JPH02111915A - Optical scanner - Google Patents

Abstract

PURPOSE:To obtain the device which has high-speed scanning functions over a wide range by fixing an imaging means consisting of an objective lens to the tip of a mechanical oscillator such as tuning fork or cantilever and optically detecting the scanning position by a mirror fixed to the tip of the oscillator as well as a Michelson interferometer. CONSTITUTION:The objective lens 25 for imaging, a reflecting prism 26, and a retroprism 27 for measuring displacement are mounted to the tip 24 of the tuning fork 23. The objective lens 25 and reflecting prism 26 at the tip of the tuning fork move back and forth along the optical axis 34 of a luminous flux when the tuning fork 23 is excited by a driving coil 35. An object 33 is displaced in such position where the surface thereof is paralleled with the oscillating direction at the tip of the tuning fork 24. As a result, the focus 36 of the objective lens 25 scans the surface of the object 33. The retroprism 27 is provided to the side face at the tip of the tuning fork 23. The amplitude at the tip of the tuning fork 23 is measured by the Michelson interferometer 37. The graph indicating the scanning position is displayed at the horizontal axis of an oscilloscope and the graph indicating the quantity of the reflected light at the vertical axis. The optical scanner suitable for the high-speed and high- accuracy scanning over a wide range is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical scanning device used in an optical figure reading device, an optical printing device, an optical drawing device, etc.

[Conventional Technique: One Light] Conventionally used optical scanning devices can be roughly divided into two types. The first method is to relatively move the optical system and the scanned proboscis, and is composed of a fixed optical system 1 and a movable stage 2, as shown in FIG. 2, for example. A focal point 4 of an optical system 1 connected to the surface of an object 3 on a moving stage 2
As the stage 2 moves, the focal position changes on the surface of the object 3. For example, when the optical system 1 is a figure reader composed of a light source 5, a collimator lens 6, an objective lens 7, a beam splitter 8, a condenser lens 9, and a photodetector 10, the focal point 4 of the objective lens 7 is It is possible to sequentially move the surface of the object 6 and continuously detect the reflectance of minute portions thereof.

The second scanning device displaces the focal position of the optical system on the focal plane by changing the angle of incidence of the incident light beam on the optical system, and uses, for example, an f-θ lens as shown in FIG. This configuration includes an objective lens 16 and an acousto-optic element 15 for changing the angle of incidence on the objective lens. Third
The light emitted from the light source 11 in i21 is filtered by filter 1.
2, collimator lens 16, beam splitter 14
, the acousto-optic element 15, and the object 17 passing through the objective lens 16.
? illuminate. The reflected light from the object 17 passes through the lens 16 and the optical element 15, is reflected by the beam splitter 14, and is guided by the condensing lens 18 to the photodetector 19. By applying ultrasonic waves to the acousto-optic element 151 from the light source side, the light enters the acousto-optic element 151, for example, as indicated by the broken line 2.
The deflection in the direction indicated by 0 causes the receiver to be displaced from the focal position 21 to 22 on the object 17.

By continuously changing the frequency of the ultrasonic waves applied to the acousto-optic element 15, the focus moves on the object 17. Part of the reflected light from the object 17 enters the beam splitter 14 in the opposite path to the illumination light, and part of it is reflected and reaches the photodetector 19.The photodetector 19 has a spatial filter. It is built-in and removes harmful reflected light.

[Problem to be solved by the invention]

The apparatus shown in FIG. 2 has the drawback that the mass of the movable parts necessary for scanning, ie, the optical system and the stage, is large, and the scanning structure becomes large. Therefore, it is suitable for devices with a slow scanning speed, but when a high-speed scanning mechanism, especially when back-and-forth scanning is required, increases the driving energy and generates vibrations. However, since existing mechanical technology can be used, the scanning position accuracy, the size of the scanning range, and the number of spots within the scanning range are large. For example, in the case of scanning using a transferred/supported object, the scanning range can be 100 mm, so if the spot diameter is 1 ttrn, the number of spots within the scanning range will reach 100,000 or more. Furthermore, the absolute precision of the scanning current may be 0.1 μm.

However, the stage has a sliding part, and the straight-line stability is about 1 μm, which does not provide very good performance, and in order to obtain high accuracy, a straight-line correction mechanism is required. For example, when scanning in the X direction, a device with a mechanism that also moves in the Y direction is used, and a mechanism that uses a laser interferometer or the like to determine the X% and Y axis coordinates of the stage and controls the position for each draw. is used. However, in a mechanism using a moving stage, the focal point of the optical system is used only on or near the light source, so the effective surface diameter is smaller than in the second method (and its size is smaller than that of the optical system). It is easy to design and manufacture since it only requires the size of a forehead microscopic mirror.

In the apparatus shown in FIG. 3, the scanning is r-θ
This is done by changing the angle of incidence of the light beam on the lens and changing the focal point position on the focal plane, but the scanning range and the spot diameter are determined by the deflection angle of the light beam of the deflection means, the orthogonality of the light beam, −
It is determined by the effective image surface diameter and numerical aperture of the θ lens. In order to realize a scanning mechanism with a wide range and minute spot size, a deflection means with a large aperture and a large deflection angle, its control means, and an f-〇 lens with a large effective image surface and a large numerical aperture are required, and these require advanced design and manufacturing. , requires inspection technology.

Examples of the deflection element include an acousto-optic element, a rotating polygonal boundary, a rotating vibrating plane boundary, and the like. Acousto-optic elements have no moving parts and are suitable for high-speed scanning, but they have the drawback of wavefront aberrations occurring due to the ultrasound propagation time and pressure within the element, and the limitations of the crystal size that can be obtained. There is an upper limit to the diameter/best deflection angle ratio, i.e. spot &j,/'F scanning range of 1 shift. ,000 times/second is possible.

When a rotating multi-plane boundary or a rotating vibration plane theory is used as a deflection means, a motor or a galvanizer is used as the rotating mechanism, so a bearing is necessarily provided in the rotating part. Due to this error in the sleeve receiver, the light incident on the f-theta lens not only has a deflection angle in the scanning direction, but also causes a deflection of a component perpendicular to the scanning direction, that is, a sagittal deflection. Therefore, when using this method to achieve high-precision scanning, sagittal detection means, such as a detection optical system,
A means for sagittal correction, such as an electro-optical element, is required.

The number of spots/scanning range value in a scanning mechanism using a rotating polygon mirror or a rotating oscillating polygon mirror is about 5,000. A scanning device using a rotating polygonal mirror, a motor, a rotating plane mirror, and a galver as a deflection element can perform repeated scanning at a maximum rate of about 200 times/second.

In this way, the optical system of the device shown in Fig. 2 is simple;
Suitable for low-speed, wide-area, high-clearance scanning, but not suitable for high-speed, frequent forest scanning. On the other hand, the device shown in Figure 3 is suitable for high-speed, small-area scanning, but is not suitable for wide-area, high-precision scanning.
.

[Means to solve the problem]

In the present invention, a device with high speed and wide range scanning capability is proposed. In the present invention, an optical system is placed at the tip of a vibrating body such as a tuning fork or a cantilever, and scanning is performed by exciting the vibrating body to move the focal point of the optical system.

The optical system is coupled with an optical system fixed at a position away from the imaging object using parallel light beams. For example, coupling can be achieved by using a configuration in which both optical systems are coaxial and the optical system at the tip of the tuning fork moves along the optical axis, or a fixed optical system has a sufficiently large input or extraction light beam system, and the optical system at the tip of the tuning fork emits or enters the optical system. The pupil is small and the optical system at the tip of the tuning fork moves in a direction perpendicular to the optical axis (,4
This is done at various times.

〔Example〕

This will be explained below based on the drawings. Figure m1 shows a phototravel device in an actual example of the present invention. This device is an optical 1
It is a device for measuring the intensity or reflectance distribution, and it is used to measure the intensity or reflectance distribution.
Al is a top view, and tbl is a front view.

In FIG. 1, the tip 24 of the tuning fork 23 includes a pair of lenses 25 and a reflection film 26 for forming an image.
A retro prism 27 for determining Ql is attached.

The reflecting prism 26 is used to align the photographing direction of the tip 24 of the tuning fork with the optical axis 64 of the measuring optical system 62. A measuring optical system 62 is arranged near the tuning fork, and is composed of a light source 270, a condenser lens 28, a beam splitter 29, a beam splitter 29, a light lens 30, a photodetector 31, etc. The reflective prism 26 at the tip of the tuning fork faces the mouth, and the light from the m11 constant optical system 62 is reflected by the reflective prism 26 and the objective lens 25 into the object 6.
Surface of 6: (Condenses light. The reflected light from the object 66 follows the optical path in the opposite direction as described above, re-enters the m11 constant optical system 62, and is transmitted to the detector 61 by the beam splitter 29 and the condensing lens 60. The light beam between the measurement optical system 62 and the objective lens 25 at the tip of the tuning fork is a parallel light beam, and its optical axis 3
Even if the optical path length along 4 changes, the result is 7'! , rc has no effect.

When the tuning fork 26 is excited by the @ moving coil 65, the objective lens 25 and the reflecting prism 26 at the tip of the tuning fork move back and forth along the optical axis 64 of the light beam, and the object 66 has a surface that is similar to the tuning fork 2.
As a result, the focal point 36 of the objective lens 25 scans the surface of the object 66. The yoke 38 is used to connect a part of the tuning fork 26 to the closed magnetic circuit, and is fixed together with the base of the tuning fork 26.
It is fixed.

The retro prism 27 is provided on the 311.1 plane at the tip of the tuning fork 23 and is used to measure the amplitude of the tip of the tuning fork 26 using a Michelson interferometer 67.

FIG. 4 is a block diagram of a circuit for controlling the apparatus shown in FIG. 1. In FIG. 4, the tuning fork is excited by the IM intensifier 40.1 drive ino V41 based on the signal from the generator g569. The vibration displacement of the tuning fork is optically measured by an interferometer 42, and a trap pulse 46 is output for each magnitude of 1/.1 of the measurement wavelength. The counting circuit 44 adds or subtracts the pulses 46, and the counted value is a value obtained by measuring displacement with a certain position as the origin and a unit displacement determined by the wavelength of the interferometer 42. /A conversion circuit 45 converts the signal into analog signal 1 and connects it to the horizontal axis input terminal of oscilloscope 46.The output of photodetector 47, which measures the amount of reflected light from an object, is connected to the vertical axis input terminal of oscilloscope 46. As a result, a chart showing the scanning position on the horizontal axis and the amount of reflected light on the vertical axis is displayed on the oscilloscope 46.In this device, the resolution of the horizontal position is about 174 wavelengths of the light used for the interferometer, or 0.3μ. can be achieved.

FIG. 5 shows an embodiment of the present invention, which relates to an apparatus for directly drawing a latent image or the like by scanning a modulated light beam onto a wafer or reticle used in a semiconductor manufacturing process. Fifth
In the figure, the light emitted from the light source 470 is transmitted to the acousto-optic element 4.
8, and passes through a first objective lens 49, a pinhole 50, a collimator lens 51, a beam splitter 52, a reflection prism 53, and a second objective lens 54.
The light is focused on the object 55 by the following. The object 55 is, for example, a wafer reticle. The reflecting prism 56 and the second objective lens 54 are fixed to the tip of the tuning fork 56.

In FIG. 5, for convenience, the axis parallel to the plane of the paper on the surface of the object 55 will be called the Y-axis, and the direction perpendicular to the plane of the paper will be called the Y-axis. In this actual case, the two tips of the tuning fork 560 vibrate in the X-axis direction as shown by arrows 57 and 58. As a result, the focus of the second objective lens 54 focuses on the surface of the object 550 in the direction of the
Scan in the axial direction. The book 55 is placed on a moving stage 59, and the object 55 is moved in the Y-axis direction. Since the tuning fork 56 and the movable stage 59 are fixed to the surface plate 62, the focus of the second objective lens 54 draws a raster locus on the surface of the object 55.

The acousto-optic element 48 is connected to the light source 470 by the output of the control circuit.
It has the function of controlling the amount of transmitted light.

The control circuit has a function of controlling the vibration of the tuning fork 56 and the feeding of the Y stage 60.

The optical interference type position detector 66 includes a first retro prism 64 attached to the tip of the tuning fork 56, a second retro prism 65 attached to the surface plate 62, and a stage 67 attached near the object 55. Third Retropriz, -66
By the optical path passing through X-axis ring of the second objective lens focus on the object book 55:
ζ is equal. In FIG. 5, 61 is an X-axis stage, 68 is a balancing weight attached to the tip of the other branch of the tuning fork with respect to the reflection prism 53 on the tuning fork and the second objective lens 54, and 69 is for driving the tuning fork. 70 is a television camera for observing and focusing on the object 55, and 71 is a photodetector for measuring the exposure amount.

FIG. 6 is a schematic diagram showing the control circuit of the apparatus shown in FIG. In FIG. 6, the reference signal emitted from the crystal oscillator 700 is counted by the variable frequency divider 710.
Compare the count with the output of U) 75 and compare it with the output of
For example, a small period pulse is generated from the output of the PU) 75. Amplifier 76 amplifies the pulse and connects it to coil 7.
Apply current to 4 and attract the tuning fork, causing it to move.

The CPU 75 uses the outputs of an interferometer 81 that measures the amplitude of the tuning fork, and an up/down counter 82 that counts interference fringes and generates the instantaneous coordinates (direction) of the tuning fork to aim for the tuning fork's pitch, and sends it to the comparator 72. The tuning fork amplitude is controlled by changing the tuning fork suction time of the stationary coil 74 by changing the output i. The CPU 75 also controls the variable frequency divider 710 to change the driving frequency of the tuning fork. - From the output of the phase comparator 76 that compares the phases of the counter 82 and the variable frequency divider 710, it is possible to know the phase difference between the driving force of the tuning fork and the amplitude of the tuning fork, and the driving frequency of the tuning fork can be adjusted to the resonant frequency of the tuning fork. It has a function to automatically adjust the settings.

The CPU 75 also operates the Y stage 80 in synchronization with the vibration of the tuning fork.
The feed rate of the PM driver 79 that drives the PM driver 79 is controlled so that the trajectory force t raster on the object 55 at the focus of the second objective lens 54 in FIG. 5 is obtained. Take notes on the drawn shapes! 7-83 K is recorded by electronic means, and the signal for each fixed displacement amount emitted by the interferometer 81 and the
The output of the up-down counter 82, which is converted into a coordinate value, C
The Y coordinate value issued by the PU 75 is read out sequentially. Based on this image signal and the signal from the photodetector 87, the side control circuit 88 and the amplitude modulator 85 control the output of the high frequency excavator 84, thereby controlling the amount of light transmitted through the acousto-optic element (AO element) 86. As described above, the tuning fork vibrates with a constant amplitude near its resonance frequency, and the light raster scans over the object by the Y stage, which is sent in synchronization with the imaging of the tuning fork.
The amount of light is controlled according to the contents of the image memory, and as a result, a +'l r-elephant or the like is drawn on the object. Note that the X stage 78 is driven by a PM driver 77.

FIG. 7 shows a configuration in which an optical grating is used as a position reference in place of the optical interference means as a sub-determining means for swinging the tuning fork in the actual example shown in FIG. 5. In FIG. 7, only the tuning fork and its width measuring means are shown, but the other parts are the same as in FIG. 5. In FIG. 7, an optical grating 90 is attached to the tip f of a tuning fork 89. Reference numeral 91 denotes a position detection optical system, which includes, for example, a light source 92 and a collimator lens 96.
, the beam splitter 94.2'' is composed of an object lens 95, a condensing lens 96, a photodetector 97, etc., and an optical grating 9
Measure the reflected light from a minute point on 0. Position detection optical system 9
1 and the base of the tuning fork 89 are attached to a surface plate and fixed to each other. When the tuning fork 89 is excited by the actual working coil 98 and the tip of the tuning fork 89 starts to vibrate, the optical grating 90
moves on the focal plane of the position detection optical system 91, and the position detection optical system 91 generates a pulse. Since the pulse is generated every time the tuning fork 89 is displaced by the interval width of the optical grating 90, the instantaneous position coordinates of the tip of the tuning fork can be obtained by counting the pulses.

Figure 8 shows a plan view of the optical grating and the output pulses of the position detection optical system. Reference numeral 101 in the enlarged view, FIG. 8 fcl, is a waveform diagram of an example of an output pulse of the position-emerging optical system, where the horizontal axis is the displacement amount, and the vertical axis is the amount of reflected light.

The tuning fork or cantilever used in the scanning mechanism of the present invention is a stable vibrating body, and its Q (direction) is large.

This means that even if there is a small fluctuation in the force that moves the vibrating body, its sensitivity is extremely small. For example, Q! Straight is 1,
000, when one effect changes in a certain period, the change in thread λA in that period is about 0.05% of the variation in driving force. In addition, it can be said that the sine wave is more elegant than the rapid motion of a tuning fork. It is possible to complement the position detection of the imaging bias and improve the accuracy.

An example of an uninvented complementation method will be explained with reference to FIG. 9. Is the song Hi 102 in FIG. 9(a) related to tuning fork, fortune, and time? It is expressed. Reference numeral 103 is an optical grating for position detection, and shows the relationship with the tuning fork amplitude. Figure 9 [b
) is part of ta+ in Figure 9? The output 106 of the position detection optical system is added to the enlarged image. Shirumata Shinpuku 104
is as shown in 105 in a very small section of the distance between adjacent gratings of the position detection optical system (considered to be a straight line, that is, uniform motion, and as shown in 107, the first pulse period T(i) and l+15:th pulse period T (i+1) are assumed to be equal. In 107, the dashed line part T(i+1) represents the assumed pulse. For example, when increasing the grating spacing by M times, first measure the pulse period T [jl'; The tuning fork position after T[i)/M time has elapsed from the rise of the i-i-1st pulse is considered to have been displaced by an amount of 17M of the grid interval. 27M, 37M, etc. conform to this.

108 shows an example of complementary pulses generated every time T(i) is divided by 1/NI, where M=4 (<M-1 complementary pulses are generated).

FIG. 10 is a block diagram showing an embodiment of a complementary pulse generation circuit. The output pulse of the position detection optical system is applied to the input terminal 109. The pulse is shaped by amplifier 110 and differentiated by free-lag flops 111, 112 and gates 113, 114. The differential waveform is the first
At the same time as the second counting circuits 115 and 118 are initialized, the count value of the first counting circuit 115, which is about to be initialized, is held in the latch 116. Reference numeral 117 is a division circuit which outputs the output 17λ1 of the latch 116 and provides an initial value for the second counting circuit 118. The second counting circuit 118 is the division circuit 11
subtract the base pulses from the value given by 7;
It has a function of outputting a pulse when the count (16) is zero and at the same time initializing itself by inputting the next reference pulse.

The zero pulse is outputted to terminal 120 via gate 119 as a complementary pulse. 122 is a reference pulse oscillation circuit, and the period of the reference pulse is sufficiently smaller than the output pulse period of the position detection optical system.

FIG. 11 is a waveform diagram showing each output of the circuit shown in FIG.
The output pulse is 0.111, and 127 is the differential waveform. 1
28 is a complementary pulse. If T(i+1) is greater than T(1), pulses 129 of M1 or more are generated, but these are removed in the second counting circuit 118.

Since the interference fringe spacing in the optical interferometer of FIG. 5 and the optical grating in FIG. 7 are equivalent in terms of complementary signal processing, the complementary method of the present invention is effective in either case.

〔Effect of the invention〕

The scanning mechanism of the present invention, which displaces a part of the optical system using a tuning fork and a cantilever, has the following characteristics because the displacement mechanism is a vibrating body that performs reciprocating motion.

(1) There are no wear parts such as bearings during reciprocating motion, and (
2) Its tip trajectory is stable.

(3) When reversing the direction of motion in reciprocating motion, kinetic energy is stored as potential energy during deceleration, and potential energy is released and converted to kinetic energy during acceleration, so the energy supplied from the outside during acceleration and deceleration is reduced. It's good to be small.

(4) Since the energy supplied from the outside to ambush the reciprocating motion is extremely small, the solid rocky structure is also small.

(5) In particular, when the object is a tuning fork, the two branches make symmetrical displacements with respect to the center line of the tuning fork, so that the moments in the support part cancel each other out.

Therefore, the amount of image leakage to the outside from the tuning fork support is extremely small.

1G) Since the displacement of the tip of the imaging body is almost a straight line, 1 displacement amount 51] Since optical interferometry can be used as a valuable means, high performance can be obtained.

(7) Since the Q value of root cutting is large and the stability of vibration is reduced, a high pre-511 bond rate can also be obtained when pre-jI11 control is used.

It has such characteristics.

Figure 1 + 2+, (bl is a top view and front view for explaining the optical scanning device of the present invention, Figure 2 is a conventionally used fixed optical system and movable stage) A front view of the optical scanning device according to
FIG. 3 is a front view of a conventional scanning optical system using an f-theta lens and an acousto-optic element, FIG. 4 is a block diagram of the control circuit of the apparatus shown in FIG. 3, and FIG. 6 is a front view of the optical scanning device, FIG. 6 is a control diagram of the device shown in FIG. 5, FIG. 7 is a front view of the amplitude 1 regulating means used in the device of the present invention, and FIG. A plan view and an output pulse waveform are shown, and FIG. 8(a) is a plan view of the optical grating, and FIG.
b) is a partially enlarged view of Fig. 8 Fa+, Fig. 8 [C1 is an output pulse waveform diagram of the positioning optical system, and Fig. 9 is a diagram for explaining the interpolation method using the present invention. Figure 9 shows the positional relationship between the position detection optical heater and the tuning fork shaker, and Figure 9 TBL shows the output of the position detection optical system. FIG. 10 is a block diagram of a complementary pulse generation circuit, and FIG. 11 is an output contour diagram of the complementary pulse generation circuit.

23...Tuning fork, 25...Objective lens, 37... Michelson interferometer.

Figure 2 5th stroke Figure 7 Figure 9 CG) Punishment - Moisou 10th flash

Claims (4)

[Claims] (1) An imaging means consisting of an objective lens is fixed to the tip of a mechanical vibrator such as a tuning fork or a cantilever, and the focal point of the imaging means is configured to scan an object or an optical image plane. An optical scanning device characterized in that the scanning position is detected optically by a mirror fixed to the tip of the vibrator and a Michelson interferometer. (2) The optical path of the Michelson interferometer includes a reflecting mirror at the tip of the vibrator and a reflecting mirror mounted on the stage, and is characterized by having a function of measuring the relative position of the tip of the vibrator and the stage. The optical scanning device according to claim 1. (3) An imaging means consisting of an objective lens is fixed to the tip of a mechanical vibrator such as a tuning fork or a cantilever, and the focal point of the imaging means is configured to scan an object or an optical image plane. An optical scanning device characterized in that the scanning position is detected by measuring reflected light or transmitted light from an optical grating fixed to the tip of the vibrator. (4) Scanning position detection in an optical scanning device in which an imaging means consisting of an objective lens is fixed to the tip of a mechanical vibrator such as a tuning fork or a cantilever, and the focal point of the imaging means scans an object or an optical image plane. The time width of one signal outputted from the means for each unit displacement amount is measured, and the displacement amount from the start point of the next signal to the next signal is further predicted based on the measured time width to perform complementary control of the position. An optical scanning device characterized in that it uses a complementary method.