Source: https://patents.google.com/patent/EP1959299B1/en
Timestamp: 2019-07-22 10:08:18
Document Index: 61848582

Matched Legal Cases: ['art 101', 'art 102', 'art 101', 'art 101', 'art 102', 'art 101', 'art 102', 'art 101', 'art 102', 'arts 101', 'art 102']

EP1959299B1 - Pattern replication with intermediate stamp - Google Patents
Pattern replication with intermediate stamp Download PDF
EP1959299B1
EP1959299B1 EP08154480A EP08154480A EP1959299B1 EP 1959299 B1 EP1959299 B1 EP 1959299B1 EP 08154480 A EP08154480 A EP 08154480A EP 08154480 A EP08154480 A EP 08154480A EP 1959299 B1 EP1959299 B1 EP 1959299B1
EP08154480A
EP1959299A2 (en
EP1959299A3 (en
2005-11-03 Application filed by Obducat AB filed Critical Obducat AB
2005-11-03 Priority to EP08154480A priority patent/EP1959299B1/en
2005-11-03 Priority to EP20050110290 priority patent/EP1731962B1/en
2008-08-20 Publication of EP1959299A2 publication Critical patent/EP1959299A2/en
2010-10-06 Publication of EP1959299A3 publication Critical patent/EP1959299A3/en
2012-12-26 Publication of EP1959299B1 publication Critical patent/EP1959299B1/en
One of the most powerful techniques for reproducing nanostructures - i.e. structures in the order of 100 nm or smaller - is nanoimprint lithography (NIL). In nanoimprint lithography an inverted copy of the surface pattern of a template - often called a stamp - is transferred into an object, comprising a substrate and, applied thereto, a film of a moldable layer often called resist, e.g. a polymer material. After heating the object to a suitable temperature above the glass transition temperature of the polymer film the stamp is pressed towards the film followed by cooling and release - often called demolding - of the stamp, after the desired pattern depth has been transferred into the film. Alternatively, the substrate is covered by a photo-resist material, i.e. a polymer which is sensitive to radiation such that it is cross-linked upon exposure to ultraviolet (UV) radiation, or a pre-polymer which is cured into a polymer upon exposure to radiation. This requires that either the substrate or the stamp is transparent to the applied radiation. In a subsequently performed process after the achieved imprint, the object - comprising the substrate and the patterned polymer film - can be post-processed e.g. by etching of the substrate within the imprinted regions to transfer the pattern to a target surface of the substrate.
JP2002 086463 discloses a method for producing a lens sheet comprising that a thermosetting resin is applied to an intermediate die subjected to templating from a die.
US2003/0071016 discloses non-stick molds, methods of forming such molds, and methods of using these molds to transfer structural patterns onto other surfaces.
GB 637105 discloses a method of manufacturing copy printing blocks from an original printing-block, in which a die is made from this original printing block, and from this die multiple copy printing blocks are produced.
EP 0813255 discloses that composite piezo-electric members having an intended structure are fabricated based on the LIGA process which includes the exposure of synchrotron radiation X-rays, development and lithography. With the intention of reducing the costs the Xray exposure mask, it is made of wire gauze having a regular pattern and formed by electrocasting.
EP 1465175 discloses a stamper used during the manufacturing of an information medium such as an optical disc comprising an uneven pattern such as grooves and prepits, a method of manufacturing the stamper, a stamper intermediate with an attached master formed during manufacture, and an information medium manufactured by the stamper.
EP 1533657 discloses a method for providing a nano-scale pattern on a substrate.
WO01/42858 discloses a device in connection with the lithography of structures of nanometre size.
Claim 1 of the invention, devised to fulfill the stated object, relates to a method of creating an intermediate polymer stamp for use in an imprint process, in which a patterned surface of the intermediate polymer stamp is pressed into a moldable layer on a substrate so as to imprint the pattern of the patterned surface into the moldable layer, said method comprising:
providing a template having a structured surface,
providing a polymer foil,
providing a radiation sensitive pre-polymer material surface layer on a surface of the polymer foil, wherein said material is photo chemically amplified, wherein the polymer material is a UV cross-linkable polymer composition, and the polymer foil is pre-coated with said polymer composition which is solid at normal room temperature,
pressing the structured surface into said surface layer to imprint an inverse of said structured surface in the surface layer,
heating the polymer foil to a temperature Tp, and, while maintaining said temperature Tp, performing said pressing and said exposing, wherein said polymer composition has an initial glass transition temperature Tg, and wherein Tp exceeds Tg,
exposing the surface layer to radiation through the polymer foil to cure the pre-polymer,
postbaking the intermediate layer while maintaining a temperature Tp, and
separating the patterned polymer foil from the template, thereby creating the intermediate polymer stamp.
In one embodiment, said exposing further comprises:
emitting said radiation to the surface layer through the polymer foil, which polymer foil is transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
In one embodiment, said second polymer composition is a UV curable pre-polymer.
In one embodiment, said step of providing a polymer foil further comprises:
dispensing the second polymer composition on the structured surface of the template, and
covering the structured surface with the polymer foil, wherein said exposing causes the second polymer composition to be bonded to the polymer foil.
providing heat to post-bake the surface layer before separating the patterned polymer foil from the template.
In one embodiment, said template is another intermediate polymer stamp created by a preceding imprint step comprising:
providing a second polymer foil having a polymer foil of a third polymer composition and an applied surface layer of a fourth polymer composition adapted for imprint,
pressing a structured surface of a primary template into said surface layer to imprint a replica of said structured surface in the surface layer,
exposing the surface layer to radiation to solidify the surface layer, and
separating the patterned second polymer foil from the template, thereby creating said another intermediate polymer stamp.
arranging the template and the polymer foil sandwiched between a stop member and a first side of a flexible membrane, and wherein
said pressing involves applying an overpressure to a medium present on a second side of the membrane.
In one embodiment, said medium is selected among the group consisting of a gas, a liquid, and a gel.
emitting radiation to said surface layer through the membrane, which membrane is transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
emitting radiation to said surface layer through said membrane, and through a transparent wall opposing said membrane, defining a back wall for a cavity for said medium, which back wall and membrane are transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
Another embodiment of the invention, devised to fulfill the stated object, relates to a method of forming a pattern in a target surface of a substrate, comprising:
a primary imprint step including a method according to any one of the e
embodiments described above for creating an intermediate polymer stamp having a patterned surface, and
a secondary imprint step comprising:
providing a substrate having a moldable layer, and
pressing the intermediate polymer stamp into the moldable layer to imprint the pattern of the patterned surface in the moldable layer.
In one embodiment, the secondary imprint step further comprises:
heating the moldable layer above its glass transition temperature Tg, and
solidifying the moldable layer by cooling it below said glass transition temperature Tg.
exposing the moldable layer to radiation for solidifying the moldable layer. In one embodiment, the secondary imprint step further comprises:
heating the intermediate polymer stamp and the substrate to a temperature Tp, and
performing, while maintaining said temperature Tp, said pressing and an additional step of exposing the moldable layer to radiation for solidifying the moldable layer.
postbaking the moldable layer while maintaining said temperature Tp.
releasing the substrate from the intermediate polymer stamp while maintaining said temperature Tp.
Figs 5-7 illustrates process steps of an embodiment of the invention;
Fig. 8 schematically illustrates an embodiment of an apparatus according to the invention, for performing the process as generally described in Figs 1-3 or 5-7;
Fig. 10 illustrates the apparatus of Figs 8 and 9, at an active process step of transferring a pattern from the template to the substrate.
The present invention as defined by the claims relates to what is herein referred to as a "two-step imprint process". This term is to be understood as a process in which in a first step one or more replicas of a template having a nanometer and/or micrometer size patterned surface is formed into one or more flexible polymer foils by an imprint process. The imprinted polymer foil may be used as a polymer stamp in a second step. Alternatively, the imprinted polymer foil is used as a stamp to make another imprint on another polymer foil, which is subsequently used in the second step. This way, the first step of the process may generate both negative polymer replicas, where the pattern is inverted to that of the original template, and flexible positive polymer replicas, where the pattern is similar to that of the original template. In the second step a so-produced replica can be used as a flexible polymer stamp to reproduce the pattern into an object surface through a subsequent performed imprint process employing thermal imprint, UV-imprint, or both.
The term "nano-imprinting process" or "imprint process" as used herein refers to a process for the creation of an inverted copy of a nano- and/or micro-structured surface pattern of a template or stamp, which is generated by pressing the stamp into a moldable layer, such as a polymer or pre-polymer, in order to deform the layer. The layer may be a separately coated film on top of a base or substrate, where the base and the layer may be of different materials. Alternatively, the layer may simply be a portion of a single material object, where the layer is defined as a portion stretching from a surface of the object down to a certain depth into the bulk of the object. The moldable layer may either be heated-up above its glass transition temperature Tg followed by cooling-down to below said glass transition temperature during the imprinting (e.g., hot embossing) process, and/or the polymer may be cured or cross-linked with the help of UV-light exposure during or after the imprinting process. The patterned surface of the template, and of the imprinted layers, may have structures on a micrometer or nanometer scale both in terms of depth and width.
The term "flexible polymer foil" refers to a flexible and ductile in the most cases transparent foil comprising a thermoplastic polymer, a thermosetting polymer, and/or a polymer, cross-linkable after exposure to radiation. Preferred embodiments of the polymer foil include polycarbonate, polymethyl methacrylate (PMMA) and cyclo-olefin copolymer (COC).
The term "replication fidelity" refers to the creation of an inverted copy of the stamp structure in which the inverted topography of the stamp surface is completely reproduced.
The first, or primary, step of the two step process will now be described with reference to Figs 1a to If of the drawings. The process of the primary step according to two different embodiments are schematically illustrated in Fig. 1. The process of Figs 1a to 1f illustrate creation of an intermediate polymer stamp using thermal imprint. However, there are other possible techniques for creating the polymer stamp as will be outlined below.
With the help of a suitable imprint process as illustrated in Fig 1b) an inversion of the pattern of template surface 2 is formed into a surface layer at surface 4 of the flexible polymer foil 3. After the template surface 2 has been placed in contact with surface 4 of polymer foil 3, the polymer foil is heated to a temperature above the glass temperature Tg of the used polymer in the surface layer of the foil. The polymer foil may be massive, i.e. having more or less the same composition throughout the entire polymer foil, or it may have a base composition of the actual polymer foil with an applied surface layer at surface 4 of another composition adapted for imprint. When the surface layer has reached its glass transition temperature, pressure is applied to press template 1 and polymer foil 3 together such that the pattern of surface 2 is imprinted in the surface layer at surface 4 of polymer foil 3. Pressing may be achieved by means of a soft press technique using a fluid or gas pressure supplied by means of a membrane, as will be explained in more detail with reference to the secondary step of the process according to the invention. Alternatively, a more conventional hard press technique may be used. Since the polymer stamp created in the primary step is not the final product, parallelism is not a crucial element of the primary step in the same manner as for the secondary step.
As mentioned, the illustrated embodiment makes use of thermal imprint, and polymer foil 3 is therefore heated before the pressure is applied, in order to soften the surface layer. Specific examples according to the above thermal primary step are given below. Alternative methods may alternatively or additionally include applied exposure of selected portions of the polymer foil to radiation.. If the material of the polymer foil is also to be cross-linked by exposure to radiation, either the material of the template 1 or that of the polymer foil 3 must be transparent to the applied radiation. Alternative embodiments include a thermally or UV-curable pre-polymer composition in the surface layer at surface 4 of polymer foil 3. In such an embodiment heating above the glass transition temperature is not necessary.
In an example of a combined heat and radiation the polymer foil, corresponding to 3 in Fig. 1, to which the template pattern is to be transferred needs to be UV-transparent. A UV-cross-linkable polymer, e.g. a negative photoresist such as SU8 from MicroChem, USA, is spin-coated onto the polymer foil, the template 1 and the coated polymer foil are brought together and covered by an imprint membrane over the polymer foil. After heating to the imprint temperature the latter is held constant during the entire rest of the imprint process to eliminate thermal expansion effects. The sandwich is now pressurized and after a typical flow time, e.g. 30 seconds, the polymer is cross-liked by UV-radiation followed by a post exposure bake of e.g. 30 seconds. No cooling is required, and the pressure can now be released directly followed by removal of imprint membrane and demolding. Again, a good negative photoresist loses its UV-absorbing properties after exposure.
In accordance with the invention, polymer stamp 5 is either used in the secondary step to transfer the pattern of surface 4 to a target substrate, or it is used in an additional primary step to produce a second inversed replica 9 into another flexible polymer foil 6 according to Figs 1d) to 1f), in a similar process as described above. A purpose behind employing a further primary step is to ensure that the final pattern to be created in the target substrate is to be an inverse of the template surface pattern. In such an embodiment, a polymer foil 6 is used which is be composed by a polymer, whose glass transition temperature and imprint temperature is lower than that of the flexible polymer stamp 5. Furthermore, the engaging surfaces 4 and 7 of polymer foil 6 and flexible polymer stamp 5 exhibit anti-adhesion properties against to each other. Anti-adhesion properties could be present from the beginning due to the chemical nature of the used polymer foils and/or be implemented by the deposition of anti-adhesion layers comprising suitable release agents on one or both polymer surfaces. Additionally, if the polymer foil 6 should be cross-linked after exposure to radiation at least one of the polymer foils 5 and 6 must be transparent to the applied radiation or alternatively transmit enough radiation to enable a cross-linking of the surface layer of foil 6, or the entire foil 6 if it is massive.
The so-produced replicas 5 or 8 having inverted or identical surface patterns to that of the original template 1, respectively, will be used as flexible polymer templates in a secondary imprint step according to the invention, as schematically illustrated in Figs 1g) to 1i) on the left hand side and the right hand side, respectively. Here, surfaces 4 or 7 of one of the flexible polymer stamps 5 or 8 will be placed in contact with a surface 16 of an object 12 comprising a substrate 13 having a target surface 17 covered by a thin moldable surface layer 14 of a radiation-sensitive material, e.g. a pre-polymer or a polymer which is cross-linkable with the help of the exposure to radiation. Surface 4 or 7 of the flexible polymer stamp 5 or 8 exhibit anti-adhesion properties against surface 16 of the moldable layer 14, due to the material compositions of the surfaces. With the help of an applied pressure forcing one of the flexible polymer templates 5 or 8 and object 12 together and applied exposure of selected portions of the polymer film 14 to radiation, an inversion of the pattern of the polymer stamp surfaces is formed in the moldable layer 14, as shown in Fig. 1h. The flexible polymer stamp 5 or 8 is transparent to the applied radiation or shows minor absorbance in order to transmit a sufficient amount of radiation necessary for curing or cross-linking the material of surface layer 14 upon exposure to radiation. After performed imprint and post-baking as shown in Fig. 1h), the flexible polymer stamp 5 or 8 can be removed from the substrate 13 mechanically or, alternatively the whole polymer stamp 5 or 8 or portions of it can be dissolved chemically with the help of one or more suitable solvents in a suitable process.
Fig. 1 is a relatively simple representation of the process according to the invention. The primary step, depicted above the dashed line, may be performed using thermal imprint directly in the massive polymer foil, UV-assisted imprint using a pre-polymer surface layer on the polymer foil, or simultaneous UV radiation at a controlled elevated temperature using a UV cross-linkable polymer surface layer on the polymer foil. If thermal imprint is used in steps 1a) to 1c), there will typically be a difference in the thermal expansion between template 1, which e.g. may be nickel, and the polymer foil 3. However, the resiliency and flexibility of polymer foil 3, which furthermore has a thickness which is substantially larger than the height of the pattern structures, guarantees that the polymer foil is stretched and contracted by the thermal expansion imposed on template 1, without damaging the pattern features on the foil surface 4. The thickness of the polymer foil is typically in the range of 50-500 µm, whereas the height or depth of the pattern structures is in the range of 5 nm to 20 µm, as will be shown by means of examples below. Other sizes are possible though.
Figs 5-7 schematically present the basic process steps of the actual pattern transfer steps, or imprint steps, in the secondary step of an embodiment of the invention. These drawings correspond to Figs 1g) to 1h), either the left hand side example or the right hand side example, but in greater detail.
In Fig. 5 a polymer stamp 10 is illustrated, which consequently may correspond to either polymer stamp 5 or 8 in Fig. 1. Polymer stamp 10 has a structured surface 11, corresponding to surface 4 or 7, with a predetermined pattern to be transferred, in which three-dimensional protrusions and recesses are formed with a feature size in height and width within a range of 1 nm to several µm, and potentially both smaller and larger. The thickness of polymer stamp 10 is typically between 10 and 1000 µm. A substrate 12 has a target surface 17 which is arranged substantially parallel to polymer stamp surface 11, with an intermediate spacing between the surfaces at the initial stage shown in Fig. 5. The substrate 12 comprises a substrate base 13, to which the pattern of polymer stamp surface 11 is to be transferred. Though not shown, the substrate may also include a support layer below the substrate base 13. In a process where the pattern of polymer stamp 10 is to be transferred to substrate 12 directly through an imprint in a polymer material, said material may be applied as a surface layer 14 directly onto the substrate target surface 17. In alternative embodiments, indicated by the dashed line, a transfer layer 15 is also employed, of e.g. a second polymer material. Examples of such transfer layers, and how they are used in the subsequent process of transferring the imprinted pattern to the substrate base 13, are described in US 6,334,960 . In an embodiment including a transfer layer 15, target surface 17 denotes the upper or outer surface of the transfer layer 15, which in turn is arranged on the substrate base surface 18.
Heater body 21 is preferably a piece of cast metal, such as aluminum, stainless steel, or other metal. Furthermore, a body 21 of a certain mass and thickness is preferably used such that an even distribution of heat at an upper side of heater device 20 is achieved, which upper side is connected to substrate 12 for transferring heat from body 21 through substrate 12 to heat layer 14. For an imprint process used to imprint 2.5" substrates, a heater body 21 of at least 2.5" diameter, and preferably 3" or more, is used, with a thickness of at least 1 cm, preferably at least 2 or 3 cm. For an imprint process used to imprint 6" substrates, a heater body 21 of at least 6" diameter, and preferably 7" or more, is used, with a thickness of at least 2 cm, preferably at least 3 or 4 cm. Heater device 20 is preferably capable of heating heater body 21 to a temperature of up to 200-300°C, though lower temperatures will be sufficient for most processes.
Another embodiment makes use of a liquid or near liquid pre-polymer material for layer 14, which is polymerizable by means of radiation. Examples of available and usable polymerizable materials for layer 14 comprise NIP-K17, NIP-K22, and NIP-K28 from ZEN Photonics, 104-11 Moonj i-Dong, Yusong-Gu, Daejeon 305-308, South Korea. NIP-K17 has a main component of acrylate, and has a viscosity at 25°C of about 9.63 cps. NIP-K22 also has a main component of acrylate, and a viscosity at 25°C of about 5.85 cps. These substances are devised to cure under exposure to ultraviolet radiation above 12 mW/cm2 for 2 minutes. Another example of an available and usable polymerizable material for layer 14 is Ormocore from Micro Resist Technology GmbH, Koepenicker Strasse 325, Haus 211, D-12555 Berlin, Germany. This substance has a composition of inorganic-organic hybrid polymer, unsaturated, with a 1-3% photopolymerisation initiator. The viscosity of 3-8 mPas at 25°C is fairly high, and the fluid may be cured under exposure of radiation with 500 mJ/cm2 at a wavelength of 365 nm. Other usable materials are mentioned in US 6,334,960 .
The thickness of layer 14 when deposited on the substrate surface is typically 10 nm-10 µm, depending on application area. The curable or cross-linkable material is preferably applied in liquid form onto substrate 12, preferably by spin coating, or optionally by roller coating, dip coating or similar. One advantage with the present invention compared to prior art step and flash methods, typically when using a cross-linkable polymer material, is that the polymer material may be spin coated on the entire substrate, which is an advantageous and fast process offering excellent layer evenness. Cross-linkable materials, such as those mentioned, are typically solid at normal room temperature, and a substrate which has been pre-coated at an elevated temperature may therefore conveniently be used. The step and flash method, on the other hand, has to use repeated dispensation on repeated surface portions, since that method is incapable of handling large surfaces in single steps. This makes both the step and flash process and the machine for carrying out such a process complex, time consuming in terms of cycle time, and hard to control.
The arrows of Fig. 5 illustrate that the polymer stamp surface 11 is pressed into surface 16 of the moldable material layer 14. At this step, heater device 20 is preferably used to control the temperature of layer 14, for obtaining a suitable fluidity in the material of layer 14. For a cross-linkable material of layer 14, heater device 20 is therefore controlled to heat layer 14 to a temperature Tp exceeding the glass temperature Tg of the material of layer 14. In this context, Tp stands for process temperature or imprint temperature, indicating that it is one temperature level common for the process steps of imprint, exposure, and postbaking. The level of constant temperature Tp is of course dependent on the type of material chosen for layer 14, since it must exceed the glass transition temperature Tg for the case of a cross-linkable material and also be suitable for postbaking the radiation-cured material of the layer. For radiation cross-linkable materials Tp typically ranges within 20-250°C, or even more often within 50-250°C. For the example of mr-L6000.1 XP, successful tests have been performed with a constant temperature throughout imprint, exposure and postbake of 100-120°C. For embodiments using radiation-curable pre-polymers, such materials are typically liquid or near liquid in room temperature, and therefore need little or no heating to become soft enough for imprinting. However, also these materials must generally go through post-baking for complete hardening after exposure, prior to separation from the polymer stamp. The process temperature Tp is therefore set to a suitable post-baking temperature level already in the imprint step beginning at the step of Fig. 5.
Fig. 6 illustrates how the structures of polymer stamp surface 11 has made an imprint in the material layer 14, which is in fluid or at least soft form, at which the fluid has been forced to fill the recesses in polymer stamp surface 11. In the illustrated embodiment, the highest protrusions in polymer stamp surface 11 do not penetrate all the way down to substrate surface 17. This may be beneficial for protecting the substrate surface 17, and particularly the polymer stamp surface 11, from damage. However, in alternative embodiments, such as one including a transfer layer, imprint may be performed all the way down to transfer layer surface17. In the embodiment illustrated in Figs 5-7, the polymer stamp is made from a material which is transparent to radiation 19 of a predetermined wavelength or wavelength range, which is usable for solidifying a selected moldable material. Such materials may e.g. be polycarbonate, COC or PMMA. For polymer stamps created using radiation as described above, the remaining layer of the radiation-sensitive surface layer in which the pattern is formed is preferably also transparent to UV radiation, or alternatively so thin that its UV absorption is low enough to let through a sufficient amount of radiation. Radiation 19 is typically applied when polymer stamp 10 has been pressed into layer 14 with a suitable alignment between polymer stamp 10 and substrate 12. When exposed to this radiation 19, solidification of the moldable material is initiated, for solidification to a solid body 14' taking the shape determined by the polymer stamp10. During the step of exposing layer 14 to radiation, heater 20 is controlled by the temperature controller to maintain the temperature of layer 14 at temperature Tp.
After exposure to radiation, a postbaking step is performed, to completely harden the material of layer 14'. In this step, heater device 20 is used to provide heat to layer 14', for baking layer 14' to a hardened body before separation of polymer stamp 10 and substrate 12. Furthermore, postbaking is performed by maintaining the aforementioned temperature Tp. This way, polymer stamp 10 and material layer 14, 14' will maintain the same temperature from the beginning of solidification of material 14 by exposure to radiation, to finalized postbaking, and optionally also through separation of polymer stamp 10 and substrate 12. This way, accuracy limitations due to differences in thermal expansion in any of the materials used for the substrate and the polymer stamp are eliminated.
The polymer stamp 10 is e.g. removed by a peeling and pulling process, as illustrated in Fig. 7. The formed and solidified polymer layer 14' remains on the substrate 12. The various different ways of further processing of the substrate and its layer 14' will not be dealt with here in any detail, since the invention as such is neither related to such further processing, nor is it dependent on how such further processing is achieved. Generally speaking, further processing for transferring the pattern of polymer stamp 10 to the substrate base 13 may e.g. include etching or plating followed by a lift-off step.
The apparatus 100 comprises a first main part 101 and a second main part 102. In the illustrated preferred embodiment these main parts are arranged with the first main part 101 on top of second main part, with an adjustable spacing 103 between said main parts. When making a surface imprint by a process as illustrated in Figs 5-7, it may be of great importance that the template and the substrate are properly aligned in the lateral direction, typically called the X-Y plane. This is particularly important if the imprint is to be made on top of or adjacent to a previously existing pattern in the substrate. However, the specific problems of alignment, and different ways of overcoming them, are not addressed herein, but may of course be combined with the present invention when needed.
The first, upper, main part 101 has a downwards facing surface 104, and the second, lower, main part 102 has an upwards facing surface 105. Upwards facing surface 105 is, or has a portion that is, substantially flat, and which is placed on or forms part of a plate 106 which acts as a support structure for a template or a substrate to be used in an imprint process, as will be more thoroughly described in conjunction with Figs 9 and 10. A heater body 21 is placed in contact with plate 106, or forms part of plate 106. Heater body 21 forms part of a heater device 20, and includes a heating element 22 and preferably also a cooling element 24, as shown in Figs 5-7. Heating element 22 is connected through connectors 23 to a energy source 26, e.g. an electrical power supply with current control means. Furthermore, cooling element 24 is connected through connectors 25 to a cooling source 27, e.g. a cooling fluid reservoir and pump, with control means for controlling flow and temperature of the cooling fluid.
In operation, apparatus 100 is further provided with a flexible membrane 113, which is substantially flat and engages seal member 108. In a preferred embodiment, seal member 113 is a separate member from seal member 108, and is only engaged with seal member 108 by applying a counter pressure from surface 105 of plate 106, as will be explained. However, in an alternative embodiment, membrane 113 is attached to seal member 108, e.g. by means of a cement, or by being an integral part of seal member 108. Furthermore, in such an alternative embodiment, membrane 113 may be firmly attached to main part 101, whereas seal 108 is disposed outwardly of membrane 113. For an embodiment such as the one illustrated, also membrane 113 is formed in a material which is transparent to radiation of a certain wavelength or wavelength range of radiation source 110. This way, radiation emitted from radiation source 110 is transmitted into spacing 103 through said cavity 115 and its boundary walls 104 and 113. Examples of usable materials for membrane 113, for the embodiment of Figs 7-9, include polycarbonate, polypropylene, polyethylene, PDMS and PEEK. The thickness of membrane 113 may typically be 10-500 µm.
Fig. 9 illustrates the apparatus embodiment of Fig. 8, when being loaded with a substrate 12 and a polymer stamp 10 for a lithographic process. For better understanding of this drawing, reference is also made to Figs 5-7. Second main part 102 has been displaced downwards from first main part 101, for opening up spacing 103. The illustrated embodiment of Fig. 8 shows an apparatus loaded with a transparent polymer stamp 10 on top of a substrate 12. Substrate 12 is placed with a backside thereof on surface 105 of heater body 21, placed on or in the second main part 102. Thereby, substrate 12 has its target surface 17 with the layer 14 of a polymerizable material, e.g. a UV cross-linkable polymer solution, facing upwards. For the sake of simplicity, all features of heater device 20, as seen in Figs 5-7 are not shown in Fig. 9. Polymer stamp 10 is placed on or adjacent to substrate 12, with its structured surface 11 facing substrate 12. Means for aligning polymer stamp 10 with substrate 12 may be provided, but are not illustrated in this schematic drawing. Membrane 113 is then placed on top of polymer stamp 10. For an embodiment where membrane 113 is attached to the first main part, the step of actually placing membrane 113 on the polymer stamp is, of course, dispensed with. In Fig. 9 polymer stamp 10, substrate 12 and membrane 113 are shown completely separated for the sake of clarity only, whereas in a real situation they would be stacked on surface 105.
Once main parts 101 and 102 are engaged to clamp membrane 113, cavity 115 is sealed. Vacuum is applied by suction from vacuum pump 117 to extract air inclusions from the surface layer of the substrate 12. Pressure source 116 is then devised to apply an overpressure to a fluid medium in cavity 115, which may be a gas, a liquid or a gel. The pressure in cavity 115 is transferred by membrane 113 to polymer stamp 10, which is pressed towards substrate 12 for imprinting the polymer stamp pattern in layer 14, cf. Fig. 6. Cross-linkable polymer solutions typically need pre-heating to overcome its glass transition temperature Tg, which may be about 60°C. An example of such a polymer is the afore mr-L6000.1 XP. When using such polymers, the apparatus 100, having combined radiation and heating capabilities, is particularly useful. However, for both these types of materials a post-baking step is generally needed to harden the radiation-solidified layer 14'. As previously mentioned, an aspect of the invention is therefore to apply a raised temperature Tp to the material of layer 14, which is higher than Tg for the case of a cross-linkable material, and also suitable for postbaking of the radiation-exposed material. Heater device 20 is activated to heat layer 14 through substrate 12, by means of heater body 21, until Tp has been reached. The actual value of Tp is naturally dependent on the material chosen for layer 14. For the example of mr-L6000.1 XP, a temperature Tp within the range of 50-150°C may be used, dependent on the molecular weight distribution in the material. The pressure of the medium in cavity 115 is then increased to 5-500 bar, advantageously to 5-200 bar, and preferably to 20-100 bar. Polymer stamp 10 and substrate 12 are thereby pressed together with a corresponding pressure. Thanks to flexible membrane 113, an absolutely even distribution of force is obtained over the whole of the contact surface between the substrate and the polymer stamp. The polymer stamp and the substrate are thereby made to arrange themselves absolutely parallel in relation to one another and, the influence of any irregularities in the surface of the substrate or polymer stamp being eliminated.
When polymer stamp 10 and substrate 12 have been brought together by means of the applied fluid medium pressure, radiation source is triggered to emit radiation 19. The radiation is transmitted through surface portion 112, which acts as a window, through cavity 115, membrane 113, and polymer stamp 10. The radiation is partly or completely absorbed in layer 14, the material of which thereby is solidified by cross-linking or curing in the perfectly parallel arrangement between polymer stamp 10 and substrate 12, provided by the pressure and membrane assisted compression. Radiation exposure time is dependent on the type and amount of material in layer 14, the radiation wavelength combined with the type of material, and of the radiation power. The feature of solidifying such a polymerizable material is well known as such, and the relevant combinations of the mentioned parameters are likewise known to the skilled person. Once the fluid has solidified to form a layer 14', further exposure has no major effect. However, after exposure the material of layer 14' is allowed to post bake, or hard bake, at the predetermined constant temperature Tp for a certain time period of e.g. 1-10 minutes, if postbaking is at all necessary to solidify the layer. For the example of mr-L6000.1 XP, postbaking is typically performed for 1-10 minutes, preferably about 3 minutes, at the common process temperature Tp of 100-120°C. For SU8, the time of exposure to radiation is between 1 and 10 seconds, where the range of 3-5 seconds has been successfully tested, and postbaking is then performed at a Tp of about 70°C for 30-60 seconds.
A first mode of the invention involves a substrate 12 of silicon covered by a layer 14 of NIP-K17 with a thickness of 1 µm. After compression by means of membrane 113 with a pressure of 5-100 bar for about 30 seconds, radiation source 110 is turned on. Radiation source 110 is typically devised to emit at least in the ultraviolet region below 400 nm. In a preferred embodiment, an air-cooled xenon lamp with an emission spectrum ranging from 200-1000 nm is employed as the radiation source 110. The preferred xenon type radiation source 110 provides a radiation of 1-10 W/cm2, and is devised to flash 1-5 µs pulses, with a pulse rate of 1-5 pulses per second. A window 112 of quartz is formed in surface 104 for passing through radiation. Exposure time is preferably between 1-30 seconds, for polymerizing fluid layer 14 into a solid layer 14', but may be up to 2 minutes.
Tests with mr-L6000.1 XP have been performed with about 1.8 W/ cm2 integrated from 200-1000 nm, with 1 minute exposure time. It should, in this context, be noted that the radiation used need not be restricted to a wavelength range within which the polymer applied in layer 14 solidifies, radiation outside that range may of course also be emitted from the radiation source used. After successful exposure and subsequent postbaking at a constant process temperature, second main part 102 is lowered to a position similar to that of Fig. 9, following which template 10 and substrate 12 are removed from the apparatus for separation and further processing of the substrate.
Advantages of the application of flexible polymer foils within a "two-step" imprint process as described above and displayed in Fig. 1 include the following:
The flexible properties of the used polymer foils alleviate complications of the pattern transfer due to different thermal expansion coefficients of the applied stamp and substrate materials used in the imprint-process. Therefore, the technique offers possibilities to transfer patterns between surfaces of materials characterized by different thermal expansion coefficients. Nevertheless, most polymers used in the application are characterized by quite similar thermal expansion factors typically ranging between 60 and 70 x 10-6 C-1 making imprints between two different polymer foils as displayed in Fig. 1e) more easy in terms of manufacturing.
The flexible and ductile properties of the used polymer foils prevent the inclusion of air during the imprint between the polymer foil - having either a patterned or non-patterned surface - and the other object - e.g. a substrate covered by a polymer film or a template, comprising silicon, nickel, quartz or a polymer material. If the foil is pressed towards one of these objects as displayed in Fig. 1b, 1e, 1h the polymer foil is acting like a membrane, pressing the air from the centre of the imprinted area to its edges where it can leave the imprinted region.
The process described above and displayed in Fig. 1 is very suitable to produce both positive (the pattern is similar to that of the original template) and negative (the pattern is inverted to that of the original template) replicas if the material properties of the different polymer materials - e.g. glass transition temperature, optical transparency, and curability after exposure to radiation - applied in the process are adapted to each other.
The invention as defined in the claims can be used in a method for transferring a pattern from a template having a structured surface to a target surface of a substrate, comprising:
heating the polymer stamp and the substrate to a temperature Tp; and
emitting pulsating radiation with a pulse duration in the range of 0.5-10 µs and a pulse rate in the range of 1-10 pulses per second.
In one embodiment, the temperature Tp is within the range of 20-250°C.
Topas 8007 from Ticona GmBH, Germany: thermoplastic random co-polymer having a glass temperature of 80°C. Topas is transparent to light with wavelengths above 300 nm and is characterized by a low surface energy. The foil is available in thicknesses of 50 - 500 µm. 130 -140 µm thick foils have been used here.
Zeonor ZF14 from Zeon Chemicals, Japan: thermoplastic polymer having a glass temperature of 136°C and a light transmittance of 92% for wavelengths above 300 nm. The used foil has a thickness of 188 µm but is available in other thicknesses ranging from 50 to 500 µm.
Zeonex E48R from Zeon Chemicals, Japan: thermoplastic polymer having a glass temperature of 139°C and a light transmittance of 92% for wavelength above 350 nm. The used foil has a thickness of 75 µm.
Polycarbonate (Bisphenol-A polycarbonate) from Bayer AG, Germany: thermoplastic polymer having a glass temperature of 150°C and a light transmittance of 91% for wavelength above 350 nm. The used foil has a thickness of 300 µm and is available in many other thicknesses up to 1 mm.
A nickel template whose surface exhibits a line pattern, having a line width of 80 nm and a height of 90 nm has been imprinted into a Zeonor ZF14 foil at 150°C and 50 bar for 3 min. None of the surfaces has been treated by any additional coating such as, e.g. anti-adhesion layers. The release temperature was 135°C, at which the Zeonor foil could mechanically be removed from the nickel surface without damaging the pattern of neither the template nor the replica. The Zeonor foil has been used as a new template, which has been imprinted into a 100 nm thick SU8 film. The SU8 film was spin-coated onto a 20nm LOR film, previously spin-coated onto a silicon substrate. Also here, none of the surfaces has been treated by an additional coating, having the purpose to improve the anti-adhesion behaviour between the SU8 film and the Zeonor foil. The imprint was performed at 70°C and 50 bar for 3 min. The SU8 film was exposed to UV-light for 4 seconds through the optically transparent Zeonor foil and baked for two more minutes. Both temperature and pressure were kept constant at 70°C and 50 bar, respectively, during the entire imprint sequence. The release temperature was 70°C at which the Zeonor foil could mechanically be removed from the SU8 film without damaging the pattern of neither the polymer template foil nor the replica film. The AFM image of an imprint result in the SU8 film deposited on a silicon wafer is shown in Fig. 2.
A nickel template whose surface exhibits a BluRay pattern having structure heights of 100 nm and widths of 150 nm - investigated by AFM - has been imprinted into a Zeonor ZF14 using the same process and the same parameters as already described in Example1. The Zeonor foil has been used as a new template, which has been imprinted into a 100 nm thick SU8 film. Also here the same process and the same parameters as already described in Example1 have been used. The AFM image of an imprint result in the SU8 film deposited on a silicon wafer is shown in Fig. 3.
A nickel template has been used whose surface contains micro-meter patterns with high aspect-ratios ranging from 1-28. The feature size ranges from 600 nm to 12 µm, at a height of 17 µm. The surface has been covered by a phosphate-based anti-adhesion film before the imprint. The nickel template has been imprinted into a polycarbonate foil at 190°C and 50 bar for 3 min. The surface of the polycarbonate foil has not been treated by an additional coating, having the purpose to improve the anti-adhesion behavior between the Ni template and the polycarbonate film. The release temperature was 130°C, at which the polycarbonate foil could mechanically be removed from the nickel surface without damaging the pattern of neither the template nor the replica. The polycarbonate foil has been used as a new template for an imprint into a Topas foil. The imprint has been performed at 120° C and 50 bar for 3 min. None of the surfaces has been disposed by an additional coating, having the purpose to improve the anti-adhesion behavior between the polycarbonate and the Topas foil. The release temperature was 70°C, at which the Topas could mechanically be removed from the polycarbonate foil without damaging the pattern of neither the template foil nor the replica foil. The Topas foil has then been used as a new template, which has been imprinted into a 6000 nm thick SU8 film spin-coated onto a silicon substrate. Also here, none of the surfaces has been treated by any additional coating, having the purpose to improve the anti-adhesion behavior between the SU8 film and the Topas foil. The imprint was performed at 70°C and 50 bar for 3 min. The SU8 film was exposed to UV-light for 4 seconds through the optically transparent Topas foil and baked for two more minutes without changing the temperature of 70°C, or the pressure of 50 bar during the entire process. The release temperature was 70°C. Afterwards the Topas foil has completely been dissolved in p-xylene at 60° C for one hour. An SEM image of the result is shown in Fig. 4.
A method of creating an intermediate polymer stamp (5; 8) for use in an imprint process, in which a patterned surface (4; 7) of the intermediate polymer stamp (5; 8) is pressed into a moldable layer (14) on a substrate (13) so as to imprint the pattern of the patterned surface (4; 7) into the moldable layer (14), said method comprising:
- providing a template (1; 5) having a structured surface (2; 4),
- providing a polymer foil (3; 6),
- providing a radiation sensitive pre-polymer material surface layer on a surface of the polymer foil, wherein said material is photo chemically amplified, wherein the polymer material is a UV cross-linkable polymer composition, and the polymer foil (3; 6) is pre-coated with said polymer composition which is solid at normal room temperature,
- pressing the structured surface (2; 4) into said surface layer to imprint an inverse of said structured surface (2; 4) in the surface layer,
- heating the polymer foil (3; 6) to a temperature Tp, and, while maintaining said temperature Tp, performing said pressing and said exposing, wherein said polymer composition has an initial glass transition temperature Tg, and wherein Tp exceeds Tg,
- exposing the surface layer to radiation through the polymer foil to cure the pre-polymer,
- postbaking the intermediate layer while maintaining a temperature Tp, and
- separating the patterned polymer foil (3; 6) from the template (1; 5), thereby creating the intermediate polymer stamp (5; 8).
The method according to claim 1, wherein said exposing further comprises:
- emitting said radiation to the surface layer through the polymer foil (3; 6), which polymer foil is transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
The method according to claim 1 or 2, wherein said second polymer composition is a UV curable pre-polymer.
The method according to claim 3, wherein said step of providing a polymer foil further comprises:
- dispensing the second polymer composition on the structured surface (2; 4) of the template (1; 5), and
- covering the structured surface (2; 4) with the polymer foil, wherein said exposing causes the second polymer composition to be bonded to the polymer foil.
The method according to claim 3 or 4, further comprising:
- providing heat to post-bake the surface layer before separating the patterned polymer foil (3; 6) from the template (1; 5).
The method according to any preceding claim, wherein the template (1; 5) is made from metal, quartz, polymer or silicon.
The method according to any preceding claim, wherein said template is another intermediate polymer stamp (5) created by a preceding imprint step comprising:
- providing a second polymer foil (3) having a polymer foil of a third polymer composition and an applied surface layer of a fourth polymer composition adapted for imprint,
- pressing a structured surface (2) of a primary template (1) into said surface layer to imprint a replica of said structured surface (2) in the surface layer,
- exposing the surface layer to radiation to solidify the surface layer, and
- separating the patterned second polymer foil (3) from the template, thereby creating said another intermediate polymer stamp (5).
- arranging the template (1; 5) and the polymer foil (3; 6) sandwiched between a stop member and a first side of a flexible membrane (113), and wherein
- said pressing involves applying an overpressure to a medium present on a second side of the membrane (113).
The method according to claim 8, wherein said medium is selected among the group consisting of a gas, a liquid, and a gel.
The method according to claim 8 or 9, further comprising:
- emitting radiation to said surface layer through the membrane (113), which membrane is transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
The method as recited in any one of claims 8-10, further comprising:
- emitting radiation to said surface layer through said membrane (113), and through a transparent wall (112) opposing said membrane (113), defining a back wall for a cavity (115) for said medium, which back wall and membrane (113) are transparent to a wavelength range of a radiation usable for solidifying said second polymer composition.
The method as recited in claim 8, wherein said exposing further comprises:
- emitting radiation from a radiation source (110) within a wavelength range of 100-500 nm.
A method of forming a pattern in a target surface of a substrate, comprising:
a primary imprint step including a method according to any one of claims 1-12 for creating an intermediate polymer stamp having a patterned surface, and
- providing a substrate (13) having a moldable layer (14), and
- pressing the intermediate polymer stamp (5; 8) into the moldable layer (14) to imprint the pattern of the patterned surface (4; 7) in the moldable layer (14).
The method according to claim 13, wherein the secondary imprint step further comprises:
- heating the moldable layer (14) above its glass transition temperature Tg, and
- solidifying the moldable layer (14) by cooling it below said glass transition temperature Tg.
- exposing the moldable layer (14) to radiation for solidifying the moldable layer (14).
- heating the intermediate polymer stamp (5; 8) and the substrate (13) to a temperature Tp, and
- performing, while maintaining said temperature Tp, said pressing and an additional step of exposing the moldable layer (14) to radiation for solidifying the moldable layer (14).
The method of claim 16, wherein the secondary imprint step further comprises:
- postbaking the moldable layer (14) while maintaining said temperature Tp.
The method of claim 16 or 17, wherein the secondary imprint step further comprises:
- releasing the substrate (13) from the intermediate polymer stamp (5; 8) while maintaining said temperature Tp.
EP08154480A 2005-06-10 2005-11-03 Pattern replication with intermediate stamp Active EP1959299B1 (en)
EP08154480A EP1959299B1 (en) 2005-06-10 2005-11-03 Pattern replication with intermediate stamp
EP05110290.3 Division 2005-11-03
EP20050110290 Division EP1731962B1 (en) 2005-06-10 2005-11-03 Pattern replication with intermediate stamp
EP1959299A2 EP1959299A2 (en) 2008-08-20
EP1959299A3 EP1959299A3 (en) 2010-10-06
EP1959299B1 true EP1959299B1 (en) 2012-12-26
EP08154480A Active EP1959299B1 (en) 2005-06-10 2005-11-03 Pattern replication with intermediate stamp
EP20050110290 Active EP1731962B1 (en) 2005-06-10 2005-11-03 Pattern replication with intermediate stamp
EP (2) EP1959299B1 (en)
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CN105372734B (en) * 2015-11-02 2018-01-19 中国科学院重庆绿色智能技术研究院 The method of micro-prism reflective material
CN107814353A (en) * 2017-10-26 2018-03-20 武汉大学 Method for preparing nanotip array on transparent flexible substrate
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JP3577903B2 (en) * 1997-08-12 2004-10-20 セイコーエプソン株式会社 Method for producing a resin plate for producing a mold manufacturing method and a resin plate
2005-11-03 CN CN 200580050071 patent/CN101198903B/en active IP Right Grant
JP5276436B2 (en) 2013-08-28
JP2004513504A (en) 2004-04-30 Substrate and a manufacturing method thereof related to the structure
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