JP2690120B2 - Optical scanning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an optical figure reading device, an optical printing device,
The present invention relates to an optical scanning device used in an optical drawing device or the like.

[Conventional technology]

Conventionally used optical scanning devices are roughly classified into two types. The first is to move the optical system and the object to be scanned relative to each other. For example, as shown in FIG. 2, the optical system 1 and the movable stage 2 are fixed. The focal point 4 of the optical system 1 which is formed on the surface of the object 3 on the moving stage 2.
The focus position changes on the surface of the object 3 as the stage 2 moves. For example, when the optical system 1 is a figure reader including 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 focus 4 of the objective lens 7 is used. Can sequentially move on the surface of the object 3 and continuously detect the reflectance of a minute portion thereof.

The second scanning device displaces the focal position of the optical system on the focal plane by changing the incident angle of the incident light beam to the optical system. For example, it is an f-θ lens as shown in FIG. The configuration includes an objective lens 16 and an acousto-optic element 15 for changing the angle of incidence on the lens. In FIG. 3, the light emitted from the light source 11 passes through the filter 12, the collimator lens 13, the beam splitter 14, the acousto-optic element 15, and the objective lens 16 to illuminate the object 17. The reflected light from the object 17 is transmitted through the objective lens 16 and the acousto-optic element 15 to form a beam.
Light is reflected by the splitter 14 and is detected by the condenser lens 18.
Guided to 19. Light incident on the acousto-optic element 15 from the light source side is, for example, broken line 20 by applying ultrasonic waves to the element.
When the object 17 is deflected in the direction indicated by, the focal point 21 on the object 17 is displaced to 22. The focal point moves on the object 17 by continuously changing the frequency of the ultrasonic wave applied to the acousto-optic element 15. A part of the reflected light from the object 17 is incident on the beam splitter 14 in a path opposite to the illumination light, and a part of the reflected light reaches the photodetector 19. The photodetector 19 has a spatial filter built therein and removes harmful reflected light and the like.

[Problems to be solved by the invention]

The apparatus shown in FIG. 2 has a drawback that the mass of the movable object required for scanning, that is, the optical system and the stage is large, and the scanning mechanism becomes large. Therefore, it is suitable for a device having a low scanning speed, but when a high-speed scanning mechanism is required, particularly when reciprocating repetitive scanning is required, driving energy is increased and vibration is generated. However, since existing mechanical technology can be used, the scanning position accuracy, the size of the scanning range, and the number of spots in the scanning range are large. For example, in the case of scanning by a moving object, the scanning range can be 100 mm, so if the spot diameter is 1 μm, the number of spots in the scanning range is 100,
Over 000 pieces. The absolute accuracy of the scanning position may be 0.1 μm. However, there is a sliding part on the stage,
The stability of going straight is about 1 μm and I can not expect very good performance,
In order to obtain high accuracy, a straightness correction mechanism is required. For example, in the case of scanning in the X direction, a device having a mechanism that moves also in the Y direction is used, and a mechanism for determining the X and Y axis coordinates of the stage using a laser interferometer and performing position control for each axis is used. To be However, in the mechanism using the movable stage, the focus of the optical system is used only on or near the optical axis, so the effective surface diameter is smaller than that of the second method, and its size is about the same as that of an optical microscope. It is easy to design and manufacture.

In the apparatus shown in FIG. 3, scanning is performed by changing the incident angle of the light beam on the f-θ lens to change the focal position on the focal plane, but the scanning range and spot diameter are determined by the deflection means. Is determined by the declination width of the luminous flux, the diameter of the luminous flux, the effective image surface diameter of the f-θ lens, and the numerical aperture. In order to realize a scanning mechanism with a wide range and a small spot size, a deflection means with a large aperture and a large deflection angle and its control means, a large effective image surface, and an f-θ lens with a large numerical aperture are required. Requires inspection technology.

Examples of the deflecting element include an acousto-optic element, a rotary polygon mirror, and a rotary vibration plane mirror. The acousto-optic element has no mechanically movable parts and is suitable for high-speed scanning, but the defect that wavefront aberration occurs in relation to the ultrasonic wave propagation time in the element and the diameter of the acousto-optic element due to the limit of the size of the obtained crystal / Maximum deflection angle ratio, that is, the upper limit of the number of spots / scanning range value. This value is roughly 5,000. A scanning device using an acousto-optic element as a deflection element can perform high repetitive scanning at a maximum of 100,000 times / sec.

When a rotary polygon mirror or a rotary oscillating plane mirror is used as the deflecting means, a motor or a gull bar is used as its rotating mechanism, so that the rotating portion necessarily has a bearing. Due to the error of the bearing portion, the incident light on the f-θ lens causes not only the deflection angle in the scanning direction but also the deflection of a component orthogonal to this, that is, sagittal. In order to realize high-precision scanning using this method, a sagittal detection unit, for example, a detection optical system,
Sagittal correction means such as electro-optical elements are required.
The number of spots / scan range value in a scanning mechanism using a rotary polygon mirror and a rotary vibration polygon mirror is about 5,000. A scanning device using a rotary polygon mirror and a motor, a rotary vibration plane mirror and a galver as a deflection element can obtain repetitive scanning at a maximum of about 200 times / sec.

As described above, the apparatus shown in FIG. 2 has a simple optical system and is suitable for low-speed wide-range and high-precision scanning, but is not suitable for high-speed scanning. On the other hand, the apparatus shown in FIG. 3 is suitable for high speed small range scanning, but is not suitable for wide range high precision scanning.

[Means for solving the problem]

In the present invention, an apparatus having a high speed and a wide range scanning function is proposed. In the present invention, an optical system is arranged at the tip of a vibrating body such as a tuning fork or a cantilever, and the focus of the optical system is moved by exciting the vibrating body to perform scanning. The optical system is coupled by parallel rays to an optical system fixed at a position apart from the vibrating body.
The coupling is, for example, 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 the incident or outgoing light beam system of the fixed optical system is sufficiently large so that the optical system at the tip of the tuning fork exits or enters. The optical system at the tip of the tuning fork with a small pupil moves in a direction orthogonal to the optical axis.

〔Example〕

This will be described below with reference to the drawings. FIG. 1 shows an optical scanning device according to an embodiment of the present invention. This device is for measuring the optical density or reflectance distribution of an object. FIG. 1 (a) is a top view and FIG. 1 (b) is a front view.

In FIG. 1, an objective lens 25 for image formation, a reflection prism 26, and a retro prism 27 for displacement measurement are attached to the tip 24 of the tuning fork 23. The reflection prism 26 is for matching the vibration direction of the tip portion 24 of the tuning fork with the optical axis 34 of the measurement optical system 32. A measurement optical system 32 including a light source 270, a condenser lens 28, a beam splitter 29, a condenser lens 30, and a photodetector 31 is arranged near the tuning fork. The opening of the measurement optical system 32 and the tip of the tuning fork are arranged. The reflection prism 26
Are facing each other, and the light from the measurement optical system 32 is a reflection prism.
26, The light is focused on the surface of the object 33 by the objective lens 25. The reflected light from the object 33 follows the above-mentioned optical path in reverse, and the measurement optical system
Re-incident on 32, beam splitter 29, condenser lens 30
Is guided to the photodetector 31 by. The light beam between the measurement optical system 32 and the objective lens 25 at the tip of the tuning fork is a parallel light beam and does not affect the image formation even if the optical path length along the optical axis 34 changes.

When the tuning fork 23 is excited by the drive coil 35, the objective lens 25 and the reflection prism 26 at the tip of the tuning fork reciprocate along the optical axis 34 of the light flux, and the surface of the object 33 becomes parallel to the vibration direction of the tip of the tuning fork 24. As a result, the objective lens
The focus 36 of 25 scans the surface of the object 33. York 38 is a tuning fork
A part of 23 and a tuning fork to form a closed magnetic circuit.
It is fixed to the surface plate with 23 bases.

The retro prism 27 is provided on the side surface of the tip of the tuning fork 23, and is for measuring the tip amplitude of the tuning fork 23 by the Michelson interferometer 37.

FIG. 4 is a block diagram of a circuit for controlling the device shown in FIG. In FIG. 4, the tuning fork is excited by the amplifier 40 and the drive coil 41 based on the signal of the oscillator 39. The vibration displacement of the tuning fork is optically measured by the interferometer 42 and is 1/1 of the measurement wavelength.
A pulse 43 is output every 4 displacements. The counting circuit 44 adds or subtracts the pulse 43, and the counted value corresponds to a value measured with a unit displacement amount determined by the wavelength of the interferometer 42 with a certain position as the origin. The count value is converted into an analog quantity by the D / A conversion circuit 45 and connected to the horizontal axis input terminal of the oscilloscope 46. A photodetector 47 that measures the amount of light reflected from the object
The output of is connected to the vertical axis input terminal of the oscilloscope 46, and as a result, a chart showing the scanning position on the horizontal axis and the reflected light amount on the vertical axis can be displayed on the oscilloscope 46. In this device, the resolution of the horizontal position can reach 0.3μ, which is about 1/4 of the wavelength of the light used for the interferometer.

FIG. 5 shows an embodiment of the present invention, and relates to an apparatus for scanning a modulated light beam on a wafer or reticle used in a semiconductor manufacturing process to directly draw a latent image or the like. In FIG. 5, the light emitted from the light source 470 is modulated by the acousto-optic device 48, and the first objective lens 49, the pinhole 50,
The light is focused on the object 55 by the second objective lens 54 via the collimator lens 51, the beam splitter 52, and the reflecting prism 53. The object 55 is, for example, a wafer, a reticle, or the like. The reflecting prism 53 and the second objective lens 54 are fixed to the tip of the tuning fork 56. In FIG. 5, for convenience, the object
An axis parallel to the paper surface of the surface of 55 is called an X axis, and a direction perpendicular to the paper surface is called a Y axis. In this embodiment, the tuning fork
The two tips of 56 vibrate in the X-axis direction as shown by arrows 57 and 58, so that the focus of the second objective lens 54 scans the surface of the object 55 in the X-axis direction of arrow 57. The object 55 is placed on the movable 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 has a function of controlling the amount of transmitted light of the light source 470 according to the output of the control circuit. The control circuit is a tuning fork
It has a function of controlling the vibration of 56 and the feed of the Y stage 60.

The optical interference type position detector 63 is attached to 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 an object 55 near a stage 67. It is an object for detecting the relative position along the X-axis of the tip of the tuning fork 56 to which the stage 67 and the second objective lens 54 are attached by the optical path passing through the third retrorhythm 66. , The relative position is equal to the X coordinate of the second objective lens focus on the object 55. In FIG. 5, 61 is X
An axis stage, 68 is a balance weight attached to the reflection prism 53 on the tuning fork and the other end of the tuning fork with respect to the second objective lens 54, and 69 is a yoke forming a magnetic path for driving the tuning fork. , And a coil, 70 is a television camera for observing and focusing the object 55, and 71 is a photodetector for measuring the exposure amount.

FIG. 6 is a block diagram showing a control circuit of the device shown in FIG. In FIG. 6, the reference signal emitted from the crystal oscillator 700 is counted by the variable frequency divider 710. The comparator 72 compares the count value with the output of the computer (CPU) 75 and generates a positive pulse for a period in which the count value is smaller than the output of the computer (CPU) 75, for example. The amplifier 73 amplifies the pulse and supplies a current to the drive coil 74 to attract and drive the tuning fork.

The CPU 75 measures the amplitude of the tuning fork by the output of the interferometer 81 that measures the amplitude of the tuning fork, the up-down counter 82 that counts the interference fringes and generates the instantaneous coordinate value of the tuning fork, and changes the output value to the comparator 72. The tuning fork amplitude is controlled by changing the tuning fork suction time width of the drive coil 74. The CPU 75 can also control the variable frequency divider 710 to change the drive frequency of the tuning fork. The CPU 75 can know the phase difference between the driving force of the tuning fork and the amplitude of the tuning fork by the output of the phase comparator 76 that compares the phases of the up / down counter 82 and the variable frequency divider 710, and the driving frequency of the tuning fork It has the function of automatically adjusting to the resonance frequency.

The CPU 75 also controls the feed speed of the PM driver 79 that drives the Y stage 80 in synchronization with the vibration of the tuning fork so that the locus of the focus of the second objective lens 54 in FIG. 5 on the object 55 becomes a raster. To do. The drawing figure is stored in the memory 83 by an electronic means, and the signal generated by the interferometer 81 for each constant displacement amount and the up / down-direction for converting it into the X coordinate value.
The output of the counter 82 and the Y coordinate value issued by the CPU 75 are sequentially read. This image signal and photodetector 87
The control circuit 88 and the amplitude modulator 85 control the output of the high-frequency oscillator 84 by the signal of the above signal to control the amount of transmitted light of the acousto-optic element (AO element) 86. As described above, the tuning fork vibrates with a constant amplitude in the vicinity of its resonance frequency, and light is raster-scanned on the object by the Y stage that is sent in synchronization with the vibration of the tuning fork, and the amount of light is controlled by the contents of the image memory. As a result, a latent image or the like is drawn as an object. The X stage 78
It is driven by the 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 the tuning fork amplitude measuring means in the embodiment shown in FIG. In FIG. 7, only the tuning fork and its amplitude measuring means are shown, but other parts are the same as in FIG. In FIG. 7, an optical grating 90 is attached to the tip of the tuning fork 89. 91 is a position detection optical system, for example, a light source 92, a collimator lens 93, a beam
It is composed of a splitter 94, an objective lens 95, a condenser lens 96, a photodetector 97, etc., and measures reflected light at a minute point on the optical grating 90. The position detection optical system 91 and the base of the tuning fork 89 are attached to a surface plate and fixed to each other. The tuning fork 89 is excited by the drive coil 98, and the tip of the tuning fork 89 starts to vibrate, and the optical grating 90 moves on the focal plane of the position detecting optical system 91.
The position detection optical system 91 generates a pulse. The pulse is a tuning fork
Since 89 is generated each time the interval width of the optical grating 90 is displaced,
The instantaneous position coordinates of the tip of the tuning fork are obtained by counting the pulses.

FIG. 8 shows a plan view of the optical grating and output pulses of the position detecting optical system. 99 in FIG. 8 (a) is a plan view of the optical grating, and 100 in FIG. 8 (b) is the optical grating. 8C is a waveform diagram of an output pulse example of the position detecting optical system, in which the horizontal axis represents the displacement amount and the vertical axis represents the reflected light amount.

The tuning fork or cantilever used in the scanning mechanism of the present invention is
It is a stable vibrating body and its Q value is large. This means that even if there is a change in the force that drives the vibrator, its sensitivity is extremely small. For example, in a vibrator having a Q value of 1,000, when the driving force changes in a certain cycle, the change in the amplitude in that cycle is about 0.05% of the fluctuation in the driving force. The vibration of the tuning fork may be called a pure sine wave. In the sine wave, the phase can be regarded as a straight line in a minute section except for the phases near the inflection points of 90 degrees and 270 degrees, and the accuracy can be improved by complementing the position detection of the tuning fork amplitude.

Explaining an embodiment of the complementing method in the present invention with reference to FIG. 9, a curve 102 in FIG. 9 (a) represents the relationship between the tuning fork amplitude and time. 103 is an optical grating for position detection, which shows the relationship with the tuning fork amplitude. FIG. 9 (b) is an enlarged view of a part of FIG. 9 (a) to which the output 106 of the position detection optical system is added. The tuning fork amplitude 104 is assumed to be a straight line as shown by 105 in a minute interval of the adjacent grating intervals of the position detection optical system, that is, it is regarded as a constant velocity motion, and as shown by 107, the i-th pulse period T (i) and the i + 1-th pulse period. T (i
+1) is assumed to be equal. The wavy line portion T'at 107
(I + 1) represents the assumed pulse. For example, when the lattice spacing is increased by M times, first, the pulse period T (i) is measured, and the number of the lattice spacing is 1 after the tuning fork position after the elapse of T (i) / M time from the rising edge of the (i + 1) th pulse. / M
Considered to have been displaced by an amount. 2 / M, 3 / M, etc. are based on this.
Reference numeral 108 shows an example of a complementary pulse generated at each time point when T (i) is divided into 1 / M, and M = 4 (M-1 complementary pulses are generated).

FIG. 10 is a block diagram showing an embodiment of a complementary pulse generating circuit. Output pulse of position detection optical system is input terminal
Applied to 109. The pulse is shaped by amplifier 110 and differentiated by flip-flops 111, 112 and gates 113, 114. The differential waveform has first and second counting circuits.
Simultaneously with the initialization of 115 and 118, 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 1 / M of the output of the latch 116 and outputs the second counting circuit.
Give an initial value of 118. The second counting circuit 118 is a division circuit
It has a function of counting down the reference pulse from the value given by 117, outputting a pulse when the count value is zero, and at the same time initializing itself by inputting the next reference pulse.
The zero pulse is output as a complementary pulse to the terminal 120 via the gate 119. Reference numeral 122 is a reference pulse transmission circuit, and the cycle of the reference pulse is sufficiently smaller than the output pulse cycle of the position detection optical system.

FIG. 11 is a waveform diagram showing each output of the circuit shown in FIG. 10, where 123 is the reference pulse, 124 is the output of the position detection optical system, and 125 and 126 are the output pulses of the flip-flops 110 and 111. , 127 are differential waveforms. 128 is a complementary pulse. T
If (i + 1) is larger than T (i), M or more pulses
129 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 both cases.

〔The invention's effect〕

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

(1) The reciprocating motion has no wear parts such as bearings, and (2) its tip locus is stable.

(3) Kinetic energy is stored as potential energy during deceleration when reversing the movement direction in reciprocating motion.
Since potential energy is released during acceleration and converted into kinetic energy, the energy supplied from outside during acceleration and deceleration may be extremely small.

(4) Since the energy supplied from the outside to sustain the reciprocating motion is extremely small, the drive mechanism is also small.

(5) When the vibrating body is a tuning fork in particular, the two branches of the tuning fork perform symmetrical displacement with respect to the center line of the tuning fork, so that the moments in the supporting portion cancel each other out, so that the tuning fork supporting portion leaks to the outside. Vibration is extremely small.

(6) Since the displacement of the tip of the vibrating body is almost linear, an optical interferometry can be used as the displacement amount measuring means, so that high position resolution can be obtained.

(7) Since the Q value of vibration is large and the stability of vibration is good, high prediction accuracy can be obtained even when the predictive control method is used.

There are such features.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are a top view and a front view for explaining an optical scanning device of the present invention, and FIG. 2 is a conventional fixed optical system and a movable mount. Front view of the optical scanning device with a gantry,
FIG. 3 is a front view of a scanning optical system using an f-θ lens and an acousto-optic device that have been conventionally used, and FIG. 4 is a block diagram of a control circuit of the device shown in FIG.
FIG. 5 is a front view of the optical scanning device of the present invention, FIG. 6 is a control block diagram of the device shown in FIG. 5, and FIG. 7 is a front view of an amplitude measuring means used in the device of the present invention. Shows a plan view of an optical element and an output pulse waveform, FIG. 8 (a) is a plan view of an optical grating, FIG. 8 (b) is a partially enlarged view of FIG. 8 (a), and FIG. 8 (c). FIG. 9 is an output pulse waveform diagram of the position detection optical system, FIG. 9 shows an optical grating and waveforms for explaining the complementary method used in the present invention, and FIG. 9 (a) is an optical grating for position detection and tuning fork amplitude. FIG. 9 (b) is a partially enlarged positional relationship diagram in which the output of the position detection optical system is added to FIG. 9 (a), and FIG. 10 is a block of a complementary pulse generation circuit. FIG. 11 and FIG. 11 are output waveform diagrams of the complementary pulse generating circuit. 23 …… Tuning fork, 25 …… Objective lens, 37 …… Michelson interferometer.

Claims (4)

(57) [Claims] 1. An image forming means composed of an objective lens is fixed to the tip of a mechanical oscillator such as a tuning fork or a cantilever, and the focus of the image forming means scans an object or an optical image plane. The optical scanning device is characterized in that the scanning position is optically detected by a mirror fixed to the tip of the vibrator and a Michelson interferometer. 2. The optical path of the Michelson interferometer includes a reflector at the tip of the oscillator and a reflector mounted on the stage, and has a function of measuring the relative position between the oscillator tip and the stage. The optical scanning device according to claim 1. 3. An image forming means comprising an objective lens is fixed to the tip of a mechanical oscillator such as a tuning fork or a cantilever, and the focal point of the image forming means scans an object or an optical image plane. The optical scanning device is 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. An optical scanning device in which an image forming means composed of an objective lens is fixed to the tip of a mechanical oscillator such as a tuning fork or a cantilever, and the focus of the image forming means scans an object or an optical image plane. One time width of the signal output from the position detecting 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 predicted based on the measurement time width and the position is complemented. An optical scanning device characterized by using a complementary system for controlling.