Manufacturing method for optical recording medium

[0001] The present invention relates to an optical recording medium, in particular an optical disk, which has a shape similar to a circular plate and is used for

Description for a round information plaque.

[0002] A traditional optical recording medium is, for example, an optical disk, such as a CD-ROM and DVD-ROM. In such optical discs, a variable row of pits is formed on a transparent substrate that is made of polycarbonate or similar material. On the substrate, a metal reflection film is formed, which is made of Al or similar material. The light beam is fed to the metal reflection film, which is the information recording surface, from the side of the surface opposite the surface on which this metal reflection film is formed. This way information is played back.

[0003] Such an optical recording medium is widely used in which information is recorded and reproduced by using a light beam. Thus, expectations for increasing its recording density are already rising today. In recent years, many optical discs have been developed that can play large volume audiovisual data or digital data. For example, research and development of a high-density ROM optical disk with a diameter of 12 centimeters is currently underway and its density is expected to increase to a memory capacity of 23.3 to 30 gigabits.

[0004] On the other hand, the DVD ROM recording medium is equipped with a security technique and, in particular, a technique to prevent unauthorized use and copying of the recorded information or similar operations. In this security technique, a BCA (burst cutting area) area is provided in which

The medium identification information used to individually identify each recording medium is overwritten in the bar code pattern. In this BCA area, during the production of the optical recording medium, medium identification information is recorded that is different for each optical recording medium, and if necessary a cryptographic key or a decoding key is recorded.

[0005] For example, in Japanese Patent Specification

Japanese Patent Laid-Open No. 10-233019 describes that the metal reflection film of an optical disk on which the row of pits has been created as the main data is partially removed by laser cutting, and the modulated data is saved separately. Thus, information identifying the medium is recorded, which is used to protect against unauthorized use and copying, or similar operations.

[0006] However, to increase the previously described recording density, the track pitch must be narrowed, or the shortest pit of a row of pits must be shortened. In addition, for a high-density optical disc, 23.3 GB or more is recorded on a 12 cm optical disc. Thus, it has been found that if a metal reflection film is formed on the substrate used for such an optical disk, which is made of an Al alloy material having a film thickness of 50 to 70nm so that it can be used in a DVD ROM optical disk, this deteriorates quality of the reproduced signal.

[0007] This is because the metal reflection film appears to be difficult to form at the bottom of a very small depression of about 0.2 μη in length. Thus, the shorter the cavity is, the deeper and smaller it becomes. Accordingly, the metal reflection film that is used in the DVD ROM optical disc could not actually be

53 / 59P27788EN00 used as a reflection film for the previously described high-density ROM optical disk.

[0008] Furthermore, when a DVD ROM optical disk is produced, the medium identification information is recorded, using a medium recording information identifying the medium, which is equipped with a YAG (yttrium-aluminum grenade) laser. However, even if the medium identification information is recorded in the bar code pattern using this medium information recording medium, the pattern could not be formed in an area where no pits are formed on the high-density ROM optical disk or on the row of pits that is recorded. with a track pitch of about 0.74μm, which is the same as in the DVD ROM optical disc. Or the reproduction noise of the medium identifying the information would increase, and thus an adequate defocus margin could not be provided.

[0009] This is because on a high-density ROM optical disk, the metal reflection film is thinner than the film on a DVD ROM optical disk. Or another material of the metal reflection film is used, and therefore the heat capacity necessary for the metal reflection film to reach its own melting point is quite different. Accordingly, a traditional media information recording device equipped with a YAG laser could not actually be used when producing a high-density ROM optical disk.

[0010] A technique related to this field can be found in WO 02/37483, which describes "OPTICAL RECORDING MEDIUM, OPTICAL RECORDING MEDIUM PRODUCTION METHOD, OPTICAL RECORDING MEDIUM PRODUCTION APPARATUS, PROGRAM, AND MEDIUM" (OPTICAL REC MEDIA , HOW TO MAKE AN OPTICAL RECORD MEDIA, THE DEVICE TO MAKE THE OPTICAL RECORD MEDIA, THE PROGRAM, AND THE MEDIA). This document shows the way

Producing an optical recording medium that has a recording capacity of 20Gb or more, including a substrate preparation step on which a row of pits is formed as master data in the main information area and a recording step of the medium identification information used to identify the optical recording medium individually by partial deletion metal reflection film in the sub-information area and creating multiple areas of the removed reflection film. However, this document does not show that the track pitch of the sub-information recording area is 0.24 μm to 0.45 μη.

[0011] It is an object of the present invention to provide a method for producing an optical recording medium in which data can be recorded more densely than on an optical DVD ROM, and using a conventional recording device to identify the medium, the information identifying the medium can be recorded so that it can be adequate defocus margin maintained.

[0012] The object is achieved by a method as defined in the appended independent claim.

[0013] Accordingly, by using a light beam having a shorter wavelength and an optical system having a larger numerical aperture for reproduction, a good quality signal can be obtained by reproducing data that has been recorded at a higher density than on a DVD ROM optical disk. In addition, even if the thermal conductivity or melting point, which is the intrinsic value of the metal reflection film, is different, using a conventional recording device to identify the medium, the medium identification information that has been recorded with an appropriate defocus margin can be evenly reproduced.

53 / 59P27788PL00

Fig. 1 is a graphical representation illustrating the result of the jitter value measurement that corresponds to the depth of the pit.

Fig. 2 is a graphical representation illustrating a distortion factor measurement result that corresponds to the film thickness for a metal reflection film that is made of an AgPdCu alloy.

Fig. 3 is a graphical representation illustrating the result of a distortion factor measurement that corresponds to the film thickness for a metal reflection film that is made of alloy A1.

Fig. 4 is a cross-sectional view of an optical disk in which a metal reflection film, which is made of an AgPdCu alloy and has a film thickness of about 100nm, is formed on the substrate where the pits are formed.

Fig. 5 is a graphical representation illustrating the result of a reflectance measurement that corresponds to the film thickness for a metal reflection film that is made of an AgPdCu alloy.

Fig. 6 is a graphical representation illustrating the result of a reflection coefficient measurement that corresponds to the film thickness for a metal reflection film that is made of an Al alloy.

Fig. 7 is a top view of the optical disk illustrating an example of its main information area and sub information area.

Fig. 8 is a block diagram illustrating the configuration of a medium identification information recording device that records medium identification information in a BCA area.

Fig. 9 is a cross-sectional view of an optical disk in which a metal reflection film is formed on the substrate where the recesses have been formed, and in addition, a resin layer is formed on the metal reflection film.

53 / 59P27788PL00

Fig. 10 is a graphical representation illustrating the result of defocus margin measurement for the recording power of the BCA area that corresponds to the track pitch of a row of pits that is formed on an optical disk that contains a 50nm metal reflection film which is made of an AgPdCu alloy.

Fig. 11 is a graphical representation illustrating the result of defocus margin measurement for the recording power of the BCA area that corresponds to the track pitch of a row of pits that is formed on an optical disk containing an Al reflection film whose thickness is 30nm.

[0014] Hereinafter, the ROM optical disk will be described as an example of the optical disk of the present invention. The present invention may also be used in various optical recording media in which the information recording layers have, for example, slight unevenness, such as an optical magnetic disk and a phase-change disk.

[0015] A ROM optical disk comprises: a main information area in which a metal reflection film is formed on a substrate where an odd row of pits forms the main data; and a sub-information area in which information is recorded which is used for the optical disk by identifying the carrier, individually identifying partial removal of the metal reflection film, and forming multiple areas with the reflection film removed. On this optical disk, information is reproduced by illuminating the metal reflection film by means of a light beam.

[0016] In general, to increase the recording density of an optical ROM disk, the track pitch must be narrower, and the shortest pit length (or shortest track length) must be significantly shortened. However, if the track pitch becomes too narrow in the RF signal characteristics

53 crosstalk increases. This interferes with securing the appropriate system margin. If the length of the shortest pit becomes too short, then the resolution of the reproduced signal decreases, thus the distortion factor of the reproduced signal decreases.

[0017] Thus, the most appropriate track spacing test is repeatedly carried out using an information reproducing device in which the wavelength λ of the light source of the light beam for reproduction is 405nm and the numerical aperture NA of the lens is 0.85. As the test result, the following measurement result was obtained. This illustrates the fact that if the track pitch is 0.24μm or more, the crosstalk signal can be virtually omitted compared to the main signal.

<td>Track distance (μη)</td><td>Distortion factor (%)</td>

<td> 0,20</td><td> 7, 6</td>

<td> 0,22</td><td> 7,0</td>

<td> 0,24</td><td> 6, 5</td>

<td> 0,26</td><td> 5, 6</td>

<td> 0,28</td><td> 5,4</td>

[0018] In addition, the most appropriate length of the shortest recess is examined using the above-described information reproducing apparatus. As a result of testing the resolution necessary to achieve the desired reproduction signal, the measurement result shown below is obtained. It turned out that if the length of the shortest pit is 0.12μη or more, the resolution of the reproduced signal can be adequately ensured.

53 / 59P27788PL00

<td>Shortest Length</td><td>Coefficient</td>

<td>Cavities (pm)</td><td>distortion (%)</td>

<td> 0, 10</td><td> 8,2</td>

<td> 0, 11</td><td> 6, 8</td>

<td> 0, 12</td><td> 6, 5</td>

<td> 0, 13</td><td> 5,4</td>

<td> 0, 14</td><td> 5, 3</td>

[0019] In this case, due to the different margins of the disk or optical drive, the distortion factor that depicts the characteristics of the optical disk must be 6.5% or less.

[0020] In this case, the information is reproduced from an optical disk with a diameter of 12 cm, using the information reproducing apparatus. To set the optical disk memory capacity to 23.3GB or more, the relational expression (shortest pit length) x (track pitch) &lt;0.0512 pm must be met. For example, if the recording capacity is 23.3GB and the shortest pit length is 0.12pm, the upper track pitch limit is about 0.43pm. In the same way, if the recording capacity is 23.3GB and the shortest pit length is 0.24μm, the upper limit of the track pitch is about 0.21pm. [0021] Next, a method for producing an optical disc 12 cm in diameter that has a recording capacity of 23.3GB or more will be described. As described above, in order to produce an optical disk with a diameter of 12 cm, which has a recording capacity of 23.3GB or more, a substrate with a track pitch of 0.24μm or more and 0.43μm or less, and the shortest length the cavities are 0.12μm or more and 0.21pm or less.

[0022] For example, to produce an optical disk with a diameter of 12 cm, which has a recording capacity of 25GB, first, a substrate is prepared in which a row of pits is formed,

Wherein the shortest pit length is 0.149 pm and the track pitch 0.32 μη. As a substrate, for example, a substrate made of polycarbonate that is made by an injection molding device may be used.

[0023] A metal reflection film is then formed on this substrate using a layer forming device. As a device for forming layers that can produce a homogeneous metal reflection film, a magnetron device such as, for example, a gas phase atomizing device can be used. for magnetron sputtering, the film-forming time can be changed, thereby controlling the film thickness for the metal reflection film. In this case, the material, film thickness, or the like for the metal reflection film will be described later.

[0024] Next, an optical disk with a metal reflection film is placed on a rotary coater. Then, the resin to be hardened by ultraviolet rays is dripped on and a 88pm thick transparent sheet made of polycarbonate is placed on it. In this state, the radiation curable resin and the deposition device using the ultraviolet device is irradiated with ultraviolet rays, while the optical disk is rotated by a rotary coater. At this point, the rotational speed of the rotary coater is controlled such that the thickness of the UV curable resin after curing is 12pm. As a result, a transparent resin layer is formed on the metal reflection film, which has a thickness of 100pm. For example, acrylic resin may be used as the UV curable resin.

[0025] In the manner described above, a metal reflection film was formed on the substrate, where it was formed

A row of pits in which the length of the shortest pit is 0.149 μm and the track pitch is 0.32 μm. A film of resin is formed on the film, which has a thickness of 100 μm, and as a consequence, an optical disk was produced.

[0026] Next, with respect to the optical disk which was produced as described above, the depth of the cavity, which corresponds to the quality of the reproduced signal, material and film thickness for the metal reflection film, and the like was examined. In particular, the manufactured optical disk was placed in the previously described information reproducing apparatus. Then, the information reproduction device uses a light beam that falls on the metal reflection film through a 100μm resin layer. In this way, the reconstructed signal was obtained from the optical disk and then it was evaluated.

[0027] First, it was examined how much the quality of the reproduced signal depends on the depth of the pit. On the optical disk manufactured in the manner described above, distortion coefficients were measured, which showed the dispersion of the reproduced signals when the depth of the pit changed. Fig. 1 is a graphical representation illustrating the result of the distortion factor measurement that corresponds to the depth of the pit. Its horizontal axis represents the depth (nm) of the pit, and the vertical axis represents the coefficient (%) of distortion. In Fig. 1, as a metal reflection film, one that was made of an Al alloy with a purity of 99% by weight and had a film thickness of about 25nm was used. However, even when the film was made of Ag98Pd1Cu1 (wt%) (hereinafter AgPdCu alloy), the same results as below were obtained.

[0028] In general, to ensure an adequate system margin, the distortion factor must be 6.5% or less. In Fig. 1, it can be seen that if the depth of the pit is set to 44nm or more and 88nm or less,

A distortion ratio of 6.5 / 59 would be 6.5% or less. In this case, the refractive index n of the resin layer formed was 1.53, and the wavelength λ of the light beam was 405nm. Thus, taking into account the measurement result described above, it can be seen that the depth D of the recess at which the desired reproduction signal could be obtained is λ / (6xn) or more, and λ / (3xn) or less.

[0029] The reason seems to be as follows. In particular, the depth of the cavity affects the amplitude of the reproduced signal, and in optical calculations, when the depth of the cavity is A / (4xn), the amplitude becomes maximum. If the refractive index n of the resin layer is 1.53 and the wavelength λ of the light beam is 405nm, it reaches its maximum when the depth of the pit is about 66nm. However, even if the amplitude slightly decreases, the distortion factor of the reproduced signal is almost unchanged. However, if the depth of the pit is less than A / (6xn), or if the depth of the pit is greater than A / (3xn), then an appropriate signal-to-noise ratio (hereinafter referred to as S / N ratio) cannot be achieved, thus deteriorating distortion factor of the reproduced signal.

[0030] Next, the appropriate film thickness for the metal reflection film was tested. First, a substrate was prepared in which the depth of the pit is A / (4xn). As a metal reflection film, two types of film were used, a metal reflection film that was made of an AgPdCu alloy and a metal reflection film that was made of an 99% pure Al alloy. Then, by changing the film thickness, the distortion factor was measured. FIG. 2 is a graphical representation illustrating the result of a distortion factor measurement that corresponds to the film thickness for a metal reflection film that is made of an AgPdCu alloy. Fig. 3

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<td>5nm</td><td>or</td><td>less,</td>

<td> 6,5%</td><td>or</td><td>less.</td>

<td> 3,</td><td colspan="2">in case of</td>

<td>alloy</td><td>Al,</td><td>if</td>

<td>40nm</td><td>or</td><td>less,</td>

<td> 6,5%</td><td>or</td><td>less.</td>

is a graphical representation illustrating the result of a distortion factor measurement that corresponds to the film thickness for a metal reflection film that is made of an Al alloy. In each figure, the horizontal axis specifies the film thickness (nm) for the metal reflection film, and the vertical axis represents the distortion coefficient (%).

[0031] As can be seen in Fig. 2, in the case of a metal reflection film made of an AgPdCu alloy, if the thickness of the film was 25nm or more and the distortion coefficient took the value On the other hand, as shown in Fig, the metal reflection film made of the film thickness was 15nm or more, the distortion factor was 6.5 In this case, the material of the metal reflection film is not particularly limited to the examples given. Other material may also be used, provided that it has a high reflectance and can be uniformly formed on the substrate by means of a layer-forming device. In addition, to improve its resistance to the rare earth metal element, such as a transition metal element such as Ti, and also be added in small amounts to the reflection film material of Ag or Al.

[0032] Next, the reflection coefficient of the metal reflection film was examined. The thinner the metal film, the smaller it will be when the amount of reflection reflected in proportion to this, the noise of the carrier also decreases. This maintains the S / N ratio unchanged. On the other hand, system noise or laser noise does not depend on the amount of light reflected. If the system noise or laser noise is much smaller than the media noise so that it can be neglected, then there will be no corrosion,

Nd or Cr, may reflect,

Then, the amount of reflected light. the light decreases,

It affected the quality of the reproduced signal even if the amount of reflected light decreases.

[0033] However, if the amount of reflected light decreases and the system noise or laser noise reaches the same level as the noise of the carrier, then when the amount of reflected light decreases, the quality of the reproduced signal will deteriorate. Furthermore, if the metal reflection film is made of a different material, even if it has the same film thickness, this will change its reflection coefficient, and thus, the film thickness at which the signal quality will deteriorate will change. In addition, if the metal reflection film becomes thicker, the reproduced signal will be worse. For example, in a magnetron sputtering device, metal atoms on the storage electrode that have been atomized by Ar ions fly into the substrate so that a metal reflection film is formed. The size of these metallic atoms also depends on the construction of the layering device, or the conditions for producing the film. However, such a film turns out to be difficult to form at the bottom of the shortest recess.

[0034] Fig. 4 shows a cross-section of an optical disk in which a metal reflection film, which is made of an AgPdCu alloy and has a film thickness of 100nm, is formed on the substrate where the pits are formed. As shown in Fig. 4, the shortest recess 11 and the long recess 12 that is longer than the shortest recess 11 are formed on substrate 1. In this case, at the bottom of the shortest recess 11, it is more difficult to form the metal reflection film 2 than at the bottom of the long recess 12.

11, after forming the metal simultaneously as a result,

Thus, the shortest recess of reflection film 2 becomes smaller and deeper than it was on substrate 1.

[0035] If this phenomenon is predicted and the write power is increased so that the shortest recess 11 can be larger, then the signal quality of the shortest recess 11

53 / 59P27788EN00 will improve. However, as the write power increases, the long recess 12 will be wider. This increases the crosstalk that comes from adjacent tracks, thus worsening the distortion factor. Because of the coefficients that can worsen the signal quality of both types of films, substrates were created that were suitable for metal reflection films made of Al alloy and AgPdCu alloy. As a result, the maximum film thickness for the Al alloy metal reflection film at which the distortion coefficient was protected against deterioration was 40 nm, and the maximum film thickness for the AgPdCu alloy metal reflection film at which it was deteriorated was about 70 nm. [0036] Based on this study, a reflection coefficient, which corresponds to the film thickness for each AgPdCu metal reflection film that is shown in Fig. 2 and the metal reflection film from Al alloy which is shown in Fig. 3, was measured. Fig. 5 is a graphical representation illustrating the result of a reflectance measurement that corresponds to the film thickness for a metal reflection film that is made of an AgPdCu alloy. FIG. 6 is a graphical representation illustrating the result of a reflectance measurement that corresponds to the film thickness for a metal reflection film that is made of an Al alloy. In each figure, the horizontal axis represents the film thickness (nm) of the metal reflection film, and the vertical axis represents the reflection coefficient (%). In this case, the refractive index n of the resin layer that was used for the measurement is 1.53 and the wavelength λ of the light beam is 405nm.

[0037] As can be seen in Fig. 5, in the case of an AgPdCu alloy metal reflection film, a reflection coefficient that corresponded to a film thickness of 25nm to 70nm, with

The desired distortion coefficient was obtained from 35% to 70%. For the Al alloy metal reflection film in Fig. 6, the reflection coefficient, which corresponded to a film thickness of 15nm to 40nm, at which the desired distortion coefficient was obtained, was from 35% to 70%. As a result, for each film, the reflection coefficient of the metal reflection film at which the quality of the reproduced signal could be guaranteed was 35% or more and 70% or less.

[0038] Then, in order to obtain a reproduction signal that has the desired distortion coefficient, in the manner described above, an odd row of grooves is created in the main information area of ​​the optical disk as main data. A detailed description will be provided of the media identification information that is created in the optical disk sub information area. FIG. 7 is a top view of the optical disk showing an example of its main information area and sub information area.

[0039] In the example shown in Fig. 7, the main information area 21 (which is the hatched part in the figure) is set in the outer circular part on the optical disk. In the ring-shaped part inside the outer circular part, the BCA area 22 is set (which is the area between the two circles depicted in the figure by the dashed line), which is the area of ​​information. In the BCA area 22, information identifying the medium 23 is recorded in a bar code pattern. A transparent layer of polycarbonate resin, or the like, is formed on the metal reflection film, and from now on, information identifying the carrier is recorded by irradiation, using a pulsed laser (e.g., YAG laser), a metal reflection film which is located at a depth of 0.1mm from the surface of the optical disk. At this point, the metal reflection film appears to be melting, and

Then accumulates at both boundary parts due to surface tension. In this way, the metal reflection film is partially removed, and therefore, several areas are created with the reflection film removed. This creates a BCA area where medium identification information is recorded, which is used to individually identify the optical disk.

[0040] Next, the method of recording medium identification information in the BCA area of ​​an optical disk will be described in more detail. In this case, the following example describes the method by which recording is made in the BCA area, with respect to a metal reflection film which is made of Ag98Pd1Cu1 (% by weight), or a metal reflection film which is made by weight), as metal reflection film as long as the same effect can be obtained, the present invention can also be applied to other types of metal reflection film, phase-change film or optical-magnetic recording film.

[0041] Fig. 8 is a block diagram illustrating the configuration of a medium identification information recording device that records the medium identification information in the BCA area. The recording medium identifying information shown in Fig. 8 is a BCA pattern recording device that is used to create the BCA area on the DVD-ROM. It contains: engine 101;

rotation control; optical pickups 103; laser drive section 104; a wave shape setting section 105; a BCA signal generating section 106; focus adjustment section 107;

preamplifier 108; and system control section 109.

[0042] The rotation control section 102 controls the rotation of the motor 101. The motor 101 rotates the optical disk 100 at a predetermined rotational speed. Section 106 generating from Al99Cr1 (% However, yes section 102 device

Which optical adjustment comes from focusing the BCA signal device generates the BCA signal by modulating the media identification information that is recorded on the optical disk 100. Based on the BCA signal, the waveform setting section 105 produces a laser modulating waveform. According to the shape of the laser modulating wave, the laser drive section 104 drives a high power laser inside the optical pickup device 103. The optical pickup device 103 focuses the light beam emitted by the high-power laser, through its built-in optical system, onto the optical disk 100. The preamplifier 108 amplifies the reproduced signal that comes from the optical pickup device 103, and then sends it to the focusing adjustment section 107. Using the amplified signal of the preamplifier 108, section 107 controls the lens inside the transducer 103 so that the light beam can be focused on the metal reflection film of the optical disk 100. The system control section 109 systematically controls the operation of the rotation control section 102, the laser drive section 104, the section 105 setting the waveform, section 106 generating the BCA signal and section 107 adjusting the focus. [0043] Next, the operation of recording the recording device of the medium identifying information that is configured as described above will be described. First, based on the instructions in section 109 of system control, section 102 of rotation control drives the motor 101 to rotate the optical disk 100. The laser drive section 104 drives the high power laser as a light source, and then, the light beam that is emitted by the high power laser is directed to the optical disk 100 from the optical pickup device 103. At this point, the focusing adjustment section 107 performs the focusing adjustment that a light beam that was emitted by a high power laser,

53 is focused on the metal reflection film of the optical disk 100.

[0044] In this case, the light reflected from the optical disk 100 is detected by the photodetector inside the optical pickup device 103. Then, the reproduced signal is transmitted as an electric signal from the photodetector. This reproduced signal is amplified by the preamplifier 108 and is introduced into the focusing section 107. In response to the amplified signal, the focus adjustment section 107 drives the lens of the optical pickup device 103 and moves it slightly in such a direction as to focus on the optical pickup 100. Thus, it controls the optical pickup device 103 so that the light beam can be focused on the metal optical film reflection layer 100.

[0045] Next, the system control section 109 allows the position detector (not shown) to detect the optical position of the transducer device 103 in the tracking direction. Based on the detected position information, it recognizes the optical pickup device 103 to be placed in the start position of the sub information recording. Then, system control section 109 instructs section 106 to generate a BCA signal to generate a BCA signal. Then, the BCA signal is sent from the waveform setting section 105, the BCA recording sequence begins, and the medium identification information is recorded in the BCA area.

[0046] On the optical disk, where a metal reflection film of AgPdCu alloy with a thickness of 50nm was created, using the previously described device recording information identifying the medium, in the part where neither row of pits or groove was created, an attempt was made to record the BCA pattern (or code pattern) bar). However, even if the laser output power increased, the area from

Melting

In addition, the removed film in which the metal reflection film was removed could not be created.

[0047] This is because the melting point of Al is 660 ° C, while the melting point of Ag is

960 ° C. This requires more energy to the metal reflection film from the AgPdCu alloy.

the thermal conductivity of Al is 237W / (mK), while the thermal conductivity of Ag is 427 ° C. Thus, a greater amount of heat is dissipated due to heat conductivity, even if the metal reflection film of the AgPdCu alloy is irradiated with a beam of light. In this case, generally, the melting point of the metal is reduced by mixing different metals. However, to ensure adequate reflection and to avoid corrosion, the weight% of Ag in the metal reflection film cannot be reduced to 97% or below this value.

[0048] Then, on an optical disk where a 50nm thick AgPdCu metal reflection film was formed, a row of pits with a track pitch of 0.24 pm was created that was used in the BCA area of ​​the DVD-ROM, and the BCA pattern was recorded in this section. At this point, the BCA pattern could not be recorded in a predetermined width, the information could not be reproduced

However, therefore, a portion of the metal reflection film of the AgPdCu alloy melts, a small portion of the removed reflection film can be formed.

This is because the metal reflection film has difficulty forming an uneven substrate on the inclined surface, and therefore, the film thickness for the metal reflection film in a portion of the surface with the inclined depression locally becomes thinner and heat conduction is suppressed.

[0049] Fig. 9 is a cross-sectional view of an optical disk in which a metal reflection film is formed on the substrate where the depressions are formed, and in addition on the metal

A reflection film is formed of a resin layer. As shown in Fig. 9, the metal reflection film 2 is formed on the substrate 1, where the recess 12 is formed, and in addition, the resin layer 3 is formed on the metal reflection film 2. In this case, the film thickness for the metal reflection film 2 which is formed on the part 4 of the inclined surface becomes thinner than the film thickness for the metal reflection film 2 which is formed on each part 5 of the bottom of the recess and part 6 of the flat plate. In this way, the amount of heat that is conducted around it becomes smaller. Therefore, the smaller the track pitch of the pits and the larger the area of ​​the portion 4 of the inclined surface becomes, the easier the heat will be conducted around. In addition, in part 4 of the inclined surface, the volume per unit of the metal reflection film 2 is less than any other part. Thus, its heat capacity necessary to reach the melting point becomes smaller, and therefore, it reaches the melting point with less irradiation power. [0050] Based on the knowledge already described, optical discs were prepared in which a 50nm thick metal reflection film made of AgPdCu was formed on each substrate where a row of pits with different track spacing was created. Then, the BCA pattern was recorded on each optical disk. FIG. 10 illustrating the result shows a graphical representation of the measurement, defocusing BCA recording power, which corresponds to the track pitch of a row of pits, optical, which contains which is formed on the disk a metal reflection film with a thickness of 50nm, which is made of an AgPdCu alloy. Its horizontal axis represents the track pitch (pm) of the row of pits, and the vertical axis represents the defocus margin (%).

[0051] As shown in Fig. 10, in the area where a row of pits was formed with a track pitch of 0.54 pm

53/59 P27788EN00 or less, a BCA pattern could be recorded, and medium identification information could be recorded. On the other hand, in the area where a row of pits were formed with a track pitch of 0.54μm or more, no defocus margin could be provided. In this case, the assessment that the BCA pattern was saved was made by setting and restoring the created optical discs in the evaluation device. It was based on whether the media identification information that was recorded in the BCA area could be accurately reproduced or not. As an evaluation device, a reproduction device was used in which the beam of light to be reproduced had a wavelength λ of 405 nm and the lens had a NA numerical aperture of 0.85.

[0052] In this case, if mass production of optical discs is considered; a number of factors should be considered, such as the film thickness dispersion for the metal reflection film and the variation in BCA recording power. Thus, an appropriate defocus margin level of 20% or more is required. In Fig. 10, the track pitch at which a defocus margin of 20% or more is obtained is 0.24Pm or wider and 0.45Pm or narrower. Thus, if the track pitch of a row of pits that is recorded in the BCA area is 0.24Pm or wider and 0.45Pm or narrower, an appropriate defocus margin may be maintained, and medium identification information may be recorded. The presumed reason for this is described below.

[0053] In particular, if the track pitch of a row of pits that is recorded in the BCA area is less than 0.45Pm, the number of pits per unit area becomes smaller, and therefore, the area portion of the inclined surface of the pits also becomes smaller. This accordingly prevents the heat conduction from stopping. Thus, if the heat capacity that is absorbed by the metal film

If the reflection pattern changes according to the defocus, the BCA pattern that has low noise cannot be saved.

[0054] On the other hand, if the track pitch is narrower than 0.24pm, the pit is too close to adjacent pits. Thus, the formation of a portion of the field between the pits becomes inappropriate, and the angle of the portion of the inclined surface of the pit decreases. In this way, the metal reflection film becomes easier to form on portions of the inclined surface of such pits, and thus, the effect of retaining heat conduction by forming the pits is reduced. In this case, in Fig. 10, the BCA pattern could be recorded and reproduced up to the point where the track pitch was 0.22 pm, while the BCA pattern could not be recorded when the track pitch was less than 0.22 pm. Thus, in Fig. 10, the dashed line is an estimated line that corresponds to a track pitch of 0.22 pm or less.

[0055] In addition, Fig. 10 shows that on an optical disk where a 50nm thick AgPdCu metal reflection film was formed, the defocus margin is dependent on the track pitch. However, on an optical disk in which the desired coefficient of distortion was obtained, the metal reflection film that was made of Ag or Ag alloy could also have a film thickness of 25nm or more and 70nm or less. In this case, if the track pitch of a row of pits that was recorded in the BCA area was 0.24 pm or wider and 0.45 pm or narrower, a defocus margin could be obtained at the same level as described above.

[0056] Similarly, the same experiment as described above was also carried out for an optical disk, where instead of a row of pits a groove was formed. Even with the groove, the metal reflection film was difficult to form in the inclined part of the groove, as was the case with the row of pits. So if the groove track pitch,

Which was recorded in the BCA area was 0.24 pm or more and 0.45 pm or less, a defocus margin could be achieved at the same level as described above.

[0057] Thus, in the case of an optical disk where the desired distortion coefficient was obtained, the metal reflection film that was made of Ag or Ag alloy had a film thickness of 25nm or more and 70nm or less if the track pitch of a row of pits or a groove that was recorded in the BCA part, was 0.24 pm or more and 0.45 pm or less, then a defocus margin could be adequately ensured.

[0058] Next, an optical disk will be described whose metal reflection film was formed using a metal reflection film which was made of Al99Cr1 (wt%) (hereinafter referred to as the Al reflection film). First, an optical disk was prepared where an Al reflection film was formed having a film thickness of 30nm. Using the previously described recording device identifying the medium, an attempt was made to record the BCA pattern in a part where neither a row of pits nor a groove was formed. In this case, a part could be formed in which the Al reflection film has been removed, and in addition, the carrier identification information that has been recorded as a BCA pattern could also be reproduced. However, the Al reflection film was thinner than this (i.e. from 50 to 70nm), which was used in the DVD-ROM, and therefore, an appropriate defocus margin could not be obtained. In addition, on an optical disk where an Al reflection film was formed with a film thickness of about 30nm, if the BCA pattern was recorded in the area where a row of pits was created with a track pitch of 0.74 pm, which was used in the BCA area of ​​the DVD-ROM , then the same result was achieved as described above.

The result is [0059] Thus, an optical disk was prepared in which an Al reflection film with a thickness of 30nm was formed on a substrate where a row of pits with different track spacing was formed. Then, the BCA pattern was saved. FIG. 11 is a graphical representation illustrating the measurement of the BCA recording power defocus margin, corresponding to the track pitch of a row of pits which formed on the optical disk which contains the Al reflection film with a film thickness of 30nm. Its horizontal axis represents the track pitch (μη) of the row of pits, and the vertical axis represents the defocus margin (%).

[0060] Even with the Al reflection film, in the same manner as described above, a defocus margin of 20% or more is required at the time of BCA recording. In Fig. 11, the track pitch at which a defocus margin of 20% or more is obtained is 0.24 pm or more and 0.45 pm or less. Thus, even on an optical disk where an Al reflection film was created with a smaller film thickness than the DVD-ROM film if the pit track pitch that is recorded in the BCA area is 0.24 pm or more and 0.45 pm or less, an adequate defocus margin can be maintained, and media identification information can be provided. this is described below.

[0061] In particular, if the wells that are recorded in the BCA area are less than 0.45 pm, the heat capacity necessary to reach the melting point becomes extremely small because the Al reflection film is thin. In this way, the edge portion of the BCA pattern is not created in the desired manner, thereby increasing the BCA signal reproduction noise. [0062] On the other hand, if the row of pits is formed with a track pitch of 0.45 pm or more, the smaller the track pitch becomes, the more likely the recorded Probable cause row pitch

53 / 59P27788EN00 is to provide a recess at the edge of the BCA pattern. In this way, the molten Al reflection film is prevented from spreading to the portion where the cavity is formed.

As a result, in the area where cavities have been created with a smaller track pitch, the noise of the BCA pattern decreases. As a result, if a row of pits is created, a track pitch of 0.45 μm or less can be recorded that implements the appropriate margin BCA pattern that defocuses.

[0063] However, if the track pitch becomes more than 0.24 μη, the smaller surface area becomes smaller the angle of the inclined recess that is formed. This reduces the force that prevents the Al reflection film from flowing, and thus, an adequate defocus margin cannot be obtained.

[0064] Thus, if a row of pits has been formed on the substrate, with a track pitch of 0.24 pm or more and 0.45 pm or less, heat control is more easily carried out even in the Al reflection film, which has a smaller film thickness. Consequently, the Al reflection film could be almost completely removed and thus, the desired BCA pattern could be saved.

[0065] In this case, Fig. 11 shows that on an optical disk where a 30nm thick Al99Cr1 metal reflection film (wt%) has been formed, the defocus margin is dependent on the track pitch. However, on an optical disk where the desired distortion coefficient was obtained, the metal reflection film that was made of Al or Al alloy could also have a film thickness of 15nm or more and 40nm or less. In this case, if the track pitch of a row of pits that was recorded in the BCA area was 0.24 pm or wider and 0.45 pm or narrower, a defocus margin could be achieved at the same level as described above.

[0066] Similarly, the same experiment as described above was also carried out on an optical disk, where instead of a row of pits a groove was formed. Even with the groove, the same result could be achieved. Thus, if the track pitch of the groove that was recorded in the BCA area was 0.24pm or wider and 0.45pm or narrower, a defocus margin could be achieved at the same level.

[0067] Next, a multi-layer optical disk will be described, which is a multi-layer optical recording medium which is formed by laminating multiple metal reflection layers, such as information recording layers. For example, on a first polycarbonate substrate having a thickness of 1.1 mm, on which a row of pits was formed, using the magnetron device described above, the first metal film was formed, a reflection spray, which is made

Al has a film thickness of the second substrate formed

45nm.

On the carrying it out, polycarbonate having a thickness of 15 pm was glued onto the cavities, so that on its side, where these cavities are not formed, contact occurs. As the adhesive, for example, a light cured resin or the like was used which ensures permanent gluing. Then, on a second polycarbonate substrate that was glued as described above, a metal reflection film was formed, which is made of AgPdCu and has a film thickness of 28nm. On top of it, a transparent resin layer is glued, which has a thickness of 70 pm. As the adhesive, for example, a pressure-sensitive adhesive sheet or the like was used.

[0068] Even in a two-layer optical disk that was produced as described above, if the track pitch of a row of pits that was recorded in the BCA area is 0.24 pm or more and 0.45 pm or less, the focus was set in time BCA recording, and thus, the BCA pattern could be recorded on both layers. As a result, the margin

Defocus could be obtained at the same level as described above.

[0069] In this case, the method of producing the multi-layer optical disk is not particularly limited to the example described previously. Before a transparent resin layer is glued, many substrates can also be made so that a multi-layer optical disk can be obtained. In this case, even if the optical disk is layered, the focus is set at the time of the BCA recording, and thus, the BCA pattern can be recorded at the desired layer. In addition, when a transparent resin layer and a polycarbonate substrate are glued, a light-cured resin and a pressure-sensitive adhesive sheet are used. However, instead of them, an adhesive and transparent carrier such as dry photopolymer may also be used. Or, without gluing the transparent resin layer, a transparent resin layer can also be formed by using only a pressure-sensitive adhesive sheet, or only a light-cured resin.

[0070] As described above, in this multilayer optical disk, several layers were glued, thereby increasing its recording density. In addition, the track pitch of a row of pits or a groove that was formed in the BCA area was set to 0.24 pm or more and 0.45 pm or less. In this way, when the BCA pattern was saved, the focus of the laser beam was set on metal reflection films in which a row of pits or a groove was formed, so that the appropriate laser power could be applied. Consequently, a BCA pattern that had low noise and the desired width could be saved. [0071] In this case, in a ROM optical disk, the shorter its writing time is, the lower its costs are. Thus, in each of the examples described above, it is desirable that a row of pits or a groove in the BCA area and a row of pits in the main information area be created simultaneously. In addition, if the track pitch of a row of pits or a groove in the BCA area

It is very different from the track pitch of a row of pits in the main information area, when a main disk is produced, the disk rotation speed must be significantly changed intermittently. Or, the main information area is adjacent to the BCA area, and therefore, the disk speed must be controlled so that it quickly becomes the desired speed. In order to maintain its linear speed at a constant level, preferably, the track pitch of a row of pits in the main information area should be equal to the track pitch of a row of pits or a groove in the BCA area.

[0072] As described earlier, the use of a light beam having a shorter wavelength and an optical system having a larger numerical aperture for reproduction, the data can be written with a higher density than on a DVD ROM optical disk. In addition, even if the thermal conductivity or melting point, which is the intrinsic value of the metal reflection film, is different, using a conventional recording device for identifying the medium, the information identifying the medium can be recorded so that an appropriate defocus margin can be maintained. Thus, the present invention may be suitably used for an optical recording medium, for example, an optical disk which has the shape of a circular plate and is used to generate information or the like.