JP4843789B2 - Nanometer displacement measuring method and apparatus by laser speckle - Google Patents

Description

  The present invention relates to a nanometer displacement measuring method using laser speckle that can be measured in a non-contact manner using a speckle interference using laser light on a rough surface object having a minute unevenness on the surface state of a member, and Relates to the device.

  Conventionally, in a measuring method of nanometer order, it is essential to be non-contact like STM (scanning tunneling microscope) or the like. In addition, the surface shape of the rough object has irregularities of several μm, and it was difficult to measure this displacement directly in units of nanometers (nm).

  If the object is a mirror surface, nanometer measurement is possible by techniques such as laser length measurement, and a method such as attaching a mirror or the like without directly measuring the displacement of the rough object is used.

  On the other hand, as a method for measuring the displacement and shape of a rough object having minute irregularities on its surface, a non-contact measurement method using the condensing property of laser light is known. For example, the surface of an object to be measured is irradiated as a probe with a laser beam, the focus position of the laser beam is fixed, the stage on which the object is mounted or the laser probe itself is relatively displaced, and the intensity of reflected light is increased. The maximum stage position coordinates are recorded, and the surface roughness of the object to be measured is measured.

  In addition, when a rough surface is irradiated with laser light, a speckled pattern called speckle is seen, and displacement measurement by speckle interferometry using this pattern has been conventionally performed. With this measurement method, the displacement of the object can be measured in units of micrometers (μm).

  Further, as disclosed in Patent Document 1, the light beam from the light source is divided into a plurality of light beams, one light beam is irradiated on the measurement rough surface, and the other light beam is irradiated on the reference rough surface. A spatial filter having a window for extracting an in-phase region of the speckle interference pattern is disposed in the optical path, and the speckle interference pattern having the same phase is selected by the filter, and a required phase is obtained. Speckle interferometers that extract information have been proposed.

  Further, as disclosed in Patent Document 2, a measurement method using electronic speckle interferometry that performs image processing by a computer has also been proposed. In Patent Document 2, a plurality of speckle images obtained by superimposing a laser beam reflected from a measurement object formed by a speckle interferometer and a laser beam not passing through the measurement object are formed and stored at predetermined time intervals. A measuring method is disclosed in which two of speckle images stored and recorded in an apparatus are taken out and a difference between the images is obtained by a computer. Thereby, the deformation caused by the measurement object at the time when the two images are recorded is seen as an interference fringe pattern. The interference fringe pattern represents the deformation distribution as contour lines, and one interference fringe corresponds to half the wavelength of the laser beam used. By repeating this one after another and adding each deformation, even non-contact, continuous measurement of submicron deformation is possible, even for large deformations or high-speed deformation distributions that cannot be measured with normal speckle interferometry. It is possible to do.

Patent Document 3 discloses a phase of an object to be observed that is phase-wrapped in a predetermined phase range based on a speckle pattern image that carries phase information of a dynamic object to be obtained, which is obtained using electronic speckle interferometry. A displacement measurement method is disclosed in which a change curve is obtained by analysis, and then the phase change curve is phase unwrapped. In this measurement method, based on a plurality of speckle pattern images obtained every predetermined time, an intensity signal in the time domain for each point of the image is obtained, a cosine component of the intensity signal is extracted, and the extracted cosine component In addition, a Hilbert transform process is performed in the time domain to obtain a sine component of the intensity signal, a phase change for each point of the image is obtained based on a ratio of the obtained sine component and the cosine component, A phase change curve is obtained, and dynamic deformation, vibration, distortion, etc. of the object to be observed are measured with high accuracy.
Japanese Patent Laid-Open No. 5-196419 JP-A-6-94434 JP 2004-109075 A

  As described above, the conventional non-contact optical displacement measuring device for object displacement can obtain nanometer-order sensitivity in the measurement of specular objects, but in the case of rough objects, a mirror is attached, etc. It was an indirect measurement.

  Also, in the case of a non-contact optical measurement device using laser speckle interference for rough surfaces, the measurement is performed by counting interference fringes, and the measurement accuracy is limited to the wavelength of light. In some cases, the measurement accuracy was of the order of submicrometers.

  In addition, the apparatus disclosed in Patent Document 1 has a complicated configuration, and measurement on the nanometer order cannot be easily performed. In the non-contact measurement method using laser light using the electronic speckle interferometry disclosed in Patent Document 2, the interference fringes are used, so the measurement accuracy is about submicron, It cannot be measured. Further, in Patent Document 3, the measurement accuracy is improved by obtaining the phase information of the object to be observed. However, the calculation in the processing is complicated, and the processing computer is required to have high performance.

  The present invention has been made in view of the above-mentioned problems of the prior art, and a method for measuring a nanometer displacement of a rough surface object by a laser speckle that has high measurement accuracy and can be easily processed by a simple optical system and apparatus. An object is to provide an apparatus.

  The present invention irradiates a laser light source such as a semiconductor laser, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, and one laser light branched by the beam splitter. The reference rough surface to be measured, the measurement rough surface irradiated with the other of the laser light, and the laser light reflected from the reference rough surface and the measurement rough surface overlapped via the beam splitter and speckle-interfered light And a displacement device for displacing the reference rough surface, the reference rough surface is displaced by a predetermined amount, and the maximum value and the minimum value of the output of the light sensor due to incidence of the speckle interference light are changed. The sensitivity of the detected displacement in this measurement range is calculated using the voltage range in which the output value changes almost linearly as the measurement range, and the position where the output value in the middle of the voltage range is obtained is calculated. See rough surface is fixed, a nanometer displacement measurement method by laser speckle to determine the displacement of the measuring rough surface by a change in the output voltage of the optical sensor.

  The present invention also provides a laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, and one laser light branched by the beam splitter is irradiated. The rough surface, the measurement rough surface irradiated with the other of the laser light, and the laser light reflected from the reference rough surface and the measurement rough surface overlap through the beam splitter and receive the speckle-interfered light. An optical sensor, and a displacement device for displacing the reference rough surface, displacing the reference rough surface by a predetermined amount, and approximately the median value of the maximum value and the minimum value of the optical sensor due to the incidence of the speckle interference light Is the reference value of the output voltage of the photosensor, the reference rough surface is displaced so that the output voltage of the photosensor becomes the reference value, and the displacement of the measurement rough surface is determined by the amount of displacement. A nanometer displacement measuring method according to the Mel laser speckle.

The present invention also provides a laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, and one laser light branched by the beam splitter is irradiated. The rough surface, the measurement rough surface irradiated with the other of the laser light, and the laser light reflected from the reference rough surface and the measurement rough surface overlap through the beam splitter and receive the speckle-interfered light. An optical sensor, and a displacement device for displacing the reference rough surface , wherein the reference rough surface is displaced by a predetermined amount by the displacement device, and a maximum value and a minimum value of the output of the optical sensor due to incidence of the speckle interference light among, the measurement range of the voltage range to be changed substantially linearly output value, to calculate the sensitivity of the detection displacement in the measurement range, obtain substantially the center of the output value of the voltage range The reference rough surface is fixed to the location, a nanometer displacement measuring apparatus by laser speckle having a processing device such as a computer for determining the displacement of the measuring rough surface by a change in the output voltage of the optical sensor.

  The present invention also provides a laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, and one laser light branched by the beam splitter is irradiated. The rough surface, the measurement rough surface irradiated with the other of the laser light, and the laser light reflected from the reference rough surface and the measurement rough surface overlap through the beam splitter and receive the speckle-interfered light. An optical sensor and a displacement device for displacing the reference rough surface, wherein the median of the maximum and minimum values of the optical sensor due to the incidence of the speckle interference light is used as a reference value for the output voltage of the optical sensor. And a laser spectrograph provided with a processing device for displacing the reference rough surface so that the output voltage of the photosensor becomes the reference value, and determining the displacement of the measurement rough surface by the amount of displacement. A nanometer displacement measuring apparatus according to Le.

  The nanometer displacement measurement method and apparatus using laser speckle according to the present invention uses the change in light intensity between interference fringes due to speckle interference of laser light, and performs displacement measurement by changing the output of the optical sensor. Measurement sensitivity is less than the wavelength of the laser beam, and nanometer-order measurement can be easily performed. Further, the output of the optical sensor is simply converted into displacement, and processing by a computer or the like is easy, and real-time measurement can be performed at high speed with a simple device.

  Further, when the reference rough surface is displaced in accordance with the displacement of the measurement rough surface, the measurement sensitivity depends on the resolution of the displacement device, the measurement range becomes the movement range of the displacement device, and the measurement range becomes wide.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 4 show a first embodiment of a nanometer displacement measuring apparatus by laser speckle according to the present invention. A displacement measuring apparatus 10 of this embodiment is a semiconductor laser 12 such as a laser diode which is a laser light source. And a converging lens 14 for converging the light from the semiconductor laser 12 to one point for condensing light. As the semiconductor laser 12, for example, a general-purpose product having a wavelength of 635 nm can be used. Furthermore, a beam splitter 16 for branching the laser beam is provided on the measurement target side, and a reference rough surface 18 having a rough surface disposed so as to face the beam splitter 16 is provided.

  At a position corresponding to one side surface of the beam splitter 16, a measurement rough surface 20, which is an object to be measured whose surface is rough, is positioned, and light such as a photodiode is opposed to the opposite surface of the beam splitter 16. A sensor 22 is arranged.

  In this embodiment, the reference rough surface 18 is attached to a displacement device 24 made of a piezoelectric element using, for example, PZT, and can be minutely displaced on the nanometer order. The displacement device 24 is connected to a control output of a computer 26 for control and processing via a D / A conversion circuit 28.

  The optical sensor 22 is connected to the light reception processing circuit 30, and the output of the light reception processing circuit 30 is input to the computer 26. Further, an oscillator 34 is connected to the semiconductor laser 12 via a laser drive circuit 32, and is oscillated and driven at a desired frequency, for example, 1 kHz. As shown in FIG. 2, in the light receiving processing circuit 30, the output of the optical sensor 22 is connected to a frequency filter circuit 38 via an AC inverting amplifier circuit 36, and is connected to a full-wave rectifier circuit 40 and a smoothing circuit 42. The output of the smoothing circuit 42 is A / D converted by the A / D conversion circuit 44 and input to the computer 26 as digital data.

  In the displacement measuring apparatus 10 of this embodiment, the laser light emitted from the semiconductor laser 12 is converged by the converging lens 14, passes through the beam splitter 16, and partially converges on the reference rough surface 18. Further, the laser beam reflected in the direction perpendicular to the reflecting surface of the beam splitter 16 is condensed on the measurement rough surface 20. The laser beam reflected by the reference rough surface 18 is partially reflected by the reflecting surface of the beam splitter 16 at a right angle and enters the optical sensor 22. Further, a part of the laser light reflected by the measurement rough surface 20 passes through the beam splitter 16 and enters the optical sensor 22, interferes with the reflected light from the reference rough surface 18, and is speckled as speckle interference. Interference fringes are formed.

  Next, a measurement processing method of the displacement measuring apparatus 10 according to the first embodiment of the present invention will be described with reference to FIG. First, the reference rough surface 18 and the measurement rough surface 20 are irradiated with laser light from the semiconductor laser 12. At that time, since the light intensity at the optical sensor 22 differs depending on the reflectance of the measurement surface, calibration is required. For this purpose, the piezoelectric element of the displacement device 24 is driven by the computer 26 with respect to the reference rough surface 18 and is largely displaced by about 50 nm (s1). At this time, the moving distance of the reference rough surface 18 by the displacement device 24 is known on the order of nm since the displacement amount of the piezoelectric element can be accurately known. Then, the output from the optical sensor 22 at this time is A / D converted (s2) and input to the computer 26, and the computer 26 stores the maximum output voltage and the minimum output voltage (s3). This is sequentially repeated to move the reference rough surface 18 by about 1000 nm (s4), and among them, as shown in FIG. 4, the median value of the measurement range a in which the output voltage change of the optical sensor 22 is almost linear is obtained. (S5). Then, in the linear measurement range a, the ratio between the known displacement amount and the output voltage is obtained and the sensitivity is calculated (s6).

  Further, the piezoelectric element of the displacement device 24 is largely displaced by about 50 nm (s7), the output voltage from the optical sensor 22 is A / D converted (s8), is calculated by the computer 26, and is the median value obtained previously. And the reference rough surface 18 is brought to the median value (s9).

  Then, the displacement measurement of the measurement rough surface 20 is started (s10). In the displacement measurement, similarly to the above, the output voltage of the optical sensor 22 is A / D converted (s11), and the displacement corresponding to the output voltage of the sensor 22 is calculated by the computer 26 from the previously obtained sensitivity (s12). . The above operation is repeated to measure the displacement of the measurement rough surface 20 within a predetermined range. After necessary data is obtained, the measurement is terminated.

  According to the displacement measuring apparatus 10 of the first embodiment, the displacement measurement of the measurement rough surface 20 is performed between the maximum value b and the minimum value c of the light intensity sensed by the sensor 22, as shown in FIG. The light intensity change is a measurement range a which is a linear portion with respect to the movement of the measurement rough surface 20, and can be easily calculated from the output voltage value. The displacement between the maximum value b and the minimum value c of the light intensity is ¼ of the wavelength of the light of the semiconductor laser 12 at the maximum because the brightness of light is caused by light interference. Therefore, for example, in the case of a laser beam having a wavelength of 630.5 nm, the maximum measurable displacement of the measurement rough surface 20 in the displacement from the maximum value b to the minimum value c is about 157.6 nm, and the most preferable linear range for measurement is about 50 nm. It is thought to be about. Thereby, the measurement of nanometer order can be easily performed from the sensitivity of the optical sensor 22 and the resolution of the output voltage, and the responsiveness is also good.

  Next, a second embodiment of the present invention will be described with reference to FIGS. Here, the same members as those in the above embodiment are denoted by the same reference numerals, and the description thereof is omitted. Similarly to the first embodiment, the displacement measuring device 10 of this embodiment is also provided with a displacement device 24 using a piezoelectric element on the reference rough surface 18 so that the reference rough surface 18 follows the displacement of the measurement rough surface 20. To do.

  A measurement processing method of the displacement measuring apparatus 10 of the second embodiment will be described with reference to FIG. First, similarly to the first embodiment, the reference rough surface 18 and the measurement rough surface 20 are irradiated with laser light. Then, in order to obtain an appropriate reference position, the piezoelectric element of the displacement device 24 is driven from the computer 26 with respect to the reference rough surface 18 and displaced largely by about 50 nm (s21). The output voltage from the optical sensor 22 at this time is A / D converted (s22) and input to the computer 26, where the maximum output voltage and the minimum output voltage are stored (s23). This is repeated sequentially to move the measurement rough surface 20 by about 1000 nm (s24), and the median value of the maximum output voltage and the minimum output voltage is obtained (s25). Further, the reference rough surface 18 is moved so that the output voltage becomes a median value.

  Then, the displacement measurement of the measurement rough surface 20 is started (s26). In the displacement measurement, similarly to the above, the output voltage of the optical sensor 22 is A / D converted (s27), and the computer 26 calculates the voltage difference from the previously obtained median value (s28). Then, the piezoelectric element of the displacement device 24 is driven by the computer 26, and the reference rough surface 18 is moved to the median side by the obtained voltage difference (s29). This operation is repeated to control the position of the reference rough surface 18 so that the output voltage always matches the median value (s30).

  If it is determined that the position of the measurement rough surface 20 is the median value, the movement distance of the reference rough surface 18 becomes the movement distance of the measurement rough surface 20 (s31). The above operation is repeated to measure the displacement of the measurement rough surface 20 within a predetermined range. After necessary data is obtained, the measurement is terminated.

  According to the second embodiment, the measurement sensitivity depends on the resolution of the displacement device 24, the measurement range is the movement range of the displacement device 24, the measurement range is widened, and the displacement of the measurement rough surface 20 is stably measured. can do.

  The nanometer displacement measuring apparatus using laser speckle according to the present invention is not limited to the above embodiment. In the optical system of the displacement measuring apparatus, an optical system such as a lens or a polarizing element is appropriately disposed. Alternatively, the beam splitter may be a polarization beam splitter, and the light of the linearly polarized semiconductor laser may be branched and deflected by combining a quarter wavelength plate. In addition, the wavelength of the laser beam and the optical element can be appropriately selected, and the arrangement of the optical system can also be appropriately set, so that the distance between the apparatus and the object to be measured can be arbitrarily changed.

  An embodiment of the displacement measuring apparatus according to the present invention will be described below. Here, as shown in FIG. 4, for the measurement range a in which the change in the output voltage of the optical sensor 22 is linear, the output measurement voltage and the displacement amount of the measurement rough surface 20 are tested on the forward and return paths of displacement. is there.

  In this experiment, as shown in FIG. 6, the measurement rough surface 20, which is known to be driven by a driving device 35 using a piezoelectric element such as PZT, was displaced by about 2 nm, and the output voltage from the optical sensor 22 was measured. The displacement of the measurement rough surface 20 was obtained by converting the control output from the computer 26 by the D / A conversion circuit 29 and giving an output voltage to the driving device 35 so that the measurement rough surface 20 was displaced by about 2 nm. In FIG. 6, the same members as those in the above embodiment are denoted by the same reference numerals.

  According to this result, although there is a slight deviation between the forward path and the return path, the result shown in FIG. 7 was obtained, and the measurement sensitivity was approximately 1 mV / nm. As a result, it was confirmed that the displacement of the surface of the measured object having a rough surface can be measured with a resolution of about 1 nm.

It is an arrangement drawing showing the outline of the nanometer displacement measuring device by the laser speckle of the first and second embodiments of the present invention. It is a block diagram of the light reception processing circuit of the displacement measuring apparatus of 1st and 2nd embodiment. It is a flowchart which shows the process of the displacement measuring apparatus of 1st embodiment. It is a graph which shows the relationship between the light intensity by the optical sensor of the displacement measuring apparatus of 1st embodiment, and the amount of displacement of a measurement rough surface. It is a flowchart which shows the process of the displacement measuring apparatus of 2nd embodiment of this invention. 1 is a layout diagram illustrating an outline of an experimental apparatus in one example of a displacement measuring apparatus according to a first embodiment of the present invention. It is a graph which shows the output voltage of the optical sensor by one Example of the displacement measuring apparatus in 1st Embodiment of this invention, and the displacement amount of a measurement rough surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Displacement measuring device 12 Semiconductor laser 14 Converging lens 16 Beam splitter 18 Reference rough surface 20 Measuring rough surface 22 Optical sensor 24 Displacement device 26 Computer 30 Light reception processing circuit 32 Laser drive circuit 34 Transmitter 35 Drive device

Claims (4)

  A laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, a reference rough surface to which one of the laser light branched by the beam splitter is irradiated, A measuring rough surface to which the other of the laser light is irradiated, a light sensor that receives speckle-interfered light that is reflected by the laser light reflected from the reference rough surface and the measuring rough surface through the beam splitter, and A displacement device for displacing the reference rough surface is provided, the reference rough surface is displaced by a predetermined amount, and the light is output almost linearly between the maximum value and the minimum value of the output of the photosensor due to the incidence of the speckle interference light. The voltage range where the value changes is taken as the measurement range, the sensitivity of the detected displacement in this measurement range is calculated, the reference rough surface is fixed at the position where the output value at the center of the voltage range is obtained, and the optical sensor is Nanometer displacement measurement method by laser speckle and obtains the displacement of the measuring rough surface by a change in the difference between the output voltage.   A laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, a reference rough surface to which one of the laser light branched by the beam splitter is irradiated, A measuring rough surface to which the other of the laser light is irradiated, a light sensor that receives speckle-interfered light that is reflected by the laser light reflected from the reference rough surface and the measuring rough surface through the beam splitter, and A displacement device for displacing the reference rough surface, displacing the reference rough surface by a predetermined amount, and determining the approximate center value of the maximum value and the minimum value of the photosensor due to the incidence of the speckle interference light. The reference rough surface is displaced so that the output voltage of the photosensor becomes the reference value as the reference value of the output voltage, and the displacement of the measured rough surface is obtained from the amount of displacement. Nanometer displacement measurement method by laser speckle. A laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, a reference rough surface to which one of the laser light branched by the beam splitter is irradiated, a measuring rough surfaces other laser light is irradiated, and a light sensor for receiving light each of said laser light reflected from said reference rough surface and the measuring rough surface has speckle interference overlap via the beam splitter, the A displacement device for displacing the reference rough surface, wherein the displacement device displaces the reference rough surface by a predetermined amount , and between the maximum value and the minimum value of the output of the photosensor due to the incidence of the speckle interference light, as measurement range a voltage range which changes linearly output value, to calculate the sensitivity of the detection displacement in the measurement range, the reference coarse in a position to obtain substantially the center of the output value of the voltage range It was fixed, nanometer displacement measurement device by laser speckle comprising the processor for determining the displacement of the measuring rough surface by a change in the output voltage of the optical sensor. A laser light source, a lens for converging the laser light at one point, a beam splitter for branching the laser light from the laser light source, a reference rough surface to which one of the laser light branched by the beam splitter is irradiated, A measuring rough surface to which the other of the laser light is irradiated, a light sensor that receives speckle-interfered light that is reflected by the laser light reflected from the reference rough surface and the measuring rough surface through the beam splitter, and A displacement device for displacing the reference rough surface, wherein the approximate value of the maximum value and the minimum value of the output of the photosensor due to the incidence of the speckle interference light is set as a reference value of the output voltage of the photosensor. A laser spectroscope comprising a processing device for displacing the reference rough surface so that an output voltage becomes the reference value and obtaining a displacement of the measurement rough surface based on a displacement amount. Nanometer displacement measuring apparatus according to Le.

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