FR2906925A1 - SUBSTRATE FOR OPTICAL RECORDING MEDIUM COMPRISING AT LEAST ONE INORGANIC PART AND METHOD OF MANUFACTURE. - Google Patents

Abstract

A substrate (1) for an optical recording medium, comprising a structured front face and a rear face, consists of a stack: - of a lower layer (2) of inorganic material, provided with first and second surfaces (2a, 2b), the first surface (2a) forming the rear face of the substrate (1) - and an upper layer (3) constituted by a material comprising at least one inorganic part and a free surface (3b) forming the front face of said substrate (1). More particularly, the material constituting the upper layer (3) is a hybrid organic-inorganic polymer.

Description

1 substrate for an optical recording medium having at least one

  inorganic part and method of manufacture.

  Technical Field of the Invention The invention relates to an optical recording medium substrate having a structured front face and a back face.

  The invention also relates to a method of manufacturing such a substrate and an optical recording medium comprising such a substrate. State of the art Currently, standard optical recording media are constituted by one or more superimposed thin layers, arranged on a substrate and optionally covered with a protective layer. The substrate and the protective layer are generally formed by a layer of polycarbonate or polymethyl methacrylate. In addition, the substrate has a non-planar face, intended to be in contact with one of the thin layers of the optical recording medium. Thus, the non-planar face of the substrate generally comprises hollow zones forming a groove and raised zones forming a track. This track makes it possible to obtain a writing and an accurate reading of the data thanks to a system of servocontrol of focusing and tracking. The substrate is generally obtained by thermal molding or injection-compression. Likewise, the thin layer (s) of the standard optical recording media are often of an organic nature. More particularly, the recordable layer is generally constituted by a synthetic dye 2906925 2 such as azo-type, cyanine-based or phthalocyanine-type dyes. Such standard optical recording media, however, have the disadvantage of being sensitive to environmental storage conditions, especially after a write operation performed using a laser beam. More particularly, the separate or cumulative actions of light, temperature and humidity can trigger a physico-chemical degradation of the optical recording medium, thereby altering said medium and the data previously recorded thereon. . OBJECT OF THE INVENTION The object of the invention is to overcome the above disadvantages. More particularly, the object of the invention is to improve the stability of the optical recording media, in particular during their storage. According to the invention, this object is achieved by the fact that an optical recording support substrate 20, comprising a structured front face and a rear face, is constituted by a stack: of a lower layer of inorganic material, provided with first and second opposed planar surfaces, the first surface forming the rear face of the substrate 25 and an upper layer consisting of a material having at least one inorganic portion and a free surface forms the front face of said substrate. According to a development of the invention, the material constituting the upper layer is a hybrid organic-inorganic polymer.

According to the invention, this object is also achieved by a method of manufacturing such an optical recording medium substrate, said method comprising at least the following steps: formation on the second surface of the lower layer, an upper layer constituted by the material comprising at least one inorganic part or by at least one of its precursors and comprising a free surface, and structuring of said free surface.

According to a particular embodiment, the upper layer is constituted by a precursor of a hybrid organic-inorganic polymer, capable of forming said polymer under the action of light radiation. According to another development, the forming step consists in depositing an upper layer of constant thickness. In this case, the structuring step is, more particularly, carried out after the step of forming the upper layer and may comprise the following successive steps: contacting said free surface of the upper layer with a structured face of a matrix transparent to said light radiation, - applying a pressure on said matrix, - exposing the upper layer to light radiation, through said matrix - and removing said matrix.

Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given as non-restrictive examples and shown in the accompanying drawings, in which: Figures 1 to 6 show schematically, in section, different steps of a method of manufacturing a substrate according to the invention. - Figure 7 shows schematically, in section, a particular embodiment of an optical recording medium according to the invention. FIG. 8 represents the topographic evolution obtained by atomic force microscopy (AFM) of the front face of a substrate according to the invention. FIG. 9 represents the topographic evolution obtained by atomic force microscopy (AFM) of the structured face of a matrix used during the structuring step of a manufacturing method according to the invention. Figure 10 shows schematically, in section, another particular embodiment of an optical recording medium according to the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS FIGS. 1 to 6 show a particular embodiment of a substrate 1 for forming the substrate of an optical recording medium. Thus, the substrate 1 comprises a structured front face intended to form the track of said support and a rear face. The substrate 1 is made from a lower layer 2 of inorganic material. The inorganic material is, for example, selected from silicon, glass, glass-ceramic, silica and quartz. In addition, the lower layer 2 has first and second plane opposite surfaces 2a and 2b.

An upper layer 3 is formed on the second surface 2b of the lower layer 2. In FIG. 1, the upper layer 3 is formed by depositing a layer of constant thickness consisting of at least one precursor 2906925 5 of a polymer organic-inorganic hybrid, capable of forming said polymer under the action of light radiation. For example, the article Hybrid inorganic-organic polymers with nanoscale building blocks: precursors, processing, properties and applications of Karl-Heinz Haas and Klaus Rose (Rev.Adv.Mater.Sci.5 (2003) 47- 52) describes particular hybrid polymers as well as their precursors and methods for obtaining said polymers. The organic-inorganic hybrid polymers described in the above-mentioned article are composite compounds comprising inorganic and organic blocks (synthons), of nanometric dimensions, and linked together by stable covalent bonds. More particularly, polymers of organic-inorganic type, also called IOP or ORMOCER s in the aforementioned article, have a main network formed of inorganic elements and hybridized by organic side groups, optionally capable of polymerizing or crosslinking. Such hybrid polymers can be obtained by a conventional sol-gel process of modified metal alkoxides, i.e., metal alkoxides also having one or more organic functions. Said sol-gel process consists, for example, in the hydrolysis and then in the polycondensation of modified silicon alkoxides. The organic functions of said resulting hybrid material are then polymerized or crosslinked, for example by heat treatment between 80.degree. C. and 180.degree. C. or by treatment with ultraviolet radiation. By way of example, the precursor may be a mixed organo-alkoxysilane precursor simultaneously comprising hydrolyzable Si-OR functions capable of forming a silica-type network and Si-R 'organic functions remaining attached to the silica-type network. The group R 'may be a polymerizable or crosslinkable group such as a vinyl, epoxy or methacrylate group. The polymerization or the crosslinking of said groups R 'makes it possible to structure and solidify the material obtained by sol-gel process. The precursor may also include a photoinitiator in the case of polymerization or crosslinking by ultraviolet radiation treatment. By way of non-limiting example, the precursor may be a material marketed by the company Micro Resist Technologies under the trade name Ormocomp in the Ormocer product range. The upper layer 3 is, for example, deposited on the second surface 2b of the lower layer 2 by a spin coating process also known under the name Anglo-Saxon spin coating. The upper layer 3 thus has a constant thickness, for example between 25 nm and 100 m, and preferably between 25 nm and 1 m. It also comprises two opposite surfaces respectively denoted 3a and 3b in FIG. 1. The surface 3a is in contact with the second surface 2b of the lower layer 2 while the surface 3b is free. At this stage of the manufacturing process, the two surfaces 3a and 3b of the top layer 3 are planar. The free surface 3b of the upper layer 3 is then structured to form the structured front face of the substrate 1 and thus form the track of the optical recording medium. More particularly, as represented in FIGS. 2 to 4, the structuring of the free surface 3b of the upper layer 3 is carried out using a matrix 4 transparent to the light radiation intended to be used for polymerizing the precursor forming the layer. In addition, the structuring is carried out before the polymerization of said precursor. The matrix 4 comprises a face 4a structured in the form of patterns having a shape complementary to that of the desired patterns for the front face of the substrate. Thus, in FIG. 1, the face 4a of the matrix 4 comprises zones 30 in relief delimited by hollow zones. The dimensions of said zones are preferably of the micrometric or nanometric order.

The matrix 4 may be of inorganic material such as quartz or silica or it may be of polymer, such as polycarbonate, polydimethylsiloxane or polymethylmethacrylate. In addition, it may be carried out, beforehand, by thermo-injection of a polymer material into a mold or by a deposition process resulting from conventional microelectronics techniques, on an inorganic substrate (photolithography and etching for example) or well by a method of direct laser writing.

As shown in FIGS. 2 to 4, the structured face 4a of the die 4 is brought into contact with the free surface 3b (arrows F1) and a pressure is applied on said die 4 (arrows F2), so as to transfer the Thus, the relief zones of the matrix 4 make it possible to form complementary recessed zones in the surface 3b of the upper layer 3 and the hollow zones of the matrix 4 form complementary raised areas in the surface 3b of the upper layer 3. Once the surface 3b is structured, the upper layer 3 is polymerized.

For this purpose, it can be exposed to light radiation through the matrix 4. The light radiation is, for example, represented by the arrow F3 in FIG. 5 and it can move on all or part of the surface 3b. of the upper layer 3.

The light radiation is, for example, ultraviolet radiation if the initially deposited precursor forms the organic-inorganic hybrid material polymer under the action of ultraviolet (UV) radiation and, more particularly, if the formation of said polymer is performed by polymerization or crosslinking of the organic functions of said precursor by treatment with UV radiation. More particularly, it is the organic functions that polymerize to form a three-dimensional network, under the action of light radiation and a photoinitiator initially contained in the precursor. Indeed, the photoinitiator agent decomposes chemically under the action of said light radiation, which triggers the polymerization or crosslinking of organic groups. The UV radiation treatment is, for example, carried out at room temperature and under atmospheric pressure. As shown in FIG. 6, once the polymer has been formed, the matrix 4 is removed so as to release the surface 3b of the top layer 3. As the top layer 3 is polymerized, the surface 3b retains the micro or nano form -structured defined by the matrix 4. This is, more particularly, illustrated by Figures 8 and 9 showing the topographic evolution of the surface 3b (curve A) of the upper layer 3, after the removal of the matrix 4, and the structured face 4a (curve B) of the matrix 4. The respective shapes of the two curves A and B confirm, in fact, that the patterns of the surface 3b of the upper layer 3 are the complementary parts of the patterns of the structured face 4a of the matrix 4. After the removal of the matrix 4, the upper layer 3 thus comprises a structured free surface 3b. This surface 3b forms the front face of the substrate 1 and is intended to form the track of an optical recording medium. In order to facilitate the removal of the matrix 4, the process may comprise, before the application of said matrix 4 on the surface 3b of the upper layer 3, a surface treatment of at least a portion of the structured face 4a of the In particular, the surface treatment may be a treatment capable of rendering the structured face 4a of the nonstick matrix. The matrix 4 can be treated, for example by plasma-assisted chemical vapor deposition (PECVD deposition), in order to obtain a deposition of a thin film 5 of non-stick material, for example hydrophobic material. The release material may have low surface energy or low surface tension. The plasma may comprise compounds based on silicon, oxygen, and carbon such as the SiOC compound, or monomeric compounds of organosiloxane or fluorinated type, such as C4F8 or SF6. Thus, as shown in FIG. 6, such a manufacturing method makes it possible to obtain a substrate 1 for an optical recording medium consisting of a stack of a lower layer 2 of inorganic material and of an upper layer 3 of which least part is inorganic. The first surface 2a of the lower layer 2 forms the rear face of the substrate 1 while the structured free surface 3b of the upper layer 3 forms the front face 10 of the substrate 1. According to an alternative, the upper layer 3 can be formed so that different. Thus, a predetermined amount of precursor may be deposited on the second surface 2b of the lower layer 2, as a ribbon of material. Then, the matrix 4 is applied to the second surface 2b comprising the ribbon of material and a centrifugal force is exerted on the assembly formed by the lower layer 2, the precursor and the matrix 4. The centrifugal force exerted then makes it possible to form the upper layer 3 and, at the same time, to structure its surface 3b. The precursor 20 is then polymerized through the die 4 before it is removed. A substrate according to the invention can be used in an optical recording medium of any type. By way of example and as shown in FIG. 7, an optical recording medium comprises a substrate 1 such as that shown in FIG. 6. In FIG. 7, the structured front face 3b of said substrate 1 is covered by a stack 6 of four thin layers forming a recording level. The stack 6 comprises successively: a reflective layer 7, a dielectric lower layer 8, an active layer 9 also called a recordable layer and, for example, constituted by an inorganic material with a phase change, and a second In addition, a protective layer (not shown in FIG. 7) may be deposited on the second dielectric layer 10. In another embodiment and as shown in FIG. 10, the optical recording medium may have an additional level of registration. In this case, an additional upper layer 3 'can be arranged between two stacks of thin layers 6 and 6'. Its formation on the first stack can be carried out in a manner equivalent to that previously described, using the matrix 4. The addition of an additional top layer 3 'between two stacks makes it possible to obtain a good optical separation of the medium and it has a typical thickness of 20 to 50 lm. A substrate 1 such as that shown in Figure 6 and more generally 20 according to the invention can advantageously replace the substrates of organic material according to the prior art. The fact of using materials comprising at least one inorganic part makes it possible, in fact, to improve the behavior of the optical recording media during their storage. The stability of said supports is thus improved in time and furthermore, the method of manufacturing such a substrate is easy to implement and is compatible with the production lines usually used in the field of optical recording and more particularly in the field of optical disks.

Furthermore, the tracking of the optical recording media comprising a substrate according to the invention is not altered compared to those according to the prior art. Thus, respective track tracks of two optical recording media were compared. The first support comprises an organic substrate according to the prior art and a stack of thin layers such as the stack 6 shown in FIG. 7. The organic substrate according to the prior art is made of polycarbonate and has a thickness of between 600 m 5 and 1100 m. The second support comprises a substrate consisting of a stack of a lower layer 2 made of glass and an upper layer 3 made of Ormocomp material and a stack 6 of thin layers identical to that of the first support. The upper layer 3 was spinced at a thickness of 50 μm and then its surface 3b was nano-structured. It has been found that the tracking made with the aid of a writing laser beam, the second optical recording medium is in accordance with that of the first optical recording medium. In addition, the respective capabilities of the first and second recording media to accept write data via a write laser beam have been compared. It has been found that, for the second optical recording medium, the signal accounting for the reflectivity contrast generated by the marks written in the active layer of the stack conforms, for the same writing parameters, to that 20 obtained with the first recording medium. Thus, the write behavior of an optical recording medium is not modified by the chemical nature of the substrate. The invention is not limited to the embodiments shown. Thus, the method of manufacturing the substrate can be adapted to any type of optical recording format, whether for the versatile digital disc also known as Digital Versatile Disc or DVD, the blue beam disc also under the Anglo-Saxon name of Blu-Ray disc or BDR, the high density digital versatile disc also under the Anglo-Saxon name of High-Density Digital Versatile Disk or HDDVD, and others.

In addition, the upper layer may be constituted by any type of material comprising at least one inorganic part. Finally, the step of structuring the free surface of the upper layer 5 can be performed by any type of process. For example, it can be performed thermally or by application of pressure.

Claims (19)

claims   1. Substrate (1) for an optical recording medium having a structured front face and a rear face, characterized in that it consists of a stack: a lower layer (2) of inorganic material, provided with first and second surfaces (2a, 2b) opposite planar, the first surface (2a) forming the rear face of the substrate (1) -and an upper layer (3) consisting of a material having at least one inorganic portion and a free surface (3b) forms the front face of said substrate (1).   2. Substrate (1) according to claim 1, characterized in that the material constituting the upper layer (3) is a hybrid organic-inorganic polymer.   3. Substrate (1) according to one of claims 1 and 2, characterized in that the inorganic material of the lower layer (2) is selected from silicon, glass, glass ceramic, silica and quartz.   4. A method of manufacturing a substrate (1) for optical recording medium according to any one of claims 1 to 3, characterized in that it comprises at least the following steps: formation on the second surface (2b) ) of the lower layer (2), an upper layer (3) constituted by the material comprising at least one inorganic part or by at least one of its precursors and comprising a free surface (3b), and structuring of said free surface (3b).   5. Method according to claim 4, characterized in that the upper layer (3) consists of at least one precursor of an organic-inorganic hybrid polymer, capable of forming said polymer under the action of radiation. luminous.   6. Method according to claim 5, characterized in that the precursor 5 comprises a main network formed of inorganic elements and hybridized with organic side groups.   7. Method according to claim 6, characterized in that the organic groups are capable of polymerizing or crosslinking.   8. Method according to one of claims 6 and 7, characterized in that the main network is obtained by performing a sol-gel process of modified metal alkoxides. 15   9. Process according to claim 8, characterized in that the modified metal alkoxides are modified silicon alkoxides.   10. Method according to any one of claims 5 to 9, characterized in that the forming step consists of depositing an upper layer (3) 20 of constant thickness.   11. The method of claim 10, characterized in that the structuring step is performed after the step of forming the upper layer (3) and comprises at least the following successive steps: - contacting said free surface (3b) of the upper layer (3) with a structured face (4a) of a matrix (4) transparent to said light radiation, - application of a pressure on said matrix (4), - exposure of the upper layer (3) ) to a light radiation, through said matrix (4) - and removal of said matrix (4). 2906925 15   12.Procédé according to claim 11, characterized in that at least a portion of the structured face (4a) of the matrix (4) undergoes a surface treatment, before the step of contacting. 5   13. The method of claim 12, characterized in that the surface treatment is a treatment capable of rendering the structured non-stick face.   14. The method of claim 13, characterized in that the surface treatment comprises depositing a thin film (5) hydrophobic on the structured face (4a) of the matrix (4).   15. Method according to any one of claims 4 to 9, characterized in that the formation of the upper layer (3) is performed at the same time as the structuring of its free surface (3b).   16. The method of claim 4, characterized in that the structuring step is a heat treatment.   17. Process according to claim 4, characterized in that the structuring step is a treatment carried out by applying a pressure.   18. An optical recording medium characterized in that it comprises a substrate (1) according to any one of claims 1 to 3. 25   19. Support according to claim 18, characterized in that it comprises two recording levels (6, 6 ') separated by an additional upper layer (3'). 15