JPH11218682A - Laser scanning microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate mechanical movement of an optical system or a sample at the time of the change of the distance between the image forming position and the sample in the direction of optical axis of incidence of laser beam to the sample to measure the surface shape of the sample at a high speed with respect to a laser scan microscope which is used for measurement and observation of the surface shape of a minute product like an LSI chip. SOLUTION: An acoustooptic polarizer 24 is provided as a means which deflects laser beam 23, and a driving signal whose frequency linearly changes from a low value to a high value is applied to the acoustooptic polarizer 24 to linearly change the angle of deflection of first-order diffracted beam 27 from a small value to a large value with time. The image forming position in the direction of the optical axis of incidence of first-order diffracted beam 27 to a sample 20 is fixed to scan the surface of the sample by first-order diffracted beam 27, and the change rate with time of the frequency of the driving signal is changed at each time of scanning of the surface of the sample 20 to repeat scanning.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser scanning microscope used for measuring or observing the surface shape of a fine product such as an LSI chip.

[0002]

2. Description of the Related Art FIG. 19 is a conceptual diagram of a main part of an example of a conventional laser scanning microscope. In FIG. 19, 1 is a sample, 2 is a laser light source, 3 is a laser light output from the laser light source 2, 4
Is a half mirror.

Reference numeral 5 denotes a deflecting element composed of a movable mirror for deflecting the laser beam 3 passing through the half mirror. 6 denotes a laser beam 3 deflected by the deflecting element 5 which is narrowed down into a spot shape so as to be perpendicular to the surface of the sample 1. This is a scanning optical system including a plurality of lenses for irradiation.

Further, reference numeral 7 denotes a light receiving optical system comprising a plurality of lenses for condensing return light 8 from the sample 1 reflected by the half mirror 4, reference numeral 9 denotes a pinhole plate having a pinhole 10, and reference numeral 11 denotes a pin. It is a light receiving element that receives return light passing through the hole 10.

In the conventional laser scanning microscope constructed as described above, the laser beam 3 output from the laser light source 2 is applied to the surface of the sample 1 via the half mirror 4, the deflection element 5, and the scanning optical system 6. The return light 8 from the surface of the sample 1 returns to the scanning optical system 6 and the deflecting element 5, is reflected by the half mirror 4, reaches the pinhole plate 9, and only the return light passing through the pinhole 10 is received by the light receiving element. The light is received at 11.

Here, the pinhole plate 9 is disposed at a position where an image of the laser spot on the surface of the sample 1 is formed. As a result, the pinhole plate 9 is out of focus on the surface of the sample 1. The return light 8 of the laser light 3 radiated in a spot shape without passing through the pinhole 10, but the return light 8 of the laser light 3 radiated in a spot shape with the surface of the sample 1 out of focus. Is hardly passed.

[0007] That is, the return light 8 of the laser beam 3 radiated in the form of a spot without any defocus on the surface of the sample 1 is received by the light receiving element 11, but the defocus is generated on the surface of the sample 1. Since the return light 8 of the laser light 3 irradiated in the form of a spot is hardly received by the light receiving element 11, when the surface of the sample 1 is scanned with the laser light 3, Only an image at the height can be obtained.

Therefore, for example, every time the sample 1 is moved in a direction orthogonal to the scanning direction by the laser beam 3, part or all of the optical system or the sample 1 is mechanically and repeatedly moved in the direction of the incident optical axis. The surface of the sample 1 is scanned with the laser light 3 by changing the distance between the image forming position of the laser light 3 with respect to the sample 1 in the direction of the incident optical axis and the sample 1, and the light receiving element 1
By observing the return light 8 by the use of 1, the surface shape of the sample 1 can be measured.

[0009]

As described above, in the conventional laser scanning microscope shown in FIG. 19, when changing the distance between the sample 1 and the image forming position of the laser beam 3 in the direction of the incident optical axis with respect to the sample 1, It is necessary to move a part or all of the optical system or the sample 1 mechanically and repeatedly.
There is a problem that a lot of time is required to measure the surface shape.

In view of the foregoing, the present invention eliminates the need for an optical system or mechanical movement of the sample when changing the distance between the sample and the imaging position of the laser beam in the direction of the incident optical axis with respect to the sample. It is an object of the present invention to provide a laser scanning microscope capable of increasing the speed of measurement of a laser beam.

[0011]

According to a first aspect of the present invention, there is provided a laser scanning microscope, comprising: a laser light source; a deflecting means for deflecting a laser beam output from the laser light source; A scanning optical microscope having an optical system for narrowing a laser beam output from a laser beam into a spot on the surface of a sample, as an deflecting means, an acousto-optic deflector to which the laser beam output from the laser light source is incident, and An acousto-optic deflector driving means capable of supplying a time-varying drive signal to the acousto-optic deflector and changing the time-change rate of the frequency of the drive signal is provided.

According to the first aspect of the present invention, since a drive signal whose frequency changes with time can be given to the acousto-optic deflector, the laser beam incident on the acousto-optic deflector is diffracted. The surface of the sample can be scanned with a laser beam that is deflected and deflected by the acousto-optic deflector.

Further, since the time change rate of the frequency of the drive signal whose time applied to the acousto-optic deflector changes with time can be changed, the time change rate of the drive signal frequency changes every scan. In this case, the surface of the sample can be scanned with the laser light by changing the imaging position of the laser light with respect to the sample in the direction of the incident optical axis for each scan.

Therefore, by changing the imaging position of the laser beam with respect to the sample in the direction of the incident optical axis for each scan, the surface of the sample is scanned with the laser beam, and the state of the spot of the return light from the sample is observed. And the surface shape of the sample can be measured.

According to a second aspect of the present invention, in the first aspect, the laser scanning microscope is formed on the surface of the sample based on the light intensity of the spot formed by the return light from the surface of the sample. The laser spot diameter measuring means for measuring the diameter of the laser spot is provided.

According to a third aspect of the present invention, there is provided a laser scanning microscope according to the second aspect, wherein the laser spot diameter measuring means includes a shutter, and the spot of the return light forms an image on the light receiving surface. And a shutter control means for controlling the shutter so that the shutter is opened when the center of the spot of the return light passes through the center of the light receiving section of the pixel of the image sensor. It is.

According to a fourth aspect of the present invention, in the laser scanning microscope according to the fourth aspect, the laser spot diameter measuring means may include a two-dimensional image in which the spot of the return light is imaged on the filter surface. A filter, an optical sensor into which return light passing through the two-dimensional filter is incident, and the pixel is opened when the center of the spot of the return light passes through the center of the filter part of the pixel of the two-dimensional filter. And two-dimensional filter control means for controlling the two-dimensional filter.

According to a fifth aspect of the present invention, there is provided a laser scanning microscope according to the first aspect, wherein the laser spot on the surface of the sample is determined from the light density of the spot formed by the return light from the surface of the sample. Laser spot diameter measurement means for measuring the diameter of the laser spot.

According to a sixth aspect of the present invention, there is provided a laser scanning microscope according to the fifth aspect, wherein the laser spot diameter measuring means comprises a photodiode in which the spot of the return light is imaged on the light receiving surface. And is configured to utilize the light density versus output current characteristics of the photodiode when the incident light amount is the same.

According to a seventh aspect of the present invention, there is provided a laser scanning microscope according to the first, second, third, fourth, fifth or sixth aspect, wherein the acousto-optic deflector driving means is provided. Has a voltage-controlled oscillator for generating a drive signal, and the voltage-controlled oscillator is provided with an input voltage having a distortion characteristic opposite to the distortion characteristic of the input voltage versus frequency characteristic,
That is.

According to the seventh aspect of the present invention, since the voltage-controlled oscillator can output a drive signal whose frequency changes linearly with time, the image forming position of the laser beam with respect to the sample in the direction of the incident optical axis. And the scanning speed can be made constant, and the scanning distortion can be eliminated.

In the present invention, the eighth invention (laser scanning microscope according to claim 8) is a method according to the first, second, third, fourth, fifth or sixth invention, wherein the surface of the sample at each time is measured. There is provided a correction means for correcting the measurement data of the surface shape of the sample using the laser spot position data obtained by measuring the position of the laser spot in advance.

According to the eighth aspect of the present invention, the measured data of the surface shape of the sample is corrected using the laser spot position data obtained by measuring the position of the laser spot on the surface of the sample at each time in advance. Therefore, the accuracy of measurement of the surface shape of the sample can be improved.

In the present invention, the ninth invention (laser scanning microscope according to claim 9) includes first, second, third, fourth, fifth, and fifth inventions.
In the sixth, seventh or eighth invention, the first acousto-optic deflector for deflecting a laser beam output from a laser light source in a first direction as the acousto-optic deflector, and A second acousto-optic deflector, which is a direction orthogonal to the first direction, and into which the first-order diffracted light output from the first acousto-optic deflector is incident.

According to the ninth aspect of the present invention, since the shape of the laser spot formed on the surface of the sample can be made circular, it is possible to observe the state of the spot formed by the return light from the surface of the sample. It can be done easily.

According to a tenth aspect of the present invention, in the ninth aspect of the present invention, the acousto-optic deflector driving means includes a first-aperture output from the second acousto-optic deflector. That is, the first and second acousto-optic deflectors are driven so that the folded light scans only the surface of the sample.

According to the tenth aspect of the present invention, unnecessary scanning can be prevented, so that the measurement of the surface shape of the sample can be further speeded up.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
The first to fourth embodiments of the present invention will be described with an example in which the present invention is applied to an incident-light laser scanning microscope.

First Embodiment FIGS. 1 to 12 FIG. 1 is a conceptual view of a main part of a first embodiment of the present invention. In FIG. A movable stage 22 is a laser light source that generates a laser beam that has been converted into a parallel light, and 23 is a laser light output from the laser light source 22.

Reference numeral 24 denotes an acousto-optic deflector (AOD) serving as a deflecting means for deflecting the laser beam 23 output from the laser light source 22, and reference numeral 25 denotes an acousto-optic deflector drive for applying a drive signal to the acousto-optic deflector 24. It is a voltage controlled oscillator (VCO) that forms the means.

Reference numeral 26 denotes a sample 2 by narrowing the first-order diffracted light 27 output from the acousto-optic deflector 24 into a spot.
0 is a scanning optical system that irradiates the surface of
9 and 30 are convex lenses.

Assuming that the focal lengths of the convex lenses 28, 29 and 30 are f ₁ , f ₂ and f ₃ respectively, the distance between the acousto-optic deflector 24 and the convex lens 28 is f ₁ , and the distance between the convex lens 28 and the convex lens 29 is Is f ₁ + f ₂ , and the distance between the convex lens 29 and the convex lens 30 is f ₂ + f ₃ .

Reference numeral 31 denotes a half mirror disposed between the convex lens 28 and the convex lens 29 for reflecting the return light 32 from the sample 20, and 33 condenses the return light 32 reflected by the half mirror 31. And a light receiving optical system for reproducing the size of the laser spot formed on the surface of the sample 20.

Reference numeral 34 denotes an image sensor serving as a laser spot diameter measuring means for measuring the diameter of the laser spot formed on the surface of the sample 20 from the diameter of the laser spot of the return light 32. CCD sensor provided.

Reference numeral 35 denotes frequency control of a drive signal output from the voltage controlled oscillator 25, shutter control of the CCD sensor 34, etc., and the scanning position of the first-order diffracted light 27 based on the value of the control voltage applied to the voltage controlled oscillator 25. And the scanning position of the first-order diffracted light 27 and the CCD sensor 34
Control to calculate the surface shape of the sample 20 from the output signal of
The calculation means 36 is the sample 2 calculated by the control / calculation means 35
Display means for displaying a surface shape of 0.

FIG. 2 is a conceptual diagram of the acousto-optic deflector 24. The acousto-optic deflector 24 has a piezoelectric element 41 and a sound absorbing material 42 bonded to one end and the other end of an acousto-optic medium 40 made of tellurium dioxide or the like. Then, a driving signal from the voltage controlled oscillator 25 is applied to the piezoelectric element 41 to ultrasonically vibrate the piezoelectric element 41, and an ultrasonic wave 43 generated by the piezoelectric element 41.
Is configured to propagate through the acousto-optic medium 40 from one end to the other end. Incidentally, reference numeral 44 denotes the zero-order diffracted light.

Here, assuming that the wavelength of the incident laser light 23 with respect to the acousto-optic medium 40 is λ, the frequency of the ultrasonic wave in the acousto-optic medium 40 is f, and the sound velocity in the acousto-optic medium 40 is v
When the incident laser light 23 is incident at a Bragg angle α, 1
The diffraction angle θ of the next-order diffracted light 27 is as shown in Expression 1.

[0038]

(Equation 1)

Therefore, for example, when a drive signal whose frequency changes linearly from low to high as shown in FIG. 3 is applied to the piezoelectric element 41, the deflection angle θ of the first-order diffracted light 27 becomes small to large. In FIG. 2, the first-order diffracted light 27 is continuously deflected from left to right in FIG. 2, and combined with the scanning optical system 26, the imaging position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis. With the first order diffracted light 27
Can scan the surface of the sample 20.

When the input voltage vs. frequency characteristic of the voltage controlled oscillator 25 is linear as shown in FIG. 4A, the voltage controlled oscillator 25 has the following characteristics as shown in FIG. When an input voltage that changes linearly with respect to a change in the input voltage is applied, the voltage-controlled oscillator 25 can output a drive signal whose frequency changes linearly with the time change of the input voltage. A constant imaging position of the folded light 27 with respect to the sample 20 in the direction of the incident optical axis and a constant scanning speed can be achieved, scanning distortion can be eliminated, and measurement accuracy of the surface shape of the sample 20 can be improved.

On the other hand, when the input voltage versus frequency characteristic of the voltage controlled oscillator 25 is non-linear as shown in FIG.
As shown in FIG. 5, when a control voltage having a distortion characteristic opposite to the distortion characteristic of the input voltage versus frequency characteristic of the voltage controlled oscillator 25 is applied, the frequency of the input voltage from the voltage controlled oscillator 25 changes with time. Can output a drive signal in which the first order diffracted light 27 changes linearly.
It is possible to stabilize the imaging position in the direction of the incident optical axis with respect to 0 and to stabilize the scanning speed, eliminate scanning distortion, and improve the measurement accuracy of the surface shape of the sample 20.

Also, without measuring the input voltage versus frequency characteristic of the voltage controlled oscillator 25, the sample 20
In the case where the laser spot position data of the surface of the sample 20 is corrected by the control / calculation means 35 using the laser spot position data beforehand by measuring the laser spot position of the surface Also, the accuracy of measurement of the surface shape of the sample 20 can be improved.

FIG. 6 illustrates the cylindrical concave lens effect of the acousto-optic deflector 24 generated when a drive signal whose frequency changes linearly from low to high as shown in FIG. FIG.

That is, as shown in FIG. 3, a drive signal whose frequency linearly changes from low to high is applied to the piezoelectric element 41 to change the frequency f of the ultrasonic wave 43 generated by the piezoelectric element 41 from low to high. When the time is continuously changed to a high value, the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is higher at a position closer to the piezoelectric element 41 and higher at a position farther from the piezoelectric element 41. , A lower frequency which is a frequency generated earlier.

Therefore, since the diffraction angles are slightly different at both ends of the light beam of the incident laser light 23, the first-order diffracted light 27 becomes a light beam having a slight spread (θ to θ + dθ), and the acousto-optic deflector 24 Shows the same effect as when a cylindrical concave lens having a curvature in the direction of deflection of the first-order diffracted light 27 is inserted.

A drive signal whose frequency changes linearly from high to low is applied to the piezoelectric element 41, and the frequency f of the ultrasonic wave 43 generated by the piezoelectric element 41 changes continuously from high to low. In the case of causing the acousto-optic deflector 24
Has the same effect as when a cylindrical convex lens having a curvature in the direction of deflection of the first-order diffracted light 27 is inserted.

In the first embodiment of the present invention, the case where the cylindrical concave lens effect of the acousto-optic deflector 24 is used has been described as an example. You may do it.

FIG. 7 shows the use of the cylindrical concave lens effect of the acousto-optic deflector 24 to scan the surface of the sample 20 with the first-order diffracted light 27 while keeping the imaging position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis constant. It is a figure for explaining what can be done.

In FIG. 7, reference numeral 27A denotes the first-order diffracted light when the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is set to 0 and scanning is stopped, and 27B denotes the acousto-optic medium 40. Change rate (d) of the frequency f of the ultrasonic wave 43
f / dt) is a first-order diffracted light when scanning is performed with a positive constant value.

That is, since the focal length F of the cylindrical concave lens due to the cylindrical concave lens effect is expressed by the following equation (2), the time change rate (d) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is obtained.
f / dt) as a positive constant value, the frequency f of the ultrasonic wave 43 generated by the piezoelectric element 41 is continuously changed from low to high to deflect the first-order diffracted light 27.
The image forming position of the sample 20 in the direction of the incident optical axis with respect to the sample 20 is separated from the image forming position when the scanning of the first-order diffracted light 27 is stopped by a distance Z that can be obtained by Expression 3.

[0051]

(Equation 2)

[0052]

(Equation 3)

Therefore, the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is set to a positive constant value, and the frequency f of the ultrasonic wave 43 generated by the piezoelectric element 41 is changed from low to high. 1st order diffracted light 2 by continuously changing
By deflecting 7, the surface of the sample 20 can be scanned with the first-order diffracted light 27 while keeping the image position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis constant.

FIGS. 8 and 9 show that when the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is changed, the first-order diffracted light 27 in the incident optical axis direction with respect to the sample 20 is changed. By changing the image position, the sample 2
FIG. 9 is a diagram for explaining that a surface of a zero can be scanned.

Here, for example, as shown in FIG. 8A, when the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is β (> 0), , 1
The imaging position of the incident optical axis direction with respect to the sample 20 of the order diffracted light 27, as shown in FIG. 9 (A), a distance Z ₁ showing the imaging position in the case of stopping the scan of the first-order diffracted light 27 on the number 4 It can be moved downward.

[0056]

(Equation 4)

On the other hand, as shown in FIG.
When the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is 2β, the first-order diffracted light 2
FIG. 9 shows an image forming position of the sample 20 in the incident optical axis direction with respect to the sample 20.
As shown in (B), it can be moved downward by the distance Z ₂ = 2 × Z ₁ shown in Formula 5 from the imaging position when the scanning of the first-order diffracted light 27 is stopped.

[0058]

(Equation 5)

Therefore, for example, the entire surface of the sample 20 is repeatedly scanned with the first-order diffracted light 27 while moving the sample 20 in a direction orthogonal to the scanning direction of the first-order diffracted light 27, and the entire surface of the sample 20 is scanned. Every time, the time change rate of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 (d
When f / dt) is changed, it is possible to repeatedly scan the entire surface of the sample 20 with the first-order diffracted light 27 by changing the imaging position of the first-order diffracted light 27 in the direction of the incident optical axis.

FIG. 10 shows an image forming position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis, a spot shape of the first-order diffracted light 27 on the surface of the sample 20, and a light intensity of the first-order diffracted light 27 on the surface of the sample 20. It is a figure showing the relation with distribution.

Here, for example, as shown in FIG. 10 (A1), when the imaging position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis is close to the surface of the sample 20, the sample 20
The spot shape of the first-order diffracted light 27 on the surface of FIG.
0 (A2), the diameter in the scanning direction is reduced, and as a result, the light intensity distribution of the first-order diffracted light 27 on the surface of the sample 20 becomes, as shown in FIG.
The light intensity distribution is such that the light intensity is not dispersed.

On the other hand, as shown in FIG. 10 (B 1), when the imaging position of the primary diffracted light 27 on the sample 20 in the direction of the incident optical axis is far from the surface of the sample 20, The spot shape of the first-order diffracted light 27 on the surface increases the diameter in the scanning direction as shown in FIG. 10 (B2). Therefore, the light intensity distribution of the first-order diffracted light 27 on the surface of the sample 20 is as shown in FIG. As shown in (B3), the light intensity distribution is such that the light intensity is dispersed.

FIG. 11 is a schematic diagram showing the structure of the light receiving optical system 33. As shown in FIG. In the light receiving optical system 33, 45 and 46 are convex lenses for collecting the return light 32 from the sample 20 reflected by the half mirror 31.
Reference numeral 46 is arranged so that the size of the laser spot formed on the surface of the sample 20 can be reproduced on the light receiving surface of the CCD camera 34.

Therefore, when the surface of the sample 20 is scanned with the first-order diffracted light 27, the spot of the return light 32 condensed by the light receiving optical system 33 has the size of the spot of the first-order diffracted light 27 formed on the surface of the sample 20. Now, CCD sensor 3
4 is scanned.

FIG. 12 is a diagram for explaining a method of controlling the shutter of the CCD sensor 34. FIG.
4 shows a part of a pixel array on the light receiving surface of the D sensor 34,
8-1, 48-2, 48-3 are pixels, 49-1, 49-
2, 49-3 are light receiving units, 50-1, 50-2, 50-3.
Denotes a light shielding portion.

FIG. 12B and FIG.
FIG. 4 is a diagram showing the movement of spots 51 and 52 of the return light 32 in the pixel row of the CCD sensor 34. The spot 51 is formed by the first-order diffracted light 27 forming a spot-like image on the surface of the sample 20 without any defocus. The spot 52 indicates a spot of the return light 32 when the first-order diffracted light 27 is out of focus on the surface of the sample 20 and forms an image.

Note that in the first embodiment of the present invention,
When the first-order diffracted light 27 forms an image on the surface of the sample 20 in the form of a spot without any defocus, the diameter of the spot in the scanning direction is the side of the light receiving sections 49-1, 49-2, and 49-3 in the scanning direction. The optical system is set to be the same as the length.

FIG. 12D shows a shutter control signal for controlling the shutter of the CCD sensor 34.
The shutter of the CD sensor 34 is opened when the shutter control signal is at the H level, and is closed when the shutter control signal is at the L level.

That is, in the CCD sensor 34, the center of the spots 51 and 52 of the return light 32 is
8-1, 48-2, and 48-3 light receiving sections 49-1 and 49-
The shutter is opened at the moment of passing through the center of 2, 49-3, and the shutter is closed during other periods, and the charge is stored in the light receiving sections 49-1, 49-2, 49-3. Is controlled to be performed intermittently.

In this case, when the first-order diffracted light 27 forms an image in the form of a spot without any defocus on the surface of the sample 20, the diameter in the scanning direction where the light intensity is not dispersed is minimized. A part of the laser spot 51 is irradiated to the light receiving units 49-1, 49-2, and 49-3 through the shutter, and relatively large electric charges are applied to the light receiving units 49-1, 49-2, and 49-3. Will be accumulated.

On the other hand, the first order diffracted light 27
When an image is formed out of focus on the surface of the laser spot, a laser spot 5 having a large diameter in the scanning direction in which the light intensity is dispersed.
2 is irradiated to the light receiving units 49-1, 49-2, and 49-3 of the CCD sensor 34 via the shutter, and
A relatively small amount of charge is stored in 9-1, 49-2, and 49-3.

Accordingly, in the CCD sensor 34, the size of the diameter of the spot of the first-order diffracted light 27 formed on the surface of the sample 20 can be extracted as an electric signal.

As described above, in the first embodiment of the present invention, the laser beam 23
Is output, and the Bragg angle α with respect to the acousto-optic deflector 24 is
And a drive signal whose frequency changes linearly with time from low to high is applied to the piezoelectric element 41 of the acousto-optic deflector 24 from the voltage controlled oscillator 25 controlled by the control / calculation means 35. You.

As a result, the first-order diffracted light 27 output from the acousto-optic deflector 24 is continuously deflected in one direction. The surface of the sample 20 can be scanned with the first-order diffracted light 27 while keeping the imaging position in the direction of the incident optical axis constant.

The return light 32 from the surface of the sample 20
Is the half mirror 3 having the same optical axis as the first-order diffracted light 27.
The light is reflected by 1 and forms an image on the light receiving surface of the CCD sensor 34 via the light receiving optical system 33.
The size of the diameter of the spot of the first-order diffracted light 27 on the surface of the sample 20 is extracted as an electric signal and transmitted to the control / calculation means 35.

The control / arithmetic means 35 determines the scanning position of the first-order diffracted light 27 from the value of the input voltage applied to the voltage controlled oscillator 25, and determines the scanning position of the first-order diffracted light 27 and the output of the CCD sensor 34. From the signal, the surface shape of the sample 20 is calculated.

Therefore, the entire surface of the sample 20 is repeatedly scanned with the first-order diffracted light 27 while moving the sample 20 in the direction orthogonal to the direction of deflection of the first-order diffracted light 27, and
When the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is changed every time the entire surface of the surface 0 is scanned, the direction of the incident optical axis of the first-order diffracted light 27 with respect to the sample 20 1st-order diffracted light 2 while changing the imaging position of
7, the surface of the sample 20 can be scanned.
6, the surface shape of the sample 20 can be displayed.

In the first embodiment of the present invention,
The display of the surface shape of the sample 20 on the display means 36 indicates the height of the image forming point of the first-order diffracted light 27 when the spot diameter of the return light 32 is minimum and the light intensity of the return light 32 is maximum. This is done by:

As described above, according to the first embodiment of the present invention, when changing the distance between the sample 20 and the imaging position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis, the optical system or the sample 20 No mechanical movement is required, and the measurement of the surface shape of the sample 20 can be speeded up.

Second Embodiment FIG. 13 and FIG. 14 FIG. 13 is a conceptual diagram of a main part of a second embodiment of the present invention.
The second embodiment of the present invention includes a flat-plate photodiode 52 on which the return light 32 is focused on a light receiving surface, instead of the CCD sensor 34 included in the first embodiment of the present invention. This is configured similarly to the first embodiment of the invention.

FIG. 14 is a graph showing the light density versus output current characteristics of the photodiode 52 when the incident light amount is the same. In the photodiode 52, when the incident light amount is the same, the spot diameter becomes smaller and the light density becomes lower. Above a certain value, the higher the light density of the spot, the lower the output current.

Here, when the most in-focus spot is formed on the surface of the photodiode 52, the output current of the photodiode 52 becomes minimum, so that the spot diameter of the spot of the first-order diffracted light 27 on the surface of the sample 20 becomes smaller. The magnitude can be taken out as an electric signal and transmitted to the control / calculation means 35.

Therefore, in the second embodiment of the present invention, similarly to the first embodiment of the present invention, the imaging position of the first-order diffracted light 27 on the sample 20 in the direction of the incident optical axis is changed by the acousto-optic deflector 24. The surface of the sample 20 is scanned with the first-order diffracted light 27 and the shape of the surface of the sample 20 can be displayed on the display means 36 while the first-order diffracted light 27 is being formed. In changing the distance from the sample 20, the optical system or the mechanical movement of the sample 20 becomes unnecessary, and the measurement of the surface shape of the sample 20 can be speeded up.

In the second embodiment of the present invention,
The display of the surface shape of the sample 20 on the display means 36 indicates the height of the imaging point of the first-order diffracted light 27 when the diameter of the spot of the return light 32 is minimum and the light density of the spot of the return light 32 is minimum. This is done by displaying.

Third Embodiment FIG. 15 FIG. 15 is a conceptual diagram of a main part of a third embodiment of the present invention.
The third embodiment of the present invention is different from the first embodiment of the present invention in that, instead of the CCD sensor 34 included in the first embodiment of the present invention, the return light 32 is imaged on the filter surface, and the return light passing through the two-dimensional filter 54 is returned. Photodiode 5 into which light is incident
5 in which the control / arithmetic means 35 controls the two-dimensional filter 54, and the others are configured in the same manner as the first embodiment of the present invention.

Here, the two-dimensional filter 54 receives the return light 3
At the moment when the center of the second spot passes through the center of the filter section of the pixel, the control / calculation means 35 is controlled so that the pixel is opened.

In the third embodiment of the present invention,
When the first-order diffracted light 27 forms an image on the surface of the sample 20 in the form of a spot without any focus shift, the diameter of the spot in the scanning direction is the same as the length in the scanning direction of the filter portion of the pixel of the two-dimensional filter 54. The optical system is set so that

Therefore, as for the return light 32 of the first-order diffracted light 27 illuminated in the form of a spot without defocusing on the surface of the sample 20, light having a high light intensity is applied to the two-dimensional filter 5.
4 is received by the photodiode 55, and the sample 2
With respect to the return light 32 of the first-order diffracted light 27 illuminated out of focus on the surface of the zero, light having a low light intensity passes through the two-dimensional filter 54 and is received by the photodiode 54.

Here, when the most in-focus spot is formed on the surface of the two-dimensional filter 54, the output current of the photodiode 55 becomes maximum, so that the diameter of the spot of the first-order diffracted light 27 on the surface of the sample 20 becomes large. Can be extracted as an electric signal and transmitted to the control / calculation means 35.

Therefore, in the third embodiment of the present invention, similarly to the first embodiment of the present invention, the imaging position of the primary diffraction light 27 on the sample 20 in the direction of the incident optical axis is changed by the acousto-optic deflector 24. The surface of the sample 20 is scanned with the first-order diffracted light 27 and the shape of the surface of the sample 20 can be displayed on the display means 36 while the first-order diffracted light 27 is being formed. In changing the distance from the sample 20, the optical system or the mechanical movement of the sample 20 becomes unnecessary, and the measurement of the surface shape of the sample 20 can be speeded up.

Note that, in the third embodiment of the present invention,
The display of the surface shape of the sample 20 on the display means 36 is performed by displaying the height of the imaging point of the first-order diffracted light 27 where the spot diameter of the return light 32 is minimum and the light intensity of the return light 32 is maximum. Will be

Fourth Embodiment FIGS. 16 to 18 FIG. 16 is a conceptual diagram of a main part of a fourth embodiment of the present invention.
In the fourth embodiment of the present invention, an acousto-optic deflector 57 and a first-order diffracted light 58 output from the acousto-optic deflector 57 are applied to the acousto-optic deflector 24 between the laser light source 22 and the acousto-optic deflector 24. A scanning optical system 59 for incidence, and a voltage-controlled oscillator 60 for generating a drive signal to be given to the acousto-optic deflector 57 are provided so that the control / arithmetic means 35 controls the voltage-controlled oscillator 60; Others are configured similarly to the first embodiment of the present invention.

Here, the acousto-optic deflector 57 is for propagating the ultrasonic wave on the horizontal plane in the X-axis direction, and the acousto-optic deflector 24 is for transmitting the ultrasonic wave on the horizontal plane in the Y-axis direction. The first-order diffracted light 27 output from the acousto-optic deflector 24 is controlled so as to scan only the surface of the sample 20 diagonally as shown in FIG. The straight lines 63A, 63B and 63C with arrows show a part of the scanning locus of the spot of the first-order diffracted light 27.

FIG. 18 is a diagram for explaining a method of controlling the voltage controlled oscillators 60 and 25 necessary for scanning only the surface of the sample 20 diagonally with the first-order diffracted light 27 as shown in FIG. 18A shows a drive signal S60 output from the voltage controlled oscillator 60, and FIG. 18B shows a drive signal S25 output from the voltage controlled oscillator 25.

In FIG. 18, 64A and 65A are drive signals S6
0, S25, necessary portions for scanning the first-order diffracted light 27 as shown by a straight line 63A with an arrow in FIG.
B and 65B represent the first-order diffracted light 2 in the drive signals S60 and S25.
7, a portion necessary for scanning as shown by a straight line 63B with an arrow in FIG. 17, 64C and 65C are drive signals S60,
In S25, the first-order diffracted light 27 is converted into a straight line 63 with an arrow in FIG.
The part necessary for scanning as shown by C is shown.

That is, the voltage controlled oscillator 60 outputs the drive signal S
Assuming that the time change rate of the frequency is constant and the unit drive signal whose frequency changes from high to low is repeatedly output as 60, first, the high frequency is fixed to the maximum frequency, and the low frequency is A unit drive signal that becomes smaller for each scan is repeatedly output, and when the lower frequency becomes the minimum frequency, the lower frequency is fixed to the minimum frequency, and the higher frequency is changed for each scan. Is controlled so as to repeatedly output a unit drive signal which is higher than the above.

On the other hand, the voltage-controlled oscillator 25 sets the time change rate of the frequency constant as the drive signal S25,
The unit drive signal whose frequency changes from low to high shall be output repeatedly.First, the low side frequency is fixed to the minimum frequency, and the unit drive signal such that the high side frequency increases with each scan. If the higher frequency becomes the maximum frequency, the higher frequency is fixed to the maximum frequency, and the unit drive signal is output repeatedly so that the lower frequency becomes lower for each scan. Is controlled.

In the fourth embodiment of the present invention having the above-described configuration, the laser light 23 which has been converted into parallel light is output from the laser light source 22 and is incident on the acousto-optic deflector 24 at a Bragg angle α. At the same time, drive signals S60 and S25 whose frequency shown in FIG. 18 linearly changes from high to low linearly with respect to the acousto-optic deflectors 57 and 24 from the voltage controlled oscillators 60 and 25 controlled by the control / arithmetic means 35. Is applied.

As a result, the first-order diffracted light 58 output from the acousto-optic deflector 57 is deflected in the X-axis direction, and the first-order diffracted light 27 output from the acousto-optic deflector 24 is formed on the surface of the sample 20. The shape of the spot becomes a circle and the sample 20
Will be scanned diagonally.

The return light 32 from the surface of the sample 20
Is reflected by the half mirror 31 and is imaged on the light receiving surface of the CCD sensor 34 via the light receiving optical system 33. In the CCD sensor 34, the diameter of the spot of the first-order diffracted light 27 on the surface of the sample 20 is reduced. It is extracted as an electric signal and transmitted to the control / calculation means 35.

The control / calculation means 35 determines the scanning position of the first-order diffracted light 27 from the value of the input voltage applied to the voltage-controlled oscillator 25, and determines the scanning position of the first-order diffracted light 27 and the output of the CCD sensor 34. From the signal, the surface shape of the sample 20 is calculated.

Accordingly, the entire surface of the sample 20 is repeatedly scanned with the first-order diffracted light 27 while moving the sample 20 in the direction orthogonal to the direction of deflection of the first-order diffracted light 27, and
When the time change rate (df / dt) of the frequency f of the ultrasonic wave 43 in the acousto-optic medium 40 is changed every time the entire surface of the surface 0 is scanned, the direction of the incident optical axis of the first-order diffracted light 27 with respect to the sample 20 Can be scanned over the entire surface of the sample 20 with the first-order diffracted light 27, and the display means 36 can display the shape of the surface of the sample 20.

Note that, in the fourth embodiment of the present invention,
The display of the surface shape of the sample 20 on the display means 36 is performed by displaying the height of the imaging point of the first-order diffracted light 27 where the spot diameter of the return light 32 is minimum and the light intensity of the return light 32 is maximum. Will be

As described above, according to the fourth embodiment of the present invention, when changing the distance between the image forming position of the first-order diffracted light 27 with respect to the sample 20 in the direction of the incident optical axis and the sample 20, the optical system or the sample 20 No mechanical movement is required, and the measurement of the surface shape of the sample 20 can be speeded up.

Since the spot shape of the first-order diffracted light 27 can be circular, the diameter of the spot of the return light 32 from the surface of the sample 20 can be easily observed.
Measurement of the surface shape of the sample 20 can be facilitated.

Note that in the fourth embodiment of the present invention,
The case where the CCD sensor 34 is used as the spot diameter measuring means has been described.
It may be configured to include the photodiode 52 provided in the embodiment, or the two-dimensional filter 54 and the photodiode 55 provided in the third embodiment of the present invention.

In the first to fourth embodiments of the present invention, the case where the present invention is applied to an epi-laser type laser scanning microscope and the incident optical axis and the reflected optical axis are coaxial will be described. However, according to the present invention, the first-order diffracted light 27, 62
Can be applied to the sample 20 obliquely from above, and can be applied to a laser scanning microscope configured so that the incident optical axis and the reflected optical axis are not coaxial.

[0108]

According to the first, second, third, fourth, fifth or sixth invention of the present invention (the laser scanning microscope according to claim 1, 2, 3, 4, 5 or 6). For example, as the deflecting means, an acousto-optic deflector on which laser light output from a laser light source is incident, and a drive signal whose frequency changes with time are given to the acousto-optic deflector, and the time change rate of the frequency of the drive signal changes. Acousto-optic deflector drive means that can change the distance between the imaging position of the laser beam with respect to the sample in the direction of the incident optical axis and the sample, eliminating the need for mechanical movement of the optical system or the sample. Therefore, the measurement of the surface shape of the sample can be speeded up.

According to the seventh aspect of the present invention, the first, second, third, fourth, and fourth laser scanning microscopes are provided.
The same effect as that of the fifth or sixth invention can be obtained, and the imaging position of the laser beam with respect to the sample in the direction of the incident optical axis and the scanning speed can be made constant, and the scanning distortion can be eliminated. Therefore, the accuracy of measurement of the surface shape of the sample can be improved.

According to the eighth aspect of the present invention, the first, second, third, fourth, and fourth laser scanning microscopes are provided.
The same effect as that of the fifth or sixth invention can be obtained, and the measurement data of the surface shape of the sample using the laser spot position data obtained by measuring the position of the laser spot on the sample surface at each time in advance. Can be corrected, so that the accuracy of measurement of the surface shape of the sample can be improved.

According to the ninth aspect of the present invention, the first, second, third, fourth, and fourth laser scanning microscopes are provided.
The same effect as that of the fifth, sixth, seventh or eighth invention can be obtained, and the shape of the laser spot formed on the surface of the sample can be made circular. It can be facilitated.

According to the tenth aspect of the present invention (the laser scanning microscope according to the tenth aspect), the same effect as that of the ninth aspect can be obtained, and unnecessary scanning is not performed. Therefore, the measurement of the surface shape of the sample can be further speeded up.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a main part of a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of an acousto-optic deflector provided in the first embodiment of the present invention.

FIG. 3 is a time chart showing a drive signal applied to a piezoelectric element of the acousto-optic deflector provided in the first embodiment of the present invention.

FIG. 4 is a diagram for explaining a control method of the voltage-controlled oscillator included in the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a control method of the voltage controlled oscillator included in the first embodiment of the present invention.

FIG. 6 is a diagram for explaining the cylindrical concave lens effect of the acousto-optic deflector provided in the first embodiment of the present invention.

FIG. 7 is a view for explaining that the surface of a sample can be scanned with the first-order diffracted light while the imaging position of the first-order diffracted light with respect to the sample in the direction of the incident optical axis can be fixed using the cylindrical concave lens effect of the acousto-optic deflector. FIG.

FIG. 8 shows that when the time change rate of the frequency of the ultrasonic wave in the acousto-optic medium of the acousto-optic deflector is changed, the imaging position of the first-order diffracted light in the direction of the incident optical axis with respect to the sample is changed. FIG. 4 is a diagram for explaining that a surface of a sample can be scanned.

FIG. 9 shows that when the time change rate of the frequency of the ultrasonic wave in the acousto-optic medium of the acousto-optic deflector is changed, the imaging position of the first-order diffracted light on the sample in the direction of the incident optical axis is changed, and FIG. 4 is a diagram for explaining that a surface of a sample can be scanned.

FIG. 10 is a diagram showing a relationship between an image forming position of the first-order diffracted light with respect to the sample in the incident optical axis direction, a spot shape of the first-order diffracted light on the surface of the sample, and a light intensity distribution of the first-order diffracted light on the surface of the sample. is there.

FIG. 11 is a schematic diagram illustrating a configuration of a light receiving optical system included in the first embodiment of the present invention.

FIG. 12 is a diagram for explaining a method for controlling the shutter of the CCD sensor provided in the first embodiment of the present invention.

FIG. 13 is a conceptual diagram of a main part of a second embodiment of the present invention.

FIG. 14 is a diagram illustrating light density versus output current characteristics of a photodiode when the amount of incident light is the same.

FIG. 15 is a conceptual diagram of a main part of a third embodiment of the present invention.

FIG. 16 is a conceptual diagram of a main part of a fourth embodiment of the present invention.

FIG. 17 is a diagram illustrating a scanning method according to a fourth embodiment of the present invention.

FIG. 18 is a diagram for describing a control method of a voltage controlled oscillator included in a fourth embodiment of the present invention.

FIG. 19 is a conceptual diagram of a main part of an example of a conventional laser scanning microscope.

[Explanation of symbols]

 24 Acoustooptic deflector 25 Voltage controlled oscillator

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitaka Oshima 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Fumiyuki Takahashi 4 Kamikadanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Fujitsu Limited (72) Inventor Hiroyuki Tsukahara 4-1-1 Kamikadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited

Claims (10)

[Claims] 1. A laser comprising: a laser light source; deflecting means for deflecting laser light output from the laser light source; and an optical system for narrowing the laser light output from the deflecting means into a spot on the surface of a sample. In the scanning microscope, an acousto-optic deflector to which a laser beam output from the laser light source is incident, and a drive signal whose frequency changes with time are given to the acousto-optic deflector as the deflection unit,
An acousto-optic deflector driving means capable of changing a time change rate of the frequency of the driving signal. 2. A laser spot diameter measuring means for measuring the diameter of a laser spot formed on the surface of the sample from the light intensity of the spot formed by the return light from the surface of the sample. The laser scanning microscope according to claim 1, wherein 3. The image sensor, wherein the laser spot diameter measuring means includes a shutter, wherein the spot of the return light is imaged on a light receiving surface, and a center of the spot of the return light is a light receiving portion of a pixel of the image sensor. 3. A laser scanning microscope according to claim 2, further comprising: shutter control means for controlling said shutter so that said shutter is opened at the moment of passing through the center of said laser scanning microscope. 4. The laser spot diameter measuring means includes: a two-dimensional filter on which a spot of the return light is imaged on a filter surface; an optical sensor to which return light passing through the two-dimensional filter is incident; The moment the center of the light spot passes through the center of the filter section of the pixel of the two-dimensional filter,
3. The laser scanning microscope according to claim 2, further comprising a two-dimensional filter control unit that controls the two-dimensional filter so that the pixel is in an open state. 5. A laser spot diameter measuring means for measuring the diameter of a laser spot on the surface of the sample from the light density of the spot formed by the return light from the surface of the sample. A laser scanning microscope as described. 6. The laser spot diameter measuring means includes a photodiode on which a spot of the return light is focused on a light receiving surface, and uses a light density vs. output current characteristic of the photodiode when an incident light amount is the same. The laser scanning microscope according to claim 5, wherein the laser scanning microscope is configured to perform the operation. 7. The acousto-optic deflector driving means includes a voltage-controlled oscillator for generating the drive signal, wherein the voltage-controlled oscillator has a distortion characteristic opposite to a distortion characteristic of an input voltage versus frequency characteristic. 7. The laser scanning microscope according to claim 1, wherein an input voltage having the following is provided. 8. A correction means for correcting measurement data of the surface shape of the sample using laser spot position data acquired by measuring the position of the laser spot on the surface of the sample at each time in advance. The laser scanning microscope according to claim 1, 2, 3, 4, 5, or 6. 9. The first acousto-optic deflector deflects a laser beam output from the laser light source in a first direction.
And a second acousto-optic deflector in which the propagation direction of the ultrasonic wave is set to a direction orthogonal to the first direction, and a first-order diffracted light output from the first acousto-optic deflector is incident thereon. And a child device.
The laser scanning microscope according to 3, 4, 5, 6, 7, or 8. 10. The acousto-optic deflector driving means, wherein the first and second acousto-optic deflectors are such that the first-order diffracted light output from the second acousto-optic deflector scans only the surface of the sample. The laser scanning microscope according to claim 9, wherein the probe is driven.