WO2013005910A1 - Local slope scanning interference microscope using an acousto-optic device - Google Patents

Abstract

The present invention relates to a scanning interference microscope. The scanning interference microscope according to the present invention comprises: a light source; a polarized beam splitter (PBS); an acousto-optic (AO) device; an AO driving unit for driving the AO device according to a modulated frequency (f_RF) for dithering within a frequency variable range (Δf) and on the basis of a center modulated frequency (f_RF0); a photodetector for detecting an interference signal of a signal light and a reference light; an RF demodulator using a modulated frequency in order to demodulate and output the interference signal; a lock-in amp using a dithering frequency (f_dithering) in order to demodulate and output a signal supplied from the RF demodulator; a function generator for generating a dithering signal having a preset amplitude (A) and the dithering frequency (f_dithering) and supplying the generated dithering signal to the AO driving unit, and supplying the dithering frequency (f_dithering) to the lock-in amp; and a controller using a signal outputted by the lock-in amp in order to detect information on a sample. The scanning interference microscope according to the present invention uses the AO device, which is capable of: varying the modulated frequency in order to obtain information on a local slope of the sample, in order to be able to accurately measure the surface of the sample; and measuring the amount of change in the overall slope of the sample caused by an external change (noise), so as to be capable of taking a more stable measurement.

Description

Local Slope Scanning Interference Microscopy Using Acousto-optic Devices

The present invention relates to a scanning interference microscope, and more particularly, to a local gradient of a sample using a signal light swept according to a modulation frequency dithered within a frequency variable range based on a modulation center frequency. By acquiring information, the present invention relates to a scanning interference microscope using an acoustic optical device capable of accurately measuring the surface of a sample irrespective of a phase change caused by external noise such as temperature change, acoustic noise, and sample inclination.

The Acosto-Opic Modulator (hereinafter, referred to as 'AOM') is an element that periodically reflects ultrasonic waves in tellurium dioxide, crystal single crystal, and the like to periodically create a refractive structure in the crystal. This acts as a diffraction grating, and when laser light is incident, it has a characteristic of being diffracted and output according to a refraction ratio period. 1 is a diagram illustrating the operation of a general acoustic-light modulator. As shown in FIG. 1, incident beams incident to the AOM are divided into zero-order beams without frequency modulation and first-order beams modulated by the variation frequency. The lights are separated and output at an angle.

When constructing an interferometer using a single AOM, a high speed and expensive A / D converter and demodulator are required to demodulate it. Therefore, in general, two AOMs are used to use a beat frequency of several kHz. As such, when two AOMs are used, beam alignment becomes difficult and manufacturing costs increase.

On the other hand, in the case of configuring the interferometer using a single AOM, since many optical elements are required to combine light again after splitting, the entire system becomes complicated and beam alignment becomes difficult, resulting in increased noise.

In addition, there is a problem in that the position and angle of the deflected light in the AOM changes when modulating the frequency of the AOM as a unique feature of the AOM. In addition, when the wavelength of the light input to the AOM is a number of wavelengths or the wavelength is changed, there is a problem that the application of the multi-wavelength interferometer is difficult because the deflection angle varies depending on the wavelength.

Figure 2 shows a heterodyne interferometer using a conventional AOM. The heterodyne interferometer shown in FIG. 2 is proposed by K. Kokkonen, et al. Under the heading "Scanning heterodyne laser interferometer for phase-sensitive absolute-amplitude measurements of surface vibrations". The heterodyne interferometer of FIG. 2 is a single-pass AOM interferometer using all the light emitted from the AOM, and three mirrors and PBSs are used to recombine two beams later, and a polarizer is used to interfere. In addition, since the angle of light emitted from the AOM is about several milliradians, it should be placed at a considerable distance to place the PBS in the center. The conventional Single-Pass AOM heterodyne interferometer described above has to use a plurality of optical elements to combine the light beams passing through the AOM, so that the structure is complicated and the beam alignment is not easy.

In particular, in the case of analyzing the surface of the sample by configuring the scanning microscope using the heterodyne interferometer of FIG. 2, if a change in the external environment such as a temperature change or a slope change occurs, this is an element for noise or the surface of the actual sample. There is a problem that it is difficult to accurately measure because there is no way to distinguish the measured value.

An object of the present invention for solving the above-described problems, the signal light is swept (sweep) according to the modulation frequency (f _RF ) dithered within the frequency variable range (Δf) on the basis of the center modulation frequency (f _RF0 ) It is an object of the present invention to provide a scanning interference microscope using an acoustic optical device that can accurately measure the surface of a sample by acquiring local gradient information of the sample.

Features of a scanning interference microscope using an acoustic optical device according to the present invention for achieving the above technical problem, the light source for providing light; A polarization beam splitter (PBS) for transmitting or reflecting light beams provided from the light source according to a polarization state; An AO device for dividing light rays provided from the PBS into first light rays and second light rays, and separating the first light rays and the second light rays at a predetermined angle and outputting the light rays; An acoustooptic device driver for driving the acoustooptic device according to a modulation frequency f _RF dithered within a frequency variable range Δf based on a center modulation frequency f _RF0 ; A sample stage on which a sample to be measured is placed; A first light beam disposed in a traveling path of the first light beam and the second light beam provided from the acoustooptical device, transmitting the first light beam and the second light beam in parallel to a sample stage, and reflecting back from the sample stage; A lens for propagating along the incident path again to provide a signal beam and a reference beam; A quadrature phase delay plate (QWP) disposed between the acoustooptic device and the lens to convert incident light rays into circularly polarized light; A photodetector for detecting and outputting an interference signal of a signal light and a reference light, which are reflected from the PBS after being output from the acoustooptic device; An RF demodulator receiving information on a modulation frequency from the acoustooptic device driver and demodulating and outputting an interference signal provided from the photodetecting device using the modulation frequency; A lock-in amplifier for demodulating and outputting a signal provided from the RF demodulator using a dithering frequency f _dithering ; A function generator for generating a dithering signal having a predetermined amplitude (A) and a dithering frequency (f _dithering ), providing the dithering signal to the acousto-optic device driver, and providing the dithering frequency (f _dithering ) to the lock-in amplifier; A control unit for detecting information about a sample using a signal output from the lock-in amplifier; The acoustooptic device driver is provided with a dithering signal from a function generator, and the modulation frequency f _RF to be dithered is determined by the amplitude A of the dithering signal. The dithering frequency f _dithering determines the speed at which the modulation frequency is dithered.

In a scanning interference microscope using the acousto-optic device having the above-mentioned characteristics, the acoustooptic device includes an Acousto Optic Modulator (AOM), an Acousto Optic Deflector (AOD), and AOFS (Acousto Optic). Frequency Shifter (AOFS) is preferably characterized in that made of any one.

In the scanning interference microscope using the acousto-optical device having the above-mentioned characteristics, the photodetecting device detects a first interference signal for light rays that are output from the acoustooptical device and then reflected by the PBS and traveling along a first path. It is preferable that it is provided with the 1st photodetecting element which outputs.

In the scanning interference microscope using the acousto-optical device having the above-mentioned characteristics, the photodetecting device detects a first interference signal for light rays that are output from the acoustooptical device and then reflected by the PBS and traveling along a first path. A first photodetecting device for outputting; And a second photodetector for detecting and outputting a second interference signal for light beams reflected from the PBS and traveling along a second path after being output from the acoustooptic device, wherein the heterodyne interferometer includes a first optical sword Preferably, a differential amplifier for outputting a difference value between the first interference signal and the second interference signal from the output device and the second photodetector to the RF demodulator.

A scanning interference microscope using an acoustooptical device having the above characteristics, the light source comprising: a laser; And an optical isolator (Optical Isolator) for aligning and outputting the light output from the laser with P waves.

In a scanning interference microscope using an acousto-optical device having the above-mentioned characteristics, the first light output from the acoustooptical device is first-order light modulated by a modulation frequency f _RF , and a second light beam. Is preferably an unmodulated zero-order light.

In a scanning interference microscope using an acoustic optical device having the above-mentioned characteristics, the heterodyne interferometer further includes a frequency multiplier, wherein the frequency multiplier converts the modulation frequency provided from the acoustic optical device driver into a frequency twice as high as that of the RF. It is preferable to output to a demodulator.

The scanning interference microscope using the acousto-optic device according to the present invention can obtain the information on the local tilt of the sample by using the acoustooptic device which can change the modulation frequency, thereby not only accurately measuring the surface of the sample, Since the reference light is irradiated to the sample surface together with the signal light, only a local gradient change, that is, a phase change (step change), can be selectively performed regardless of the overall gradient change of the sample due to external noise or the condition of the tilted sample. The measurement is possible, which makes the measurement more stable.

In addition, the scanning interference microscope using the acousto-optic device according to the present invention uses a dual-path AOM, so that not only an optical system having a simple structure without an additional optical system can be configured, but also the noise and the uniqueness of the two interference light beams are used. Balanced Detection can be implemented to remove all DC components. In addition, the scanning interference microscope using the acoustic optical device according to the present invention uses a signal light and a reference light having a pseudo-common-path, thereby making it possible to accurately measure insensitive to changes in the external environment.

1 is a diagram illustrating the operation of a general acoustic-light modulator.

Figure 2 shows a heterodyne interferometer using a conventional AOM.

3 is a block diagram schematically showing the configuration of a scanning interference microscope using an acoustic optical device according to the first embodiment of the present invention.

FIG. 4 is a view illustrating a second light beam and a first light beam swept provided in a sample stage in a scanning interference microscope using an acoustic optical device according to the present invention.

5 is a view for explaining a method for measuring the local tilt of the sample with a scanning interference microscope using an acoustic optical device according to the present invention.

FIG. 6 is a diagram illustrating light rays incident to the acoustooptic device and light rays modulated and output by the acoustooptic device.

7 is a block diagram illustrating input and output signals of the RF demodulator 380 and lock-in amplifier 386 according to the present invention.

8 is a block diagram schematically showing the configuration of a scanning interference microscope using an acoustic optical device according to a second embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail the structure and operating principle of a scanning interference microscope using an acoustic optical device according to a preferred embodiment of the present invention.

First embodiment

3 is a block diagram schematically illustrating a scanning interference microscope using an acoustic optical device according to a first embodiment of the present invention. Referring to FIG. 3, the scanning interference microscope 30 according to the present invention includes a light source 300, a PBS 310, an acoustic optical device 320, an acoustic optical device driver 330, a sample stage 340, and a lens. 350, QWP 360, first photodetector 370, second photodetector 372, differential amplifier 374, RF demodulator 380, function generator 384, lock-in amplifier 386, and controller ( 390). In the scanning interference microscope using the acoustooptic device according to the preferred embodiment of the present invention, the diffraction angle of the first light beam modulated from the acoustooptical device is fine according to the modulation frequency f _RF dithered by the acoustooptic device driver. It is characterized in that the local gradient information of the sample is obtained by using a phenomenon in which the signal beam is swept from the sample measuring point.

The light source 300 provides a beam of light composed of a single linear polarization wave, and includes a laser 302 and an optical isolator 304 that aligns and outputs the light output from the laser into P waves. Therefore, the light source 300 provides the PBS 410 with light beams aligned with P waves.

The polarization beam splitter (PBS) 310 transmits or reflects incident light according to a polarization state. The polarization beam splitter (PBS) 310 transmits the P wave as it is and reflects the S wave perpendicular to the incident angle. Therefore, the PBS transmits the P wave provided from the light source 300 as it is and provides it to the acoustic optical device 320.

The acoustooptic device 320 vibrates at the dithered modulation frequency f _RF provided from the acoustooptic device driver 330, and as a result, a part of the incident light beams has the original frequency f ₀ without modulation. (Zero-order) light beams are output, and a part of the light beams incident is modulated by the modulation frequency f _RF and output as first-order light beams. In this case, since the modulated primary light beams are diffracted and output, the _zero order light beams having a frequency of f ₀ and the primary light beams having a frequency of f ₀ + f _RF are separated from each other at a predetermined angle and output. Here, the modulated primary light is defined as first light, and the unmodulated zero order light is defined as second light.

As the modulation frequency f _RF provided by the acoustooptic device driver 330 is dithered, the acoustooptic device 320 finely varies the diffraction angle of the first light beam. The modulation frequency f _RF is a variable frequency finely dithered within the frequency variable range Δf on the basis of the center modulation frequency f _RF0 and is input from the acoustooptic device driver. In the present invention, as the modulation frequency is dithered within a frequency variable range around the center modulation frequency, the first light beams passing through the acoustooptical device are swept based on the sample measuring point. The magnitude of the sweep of the first light from the measurement point of the sample is determined according to the frequency variable range of the modulation frequency, and the speed at which the first light is swept is determined according to the dithering speed of the modulation frequency. Here, the dithering speed means a speed at which the modulation frequency is repeated within a frequency variable range on the basis of the center modulation frequency.

The first light beam is swept by only a few nm, thereby obtaining a signal beam including a local slope of the sample. The signal light thus obtained is demodulated into I and Q values by the RF demodulator, and only the signal having the same frequency as the dithering frequency is detected and output by the lock-in amplifier. Here, the acousto-optic device 320 is an acoustic-optic modulator (AOM) capable of sweeping the first light beam according to the modulation frequency and the variable frequency provided by the acoustooptic device driver 330, and the sound. Optical-Optic Deflector (AOD), Acousto Optic Frequency Shitfter (AOFS) and the like can be used.

On the other hand, the light waves of the P-waves incident on the acoustooptic device become S-waves in a linearly polarized state rotated 90 ° from the P-wave by the characteristics of the acoustooptic device as they pass through the acoustooptic device.

Meanwhile, the acoustooptic device driver 330 drives the acoustooptic device according to a modulation frequency f _RF dithered within a frequency variable range Δf based on a center modulation frequency f _RF0 , and controls the signal light. Information about the modulation frequency f _RF is provided to the RF demodulator 380 for detection. The modulation frequency is dithered according to the dithering signal provided from the function generator. The frequency variable range Δf is determined by the amplitude A of the dithering signal and the dithering speed is determined by the dithering frequency f _dithering of the dithering signal. . Here, the dithering speed means a speed at which the modulation frequency is repeatedly changed within a frequency variable range on the basis of the center modulation frequency f _RF0 .

The function generator 384 generates a sinusoidal dithering signal having a desired dithering frequency (f _dithering ) and an amplitude (A), and provides the sinusoidal dithering signal to an acoustooptic device driver, and dithering frequency (f _dithering ). Information about this is provided to the Lock-In AMP (386). The dithering frequency f _dithering determines how fast the first diffracted light is to be reciprocated and diffracted or laterally moved, and the amplitude A of the dithering signal determines the frequency variable range.

The sample stage 340 is placed a sample to be measured.

Since the quarter-wave phase delay plate QWP (Quater-Wave Plate; 360) is aligned at 45 °, when the linearly polarized light of S wave is incident, it is converted into circularly polarized light and outputted. It converts into linearly polarized light of P wave and outputs it. The QWP 360 is disposed in the paths of the first and second light beams provided from the acoustooptic device, and converts the linearly polarized light reflected from the acoustooptic device 320 into circular polarized light or outputs the sample stage. The circularly polarized light reflected from the light is converted into linearly polarized light and output.

On the other hand, the lens 350 is disposed in the path of the first and second light beams provided from the acoustooptic device, and transmits the first and second light beams in parallel to the sample stage. FIG. 4 is a view illustrating a second light beam and a first light beam swept provided in a sample stage in a scanning interference microscope using an acoustic optical device according to the present invention. Referring to FIG. 4, the second light rays of the zeroth order light and the first light rays of the first order light incident in parallel are incident on the sample stage 340 with a difference of several micrometers (μm). Since the first and second beams incident in parallel become signal beams and reference beams, respectively, there are only a few micro-differences, so that they proceed in a common common path. . Therefore, the scanning microscope using the acousto-optic device according to the present invention has the same path of the signal light and the reference light, which can eliminate the factors for the noise, thereby enabling stable measurement.

On the other hand, the first light beam passing through the lens is diffracted by the modulation frequency provided from the acoustooptic device driver and then incident in parallel to the sample stage 340, having a Δd of several nanometers (nm) and sweeping at the measurement point. sweep). 5 is a view for explaining a method for measuring the local tilt of the sample with a scanning interference microscope using an acoustic optical device according to the present invention. Referring to FIG. 5, the first light that is swept has a phase difference Δφ as shown in Equation 1 by a local slope of the sample.

Equation 1

Here, Δz is the path difference of the first light to be swept,

It is expressed as Where A is determined by the slope of the sample and the range over which the modulation frequency is varied relative to the center modulation frequency,

Is the frequency associated with the sweep of the variable frequency Δf.

In addition, referring to FIG. 5, the local gradient tan θ may be represented by Equation 2.

Equation 2

Therefore, the local gradient is expressed by Equation 3 using Equations 1 and 2.

Equation 3

That is, it is possible to measure the local slope of the first light swept through the equation (3). The measured local gradient enables the scanning microscope using the acoustic optical device according to the present invention to accurately analyze the sample surface.

On the other hand, the first and second light beams reflected from the sample stage 340 proceeds along the incident path that was first incident, and is remodulated by the acoustooptic device 320. At this time, each of the light beams re-entered into the acousto-optic device 320 is output by being divided into non-modulated zero order light beams and primary light beams modulated by the modulation frequency. Accordingly, as the light beams once frequency-modulated are frequency-modulated again, the frequency difference between the two light beams output from the acoustooptical device, that is, the beat frequency, becomes twice the modulation frequency f _RF of the acoustooptic device. In addition, the light beams passing through the QWP 360 are converted to S waves by rotating 90 °.

FIG. 6 is a view illustrating light rays incident to the acoustooptic device and light rays modulated and output by the acoustooptical device, and FIG. 6A illustrates a single pass through the acoustooptical device. Figure 6 shows the rays of light in the AOM, and FIG. 6 (b) shows the rays of light in a double pass AOM that are reflected by the mirrors and then incident back into the acousto-optic device after passing through the acoustooptic device. . Referring to FIG. 6A, the light beam a1 of the P-polarized light having the frequency f ₀ is incident on the acoustic optical device 60, and divided into the light beam a2 incident on the acoustic optical device. That is, the 0th order light beam a3 has a frequency f ₀ , and the 1st order light beam a2 is modulated to have a frequency f ₀ + f _RF . The zeroth order light beam a3 output from the acousto-optic device is rotated 45 ° while passing through the QWP 62, is converted into circularly polarized light, and enters the mirror 66, and the primary light beam a2 output from the acoustooptical device. Is rotated 45 ° while passing through the QWP 62, converted into circularly polarized light, and is incident on the mirror 64.

Referring to (b) of Figure 6, the primary beams (b1), each mirror of the 0th-order beams (b2) and the frequency (f ₀ + f _RF) of the same frequency (f ₀₎ of Fig. 6 (a) Reflected at 66 and 64, it passes through QWP 62 and reenters the acoustooptic device 60. The zeroth order rays b2 reentered into the acousto-optic device are divided into the zeroth order rays b4 passing through the acousto-optic device as it is, and the primary rays of light modulated at the modulation frequency f _RF of the acousto-optic device b6. A certain angle is output apart. That is, the zero order of the frequency (f ₀₎ beams (b2) is output is divided into the 0th-order beams (b4) and the first frequency beams (b6) of (f ₀ -f _RF) of the frequency (f _0). On the other hand, the primary light beam (b1) re-entered into the acoustic optical device is the primary light beam (b5) passing through the acoustic optical device as it is and the primary light beam (b3) modulated at the modulation frequency (f _RF ) of the acoustic optical device The output is divided by a certain angle from each other. That is, as the primary beams (b3) of the frequency (f ₀ + f _RF) of the primary beams (b1) has a frequency (f ₀ + f _RF) of the 0th-order beams (b5) and the frequency (f ₀ + 2f _RF) The output is divided. Here, the frequency zero-order beams (b4) of the primary beams (b3) and the frequency (f ₀₎ of (f ₀ + 2f _RF) proceeds along the same first path to each other, the frequency (f ₀ + f _RF) The zeroth order light beam b5 and the first order light beam b6 of the frequency f ₀ -f _RF also travel along the same second path, and the first path and the second path are spaced apart from each other by a predetermined angle.

On the other hand, Figure 6 (c) shows the light beams (sweep) is swept by the modulation frequency that is changed from the acoustic optical device driver. Referring to (c) of FIG. 6, light rays in the dual path shown in FIG. 6 (b) are almost similar to those of the light rays output from the acoustooptic device due to a variable modulation frequency (f _RF ± Δf). The frequency value fluctuates minutely. From the acoustooptic device, the zeroth order light c2 has a frequency f ₀ , and the primary order light c1 is modulated to have a frequency f ₀ + f _RF ± Δf. When the above-mentioned light beam is reflected back through the mirror and re-entered into the acoustic optical device again, the re-entered zeroth light beam (c2) is the zeroth light beam (c4) passing through the acoustic optical device as it is and the modulation frequency of the acoustic optical device ( f _RF ± Δf) divided by the primary light beam (c6) modulated by a predetermined angle is output to each other. In other words, the frequency (f ₀₎ of the 0th-order beams (c2) is a frequency (f ₀₎ of the 0th-order beams (c4) and the frequency _{(f 0 - (f RF ±} Δf)) 1 primary beams (c6) as a divided output of do. On the other hand, the primary light beam (c1) re-entered into the acoustic optical device is a primary light beam (c3) modulated at the modulation frequency (f _RF ± Δf) of the acoustic optical device and the zeroth light beam (c5) passing through the acoustic optical device as it is The output is separated by a certain angle. That is, the primary frequency of _{(f 0 + f RF ± Δf} ) beams (c1) is the frequency zero-order beams (c5) and the frequency _{(f 0 +2 (f RF ±} Δf) of _{(f 0 + f RF ± Δf} ) The output is divided into the primary rays of light c3). Here, the frequency _{(f 0 +2 (f RF ±} Δf)) 1 primary beams (c3) and the frequency zero-order beams (c4) of (f ₀₎ of the proceeds along the same first path to each other, the frequency (f ₀ The zeroth order c5 of + f _RF ± Δf and the first order c6 of frequency f ₀ − (f _RF ± f) also travel along the same second path. The two paths are spaced at a certain angle from each other. In addition, since the angle of the light beam swept by Δf is minute, there is only a slight difference and only the light beams swept are changed to a level detectable by one photodetector. 6C is somewhat exaggerated for convenience of description.

All the light beams incident on the PBS 310 are S-polarized states, and the light incident along the first path 'a' is reflected by the PBS and proceeds to the first photodetector 370. Light incident along b ') is reflected by the PBS and proceeds to the second photodetector 372.

The first photodetector 370 has a first light beam b3 having a frequency f ₀ +2 (f _RF ± Δf) and a zero light beam b4 having a frequency f ₀ , and the frequency 2 ( The interfering signal I ₁ of f _rf ± Δf is output to the demodulator 380. On the other hand, in the second photodetecting device 372, the zeroth order light b5 of frequency f ₀ + f _RF ± Δf and the first light beam b6 of frequency f ₀ − (f _RF ± Δf) are incident and are incident. The second interference signal I ₂ of frequency 2 (f _RF ± Δf) for the light beams is output to a differential amplifier 374. Here, the second photodetector 372 includes a D-Shaped mirror disposed obliquely on a path through which the rays reflected from the PBS travel and a photodetector disposed on a path through the rays reflected from the D-Shaped mirror. Can be.

The first interference signal and the second interference signal described above may be represented by equations (4) and (5).

Equation 4

Equation 5

Here, Is is the DC component of the interference signal and I _L corresponds to the noise component of the interference signal.

The differential amplifier 374 receives first and second interference signals from the first photodetector 370 and the second photodetector 372, respectively, and detects a difference value I ₁ -I ₂ of the input interference signals. And output to the demodulator 380. On the other hand, in general, the unmodulated zeroth order light output from the AOM and the first modulated first order light beam have a phase difference of 90 °. Accordingly, the phase difference between the first interference signal and the second interference signal described above is 180 ° due to the second modulation.

), And as a result, equation (5) can be rearranged into equation (6).

Equation 6

Based on the above-described mathematical basis, the output signals I ₁ -I ₂ of the differential amplifier 474 are represented by Equation 7 below. Accordingly, the differential amplifier according to the first embodiment of the present invention obtains twice the interference signal from which both the DC signal and the noise signal are removed as the same result of the balanced detection.

Equation 7

The modulation frequency f _RF provided from the acoustooptic device driver is converted into a double frequency (2 f _RF ) through a frequency doubler 382 and provided to the RF demodulator 380. The RF demodulator 380 RF demodulates the interference signal provided from the photodetector using the double modulation frequency (2 f _RF ) to detect the I signal and the Q signal for the signal light to the lock-in amplifier 386. Output

The lock-in amplifier 386 detects a signal having the same frequency as the dithering frequency among the I and Q signals input from the RF demodulator and outputs the dithering frequency provided from the function generator to the control unit 390.

7 is a block diagram illustrating input and output signals of the RF demodulator 380 and lock-in amplifier 386 in accordance with the present invention. As shown in FIG. 7, the RF demodulator 380 receives and demodulates interference signals and modulation frequency information, and outputs the demodulated signals as I values and Q values. The lock-in amplifier 386 has a dithering frequency among the signals output from the RF demodulator. Detects and outputs signals of the same frequency. Here, the I value and the Q value are as shown in Equations 8 and 9.

Equation 8

Equation 9

Using the above-described I and Q values, amplitude and phase can be detected according to equations (10) and (11).

Equation 10

Equation 11

The I and Q values output from the lock-in amplifier 386 are provided to the controller 390 to detect phase and amplitude. The control unit 390 may include an A / D converter 392 and a computer 394 for converting analog signals provided from the lock-in amplifier into digital signals, and the computer 394 may be provided from the A / D converter. Store the I and Q values of the digital signals and detect the phase and amplitude from them.

The scanning interference microscope using the acousto-optic device having the above-described configuration can accurately measure the surface of the sample by acquiring information on the local tilt of the sample by using the acoustooptic device capable of varying the modulation frequency. In addition, it is possible to measure the overall gradient change of the sample due to external noise, thereby making the measurement more stable. In addition, the scanning interference microscope using the acousto-optic device according to the present invention can implement balanced detection capable of removing both noise and DC components using an optical system having a simple structure. In addition, the scanning interference microscope using the acoustic optical device according to the present invention uses a signal light and a reference light having a pseudo-common-path, thereby making it possible to accurately measure insensitive to changes in the external environment.

Second embodiment

Hereinafter, the structure and operation of the scanning interference microscope using the acoustic optical device according to the second embodiment of the present invention will be described in detail. The scanning interference microscope according to the second embodiment is almost similar to the structure of the scanning interference microscope of the first embodiment, but differs from the scanning interference microscope of the first embodiment in that balanced detection is not performed. Due to this difference, the scanning interference microscope according to the second embodiment does not implement balanced detection, but has a simpler structure.

8 is a structural diagram illustrating a biochip readout sensor according to a second exemplary embodiment of the present invention. Referring to FIG. 8, the scanning interference microscope 70 according to the second embodiment of the present invention includes a light source 700, a PBS 710, an acoustic optical device 720, an acoustic optical device driver 730, and a sample stage ( 740, lens 750, QWP 760, photodetector 770, RF demodulator 780, function generator 784, lock-in amplifier 786, and controller 790.

The light source 700, the PBS 710, the acoustic optical device 720, the acoustic optical device driver 730, the sample stage 740, the lens 750, the RF demodulator 780, the function generator 784, lock-in Since the amplifier 786 and the control unit 790 are the same as those in the first embodiment, overlapping description is omitted.

In the scanning interference microscope 70 according to the present embodiment, only the light beams traveling in the same path among the light beams reflected from the sample stage and the reference light are passed through the acoustic optical device 720 to the PBS 710. It is characterized by detecting. Accordingly, the photodetecting device 760 has a signal of frequency f ₀ and a reference light of frequency f ₀ + 2 (f _RF0 ± Δf) incident from the PBS, and have a frequency of 2 (f _RF0 ± Δf). The interference signal is detected and converted into an electrical signal and output to the RF demodulator 780.

The acoustooptic device modulation frequency (f _RF) provided by the drive unit multiplier; is converted via (Frequency Doubler 782) at a frequency (2 f _RF) of twice is provided to the RF demodulator (780). The RF demodulator 780 demodulates the interference signal provided from the photodetector using the double frequency (2 f _RF ), detects the I signal and the Q signal for the signal light, and outputs the signal to the lock-in amplifier 386. . The lock-in amplifier detects a signal having the same frequency as the dithering frequency among the I and Q signals provided from the RF demodulator by using the dithering frequency which is a reference signal and outputs the signal to the controller 790.

Although the present invention has been described above with reference to preferred embodiments thereof, this is merely an example and is not intended to limit the present invention, and those skilled in the art do not depart from the essential characteristics of the present invention. It will be appreciated that various modifications and applications which are not illustrated above in the scope are possible. And differences relating to such modifications and applications should be construed as being included in the scope of the invention as defined in the appended claims.

Scanning interference microscope using the acoustic optical device according to the present invention is widely applicable to all fields for sample surface analysis.

Claims (8)

1. A light source for providing light;

   A polarization beam splitter (PBS) for transmitting or reflecting light beams provided from the light source according to a polarization state;

   An AO device for dividing light rays provided from the PBS into first light rays and second light rays, and separating the first light rays and the second light rays at a predetermined angle and outputting the light rays;

   An acoustooptic device driver for driving the acoustooptic device according to a modulation frequency f _RF dithered within a frequency variable range Δf based on a center modulation frequency f _RF0 ;

   A sample stage on which a sample to be measured is placed;

   A first light beam disposed in a traveling path of the first light beam and the second light beam provided from the acoustooptical device, transmitting the first light beam and the second light beam in parallel to a sample stage, and reflecting back from the sample stage; A lens for propagating along the incident path again to provide a signal beam and a reference beam;

   A quadrature phase delay plate (QWP) disposed between the acoustooptic device and the lens to convert incident light rays into circularly polarized light;

   A photodetector for detecting and outputting an interference signal of a signal light and a reference light, which are reflected from the PBS after being output from the acoustooptic device;

   An RF demodulator receiving information on a modulation frequency from the acoustooptic device driver and demodulating and outputting an interference signal provided from the photodetecting device using the modulation frequency;

   Lock-in amplifier for detecting and outputting a signal of the same frequency and the dither frequency (f _dithering) from the signal provided from the RF demodulator;

   A function generator for generating a dithering signal having a predetermined amplitude (A) and a dithering frequency (f _dithering ), providing the dithering signal to the acousto-optic device driver, and providing the dithering frequency (f _dithering ) to the lock-in amplifier;

   A control unit for detecting information about a sample using a signal output from the lock-in amplifier;

   The acoustooptic device driver is provided with a dithering signal from a function generator, and the modulation frequency f _RF swept is determined in a frequency variable range according to the amplitude A of the dithering signal, and the dithering frequency of the dithering signal ( Scanning interference microscope using an acousto-optical device, characterized in that the dithering speed is determined according to f _dithering ).
2. The method of claim 1, wherein the acoustooptic device comprises one of an acoustic-optic modulator (AOM), an acoustic-optic deflector (AOD), and an acoustico optic frequency shifter (AOFS). Scanning interference microscope using an acoustic optical device, characterized in that.
3. The light detecting device of claim 1, wherein the photodetecting device detects and outputs a first interference signal for light rays that are output from the acoustooptical device and then reflected from a PBS and traveling along a first path. Scanning interference microscope using the acoustic optical device, characterized in that provided as a first light detecting element.
4. The photodetecting device of claim 1, wherein the photodetecting device comprises:

   A first photodetecting device for detecting and outputting a first interference signal for light beams reflected from the PBS and traveling along a first path after being output from the acoustooptic device; And

   A second photodetecting device for detecting and outputting a second interference signal for light beams reflected from the PBS and traveling along a second path after being output from the acoustooptic device;

   Equipped with

   The heterodyne interferometer further includes a differential amplifier for outputting a difference value between the first and second interference signals from the first and second photodetectors to the RF demodulator. Interference microscope.
5. The method of claim 1, wherein the light source

   laser; And

   An optical isolator for aligning and outputting the light output from the laser with P waves;

   Scanning interference microscope using an acoustic optical device, characterized in that consisting of.
6. The method of claim 1, wherein the first light output from the acoustooptical device is first-order light modulated by a modulation frequency f _RF , and the second light is unmodulated zero-order. Scanning interference microscope using an acoustic optical device, characterized in that the light.
7. The method of claim 1, wherein the heterodyne interferometer further comprises a frequency multiplier,

   The frequency multiplier is a scanning interference microscope using an acoustic optical device, characterized in that for converting the modulation frequency provided from the acoustooptic device driver to a frequency of 2 times to output to the RF demodulator.
8. The scanning interference microscope of claim 1, wherein the information of the sample detected by the controller comprises information about a local slope of the sample.

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