JP2009288159A - Distance measuring device, and optical interferometer and optical microscope equipped with this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distance measuring device which can perform highly accurate measurement of a distance along an optical axis to a measuring object placed on the optical axis. <P>SOLUTION: The distance measuring device includes a transparent electrode 44 which is disposed opposite to the electroconductive measuring object 2 on the optical axis of measuring light L<SB>1</SB>of a laser interferometer 1 and a signal processing circuit 52 as a capacitance detecting means which detects the capacitance between the transparent electrode 44 and the measuring object 2. Based on the detected capacitance, the distance measuring device calculates the distance D along the optical axis between the transparent electrode 44 and the measuring object 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a distance measuring device for measuring a distance, and more particularly, to a distance measuring device for measuring a distance along an optical axis to an object to be measured placed on the optical axis, and an optical equipped with the same. The present invention relates to an interferometer and an optical microscope.

  In recent years, there has been an increasing demand in the industry for parts that require nanometer precision and manufacturing equipment that manufactures such high precision parts. Manufacturing apparatuses equipped with a laser interferometer capable of measuring the position of a movable part with a precision of nanometers, and the like.

For example, a flat stage apparatus including a laser interferometer that measures the displacement of a stage that is movably provided in a two-dimensional direction is known (see Patent Document 1).
In general, a laser interferometer splits light from a light source into measurement light and reference light, irradiates the measurement light on a measurement object (such as a standard surface of a stage) and irradiates the reference surface with the reference light. The measurement light reflected from the measurement object and the reference light reflected from the reference surface are overlapped to detect interference fringes generated by the optical path difference. Then, the displacement of the object to be measured is calculated based on the phase of the interference fringes that changes according to the displacement of the object to be measured.
For example, when the measurement light is irradiated perpendicularly to the object to be measured, the fringe spacing of the generated interference fringes is half the wavelength of the measurement light. When a frequency-stabilized He-Ne laser light source having a wavelength of 633 nm is used as the light source, the interference fringe interval is 316.5 nm in principle, but the detected interference fringe signal is inserted into the interpolation means (interpolator). Thus, the displacement of the stage or the like can be measured with an accuracy of nanometers by executing the interpolation process of 317 divisions or more.

JP 2007-25887 A

As in the flat stage apparatus of Patent Document 1, when positioning the stage, before the apparatus is turned off and after the apparatus is turned on again, the stage itself is reproducible to ensure the reproducibility of the stage position. Sometimes you want to know the origin position.
However, the above-described laser interferometer can measure the relative displacement of the stage with respect to the sensor head that irradiates the stage with measurement light, but cannot measure the absolute position of the stage (such as the origin position).
Therefore, in the flat stage device of Patent Document 1, an optical switch for detecting the stage is provided separately from the laser interferometer, and the stage position detected by this switch is used as the origin of measurement by the laser interferometer. The

However, in the above-described planar stage apparatus, the optical switch is disposed at a position not on the optical axis of the measurement light in order to avoid interference with the measurement light of the laser interferometer. The origin position includes an Abbe error. For this reason, it is difficult to position the stage with high accuracy.
Such problems are not limited to the setting of the origin position when positioning the stage in a flat stage device, but are measured from the sensor head when measuring the surface shape of the workpiece being measured using a laser interferometer. The same occurs in the measurement of the distance to a place, the measurement of the distance to the measurement place when observing the object to be measured using an optical microscope, and the like.
That is, when the object to be measured is irradiated with measurement light or illumination, the position of the object to be measured is measured by the reflected light, or the surface shape of the object to be measured is measured or observed along the optical axis of the reflected light. When the distance to the measured object is measured by the conventional method, there is a common problem that the Abbe error is included in the measured value.

  An object of the present invention is to provide a distance measuring device capable of measuring a distance along the optical axis to a measurement object placed on the optical axis with high accuracy, and an optical interferometer and an optical microscope provided with the distance measuring device. That is.

  The distance measuring device of the present invention is a distance measuring device that measures the distance along the optical axis to a conductive object to be measured placed on the optical axis, and is a predetermined dimension with respect to the object to be measured. A transparent electrode provided at a position on the optical axis far away; and a capacitance detecting means for detecting a capacitance between the transparent electrode and the object to be measured. Based on this, a distance along the optical axis between the transparent electrode and the object to be measured is calculated.

  According to this configuration, when the object to be measured is irradiated with measurement light or illumination, the position of the object to be measured is measured by the reflected light, or the surface shape of the object to be measured is measured or observed. Since the transparent electrode is provided on the optical axis of the reflected light from, the distance to the object to be measured along the optical axis can be measured with high accuracy. Conventionally, in order to avoid interference with reflected light, a switch is provided at a position not on the optical axis, and the position of the measured object detected by the switch is set as the origin position of the measured object, and the distance to the measured object is set. Although it was measured, there was a problem that the Abbe error was included in the measured value because the switch was not on the optical axis. On the other hand, in the present invention, since the transparent electrode is disposed on the optical axis, interference between the transparent electrode and the reflected light does not occur, and the measured location measured by the transparent electrode is separated from the measured object. It can be matched with the position where the reflected light is generated. Therefore, the distance along the optical axis can be directly measured by the transparent electrode, and high-accuracy measurement without Abbe error is possible.

An optical interferometer according to the present invention includes the distance measuring device.
Here, as the optical interferometer, for example, an optical that measures the surface of the object to be measured and measures the distance to the surface of the object to be measured along the optical axis of the measurement light or the surface shape of the object to be measured. It can be an interferometer. The former includes, for example, a displacement measuring device that measures the displacement of a stage that is movably provided in a predetermined direction, and the latter measures surface properties having fine irregularities such as a circuit board pattern. Such as a surface texture measuring device.

  According to this configuration, when measuring an object to be measured with an optical interferometer, the conventional optical interferometer could not measure the absolute distance to the object to be measured. Since it is provided with a transparent electrode disposed on the optical axis of light, and a capacitance detecting means for detecting a capacitance between the transparent electrode and the measured object, an absolute distance to the measured object is provided. The distance can be measured with high accuracy.

The optical microscope of the present invention includes the distance measuring device.
According to this configuration, when the object to be measured is measured with an optical microscope, the capacitance between the transparent electrode disposed on the optical axis of the objective lens of the optical microscope and the object to be measured is measured. Therefore, the absolute distance to the object to be measured can be measured with high accuracy while observing the object to be measured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a schematic diagram showing an overall configuration of a Michelson type laser interferometer 1 as an optical interferometer of the present embodiment.
The laser interferometer 1 can be used, for example, as a displacement measuring device that measures the displacement of a table that is movably provided in the table device. Hereinafter, a case where the displacement of the measurement object 2 such as a table is measured will be described.

[Overall configuration of laser interferometer]
The laser interferometer 1 uses a measurement light L _{1 as} an object to be measured 2 based on the laser light supplied from the light source unit 3 as a light source unit 3 that generates laser light and a measurement unit that is disposed opposite the object to be measured 2. The sensor head unit 4 that receives the measurement light L ₁ reflected from the object to be measured 2 and the signal processing unit 5 that processes the signal output from the sensor head unit 4 are provided. It is assumed that the DUT 2 is formed from a conductive material.

  The light source unit 3 includes a laser light source 31 that generates laser light, a lens 32 that condenses the laser light, and a polarization plane preserving fiber 33 that propagates while maintaining the polarization plane of the collected laser light in a certain direction. Prepare. This polarization plane preserving fiber 33 is connected to the sensor head unit 4.

The sensor head unit 4 is divided into a collimator lens 41 that converts incident laser light into parallel light L ₀ , a polarization beam splitter 42 that splits the parallel light L ₀ into measurement light L ₁ and reference light L ₂ . a first lambda / 4 plate 43 and the transparent electrode 44 disposed on the optical axis of the measurement light L _1, the second lambda / 4 plate 45 which is disposed on the optical axis of the split reference light L ₂ and A reference mirror 46, and a polarizing plate 47 and a phase detector 48 disposed on the opposite side of the reference beam 46 with respect to the polarization beam splitter 42 are provided.

The measurement light L ₁ split by the polarization beam splitter 42 travels straight through the polarization beam splitter 42. Along parallel light L ₀ and the optical axis of the measurement light L _1, a collimator lens 41, a polarization beam splitter 42, the first lambda / 4 plate 43, a transparent electrode 44 are disposed linearly in order. Here, the first lambda / 4 plate 43 and the transparent electrode 44 is transmitted through the measurement light _{L 1.} Further, the transparent electrode 44 is fixed to the outer periphery of the sensor head portion 4 and is disposed so as to face the object to be measured 2 at a distance D. Further, the transparent electrode 44 and the first λ / 4 plate 43 transmit the measurement light L ₁ reflected from the DUT 2 again. The polarization beam splitter 42 reflects the measurement light L ₁ from the DUT 2 toward the polarizing plate 47.

The transparent electrode 44 is a disk-like electrode manufactured by forming a thin film of indium tin oxide, for example, on a transparent glass substrate, and is an electrode that is transparent and conductive to visible light. The transparent electrode 44 has an electrode surface perpendicular to the optical axis of the measurement light L _1. An electrostatic capacity corresponding to the distance D is generated between the transparent electrode 44 and the DUT 2. The transparent electrode 44 is electrically connected to the signal processing unit 5.

On the other hand, the reference light L ₂ divided by the polarization beam splitter 42 is reflected by the polarization beam splitter 42 in the direction perpendicular to the measurement light L ₁ . Along the optical axis of the reference light L _2, reference mirror 46, the second lambda / 4 plate 45, the polarization beam splitter 42, a polarizing plate 47, phase detector 48 are arranged in a straight line in order.
Second lambda / 4 plate 45 transmits the reference light L ₂ from the polarization beam splitter 42, further again transmits reference light L ₂ reflected by the reference mirror 46. The polarization beam splitter 42 is configured to cause the reference light L ₂ from the reference mirror 46 to travel straight toward the polarizing plate 47.

The polarizing plate 47 transmits the measurement light L ₁ and the reference light L ₂ and causes them to interfere with each other to generate interference light L ₃ .
The phase detector 48 receives the interference light L ₃ and outputs a Lissajous signal S ₁ (two-phase sine wave signal having a phase difference of 90 °) to the signal processor 5 while changing according to the displacement of the DUT 2. It is like that.

The signal processing unit 5, detects the interpolator 51 Lissajous signals S ₁ from the phase detector 48 is input, the capacitance Cm generated between the transparent electrode 44 and the object 2 (see FIG. 2) and it comprises a signal processing circuit 52 for outputting an origin signal S _2, and a counter 53 which these Lissajous signals S ₁ and the origin signal S ₂ is input.
The interpolator 51 interpolates the Lissajous signal S ₁ and outputs a two-phase rectangular wave signal S ₃ having a 90 ° phase difference that changes according to the displacement of the DUT 2 to the counter 53.

[Configuration of signal processing circuit]
FIG. 2 is a block diagram showing the configuration of the signal processing circuit 52 as the capacitance detecting means.
The signal processing circuit 52 has a structure in which function of generating pulsed origin signal S ₂ to the signal processing circuit of the conventional electrostatic capacitance displacement meter is added. That is, the signal processing circuit 52 has a function of outputting the origin signal S ₂ towards the counter 53 passes through the detected electrostatic capacitance Cm is set thresholds.
Specifically, as shown in FIG. 2, the signal processing circuit 52 includes a sine wave signal transmitter 521 that generates a sine wave voltage having a constant amplitude V ₀ , a sine wave signal transmitter 521, and a transparent electrode 44. Capacitance Cr 522 connected in series between them and RMS-DC conversion as amplitude detection means for detecting the detected capacitance Cm and the amplitude Vm of the voltage divided by the capacitance Cr of capacitor 522 A circuit 523, a variable reference voltage source 524 that generates a variable voltage Vr, a comparator 525 that detects the coincidence and mismatch of the two values when the amplitude Vm and the variable voltage Vr are applied, and detects a change in the output of the comparator 525; and a rise and fall detecting circuit 526 to be output to the counter 53 a detection signal as an origin signal S _2. Here, as the RMS-DC conversion circuit 523, a commercially available IC chip AD637 (manufactured by Analog Device) can be adopted.

In FIG. 1, the counter 53 counts the two-phase rectangular wave signal S ₃ from the interpolator 51 and calculates the displacement of the DUT 2 by calculating this count value. Further, the counter 53 resets the count value at the timing when the origin signal S ₂ is input, so as to detect the origin position of the object 2.

In the present embodiment, the transparent electrode 44 arranged on the optical axis of the measurement light L ₁ of the laser interferometer 1 and the capacitance detection for detecting the capacitance between the transparent electrode 44 and the DUT 2. The signal processing circuit 52 as a means constitutes the distance measuring device of the present invention that measures the distance D along the optical axis of the measuring light L ₁ between the DUT 2 and the transparent electrode 44.

[Measurement method of displacement of measured object]
Next, a method for measuring the displacement of the DUT 2 using the laser interferometer 1 will be described.
In FIG. 1, the laser light emitted from the laser light source 31 enters the sensor head unit 4 via the lens 32 and the polarization plane preserving fiber 33. The laser light incident on the sensor head unit 4 is converted into parallel light L ₀ by the collimator lens 41 and is incident on the polarization beam splitter 42. The parallel light L ₀ is divided into the measurement light L ₁ and the reference light L ₂ by the polarization beam splitter 42.

The measurement light L ₁ passes through the first λ / 4 plate 43 and the transparent electrode 44 and irradiates the DUT 2. The measurement light L ₁ reflected by the DUT 2 passes through the transparent electrode 44 and the first λ / 4 plate 43 again, is reflected by the polarization beam splitter 42, and enters the polarizing plate 47. On the other hand, the reference light L ₂ passes through the second λ / 4 plate 45 and enters the reference mirror 46, and is reflected by the reference mirror 46. The reflected reference light L ₂ passes through the second λ / 4 plate 45 and the polarization beam splitter 42 again and enters the polarizing plate 47. Then, the measurement light L ₁ and the reference light L ₂ incident on the polarizing plate 47 are transmitted through the polarizing plate 47 to become interference light L ₃ . The interference light L ₃ is received by the phase detector 48.

In the phase detector 48, Lissajous signals S ₁ which varies in accordance with the displacement of the object to be measured 2 is output. The Lissajous signal S ₁ is interpolated by the interpolator 51 to become a two-phase rectangular wave signal S ₃ having a 90 ° phase difference that changes according to the displacement of the DUT 2. The two-phase square wave signal _{S 3} is counted by the counter 53. Since the count value changes in proportion to the displacement of the DUT 2, the displacement of the DUT 2 can be calculated by calculating the counter value.

[Measurement method of displacement of measured object]
Next, a method for detecting the origin position of the DUT 2 will be described.
In FIG. 2, a sinusoidal voltage having a constant amplitude (V ₀ ) is applied to the capacitor 522 and the transparent electrode 44 by the sinusoidal signal transmitter 521. Since the electrostatic capacitance Cm between the transparent electrode 44 and the DUT 2 changes according to the distance D, the amplitude Vm of the voltage divided by the electrostatic capacitance Cm and the electrostatic capacitance Cr of the capacitor 522 is also obtained. It will change according to the distance D. Then, the RMS-DC conversion circuit 523 detects the amplitude Vm of the divided voltage.
The amplitude Vm is expressed by the following equation (1).

Here, ε _r is the relative dielectric constant of air, ε ₀ is the dielectric constant in vacuum, and S is the area of the transparent electrode 44 facing the object 2 to be measured.
FIG. 3 shows the relationship between the distance D and the amplitude Vm. In Figure 3, when the distance in a state where the object 2 is in the home position and D _0, the value of the amplitude Vm corresponding to the distance D ₀ is uniquely determined.

Further, the amplitude Vm and the variable voltage Vr generated using the variable reference voltage source 524 are applied to the comparator 525. Here, by varying voltage Vr is set a variable voltage Vr to a value of the amplitude Vm corresponding to the distance D ₀ shown in FIG. 3, the comparator 525 a voltage Vr corresponding to the distance D ₀ in the origin position as a threshold The output of can be changed. That is, the output of the comparator 525 can be changed depending on whether the distance D is larger or smaller than the distance D _{0 at an} arbitrary origin position. The change in the output of the comparator 525 is detected using the rising / falling detection circuit 526, and a pulsed origin signal S ₂ is generated and applied to the counter 53. Counter 53, the origin signal S ₂ is input, resets the count value at that timing.
As described above, the signal processing circuit 52 generates the pulsed origin signal S ₂ at the moment when the distance D between the transparent electrode 44 and the DUT 2 becomes the distance D ₀ corresponding to the origin position. The origin position of the measurement object 2 can be detected.

According to this embodiment, the following effects can be achieved.
(1) When the measurement light L ₁ is applied to the measurement object 2 and the displacement of the measurement object 2 is measured by the measurement light L ₁ that reflects the measurement object 2, the measurement light L from the measurement object 2 is measured. _{Since the} transparent electrode 44 is provided on the optical axis ₁ , the distance D from the transparent electrode 44 along the optical axis of the measurement light L ₁ to the DUT 2 can be measured with high accuracy. Conventionally, in order to avoid interference with the measurement light L ₁ from the measurement object 2, a switch is provided at a position not on the optical axis of the measurement light L ₁ , and the position of the measurement object 2 detected by the switch is determined. Although the absolute distance to the DUT 2 was measured as the origin position, there was a problem that the Abbe error was included in the measured value because the switch was not on the optical axis. In contrast, in the present embodiment, since disposing the transparent electrode 44 on the optical axis of the measurement light L _1, not interference occurs between the transparent electrode 44 and the measurement light L _1, and the distance at the transparent electrode 44 It is possible to make the measurement location of the DUT 2 at which the measurement is made coincide with the position where the measurement light L ₁ is reflected. Therefore, direct measure the distance D along the optical axis of the measurement light L ₁ by the transparent electrode 44 can be measured the position of the origin of the object 2 with high accuracy.

(2) Since the signal processing circuit 52 for detecting the capacitance Cm is provided, the distance between the transparent electrode 44 and the DUT 2 is set by setting the signal processing circuit 52 to a measurement range of about 0 to 10 micrometers. D can be detected with an accuracy of 10 nanometers, and the origin position of the DUT 2 can be measured with an accuracy of 10 nanometers.

(3) using a frequency-stabilized He-Ne laser light source as a laser light source 31 a wavelength 633 nm, by performing the interpolation of the 317 or more divisions with respect Lissajous signals S ₁ at the interpolator 51, the object 2 Can be measured with nanometer precision.

[Modification of this embodiment]
Further, the laser interferometer of the present embodiment may be used as a surface texture measuring device that measures the surface texture of a processed part. For example, the laser interferometer of this embodiment can be applied to the measurement of the surface shape of a processed part having fine irregularities such as a metal pattern of a circuit board using a laser interferometer. That is, a transparent electrode is disposed on the optical axis of the measurement light emitted from the sensor head of the laser interferometer, and the distance to the measurement location is measured while measuring the surface shape.
In the case of the surface texture measuring apparatus having such a configuration, when the measurement light is irradiated to the measurement object and the surface shape of the measurement object is measured by the reflected light, the optical axis of the measurement light from the measurement object Since the transparent electrode is provided on the top, the distance to the object to be measured along the optical axis of the measurement light can be measured with high accuracy. Therefore, the measurement location of the measurement object measured by the transparent electrode can coincide with the measurement location of the measurement object by the laser interferometer. Therefore, the absolute distance to the measurement location measured by the laser interferometer can be measured with high accuracy.

[Second Embodiment]
Next, an optical microscope 1A provided with a distance measuring device according to a second embodiment of the present invention will be described with reference to the drawings.
FIG. 4 is a side view showing the overall configuration of the optical microscope 1A. FIG. 5 is a partially enlarged view of the optical microscope 1A shown in FIG.
The optical microscope 1A is a normal optical microscope in which the transparent electrode 62 is disposed between the objective lens 61 and the sample 2A, so that the distance from the measurement site of the sample 2A observed through the objective lens 61 to the transparent electrode 62 is increased. the D ₁ are those having a function of measuring (Figure 5). Here, the sample 2A as an object to be measured of the present invention is made of a conductive substance.

In FIG. 4, the optical microscope 1 </ b> A includes a frame 63 formed in an L-shaped side surface, an observation head 64 supported by the upper part of the frame 63 so as to be movable up and down, and an optical axis of the objective lens 61 at the lower part of the frame 63. And a table 65 which is supported so as to be movable in two orthogonal directions and on which the sample 2A can be placed.
In the observation head 64, an observation optical system having an objective lens 61 and an eyepiece lens 66 is formed. A transparent electrode 62 formed in a thin film on a transparent glass substrate 67 is supported on the frame 63 through a support arm 68 so as to be movable up and down along the moving direction of the observation head 64. The transparent electrode 62 is disposed on the optical axis of the objective lens 61.
Although not shown, the transparent electrode 62 is electrically connected to a signal processing circuit as a capacitance detecting means for detecting the capacitance between the transparent electrode 62 and the sample 2A.

  According to the present embodiment, when the sample 2A, which is the object to be measured, is irradiated with natural light or illumination, and the surface shape of the sample 2A is observed by the reflected light, the measured portion of the sample 2A is positioned at the eyepiece 66. The distance to the measurement location can be measured with high accuracy by the transparent electrode 62 provided on the optical axis of the objective lens 61 while visually observing. In addition, the distance to the measurement location can be continuously measured while operating the table 65 to scan the surface of the sample 2A.

[Modification of the present invention]
It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

In the above-described embodiment, the case of a Michelson type laser interferometer has been described as the optical interferometer. However, the present invention is not limited to this. In other words, any optical interferometer may be used as long as it irradiates the measurement object with measurement light and measures the position or surface shape of the measurement object from the interference fringes between the reflected light and the reference light. An interferometer or a grazing incidence interferometer may be used.
The distance measuring device of the present invention is not limited to a laser interferometer and an optical microscope, and can be applied to, for example, a length measuring device, a stage device, a shape measuring device, and the like.

In addition, the best configuration, method and the like for carrying out the present invention have been disclosed above, but the present invention is not limited to this. That is, the invention has been illustrated and described with particular reference to certain specific embodiments, but without departing from the spirit and scope of the invention, Various modifications can be made by those skilled in the art in terms of material, quantity, and other detailed configurations.
Therefore, the description limited to the shape, material, etc. disclosed above is an example for easy understanding of the present invention, and does not limit the present invention. The description by the name of the member which remove | excluded the limitation of one part or all of such is included in this invention.

  The present invention can be used for laser interferometers, length measuring devices, stage devices, surface shape measuring devices, and the like.

The schematic diagram which shows the whole structure of the optical interferometer which concerns on 1st Embodiment of this invention. The block diagram which shows the structure of the signal processing circuit in the said optical interferometer. The graph which shows the relationship between the distance and amplitude of a transparent electrode and to-be-measured object in the said optical interferometer. The side view which shows the whole structure of the optical microscope which concerns on 2nd Embodiment of this invention. The elements on larger scale of the optical microscope of FIG.

Explanation of symbols

1 ... Laser interferometer (optical interferometer)
1A ... Optical microscope 2 ... Object to be measured 2A ... Sample (object to be measured)
44, 62 ... transparent electrode 52 ... signal processing circuit (capacitance detection means).

Claims (3)

A distance measuring device for measuring a distance along the optical axis to a conductive object to be measured placed on the optical axis,
A transparent electrode provided at a position on the optical axis that is a predetermined dimension away from the object to be measured;
A capacitance detecting means for detecting a capacitance between the transparent electrode and the object to be measured;
A distance measuring apparatus that calculates a distance along the optical axis between the transparent electrode and the object to be measured based on the detected capacitance.   An optical interferometer comprising the distance measuring device according to claim 1.   An optical microscope comprising the distance measuring device according to claim 1.

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