JP2992075B2 - Light beam scanning device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device used for performing precise measurement of a shape, dimensions, and the like by scanning a laser beam.

[Prior Art] With the recent advance in precision processing technology, fine patterns on the order of microns have been formed, and the need for precise measurement of shapes, dimensions, and the like has increased. In this type of measurement, in order to increase the spatial resolution of the measurement, scanning of a light beam (laser light) that scans a predetermined range with a laser beam condensed to a minute spot diameter in a minute scanning step (for example, 0.01 μm). Equipment is required. A scanning device for controlling the scanning of a light beam is required to constitute a scanning device. Conventionally, the most commonly used scanning devices include an acousto-optic deflecting device, a galvanometer mirror, and a polygon mirror. When scanning a light beam one-dimensionally, a scanning device having a configuration in which one scanning element and various lenses are combined is used. Further, when scanning a light beam two-dimensionally, a scanning device having a configuration in which two scanning elements and various lenses are combined is used. For example, a scanning device combining two acousto-optic deflecting elements is reported in “Laser Research” Vol. 15, No. 8, page P636. A scanning device combining one acousto-optic deflecting element and one galvanomirror is a laser. It has been put into practical use as a Tech 1LM11 model.

[Problems to be solved by the invention]

In a conventional two-dimensional or one-dimensional light beam scanning device,
The scanning direction and the scanning range are set in advance. For example, in two-dimensional scanning, the scanning directions of two scanning elements are arranged so as to be orthogonal to each other (X and Y axes), and raster scanning is generally performed. Also, in one-dimensional scanning, the scanning direction (X-axis) of the scanning element can be performed only in the initially set direction, and the scanning direction cannot be changed. In the two-dimensional scanning, it is possible to change the X-axis and Y-axis scanning directions by simultaneously driving the X-axis and the Y-axis. Therefore, it is difficult to convert the scanning direction to an arbitrary direction. Furthermore, also in the range to be scanned, only the range in which the scanning characteristics are uniform can be scanned. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a light beam scanning device capable of freely changing the scanning direction with a simple mechanism.

[Means for solving the problem]

To achieve the above object, the present invention comprises the following means.

A scanning optical system including first and second at least two types of scanning elements having different scanning ranges and different scanning resolutions in an optical path from a laser light source to an objective lens, and a reflecting surface between an incident surface and an emitting surface. A scanning control unit for driving the first and second scanning elements, and a rotation control unit for rotating the scanning direction conversion element are provided. The first scanning element scans a first area in the incident surface of the scanning direction conversion element,
The second scanning element is located within the plane of incidence of the scanning direction conversion element,
Scanning a second area within the first area and having a narrow scanning range, and causing a light beam scanned in the first area or the second area to enter the scanning direction conversion element; The control unit rotates the scanning direction conversion element with the axis parallel to the optical axis as the rotation axis while the incident surface and the emission surface of the scanning direction conversion element are kept perpendicular to the optical axis. In other words, the scanning direction of the light beam emitted from the emission surface is changed.

At this time, the scanning direction conversion element has a configuration in which an equilateral triangular prism having an apex angle of 60 ° and a right angle prism having an apex angle of 30 ° and 60 ° are overlapped with each other, and one surface of the equilateral triangular prism is positioned with respect to the optical axis. The vertical surface is set to be the entrance surface, one surface of the right-angle prism is set to be perpendicular to the optical axis to be the exit surface, and the other surface is set to be parallel to the optical axis to be the reflective surface. It is assumed that.

[Action]

Two types of light beam scanning elements having different scanning ranges and different scanning resolutions are provided in the optical path from the laser light source to the objective lens. The first scanning element has a large scanning angle and relatively low scanning resolution, and scans a relatively wide range two-dimensionally or one-dimensionally in coarse steps. This scan is a prescan-like operation for measuring a rough shape or the like of an object to be measured, and for determining a measurement position of a portion to be precisely measured. The second scanning element has a small scanning angle and high scanning resolution, and has a two-dimensional or one-dimensional range smaller than the scanning range of the first scanning element.
Scans dimensionally. This scan is a precise scan, and a precise scan is performed at the measurement position determined by the coarse scan to measure the size, shape, and the like. At this time, only one of the first and second scanning elements is operated, and when one of the scanning elements is performing the scanning operation, the scanning operation of the other scanning element is stopped. At this time, since the direction of the light beam scanned by the first and second scanning elements is a preset direction (X axis or Y axis), the scanning direction can be freely changed by the scanning direction conversion element. The scanning direction conversion element includes one regular triangular prism and one
A light beam incident on one surface of an equilateral triangular prism is reflected by the bottom surface of the right angle prism, and a V-shaped reflection path is taken inside the prism. Out of the surface. At this time, if the bottom surface of the right-angle prism is rotated in a plane perpendicular to the optical axis, the scanning direction can be changed by an angle twice as large as the rotation angle. The beam can be scanned, and the light beam can be scanned in a direction orthogonal to a member generally formed also in an axial direction other than the X and Y axes.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First
The figure is a block diagram for explaining the operation of the present invention.
Reference numeral 10 denotes a laser light source, which is composed of, for example, a He-Ne laser tube or a semiconductor laser, and emits laser light 100. 11 and 1
Reference numeral 2 denotes a first scanning element, which is formed of, for example, a galvanometer mirror, has a large scanning angle, and has a scanning characteristic that the scanning resolution is not so high. One 11 of the first scanning elements scans in the X-axis direction, and the other 12 of the first scanning elements scans in the Y-axis direction, and performs two-dimensional raster scanning on the XY plane. Reference numeral 13 denotes a second scanning element, which comprises, for example, an acousto-optic deflecting element, has a small scanning angle and high scanning resolution, and performs scanning in the X-axis direction, for example. The scanning by the second scanning element 13 is inside the scanning area by the first scanning elements 11 and 12, and scans a narrow range. The arrangement of the scanning elements may be other than that shown in FIG. 1, and the number of the scanning elements may be one for the first scanning element and two for the second scanning element. A beam splitter 105 transmits most of the light beam scanned by the first and second scanning elements. A scanning optical system 110 includes first and second scanning elements 11, 12, and 13, a beam splitter 105, and many other lenses (not shown).
Of the beam shape conversion and the scanning width are set. Reference numeral 14 denotes a scanning controller, which includes a first scanning controller 120 for driving the first scanning elements 11 and 12 and a second scanning controller 130 for driving the second scanning element 13. At this time, the first scanning control unit 120 outputs drive signals 122 and 124 of two channels. The signal 122 is a ramp signal whose voltage continuously changes, and continuously changes the scanning angle of the first scanning element 11. The signal 124 is a step voltage signal in which the voltage changes stepwise, and changes the voltage in synchronization with the cycle of the signal 122.
The scanning angle of the scanning element 12 is changed stepwise. The second scan control unit 130 outputs a drive signal 132 for one channel. The signal 132 is a ramp voltage signal like the signal 122, and continuously changes the scanning angle of the second scanning element 13. In the above scanning drive signal, the first scanning control unit 12
When 0 is performing the scanning operation, the second scanning control unit 130
Causes only one of them to be in a scanning state, such that the scanning operation is stopped.

Reference numeral 15 denotes a scanning direction conversion element, the shape and operation of which will be described later in detail, but the control signal 162 emitted from the rotation control unit 16 causes the scanning direction conversion element 15 to move around the optical axis 107 by a predetermined angle. Rotate. Scanning optical system 11
When a light beam scanned two-dimensionally or one-dimensionally by 0 enters the incident surface 150 of the scanning direction conversion element 15, the light exiting surface 152
The scanning direction of the light beam emitted from the scanning direction conversion element
It is rotated by twice the angle of 15 rotations. The light beam whose scanning direction has been changed enters the objective lens 17, is condensed to a minute spot diameter, and is scanned in an arbitrary direction on the surface of the device under test 18. The light beam reflected by the DUT 18 passes through the objective lens 17 and the scanning direction conversion element 15,
The light is reflected by the beam splitter 105 and detected by the light receiver 170. The light intensity of the reflected light detected by the light receiver 170 is photoelectrically converted, and the data processing unit 180 performs arithmetic processing for various measurements such as shape and size.

FIG. 2 shows a specific configuration example of the scanning direction conversion element 15.

20 is a regular triangular prism with a vertical angle of 60 °, 21 is a vertical angle of 30 °, 60
The scanning direction conversion element 15 is formed by superposing the two prisms 20 and 21 as shown in FIG. The surface 200 of the equilateral triangular prism 20 is a light beam incident surface, and is set to be a surface perpendicular to the traveling direction Z (optical axis) of the light beam.
The surface 210 of the right triangle 21 is the exit surface of the light beam and the entrance surface 200
Similarly to the above, it is set on a plane perpendicular to the optical axis. Incident surface 200
Is set perpendicular to the optical axis in order to prevent deformation of the beam shape due to astigmatism when the incident light beam is divergent light or convergent light. The bottom surface 220 of the right-angle prism 21 is a reflection surface, which is a surface parallel to the optical axis. The light beam 230 incident on the incident surface 200 is transmitted through the incident surface, reflected on the other surface 240 of the equilateral triangular prism 20, reflected on the reflecting surface 220, and reflected again on the other surface 250 of the right-angle prism 21. The light exits from the exit surface 210 as an exit light 260 on an optical path parallel to the incident light 230. At this time, the path from the incidence to the emission is a V-shaped path as shown. The optical axis height of the outgoing light 260 in the Y-axis direction with respect to the incident light 230 is equal to the reflection surface 22 of the incident light 230.
It is determined by the position in the optical axis height direction from 0, and the optical axis height position of the outgoing light 260 changes with twice the change in the optical axis height position of the incident light in the Y axis direction. At this time, even if the incident position of the incident light 230 changes in the X-axis direction, the output positions of the output light 260 in the X-axis direction and the Y-axis direction do not change.

FIGS. 3A and 3B show the scanning area of the scanning beam on the incident surface of the scanning direction conversion element 15. FIG. Reference numeral 30 denotes a diagram when the incident surface 200 of the regular triangular prism 20 is viewed from the incident direction, and has a square cross-sectional shape. An area 31 in FIG. 3A is a two-dimensional area scanned by the first scanning elements 11 and 12, and is called a first area. As described above, this first area 31 is a rough scan in a wide range. The area 32 in FIG. 3B is a one-dimensional area scanned by the second scanning element 13 and is called a second area. The second area 32 is inside the first area 31 and precisely scans a smaller area.

As described above, in the first and second regions 31 and 32, the scanning beam is scanned only in the X-axis or Y-axis direction, and scanning in the other axis directions is not performed.

Next, the scanning direction conversion operation by the scanning direction conversion element 15 will be described.

FIG. 4 (a) is a view for explaining the scanning direction on the plane of the incident surface 200, where α is scanning rightward on the incident surface in the X-axis direction,
β represents the downward scanning in the Y-axis direction on the incident surface. (A) to (h) of FIG.
FIG. 14 is a diagram showing the position of the reflecting surface 220 when the reflecting surface 220 of FIG. 21 is rotated and the scanning direction of the emitted light beam when viewed from the incident surface side. Scanning direction conversion element shown in FIG.
In 15, the reflecting surface 220 is in a plane in the X-axis direction, and by rotating the entire scanning direction conversion element 15 in a plane perpendicular to the optical axis, the reflecting surface 220 is rotated.
At this time, the reflection surface 200 is always kept parallel to the optical axis.

(A) of FIG. 4 (b) is a reference state where the rotation angle θ is 0 °, (b) is θ = 45 °, (c) is θ = 90 °, and (d) is θ.
= 135 °, (e) is θ = 180 °, (f) is θ = 225 °,
(G) shows a state in which θ = 270 °, and (h) shows a state in which θ = 315 °. One rotation is performed in the next state (a).

In the state (a), the scanning beam α scanned in the X-axis direction
Is emitted in that state, and the scanning beam β scanned in the Y-axis direction is emitted in the same Y-axis direction but with the scanning direction reversed. This scanning direction is represented by.

In the state of (b), the scanning direction of the incident scanning beam α is
It is rotated 90 ° and scanned in the Y-axis direction. This scanning direction is represented by β. The incident scanning beam β is also rotated in the scanning direction by 90 ° and scanned in the X-axis direction.
At this time, the direction of the X axis is reversed. This scanning direction is represented by. Even in other angle states, the scanning direction is converted to the scanning direction shown in the figure. From the above, it is understood that the scanning direction is converted at twice the rotation angle of the reflection surface 220.

The conversion of the scanning direction according to the present invention is not the conversion of the direction in the same direction, for example, α, but the conversion that causes the change in the azimuth, such as from the α direction to the β direction.

The scanning direction conversion operation described above can also be realized by a conventionally known image rotating prism (Dove prism). The Dove prism has a defect that the beam shape becomes elliptical due to astigmatism when divergent light or convergent light is incident because the entrance surface and the exit surface are inclined surfaces inclined 45 ° from the vertical surface. Depending on the configuration of the scanning optical system, parallel light may be incident. In this case, a Dove prism may be used.

FIGS. 5A, 5B, and 5C show examples of the scanning beam when the scanning direction is changed. As is apparent from the description of FIG. 4, in order to cause rotation in the direction of ± 90 ° unless the direction of the scanning direction (for example, the relationship with α) is taken into consideration, the reflecting surface 220 must be rotated by ± 45 °. It will be good.

In FIG. 5A, a line 50 indicates a reference scanning beam scanned in the X-axis direction. Line 51 is a scanning beam having an inclination of 45 ° with respect to the X axis, and is obtained when the reflecting surface 220 is rotated in the positive direction (forward direction) by 22.5 °. Line 52 is a scanning beam having an inclination of -45 ° with respect to the X axis, and is obtained when the reflecting surface 220 is rotated in the negative direction (reverse direction) by 22.5 °. In this way, the reflecting surface 220 may be rotated in the forward or reverse direction by half the angle with respect to the scanning direction.

FIG. 5B shows an example in which the scanning direction of the scanning beam scanned by the first scanning elements 11 and 12 is changed.

The two-dimensional area 500 is a scanning range corresponding to the above-described first area. When the angle of the reflecting surface 220 is 0 °, the first scanning area incident on the incident surface 200 is obtained by transmitting through the emitting surface 210. .
A line 53 inside the region 500 is a scanning beam that is raster-scanned in the X-axis direction, and a line 54 is a scanning beam that is also raster-scanned in the X-axis direction.

The line 55 is a line 56 when the scanning direction indicated by the line 53 is changed.
Is a case where the scanning direction indicated by the line 54 is converted. In any case, the direction is converted around the center position of the area 500 on the X axis.

FIG. 5C shows a case where the scanning operation by the first scanning elements 11 and 12 is stopped and the second scanning element 13 is operated.
Reference numeral 57 denotes a scanning beam in the X-axis direction when the rotation angle of the reflection surface 220 is 0 °. Line 50 is the scanning beam whose scanning direction has been changed by rotating the reflecting surface. Thus, by rotating the reflection surface 220, scanning of the scanning beam in an arbitrary direction becomes possible.

FIG. 6 shows an embodiment of application to measurement when the light beam scanning device of the present invention is used.

FIG. 6 is a schematic view of the magnetic head as viewed from above. 61 is a portion called a slider, 62 is a portion called a track portion, and 63 is a portion called a nose, around which a coil is wound. The track section 62 has a gap 64
Are formed. In the above magnetic head, it is important to measure the width of the gap 64 (about 0.5 μm in the X direction) and the width of the track section 62 (about 15 μm in the Y direction).

Here, a two-dimensional area surrounded by a dotted line 600 is a scanning range of the first scanning elements 11 and 12, and a wide area of, for example, 1 mm square is roughly scanned to determine the position of the gap 64. When the position to be measured is determined, the second scanning element 13 is driven to
Precise scanning of the scanning range (X direction) shown in 65
Measure 64 dimensions. Next, when measuring the width of the track portion 62, the scanning position is slightly shifted in the X-axis direction, and then the scanning direction conversion element 15 is rotated by 45 ° to perform scanning in the Y-axis direction indicated by the line 66. . This scan is a scan 65 in the X-axis direction.
Has the same scanning accuracy as.

FIG. 7 shows an embodiment of the scanning optical system constituting the light beam scanning device of the present invention.

71 and 74 are cylindrical lenses of focal length f _1, 72
And 73 is the focal length of f ₂ convex lens 75 focal length f _3,
76 is a convex lens having a focal length of f ₄ , 77 is a convex lens having a focal length of f ₅ , and 78 is an objective lens having a focal length of f ₀ . The second scanning element 13 includes an acousto-optic element (hereinafter abbreviated as AO), and scans the second area in the X-axis direction. The first scanning element 11 and
12 is composed of a galvanometer mirror, GMY of 12 is in the Y-axis direction, 1
One GMX scans the first area in the X-axis direction.

The laser beam 100 having a circular cross section emitted from the laser light source 10 is converted by the cylindrical lens 71 and the convex lens 72 into a sheet-like beam having a fan shape in a plane parallel to the paper surface. When this sheet-like beam exits the convex lens 72, it enters the AO 13 as parallel light in a plane parallel to the paper. At this time, in a plane perpendicular to the paper surface, the light is convergent light after exiting the convex lens 72, and is focused at the center of the AO13. AO
The beam emitted from 13 is a convex lens in a plane parallel to the paper.
After being converted into convergent light at 73 and reflected by GMY12, it is transmitted through a cylindrical lens 74 and condensed at its focal position 700. At this time, on the surface perpendicular to the paper, the divergent light emitted from the AO13 is converted into parallel light by the convex lens 73, and GMY1
After being reflected at 2, it is refracted by the cylindrical lens 74 and condensed at its focal position 700. In the optical path after the rear focal position 700 of the cylindrical lens 74, the light beam again has a circular cross section. Note that GMY12 is disposed at the front focal position of the cylindrical lens 74, and the focal position of the convex lens 73 and the focal position of the cylindrical lens 74 are the same point 700.
Arrange so that Also, with the cylindrical lens 71
74 is disposed so that the refraction surfaces are different from each other by 90 °. The reason why the sheet beam is used for the AO13 is to allow the interaction between the ultrasonic wave and the light wave to be sufficiently performed inside the AO13 and to increase the diffraction efficiency by the AO13.

The laser light whose cross section is converted into a circular beam at the point 700 is converted into parallel light by the convex lens 75, reflected by the GMX11, converted into convergent light again by the convex lens 76, transmitted through the beam splitter 105, and diverged as The light enters the entrance surface 150 of the scanning direction conversion element 15. At this time, the reflection surface 220 of the scanning direction conversion element 15 is rotated as described above. The laser beam transmitted through the emission surface 152 of the scanning direction conversion element 15 enters the convex lens 77, is converted into parallel light again by the convex lens 77, and enters the convex lens 78. Then, the light is condensed to a minute spot diameter by the objective lens 78, is irradiated on the object to be measured 180, and scans the object plane. The reflected light from the device under test 180 passes through the objective lens 78, the convex lens 77, and the scanning direction conversion element 15, is reflected by the beam splitter 105, and detected by the light receiver 170.

The range scanned at this time is determined by the scanning angle of each scanning element and the focal length of the lens used.
When the angle to be scanned was theta _a by AO13, scan range D _A0 which is scanned over the DUT _{surface, D A0 = f 2 · f} 4 · f 0 · θ a / (f 3 · f 5) Becomes Further, if the angle of theta _x scanned by GMX11, scan range D _gx scanned over the DUT surface becomes _{D gx = f 4 · f 0} · θ gx / f 5.

Further, assuming that the angle scanned by the GMY12 is θ _y , the scanning range D _gy scanned on the object surface is D _gy = 2f ₁ · f ₄ · f ₀ · θ _gy / (f ₃ · f ₅ ).

〔The invention's effect〕

According to the present invention, two types of scanning elements having different scanning angles and different scanning step resolutions are combined to form a hybrid type, and an electric system using a wide range and a narrow range scanning in the same optical path is used. It is possible to switch freely just by switching the signal. At this time, in scanning over a wide range, the approximate shape of the object is measured, and the position of the portion to be measured precisely is determined. In scanning in a narrow range, precise scanning is performed to precisely measure the shape and dimensions of a portion to be measured.

Further, the scanning direction of the scanning beam can be freely changed, and the scanning of the light beam is performed in any direction other than the X-axis and the Y-axis which are orthogonal to each other, and the light beam is formed in any direction. It is possible to measure the shape of the object being performed with a simple device.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining the operation of the present invention, FIG. 2 is a diagram showing a specific configuration of the scanning direction conversion element according to the present invention, and FIG. FIG. 4, FIG. 4 is a diagram for explaining the conversion of the scanning direction caused by the rotation of the scanning direction conversion element, FIG. 5 is a diagram showing an example of the conversion of the scanning direction, and FIG. FIG. 7 is a diagram showing an application example when the present invention is applied to FIG. 7, and FIG. 7 is a diagram showing a specific configuration of a scanning optical system. 10 laser light source 11, 12 first light beam scanning element, 13 second light beam scanning element, 14 scanning control unit, 15 scanning direction conversion element, 16 rotation control Part, 17 ... objective lens, 20 ... equilateral triangle prism, 21 ... right angle prism.

Claims (2)

(57) [Claims] An optical path extending from a laser light source to an objective lens has a common optical axis, and has first and second scanning elements having different scanning ranges and different scanning resolutions; A scanning control unit configured to drive the first and second scanning elements and a rotation control unit configured to rotate the scanning direction converting element. The first scanning element scans a first area in the incident surface of the scanning direction conversion element, and the second scanning element scans the first area in the incident plane of the scanning direction conversion element. Partial or partial sharing second
Scan the area of, the incident surface of the scanning direction conversion element,
With the emission surface kept perpendicular to the optical axis, the rotation control unit rotates the scanning direction conversion element about an axis parallel to the optical axis as a rotation axis, and passes through the first and second scanning elements. A light beam scanning device for converting a scanning direction of a light beam incident on an incident surface of a scanning direction conversion element and emitting the light beam from an emission surface of the scanning direction conversion element. 2. A scanning direction conversion element comprising an equilateral triangular prism superposed on a 90 ° apex angle of a right angle prism having a vertex angle of 30 °. The opposite surface is a reflection surface, the opposite surface with a vertical angle of 30 ° is an emission surface, the surface of an equilateral triangular prism parallel to the emission surface is an incidence surface, and the incidence surface is installed orthogonal to the optical axis. 2. The light beam scanning device according to claim 1, wherein: