JPH11271020A - Interference microscope apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an uneven image of an observation object surface, without mechanically moving a reference mirror. SOLUTION: A semiconductor laser capable of wavelength sweeping is used as a laser light source 1. A fringe scan control part 16 outputs a fringe scan signal generating phase change between an object light and a reference light to a laser control part 17, which controls the laser light source 1. Since the phase of a reference light 34 can be changed, it is unnecessary to move a reference mirror, and unevenness of an observation object surface 4 can be observed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference microscope apparatus for imaging irregularities on an observation object surface using light.

[0002]

2. Description of the Related Art A conventional apparatus for causing an object light and a reference light to interfere with each other and observing irregularities on an observation object surface by using the phase of the light is disclosed in V.S. R. Tychinsky, I .; N. Mas
alov, V .; L. Pankov and D.C. V. U
Blinsky: OPTICSComm. , Vol. 7
4, (1989), p. 37-40. Is known.

FIG. 4 shows this phase interference microscope apparatus.
A laser oscillator 221 that generates a coherent plane wave of a constant wavelength, and a half mirror 222 that splits a laser beam generated from the laser oscillator 221 into an object beam 240 and a reference beam 250 are provided. The first lens 22 is located in the optical path of the object light 240 reflected by the half mirror 222.
The object light 240 is incident on the observation object 224 through the first lens 223. The object light 240 incident on the observation object 224 is reflected on the surface of the observation object 224, and the reflected light enters the optical path of the reflected light 260 that has passed through the first lens 223 again via the third lens 230. For example, a photodetector 225 such as a CCD is provided.

On the other hand, a second lens 226 is disposed in the optical path of the reference light 250 transmitted through the half mirror 222,
The reference light 250 enters the reference plane mirror 227 through the second lens 226. Then, the reference plane mirror 227
Is reflected by the half mirror 222 again through the second lens 226, and enters the photodetector 225.

The photodetector 225 detects a signal in which object light, which is reflected light of the observation object 224, and reference light, which is reflected light of the reference plane mirror 227, interfere with each other. The photodetector 225 has a memory 22 for storing a result detected by the photodetector 225.
8 is connected to the memory 228 and the computer 22
9 is connected. The computer 229 has the memory 22
8, a phase image is calculated from the interference intensity.

At this time, if the wavelength of the laser beam generated by the laser oscillator 221 is λ and the phase resolution is m,
The resolution D of the irregularities on the surface of the observation object 224 is obtained by the following equation. D = m · λ / 4π

In the above equation, when the wavelength λ = 633 nm and the phase resolution m = 5 °, the resolution of the unevenness is D = 4 nm
And the resolution of the unevenness becomes very high. Observation object 22
In the case where the direction perpendicular to the surface of No. 4 is the Z axis and the two directions parallel to the surface of the observation object 224 are the X and Y axes, the resolution in the Z axis direction is very high in this method. The resolution in the direction is the same as that of a normal optical microscope, which is about the wavelength λ of laser light.

In order to increase the resolution in the X and Y directions, V.V. R. Tychinsky: OPTICS Co
mm. , Vol. 74, (1989), p. 41-4
A method using a phase as described in No. 5 has been proposed. In this method, the reference light is reflected by the reference plane mirror 227, and the phase of the observation object 224 is measured with reference to the phase. In order to obtain this phase, the reference plane mirror 227 is moved by a distance obtained by dividing the distance of 波長 of the wavelength by 4 to 5 to obtain a plurality of interference images. I do. Next, an outline of the most basic method of this calculation will be described.

In the case where an image pickup device comprising a CCD is used as the photodetector 225, one pixel on the CCD corresponds to a point (x, y) on the observation object. The phase change of the reference light due to the movement of the reference plane mirror 227 is α, and the phase of the light reflected by the observation object 224 is θ. The intensity I of the interference light of each pixel of the CCD of the observation object 224 is obtained from Expression 1 as the intensity Ir of the reference light and the intensity Im of the object light. I = Ir + Im + γ2 (Im / Ir) 1/2 · cos (θ + α) (1) In this expression, γ is a constant satisfying 0 ≦ γ ≦ 1.

For example, when the reference plane mirror 227 is moved to give a phase change of α = 0, 90, 180, 270 °, the intensity I (α) of the interference light with respect to each phase change is given by the following equation (2). ) To (5). I (0) = Ir + Im + γ2 (Im / Ir) 1/2 · cos (θ + 0) = Ir + Im + γ2 (Im / Ir) 1/2 · cos (0) Equation (2) I (90) = Ir + Im + γ2 (Im / Ir) 1/2 · cos (θ + 90) = Ir + Im−γ2 (Im / Ir) 1/2 · sin (θ) Equation (3) I (180) = Ir + Im + γ2 (Im / Ir) 1/2 · cos (θ + 180) = Ir + Im−γ2 (Im / Ir) 1/2 · cos (θ) Equation (4) I (270) = Ir + Im + γ2 (Im / Ir) 1/2 · cos (θ + 270) = Ir + Im + γ2 (Im / Ir) 1/2・ Sin (θ) ... Equation (5)

Here, when the equations (2)-(4), which is the cos component, and the equations (5)-(3), which are the sin components, are calculated, the cos component is 2 · γ2 (Im / Ir) 1 / 2 · cos (θ) Expression (6) The sin component is given by 2 · γ2 (Im / Ir) 1/2 · sin (θ) Expression (7). Therefore, sin component / cos component = sin (θ) / cos (θ)
= Tan (θ). By rearranging the above equations, equation (8) is obtained. tan (θ) = (I (270) −I (90)) / (I (0) −I (180)) Equation (8)

From equation (8), the phase of each CCD pixel reflecting the unevenness of the observation object 224 is obtained. This is nothing but the fact that a two-dimensional phase image reflecting the unevenness of the observation object 224 is obtained.

[0013]

However, since the wavelength λ normally used is about 0.5 μm, the moving distance of the reference plane mirror 227 for one image is 0.05.
It is a very small distance of μm. In order to accurately obtain a phase image, it is necessary to move this minute distance accurately, but to achieve this, it is necessary to use an expensive stage such as a stage using a piezoelectric element (piezo stage). However, during the measurement of the phase image, it is necessary to avoid mechanical vibrations as much as possible, and it is difficult to perform the measurement using a moving mechanism such as an expensive stage as described above.

The present invention has been made in consideration of such a conventional problem, and it is possible to reliably obtain the unevenness of the observation observation surface even in a structure that does not require a moving mechanism such as a stage. It is an object of the present invention to provide an interference microscope device capable of performing the above.

[0015]

In order to achieve the above object, the present invention is directed to a laser light source capable of sweeping a wavelength, a laser controller for controlling a wavelength sweep of the laser light source, and a laser light source. Light splitting means for splitting the emitted laser light into object light and reference light, an observation object surface irradiated with the object light, object light irradiation means for irradiating the observation object surface with the object light, and the light A reference mirror whose distance to the splitting unit is different from the distance between the observation object surface and the light splitting unit, and which is irradiated with the reference light; and a reference light irradiating unit which forms the reference light on the reference mirror. Interference light imaging means for irradiating the object light reflected on the observation object surface and the reference light reflected on the reference mirror with interference light synthesized by the light splitting means, and imaging of the interference light imaging means With the image sensor installed at the position A fringe scanning control unit for outputting a fringe scan output signal to provide a desired phase change between the reference beam and the object beam to the laser control unit,
A plurality of desired phase changes are instructed to the fringe scan control unit, an arithmetic control unit that captures images corresponding to each of the plurality of phase changes from the image sensor, and a plurality of images obtained by the arithmetic control unit. It is characterized by comprising an image memory for storing, and a phase image calculating means for calculating a phase image corresponding to the unevenness of the observation object surface from a plurality of images stored in the image memory.

According to the present invention, the arithmetic control means instructs the fringe scan control section to change the phase,
The fringe scan control unit outputs a fringe scan output signal to the laser control unit. This allows the laser control unit to:
The wavelength of the laser light from the laser light source is swept so as to change the phase between the object light and the interference light. Therefore, the phase image can be measured without moving the reference mirror in the X and Y directions. For this reason, even if a moving mechanism such as a stage is unnecessary, it is possible to image the unevenness of the observation object surface.

According to a second aspect of the present invention, in the first aspect, an interference light splitting means for splitting the interference light is disposed between the light splitting means and the interference light imaging means. In the optical path of the split interference light split by the interference light splitting means, a photodetector that detects the split interference light and a phase change between the split interference light detected by the photodetector and the fringe scan output signal And a proportional coefficient detecting section for detecting and storing the proportional coefficient in advance and outputting the proportional coefficient to the fringe scan control section.

According to the present invention, the proportional coefficient detector detects and stores the proportional coefficient between the fringe scan output signal and the divided interference light detected by the photodetector. The stored proportional coefficient is output to the fringe scan control unit, and thereafter, the fringe scan control unit outputs a fringe scan output signal corrected based on the proportional coefficient to the laser control unit. Therefore, the wavelength sweep of the laser light source can be accurately controlled in real time.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the laser light source is a semiconductor laser,
The laser control unit controls the temperature of the semiconductor laser based on the fringe scan output signal.

According to the present invention, since the wavelength of the laser beam from the semiconductor laser is swept by controlling the temperature of the semiconductor laser, the wavelength sweep can be performed accurately and easily.

[0021]

(Embodiment 1) FIG. 1 shows an interference microscope apparatus according to Embodiment 1 of the present invention. This interference microscope apparatus includes a laser light source 1 whose wavelength can be swept, a laser controller 17 for controlling the wavelength sweep of the laser light source 1, and a laser light 31 emitted from the laser light source 1 converted into an object light 32 and a reference light 33. Half mirror 2 as light splitting means for splitting
The distance between the observation object surface 4 to which the object light 32 is irradiated, the objective lens 3 as object light irradiation means for irradiating the observation object surface 4 with the object light 32, and the half mirror 2
A reference mirror 6, which is arranged at a position different from the distance between the reference mirror 33 and the half mirror 2 and is irradiated with the reference light 33, an objective lens 5 as reference light irradiation means for irradiating the reference mirror 6 with the reference light 33, An imaging lens 10 as interference light imaging means for imaging an interference light 34 synthesized by the half mirror 2 with the object light reflected by the observation object surface 4 and the reference light reflected by the reference mirror 6; And a fringe scan control unit 16 that outputs a fringe scan output signal for providing a desired phase change between the object light 32 and the reference light 33 to the laser control unit 17.
And a computer 12 as an arithmetic control unit for instructing the fringe scan control unit 16 to perform a plurality of desired phase changes and capturing images corresponding to each of the plurality of phase changes from the image sensor 11, and the computer 12. An image memory 13 for storing a plurality of images, and a phase image calculating means 14 for calculating a phase image corresponding to the unevenness of the observation object surface 4 from the plurality of images stored in the image memory 13 are provided. Note that a display unit 15 that displays a phase image is connected to the phase image calculation unit 14.

In such a configuration, the laser beam 31 emitted from the laser light source 1 capable of sweeping the wavelength is
As a result, the light is split into the object light 32 and the reference light 33. The object light 32 is applied to the observation object surface 4 by the objective lens 3. On the other hand, the reference light 33 is applied to the reference mirror 6 via the objective lens 5. The object light and the reference light respectively reflected by the observation object surface 4 and the reference mirror 6 return to the half mirror 2, and the combined interference light is generated again. This interference light 3
4 is incident on the image sensor 11 via the imaging lens 10.
The imaging element 11 is provided in a conjugate positional relationship with the observation object plane 4. As the imaging device 11, for example, a two-dimensional CCD
Etc. can be used. Further, since the reference mirror 6 is a plane mirror, the image pickup device 11 can obtain an interference image reflecting the unevenness of the observation object surface 4.

In such an embodiment, the optical path length between the half mirror 2 and the observation object plane 4 differs from the optical path length between the half mirror 2 and the reference mirror 6 by nL. n is the refractive index of air. In FIG. 1, the reference mirror 6 and n
A dotted line position A corresponds to the observation object plane 4 at a position where the optical path length differs by L.
Is a position equivalent to

Therefore, the phase difference Φ between the object light and the reference light incident on the image sensor 11 can be obtained by the equation (9) as the wavelength λ of the laser light source 1. Φ = 2π · 2nL / λ = 4πnL / λ Equation (9)

The coefficient 2 before nL in equation (9) indicates that the optical path length difference is doubled due to reciprocation of light. Here, in Expression (9), when nL is a constant, that is, the reference mirror 6 does not move, and when λ is a variable, the derivative dΦ of Φ and α in Expression (1) can be regarded as equivalent, and α = dΦ = − (4πnL / λ2) dλ Expression (10) In the equation (10), when the wavelength λ slightly changes, the change amount dλ of the wavelength, the object light 32 and the reference light 33
Can be regarded as proportional to the phase change α (dΦ). In the present embodiment, this relationship is used, and therefore, the optical path length difference between the object light 32 and the reference light 33 is 2 nL.
Sweeps the wavelength of the laser light source 1 because
The phase α of the interference light 34 can be changed without mechanically moving the reference mirror 6.

Next, the equation (10) in this embodiment is
Will be described using specific numerical values. A semiconductor laser can be used as the laser light source 1 whose wavelength can be swept. This is because a semiconductor laser has a property that its wavelength can be changed by temperature or injection current. In this embodiment, a description will be given using a visible laser (red, about λ = 680 nm) as a semiconductor laser.

In order to obtain a phase image corresponding to the unevenness of the observation object surface 4 by applying the above-described equations (1) to (8), the phase change α needs to change from 0 to 2π. When the wavelength sweep of the semiconductor laser is performed by changing the temperature, the wavelength change (wavelength temperature characteristic) dλ / dT generated by the semiconductor laser having the wavelength of 680 nm by the temperature change of 1 ° C. is dλ / dT = 0.068 nm / ° C.
It is about. Here, when L = 3.4 mm, n = 1, and temperature change ΔT, Expression (10) is expressed as follows: α = − (4πnL / λ2) dλ = − (4πnL / λ2) · (dλ / dT) · ΔT = − (4π · 3.4 mm / (680 nm) 2) · 0.068 nm / ° C. ΔT = −2π · ΔT Expression (11) That is, by changing the temperature of the semiconductor laser by ΔT = 1 ° C. under the condition of L = 3.4 mm, the phase change α can be changed by about 2π.

Since the wavelength temperature characteristic dλ / dT of the semiconductor laser actually varies, and L may change by several mm due to the exchange of the objective lens 3, the equation (1)
The proportional coefficient of 1) is not always -2π and changes.
The treatment for this will be described in a second embodiment described below.
In this embodiment, a description will be given below on the assumption that the proportionality coefficient is -2π.

An instruction value of the phase change α of the equation (11), for example, α
= 0 °, 90 °, 180 °, 270 ° are transmitted. The fringe scan control unit transmits a fringe scan output signal corresponding to the indicated value of the phase change α, that is, the set temperature of the semiconductor laser, to the laser control unit 17 based on Expression (11).

The laser controller 17 controls the temperature of the semiconductor laser as the laser light source 1 so as to reach the set temperature. The temperature of the semiconductor laser can be controlled by a heating / cooling element such as a Peltier element such that a temperature sensor installed near the semiconductor laser reaches a set temperature.
When the semiconductor laser is stabilized at the set temperature, a trigger signal is input from the laser control unit 17 to the computer 12 via the fringe scan control unit 16, and the interference image of the image sensor 11 is captured by the computer 12 and stored in the image memory 13. It is memorized. By executing this process for each phase change α, the image memory 13 stores a plurality of interference images.

The phase image calculation device 14 calculates the above equation (2)
To (8) to obtain a phase image reflecting the unevenness of the observation object surface 4. The display unit 15 displays the phase image, and an external storage device (not shown) stores the phase image.

In such an embodiment, the fringe scan controller 16 outputs a fringe scan output signal (set temperature of the semiconductor laser) corresponding to the instruction value of the phase change α to the laser controller 17 and Of the observation object 4 without moving the reference mirror 6
Can be obtained.

(Embodiment 2) In this embodiment 2,
This is to deal with a case where the proportionality coefficient between α and ΔT in equation (11) in the first embodiment varies. FIG. 2 shows the configuration of this embodiment, and the same elements as those of the first embodiment are assigned the same reference numerals.

In this embodiment, a half mirror 2 as a light splitting means and an imaging lens 1 as an interference light imaging means
A half mirror 7 as interference light splitting means for splitting the interference light between 0 and 0 is arranged. In the optical path of the split interference light 35 split by the half mirror 7, a photodetector 9 for detecting the split interference light 35, a phase change of the split interference light detected by the photodetector 9, and a fringe scan output signal And a proportional coefficient detecting unit 18 that detects in advance the proportional coefficient between and stores the proportional coefficient and outputs the detected coefficient to the fringe scan control unit 16. Reference numeral 8 denotes an imaging lens serving as a division interference light imaging unit that forms the division interference light 35 on the photodetector 9, and reference numeral 21 denotes a pinhole.

The causes of the variation of the proportional coefficient in the equation (11) are L and dλ / dT. Among them, L is a variation when the objective lens 3 is replaced, and dλ / dT is a variation in individual characteristics of the semiconductor laser. On the other hand, in the present embodiment, a measure is taken by directly obtaining the proportionality coefficient of Expression (11) before measuring the phase image.

In the first embodiment, the computer 12
From the fringe scan controller 16
Sent to. Thereby, the fringe scan control unit 1
A fringe scan output signal (set temperature) is output from 6 to the laser control unit 17, and the temperature information of the semiconductor laser is input to the proportional coefficient output unit 18 via the fringe scan control unit 16 in real time. At the same time, proportional coefficient detector 1
Reference numeral 8 captures an interference signal received by the photodetector 9. At this time, even if the variation between L and dλ / dT is considered, 1
Wavelength sweeping is performed to such an extent that an interference signal having a cycle or more can be received by the photodetector 9.

At this time, the data obtained by the proportional coefficient detector 18 is represented as a graph of the temperature and the interference signal as shown in FIG. An offset of the interference signal is obtained from the average value of the maximum value Imax and the minimum value Imin of the amplitude of the interference signal. Temperature change ΔT1 (α =
π) can be obtained to obtain a proportional coefficient between the temperature change ΔT.

When there are three cross points with the offset, ΔT2 (α = 2π) can also be obtained.
The average value of the proportional coefficient between 1 and ΔT2 can also be obtained.
The proportional coefficient thus obtained is stored in the proportional coefficient detecting section 18, and thereafter the fringe scan control section 16 corrects the fringe scan output signal to be output to the laser control section 17 based on the stored proportional coefficient.

In such an embodiment, since the proportional coefficient of equation (11) is directly obtained before measuring the phase image, L and dλ
Even if the proportional coefficient varies due to the variation of / dT, it is possible to deal with the variation in real time, and the unevenness of the observation object surface 4 can be reliably obtained.

[0040]

As described above, according to the first aspect of the present invention, the fringe scan control unit outputs a fringe scan output signal to the laser control unit according to a command from the arithmetic control unit, and the laser control unit outputs the object light and the fringe scan signal. Since the wavelength of the laser light from the laser light source is swept so that the phase can be changed between the interference light and the interference light, the unevenness of the observation object surface can be imaged. Therefore, fringe scanning can be performed without mechanically moving the reference mirror.

According to the second aspect of the present invention, the proportional coefficient detector detects and stores the proportional coefficient between the fringe scan output signal and the divided interference light detected by the photodetector, and stores the proportional coefficient in the fringe scan controller. Since the output is performed, the wavelength sweep of the laser light based on the proportional coefficient can be accurately controlled in real time.

According to the third aspect of the invention, since the wavelength of the laser beam from the semiconductor laser is swept by controlling the temperature of the semiconductor laser, the wavelength sweep can be performed accurately and easily.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a second embodiment.

FIG. 3 is a characteristic diagram of a temperature and an interference signal obtained in a second embodiment.

FIG. 4 is a block diagram showing a configuration of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 7 Half mirror 3 5 Objective lens 4 Observation object plane 6 Reference mirror 9 Photodetector 10 Imaging lens 11 Image sensor 12 Computer 13 Image memory 16 Fringe scan controller 17 Laser controller 18 Proportional coefficient detector

Claims (3)

[Claims] 1. A laser light source capable of sweeping a wavelength, a laser control unit for controlling a wavelength sweep of the laser light source, and a light splitting unit for splitting laser light emitted from the laser light source into object light and reference light. The observation object surface irradiated with the object light, the object light irradiation unit that irradiates the observation object surface with the object light, and the distance between the light division unit and the distance between the observation object surface and the light division unit. A reference mirror disposed at a different position and illuminated with the reference light, reference light irradiating means for irradiating the reference mirror with the reference light, object light reflected on the observation object surface, and a reference reflected on the reference mirror Interference light imaging means for forming an image of the interference light in which the light is combined by the light splitting means; an image pickup device provided at an image forming position of the interference light imaging means; That gives the desired phase change to the A fringe scan control unit that outputs a scan output signal to the laser control unit, and commands a plurality of desired phase changes to the fringe scan control unit, and captures images corresponding to each of the plurality of phase changes from the image sensor. Arithmetic control means, an image memory for storing a plurality of images obtained by the arithmetic control means, and a phase image for calculating a phase image corresponding to the unevenness of the observation object surface from the plurality of images stored in the image memory An interference microscope apparatus comprising: a calculation unit. 2. An interference light splitting means for splitting the interference light is disposed between the light splitting means and the interference light imaging means,
In the optical path of the split interference light split by the interference light splitting means, a photodetector that detects the split interference light and a phase change of the split interference light detected by the light detector and the fringe scan output signal 2. The interference microscope apparatus according to claim 1, further comprising a proportional coefficient detecting unit that detects, stores, and outputs the proportional coefficient between the fringe scan control units. 3. The laser light source is a semiconductor laser,
The interference microscope apparatus according to claim 1, wherein the laser controller controls a temperature of the semiconductor laser based on the fringe scan output signal.