HK1114185B - Method for imprint lithography at constant temperature - Google Patents

Description

Imprint lithography method at fixed temperature

Technical Field

The present invention relates to a method for imprinting a lithographic structure on a micro-or nano-scale. In particular, the invention relates to fixed temperature imprint lithography at a fixed temperature to improve accuracy.

Background

The trend in microelectronics, as well as in micromachines, is toward smaller and smaller dimensions. Some of the most interesting techniques for fabricating micron or submicron structures include different types of lithography.

Photolithography generally involves the step of coating a substrate with a photosensitive resist material to form a resist layer on the substrate surface. The resist layer is then exposed to radiation at selected portions, preferably through the use of a mask. A subsequent development step removes portions of the resist, thereby forming a pattern in the resist corresponding to the mask. Removing portions of the resist exposes the substrate surface, which may be treated by etching, doping or metallization. For fine scale replication, lithography is limited by diffraction, which depends on the wavelength of the radiation used. To produce structures with dimensions smaller than 50nm, short wavelengths are required, so that the material requirements for optical systems become outstanding.

An alternative technique is the embossing technique. In an imprint lithography process, a substrate to be patterned is covered by a moldable (moldable) layer. The pattern to be transferred to the substrate is defined in advance three-dimensionally on a stamp (stamp) or template. The template is in contact with a moldable layer, which is preferably softened by heating. The template is then pressed into a softening layer, thereby forming an imprint of the template pattern in the mold layer. The layer is cooled until hardened to a satisfactory extent, after which the template is separated and removed. Subsequent etching may be employed to replicate the template pattern in the substrate. The step of heating and cooling the combined template and substrate may cause movement in the joining surfaces due to thermal expansion. The larger the area to be imprinted, the larger the actual expansion and contraction, which makes it more difficult to imprint larger surface areas.

A different form of imprint technique, commonly referred to as step and flash (step and flash) imprint technique, is proposed by Willson et al in U.S. patent No.6334960 and by mannini et al in U.S. patent 6,387,787. Similar to the imprint technique briefly described above, this technique involves a template having a structured surface that defines a pattern to be transferred to a substrate. The substrate is covered with a layer of polymerizable fluid, prepolymer, wherein a template is pressed into the prepolymer layer such that the liquid fills the recesses in the pattern structure. The template is made of a material that is transparent to the wavelength range of radiation that may be used to polymerize the polymerizable fluid, typically ultraviolet light. Radiation is applied to the liquid through the template and the liquid solidifies. The template is then removed, after which the pattern of the template is replicated within a layer of solid polymer material formed from the polymer liquid. Further processing transfers the structure within the layer of solid polymer material to a substrate.

WO02/067055 of the University of Texas System director discloses a System for applying step and flash imprint techniques. Among other things, this document relates to production scale step and flash equipment devices, also known as steppers (steppers). The template used in such an apparatus has a rigid body of transparent material, typically quartz. The template is made in the stepper by flexure means which allow the template to rotate about X and Y axes which are perpendicular to each other in a plane parallel to the surface of the substrate to be imprinted. The mechanism also relates to a piezoelectric actuator for controlling parallelism and gap between the template and the substrate. However, such systems cannot process large substrate areas in a single imprint step. One step and flash system offered on the market is IMPRIO100, offered by Molecular Imprints, Inc, 1807-Cforest Braker Lane, Austin, Tx78758, U.S.A. The template image area of the system is 25 x 25mm, and the road width (street width) is 0.1 mm. Although such systems can handle substrate wafers as large as 8 inches, the imprint process must be repeated by: the template is raised using an X-Y translation stage, moved laterally, and lowered again to the substrate. Furthermore, for each of these steps, realignment and redistribution of the polymerizable fluid must be performed. This technique is therefore very time consuming and not optimal for mass production. Furthermore, in addition to the problems of repetitive alignment errors and the requirement for high precision of the translation stage, this technique suffers from the drawback that it is not possible to produce continuous structures having an area larger than the size of the template. In summary, this means that the production costs of such a technique are too high to be of interest for use in mass production of fine structure devices.

Another disadvantage of the prior art for uv assisted imprinting is that in many cases it is desirable to use an opaque template. Nickel is commonly used as a template material due to its excellent material properties. However, the nickel template is of course opaque and therefore the ultraviolet radiation must be supplied through the substrate. In this case, a substrate of, for example, glass or quartz or a suitable plastic material may be used. Furthermore, the use of different materials in the template and the substrate typically means that they have different coefficients of thermal expansion. This in turn causes problems during the heating and cooling steps, limiting the accuracy of the process.

Disclosure of Invention

It is therefore an object of the present invention to provide a method and apparatus for improving the fabrication of structures containing micro-or nano-scale three-dimensional features. Aspects of the object relate to providing an improved method of transferring a pattern to a substrate with improved accuracy, a method involving a simplified production process, and a method of continuous structures that can be imprinted on substrates having a width of 1 inch or more, even 8 inches, 12 inches and more in diameter.

According to the invention, this object is achieved by a method for transferring a pattern from a template having a structured surface to a substrate carrying a surface layer of a material cured by irradiation, the method comprising:

arranging the template and substrate parallel to each other in an imprint apparatus, the structured surface facing the surface layer;

heating the template and the substrate to a temperature Tp using a heating device; and

while maintaining said temperature Tp, the steps of:

pressing the template against the substrate, thereby imprinting the pattern into the layer;

exposing the layer to radiation to cure the layer; and

the layer is post-baked.

In one embodiment, the material is a crosslinkable thermoplastic polymer having a glass temperature Tg, and wherein Tp is greater than Tg.

In one embodiment, the material is a uv-crosslinkable thermoplastic polymer having a glass temperature Tg, wherein the temperature Tp is greater than the temperature Tg and wherein the radiation is uv radiation.

In one embodiment, the material is photochemically amplified.

In one embodiment, the method comprises:

the surface layer is applied to the substrate by spin coating the material before arranging the template and substrate parallel to each other.

In one embodiment, the material is an ultraviolet curable thermoplastic prepolymer, and wherein the radiation is ultraviolet radiation.

In one embodiment, the method comprises:

sandwiching the template and the substrate between a barrier member (stop member) and a first side of a flexible membrane, and wherein

Pressing the template against the substrate involves applying an overpressure to the medium on the second side of the membrane to achieve this.

In one embodiment, the medium comprises a gas.

In one embodiment, the medium comprises air.

In one embodiment, the medium comprises a liquid.

In one embodiment, the medium comprises a gel.

In one embodiment, the method comprises:

emitting radiation through the template towards the layer, the template being transparent to a wavelength range of radiation used to cure the material; and

heating the substrate by direct contact with the heating device.

In one embodiment, the method comprises:

emitting radiation through the substrate towards the layer, the substrate being transparent to a wavelength range of radiation used to cure the material; and

heating the template by direct contact with the heating device.

In one embodiment, the method comprises:

emitting radiation through the film towards the layer, the film being transparent to a wavelength range of radiation used to cure the material.

In one embodiment, the method comprises:

emitting radiation through the film and through a transparent wall opposite the film towards the layer, the wall defining a rear wall of a cavity for the medium, the rear wall and the film being transparent to a wavelength range of the radiation for curing the material.

In one embodiment, the step of exposing the layer comprises:

radiation is emitted from the radiation source in the wavelength range of 100 to 500 nm.

In one embodiment, the method comprises:

pulsed radiation is emitted with a pulse duration in the range of 0.5 to 10 mus and a pulse rate in the range of 1 to 10 pulses per second.

In one embodiment, the method comprises:

clamping (clamp) the substrate and template together before disposing the template and substrate between the blocking member and the flexible membrane.

In one embodiment, the method comprises:

applying a vacuum between the template and the substrate before exposing the layer to radiation, thereby extracting air inclusions from the surface layer.

In one embodiment, the structured surface comprises protrusions defining a pattern, which protrusions are opaque to the radiation, whereby the step of exposing the layer to radiation involves curing portions of the layer between the protrusions.

In one embodiment, the protrusion comprises a layer of opaque material.

In one embodiment, a layer of opaque material is applied over the protrusions as the outermost layer.

In one embodiment, the temperature Tp is in the range of 50 to 250 ℃.

Drawings

The invention will be described in more detail below with reference to the accompanying drawings, on which:

FIGS. 1-3 schematically illustrate the main process steps for transferring a pattern from a template to a substrate, wherein radiation is applied through a transparent template to cure a polymerizable fluid on the substrate surface;

4-6 schematically illustrate corresponding process steps for transferring a pattern from a template to a substrate, wherein radiation is applied through a transparent template to cure a polymerizable fluid on the substrate surface;

FIG. 7 schematically illustrates an apparatus according to an embodiment of the invention for performing a process generally as described in FIGS. 1-3 or 4-6;

FIG. 8 schematically illustrates the apparatus of FIG. 7 when loaded with a template and substrate at an initial step in the process;

FIG. 9 shows the apparatus of FIGS. 7 and 8 at an efficient process step for transferring a pattern from a template to a substrate;

FIGS. 10-12 illustrate an alternative embodiment of an imprinting process according to the present invention; and

fig. 13-14 show test results for 2.5 "substrates imprinted with a single imprinting step according to the present invention, with AFM photographs taken near the center and edge of the substrate, respectively.

Detailed Description

Generally, the present invention relates to a method of transferring a pattern from a template to a substrate by creating a relief image of a structure on a surface of the template on the surface of the substrate. The surface of the template and the surface of the substrate are arranged generally parallel to each other in the present process, and the transfer of the pattern is achieved by pressing the structured template surface into a formable layer disposed on the substrate surface. The formable layer is treated to solidify so that its shape is forced to resemble the surface of the template. The template may thereafter be removed from the substrate and its layer, which is now an inverse topographical replica of the template. Further processing may be required in order to fix the transferred pattern in the substrate. Typically, wet or dry etching is performed to selectively etch the surface of the substrate beneath the cured layer, thereby transferring the pattern in the cured layer to the substrate surface. These are prior art and are described in detail in prior art documents, such as the aforementioned U.S. patent No. 6334960.

Fig. 1-3 schematically represent the basic process steps of an actual pattern transfer step, or imprinting step, of an embodiment of the present invention.

In fig. 1, a template 10 is shown, the template surface 11 having a structure in which three-dimensional protrusions and recesses are formed, the characteristic dimensions of height and width being in the range of 1nm to a few μm, and possibly smaller and larger. The thickness of the template 10 is typically between 10 and 1000 μm. The substrate 12 has surfaces 17 that are aligned substantially parallel to the template surface 11 with an intermediate spacing between the surfaces in an initial step as depicted in fig. 1. The substrate 12 comprises a substrate base 13 to which the pattern of the template surface 11 is to be transferred. Although not shown, the substrate may also include a support layer under the substrate base 13. In a process in which the pattern of template 10 is transferred directly to substrate 12 by imprinting in a polymeric material, the material may be applied directly onto substrate base surface 17 as surface layer 14. In an alternative embodiment, shown by dashed lines, a transfer layer 15 of, for example, a second polymeric material is also used. Examples of such transfer layers and how they are used in a subsequent process for transferring an imprinted pattern to the substrate base 13 are also described in US 6334960. In embodiments including a transfer layer 15, the substrate surface 17 represents the upper or outer surface of the transfer layer 15, which in turn is disposed on a substrate base surface 18.

The substrate 12 is disposed on the heating device 20. The heating means 20 preferably comprise a heating body 21 of metal, for example aluminium. The heating element 22 is connected to or comprised in the heating body 21 for transferring thermal energy to the heating body 21. In one embodiment, the heating element 22 is an electric immersion heater inserted into a socket in the heating body 21. In another embodiment, the electric heating coil is disposed inside the heating body 21, or attached to the lower surface of the heating body 21. In another embodiment, the heating element 22 is a channel formed in the heating body 21 for conveying a heating fluid through said channel. The heating element 22 is further provided with a connector 23 for connection to an external energy source (not shown). In the case of electrical heating, the connector 23 is preferably a galvanic contact for connection to a current source. For embodiments having a shaped channel for conveying a heating fluid, the connector 23 is preferably a tube for attachment to a source of heating fluid. The heating fluid may be, for example, water or oil. Another option is to use an IR radiation heater as heating element 22, designed to emit infrared radiation onto the heating body 21. In addition, a temperature controller is included in heating body 20 (not shown), including means for heating element 22 to a selected temperature and maintaining the temperature within a certain temperature tolerance. Different types of temperature controllers are well known in the art and are therefore not discussed in further detail.

The heating body 21 is preferably a piece of cast metal, such as aluminum, stainless steel or other metal. In addition, a body 21 of a certain mass and thickness is preferably used, so that an even distribution of heat at the upper side of the heating device 20 is achieved, which upper side is connected to the base plate 12 for transferring heat from the body 21 through the base plate 12 to heat the layer 14. For the imprint process for imprinting a 2.5 "substrate, a heating body 21 having a diameter of at least 2.5", preferably 3 "or more, and a thickness of at least 1cm, preferably at least 2 or 3cm, is used. For the imprint process for imprinting a 6 "substrate, a heating body 21 having a diameter of at least 6", preferably 7 "or more, and a thickness of at least 2cm, preferably at least 3 or 4cm is used. The heating body 20 is preferably capable of heating the heating body 21 to temperatures of up to 200-300 c, although lower temperatures are sufficient for most processes.

For the purpose of providing a controlled cooling of layer 14, heating device 20 may further be provided with a cooling element 24 connected to or included in heating body 21 for transferring thermal energy from heating body 21. In a preferred embodiment, the cooling element 24 comprises one or more channels shaped in the heating body 21 for conveying a cooling fluid through said channel or channels. The cooling element 24 is also provided with a connector 25 for connection to an external cooling source (not shown). Preferably, said connector 25 is a pipe for attachment to a source of cooling fluid. The cooling fluid is preferably water, but may alternatively be oil, for example insulating oil.

The preferred embodiment of the present invention utilizes a radiation crosslinkable thermoplastic polymer solution material for layer 14, which is preferably spin-coatable. These polymer solutions may also be photochemically amplified. An example of such a material is mr-L6000.1XP from Micro Resist Technology, which is uv-crosslinkable. Other examples of such radiation-crosslinkable materials include negative photoresist materials such as Shipley ma-N1400, SC100, and MicroChem SU-8. Spin-coatable materials are advantageous because they allow for complete and accurate coating of the entire substrate.

Another embodiment utilizes a liquid or near liquid prepolymer material for layer 14 that is crosslinkable by radiation. Examples of existing and useful polymerizable materials for layer 14 include NIP-K17, NIP-K22, and NIP-K28 from ZENPHOTONICES, 104-11Moonj i-Dong, Yusong-Gu, Daejeon305-308, South Korea. NIP-K17 has a major component of acrylate and has a viscosity of about 9.63cps at 25 ℃. NIP-K22 also has a major component of acrylate and has a viscosity of about 5.85cps at 25 ℃. These materials were designed at 12mW/cm²Cured for 2 minutes of uv radiation exposure.

Another example of a current and useful crosslinkable polymeric material for layer 14 is Ormocore from Micro Resist technology GmbH, Koepenicker Strass 325, Haus211, D-12555Berlin, Germany. The material has a composition of inorganic-organic hybrid polymer, unsaturated, with 1-3% of photo-crosslinking initiator. The viscosity of 3-8mPas at 25 ℃ is quite high, and the fluid can be 500mJ/cm at 365nm²Is cured under exposure to the radiation of (a). Other useful materials are mentioned in US 6334960.

Common to these materials, and to any other material useful for carrying out the present invention, is that they have the ability to be cured when exposed to radiation, particularly ultraviolet radiation, for example by crosslinking a polymer solution material or curing a prepolymer. Such materials for layer 14 are collectively referred to herein as radiation polymerizable.

The thickness of the layer 14 when deposited on the substrate surface is typically 10nm-10 μm, depending on the field of application. The polymerizable material is preferably applied to the substrate 12 in liquid form, preferably by spin coating, or alternatively by roll coating, dip coating, or the like. One advantage of the present invention over the prior art step and flash process, which is typical when using crosslinkable polymeric materials, is that the polymeric material can be spin coated over the entire substrate, which is an advantageous and fast process that provides excellent layer uniformity. Crosslinkable materials such as those described are generally solid at normal room temperature and therefore substrates that have been pre-coated at high temperatures may be conveniently used. Step and flash methods, on the other hand, must utilize repetitive dispensing by dripping on repetitive surface portions, since the method cannot process large surfaces in a single step. This makes the step and flash process and the machinery for performing such process complicated and difficult to control.

A preferred embodiment of the method according to the invention will now be described with reference to fig. 1-3. According to the invention, the process steps of imprinting, curing the imprinting material by radiation and post-baking the material are carried out at a fixed temperature.

The arrows in FIG. 1 show the pressing of the template surface 11 into the surface 16 of the layer of polymerizable material 14. At this step, a heater device 20 is preferably used to control the temperature of the layer 14 for obtaining a suitable viscosity in the material of the layer 14. For the crosslinkable material of the layer 14, the heating device 20 is thus controlled to heat the layer 14 to a temperature Tp that exceeds the glass temperature Tg of the material of the layer 14. In this context, Tp represents the process temperature, meaning that it is a common temperature level for the imprinting, exposure and post-baking process steps. The level of the fixed temperature Tp depends, of course, on the type of material selected for the layer 14, since it must exceed the glass transition temperature Tg for the case of a cross-linkable material and is also suitable for post-baking a radiation-cured material layer. For radiation crosslinkable materials, Tp is typically in the range of 50-250 ℃. For the mr-L6000.1XP example, successful testing has been performed at a fixed temperature throughout the 100-120 ℃ imprint, exposure, and post bake. For embodiments using radiation curable prepolymers, such materials are typically liquid or near liquid at room temperature and therefore require little or no heating to become soft enough for imprinting. However, all of these materials typically undergo a post bake before being separated from the template for complete hardening after exposure. The process temperature Tp is thus set to a suitable post-bake temperature level already in the imprinting step starting from the step of fig. 1.

Fig. 2 shows how the structure of the template surface 11 forms an imprint in the material layer 14, the material layer 14 being in a fluid or at least soft form, where the fluid is forced to fill the concave shape in the template surface 11. In the illustrated embodiment, the highest protrusions in the template surface 11 do not penetrate down to the substrate surface 17. This is beneficial for protecting the template surface 17 and in particular the template surface 11 from damage. However, in alternative embodiments, such as one that includes a transfer layer, the embossing may be performed down to the transfer layer surface 17. In the embodiment shown in fig. 1-3, the template is made of a material that is transparent to radiation 19 of a predetermined wavelength or range of wavelengths, which may be used to cure selected polymerizable materials. Such materials may be, for example, quartz or various forms of polymers, depending on the wavelength of the radiation. Since the template is typically very thin, typically less than one millimeter, and even with the use of uv sensitive materials in layer 14, a glass template may be used since there will be very little absorption in the template material. Radiation 19 is typically applied when template 10 is pressed into layer 14 with proper alignment between template 10 and substrate 12. When exposed to this radiation 19, curing of the polymerizable material is initiated for curing to a solid 14' taking the shape determined by the template 10. During the step of exposing layer 14 to radiation, heater 20 is controlled to maintain the temperature of layer 14 at temperature Tp.

After exposure to radiation, a post-bake step is performed to fully harden the material of layer 14'. In this step, heater device 20 is used to provide heat to layer 14 'for baking layer 14' into a hardened body prior to separating template 10 and substrate 12. Further, the post-baking is performed by maintaining the temperature Tp. In this way, the template 10 and the material layers 14, 14' will remain at the same temperature from the exposure to radiation to cure the material 14 to the final post bake, and optionally also until separation of the template 10 and substrate 12. In this way, accuracy limitations due to differences in thermal expansion in any of the materials used for the substrate and template are eliminated.

The form 10 is removed, for example, by a peeling and pulling (peeling and pulling) process. The formed and cured polymer layer 14' remains on the substrate 12. Various different methods of further processing the substrate and its layers 14' will not be discussed in detail here, since the invention as described is not only not concerned with such further processing, but is also not dependent on how such further processing is achieved. In general, further processing for transferring the pattern of the template 10 to the substrate base 13 may, for example, include etching or plating and subsequent lift-off steps.

Fig. 4-6 schematically represent the basic process steps of an actual pattern transfer step or imprinting step of an alternative embodiment of the present invention. The only practical difference from the embodiment of fig. 1-3 is that in this embodiment the radiation 19 is applied through the substrate 12, rather than through the template 10, while the same reference numerals are used. In addition, a heating device 20 is coupled to template 10 for heating layer 14 through template 10. In one embodiment as shown in fig. 4-6, an opaque template may be used, which has certain advantages. One is that this makes it possible to use a nickel template suitable for imprinting. The heating device 20 of fig. 4-6 includes the same features as the heating device of fig. 1-3, for which the same reference numerals are used. The features of fig. 4-6 will not be described further.

Fig. 7 schematically shows a preferred embodiment of the apparatus according to the invention, an embodiment which can also be used for carrying out the method according to the invention. It should be noted that the figures are merely schematic for the purpose of distinguishing the different features thereof. In particular, the dimensions of the different features are not on a common scale.

The device 100 comprises a first main part 101 and a second main part 102. In the shown preferred embodiment the main parts are arranged such that the first main part 101 is on top of the second main part 102, with an adjustable space 103 between said main parts. When forming a surface imprint by a process as described in fig. 1-6, it is of paramount importance that the template and substrate are correctly aligned in a lateral direction, commonly referred to as the X-Y plane. This is particularly important if the imprint is formed on top of or close to a pre-existing pattern in the substrate 10. However, the specific problems of alignment and different methods of solving them are not discussed here, but the invention can of course be combined if desired.

The first upper main portion 101 has a downwardly facing surface 104 and the second lower main portion 102 has an upwardly facing surface 105. The upwardly facing surface 105, or a portion thereof, is substantially planar and is placed on a plate 106 or formed as part of a plate 106, the plate 106 serving as a support structure for a template or substrate used in an imprint process, as will be more fully described in connection with fig. 8 and 9. The heating body 21 is placed on the plate 106, or forms part of the plate 106. The heating body 21 forms part of a heating body 106 and comprises a heating element 22 and preferably also a cooling element 24, as shown in fig. 1-6. The heating element 22 is connected via a connector 23 to an energy source 26, for example a power supply provided with current control means. In addition, the cooling element 24 is connected to a cooling source 27, such as a cooling fluid container and a pump, by means of a connector 25, and has control means for controlling the flow and temperature of the cooling fluid.

In the shown embodiment the means for adjusting the space 103 is provided by a piston member 107, the piston member 107 being attached to the plate 106 at its outer end. The piston member 107 is displaceably connected to a cylinder member 108, which is preferably held fixed relative to the first main part 101. As indicated by the arrows in the figure, the means for adjusting the space 103 are designed to displace the second main part 102 closer to or further away from the first main part 101 by a movement substantially perpendicular to the substantially flat surface 105, i.e. the Z-direction. The displacement may be effected manually, but is preferably assisted by the use of a hydraulic or pneumatic arrangement. The illustrated embodiment may be varied in this regard in a number of ways, such as by affixing the plate 106 to a cylindrical member surrounding a fixed piston member. It should further be noted that the displacement of the second main part 102 is mainly used for loading and unloading templates and substrates to the apparatus 100 and for setting the apparatus in an initial working position. However, the movement of the second main portion 102 is preferably not included in the actual embossing process as described in the illustrated embodiment, as will be described.

The first main portion 101 includes a peripheral sealing member 108 surrounding the surface 104. Preferably, the sealing member 108 is an annular seal, such as an O-ring, but may alternatively be composed of several interconnected sealing members that together form a continuous seal 108. The sealing member 108 is disposed in a recess 109 outward of the surface 104, and is preferably separable from the recess. The device further comprises a radiation source 110, which in the embodiment shown is arranged in the first main portion 101 behind the surface 104. The radiation source 110 is connectable to a radiation source driver 111, which preferably comprises or is connected to a power source (not shown). The radiation source driver 111 may be included in the apparatus 100, or may be an externally connectable component. The surface portion 112 of the surface 104 disposed proximate to the radiation source 110 is formed in a material that is transparent to the radiation of a certain wavelength or range of wavelengths of the radiation source 110. Thus, radiation emitted from the radiation source 110 is transmitted towards the space 103 between the first main portion 101 and the second main portion 102, through said surface portion 112. The surface portion 112 serving as the window may be formed of available fused silica, quartz, or sapphire.

In operation, the apparatus 100 is also provided with a flexible membrane 113 which is substantially flat and engages the sealing member 108. In a preferred embodiment, the sealing member 113 is a separate member from the sealing member 108 and is engaged with the sealing member only by applying opposing pressure from the surface 105 of the plate 106, as will be explained. However, in alternative embodiments, the membrane 113 is attached to the sealing member 108, for example by a bonding agent, or is an integral part of the sealing member 108. Additionally, in such alternative embodiments, the film 113 may be securely affixed to the first main portion 101, with the sealing member 108 disposed outside of the film 113. For embodiments such as that shown, film 113 is also formed of a material that is transparent to the radiation of a certain wavelength or range of wavelengths of radiation source 110. In this way, radiation emitted from the radiation source 110 is transmitted into the space 103 through said cavity 115 and its boundary walls 104 and 113. Examples of useful materials for the membrane 113 of the embodiment of fig. 7-9 include polycarbonate, polypropylene, polyethylene, PDMS, and PEEK. The thickness of the film 113 is usually 10 to 500. mu.m.

A duct 114 is formed in the first main part 101 to allow a fluid medium, either a gas, a liquid or a gel, to be transported to the space delimited by the surface 104, the sealing member 108 and the membrane 113, which space acts as a cavity 115 for said fluid medium. The conduit 114 may be connected to a pressure source 116, such as a pump, which may be external or internal to the device 100 as part of the device 100. The pressure source 116 is designed to apply an adjustable pressure, in particular an overpressure, to the fluid medium contained in said cavity 115. The embodiment shown is suitable for use with a gaseous pressure medium. Preferably, the medium is selected from the group comprising air, nitrogen and argon. If a liquid medium is used, it is preferable to have the film attached to the sealing member 108. Such a liquid may be hydraulic oil. As mentioned, another possibility is to use a gel as the medium.

FIG. 8 illustrates the apparatus embodiment of FIG. 7 when loaded with a substrate and a template for a lithographic process. For a better understanding of the figure, reference is also made to fig. 1-3. The second main portion 102 is displaced downwards from the first main portion 101 for opening the space 103. As shown in fig. 1-6, the template or substrate is transparent to radiation of a certain wavelength or range of wavelengths of radiation source 110. The embodiment shown in fig. 8 shows an apparatus loaded with a transparent template 10 on top of a substrate 12. The substrate 12 is placed on or in the second main part 102 with its back side on the surface 105 of the heating body 21. Thus, the substrate 12 has its substrate surface 17 facing upwards with a layer 14 of polymerizable material, for example an ultraviolet cross-linkable polymer solution. For simplicity, all features of the heating device 20 as shown in fig. 1-6 are not shown in fig. 8. Template 10 is placed on or adjacent to substrate 12 with structured surface 11 facing substrate 12. Means for aligning the template 10 with the substrate 12 may be provided, but are not shown in this schematic drawing. The film 113 is then placed on top of the template 10. For embodiments in which the film 113 is attached to the first main portion, the step of actually placing the film 113 on the template 113 may of course be omitted. In fig. 8, template 10, substrate 12 and film 113 are shown completely separated for clarity only, and in actual practice they would be stacked on surface 105.

Fig. 9 shows the operational position of the device 100. The second main portion 102 is raised to a position where the membrane 113 is clamped between the sealing member 108 and the surface 105. In practice, template 10 and substrate 12 are very thin, typically less than one millimeter, and the actual bending of membrane 113 as shown is minimal. However, surface 105 may alternatively be designed with a raised perimeter portion where it contacts sealing member 108 through film 113 to compensate for the combined thickness of template 10 and substrate 12.

Once the main portions 101 and 102 are engaged to clamp the membrane 113, the cavity 115 is sealed. The pressure source 116 is then designed to apply an overpressure to the fluid medium in the cavity 115, which medium may be a gas, a liquid or a gel. The pressure in cavity 115 is transferred by membrane 113 to template 10, which is pressed against substrate 12 for imprinting the template pattern in layer 14, see fig. 2. For a pre-polymer material of the layer 14 having a sufficient viscosity at room temperature, typically between 20 and 25 c, the imprint can be formed directly. However, the crosslinkable polymer solution typically requires preheating to overcome its glass transition temperature Tg, which may be about 60 ℃. One example of such a polymer is mr-L6000.1XP, described previously. When such polymers are used, an apparatus 100 having combined radiation and heating capabilities is particularly useful. However, for these types of materials, a post-bake process is typically required to harden the radiation-cured layer 14'. As previously mentioned, it is therefore an aspect of the invention to apply an elevated temperature Tp to the material of the layer 14, in the case of a cross-linkable material, Tp being above Tg, and also suitable for post-bake radiation exposed materials. Heating device 20 is activated to heat layer 14 by heating body 21 through substrate 12 until Tp is reached. The actual value of Tp naturally depends on the material chosen for layer 14. For the example of mr-L6000.1XP, a temperature Tp in the range of 50-150 ℃ may be used, depending on the molecular weight distribution in the material. The pressure of the medium in the chamber 115 is then increased to 5-500bar, advantageously to 5-200bar, and preferably to 20-100 bar. Thereby pressing the template 10 and the substrate 12 together with a corresponding pressure. Due to the flexible membrane 113 an absolutely evenly distributed force is obtained over the entire contact surface between the substrate and the template. Thereby allowing the template and the substrate to be aligned absolutely parallel with respect to each other and eliminating the effect of any irregularities in the surface of the substrate or template.

The radiation source is triggered to generate radiation 19 when the template 10 and substrate 12 are pressed together by the applied fluid medium pressure. The radiation is transmitted through the surface portion 112, which acts as a window, through the cavity 115, the membrane 113 and the template 10. The radiation is partially or completely absorbed in the layer 14, whereby the material of the layer 14 is cross-linked or hardened and cured, provided by pressure and film assisted compressive forces with a completely parallel alignment between the template 10 and the substrate 12. The radiation exposure time depends on the type and amount of material in the material layer 14, the wavelength of the radiation associated with the type of material and the type of radiation source. The characteristics of curing such polymerizable materials are well known as described, and the relevant combinations of the parameters are similarly well known to those skilled in the art. Once the fluid has cured to form layer 14', further exposure has no significant effect. However, the material of the layer 14' is allowed to be post-baked after exposure at a predetermined fixed temperature Tp, or hard-baked for a certain time, e.g. 1-10 minutes. For the example of mr-L6000.1XP, the post-baking is typically carried out at a common process temperature Tp of 100-120 ℃ for 1-10 minutes, preferably about 3 minutes.

With the apparatus 100 according to the invention, the post-baking is performed in the imprinter 100, which means that the substrate does not need to be taken out of the apparatus and put into a separate oven. This saves one process step, which makes it possible to save time and costs in the imprint process. Providing for performing a post-bake process while still maintaining the stamp 10 at a fixed temperature Tp, and possibly also with a selected pressure towards the substrate 10, also allows for a high accuracy in the resulting structure pattern in the layer 14, which allows for the production of finer structures. After pressurization, exposure and post-baking, the pressure in the cavity 115 is reduced and the two main portions 101 and 102 are separated from each other. In one embodiment, the cooling element 24 of the heating device 20 may be used to cool the substrate 112 after separation of the main portion. The substrate is then separated from the template and subjected to further processing in accordance with that previously known for imprint lithography.

Fig. 8 and 9 illustrate a process similar to that of fig. 1-3. Again, it should be noted that with a transparent substrate 12, the template 10 may be placed on the surface 105 of the heating body 21, with the substrate on top of the template 10, as shown in fig. 4-6.

Fig. 10-12 illustrate alternative methods of utilizing the apparatus 100 according to embodiments of the present invention. The same reference numerals are used for similar features as in fig. 1-3. In fig. 10-12, however, a transparent template 200 is used, which is preferably made of glass or quartz. The stencil 200 has a structured surface facing the substrate 12 with protrusions 201 defined by an opaque raised pattern. Preferably, this is achieved by including a layer of opaque material in the projections. The preferred embodiment shown includes an opaque layer 202 covering the outer end surfaces of the projections 201. Preferably, layer 202 is a metal layer. In one embodiment, the template 200 is fabricated by first applying a metal mask 202 over selected areas of the template surface, followed by an etching process for defining the recesses between the masked portions. The mask is not removed after the etching step, but rather the mask 202 remains on the template to define the non-transparent outer end surfaces of the template projections 201. The manufacture of the template 200 by this process also ensures that a nearly completely uniform common plane of the outer end surfaces of the protrusions 201 is achieved, since the template manufacturing process is adapted to a flat template body having a planar surface. It should be noted that the dimensions shown in fig. 1-12 are exaggerated for ease of understanding. For example, layer 202 may be only a few atomic monolayers thick.

In fig. 10, the template 200 is pressed into a layer 214 on the substrate 12, preferably by using the apparatus described with reference to fig. 7-9. The material of the layer 214 is in this case for example an ultraviolet curable prepolymer or an ultraviolet crosslinkable negative resist, which may be of any known type. The heating device 20 is controlled to raise the temperature of the substrate 12 to the appropriate process temperature Tp. In the case of a cross-linkable material, the heating device 20 is arranged to preheat the layer 214 through the substrate 12 such that the material of the layer 214 exceeds the glass transition temperature Tg to an elevated temperature Tp. Due to the imprinting technique using the film and the air pressure as described above, uniform pressure is achieved over the entire bonding surfaces of the template 200 and the substrate 12. Preferably, the stamp 200 is pressed into the layer 214 so that the outer ends of the protrusions 201 are extremely close to the substrate layer 17, preferably only a few nanometers.

In fig. 11, the template 200 has been fully pressed into the layer 214 and radiation 19 is applied through the template 200 towards the substrate 12. Radiation that reaches layer 202 is blocked and reflected and does not reach the underlying layer portion 214'. However, radiation falling between the protrusions 201 will reach the layer 214 and a hardening or curing process is initiated in the layer portion 214 "and the layer 214 is maintained at a temperature Tp. Preferably, the post-baking process is performed using the heating device 20 at the same temperature Tp for completing the curing process.

In the step shown in fig. 12, template 200 is separated and removed from template 12, leaving imprinted layer 214. In this shape, the substrate 12 is exposed to a negative resist developer fluid. The particular type of fluid may be any known type, although those skilled in the art will recognize that the type of developer must be selected according to the resist polymer used. The developer will remove only the portions 214' not exposed to the radiation and will remain as a very thin layer only at the bottom of the recesses in the polymer layer formed by the protrusions 201. In the prior art, an ashing or etching process has to be applied to remove the polymer portion 214' remaining in the concave shape and being solid, which process is significantly easier and faster than the prior art process. In addition, the ashing or etching of patterned polymer layer 14 will remove material from all portions of layer 214, i.e., portions 214 and 214 ', whereas the proposed method removes only portions 214' that are not exposed to radiation.

An embodiment of the system according to the invention further comprises mechanical clamping means for clamping together the substrate 12 and the template 10. This is particularly preferred in embodiments having an external alignment system for aligning the substrate and the template prior to pattern transfer, wherein the aligned stack comprises the template and the substrate and the aligned stack has to be transferred into the imprint apparatus. The system may further comprise means for applying a vacuum between the template and the substrate to extract air inclusions from the polymerizable layers of the stacked stack (sandwich) prior to hardening the polymerizable material by ultraviolet radiation.

In a preferred embodiment, the template surface 11 is preferably treated with an anti-adhesive layer to prevent the cured polymer layer 14' from sticking to it after the imprinting process. Examples of such tie layers include fluorine-containing groups, as presented in WO03/005124 and invented by one of the inventors of the present invention. WO03/005124 is also incorporated herein by reference.

The first mode of the invention with a transparent template has been successfully tested by the present inventors, which relates to a substrate 12 of silicon covered by a layer 14 with a NIP-K17 thickness of 1 μm. A template of glass or fused silica/quartz with a thickness of 600 μm was used.

The second mode of the invention with a transparent template has been successfully tested by the present inventors, which relates to a substrate 12 of silicon covered by a layer 14 with a NIP-K17 thickness of 1 μm. A template of, for example, nickel or silicon having a thickness of about 600 μm is used, although any other suitable non-transparent material may be used.

After a compression of about 30 seconds with 5-100bar through the membrane 113, the radiation source 110 is switched on. Radiation source 110 is typically designed to emit at least in the ultraviolet region below 400 nm. In a preferred embodiment, an air-cooled xenon lamp with an emission spectrum in the range of 200-1000nm is used as the radiation source 110. The preferred xenon-type radiation source 110 provides 1-10W/cm²And is designed to flash 1-5 mus pulses at a frequency of 1-5 pulses per second. A window 112 of quartz is formed in the surface 104 for passing radiation. The exposure time is preferably between 1 and 30 seconds for polymerizing the fluid layer into the solid layer 14', but may be up to 2 minutes.

The mr-L6000.1XP test has been performed with a cumulative total of about 1.8W/cm from 200 and 1000nm²And was performed with an exposure time of 1 minute. In this context, it should be noted that the radiation used need not be limited to the wavelength range in which the polymer applied in layer 14 is cured, in which rangeThe radiation outside the enclosure can of course also be emitted from the radiation source used. After a successful exposure at a fixed process temperature and a subsequent post-bake, the second main portion 102 is lowered to a position similar to that of fig. 8, and the template 10 and substrate 12 are subsequently removed from the apparatus for separation and further processing of the substrate.

The present invention brings a new embossing method that combines uv and thermal NIL, allowing a complete embossing process for uv-crosslinkable thermoplastic polymers at a fixed temperature. The method according to the invention thus overcomes the problem of differential thermal expansion in the template and substrate materials. As a result, high-precision large-area imprinting can be performed with different template and substrate materials. In addition, the method allows the use of spin-coatable uv-crosslinkable polymers with a uniform thickness distribution on wafer level, which is difficult to achieve with dispensing low viscosity uv-hardenable prepolymers.

The general process scheme comprises three main steps: a thermal embossing process followed by uv post exposure and hard bake to fully harden the polymer. In a preferred embodiment, a photochemically amplified polymer, such as mr-L6000.1XP, is used.

The three steps were combined at a fixed temperature and the following process scheme was given. The template and substrate are heated to a temperature Tp, which is greater than Tg for the crosslinkable material. Preferably, this is done by bringing the template into contact with the substrate in a stacked arrangement and any heating of the template or the substrate by the heating means. In this way, the template and the substrate, in particular the layer on the substrate to be imprinted, are heated to a common temperature by thermal conduction. The template-substrate stack is then exposed to high pressure to imprint the template pattern into the polymer layer. After a period of time, typically 30-60 seconds, a UV flood exposure is initiated to initiate hardening of the polymer. Before releasing the pressure, the temperature is kept fixed at Tp to hard bake the polymer until it is fully cured. Different template and substrate materials can be readily used to produce high precision large area imprinting. The possibility of using a cheap replicated nickel template makes large area imprinting significantly more cost effective and easy to implement, showing a good prospect for this approach.

The inventors successfully imprinted the entire area of the 2.5 "glass substrate with a blue-light nickel template, with a line width of about 140 nm. The imprint quality shows no tendency to decrease due to thermal effects when moving towards the edge of the substrate. This is clearly visualized in fig. 13 and 14, which show AFM (atomic force microscope) images of the results obtained.

FIG. 13 shows an AFM image 137 of a region near the center of a blue imprint on a 2.5 "glass substrate. On the left side of fig. 13, the AFM depth analysis structure over the area of 137 is shown, measured along the horizontal line in fig. 137. The selected points along the line are indicated by reference numerals 131 and 136 and are shown in the map 137 and the depth analysis map. As can be seen from the latter, the grooves formed in the imprinting process according to the present invention are deep and smooth.

In addition, fig. 14 shows a corresponding plot 147 for a region of the same imprint substrate located a few millimeters inward from the substrate edge. Similar to fig. 13, the points selected along the horizontal line of fig. 147 are indicated by reference numerals 141 and 146, and are shown in the depth analysis maps on the left of fig. 147 and fig. 147. Also in fig. 14, it can be seen that the grooves formed in the imprinting process according to the present invention are also deep and smooth near the 2.5 "glass substrate edge and show no tendency to be uneven or deformed due to thermal expansion.

By performing a single process comprising three main process steps in one process and in the same machine without taking the substrate out of the machine between these main steps, it is possible to perform an imprint of excellent quality on a large substrate surface. Since the entire substrate surface is imprinted in one step, the polymer layer 14 can be spin coated on the substrate and a continuous structure can be created over the entire substrate surface. All this is not possible with the so-called step and flash method. The disclosed apparatus and method are therefore particularly advantageous for large area imprinting and have the stated great advantages for step and flash processes, and the present invention can be used for single-step imprinting of 8 inch, 12 inch and even larger disks by using a membrane to transfer fluid pressure. With a single imprinting and exposure step of the present invention, even full flat panel displays having dimensions above about 400 x 600mm can be patterned.

The invention thus provides a technique which for the first time makes radiation assisted polymerisation imprinting attractive for mass production. The invention is suitable for forming patterns in substrates for the production of, for example, printed wiring boards or circuit boards, electronic circuits, micromechanical or electromechanical structures, magnetic and optical storage media, etc. The embodiments described herein relate to a combination of radiation exposure of an ultraviolet cross-linked polymer or ultraviolet curable prepolymer and a heater. However, with the goal of providing a solution to overcome the problems caused by thermal expansion due to the use of different template and substrate materials, the skilled person will appreciate that the present invention may be equally effectively implemented in methods involving radiation of other wavelength ranges to which the resist material for the imprint layer on the substrate is cured accordingly. Furthermore, although the present invention is particularly preferred for use in imprint processes involving templates and substrates formed of different materials, the technical effect of not requiring removal of the substrate from the imprint machine during post-baking and convenient control using a fixed temperature can also be achieved when the same material is used in the template and substrate.

The term fixed temperature is meant to be substantially fixed, meaning that even if the temperature controller is set to maintain a certain temperature, the actual temperature achieved will inevitably fluctuate within a certain range. The stability of this fixed temperature depends mainly on the accuracy of the temperature controller and the inertness of the whole device. Furthermore, it should be understood that even though the method according to the invention can be used for imprinting extremely fine structures up to 1nm, slight temperature variations will not have a significant effect as long as the template size is not too large. Assuming that the width of the structures at the periphery of the template is x and a reasonable spatial tolerance is a fraction of this width, e.g., y ═ x/10, then y becomes a parameter for setting the temperature tolerance. In practice, the effect that a difference in thermal expansion will have can be readily calculated by applying the respective coefficients of thermal expansion of the materials of the template and substrate, the dimensions of the template, which are commonly referred to as the radius, and the spatial tolerance parameter y. From this calculation, the appropriate temperature tolerance of the temperature controller can be calculated and applied to the machine to perform the process.

The invention is defined by the appended claims.

Claims (20)

1. A method for transferring a pattern from a template having a structured surface to a substrate bearing a surface layer of radiation-cured material, comprising:

arranging the template and substrate parallel to each other in an imprint apparatus, the structured surface facing the surface layer;

heating the template and the substrate to a temperature Tp using a heating device; and

while maintaining said temperature Tp, the following steps are performed:

pressing the template against the substrate, thereby imprinting the pattern into the layer;

exposing the layer to radiation to cure the layer; and

post-baking the layer;

wherein the material is a uv-crosslinkable thermoplastic polymer having a glass temperature Tg, wherein the temperature Tp is greater than the temperature Tg, and wherein the radiation is uv-radiation.

2. The method of claim 1, wherein the material is photochemically amplified.

3. The method of claim 1, comprising:

the surface layer is applied to the substrate by spin coating the material before arranging the template and substrate parallel to each other.

4. The method of claim 1, comprising:

sandwiching the template and the substrate between a barrier member and a first side of a flexible membrane, and wherein

Pressing the template against the substrate involves applying an overpressure to the medium on the second side of the membrane.

5. The method of claim 4, wherein the medium comprises a gas.

6. The method of claim 4, wherein the medium comprises air.

7. The method of claim 4, wherein the medium comprises a liquid.

8. The method of claim 4, wherein the medium comprises a gel.

9. The method of claim 1, comprising:

emitting radiation through the template towards the layer, the template being transparent to a wavelength range of radiation used to cure the material; and

heating the substrate by direct contact with the heating device.

10. The method of claim 1, comprising:

emitting radiation through the substrate towards the layer, the substrate being transparent to a wavelength range of radiation used to cure the material; and

heating the template by direct contact with the heating device.

11. The method of claim 4, comprising:

emitting radiation through the film towards the layer, the film being transparent to a wavelength range of radiation used to cure the material.

12. The method of claim 4, comprising:

emitting radiation through the film and through a transparent wall opposite the film towards the layer, the wall defining a rear wall of a cavity for the medium, the rear wall and the film being transparent to a wavelength range of the radiation for curing the material.

13. The method of claim 1, wherein exposing the layer comprises:

radiation is emitted from the radiation source in the wavelength range of 100 to 500 nm.

14. The method of claim 13, comprising:

pulsed radiation is emitted with a pulse duration in the range of 0.5 to 10 mus and a pulse rate in the range of 1 to 10 pulses per second.

15. The method of claim 4, comprising:

clamping the substrate and template together prior to disposing the template and substrate between the barrier member and the flexible membrane.

16. The method of claim 1, comprising:

applying a vacuum between the template and the substrate before exposing the layer to radiation, thereby extracting air inclusions from the surface layer.

17. The method of claim 1, wherein the structured surface comprises a pattern of protrusions that are opaque to the radiation, whereby exposing the layer to radiation involves curing portions of the layer between the protrusions.

18. The method of claim 17, wherein the protrusion comprises a layer of opaque material.

19. The method of claim 17, wherein a layer of opaque material is coated on the projections as an outermost layer.

20. The process of claim 1, wherein the temperature Tp is in the range of 50 to 250 ℃.