WO2015020135A1 - Optical recording medium - Google Patents

Abstract

The present invention addresses the problem of providing an optical recording medium such that the extinction coefficient (k) of recording layers can be reduced in order to achieve further improvement of transmissivity. In order to resolve the problem, an optical recording medium according to one embodiment of the present invention is equipped with recording layers comprising: auxiliary recording films for which the extinction coefficient (k) of light in the 405 nm wavelength is less than or equal to 0.012; and main recording films which are disposed adjacent to the auxiliary recording films, and which can propagate heat generated by absorption of recording-use laser light to the auxiliary recording films. As a result, it is possible to provide an optical recording medium comprising recording layers of high transmissivity, and multi-layering becomes possible.

Description

Optical recording medium

The present invention relates to an optical recording medium having a high transmittance recording layer and suitable for multilayer recording layers.

In recent years, in the field of optical discs, development of write-once type multilayer optical recording media compatible with blue lasers has been promoted for the purpose of high density recording and large capacity. In a multilayer optical recording medium, high transmittance is required for each film so that laser light with sufficient power can be incident on the recording film farthest from the laser incident surface when multilayered. Yes. *

In general, it is possible to increase the transmittance by reducing the film thickness. However, since the recording film greatly affects the recording characteristics, it is impossible to reduce the film thickness by giving priority only to the transmittance. On the other hand, by reducing the light absorptivity of the recording film, it is possible to improve the transmittance while maintaining a film thickness that can ensure recording characteristics. *

For example, in Patent Document 1 below, the ratio of nitrogen in metal nitride is controlled in the step of forming a recording layer by reactive sputtering in an atmosphere containing argon and nitrogen with an alloy target made of metal constituting metal nitride. It is described that the light absorption rate of the recording layer is changed. Further, Patent Document 2 described below describes that when the bismuth oxide-based recording layer is formed by sputtering, increasing the amount of argon introduced increases the light absorption rate of the recording layer.

JP 2006-182030 A JP 2008-68491 A

However, in the methods described in Patent Documents 1 and 2, there is a limit to a decrease in the light absorption rate with respect to light having a wavelength of 405 nm, for example, and thus there is a limit to an increase in transmittance. *

In view of the circumstances as described above, an object of the present invention is to provide an optical recording medium in which the extinction coefficient (k) of the recording layer can be reduced to further improve the transmittance.

An optical recording medium according to an aspect of the present invention includes a recording layer, and the recording layer includes an auxiliary recording film and a main recording film. The auxiliary recording film has a light extinction coefficient (k) of 0.012 or less at a wavelength of 405 nm. The main recording film is disposed adjacent to the auxiliary recording film, and is configured to be able to propagate heat generated by absorption of a recording laser beam to the auxiliary recording film. *

According to the above optical recording medium, an optical recording medium having a recording layer with high transmittance can be provided, and multilayering is possible. The main recording film can generate heat necessary for forming the recording mark portion on the auxiliary recording film. *

The auxiliary recording film may have a recess formed in the vicinity of the interface with the main recording film in the recording mark portion after recording. The concave portion is a gap observed in a state where the recording mark portion is recessed in the back direction when viewed from the cross section. The area where the concave portion is formed can change the reflectance of the recording / reproducing light with respect to the other areas. Therefore, the concave portion can assist the function as a recording mark, and the recording characteristics can be improved. *

The auxiliary recording layer may have a light extinction coefficient (k) of less than 0.005 at a wavelength of 405 nm. *

Thereby, an optical recording medium having an auxiliary recording film with a very high transmittance can be provided, and further multilayering is possible. Further, the auxiliary recording film can have a structure in which oxygen deficient portions are suppressed, and a stable structure can be maintained over a long period of time even by irradiation with reproduction light or the like. *

Specifically, the auxiliary recording film may be an inorganic film of at least one of NbO-based and BiO-based. Thereby, an auxiliary recording layer having an extinction coefficient (k) of less than 0.005 can be formed relatively easily. *

The auxiliary recording film may be a sputtered film formed in an atmosphere containing at least argon and oxygen.
Sputtering in an atmosphere containing at least argon, which is the carrier gas during sputtering, and oxygen that reduces oxygen vacancies suppresses the formation of oxygen vacancies, and an auxiliary recording film with high transmittance can be obtained. Is possible

In this case, the auxiliary recording film may contain at least argon gas and oxygen gas. That is, the auxiliary recording film can be formed by involving argon and oxygen contained in the atmosphere during sputtering. Thereby, gas emission or the like occurs from the auxiliary recording film when the recording laser light is irradiated, and the shape change or the like of the auxiliary recording film can be caused. Therefore, the recording characteristics of the optical recording medium can be improved. *

More specifically, the auxiliary recording film may have a concave portion containing the gas in a recording mark portion formed by the heat of the recording laser beam. As described above, the gas in the auxiliary recording film is released by the heat of the recording laser beam, and a recess can be formed. Therefore, the optical recording medium can use the concave portion as a recording mark in addition to the phase change of the main recording film, and can further improve the recording characteristics. *

Alternatively, the auxiliary recording film may further contain nitrogen gas. Thereby, the extinction coefficient (k) in the recording / reproducing light can be set to 0 or a value close to 0. Also in this case, the gas in the auxiliary recording film is released by the heat of the recording laser beam, and a recess can be formed. Therefore, the optical recording medium can use the concave portion as a recording mark in addition to the phase change of the main recording film, and can further improve the recording characteristics. *

The main recording film may be a film made of a material containing at least one of iron, germanium, copper, tin, and manganese. *

By using the above material for the main recording film, the phase can be changed from amorphous to crystalline by the heat of the recording laser beam, and the recording mark portion can be easily formed. *

Alternatively, the optical recording medium further includes a first optical adjustment film and a second optical adjustment film which are disposed adjacent to the main recording film and the auxiliary recording film, respectively, and are made of a metal oxide. The laminated structure of the first optical adjustment film, the main recording film, the auxiliary recording film, and the second optical adjustment film has the second optical adjustment film as a light incident surface, and the first optical adjustment film. A recording / reproducing layer having a transmittance of 93% or more with respect to light having a wavelength of 405 nm when the optical adjusting film of FIG. The first and second optical adjustment films can adjust optical characteristics such as the transmittance of the optical recording medium and the reflectance necessary for recording and reproducing information. Further, the recording / reproducing layer can provide an optical recording medium having a high transmittance. *

Further, the optical recording medium further includes a guide layer having a guide groove for tracking control, and a planarization layer made of a transparent resin disposed between the guide layer and the first optical adjustment film, Four or more recording / reproducing layers may be laminated on the planarizing layer via an intermediate layer. Thereby, since each film included in the recording / reproducing layer can be formed as a flat film without a guide groove, multilayering can be easily realized.

1 is a schematic cross-sectional view showing an optical recording medium according to a first embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the guide layer of the said optical recording medium. It is a schematic diagram which shows the guide track of the said guide layer. It is a schematic sectional drawing which shows the layer structure of the recording / reproducing layer of the said optical recording medium. It is a simulation model for measuring the extinction coefficient of a recording film, which will be described in an embodiment of the present invention. It is a sample block diagram for the transmittance | permeability measurement of the optical recording medium demonstrated in the Example of this invention. It is an experimental result which shows the relationship between the film-forming conditions of an auxiliary recording film, and an extinction coefficient demonstrated in the Example of this invention. It is a schematic sectional drawing which shows the principal part of the optical recording medium which concerns on the 2nd Embodiment of this invention. 5 is a graph showing the relationship between recording power, i-MLSE (Integrated-Maximum Likelihood Sequence Estimation), and modulation degree for each of the optical recording media according to an example of the present embodiment and a comparative example. 6 is a graph showing the relationship between recording power, i-MLSE, and modulation (Modulation) for each of optical recording media according to another example of the present embodiment and another comparative example. FIG. 11 is a cross-sectional TEM (Transmission Electron Microscope) view of the recording / reproducing layer of the optical recording medium according to the embodiment shown in FIG. 10. 10 is a graph showing a TDS (Thermal Desorption Method) analysis result of the auxiliary recording film when the gas introduction amount at the time of sputtering in the sample according to the example shown in FIG. 9 is changed. 10 is a graph showing the relationship between the oxygen flow rate during the formation of an auxiliary recording film according to the example shown in FIG. 9, i-MLSE, modulation degree, and recording power. 11 is a graph showing the relationship between the oxygen flow rate during the formation of an auxiliary recording film according to the example shown in FIG. 10, i-MLSE, modulation degree, and recording power. 2A and 2B are schematic diagrams of a recording film of the optical recording medium, in which A shows a configuration after film formation and before recording light irradiation, and B shows a configuration after recording light irradiation. It is a graph which shows the result of having analyzed the auxiliary recording film by TDS.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. *

First Embodiment FIG. 1 is a schematic cross-sectional view showing an optical recording medium according to an embodiment of the present invention. *

[Configuration of Optical Recording Medium] The optical recording medium 11 of the present embodiment is configured by a guide layer separation type multilayer optical disc having a guide layer 112 and a plurality of recording / reproducing layers 113. The illustrated optical recording medium 11 has four recording / reproducing layers 113. Such a multilayer structure can be achieved by reducing the extinction coefficient of the auxiliary recording film so that the recording laser light reaches the recording layer on the back side. However, the present invention is not limited to this, and one to three layers or five or more recording / reproducing layers may be provided. The optical recording medium 11 has a disk shape, and a center hole is formed in the central portion. *

In the optical recording medium 11, a light-transmitting buffer layer 116 and an intermediate layer 114 are interposed between the guide layer 112 and the nearest recording / reproducing layer 113 and between the adjacent recording / reproducing layers 113. Are layered. These layers are a protective layer (cover layer) 115, a recording / reproducing layer 113 (L3), and an intermediate layer 114 from the side on which recording / reproducing light R1 and guide light R2 from an optical pickup in a recording / reproducing apparatus (not shown) are incident. The recording / reproducing layer 113 (L2), the intermediate layer 114, the recording / reproducing layer 113 (L1), the intermediate layer 114, the recording / reproducing layer 113 (L0), the buffer layer 116, and the guide layer 112 are laminated in this order. *

The recording / reproducing light R1 and the guide light R2 are controlled so as to be focused on the target recording / reproducing layer 113 and the guide layer 112 via the objective lens 60. Laser beams having different wavelengths are used for the recording / reproducing light R1 and the guide light R2. Typically, blue laser light is used for the recording / reproducing light R1, and red laser light is used for the guide light R2. . *

(Guide Layer) FIG. 2 is a schematic cross-sectional view showing the configuration of the guide layer 112, and FIG. 3 is a schematic diagram showing the guide track of the guide layer 112. *

As shown in FIGS. 2 and 3, the guide layer 112 follows the uneven shape of the uneven portion 111 and the plastic substrate 110 such as a disk-shaped polycarbonate having a spiral uneven portion 111 (guide groove) on one surface. Thus, it has a laminated structure with the reflective film 120 covering the concavo-convex portion 111. *

The substrate 110 is typically molded using a molding die such as a stamper, and has an outer diameter of 120 mm and a thickness of 1.1 mm. The reflective film 120 is formed of a sputtered film of a metal material having a high reflectance with respect to red laser light, such as silver (Ag) or an alloy thereof. The thickness of the reflective film 120 is not particularly limited, and is, for example, 20 nm to 100 nm, and in this embodiment, 80 nm. *

A guide track 121 for tracking control is formed on the surface of the guide layer 112 facing the recording / reproducing layer 113 as shown in FIGS. The guide track 121 has a land / groove structure formed in a spiral shape. The land is formed between the grooves, and the groove is formed between the lands. In the following description, in the guide track 121, a track closer to the laser light source (optical pickup) is referred to as “groove” or “on-groove portion”, and a track farther from the laser light source is referred to as “land”. Alternatively, it is referred to as an “in-groove part”. *

The guide track 121 includes a land-based guide track (in-groove portion 121L) and a groove-based guide track (on-groove portion 121G), and means for switching between the land track and the groove track every round is used. A so-called “double spiral track” may be configured. In the present embodiment, the in-groove portion 121L and the on-groove portion 121G are continuously formed in a spiral shape from the inner peripheral side to the outer peripheral side of the optical recording medium 11, but are not limited thereto. For example, the in-groove portion 121L and the on-groove portion 121G may be continuously formed in a spiral shape so that they are alternately switched at a predetermined period (for example, every circumference) from the inner circumference side to the outer circumference side of the optical recording medium 11. . *

The in-groove portion 121L is surrounded by a pair of side walls 121s that form a boundary with the on-groove portion 121G. The side wall 121s is typically formed with a tapered surface, but may be formed with a surface perpendicular to the surface of the substrate 110. The taper angle of the side wall 121s is not particularly limited, and is appropriately set according to the draft angle of the stamper mold, the uneven height of the uneven portion 111, the thickness of the reflective film 120, and the like. *

In the guide track 121, physical address information is formed by wobbling or pit rows on the side wall surface. The in-groove portion 121L and the on-groove portion 121G are formed with a track pitch (0.64 μm) corresponding to red laser light used for recording / reproduction of a DVD (Digital Versatile Disk), for example. The average pitch between the land and the groove is 0.32 μm, which corresponds to the track pitch of the guide track 121. Hereinafter, the laser beam of the red laser beam is referred to as “guide light”. *

In the recording / reproducing apparatus for driving the optical recording medium 11, for example, in each of the land and groove of the guide track 121, the push-pull method (PP: Push-Pull), the differential push-pull method (DPP: Differential-Push-Pull), Tracking control is performed by a three-beam method or the like. By performing tracking control in each of the land and groove of the guide track 121, information recording on the recording / reproducing layer 113 can be performed at a track pitch of 0.32 μm. *

(Recording / Reproducing Layer) FIG. 4 is a schematic sectional view showing the layer structure of the recording / reproducing layer. *

The recording / reproducing layers 113 (L0 to L3) of the respective layers have the same layer structure and are laminated with the intermediate layer 114 interposed therebetween. The recording / reproducing layer 113 (L0) closest to the guide layer 112 is formed on the buffer layer 116 (flattening layer) formed with a thickness larger than the depth of the guide track 121 covered with the reflective film 120. . Therefore, the recording / reproducing layer 113 and the intermediate layer 114 formed on the buffer layer 116 are sequentially laminated on a flat plane without a groove (guide track). *

Each recording / reproducing layer 113 has a laminated structure of a first optical adjustment film 131, a main recording film 132, an auxiliary recording film 133, and a second optical adjustment film 134. *

The auxiliary recording film 133 records information at a track pitch (0.32 μm) corresponding to blue laser light having a wavelength of 380 to 450 nm (405 nm in this example) used for recording / reproducing of a Blu-ray Disc (registered trademark), for example. Is a layer. Hereinafter, this blue laser light is referred to as “recording / reproducing light” or “recording light”. *

In the present embodiment, the auxiliary recording film 133 is made of a material containing at least Bi (bismuth) and O (oxygen). By using such a material, it is possible to form a write-once type inorganic recording layer that can write information but cannot rewrite information. *

As a material containing at least Bi and O, Bi-MO (where M is Mg (magnesium), Ca (calcium), Y (yttrium), D)
y (dysprosium), Ce (cerium), Tb (terbium), Ti (titanium), Zr (zirconium), V (vanadium), Nb (niobium), Ta (tantalum), Mo (molybdenum), W (tungsten), Mn (manganese), Fe (iron), Zn (zinc), Al (aluminum), In (indium), Si (silicon), Ge (germanium), Sn (tin), Sb (antimony), Li (lithium), Na (sodium), K (potassium), Sr (strontium), Ba (barium), Sc (scandium), La (lanthanum), Nd (neodymium), Sm (samarium), Gd (gadolinium), Ho (holmium), Choose from Cr (chromium), Co (cobalt), Ni (nickel), Cu (copper), Ga (gallium), Pb (lead) Material mainly containing at least one element) are and the like.

The auxiliary recording film 133 is typically formed on the main recording film 132 by a sputtering method. The thickness of the auxiliary recording film 133 is not particularly limited, and is, for example, 10 nm to 70 nm, and is appropriately set according to the layer position and the number of layers of the recording / reproducing layer 113. *

As will be described later, the auxiliary recording film 133 is a BiO-based inorganic recording film made of a sputtered film in which a Bi-based oxide target is formed in an atmosphere containing argon, oxygen, and nitrogen. In this embodiment, the Bi— It is composed of a Ge—O based inorganic material. The auxiliary recording film 133 has an extinction coefficient (k) of 0 or more and 0.012 or less with respect to light having a wavelength of 405 nm. *

The main recording film 132 is for compensating for heat absorption efficiency that is insufficient with the auxiliary recording film 133 alone, and is disposed adjacent to the auxiliary recording film 133. The main recording film 132 may be disposed adjacent to the recording / reproducing light incident side of the auxiliary recording film 133 or may be disposed adjacent to the opposite side thereof. In the example shown in FIG. 4, the main recording film 132 is disposed between the auxiliary recording film 133 and the first optical adjustment film 131, but between the auxiliary recording film 133 and the second optical adjustment film 134. It may be arranged. *

The main recording film 132 is made of an inorganic material or an organic dye material, and functions as a light absorption film that propagates heat generated by the absorption of the recording / reproducing light R1 to the auxiliary recording film 133, so that the heat storage property of the auxiliary recording film 133 is achieved. To improve. In the present embodiment, the main recording film 132 is made of iron oxide (Fe <SUB> 3 </ SUB> O <SUB> 4 </ SUB>) having a thickness of 1 nm to 10 nm. *

The first optical adjustment film 131 is, for example, a reflection film for the purpose of adjusting the transmittance of the recording / reproducing layer 113 and ensuring the reflectance necessary for reproducing information (record marks) recorded on the auxiliary recording film 133. It is disposed between 120 and the auxiliary recording film 133. The first optical adjustment film 131 is made of a metal oxide material, for example, SnO <SUB> 2 </ SUB> series, TiO <SUB> 2 </ SUB> series, SiO <SUB> 2 </ SUB>. And ZnO—SnO <SUB> 2 </ SUB> glass materials. *

The first optical adjustment film 131 also has a function as a boundary layer that partitions the main recording film 132 and the buffer layer 116 or the intermediate layer 114. As a result, the main recording film 132 and the buffer layer 116 or the intermediate layer 114 can be appropriately separated. *

The first optical adjustment film 131 is typically formed on the buffer layer 116 or the intermediate layer 114 by a sputtering method. The thickness of the first optical adjustment film 131 is not particularly limited, and is, for example, 10 nm to 100 nm, and is appropriately set according to the target reflectance, the layer position of the recording / reproducing layer 113, the number of layers, and the like. *

The second optical adjustment film 134 is for assisting the function of adjusting the optical characteristics of the recording / reproducing layer 113 by the first optical adjustment film 131, and is a laser beam incident side of the auxiliary recording film 133, that is, the reflection film 120. It is arranged on the opposite side to the side. The second optical adjustment film 134 is made of a metal oxide material. In the present embodiment, the second optical adjustment film 134 is made of the same material as the first optical adjustment film 131. *

The second optical adjustment film 134 also has a function as a protective layer for preventing a mixing phenomenon in which the solvent of the photocurable resin used when forming the intermediate layer 114 penetrates the auxiliary recording film 133. *

The second optical adjustment film 134 is typically formed on the auxiliary recording film 133 by a sputtering method. The thickness of the second optical adjustment film 134 is not particularly limited, and is, for example, 5 nm to 100 nm. The thickness of the first optical adjustment film 131, the target reflectance, the layer position of the recording / reproducing layer 113, or the number of layers thereof, etc. It is set appropriately according to *

The intermediate layer 114, the protective layer 115, and the buffer layer 116 are made of a resin material that is transparent to the guide light and the recording / reproducing light, for example, an ultraviolet curable resin material. The intermediate layer 114, the protective layer 115, and the buffer layer 116 are typically formed by a coating method such as a spin coating method. The thicknesses of the intermediate layer 114, the protective layer 115, and the buffer layer 116 are not particularly limited, and are appropriately set according to optical characteristics such as a desired transmittance. The buffer layer 116 corresponds to the first transparent resin layer, and the intermediate layer 114 corresponds to the second transparent resin layer. *

[Method for Manufacturing Optical Recording Medium] Next, a method for manufacturing the optical recording medium 11 will be described as described above. *

First, a substrate constituting the guide layer 112 is manufactured. The guide track 121 is produced by forming the reflective film 120 on the surface of the concavo-convex portion 111 of the substrate 110. The substrate 110 is typically formed by injection molding. The reflective film 120 is typically formed by sputtering. *

Subsequently, the buffer layer 116 is formed on the guide track 121. The buffer layer 116 is formed by applying an ultraviolet curable resin to the guide layer 112 to form a coating film, and irradiating the ultraviolet ray to cure the coating film. *

Next, the first optical adjustment film 131 and the main recording film 132 are sequentially formed on the buffer layer 116. The first optical adjustment film 131 and the main recording film 132 are each formed by sputtering. The first optical adjustment film 131 and the main recording film 132 may be sequentially formed using different targets in the same sputtering apparatus, or may be formed by separate sputtering apparatuses. *

Subsequently, an auxiliary recording film 133 is formed on the main recording film 132. The auxiliary recording film 133 is formed by sputtering a Bi-based oxide target in an atmosphere containing argon, oxygen, and nitrogen. Thereby, the extinction coefficient (k) of the recording film to be formed can be reduced and the transmittance can be increased. *

In the present embodiment, the extinction coefficient (k) of the auxiliary recording film to be formed can be controlled by the flow rate ratio of oxygen and nitrogen. For example, the extinction coefficient (k) is a value close to 0 as much as possible. can do. Thereby, an auxiliary recording film having a high transmittance can be obtained. *

The type of the sputtering apparatus is not particularly limited, and for example, an RF magnetron sputtering apparatus can be used. Argon functions as a sputtering gas for discharge, and oxygen and nitrogen function as gases that suppress oxygen vacancies. *

The flow rate ratio of oxygen and nitrogen is not particularly limited, and can be, for example, 6: 1 or more and 1: 6 or less. In this case, the argon flow rate may or may not be fixed. By setting the flow rate ratio of oxygen and nitrogen within the above range, the light extinction coefficient (k) at a wavelength of 405 nm is made of a BiO-based inorganic recording film having a value of 0 or more and 0.012 or less, such as Bi, Ge, or O. An inorganic recording film can be formed. In addition to Bi, Ge, and O, an atmospheric gas at the time of sputtering may be present in the film to be formed. *

The pressure at the time of film formation (sputtering pressure) is not particularly limited, and is set according to the flow rate of gas (argon, oxygen, and nitrogen) introduced into the vacuum chamber, for example, 0.1 Pa or more and 5 Pa or less. *

The sputter rate is not particularly limited, but by relatively reducing the sputter rate, oxides and nitrides are easily generated stably, and as a result, the composition having a high extinction coefficient (k) such as metal Bi is reduced. For example, by setting the sputtering rate to 0.57 [nm / s] or more and 1.51 [nm / s] or less, the extinction coefficient (k) is 0 or more and 0.012 or less for light with a wavelength of 405 nm. An auxiliary recording film can be obtained. *

Next, the second optical adjustment film 134 and the intermediate layer 114 are sequentially formed on the auxiliary recording film 133. The second optical adjustment film 134 is formed by a sputtering method. The intermediate layer 114 is formed on the second optical adjustment film 134 by applying an ultraviolet curable resin to form a coating film, and irradiating with ultraviolet rays to cure the coating film. *

Subsequently, as described above, the first optical adjustment film 131, the main recording film 132, the auxiliary recording film 133, and the second optical adjustment film 134 are repeatedly formed in order. Thereby, the multilayer optical recording medium 11 shown in FIG. 4 is produced. *

According to this embodiment, each auxiliary recording film 133 has a very small extinction coefficient (k) with respect to light having a wavelength of 405 nm, so that the transmittance of each recording / reproducing layer 113 can be increased. it can. Thereby, recording / reproducing light having sufficient power can be incident on the recording / reproducing layer (L0) located at the innermost layer from the laser incident surface, and further multilayering of the recording / reproducing layer can be realized. *

In addition, since the optical recording medium 11 of the present embodiment is constituted by a so-called guide layer separation type optical recording medium, the first optical adjustment film 131, the main recording film 132, the auxiliary recording film 133, and the second optical adjustment. The film 134 and the like can be formed of a flat film without a guide groove, whereby a multi-layer can be easily realized.

Examples of the present invention will be described below. Of course, the present invention is not limited to the following examples. *

Example 1 A thin film constituting an auxiliary recording film was formed on a polycarbonate substrate under the following sputtering conditions, and its extinction coefficient (k) was measured. (Sputtering conditions)-Sputtering equipment: Unaxis magnetron sputtering equipment "DVD Sprinter 13PC" Target: Bi <SUB> 2 </ SUB> O <SUB> 3 </ SUB> -GeO <SUB> 2 <・ Power supply: RF (13.56 MHz) ・ Argon (Ar) flow rate: 10 [sccm] ・ Oxygen (O <SUB> 2 </ SUB>) flow rate: 30 [sccm] ・ Nitrogen (N <SUB> 2 </ SUB>) Flow rate: 5 [sccm] RF power: 1 [kW] Vacuum degree (in-chamber pressure during film formation): 0.74 [Pa] Sputtering rate: 1.50 [nm / sec]

The extinction coefficient (k) is defined as follows according to the Lambert-Beer law. I = I <SUB> 0 </ SUB> exp (-αz) (1) α = 4πk / λ (2) where I is the light intensity and I <SUB> 0 </ SUB> is the first The light intensity, z is the depth of penetration into the substance, α is the absorption coefficient, and λ is the wavelength. *

Here, the extinction coefficient (k) at a wavelength of 405 nm of the formed auxiliary recording film was measured by the following procedure. (Procedure 1) Using a Hitachi spectrophotometer “U-4100” (manufactured by Hitachi High-Technologies Corporation), the transmittance of light having a wavelength of 405 nm incident perpendicularly to the thin film and the substrate while changing the thickness of the thin film ( Measured value) was measured. (Procedure 2) Using the simulation model shown in FIG. 5, the thickness d of the thin film (corresponding to “z” in the above equation (1)) is changed, and light is incident perpendicularly to the thin film and the substrate (λ = 405 nm). The transmittance (Sim value) was obtained. (Procedure 3) A simulation profile having the highest correlation between the measured transmittance value obtained as described above and the Sim value is obtained by fitting by a non-linear least square method, and the value of k at that time is determined as an extinction coefficient (k ). The numerical values of the extinction coefficient (k) shown in the following examples are all measured in consideration of measurement variations and the average value is adopted. When there was an obvious abnormal value among the three measurement data, remeasurement was performed. As a result, the extinction coefficient (k) of the thin film was 0.0076. *

Further, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is produced, and a wavelength 405 nm perpendicularly incident on the laminated body
The light transmittance of was measured. As a result, the transmittance was 93.7%.

Here, the stacked body 20 includes a first optical adjustment film 31 having a thickness of 30 nm, a main recording film 32 having a thickness of 2 nm, an auxiliary recording film 33 having a thickness of 35 nm, and a second optical adjustment film having a thickness of 57 nm on the substrate. 34 were formed by sputtering in order. The first and second optical adjustment films 31 and 34 are SnO <SUB> 2 </ SUB> -based metal oxides, and the main recording film 32 is Fe <SUB> 3 </ SUB> O <SUB> 4 </ SUB>. A Hitachi spectrophotometer “U-4100” (manufactured by Hitachi High-Technologies Corporation) was used for the transmittance measurement, and the second optical adjustment film 34 was used as the light incident surface for the transmittance measurement. The adjustment film 31 was used as the light emission surface. *

Example 2 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate was 10 [sccm], the degree of vacuum was 0.81 [Pa], and the sputtering rate was 1.45 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 56.5 nm. The transmittance of the laminate 30 at a wavelength of 405 nm was measured under the same conditions as in Example 1. As a result, the transmittance was 94.3%. *

Example 3 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate was 30 [sccm], the degree of vacuum was 1.10 [Pa], and the sputtering rate was 1.40 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 56 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 94.2%. *

Example 4 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate was 50 [sccm], the degree of vacuum was 1.70 [Pa], and the sputtering rate was 1.35 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 was produced, and the thickness of the second optical adjustment film 34 was changed to 55 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 94.2%. *

Example 5 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate is 70 [sccm], the degree of vacuum is 2.90 [Pa], and the sputtering rate is 0.87 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 54 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 94.1%. *

Example 6 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate was 100 [sccm], the degree of vacuum was 6.00 [Pa], and the sputtering rate was 0.62 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 53.5 nm. The transmittance of the laminate 30 at a wavelength of 405 nm was measured under the same conditions as in Example 1. As a result, the transmittance was 94.1%. *

Example 7 Example 1 except that the oxygen flow rate is 5 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 0.77 [Pa], and the sputtering rate is 1.51 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 was manufactured, and the thickness of the second optical adjustment film 34 was changed to 58 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 94.1%. *

Example 8 Example 1 except that the oxygen flow rate is 10 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 0.84 [Pa], and the sputtering rate is 1.22 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 was produced, and the thickness of the second optical adjustment film 34 was changed to 57 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 94.2%. *

Example 9 Example 1 except that the oxygen flow rate is 50 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 1.60 [Pa], and the sputtering rate is 0.87 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was less than 0.005. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 54.5 nm. The transmittance of the laminate 30 at a wavelength of 405 nm was measured under the same conditions as in Example 1. As a result, the transmittance was 93.9%. *

Example 10 Example 1 except that the oxygen flow rate is 70 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 2.50 [Pa], and the sputtering rate is 0.79 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.0084. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 53.5 nm. The transmittance of the laminate 30 at a wavelength of 405 nm was measured under the same conditions as in Example 1. As a result, the transmittance was 93.7%. *

Example 11 Example 1 except that the oxygen flow rate is 100 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 4.70 [Pa], and the sputtering rate is 0.57 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.0118. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 52 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 93.4%. *

Comparative Example 1 Example 1 except that the oxygen flow rate is 0 [sccm], the nitrogen flow rate is 0 [sccm], the degree of vacuum is 0.11 [Pa], and the sputtering rate is 4.08 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.06. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 53 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 89%. *

Comparative Example 2 Example 1 except that the oxygen flow rate is 10 [sccm], the nitrogen flow rate is 0 [sccm], the degree of vacuum is 0.17 [Pa], and the sputtering rate is 1.91 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.016. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 54 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 93.2%. *

Comparative Example 3 An auxiliary recording film under the same conditions as in Example 1 except that the nitrogen flow rate was 0 [sccm], the degree of vacuum was 0.67 [Pa], and the sputtering rate was 1.56 [nm / sec]. The extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.032. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 53 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 92.8%. *

(Comparative Example 4) Example 1 except that the oxygen flow rate is 50 [sccm], the nitrogen flow rate is 0 [sccm], the degree of vacuum is 0.90 [Pa], and the sputtering rate is 1.32 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.041. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 was manufactured, and the thickness of the second optical adjustment film 34 was changed to 51 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 92.5%. *

Comparative Example 5 Example 1 except that the oxygen flow rate is 0 [sccm], the nitrogen flow rate is 10 [sccm], the degree of vacuum is 0.16 [Pa], and the sputtering rate is 2.27 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.02. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 was produced, and the thickness of the second optical adjustment film 34 was changed to 55 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 93.1%. *

Comparative Example 6 Example 1 except that the oxygen flow rate is 0 [sccm], the nitrogen flow rate is 30 [sccm], the degree of vacuum is 0.69 [Pa], and the sputtering rate is 1.88 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.0282. *

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as an auxiliary recording film 33 was prepared, and the thickness of the second optical adjustment film 34 was changed to 54 nm. 1 and the transmittance of the laminate 30 at a wavelength of 405 nm were measured. As a result, the transmittance was 92.9%. *

Comparative Example 7 Example 1 except that the oxygen flow rate was 0 [sccm], the nitrogen flow rate was 50 [sccm], the degree of vacuum was 1.00 [Pa], and the sputtering rate was 1.65 [nm / sec]. A thin film constituting the auxiliary recording film was formed under the same conditions as in Example 1, and the extinction coefficient (k) was measured. As a result, the extinction coefficient (k) of the thin film was 0.031.

Subsequently, as shown in FIG. 6, a laminated body 30 including a thin film having a thickness of 35 nm formed under the above conditions as the auxiliary recording film 33 is manufactured, and the thickness of the second optical adjustment film 34 is set to 53.5 nm. The transmittance of the laminate 30 at a wavelength of 405 nm was measured under the same conditions as in Example 1. As a result, the transmittance was 92.8%. *

The results of Examples 1 to 11 and Comparative Examples 1 to 7 are summarized in Table 1. FIG. 7 is a bar graph comparing the extinction coefficients (k) of Examples 1 to 4 and Comparative Examples 1 to 7. *

As shown in Table 1, according to the auxiliary recording films (Examples 1 to 11) formed by sputtering a Bi-based oxide target in an atmosphere containing argon, oxygen and nitrogen, Comparative Examples 1 to 7 and In comparison, the extinction coefficient (k) can be reduced, and the transmittance when the medium is constructed can also be increased. *

The reason why the extinction coefficient (k) can be reduced by simultaneous introduction of nitrogen is that sputtering to the target becomes stable, oxygen deficient portions in the sputtered film are reduced, and oxide is uniformly generated. It is believed that there is. The oxide recording layer loses its transmittance due to oxygen deficiency during film formation. For this reason, oxygen vacancies are usually suppressed by sputtering film formation in an oxygen atmosphere. At this time, it is effective to introduce nitrogen in addition to oxygen at the same time, whereby a recording film having a high transmittance in which the extinction coefficient (k) becomes 0 or a value close to 0 can be formed. *

Further, the sputtering rate is reduced by further adding nitrogen to Ar and oxygen as the atmospheric gas. As a result, oxygen vacancies in the auxiliary recording film are reduced, stable products of oxides and nitrides are easily formed, and the composition having a high extinction coefficient (k) such as metal Bi is reduced. It is considered that the extinction coefficient (k) can be reduced. *

For example, as in Examples 1 to 11, BiO having a small extinction coefficient (k) is formed by forming a film at a relatively low sputtering rate of 0.57 [nm / s] to 1.51 [nm / s]. A system auxiliary recording film can be formed. *

Further, as in Examples 1 to 11, by setting the flow ratio of oxygen and nitrogen to 6: 1 or more and 1: 6 or less, the light extinction coefficient (k) at a wavelength of 405 nm is 0 or more and 0.012 or less. A BiO-based auxiliary recording film can be formed. As described above, the extinction coefficient (k) of the auxiliary recording film to be formed can be controlled by the flow ratio of oxygen and nitrogen, so that the auxiliary recording film having the desired extinction coefficient (k) can be easily obtained. While being able to form, the dependence by the material physical property of an extinction coefficient (k) can be reduced. *

Furthermore, according to the experiments by the present inventors, it was confirmed that the samples according to Examples 1 to 11 had a smaller change in optical characteristics with time than the samples according to Comparative Examples 1 to 7. That is, the extinction coefficient (k) of the auxiliary recording films according to Examples 1 to 11 being 0.012 or less means that most of the auxiliary recording films are made of oxide. For this reason, further oxidation of the metal component contained in the auxiliary recording film is effectively suppressed, thereby suppressing, for example, a sensitivity shift with respect to the recording laser beam and ensuring excellent reliability over a long period of time. It will be possible. The sensitivity shift is a change in characteristics with time, and the sensitivity of the recording film such as the degree of modulation varies with respect to a constant recording laser beam. *

Subsequently, another embodiment of the present invention will be described. *

Second Embodiment Since the recording / reproducing layer 113 according to the first embodiment has a high transmittance as described above, the heat of the laser beam can be used efficiently, and sufficient recording characteristics are exhibited. On the other hand, further improvement in recording characteristics is desired. Therefore, an object of the present embodiment is to provide an optical recording medium that can realize further improvement in recording characteristics in addition to the above-described problem of improvement in transmittance. *

FIG. 8 is a schematic cross-sectional view showing the main part of an optical recording medium according to the second embodiment of the present invention. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. *

[Configuration of Optical Recording Medium] The optical recording medium 21 of the present embodiment is different from the first embodiment in the configuration of the recording / reproducing layer 213. That is, the optical recording medium 21 is constituted by a guide layer separation type multilayer optical disc having a guide layer 112 and a plurality of recording / reproducing layers 213, similarly to the optical recording medium 11 of the first embodiment. Also in the optical recording medium 21, a light-transmitting buffer layer 116 and intermediate layer 114 are provided between the guide layer 112 and the nearest recording / reproducing layer 213 and between adjacent recording / reproducing layers 213. Are layered. *

(Recording / Reproducing Layer) The recording / reproducing layer 213 of this embodiment will be described with reference to FIG. *

Each recording / reproducing layer 213 has a laminated structure of a first optical adjustment film 231, a recording layer 235, and a second optical adjustment film 234. The recording layer 235 includes a main recording film 232 and an auxiliary recording film 233. *

The auxiliary recording film 233 has an extinction coefficient (k) of 0.012 or less with respect to light having a wavelength of 405 nm. As will be described later, the auxiliary recording film 233 can be involved in improving the recording characteristics by changing its shape upon irradiation with recording light. *

In the present embodiment, the auxiliary recording film 233 is composed of an inorganic film such as NbO-based or BiO-based, for example. Examples of the NbO-based inorganic film include an inorganic film made of a material containing at least Nb (niobium) and O. Specifically, examples of the material containing at least Nb and O include a material containing SnNbOx or SnNbNOx as a main component. Examples of the BiO-based inorganic film include an inorganic film made of a material containing at least Bi and O. Examples of the material containing at least Bi and O include the materials described in the first embodiment. *

The auxiliary recording film 233 is typically formed on the main recording film 232 by a sputtering method. The thickness of the auxiliary recording film 233 is not particularly limited and is, for example, 10 nm to 70 nm. The auxiliary recording film 233 is made of, for example, a sputtered film formed in an atmosphere containing argon and oxygen. As a result, the oxidation of the material of the auxiliary recording film 233 is promoted, and the auxiliary recording film 233 with few oxygen vacancies or no oxygen vacancies is formed. As a result, the extinction coefficient (k) of the auxiliary recording film 233 is suppressed to 0.012 or less. *

Further, the auxiliary recording film 233 can be a sputtered film formed in an atmosphere containing argon, oxygen, and nitrogen. As a result, the extinction coefficient (k) can be easily controlled as described above. For example, the extinction coefficient (k) of the auxiliary recording film 233 can be suppressed to less than 0.005. *

On the other hand, the auxiliary recording film 233 contains argon gas and oxygen gas, or argon gas, oxygen gas and nitrogen gas. These gases are considered to be atmospheric gases entrained in the film when the auxiliary recording film 233 is formed. By including such a gas, the auxiliary recording film 233 can have a recess formed in the recording mark portion and containing the gas after irradiation with the recording laser beam. The recess will be described later. *

The main recording film 232 is disposed adjacent to the auxiliary recording film 233. The main recording film 232 can compensate for the heat absorption efficiency that is insufficient with the auxiliary recording film 233 alone, and can cause a phase change due to the heat of the recording light to form a recording mark. The main recording film 232 may be disposed adjacent to the recording / reproducing light incident side of the auxiliary recording film 233, or may be disposed adjacent to the opposite side thereof. Alternatively, it may be disposed between the auxiliary recording film 233 and the second optical adjustment film 234. *

The main recording film 232 is made of an inorganic material or an organic dye material, and propagates heat generated by absorption of recording / reproducing light to the auxiliary recording film 233. Thereby, the heat storage property of the auxiliary recording film 233 can be improved, and the formation of the concave portion of the auxiliary recording film 233 can be promoted. The main recording film 232 is a film made of a material containing at least one of Fe, Ge, Cu, Sn, and Mn, for example. Examples of such a material include a material mainly composed of Fe <SUB> 3 </ SUB> O <SUB> 4 </ SUB>, CuO, Ge, Sn, Mn and the like. The thickness of the main recording film 232 is not particularly limited and is, for example, 1 nm to 10 nm. *

Each of the first optical adjustment film 231 and the second optical adjustment film 234 is a film that is disposed adjacent to the recording layer 235 and made of a metal oxide. *

The first optical adjustment film 231 is a film corresponding to the first optical adjustment film 131, and is disposed, for example, between the reflective film 120 and the auxiliary recording film 233. The first optical adjustment film 231 has a function of adjusting the transmittance of the recording / reproducing layer 213, a function of ensuring a reflectance necessary for reproducing the recording mark, and a function of the main recording film 232 and the buffer layer 116 or the intermediate layer 114. It functions as a boundary layer that separates the spaces. The first optical adjustment film 231 includes, for example, a SnO <SUB> 2 </ SUB> system, a TiO <SUB> 2 </ SUB> system, a SiO <SUB> 2 </ SUB> system, and a ZnO-SnO <SUB>. 2 </ SUB> glass material. The first optical adjustment film 231 is typically formed on the buffer layer 116 or the intermediate layer 114 by a sputtering method, and has a thickness of, for example, 10 nm to 100 nm. *

Similar to the second optical adjustment film 134, the second optical adjustment film 234 functions to assist the adjustment function of the optical characteristics of the recording / reproducing layer 213 by the first optical adjustment film 231 and to prevent the mixing phenomenon. As a protective layer. The second optical adjustment film 234 is disposed on the laser light incident side of the auxiliary recording film 233, that is, on the side opposite to the reflection film 120 side. In the present embodiment, the second optical adjustment film 234 is made of the same material as the first optical adjustment film 231. The second optical adjustment film 234 is typically formed on the auxiliary recording film 233 by a sputtering method and has a thickness of, for example, 5 nm to 100 nm. *

The recording / reproducing layer 213 having such a configuration has a transmittance with respect to light having a wavelength of 405 nm when the second optical adjustment film 234 is a light incident surface and the first optical adjustment film 231 is a light emission surface, for example, 93%. This can be done. *

The optical recording medium 21 configured as described above can be manufactured in the same manner as the optical recording medium 11 of the first embodiment. *

[Method of manufacturing optical recording medium]

First, a substrate constituting the guide layer 112 is manufactured. *

Next, the first optical adjustment film 231 and the main recording film 232 are sequentially formed on the buffer layer 116. The first optical adjustment film 231 and the main recording film 232 are each formed by sputtering. *

Subsequently, an auxiliary recording film 233 is formed on the main recording film 232. In this embodiment, the auxiliary recording film 233 can be formed by sputtering in an atmosphere containing argon, oxygen, and nitrogen. Argon functions as a sputtering gas for discharge, and oxygen and nitrogen function as gases that suppress oxygen vacancies. Thereby, oxygen vacancies in the auxiliary recording film 233 can be suppressed, and the extinction coefficient (k) of the recording layer 235 to be formed can be reduced. *

Also in this embodiment, the extinction coefficient (k) of the formed auxiliary recording film 233 can be controlled by the flow ratio of oxygen and nitrogen. For example, the extinction coefficient (k) is 0 or a value close to 0. Can be. As a result, an auxiliary recording film having high transmittance and no oxygen deficiency can be obtained. The flow rate ratio of oxygen and nitrogen is not particularly limited, and can be, for example, 6: 1 or more and 1: 6 or less. In this case, the argon flow rate may or may not be fixed. By setting the flow ratio of oxygen and nitrogen within the above range, an auxiliary recording film having an extinction coefficient (k) of light at a wavelength of 405 nm of 0.012 or less can be formed. *

In the case where Nb, Sn, and O are included, the auxiliary recording film 233 is formed by sputtering an alloy target including these materials in the above atmosphere. On the other hand, the auxiliary recording film 233
Is made of a material containing Bi, Ge, and O, the auxiliary recording film 233 is formed by sputtering a Bi—Ge—O-based oxide target in the above atmosphere. The pressure at the time of film formation (sputtering pressure) is not particularly limited, and is set according to the flow rate of gas (argon, oxygen, nitrogen, etc.) introduced into the vacuum chamber, for example, set to 0.1 Pa or more and 5 Pa or less. .

The sputter rate is not particularly limited, but by making the sputter rate relatively low, oxides and nitrides are easily generated stably, and as a result, the composition having a high extinction coefficient (k) decreases. Further, by setting the sputtering rate to 2.0 [nm / s] or less, the film can be formed while the atmospheric gas is involved in the film, and the auxiliary recording film 233 containing the gas can be formed. *

Next, the second optical adjustment film 234 and the intermediate layer 114 are sequentially formed on the auxiliary recording film 233. The second optical adjustment film 234 is formed by a sputtering method. The intermediate layer 114 is formed on the second optical adjustment film 234 by applying an ultraviolet curable resin to form a coating film, and irradiating with ultraviolet rays to cure the coating film. *

Subsequently, as described above, the first optical adjustment film 231, the main recording film 232, the auxiliary recording film 233, and the second optical adjustment film 234 are repeatedly formed in order. Thereby, the multilayer optical recording medium 21 shown in FIG. 8 is produced. *

The operational effects of the recording layer 235 manufactured as described above will be described while showing a plurality of experimental results. *

[Operation Effect of Recording Layer] FIGS. 9 and 10 are experimental results showing the difference in optical characteristics depending on the presence or absence of the auxiliary recording film 233. 9 and 10, the horizontal axis represents recording light power (Write ［power) [mW], the left vertical axis represents i-MLSE [%], and the right vertical axis represents modulation (Modulation). FIG. 9 shows an experimental result of a sample using Ge for the main recording film 232 and NbSnOx for the auxiliary recording film 233. FIG. 10 shows Fe <SUB> 3 </ SUB> O <SUB for the main recording film 232. > 4 </ SUB> shows the experimental results of the samples using GeBiOx for the auxiliary recording film 233, respectively. *

9 and 10, the data plotted with circles indicate the results of i-MLSE, and the data plotted with squares indicates the results of the degree of modulation. Among these data, the data indicated by the solid line between the plots is the experimental result of the sample (Example) having the auxiliary recording film 233, and the data indicated by the broken line between the plots is the sample not having the auxiliary recording film 233. It is an experimental result of (comparative example). Note that i-MLSE is an evaluation value of error rate correlation used as an evaluation index of the quality of a binarized reproduction signal, and a lower value indicates better recording characteristics. *

As for the modulation degree, as shown in FIGS. 9 and 10, the modulation degree tends to increase as the recording light power increases. It is confirmed that the example having the auxiliary recording film 233 has a high degree of modulation even in a region where the recording power is low and shows a gradual change in the degree of modulation compared to the comparative example having no auxiliary recording film 233. It was done. Thereby, it was confirmed that the auxiliary recording film 233 can broaden the range of intensity that can be taken as recording light (increase the margin of recording light power). *

On the other hand, with respect to i-MLSE, as shown in FIG. 9 and FIG. 10, the example showed a good value within a predetermined recording light power range, but the comparative example was measured at any recording light power. It was out of range. From this result, it can be seen that the presence or absence of the auxiliary recording film has a great influence on the recording characteristics of the recording / reproducing layer. *

Here, FIG. 11 is a TEM (Transmission Electron Microscope) photograph showing the cross-sectional structure of the recording / reproducing layer after irradiation of the recording light in the sample according to the example shown in FIG. In the figure, M represents a recording mark portion, and R3 represents the incident direction of recording light. As shown in FIG. 11, it was confirmed that a recess 233a was formed in the vicinity of the interface with the main recording film 232 in the region where the recording mark M of the auxiliary recording film 233 was formed. In addition, a recessed part is the block | closed space | gap part, and when it observes from the cross section of the vertical direction like FIG. 8, it expresses that the 233a part of FIG. In FIG. 11, it is confirmed that the recording mark portion is spread and deformed in the R3 direction and the opposite direction due to the presence of the concave portion 233a. *

From this result, the shape change of the auxiliary recording film 233 due to the concave portion 233a is closely related to the detection of a significant reproduction signal and greatly contributes to the good recording characteristics (i-MLSE characteristics) of the recording / reproduction layer. Inferred. Next, the principle of forming the recess 233a will be considered. *

FIG. 12 is an experimental result showing the relationship between the oxygen flow rate introduced during sputtering deposition of the auxiliary recording film (NbSnOx) 233 and the oxygen release amount by TDS analysis (Thermal-Desorption Method) in the sample according to the embodiment shown in FIG. It is. In the figure, the horizontal axis represents the oxygen flow rate [sccm] at the time of sputtering, and the vertical axis represents the intensity of detected oxygen amount [au: arbitrary unit] in the TDS analysis. *

From the result of FIG. 12, the amount of oxygen detected from the auxiliary recording film increases substantially in proportion to the amount of introduced oxygen. This indicates that the auxiliary recording film immediately after film formation (unrecorded) contains a process gas for film formation. According to the experiments by the present inventors, it was confirmed by the same experiment that not only oxygen but also other process gases (argon and nitrogen) were detected. FIG. 16 shows the result of TDS analysis of the auxiliary recording film when the film is formed with argon, nitrogen, and oxygen process gases. According to the figure, as the three process gases including the reaction-inactive argon gas are detected at substantially the same temperature as the heating is performed (the pressure on the vertical axis of the graph increases), these gases are It is considered that they are not generated by a chemical reaction but originally exist in the auxiliary recording film. *

From these results, in the concave portion 233a of the auxiliary recording film 233, the heat accumulated in the main recording layer 232 by the irradiation of the recording light propagates to the auxiliary recording film 232, and the gas component in the auxiliary recording film is transferred to the outside by the heat. By being released, it is considered that the recording mark portion is formed to assist the deformation. Such a recess does not necessarily have to exist in the entire area of the recording mark portion, and has a function of sufficiently assisting deformation of the recording mark portion even if it exists partially. *

Next, the relationship between the gas flow rate during sputtering of the auxiliary recording film 233 and the recording characteristics will be described. *

FIG. 13 is a graph showing the relationship between the oxygen flow rate during deposition of the auxiliary recording film (NbSnOx) 233, i-MLSE, modulation factor, and recording light power (Pw) in the sample according to the example shown in FIG. The horizontal axis represents the oxygen flow rate [sccm], the left vertical axis represents i-MLSE [%] and recording power [mW], and the right vertical axis represents the degree of modulation. On the other hand, FIG. 14 shows the relationship between the oxygen flow rate during formation of the auxiliary recording film (GeBiOx) 233, i-MLSE, modulation factor, and recording light power (Pw) in the sample according to the embodiment shown in FIG. The horizontal axis represents the oxygen flow rate [sccm], the left vertical axis represents i-MLSE [%] and recording power [mW], and the right vertical axis represents the degree of modulation. In each figure, the circle plot indicates the recording light power, the square plot indicates i-MLSE, and the triangle plot indicates the modulation degree result. *

From this result, it was found that as the oxygen flow rate increased, the modulation degree increased and the recording power and i-MLSE tended to decrease. Therefore, it was confirmed that the larger the oxygen flow rate, the better the recording characteristics and the recording of information with a relatively low laser power. This is presumably because the amount of gas contained in the auxiliary recording film 233 increases as the gas flow rate during sputtering increases, and the degree of shape change due to the formation of the recess 233a increases during the formation of the recording mark portion. That is, as the amount of gas contained in the auxiliary recording film 233 increases, better recording characteristics can be obtained. *

The formation principle of the recording mark portion that can be derived from the above experimental results will be described with reference to schematic diagrams. *

FIG. 15 is a schematic diagram of the recording layer 235 according to this embodiment. A shows a configuration after film formation and before recording light irradiation, and B shows a configuration after recording light irradiation. *

As shown in FIG. 15A, the unrecorded auxiliary recording film 233 contains a gas G in the film. As described above, these gases are considered to be atmospheric gases entrained in the film during sputtering. *

As shown in FIG. 15B, when the recording light R3 is irradiated to the recording layer 235, the main recording film 232 that easily absorbs heat undergoes a phase change from amorphous to crystalline, thereby forming a recording mark M2. At the same time, the heat accumulated in the main recording film 232 propagates to the auxiliary recording film 233, and the gas G contained in the auxiliary recording film 233 expands and is released near the interface with the main recording film 232. *

As a result, a concave portion 233a that accommodates the gas G is formed near the interface between the auxiliary recording film 233 and the main recording film 232. The recess 233a is formed adjacent to the recording mark M2 and functions as the recording mark M1. The recording marks M1 and M2 function as one recording mark portion M during reproduction. At this time, no phase change from amorphous to crystalline occurs in the auxiliary recording film 233, but the phase change may occur. *

Therefore, according to the present embodiment, the recording mark portion M can be formed by the shape change of the auxiliary recording film 233 in addition to the phase change of the main recording film 232 by the irradiation of the recording light R3. Thereby, the recording characteristics of the optical recording medium 21 can be enhanced. *

Further, as shown in FIGS. 9 and 10, since the change of the modulation degree with respect to the recording light power is gentle, a stable modulation degree is ensured regardless of the fluctuation of the recording light power. Thereby, a stable recording mark portion can be formed. *

Furthermore, since each auxiliary recording film 233 has almost no extinction coefficient (k) with respect to light having a wavelength of 405 nm, it is possible to improve the durability (storability) of the recording layer with respect to the environmental load. Moreover, according to the present embodiment, since the sensitivity of the recording light in each recording layer is ensured while preventing a decrease in transmittance due to the multilayered recording layer, a multilayer optical recording medium having stable recording / reproducing characteristics is obtained. Can be provided. *

The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. *

For example, in the above embodiment, the guide layer separation type optical recording medium has been described as an example. However, instead of this, an optical recording medium in which a guide groove for tracking control is formed in the recording / reproducing layer is similarly used. Applicable. *

In the above embodiments, the multilayer optical recording medium having a plurality of recording layers has been described as an example. However, the present invention is not limited to this, and can be similarly applied to a single-layer optical recording medium having a single recording layer. It is. *

Furthermore, the present invention may include the following description. (1) An optical recording medium comprising a recording layer having an auxiliary recording film containing at least argon gas, oxygen gas, and nitrogen gas, and a main recording film disposed adjacent to the auxiliary recording film. (2) The optical recording medium according to (1), wherein the optical recording medium has a concave portion formed in the vicinity of the interface between the auxiliary recording film and the main recording film in at least a part of the recording mark portion after recording. recoding media. *

Alternatively, the following description may be included. (1) A method of manufacturing an optical recording medium, in which a BiO-based auxiliary recording film is formed on a substrate by preparing a substrate and sputtering a Bi-based oxide target in an atmosphere containing argon, oxygen, and nitrogen. (2) The method for manufacturing an optical recording medium according to (1), wherein the step of forming the auxiliary recording film includes setting the flow rate ratio of oxygen and nitrogen to 6: 1 or more and 1: 6 or less. An optical recording medium manufacturing method for forming a film. (3) The method for manufacturing an optical recording medium according to (1) or (2), wherein the step of forming the auxiliary recording film includes 0.57 [nm / s] or more and 1.51 [nm / s]. The method for producing an optical recording medium, wherein the auxiliary recording film is formed at the following sputtering rate. (4) The method of manufacturing an optical recording medium according to any one of (1) to (3), wherein the step of preparing the substrate includes:
A base material having a surface on which a guide groove for tracking control is formed, a metal reflective film is formed on the surface of the guide groove, and a transparent resin that covers the guide groove on the metal film A method for producing an optical recording medium, comprising forming a flattening film. (5) The method of manufacturing an optical recording medium according to (4), further comprising: forming an optical adjustment film made of a metal oxide on the planarizing film before forming the auxiliary recording film Is formed by a sputtering method, and a light absorbing film capable of generating heat by absorbing a recording laser beam is formed on the optical adjustment film by a sputtering method. (6) a first optical adjustment film made of a metal oxide, a BiO-based auxiliary recording film having a light extinction coefficient (k) of 0 to 0.012 at a wavelength of 405 nm, An optical recording medium comprising: a light absorbing film that is disposed between the optical adjustment film and the auxiliary recording film and capable of propagating heat generated by absorption of a recording laser beam to the auxiliary recording film. (7) The optical recording medium according to (6), further including a second optical adjustment film disposed on the auxiliary recording film and configured of a metal oxide, An optical recording medium having a transmittance of 93% or more for light having a wavelength of 405 nm when the adjustment film is a light incident surface and the first optical adjustment film is a light emission surface. (8) The optical recording medium according to (6) or (7), wherein the auxiliary recording film is a sputtered film formed from a Bi-based oxide target in an atmosphere containing argon, oxygen, and nitrogen. Optical recording medium. (9) The optical recording medium according to any one of (6) to (8), wherein the guide layer has a guide groove for tracking control, the guide layer, the first optical adjustment film, An optical recording medium further comprising a planarizing layer made of a transparent resin disposed between the two. (10) The optical recording medium according to any one of (6) to (9), wherein the auxiliary recording film includes a plurality of auxiliary recording films.

11, 21 ... Optical recording medium 110 ... Base material 112 ... Guide layer 113 ... Recording / reproducing layer 114 ... Intermediate layer 115 ... Protective layer 116 ... Buffer layer 120 ... Reflective film 121 ... Guide track 131, 231 ... First optical adjustment film 132,232 ... main recording film 133,233 ... auxiliary recording film 134,234 ... second optical adjustment film 235 ... recording layer M ... recording mark section

Claims (11)

1. An auxiliary recording film having an extinction coefficient (k) of light at a wavelength of 405 nm of 0.012 or less, and heat generated by absorption of a recording laser beam are disposed adjacent to the auxiliary recording film, and are supplied to the auxiliary recording film. An optical recording medium comprising a recording layer having a main recording film capable of propagating. *
2. The optical recording medium according to claim 1, wherein the auxiliary recording film has a recess formed in the vicinity of an interface with the main recording film in a recording mark portion after recording. *
3. 2. The optical recording medium according to claim 1, wherein the auxiliary recording film has an extinction coefficient (k) of light at a wavelength of 405 nm of less than 0.005. *
4. 2. The optical recording medium according to claim 1, wherein the auxiliary recording film is an inorganic film of at least one of NbO-based and BiO-based. *
5. 5. The optical recording medium according to claim 4, wherein the auxiliary recording film is a sputtered film formed in an atmosphere containing at least argon and oxygen. *
6. The optical recording medium according to claim 1, wherein the auxiliary recording film includes at least argon gas and oxygen gas. *
7. The optical recording medium according to claim 6, wherein the auxiliary recording film has a concave portion containing the gas in a recording mark portion formed by heat of the recording laser beam. *
8. The optical recording medium according to claim 6, wherein the auxiliary recording film further contains nitrogen gas. *
9. The optical recording medium according to claim 1, wherein the main recording film is a film made of a material containing at least one of iron, germanium, copper, tin, and manganese. *
10. 2. The optical recording medium according to claim 1, wherein the first optical adjustment film and the second optical adjustment film are disposed adjacent to the main recording film and the auxiliary recording film, respectively, and are made of a metal oxide. And a laminated structure of the first optical adjustment film, the main recording film, the auxiliary recording film, and the second optical adjustment film, wherein the second optical adjustment film is a light incident surface. An optical recording medium constituting a recording / reproducing layer having a transmittance of 93% or more for light having a wavelength of 405 nm when the first optical adjustment film is used as a light emitting surface. *
11. 11. The optical recording medium according to claim 10, wherein: a guide layer having a guide groove for tracking control; and a planarization layer made of a transparent resin disposed between the guide layer and the first optical adjustment film An optical recording medium in which four or more layers of the recording / reproducing layer are laminated on the planarizing layer via an intermediate layer.

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