JP2004265519A - Method of manufacturing optical disk substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that it is required for recording a micro mark to make an optical spot micro because a resist conventionally used in a process to manufacture an optical disk substrate had a reactivity almost proportional to the strength distribution of exposure light spot, and even though there is an optical super-resolution technology therefor, a side lobe is formed outside a main spot and the resist is exposed by the side lobe. <P>SOLUTION: A material having high linear reactivity against a temperature is used as a resist or a mask and a pattern is created with heat generated by absorbing an incident light. A portion in which the temperature becomes not lower than a reaction threshold reacts and a recording pattern can be made smaller. By combining a sample using such material with the optical super-resolution technology, recording with the side lobe by the optical super-resolution can be suppressed and the size of the optical spot can be reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk manufacturing technique, and particularly to an apparatus and a manufacturing method for manufacturing a substrate using laser light.
[0002]
[Prior art]
Optical discs are broadly classified into read-only (ROM), write-once (WORM), and rewritable (rewritable memory or random access memory) RAMs, depending on the application. Among them, the ROM has holes (pits) formed on the substrate corresponding to the recording data. In WORM and RAM, a groove (groove groove) corresponding to a track is formed on the substrate, and user data is recorded along the groove. In addition to grooves, WORM and RAM are provided with pits indicating information such as the characteristics of the disk and address information.
[0003]
A disk substrate having pits and grooves as described above is generally manufactured by the following process; 1. apply a photosensitive resist to a glass substrate; 2. The substrate is rotated, and a laser beam focused by an objective lens is incident on the substrate to expose the resist. 3. develop the substrate to form a pattern; Ni plating is performed, and the resultant is used as a mold. The molten polycarbonate is poured into the mold to prepare a mold. An apparatus for exposing with laser light is called a cutting apparatus.
[0004]
In the above item 2, when forming a groove, the incident laser light is DC light, and when forming a pit, pulse light under appropriate conditions is used. The conditions are optimized in consideration of the photosensitivity of the resist and the like.
[0005]
In the resist used in the above process, most of the region irradiated with light undergoes a photoreaction, so that it is necessary to reduce the spot size of incident light in order to form a small pattern. The diameter of the spot when condensed is approximately equal to λ / NA, where λ is the light wavelength and NA is the numerical aperture of the objective lens. Therefore, in order to reduce the spot, it is necessary to shorten the wavelength and / or increase the NA. As a next-generation optical disk, a method of recording a capacity of 20 to 30 GB on a disk having a diameter of 120 mm is being studied. To realize this capacity, the shortest mark length needs to be about 0.15 to 0.2 mm and the track pitch needs to be about 0.3 to 0.35 mm. In order to produce a pit of this size, the light wavelength is set to 250 to 270 nm and the NA is set to about 0.9.
[0006]
On the other hand, phase change recording is considered as a rewritable medium. Phase change recording is a mark that uses a phenomenon in which a part of the recording film is melted by the heat generated by absorbing the incident laser light and becomes amorphous in the process of rapidly cooling, when the recording film is initially in a crystalline state. Is a method of recording. This method is used in, for example, a CD-RW, a DVD-RAM, a DVD-RW, and a DVD + RW, and recording is performed by a drive similarly to reproduction. For the next-generation drive, use of a blue-violet laser having a wavelength of 400 to 410 nm and an objective lens having an NA of 0.65 to 0.85 is being studied.
[0007]
The above is summarized in FIG. FIG. 2A shows an example of a cutting device. When the resist having the reaction threshold value 22 is exposed to the light spot of the intensity profile 21, a mark having a mark size 24 with respect to the light spot size 23 is recorded. On the other hand, the case where the reaction threshold is high, such as a phase change record, is shown in FIG. As described above, since the light spot of the drive is larger than that of the cutting device, the size of the intensity profile 25 is large, but since the threshold 26 is high, a mark having a large light spot size 27 and a size substantially equal to the mark size 24 is obtained. 28 are recorded.
[0008]
Further, an optical super-resolution technique for reducing a spot size by shielding a part of an objective lens from light is reported in, for example, Applied Optics Vol. 29, pp. 3046 to 3051 (1990). In this method, a part of the optical path of the incident optical system is shielded by a mask, and the light spot size is reduced by utilizing the interference effect of light passing through the mask. As a result, the intensity profile of the light spot becomes as shown in FIG. The main spot 34 is smaller than the normal light spot profile 31 shown in FIG. At the same time, a side lobe 35 is generated in the light spot shown in FIG.
[0009]
[Problems to be solved by the invention]
As described above, in the current cutting apparatus, the density of the recording data is increased by shortening the wavelength and increasing the NA, but λ / NA is about 280 to 290 nm, which is larger than the recording mark. On the other hand, the reactivity of the photosensitive resist is almost proportional to the amount of light exposed, so that a margin for producing a substrate for a next-generation optical disk with this spot size was very small. Even when the apparatus and exposure conditions were adjusted in detail, the jitter was 9% or more when a ROM substrate having a diameter of 120 mm and a capacity equivalent to 25 GB was manufactured and measured. On the other hand, when phase change recording of the same capacity is performed using a drive having a light source wavelength of 400 nm and an objective lens NA of 0.85, the jitter is about 7% even though λ / NA is about 1.6 times. Met.
[0010]
In optical super-resolution, side lobes occur as described above. In normal exposure, as shown in FIG. 3A, a mark having a size 33 determined by the reaction threshold value 32 of the resist is recorded. In the optical super-resolution, as shown in FIG. 3B, a mark 37 formed by the main spot 34 and a mark 38 formed by the side lobe 35 are formed. In order not to form the mark 38, the height of the side lobe 35 needs to be smaller than the reaction threshold value 36 of the resist. For this purpose, the recording laser power must be reduced or the intensity ratio between the main spot 34 and the side lobe 35 in the light spot profile must be increased. However, when the laser power is reduced, the amount of exposure is reduced, so that the reaction of the resist does not sufficiently proceed due to the limitation of the sensitivity of the resist, and a pattern is not formed. Also, since the size of the main spot and the side lobe intensity are in a trade-off relationship, if the intensity ratio between the main spot and the side lobe is increased, the size of the main spot will eventually increase, reducing the effect of optical super-resolution. This makes it impossible to increase the density of recording data. For these reasons, it has not been possible to use optical super-resolution techniques in drives and cutting devices.
[0011]
[Means for Solving the Problems]
In order to record marks with a reproducibility smaller than the ratio of the light source wavelength λ of the cutting device to the NA of the objective lens λ / NA, it is necessary to use a substance whose reactivity to exposure shows a large nonlinearity to the intensity of the irradiated light. Used as a resist or mask. As described in the above-mentioned problem, in the phase change recording, a mark smaller than λ / NA can be recorded with good reproducibility, because a mark having a high intensity in the intensity profile of the irradiated light spot is used. This is because the recording film melts and the mark size becomes equal to or smaller than that. Usually, a resist used for exposure also has non-linearity, but the non-linearity is so small that a small mark cannot be recorded.
[0012]
One of the measures is to use a material exhibiting non-linear chemical reactivity with temperature as a resist. For example, Au ₂ O ₃ releases oxygen at a temperature of 250 ° C. to become Au. Therefore, when Au ₂ O ₃ is formed on a substrate and laser light is incident thereon, heat is generated by light absorption. When light of appropriate power is incident, a part of the incident light spot becomes 250 ° C. or higher, As shown in FIG. 2B, Au is a region smaller in size than the light spot. Since Au ₂ O ₃ and Au have different reactivities to acids and alkalis, it is possible to dissolve one of Au ₂ O _{3 and} Au and leave the other pattern by developing with an appropriate chemical. As such a material, PtO and Ag ₂ O can be used in addition to Au ₂ O ₃ .
[0013]
In addition, a material that oxidizes at a certain temperature or higher with the same configuration and principle as described above can be used as the resist. Such materials include Si, Fe, Zn, Mn, W, and Ru.
[0014]
FIG. 4 shows a table summarizing the reaction temperature, the substance after the reaction, the example of the developer, and the substance of the pattern remaining after the development for the above materials.
[0015]
In the above-mentioned method, the above-mentioned material or a substance reacted with the above-mentioned material remains as a pattern. This pattern itself may be used as a groove or a pit, and the pattern may be used as a mask for reactive ion etching (RIE). It is also possible to form a concavo-convex pattern by performing the treatment.
[0016]
As another method of recording a mark smaller than the light spot, a method of exposing a material using a material showing a remarkable change in refractive index with temperature as a mask can be considered. For example, a resist is applied on a substrate, and a metal or semiconductor mask film is formed thereon. Laser light is incident on the sample, and the mask film absorbs the light to generate heat, thereby changing the refractive index. Here, for example, if the sample is manufactured so that the transmittance of the light in the region where the temperature is increased is high, the light is transmitted through a part of the light spot and the resist is exposed. The threshold and the transmittance depend on exposure conditions such as the material and thickness of the mask film and the power of incident light. As such a mask material, for example, a composite material used for a phase change recording film, such as Sb, Te, In, Sn, Se, or GeSbTe or AgInSbTe, can be considered. FIG. 5 shows the melting points of these materials. When these materials melt, the transmittance increases. Under appropriate conditions, the incident laser light melts some areas within the light spot and exposes the resist.
[0017]
The refractive index changes of these materials are all reversible. Although it is possible in principle to use a substance showing an irreversible change as the mask layer, in this case, after exposing a certain track, exposing the adjacent track, the transmittance of the previously exposed track becomes high. As a result, the track is exposed again, that is, cross-light occurs, so that it is impossible to reduce the track pitch.
[0018]
By combining the above-described method using the non-linear mask and the optical super-resolution technique, it is possible to further increase the data density. FIG. 1 shows an explanatory diagram. If the response threshold 12 of the resist is higher than the side lobe 15 as in (b), the side lobe does not contribute to the exposure, and the main spot 14 is smaller than the normal spot 11. The mark 16 formed is smaller than the mark 13 formed by the normal light spot 11. With this effect, a further increase in capacity can be achieved.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
(First form)
An embodiment of the present invention will be described. Here, a case where Au ₂ O ₃ is used as a resist will be described. An explanatory diagram of the process is shown in FIG. As shown in (a), Au is sputtered in an Ar gas containing oxygen on a glass substrate 62 to form an Au ₂ O ₃ film 61. Here, the thickness of Au ₂ O ₃ was about 20 nm. Next, as shown in (b), a laser beam is irradiated, and the heat generated thereby forms an Au mark array 63 in the Au ₂ O ₃ film.
[0020]
In the cutting device, in order to utilize the optical super-resolution effect, a central portion of a parallel light beam having a diameter of about 4 mm incident on the objective lens was shielded by a circle having a diameter of 2 mm. Cr was used for the light-shielding mask. At this time, the diameter of the main spot was 80% as compared with the case where no light was shielded, and the intensity ratio between the main spot and the lobe was about 5: 1 again. The wavelength of the light source of the cutting device is 260 nm, and the numerical aperture (NA) of the objective lens is 0.9.
[0021]
At the time of recording, a recording waveform composed of a train of laser pulses shorter than at least the mark length as used in phase change recording was used. The reason is that mark recording uses a phenomenon in which reactivity is developed depending on temperature, and therefore, it is necessary to improve the quality of recorded marks by controlling the temperature distribution in the Au ₂ O ₃ film at the time of recording. It is. FIG. 7 shows examples of recording waveforms of the 2 Tw mark and the 5 Tw mark. As shown, the nTw mark was recorded with n-1 laser pulses. The power levels P1, P2, and P3 of the laser pulse train were defined as shown in the figure. Regarding the pulse length, the length of the first pulse was defined as tfp, and the lengths of the P1 level and P2 level of the multi-pulse portion were defined as tp1 and tp2, respectively. Here, the length of Tw is 0.075 μm, the track pitch is 0.32 μm, tfp = tp1 = tp2 = Tw / 2, P1 = 4 mW, and P2 = P3 = 0.5 mW. Under these conditions, a recording capacity of about 25 GB can be achieved with a disc having a diameter of 120 mm. At the time of recording, the disk linear velocity was 3 m / s.
[0022]
The substrate after the processing of FIG. 6B was immersed in hydrochloric acid to dissolve Au ₂ O ₃ , leaving only the Au pattern as shown in FIG. 6C. This was subjected to a reactive ion etching (RIE) process using C ₂ F ₆ gas to etch the glass substrate 62. At this time, Au is also etched by RIE, but since the etching rate is much slower than the etching rate of the glass substrate, Au can be used as a mask to form a pattern as shown in FIG. By optimizing the RIE conditions, a pit having a desired depth can be produced. Here, a pit having a depth of 80 nm was formed. The substrate thus produced was used as a master for producing the substrate.
[0023]
An Ag alloy was sputtered onto a polycarbonate substrate prepared from the master of (d), and a disk having a 0.1 mm-thick polycarbonate sheet attached thereto was evaluated with a disk evaluation machine having a light source wavelength of 400 nm and an objective lens NA of 0.85. When reproduced at a linear velocity of 4.92 m / s, about 4.5% jitter was obtained.
[0024]
Further, by using the above-described method and the above-described cutting apparatus, recording was performed at a Tw length of 0.05 μm and a track pitch of 0.24 μm to prepare a substrate. This substrate was reproduced by the same disk evaluation machine as above, and the error rate was measured using PRML (Partial Response Most Likelihood) signal processing. The error rate was about 10 ⁻⁶ without error correction processing, which was a practical level. Was confirmed. Under these conditions, a recording capacity of about 50 GB can be achieved with a disc having a diameter of 120 mm.
[0025]
Next, exposure was performed with a Tw length of 0.04 μm and a track pitch of 0.2 μm. This condition corresponds to a capacity of about 75 GB for a disc having a diameter of 120 mm. Exposure conditions are the same as those described above. When the fluctuation of the edge of the mark was measured by an atomic force microscope (AFM), the ratio of the standard deviation of the fluctuation to Tw (corresponding to the jitter) was about 7.2%.
[0026]
(2nd form)
Here, the process of dissolving Au ₂ O ₃ with hydrochloric acid in the first embodiment is omitted. Au and Au ₂ O ₃ are both etched by RIE using C ₂ F ₆ gas, but Au ₂ O _{3 has} a higher etch rate. Therefore, the Au pattern remains while the entire Au ₂ O ₃ portion is etched to SiO ₂ . Since the etch rate of SiO ₂ is very large, the etching proceeds very quickly after Au ₂ O ₃ is completely etched. Therefore, if the thickness of Au ₂ O ₃ is appropriately set, a pit having an appropriate depth can be manufactured. This can reduce the process by one step, making mastering easier.
[0027]
Here, the thickness of Au ₂ O ₃ was 30 nm, and P1 was 7 mW. Other conditions are the same as those of the first embodiment. After the exposure, an RIE process was performed to produce pits having a depth of 80 nm. When the substrate exposed under the conditions corresponding to the capacity of 25 GB was measured under the same conditions as in the first embodiment, the jitter was about 4.9%.
[0028]
(Third form)
An example in which PtO ₂ , Ag ₂ O, and MoO ₃ are used as a resist will be described. Each of the above materials was sputtered on a glass substrate. All film thicknesses were about 20 nm. P1 was 8.5 mW for PtO ₂ , 3 mW for Ag ₂ O, and 4.8 mW for MoO ₃ . After the exposure, each sample was immersed in the liquid shown in FIG. 4 to leave a pattern of Pt, Ag, and MoO ₃ respectively. Using the sample as a master, a disk substrate was produced. Other conditions were the same as those of the first embodiment. When the disc was reproduced under the same conditions as in the first embodiment, the jitter at the mark size of 25 GB capacity described in the first embodiment was 4.4% for PtO ₂ , 4.9% for Ag ₂ O, and MoO ₃ Was 5.2%.
[0029]
(4th form)
An example using Al, Sn, Se, Te, Sb, Si, W, and Ru as a resist will be described. Each of the above materials was sputtered on a glass substrate. All film thicknesses were 20 nm. After the exposure, each sample was immersed in the liquid shown in FIG. 4 to form a pattern. Using the sample as a master, a disk substrate was produced. Except for the condition of the exposure power P1, it was the same as that of the first embodiment. The mark size was set so that the capacity of a 120 mm disk described in the first embodiment was 25 GB. The disc was reproduced under the same conditions as in the first embodiment. FIG. 8 shows the value of P1 for each material and the value of jitter obtained as a result of reproduction. It can be seen that practical jitter values were obtained for all the materials.
[0030]
(Fifth form)
The case where Sb, Te, In, Sn, Se, and Sb ₇ Te ₃ are used will be described. FIG. 9 is an explanatory diagram of a process when these materials are used. The state of the sample before exposure is (a). A resist 93 is applied on a glass substrate 94 by a spin coater, and a mask layer 92 and a protective film 91 are formed thereon by sputtering. Here, the resist 93 is a normal organic resist material that reacts by light absorption. The protective film 91 is necessary to prevent the mask layer 92 from being oxidized. This sample is exposed by a cutting device as shown in FIG. The laser beam spot scans in the direction of the arrow in FIG. Although the transmittance of the mask material 92 is substantially 0% at room temperature, a part of the mask layer is melted by the incidence of the laser beam, and a high transmittance region 95 is generated. Therefore, the resist 93 is exposed only at the position where the laser pulse is applied, and an exposure pattern 96 is formed. (C) After dissolving the protective film 91 and the mask layer 92 as shown in (d), the exposed resist is developed to obtain the concavo-convex pattern (e).
[0031]
The structure of the actually manufactured sample was glass substrate / resist (80 nm) / mask material (40 nm) / SiO ₂ (40 nm). As in the first embodiment, the specifications of the cutting device were a wavelength of 260 nm and an NA of the objective lens of 0.9. The same recording waveform as that of the first embodiment was used. However, only the recording power P1 was optimized by the material. The mark size was the condition for the capacity of 25 GB described in the first embodiment. A disk substrate was manufactured using the sample of FIG. 9E as a master.
[0032]
FIG. 10 shows the P1 value of each material and the jitter value obtained by reproducing the disk substrate. Practical jitter values were obtained for all materials.
[0033]
【The invention's effect】
The optical super-resolution technique can be used for a drive or a cutting device, and high density of recorded data can be achieved.
[0034]
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of reduction of a recording mark by a combination of optical super-resolution and a nonlinear resist or a nonlinear mask. (A) When a non-linear resist or non-linear mask is used, (b) When optical super-resolution is used in combination with (a).
FIG. 2 shows a light spot size and a recording mark size when a cutting device and an optical disk drive are used. (A) Cutting device, (b) Optical disk drive.
FIG. 3 is a recording mark when optical super-resolution is used in the related art. (A) Conventional technology, (b) A case where recording is performed on a conventional resist using optical super-resolution.
FIG. 4 shows a nonlinear resist material and its characteristics.
FIG. 5 shows a nonlinear mask material and its melting point.
FIG. 6 is an explanatory diagram of a process when a non-linear resist is used.
FIG. 7 is a recording laser waveform according to the present invention.
FIG. 8 shows a laser recording power P1 for each nonlinear resist material and a jitter value when a recording mark is reproduced.
FIG. 9 is an explanatory diagram of a process when a non-linear mask is used.
FIG. 10 shows a laser recording power P1 for each nonlinear resist material and a jitter value when a recording mark is reproduced.
[Explanation of symbols]
11: intensity distribution of a light spot in the prior art, 12: reaction threshold value of a non-linear resist or a non-linear mask, 13: recording mark when a non-linear resist or a non-linear mask is used in the prior art, 14: main spot in optical super-resolution, 15: side lobe in optical super-resolution, 16: recording mark when optical super-resolution and non-linear resist or non-linear mask are used,
21: Intensity distribution of light spot in cutting device, 22: Response threshold of conventional resist, 23: Light spot size of cutting device, 24: Mark recorded by cutting device, 25: Intensity distribution of light spot of optical disk drive, 26 : Response threshold of the recording film of the medium to be recorded by the optical disk drive; 27: optical spot size of the optical disk drive; 28: mark recorded by the optical disk drive;
31: intensity distribution of the light spot of the conventional cutting device, 32: reaction threshold value of the conventional resist, 33: mark recorded by the conventional cutting device, 34: light spot of the optical spot when the optical super-resolution is used for the cutting device Main spot, 35: side lobe in optical super-resolution, 36: response threshold of non-linear resist or non-linear mask, 37: mark recorded in main spot, 38: part recorded in side lobe,
61: nonlinear resist, 62: substrate, 63: exposed portion in nonlinear resist,
91: protective film, 92: non-linear mask layer, 93: resist, 94: substrate, 95: high transmittance region in the non-linear mask, 96: exposed portion in the resist.

Claims (1)

In an optical disk substrate manufacturing method for manufacturing an optical disk substrate by making a focused laser beam incident, a part of the light incident on the objective lens of the cutting device is shielded, and the sample to be exposed is
A thin film of at least one kind of oxide of Au, Pt, Ag, and Mo;
Or / and at least one thin film of Al, Sn, Se, Te, Sb, Si, W, Ru
And / or a method for producing an optical disk substrate, comprising a thin film of Sb, Te, In, Sn, Se or a composite material of the above materials.

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