WO1994010684A1

WO1994010684A1 - Optically readable information disc including visible ornamental hologram, and method of fabricating same

Info

Publication number: WO1994010684A1
Application number: PCT/US1993/009967
Authority: WO
Inventors: James Scott Wise; Randall Ray Mcbride; Brian Kevin Harden
Original assignee: Pmdc, Inc.
Priority date: 1992-10-27
Filing date: 1993-10-19
Publication date: 1994-05-11
Also published as: AU5364094A

Abstract

An optically readable information disc such as a compact disc, comprises an optically transparent disc-shaped substrate including an optically readable information signal and at least one visible, ornamental hologram. The visible, ornamental hologram provides an additional avenue for creative expression in the disc medium itself. The holograms are preferably formed on a father disc, which is a negative metal copy of the glass master on which the digital information signal is formed. A holographic image is formed in an imagable layer on the father disc. Mother discs are formed from the father disc and stampers are formed from the father discs such that the stampers include the information signal and the hologram therein. Optically readable information discs are then formed from the stamper using conventional techniques.

Description

OPTICALLY READABLE INFORMATION DISC INCLUDING VISIBLE ORNAMENTAL HOLOGRAM, AND METHOD

OF FABRICATING SAME

Field of the Invention

This invention relates to optically readable information discs such as compact discs and methods of manufacturing the same.

Background ofthe Invention

Optically readable information discs are widely used in consumer and industrial products, for storing and optically reading encoded information. Examples of optically readable information discs are compact discs for digital audio information and laser discs for analog or digital video information. Variations of the compact disc include the interactive compact disc (CD-I) , the video compact disc (CD-V) and the CD-ROM for storing alphanumeric information. Although the physical characteristics of all optically readable information discs may vary somewhat, they generally include an optically transparent disc¬ shaped substrate, having a center hole and an information area, concentric to the center hole, in which information is stored. The information is typically stored as a spiral of pits; however, concentric tracks of pits may also be used. An optically reflective layer such as a layer of metal covers at least the data area, and a protective layer such as a lacguer layer covers the optically reflective area. A printed label may be formed on the protective layer. Single sided and double sided discs may be produced. Data is read from the disc by passing a focused optical radiation beam, typically a laser beam, through the transparent substrate so that it passes through the pits and reflects back through the substrate from the optically reflective layer. As the laser beam strikes the pits and the areas between pits, the returning variable intensity beam carries the information on the disk. The returning beam is detected and then processed.

Optically readable information discs can store large amounts of information with low error rate and minimal effects of aging. For example, a compact disc can hold five billion pits of audio data to deliver high fidelity sound which does not degrade with use. Moreover, optically readable information disks are conducive to mass production. Unlike tapes which must be cycled through their entire length during duplication, the pits in an optically readable information disc may be simultaneously formed in one operation. The manufacturing process for optically readable information discs is well known. Although some minor variations may exist for different types of optically readable information discs, the basic processes are similar. A process for making compact discs will now be summarized. A detailed description of the compact disc manufacturing process is provided in a textbook entitled Principles of Digital Audio by K. C. Pohlmann, published by Howard W. Sams and Company, Inc., 1985, in Chapter 7 entitled The Compact Disc, pp. 215-263, the disclosure of which is hereby incorporated herein by reference. The compact disc manufacturing process typically involves three general steps: tape mastering, compact disc mastering, and compact disc duplication. The tape mastering process produces a master audio tape or other source which contains the information to be encoded onto the compact disc, in the appropriate digitally encoded format.

Compact disc mastering begins with a glass plate, about 240 millimeters in diameter and 6 millimeters thick, which is lapped and polished to produce a smooth, defect free surface. An adhesive is applied, followed by a coat of photoresist which is typically applied by a spin coating process. The photoresist is cured and the plate is then placed in a cutting machine. The cutting machine is a laser cutter which cuts the data pits into the photoresist layer on the glass master plate. The cutting machine typically uses a laser which is intensity modulated to create the cutting signal corresponding to the data on the master tape. The exposed photoresist is then developed to thereby etch away the exposed areas of the photoresist. After development, a thin layer of silver or nickel is deposited on the photoresist. The silver or nickel layer is used as a base for electroplating a thick nickel layer. The metal coatings are then separated from the glass plate and the glass plate is recycled. Residual photoresist, and the silver layer if present, are removed from the nickel disc, hereinafter referred to as a "father". Typically, the father is not used to directly produce compact discs. Rather, multiple negative copies of the father, called "mothers", are produced, using an electroplating process on the father. Then, from each metal mother, multiple "stampers" are produced by electroplating nickel on the mothers. The stampers are actually used to produce the compact discs. The back side of the stamper is polished. A center hole is formed therein, and the outside diameter is typically trimmed to produce the finished stamper.

Compact discs are produced by injection molding a polycarbonate resin on the stamper. After molding, a reflective layer, typically a layer of aluminum about 40-100 nanometers thick, is evaporated or sputtered onto the molded disc surface to provide greater reflectivity. The aluminum layer is covered by an acrylic or other lacguer layer using a spin coating machine. This layer protects the aluminum layer from scratches and oxidation. If necessary, the center hole may again be punched to the final center hole diameter. The label is then printed directly on the lacquer layer. The finished discs are then inspected and packaged.

The compact disc manufacturing process, and improvements thereto, are also described in many United States patents. See, for example, the following United States patents, all assigned to U.S. Phillips Corporation: U.S. Patent No. 3,894,179 to Jacobs et al. entitled Method of Manufacturing an Information Carrier; U.S. Patent No. 4,474,650 to De Laat entitled Method of Manufacturing a Mother Matrix; U.S. Patent No. 4,477,328 to Broeksema et al. entitled Optically readable Information Disk and Method of Manufacturing Same ; U.S. Patent no. 4,507,180 to van der Werf et al., entitled Method of Electrodepositing a Homogeneously Thick Metal Layer, Metal Layer Thus Obtained and the Use of the Metal Layer Thus Obtained, Device for Carrying Out the Method and Resulting Matrix; U.S.

Patent No. 4,861,699 to Wijdenes et al. entitled Method of Making a Master Disk Used in Making Optical Readable Information Disks ; and U.S. Patent No. 4,931,147 to Legierse et al. entitled Method of Manufacturing a Metal Matrix. An optical disc in which data is recorded as radially contiguous Fourier and Fresnel holograms is also described in U.S. Patent 5,111,455 to Psaltis et al. entitled Holographic Information Storage System .

With the widespread acceptance of optically readable information discs in the consumer and industrial product fields, manufacturers of these discs continue to seek innovative ways to manufacture discs having enhanced marketing appeal. Much effort has focused on the packaging of the discs as a marketing tool. For example, multicolor labels have been printed on the discs, to enhance their marketability.

Innovative art work has also been used in the packaging for the disc. For example, U.S. Patent 4,996,681 to Cocco et al. entitled Integral Card for Protectively Enclosing an Optical Disc and a Visual Information Bearing Area , describes a data storage disc including a cover having a visually discernable information bearing layer. The information bearing layer may be an image or photograph of a person and may also include machine readable information such as bar graphs or holograms. An article appearing in Billboard Magazine on

March 21, 1992, entitled Specialized CD Packaging; Many Promo Only Items Now Going Public, describes the proliferation of aesthetically oriented, often ingenious compact disc packages which are making a successful transition from the promotion-only universe to the retail environment. The article describes the use of a heat sensing material in the packaging of the compact disc, so that the heat sensing material changes colors as the user touches it. Holograms have also been used on the CD cover. Metal encased boxes have also been used for the CD cover.

Summary ofthe Invention

The invention is an optically readable information disc such as a compact disc which comprises an optically transparent disc-shaped substrate including concentric data and hologram areas. The data area contains an optically readable information signal, such as one or more of a digital audio, digital or analog video or digital data signal. The hologram area contains at least one visible, ornamental hologram. By "visible" it is meant that the hologram is visible to the naked eye without magnification. By "ornamental" it is meant that the hologram forms an aesthetically pleasing indicia.

The optically readable information disc including visible ornamental holograms, provides an additional avenue for creative expression in the disc medium itself. Holograms are formed in the disc to enhance the marketability and uniqueness thereof. The holograms are formed outside the data area of the disk, which contains the optically readable information signal. In other words, the holograms and the optically readable information signal are preferably formed in nonoverlapping relationship. The hologram area is typically one or more rings which are concentric with the data area. An inner hologram ring may be formed between the data area and the center hole, and an outer hologram ring may also be formed between the data area and the outer edge of the disc. The hologram areas may include one or more hologram images.

The optically readable information disc including at least one visible ornamental hologram is manufactured by forming a stamper disc having a digital information signal and a holographic image at one face thereof, and then injection molding or otherwise forming optically transparent disc shaped substrates from the stamper disc using well known compact disc duplication techniques. Alternatively, the hologram may be formed on the pin or center bushing which holds the stamper in the mold, or in the stamper mold itself. The optically reflective layer which is formed on the transparent disc-shaped substrate may cover the hologram area as well as the data area so that the visible hologram may be viewed from the bottom of the compact disc by reflection from the reflective layer. Alternatively, the hologram area may be free of an optically reflective area and label so that the hologram may be viewed from both sides of the disc.

The holographic image or images may be formed on the glass master along with the optically readable information signal. However, because hologram formation typically has differing requirements from the data pit formation, the hologram is preferably formed separately from the information signal. In particular, the hologram is preferably formed on the father which, as described above, is a negative metal copy of the glass master. An imagable photoresist layer is formed on the father. A holographic image is then formed in the imagable layer, outside the data area.

The holographic image may be formed by creating an optical interferometric pattern of an object in the imagable layer using well known hologram fabrication techniques. Alternatively, a hologram signal may be generated on a computer and imaged onto the imagable layer. Such a hologram is typically referred to as a "computer generated" hologram. The father, with the holographic image thereon, is then used to form a mother and a stamper as described above. The mother and stamper include the optically readable information signal and the hologram therein. The stamper is then used to form optically readable information discs in a manner already described. Accordingly, the manufacturing process for the optically readable information disc including a visible ornamental hologram is compatible with existing disc manufacturing processes, thereby providing a disc with enhanced marketability at nominal additional cost. Brief Description the Drawings Figures 1A and IB are a bottom view and a side, cross-sectional view, respectively, of an optically readable information disc including a visible ornamental hologram according to the present invention.

Figures 2A-2L are side, cross-sectional views of the optically readable information disc of Figures 1A and IB during intermediate fabrication steps.

Detailed Description of Preferred Embodiments The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout.

Referring now to Figures 1A and IB, a bottom view and a side, cross-sectional view, respectively, of an optically readable information disc according to the invention, are illustrated. As shown, optically readable information disc 10 includes an optically transparent disc-shaped substrate 11 including a concentric data area 12 and one or more hologram areas 13a, 13b. The data area contains an optically readable information signal 19 and the hologram areas 13a, 13b contain at least one visible, ornamental hologram 14. The information signal 19 and the at least one visible ornamental hologram 14 are preferably in nonoverlapping relationship. It will be understood by those having skill in the art that holograms 14 are visible to the naked eye and are aesthetically ornamental. One example of an aesthetically ornamental indicia is a trademark or logo of the recording artist or record company. Various musical symbols are shown in the outer hologram area 13b and a spoke design is shown in the inner hologram area 13a. However, it will be understood by those having skill in the art that the holograms may be identical or different and that a single hologram or many holograms may be formed, limited only by the aesthetic creativity of the artist or designer.

As is well known to those having skill in the art, the optically readable information signal 19 in the data area 12 comprises a series of pits, typically on the order of microns in length, and typically not visible to the naked eye. For purposes of illustration only, a spiral 19a of pits 19 is shown, as is a pair of concentric tracks 19b of pits. The compact disc typically uses a spiral track 19a, while other optically readable information discs may use concentric tracks 19b. As is well known to those having skill in the art, the pits 19 form an information signal which may be a digital audio signal, a digital video signal, an analog video signal (an FM analog signal generated by the pits), a digital data signal, or a combination thereof.

Figure IB illustrates a side cross-sectional view of disc 10 including the transparent substrate 11, reflective layer 15, protective layer 16 and printed label 17. The printed label side of the disc 10 is typically regarded as the front face 10a, while the transparent side is typically regarded as the back face 10b. According to the invention, ornamental holograms 14 are visible to the naked eye when viewing the back face 10b of the optically readable information disc 10. It will be understood by those having skill in the art that the ornamental holograms 14 may also be visible when viewing the front face 10a, as long as they are not obscured by the reflective layer 15, protective layer 16, and/or printed label 17.

The dimensions of the data and hologram areas will now be described with reference to the standard compact disc. The dimensions may differ for other optically readable information discs. In the compact disc, the diameter of the outer edge 10c is 120 millimeters and the diameter of inner edge lOd, which forms center aperture 18, is 15 millimeters. The data area 12 has an inner diameter of 40 millimeters.

Accordingly, the inner hologram area 13a may extend from the 15 millimeter diameter to the 40 millimeter diameter.

The data area 12 may extend from the 40 millimeter diameter all the way to the outer edge of the compact disc 10c. However, typically, less than the full diameter of the compact disc is used to store the information signal, so that an outer area 13b which is free of the information signal will remain. This outer area is used for an outer hologram area.

Accordingly, as shown in Figures 1A and IB, the data and hologram areas form rings, with the data area 12 forming a central ring and the hologram areas 13a and 13b forming inner and outer rings, respectively. The compact disc may include a hologram area 13a or hologram area 13b, or both. Additional hologram areas may also be included.

An alternate fabrication technique forms a hologram on the center bushing (which is typically 25- 38 millimeters in diameter) that holds the stamper in the mold. The hologram may also be formed on any other part of the mold. These locations may be particularly advantageous for holograms which do not change from disc to disc, such as a manufacturer or record company logo.

Referring now to Figures 2A-2L, a preferred process for manufacturing an optically readable information disc including a visible, ornamental hologram will be described. The disc is manufactured by forming a stamper disc having an information signal and a holographic image at one face thereof preferably in nonoverlapping relationship. Optically transparent disc-shaped substrates are then formed on the one face of the stamper disc, such that the disc-shaped substrates include the information signal and the holographic image at a first face thereof. An optically reflective layer is formed on the first face of the disc shaped substrate, such that the holographic image forms a visible ornamental hologram when viewed through the disc-shaped substrate.

The stamper disc may be formed from a glass master having an information signal and a holographic ^' image thereon. However, preferably, according to the invention, the holographic image is formed on the father disc which is formed from the glass master. In other words, preferably, the information signal is formed on the glass master and a father disc is formed therefrom. Then, an imagable layer is formed on the father disc and a holographic image is formed in the imagable area outside the information signal area. Then, a stamper is formed from the father disc, preferably by forming a mother disc and then forming a stamper disc, having information and a holographic image therein. Compact discs are then formed from the stamper discs using well known techniques.

In particular, referring now to Figure 2A, a conventional glass master 25 includes a pattern of developed photoresist 26 thereon which is formed by laser exposure, and development. The photoresist 26 is typically between about 125-175 nanometers thick. As shown in Figure 2B, a thin silver layer 27 is evaporated onto glass master 25 and a nickel father 28 is plated on the thin silver layer 27. As shown in Figure 2C, the father 28 is then separated from the glass master, and the silver layer 27 and photoresist 26 are removed.

The holographic image is then formed on the father as will now be described. Referring to Figure 2D, a relatively thick layer of photoresist 29, on the order of microns thick, is coated on father 28. Then, the desired visible, ornamental holographic images are formed on the father 28 in the hologram areas thereof. As shown in Figure 2E, holographic imaging may take place by directing a pair of laser beams 31a and 31b from laser 30 onto the surface of photoresist 29. Beam 31a reflects from an object 32 to be formed as a hologram, and beam 31b passes directly onto photoresist 29. The resultant interference between beams 31a and 31b at the surface of the photoresist 29 creates a holographic image 33 in photoresist 29. It will be understood by those having skill in the art that multiple objects 32 may be used to expose multiple portions of the hologram areas to create multiple holographic images 33 in the photoresist layer 29. Alternatively, a single object may be repetitively directed onto photoresist layer 29. The details for creating an interferometric holographic image on photoresist layer 29 are well known to those having skill in the art and need not be described further herein.

Referring now to Figure 2F, an alternative technique for forming holographic images 33 in photoresist layer 29 is shown. A computer is used to generate the required exposure patterns for a desired hologram image. A computer 34 is then used to control laser 30 to selectively expose photoresist layer 29 in a manner which creates the necessary pattern therein. These holograms are typically referred to as "computer generated holograms" and need not be described further herein. The holographic images 33 formed by interferometric techniques (Figure 2E) or computer generated techniques (Figure 2F) are then developed by immersion in a standard dilute developer solution.

Referring now to Figure 2G, the photoresist 29 outside the hologram areas is then removed. The photoresist may be removed by masking the hologram areas, shining ultraviolet light through the unmasked portions and rinsing in developer solution. In particular, as shown in Figure 2G, a central masking fixture 35 formed of an opaque material, is placed on the father. Central pedestal 35a mechanically contacts the father in the area that will eventually become the disc center hole. Accordingly, fixture 35 is slightly recessed in the hologram area so that the hologram is shielded from the ultraviolet light but the fixture 35 does not touch or contact the hologram 33.

When an outer hologram area is produced on the disc, an edge masking fixture 37 is used. The edge masking fixture 37 contacts the father at an edge pedestal 37a but not over the holograms. The center masking fixture 35 is typically 40 millimeters wide with a central pedestal 35a about 5 millimeters wide and about 0.25 millimeters tall. Edge masking fixture 37 is typically 130 millimeters in diameter with an edge pedestal 37a about 5 millimeters wide and about

0.25 millimeters tall. The inner diameter of the edge pedestal 37 will vary depending upon the width of the outer hologram area.

The father is then exposed to ultraviolet light 36 for about one minute. The fixture or fixtures 35 and/or 37 are removed and the father is rinsed by pouring about 2.5 liters of standard developing solution directly on the surface of the father. The solution is typically a water solution with 2.5 grams NaOH per liter and 12.6 grams Na₄P₂θ₇ per liter. The photoresist which was exposed to the ultraviolet light is thereby washed away leaving the desired hologram visibly intact on the surface of the father as shown in Figure 2H.

The father 28 is then thoroughly rinsed with deionized water to stop the development and to remove all residual developer from the surface of the father. The father 28 is then dried using a high speed spin-dry to remove all water from the father's surface and leave a dry, stain-free surface.

Then, referring to Figure 21, approximately 1000 Angstroms of silver 38 are evaporated onto the surface of the father containing the hologram. The silver layer provides the necessary electrical contact for a subsequent electroplating process. The silvered father is electroplated with nickel to create a mother 39.

The father 28 and mother 39 are then separated from each other as shown in Figure 2J. The mother 39 contains the holographic images and the information signal in its nickel layer. The mother is cleaned of all residual photoresist and silver by exposing the mother to about two minutes of ultraviolet light so that all residual photoresist will be removed from the surface by a caustic solution. The residual silver and photoresist are removed by pouring a solution of ammonium hydroxide and hydrogen peroxide over the mother. The mother is then thoroughly rinsed with deionized water. The holographic image is now clearly visible in the nickel surface of the mother.

Compact discs are then fabricated from the mother 39 using standard manufacturing processes. As shown in Figure 2K, a nickel stamper 40 is electroplated from the nickel mother using standard electroplating processes. Then, as shown in Figure 2L, the stamper 40 is mounted in an injection molding machine where an optically transparent disc-shaped substrate 11 is pressed from optically clear polycarbonate material. The hologram image information which was part of the stamper is formed directly in the polycarbonate disc.

The polycarbonate disc is then metallized with aluminum and the metallized disc is spin-coated" with a protective lacquer coating. A printed label is formed on the lacquer coating to produce the disc shown in Figures 1A and IB. The center hole 18 is then punched if necessary and the disc is packaged. An aesthetically improved optically readable information disc is thereby provided.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims

THATWHICH IS CLAIMED:

1. An optically readable information disc comprising: an optically transparent disc-shaped substrate including concentric data and hologram areas; wherein said data area contains an optically readable information signal; and wherein said hologram area contains at least one visible, ornamental hologram.

2. The optically readable information disc of Claim 1 wherein said concentric data and hologram areas are located at a first face of said substrate, said disc further comprising: an optically reflective layer on said first face, covering said concentric data and hologram areas; a protective layer on said optically reflective layer, opposite said substrate; and a printed label area on said protective area, opposite said optically reflective layer.

3. The optically readable information disc of Claim 2 wherein said substrate further includes a central aperture, and wherein said aperture and said data and hologram areas are concentric.

4. The optically readable information disc of Claim 1 wherein said concentric data and hologram areas comprise first and second concentric rings, respectively, and wherein said second ring is within said first ring.

5. The optically readable information disc of Claim 1 wherein said concentric data and hologram areas comprise first and second concentric rings, respectively, and wherein said first ring is within said second ring.

6. The optically readable information disc of Claim 1 wherein said data area comprises a central ring, and wherein said hologram area comprises inner and outer concentric rings surrounding said central ring.

7. The optically readable information disc of Claim 1 wherein said information signal comprises a spiral of pits in said substrate.

8. The optically readable information disc of Claim 1 wherein said information signal comprises a plurality of concentric tracks of pits in said substrate.

9. The optically readable information disc of Claim 1 wherein said information signal comprises at least one of a digital audio signal, analog video signal, digital video signal and a digital data signal.

10. An optically readable digital information disc including at least one visible, ornamental hologram.

11. A method of manufacturing an optically readable information disc comprising the steps of: forming a stamper disc having an optically readable information signal and a holographic image at one face thereof; and forming an optically readable information disc including said optically readable information signal and said holographic image from said stamper disc.

12. The method of Claim 11 wherein said optically readable information disc forming step comprises the steps of: forming an optically transparent disc-shaped substrate on said one face of said stamper disc such that said disc-shaped substrate includes said information signal and said holographic image at a first face thereof; and forming an optically reflective layer on said first face of said disc-shaped substrate such that said holographic image forms a hologram when viewed through said disk shaped substrate.

13. The method of Claim 11 when said step of forming an optically readable information disc from said stamper is repeatedly performed, to produce a plurality of optically readable information discs including said information signal and said holographic image.

14. The method of Claim 11 wherein said stamper disc forming step comprises the steps of: forming a father disc having an information signal in one face thereof; forming an imagable layer on said one face of said father disc; forming a holographic image in said imagable layer; and forming a stamper from said father disc such that said stamper includes said information signal and said holographic image at a first face thereof.

15. The method of Claim 14 wherein said step of forming a stamper from said father disc comprises the steps of: forming a mother disc on said one face of said father disc, such that said mother disc includes said information signal and said holographic image; and

forming said stamper from said mother disc.

16. The method of Claim 14 wherein said holographic image forming step comprises the step of: creating an optical interferometric pattern of an object in said imagable layer.

17. The method of Claim 14 wherein said holographic image forming step comprises the step of: generating a hologram signal on a computer; and imaging the computer generated signal into said imagable layer.

18. The method of Claim 14: wherein said imagable layer forming step comprises the step of forming a photoresist layer over all of said one face of said father disc; and wherein said holographic image forming step is followed by the steps of: masking said holographic image in said photoresist layer; exposing said father disc to radiation to develop the unmasked portion of said photoresist layer; and removing the developed photoresist from said father disc, such that said holographic image in said photoresist layer remains.

19. An optically readable information disc which is manufactured by the method of Claim 11.

20. A method of manufacturing a stamper for optically readable information discs, comprising the steps of: forming an information signal on a master disc; forming a father disc from said master disc, said father disc having said information signal in one face thereof; forming an imagable layer on said one face of said father disc; forming a holographic image in said imagable layer; forming a mother disc on said one face of said father disc, such that said mother disc includes said information signal and said holographic image at a predetermined face thereof; and forming a stamper from said mother disc such that said stamper includes said information signal and said holographic image at a first face thereof.

21. The method of Claim 20 wherein said holographic image forming step comprises the step of: creating an optical interferometric pattern of an object in said imagable layer.

22. The method of Claim 20 wherein said holographic image forming step comprises the step of: generating a hologram signal on a computer; and imaging the computer generated signal into said imagable layer.

23. The method of Claim 20: wherein said imagable layer forming step comprises the step of forming a photoresist layer over all of said one face of said father disc; and wherein said holographic image forming step is followed by the steps of: masking said holographic image in said photoresist layer; exposing said father disc to radiation to develop the unmasked portion of said photoresist layer; and removing the developed photoresist from said father disc, such that said holographic image in said photoresist layer remains.

24. The method of Claim 23 wherein said information signal defines a ring on said one face of said father disc- wherein said step of forming a holographic image in said imagable layer comprises the step of forming a holographic image in said imagable layer, inside said ring; and wherein said masking step comprises the step of masking said holographic image inside said ring.

25. The method of Claim 23 wherein said information signal defines a ring on said one face of said father disc- wherein said step of forming a holographic image in said imagable layer comprises the step of forming a holographic image in said imagable layer, outside said ring; and wherein said masking step comprises the step of masking said holographic image outside said ring.

26. The method of Claim 20 wherein said stamper forming step is followed by the step of: forming an optically readable information disc from said stamper, such that said optically readable information disc includes said information signal and said holographic image.

27. The method of Claim 20 wherein said step of forming an optically readable information disc from said stamper is repeatedly formed, to produce a plurality of optically readable information discs.

28. The method of Claim 26 wherein said optically readable information disc forming step comprises the steps of: forming an optically transparent disc-shaped substrate on said one face of said stamper disc such that said disc-shaped substrate includes said information signal and said holographic image at a first face thereof; and forming an optically reflective layer on said first face of said disc-shaped substrate such that said holographic image forms a hologram when viewed through said disk shaped substrate.

29. An optically readable information disc which is manufactured by the method of Claim 20.

30. An optically readable information disc which is manufactured by the method of Claim 26.