WO2008047293A2

WO2008047293A2 - Stamper and method of manufacturing a stamper

Info

Publication number: WO2008047293A2
Application number: PCT/IB2007/054180
Authority: WO
Inventors: Mattheus I. Bos; Dirk Burdinski; Alexander M. Van Der Lee; Milan Saalmink; Albert H. J. Immink
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-10-17
Filing date: 2007-10-15
Publication date: 2008-04-24
Also published as: WO2008047293A3; TW200830308A

Abstract

The present invention relates to a stamper (10) for optical disc manufacturing, having a stamper substrate (12), a substrate surface (14) comprising Ni and/or NiO, and a self-assembled monolayer (16) at least partly covering the substrate surface. The present invention further relates to manufacturing methods for stampers (10) and optical discs (22).

Description

STAMPER AND METHOD OF MANUFACTURING A STAMPER

FIELD OF THE INVENTION

The present invention relates to a stamper for optical disc manufacturing and to a method of producing such a stamper. Particularly, the invention relates to a stamper having a modified surface.

BACKGROUND OF THE INVENTION

Manufacturing of a ROM disc can be performed by the so-called 2P (photo- polymerization) replication process. The process can be used to produce many identical disc replications from a single stamper. This allows cheap mass-production of discs. In the replication process with a TwoDOS (two dimensional optical storage) nickel stamper in the 2P process so-called "pit moge" is observed. This causes defects on the stamper and the replicated discs. The stamper consists of pillars with a high aspect ratio, a height of approximately 80-60 nm, and a diameter of approximately 80-60 nm. After replication it can be observed that some pillars have broken off the stamper. This can be attributed to a too high adhesion between the stamper and the 2P lacquer and a too low strength of the pillars on the Nickel stamper.

Another problem arises when replicating in thin films of a thickness less than 100 μm. Since the adhesion between the lacquer and the stamper is too high, the yield of the replication process is very low. For manufacturing of dual layer BD-R (Blu-ray recordable) or BD-RE (BIu- ray rewritable) also a 2P replication process is used for forming the layer 1 (Ll) groove structure. The nature of the layer 0 (LO) stack does not allow UV curing through it, as it is not UV transparent. Thus, in difference to the single layer case where curing is performed through the disc, a metal stamper cannot be used for replication. Instead, a transparent stamper is needed. The same adhesion problems as detailed above exist with these transparent stampers.

There is a special polymer that can be used for making a transparent stamper with low adhesion, known as Zeonor™. This material has a major drawback. The low adhesion property is lost after the first replication, meaning that it needs to be replaced after each replication. In combination with high material cost, this process is very expensive.

It is therefore an object of the present invention to provide a stamper, a stamper manufacturing method, and the related disc manufacturing method, such that "pit moge" is avoided and on the basis of which the yield of the replication process can be increased, both for single and dual layer disc replication.

SUMMARY OF THE INVENTION

This object is solved by the stamper according to claim 1, and by the manufacturing methods according to claims 8, 13, and 14. Further advantageous developments are outlined in the dependent claims.

In accordance with the invention there is provided a stamper for optical disc manufacturing, having a stamper substrate, a substrate surface comprising Ni and/or NiO, and a self-assembled monolayer at least partly covering the substrate surface. It has been found that the modification of the surface of the nickel stamper with a self-assembled monolayer of suitable molecules dramatically reduces the adhesion between the stamper and the laquer and hence the number of defects in the replica. The stability of the stamper in the replication process at the same time is increased tremendously, when compared to an unmodified stamper. As a result of the modification the nickel surface becomes hydrophobic, which reduces the friction during release of the imprinted product from the stamper and thus reduces the risk of break off of smaller features.

Preferably, the self-assembled monolayer is based on a compound from the group comprising phosphonic acids (RPO3H2), phosphinic acids (RPO₂H₂), sulfonic acids (RSO₃H), sulfuric acids (RSO₂H), boronic acids (RB(OH)₂), carboxylic acids (RCO₂H). It is also possible that the self-assembled monolayer is based on a silicon-oxo derivative from the group comprising trihydroxysilyl (RSi(OH)₃), dihydroxysilyl (R¹R²Si(OH)₂), monohydroxysilyl (R¹R²R³SiOH) compounds or reactive precursors thereof, including but not limited to alkoxy (R¹Si(OR)₃, R¹R²Si(OR)₂, R¹R²R³SiOR) or chloro derivatives R¹SiCl₃, R¹R²SiCl₂, R¹R²R³SiCl). According to further embodiments of the present invention, the self-assembled monolayer is based on an alkanethiol compound (RSH).

The present invention is particularly useful in the case that the stamper substrate comprises Ni. Thus, a conventional Ni stamper can be modified in accordance with the present invention, namely by depositing a self- assembled monolayer onto the surface. According to a further embodiment, the stamper substrate comprises a substrate bulk layer and a substrate surface layer, the substrate bulk layer material being different from Ni, and the substrate surface layer comprising Ni and/or NiO. Thus, also stampers made from a different material than Ni can be used, while the advantages investigated in relation to self-assembled monolayers on Ni and/or NiO surfaces are nevertheless obtained.

In this context it can be particularly useful that the substrate bulk layer is transparent and the substrate surface layer has a thickness in the range between 5 and 50 nm. Transparent stampers are needed for UV curing of a photo polymer in the case of dual layer optical disc manufacturing.

In accordance with a further aspect of the present invention there is provided a method of manufacturing a stamper for optical disc manufacturing, comprising the steps of: providing a stamper substrate having a surface comprising Ni and/or NiO, and depositing a self-assembled monolayer onto the substrate surface. Preferably, the step of depositing comprises adsorbing molecules from the gas phase.

It is also possible that the step of depositing comprises adsorbing molecules from the liquid phase.

According to a preferred embodiment of the stamper manufacturing method the step of providing a stamper substrate comprises providing a substrate bulk layer and sputtering a substrate surface layer comprising Ni onto the substrate bulk layer. The sputtering technique is particularly useful in order to deposit very thin layers. Since thin layers are needed if the stamper has to retain transparancy in order to be adepted for the manufacturing process, the sputtering of Ni layers is particularly useful in connection with the present invention.

According to a still further embodiment, before the step of depositing the self- assembled monolayer onto the substrate surface, a step of oxidizing Ni is performed. Since several of the substances herein for forming self assembled monolayers are particularly adapted for forming self assembled monolayers on NiO surfaces, the oxidizing of the Ni leads to the desired surface quality. However, it is also in the scope of the present invention to use Ni surfaces and to even avoid an oxidation of the surface before applying a self assembled monolayer.

The present invention further relates to a method of manufacturing a stamper using a stamper according to the present invention. Thus, the present invention is also adapted for the stamper manufacturing family process. In this sense, the father stamper may be modified in accordance with the invention; further, the resulting mother stamper can be modified accordingly, and also the stampers resulting from the mother stamper, which are used for disc production on large scale, are modified in accordance with the present invention.

The present invention further relates to a method of manufacturing an optical disc unsing a stamper according to the present invention.

Still further, the present invention relates to an optical disc manufactured by such a disc manufacturing method. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment described herein after.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a conventional method of manufacturing a conventional Ni stamper.

Figure 2 illustrates a conventional method of manufacturing a conventional Ni stamper in a family manufacturing process.

Figure 3 illustrates a conventional 2P replication process. Figure 4 shows a SEM photograph of a conventional stamper after one replication process.

Figure 5 shows a SEM photograph of a replica manufactured by a conventional stamper.

Figure 6 shows an AFM image of a replica manufactured by a conventional stamper. Figure 7 illustrates a conventional 2P replication process producing holes in the replica.

Figure 8 illustrates a first embodiment of a stamper according to the present invention.

Figure 9 illustrates a second embodiment of a stamper according to the present invention.

Figure 10 illustrates a third embodiment of a stamper according to the present invention.

Figure 11 shows a diagram illustrating the dependence of UV transmission of a sputtered Ni layer from sputtering time. Figure 12 illustrates (a) a conventional 2P replication process bearing low aspect ratio features, (b) a conventional 2P replication process using a conventional stamper bearing high aspect ratio features, and (c) a 2P replication process according to the present invention using a stamper according to the present invention bearing high aspect ratio features.

Figure 13 illustrates a conventional 2P replication process producing debris on the replica.

Figure 14 shows a flow diagram illustrating a method of manufacturing a stamper according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 illustrates a conventional method of manufacturing a conventional Ni stamper. Figure 2 illustrates a conventional method of manufacturing a conventional Ni stamper in a family manufacturing process. As can be seen in Figure 1, the stamper is made by illumination with a focussed laser beam 24 of a photo-sensitive resist layer 26 that was spin-coated on top of a glass substrate 28 (step a). The photo-resist is etched away completely at the positions where it was illuminated. The glass substrate is used as an etching-stop. Note that the thickness of the photo-resist layer will determine the pit-depth of the final disc and therefore it should have a good thickness uniformity (step b). After the etching a thin layer of nickel or nickel-alloy 30 is deposited on top of the structured photo-resist layer in a sputtering process (step c). The metallized glass master is electroplated to form a thick nickel father stamper 10 (step d) which can be removed from the glass substrate. This father stamper 10 can be used to press a final disc. Referring to Figure 2, for large scale production two additional electroplating steps are applied to create a mother stamper 10' in a family-process (step a) from which more than one stamper 10" can be created (step b). In the latter case the stampers are oxidized prior to electroplating to allow proper separation of the stampers.

Figure 3 illustrates a conventional 2P replication process. A photo-polymer liquid lacquer 32 is deposited on the stamper 10 after which a polycarbonate substrate 34 is pressed against the stamper (step a). The lacquer is cured by ultra-violet (UV) light through the transparante substrate (step b). After curing the newly formed disc 22' can be released from the stamper (step c) and an aluminum 38 and additional protective layer 40 can be deposited on top of the lacquer (step d).

Another replication process that is not illustrated in the drawings is a glass-2P replication process. In contrast to the process of Figure 3 that uses a polycarbonate substrate, a glass substrate is used on which the photo-polymer can be disposed. Further steps are comparable to the method illustrated in Figure 3.

Yet another replication process that is not illustrated in the drawings is injection moulding. The Nickel stamper is mounted on a press to form one half of the mould. The other half is a flat plate to form the optically flat surface at the read-out side of the disc. Molten polycarbonate of optical quality is injected into the cavity formed between the nickel stamper and the flat surface. After cooling down the newly formed disc is released from the mould. The whole replication procedure takes only around 3 seconds which makes mass- manufacturing of discs very cheap. After the replication the transparant disc is sputter-coated with an aluminum layer to form the mirror.

When very small structures must be replicated, as is the case in TwoDOS, the pillars on the stamper (which form the pits in the disc) become very vulnerable to mechanical forces. The strength of these pillars is proportional to the cross-sectional area of the pillars, which decreases quadratically when reducing the diameter of the pits. During the separation of the nickel stamper from the glass-substrate forces act on the pillars that are proportional to the surface area of the sidewall. This decreases only linearly when reducing the diameter of the pits. Therefore, at some moment when decreasing the pit diameter the pits show an increased probability to break off or wrench off during the stamper-substrate separation. A similar problem can occur when separating the disc and the stamper during the replication process. It appears that for the EBR-mastered discs at a lattice constant CC_H = 138 nm with pit diameters equal to about 100 nm the break-off problem indeed occurs during the replication process. This phenomenon is called "pit-moge", a term partly coming from the Japanese language. It appears primarily for pits with a high wall-angle. Here separation forces apparently are larger and the probability of pit-moge increases. Furthermore, also pits with a high aspect ratio are more susceptible to pit-moge, which is no surprise because for deep pits the force on the surface during separation is larger.

Figure 4 shows a SEM photograph of a conventional stamper after one replication process. The photo shows the typical defects caused by pit-moge by the example of a stamper after a first replication. It is clear that some pillars within the circles are missing because the broad spirals should be identical.

Figure 5 shows a SEM photograph of a replica manufactured by a conventional stamper. Not only the pillars on the stamper may break-off, as illustrated in Figure 4, but it is also possible that the UV-curable polymer that is between the pillars may stick to the stamper and break from the disc during separation of the disc from the stamper. This causes large holes in the disc and it especially occurs at places on the disc with large number of pits because there the structures between pits are most narrow and thus most fragile.

Figure 6 shows an AFM image of a replica manufactured by a conventional stamper. This atomic force microscopy (AFM) image of a replica of a different stamper than shown in Figure 4 clearly shows bumps 42 instead of pits 44. This can be explained by the fact that during break-off of the pillars from the stamper some extra material of the stamper surface was torn off. The newly formed irregular hole in the stamper causes a bump in the replica. Figure 7 illustrates a conventional 2P replication process producing holes in the replica. Here the origin of the disc damage due to stamper 10 separation is shown. A part 46 of the disc 22 sticks with the stamper when separating the stamper from the disc.

Figure 8 illustrates a first embodiment of a stamper according to the present invention. The stamper 10 comprises a substrate 12 with a substrate surface 14. The substrate surface 14 comprises Ni and/or NiO, depending on the manufacturing process. In any case, a self assembled monolayer 16 is deposited on the substrate surface 14, while the nature of the self assembled monolayer is preferably chosen in dependence on the substrate surface properties. In the case of a surface consisting of Ni or mainly of Ni, alkanethiol compounds can be deposited. In the more common case, where the surface is oxidized, either due to natural oxidation or by induced oxidation, alkanephosphonic acids are a preferred basis for the self assembled monolayers. Further materials can be used as mentioned below.

Figure 9 illustrates a second embodiment of a stamper according to the present invention. In this case, the stamper 10 comprises a substrate bulk layer 18 and a substrate surface layer 20. The substrate surface layer comprises Ni and/or NiO so that a self assembled monolayer 16 can be supplied that is identical to the self assembled monolayers being appliable to conventional Ni stampers. The present embodiment is particularly useful in the case that a transparent stamper has to be used for the manufacturing process, especially for dual layer optical discs. In this case, the bulk layer is transparent, and the substrate surface layer 20 is sputtered on the bulk layer up to a thickness of for example 10 mm, thereby leaving sufficient transparency.

In contrast to Figure 9, the stamper 10 shown in Figure 10 is based on a glass substrate 48 that supports a 2P replication layer 50. Thus, also a transparent stamper is obtained on which a thin substrate surface layer 20 and a self assembled monolayer 16 can be deposited.

Figure 11 shows a diagram illustrating the dependence of UV transmission of a sputtered Ni layer from sputtering time. It is illustrated that the transparency of the Ni layer that is deposited on the stamper bulk layer can be well controlled by selecting the appropriate sputter time. In the example given in Figure 11, the transparency after approximately 6 sec still has a relative value of 50 %, while after 15 sec of sputter time only a relative transparency of 30 % is left. Depending on the replication process requirements, the transparency can thus be adjusted as needed. Figure 12 illustrates (a) a conventional 2P replication process bearing low aspect ratio features, (b) a conventional 2P replication process using a conventional stamper bearing high aspect ratio features, and (c) a 2P replication process according to the present invention using a stamper according to the present invention bearing high aspect ratio features. In Figure 12a no problems are observed. The stamper 10 is pressed to the prepolymer substrate 52, and it is removed from the polymer substrate 54 after curing. In

Figure 12b the problems underlying the present invention are observed, since the stamper 10 has smaller structures for providing a higher aspect ratio. As can be seen, the smaller structures brake off when the stamper 10 is removed from the polymer substrate 54. These problems are avoided in accordance with Figure 12c, where, before pressing the stamper 10 to the prepolymer substrate 52, a self assembled monolayer 16 (not visible in this illustration) is deposited on the stamper c. Due to the "anti-stick" effect of this layer, the small structures of the stamper 10 are retained even after separation of the stamper 10 from the polymer substrate 54.

Figure 13 illustrates a conventional 2P replication process producing debris on the replica. This is another artefact that can be observed along the side of many pits. The hypothesis for the origin of this debris is that it is induced by scraping of the pillars at the sides of the just-formed-pits in the disc during the separation of the disc from the stamper. This is another effect of pillars that have a very high wall-angle (the drawing even shows an angle larger than 90°). Also this debris effect can be mitigated by using a stamper according to the present invention.

Figure 14 shows a flow diagram illustrating a method of manufacturing a stamper according to the present invention. In a first step SOl a stamper substrate is provided having a surface comprising Ni and/or NiO. Subsequently, a self assembled monolayer is deposited onto the substrate surface in step S02, thereby providing a stamper that shows no problems in the 2P replication process due to sticking effects.

In the following, particular properties of the self-assembled monolayers used with the present invention are described. In the case of nickel surfaces, self-assembled monolayers (SAMs) of alkanethiols have been investigated in great detail.^1"3 Modification of nickel surfaces with alkanethiol SAMs provides surfaces with a water contact angle well above 100° indicating significant hydrophobicity and low friction properties.

2 Ni + H-S-R --> Ni-S-R + Ni-H (1)

The stability of such alkanethiol SAMs is, however, relatively low due to their chemical reactivity. As exemplified in the case of cyclohexanethiol SAMs on the Ni(111) surface, the C-S bond can be broken easily, resulting in the ultimate loss of the alkane (cyclohexane in this case) tail group and thus the loss of the surface protecting properties of the SAM.¹ It has further been shown that alkanethiol SAMs on nickel surfaces are prone to oxidation by oxygen from ambient and that such oxidation processes reduce the stability of such monolayer.²'³ Surface reaction with air dioxygen in general is problematic for all modification processes that require an oxygen- free nickel surface as it is the case for alkanethiols. In contrast to reduced nickel surfaces, oxidized surfaces produce only low quality monolayers with a significant content of alkanesulfinate (n = 2) and alkanesulfonate (n = 3) components.² "NiO" + H-S-R -> Ni-S(O)_n-R (2)

In spite of the above mentioned problems with alkanethiol SAMs, stampers with such monolayers are understood to be within the limits of the present invention.

Particularly useful embodiments of the invention take advantage of the natural oxide layer, which is formed on nickel surfaces exposed to the ambient. The use of alkanephosphonic acids (RPO3H2) as SAM-forming molecules is proposed. In a simplified way, the first step of the formation of SAMs of these molecules on oxidized and hydroxylated nickel surfaces may be described as a condensation reaction as shown in equation 3.

Ni-O-H + H-O-P(O)(OH)-R -> Ni-O-P(O)(OH)-R + H₂O (3) The formation of alkanephosphonic acid monolayers on other metals that easily form surface oxides or metal oxides is well known in the literature. Among those materials are, for instance, silicon, aluminum, indium tin oxide (ITO), and indium zinc oxide (IZO). Due to their hydrophobic nature, those SAMs have proven useful as protective layers against chemical corrosion processes, such as wet or dry chemical etching.^4"12 Alternatively the use of other organic or heteroorganic acids for the formation of release layers on nickel stampers is proposed. Such other acids may include phosphinic acids (RPO₂H₂), sulfonic acids (RSO₃H), sulfuric acids (RSO₂H), boronic acids (RB(OH)₂), carboxylic acids (RCO₂H), or organic silicon-oxo derivatives. Silicon-oxo derivatives may include trihydroxysilyl (RSi(OH)₃), dihydroxysilyl (R¹R²Si(OH)₂), monohydroxysilyl

(R¹R²R³SiOH) compounds or reactive precursors of those, including but no limited to alkoxy (R¹Si(OR)₃, R¹R²Si(OR)₂, R¹R²R³SiOR, with R = methyl, ethyl,...) or chloroderivatives R¹SiCl₃, R¹R²SiCl₂, R¹R²R³SiCl) or alike. Alkanethiols or suitable derivatives may also be used to form such monolayers. R, R¹, R², and R³, as mentioned above, independent from each other represent hydrocarbon or halogenated hydrocarbon containing groups. The term hydrocarbon as used herein can denote straight-chained, branched and cyclic aliphatic and aromatic groups, and can typically include alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, aryl, arylalkyl, arylalkenyl and arylalkynyl. The term "hydrocarbon containing group" also allows for the presence of atoms other than carbon and hydrogen, typically for example, oxygen and/or nitrogen.

The term hydrocarbon as explained above can denote straight-chained, branched and cyclic aliphatic and aromatic groups, and can typically include alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, aryl, arylalkyl, arylalkenyl and arylalkynyl. Suitably, the hydrocarbon groups can contain up to 35 carbon atoms, typically up to 30 carbon atoms, and more typically up to 20 carbon atoms. Corresponding halogenated hydrocarbons can also be employed, especially fluorinated hydrocarbons. In a preferred case where R represents a fluorinated alkyl group, this can be represented by the general formula F(CF₂)_k(CH₂)i, where k is typically an integer having a value between 1 and 30 and 1 is an integer having a value of between 0 and 6. More preferably, k is an integer of between 5 and 20, and particularly between 8 and 18. It is of course recognized that although the above are given as preferred ranges for the values of k and 1, the particular choice of k and 1 will depend on the purpose to which the surface to be treated is to be put. It will also be appreciated that the term "hydrocarbon containing group" also allows for the presence of atoms other than carbon and hydrogen, typically O or N, as explained above.

The above hydrocarbon groups can also be further substituted by substituents well known in the art, such as Chalky!, phenyl, Ci-βhaloalkyl, hydroxy, Ci_6alkoxy, Ci_ βalkoxyalkyl, Ci_6alkoxyCi_6alkoxy, aryloxy, keto, C₂_6alkoxycarbonyl, C₂. 6alkoxycarbonylCi_6alkyl, C2-6alkylcarbonyloxy, arylcarbonyloxy, arylcarbonyl, amino, mono- or di- (Ci_6)alkylamino, or any other suitable substituents known in the art.

Those self-assembled monolayers may be formed in various ways. The molecules may be adsorbed to the nickel surface from the gas phase, provided that the molecules used exhibit a sufficiently high vapor pressure. The molecules may alterantively be adsorbed from a solution in a suitable solvent. The solvent can have a significant impact on the quality of the obtained SAM. The choice of solvent should be made according to its capability to dissolve the SAM-forming molecules, to its extent of interaction with those molecules and its inertness toward the nickel surface.³ Alternative ways of forming such a monolayer may also be envisioned.

A first example of manufacturing a stamper for single layer disc replication is described in the following. The surface of a standard nickel stamper (with a diameter of about 17 cm) has been modified as described above. From the surface of the stamper were removed all organic protective layers and organic impurities by washing it subsequently with water, ethanol, and n-heptane, and drying it in a stream of nitrogen. It was further exposed to an argon plasma (300 W, 0.25 mbar, 1 min) followed by an oxygen plasma (200 W, 0.20 mbar, 30 s) to allow for the formation of an oxide layer on the surface of the stamper. It was subsequently immersed in a solution of octadecanephosphonic acid (ODPA, 0.01 mol L^"1, about 100 mL) in ethanol for at least a few minutes. Immersion times of up to 3 days have been employed to obtain high quality SAMs. After removal from the ODPA solution, the stamper was rinsed with ethanol to remove any excess of ODPA and dried in a stream of nitrogen. The stamper was subsequently heated to about 80-100 ⁰C for about 20 minutes to complete SAM formation. This optional heating step was found to be suitable to increase the durability of the SAM-modified surface. Temperatures of up to 200 ⁰C or even above can be suitable in the heating step. Higher temperatures may be useful to allow for applying significantly shorter heat exposure times. So modified stampers were used in the above described replication process. With the modified stamper, a dramatic reduction of the described problems was achieved, when compared to a process, in which a not-modified stamper was used. As a second example, for the replication of dual layer BD-R the surface of a polycarbonate substrate was modified. First the injection moulded polycarbonate disc was sputtered with a thin layer of nickel (~10 nm). For activation of the nickel surface, the substrate was exposed to an atmospheric plasma jet using pressurized air (performed on our own designed hardware). It was subsequently immersed in a solution of octadecanephosphonic acid (ODPA) in ethanol (2.5 mmol L^"1) for at least a few minutes. Immersion times of up to several days were employed to obtain high quality SAMs. After removal from the ODPA solution, the stamper was rinsed with ethanol to remove any excess of ODPA and spun dry on a Headway™ spinner. After spinning, substrates were placed in 100°C oven for about 45 minutes. Such modified stampers were used in the replication process as described above. With the modified stamper, a dramatic reduction of the described problems (release of stamper from substrate, groove shape takover, etc) was achieved, when compared to a process in which a non-modified stamper was used.

Summarizing, this invention describes a method to overcome the problems occurring when replicating small structures with high aspect ratios in a 2P replication process for optical storage disks. For small structures with a high aspect ratio the contact surface with the 2P material is large compared to the diameter of the structure. This leads to high adhesion (between 2P and stamper material) and low cohesion (in the stamper material), resulting in defects in the replication process. A solution to this is given by the application of an "anti- stick" layer to the stamper. It has been found that the modification of the surface of the nickel stamper with a self-assembled monolayer of suitable molecules dramatically reduces the adhesion between the 2P lacquer and the stamper and thus the number of defects in the replica and the stamper.

References

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Claims

CLAIMS:

1. A stamper (10) for optical disc manufacturing, having a stamper substrate

(12), a substrate surface (14) comprising Ni and/or NiO, and a self-assembled monolayer (16) at least partly covering the substrate surface.

2. A stamper according to claim 1, wherein the self-assembled monolayer (16) is based on a compound from the group comprising phosphonic acids (RPO3H2), phosphinic acids (RPO₂H₂), sulfonic acids (RSO₃H), sulfuric acids (RSO₂H), boronic acids (RB(OH)₂), carboxylic acids (RCO₂H).

3. A stamper according to claim 1, wherein the self-assembled monolayer (16) is based on a silicon-oxo derivative from the group comprising trihydroxysilyl (RSi(OH)₃), dihydroxysilyl (R¹R²Si(OH)₂), monohydroxysilyl (R¹R²R³SiOH) compounds or reactive precursors thereof, including but not limited to alkoxy (R¹Si(OR)₃, R¹R²Si(OR)₂, R¹R²R³SiOR) or chloro derivatives R¹SiCl₃, R¹R²SiCl₂, R¹R²R³SiCl).

4. A stamper according to claim 1, wherein the self-assembled monolayer (16) is based on an alkanethiol compound (RSH).

5. A stamper according to claim 1, wherein the stamper substrate (12) consists of Ni.

6. A stamper according to claim 1, wherein the stamper substrate (12) comprises a substrate bulk layer (18) and a substrate surface layer (20), the substrate bulk layer material being different from Ni, and the substrate surface layer comprising Ni and/or NiO.

7. A stamper according to claim 6, wherein the substrate bulk layer (18) is transparent and the substrate surface layer (20) has a thickness in the range between 5 and 50 nm.

8. A method of manufacturing a stamper (10) for optical disc manufacturing, comprising the steps of: providing a stamper substrate (12) having a surface (14) comprising Ni and/or NiO, and depositing a self-assembled monolayer (16) onto the substrate surface.

9. A method according to claim 8, wherein the step of depositing comprises adsorbing molecules from the gas phase.

10. A method according to claim 8, wherein the step of depositing comprises adsorbing molecules from the liquid phase.

11. A method according to claim 8, wherein the step of providing a stamper substrate (12) comprises providing a substrate bulk layer (18) and sputtering a substrate surface layer (20) comprising Ni onto the substrate bulk layer.

12. A method according to claim 8, wherein, before the step of depositing the self- assembled monolayer (16) onto the substrate surface (14), a step of oxidizing Ni is performed.

13. A method of manufacturing a stamper (10) using a stamper according to claim 1.

14. A method of manufacturing an optical disc (22) using a stamper (10) according to claim 1.

15. An optical disc (22) manufactured in accordance with claim 14.