The laser light emitted from the laser light source 31 is demultiplexed into the measurement laser light 5 and the reference laser light 6, the measurement laser light 5 is irradiated onto the reflector 32, and the measurement laser light 5 reflected by the reflector 32 is referred to. Laser light interference optical system 33 that combines and interferes with laser light 6 to output interference laser light, laser light detector 21 that detects the interference laser light output from laser light interference optical system 33, and laser light detection And a movement amount calculation unit 23 for calculating the movement amount of the objective lens 14 based on the change of the intensity of the interference laser light detected by the detector 21 due to the movement of the objective lens 14.

  Here, the movement amount measuring device 30 is a part related to the calculation of the movement amount of the objective lens 14, and in FIG. 1, it has a laser light source 31, a laser light interference optical system 33, a laser light detector 21, and a movement amount calculation unit 23. Configured. The laser beam interference optical system 33 is a part related to laser beam interference. In FIG. 1, the laser beam interference optical system 33 includes a beam splitter 35 to 38 (37 may be a reflecting mirror), a beam splitter 34, a beam splitter 13, and a reflector 32. Configured. Further, the intensity of the interference laser light periodically changes with respect to the optical path length difference between the measurement laser light 5 and the reference laser light 6 (see FIG. 4), and also periodically changes with the amount of movement of the objective lens 14. Therefore, when this is the waveform of the interference wave, the movement amount can be calculated from the change in the wave number (cycle number) of the interference wave and the phase difference. If comprised like this aspect, since the movement amount of an objective lens is measured using the waveform of the interference wave of a laser beam with high coherence property, the movement amount can be measured accurately.

  A confocal microscope according to a sixth aspect of the present invention includes the low coherence interferometer according to any one of the first to fifth aspects. When configured in this way, since the coherence interferometer of the above aspect is provided, when used for three-dimensional shape measurement or film thickness measurement of a measurement target, it is possible to suppress the influence on the measurement accuracy due to disturbance (for example, temperature change and vibration), It is possible to provide a confocal microscope that enables high-precision measurement that does not depend on the measurement range and is not affected by the surface state of the measurement target.

The optical microscope according to the seventh aspect of the present invention includes a movement amount measuring device 30 for measuring the movement amount of the objective lens 14 in the optical axis direction, and the movement amount measuring device 30 emits laser light. The laser light source 31 includes a reflector that is formed on or near the optical axis and reflects the laser light.
If comprised in this way, the moving amount measuring device which concerns on this aspect can suppress the influence on the measurement accuracy by disturbance (for example, a temperature change or vibration), can perform the high precision measurement which is not dependent on a measurement range, and is a measuring object. Since it is not affected by the surface condition (surface roughness, slope, absorption, etc.) of the surface, an optical microscope capable of measuring the amount of movement of the objective lens with high accuracy can be provided.

The optical microscope according to the eighth aspect of the present invention includes a movement amount measuring device for measuring the movement amount of the objective lens in the optical axis direction. The movement amount measuring device includes a laser light source that emits laser light, And a reflector that is provided in the vicinity of the objective lens and reflects the laser light that moves integrally with the objective lens.
If comprised in this way, the moving amount measuring device which concerns on this aspect can suppress the influence on the measurement accuracy by disturbance (for example, a temperature change or vibration), can perform the high precision measurement independent of a measurement range, and is a measuring object. Since it is not affected by the surface condition (surface roughness, slope, absorption, etc.) of the surface, an optical microscope capable of measuring the amount of movement of the objective lens with high accuracy can be provided.

According to the present invention, in the three-dimensional shape measurement or film thickness measurement of the measurement object, the influence of disturbance (for example, temperature change or vibration) on the measurement accuracy can be suppressed, and the surface state of the measurement object is independent of the measurement range. It is possible to provide a low-coherence interferometer that enables highly accurate measurement that is not affected.
In addition, it is possible to provide an optical microscope capable of measuring the amount of movement of the objective lens with high accuracy.

3 is a diagram illustrating a configuration example of a low coherence interferometer in Embodiment 1. FIG. It is a figure for demonstrating the interference by white light. It is a schematic diagram of a reflecting film. It is a figure for demonstrating the interference by a laser beam. 6 is a diagram for explaining formation of a reflective film in Example 2. FIG. 6 is a diagram for explaining formation of a reflective film in Example 3. FIG. 10 is a diagram illustrating a configuration example of a low coherence interferometer in Embodiment 4. FIG. It is a figure for demonstrating installation of the reflective mirror in Example 5. FIG. It is a figure for demonstrating installation of the reflective mirror in Example 6. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  In this embodiment, an example in which a reflection film is formed on the surface of an objective lens and an interference objective lens in which an optical demultiplexer / multiplexer is integrated with an objective lens will be described.

  FIG. 1 shows a configuration example of a low coherence interferometer 1 in the present embodiment. The low coherence interferometer 1 includes an XY stage 10 on which a measurement target 2 is mounted, an objective lens 14 that can move in the optical axis direction, and an irradiation optical system that emits low coherence light and irradiates the measurement target 2 through the objective lens 14. In the middle of the irradiation optical system, the low-coherence light directed toward the measuring object 2 is split into the object light 3 that irradiates the measuring object 2 and the reference light 4 that irradiates the reference mirror 17, and the measuring object 2 An optical demultiplexing / multiplexing unit 16 for combining the reflected object beam 3 and the reference light 4 reflected by the reference mirror 17 to output low coherence interference light, and a low output from the optical demultiplexing / multiplexing unit 16. A detection optical system that guides coherence interference light to the low-coherence light detector 20 and a movement amount measuring device 30 for measuring the movement amount of the objective lens 14 in the optical axis direction are configured. In the irradiation optical system, a low-coherence light source 11, a collimator lens 12, a beam splitter 34, and a beam splitter 13 are arranged in this order on the optical axis of low-coherence light emitted from the low-coherence light source 11. The objective lens 14, the optical demultiplexer / multiplexer 16 and the XY stage 10 are arranged in this order on the optical axis of the low-coherence light reflected by. In the detection optical system, the objective lens 14, the beam splitter 13, the imaging lens 18, and the low coherence light detector 20 are arranged in this order on the optical axis of the low coherence interference light output from the optical demultiplexer / multiplexer 16. ing. The movement amount measuring device 30 measures the movement amount of the objective lens 14 in the optical axis direction. The movement amount measuring device 30 includes a laser light source 31, a laser light interference optical system 33, a laser light detector 21, and a movement amount calculation unit 23. It is comprised. The laser beam interference optical system 33 is a part related to laser beam interference, and includes a beam splitter 35 to 38, a beam splitter 34, a beam splitter 13, and a reflection film 32 as a reflector. Hereinafter, the configuration and operation of the low coherence interferometer 1 in the present embodiment will be described.

  The measurement object 2 is mounted on the XY stage 10 and is subjected to measurement of a three-dimensional shape by the low coherence interferometer 1. In this embodiment, the XY stage 10 is fixed in the Z direction (the optical axis direction of the objective lens 14), but is movable in the XY direction (in a plane perpendicular to the optical axis). For example, in the XY direction, It is driven by a stepping motor or the like. The low coherence light source 11 emits low coherence light having a short coherence length (for example, a halogen lamp light source). For example, a white light source such as a halogen lamp can be used. The halogen lamp emits white light mixed from near infrared light to visible light, and the coherence length is, for example, about several μm. In this embodiment, this white light is used as the low coherence light. When such white light is used, interference fringes are locally generated when the optical path lengths of the object light 3 irradiated and reflected on the measurement object 2 and the reference light 4 irradiated and reflected on the reference mirror 17 are substantially the same. By analyzing the obtained interference fringes, the three-dimensional shape of the measuring object 2 can be accurately measured. In this embodiment, the low coherence interferometer is a Michelson interferometer. Further, a low-coherence interferometer with a limited wavelength band can be obtained by using a filter that limits the wavelength band of the light source.

  FIG. 2 is a diagram for explaining interference due to white light. The horizontal axis represents the optical path length difference, and the vertical axis represents the detected light intensity. When the optical path lengths of the object light 3 and the reference light 4 coincide, the interference becomes maximum, and the maximum intensity is obtained. In the vicinity where the difference between the optical path lengths of the object beam 3 and the reference beam 4 is zero, the interference becomes maximum and the maximum intensity is obtained. When the optical path length difference is within the coherence length of white light (within ± lc), interference occurs locally, and interference fringes are generated in which the detected light intensity varies periodically due to the change in the optical path length difference. The peak of the interference wave draws an envelope and gradually decreases as the optical path length difference increases, and the interference disappears when the optical path length difference is ± lc. The number of interference fringes is about several.

  Returning to FIG. 1, in the irradiation optical system, the collimator lens 12, the beam splitter 34, and the beam splitter 13 are arranged in this order on the optical axis of the low coherence light emitted from the low coherence light source 11. An objective lens 14, an optical demultiplexer / multiplexer 16 and an XY stage 10 are arranged in this order on the optical axis of the low coherence light reflected by the beam splitter 13. The low coherence light emitted from the low coherence light source 11 becomes a substantially parallel light beam by the collimator lens 12, passes through the beam splitter 34, is reflected by the beam splitter 13, becomes a substantially parallel light beam, and enters the objective lens 14. The beam splitter 34 is for combining the measurement laser beam 5 from the laser beam interference optical system 33 described later with white light. The beam splitter 13 reflects a part of white light and transmits a part thereof. For example, the reflectance is 50% and the transmittance is 50%. Note that low-coherence light from the low-coherence light source 11 may be transmitted through an optical fiber and projected onto the collimator lens 12 by a diffusion lens at the output end of the optical fiber.

  The objective lens 14 focuses the low coherence light on the measurement object 2. The optical axis of the low coherence light reflected from the beam splitter 13 coincides with the optical axis of the objective lens 14. In the present embodiment, the objective lens 14 has a configuration of an interference objective lens 15 (within the one-dot chain line in the figure), and is configured integrally with the optical demultiplexer-multiplexer 16 and the reference mirror 17. The optical demultiplexer / multiplexer 16 demultiplexes the low-coherence light that has passed through the objective lens 14 into the object light 3 that irradiates the measurement object 2 and the reference light 4 that irradiates the reference mirror 17, and is reflected by the measurement object 2. Then, the returned object beam 3 and the reference beam 4 reflected by the reference mirror 17 are combined to output low coherence interference light. The optical demultiplexer-multiplexer 16 can use, for example, a beam splitter that reflects part of white light and transmits part of it. For example, the reflectance is 50% and the transmittance is 50%. A light beam incident on the beam splitter 16 through the objective lens 14 is demultiplexed into the object light 3 and the reference light 4. The object light 3 transmitted through the beam splitter 16 is irradiated onto the measurement object 2, reflected by the measurement object 2, and returned to the beam splitter 16. The reference light 4 reflected by the beam splitter 16 is irradiated on the reference mirror 17, reflected by the reference mirror 17, and returned to the beam splitter 16. The object light 3 reflected and returned by the measurement object 2 and the reference light 4 reflected and returned by the reference mirror 17 are combined by the beam splitter 16 to become low coherence interference light, which is output toward the objective lens 14. Is done.

  The light beam is transmitted through the beam splitter 16, irradiated to the measurement object 2, reflected by the measurement object 2, returned to the beam splitter 16, reflected by the beam splitter 16, and irradiated to the reference mirror 17. When the optical path length of the reference light 4 reflected by the reference mirror 17 and returning to the beam splitter 16 becomes substantially equal, the object light 3 is focused on the measurement object 2 and the reference light 4 is focused on the reference mirror 17. A splitter 16 and a reference mirror 17 are arranged. When the optical path length of the object light 3 and the optical path length of the reference light 4 substantially coincide with each other, white light interference fringes are locally generated. When the height difference of the surface of the measuring object 2 is within the coherence length of white light, the image detected by the low coherence light detector 20 has interference fringes in the plane, and therefore the position of the objective lens 14 is moved. The surface shape can be calculated by interference fringe analysis.

  The objective lens 14 is configured to be movable in the optical axis direction (Z direction). In this embodiment, the XY stage 10 is fixed and the objective lens 14 is moved. For example, it can be moved in the Z direction by a stepping motor, a piezoelectric actuator (not shown), or a combination thereof. The use of a piezo actuator is preferable because a capacitance sensor for measuring the amount of movement can be installed in the vicinity of the objective lens 14 and the amount of movement can be measured with high accuracy. Thereby, when the height difference of the measurement target surface is equal to or greater than the coherence length of the white light, the interference fringe image detected by the low coherence photodetector 20 while moving the position of the objective lens 14 (may be scanned). The three-dimensional shape of the measuring object 2 can be accurately measured by analyzing and analyzing the Z-direction position dependency of the detection intensity at each pixel of the image based on these interference fringes.

  In the detection optical system, the objective lens 14, the beam splitter 13, the imaging lens 18, and the low coherence light detector 20 are arranged in this order on the optical axis of the low coherence interference light output from the beam splitter 16. The low coherence interference light output from the beam splitter 16 passes through the objective lens 14 to become a substantially parallel light beam and enters the beam splitter 13. The white light transmitted through the beam splitter 13 passes through the imaging lens 18 and enters the low coherence photodetector 20. The low coherence light detector 20 detects low coherence interference light, and for example, a CCD camera can be used. The general CCD camera 20 has sensitivity from near infrared to visible light, but light having a wavelength away from low coherence interference light (portion where interference fringes are generated) may be blocked by a wavelength band filter. The CCD camera 20 captures an interference fringe image using low coherence interference light. The CCD camera 20 can measure the three-dimensional shape of the measurement object 2 with high accuracy by analyzing the obtained interference fringe image by the white light interference analysis unit 24 in the analysis device 22. For example, a personal computer (PC) can be used as the analysis device 22.

  The movement amount measuring device 30 measures the movement amount of the objective lens 14 in the optical axis direction. The movement amount measuring device 30 includes a laser light source 31, a laser light interference optical system 33, a laser light detector 21, and a movement amount calculation unit 23. The laser beam interference optical system 33 is a part related to laser beam interference, and includes a beam splitter 35 to 38 (37 may be a reflecting mirror), a beam splitter 34, the beam splitter 13, and a reflection film 32 as a reflector. Configured. The laser light source 31 emits laser light. The reflective film 32 reflects the laser light.

  FIG. 3 shows a schematic diagram of the reflective film 32. The reflective film 32 is formed on the objective lens 14. For example, the objective lens 14 is formed on the surface opposite to the measurement target 2. It is preferable to select a wavelength of the reflected light by using a general dielectric multilayer film (for example, used for a dichroic mirror) for the reflection film 32. For example, the reflective film 32 made of a multilayer film in which two layers having different refractive indexes are laminated alternately on the surface of the objective lens 14 is formed. The multilayer film is formed by alternately stacking the high refractive index layers P1 and the low refractive index layers P2 by vapor deposition, for example. The laser light is efficiently reflected by adjusting the film thicknesses of the two layers so that the optical path length matches the wavelength of the laser light. Thus, the reflection film 32 is formed in close contact with the objective lens 14 so as to include the optical axis thereof, that is, to intersect the optical axis. The laser beam is locally irradiated on the optical axis of the reflective film 32 and satisfies Abbe's principle. Therefore, disturbance (for example, temperature change and vibration) is not easily affected by the measurement accuracy. Further, the amount of movement of the objective lens 14 itself is measured by measuring the reflected light from the reflective film 32. In addition, by measuring with a laser beam, high-precision measurement independent of the measurement range is possible. Further, since the amount of movement of the objective lens 14 is measured using the reflected light from the reflective film 32 formed on the objective lens 14, it is influenced by the surface state (surface roughness, slope, absorption, etc.) of the surface of the measuring object 2. Absent.

  Returning to FIG. 1, for example, a He—Ne laser can be used as the laser light source 31. Laser light (wavelength 632.8 nm) emitted from the He—Ne laser 31 is incident on the laser light interference optical system 33. Instead of the He-Ne laser, a semiconductor laser of each wavelength, an Nd-YAG laser (wavelength 1064 nm), or the like may be used. If the wavelength of the laser light is far from the wavelength of the low-coherence light (the wavelength in the interference range) or the wavelength band of the filter that limits the wavelength band, it is preferable because the laser light does not affect the interference fringes of the white light. The laser beam interference optical system 33 receives the laser beam emitted from the laser light source 31 and demultiplexes it into the measurement laser beam 5 and the reference laser beam 6 by the beam splitter 35. The reference laser beam 6 reaches the beam splitter 38 from the beam splitter 35. The measurement laser beam 5 is reflected by the beam splitter 36 and is incident on the low coherence optical system by the beam splitter 34, and thereafter, similarly to the low coherence beam (in this embodiment, the optical axis of the measurement laser beam 5 and the optical axis of the low coherence beam). Are reflected by the beam splitter 13, reflected by the reflecting film 32 formed on the objective lens 14, reflected by the beam splitter 13 and the beam splitter 34, and then separated from the low-coherence optical system. Is reflected by a beam splitter 37 (or a reflecting mirror) and then enters a beam splitter 38. The beam splitter 38 combines the measurement laser beam 5 and the reference laser beam 6 and outputs an interference laser beam.

  The interference laser light enters the laser light detector 21 and is detected. For example, a photoelectric sensor can be used as the laser light detector 21. The detection signal from the photoelectric sensor 21 is transmitted to the analysis device 22, and the analysis device 22 analyzes the interference fringes of the laser light by the movement amount calculation unit 23, whereby the movement amount of the objective lens 14 can be measured with high accuracy. The analysis device 22 can be a personal computer (PC). These beam splitters 34 to 38, the beam splitter 13, and the reflection film 32 constitute a laser beam interference optical system 33. When the difference between the optical path length of the measurement laser beam 5 and the optical path length of the reference laser beam 6 in the laser beam interference optical system 33 is changed, the interference laser beam intensity periodically changes. When these two optical path lengths match or when the difference between the two optical path lengths is an integral multiple of a half wavelength of the laser light, the intensity of the interference laser light is maximized. In addition, the laser beam may be irradiated and reflected locally on the reflection film 32. In this embodiment, the laser beam is irradiated on the center of the beam splitter 13 and travels on the optical axis toward the center of the objective lens 14 to generate light. Reflected from the reflective film 32 on the axis. It is preferable to irradiate the laser beam on the optical axis (that is, reflect it by the reflection film 32 on the optical axis) because the Abbe's principle is satisfied. Since Abbe's principle is approximately satisfied, disturbance (for example, temperature change and vibration) can suppress the influence on measurement accuracy.

  FIG. 4 is a diagram for explaining interference due to laser light. The horizontal axis indicates the amount of movement in the Z direction, and the vertical axis indicates the detected light intensity. The wavelength of the interference fringes is ½ of the wavelength of the laser light. Thus, since the interference fringes are repeated with respect to the movement amount, the movement amount of the objective lens 14 can be measured by the number of the interference fringes and the phase difference. That is, the movement amount measuring device 30 transmits the detected light intensity of the interference laser light detected by the laser light detector 21 to the movement amount calculating unit 23, and the movement amount calculating unit 23 is detected by the laser light detector 21. The amount of movement of the objective lens 14 is calculated based on the change in the intensity of the interference laser beam due to the movement of the objective lens 14. The intensity of the interference laser light changes periodically with respect to the optical path length difference between the measurement laser light 5 and the reference laser light 6 and periodically changes with the amount of movement of the objective lens 14. If it is a waveform, the amount of movement can be calculated from the wave number (cycle number) of the interference wave and the change in phase difference.

  As described above, according to the present embodiment, in the three-dimensional shape measurement or the film thickness measurement of the measurement object, the measurement is performed using the reflected light from the reflection film formed on the optical axis. ) Is suppressed, and the coherence length of the laser beam used for the measurement is long, so that highly accurate measurement independent of the measurement range can be performed. Further, since the amount of movement of the objective lens is measured using the reflected light from the reflective film formed on the objective lens, it is not affected by the surface state (surface roughness, slope, absorption, etc.) of the measurement target surface.

  FIG. 5 is a diagram for explaining the formation of the reflective film 32 in the second embodiment. In the first embodiment, the objective lens 14 is described as one, but in the second embodiment, an example in which an objective lens composed of a plurality of lenses is used and the reflective film 32 is formed on one objective lens 14A will be described. Differences from the first embodiment will be mainly described. A reflective film 32 is formed on the surface of the objective lens 14 opposite to the measurement target 2 on the side opposite to the measurement target 2 of the lens 14A. A reflective film 32 is formed on the surface of the lens 14A. The reflective film 32 is formed of a multilayer film in which two layers having different refractive indexes are laminated alternately. The lens 14A is held by the housing 40B, and the housing 40B is attached to the low coherence interferometer by a revolver 40A. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment are obtained.

  FIG. 6 is a diagram for explaining the formation of a reflective film in Example 3. In the first embodiment, an example in which the reflection film 32 that reflects the laser light is formed on the objective lens 14 has been described. In this embodiment, an example in which the multilayer film 32B formed on the transparent substrate 42 is used as a reflector will be described. Differences from the first embodiment will be mainly described. For example, the multilayer film 42 is formed by vapor-depositing a multilayer film in which two layers having different refractive indexes are alternately laminated on a transparent substrate such as a glass substrate. For example, the revolver 40A is attached to the opposite side of the measurement object 2 of the housing 40B equipped with the objective lens 14, and the multilayer filter 42 is sandwiched between the housing 40B and the revolver 40A. Thereby, the laser light irradiated to the multilayer filter 42 is reflected by the reflective film 32B made of the multilayer film. Light having a wavelength in the vicinity of the white interference fringes passes through the multilayer filter 42. Since the multilayer film 32B is formed on the transparent substrate, the multilayer film 32B can be formed and handled more easily than directly forming on the objective lens. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment are obtained.

  In the first embodiment, the example in which the reflecting film 32 that reflects the laser light is formed on the objective lens 14 has been described. In this embodiment, an example in which the reflecting mirror 43 is formed on the objective lens mounting member 40 (40A or 40B) will be described. . Therefore, although the reflective film 32 is disposed on the surface of the objective lens 14 in the first embodiment, the reflective mirror 43 is disposed on the objective lens mounting member 40 that moves integrally with the objective lens 14 in the present embodiment.

  FIG. 7 shows a configuration example of the low coherence interferometer 1A in the fourth embodiment. FIG. 7A shows an example of the configuration of the low coherence interferometer 1A, and FIG. 7B shows an example of the installation part of the reflecting mirror 43. Differences from the first embodiment will be mainly described. The objective lens attachment member 40 is a member for attaching the objective lens 14 to the low coherence interferometer 1A, and includes a housing 40B for holding the objective lens 14 and a revolver 40A for attaching the housing 40B to the low coherence interferometer 1A. Including. The objective lens 14 is held by the housing 40B, and the housing 40B is attached to the low coherence interferometer 1A. For example, the reflecting mirror 43 is disposed on the surface of the revolver 40A opposite to the measurement target 2, moves integrally with the objective lens 14, and measures the movement amount of the objective lens 14 using laser reflected light. It is possible to accurately measure the amount of movement without depending on the condition and without being affected by the surface condition of the surface to be measured. Further, since the revolver 40A is in a position that does not prevent the object light 3 from entering the objective lens 14, it does not affect the observation of white interference fringes. The reflecting mirror 43 is installed perpendicular to the optical axis of the objective lens 14, and the reflected light of the laser light incident on the reflecting mirror 43 returns the optical path of the incident light. Since the reflecting mirror 43 is disposed in the vicinity of the objective lens 14, it can be said that although it does not strictly satisfy the Abbe principle, it approximately satisfies the Abbe principle. Therefore, disturbance (for example, temperature change and vibration) can suppress the influence on measurement accuracy. Further, as compared with the formation of the reflection film 32 on the objective lens 14, the reflection mirror 43 can be easily attached to the revolver 40A because it only has to be attached.

  Further, the beam splitter 34 (see FIG. 1) is removed from the optical system of the first embodiment, and the beam splitter 13 reflects white light and laser light toward the objective lens 14. The laser light is irradiated to the local area toward the end of the beam splitter 13 and reflected toward the reflecting mirror 43. Therefore, the laser light is not incident on the objective lens 14 and does not affect the interference of the low coherence light. Reflected light from the reflecting mirror 43 is reflected by the beam splitter 13 and travels toward the beam splitter 36, and low-coherence interference light output from the objective lens 14 passes through the beam splitter 13 and travels toward the imaging lens 18.

  Laser light (wavelength 632.8 nm) emitted from the He-Ne laser 31 is incident on the laser light interference optical system 33A. Instead of the He-Ne laser, a semiconductor laser of each wavelength, an Nd-YAG laser (wavelength 1064 nm), or the like may be used. The laser beam interference optical system 33 </ b> A receives the laser beam emitted from the laser light source 31 and demultiplexes the laser beam into the measurement laser beam 5 and the reference laser beam 6 by the beam splitter 35. The reference laser beam 6 reaches the beam splitter 38 from the beam splitter 35. The measurement laser light 5 passes through the beam splitter 36 and is incident on the low coherence optical system by the beam splitter 13 and then travels along the optical path of the low coherence light. However, in this embodiment, the measurement laser light 5 is locally incident on a portion near the end of the beam splitter 13, and the optical axis of the measurement laser light 5 and the optical axis of the low coherence light are parallel, but do not coincide. The measurement laser beam 5 reflected by the beam splitter 13 is reflected by the reflecting mirror 43 provided on the surface opposite to the measuring object 2 of the revolver 40A, then reflected by the beam splitter 13, and separated from the low coherence optical system. Are reflected by the beam splitter 36 and the beam splitter 37 (which may be a reflecting mirror) and enter the beam splitter 38. The beam splitter 38 combines the measurement laser beam 5 and the reference laser beam 6 and outputs an interference laser beam. The interference laser light enters the laser light detector 21 and is detected.

  The movement amount measuring device 30 includes a laser light source 31, a laser light interference optical system 33, a laser light detector 21, and a movement amount calculation unit 23. The laser beam interference optical system 33 is a part related to laser beam interference, and includes a beam splitter 35 to 38, the beam splitter 13, and a reflecting mirror 43 as a reflector.

  The other configuration is the same as that of the first embodiment, and white light interference fringes are locally generated, and the amount of movement of the objective lens 14 is measured by measuring the reflection of the laser beam from the reflecting mirror 43 disposed in the revolver 40A. By doing so, the movement amount of the objective lens 14 can be measured. The reflecting mirror 43 is provided in the vicinity of the objective lens 14 and moves integrally with the objective lens 14. Therefore, in the three-dimensional shape measurement or film thickness measurement of the measurement object, the influence of disturbance (for example, temperature change or vibration) on the measurement accuracy can be suppressed, and high-precision measurement independent of the measurement range can be performed.

  FIG. 8 is a diagram for explaining the installation of the reflecting mirror 43 in the fifth embodiment. In the fourth embodiment, an example in which the reflecting mirror 43 is installed in the revolver 40A has been described. In this embodiment, an example in which the reflecting mirror 43 is installed in the housing 40B of the objective lens 14 will be described. That is, the reflecting mirror 43 is fixed at a position in close contact with the housing 40B of the objective lens 14, the revolver 40A is drilled, and the laser beam reflected by the beam splitter 13 is irradiated to the reflecting mirror 43 through the hole 44. , Reflected from the reflecting mirror 43 and returned to the beam splitter 13. If the position of the reflecting mirror 43 is the same height (Z coordinate) as the objective lens 14, the influence of disturbance (for example, temperature change and vibration) on the measurement accuracy can be further suppressed. Other configurations are the same as those of the fourth embodiment, and the same effects as those of the fourth embodiment are obtained.

  FIG. 9 is a diagram for explaining the installation of the reflecting mirror 43 in the sixth embodiment. FIG. 9A is a view of the objective lens 14 and the revolver 40A as viewed from the side, and FIG. 9B is a view of these as viewed from the top. In the fourth embodiment, an example in which the reflecting mirror 43 is installed on the revolver 40A has been described. In the present embodiment, an example in which the reflecting mirror 43 is installed between the housing 40B of the objective lens 14 and the revolver 40A will be described. That is, the low-coherence light reflected by the beam splitter 13 is installed in a position where the reflecting mirror 43 is in close contact with the housing 40B of the objective lens 14 and sandwiched between the housing 40B and the revolver 40A. The light is irradiated to the reflecting mirror 43 through the hole 44, reflected from the reflecting mirror 43, and incident on the beam splitter 13. Other configurations are the same as those of the fourth embodiment, and the same effects as those of the fourth embodiment are obtained.

  Further, the laser beam interference optical system of the present invention can be incorporated into a confocal microscope. Since such a confocal microscope includes the coherence interferometer of the present invention, when used for measuring a three-dimensional shape or a film thickness of a measurement target, it is possible to suppress the influence on the measurement accuracy due to disturbance (for example, temperature change and vibration), High-accuracy measurement that does not depend on the measurement range and is not affected by the surface condition of the measurement object becomes possible.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it is obvious that various modifications can be made to the embodiments without departing from the spirit of the present invention. .

  For example, the positional relationship and the configuration order of the optical components constituting the low coherence interferometer in the above embodiments can be changed. For example, in the first or fourth embodiment, the example in which the low coherence interferometer is configured by a Michelson interferometer has been described. However, the vertical relationship between the positions of the optical demultiplexing multiplexer and the objective lens may be reversed. In addition, the low coherence interferometer is composed of a linic interferometer having two objective lenses, an object lens objective lens and a reference beam objective lens, with the vertical relationship between the position of the optical demultiplexer / multiplexer and the objective lens reversed. It is also possible to configure the optical demultiplexing / multiplexing device with a Mirau type interferometer in which the objective lens housing is formed. In the fourth embodiment, the example in which the reflecting mirror is disposed on the upper surface of the revolver has been described. However, the reflecting mirror may be disposed on the bottom of the hole opened from the upper surface of the revolver. In this case, if the position of the hole bottom, that is, the position of the reflecting mirror 43 is set to the same height (Z coordinate) as that of the objective lens 14, the influence on the measurement accuracy due to disturbance (for example, temperature change or vibration) can be suppressed. Further, instead of the reflective film 32 of the first embodiment, a reflecting mirror may be locally provided on the surface of the objective lens 14 on the optical axis of the objective lens 14. In this case, a part of the low-coherence light and the low-coherence interference light is prevented from passing through the objective lens 14, but since it is local, the influence of white light on the interference fringes is small. In addition, the configuration and arrangement of the reflecting film and the reflecting mirror, and the selection and arrangement of other components constituting the other low-coherence interferometer can be appropriately changed.

  The present invention is used in a three-dimensional shape and film thickness measuring instrument and an optical microscope.

1,1A Low coherence interferometer 2 Measurement object 3 Object light 4 Reference light 5 Measurement laser light 6 Reference laser light 10 XY stage 11 Low coherence light source (halogen lamp)
12 Collimator lens 13 Beam splitter 14, 14A Objective lens 15 Interference objective lens 16 Optical demultiplexer / multiplexer (beam splitter)
17 Reference mirror 18 Imaging lens 20 Low coherence photodetector (CCD camera)
21 Laser Light Detector 22 Analyzing Device 23 Movement Amount Calculation Unit 24 White Light Interference Analysis Unit 30 Movement Amount Measuring Device 31 Laser Light Source (He-Ne Laser)
32, 32A, 32B Reflector (reflective film)
33, 33A Laser beam interference optical system 34 Beam splitter 35-38 Beam splitter 40 Objective lens mounting member 40A Revolver 40B Housing 42 Multilayer filter 43 Reflector (reflecting mirror)
44 hole P1 high refractive index layer P2 low refractive index layer

Claims (8)

A low coherence interferometer used for measuring a three-dimensional shape or a film thickness of a measurement object;
A low coherence light source that emits low coherence light with a short coherence length;
An objective lens that focuses the low-coherence light on a measurement object and is movable in the optical axis direction;
The object light and the reference, which are demultiplexed into the object light that irradiates the measurement object and the reference light that irradiates the reference mirror, and reflected by the measurement object before or after passing through the objective lens An optical demultiplexer that combines the reference light reflected by the mirror and outputs low coherence interference light;
A low coherence photodetector that detects low coherence interference light output from the optical demultiplexer;
A moving amount measuring device for measuring the moving amount of the objective lens in the optical axis direction;
The movement amount measuring device includes a laser light source that emits laser light, and a reflector that is formed on or near the optical axis and reflects the laser light;
Low coherence interferometer. The reflector is a reflective film formed on the objective lens on the optical axis;
The low coherence interferometer according to claim 1. A low coherence interferometer used for measuring a three-dimensional shape or a film thickness of a measurement object;
A low coherence light source that emits low coherence light with a short coherence length;
An objective lens that focuses the low-coherence light on a measurement object and is movable in the optical axis direction;
The low-coherence light before or after passing through the objective lens is demultiplexed into object light for irradiating the measurement target and reference light for irradiating a reference mirror, and the object light reflected by the measurement target and the reference An optical demultiplexer that combines the reference light reflected by the mirror and outputs low coherence interference light;
A low coherence photodetector that detects low coherence interference light output from the optical demultiplexer;
A moving amount measuring device for measuring the moving amount of the objective lens in the optical axis direction;
The movement amount measuring device includes a laser light source that emits laser light, and a reflector that is provided near the objective lens and reflects the laser light that moves integrally with the objective lens;
Low coherence interferometer. The reflector is a reflector formed on an objective lens mounting member for mounting the objective lens to the low coherence interferometer;
The low coherence interferometer according to claim 3. The moving amount measuring device is
The laser light emitted from the laser light source is demultiplexed into measurement laser light and reference laser light, the measurement laser light is irradiated to the reflector, and the measurement laser light reflected by the reflector is used as the reference laser light. A laser beam interference optical system that outputs the interference laser beam by combining and interfering;
A laser light detector for detecting the interference laser light output from the laser light interference optical system;
A movement amount calculating unit that calculates a movement amount of the objective lens based on a change in the intensity of the interference laser light detected by the laser light detector due to the movement of the objective lens;
The low coherence interferometer according to any one of claims 1 to 4. A low coherence interferometer according to any one of claims 1 to 5;
Confocal microscope. A moving amount measuring device for measuring the moving amount of the objective lens in the optical axis direction;
The movement amount measuring device includes a laser light source that emits laser light, and a reflector that is formed on or near the optical axis and reflects the laser light;
Optical microscope. A moving amount measuring device for measuring the moving amount of the objective lens in the optical axis direction;
The movement amount measuring device includes a laser light source that emits laser light, and a reflector that is provided near the objective lens and reflects the laser light that moves integrally with the objective lens;
Optical microscope.

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