JP2010043954A - Dimension measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dimension measuring apparatus which can adjust a focal position of a measuring light beam in a short time in the measurement of surface height of an object under measurement using white light interference. <P>SOLUTION: The dimension measuring apparatus 1 includes: a white light source 2; a light beam dividing means 3 for dividing the light emitted from the white light source 2 into the measuring light beam having optical path length in accordance with the surface height of the object under measurement and a reference light beam; a reference light beam scanning optical system 5 for changing the optical path length of the reference light beam emitted from the light beam dividing means 3; a varifocal lens 41 arranged within the measuring light beam; a detector 6 for detecting an interference signal which occurs when the optical path length of the measuring light beam and the optical path length of the reference light beam are nearly equal and outputting a signal corresponding to the interference signal; and a controller 7 which adjusts the focal length of the varifocal lens 41 so that the measuring light beam focuses on a position at which the measuring light beam is reflected when the optical path length of the reference light beam and the optical path length of the measuring light beam are equal and determines the optical path length of the reference light beam corresponding to the maximum value of the interference signal, thereby determining the surface height of the object under measurement. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a dimension measuring apparatus that measures the dimension of an object to be measured, and more particularly to a dimension measuring apparatus that measures the surface height of an object to be measured using white interference.

  Conventionally, a method using the principle of white interference has been proposed as a method for accurately measuring the surface height of an object to be measured without contact. In such a method, the light emitted from the white light source is divided into a measurement light beam directed to the object to be measured and a reference light beam directed to the reference mirror, and these light beams are respectively reflected on the surface of the object to be measured or the reference mirror. After the reflection, it is detected again together. At that time, when the optical path length of the measurement light beam is equal to the optical path length of the reference light beam, the amplitude of the white interference fringe is maximized. Therefore, this method measures the surface height of the object to be measured by moving the reference mirror, measuring the position of the reference mirror when the amplitude of the white interference fringe is maximum, and examining the optical path length of the reference beam. Can be measured.

  Here, when the measurement range of the dimension to be measured is wide (that is, when the change in the surface height of the object to be measured is wide), the measurement light beam is optically focused at any position within the measurement range. Even if the system is adjusted, if the surface of the object to be measured is positioned at a position far from the position where the measurement light beam is focused, the spot size of the measurement light beam on the surface is blurred and large. In addition, since the light reflected or scattered in the spot contributes to the generation of white interference fringes, the measurement method cannot measure the surface height for a fine structure when the spot size increases. Therefore, an objective lens placed in the measurement beam is irradiated by irradiating the measurement object with laser light so that the measurement beam is focused on the surface of the measurement object, observing the return light and performing autofocus. A dimension measuring method is known in which the focal position of the measurement light beam is adjusted by moving the lens in the optical axis direction (see, for example, Patent Document 1).

JP 2000-146532 A

  In the method as described in Patent Document 1, an element whose length is changed by voltage application such as a mechanical movement mechanism or a piezoelectric element is used to move the objective lens. However, in such a method, since the time required for adjusting the focal position depends on the mechanical mechanism or the response speed of the piezo element, it is difficult to reduce the time required for measurement. In particular, when the range of dimensions to be measured is wide and the adjustment range of the focus position of the measurement light beam is wide, the moving distance of the objective lens becomes long, so the time required for adjusting the focus position of the measurement light beam becomes long. . In addition, heat generated by the voltage applied to drive the piezo element and vibration associated with the operation of the mechanical mechanism may cause noise, which may reduce measurement accuracy.

  In view of the above problems, an object of the present invention is to provide a dimension measuring apparatus capable of adjusting the focal position of a measurement light beam in a short time in measuring the surface height of an object to be measured using white interference. .

According to one embodiment of the present invention, a dimension measuring device for measuring the surface height of an object to be measured is provided. Such a dimension measuring apparatus includes a white light source, a light beam splitting element that splits light emitted from the white light source into a measurement light beam and a reference light beam having an optical path length corresponding to the surface height of the object to be measured, and a light beam splitting element Reference light scanning optical system that changes the optical path length of the reference light beam emitted from the lens, and a variable-focus lens that is arranged in the measurement light beam and can change the focal length without mechanical movement in the optical axis direction of the measurement light beam A detector that detects an interference signal generated when the optical path length of the measurement light beam and the optical path length of the reference light beam are substantially equal, and outputs a signal corresponding to the interference signal, and the optical path length of the reference light beam and the optical path length of the measurement light beam By adjusting the focal length of the variable focus lens so that the measurement light beam is focused at a position where the measurement light beam is reflected when they are equal, and obtaining the optical path length of the reference light beam corresponding to the maximum value of the interference signal, Surface height of measured object And a controller for determining the.
In the dimension measuring device according to the present invention, the variable focus lens is preferably a liquid lens.

  In the dimension measuring apparatus according to the present invention, the reference beam scanning optical system is symmetrical with respect to the rotation member, the drive unit that rotates the rotation member at a predetermined rotation speed, and the rotation axis of the rotation member. When a reference light beam is incident on one of the first and second reflecting elements and the first and second reflecting elements disposed on the rotating member, one of the reflecting elements The reference light beam is guided so that the reference light beam reflected by the light beam is incident on the other reflection element of the first and second reflection elements in a direction parallel to and opposite to the incident direction of the reference light beam with respect to the one reflection element. It is preferable to change the optical path length of the reference light beam by rotating the rotating member. In this case, the controller detects that either the first or second reflective element has reached the predetermined position, and that either of the first or second reflective element has reached the predetermined position. The optical path length of the reference light beam is measured by multiplying the elapsed time since the detection by the rotational speed of the rotating member to determine the detected position of the reflecting element, and according to the measured optical path length of the reference light beam. It is preferable to adjust the focal length of the variable focus lens. Alternatively, the dimension measuring device according to the present invention includes a rotational position detector such as a rotary encoder that detects the rotational position of the rotating member, and the controller first determines the rotational position of the rotating member detected by the rotational position detector. Alternatively, it is preferable that the optical path length of the reference light beam is measured by specifying the position of the second reflecting element, and the focal length of the variable focus lens is adjusted according to the measured optical path length of the reference light beam.

  Further, the dimension measuring apparatus according to the present invention is disposed outside the measurement light beam and irradiates the reference light so as to be obliquely incident on the variable focus lens, and is disposed outside the measurement light beam and transmitted through the variable focus lens. And a second detector for receiving a reference light and outputting a signal corresponding to the light receiving position of the reference light, and the controller is a reference table showing a relationship between the light receiving position of the reference light and the focal length of the variable focus lens. Measure the focal length of the variable focal length lens and adjust the focal length of the variable focal length lens so that the amount of deviation between the measured focal length and the focal length of the variable focal length lens to be set is small. It is preferable to do.

  According to another embodiment of the present invention, a dimension measuring method for measuring the surface height of an object to be measured is provided. According to the dimension measuring method, the light emitted from the white light source is divided into a measurement light beam having a light path length corresponding to the surface height of the object to be measured and a reference light beam by the light beam dividing element, and emitted from the light beam dividing element. The step of changing the optical path length of the reference light beam, the step of measuring the optical path length of the reference light beam, and the position where the measured light beam is reflected when the optical path length of the measured reference light beam is equal to the optical path length of the measurement light beam. Adjusting the focal length of the variable focus lens, which is arranged in the measurement luminous flux so that the measurement luminous flux is focused and can change the focal length without mechanical movement in the optical axis direction of the measurement luminous flux, and measurement Detecting an interference signal generated when the optical path length of the light beam and the optical path length of the reference light beam are substantially equal, outputting a signal corresponding to the interference signal, and determining the optical path length of the reference light beam corresponding to the maximum value of the interference signal. By Mel, and a step of determining the surface height of the object.

  ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the dimension measuring apparatus which can adjust the focus position of measurement light in a short time in the measurement of the surface height of the to-be-measured object using white interference.

Hereinafter, an embodiment in which the present invention is applied to a dimension measuring device for measuring the surface height of an object to be measured such as a mold will be described with reference to the drawings.
The dimension measuring apparatus to which the present invention is applied divides light emitted from a white light source into a measurement light beam and a reference light beam that are directed to the object to be measured by an optical coupler. The measurement light beam is reflected or scattered by the surface of the object to be measured, and then combined with the reference light beam again by the optical coupler and detected by the detector. Then, the dimension measuring apparatus measures the optical path length of the reference light beam when the amplitude of the white interference fringe generated between the two light beams is maximized, and measures the surface height of the object to be measured. This measuring apparatus changes the focal length of a lens with a variable focal length arranged in the optical path of the measurement light beam according to the optical path length of the reference light beam, so that when the white interference fringe is observed, The focal point is formed on the surface of the object to be measured.

FIG. 1 is a diagram showing a schematic configuration of a dimension measuring apparatus 1 to which the present invention is applied. The dimension measuring apparatus 1 includes a white light source 2, an optical coupler 3, an object scanning optical system 4, a reference light scanning optical system 5, a detector 6, a controller 7, and optical fibers 8 to 11.
In the dimension measuring apparatus 1, the white light emitted from the white light source 2 is transmitted to the optical coupler 3 through the optical fiber 8. The white light is split by the optical coupler 3 into a measurement light beam directed toward the object 12 to be measured and a reference light beam directed toward the reference light scanning optical system 5. After passing through the optical fiber 9, the measurement light beam is imaged on the measurement point on the surface of the measurement object 12 by the measurement object scanning optical system 4. Then, the measurement light beam reflected or scattered at the measurement point on the surface of the measurement object 12 enters the optical coupler 3 again through the measurement object scanning optical system 4 and the optical fiber 9. On the other hand, the reference light beam passes through the optical fiber 10 and then enters the reference light scanning optical system 5 having an optical path length adjustable within a predetermined range. The reference light beam passes through the reference light scanning optical system 5 and then enters the optical coupler 3 through the optical fiber 10 again. Then, the measurement light beam and the reference light beam are combined together by the optical coupler 3, and then enter the detector 6 through the optical fiber 11. The detector 6 detects a white interference fringe generated when the optical path length of the measurement light beam and the optical path length of the reference light beam are substantially equal, converts the white interference fringe into an electric signal, and sends the electric signal to the controller 7. The controller 7 obtains the optical path length of the reference light beam when the amplitude of the white interference fringe is maximized. Then, the controller 7 calculates the difference between the optical path length and the optical path length of the reference light beam with respect to the reference surface of the standard product whose height is known in advance, and obtains the height of the measurement point on the surface of the object 12 to be measured.
Hereinafter, each part of the dimension measuring apparatus 1 will be described in detail.

  The white light source 2 is a light source that has a short coherence length and can emit light having a broad wavelength. As the white light source 2, for example, a laser diode, LED, SLD (super luminescent diode), SOA (Semiconductor Optical Amplifier) light source, ASE (Amplified Spontaneous Emission) light source, or the like can be used. The center wavelength of the light emitted from the white light source 2 can be set to 750 nm, 1300 nm, 1550 nm, and the like, for example. In the present embodiment, a laser diode having a center wavelength of 1550 nm is used as the white light source 2.

  The optical coupler 3 divides white light incident via the optical fiber 8 into a measurement light beam emitted to the optical fiber 9 and a reference light beam emitted to the optical fiber 10. On the other hand, the measurement light beam incident via the optical fiber 9 and the reference light beam incident via the optical fiber 10 are combined and emitted to the optical fiber 11. As the optical coupler 3, for example, various known optical couplers having such a function can be used.

FIG. 2 shows a schematic configuration diagram of the measurement object scanning optical system 4. As shown in FIG. 2, the measurement object scanning optical system 4 includes a variable focus lens 41, a lens driver 42, a condensing lens 43, a scanning mirror 44, and an actuator 45. Then, the measurement object scanning optical system 4 forms an image of the measurement light beam emitted from the optical fiber 9 on an arbitrary measurement point on the surface of the measurement object 12. Then, the measurement object scanning optical system 4 collects the measurement light beam reflected or scattered at the measurement point and makes it incident on the optical fiber 9 again.
Hereinafter, each part of the measurement object scanning optical system 4 will be described.

The variable focus lens 41 is a lens that can change the focal length without having a component that moves along the optical axis of the measurement light beam, and is disposed on the optical path of the measurement light beam emitted from the optical fiber 9. The variable focus lens 41 changes the position where the measurement light beam is focused in accordance with the focal length.
As the variable focus lens 41, for example, a liquid lens in which two kinds of liquids (for example, oil and aqueous solution) that have different refractive indexes and do not mix with each other can be used. In such a liquid lens, each liquid layer is formed in a direction perpendicular to the optical axis, and an interface between the liquid layers functions as a refractive surface. Therefore, in such a liquid lens, the refractive power according to the refractive index of each liquid and the curvature radius of the interface can be obtained. In this liquid lens, when a voltage is applied from the outer periphery of the liquid lens, the radius of curvature of the interface changes according to the applied voltage, and the refractive power at the interface changes. Therefore, the focal length of the liquid lens can be adjusted by adjusting the applied voltage.
Such a liquid lens can adjust the focal length without moving the entire lens or a part thereof along the optical axis of the measurement light beam. Therefore, the focal length of the liquid lens can be adjusted to a desired value at high speed. As the variable focus lens 41, a lens whose focal length can be changed without mechanically moving the entire lens or a part of the lens components, such as a lens using liquid crystal as a medium, may be used. .

  The lens driver 42 is a driver for adjusting the focal length of the variable focus lens 41, and converts the AC voltage or the DC voltage supplied from the power supply circuit into a desired DC voltage included in a predetermined voltage range. Etc. The lens driver 42 is connected to the controller 7 via a signal line, and applies a voltage determined according to the focal length adjustment signal received from the controller 7 to the variable focus lens 41.

The condensing lens 43 is disposed between the variable focus lens 41 and the scanning mirror 44, and cooperates with the variable focus lens 41 to form an image of the measurement light beam on or near the surface of the measurement object 12. Therefore, the area of the spot that the measurement light beam connects on the object to be measured 12 is reduced, so that the resolution of the dimension measuring apparatus 1 can be increased. Further, the condensing lens 43 condenses the measurement light beam reflected or scattered at the spot through the scanning mirror 44 and makes it incident on the optical fiber 9 through the variable focus lens 41.
The scanning mirror 44 is arranged so as to reflect the measurement light beam transmitted through the condenser lens 43 toward an arbitrary measurement point on the surface of the object to be measured. The scanning mirror 44 rotates along each of a surface substantially parallel to the surface of the object to be measured 12 and a surface substantially orthogonal to the surface and parallel to the optical axis of the measurement light beam emitted from the condenser lens 43. The direction of the reflecting surface of the scanning mirror 44 can be adjusted. By adjusting the direction of the reflecting surface of the scanning mirror 44, the measurement light beam can scan the surface of the object 12 to be measured two-dimensionally.
The actuator 45 adjusts the direction of the reflecting surface of the scanning mirror 44 according to the control signal received from the controller 7.

  FIG. 3 shows a schematic configuration diagram of the reference light scanning optical system 5. As shown in FIG. 3, the reference light scanning optical system 5 includes a rotary table 51, four corner cube prisms 53 to 56 arranged on the rotary table 51, and a fixed mirror 57 arranged around the rotary table. To 66 and an actuator 67. The reference light scanning optical system 5 is configured such that the reference light beam emitted from the optical fiber 10 enters the optical fiber 10 again after passing through a predetermined optical path. The reference light scanning optical system 5 adjusts the optical path length difference between the optical path length of the measurement light beam and the optical path length of the reference light beam by changing the optical path length of the optical path.

The rotary table 51 is rotatable around the rotary shaft 52. The rotary table 51 is driven by the actuator 67 and rotates at a constant rotational speed during the measurement operation. For example, the rotary table 51 rotates at 6000 rpm during the measurement operation.
The four corner cube prisms 53 to 56 are arranged on the rotary table 51 so as to be equidistant from the rotary shaft 52 and equidistant from each other. Specifically, the corner cube prisms 53 and 55 are arranged so as to be symmetrical about the rotation axis 52. Similarly, the corner cube prisms 54 and 56 are also arranged so as to be symmetric with respect to the rotation axis 52. The angle formed by the surfaces parallel to the entrance surfaces of the corner cube prisms adjacent to each other is a right angle. Furthermore, when the incident surface of each corner cube prism is located on the right side of the turntable 51, it faces the end surface of the optical fiber 10, and is arranged so that the reference light beam emitted from the end surface enters the corner cube prism. .

  The fixed mirrors 57 to 66 are arranged so as to surround the rotary table 51. Each fixed mirror 57 to 66 functions as a light direction changing member that changes the direction of the reference light beam emitted from the corner cube prism. When the reference light beam emitted from the optical fiber 10 enters one of the corner cube prisms, the fixed mirrors 57 to 66 change the direction of the reference light beam emitted from the corner cube prism, and change to the adjacent corner cube prism. Make it incident. Therefore, the reference light beam enters the optical fiber 10 again via the fixed mirrors 57 to 66 and the corner cube prisms 53 to 56. At that time, the reference light beam is incident on the two corner cube prisms arranged symmetrically about the rotation axis 52 in parallel and in opposite directions. For this reason, when the position of the rotary shaft 52 of the turntable 51 is shifted, the distance between one of the two corner cube prisms and the fixed mirror disposed opposite thereto is increased according to the shift amount. However, the distance between the other corner cube prism and the fixed mirror disposed opposite thereto is conversely shortened in accordance with the amount of deviation. Therefore, even if the position of the rotating shaft 52 is shifted, the optical path length itself of the reference light beam does not change.

As an example, as shown in FIG. 3, when the corner cube prism 53 is positioned facing the end face of the optical fiber 10 and the reference light beam emitted from the optical fiber 10 enters the corner cube prism 53, The propagation path will be described.
The reference light beam is emitted from the optical fiber 10 and then enters the corner cube prism 53. The reference light beam is reflected by the corner cube prism 53 in the direction parallel to the incident direction and in the opposite direction. Thereafter, the reference light beam is reflected by the fixed mirror 57 so as to be perpendicular to the incident direction and travels toward the fixed mirror 58. Thereafter, the reference light beams are sequentially reflected by the fixed mirrors 58 and 59 so as to be perpendicular to the incident direction, and the traveling direction is rotated 180 degrees toward the corner cube prism 54. When the reference light beam is incident on the corner cube prism 54, the reference light beam is reflected in a direction parallel to and opposite to the incident direction and travels toward the fixed mirror 60. The reference light beams are respectively reflected at right angles by the fixed mirrors 60 to 62, and the traveling direction is rotated 270 degrees counterclockwise. Thereafter, the reference light flux goes to the corner cube prism 55. The reference light beam is reflected by the corner cube prism 55 in the direction opposite to the incident direction and travels toward the fixed mirror 63. The reference light beams are reflected at right angles by the fixed mirrors 63 to 65, respectively, and the traveling direction rotates 270 degrees counterclockwise. Thereafter, the reference light flux goes to the corner cube prism 56. The reference light beam is reflected by the corner cube prism 56 in the direction opposite to the incident direction and travels toward the fixed mirror 66. Since the reference light beam is perpendicularly incident on the fixed mirror 66, it is reflected by the fixed mirror 66, and then travels in the reverse direction along the path that has passed through it. Then, the reference light beam again passes through the corner cube prisms 53 to 56 and the fixed mirrors 57 to 65, is then emitted from the reference light scanning optical system 5, and enters the optical fiber 10.

  Here, for example, it is assumed that the position of the rotation shaft 52 is shifted by a distance a in a direction approaching the optical fiber 10. In this case, the optical path length of the optical path from the end face of the optical fiber 10 to the fixed mirror 57 via the corner cube prism 53 is shortened by 2a. However, as described above, the corner cube prism 55 is arranged symmetrically with the corner cube prism 53 with respect to the rotation axis 52. The direction in which the reference light beam enters the corner cube prism 53 and the direction in which the reference light beam enters the corner cube prism 55 are parallel and opposite to each other. Therefore, the optical path length of the optical path from the fixed mirror 62 to the fixed mirror 63 via the corner cube prism 55 is increased by 2a. Therefore, even if the position of the rotating shaft 52 is deviated, it can be seen that the optical path length deviations cancel each other between the corner cube prisms 53 and 55 and the fixed mirror disposed facing them.

Further, it is assumed that the position of the rotating shaft 52 is perpendicular to the traveling direction of the reference light beam emitted from the optical fiber 10 and is shifted by a distance b in a direction approaching the optical fiber 10. In this case, the optical path length of the optical path from the fixed mirror 59 to the fixed mirror 60 via the corner cube prism 54 is increased by 2b. However, as described above, the corner cube prism 56 is arranged symmetrically with the corner cube prism 54 with respect to the rotation axis 52. The direction in which the reference light enters the corner cube prism 54 and the direction in which the reference light enters the corner cube prism 56 are parallel and opposite to each other. Therefore, the optical path length of the optical path from the fixed mirror 65 to the fixed mirror 66 via the corner cube prism 56 is shortened by 2b. Therefore, in this case as well, even if the position of the rotating shaft 52 is shifted, it can be seen that the optical path length shifts cancel each other between the corner cube prisms 54 and 56 and the fixed mirror disposed opposite thereto. .
As described above, even if the position of the rotation shaft 52 is shifted along the direction parallel or perpendicular to the traveling direction of the reference light beam emitted from the optical fiber 10, the center point with respect to the rotation shaft 52. Since the deviation of the optical path length between the two corner cube prisms arranged symmetrically and the fixed mirror arranged opposite to each other cancels each other, the total length of the optical path of the reference beam may not change. I understand.

  On the other hand, when the distance between the end face of the corner cube prism at the position facing the end face of the optical fiber 10 changes due to the rotation of the turntable 51, the other corner cube prism and the fixed mirror disposed facing the corner cube prism are changed. The distance also changes by the same amount. For example, in FIG. 3, it is assumed that the distance between the corner cube prism 53 and the end face of the optical fiber 10 is increased by c due to the rotation of the turntable 51. In this case, since the distance between each corner cube prism and the fixed mirrors (for example, the corner cube prism 54 and the fixed mirrors 59 and 60) arranged opposite to each other is also increased by c, the optical path length of the reference light beam as a whole is increased. 8c longer. In this way, by rotating the turntable 51, the optical path length of the reference light beam can be greatly changed to eight times the moving distance of the corner cube prism.

  The actuator 67 operates the rotary table 51 in accordance with a control signal from the controller 7. Therefore, various known motors can be used as the actuator 67. However, it is preferable that the rotary table 51 rotates at a constant speed (for example, 6000 rpm) during the measurement operation. Moreover, it is preferable that the rotational speed of the turntable 51 can be changed according to a use. Therefore, it is preferable to use a motor having a small speed fluctuation rate (for example, a speed fluctuation rate of 0.01% or less) at a plurality of set rotational speeds as the actuator 67. Further, in order to detect the rotational position of the rotary table 51, a rotational position detector such as a rotary encoder can be used.

The detector 6 outputs the detected light quantity as an electrical signal. As the detector 6, for example, a semiconductor detection element such as a photodiode, CCD, or C-MOS can be used. In this embodiment, a detector in which CCD elements are arranged in a two-dimensional array is used as the detector 6. The detector 6 samples at predetermined time intervals, and converts the detected light amount at each sampling time into an electrical signal. Furthermore, the detector 6 is electrically connected to the controller 7 and transmits the electrical signal to the controller 7 sequentially.
Here, when white interference occurs between the reference light beam and the measurement light beam, the optical path difference between the light beams changes according to the movement of the corner cube prism, and thus the corresponding electrical signal according to the change in the light amount due to the optical path difference. Also fluctuate. Moreover, since the position of the corner cube prism changes with the rotation of the rotary table, the position changes with time. Therefore, the white interference fringes are observed in the temporal change of the electric signal output from the detector 6.

  The optical fibers 8 to 11 are arranged between the optical coupler 3, the white light source 2, the measurement object scanning optical system 4, the reference light scanning optical system 5, and the detector 6, respectively, and transmit a light beam between the devices. As the optical fibers 8 to 11, various known optical fibers can be used. However, it is preferable that the optical fibers 8 to 11 have a transmission loss as small as possible with respect to the wavelength of light emitted from the white light source 2.

The controller 7 is configured by a so-called PC, and includes a calculation device such as a CPU, a semiconductor memory such as a ROM and a RAM, a storage device including a magnetic disk, an optical disk, and a reading device thereof, RS232C, Ethernet (registered trademark), and the like. A communication device including software such as an electronic circuit and a device driver configured according to the communication standard, and a computer program stored in the storage device and executed on the CPU.
Then, the controller 7 obtains the height of the measurement point on the surface of the object 12 to be measured by measuring the optical path length of the reference light beam from the light amount detected by the detector 6. The controller 7 is electrically connected to each part of the dimension measuring apparatus 1 and controls them. In particular, the controller 7 measures the optical path length of the reference light beam, and when the optical path length of the reference light beam and the optical path length of the measurement light beam are equal, the variable-focus lens so that the measurement light beam is focused at a position where the measurement light beam is reflected. The focal length of 41 is adjusted.

  Here, the controller 7 obtains the position of the corner cube prism when the white interference fringe signal is acquired from the detector 6 in order to measure the optical path length of the reference light beam. When the rotary table 51 of the reference light scanning optical system 5 is rotating, the reference light beam does not reach the detector 6 depending on the position of the corner cube prism. In other words, the reference light beam reaches the detector 6 only when the reference light beam emitted from the optical fiber 10 enters the incident surface of any corner cube prism. In the detector 6, the amount of light when the reference light beam is received is much larger than the amount of light when the reference light beam is not received. Therefore, the electric signal corresponding to the light amount transmitted from the detector 6 to the controller 7 is also larger than the signal when the reference light beam is not received during the period when the reference light beam is received. Therefore, the controller 7 estimates the position of the corner cube prism by examining the temporal change of the electrical signal corresponding to the amount of light received from the detector 6, and obtains the optical path length of the reference light beam.

Therefore, first, the position p ₁ closest to the optical fiber 10 of the corner cube prism when the reference light beam can be incident on the incident surface of any corner cube prism is measured in advance and stored in the storage device of the controller 7. .
On the other hand, during the measurement operation, for example, it is assumed that the rotary table 51 rotates clockwise at a constant speed in FIG. In this case, for example, the controller 7 detects a time t ₁ when the amount of change of the electrical signal per time exceeds a predetermined threshold. In order to prevent detection of a signal change due to white light interference, it may be added to the detection condition at time t ₁ that the average value of the electrical signal in a certain period before time t ₁ is lower than a predetermined value.
The controller 7 estimates that any corner cube prism is at the position p ₁ at time t ₁ . The position of the corner cube prism at an arbitrary time t after time t ₁ is obtained as follows. By multiplying the time difference between the time t and the time t ₁ by the rotation speed of the rotary table 51, an angle β at which the corner cube prism rotates from the time t ₁ to the time t is obtained. Then, the controller 7 sets the position rotated by the angle β clockwise from the position p ₁ as the position of the corner cube prism at the time t. When the position of the corner cube prism is obtained, the distance between each fixed mirror of the reference light scanning optical system and each corner cube prism is obtained. Therefore, the controller 7 obtains the optical path length of the reference light beam based on the position of the corner cube prism. be able to. When the rotation position detector can detect the rotation position of the turntable 51, the controller 7 specifies the position of each corner cube prism from the rotation position and the positional relationship of each corner cube prism on the turntable. The optical path length of the reference light beam may be obtained.

The controller 7 sequentially transmits a focal length adjustment signal corresponding to the optical path length to the lens driver 42 so that the focal position of the measurement light flux changes following the change in the optical path length of the obtained reference light flux.
Here, the focal length of the variable focus lens 41 corresponding to the optical path length of the reference light beam is determined as follows. First, the focal length of the variable focus lens 41 is changed variously, and the focal position of the measurement light beam corresponding to each focal length and the optical path length of the measurement light beam when the measurement light beam is reflected at the focal position are measured in advance. Further, assuming that the optical path length of the measurement light beam at this time is equal to the optical path length of the reference light beam, the focal length representing the relationship between the focal length of the variable focus lens 41 and the optical path length of the corresponding reference light beam based on the measurement result− Create a reference optical path length correspondence table. A focal length-reference optical path length correspondence table is stored in advance in the storage device of the controller 7. The controller 7 can determine the focal length of the variable focus lens 41 by referring to the obtained optical path length and focal length-reference optical path length correspondence table of the reference light beam.
The controller 7 may determine the focal length of the variable focus lens 41 according to a paraxial optical calculation or simulation result for the optical system of the dimension measuring apparatus 1.

Further, the controller 7 obtains the surface height of the object to be measured from the white interference fringes generated according to the optical path difference between the reference light beam and the measurement light beam.
Since the light emitted from the white light source 2 has a short coherence length, the white interference fringes can be observed by the detector 6 only when the optical path difference between the measurement light beam and the reference light beam is substantially equal. Then, when the optical path lengths of both light fluxes coincide, the amplitude of the white interference fringe is maximized. Therefore, the controller 7 obtains the position of the corner cube prism when the amplitude of the white interference fringe becomes maximum for the reference surface of the reference product whose surface height is known in advance and the measurement point of the object 12 to be measured. The controller 7 obtains an optical path difference corresponding to the difference in position and adds the optical path difference to the surface height of the reference surface to determine the surface height of the measurement point of the object to be measured.
In order to accurately obtain the time at which the amplitude of the white interference fringes is maximized, the controller 7 removes a high-frequency component corresponding to the period of the white interference fringes from the electrical signal received from the detector 6, for example. A low-pass filtering process is performed to obtain an envelope of the electric signal. Then, the controller 7 sets the time when the amplitude of the envelope becomes maximum as the time when the amplitude of the white interference fringe becomes maximum.

FIG. 4 shows an operation flowchart of the dimension measuring apparatus 1 when measuring the surface height of the DUT 12. The operation of the dimension measuring device 1 is controlled by the controller 7.
As a preliminary preparation, the above-mentioned reference product is installed in the dimension measuring apparatus 1, and the position Pr of the corner cube prism corresponding to the maximum value of the amplitude of the white interference fringe when the reference surface is irradiated with the measurement light beam is obtained. Stored in the storage device.
When the measurement operation is started, the controller 7 controls the actuator 67 of the reference light scanning optical system 5 to rotate the rotary table 51 at a predetermined speed (step S101). Next, the actuator 43 of the measurement object scanning optical system 4 is controlled to adjust the direction of the scanning mirror 44 so that the measurement light beam is spotted at an arbitrary measurement point of the measurement object 12 (step S102).

  Thereafter, as described above, the controller 7 obtains the position of the corner cube prism on the rotary table 51 from the change in the amount of received light, and sequentially measures the optical path length of the reference light beam (step S103). The controller 7 transmits a focal length adjustment signal to the lens driver 42 so as to change the focal length of the variable focus lens 41 in synchronization with the change in the optical path length of the measured reference light beam (step S104). Then, the focal length of the variable focus lens 41 is adjusted so that the measurement light beam is focused at a position where the measurement light beam is reflected when the optical path length of the reference light beam is equal to the optical path length of the measurement light beam.

  Next, white interference fringes generated according to the difference between the optical path length of the measurement light beam and the optical path length of the reference light beam are detected by the detector 6 (step S105). The detector 6 transmits an electric signal corresponding to the white interference fringe to the controller 7.

Next, the controller 7 determines the relationship between the electrical signal received from the detector 6 and the position of the corner cube prism (step S106). As described above, the controller 7 detects, for example, a time when the electrical signal suddenly changes, and associates the time with the limit position of the corner cube prism that can receive the reference light beam by the detector 6. The relationship between the signal and the position of the corner cube prism can be determined. Then, the controller 7 measures a time at which the amplitude of the periodic vibration of the electrical signal becomes maximum, that is, a time t _{p at} which the amplitude of the white interference fringe becomes maximum, and the position P of the corner cube prism at that time. _p is obtained (step S107). Thereafter, the controller 7 includes position P _p of the corner cube prism obtained in step S105, the position P _r of the corner cube prism obtained in the same manner with respect to the reference plane, the optical path difference between the reference beam corresponding to the difference between the position Is obtained (step S108). And the controller 7 determines the surface height of the to-be-measured object 12 in a measurement position by adding the optical path difference to the surface height of a reference plane (step S109).
The controller 7 can measure the surface height at each point on the surface of the object to be measured 12 by repeating the processes of steps S101 to S109.

  As described above, the dimension measuring apparatus to which the present invention is applied always measures the optical path length of the reference light beam during the measurement operation, and follows the optical path length of the measured reference light beam to focus the measurement light beam. To change. Therefore, when the white interference fringe is obtained between the measurement light beam and the reference light beam, the dimension measuring apparatus can focus the measurement light beam on the surface of the object to be measured. Therefore, such a dimension measuring device can measure the surface height using light reflected or scattered in a narrow range on the surface, so that the surface height can be measured with very high resolution. Further, the dimension measuring apparatus uses a variable focus lens that can change the focal length without mechanical position movement, such as a liquid lens, in order to adjust the focal position of the measurement light beam. Therefore, even if the dimension measuring apparatus changes the optical path length of the reference light beam at high speed, the focus position of the measurement light beam can follow the change, so that the time required for measurement can be shortened. Further, the variable focus lens that can change the focal length without mechanical movement has a small amount of heat generated due to the change in the focal length, and does not generate vibration due to the adjustment of the focal length. Therefore, since noise generation during the measurement operation can be suppressed, the dimension measuring apparatus can measure the surface height of the object to be measured with high accuracy.

In addition, this invention is not limited to said embodiment. For example, in the measurement object scanning optical system, the focal length of the variable focus lens is measured during the measurement of the surface height of the measurement object, and the controller 7 feedback-controls the variable focus lens using the measured focal length. You may do it.
FIG. 5 shows a schematic configuration diagram of another embodiment of the measurement object scanning optical system capable of feedback control of the focal length of the variable focus lens. The measured object scanning optical system 40 shown in FIG. 5 is different from the measured object scanning optical system 4 shown in FIG. 2 in that the focal length confirmation light source 46 and the position detector are arranged opposite to each other with the focus variable lens 41 interposed therebetween. It differs in having 47. In FIG. 5, among the components included in the measurement object scanning optical system 40, those having the same function and configuration as the measurement object scanning optical system 4 shown in FIG. The same reference numerals as those of the constituent elements to be used are attached.
Hereinafter, the difference between the measurement object scanning optical system 40 and the measurement object scanning optical system 4 will be described.

The focal length confirmation light source 46 is a light source used for measuring the focal length of the variable focus lens 41, and is configured by a laser diode, for example. Further, the focal length confirmation light source 46 is arranged outside the measurement light beam so that a light beam irradiated from the focal length confirmation light source 46 (hereinafter referred to as a reference light beam) is obliquely incident on the variable focal length lens 41. Its light emitting surface is directed.
The position detector 47 is a detector capable of detecting the position of the received light beam. For example, a position detection element (PSD) or a light receiving element array in which a plurality of light receiving elements are arranged in a one-dimensional or two-dimensional manner. It can be. The position detector 47 is arranged on the opposite side of the focal length confirmation light source 46 with the variable focus lens 41 interposed therebetween so as to receive the reference light beam that has passed through the variable focus lens 41. A position detector 47 is also arranged outside the measurement beam.

  Here, the reference light beam is refracted by the variable focus lens 41, and its refraction angle changes according to the focal length of the variable focus lens 41. Therefore, the focal length of the variable focus lens 41 is changed variously, the light receiving position of the reference light beam on the position detector 47 corresponding to each focal distance is measured, and the relationship between each focal distance and the corresponding light receiving position is measured. A focal length-light reception position correspondence table is created in advance. A focal length-light receiving position correspondence table is stored in advance in the storage device of the controller 7. Note that the reference light beam is incident on a position away from the principal point of the variable focus lens 41 so that the light receiving position of the position detector 47 changes as much as possible according to the change in the focal length of the variable focus lens 41. A focal length confirmation light source 46 is preferably disposed.

  The position detector 47 is electrically connected to the controller 7, and the position detector 47 sequentially transmits a signal indicating the light receiving position to the controller 7 when measuring the surface height of the DUT 12. The controller 7 can measure the actual focal length of the variable focus lens 41 by referring to the focal length-light receiving position correspondence table based on the light receiving position received from the position detector 47. Therefore, the controller 7 adjusts the focal point so that when the actual focal length of the variable focus lens 41 deviates from the focal length to be set based on the light receiving position received from the position detector 47, the deviation amount is reduced. Feedback control for changing the voltage applied to the variable lens 41 can be performed. Therefore, the controller 7 can more accurately focus the measurement light beam on the surface of the object to be measured.

Further, in the reference light scanning optical system, a corner cube mirror or a reflecting element in which two reflecting surfaces are arranged at right angles, such as a right angle prism or a right angle mirror, may be used instead of the corner cube prism.
Further, instead of the fixed mirrors 57 to 66, a waveguide may be used as the light direction changing member. The waveguide changes the direction of the reference light beam so that the reference light beam emitted from each corner cube prism enters the adjacent corner cube prism. However, also in this case, the waveguide is configured such that the incident directions of the reference light beams to the two corner cube prisms arranged symmetrically with respect to the rotation axis of the rotary table are parallel to each other and opposite to each other. .

Further, a mechanism for detecting that the corner cube has reached a predetermined position in order to accurately associate the position of the corner cube prism with the electrical signal corresponding to the amount of light detected by the detector is provided with a reference light scanning optical system. 5 may be provided separately. For example, a hole penetrating the rotary table 51 along the rotation axis is formed at a predetermined position of the rotary table 51. Then, a light source such as an LED and a light receiving sensor are installed facing the light source across the rotary table 51, and when the hole formed in the rotary table 51 reaches a predetermined position, the light from the light source is The light source and the light receiving sensor are arranged so as to reach the light receiving sensor through the hole. When the light receiving sensor detects light from the light source, it transmits a detection signal to the controller 7. The controller 7 can associate the position of the corner cube prism with the electrical signal by associating the time at which the detection signal from the light receiving sensor is received with the electrical signal corresponding to the amount of light at that time.
In addition, when a rotation position detector such as a rotary encoder is attached to the rotation shaft 52 of the rotation table 51 in order to detect the rotation position of the rotation table 51, the controller 7 can detect the rotation table obtained by the rotation detector. The position of the corner cube prism obtained from the rotation position may be associated with an electrical signal corresponding to the amount of light detected by the detector.

Furthermore, the reference light scanning optical system may be configured by a system in which one reflecting element that reflects the reference light beam simply moves back and forth along the optical axis of the reference light beam.
FIG. 6 shows a schematic configuration diagram of another embodiment of the reference beam scanning optical system having such a configuration. In the reference light scanning optical system 50 shown in FIG. 6, the reference light beam emitted from the optical fiber 10 is configured to be vertically reflected by the movable mirror 71 and incident on the optical fiber 10 again.

  The movable mirror 71 is attached to the support member 72. The movable mirror 71 and the support member 72 are installed on a piezo fine movement stage 75 that allows a fine adjustment of the position of the movable mirror 71 although the movement range is narrow. The movable mirror 71 and the support member 72 are installed on a coarse movement stage 76 that has a relatively large movement range and roughly determines the position of the movable mirror 71 together with the piezo fine movement stage 75. The piezo fine movement stage 75 and the coarse movement stage 76 are electrically connected to a piezo controller 77 and a stage controller 78, respectively. The piezo fine movement stage 75 and the coarse movement stage 76 move the movable mirror 71 along the optical axis of the reference light beam based on drive signals from the piezo controller 77 and the stage controller 78. The piezo controller 77 and the stage controller 78 are electrically connected to the controller 7 and operate according to a control signal from the controller 7.

A corner cube 73 is attached to the back surface of the support member 72. Further, a position measurement interferometer 74 for the movable mirror 71 is installed behind the support member 72 (that is, on the opposite side of the optical fiber 10 with the support member 72 as the center). Then, the position measurement interferometer 74 is irradiated toward the corner cube 73, reflected by the corner cube 73, and the interference observed between the coherent light returned to the position measurement interferometer 74 and the reference light. The amount of movement of the movable mirror 71 can be measured by counting the number of moving stripes.
The controller 7 can determine the optical path length of the reference light beam based on the amount of movement of the movable mirror 71 from the reference position measured by the position measurement interferometer 74.
In the reference light scanning optical system 50, a corner cube mirror, a right angle prism, a right angle mirror, or the like may be used instead of the corner cube prism 73.
As described above, various modifications can be made within the scope of the present invention according to the embodiment to be implemented.

It is a schematic block diagram of the dimension measuring apparatus which concerns on one Embodiment of this invention. It is a schematic block diagram of an example of a measurement object scanning optical system. It is a schematic block diagram of an example of a reference beam scanning optical system. It is an operation | movement flowchart of the dimension measuring apparatus at the time of measuring the surface height in the arbitrary measurement points of the surface of to-be-measured object. It is a schematic block diagram of another example of a measurement object scanning optical system. It is a schematic block diagram of another example of a reference light scanning optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Size measuring device 2 White light source 3 Optical coupler (light beam splitting element)
DESCRIPTION OF SYMBOLS 4 Measuring object scanning optical system 5 Reference light scanning optical system 6 Detector 7 Controller 8-11 Optical fiber 12 Measured object 41 Variable focus lens 42 Lens driver 43 Condensing lens 44 Scanning mirror 45 Actuator 46 Focal length confirmation light source 47 Position Detector 51 Rotary table (Rotating member)
52 Rotating shaft 53 to 56 Corner cube prism 57 to 66 Fixed mirror (ray direction changing member)
67 Actuator

Claims (5)

A dimension measuring device for measuring the surface height of an object to be measured,
A white light source,
A light beam splitting element for splitting light emitted from the white light source into a measurement light beam and a reference light beam having an optical path length corresponding to the surface height of the object to be measured;
A reference light scanning optical system that changes an optical path length of the reference light beam emitted from the light beam splitting element;
A variable focus lens arranged in the measurement beam and capable of changing a focal length without mechanical movement in the optical axis direction of the measurement beam;
A detector that detects an interference signal generated when the optical path length of the measurement light beam and the optical path length of the reference light beam are substantially equal, and outputs a signal corresponding to the interference signal;
The focal length of the variable focus lens is adjusted so that the measurement light beam is focused at a position where the measurement light beam is reflected when the optical path length of the reference light beam is equal to the optical path length of the measurement light beam, and the interference A controller for determining the surface height of the object to be measured by determining the optical path length of the reference light beam corresponding to the maximum value of the signal;
A dimension measuring apparatus comprising:   The dimension measuring apparatus according to claim 1, wherein the variable focus lens is a liquid lens. The reference light scanning optical system includes:
A rotating member;
A driving section for rotating the rotating member at a predetermined rotation speed;
A first reflecting element and a second reflecting element arranged on the rotating member so as to be symmetrical with each other about the rotation axis of the rotating member;
When the reference light beam is incident on one of the first and second reflective elements, the reference light beam reflected by the one reflective element is reflected on the first and second reflective elements. A light beam direction changing member that guides the reference light beam so as to be incident on the other reflection element in a direction parallel to and opposite to the incident direction of the reference light beam with respect to the one reflection element, and rotates the rotating member By changing the optical path length of the reference light flux,
The controller detects that either the first or the second reflecting element has reached a predetermined position, and either the first or the second reflecting element has reached a predetermined position. By multiplying the elapsed time from the detection of the rotational speed of the rotating member to specify the position of the detected reflective element, or the controller uses the rotational position detector to detect the first or the second. By specifying the position of the reflective element, the optical path length of the reference beam is measured, and the focal length of the variable focus lens is adjusted according to the measured optical path length of the reference beam.
The dimension measuring apparatus according to claim 1 or 2. A second light source disposed outside the measurement light beam and irradiating a reference light so as to be obliquely incident on the variable focus lens;
A second detector that is disposed outside the measurement light beam, receives the reference light transmitted through the variable focus lens, and outputs a signal corresponding to a light receiving position of the reference light;
The controller measures the focal length of the variable focus lens by referring to a reference table indicating the relationship between the light receiving position and the focal length of the variable focus lens, and tries to set the measured focal length. The dimension measuring apparatus according to any one of claims 1 to 3, wherein a focal length of the variable focal lens is adjusted so that a shift amount of a focal length of the variable focal lens is small. A dimension measuring method for measuring the surface height of an object to be measured,
Splitting the light emitted from the white light source into a measurement light beam and a reference light beam having an optical path length corresponding to the surface height of the object to be measured by a light beam splitter;
Changing an optical path length of the reference light beam emitted from the light beam splitting element;
Measuring the optical path length of the reference beam;
The measurement light beam is disposed in the measurement light beam so that the measurement light beam is focused at a position where the measurement light beam is reflected when the optical path length of the measured reference light beam is equal to the optical path length of the measurement light beam. Adjusting the focal length of the variable focus lens capable of changing the focal length without mechanical movement in the optical axis direction;
Detecting an interference signal generated when the optical path length of the measurement light beam and the optical path length of the reference light beam are substantially equal, and outputting a signal corresponding to the interference signal;
Obtaining a surface height of the object to be measured by obtaining an optical path length of the reference light beam corresponding to a maximum value of the interference signal;
A dimension measuring method characterized by comprising:

Images