JP6761160B2 - Dimension measuring device - Google Patents

Description

The present invention relates to an etalon and a dimensional measuring device, and more particularly to a dimensional measuring device including an etalon and measuring the size of an object to be measured by utilizing the principle of low coherence interferometry.

Patent Document 1 discloses a scanning white interferometry method that utilizes the principle of low coherence interference as a method for accurately measuring the size (surface height) of an object to be measured without contact.

The white interferometry utilizes a white light source with a wide spectrum and a short coherent length. That is, the white light emitted from the white light source is divided into a measurement light and a reference light, the divided measurement light is irradiated to the object to be measured, and the divided reference light is irradiated to the reference mirror. Then, the measurement light reflected by the object to be measured and the reference light reflected by the reference mirror are interfered with each other to form an interference fringe, and the size of the object to be measured at the position irradiated with the measurement light is measured based on the interference fringe. To do.

The interference fringes are formed when the optical path length of the measurement light and the optical path length of the reference light are substantially equal, and the amplitude of the interference fringes becomes maximum when the optical path lengths of the measurement light match. Therefore, the dimensions of the object to be measured are measured by moving the reference mirror to change the optical path length of the reference light and measuring the optical path length of the reference light when the amplitude of the interference fringes is maximized. According to the white interferometry, the size of the object to be measured can be measured with nanometer accuracy by changing the optical path length of the reference light with high accuracy.

By the way, Patent Document 2 discloses a low coherence interferometer using Fabry-Perot Etalon (hereinafter referred to as Etalon). Etalon is formed by arranging two parallel flat plates on which a reflective film and an antireflection film are formed, so that the reflective films face each other with a gap.

Etalon reflects the light incident from one of the parallel plates by the reflective films of each other to cause multiple interference. As a result, light having transmitted peaks at regular intervals in the wavelength region and having a narrow half-value full width transmitted waveform is emitted from the other parallel plate with a delay at regular intervals, so that the reference light that interferes with the measurement light is effective. Optical path length can be lengthened discretely.

The light transmission characteristic of such etalon is determined by the free spectrum range (hereinafter referred to as FSR) and finesse (FSR / full width at half maximum) indicating the period of the transmission waveform. Therefore, in order to obtain the desired FSR and finesse, it is necessary to align the reflective films with high accuracy.

Patent Document 3 proposes an etalon having high performance by adjusting the parallelism between opposing surfaces of a pair of parallel flat plates constituting the etalon with high accuracy.

According to Patent Document 3, a pair of holder portions for separately holding a pair of parallel flat plates arranged to face each other and a housing portion provided outside the pair of holder portions are provided. Then, at least one of the pair of holder portions has a receiving portion with which the corresponding parallel flat plate abuts on the inner peripheral portion thereof, and at least a position where the outer peripheral portion of the parallel flat plate abuts on the receiving portion and at least the outer peripheral portion of the parallel flat plate. An inclined surface is provided on one side. The housing portion has a fitting hole, and at least one of the pair of holder portions is fitted into the fitting hole, and the pair of parallel flat plates are in contact with each other through the inclined surface. By tilting, at least one of the pair of holders is slidably held in the direction along the central axis of the housing to the extent that the parallelism of the pair of parallel flat plates can be adjusted.

JP-A-2009-222705 Japanese Patent No. 5228828 Japanese Patent No. 50489939

However, since etalon is composed of a pair of parallel plates, it is not easy to align the reflective films with high accuracy. Further, since the etalon of Patent Document 3 requires a holder portion and a housing portion having a receiving portion and an inclined surface, there is also a problem that the structure is complicated.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an etalon having a simple structure capable of easily aligning reflective films with high accuracy, and a dimensional measuring device provided with the etalon. And.

One aspect of the present invention is a spherical surface in an etalon that emits light having a transmitted waveform having transmitted peaks at regular intervals in a wavelength region by causing multiple interference of light inside the invention in order to achieve the object of the present invention. A ball lens having a light incident surface forming a part of the light incident surface and a light emitting surface forming another part of the spherical surface and facing the light incident surface, and a first reflective film provided on the light incident surface. To provide an etalon comprising a second reflective film provided on the light emitting surface and an optical system for condensing the light at the center of the ball lens via the light incident surface.

One aspect of the present invention has transmitted peaks at regular intervals in a wavelength region by causing multiple interference between a light source that emits light and light from the light source inside the light source in order to achieve the object of the present invention. Etalon that emits light with a transmitted waveform, light dividing means that divides the light emitted from the etalon into measurement light and reference light, and measurement light emitted from the light dividing means are used as objects to be measured. A reference light path length changing means that has a measuring light irradiating means to irradiate and a reflecting mirror that reflects the reference light emitted from the light dividing means, and changes the optical path length of the reference light by moving the reflecting mirror. , The light detection means for detecting the interference light obtained by combining the measurement light reflected by the object to be measured and the reference light reflected by the reflector, and the measurement subject based on the interference light detected by the light detection means. A dimensional measuring device including a calculation means for calculating the dimensions of an object, wherein the etalon forms a light incident surface forming a part of a spherical surface and a light incident surface forming another part of the spherical surface. A ball lens having facing light emitting surfaces, a first reflecting film provided on the light incident surface, a second reflecting film provided on the light emitting surface, and the light incident surface. Provided is a dimensional measuring device including an optical system for condensing light from the light source at the center of a ball lens.

According to one aspect of the etalon and the dimension measuring device of the present invention, since the etalon is formed by a ball lens, the distance between the first reflective film provided on the light incident surface and the second reflective film provided on the light emitting surface is large. , It is uniquely determined by the diameter of the ball lens. Therefore, the first reflective film and the second reflective film can be easily aligned with high accuracy. Further, since the etalon is composed of a ball lens, it is possible to provide a dimensional measuring device including the etalon having a simple structure.

According to the present invention, it is possible to provide an etalon having a simple structure capable of easily aligning reflective films with high accuracy, and a dimension measuring device including the etalon.

Configuration diagram of the dimension measuring device of the embodiment to which the etalon and the dimension measuring device of this invention are applied Side view showing the composition of Etalon Graph showing an example of the transmission characteristics of etalon The figure which shows an example of the transmission property of etalon The figure which showed the frequency which shows the peak of the transmittance in the transmittance characteristic of etalon shown in FIG. 4 based on "frequency-electric field". Flow chart showing the operation of the dimensional measuring device

Hereinafter, preferred embodiments of the etalon and dimensional measuring apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a dimension measuring device 10 of an embodiment to which the etalon and the dimension measuring device of the present invention are applied.

[Dimension measuring device 10]
The dimension measuring device 10 includes a broad spectrum light source (hereinafter, abbreviated as a light source) 12, an etalon 14, a circulator 16, a beam splitter (light dividing means) 18, and a measuring object scanning optical system (measuring light irradiating means) 20.

Further, the dimension measuring device 10 includes a reference optical path length changing device (reference optical path length changing means) 22 having a reference mirror 24, a detector (light detecting means) 26, a frequency amplifier 28, a controller (calculation means) 30, and light. It has fibers 32, 34, 36, 38, 40, 42.

In the dimensional measuring device 10, white light emitted from the light source 12 enters the etalon 14 via the optical fiber 32 and the lens 32A.

The etalon 14 has a discrete light transmission band with respect to the frequency of light, receives white light from the light source 12, and emits only intensity-modulated light 15 having a specific light frequency component. Etalon 14 will be described later (see FIGS. 2 to 5).

The intensity-modulated light 15 emitted from the etalon 14 enters the beam splitter 18 via the collimator 34A, the optical fiber 34, the circulator 16, and the optical fiber 36.

Then, the intensity-modulated light 15 is split into a measurement light directed toward the object scanning optical system 20 and a reference light directed toward the reference optical path length changing device 22 by the beam splitter 18, and then emitted in each direction.

The measurement light emitted from the beam splitter 18 is incident on the measurement object scanning optical system 20 via the optical fiber 38, and is imaged on the measurement point on the surface of the measurement object 44 by the lens 46 of the measurement object scanning optical system 20. Will be done. Then, the measurement light reflected or scattered at the measurement point is returned to the beam splitter 18 via the measurement object scanning optical system 20 and the optical fiber 38.

On the other hand, the reference light emitted from the beam splitter 18 is incident on the reference optical path length changing device 22 via the optical fiber 40, and is incident on the reference mirror 24 via the collimator lens 48 of the reference optical path length changing device 22. Then, the reference light emitted from the reference mirror 24 is reflected by the reflecting mirror 25, then re-enters the reference mirror 24 and is emitted from the reference mirror 24. The reference light (hereinafter, also referred to as reflected light) is returned to the beam splitter 18 via the collimator lens 48 and the optical fiber 40.

Here, reference numeral 58 indicates reference light incident on the reference mirror 24, and reference numeral 60 indicates reflected light emitted from the reference mirror 24. In the specification, the reference light 58 and the reflected light 60 may be described separately, but the reflected light 60 is a part of the reference light 58.

On the other hand, the measurement light and the reference light returned to the beam splitter 18 are combined by the beam splitter 18 and then incident on the detector 26 via the optical fiber 36, the circulator 16, and the optical fiber 42. The detector 26 detects the interference light in which the measurement light returned to the beam splitter 18 and the reference light are combined.

Hereinafter, each part of the dimension measuring device 10 will be described in detail.

<Light source 12>
The light source 12 is a white light source having a short coherent length and capable of emitting light having a wide band wavelength. As the light source 12, for example, an LED (Light Emitting Diode), an SLD (Super Luminescence Diode), a halogen lamp, and an optical frequency com (however, when an optical frequency com is used, the length of the etalon and the repetition frequency of the intensity-modulated light must match. You can use it. The central wavelength of the light emitted from the light source 12 can be set to, for example, 750 nm, 1300 nm, 1550 nm, or the like.

<Etalon 14>
FIG. 2 is a side view showing the configuration of the etalon 14.

A true spherical ball lens is applied as the etalon 14. The etalon 14 has transmission peaks at regular intervals in the wavelength region by multiple interference of white light 13 incident on the inside of the light source 12 on spherical reflecting surfaces facing each other, and transmits with a narrow half-value full width. The intensity-modulated light 15 of the waveform is emitted.

Further, the etalon 14 is a Fabry-Perot type etalon whose diameter is the distance between interferences, and is a pair of reflective coatings (first reflective film, second reflective film) 14A such as gold plating arranged apart from each other. , 14B, and a reflection region 14C between the reflection coat 14A and the reflection coat 14B.

The reflection coat 14A is provided on a spherical light incident surface 14a that forms a part of the spherical surface of the ball lens. Further, the reflection coat 14B is a light emitting surface 14b that forms another part of the spherical surface of the ball lens, and is provided on the spherical light emitting surface 14b facing the light incident surface 14a.

The white light 13 incident on the reflection region 14C from the reflection coat 14A is focused on the center P of the etalon 14 by the lens 32A (optical system). That is, the lens 32A is pre-positioned at a position where the focal point of the lens 32A coincides with the center P of the etalon 14.

The white light 13 focused on the center P of the etalon 14 diffuses, then reaches the reflection coat 14B, and is reflected by the reflection coat 14B toward the reflection coat 14A.

The white light 13 is repeatedly reflected in the reflection region 14C between the reflection coat 14A and the reflection coat 14B, and a specific wavelength component (frequency component) is strengthened by the interference effect to pass through the reflection coat 14B and is emitted from the etalon 14. Will be done. The characteristics of the intensity-modulated light 15 emitted from the etalon 14 are specified by the FSR (Free Spectral Range) and the finesse (FSR / full width at half maximum: Finesse).

FIG. 3 is a graph showing an example of the transmission characteristics of Etalon 14. The horizontal axis of FIG. 3 shows the fringe order (m, m + 1, m + 2), and the vertical axis shows the transmittance of etalon 14.

The spacing between adjacent light transmission bands with respect to frequency is constant. That is, the characteristics of the etalon 14 are determined based on the FSR representing the interval between the transmission bands of the etalon 14 and the FWHM which is the full width at half maximum of the transmission peak. Finesse is an index showing the degree of sharpness of the interference fringes.

FIG. 4 is a diagram showing an example of the transmittance of Etalon 14, where the horizontal axis represents frequency and the vertical axis represents transmittance. As shown in FIG. 4, the frequencies showing the peak transmittance appear discretely. Also, the spacing between adjacent transmittance peaks is determined based on the FSR.

FIG. 5 is a diagram showing the frequency showing the peak of the transmittance in the transmission characteristics of the etalon 14 shown in FIG. 4 based on the “frequency-electric field”.

When the etalon 14 composed of a ball lens has a ball lens diameter D of 10 mm, a refractive index of 2.0, a wavelength of λ of 1500 nm, and a velocity of intensity-modulated light 15 of c, the FSR is λ ^{2 in the} wavelength device. / 2nD = 0.056 nm, and c / 2nD = 7.5 GHz in the frequency region. Therefore, the dimension measuring device 10 using the etalon 14 can obtain the same effect as the measurement using the optical comb by utilizing the periodicity of the intensity-modulated light 15 from the etalon 14.

<Beam splitter 18>
The beam splitter 18 of FIG. 1 divides the intensity-modulated light 15 incident through the optical fiber 36 into a measurement light emitted to the optical fiber 38 and a reference light emitted to the optical fiber 40. Further, the beam splitter 18 synthesizes the measurement light returned via the optical fiber 38 and the reference light returned via the optical fiber 40, and outputs the light to the optical fiber 36. As the beam splitter 18, for example, various known optical couplers having such a function can be used.

<Measuring object scanning optical system 20>
The object scanning optical system 20 forms an image of the measurement light emitted from the optical fiber 38 at an arbitrary measurement point on the surface of the object 44 via the lens 46. Then, the measurement object scanning optical system 20 collects the measurement light reflected or scattered at the measurement point and causes it to enter the optical fiber 38. Therefore, the object scanning optical system 20 includes a lens 46, a scanning mirror (not shown), and an actuator (not shown) for driving the scanning mirror. The actuator adjusts the orientation of the reflecting surface of the scanning mirror according to the control signal received from the controller 30.

Further, the object scanning optical system 20 is provided with a semitransparent reflector 50 for creating a 0-point signal RS in the controller 30. Since the reflector 50 is arranged at a position having the same length as the reference optical path length, interference fringes having an optical path difference of 0 are formed by the detector 26. The reference numeral TS is a target signal.

<Reference optical path length changing device 22>
The reference optical path length changing device 22 is configured such that the reference light emitted from the optical fiber 40 passes through a predetermined optical path and then re-enters the optical fiber 40. Then, the reference optical path length changing device 22 changes the optical path length of the optical path to adjust the optical path difference between the optical path length of the measurement light and the optical path length of the reference light.

Therefore, the reference optical path length changing device 22 includes a reference mirror 24 and a linear drive unit 54 that reciprocates the reference mirror 24 along the optical axis of the reference light 58.

<< Reference mirror 24 >>
A corner cube prism is used as the reference mirror 24. The optical path length of the reference light 58 is changed by moving the reference mirror 24 along the optical axis of the reference light 58 by the linear motion drive unit 54.

<Detector 26>
The detector 26 outputs the detected amount of light as an electric signal. As the detector 26, for example, a semiconductor detection element such as a photodiode, CCD (Charge Coupled Device) or C-MOS (Complementary Metal Oxide Semiconductor) is used. Further, the detector 26 samples at predetermined time intervals and converts the detected light amount at each sampling time into an electric signal. Further, the detector 26 is electrically connected to the controller 30 via the frequency amplifier 28, and sequentially transmits the electric signal to the controller 30.

<Controller 30>
The controller 30 is composed of a so-called PC (Personal Computer), and includes a computing device such as a CPU (Central Processing Unit), a semiconductor memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory), or a magnetic disk or an optical disk. A storage device consisting of these readers, a communication device consisting of software such as an electronic circuit and a device driver configured based on communication standards such as RS232C and Ethernet (registered trademark), and a CPU stored in the storage device. It has a program to be executed.

Then, the controller 30 calculates the height of the measurement point of the object to be measured 44 by measuring the optical path length of the reference light from the amount of light detected by the detector 26.

Further, the controller 30 is electrically connected to each part of the dimension measuring device 10 and controls them in an integrated manner.

Further, the controller 30 calculates the position of the reference mirror 24 when the signal of the interference fringe is acquired from the detector 26 in order to measure the optical path length of the reference light.

<Optical fiber 32-42>
The optical fibers 32 to 42 are arranged between the light source 12, the etalon 14, the circulator 16, the beam splitter 18, the object scanning optical system 20, the reference optical path length changing device 22, and the detector 26, and transmit light between the devices. To transmit. Various known optical fibers can be used as the optical fibers 32 to 42, but it is preferable that the transmission loss is as small as possible with respect to the wavelength of the light emitted from the light source 12.

[Action of dimension measuring device 10]
FIG. 6 is a flowchart showing the operation of the dimension measuring device 10 when measuring the dimensions of the object to be measured 44. The operation of the dimension measuring device 10 is controlled by the controller 30.

As a preliminary preparation, a reference product having known dimensions is installed in the dimension measuring device 10, and the position PR of the reference mirror 24 corresponding to the maximum value of the amplitude of the interference fringes when the reference surface is irradiated with the measurement light is calculated. It is stored in the storage device of the controller 30.

When the measurement operation is started, the controller 30 controls the linear drive unit 54 to move the reference mirror 24 at a predetermined speed along the optical axis of the reference light (step S101).

Next, the actuator of the measurement object scanning optical system 20 is controlled to adjust the orientation of the scanning mirror so that the measurement light connects spots at an arbitrary measurement point of the measurement object 44 (step S102).

Next, the detector 26 detects the interference fringes generated according to the difference between the optical path length of the measurement light and the optical path length of the reference light (step S103). The detector 26 transmits an electric signal corresponding to the interference fringes to the controller 30.

Next, the controller 30 associates the electrical signal received from the detector 26 with the position of the reference mirror 24 (step S104).

Then, the controller 30 measures the time when the amplitude of the periodic vibration of the electric signal becomes maximum, that is, the time TP when the amplitude of the interference fringes becomes maximum, and calculates the position PP of the reference mirror 24 in the time TP. (Step S105).

After that, the controller 30 determines the optical path difference of the reference light 58 corresponding to the difference between the position PP of the reference mirror 24 obtained in step S105 and the position PR of the reference mirror 24 similarly obtained with respect to the reference plane. Is calculated (step S106).

Then, the controller 30 calculates the surface height of the object to be measured 44 at the measurement position by adding the optical path difference to the surface height of the reference plane (step S107).

Then, the controller 30 repeatedly carries out the above steps S101 to S107, and measures the surface height at each point on the surface of the object to be measured 44 for each irradiation position of the measurement light.

By the way, in the dimension measuring device 10 using the etalon 14, the intensity-modulated light 15 (see FIGS. 4 and 5) irradiates the object to be measured 44 and the reference mirror 24. Therefore, the measurable range is expanded as compared with a general dimensional measuring device in which low coherence light is applied to the object to be measured 44 and the reference mirror 24.

That is, the measurable range of the dimension measuring device 10 using the intensity-modulated light 15 emitted from the etalon 14 is determined according to the FSR (see FIG. 3) of the etalon 14.

Specifically, the position of the object to be measured 44 in which the optical path length of the measurement light and the optical path length of the reference light are equal to each other, which can be measured by a dimension measuring device using a general low coherence light that does not use the etalon 14 (hereinafter, In addition to "zero point position") ", from the zero point position," N x nd (where "N" represents an integer of 1 or more, "n" represents the refractive index of the reflection region 14C of the etalon 14, and " “D” represents the distance between the reflective coat 14A and the reflective coat 14B of the etalon 14) ”, which makes it possible to measure the positions apart.

Therefore, according to the dimension measuring device 10, "L = (L ₀ + N × nd (where" L ₀ "represents the zero point position," N "represents an integer greater than or equal to 0," and "n" represents the etalon 14. It represents the refractive index of the reflection region 14C, and "d" represents the distance between the reflection coat 14A and the reflection coat 14B of the etalon 14) ", which enables measurement for each discrete position L. The discrete position L indicates a position separated from the zero point position L _{0 on the} object to be measured 44 by "N × nd" in the direction in which the intensity-modulated light 15 is directed toward the object to be measured 44.

〔effect〕
According to the etalon 14 and the dimensional measuring device 10 of the embodiment, since the etalon 14 is configured by the ball lens as shown in FIG. 2, the distances between the reflective coats 14A and 14B provided on the light incident surface 14a and the light emitting surface 14b, respectively. Is uniquely determined by the diameter of the ball lens. Therefore, the reflective coats 14A and 14B can be easily aligned with each other with high accuracy. Further, since the etalon 14 is composed of a ball lens, it is possible to provide a dimensional measuring device 10 having an etalon having a simple structure.

When the focal point of the lens 32A and the center P of the etalon 14 are deviated from each other, an optical path length difference is generated according to the deviating amount, which affects the measurement accuracy. Therefore, when assembling the dimension measuring device 10, it is necessary to adjust the optical axis so that the focus of the lens 32A is aligned with the center P of the etalon 14 in advance.

In this optical axis adjustment work, the lens 32A is moved in the vertical direction and the front-back direction with respect to the optical axis of the white light 13. At this time, if the focal point of the lens 32A and the center P of the etalon 14 do not match, interference fringes occur in the light emitted from the etalon 14, but the focal point of the lens 32A and the center P of the etalon 14 match. If this happens, the interference fringes disappear. By positioning the lens 32A at this position, the optical axis adjustment work is completed.

10 ... Dimension measuring device, 12 ... light source, 13 ... white light, 14 ... etalon, 14A, 14B ... reflective coat, 14C ... reflective area, 14a ... light incident surface, 14b ... light emitting surface, 15 ... intensity modulated light, 16 ... Circulator, 18 ... Beam splitter, 20 ... Measurement object scanning optical system, 22 ... Reference optical path length changing device, 24 ... Reference mirror, 25 ... Reflector, 26 ... Detector, 28 ... Frequency amplifier, 30 ... Controller, 32 , 34, 36, 38, 40, 42 ... Optical fiber, 44 ... Object to be measured, 46 ... Lens, 48 ... Collimeter lens, 50 ... Reflector, 54 ... Linear drive unit, 58 ... Reference light, 60 ... Reflected light

Claims (1)

A light source that emits light and
Etalon, which emits transmitted waveform light having transmitted peaks at regular intervals in the wavelength region by multiplex interference of light from the light source inside the light source.
An optical dividing means that divides the light emitted from the etalon into measurement light and reference light and emits the light.
A measurement light irradiating means that irradiates an object to be measured with the measurement light emitted from the light dividing means,
A reference optical path length changing means that has a reflecting mirror that reflects the reference light emitted from the light dividing means and changes the optical path length of the reference light by moving the reflecting mirror.
An optical detection means for detecting interference light in which the measurement light reflected by the object to be measured and the reference light reflected by the reflector are combined.
A dimensional measuring device including a calculation means for calculating the size of the object to be measured based on the interference light detected by the photodetecting means.
The etalon is
A ball lens having a light incident surface forming a part of a spherical surface and a light emitting surface forming another part of the spherical surface and facing the light incident surface.
A first reflective film provided on the light incident surface and
A second reflective film provided on the light emitting surface and
An optical system that collects light from the light source at the center of the ball lens via the light incident surface.
A dimensional measuring device provided with.

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