JP3688480B2 - Optical disc master exposure system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc master exposure apparatus, and more particularly to a recording medium in which a relatively narrow pit portion and a relatively wide groove groove portion such as MD (Mini Disc) HB (Hydrid Disc) exist on the same disc. The present invention relates to an optical disc master exposure apparatus that exposes a master disc, or an optical disc master exposure device that exposes a groove groove that is relatively wider than a spot diameter and has a steeper wall angle.
[0002]
[Prior art and problems to be solved by the invention]
2. Description of the Related Art Conventionally, several methods have been proposed for exposing an original disc of a recording medium in which a relatively narrow pit portion and a relatively wide groove groove portion are present on the same disc. As one of them, Japanese Patent Publication No. 8-7883 discloses a method of exposing a groove groove with a plurality of spots shifted from the center. A diffraction grating or a prism has been used as means for realizing a plurality of spots with shifted centers. However, when using any of these methods, in order to expose a master having pit / groove grooves on the same substrate, two optical paths corresponding to each are required, and the positional relationship of each spot with respect to room temperature and vibration Becomes unstable. In addition, the loss of laser power is large. Furthermore, since the relative intensity adjustment of a plurality of spots cannot be easily performed, the shape of both wall surfaces of the groove groove is asymmetrical, and there is a problem that the disk tends to have a track error.
[0003]
As another conventional example, Japanese Patent No. 2643159 discloses a groove having a width wider than the spot size by oscillating a recording beam in the disk radial direction and performing multiple exposure of the groove groove area. A recording method is disclosed. Here, the structure of a general acousto-optic element is shown in FIG. 8, and the general acousto-optic element will be described with reference to FIG. In the figure, a high frequency fc voltage is applied from a high frequency signal generator 81 to a vibrator 82. The acousto-optic medium 83 generates an ultrasonic traveling wave 84 that travels from the bottom to the top in the figure by the vibration of the vibrator 82. At this time, when an incident beam enters the acoustooptic medium 83 from the left in the figure, diffracted light by the ultrasonic traveling wave 84 is generated in the right direction in the figure. When the wavelength of the incident beam is λo, the excitation frequency is fc, the velocity of the ultrasonic traveling wave is vs, and the separation angle between the incident beam and the diffracted light is θ, θ is θ = λo · fc / vs (1). Represented.
[0004]
Further, the diffracted light intensity varies depending on the voltage intensity applied to the vibrator 82. Here, the state of the diffracted light of the acoustooptic device in this conventional example will be considered. In order to vibrate the recording beam at the frequency fm in the disk radial direction, the excitation frequency fc in FIG. 9 may be FM-modulated at a speed fm over a certain frequency range (± Δfc). When fm is relatively small, the diffracted light is deflected at a speed of fm according to the above equation (1). However, when fm becomes large and the state as shown in FIG. 9 is reached, the deflection operation stops. That is, in FIG. 9, the lower light beam has a small diffraction angle due to fc−Δfc, whereas the upper light beam has a large diffraction angle due to fc + Δfc. The light beam near the central optical axis is in the middle. At this moment, the entire diffracted light enters the objective lens as divergent light that is not deflected from the original fc state. Further, since the upper and lower density is reversed at the next moment (after 1 / (2 fm) seconds), the diffracted light is now converged light. Eventually, the focused spot on the board surface only repeats the defocused state at high speed, and it becomes impossible to expose the wide groove by deflection.
[0005]
When this phenomenon is confirmed using specific numerical values, according to this Japanese Patent No. 2643159, the vibration frequency fm (symbol fo in the patent) required for the spot size d and the disk linear velocity v is Fm> v / d = (1.25 m / sec) / (0.5 μm) = 2.5 MHz (2). In the state of FIG. 9, assuming that the incident beam diameter in the traveling direction is dm, dm = vs / 2fm = (4260 m / sec) / (2 * 2.5 MHz) = 0.852 mm (3) (Note that the acoustooptic medium TeO ₂ Vs = 4260 m / sec). In the state of FIG. 9, since the diffracted light only repeats divergence and convergence as described above, dm has a diameter smaller than 0.852 mm (for example, 0.1 mm) in order to obtain a deflection speed that satisfies the above equation (2). Below). This usually requires dm> 1 mm and cannot be realized with an actual master exposure optical system.
[0006]
Furthermore, as another conventional example, Japanese Patent Laid-Open No. 4-26940 discloses an apparatus that selectively outputs one beam and two beams on both sides using an acousto-optic element. In this conventional method, the two beams on both sides are generated by transmitted light (0th-order light) and diffracted light (first-order light), but the separation angle between the 0th-order light and the primary light in the acoustooptic device is Usually about 1 °. In addition, the separation angle for overlapping a certain portion of the spot on the board surface formed by the 0th-order light and the first-order light as in the conventional method is about 1 '. Therefore, in a normal acoustooptic device, a desired configuration is obtained. Cannot be obtained. Further, from the above equation (1), in order to obtain a small separation angle, the excitation frequency fc may be decreased or a medium having a high ultrasonic traveling wave velocity vs may be used. Is also unrealistic.
[0007]
As still another conventional example, Japanese Patent Laid-Open No. 7-169115 discloses an exposure in which a plurality of signals having different frequencies are input to an AO (Acoustic Optic) deflector and a wide groove is exposed with a plurality of focused beams. In the apparatus, a method is disclosed in which the spatial frequency on the master corresponding to the frequency of the beat signal generated by a plurality of signals is set to at least twice the spatial frequency corresponding to the signal band of the optical disc. As described in this conventional example, fluctuation of the reproduction signal due to the beat signal occurs. However, since fluctuation is twice or more the frequency of the information signal, there is no practical problem. Therefore, the S / N of the reproduction signal is deteriorated as compared with the case where there is no beat signal. In recent high-density recording masters, the track pitch and groove width are narrowed, and the information signal frequency is increasing. Therefore, in order to reduce the groove groove width, the difference between the two frequencies must be reduced. At this time, the beat signal frequency is lowered. Therefore, there are cases where the beat signal frequency cannot be set to more than twice the information signal as in this conventional example.
[0008]
Furthermore, in general, when exposing a groove groove wider than the spot diameter, the exposure power is increased or the beam diameter incident on the condenser lens is decreased to reduce the NA (effective numerical aperture). there were. When the exposure power is increased, the wall surface shape of the groove groove becomes the same as the lower part of the intensity distribution shape of the focused spot, so that the groove wall shape becomes a sagging wall surface. The same is true when the NA is lowered. Eventually, in such a system, the tracking error signal, which is the role played by the groove, becomes unstable, resulting in a disc that is likely to cause track deviation.
[0009]
The present invention is for solving these problems, and wide groove exposure with a steep groove wall shape is possible, and the relative positional relationship between the spot at the pit exposure and the spot at the groove exposure is stable. It is an object of the present invention to provide an optical disc master exposure apparatus.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention condenses a laser beam from an exposure laser onto an exposure master that is rotated and moved by applying a photoresist by an objective lens, Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes groove grooves, acousto-optic elements arranged in the optical path between the exposure laser and the objective lens, and a plurality of high-frequency signals that supply drive signals having different frequencies to the acousto-optic elements And a high-speed switch element and a pulse signal generator that sequentially and circulates one of the drive signals generated from the high-frequency signal generator to supply the acousto-optic element. Therefore, wide groove exposure with a steep groove wall shape is possible, and the relative positional relationship between the spot at the time of pit exposure and the spot at the time of groove exposure is stabilized, and an effect of reducing laser power loss can be obtained. Moreover, since the intensity balance of two diffracted lights can be adjusted easily, it can be set as a symmetrical groove wall surface shape. Furthermore, since a plurality of stable spots can be formed even from a realistic thick beam diameter, the application range is wide, and the interval between the plurality of spots is due to the difference in the corresponding drive signal frequency. Easy and highly accurate. Also pit Part Since the exposure can be switched instantaneously between the groove groove and the groove groove, it is suitable for exposure such as HB. Furthermore, a simple high-frequency signal generator having no modulation function can be used.
[0011]
In addition, the beam diameter of the laser beam incident on the acoustooptic device is dm, the switching frequency required to select and drive the drive signals from a plurality of high-frequency signal generators one by one, fm, and the supersonic wave generated inside the acoustooptic device Assuming that the velocity of the traveling acoustic wave is vs, the condition of dm ≧ vs / fm is satisfied. Therefore, the intensity fluctuation of a plurality of spots is small, and uniform groove exposure without fluctuation and noise can be performed.
[0012]
Furthermore, the laser beam from the exposure laser is condensed by the objective lens onto the exposure master that is rotated and moved by applying the photoresist. Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes a groove, an acousto-optic device disposed in an optical path between an exposure laser and an objective lens, a pulse signal generator that generates a multi-stage pulse signal, and a pulse signal generator And an FM modulation circuit that generates an FM modulated wave in which the frequency of the drive signal supplied to the acousto-optic element is changed in a multistep manner using the pulse signal generated from the above. Therefore, the pit Part It is not necessary to change the frequency of the high-frequency signal in order to position the groove at the center of the groove, and the relative phase relationship of the plurality of high-frequency signals can be further stabilized, thereby enabling uniform groove exposure without fluctuations and noise. .
[0013]
In addition, assuming that the beam diameter of the laser beam incident on the acoustooptic device is dm, the cycle frequency of the multistage pulse of the pulse signal generator is fm, and the velocity of the ultrasonic traveling wave generated inside the acoustooptic device is vs, dm ≧ The condition of vs / fm is satisfied. Therefore, the intensity fluctuation of a plurality of spots is small, and uniform groove exposure without fluctuation and noise can be performed.
[0016]
In addition, the laser beam from the exposure laser is focused by the objective lens onto the rotating exposure master that is coated with the photoresist and rotated and moved. Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes a groove, an acoustooptic element disposed in an optical path between an exposure laser and an objective lens, a high-frequency signal generator that supplies a drive signal to the acoustooptic element, and a plurality of frequencies A modulation signal generator that generates a continuous signal having components, and an AM modulation that generates an AM modulated wave in which the amplitude of the drive signal supplied to the acoustooptic device is changed using the modulation signal generated from the modulation signal generator It is characterized by providing a circuit. Therefore, the pit Part Therefore, it is not necessary to change the frequency of the high-frequency signal to position the groove at the center of the groove groove, and uniform groove exposure without fluctuations and noise can be achieved.
[0017]
Furthermore, the beam diameter of the laser beam incident on the acoustooptic device is dm, the frequency of the lowest frequency component of the modulation signal from the modulation signal generator is Δfc, and the velocity of the ultrasonic traveling wave generated inside the acoustooptic device is Assuming vs, the condition of dm ≧ vs / 2Δfc is satisfied. Accordingly, uniform groove exposure is possible with less intensity fluctuation of the plurality of spots.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In an optical disc master exposure apparatus that focuses a laser beam from an exposure laser on an exposure master that is coated with a photoresist and rotates and moves by an objective lens and exposes a pit row or groove groove, the exposure laser and the objective lens One signal among the acousto-optic elements arranged in the optical path between them, a plurality of high-frequency signal generators supplying drive signals having different frequencies to the acousto-optic elements, and the drive signals generated from the high-frequency signal generators Are sequentially and circulated to supply the acousto-optic element with a high-speed switch element and a pulse signal generator.
[0019]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an optical disc master exposure apparatus according to a first embodiment of the present invention. In the figure, an optical disk master exposure apparatus according to the present embodiment includes an exposure laser light source 11, reflection mirrors 12, 13, 14, acoustooptic elements 15, 16, lens pairs 17, 18, an objective lens 19, A high-frequency signal generator 20 and a high-speed switch element 21 are included. Further, the exposure master 22 is rotated by a motor 23 and is moved together with the motor 23 in the direction of the arrow in the drawing by a driving means (not shown). Further, the acoustooptic device driving unit 24 includes two high-frequency signal generators 25 and 26, a pulse signal generator 27, and two high-frequency signal generators 25 and 26 according to the pulse wave supplied from the pulse signal generator 27. And a high-speed switch element 28 that alternately switches the high-frequency signals fc1 / fc2 from.
[0020]
Laser light from the exposure laser light source 11 is reflected by the reflection mirror 12 and is incident on the first acousto-optic element 15 via the lens 17. Then, transmission / non-transmission is selected by the acoustooptic device 15. When the pit row is exposed, the signal from the high-frequency signal generator 20 is applied to the acousto-optic device 15 by turning on / off the high-speed switch element 21 at a timing corresponding to the pit row. Further, at the time of groove exposure, a constant high-frequency signal is applied to the acousto-optic element 15 by always turning on the high-speed switch element 21. Since the incident beam diameter is narrowed down by the lens pair 17 and 18 and enters the acoustooptic device 15, it is possible to cope with high-speed ON / OFF operations such as during pit exposure. Laser light, which is diffracted light from the acoustooptic device 15, is subsequently reflected by the reflecting mirror 13 through the lens 18, enters the second acoustooptic device 16, and is angularly separated into two light beams. The two light beams are reflected by the reflecting mirror 14 to form two spots on the exposure master disk 22 on which the photoresist is applied by the objective lens 19. The exposure master 22 is rotated about a shaft in a certain direction by a motor 23, and is moved together with the motor 23 in the direction of an arrow by a driving mechanism (not shown). Further, since the objective lens 19 is always kept at a constant distance from the exposure master by a focus adjustment mechanism (not shown), even if the exposure master 22 rotates and moves, the same spot condensing state is obtained over the entire surface of the exposure master 22. Can be exposed.
[0021]
Next, in the acoustooptic device driving unit 24, signals of different frequencies fc1 and fc2 are constantly generated from the two high-frequency signal generators 25 and 26, respectively. The high speed switching element 28 is alternately switched by the pulse wave of the frequency fm from the pulse signal generator 27 to supply fc1 / fc2 to the acoustooptic element 16 alternately. As shown in FIG. 2, the sparse horizontal lines of the acoustooptic device 16 schematically represent ultrasonic traveling waves generated by this operation. When this sparse / dense is made to correspond to the low / high frequency, the angle of the diffracted light that passes through the sparse part of the incident beam incident on the exposure master 22 passes through the dense part according to the above-described equation (1). Smaller than the angle of the diffracted light. Therefore, the incident beam incident on the exposure master 22 is angularly separated into two beams of diffracted light A and B as shown in FIG.
[0022]
Actually, since there is an intensity characteristic (diffraction efficiency) of the diffracted light depending on the diffraction angle, it is necessary to adjust the intensity balance of the two diffracted lights. Also at this time, in this embodiment, the balance can be easily adjusted by changing the voltage level of fc1, fc2, or the pulse duty of fm. Switching from two beams to one beam is instantaneously possible by setting the output of the pulse signal generator 27 to a constant level of 1 (or 0) and selecting only fc1 (or fc2). However, for example, when a wide groove is exposed with two beams and a pit is exposed with one beam, fc1 (or fc2) is set to (fc1 + fc2) / 2 to position the pit row at the center of the groove groove. Need to change.
[0023]
The case of two beams has been described above, but the effect can be obtained with the same configuration in the case of three or more beams. For example, in the case of three beams, one of the signals from three high-frequency signal generators is selected, and sequentially and circulated and applied to the acousto-optic device. As a means for selecting, it is possible to easily realize such as configuring a normal multiplexer by combining the high-speed switch elements described above.
[0024]
Considering the intensity fluctuations of the diffracted beams A and B, the ultrasonic traveling wave travels at a speed vs from the bottom to the top in FIG. Therefore, the relationship between the incident beam diameter dm and the switching frequency fm is expressed as dm = vs / fm (4) when the density period exactly matches the incident beam diameter as shown in FIG. Under this condition, if the intensity distribution in the radial direction of the incident beam is constant, the intensities of the diffracted lights A and B are always constant regardless of the upper and lower positions of the ultrasonic traveling wave. Alternatively, when dm <vs / fm (5), the intensities of the diffracted beams A and B are alternately repeated. When dm> vs / fm (6), the intensity of the diffracted beams A and B is not changed when dm is an integral multiple of (vs / fm). As a result, the intensities of the diffracted beams A and B are always logically constant when dm = n (vs / fm) (n = 1, 2, 3,...) (7). In actual exposure, the exposed photoresist portion has a certain degree of thermal capacity, and therefore, if dm ≧ vs / fm (8), the groove shape is not adversely affected.
[0025]
Moreover, switching the high frequency of fc1 and fc2 supplied from the high frequency signal generators 25 and 26 with the pulse wave fm as shown in FIG. 1 results in Δfc = (fc1 + fc2) / 2 as a result. This is equivalent to FM modulation with the pulse wave fm in the frequency range of ± | fc1-fc2 | / 2. Therefore, as shown in FIG. 3 of the second embodiment of the present invention, a pulse modulation wave corresponding to a speed of fm and a level of Δfc is applied from the pulse signal generator 32 from the outside using the FM modulation circuit 31. Thus, the acoustooptic device equivalent to that of the first embodiment can be driven. In this embodiment, switching from 2 beams to 1 beam can be instantaneously performed by setting the output of the pulse signal generator 32 to a constant level of 0. Further, unlike the first embodiment, it is not necessary to change the frequency of the high frequency signal in order to position the pit row at the center of the groove groove.
[0026]
The case of two beams has been described above, but the effect can be obtained with the same configuration in the case of three or more beams. For example, in the case of three beams, three beams can be easily formed by making the output of the pulse signal generator 32 repeat a three-stage pulse shape. Further, if dm ≧ vs / fm (8) in the above formula, the intensity fluctuation of the diffracted light does not adversely affect the groove shape.
[0027]
As described above, when the parallel light beam of the laser is modulated as the diffracted light of the acoustooptic device, and it is narrowed down to a minute spot by the objective lens, the signal applied to the acoustooptic device and the spot intensity distribution on the board surface are: It is proved experimentally and logically that it is related to the Fourier transform. That is, the frequency spectrum shape when the applied signal is sampled in the section (dm / vs) where the traveling wave of the ultrasonic wave passes through the incident beam has a correlation with the spot intensity distribution formed by the objective lens.
[0028]
FIG. 4 shows the frequency spectrum shape, and FIG. 5 shows the relationship with the spot intensity distribution formed by the objective lens. 4A and 5A show the acoustooptic device driven at a normal single frequency. In this case, only one frequency spectrum is generated, and only one board spot is generated. 4 (b) and 5 (b) are systems in which the spot is vibrated in the groove width direction to expose the wide groove as described in the prior art, but as the vibration speed increases, the same figure is obtained. In addition, side lobes are generated before and after the center frequency fc. As a result, the low-strength side lobes appear at both ends of the main spot, and wide groove exposure cannot be performed. FIGS. 4C and 5C show the cases of the first and second embodiments of the present invention. With the two main spots, wide groove exposure is always possible. However, since the applied signal is FM modulation that changes in a pulse shape, side lobes are generated at both ends for each of fc1 and fc2 (indicated by dotted lines). The side lobe sandwiched between the two main spots is not a problem in exposure, but the side lobe generated at both ends is a problem because the groove cross-sectional shape is distorted. Therefore, as the third and fourth embodiments of the invention, when two frequencies are simply added and added to the acousto-optic element as shown in FIGS. 4D and 5D, there is no side lobe. Two spots are generated.
[0029]
FIG. 6 shows the configuration of the third embodiment of the present invention. In the figure, an adder 61 adds the high-frequency signals fc1 and fc2 from the high-frequency signal generators 62 and 63. Actually, since there is an intensity characteristic (diffraction efficiency) of the diffracted light depending on the diffraction angle, it is necessary to adjust the intensity balance of the two diffracted lights. Also at this time, in this embodiment, the intensity balance can be easily adjusted by changing the voltage levels of the high frequencies fc1 and fc2. Note that switching from 2 beams to 1 beam is instantaneously possible by selecting only fc1 (or fc2). However, for example, when a wide groove is exposed with two beams and a pit is exposed with one beam, fc1 (or fc2) is set to (fc1 + fc2) / 2 to position the pit row at the center of the groove groove. Need to change.
[0030]
The case of two beams has been described above, but the effect can be obtained with the same configuration in the case of three or more beams. For example, in the case of three beams, it can be easily realized by adding signals from three signal generators using two adders and applying them to the acousto-optic device.
[0031]
Here, the addition of two signals as in the third embodiment generates a beat signal 64 equal to the difference frequency. The shape of the ultrasonic traveling wave in FIG. 6 is schematic. Actually, two signals strengthen each other at a long horizontal line, and a large refractive index difference is generated. At a short horizontal line, they are weakened. The traveling wave has a small refractive index difference. The intensity of the diffracted light increases when the difference in refractive index of the traveling wave is large. Therefore, in order to obtain a constant intensity at all times, it is sufficient that the incident beam diameter dm coincides with the beat cycle vs / | fc1-fc2 | as shown in FIG. That is, dm = vs / | fc1-fc2 | (9) may be satisfied. At this time, since the diffracted light averages the beat signal in the dm section, a constant intensity is always obtained regardless of the phase of the traveling wave. In actual exposure, the exposed photoresist portion has a certain degree of thermal capacity. Therefore, if dm ≧ vs / | fc1−fc2 | (10), the groove shape is not adversely affected. When three or more beams are generated, it is only necessary that the cycle of the beat signal generated by the two closest signals satisfies the expression (10).
[0032]
Further, adding the high frequencies fc1 and fc2 is equivalent to AM modulation of the center frequency fc = (fc1 + fc2) / 2 with a signal having a frequency of Δfc = (fc1−fc2) / 2. Therefore, as can be seen from FIG. 7 showing the fourth embodiment of the present invention, by adding a modulation wave corresponding to Δfc from the signal generator 72 using the AM modulation circuit 71 from the outside, Acoustooptic device driving equivalent to that in the embodiment can be performed. Note that switching from 2 beams to 1 beam is possible instantaneously by setting the output of the signal generator 72 to a constant level of 0. Further, unlike the third embodiment, it is not necessary to change the frequency of the high frequency signal in order to position the pit at the center of the groove groove.
[0033]
The case of two beams has been described above, but the effect can be obtained with the same configuration in the case of three or more beams. For example, in the case of three beams, the center frequency fc can be easily realized by AM multiplex modulation using three different frequencies. Also, assuming that the lowest frequency among a plurality of modulation signals at the time of AM multiplex modulation is Δfc, if dm ≧ vs / 2Δfc (11) is satisfied, the intensity variation of the diffracted light will adversely affect the groove shape. There is nothing.
[0034]
The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications and substitutions are possible within the scope of the claims.
[0035]
【The invention's effect】
As described above, according to the present invention, the laser beam from the exposure laser is condensed by the objective lens on the exposure master disk that is coated with the photoresist and rotates and moves, Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes groove grooves, acousto-optic elements arranged in the optical path between the exposure laser and the objective lens, and a plurality of high-frequency signals that supply drive signals having different frequencies to the acousto-optic elements And a high-speed switch element and a pulse signal generator that sequentially and circulates one of the drive signals generated from the high-frequency signal generator to supply the acousto-optic element. Therefore, wide groove exposure with a steep groove wall shape is possible, and the relative positional relationship between the spot at the time of pit exposure and the spot at the time of groove exposure is stabilized, and an effect of reducing laser power loss can be obtained. Moreover, since the intensity balance of two diffracted lights can be adjusted easily, it can be set as a symmetrical groove wall surface shape. Furthermore, since a plurality of stable spots can be formed even from a realistic thick beam diameter, the application range is wide, and the interval between the plurality of spots is due to the difference in the corresponding drive signal frequency. Easy and highly accurate. Also pit Part Since the exposure can be switched instantaneously between the groove groove and the groove groove, it is suitable for exposure such as HB. Furthermore, a simple high-frequency signal generator having no modulation function can be used.
[0036]
In addition, the beam diameter of the laser beam incident on the acoustooptic device is dm, the switching frequency required to select and drive the drive signals from a plurality of high-frequency signal generators one by one, fm, and the supersonic wave generated inside the acoustooptic device Assuming that the velocity of the traveling acoustic wave is vs, the condition of dm ≧ vs / fm is satisfied. Therefore, the intensity fluctuation of a plurality of spots is small, and uniform groove exposure without fluctuation and noise can be performed.
[0037]
Furthermore, the laser beam from the exposure laser is condensed by the objective lens onto the exposure master that is rotated and moved by applying the photoresist. Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes a groove, an acousto-optic device disposed in an optical path between an exposure laser and an objective lens, a pulse signal generator that generates a multi-stage pulse signal, and a pulse signal generator And an FM modulation circuit that generates an FM modulated wave in which the frequency of the drive signal supplied to the acousto-optic element is changed in a multistep manner using the pulse signal generated from the above. Therefore, it is not necessary to change the frequency of the high-frequency signal in order to position the pit row at the center of the groove groove, and the relative phase relationship of the plurality of high-frequency signals can be further stabilized, so that uniform groove exposure without fluctuations and noise can be achieved. Is possible.
[0038]
In addition, assuming that the beam diameter of the laser beam incident on the acoustooptic device is dm, the cycle frequency of the multistage pulse of the pulse signal generator is fm, and the velocity of the ultrasonic traveling wave generated inside the acoustooptic device is vs, dm ≧ The condition of vs / fm is satisfied. Therefore, the intensity fluctuation of a plurality of spots is small, and uniform groove exposure without fluctuation and noise can be performed.
[0041]
In addition, the laser beam from the exposure laser is focused by the objective lens onto the rotating exposure master that is coated with the photoresist and rotated and moved. Part Or Wider than the spot diameter of the laser beam In an optical disk master exposure apparatus that exposes a groove, an acoustooptic element disposed in an optical path between an exposure laser and an objective lens, a high-frequency signal generator that supplies a drive signal to the acoustooptic element, and a plurality of frequencies A modulation signal generator that generates a continuous signal having components, and an AM modulation that generates an AM modulated wave in which the amplitude of the drive signal supplied to the acoustooptic device is changed using the modulation signal generated from the modulation signal generator It is characterized by providing a circuit. Therefore, it is not necessary to change the frequency of the high-frequency signal in order to position the pit row at the center of the groove groove, and uniform groove exposure without fluctuation and noise can be achieved.
[0042]
Furthermore, the beam diameter of the laser beam incident on the acoustooptic device is dm, the frequency of the lowest frequency component of the modulation signal from the modulation signal generator is Δfc, and the velocity of the ultrasonic traveling wave generated inside the acoustooptic device is Assuming vs, the condition of dm ≧ vs / 2Δfc is satisfied. Accordingly, uniform groove exposure is possible with less intensity fluctuation of the plurality of spots.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an optical disc master exposure apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a part of the configuration of the first embodiment.
FIG. 3 is a diagram showing a part of the configuration of a second exemplary embodiment of the present invention.
FIG. 4 is a diagram showing a frequency spectrum shape.
FIG. 5 is a diagram showing a relationship with a spot intensity distribution formed by an objective lens.
FIG. 6 is a diagram showing a part of the configuration of a third exemplary embodiment of the present invention.
FIG. 7 is a diagram showing a part of the configuration of a fourth exemplary embodiment of the present invention.
FIG. 8 is a diagram showing a configuration of a general acoustooptic device.
FIG. 9 is a diagram showing a configuration of an acousto-optic element in a conventional example.
[Explanation of symbols]
11 Laser light source for exposure
16 Acoustooptic device
19 Objective lens
25, 26 High-frequency signal generator
27 Pulse signal generator
28 High-speed switch element

Claims (6)

The laser beam from the exposure laser objective lens condenses on exposed master which photoresist is applied to rotate and move, an optical disk master exposure than the spot diameter of the pit portion or the laser beam for exposing the wide groove groove In the device
An acoustooptic device disposed in an optical path between the exposure laser and the objective lens;
A plurality of high-frequency signal generators for supplying drive signals having different frequencies to the acoustooptic device;
An optical disk master exposure apparatus, comprising: a high-speed switch element that sequentially and circulates one of driving signals generated from the high-frequency signal generator and supplies the acousto-optic element to the acoustooptic element; and a pulse signal generator . A beam diameter of a laser beam incident on the acoustooptic device is dm, a switching frequency required to select and drive the drive signals from the plurality of high frequency signal generators one by one is generated in the acoustooptic device If the velocity of the ultrasonic traveling wave is vs,
dm ≧ vs / fm
2. An optical disc master exposure apparatus according to claim 1, which satisfies the following condition. The laser beam from the exposure laser objective lens condenses on exposed master which photoresist is applied to rotate and move, an optical disk master exposure than the spot diameter of the pit portion or the laser beam for exposing the wide groove groove In the device
An acoustooptic device disposed in an optical path between the exposure laser and the objective lens;
A pulse signal generator for generating a multi-stage pulse signal;
And an FM modulation circuit that generates an FM modulated wave in which the frequency of the drive signal supplied to the acoustooptic device is changed in a multistep manner using the pulse signal generated from the pulse signal generator. Optical disc master exposure device. When the beam diameter of the laser beam incident on the acoustooptic device is dm, the cycle frequency of the multi-stage pulse of the pulse signal generator is fm, and the velocity of the ultrasonic traveling wave generated inside the acoustooptic device is vs.
dm ≧ vs / fm
4. The optical disk master exposure apparatus according to claim 3, wherein the following condition is satisfied. The laser beam from the exposure laser objective lens condenses on exposed master which photoresist is applied to rotate and move, an optical disk master exposure than the spot diameter of the pit portion or the laser beam for exposing the wide groove groove In the device
An acoustooptic device disposed in an optical path between the exposure laser and the objective lens;
A high frequency signal generator for supplying a dynamic signal drive to the acousto-optic device,
A modulation signal generator for generating a continuous signal having a plurality of frequency components;
An optical disc master exposure comprising: an AM modulation circuit that generates an AM modulated wave in which an amplitude of a drive signal supplied to the acoustooptic device is changed using a modulation signal generated from the modulation signal generator apparatus. The beam diameter dm of the laser beam incident on the acousto-optic device, the lowest frequency of the frequency component △ fc, the speed of ultrasonic traveling waves generated within the acousto-optic device of the modulation signal from the modulation signal generator Is vs.
dm ≧ vs / 2Δfc
6. An optical disc master exposure apparatus according to claim 5, wherein the following condition is satisfied.

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