JP2690111B2 - Two-dimensional laser scanning optical device - Google Patents

Description

The present invention relates to an optical device for performing two-dimensional scanning of laser light.

[Background of the Invention]

Due to the progress of precision processing technology in recent years, the miniaturization, high density, and high precision of the work piece have advanced, and
Dimensional patterns are being created. Along with this, the need for precise measurement of the shape, dimensions, etc. of a two-dimensional pattern formed with submicron precision has increased, and when performing optical measurement, it is possible to realize an optical device that can perform stable two-dimensional scanning in a minute area. Is desired.

[Conventional technology]

The following two methods are often used to focus laser light on a minute spot diameter and perform two-dimensional scanning.

 A method of moving a sample two-dimensionally and scanning.

A method of electrically scanning laser light using a deflection device.

In this method, the laser beam is fixed and the stage on which the object to be measured is placed is mechanically scanned. In this method, the object to be measured is fixed and the laser light is two-dimensionally scanned. As a polarizing device for scanning, a polygon mirror, a galvano mirror, or an acousto-optic deflecting element is often used. An optical device that two-dimensionally scans a laser beam by electrical control has been realized by combining a polarizing element and a galvanometer mirror.

[Problems to be solved by the invention]

The method described in the prior art has a low scanning speed, mechanical vibrations are generated during scanning, and it is difficult to set a scan position for each minute distance of about 0.01 micrometer (hereinafter referred to as μm). The method in which the acousto-optic deflection element described in the prior art is combined with the luvano mirror is
The scanning speed is faster than that of the conventional method, but the deflection angle of the galvanomirror is relatively large. Therefore, when scanning a minute area such as several tens of μm in steps of about 0.01 μm, the galvanomirror It is difficult to stably set a minute shake angle, and it is not suitable for stable two-dimensional scanning in a minute area.

The object of the present invention is to solve the above-mentioned problems and to solve the problem of several tens of μm
It is an object of the present invention to provide an optical device capable of performing stable two-dimensional scanning with a scan step of about 0.01 μm in a small area of about 0.01 μm.

[Means for solving the problem]

In order to achieve the above object, the present invention has the following configuration.

First light deflection of laser light emitted from a laser light source by a first optical element group including an acousto-optical element driven by a first drive signal source and a lens for controlling an optical operation of the acousto-optical element. And an optical path conversion prism that causes a laser beam to be incident on the V-shaped reflection path inside the medium by a piezo translator driven by a second drive signal source and emits the laser beam in the same direction as the incident direction. To drive the second light beam in the direction perpendicular to the first light deflection.
The second optical element group including the objective lens collects the laser beam scanned by the first optical deflection and the second optical deflection to perform two-dimensional scanning.

Furthermore, the laser light emitted from the laser light source is driven by the first piezo translator operated by the first drive signal source to drive the above-mentioned optical path conversion prism to perform the first light deflection, and the second light deflection is performed. A second piezo translator that is operated by a drive signal source drives the above-mentioned optical path conversion prism, and a second piezo translator moves in a direction perpendicular to the first light deflection.
Optical deflection is performed, the laser light scanned by the first optical deflection and the second optical deflection is condensed by an optical element group including an objective lens, and two-dimensional scanning is performed.

[Action]

When using the Dove prism as an example of the optical path changing prism, when the position of the light beam incident on the Dove prism is fixed and the prism bottom position that causes total reflection of the Dove prism is moved, the light beam that has passed through the Dove prism is not moved. The light is emitted to a position shifted by twice the movement amount with respect to the position. Therefore, scanning can be performed by moving the Dove prism by a small amount by the piezo translator.

On the other hand, the acousto-optic element can perform scanning with a minute change in the diffraction angle according to the applied electric signal, and the acousto-optic element + dove prism or the combination of the dove prism + dove prism can perform a two-dimensional scan of a minute area. Can be done.

Both the acousto-optic element and the piezo translator that drives the dove prism are driven by electric signals. The acousto-optic element can make a change of 10 ^-3 mrad and the piezo translator can make a change of 10 ^-3 μm per unit change of the electric signal. Therefore, the two-dimensional scanning is performed with an arbitrary trajectory according to the electric signal driven with a scanning accuracy of the order of 10 ⁻³ μm.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1 shows a block diagram for explaining the operation of the first embodiment of the present invention, and the case where a Dove prism is used as an optical path changing prism will be described.

Reference numeral 10 is a laser light source, 11 is laser light emitted from the laser light source 10, and the laser light source 10 is, for example, a He—Ne laser, an Ar laser, a semiconductor laser, or the like. 12 is an acousto-optical element (abbreviated as A / O below), 13 is a first optical element group 14 including various lenses for controlling the optical operation of A / O 12, and is for driving A / O 12. Is a first drive signal group. When an ultrasonic traveling wave is applied to the A · O12, the photoelastic effect of the A · O medium causes a periodic fluctuation of the refractive index in the medium, so that it acts as a diffraction grating for light and diffracts incident light. At this time, the diffraction angle of A · O12 is controlled by the electric signal from the first drive signal source 14. This A
The light deflection by O12 is called the first light deflection. For example, the deflection direction is the X direction in the plane parallel to the paper surface.

Reference numeral 15 is a DOVE PRISM, 16 is a piezo translator, and 17 is a second drive signal source for driving the piezo translator 16. The Dove prism 15 is moved by the piezo translator 16. If the moving direction is, for example, the Z direction perpendicular to the paper surface, the second light deflection is also performed in the Z direction. Control of this deflection amount and deflection position Is performed by the electric signal from the second drive signal source 17. The deflection direction of the second light deflection is perpendicular to the deflection direction of the first light deflection described above.

Reference numeral 18 denotes a second optical element group including an objective lens 19, which condenses the laser light 100, which is two-dimensionally scanned in the X and Z directions, to a minute spot diameter, and also focuses this focused light in a minute area in two dimensions. In order to scan, an operation of reducing the deflection amount of the laser light 100 according to a constant ratio is performed. Point 101
Is the focal position of the objective lens 19, and the focused light spot 2 on the XZ plane.
Perform a dimensional scan. When performing this two-dimensional scan, the stability of the piezo translator 16 is particularly important.
It is especially important that there is no hysteresis, good linearity of movement, and fast operation speed.
Truments Piezo Translator, Model DPT / AX100
Is suitable for this purpose. In addition, A ・ O12 also needs high-precision deflection characteristics.
ADM-40 is suitable for this purpose.

FIG. 2 shows an optical path diagram for explaining the light deflection operation by the Dove prism 15. FIG. 2 (a) shows the case where the dove prism 15 is at the set reference position, and FIG. 2 (b) shows the dove prism.
This is the case where 15 is shifted in the Z direction from the reference position by h in conjunction with the movement of the piezo translator.

If the laser light 200 incident on the Dove prism 15 placed at the reference position in FIG. 2 (a) enters the center of the Dove prism 15 in the height direction, it travels along the refraction path as shown in FIG. Emitted light 2 is totally reflected at the central portion 201 in the vertical direction.
02 is emitted at the same height as the incident light 200.

In the case of FIG. 2B in which the total reflection surface of the dove prism 15 is shifted in the Z direction by h, the incident light beam 200 is incident downward by h from the central portion of the dove prism 15 in the height direction ( The Z direction position of the incident ray 200 is fixed). The refracted ray travels along the path shown in the figure, and is totally reflected at a position 203 on the left side of the central portion in the longitudinal direction. It is emitted to the position. In this way the piezo translator 16
By using, to shift the total reflection surface of the dove prism 15 in the Z direction by h, the position of the emitted light can be changed in the Z direction by a size of 2h and the light can be deflected.

FIG. 3 shows a structural example of the optical system of the block diagram shown in FIG.

Reference numerals 30 and 33 denote cylindrical lenses having the same focal length and f _c . Reference numerals 31 and 32 are convex lenses having focal lengths f ₁ and f ₂ , respectively, and between the convex lens 31 and the convex lens 32, A ·
Place O12. The above lens groups 30, 31, 32, and 33 are AO
It is a first optical element group 13 for controlling the optical operation of 12.

In order to perform the deflection operation by the diffraction of A · O12 in the optimum state, it is necessary to sufficiently interact the ultrasonic traveling wave and the light wave propagating in the medium of A · O12. Therefore, the cylindrical lens 30 and the convex lens The combination of 31 converts the beam diameter and the beam shape of the linearly polarized laser light 11 having a circular shape emitted from the laser beam 10 according to the focal length ratio f ₁ / f _C. The converted beam 300 has a sheet shape having a substantially one-dimensional spread due to the action of the cylindrical lens 30. The beam shape shown in the drawing represents a shape in the plane in the X direction parallel to the paper surface, and is a beam shape that is focused at the midpoint position 301 of A · O12 in the Z direction surface perpendicular to the paper surface.

The sheet-shaped beam 300 diffracts at A · O12, and the convex lens 32 and the cylindrical lens 33 convert the sheet-shaped beam again to convert it into a circular beam shape. The light refracting surface of the cylindrical lens 33 is
It is set in a direction perpendicular to the light refracting surface of the cylindrical lens 30. The position 302 is the focal point of the circularly focused beam, and the 1st-order diffracted light diffracted by A · O 12 and the 0th-order light that is not diffracted are separated, but the 1st-order diffracted light is used as the deflected beam.

34 is a polarizing beam splitter (PBS), 15 is the above-mentioned Dove prism, 35 is a convex lens having a focal length f ₃ , and 36 is
1/4 wavelength plate, 19 is an objective lens having a focal length f ₀ , 37 is P
Photodetector consisting of iN photodiode, 38 is a small 2
An object to be measured having a dimensional pattern. Here, the DUT 38 is placed at the focal position of the objective lens 19, and the reflected light is detected by the photodetector 37. A polarization beam splitter 34 and a Dove prism 15 are arranged in the optical path of a circular beam divergent light beam 303. Here, the Dove prism 15 is moved in a plane perpendicular to the plane of the paper, and the second light is deflected in the plane perpendicular to the plane of the paper (Z direction). In the above-mentioned A · O12, the first light deflection is performed in the X direction in the plane parallel to the paper surface.

The convex lens 35 converts the divergent light 303 into parallel light 304, and the objective lens 19 condenses it into a minute spot diameter of about 1 μm.
Two-dimensional scanning is performed on a minute area in the XZ plane at the focus position. Here, the convex lens 35 and the objective lens 19 are the second optical element group 18. Although the quarter-wave plate is arranged in the optical path of the parallel beam 304, it may be arranged on the left side of the convex lens 35.

FIG. 4 shows an optical path diagram for explaining optical path conversion by scanning with the configuration of the optical system shown in FIG. 3, and FIG.
Is an optical path diagram for explaining light deflection in the X direction by A · O12, and FIG. 4B is an optical path diagram for explaining light deflection in the Z direction by the Dove prism 15. In both FIGS. 4 (a) and 4 (b), the cylindrical lens 30, the convex lens 31, the polarization beam splitter 34, and the 1/4 wavelength plate 36 shown in FIG. 3 are not related to the explanation of the optical path. Omitted.

In FIG. 4 (a), the diffracted first-order light 400 diffracted by A · O12 travels at a diffraction angle of θ and is converted by the convex lens 32 into parallel light 401 traveling in the parallel optical path. The cylindrical lens 33 has no refracting action on the parallel light 401, and the dove prism 15 also has no optical path changing action in the X direction on the parallel light 401 deflected in the X direction. The parallel light 401 is refracted by the convex lens 35, and the objective lens 19
Then, the light is focused into a small spot diameter, converted into parallel light again, and scanned in the X direction. First applied to A · O12
If the change in the diffraction angle of the A · O12 by the driving signal of the driving signal source 14 and theta _d, a change in deflection amount at the focal position of the objective lens 19 D _X has the formula _{D X = (f 0 / f} 3) × It is represented by f ₂ × θ _d .

In FIG. 4B, the optical path in the Z direction is A.
At O12, the diffraction effect is not performed and the light beam 402 goes straight.
In the Dove prism 15, the light beam 402 is refracted as described with reference to FIG.
The refracted light is emitted to a position shifted by a distance, and parallel light 403 traveling in parallel is obtained. The parallel light 403 is condensed by the convex lens 35 and the objective lens 19 into a minute spot diameter in the same manner as described with reference to FIG. Piezo translator driving the Dove prism 15
When the movement amount of the Dove prism 15 by the drive signal of the second drive signal source 17 applied to 16 is h, the deflection amount D _{Z at} the focus position of the objective lens 19 is expressed by the formula D _Z = (f ₀ / f ₃ ) × 2h …….

Since the deflection amounts D _X and D _Z in the equation can be changed by (f ₀ / f ₃ ), the convex lens 35 and the objective lens that form the second optical element group according to the desired deflection amount.
You can set a focal length of 19.

(Example of Second Example) Next, a two-dimensional scanning optical system using two Dove prisms will be described. In the first embodiment, the scanning in the X direction was performed by using A.O12, but it is also possible to scan by using a Dove prism instead of A.O12.

FIG. 5 shows a block diagram for explaining the operation of the second embodiment in which two-dimensional scanning is performed using two Dove prisms. Reference numeral 10 denotes the above-mentioned laser light source, which emits the laser light 11. A first Dove prism 51 deflects the first light in the X direction. Reference numeral 52 denotes a first piezo translator (hereinafter abbreviated as PZT) for moving the first Dove prism 51, 5
Reference numeral 3 is a first drive signal source for driving the first PZT 52. A second Dove prism 54 deflects the second light in the Z direction. 55 is a second PZT for moving the second Dove prism 54, and 56 is a second drive signal source for driving the second PZT 55. 57 includes the objective lens 19 and includes the first and second
This is an optical system for controlling the optical operation of the Dove prisms 51 and 54.

In the above configuration, the first and second Dove prisms 51 and
As shown in the drawing, 54 is arranged so that the positions of the bottom surfaces of the dove prisms that cause total reflection are perpendicular to each other. In either case, it is necessary to move the bottom surface positions of the dove prisms.
The second PZT 55 is configured to move in the X direction, and the second PZT 55 is configured to move in the Z direction.

FIG. 6 shows a structural example of the optical system of the block diagram shown in FIG. Reference numeral 60 denotes a convex lens, which is a divergent light obtained by expanding the beam diameter of the circular laser light 11 emitted from the laser light source 10.
Create 600. The above-mentioned first Dove prism 51 and second Dove prism 54 are arranged in the optical path of this divergent light 600. 61
Is a convex lens with a focal length f ₃
And the parallel light 60 is converted by the objective lens 19 having the focal length f _0.
1 is condensed and focused on a minute spot, and the DUT 38 is placed at the focal position to perform a two-dimensional scan. In FIG. 6, a polarization beam splitter, a 1/4 wavelength plate and a photodetector which are useful for detecting reflected light are omitted.

FIG. 7 is a diagram for explaining optical path conversion by scanning by the configuration of the optical system shown in FIG. 6, and FIG. 7 (a) is an optical path diagram of X direction scanning by the first Dove prism 51, FIG. (B) is an optical path diagram of Z-direction scanning by the second Dove prism 54.

In FIG. 7A, when the bottom surface of the first Dove prism 51 that causes total reflection is shifted from the reference position by h _{X in the} X direction, the emitted light 700 is shifted by 2 h _X from the reference position. Second
The dove prism 54 has no optical path changing action in the X direction, goes straight, is refracted by the convex lens 61, and is refracted again by the objective lens 19 to proceed in parallel. First drive signal source 53
When the moving amount of the first Dove prism 51 due to the drive signal of H _x is h _X , the deflection amount D _{X at} the focus position of the objective lens 19 is expressed by the formula D _X = (f ₀ / f ₃ ) × 2h. .

In FIG. 7B, the optical path in the Z direction is the first
Since the dove prism 51 of No. 3 has no optical path changing action, it goes straight, and when the bottom surface of the second dove prism 54 that causes total reflection is shifted in the Z direction from the reference position by h _Z , the emitted light 701 becomes 2 h _Z from the reference position. It is shifted and refracted by the convex lens 61 and the objective lens 19 as in the case of FIG. 7A, and the focal plane of the objective lens 19 is scanned in the Z direction. If the amount of movement of the second Dove prism by the drive signal of the second drive signal source 56 is h _Z , the deflection amount D _{Z at} the focus position of the objective lens 19 is given by the formula D _Z = (f ₀ / f ₃ ) × 2h _Z: Represented by.

Also in the case of the second embodiment, if the amount of movement by the piezo translator is determined, the focal length ratio of the convex lens 61 and the objective lens 19 is arbitrarily set to obtain the desired amount of 2
A dimensional scan is performed.

Next, drive signals for performing the two-dimensional scan described in the first and second embodiments will be described.

FIG. 8 shows an example of drive signals for performing raster scan in the case described in the first embodiment. Signal 80 is first
A · O12 is driven by a signal generated from the drive signal source 14 of. The signal 81 is a signal emitted from the second drive signal source 17.
Drive the PZT16. The drive signal 80 has a voltage level of V _{X1 to} V _X2.
With the ramp wave changing in the range up to, the diffraction angle change of θ _d described above is performed in this voltage range, and the X position is scanned according to the applied voltage value. Drive signal 81 is drive signal 80
Is a signal whose voltage changes stepwise in synchronism with, and is scanned to the Z position according to the applied voltage values V _Z1 , V _Z2 , ....

In the case of this embodiment, after scanning one line in the X direction,
The position in the Z direction is shifted to scan another line, and this operation is sequentially repeated to perform raster scan. Even when the two Dove prisms described in the second embodiment are used, the first Dove prism 51 may be driven by the ramp signal of the drive signal 80. Further, the voltage of the drive signal may be set according to the desired scan format.

Although the example using the Dove prism has been described above as an example of the optical path changing prism, another example of the optical path changing prism is shown in FIG. 91 is a first prism with an apex angle of 60 ° and a regular triangular cross section, and 92 is an apex angle of 30 °, 60
This is the second prism that makes an angle of 90 °, and the above two prisms are used as shown in the figure. First prism 91
The laser light 93 that is incident on the first prism 91 is perpendicularly incident on the first prism 91, causes a V-shaped reflection path inside the medium as in the case of the Dove prism, and is emitted from the second prism 92. 94 is emitted in the same direction as the incident direction from the vertical surface of the second prism 92.

In the case of the present embodiment as well, when driven by the piezo translator as in the case of the Dove prism, the positions of the incident light beam and the outgoing light beam are shifted by twice the movement amount. When the prism of this embodiment is used, the optical system may be replaced with the Dove prism of the optical system described above.

〔The invention's effect〕

As is clear from the above description, according to the present invention, it is possible to stably perform a two-dimensional scan on a minute area with a simple optical system configuration, and to improve the shape and size of a minute two-dimensional micro pattern. It is possible to detect with accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a first embodiment of the present invention,
2 is an optical path diagram for explaining the operation of light deflection by the Dove prism, FIG. 3 is an optical path diagram showing an example of the configuration of the optical system of the block diagram shown in FIG. 1, and FIG. 4 is shown in FIG. FIG. 5 is an optical path diagram for explaining the optical path of light deflection by the optical system, FIG. 5 is a block diagram for explaining the second embodiment of the present invention, and FIG. 6 is a structural example of the optical system of the block diagram shown in FIG. FIG. 7 is an optical path diagram for explaining an optical path of light deflection by the optical system shown in FIG. 6, FIG. 8 is a waveform diagram showing an example of a drive signal, and FIG. 9 is a second optical path conversion prism. FIG. 3 is an optical path diagram for explaining the example of FIG. 10 ... Laser light source, 12 ... Acousto-optic element, 15 ... Dove prism, 16 ... Piezo translator, 19 ... Objective lens, 51 ... First dove prism, 54 ... Second dove prism, 91 ...... First prism, 92 ...... Second prism.

Claims (2)

(57) [Claims] 1. A first optical element group including a laser beam emitted from a laser light source, the acousto-optical element driven by a first drive signal source, and a lens for controlling an optical operation of the acousto-optical element. The piezo translator driven to perform the first light deflection and driven by the second drive signal source causes the incident laser light to have a V-shaped reflection path inside the medium and is directed in the same direction as the incident direction. The optical path conversion prism to be emitted is driven to perform the second light deflection in the direction perpendicular to the first light deflection, and the laser light scanned by the first light deflection and the second light deflection is A two-dimensional scanning optical device for laser light, characterized in that a second optical element group including an objective lens collects the light to perform two-dimensional scanning. 2. A laser beam emitted from a laser light source is a first piezo translator which is operated by a first drive signal source, and the incident laser beam is V inside the medium.
A second optical path conversion prism that drives a first optical path conversion prism that causes a reflection path of the mold to be emitted in the same direction as the incident direction, and causes the second optical path conversion prism to operate. The second optical path conversion prism is driven by the piezo translator to perform the second optical deflection in the direction perpendicular to the first optical deflection, and the scanning is performed by the first optical deflection and the second optical deflection. A two-dimensional scanning optical device for laser light, characterized in that laser light is condensed by an optical element group including an objective lens to perform two-dimensional scanning.