Optical recording medium

ES 2 339 019 T3

DESCRIPTION

Optical recording medium and reproduction procedure of the optical recording medium.

The present invention describes an optical recording medium, particularly an optical disk which is similar in shape to a circular platter and is used to reproduce information.

As a conventional medium of optical recording, for example, there is an optical disk, such as a CD-ROM and a DVD-ROM. In such an optical disk, an uneven row of pits is formed on a transparent substrate which is made of polycarbonate or the like. On the substrate, a metal reflection film is formed which is made of Al or the like. From the side of the surface opposite the surface on which this metal reflection film is formed, a beam of light is applied to the metal reflection film which is an information record surface. In this way, the information is reproduced.

Such a means of optical recording has been widely used in which information is recorded and reproduced by applying a beam of light. Thus, expectations have become greater of raising the density of the recording from now on. In recent years, a variety of optical discs have been developed which can reproduce large capacity digital data or audio-visual data. For example, research and development for a high-density ROM optical disk is now being carried out, in which the density of an optical disk having a diameter of 12 centimeters is expected to become higher than a capacity of 23.3 to 30 gigabit storage.

On the other hand, a DVD ROM recording medium is provided with a security technique, specifically, the technique of preventing someone from using and copying the illegally recorded information or from performing such acts. Like that security technique, a BCA area (or burst cut area) is provided where the Media Identification Information which is used to identify each recording media individually is overwritten in a barcode pattern. In this area of ​​BCA, when an optical recording medium is manufactured, the identification information of the medium that differs for each optical recording medium is recorded, and if necessary, a cryptographic key or a decoding key is recorded.

For example, Japanese published patent no. 10-233019 specifically reveals that a metal reflection film of an optical disk in which a row of pits is formed as the main data is partially removed by laser clipping, and the modulated data is individually recorded. Thus, the identification information of the medium is recorded, which is used to protect against illegal use and copying, or as such an act.

However, to increase the above-described density, the site between the tracks has to be narrow, or the shortest pit in a row of pit needs to be shortened. Also, relative to a high-density optical disc, 23.3 GB or more data is recorded on a 12 cm-diameter optical disc. Therefore, it has been found that if on a substrate used for such an optical disk, a metal reflection film is formed which is made of an Al alloy material having a film thickness of 50 to 70 nm. so that it can be used in a DVD ROM optical disc, which deteriorates the quality of a reproduced signal.

This is because a film of metal reflection appears to be difficult to form at the bottom of a tiny pit about 0.2 µm long. Thus, the shorter a bite becomes, the deeper and smaller it tends to be. Therefore, as a metal reflection film for the above-described high-density ROM optical disc, a metal reflection film which is used in a DVD ROM optical disc could not be as widely used as it is.

Furthermore, when a DVD ROM optical disc is manufactured, the identification information of the medium is recorded, using a medium-identification-information recording apparatus which is provided with a YAG (yttrium aluminum garnet) laser. However, even if the identification information of the medium is recorded in a bar code pattern using this medium-identification-information recording apparatus, in an area where the pits are not forming on a high-density optical disk ROM. or in a row of pits which is recorded in a track location of 0.74 pm which is the same as the DVD ROM optical disc, then the pattern could not be formed. Or, the noise of the reproduction of the identification information of the medium would be louder, and therefore, an adequate margin of blur could not be ensured.

This is because in a high-density ROM optical disc, a metal reflection film is thinner than that of a DVD ROM optical disc. Or, the material of a metal reflection film type in use is different, and thus, the necessary heat capacity until the metal reflection film reaches its melting point is largely different. Consequently, a conventional medium-identification-information recording apparatus provided with a YAG could not be used like this when a high-density ROM optical disk is manufactured.

Prior state of the art, where claim 1 is delimited, can be found in document WO02 / 37483 A1, revealing "An optical recording medium, an optical recording medium production method, optical recording medium production apparatus, program, and a half ”.

ES 2 339 019 T3

It is an object of the present invention to provide an optical recording medium in which data can be recorded with higher density than on a DVD ROM optical disc, and using a conventional medium-identification-information recording apparatus, the identification information The middle can be recorded so that an adequate blur margin can be ensured.

In an optical recording medium according to the present invention, a series of pits or a groove is formed in a secondary information area on the substrate, and the site of the series of pits or grooves is determined to be 0.24 μm. or wider and 0.45 pm or narrower. Therefore, by using a beam of light to reproduce having a shorter wavelength and an optical system having a higher numerical aperture, data can be recorded at a higher density than on a DVD ROM optical disc. In addition, although the thermal conductivity or the melting point which is the intrinsic value of the metal reflection film is different, using a conventional medium-identification-information recording apparatus, the identification information of the medium can be recorded accordingly. so that an adequate blur margin can be ensured.

By a manufacturing method for an optical recording medium in accordance with the present invention, a series of pits or a groove is formed in the secondary information area on the substrate, and the site of the series of pits or groove track it is determined at 0.24 pm or wider and 0.45 pm or narrower. Therefore, by using a beam of light to reproduce having a shorter wavelength and an optical system having a higher numerical aperture, data can be recorded at a higher density than on a DVD ROM optical disc. In addition, although the thermal conductivity or the melting point which is the intrinsic value of the metal reflection film is different, using a conventional medium-identification-information recording apparatus, the identification information of the medium can be recorded accordingly. so that an adequate blur margin can be ensured.

By this reproductive method for an optical recording medium according to the present invention, the information is reproduced by applying a light beam to the metal reflection film of the optical recording medium that includes an area of ​​secondary information where the row of pits or the groove is formed in the area of ​​secondary information on the substrate and the track site of the row of pits or the groove is determined at 0.24 µm or wider and 0.45 pm or narrower. Therefore, by using a light beam for reproduction that has a shorter wavelength and an optical system that has a higher numerical aperture, a good quality signal can be obtained by reproducing the data that has been recorded at a density. higher than a DVD ROM optical disc. In addition, although the thermal conductivity or the melting point which is the intrinsic value of the metal reflection film is different, using a conventional recording apparatus of the medium-identification information, the identification information of the medium that has been recorded on an adequate blurring range can be constantly reproduced.

Figure. 1 is a graphical representation, showing a result of the measurement of the fluctuation value which corresponds to the depth of a pit.

Figure. 2 is a graphical representation, showing a measurement result of the fluctuation value which corresponds to the film thickness of a metal reflection film which is made of an AgPdCu alloy.

Figure. 3 is a graphical representation, showing a result of the measurement of the fluctuation value which corresponds to the film thickness of a metal reflection film which is made of an A1 alloy.

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

Figure. 5 is a graphical representation, showing a reflection ratio measurement result which corresponds to the film thickness of a metal reflection film which is made of an AgPdCu alloy.

Figure. 6 is a graphical representation, showing a reflection ratio measurement result which corresponds to the film thickness of a metal reflection film which is made of an Al alloy.

Figure. 7 is a top view of an optical disc, showing an example of its main-information area and the sub-information area.

Figure. 8 is a block diagram, showing the configuration of a medium-identification-information recording apparatus which records the identification information of the medium in a BCA area.

Figure. 9 is a sectional view of an optical disk in which a metal reflection film is formed on a substrate where the pits are formed, and furthermore, it is formed with a resin layer on the metal reflection film.

Figure. 10 is a graphical representation, showing a result of the measurement of the margin of the defocusing of a power of the BCA recording which corresponds to the height of the track of a row of pits which are

ES 2 339 019 T3 formed in an optical disk that includes a 50 nm metal reflection film which is made of an alloy of AgPdCu.

Figure. 11 is a graphical representation, showing a result of the measurement of the defocusing margin of a power of the BCA recording which corresponds to the height of the track of a row of pits which are formed in an optical disk that includes a Al reflection film whose film thickness is 30 nm.

Hereinafter, a ROM MEMORY optical disc will be described as an example of the optical disc according to the representation of the present invention. Herein, an optical recording medium which is applied according to the present invention is not especially limited to this example. The present invention can also be applied to various optical recording media which information recording layer has, for example, a minute irregularity, such as an optical magnetic disk and a phase-change disk.

The optical disk of the ROM MEMORY includes: a main information area in which a film of metal reflection is formed on a substrate where an uneven row of pits is formed as main data; and a secondary information area in which the identification information of the medium that is used to identify the optical disc individually is recorded by removing the film from the metal reflection partially and forming a plurality of reflecting film removed areas. In this optical disk, the information is reproduced by irradiating the metal reflector film with a beam of light.

Generally, in order to raise the density of a ROM optical disk, the height between the tracks has to be narrowed, and the shortest pit length (or shortest mark length) needs to be shortened extremely. However, if the height of the track becomes too narrow, the crosstalk becomes a larger characteristic RF-signal. This prevents ensuring an adequate system margin. If the shortest length of the sting becomes too short, then the resolution of a reproduced signal drops, thereby worsening the value of the jitter of the reproduced signal.

Therefore, an examination is repeatedly made of the most suitable track height, using an information reproduction apparatus in which the wavelength λ of a light source of a light beam for reproduction is 405 nm and A numerical aperture NA of an objective lens is 0.85. As a result of such an examination, the following resulting measurements are obtained. This presents the fact that if a track height is 0.24 pm or wider, the crosstalk signal can be practically abandoned, compared to a main signal.

<td>track height (pm)</td><td>Fluctuation value (%)</td><td></td>

<td> 0.20</td><td colspan="2"> 7.6</td>

<td> 0.22</td><td> 7.0</td><td></td>

<td> 0.24</td><td> 6.5</td><td></td>

<td> 0.26</td><td> 5.6</td><td></td>

<td> 0.28</td><td> 5.4</td><td>i</td>

In addition, the suitable shortest bite length is examined, using the information reproduction apparatus described above. As a result of studying a resolution necessary to obtain a desirable reproduction signal, a measurement result is obtained as follows. It turns out that if the shortest sting length is 0.12 pm or longer, the resolution of the playback signal can be suitably stable.

<td>Shortest bite length (pm)</td><td>Fluctuation value (%)</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>

Here, in the consideration of different margins of an optical disc or of a drive, a jitter value showing characteristics of an optical disc needs to be 6.5% or below.

Here, the information on a 12 cm-diameter optical disc is reproduced, using the information reproducing apparatus. In order to determine the storage capacity of the optical disk at 23.3 GB or above, an expression

ES 2 339 019 T3 related (the shortest pit length) x (the runway height) &lt;0.0512 pm² it has to be satisfied. For example, if the recording capacity is 23.3 GB and the shortest sting length is 0.12 pm, the upper limit of the track height is about 0.43 pm. Likewise, if the recording capacity is 23.3 GB and the shortest pit length is 0.24 pm, the upper limit of the track height is about 0.21 pm.

Next, a manufacturing method will be described for a 12 cm-diameter optical disk that has a recording capacity of 23.3 GB or higher. As described above, in order to create a 12 cm-diameter optical disc that has a recording capacity of 23.3 GB or greater, a substrate has to be used in which the track height is 0.24 pm or wider and 0.43 pm or greater. narrower, and its shortest sting length is 0.12 pm or longer and 0.21 pm or shorter.

For example, in order to create a 12 cm-diameter optical disk that has a recording capacity of 25 GB, first, a substrate is prepared where a row of pits is formed that has a shorter pite length of 0.149 pm and a track line from 0.32 pm. Like this substrate, for example, a substrate made of polycarbonate can be used which is created by an injection molding machine.

Next, a film of metal reflection is formed on this substrate, using a film-forming apparatus. As the film-forming apparatus, one that can form a film of metal reflection uniformly, such as a magnetron bombardment apparatus and a vapor deposition apparatus, can be used. For example, using a magnetron bombardment apparatus, the time for film formation can be varied, thereby controlling the film thickness of the metal reflection film. Enclosed, the material, the film thickness, or the like, of the metal reflection film will be described later.

Next, the optical disk is placed in a rotation coater, with the metal reflection film continued. Then, a resin that will harden by ultraviolet rays is dripped, and on top of it, an 88 pm thick transparent sheet which is made of polycarbonate is placed. In this state, the resin hardener ultraviolet ray is irradiated with the ultraviolet rays while the optical disk is being rotated by the spin coater. At this time, the rotation speed of the rotation coater is controlled, so that the thickness of the resin cured by the UV ray after it has cured becomes 12 pm. Consequently, a transparent resin layer having a film thickness of 100 µm is formed on the metal reflection film. For example, an acrylic resin can be used as this UV hardened resin.

As described above, the metal reflection film was formed on the substrate where the row of pits was formed having a shorter pit length of 0.149 pm and a track height of 0.32 pm. On top of it, the resin layer having a film thickness of 100 pm is formed, and therefore, an optical disk is manufactured.

Next, with respect to the optical disc that was being manufactured as described above, a study was made of the depth of a pit corresponding to the quality of a reproduced signal, the material and the film thickness of the reflection film of metal, and the like. Specifically, the manufactured optical disk was determined in the information reproducing apparatus described above. Then, this information reproducing apparatus allowed a beam of light to be incident on the metal reflection film through the 100 pm thick resin layer. Thus, a reproduced signal was obtained from the optical disk, and then it was evaluated.

First, an examination was made of how much quality of a reproduced signal depended on the depth of a bite. In the optical disk that was manufactured as described above, the fluctuation values ​​that were measured showed the scattering of signals reproduced when the depth of a pit varied. Figure. 1 is a graphical representation, showing a result of the measurement of the value of a fluctuation which corresponds to the depth of a bite. Its horizontal axis is the depth (nm) of a bite and the vertical axis is the value (%) of a fluctuation. In figure. 1, as the metal reflection film, was the one used which was made of an aluminum alloy with a purity of 99 wt% and had a film thickness of 25 nm. However, even when the one that was made from an Ag98Pd1Cu1 (wt%) (hereinafter referred to as the AgPdCu alloy), the same result as the following was obtained.

Generally, in order to ensure an adequate margin of the system, the value of a fluctuation has to be 6.5% or less. In figure. 1, it could be seen that if the depth of a pit is determined at 44 nm or higher and at 88 nm or lower, the value of a fluctuation would be 6.5% or lower. In addition, a refractive index n of the created resin layer was 1.53, and a wavelength λ of the light beam was 405 nm. Therefore, taking the measurement result described above into consideration, you could see that a depth D of a pit at which a desirable reproduction signal could be obtained is d / (6xn) or higher, and d / (3xn) or lower.

This appears to be for the following reason. Specifically, the depth of a pit affects the amplitude of a reproduced signal, and in an optical calculation, when the depth of a pit is d / (4xn), the amplitude becomes maximum. If the index of refraction n of the resin layer is 1.53 and the wavelength λ of the light beam is 405 nm, this becomes maximum when the depth of the pit is above 66 nm. But, even if the amplitude becomes a little smaller, the value of the jitter of a reproduced signal is almost unchanged. But nevertheless,

ES 2 339 019 T3 if the depth of the pit is below d / (6xn), or if the depth of the pit is above d / (3xn), then a suitable signal-to-noise ratio (below, referred to as the S / n ratio) cannot be obtained, thereby worsening the fluctuation value of the reproduced signal.

Next, a study was made of a suitable film thickness of a metal reflection film. First, a substrate was prepared in which the depth of a pit is d / (4xn). As the metal reflection film, two types were used which were a metal reflection film that was made of AgPdCu alloy and a metal reflection film that was made of an aluminum alloy with a purity 99 wt%. Then, the value of a fluctuation was measured when its film thickness was varied. Figure. 2 is a graphical representation, showing a result of the measurement of the fluctuation value which corresponds to the film thickness of the metal reflection film which is made of the AgPdCu alloy. Figure. 3 It is a graphical representation, showing a result of the measurement of the fluctuation value which corresponds to the thickness of the film of the metal reflection film which is made of aluminum alloy. In each figure, the horizontal axis is the film thickness (nm) of the metal reflection film, and the vertical axis is the value (%) of a fluctuation.

As can be seen in the figure. 2, In the case of AgPdCu alloy metal reflection film, if its film thickness was 25 nm or more and 75 nm or less, the value of a fluctuation became 6.5% or lower . Moreover, as shown in the figure. 3, In the case of aluminum alloy metal reflection film, if the thickness of the film was 15 nm or more and 40 nm or less, the value of a fluctuation became 6.5% or less. Here, the material of a metal reflection film is not limited especially to those examples. Other material can also be used, as long as it has a high reflactance ratio and can be uniformly formed on a substrate by a film-forming apparatus. Furthermore, in order to improve its corrosion resistance, a rare earth metallic element such as Nd, or a transition metallic element such as Ti and Cr, can also be added in a small amount to the Ag or Al film material. aluminum reflection.

Next, the reflection ratio of a metal reflection film was examined. The thinner a metal reflection film becomes, the smaller the amount of reflected light. Then, when the amount of reflected light becomes smaller, in proportion to this, an average noise also lower. This keeps the S / N ratio unchanged. On the other hand, a system noise or a laser noise does not depend on the amount of reflected light. If the noise of the system or the noise of the laser is far lower than the average noise so it can be neglected, then this will not affect the quality of a reproduced signal, although the amount of reflected light becomes smaller.

However, if the amount of reflected light becomes smaller, and the system noise or laser noise reaches the same level as the average noise, then the quality of the reproduced signal will deteriorate as the amount of reflected light decreases. . Besides, if the metal reflection film is made of a different material even though it has the same film thickness, this will change its reflection ratio, and therefore, the film thickness will change in which the quality of the signal gets worse. Also, if the metal reflection film becomes thicker, the reproduced signal will become worse. For example, in a magnetron bombardment apparatus, metal atoms in a target that have been bombarded by Ar ions come flying over a substrate, so that a film of reflection from the metal is formed. The size of these metal atoms also depends on the structure of a film-forming apparatus, or the film-forming conditions. But such a film tends to be difficult to form on the bottom of the shorter sting.

Figure. 4 is a 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 100 nm is formed on a substrate where the pits are formed. As the picture shows. 4, a shorter pit 11 and a long pit 12 that is longer than the shorter pit 11 are formed on a substrate 1. In this case, at the bottom of the shorter pit 11, a film of metal reflection 2 is more difficult to form than at the bottom of the long pit 12. Therefore, the shorter pit 11 after the metal reflection film 2 has been formed to become smaller, and at the same time, deeper than it was on substrate 1.

If you anticipate this phenomenon, and thus make a higher recording power so that the shorter sting 11 can be higher, then the signal quality of the shorter sting 11 will improve. However, when the recording power becomes larger, the long pit 12 will become wider. This causes greater crosstalk which comes from adjacent tracks, thus making the value of a jitter worse. In consideration of the factors that can worsen the signal quality of both types of films, the substrates were formed that were suitable for metal reflection films of an aluminum alloy and an AgPdCu alloy. Consequently, the maximum film thickness of the aluminum alloy metal reflection film in which the value of a fluctuation was prevented from deteriorating was 40 nm, and the maximum film thickness of the reflection film of the AgPdCu alloy metal in which it was prevented from deterioration was 70 nm.

Based on this study, a reflection ratio was measured which corresponded to the film thickness of each of the AgPdCu alloy metal reflection films that is shown in the figure. 2 and the aluminum alloy metal reflection film which is shown in figure. 3. Figure. 5 is a graphic representation, showing a result of the measurement of the reflection ratio which corresponds to the thickness of the film of

ES 2 339 019 T3 a metal reflection film which is made of an alloy of AgPdCu. Figure. 6 is a graphical representation, showing a result of the measurement of the reflection ratio which corresponds to the film thickness of a metal reflection film which is made of an aluminum alloy. In each figure, the horizontal axis is the film thickness (nm) of the metal reflection film, and the vertical axis is the reflection ratio (%). Here, 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 405 nm.

As can be seen in the figure. 5, in the case of the AgPdCu alloy metal reflection film, the reflection ratio that corresponded to a film thickness of 25 nm to 70 nm in which a desirable fluctuation value was obtained were as follows 35% to 70%. In the case of the aluminum alloy metal reflection film in figure. 6, the reflection ratio corresponding to a film thickness of 15 nm to 40 nm in which a desirable fluctuation value was obtained was 35% to 70%. As a result, for each film, the metal reflection film reflection ratio in which the quality of a reproduced signal could be guaranteed was 35% or higher and 70% or low.

Next, to obtain a reproduction signal having a desirable jitter value as described above, an uneven row of pits is formed as main data in a main-information area of ​​an optical disk. A detailed description will be given of the identification information of the medium which is formed in a secondary-information area of ​​the optical disk. Figure. 7 is a top view of an optical disc, showing an example of its primary-information area and secondary-information area.

In the example shown in the figure. 7, a main-information area 21 (which is in a shaded part in the figure) is determined in the outer circular part in the optical disk. Inside the ring-shaped part of the outer circular part, an area BCA 22 (which is the area between two circles shown by the dashed lines in the figure) is determined which is an area of ​​information- secondary. In the BCA area 22, the identification information of the medium 23 is recorded in a bar code pattern. A layer of the transparent polycarbonate resin or the like is formed on the metal reflection film, and after that, the identification information of the medium 23 is recorded by irradiating, with a pulse laser (that is, a laser of YAG), the film of metal reflection which is stretched to a depth of 0.1 mm from the surface of the optic disk. At this time, the reflection film of the metal seems to melt, and then, it accumulates on both parts of the border by surface tension. In this way, the reflection film of the metal is partially removed, and thus, several removed areas of reflection-film are formed. This creates a BCA area where the identification information of the medium is recorded that is used to identify the individual optical disc.

Next, the method of recording the identification information of the medium in the BCA area of ​​an optical disc will be described in detail. Here, in the following example, a method by which an etching is made in the BCA area is described, with respect to a metal reflection film which is made of Ag98Pd1Cu1 (% wt), or to a reflection film of metal which is made of Al99Cr1 (% wt), like the metal reflection film. However, as long as the same effect can be obtained, the present invention can also be applied to different types of metal reflection films, phase-change film, or magnetic register optical film.

Figure. 8 is a block diagram, showing the configuration of a medium-identification-information recording apparatus which records the identification information of the medium in a BCA area. The medium-identification-information recording apparatus shown in figure. 8 is a BCA-pattern recording device that is used to create a BCA area on a DVD-ROM. Includes: a 101 motor; a rotation control section 102; an optical pickup 103; a laser drive section 104; a waveform determining section 105; a BCA-signal generation section 106; a focus control section 107; a preamplifier 108; and a system control section 109.

The rotation control section 102 controls the rotation of the motor 101. The motor 101 rotates an optical disk 100 at a predetermined rotational speed. The BCA-signal generation section 106 creates a BCA signal by modulating the identification information of the medium which is recorded on the optical disk 100. Based on the BCA signal, the waveform determination section 105 creates a waveform from laser modulation. Depending on the waveform of the laser modulation, the laser drive section 104 drives a high-power laser within the optical pickup 103. The optical pickup 103 converges a beam of light emitted from the high-power laser, through its built-in optical system, on the optical disk 100. The preamplifier 108 amplifies a reproduced signal which comes from the optical pickup 103, and then outputs it to the focus control section 107. Using the amplified signal coming from the preamplifier 108, the focus control section 107 controls the interior of the objective lens of the optical pickup 103, so that a beam of light can converge 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 waveform determining section 105, the BCA generation section -signal 106, and the focus control section 107.

Next, a recording operation of the medium-identification-information recording apparatus which is configured as described above. First, based on an instruction from the system control section 109, the rotation control section 102 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, a beam of light which is emitted from

ES 2 339 019 T3 the high power laser is applied to the optical disk 100 of the optical pickup 103. At this time, the focus control section 107 executes the focus control so that the beam of light that has been emitted from the laser high power converge on the optical disk 100 metal reflection film.

Here, the reflected light from the optical disk 100 is detected by a photodetector within the optical pickup 103. Then, a reproduced signal is emitted as an electrical signal from the photodetector. This reproduced signal is amplified through the preamplifier 108 and is input to the control section of the focus 107. In response to the amplified signal, the focus control section 107 drives the objective lens from the optical pickup 103 and moves it slightly in a focus direction on the optic disk 100. Thus, it controls the optical pickup 103 for the light beam. can converge on the metal reflection film of the optical disk 100.

Next, the system control section 109 allows a position detector (not shown) to detect the position of the optical pickup 103 in a tracking direction. Based on the positional information detected, it recognizes the optical pickup 103 to be located in an initial position of the recording of the secondary information. Next, the system control section 109 instructs the BCA signal generation section 106 to generate a BCA signal. Then, the BCA signal is output from the waveform determining section 105, beginning of a BCA recording sequence, and the identification information of the medium is recorded in the BCA area.

On an optical disk where a film made of metal reflection of 50 nm thickness made of an alloy of AgPdCu was formed, using the medium-identification-information recording apparatus described above, an attempt to record a BCA pattern ( or a barcode pattern) was made in a part where neither a row of pits nor the groove was formed. However, even if the output power of a laser was increased, a reflection-film removed area in which the metal reflection film was removed could not be created.

This is because the melting point of Al is 660 ° C while the melting point of Ag is 960 ° C. This takes a larger amount of energy to melt the metal reflection film of an AgPdCu alloy. Furthermore, the thermal conductivity of Al is 237 W / (mK) while the thermal conductivity of Ag is 427 ° C. Therefore, a larger amount of heat is diffused by heat conduction, although the metal reflection film of an AgPdCu alloy is radiated with a beam of light. Here, in general, the melting point of metal is lowered by mixing a different metal. However, in order to ensure adequate reflection ratio and avoid corrosion, the wt% of Ag in the metal reflection film cannot be reduced to 97% or below.

Next, in the optical disk where the 50 nm thick metal reflection film made of an AgPdCu alloy, a row of pits was formed at a track height of 0.24 pm which was used in the BCA area of a DVD-ROM, and a BCA pattern was recorded on that part. At this time, the BCA pattern could not be recorded in a predetermined width, and thus, the information could not be reproduced. However, a part of the reflection film of the AgPdCu alloy metal melts, and a small part of the reflection film withdrawn could be formed. This is because a metal reflection film tends to be difficult to form on an inclined surface of an uneven substrate, and thus, the film thickness of the metal reflection film on a portion of the inclined surface of the Pit becomes thin locally and heat conduction is impeded.

Figure. 9 is a sectional view of an optical disk in which a metal reflection film is formed on a substrate where pits are formed, and furthermore, a resin layer is formed on the metal reflection film. As shown in the figure. 9, the metal reflection film 2 is formed on the substrate 1 where the pit 12 is formed, and furthermore, a resin layer 3 is formed on the metal reflection film 2. In this case, the film thickness of the metal reflection film 2 which is formed on an inclined surface part 4 becomes thinner than the film thickness of the metal reflection film 2 which it is formed in each of a part of the bottom of the pit 5 and of a part of the flat plate 6. In such a way, the amount of heat that is conducted around becomes smaller. Therefore, the narrower the track height of a row of pits becomes and the larger the area of ​​the inclined surface part 4 becomes, the easier the heat will be conducted around. Furthermore, in the inclined surface part 4, the per unit volume of the metal reflection film 2 is smaller than any other part. Therefore, its thermal capacity necessary to reach the melting point becomes smaller, and thus, it reaches the melting point with a lower irradiation power.

Based on the knowledge previously described, the optical discs were prepared in which a film of metal reflection of a thickness of 50 nm made in an alloy of AgPdCu was formed on each substrate where a row of pits was formed at various heights. track. Then, a BCA pattern was recorded on each optical disc. Figure. 10 is a graphical representation, showing a result of the measurement of the blur margin and a recording power of BCA which correspond to the height of the track of a row of pits which are formed in an optical disk that includes a film of the reflection of the 50 nm metal which is made from an alloy of AgPdCu. Its horizontal axis is the track height (um) of a row of pits and the vertical axis is the blur margin (%).

As shown in the figure. 10, in the area where a row of pits was formed at a track height of 0.54 pm or less, a BCA pattern could be recorded, and the identification information of the medium could be recorded. On the other hand, in the area where a row of pits was formed at a track height of 0.54 µm or more, no margin of blurring could be ensured. Here, the judgment that a BCA pattern was

ES 2 339 019 T3 recorded, was made by determining and reproducing the optical discs created in an evaluation machine. It was done based on whether or not the identifying information of the medium that was recorded in the BCA area could be accurately reproduced. As the evaluation machine, a reproduction apparatus was used in which a beam of light for reproduction had the wavelength λ of 405 nm and an objective lens had a numerical aperture NA of 0.85.

Here, if you take the mass production of optical discs into consideration; you have to consider a number of factors, such as the film thickness dispersion of a metal reflection film, and a variation in a BCA recording power. Therefore, a blur margin of 20% or higher is required as your adequate level. In the figure. 10, the runway height at which a 20% or higher blur margin is obtained is 0.24 pm or wider and 0.45 pm or narrower. Therefore, if the track height of a row of pits which is recorded in the BCA area is 0.24 pm or wider and 0.45 pm or narrower, the adequate blur margin can be ensured, and the information of Media identification can be recorded. The presumable reason for this is described below.

Specifically, if the track height of a row of pits which is recorded in the BCA area is beyond 0.45 pm, the number of pits per unit area becomes smaller, and thus, the area of ​​the parts. of the inclined surface of pitting also becomes smaller. This prevents heat conduction from being properly cut. Therefore, if the thermal capacity that is absorbed by a metal reflection film varies according to defocusing, a BCA pattern in which noise is low cannot be recorded.

On the other hand, if the runway height is narrower than 0.24 pm, a pit is also closer to its adjacent pit. Therefore, the formation of a part of the earth between the pits becomes inadequate, and the angle of the part of the inclined surface of a pits becomes narrower. Thus, a film of metal reflection becomes easier to form on the sloping surface portions of such pits, and thus, the effect of cutting off the heat conduction by the formation of pits is reduced. Here in the figure. 10, a BCA pattern could be recorded and played back to the point where the track height was 0.22 pm, while a BCA pattern could not be recorded when the track height was narrower than 0.22 pm. Therefore, in the figure. 10, a dotted line is an estimated line which corresponds to a runway height of 0.22 pm or less.

Also, the figure. 10 shows that in an optical disk where a 50 nm thick metal reflection film made of an AgPdCu alloy was formed, the defocusing margin is dependent on the height of the track. However, in an optical disk where a desirable fluctuation value was obtained, a metal reflection film which was made from Ag or an Ag alloy may also have a film thickness of 25 nm or greater and 70 nm or less. In that case, if the track height of a row of pits which was recorded in a BCA area was 0.24 pm or higher and 0.45 pm or narrower, a blur margin could be obtained at the same level as described. previously.

Similarly, instead of a row of pits, the same experiment as described above was also conducted on an optical disk where a track was formed. Even in the case of a track, a film of metal reflection tends to be difficult to form on the sloping part of the track, as is the case with a row of pits. Thus, if the track height of a groove that was recorded in a BCA area was 0.24 pm or wider and 0.45 pm or narrower, a blurring margin could be obtained at the same level as described above.

Therefore, in the case of an optical disk where a desirable fluctuation value was obtained, a metal reflection film which was made of Ag or an Ag alloy had a film thickness of 25 nm or more. and 70 nm or less, if the track height of a row of pits or a groove which was recorded in a part of BCA was 0.24 pm or wider and 0.45 pm or narrower, then a margin of blur could be adequately insured.

Next, an optical disk will be described in which the metal reflection film was created using a metal reflection film that was made from an Al99Cr1 (wt%) (hereinafter referred to as the metal reflection film). aluminum). First, an optical disk was prepared where aluminum reflection film having a film thickness of 30 nm was formed. Using the above-described medium-identification-information recording apparatus, an attempt to record a BCA pattern was made 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 aluminum reflection film was removed, and furthermore, the identification information of the medium that was recorded as the BCA pattern could also be reproduced. However, the aluminum reflection film was thinner than that (ie 50 to 70 nm) that was used on a DVD-ROM, and thus, an adequate defocusing range could not be obtained. Also, in the optical disk where the aluminum reflection film was formed with a film thickness of 30 nm, if a BCA pattern was recorded in the area where a row of pits was formed at the 0.74 pm heights of the track which was used in the BCA area of ​​the DVD-ROM, then the same result as described above was obtained.

Therefore, an optical disk was prepared where the aluminum reflection film with a film-thickness of 30 nm was formed on a substrate where a row of pits was formed at various heights of the track. Then a BCA pattern was recorded. Figure. 11 is a graphical representation, showing a result of the measurement of the

ES 2 339 019 T3 margin of defocusing of a BCA recording power which corresponds to the height of the track of a row of pits which are formed in an optical disk that includes a film of reflection of aluminum which has a thickness of the 30 nm film. Its horizontal axis is the track height (nm) of a row of pits, and the vertical axis is the blur margin (%).

Even in the case of aluminum reflection film, in the same way as described above, a blur margin of 20% or higher is required at the time of BCA recording. In the figure. 11, the track height at which a blur margin of 20% or higher is obtained is 0.24 pm or wider and 0.45 µm or narrower. Therefore, even in the optical disc where the aluminum reflection film with a film thickness thinner than that of a DVD-ROM is formed, if the height of the pitting track which is recorded in the area of BCA is 0.24 pm or wider and 0.45 pm or narrower, an adequate blur margin can be ensured, and the identification information of the medium can be recorded. The presumable reason for this is described below.

Specifically, if the track height of a row of pits that is recorded in the BCA area is beyond 0.45 jum, the thermal capacity necessary to reach the melting point becomes extremely small, because the reflection film aluminum is thin. Thus, the edge portion of a BCA pattern is not desirably formed, thus making the signal noise of the BCA reproduction louder.

On the other hand, if a row of pits is formed in a track height of 0.45 μm or narrower, the narrower the track height becomes, the more likely a pit is formed at the edge of a BCA pattern. . Thus, the molten film of the aluminum reflection remains flowing in the part where a pit is formed. Therefore, in the area where the pits are formed at a narrower height of the track, the noise of a BCA pattern becomes lower. As a result, if a row of pits is formed at a track height of 0.45 pm or narrower, a BCA pattern that performs an adequate margin of blur can be recorded.

However, if the track height becomes narrower than 0.24 pm, the angle of the inclined surface of a pit which is formed becomes narrower. This weakens the force that prevents the film from reflecting off the flowing aluminum, and thus, an adequate defocusing margin cannot be obtained.

Therefore, if a row of pits is formed in a substrate at a track height of 0.24 pm or more and 0.45 pm or less, heat control is easily conducted even in an aluminum reflection film that have a thin film thickness. Therefore, the aluminum reflection film could be almost completely removed, and thus, a desirable BCA pattern could be etched.

Here, the figure. 11 shows that in an optical disk where a 30 nm thick metal reflection film made of Al99CM (wt%) was formed, the defocusing margin is dependent on the height of the track. However, in an optical disk where a desirable fluctuation value was obtained, a metal reflection film that was made of aluminum or an aluminum alloy might also have a film thickness of 15 nm or greater and of 40 nm or less. In that case, if the track height of a row of pits that was recorded in a bCa area was 0.24 pm or wider and 0.45 pm or narrower, a blur margin could be obtained at the same level as described. previously.

Similarly, instead of a row of pits, the same experiment as described above was also conducted on an optic disk where a groove was formed. Even in the case of a groove, the same effect could be produced. Thus, if the track height of a groove that was recorded in a BCA area was 0.24 µm or wider and 0.45 pm or narrower, a margin of blurring could be obtained at the same level.

Next, a multi-layer optical disk will be described which is a multi-layer recording medium that is formed by laminating a plurality of metal reflection films as layers of the information record. For example, in a first polycarbonate substrate that has a thickness of 1.1 mm where a row of pits is formed, a first film of metal reflection which is made of aluminum and has a film thickness of 45 nm is formed. , using the magnetron bombardment apparatus described above. On it, a second polycarbonate substrate having a thickness of 15 µm where the pits are formed is glued, so that this side where the pits are not formed comes into contact. As the adhesive, for example, a resin that will harden by light or the like is used which is a strong contact adhesive. Then, on the second polycarbonate substrate which has been glued in such a way as described above, a film of metal reflection is formed which is made of AgPdCu and has a film thickness of 28 nm. On top of it, a layer of transparent resin is glued which has a thickness of 70 μιη. As the adhesive, for example, a pressure-sensitive adhesive sheet or the like is used.

Even on the double-layer optical disc which was created in such a way as described above, if the track height of a row of pits that was recorded in a BCA area is 0.24 μm or wider and 0.45 pm or narrower, a focus was adjusted at the time of a BCA recording, and thereby, a BCA pattern could be recorded on both layers. Therefore, a margin of blur could be obtained at the same level as described above.

ES 2 339 019 T3

Here, the method of creating a multilayer optical disc is not especially limited to the example described above. Before a layer of the transparent resin is glued, a plurality of substrates can also be formed, so that a multilayer optical disk can be obtained. In this case, even if an optical disc is layered, a focus is set at the time of a BCA recording, and in such a way that a BCA pattern can be recorded on a desired layer. In addition, when a layer of the transparent resin and a polycarbonate substrate are glued, a light-hardened resin and a pressure-sensitive adhesive sheet are used. But instead, an adhesive and a transparent medium, such as a dry photopolymer, can also be used. Or, without gluing a layer of the transparent resin, a layer of the transparent resin can also be formed using only a pressure sensitive adhesive sheet, or only a light-hardened resin.

As described above, in this multilayer optical disc, the various layers were glued together, thereby increasing their recording density. Furthermore, the track height of a row of pits or the furrow which were formed in the BCA area was determined between 0.24 pm or wider and 0.45 pm or narrower. Thus, when a BCA pattern was engraved, the focus of a laser light beam was adjusted to the reflection films of the metal in which the row of pits or the groove was formed, so that a laser power adequate could be applied. Therefore, a BCA pattern could be recorded which had a low noise and a desired width.

Here, in an optical disk ROM, the shorter its recording time becomes, the lower its costs. Therefore, in each of the examples described above, it is desirable that a row of pits or the groove in the BCA area and a row of pits in the main information area be formed simultaneously. Also, if the track height of a row of pits or groove in the BCA area is largely different from the track height of a row of pits in the main info area, when a master disc is manufactured, the rotational speed of the disc has to be largely discontinuously changed. Or, the main information area is adjacent to the BCA area, and thus the rotational speed of the disk needs to be controlled so that it becomes a desired rotational speed as fast as possible. To make its linear velocity constant, preferably, the height of the track of a row of pits in the main information area should be equal to the height of the track of a row of pits or of a groove in the area of ​​BCA.

As described above, according to the present invention, using a beam of light for reproduction having a shorter wavelength and an optical system having a higher numerical aperture, data can be recorded at a higher density than a DVD ROM optical disc. In addition, although the thermal conductivity or the melting point which is the intrinsic value of a metal reflection film is different, using a conventional medium-identification-information recording apparatus, the identification information of the medium can be recorded. so that an adequate defocusing margin can be ensured. Therefore, the present invention can be conveniently applied to an optical recording medium, for example, an optical disk which has a circular plate shape and is used to generate information, or the like.