JP2005353255A - Optical information recording medium, exposure method of master plate for information recording medium, stamper for information recording medium and substrate for information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform multi-valued recording to have large capacity without being limited by the size of a light spot for recording and to obtain stable tracking characteristics. <P>SOLUTION: Cells 22 each having a fixed area are continuously formed in a track 21 of an optical information recording medium 20 such as an optical disk, an uneven multi-valued data pattern 10 is formed at a center part of each cell 22 and uneven patterns 11 for tracking are formed at four corners of each cell 22. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical information recording medium such as an optical disc, an exposure method for a master for the information recording medium, an information recording medium stamper, and an information recording medium substrate.

  Conventionally, in an optical disk, binary digital data is formed on a spiral or concentric track by forming embossed uneven pits (ROM disk) or holes in an inorganic / organic recording film (recordable disk). , Recorded due to the difference in crystal state (phase change disc).

  When reproducing these recorded data, a track is irradiated with a laser beam to detect a difference in intensity of the reflected light and obtain a reproduction signal. Then, the obtained reproduction signal is judged based on, for example, a certain threshold value, and binary data is detected.

  ROM disks, such as CDs, CD-ROMs, DVD-ROMs, etc., can be produced in large quantities at low cost by transferring uneven pits formed on the master to a molding plate and used for distribution. The

  The concave and convex pits of the master are formed by forming a resist on a glass substrate or the like, irradiating this with a laser beam to form a latent image, and developing. The write-once disc or phase change disc is guided from a master disc in which guide grooves for tracking are formed in the same way as a ROM disc, such as CD-R, CD-RW, DVD-R, DVD + RW, etc. A groove or the like is transferred to a molding plate, and a recording material such as an inorganic / organic recording film is formed thereon, and information is recorded by a user in a recording / reproducing apparatus (CD-R drive or the like).

As a method of increasing the capacity of such an information recording medium, there is a method of miniaturizing guide grooves or pits. However, the wavelength of the laser beam is determined by the wavelength λ and the numerical aperture NA of the condensing lens, so the wavelength of 405 nm (NA = 0.85) is the limit at present. Here, when the NA of the condensing lens is increased to 0.85, the distance between the pickup and the substrate is shortened, and there are problems such as an increase in danger due to a collision and an increase in the influence of dust. In addition, there is a problem that compatibility with DVD media that are widely used at present is difficult (the lens NA of the DVD drive is 0.65).

  As another method of increasing the capacity of the information recording medium, a method of recording multi-value data of three or more values instead of binary data is considered. In the technique described in Patent Document 1, six-value data is obtained with one recording bit by changing the size of the recording bit of the phase change disk.

  12A to 12D are explanatory diagrams of an information recording medium capable of recording multi-value data, FIG. 12A is an enlarged view of a recording track portion of the recording medium, and FIG. 12B is a recording medium. 20 is an optical information recording medium, 21 is a track on which data is recorded, 22 is a cell formed on the track 21 in a certain area, 23 is a light spot of a reproduction beam, and 24 is a cell 22. A recorded recording bit 25 is a substrate of the optical information recording medium 20.

  A recording material, a reflective film, a protective film, and the like are formed on the substrate 25 on which the track 21 is formed, and the optical information recording medium 20 is created. The optical information recording medium 20 is irradiated with a condensed light spot 23 by an information recording device (not shown) to form a recording bit 24. The recording bits 24 are formed in different sizes one by one in the cells 22 formed on the track 21.

  When the optical information recording medium 20 is reproduced by an information reproducing apparatus, as shown in FIGS. 12 (c) and 12 (d), the amount of reflected light of the RF signal changes according to the size of the recording bit 24. It is converted to a predetermined level, and information is reproduced based on the converted data. In this case, a value of 0 to 5 can be expressed in each cell 22, and a larger amount of information can be recorded as compared with a conventional value of 0 to 1.

  As a conventional example of a ROM disk for recording multi-value information, there is a method for obtaining multi-value information by making a pit depth into a plurality of stages (see Patent Document 2), and a multi-value by making a pattern width into a plurality of stages. There are a method for obtaining information (see Patent Document 3) and a method for obtaining multi-value information by setting the pit length in a plurality of stages (see Patent Document 4).

  The multi-value information recording described in Patent Document 3 will be described with reference to FIGS. In this method, the pattern width is set in a plurality of stages and multi-value recording is performed. FIG. 13A shows the recording pattern 30, FIG. 13B shows the reproduced RF signal, and FIG. 13C shows the detection level. In this example, five values of 0 to 4 are recorded. .

In addition, as described in Patent Document 5, for the purpose of improving tracking characteristics of a ROM disk for recording multi-value information, the multi-value pattern and the multi-value pattern are connected by a shallow groove. Some are configured.
Japanese Patent No. 2642422 JP-A-8-77599 JP-A-6-124450 JP 2002-8233 A JP 2003-233932 A

  In the conventional technique, in the method described in Patent Document 2, multi-level recording is performed by changing the pit depth in a plurality of stages. However, it is difficult in practice to stably form patterns with different depths, and it is impossible to adopt them for inexpensive ROM disks.

  In the method described in Patent Document 3, multi-value recording is performed with a pattern width set in a plurality of stages. However, there is a limit to creating a narrow groove. If a groove with a width of 100 nm can be formed, pits with a width of 80 nm narrower than the groove can be formed with the same exposure apparatus. Moreover, when considering the amount of light reflected from the cell, the 80 nm wide pit has a length of about 80 nm, and in order to realize a reflected light amount equivalent to this pit in the groove whose length is the cell length, It needs to be a fraction of that of a pit. Actually, since a groove having such a width cannot be formed, the amount of reflected light in the narrowest groove is reduced, so that only a ROM disk having a small dynamic range can be produced.

  In the method described in Patent Document 4, it is necessary to change the length of the pits on the order of nanometers (nm), an extremely high-precision and expensive electron beam drawing apparatus is required, and the formation of the substrate is equivalent. Since accuracy is required, it is impossible to realize an inexpensive ROM disk.

  In the method described in Patent Document 5, the tracking characteristic is obtained by setting the cell center pattern to a depth λ / 4n (n is the refractive index of the substrate) and the guide groove around the cell center pattern to λ / 8n. Although improved, there is a problem that even if λ / 8n, the RF signal is reduced by 50% in the case of λ / 4n, so that only a ROM disk with a small dynamic range can be created. Further, similarly to the method described in Patent Document 1, it is difficult to create a plurality of depths with a single master, and thus it is impossible to employ it for an inexpensive ROM disk.

  An object of the present invention is to solve the problems of the prior art, and is not limited to the size of the light spot for recording, and the optical information can be recorded in a multi-valued manner with a large capacity and a stable tracking characteristic can be obtained. An object of the present invention is to provide a recording medium, an exposure method for an information recording medium master, an information recording medium stamper, and an information recording medium substrate.

  In order to achieve the object, according to the first aspect of the present invention, a cell which is a two-dimensional region having a constant area virtually exists continuously along a track in a spiral shape, and the reflection in one cell. In an optical information recording medium in which digital data of three or more values is recorded by changing the amount of light, irregularities corresponding to the recording data are formed at the center of the cell, and irregularities for tracking are formed at the four corners of the cell. With this configuration, since tracking patterns are formed at the four corners of the cell, a stable push-pull signal is output and a stable tracking characteristic can be obtained. In addition, since the tracking patterns are formed at the four corners of the cell, the decrease in the RF signal due to the four corner patterns is small, so the dynamic range of the reflectance change can be increased and the multi-level level can be easily determined. it can.

  According to a second aspect of the present invention, in the optical information recording medium according to the first aspect, the cells adjacent in the radial direction in the optical information recording medium are aligned in the circumferential direction, and the unevenness is common to the four adjacent cells. It is formed at the corner of the cell and the unevenness is shared by the four adjacent cells. With this configuration, cells that exist virtually continuously along the track are aligned in the circumferential direction. In addition, by sharing the tracking irregularities formed at the four corners with the adjacent cells, it is possible to obtain a stable tracking characteristic and a multi-value level having a large dynamic range.

  According to a third aspect of the present invention, in the optical information recording medium of the first aspect, the cells adjacent in the circumferential direction of the optical information recording medium share the irregularities formed at the four corners of the cell, and In the information recording medium, the unevenness is not shared with the cells adjacent in the radial direction, and by this configuration, the tracking unevenness is not shared with the cells adjacent in the radial direction, and the tracking unevenness is formed separately. In the CLV (Constant Linear Velocity) recording type optical information recording medium in which cells adjacent in the radial direction are not aligned in the circumferential direction, a stable tracking characteristic and a multi-value level with a large dynamic range can be obtained. And a large-capacity optical information recording medium can be realized.

  According to a fourth aspect of the present invention, in the optical information recording medium according to any one of the first to third aspects, the depths of the irregularities at the center of the cell and the irregularities formed at the four corners of the cell are the same. By making the uneven area variable, digital data of three values or more is recorded by changing the amount of reflected light in one cell. With this configuration, the depth of all the uneven patterns in the surface can be reduced. Since it is possible to record digital data having three or more values in a single cell, a large-capacity recording medium that is easy to create and inexpensive can be created.

  According to a fifth aspect of the present invention, in the optical information recording medium according to the first to third aspects, the concave and convex portions formed at the four corners of the cell have a concave and convex shape longer in the track direction than in the radial direction. As a result, the concavo-convex portions formed at the four corners of the cell are concavo-convex longer in the track direction than in the radial direction, so that the push-pull signal can be improved without lowering the RF signal compared to the circular pattern.

  The invention according to claim 6 is the optical information recording medium according to any one of claims 1 to 3, wherein the shape of the uneven portions formed at the four corners of the cell is constant regardless of the shape of the uneven portions at the center of the cell. With this configuration, the uneven pattern formed at the four corners of the cell is made constant regardless of the pattern size at the center of the cell, so that fluctuations in the push-pull signal can be reduced, resulting in stable tracking characteristics. It is done.

  A seventh aspect of the present invention is the optical information recording medium according to any one of the first to third aspects of the present invention, characterized in that the radial cross-sections of the concavo-convex portions formed at the four corners of the cell are V-shaped. Since the center pattern of the cell is trapezoidal and the tracking pattern is V-shaped at the four corners of the cell, the RF signal and push-pull signal can be increased. A multi-value level with a large range can be obtained.

  According to an eighth aspect of the present invention, in the optical information recording medium according to any one of the first to third aspects, the unevenness at the center of the cell and the unevenness formed at the four corners of the cell are provided separately. By separating the pattern at the center of the cell and the pattern for tracking at the four corners of the cell, the interference between the pattern at the center of the cell and the pattern at the four corners can be prevented. The variation in the pattern size at the center of each can be reduced.

  According to the ninth aspect of the present invention, a cell that is a two-dimensional region having a constant area virtually exists continuously along a track in a spiral shape, and a ternary value is obtained by changing the amount of reflected light in one cell. 9. The method for exposing a master of an optical information recording medium according to claim 1, wherein the digital data is recorded, wherein the central portion of the cell and the corner of the cell are alternately exposed. With this exposure method, the cell center pattern and the four corner tracking patterns can be exposed with one exposure beam by alternately exposing the center of the cell and the corner of the cell. . Further, since the relative positions of the cell center pattern and the tracking patterns at the four corners can be made constant as compared with the exposure with two beams, a highly accurate multi-value master can be created.

  According to a tenth aspect of the present invention, in the exposure method for an information recording medium master according to the ninth aspect, the exposure beam is intermittently irradiated when the corner of the cell is exposed. Thus, by intermittently irradiating the exposure beam, the pattern length can be increased without increasing the pattern width, so that a pattern that can improve the push-pull signal can be formed.

  The invention according to claim 11 is produced from the master disc exposed by the exposure method of the master disc for information recording medium according to claim 9 or 10, and is stable by the configuration of the stamper for the information recording medium. An information recording medium capable of obtaining a multilevel signal having a large tracking characteristic and dynamic range can be created.

  According to a twelfth aspect of the present invention, the information recording medium stamper according to the eleventh aspect of the present invention is used, and the multi-level signal having a stable tracking characteristic and a large dynamic range is obtained by the configuration of the information recording medium substrate. Can be created.

  According to the present invention, since tracking patterns are formed at the four corners of the cell, a stable push-pull signal is output and a stable tracking characteristic is obtained. In addition, since the tracking patterns are formed at the four corners of the cell, the decrease in the RF signal due to the four corner patterns is small, so the dynamic range of the reflectance change can be increased and the multi-level level can be easily determined. An optical information recording medium that can be used can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol was attached | subjected to the member corresponding to the member mentioned already in the following description.

  In the conventional technique, as shown in FIG. 12, when an objective lens NA 0.65 equivalent to a DVD drive is assumed with a blue laser beam having a wavelength of 405 nm, the cell is up to a track pitch of 0.46 μm and a cell length of about 0.23 μm. Even if it is made smaller, it is possible to reproduce a reflected light level of about eight values. As shown in FIG. 10, when a multi-value signal is created with a pattern area as in the technique described in Patent Document 1.

  In FIG. 10, 10 is an uneven and circular multi-value data pattern formed for each cell 22 of the track 21. In the layer change material, a crescent-shaped narrow pattern ( (See FIG. 12), but since the recorded pattern cannot be erased on the master, as shown in FIGS. 11 (a) and 11 (b), the size of the circular pattern can be varied to change the multi-value data. Pattern 10 is created.

  In the case of this conventional technique, as shown in FIGS. 11A and 11B, when there is no concavo-convex pattern as in level 7 or when the concavo-convex pattern is small as in levels 6 and 5, push is performed. There is a problem that the pull signal becomes small.

  FIG. 1 is an enlarged view of a recording track portion of an optical information recording medium for explaining Embodiment 1 of the present invention. In Embodiment 1, as shown in FIG. In addition to the uneven multi-value data pattern 10 formed in the center of the cell 22 provided on the track 21 with a constant area, the uneven pattern 11 for tracking is formed at the four corners of the cell 22.

  RF signals are obtained as shown in FIGS. 2A and 2B by optical reading and photoelectric conversion by scanning the light spot 23 of the reproduction beam with respect to the multi-value data pattern 10.

  By providing the tracking pattern 11 at the four corners of the cell 22 farthest from the center of the light spot 23 of the reproduction beam, the RF signal is reduced by about 10% as shown in FIG. The signal is improved by about 50% (pattern depth is 40 nm corresponding to λ / 6n).

  In the optical information recording medium of Embodiment 1, the deflection of one exposure beam is controlled as shown in FIG. 5C, and the intensity of the exposure beam is controlled as shown in FIG. ) Can be exposed to the cell 22 portion.

  In addition, as in the optical information recording medium according to Embodiment 2 of the present invention shown in FIG. 3A, by exposing the four corner patterns 11 to be elongated, it is possible to suppress the decrease in the RF signal and improve the push-pull signal. it can. FIG. 3B is a cross-sectional view taken along the line i-i ′ in FIG. 3A to show the depth (height) of the pattern.

  Also in the second embodiment, as in the first embodiment, as shown in FIGS. 4A and 4B, optical reading and photoelectric conversion by scanning the light spot 23 of the reproduction beam with respect to the multi-value data pattern 10 are performed. An RF signal is obtained.

  In the optical information recording medium of the second embodiment, the deflection of one exposure beam is controlled as shown in FIG. 6C, and the intensity of the exposure beam is controlled as shown in FIG. ) Patterns 10 and 11 can be exposed to the cell 22 portion.

  Further, by controlling the deflection and intensity of one exposure beam as shown in FIGS. 6C and 6D, the pattern shown in FIG. 6A can be exposed. In this case, even if intensity modulation is not analog modulation but digital modulation, the pattern shown in FIG.

  FIG. 7 is an enlarged view of a recording track portion of an optical information recording medium for explaining Embodiment 3 of the present invention. In Embodiment 3, as shown in FIG. In addition to the concavo-convex multi-value data pattern 10 formed at the center of the cell 22, tracking concavo-convex patterns 11 are formed at the four corners of the cell 22, and the cell 22 adjacent in the track direction has one tracking Although the uneven pattern 11 for use is shared with the adjacent cell 22, the adjacent cell 22 in the radial direction has a separate uneven pattern 11 for tracking for each cell.

  In the CAV (Constant Angular Velocity) recording type optical information recording medium, the cells 22 are aligned in both the circumferential direction and the radial direction as in the first and second embodiments. The concavo-convex pattern 11 can be shared with the adjacent cells 22, but in a CLV (Constant Linear Velocity) recording type optical information recording medium, cells adjacent in the radial direction are arranged in the circumferential direction. Since they are not aligned, as shown in FIG. 7, the cells 22 adjacent to each other in the radial direction are provided with different uneven patterns 11 for tracking for each cell.

  In the optical information recording medium of Embodiment 3, when performing laser exposure, the deflection of one exposure beam is controlled as shown in FIG. 8C, and the intensity of the exposure beam is controlled as shown in FIG. 8B. Thus, the patterns 10 and 11 in FIG. 8A can be exposed to the cell 22 portion. FIG. 8C means that the exposure beam is temporarily separated into two evenly in the radial direction. By inputting a signal in which two frequencies are superimposed on a deflecting element whose deflection angle changes depending on the input frequency, the exposure beam is equally divided into two in the radial direction.

  Further, in the case of electron beam exposure, since the exposure beam intensity cannot be analog-modulated and the exposure beam cannot be divided into two, the deflection of one exposure beam is as shown in FIG. Further, by controlling the intensity (ON / OFF control) of the exposure beam as shown in FIG. 13B, the patterns 10 and 11 shown in FIG. 9A can be exposed to the cell 22 portion.

  Next, the present invention will be described in more detail by way of specific examples.

Example 1
In Example 1, a glass master was coated with a resist, and was exposed with a laser beam having a wavelength of 257 nm so that one track had 600,000 cells at a rotation speed of 600 rpm and a track pitch of 0.46 μm. The exposure beam intensity and the deflection control in the radial direction of the exposure beam were controlled as shown in FIGS. 5B and 5C. As a multi-value data pattern in the center of the cell, an uneven pattern having 0 to 7 values (pattern width 80 nm to 230 nm) was exposed by controlling the irradiation time from 0 nsec to 80 nsec. Further, a 140 nm uneven pattern was exposed as a tracking pattern for the four corners.

  The master was developed to create a pattern, and this master was electroformed and electroformed and peeled to create a stamper having a pattern as shown in FIG. 3A on the surface. A polycarbonate (PC) substrate having a thickness of 0.6 mm was formed by molding from this stamper. A reflective film was formed by sputtering Al on the substrate, and the two sheets were laminated to form an information recording medium.

  When the information recording medium was reproduced by a reproducing drive equipped with a pickup having a wavelength of 405 nm and NA of 0.65, the information recording medium can be stably tracked and has a value of 0 to 7 as shown in FIGS. 4 (a) and 4 (b). Playback was successful.

  Next, a comparative example of the present invention will be described.

  An information recording medium was prepared in the same manner as in Example 1. However, the pattern has the structure shown in FIG. 10 without the four corner patterns. When this was reproduced with a reproducing drive equipped with a pickup with a wavelength of 405 nm and NA 0.65, the tracking was lost at the point where seven values were continuous, and reproduction could not be performed.

(Example 2)
In Example 2, an information recording medium was prepared in the same manner as in Example 1. However, the intensity of the exposure beam and the deflection control in the radial direction of the exposure beam were controlled as shown in FIGS. 6B and 6C. As a result, the tracking pattern at the four corners was a pattern having a width of 80 nm and a length of 160 nm as shown in FIG. When this was reproduced with a reproduction drive equipped with a pickup with a wavelength of 405 nm and NA 0.65, the RF signal was 2% stronger than in Example 1 and the push-pull signal was also improved by 15%.

(Example 3)
In Example 3, an information recording medium was prepared in the same manner as in Example 1. However, the exposure beam intensity was made weaker than in Example 2, and exposure was performed so that the bottom width of the tracking pattern at the four corners was about 0 to 30 nm. The opening width of the tracking pattern at the four corners was a pattern of 75 nm in the radial direction and 160 nm in the circumferential direction. When this was reproduced by a reproducing drive equipped with a pickup with a wavelength of 405 nm and NA 0.65, the RF signal was hardly changed, but the push-pull signal was improved by 40% from that of Example 2.

Example 4
In Example 4, an information recording medium was prepared in the same manner as in Example 1. However, the intensity of the exposure beam and the deflection control in the radial direction of the exposure beam were controlled as shown in FIGS. 6 (c) and 6 (d). As a result, the tracking patterns at the four corners became a pattern with a width of 80 nm and a length of 160 nm as shown in FIG. 3A, and the same pattern as in Example 2 could be formed.

(Example 5)
A glass master was coated with a resist and exposed with a laser beam having a wavelength of 257 nm so that the linear velocity was 1 m / sec, the track pitch was 0.46 μm, and the cell length was 0.23 μm. The exposure beam intensity and the deflection control in the radial direction of the exposure beam were controlled as shown in FIGS. 8B and 8C. By controlling the irradiation time from 0 nsec to 80 nsec as a multi-value data pattern in the center of the cell, a concavo-convex pattern having 0 to 7 values (pattern width 80 nm to 230 nm) was exposed as shown in FIG.

  Further, a pattern having a width of 80 nm and a length of 160 nm was exposed as shown in FIG. When this was reproduced by a reproducing drive equipped with a pickup of wavelength 405 nm and NA 0.65, a push-pull signal equivalent to that in Example 2 was obtained, and the RF signal was reduced by about 5%, but the recording capacity was about doubled. Improved.

(Example 6)
In Example 6, a glass master was coated with a resist and exposed to an electron beam with a beam diameter of 80 nm so that the linear velocity was 1 m / s, the track pitch was 0.46 μm, and the cell length was 0.23 μm. The exposure beam intensity and the deflection control in the radial direction of the exposure beam were controlled as shown in FIGS. 9B and 9C. By controlling the irradiation time from 0 nsec to 30 nsec as a multi-value data pattern at the center of the cell, a concavo-convex pattern having 0 to 7 values (pattern width 80 nm to 200 nm) was exposed as shown in FIG.

  Further, as a tracking pattern for the four corners, the concave and convex pattern was exposed as shown in FIG. 9A by alternately irradiating both sides of the cell in the radial direction intermittently as shown in FIG. 9B. When this was reproduced by a reproducing drive equipped with a pickup with a wavelength of 405 nm and NA 0.65, a push-pull signal and an RF signal equivalent to those in Example 5 were obtained.

  In the above-described embodiment, even if it is described that a pattern is created by exposure with a laser exposure machine, the pattern creation method is not limited thereto. For example, electron beam exposure can be applied to the exposure beam control in the second and fourth embodiments.

  Further, the tracking irregularities formed at the four corners of the cell may have a V-shaped cross section in the disk radial direction of the information recording medium.

  The present invention is applied to an optical information recording medium such as an optical disk, and is particularly useful for an information recording method such as a recording medium (ROM disk) for recording and reproducing multi-value information in advance.

FIG. 2 is an enlarged explanatory view of a recording track portion of an optical information recording medium for explaining Embodiment 1 of the present invention. Explanatory drawing which shows the relationship between the pattern in Embodiment 1, an output level, RF signal, etc. FIG. 6 is an enlarged explanatory view of a recording track portion of an optical information recording medium for explaining Embodiment 2 of the present invention. Explanatory drawing which shows the relationship between the pattern in Embodiment 2, an output level, and RF signal Explanatory drawing of pattern formation by the exposure beam in Embodiment 1 Explanatory drawing of pattern formation by the exposure beam in Embodiment 2. FIG. 6 is an enlarged explanatory view of a recording track portion of an optical information recording medium for explaining Embodiment 3 of the present invention. Explanatory drawing of pattern formation by the exposure beam in Embodiment 3 Explanatory drawing of pattern formation by the other exposure beam in Embodiment 3. Expansion explanatory drawing of the recording track part of the conventional optical information recording medium Explanatory drawing which shows the relation of the pattern of conventional example, output level, RF signal Explanatory drawing of the information recording medium which can record the conventional multi-value data Explanatory drawing which shows the relationship between the pattern and output level of the conventional optical information recording medium

Explanation of symbols

10 Multi-value data pattern 11 Tracking pattern 20 Optical information recording medium 21 Track 22 Cell 23 Light spot of reproduction beam

Claims (12)

Light in which cells, which are two-dimensional regions having a constant area, virtually exist continuously along a track in a spiral shape, and digital data of three or more values is recorded by changing the amount of reflected light in one cell. In an information recording medium,
An optical information recording medium, wherein irregularities corresponding to recording data are formed at the center of the cell, and irregularities for tracking are formed at the four corners of the cell.   The cells adjacent in the radial direction in the optical information recording medium are aligned in the circumferential direction, the irregularities are formed at the corners of the cells common to the four adjacent cells, and the irregularities are formed in the four adjacent cells. 2. The optical information recording medium according to claim 1, wherein the optical information recording medium is shared.   The cells adjacent in the circumferential direction in the optical information recording medium share the irregularities formed at the four corners of the cells, and the cells adjacent in the radial direction in the optical information recording medium do not share the irregularities. The optical information recording medium according to claim 1, wherein:   By making the depth of the unevenness at the center of the cell and the unevenness formed at the four corners of the cell the same, and making the area of the unevenness at the center of the cell variable, within the one cell 4. The optical information recording medium according to claim 1, wherein digital data having three or more values is recorded by changing the amount of reflected light.   4. The optical information recording medium according to claim 1, wherein the concavo-convex portions formed at the four corners of the cell have a concavo-convex shape longer in the track direction than in the radial direction.   The optical information recording medium according to claim 1, wherein the shape of the uneven portions formed at the four corners of the cell is constant regardless of the shape of the uneven portions at the center of the cell.   The optical information recording medium according to claim 1, wherein a radial cross section of the concavo-convex portion formed at four corners of the cell is V-shaped.   The optical information recording medium according to claim 1, wherein the unevenness at the center of the cell and the unevenness formed at the four corners of the cell are provided separately.   A cell that is a two-dimensional region having a constant area virtually exists continuously along a track in a spiral shape, and digital data of three or more values is recorded by changing the amount of reflected light in one cell. 1. The method for exposing a master of an optical information recording medium according to claim 1, wherein the center of the cell and the corner of the cell are alternately exposed. Exposure method. 10. The exposure method for an information recording medium master according to claim 9, wherein when exposing the corner of the cell, the exposure beam is irradiated intermittently.   11. A stamper for an information recording medium, wherein the stamper is produced from a master exposed by the exposure method for an information recording medium master according to claim 9.   An information recording medium substrate made from the information recording medium stamper according to claim 9.

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