JP4196634B2 - Optical recording medium master exposure apparatus and optical recording medium master exposure method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium master exposure apparatus that performs pattern exposure corresponding to recording information by irradiating light from an exposure light source onto an optical recording medium master coated with a photoresist, and an exposure method for the optical recording medium master. .
[0002]
[Prior art]
  CD (Compact Disc,Registered trademark), MD (Mini Disc,Registered trademark), DVD (Digital Versatile Disc,Registered trademarkThe optical recording medium master for producing optical recording media such as various optical disks, magneto-optical disks, etc. is coated with a photoresist on, for example, a disc-shaped master substrate, and the surface has irregularities corresponding to recording information. The pattern is formed by exposure and development, that is, formed by so-called cutting.
  A mastering apparatus that performs this cutting, ie, an optical recording medium master exposure apparatus, is a laser beam having a wavelength of about 400 nm emitted from an exposure light source, for example, an ultraviolet wavelength such as a Kr laser (λ = 413 nm) or an Ar laser (λ = 351 nm). An exposure process is performed by narrowing down and irradiating a diffraction-limited microspot on a master plate coated with a resist through an objective lens using a continuous wave solid-state laser light source in the region.
[0003]
Various optical recording media as described above are required to have finer pit or groove processing dimensions as the recording density is increased to increase the recording capacity. However, when a dimension of 0.25 μm or less is required as the processing dimension of the pit, a lens having a numerical aperture NA close to 1 at the wavelength of the gas laser used in the optical recording medium master exposure apparatus described above. However, the laser beam cannot be sufficiently narrowed down. Therefore, at present, it is extremely difficult to accurately process to a size of 0.25 μm or less in the production of an optical recording medium master.
[0004]
For example, an ultraviolet laser beam having a wavelength of 266 nm is generated using a semiconductor laser pumped high power green laser having a wavelength of 532 nm as a pumping light source and using a second harmonic generator having an external resonator structure, and the numerical aperture NA = 0 as the beam spot size. .9 aberration-free objective lens is used to obtain an Airy spot of 0.36 μm (see, for example, Patent Document 1).
[0005]
In recent years, the trend toward higher density of optical disks has further accelerated, and at present, formation of finer pits, for example, 0.2 μm or less is essential, and a light source with a shorter wavelength is required. As a continuous oscillation laser light source having stability, low noise, and beam quality that can be used for an optical recording medium master exposure apparatus, a BaB is included in a resonator of an argon gas laser.₂O_FourA Deep UV oscillation water-cooled argon gas laser (an output of 40 mW at a wavelength of 229 nm and an output of 100 mW at a wavelength of 238 nm) in which a nonlinear optical crystal such as (BBO) is installed is commercially available. However, the wavelength ratio is 229/266 = 0.86, and in order to obtain a resolution of 0.2 μm or less, it is necessary to use an objective lens with a higher NA. In addition, since a large amount of cooling water is used, there is an inconvenience that requires measures to avoid vibration in the built-in equipment.
[0006]
Further, as a high NA optical system, a technical study of means using a near field optical system using a solid immersion lens (SIL) of NA> 1 has been made. However, the working distance is as narrow as 100 nm or less, for example, several tens of nanometers, and attention must be paid to dust and dust mixing, surface smoothness of the optical recording medium master, and the rotation speed of the optical recording medium master. There is a problem that it cannot be raised too much.
[0007]
Recently, a micropit processing method using an electron beam exposure apparatus has been proposed as another means for increasing the resolution (see, for example, Patent Document 2).
[0008]
However, since an electron beam exposure apparatus uses an electron beam, a vacuum apparatus is required, and a large-scale apparatus such as a high-precision high-rotation mechanism for a glass master is provided in a vacuum.
[0009]
On the other hand, in recent years, several high-power Ti: Sapphire (titanium sapphire) ultrashort pulse laser light sources having a repetition rate of 1 MHz to 100 MHz in a car lens mode lock system are commercially available. This Ti: Sapphire ultrashort pulse laser light source is pumped by a semiconductor laser pumped high-power green laser, and oscillates at a central wavelength of 760 nm to 840 nm, for example, 800 nm. Can be obtained stably. The transverse mode of the beam is TEM00 and the noise is 0.1% or less.
[0010]
In addition, for example, Tsunami series by Spectra Physics, Mira series by Coherent, etc., those having a repetition frequency of 80 MHz and a pulse width (FWHM) of 100 fs or less and an average output of 1 W or more have been put into practical use.
[0011]
In addition, a two-photon absorption process is generated using such an ultrashort pulse laser light source, and a pattern finer than the diffraction limit can be formed by super-resolution characteristics using a nonlinear optical effect (for example, non-patent literature) 1).
[0012]
For example, an example in which a dot-shaped pattern having a width of 120 nm is formed using a laser having a wavelength of 780 nm, a repetition frequency of 76 MHz, a pulse width of 150 fs, and an objective lens having a numerical aperture NA of 1.4 is reported (for example, see Non-Patent Document 2). .)
However, at present, a technique for forming a modulation signal of recording information for an optical recording medium on a resist by pattern exposure using a two-photon absorption process and using it for exposure of an optical recording medium master has not been realized.
[0013]
[Patent Document 1]
JP-A-7-98891
[Patent Document 2]
Japanese Patent No. 3233650
[Non-Patent Document 1]
Edited by Satoshi Kawada, Spectroscopical Society of Japan, Series 38 “Super-Resolution Optics”, Society Publishing Center, March 20, 1999, Chapter 5, page 79
[Non-Patent Document 2]
S. Kawata et al, “Fine features for functional microdevices”, Nature, 2001, Vol. 412, p. 697)
[0014]
[Problems to be solved by the invention]
The present invention has been made in view of the above-described circumstances, and an optical recording medium master exposure apparatus and an optical recording medium exposure capable of forming fine pits with high accuracy and greatly improving productivity. The purpose is to provide a method.
[0015]
[Means for Solving the Problems]
The present invention relates to a modulation unit that modulates light intensity from an exposure light source corresponding to recording information, and a condensing optical system that condenses the light modulated by the modulation unit onto a photoresist on an optical recording medium master. And an optical recording medium master exposure apparatus for pattern exposure of a photoresist according to recording information, wherein the exposure light source is an ultrashort pulse having a repetition frequency of 1 to 20 times the clock frequency of the recording information. A laser is used, and a frequency dividing optical system that divides the laser beam emitted from the ultrashort pulse laser is provided.
[0016]
Further, according to the present invention, in the above-described configuration, the repetition frequency of the ultrashort pulse laser is set to an integer multiple of 1 to 20 times the clock frequency of the recording information, and the resonator length of the ultrashort pulse laser is made variable. An external synchronization mechanism is provided in which the repetition frequency of the pulse laser is mode-locked in synchronization with the clock frequency of the recording information to generate pulse oscillation.
[0017]
Furthermore, the present invention provides high-order harmonic generation means for emitting light having a wavelength shortened by wavelength conversion using a nonlinear optical element with an ultrashort pulse laser light source as an excitation light source between the exposure light source and the frequency dividing optical system. It is set as the structure which provides.
[0018]
The exposure method for an optical recording medium master according to the present invention performs exposure using the above-described optical recording medium master exposure apparatus.
That is, light intensity modulation is performed on the light from the exposure light source corresponding to the recording information, and the light modulated by the modulation means is condensed on the photoresist on the optical recording medium master, and the photoresist is used as the recording information. An exposure method of an optical recording medium master that performs pattern exposure in response, wherein the exposure light source is composed of an ultrashort pulse laser having a repetition frequency of 1 to 20 times the clock frequency of the recording information, and the ultrashort pulse laser A frequency dividing optical system for dividing the emitted laser light is provided.
[0019]
Further, according to the present invention, in the exposure method described above, the external synchronization in which the repetitive frequency of the ultrashort pulse laser is an integer multiple of 1 to 20 times the clock frequency of the recording information and the resonator length of the ultrashort pulse laser is variable. A mechanism is provided so that the repetition frequency of the ultrashort pulse laser is mode-locked in synchronization with the clock frequency to generate a pulse oscillation.
[0020]
Further, the present invention provides a method for shortening the wavelength of light emitted from an exposure light source by wavelength conversion using a nonlinear optical element by high-order harmonic generation means using the exposure light source as an excitation light source. The light is emitted and incident on the frequency dividing optical system.
[0021]
As described above, the optical recording medium master exposure apparatus and the optical recording medium master exposure method according to the present invention uses an ultrashort pulse laser light source as an exposure light source, and the repetition frequency thereof is one or more times the clock frequency of recording information. A frequency dividing optical system that divides the laser beam emitted from the ultrashort pulse laser is set to 20 times or less.
[0022]
  The clock frequency of the recording information signal of the optical disc is CD(Registered trademark)In case of 4.3MHz, DVD(Registered trademark)In the case of 26 MHz. In recent years, the so-called Blu-ray Disc has been attracting attention as a high-density disc and is being developed with a reproduction light wavelength λ of 405 nm and an objective lens NA of 0.85.(Registered trademark)In this case, it is 66 MHz. For example, Blu-ray Disc(Registered trademark)In this case, since it is 66 MHz, it is almost the same as the repetition frequency of the ultrashort pulse laser, so it is necessary to match the timing of information data signal and laser pulse oscillation.
[0023]
However, according to the present invention, as described above, the pulse interval is reduced by providing the frequency dividing optical system that makes the pulse repetition frequency of the ultrashort pulse laser 2 times, 4 times, 8 times,. Is superimposed on the recording information, the deviation of exposure per pulse can be reduced, the occurrence of pattern defects can be avoided, and an increase in the jitter of a reproduction signal, for example, due to the pattern defects can be suppressed. Therefore, by using an ultrashort pulse laser, it is possible to form a fine pattern with high accuracy as compared with the conventional case.
Further, by setting the repetition frequency to 20 times or less, it is possible to avoid a decrease in pattern formation accuracy due to a decrease in the peak output of the ultrashort pulse laser. That is, by dividing the laser light emitted from the ultrashort pulse laser light source and shortening the wavelength by high-order harmonic generation means, the peak output is reduced, but the repetition frequency is 20 times or less. Can sufficiently secure the output of the ultrashort pulse laser, efficiently generate the two-photon absorption process described later, and can perform pattern exposure with a fine spot size.
[0024]
  In the present invention, when the repetition frequency of the ultrashort pulse laser is set to an integer multiple of 1 to 20 times the clock signal of the recording information, the external length for adjusting the resonator length of the ultrashort pulse laser light source used as the exposure light source A synchronization mechanism is provided, whereby the resonator length is adjusted, the repetition frequency can be synchronized with the clock signal, and the jitter of the reproduction signal can be suppressed to 10% or less.
  By synchronizing in this way, the light from the ultrashort pulse laser light source is used as the exposure light source, and the CD(Registered trademark), DVD(Registered trademark), Blu-ray Disc(Registered trademark)It is possible to reliably perform pattern exposure synchronized with information signals recorded on various optical recording media.
[0025]
In another aspect of the present invention, high-order harmonic generation means is provided between the exposure light source and the modulation means, and the wavelength is shortened by wavelength conversion using a nonlinear optical element with an ultrashort pulse laser light source as an excitation light source. An exposure light source having a shorter wavelength can be obtained by emitting the emitted light.
[0026]
As described above, according to the optical recording medium master exposure apparatus and the optical recording medium master exposure method according to the present invention, an exposure light source that emits an ultrashort pulse laser beam having a high repetition frequency that can be regarded as pseudo continuous light or the like. The ultra-short pulse laser light having a short wavelength is emitted by the high-order harmonic generation means using the excitation means as the excitation means, and the light modulated by the light intensity modulation means is made into a diffraction-limited spot size by a predetermined condensing optical system. By condensing and irradiating the photoresist, it is possible to expose a concavo-convex pattern such as a pit having a finer pattern than in the past.
[0027]
In the above-described present invention, the frequency dividing optical system is composed of a polarizing beam splitter and an optical delay circuit, and this frequency dividing optical system is provided at the subsequent stage of the light source composed of the ultrashort pulse laser, and the higher order harmonics. In the case where the generating means is provided, this frequency-dividing optical system is provided in the subsequent stage, so that it is possible to use laser light with high efficiency and high efficiency with little power loss.
[0028]
That is, the average output power of high-order harmonic light is proportional to the square of the fundamental wave power. Therefore, if the ultra-short pulse laser beam with a relatively low repetition frequency that provides high output is incident to generate high-order harmonics with high efficiency, and then this pulse train is divided several times, the same input fundamental wave power Therefore, pulse oscillation with a high output and a high repetition frequency is possible, and it is not necessary to have a device configuration that takes into account the timing of the clock of recording information.
[0029]
In this case, the high-order harmonic generation means for shortening the wavelength is a nonlinear optical process, whereas the process through the frequency dividing optical system is a linear optical process, so that it is possible to reduce output loss. Have advantages.
[0030]
Further, according to the present invention, in the above-described optical recording medium master exposure apparatus or optical recording medium master exposure method, the photoresist is exposed by a two-photon absorption process. By using an ultrashort pulse laser light source with very high peak output (peak output) as an exposure light source and condensing the beam with a condensing optical system, a two-photon absorption process occurs very efficiently in the resist. . For example, when the repetition frequency is 1 GHz and the average power of the laser after emission from the objective lens is 10 mW, the light intensity in the beam spot on the surface of the photoresist is 100 GW / cm with a peak output.²It extends to.
[0031]
The two-photon absorption process is one of nonlinear optical phenomena, and the exposure of the resist is given by the square of the intensity distribution of the beam spot. The two-photon absorption cross section of the resist is 10^-46~Ten^-47cm^FourAlthough it is a small value of about s / photon, the sensitivity of the resist is low, but absorption of several percent occurs.
[0032]
  Thus, in order to cause two-photon absorption with high efficiency, the peak output of the ultrashort pulse laser beam must be high.RanaYes.
  In the present invention, pulse oscillation with a high repetition frequency is used, and the pulse width (FWHM) is at least 1 ps (1 × 10 10).^-12However, by defining the pulse width in this way, two-photon absorption could be efficiently caused.
[0033]
When the resist is exposed, the light absorption distribution of the light source in the resist surface is proportional to the beam intensity distribution in the case of normal absorption, and is proportional to the square of the beam intensity distribution in the case of two-photon absorption. The light absorption distribution is shown in FIG. In FIG. 6, I indicates the beam intensity distribution, which corresponds to the case of normal absorption. I2 represents the square of the beam intensity distribution and corresponds to the case of two-photon absorption. The Airy spot diameter d is
d = 1.22λ / NA
It becomes. When the numerical aperture NA of the objective lens is NA = 0.9 and the wavelength λ = 267 nm, the spot size is 0.36 μm. In the case of two-photon absorption, the beam spot is approximately 1 / √2 = 0.7 times. That is, this corresponds to the beam spot size during normal exposure using an exposure light source having a wavelength of 190 nm. As a result, the recording linear density is about 1.4 times that in the case of one-photon (normal) exposure.
[0034]
The present invention also relates to the above-described optical recording medium master exposure apparatus and optical recording medium master exposure method, wherein the spot shape of the laser light emitted from the condensing optical system and condensed on the photoresist The shape is an ellipse extending in the scanning direction.
[0035]
For example, in order to expose a linear pattern such as a groove, the pulse interval (reciprocal of the repetition frequency) and scanning speed (linear speed in the case of a disk-shaped optical recording medium master) must be optimized in accordance with the resist sensitivity. Don't be. However, since the pulse interval is uniquely fixed by the clock, it is difficult to expose a linear pattern. According to the present invention described above, the beam spot emitted from the focusing optical system and focused on the resist is elongated in the beam scanning direction. This linear pattern can be easily obtained.
[0036]
As described above, in the present invention, since the ultrashort pulse laser is used as the exposure light source and the beam is further narrowed down to the diffraction limit by the condensing optical system, two-photon absorption can be performed with high efficiency, and 2 Photosensitivity of the resist is given by the square of the intensity distribution of the beam spot due to the photon absorption process, and it has super-resolution characteristics using non-linear effects, and records smaller pits that are finer than the diffraction limit. Is possible.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an optical disk master exposure apparatus according to the present invention will be described with reference to the drawings.
[0038]
FIG. 1 shows a schematic block diagram of an example of an exposure apparatus for an optical recording medium master according to the present invention. In this example, modulation means 3 that modulates light intensity from the exposure light source 1 corresponding to recording information, and light modulated by the modulation means 3 are converted into a disk-shaped optical recording medium master 11 in the illustrated example. A condensing optical system 9 for condensing light on the upper photoresist 12 is provided, and the photoresist 12 is subjected to pattern exposure according to recorded information.
[0039]
  In FIG. 1, 1 is an exposure light source made of an ultrashort pulse laser, and 15 is a diagram to be described later.51 is a frequency dividing optical system, 4 is a chirp correction optical system, 5 is a beam expander, 6 is an autofocus optical system, and an example is described in detail in the following embodiments. / 4 wavelength plate, 8a is an objective lens, 8b and 8c are electromagnetic actuators. 1a, 1b and 1c are mirrors. The optical recording medium master 11 is fixed to the mounting table 10. The mounting table 10 is a rotating means 1 in this example.3The condensing optical system 9 is moved in the radial direction of the optical recording medium master 11 by being arranged on a moving optical table (not shown), for example, as shown by the arrow a. The exposure light can be irradiated over the entire surface of the recording medium master.
[0040]
  Figure5A schematic diagram of an example of the frequency dividing optical system is shown in FIG. Figure5In A, reference numerals 60 and 70 denote frequency dividing circuits. The light L11 emitted from the exposure light source composed of the ultrashort pulse laser is separated by the beam splitter 61 into 50:50. If this light is s-polarized light, a polarizing beam splitter 67 through which the light transmitted through the beam splitter 61 passes is disposed. The light reflected by the beam splitter 61 enters the half-wave plate 66 through the lens 62, mirrors 63 and 64, and the lens 65 to be p-polarized light, and is completely reflected by the polarization beam splitter 67.
  Similarly, in the frequency dividing optical system 70, the light L12 emitted from the beam splitter 71 and the frequency dividing optical system 60 is separated into 50:50 by the beam splitter 71. If this light is s-polarized light, a polarization beam splitter 77 that transmits the light transmitted through the beam splitter 71 is disposed. The light reflected by the beam splitter 71 is incident on the half wavelength 76 through the lens 72, mirrors 73 and 74, and the lens 75 to be p-polarized light, and is completely reflected by the polarization beam splitter 77.
[0041]
Here, the lenses 62 and 65, 72 and 75 form an afocal (telescope) system, and are arranged so that both beam parameters coincide with each other. The half-wave plates 66 and 76 are installed by rotating their optical axes by 45 °, and rotate the polarization plane of incident light by 90 ° so as to be totally reflected by the polarization beam splitters 67 and 77 as described above. It is.
Further, the mirrors 63 and 64, 73 and 74 can be replaced with right-angle prisms or corner cubes.
[0042]
  In the frequency dividing optical system 60, an optical delay circuit is configured by appropriately selecting a difference in optical path length between two lights obtained by dividing the incident light L11 by the beam splitter 61. This difference in the optical path length of the beam is adjusted with high accuracy so that the pulse transit time is equal to ½ of the pulse train interval of the incident light L11 (that is, the reciprocal of the repetition frequency of the ultrashort pulse laser). The figure5In B, as schematically shown in the pulse train conversion process, the incident pulse train p11 can be converted into a pulse train p12 whose interval is halved, that is, whose frequency is doubled.
[0043]
For example, if the repetition frequency is 66 MHz, the interval between pulse trains is 15.152 ns (10 −9 seconds), and the optical path length is 2.2712 m (light speed = 2.998 × 10 8 m / s).
Further, instead of the beam splitter 61, a half-wave plate whose optical axis is rotated with respect to the polarization plane of the 22.5 ° incident pulse laser beam is provided to rotate the polarization plane by 45 °, and the polarization beam splitter. And may be combined.
[0044]
Further, in the frequency dividing optical system 70 at the subsequent stage of the frequency dividing optical system 60, by accurately adjusting the optical path length difference to be equal to ½ of the interval of the pulse train p12, as shown in FIG. It is possible to emit a pulse train p13 in which the interval of the pulse train p12 emitted from the frequency dividing circuit 60 is further halved. In this case, the optical path difference is 1.1356 m.
[0045]
The pulse train obtained in this way is divided into pulse trains having a peak power of 1/2 and a repetition frequency twice when passing through the frequency divider circuit 60, and a peak power of 1/4 when passing through the frequency divider circuit 70. The repetition frequency is divided into four times the pulse train. When the above-mentioned 66 MHz ultrashort pulse laser is incident, the repetition frequency becomes 264 MHz. However, although the polarization planes of the pulses p12 and p13 are horizontal polarization and vertical polarization inclined by 90 °, there is no direct influence on the exposure apparatus and the exposure method.
[0046]
  A schematic waveform of a pulse signal from this ultrashort pulse laser light source and frequency dividing optical system is shown.2A schematic waveform in a state in which the pulse signal is superimposed on the signal waveform S of the recording information by A and the modulation means 3 is shown in FIG.2Shown in B. Figure2As shown in A, the interval between the pulses P is appropriately selected, and the frequency is plotted.21 to 20 times or less of the clock signal C of the recording information shown in C, and in the example shown, the frequency is doubled.2As shown in B, it is superimposed on the signal S of the recording information. Figure2In B, the pulse waveform is shown as a broken line P '. In this way, when the repetition frequency of the pulse train is an integer multiple of 1 to 20 times the clock frequency of the recording information, the recording information and the recording information By performing synchronized exposure, the pattern exposure of the photoresist can be performed in accordance with the recorded information.
[0047]
FIG. 4 shows a schematic schematic configuration diagram of an example of an external synchronization mechanism and an exposure light source suitable for use in the embodiment of the present invention. In FIG. 4, 30 is an ultrashort pulse laser light source using, for example, Ti: Sapphire, and 50 is an external synchronization mechanism.
First, excitation light Li0 such as a semiconductor laser (not shown) enters a laser medium 34 such as Ti: Sapphire via a lens 31 and a spherical mirror 32. The light emitted from the laser medium 34 is reflected by the spherical mirror 33, further reflected by the high reflection mirror 35, and then incident on the dispersion compensation prisms 36 a and 36 b. Then, the light is reflected by the high reflection mirror 38 through the slit 37. Then, the light passes again through the slit 37 and is returned to the laser medium 34 via the dispersion compensating prisms 36 b and 36 a, the high reflection mirror 35, and the spherical mirror 33. As the exposure light, the light returned from the laser medium 34 to the spherical mirror 32 is extracted outside as output light Li2 through an output window (output coupler) 39 and a beam splitter 40.
[0048]
In this external synchronization mechanism, a part of output light is detected by a beam splitter 40 by a photodetector 41 made of a high-speed photodiode or the like. Then, the phase detector 43 compares the phase of the output from the photodetector 41, that is, the electrical signal generated by the laser pulse oscillation, and the output of the clock signal generator 42 of the information signal output device recorded on the optical recording medium. Here, when the clock signal is an integer multiple of 2 or more, phase comparison with a clock signal that is an integral multiple of the signal of the clock signal generator 42 is performed. Then, the signal output from the phase detector 43 is input to a control unit 44 composed of a PLL (Phase Lock Loop) circuit or the like, and the control signal converted into a predetermined control amount is input to the piezo drive unit 45 to The resonator length of the laser resonator can be finely adjusted by slightly moving the piezo element 46 fixed to the high reflection mirror 38 in the optical axis direction. The resonator length in this example is the length of the optical path from the spherical mirror 32 to the high reflection mirror 38.
[0049]
  With such a configuration, the jitter between the clock signal of the recording information and the laser oscillation pulse can be reduced to 1 ps or less.
  Since the optical modulator driving signal of the information recording signal is also transmitted in synchronization with the clock signal, the pulse oscillation of the ultrashort pulse laser can be timed. When the repetition frequency of the ultra-short pulse laser light source is 1 times that of the clock signal, that is, synchronized, when the photoresist is recorded using, for example, a (1,7) modulation code, the 2T shortest pit is irradiated with 2 pulses. Is done. If the frequency is twice that of the clock signal, the aforementioned Blu-ray Disc(Registered trademark)In the case of external synchronization with 132 MHz, the optical system in the ultrashort pulse laser device may be arranged so that the resonator length R is R = c / 2L = 1136 mm (c is the speed of light), and the 2T shortest pit is obtained. Is the figure above2As shown in B, four pulses are irradiated.
[0050]
If the repetition frequency of laser oscillation is increased, the peak output of the pulse decreases even if the average output is the same, so that the efficiency of generation of higher harmonics in the subsequent stage and the two-photon absorption of the resist decreases. Therefore, the repetition frequency of the ultrashort pulse laser light source is selected to be 20 times or less the frequency of the clock signal.
Further, when the repetition frequency is an integer multiple of 10 times the frequency of the clock signal, the deviation from the clock can be 1/10 or less of the cycle, and the jitter of the reproduction signal can be 10% or less. Exposure can be performed without providing an external synchronization mechanism.
[0051]
Further, according to the present invention, in the above-described configuration, the wavelength is shortened by wavelength conversion using a nonlinear optical element with an ultrashort pulse laser light source as an excitation light source between the exposure light source 1 and the modulation means 3 as shown in FIG. The high-order harmonic generation means 2 that emits the emitted light is provided.
[0052]
  A schematic configuration of an example of the high-order harmonic generation means 2 is illustrated.3Shown in
  Figure3, 26 denotes a second harmonic (SHG) generator, 27 denotes a delay line unit, and 28 denotes a third harmonic (THG) generator. The light Li incident on the second harmonic generation unit 26 enters the nonlinear optical crystal 20 through the condensing lens 19a, is reflected by the harmonic separator 21a through the condensing lens 19b, and is extracted as L2-1. If the harmonic separator 21a is not provided, the light enters the delay line unit 27.
[0053]
The light incident on the delay line unit 27 is divided into a fundamental wave L1 and a second harmonic L2-2 by the harmonic separator 21b. The fundamental wave is reflected by the mirrors 22a and 22b and is incident on the third harmonic generation unit 28, and the second harmonic L2-2 is reflected by the mirrors 22c, 22d and 21c via the half-wave plate 23. The light enters the third harmonic generation unit 28.
[0054]
For example, as described in F. Rotermund, et al: “Generation of the fourth harmonic of a femtosecond Ti: Sapphire laser” Optics Letters, July 1, 1998, Vol. 23, No. 13, p1040 Using an 800 nm Ti: Sapphire ultrashort pulse laser (repetition frequency 82 MHz, pulse width 85 fs, average output 1.9 W), nonlinear optical crystal LiB_ThreeO_FiveBy using a second harmonic generation (SHG) device using (LBO) type I critical phase matching, the center wavelength is 400 nm, the pulse width is slightly expanded due to group velocity dispersion, for example, 100 fs, and the average output exceeds 600 mW. Short pulse laser light can be obtained.
[0055]
  When using type I phase matching in the second harmonic generation, the polarization planes of the fundamental wave and the second harmonic are rotated by 90 °.3As shown in FIG. 1, by providing a half-wave plate 23 that aligns with the fundamental wave L1 before entering the second nonlinear optical crystal 24 that uses type I phase matching, the second harmonic L2-2 The polarization plane can be adjusted to the fundamental wave.
[0056]
Further, since the second harmonic L2-2 is emitted behind the fundamental wave L1 due to the chromatic dispersion in the first nonlinear optical crystal 20, the delay line unit 27 causes the second nonlinear optical crystal 24 to emit light. The fundamental wave L1 is delayed before entering. The means for delaying is made by separating both waves by the harmonic separator 21b, and combining them again by lengthening only the optical path length of the fundamental wave L1 by a length corresponding to the delay time.
[0057]
  And figure3As shown in FIG. 3, the third harmonic generation unit 28 causes the combined wave to enter the nonlinear optical crystal 24 and emit the third harmonic L3 to the outside by sum frequency mixing. 19c and 19d are condensing lenses, 21d is a mirror, 25 is a beam stopper, and Lo is unnecessary light.
  The lenses 19a to 19d are arranged to increase the beam intensity in the crystal and improve the conversion efficiency.
[0058]
In the case of ultra-short pulse laser light, the peak output is very high, and the second harmonic generation, which is a second-order nonlinear optical phenomenon, increases its conversion efficiency in proportion to the intensity of the laser. High efficiency can be obtained even if the optical path is set once through the optical crystal. However, in the case of high-order harmonic generation using an ultrashort pulse laser, there is group velocity dispersion of the nonlinear optical crystal. Therefore, if the crystal is thick, group velocity mismatch occurs and effective wavelength conversion is not performed. For example, the crystal length of LBO needs to be 1.5 mm or less when the pulse width is 100 fs and the center wavelength is 800 nm.
[0059]
Furthermore, in the above-described third harmonic generation unit 28, for example, by sum frequency mixing (SFM) of, for example, a fundamental wave having a center wavelength of 800 nm and a second harmonic having a center wavelength of 400 nm emitted from the above-described higher-order harmonic generation unit. In addition, an ultrashort pulse laser beam having a center wavelength of 267 nm, a pulse width of 115 fs, and an average output of about 150 mW can be obtained. This sum frequency mixing is a second-order nonlinear optical phenomenon similar to the second harmonic generation. For example, the type I critical phase matching of the nonlinear optical crystal BBO can be used. It is necessary to set it to 3 mm or less.
[0060]
Further, by adding a nonlinear optical crystal (BBO) for sum frequency mixing, fourth-order harmonics can be generated, and a light source with a wavelength of 204 nm can be obtained. A pulse width of 340 fs and an average output of 15 mW are obtained. Therefore, it can be used as an exposure light source by applying to the optical recording medium master exposure apparatus and the optical recording medium master exposure method of the present invention with sufficient average output power up to the fourth harmonic light as the wavelength.
[0061]
As described above, in the present invention, when pulse oscillation with a high repetition frequency is used, the pulse width (FWHM) is at least 1 ps (1 × 10 10).^-12However, by defining the pulse width in this way, two-photon absorption could be efficiently caused.
[0062]
In the present invention, the following effects can be obtained by setting the absorption peak wavelength of the photoresist to half or less of the wavelength of the exposure light source.
As described above, normal absorption (one-photon absorption) can be efficiently suppressed by using a material that is transparent in the wavelength range of the exposure light source and has absorption at half the wavelength as the photoresist. .
In the two-photon absorption, two photons are absorbed simultaneously, and the resist electrons are shifted to a level higher by twice the energy of one photon. In terms of absorption spectrum, this corresponds to excitation with light having a wavelength half the wavelength of the exposure light source (one photon), so that the resist for absorption of two photons has an absorption peak wavelength that is half or less of the wavelength of the exposure light source. Thus, two-photon absorption can be efficiently generated and finer pattern exposure can be performed.
[0063]
  When exposure is performed over the entire thickness of the photoresist, it is desirable that half the wavelength of the exposure light source be slightly longer than the absorption peak of the photoresist.
  For example, a CD with a photoresist thickness of about 100 nm(Registered trademark)When an exposure master is exposed, if an exposure light source and a photoresist that have an absorption coefficient of several percent of the absorption coefficient at the absorption peak wavelength are selected, the two-photon absorption is not achieved only near the resist surface, and the total thickness Absorptive absorption can occur. Also, Blu-ray Discs with a photoresist thickness of about 40 nm(Registered trademark)For masters, etc., pattern exposure that causes absorption over the entire thickness of the resist by selecting an exposure light source and a photoresist having an absorption coefficient of about 10%, and exposes the surface of the master substrate after development. Can be performed.
[0064]
It should be noted that the bandwidth (FWHM) δλ of the ultrashort pulse laser beam is, for example, a pulse width δt of 100 fs and sech²Δλ · δt = 0.315 · λ for a Fourier transform limit pulse of the shape²/ C (c: speed of light) and δλ = 6.7 nm. Therefore, when using a high NA lens with NA of 0.5 or more, it is necessary to use an achromatic lens such as an achromatic lens used in a microscope or the like as the objective lens. Further, chromatic aberration occurs only in the refraction system, and the above problem can be avoided by using a condensing optical system using an aspheric concave mirror.
[0065]
In the present invention, the beam spot emitted from the condensing optical system and condensed on the resist is elongated in the beam scanning direction. As a result, the distribution of the amount of light to be irradiated is spread and averaged, and a linear pattern such as a groove can be easily obtained.
In order to make the beam spot into an ellipse, for example, the beam expander 5 described in FIG. 1 has an anamorphic optical system, that is, the beam diameter in the direction perpendicular to the beam scanning direction is further enlarged. Anything is acceptable.
Specifically, it is desirable to use a cylindrical lens, a cylindrical concave mirror, an anamorphic prism, or the like to make the ratio of the beam expansion ratio about several times.
[0066]
Further, as the modulation means for light intensity modulation described in FIG. 1 described above, an acoustic utilizing the fact that light is Bragg diffracted by an ultrasonic wave in an acousto-optic element driven by a piezoelectric element modulated by a recording information signal. An electro-optic modulation element using an optical effect or a Pockles effect modulated by a recording information signal is suitable.
[0067]
All optical elements such as the lens, wave plate, and optical modulator described above have positive group velocity dispersion, so they passed through even though the pulse width was adjusted to be minimal when the exposure light source was emitted. The ultrashort pulse laser beam is always chirped when irradiated to the photoresist of the optical recording medium master, and the pulse width is expanded.
[0068]
Therefore, as the chirp correction optical system 4 shown in FIG. 1, a chirp correction optical system having negative group velocity dispersion is used to give a negative chirp in advance to the ultrashort pulse light after being emitted from the exposure light source, thereby canceling this. Thus, it is necessary to obtain the shortest pulse on the resist. As the chirp correction optical system 4, a dispersion prism pair, a grating pair, or a chirp mirror can be used.
[0069]
The pulse width required for adjusting the pulse width can be measured by an autocorrelator using a conventional second harmonic generation method.
[0070]
[Example 1]
Next, an example of the optical recording medium master exposure apparatus of the present invention will be described with reference to FIG. In this example, an exposure light source 1 composed of a Ti: Sapphire ultrashort pulse laser light source, high-order harmonic generation means 2 using this ultrashort pulse laser as an excitation light source, and the high-order harmonic generation means 2 are emitted. A frequency-dividing optical system 15 that divides light, and a negative group velocity dispersion that corrects in advance positive group velocity dispersion experienced when a pulse output from the frequency-dividing optical system 15 passes through various optical components. A chirp correction optical system 4, a modulation means 3 as a modulation means for performing light intensity modulation by switching at high speed with an electrical pulse signal corresponding to supplied data, and modulation by the modulation means 3 A condensing optical system 9 and a beam expander 5 are provided for condensing the emitted light to a diffraction-limited spot size and irradiating it on an optical recording medium master 11 coated with a photoresist 12.
[0071]
  The ultra-short pulse laser light source has a repetition frequency of the aforementioned Blu-ray Disc.(Registered trademark)A Ti: Sapphire laser having a central frequency of 816 nm, a pulse width of 80 fs, and an average output of 0.8 W, that is, an ultrashort pulse laser using Ti: Sapphire as the laser medium 34 described with reference to FIG.
[0072]
  And the above figure3The second harmonic wave having a wavelength of 408 nm or the wavelength 272 is obtained using the high-order harmonic wave generation means 3 described in 1).nThe third harmonic of m was generated. In this example, a type I phase-matching LBO crystal is used as the nonlinear optical crystal 20 of the second harmonic generation unit 26 shown in FIG. The nonlinear optical crystal 24 of the third harmonic generation unit 28 is type I BBO. The various lenses 19a to 19d are arranged to increase the beam intensity in the crystal and improve the conversion efficiency. The second harmonic light had an average output of 300 mW and a pulse width (FWHM) of 100 fs, the third harmonic light had an average output of 60 mW and a pulse width of 120 fs with a pulse width of 1 ps or less.
[0073]
  As the frequency dividing optical system 15, the above-mentioned figure.5An optical system of ¼ frequency division provided with the frequency dividing circuits 60 and 70 described in the above was provided. By passing this frequency dividing optical system 15, it is possible to obtain an output with a repetition frequency of 528 MHz and an average power of 15 mW. In this embodiment, the pulse laser beam is used as a clock signal for recording information without providing an external synchronization mechanism. It was possible to perform pattern exposure with a good shape.
  In this case, in the first-stage frequency divider 60, the optical path difference is 1.1356 m, and the afocal lenses 62 and 65 have a focal length of 300 mm. In the second-stage frequency divider 70, the optical path difference is 0.5678 m, and the lenses 72 and 75 have a focal length of 160 mm. A half mirror was used for separating the pulsed light, and a 0th order half-wave plate for the second harmonic 408 nm and a polarizing beam splitter were used for multiplexing. The optical path length was adjusted by placing two reflecting mirrors on a stage with a micrometer. An ultrashort pulse laser was detected with a light speed photodetector having a band of 1.2 GHz and measured with a spectrum analyzer, and the center frequency was adjusted to be the narrowest at 528 MHz.
[0074]
As the chirp correction optical system 4, a Breswster prism pair was used.
The light is reflected at 90 ° by the mirror 1 a and sent to the modulation means 3. As the light intensity modulator of the modulation means 3, an electro-optic element EOM having a signal modulation band of 80 MHz was used. Although not shown, the modulation means 3 is supplied with a pit recording signal from a so-called formatter in which data recorded on the optical recording medium master generates an electrical pulse signal. Light is modulated according to this data.
[0075]
This light-modulated light is reflected by 90 [deg.] By the mirror 1b, and passes through the quarter-wave plate 7 via the beam expander 5 and the autofocus optical system 6 through, for example, a polarization beam splitter (hereinafter referred to as PBS) 6a. After 90 ° reflection at 1c, the light is transmitted through an objective lens 8a having a high numerical aperture NA and irradiated onto an optical recording medium master 11 on which a photoresist 12 has been applied in advance.
As the photoresist 12, for example, an i-line resist (such as JSR Corporation PFRIX 1110G) or a KrF laser mastering resist (such as Nippon Zeon Corporation DVR-100) can be used.
[0076]
At this time, the objective lens 8a uses incident light, for example, a lens having a high numerical aperture NA value corrected for aberration for the wavelength λ = 267 nm, and irradiates the focused beam to the diffraction limit. As the objective lens 8a, an achromatic objective lens made of synthetic quartz, meteorite, or the like whose material sufficiently transmits light in this wavelength region was used. The optical recording medium master 11 is fixed on a mounting table 10 that rotates in a direction indicated by an arrow a by a rotating means 13 such as a spindle motor.
[0077]
On the other hand, the high-order harmonic generation means 2 emits the third harmonic light having the wavelength λ = 272 nm and simultaneously emits the light having the second harmonic wavelength λ = 408 nm. The optical path of this light is also an optical path that passes through each optical element described above, and is applied to the optical recording medium master 11.
The return light reflected from the optical recording medium master 11 enters the PBS 6a through the objective lens 8a, the mirror 1c, and the quarter wavelength plate 7. Here, since the return light passes through the quarter-wave plate 7 twice, it is reflected by the PBS 6a. Thus, the PBS 6a of the autofocus optical system 6 sends the return light to the focus error amount detection element 6c via the wavelength selection element 6b. The wavelength selection element 6b is for blocking the exposure wavelength light by using a multilayer interference film or the like because the third harmonic light as the exposure wavelength is also reflected by the PBS 6a in a considerable amount.
[0078]
The focus error amount detection element 6c optically detects a positional deviation amount from the best focus position when the exposure light is focused on the optical recording medium master 11 using, for example, an astigmatism method. The detected amount is converted into an electric signal. The detected electrical signal is supplied to a drive control unit 6d that forms part of the autofocus servo system 6.
Here, the above-mentioned astigmatism method is a method in which a cylindrical lens is arranged behind the detection lens and the astigmatism is positively used and detected by a photodetector. Since this cylindrical lens has a lens action only in a single direction and has only the same action as a parallel plate in a direction perpendicular to this single direction, it converges at a position other than the focus position of the detection lens and this cylindrical lens. Instead, a focus error signal is detected by forming a thin beam image. By controlling the focus error signal to be zero, the focus of the objective lens is maintained at an optimum position.
[0079]
  Drive controller6dThen, based on the electrical signal, a drive signal for correcting the positional deviation is generated and output to the electromagnetic actuators 8b and 8c that finely move the objective lens 8a up and down. The electromagnetic actuators 8b and 8c move the objective lens 8a in the vertical direction indicated by the arrow b in response to the drive signal, that is, in the direction close to or away from the photoresist, thereby optimizing the focus position of the optical recording medium master 11. It is possible to perform exposure while automatically adjusting the position and suppressing loss.
[0080]
Here, for example, when a non-aberration lens having a numerical aperture NA = 0.9 is used as the objective lens with a laser beam spot size, the airy disc can be reduced to 0.36 μm. Therefore, exposure corresponding to a spot size of 0.36 × (1√2) ≈0.25 (μm) could be performed by generating a two-photon absorption process.
[0081]
At this time, as described above, the beam expander 5 is formed as an anamorphic optical system, so that the spot shape is enlarged and elongated in the beam scanning direction. Thus, the groove pattern could be exposed as a fine pattern.
[0082]
The laser beam thus formed is rotated and scanned on the optical recording medium master 11 by the rotating means 13, and at the same time, the optical system including the objective lens is moved in the radial direction from the center of the disk (the center of the master), so that the beam is spirally formed. Can be scanned on the master, and the photoresist can be exposed to form pits with high density.
The photoresist 12 may be a positive resist for g-line or i-line, in addition to the above-mentioned i-line. Since the exposure of the resist is photon mode recording, the exposure amount is determined by the integrated amount of photons per unit area even in the case of ultra-short pulse light with a high repetition frequency. According to the present invention, unlike the case of continuous light irradiation, the thermal mode is hardly involved. That is, it is possible to suppress unnecessary expansion of the resist due to temperature rise and change in reaction speed, and finer pits can be formed.
[0083]
In the first embodiment, the case where the center wavelength is 816 nm has been described. However, the Ti: Sapphire ultrashort pulse laser can oscillate from 760 nm, and in this case, the same means as described above (the center design wavelength needs to be all changed). Therefore, 380 nm second harmonic light and 253 nm third harmonic light can be used. However, since the efficiency is somewhat reduced, it is necessary to increase the output of the excitation green laser that excites the laser medium of the ultrashort pulse laser light source.
[0084]
Further, by adding a nonlinear optical crystal (for example, BBO) for sum frequency mixing, a fourth harmonic (wavelength near 200 nm) could be generated. In this case, as a beam spot size, an Airy spot of 0.28 μm was obtained using a non-aberration objective lens having a numerical aperture NA of 0.9. Therefore, exposure corresponding to a spot size of 0.28 × (1 / √2) ≈0.2 (μm) can be performed. In this case, a resist for KrF laser (wavelength 248 nm) or ArF laser (wavelength 192 nm) can be applied as a highly sensitive resist.
[0085]
  In the first embodiment described above, the third harmonic generation means is described as an example of the higher harmonic generation means.3Since the second harmonic generation unit and the sum frequency mixing unit are independently separated from each other in the high-order harmonic generation unit described in, the second harmonic can also be used as the exposure light source. In this case, the second harmonic generation has higher conversion efficiency than the third harmonic generation, and not only can high exposure power be obtained with the same laser power for excitation, but also the wavelength of the laser light is close to the visible light range, Various glass materials can be used, the lens design is easy, and the limitation of optical elements is reduced.
[0086]
[Example 2]
Next, a second embodiment according to the present invention will be described.
In this example, the configuration of the optical recording medium master exposure apparatus is exactly the same as that of the first embodiment, but in this example, the exposure light source has a repetition frequency of 66 MHz, a center wavelength of 816 nm, a pulse width of 80 fs, and an average output of 1.5 W. An ultrashort pulse laser source using Ti: Sapphire as the laser medium was used. In order to increase the laser power intensity of high-order harmonics, the focal length of the condensing lens in front of each nonlinear optical crystal is shortened, the beam spot diameter is reduced, and the wavelength conversion efficiency is increased.
[0087]
  And in this example, the dividing optical system15, only the divide-by-2 optical circuit was used. That is, the previous figure5Only the frequency dividing circuit 60 described in the above item is provided between the high-order harmonic generation means 2 and the chirp correction optical system 4. The optical path difference of the frequency dividing circuit 60 is set to 2.2712 m, and the focal lengths of the afocal lenses 62 and 65 are 600 mm. A half mirror was used for separation of the pulse beam, and a zero-order half-wave plate for the third harmonic 267 nm and a polarizing beam splitter were used for multiplexing.
[0088]
When irradiating a photoresist for ArF laser, for example, a fluororesin resist, for example, as a photoresist, using an ultrashort pulse light of 130 fs having a wavelength of 272 nm and a pulse width of 1 ps or less emitted from the third harmonic generation unit 28, The light intensity in the beam spot on the resist surface is 100 GW / cm at the peak output²In addition, two-photon absorption remarkably occurred and several percent absorption, that is, a photoreaction which is a resist exposure process was allowed to proceed. In this example, a non-aberration objective lens with NA = 0.9 is used as the objective lens, and an Airy spot of 0.36 μm can be obtained. By generating a two-photon absorption process, 0.36 × (1 √2) = Expiration with an Airy spot size of 0.25 μm could be performed.
[0089]
Resist exposure is given by the square of the intensity distribution of the beam spot. In the above resist, normal absorption does not occur because it is transparent to light with a wavelength of 272 nm. Only the two-photon absorption process occurs locally only in places where the intensity distribution is high. This can be replaced by a resist for ArF laser (193 nm) (for example, ZERF Corporation ZARF001) or a KrF laser resist (for example, JSR Corporation KRFM89Y).
[0090]
Also in this case, by making the beam expander 5 an anamorphic optical system, the groove width is made larger than that of the prior art by enlarging the beam expander 5 in the beam scanning direction into an elliptical spot shape. The groove pattern could be exposed as a fine pattern.
[0091]
  Further, in this example, the second harmonic generation unit and the sum frequency mixing unit are separately separated from each other as the high-order harmonic generation unit.3The second harmonic (wavelength 403 nm) can also be used as the exposure light source. In this case, it is desirable to use a photoresist for KrF (wavelength 248 nm) or i-line (wavelength 365 nm) as the photoresist used.
[0092]
Since the two-photon absorption cross-sectional area is a very small value, an organic dye having a high two-photon absorption cross-sectional area added to the resist as a sensitizer can be used in order to increase the sensitivity of the resist. In addition to the same advantages as in the case of Example 1, the range of applicable photoresist selections is expanded.
[0093]
In the first embodiment described above, the repetition frequency of the ultrashort pulse laser is set to be twice the frequency of the clock signal of the recording information, and further, by providing a divide-by-4 optical system, the repetition frequency of the pulse is set to the frequency of the clock signal. As a result, pattern exposure could be performed with a good shape without providing an external synchronization mechanism.
On the other hand, in Embodiment 2 described above, the repetition frequency of the ultrashort pulse laser is set to one time the frequency of the clock signal of the recording information, and the frequency dividing optical system is a frequency dividing optical system, whereby the clock of the recording information is obtained. By obtaining a pulsed laser beam having a frequency twice that of the signal and synchronizing the exposure pulse with the clock signal by an external synchronization mechanism in this case, the pattern exposure can be performed with a good shape.
[0094]
On the other hand, if the repetition frequency is too high, the peak output is lowered, it becomes difficult to generate two-photon absorption, and pattern exposure with high resolution cannot be performed. Therefore, at present, the upper limit is about 20 times the clock signal of the recording information of the optical recording medium to be exposed, so that it is possible to surely expose a fine pattern.
[0095]
In the above-described embodiment and each example, the Ti: Sapphire ultrashort pulse laser is taken as an example of the light source means, but various other ultrashort pulse laser light sources can be used.
For example, an Nd: Vanadete ultrashort pulse laser can be pumped with a semiconductor laser, and a laser with a center wavelength of 1064 nm, a pulse width of 7 ps, an average output number W and a repetition frequency of 25 MHz to 1 GHz using a semiconductor saturable absorption mirror (SESAM) is commercially available. Yes. A center wavelength of 917 nm is also available. Nd: YAG, Nd: YLF, or the like can also be used as the laser medium. Further, in an ultrashort pulse laser using a solid laser medium such as Cr: LiSAF or Nd: Glass, the pulse width is 100 fs or less, and the center wavelengths are 850 nm and 1058 nm.
[0096]
In addition, the higher harmonic generation means includes sum frequency mixing, second harmonic generation, fourth harmonic generation, etc., and nonlinear crystal optical elements include KDP, KTP, LN, and their periodic polarization inversion in addition to BBO. Type KTP (PPKTP), PPLN, LBO, LiIO_ThreeAnd CBO.
[0097]
Further, the exposure of minute pits and grooves has been described above as an example. However, since it can be handled in the same manner as the conventional continuous light source, not only the formation of minute pits and grooves but also the acousto-optic effect or Pockels A wobbling address can be similarly formed using an optical deflector utilizing the effect.
[0098]
Furthermore, the present invention is not limited to an exposure apparatus and exposure method for a disk-shaped optical recording medium master, and an XY linear scanning system using a high-precision linear actuator instead of the rotating means 13 shown in FIG. In addition to these laser drawing apparatuses and these rotation systems and XY linear scanning systems, the present invention is also applied to a three-dimensional microfabrication apparatus provided with a z-direction slide mechanism.
[0099]
【The invention's effect】
In the optical recording medium master exposure apparatus and optical recording medium exposure method according to the present invention, the ultrashort pulse laser beam output from the exposure light source or the short wavelength output from the high-order harmonic generation means using this as an excitation light source. By adjusting the pulse repetition frequency using the frequency division optical system or the frequency division optical system and an external synchronization mechanism in accordance with the clock frequency of the information signal recorded on the optical recording medium, the ultrashort pulse laser light It is possible to perform pattern exposure with a good shape corresponding to the signal, and to obtain an optical recording medium in which the jitter of the reproduction signal is suppressed to about 10% or less. In particular, a two-photon absorption process is generated by using a pulse laser having a shorter wavelength by means of higher-order harmonic generation means, and pattern exposure such as fine pits of about 0.25 μm or less is performed with high accuracy compared to the prior art. It can be carried out.
[0100]
Further, in the present invention, the frequency dividing optical system is composed of a polarizing beam splitter and an optical delay circuit, and this frequency dividing optical system is provided in the subsequent stage of the light source composed of an ultrashort pulse laser, thereby reducing power loss and high efficiency. This makes it possible to use an effective laser beam.
In addition, when high-order harmonic generation means is provided, this frequency-dividing optical system is provided at the subsequent stage, so that high-order harmonic generation means has a laser beam with a relatively high peak output from the ultrashort pulse laser. And the peak output of the pulsed laser light finally obtained as the exposure light can be secured.
[0101]
Also, the pulse width of the ultrashort pulse laser is 1 × 10^-12By setting it to 2 seconds or less, the two-photon absorption process can be generated more efficiently, and finer pits can be formed below the diffraction limit of the wavelength of the exposure light source.
[0102]
Furthermore, in the present invention, by making the beam spot of the laser beam irradiated onto the optical recording medium master disk into an oval shape, the pattern signal extending in the scanning direction of the groove or the like can be subjected to pattern exposure with a good shape. Can do.
[0103]
According to the present invention, since the far field optical system can be adopted instead of the near field optical system using the high numerical aperture SIL as described above, the working distance can be sufficiently widened and the rotation at the time of exposure can be ensured. By increasing the number, productivity can be significantly improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an example of an optical recording medium master disc exposure apparatus.
[Figure 2]A is a schematic explanatory view of a pulse waveform of an ultrashort pulse laser beam. B is a schematic explanatory diagram of the waveform of the information signal and the pulse waveform of the ultrashort pulse laser beam. C is a schematic explanatory view of a pulse waveform of a clock signal.
[Fig. 3]It is a typical block diagram of an example of a high order harmonic generation means.
FIG. 4 is an explanatory diagram of an external synchronization mechanism.
[Figure 5]FIG. 2A is a schematic configuration diagram of an example of a frequency dividing optical system. B is an explanatory view of a schematic waveform of an example of a pulse train.
FIG. 6 is a diagram showing the amount of airy spot absorption in a photoresist.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Exposure light source, 1a ... Mirror, 1b ... Mirror, 1c ... Mirror, 2 ... Higher harmonic generation means, 3 ... Modulation means, 4 ... Chirp correction optical system, 5 ... Beam expander, 6 ... Auto focus optical system , 6a ... polarization beam splitter, 6b ... wavelength selection element, 6c ... focus error amount detection element, 6d ... drive control unit, 7 ... quarter wave plate, 8a ... objective lens, 8b ..., electromagnetic actuator, 8c ... electromagnetic actuator , 9 ... Condensing optical system, 10 ... Mounting table, 11 ... Optical recording medium master, 12 ... Photoresist, 13 ... Rotating means, 15 ... Frequency dividing optical system, 19a ... Lens, 19b ... Lens, 19c ... Lens, 19d ... Lens, 20 ... Nonlinear optical crystal, 21a ... Harmonic separator, 21b ... Harmonic separator, 21c ... Harmonic separator, 21d ... -Monic separator, 22a ... high reflection mirror, 22b ... high reflection mirror, 22c ... high reflection mirror, 22d ... high reflection mirror, 23 ... 1/2 wavelength plate (HWP), 24 ... nonlinear optical crystal, 25 ... beam stopper, 26: Second harmonic (SHG) generating unit, 27: Delay line unit, 28: Third harmonic (THG) generating unit, 31: Lens, 32: Spherical mirror, 33: Spherical mirror, 34: Laser medium, 35 ... high reflection mirror, 36a ... dispersion compensation prism, 36b ... dispersion compensation prism, 37 ... slit, 38 ... high reflection mirror, 39 ... output window, 40 ... beam splitter, 41 ... photodetector, 46 ... piezo element, 60 ... Frequency divider, 61 ... beam splitter, 62 ... lens, 63 ... mirror, 64 ... mirror, 65 ... lens, 66 ... 1/2 wavelength plate, 67 ... polarizing beam sp Ritter, 70 ... frequency divider, 71 ... beam splitter, 72 ... lens, 73 ... mirror, 74 ... mirror, 75 ... lens, 76 ... half-wave plate, 77 ... polarization beam splitter

Claims (14)

There are provided modulation means for modulating the light intensity from the exposure light source corresponding to the record information, and a condensing optical system for condensing the light modulated by the modulation means on the photoresist on the optical recording medium master. An optical recording medium master exposure apparatus that pattern-exposes the photoresist in accordance with the recording information,
The exposure light source comprises an ultrashort pulse laser having a repetition frequency of 1 to 20 times the clock frequency of the recording information,
An optical recording medium master exposure apparatus, comprising a frequency division optical system for dividing a laser beam emitted from the ultrashort pulse laser. The repetition frequency of the ultrashort pulse laser is an integer multiple of 1 to 20 times the clock frequency of the recording information,
The resonator length of the ultrashort pulse laser is variable, and an external synchronization mechanism is provided that performs pulse locking by mode-locking the repetition frequency of the ultrashort pulse laser in synchronization with the clock frequency. Item 4. The optical recording medium master exposure apparatus according to Item 1. Between the exposure light source and the frequency dividing optical system, there is provided high-order harmonic generation means for emitting light having a wavelength shortened by wavelength conversion using a nonlinear optical element using the ultrashort pulse laser light source as an excitation light source. optical recording medium master exposure apparatus according to claim 1 or 2, characterized in that it is. 3. The optical recording medium master disc exposure apparatus according to claim 1, wherein the frequency dividing optical system includes a polarization beam splitter and an optical delay circuit. 4. The optical recording medium master disc exposure apparatus according to claim 3 , wherein the frequency dividing optical system includes a polarization beam splitter and an optical delay circuit. The optical recording medium master disk exposure apparatus according to claim 1 or 2 , wherein the exposure of the photoresist is performed by a two-photon absorption process. 4. The optical recording medium master exposure apparatus according to claim 3 , wherein the exposure of the photoresist is performed by a two-photon absorption process. 7. The optical recording medium master disc exposure apparatus according to claim 6 , wherein a pulse width of the exposure light source is 1 × 10 ⁻¹² seconds or less. 8. The optical recording medium master exposure apparatus according to claim 7 , wherein a pulse width of the exposure light source is 1 × 10 ⁻¹² seconds or less. Is emitted from the light converging optical system, the spot shape of said photoresist is focused laser beam, according to claim 6, characterized in that are oblong shape extending in the scanning direction of the laser beam Optical recording medium master exposure apparatus. Is emitted from the light converging optical system, the spot shape of said photoresist is focused laser beam, according to claim 7, characterized in that are oblong shape extending in the scanning direction of the laser beam Optical recording medium master exposure apparatus. The light from the exposure light source is subjected to light intensity modulation corresponding to the recording information, the light modulated by the modulating means is condensed on the photoresist on the optical recording medium master, and the photoresist is used as the recording information. An exposure method for an optical recording medium master that performs pattern exposure according to the method,
The exposure light source comprises an ultrashort pulse laser having a repetition frequency of 1 to 20 times the clock frequency of the recording information;
An exposure method for an optical recording medium master, comprising a frequency division optical system for dividing a laser beam emitted from the ultrashort pulse laser. The repetition frequency of the ultrashort pulse laser is an integer multiple of 1 to 20 times the clock frequency of the recording information,
The ultrasonic resonator length of the short pulse laser to provide a external synchronization mechanism for varying the repetition frequency of the ultrashort pulse laser with mode locking in synchronization with the clock frequency, claim 12, characterized in that to pulsed An exposure method for an optical recording medium master as described in 1. The light emitted from the exposure light source is made to have a short wavelength by wavelength conversion using a non-linear optical element by the high-order harmonic generation means using the exposure light source as an excitation light source, and is incident on the frequency dividing optical system. 14. An exposure method for an optical recording medium master according to claim 12 or 13 .

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