Abstract:
A method for forming a stamper used in the manufacture of CDs, DVDs, and other types of optical disks comprises forming a substrate by rolling. A layer of material is deposited (e.g. by plating) onto the substrate. Thereafter, a resist layer is formed on the layer of material and patterned. Because the substrate is formed by rolling, it is relatively inexpensive to form the substrate to a desired thickness. Because the layer of material is formed by deposition (e.g. plating), it is relatively inexpensive to ensure that the layer has a very smooth surface (i.e. without necessitating a great deal of polishing).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention pertains to stampers used to manufacture optical data storage media such as CDs and DVDs and methods for making such stampers. (As used herein, optical media includes magneto-optic, phase change and dye based media as well as other types of optical media.)  
         [0002]     It is known in the art to use “stampers” to make optical data storage devices. Stampers are discussed, for example, by Boomaars, “The Key to Mastering the In-House Solution”, published in April, 2003, One to One, pages 63-64, incorporated by reference. See also EP 0 995 193 B1, EP 0 986 813 B1 and U.S. Pat. No. 6,238,846.  
         [0003]      FIGS. 1A  to  1 H schematically illustrate in cross section a first prior art method for making a stamper used to form an optical data storage device. Referring to,  FIG. 1A , one spin-coats a silane-based adhesion layer  11  and then a DNQ-based Novo-lacquer photoresist layer  10  onto a 1.6 mm thick glass substrate  12 . One then “prebakes” and then patterns photoresist layer  10  by selective exposure with a laser beam. (The laser wavelength is between 250 and 450 nm.) One then develops the resist, thereby removing portions  10   a  and  10   b  of photoresist  10  on substrate  12  ( FIG. 1B ). The structure shown in  FIG. 1B  is sometimes known as a “master”  13 . (It will be appreciated that  FIG. 1B  only shows a small portion of master  13 , and that a full cross section would show numerous areas where portions of photoresist  10  are removed. It will also be appreciated that the figures are not to scale.)  
         [0004]     One then applies a thin NiV film  14  to master  13  ( FIG. 1C ) by evaporation or sputtering. One then plates a Ni layer  16  (about 300 μm thick) onto NiV film  14 . Ni layer  16  is then separated from the master ( FIG. 1D ). (The surface of NiV film  14  is then cleaned to remove any residual photoresist that might cling thereto.) Ni layer  16  contains protrusions  16   a ,  16   b  at locations corresponding to the locations of removed portions  10   a ,  10   b  of photoresist layer  10 . Ni layer  16  is sometimes referred to as a “father”  17 .  
         [0005]     The surface of Ni layer  16  is oxidized to facilitate separating father  17  from a subsequently formed structure. One then plates a Ni layer  18  onto Ni layer  16  ( FIG. 1E ) and then separates Ni layer  18  from layer  16 . Ni layer  18  comprises depressions  18   a ,  18   b  at locations corresponding to the locations of protrusions  16   a ,  16   b . Layer  18  is sometimes referred to as a “mother”  19  ( FIG. 1F ).  
         [0006]     The surface of layer  18  is then oxidized, and a Ni layer  20  ( FIG. 1G ) is plated onto mother  19 . One then separates Ni  20  from mother  19 . Ni layer  20  has protrusions  20   a ,  20   b  at locations corresponding to the locations of depressions  18   a ,  18   b . Layer  20  is sometimes referred to as a “son” or “stamper”  22  ( FIG. 1H ).  
         [0007]     During manufacturing of CDs and DVDs, stamper  22  is placed into an injection mold  24  ( FIG. 2 ). ( FIG. 2  shows only a small number of protrusions on stamper  22  for ease of illustration. It will be appreciated that a stamper typically includes a much larger number of protrusions.) The injection mold is filled with molten polycarbonate  26  via a centrally defined opening  22   a  in stamper  22 . After polycarbonate  26  cools, it is removed from mold  24 . At this point, polycarbonate  26  contains depressions at locations corresponding to the locations of protrusions  20   a ,  20   b . These depressions serve as servo information for the CD or DVD being formed. For the case of read-only CDs and DVDs, the depressions can also correspond to content data and encoding data for error correction. (Content data can include video or still images, sound recordings, computer data in digital form or software.) After being removed from the injection mold, polycarbonate  26  is covered with a thin transparent protective layer (not shown). In addition to protecting polycarbonate  26 , this protective layer also ensures that any dust or other undesired particle is not near the focal point of a laser used to read data in the CD or DVD. (For the case of write-once or read/write optical media, one deposits a dye based, magneto-optic or phase change optical recording layer on the polycarbonate substrate before depositing the above-mentioned protective layer. Data can be recorded in and read from this optical recording layer.)  
         [0008]     It is known to use one master to form a number of fathers, one father to form a number of mothers, and one mother to form a number of sons.  
         [0009]     The above-described method for manufacturing stampers for CDs and DVDs accounts for over 95% of the CDs and DVDs manufactured today. While this procedure is adequate for producing optical media, it is complicated and expensive. In particular, the plating processes and the glass substrate starting material are expensive.  
         [0010]      FIGS. 3A  to  3 B illustrate a second prior art method for forming a stamper. Referring to  FIG. 3A , one sputters or evaporates a Ni seed layer  30  (e.g. a few hundred angstroms thick) onto a glass substrate  32  and then plates a nickel layer  34  (about 300 μm thick) onto seed layer  30 . One then peels nickel layer  34  off of substrate  32 . Layer  34  is then stamped to bring it to a desired diameter. Thereafter, one applies a cross-linked undercoat  35  and a DNQ-based image-reversal polymer photoresist layer  36  onto nickel layer  34  ( FIG. 3B ). Photoresist layer  36  is then pre-baked. A laser beam is then used to write a pattern in photoresist layer  36 . After a bake step layer  36  is developed and hard-baked. A thin metalization layer  38  is then deposited over patterned photoresist layer  36 .  
         [0011]     The structure comprising nickel layer  34 , undercoat  35 , patterned photoresist layer  36  and metalization layer  38  is a stamper  40 . Stamper  40  is placed in a mold along with molten polycarbonate as discussed above in relation to  FIG. 2  to form a CD or a DVD. The polycarbonate then cools and hardens. Depressions form in the polycarbonate at locations corresponding to the pattern formed in photoresist layer  36 . The depressions constitute content information and/or tracking and servo structures within the CD or DVD. The above-mentioned process is discussed in PCT Patent Application WO 02/09103, published on Jan. 31, 2002, incorporated herein by reference.  
         [0012]     As mentioned above, a thin transparent protective layer is bonded to the polycarbonate substrate during the manufacture of the CD or DVD. For the case of read-write or write-once media, a recording layer such as a dye based, magneto-optic or phase change layer is formed over the polycarbonate prior to depositing the protective layer.  
         [0013]     While the above-described process provides adequate results, it is also expensive. For example, forming nickel layer  34  by plating is expensive. Accordingly, it would be desirable to provide a less expensive process for making stamper  40 .  
         [0014]     One might be tempted to form nickel layer  34  by another process, such as rolling. Unfortunately, substrates formed by rolling have many surface defects that would have to be removed by polishing. Such polishing would be excessively expensive. Accordingly, manufacturers tolerate the expense of forming nickel layer  34  by plating because plating results in a very smooth layer.  
         [0015]     It would be desirable to provide a smooth substrate for a stamper while minimizing the expense of plating or other deposition process.  
         [0016]     Another type of process for making a stamper is discussed in U.S. Pat. No. 5,783,371. In the &#39;371 process, a photoresist layer is formed on a substrate and patterned. The substrate is then machined with an ion beam using the photoresist as a mask. This type of process requires ion beam machining apparatus. It is not believed that the &#39;371 process is in commercial use. This process fundamentally differs from the process of  FIGS. 1 and 3  in that it relies on etching a substrate to pattern the substrate rather than depositing material over a substrate covered with patterned resist.  
       SUMMARY  
       [0017]     A method for manufacturing a stamper in accordance with a first embodiment of the invention comprises forming a substrate by a rolling operation (e.g. by rolling an ingot of material). The substrate is typically a metal such as Ni, Cu, or alloys thereof.  
         [0018]     A first layer is then deposited on the substrate, e.g. by plating. In one embodiment, deposition comprises electroless plating of a metallic material such as a NiP alloy or other hard material. In another embodiment, deposition is accomplished by electroplating. Alternatively, a vacuum deposition process such as sputtering, evaporation, ion beam deposition, etc., can be used. Optionally, the surface of the first layer is subjected to one or more polishing steps.  
         [0019]     Thereafter, the top surface of the stamper is patterned. In one embodiment, this is accomplished by depositing a layer of resist on the first layer. The resist is preferably negative resist, but positive resist can be used as well. In one embodiment, the resist is patterned by selectively exposing the resist to a laser beam and then developing the resist. In another embodiment, instead of using a laser beam, another form of radiation is used, e.g. an e-beam. Alternatively, it can be patterned using a mask and a light source (e.g. visible light, UV light or X-rays). In one embodiment, a metallic layer is deposited (e.g. by sputtering or other vacuum deposition technique) onto the patterned resist.  
         [0020]     Optionally, the resist can be “prebaked” (baked before being exposed) and/or baked after being exposed. This enhances the mechanical stability of the resist.  
         [0021]     After patterning of the resist, the stamper is inserted into a mold along with a molten material (e.g. polycarbonate). When the polycarbonate cools, it is removed from the mold. The polycarbonate surface reflects the pattern formed in the resist layer. (Instead of using molten polycarbonate, other types of fluid could be placed in the mold to thereafter harden.)  
         [0022]     Advantageously, the stamper is provided without having to form most of the thickness of the stamper by a deposition process. Instead, a rolling process is used to form a large part of the stamper thickness. However, because a surface of the stamper is formed by deposition, this surface is very smooth, so that it is unnecessary to perform a great amount of polishing.  
         [0023]     In one version of the first embodiment in which the resist is patterned using light, a light insensitive layer can be provided between the first layer and the resist. The light-insensitive layer is typically transparent to the light used to expose the resist.  
         [0024]     In accordance with a second embodiment of the invention, a substrate (typically metallic) is plated with an overcoat layer (typically a hard material, e.g. a metal such as a NiP alloy). (In lieu of plating, other deposition techniques such as vacuum deposition can be used to provide the overcoat layer.) The substrate can be manufactured using a rolling process. Typically, a light-insensitive layer (e.g. a polymer) is deposited on the overcoat layer. A resist layer is then deposited thereon. The resist layer is then patterned.  
         [0025]     The light-insensitive layer can be a material (e.g. a dielectric) other than a polymer. This layer is typically transparent to light having the wavelength used to pattern the photoresist. It is also typically electrically non-conductive.  
         [0026]     A layer of material is then deposited over the patterned resist. In one embodiment, this is accomplished by vacuum depositing a first metal layer over the substrate and patterned resist (e.g. by evaporation or sputtering), and a second metal layer (e.g. Ni or NiP) is plated onto the first metal layer. The second metal layer is then removed from the substrate and resist. The second metal layer can be used as a father.  
         [0027]     The surface of the second metal layer can then be oxidized and plated with a third metal layer to form a mother. The third metal layer is then separated from the second metal layer, oxidized, and plated with a fourth metal layer to form a son. The fourth metal layer is separated from the third metal layer and used as a stamper.  
         [0028]     One version of this second embodiment permits replacing glass substrate  12  ( FIG. 1A ) with a less expensive metallic substrate covered with the light insensitive layer. Further, this structure is not as fragile as glass substrate  12 . If glass substrate  12  fractures while it is within laser patterning equipment, removing broken pieces of glass from the equipment can be a time-consuming task. Because the metallic substrate is not as fragile as glass, it does not have this disadvantage.  
         [0029]     If one merely substituted a photoresist-covered metallic substrate for a photoresist-covered glass substrate, the minimum feature pitch size that could be achieved would be larger than the corresponding minimum feature pitch size that could be achieved with photoresist on glass. Therefore, the data storage density that could be achieved using a metallic substrate would be degraded. Moreover, the cross section of the resultant pit or protrusion will not meet the requirements for the desired data density or polycarbonate molding process. This is because a laser interacts with a metallic substrate differently than with a glass substrate. By providing the above-mentioned light-insensitive layer between the metallic substrate and the photoresist, a smaller minimum feature pitch size and the desired pit or protrusion cross section can be achieved. Therefore, one can replace a glass substrate with a much less expensive metal substrate coated with the light-insensitive layer with reduced or no sacrifice in data storage density.  
         [0030]     One can essentially use the polymer-coated metallic substrate in the process of  FIGS. 1A  to  1 H in lieu of the more expensive glass substrate  12  without having to make substantial modifications to the patterning process. Since 95% of stamper manufacturing uses the method of  FIGS. 1A  to  11 H, this represents a significant saving for the CD and DVD industry.  
         [0031]     In a third embodiment of the invention, instead of using a metallic substrate covered with a light insensitive layer, the surface of the metallic substrate is made substantially non-reflective of the laser light used to expose the photoresist. For reasons described below, this is an alternative method for reducing the minimum feature pitch size that can be achieved in the photoresist compared to what would be achieved if the photoresist was directly applied to a reflective metallic substrate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]      FIGS. 1A  to  1 H illustrate a first method in accordance with the prior art for forming a stamper.  
         [0033]      FIG. 2  schematically illustrates in cross section a stamper being used to form a CD or a DVD.  
         [0034]      FIGS. 3A and 3B  illustrate a second method in accordance with the prior art for forming a stamper.  
         [0035]      FIGS. 4A  to  4 C illustrate a method in accordance with a first embodiment of the invention for forming a stamper.  
         [0036]      FIGS. 5A  to  5 C illustrate a method in accordance with a second embodiment of the invention for forming a substrate used to manufacture a master.  
         [0037]     These figures are schematic and not to scale. 
     
    
     DETAILED DESCRIPTION  
       [0038]     Referring to  FIG. 4A , a method in accordance with one embodiment of our invention includes providing a sheet  100 . Sheet  100  is typically metallic, and is formed by rolling. During rolling, an ingot of material is fed through rollers  101  to form sheet  100 . (Although only two pairs of rollers are shown in  FIG. 4A , typically more than two pairs of rollers are used during this process.) As the material passes through the rollers, it becomes progressively thinner until it is in the form of sheet  100 . Sheet  100  can be a metal such as a spinodal copper alloy. (Spinodal structures are discussed by D. E. Laughlin and W. A. Soffa in “Spinodal Structures”, Metals Handbook, Ninth Edition: Volume 9, Metallography and Microstructures, American Society for Metals, pages 652-654 (1985), incorporated herein by reference.) Spinodal structures have the advantage of being bendable without distortion. However, sheet  100  can be other materials as well, e.g. nickel, stainless steel or brass. In one embodiment, sheet  100  is 277 μm thick, plus or minus 3 μm. However, this thickness is merely exemplary.  
         [0039]     Optionally, after rolling, sheet  100  can be lapped or ground, e.g. using a grinding stone comprising diamond particles embedded in epoxy. In another embodiment, such lapping or grinding is not performed.  
         [0040]     Sheet  100  is cleaned. A layer  102  is then deposited on sheet  100  ( FIG. 4B ). In one embodiment, layer  102  is metallic, e.g. Ni or a Ni alloy. For example, layer  102  can be an alloy comprising Ni and P electroless plated onto sheet  100 . (The NiP alloy is amorphous and harder than pure Ni. In one embodiment, the NiP contains from 7 to 12 wt. % P.) A “strike” voltage can be applied to sheet  100  to facilitate initiating of plating. (In lieu of electroless plating, electroplating, vacuum deposition or other deposition techniques can be used.) Layer  102  is then polished and cleaned. Polishing can be accomplished using one or more polishing steps, and can be performed using mechanical polishing, chemical polishing, or chemical mechanical polishing. Preferably, a single polishing step using chemical mechanical polishing is used. In one embodiment, polishing is performed using a colloidal silica or alumina slurry. The slurry can have one or more additives to improve the slurry performance. One example of a slurry is discussed in U.S. Pat. No. 6,149,696, issued to Kang Jia, incorporated herein by reference.  
         [0041]     In one embodiment, the thickness of the plated sheet is 295 μm plus or minus 5 μm. In yet another embodiment, the thickness tolerance is plus or minus 3 μm. The Ra, Rz and Rmax are typically 3, 30 and 50 nm, respectively. (The Ra, Rz and Rmax are well-known measures of roughness.) However, these values are merely exemplary.  
         [0042]     Either before or after plating (but preferably before cleaning and plating), sheet  100  can be formed into the shape of a disk, e.g. by a punching operation. At the conclusion thereof, the OD of the disk is typically about 180 mm plus or minus 0.3 mm. Again, this diameter is merely exemplary.  
         [0043]     The disk is then cleaned. Thereafter, a light-insensitive layer  103  (discussed below) and a resist layer  104  are applied to layer  102 . Resist layer  104  can be applied by spin coating. Resist  104  can be positive or negative resist, and can be 182.5 nm thick plus or minus 2.5 nm. (Again, these values are merely exemplary.) In one embodiment, resist layer  104  comprises a 15 vol. % solution of Clariant AZ 5214E in AZ Thinner ERB Solvent (propylene glycol monomethyl ether acetate). Resist layer  104  is then heated, e.g. to partially or completely evaporate solvents from layer  104 . Thereafter, a laser is used to expose resist layer  104 . The laser wavelength can be from 405 to 430 nm, but these values are merely exemplary. Layer  104  is then developed.  
         [0044]     In lieu of laser exposure, other forms of radiation can be used to expose layer  104 . For example, layer  104  can be exposed by being subjected to an e-beam. Alternatively, layer  104  can be exposed using a lithographic mask and UV light or X-rays. Other types of light can be used to expose layer  104  as well.  
         [0045]     As explained below, light-insensitive layer  103  facilitates forming smaller features in resist layer  104  for the case in which the resist is exposed using light. However, in embodiments in which light is not used to expose the resist, or in embodiments in which the advantages of layer  103  are not needed, layer  103  can be omitted.  
         [0046]     After developing, layer  104  is hard-baked and coated with a metalization layer  106  ( FIG. 4C ). At this point in the process, the resulting structure constitutes a stamper  108 . The hard bake and deposition of metalization layer  106  make stamper  108  more robust. Thereafter, a punching operation is performed so stamper  108  has an ID and an OD that meets the requirements of the mold within which it is to be used. (The ID and OD are typically 138 mm and 25 mm, respectively, but these dimensions are merely exemplary.)  
         [0047]     Stamper  108  is then placed in a mold, along with molten polycarbonate material as discussed above with respect to  FIG. 2 . As indicated in  FIG. 4C , stamper  108  includes protrusions  104   a  corresponding to the remaining portions of resist layer  104 . These protrusions cause corresponding indentations in the polycarbonate material. These indentations are closely spaced in a spiral or concentric configuration to serve as servo information and/or content data and/or error correction data in the optical medium being manufactured.  
         [0048]     Also as discussed above, a thin transparent protective layer is then applied to the polycarbonate material. For the case of read-write or write-once media, a recording layer such as a magneto-optic layer, a dye based layer or a phase change recording layer is deposited on the polycarbonate before depositing the protective layer. (The resulting optical media can include other layers as well.)  
         [0049]     One advantage of the above-described method is that it is much easier and much less expensive to produce a stamper without relying on plating to provide the most of the stamper thickness. By depositing a layer onto a substrate produced by rolling, one can achieve the benefit of having a very smooth surface without having to perform a great deal of polishing.  
         [0050]      FIGS. 5A  to  5 C illustrate a method in accordance with another embodiment of the invention for forming a stamper. Referring to  FIG. 5A , metallic sheet (typically about 1.6 mm thick, and typically comprising an alloy of mostly Al with Mg) is stamped into disk-shaped substrates such as substrate  200 . The sheet can be formed by rolling. In one embodiment, the substrates have an OD of 180 mm. Optionally, after stamping, the substrate edges can be chamfered to facilitate handling the substrates without damaging them.  
         [0051]     Optionally, the surface of substrate  200  can be subjected to grinding and/or lapping.  
         [0052]     Substrate  200  is then cleaned. Thereafter, a NiP alloy layer  202  is electroless plated onto substrate  200 . A strike voltage can be applied to substrate  200  to facilitate initiation of the plating. (In an alternative embodiment, instead of electroless plating, other deposition methods such as electroplating or vacuum deposition can be used. Also, instead of using NiP to form layer  202 , other hard alloys or elements, e.g. Cr, can be formed on substrate  200 .) Layer  202  can then be polished and cleaned as described above with respect to layer  102 . A light-insensitive layer  204  (typically electrically non-conductive, e.g. a polymer or an inorganic dielectric material) and a resist layer  206  are then deposited on NiP layer  202 . Resist layer  206  can be positive resist or negative resist, but negative resist is preferred. In one embodiment, resist layer  206  comprises the above-mentioned solution comprising Clariant AZ 5214E, and has a thickness of 190 nm plus or minus 2.5 nm. Alternatively, resist layer  205  can have a thickness of 187.5 plus or minus 2.5 nm. Again, these parameters are merely exemplary.  
         [0053]     Resist layer  206  is baked, and then a pattern is written into resist layer, e.g. using a laser (e.g. having a wavelength between 405 and 430 nm) to expose portions of the resist followed by development. However, other techniques and forms of radiation can be used to expose resist layer  206 , e.g. an e-beam, or a light source in combination with a lithographic mask. The light source can provide x-rays, ultraviolet light, or visible light. After exposure, resist layer  206  is developed and hard-baked, leaving resist protrusions  206   a ,  206   b  on top of layer  204 .  
         [0054]     After resist layer  206  is patterned, a layer of material  208  is deposited thereon ( FIG. 5C ). Layer  208  can be a metal such as Ni or an alloy thereof, deposited by a vacuum deposition process such as sputtering, evaporation or ion beam deposition. The structure of  FIG. 5C  can be used as a master in lieu of master  13  discussed above ( FIG. 1B ), and can be used to form a stamper as described above with reference to  FIGS. 1C  to  1 H. In such a process, one can plate a material such as Ni or a Ni alloy onto layer  208  in a manner similar to layer  16  discussed above. The advantage of using the structure of  FIG. 5C  as a master instead of the structure of  FIG. 1B  is that glass substrate  12  is more expensive than substrate  202 . (After plating, one typically separates the deposited Ni from resist  206  and layer  204 , and cleans the Ni to remove any residual portions of layers  204  and  206  if necessary.)  
         [0055]     Layer  204  helps reduce the minimum feature size that can be formed in resist layer  206  and optimize the cross section profile of the protrusions or pits that can be formed in resist layer  206 . If one formed resist  206  directly on NiP layer  202 , light reflecting off layer  202  would form a standing wave such that destructive interference would occur at the interface between resist  206  and NiP layer  202 . Providing layer  204  ensures that the point of maximum destructive interference is not located at the bottom of resist layer  206 . This facilitates forming smaller features and optimal cross section profiles in resist layer  206 . In order to perform this function, layer  204  should be transparent, at least for light having the wavelength used to pattern resist layer  206 . (In one embodiment, layer  204  has a thickness that prevents the point of maximum destructive interference from being within resist layer  206 .)  
         [0056]     As mentioned above, layer  204  can be a polymer or a dielectric material. For the case of a polymer, layer  204  can be applied by a spinning process. For example, layer  204  can comprise a solution of 4 vol. % Clariant AZ 5214E in AZ Thinner ERB Solvent that has been heated (or otherwise subjected to a cross-linking reaction). In such an embodiment, layer  204  can be 30 nm plus or minus 2 nm thick. For the case of a dielectric material, layer  204  can be sputtered. One example of a material that can be used for layer  204  is oxidized or partially oxidized NiP.  
         [0057]     In lieu of making layer  204  transparent, if layer  204  is non-reflective (e.g. light absorptive), at least at the wavelength used to pattern resist  206 , the above-mentioned reflection and interference will be prevented or minimized. For example, layer  204  can be black. Alternatively, if substrate  202  is non-reflective, layer  204  need not be formed. (This discussion of layer  204  also applies to layer  103 .)  
         [0058]     Alternatively, instead of forming NiP layer  202 , substrate  200  is subjected to an anodizing step to form an oxidized surface layer thereon. In one embodiment, the oxidized surface layer renders layer  204  unnecessary.  
         [0059]     In yet another embodiment, layer  202  can be a plated composite material containing a mixture of one or more metallic phases and one or more dielectric phases, e.g. a mixture of NiP and teflon (PTFE) deposited from a plating bath. The percentage of the dielectric material can be adjusted to achieve specific optical reflective and absorptive properties to thereby render layer  204  unnecessary.  
         [0060]     In yet another embodiment, alloys or compounds containing one or more dielectric phases (e.g. oxides or amides) can be used to form layer  202 . (The amide can be a metal nitride.) The percentage of the dielectric phase can be selected to achieve desired optical reflective and absorptive properties to thereby render layer  204  unnecessary. (Again, the above-mentioned techniques can be used to render layer  103  unnecessary.)  
         [0061]     If radiation other than light is used to pattern resist layer  206 , layer  204  can be eliminated. Similarly, if the advantages of layer  204  are not needed, layer  204  can be eliminated.  
         [0062]     As mentioned above, methods in accordance with the invention have a number of advantages over the prior art processes discussed above with respect to  FIGS. 1 and 3 . Methods in accordance with the invention also have advantages with respect to the above-described &#39;371 patent. For example, it will be appreciated that embodiments of the above-described methods do not typically require exotic and expensive ion machining apparatus for machining substrates or otherwise etching substrates.  
         [0063]     While the invention has been described with respect to specific embodiments, those skilled in the art will appreciate that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, different types of laser beams (having different wavelengths), and different types of resist can be used. (The laser beam wavelength and resist type can be selected depending upon the size of the feature pitch one uses during the process.) The process of exposing and developing resist can comprise an “image reversal process” as described in U.S. Pat. No. 6,423,477, issued to Engelen or U.S. Pat. No. 6,159,664, Reuhman-Huisken (each incorporated herein by reference). In lieu of rolling, the metallic substrates used during the above-described methods can be formed by casting, molding or extruding. (Materials other then metal, e.g. plastic, can be used to form the substrates.) In some embodiments of the invention, the above-described light-insensitive layers are not formed. It will also be appreciated that additional layers can be formed during the above-described methods. Accordingly, all such changes come within the invention.