JP4515413B2 - Imprint lithography - Google Patents

Description

  The present invention relates to imprint lithography.

  A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus is conventionally used in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures.

  It is desirable to reduce the size of lithographic pattern features because this can increase the density of features on any substrate area. In photolithography, improved resolution can be achieved by using shorter wavelength radiation. However, there are problems associated with such a decrease. Current systems have begun to employ light sources in the wavelength region of 193 nm, but even at that level, the diffraction limit becomes an obstacle. At shorter wavelengths, the transparency of the material is very low. Optical lithographic machines that can improve resolution require complex optics and scarce materials and are therefore very expensive.

  A new method of printing features less than 100 nm, known as imprint lithography, involves transferring a substrate to a pattern by imprinting the pattern onto an imprintable medium using a physical mold or template. . The imprintable medium may be a substrate or a material that is coated on the surface of the substrate. The imprintable medium can function or be used as a “mask” that transfers the pattern to the underlying surface. The imprintable medium can be provided as a resist that is attached to a substrate, such as a semiconductor material, to which the pattern defined by the template is transferred. Thus, imprint lithography is basically a micrometer or nanometer scale molding process in which the template topography defines the pattern produced on the substrate. The pattern can be layered as in the optical lithography process, so in principle imprint lithography can be used for applications such as IC manufacturing.

  The resolution of imprint lithography is limited only by the resolution of the template manufacturing process. For example, imprint lithography can be used to generate features in the sub-50 nm range with significantly improved resolution and line edge roughness than is achievable with conventional optical lithography processes. it can. Also, the imprint process does not require expensive optics, advanced illumination sources, or special resist materials that are normally required in optical lithography processes.

  In a conventional imprint lithography apparatus, a template provided with a pattern is attached to an actuator. An actuator moves the template toward the substrate and pushes the template onto the substrate. The force pressed against the substrate through the template can be very large. This can cause the substrate and / or template to be deformed, for example several hundred nanometers, which can lead to damage of the pattern imprinted on the substrate.

  Generally, the imprint template is left for a long time after contacting the imprintable material of the substrate. This is because the imprintable material is sufficiently allowed to flow into all the depressions of the template pattern. This large amount of time is one reason why imprint lithography currently takes longer than optical lithography. Speed is an important factor in the economic feasibility of an imprint lithography machine, and the large amount of time that the fluid can flow into the template can be disadvantageous.

According to a first aspect, in a lithographic apparatus,
A template holder configured to hold an imprint template;
A substrate table arranged and configured to receive a substrate;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A lithographic apparatus is provided having a detector configured to detect radiation scattered from an interface between an imprint template and an imprintable material provided on a substrate.

According to a second aspect, a lithographic apparatus comprising:
A template holder configured to hold an imprint template;
A substrate table arranged and configured to receive a substrate;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A lithographic apparatus is provided having a detector configured to detect radiation reflected by the substrate.

According to a third aspect, there is a method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
A method is provided that includes detecting radiation scattered from an interface between an imprint template and an imprintable material on a substrate.

According to a fourth aspect, there is a method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
Detecting radiation reflected by the substrate.

  One or more embodiments of the present invention are applicable to any imprint lithography process that imprints a patterned template onto a flowable imprintable medium, for example as described herein. It can be applied to high temperature and UV imprint lithography.

  Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings. Corresponding reference symbols indicate corresponding parts in the drawings.

  There are two main approaches to imprint lithography, commonly referred to as high temperature imprint lithography and UV imprint lithography. There is also a third type of “imprint” lithography known as soft lithography. Examples of these are illustrated in FIGS. 1a to 1c.

  FIG. 1a shows a layer of molecules 11 (usually inks such as thiols) from a flexible template 10 (usually made from polydimethylsiloxane (PDMS)) on a substrate 12 and a planarization and transfer layer 12 ′. 1 schematically illustrates a soft lithographic process including transfer to a resist layer 13 supported on the substrate. The template 10 has a pattern of features on its surface and a molecular layer is disposed on the features. When the template 10 is pressed against the resist layer 13, the layer of molecules 11 adheres to the resist. When the template is removed from the resist, the layer of molecules 11 adheres to the resist and the remaining layers of the resist are etched, so that areas of the resist not covered by the transferred molecular layer are etched to the substrate.

  The template 10 used for soft lithography is easily deformable and is therefore not suitable for high resolution applications, for example on the nanometer scale. This is because the deformation of the template can adversely affect the imprinted pattern. Furthermore, when manufacturing a multilayer structure that overlaps the same region multiple times, soft imprint lithography cannot provide overlay accuracy on the nanometer scale.

  High temperature imprint lithography (or high temperature embossing) is also known as nanoimprint lithography (NIL) when used on a nanometer scale. This process uses a relatively hard template made from, for example, silicon or nickel, which is more resistant to wear and deformation. This is described, for example, in US Pat. No. 6,482,742 and illustrated in FIG. 1b. In a typical high temperature imprint process, the solid template 14 is imprinted onto a thermosetting or thermoplastic polymer resin 15 that is molded onto the surface of the substrate. The resin can be baked, for example, by spin-coating onto the substrate surface, more typically (as in the example shown) to the planarization and transfer layer 12 '. It is to be understood that the term “hard” when describing an imprint template includes materials that are generally considered between “hard” and “soft” materials, such as “hard” rubber. The suitability of a particular material for use as an imprint template is determined by application requirements.

  If a thermosetting polymer resin is used, the resin is heated to a temperature such that upon contact with the template, the resin can flow to flow into the pattern features defined on the template. Next, the temperature of the resin is raised to heat cure (eg, crosslink) the resin so that it solidifies and corresponds irreversibly to the desired pattern. Thus, the template can be taken out and the resin with the pattern formed can be cooled.

  Examples of thermoplastic polymer resins used in high temperature imprint lithography processes are poly (methyl methacrylate), polystyrene, poly (benzyl methacrylate) or poly (cyclohexyl methacrylate). The thermoplastic resin is heated so that it can flow freely just before imprinting with the template. Usually, it is necessary to heat the thermoplastic resin to a temperature well above the glass transition temperature of the resin. The template is pressed into the flowable resin and sufficient pressure is applied to ensure that the resin flows into all of the pattern features defined on the template. Next, with the template in place, the resin is allowed to cool below the glass transition temperature, after which the resin irreversibly corresponds to the desired pattern. The pattern is composed of features that have been relieved from the residual resin layer, and the residual layer can be removed with a suitable etching process, leaving only the pattern features.

  Once the template is removed from the solidified resin, a two-stage etching process is typically performed as shown in FIGS. 2a-2c. The substrate 20 has a planarization and transfer layer 21 immediately above it, as shown in FIG. 2a. There are two purposes for planarization and transfer layer. This serves to provide a surface that is approximately parallel to that of the template, which helps to ensure that the contact between the template and the resin is parallel and printed as described herein. The aspect ratio of the feature is also improved.

  After removing the template, a solidified resin residual layer 22 is formed in a desired pattern and remains on the planarization and transfer layer 21. Since the first etching is isotropic and removes a part of the residual layer 22, the height of the feature 23 is L1, as shown in FIG. The second etch is anisotropic (or selective) and improves the aspect ratio. The anisotropic etching removes the portion of the planarization and transfer layer 21 that is not covered by the solidified resin and increases the aspect ratio of the feature 23 to (L2 / D) as shown in FIG. 2c. The resulting polymer thickness contrast left on the substrate after etching can be used, for example, as a step in a stripping process, for example as a mask for dry etching, if the imprinted polymer is sufficiently resistive.

  High temperature imprint lithography requires pattern transfer to be performed at a relatively high temperature and requires a relatively large temperature difference to ensure that the resin is sufficiently solid before removing the template. There is a disadvantage that there are things. A temperature difference between 35 ° C and 100 ° C may be required. For example, expansion due to a temperature difference between the substrate and the template may lead to distortion of the transferred pattern. This pattern distortion can be exacerbated by the relatively high pressure required in the imprint step due to the viscous nature of the imprintable material, which induces mechanical deformation in the substrate and further distorts the pattern. There is a possibility.

  On the other hand, UV imprint lithography does not have such high temperatures and temperature differences and does not require such viscous imprintable materials. Rather, UV imprint lithography involves the use of partially or totally transparent templates and monomers such as UV curable liquids, usually acrylates or methacrylates. In general, any photopolymerizable material such as a mixture of monomers and initiator can be used. The curable liquid may include, for example, a dimethylsiloxane derivative. Such materials are less viscous than the thermosetting and thermoplastic resins used in high temperature imprint lithography, and as a result, fill the template pattern features much faster. Low temperature and low pressure operation is also preferred for higher throughput capabilities.

  An example of a UV imprint process is illustrated in FIG. The quartz template 16 is applied to the UV curable resin 17 in a manner similar to the process of FIG. Rather than a temperature increase such as high temperature embossing using a thermosetting resin, or temperature cycling when using a thermoplastic resin, UV radiation is passed through the quartz template to polymerize and then cure the resin. Apply. After removing the template, the remaining steps of etching the remaining layer of resist are the same or similar to the embossing process described herein. Commonly used UV curable resins are much less viscous than typical thermoplastics and therefore lower imprint pressures can be used. UV imprint lithography is suitable for applications that require high overlay accuracy, because lower pressure reduces physical deformation and further reduces deformation due to higher temperatures and temperature changes. Also, the transparent nature of the UV imprint template allows the optical alignment technique to be simultaneously adapted for imprinting.

  This type of imprint lithography primarily uses UV curable materials and is therefore commonly referred to as UV imprint lithography, but other wavelengths of radiation are used to cure appropriately selected materials (eg, polymerization). Or activating the cross-linking reaction). In general, any radiation capable of initiating such a chemical reaction may be used if a suitable imprintable material is available. Alternative “activating radiation” includes, for example, visible light, infrared radiation, x-ray radiation and electron beam radiation. In the general description herein, reference to UV imprint lithography and the use of UV radiation does not exclude these and other possibilities of actinic radiation.

  Low-line printing systems have been developed as an alternative to imprint systems that use planar templates that are maintained substantially parallel to the substrate surface. While the template is formed on a roller, other imprint processes have been proposed for both high temperature and UV low line printing systems that are very similar to imprints using planar templates. Unless specifically limited by context, references to imprint templates include references to roller templates.

  A development, especially known as step-and-flash imprint lithography (SFIL), that can be used to form patterns in a small step on a substrate in a manner similar to conventional optical steppers used in, for example, IC manufacturing, etc. UV imprint technology. This involves imprinting the template into a UV curable resin, “flashing” the UV radiation through the template, curing the resin under the template, removing the template, and stepping into the adjacent area of the substrate. It includes printing a small area of the substrate at a time by iterating. The small field size of such a step-and-repeat process can help reduce pattern distortion and CD variation, so SFIL is especially useful in the manufacture of ICs and other devices that require high overlay accuracy. Suitable.

  In principle, UV curable resins can be applied to the entire substrate surface, for example by spin coating, but this can be problematic due to the volatile nature of UV curable resins.

  One approach to addressing this problem is the so-called “drop-on-demand” process, where the resin is dispensed into the target portion of the substrate in small droplets just prior to imprinting with the template. This liquid dispensing is controlled so that a predetermined amount of liquid adheres to a specific target portion of the substrate. The liquid can be dispensed in various patterns and a carefully controlled combination of liquid volume and pattern placement can be used to limit pattern formation to the target area.

  As mentioned above, dispensing resin on demand is not trivial. Carefully control the size and spacing of the droplets to make sure there is enough resin to fill the template features while minimizing excess resin that can lead to undesirable thickness or uneven residual layers Guarantee to do. This is because there is no place for the resin to flow when adjacent droplets come into contact with each other.

  Although this specification refers to depositing a UV curable liquid on a substrate, the liquid can also be deposited on a template and generally the same techniques and considerations apply.

FIG. 3 shows the relative dimensions of the template, imprintable material (curable monomer, thermosetting resin, thermoplastic resin, etc.), and substrate. The ratio between the width D of the substrate and the thickness t of the curable resin layer is on the order of 10 ⁶ . It will be appreciated that the dimension t must be greater than the depth of the protruding feature on the template to prevent the feature from protruding from the template and damaging the substrate.

  The residual layer remaining after stamping is useful to protect the underlying substrate, but as mentioned herein, the source of the problem, especially when high resolution and / or overlay accuracy is required. Sometimes it becomes. The initial “breakthrough” etch is isotropic (non-selective) and therefore also erodes imprinted features and even residual layers to some extent. This is exacerbated when the residual layer is excessively thick, non-uniform, or both. This problem leads to fluctuations in the thickness of the line finally formed on the underlying substrate (ie fluctuations in critical dimensions). The uniformity of the thickness of the lines etched into the transfer layer in the second anisotropic etching is determined by the aspect ratio and shape integrity of the features remaining in the resin. If the residual resin layer is non-uniform, a non-selective first etch may leave some of these features in a “rounded” top, so that the features are second and subsequent It is not well defined enough to ensure good uniformity of line thickness in the etching process. In principle, the above-mentioned problems can be mitigated by ensuring that the residual layer is as thin as possible, but this has undesirably high pressure (possibly increasing the deformation of the substrate) and comparison It may be necessary to apply a long imprint time (sometimes reducing throughput).

  Templates are a critical component of an imprint lithography system. As described herein, the resolution of features on the template surface is a limiting factor in the achievable resolution of features printed on the substrate. Templates used for high temperature and UV lithography are typically formed in a two-step process. Initially, a desired pattern is written, for example using electron beam writing, to give a high resolution pattern in the resist. The resist pattern is then transferred to a thin layer of chromium, which forms a mask with a final anisotropic etching step to transfer the pattern to the template support material. Other techniques such as ion beam lithography, X-ray lithography, extreme UV lithography, epitaxial growth, thin film deposition, chemical etching, plasma etching, ion etching or ion milling can also be used. In general, use techniques that allow very high resolution. This is because the template is actually a 1x mask and the resolution of the transferred pattern is limited by the resolution of the pattern on the template.

  The peeling characteristics of the template can also be a consideration. The template can be treated, for example, with a surface treatment material to form a thin release layer having a low surface energy on the template (a thin release layer may be applied to the substrate).

  Another consideration in the development of imprint lithography is the mechanical durability of the template. Templates can be subjected to high forces during resist stamping and can also be subjected to extreme pressures and temperatures for high temperature lithography. This causes wear of the template and can adversely affect the shape of the pattern imprinted on the substrate.

  In high temperature imprint lithography, there is a potential advantage in using a template of the same or similar material as the substrate to reduce the difference in thermal expansion. In UV imprint lithography, the template is at least partially transparent to actinic radiation and therefore uses a quartz template.

  Although the text specifically refers to the use of imprint lithography in the manufacture of ICs, it should be understood that the imprint apparatus and methods described herein may have other applications. For example, it can be used in the manufacture of integrated optical systems, magnetic domain memory guidance and detection patterns, hard disk magnetic media, flat panel displays, thin film magnetic heads and the like.

  The description herein specifically refers to the use of imprint lithography to transfer the pattern of the template to the substrate through an imprintable resin that acts substantially as a resist, but in some situations imprinting The printable material event may be a functional material, for example, having electrical conductivity, optical linear or non-linear response, and the like. For example, the functional material can form a conductive layer, a semiconductor layer, a dielectric layer, or a layer having other desirable mechanical, electrical, or optical properties. Some organic substrates can also be suitable functional materials. Such applications are within the scope of the present invention.

  FIG. 4 schematically depicts an imprint lithography apparatus having a substrate table 30 and a template holder (not shown for clarity and clarity) that holds an imprint template 31. The substrate 32 is held on a substrate table 30 and an area of imprintable material 33 is provided. For ease of illustration, only a portion of the substrate table 30 and substrate 32 is shown in FIG.

  The imprint template 31 is movable in the z direction from the disengagement position that is not in contact with the imprintable material 33 to the imprint position where the imprint template 31 is pushed into the imprintable material 33 (FIG. 4). Marked with standard Cartesian coordinates). When the imprint template 31 is in the imprint position, this causes the imprintable material 33 to flow into the depressions that form the pattern on the imprint plate (the depressions are not shown in FIG. 4). As a result, the pattern on the imprint template 31 is transferred to the imprintable material 33.

  The imprintable material 33 is illustrated as extending just beyond the edge of the imprint template 31. In some arrangements, the imprintable material is provided over the entire top surface of the substrate 32.

  A light emitting diode (LED) having a radiation output unit 34 is provided on one side of the imprint template 31 and arranged to emit radiation at a wavelength of 400 nanometers in the direction of the imprint template. Alternatively or additionally, radiation can be supplied to the radiation output 34 from a remote radiation source. In some embodiments, a beam stop 38 is provided on the opposite side of the imprint template 31 and is arranged to capture radiation reflected by the imprint template 31 and the substrate 32. The condensing lens 36 is disposed on the imprint template 31, and the condensing lens 36 is disposed and configured to focus the image of the imprint template 31 on a charge coupled device (CCD) camera 37.

  In use, once the imprint template 31 has been moved to the imprint position, ie, pushed into the imprintable material 33, the LED 34 is switched on and the beam of radiation 35 is directed to the top surface of the imprint template 31. The beam of radiation 35 passes through the imprint template 31, reflects off the surface of the substrate 32, passes back through the imprint template, and enters the beam stop 38. A portion of the radiation beam 35 is scattered at the interface between the imprint template 31 and the imprintable material 33. The scattered radiation represented by the arrow is condensed on the CCD camera 37 by the condenser lens 36. The scattered radiation 39 is used to determine whether the imprintable material 33 has sufficiently flowed into the depressions that form the pattern below the imprint template 31.

  5a to 5c schematically show details of the imprint template and substrate shown in FIG. Referring initially to FIG. 5 a, the imprint template 31 is in a disengaged position and is placed on the substrate 32. An imprintable material 33 is provided on the substrate 32. The imprintable material 33 is in the form of two droplets rather than a continuous layer of equal depth. Droplets of imprintable material 33 often arise due to the surface tension of the imprintable material. In fact, the imprintable material 33 is often intentionally provided in the form of a droplet, for example in a configuration that is believed to accelerate the imprint process. The droplets of imprintable material 33 are shown to have dimensions similar to the recesses 40 that form the pattern on the underside of the imprint template. However, this is only for ease of illustration, and in practice the droplets of imprintable material 33 are typically much larger than the depressions 40.

  In FIG. 5 b, the imprint template 31 has been moved to the imprint position and is pressed onto the imprintable material 33. As time passes, this pressure forces the imprintable material 33 to flow into the depression 40 below the imprint template 31. At the end of this flow, the imprintable material 33 has fully filled all of the depressions 40 so that when the imprint template 31 moves to the disengaged position, it is formed by the depressions 40 below the imprint template. The patterned pattern is held by the imprintable material 33. FIG. 5b shows the midpoint of the flow. At this intermediate point, the imprintable material 33 does not sufficiently fill the recess 40 of the imprint template 31, leaving a region of gas 42 (bubbles) in the recess.

  The beam of radiation 35 scatters when it intersects the interface between the bubble 42 and its surroundings. As shown in FIG. 4, the scattered radiation is indicated by an arrow 39. The scattered radiation 39 is imaged by the CCD camera 37, indicating that the flow of the imprintable material 33 has not ended.

  The reason why scattering occurs can be understood by referring to the reflectance of the gas 42 compared to the reflectance of the imprint template 31 and the imprintable material 33. A typical refractive index of gas 42, which may be nitrogen or air, for example, is 1. A typical refractive index of the imprint template 31 that is conventionally made of quartz is 1.9. The typical index of refraction of imprintable material 33, which typically includes silicon containing monomer, is 1.6. The reflection of radiation occurs at the interface between the two materials when there is a large difference between the refractive indices of the two materials. Thus, the beam of radiation 35 is reflected when it reaches the interface between the imprint template 31 and the bubble 42 and the interface between the bubble 42 and the imprintable material 33. Since there are several interfaces, which are arranged at different angles, many reflections occur and cause scattered radiation 39. Scattering of radiation from the bubble 42 is detected by the CCD camera 37 (see FIG. 4). To avoid complicating FIG. 5b, the path of the beam of radiation 35 to the bubble 42 is not shown.

  Referring to FIG. 5c, when the flow of imprintable material 33 is finished, the recess 40 is almost completely filled with the imprintable material and there are no or few bubbles. Since the reflectance of the imprint template 31 is close to the refractive index of the imprintable material 33, the amount of reflection generated at the interface between the imprint template and the imprintable material is small. The beam of radiation 35 passes through this interface almost undisturbed and does not produce significant scatter, so little or no scattered radiation is detected by the CCD camera 37 (see FIG. 4). In some cases, the amount of residual radiation may be scattered at the interface due to a relatively small difference between the refractive index of the imprint template and the refractive index of the imprintable material. However, this is small compared to the amount of radiation scattered by the presence of bubbles.

  In general, the degree of scattering detected by the CCD camera 37 provides an indication of the number and / or size of the bubbles 42 located under the imprint template 31.

  In some embodiments, the point in time when the imprintable material 33 has been allowed to flow into the recess of the imprint template 31 can be measured. This measurement can be performed automatically, for example by comparing the overall intensity of the image detected by the CCD camera 37 or the contrast of the image viewed by the CCD camera. Thereby, imprint lithography can be performed more efficiently. This is because when the flow of the imprintable material 33 is completed, the imprint template 31 can be immediately moved to the disengagement position. In typical imprint lithography, it may not be known when the flow of imprintable material is finished, resulting in the imprint template remaining longer than necessary at the imprint location. Therefore, the time required for performing imprint lithography is shortened, and the productivity of imprint lithography can be improved accordingly.

  Further, in some embodiments, an indication can be provided that a defect is present in the imprinted pattern. For example, if bubbles are trapped under the imprint template and have not moved from under the template within the maximum time allowed for the flow of imprintable material. These bubbles can cause imperfections in the imprint pattern. By detecting the presence of bubbles, in certain embodiments, imprint patterns with defects can be identified. A defective imprint pattern can be reworked or discarded, for example. In conventional imprint lithography systems, defective patterns cannot be identified until the device is finished and the device is tested.

  After the flow of the imprintable material is completed, the imprint template 31 is returned to the disengagement position. Next, the imprintable material 33 is illuminated with UV radiation to activate a chemical reaction that fixes the imprint pattern to the imprintable material 33 (ie, cures the imprintable material). In some embodiments, the CCD camera 37 and the condenser lens 36 are operable in the x and / or y directions and leave the imprint template 31 before performing illumination with UV radiation. In certain embodiments, CCD camera 37 and / or condenser lens 36 are transparent to UV radiation, which is directed to imprintable material 33 through one or both. In some embodiments, the UV radiation can be directed to the imprintable material 33 at an angle so that the CCD camera 37 does not need to move or be transparent to the UV radiation. In some embodiments (not shown), the CCD camera is positioned to view the imprint template at an angle rather than substantially at a right angle so that the UV radiation can illuminate the imprint template at a substantially right angle. Can do.

  As described above, the output of the CCD camera 37 can be automatically analyzed. This is done, for example, by adding all the outputs of the CCD camera 37 together to provide a single intensity value. The controller C compares this intensity value with a threshold value, and if the single intensity value falls below the threshold value, it can be interpreted as an indication that the flow of imprintable material 33 has ended. can do. Next, the control device C provides an output signal indicating that the imprint template 31 may be moved to the disengagement position. It will be appreciated that in this arrangement, the CCD camera 37 may be replaced with a single large area photodiode.

  In one arrangement, the controller C can be used to analyze the contrast of the image detected by the CCD camera 37 (ie, the difference in intensity seen by different pixels of the camera). The radiation scattered from the bubbles is unevenly distributed and does not provide a uniform intensity on the CCD camera 37. That is, the amount of contrast is an indication of the number and / or size of the bubbles 42 trapped under the imprint template 31. When the scattering is eliminated or significantly reduced, what remains is some background illumination of the CCD camera 37, which is almost uniform. Thus, if the contrast drops below the threshold, this can be interpreted as indicating that the flow of imprintable material 33 has ended. Next, the control device C provides an output signal indicating that the imprint template 31 may be moved to the disengagement position.

  In general, all bubbles 42 may not be eliminated by the flow of imprintable material 33. Thus, the threshold is found to correspond to an imprint pattern having a level that indicates that most of the bubbles 42 have been eliminated, or a required form (ie, not excessively damaged by the presence of bubbles). You can set the value to

  Referring to FIG. 6, an imprint lithography apparatus according to another embodiment of the present invention is schematically illustrated. The imprint lithography apparatus has a substrate table 30 and a template holder that holds an imprint template 31 (not shown for ease of illustration and clarity). The substrate 32 is held on a substrate table 30 and an area of imprintable material 33 is provided. The imprint template 31 can operate in the z direction. An LED having a radiation output unit 34 is provided on one side of the imprint template 31 and is arranged and configured to emit radiation at a wavelength of 400 nanometers in the direction of the beam splitter 45. Alternatively or additionally, radiation can be supplied to the radiation output 34 from a remote radiation source. The beam splitter 45 is arranged and configured to guide the radiation from the LED 34 toward the imprint template 31. The condensing lens 36 is arranged on the beam splitter 45 and arranged so as to focus the image of the imprint template 31 on the CCD camera 37.

  In use, once the imprint template 31 is moved to the imprint position, the LED 34 is switched on and the beam of radiation 46 is directed to the lower surface of the imprint template via the beam splitter 45. If bubbles exist between the imprint template 31 and the imprintable material 33, the beam 46 is scattered as indicated by an arrow 47. Generally, the scattered radiation 47 is not collected by the condenser lens 36 and is therefore not detected by the CCD camera 37.

  When the flow of the imprintable material 33 into the depression of the imprint template 31 is completed, bubbles are eliminated or the number of the bubbles is reduced at the interface between the imprint template and the imprintable material. Thus, the beam of radiation 46 is no longer scattered and reflects off the top surface of the substrate 32 as indicated by arrow 48. The reflected radiation is collected by the condenser lens 36 and detected by the CCD camera 37.

  The presence and amount of radiation detected by the CCD camera 37 provides an indication of whether the flow of the imprintable material 33 into the depression of the imprint template 31 has been completed. The measurement provided by the CCD camera 37 is different from the measurement provided in the embodiment illustrated with respect to FIGS. 4 and 5 in the sense that the presence of bubbles reduces the amount of radiation detected by the CCD camera 37. The opposite (in the embodiment described above, the presence of bubbles increased the amount of detected radiation). Accordingly, the CCD camera 37 can be interpreted as indicating that the flow of the imprintable material 33 has ended when the total intensity output from the CCD camera rises above the threshold. When the output from the CCD camera 37 rises above the threshold, the control device C provides an output signal indicating that the imprint template 31 may be moved to the disengagement position. If a single total intensity output is used, the CCD camera 37 can be replaced with a single large area photodiode.

  In one arrangement, the contrast of the radiation detected by the CCD camera 37 can be used to obtain an indication of when the flow of imprintable material 33 has ended. The reflection of the radiation 46 beam from the surface of the substrate 32 illuminates the CCD camera 37 almost uniformly (that is, the contrast is low) together with the reflection seen from the surface of the imprint template 31. However, if air bubbles are present between the imprint template 31 and the imprintable material 33 while the imprintable material 33 flows, most of the radiation incident on the imprint template and the imprintable material is scattered and detected. The amount of radiation emitted is reduced. Although most of the scattered radiation does not enter the CCD camera 37, the small amount incident on the CCD camera is important compared to the amount of reflected radiation incident on the CCD camera. Therefore, the scattered radiation causes the radiation on the CCD camera 37 to be unevenly distributed. That is, the amount of contrast increases. When the flow of imprintable material 33 ends, the amount of reflected radiation increases and the amount of scattered radiation decreases, which is seen as a decrease in the contrast of the radiation incident on the CCD camera 37. Thus, if the contrast seen by the CCD camera 37 falls below the threshold, this is interpreted by the controller C to indicate that the flow of imprintable material 33 has ended. Thus, the control device C provides an output signal indicating that the imprint template 31 may be moved to the disengagement position.

  A proportion of the beam of radiation 46 passes through the beam splitter 45 and a proportion of the beam of radiation 48 is reflected by the beam splitter. The unwanted beam is directed to a beam stop (not shown), which is arranged to absorb the beam without reflection. In some cases, an appropriate deflector plate can be used in combination with a deflecting beam splitter to minimize the amount of unwanted beam energy or even substantially eliminate unwanted beams.

  In the described embodiment, for ease of illustration, the beam of radiation 35, 46 is shown as only intersecting a narrow portion of the imprint template 31. In practice, it will be appreciated that the beam of radiation 35, 46 may be sufficiently wide to illuminate the entire imprint template. In some cases, it is desirable that only a part of the imprint template 31 is illuminated and measured. When this is performed, the measured value can be interpreted as representing the entire imprint template 31.

  In the described embodiment, the output of the CCD camera 37 is compared to a threshold value across the surface of the CCD camera. In one arrangement, the output of the CCD camera can be viewed as a set of adjacent areas (eg, nine rectangles of equal size). When doing this, the output of each zone can be compared separately to a threshold. This provides spatial information regarding the location of areas where imprintable material flow is incomplete. This information can be used to improve the imprint process. For example, once the location of an area where imprintable material flow is incomplete is known, additional imprint pressure can be applied to the area.

  The LED 34 is arranged to emit 400 nanometer radiation, but other suitable wavelengths or wavelength widths may be used. In addition, radiation sources other than LEDs may be used. In general, the wavelength used is long enough not to cause the effect of the imprintable material, but short enough to scatter from a small bubble (ie, a bubble that is significantly smaller than the size of the feature on the imprint template). Must-have. A suitable range of radiation wavelengths is 400 to 700 nanometers. In some embodiments, no infrared radiation is used. This is because it is absorbed by the imprintable material or substrate and can cause undesirable heating.

  The described embodiments can be used in the context of conventional imprintable materials such as photopolymerizable materials such as monomer mixtures, initiators and silicon. Usually the monomer may comprise, for example, acrylate or methacrylate. If desired, the refractive index of the imprintable material can be increased by increasing the proportion of silicon in the material. This reduces the refractive index difference between the imprint template 31 and the imprintable material 33, thereby improving operation. The refractive indices of the imprint template 31 and the imprintable material 33 can be adjusted so that they match (ie, are approximately equal). Another way to reduce the refractive index difference between the imprint template 31 and the imprintable material 33 is to create the imprint template from a material having a lower refractive index. One material that can be used to do this is plastic. However, plastics can be damaged over time due to exposure to ultraviolet radiation.

  An anti-reflective coating at the wavelength of the beam of radiation may be provided on the top surface of the imprint template 31 to increase the proportion of the beam of radiation 35, 46 that provides a useful signal.

  While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The description is not intended to limit the invention.

An example of a conventional soft lithography process is shown. 1 illustrates an example of a conventional high temperature lithography process. An example of a conventional UV lithography process is shown. 2 illustrates a two-stage etching process used when forming a pattern in a resist layer using high temperature and UV imprint lithography. 1 schematically illustrates a template and a typical imprintable resist layer deposited on a substrate. 1 schematically depicts an imprint lithography apparatus according to an embodiment of the invention. FIG. 5 schematically shows details of the imprint template and the substrate shown in FIG. 4 and shows a state in which the template is in a disengagement position. FIG. 5 schematically shows details of the imprint template and the substrate shown in FIG. 4 and shows a state in which the template is in an imprint position. FIG. 5 schematically shows details of the imprint template and the substrate shown in FIG. 4 and shows a state in which the template is in an imprint position. 3 schematically depicts an imprint lithography apparatus according to another embodiment of the invention.

Claims (26)

A lithographic apparatus comprising:
A template holder configured to hold an imprint template;
A substrate table arranged and configured to receive a substrate;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A detector configured to detect radiation scattered by the presence of bubbles at the interface between the imprint template and the imprintable material provided on the substrate;
The total amount of radiation incident on the detector is compared to a threshold set at a level indicating that a predetermined amount of the bubble has been removed, and output when the total amount of radiation falls below the threshold. A lithographic apparatus comprising: a controller configured to generate the apparatus. A lithographic apparatus comprising:
A template holder configured to hold an imprint template;
A substrate table arranged and configured to receive a substrate;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A detector configured to detect radiation scattered by the presence of bubbles at the interface between the imprint template and the imprintable material provided on the substrate;
Compare the contrast of the radiation incident on the detector with a threshold set at a level indicating that a predetermined amount of the bubble has been removed, and generate an output when the contrast drops below the threshold A lithographic apparatus comprising: a control device configured as described above . 3. An apparatus according to claim 1 or claim 2 , wherein the detector comprises a charge coupled device (CCD) camera or one or more photodiodes. The apparatus according to claim 1 or 2 , comprising a radiation output configured to direct UV radiation onto the imprintable material at an angle so that UV radiation is incident on the detector. The apparatus according to claim 1 or 2 , wherein the detector is translatable and can be moved away from the imprint template. 3. An apparatus according to claim 1 or claim 2 , wherein the detector is arranged to produce a plurality of outputs, each output representing a different area of the detector. 3. An apparatus according to claim 1 or claim 2 , wherein the radiation output is configured to provide radiation at a wavelength or band of wavelengths in the range of 400 to 700 nanometers. The radiation output unit is arranged and configured to direct radiation to the imprint template so that the radiation is incident on the imprint template at a certain angle, and the angle reflects the radiation reflected from the substrate to the detector. 3. An apparatus according to claim 1 or claim 2 , wherein the apparatus is large enough not to be incident. The apparatus according to claim 1 or 2 , wherein a refractive index of the imprintable material and a reflectance of the imprint template substantially coincide with each other. A lithographic apparatus comprising:
A template holder configured to hold an imprint template;
A substrate table arranged to hold a substrate provided with imprintable material;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A detector configured to detect radiation reflected by the substrate;
The radiation reflected by the substrate provides an indication of whether the flow of the imprintable material into the recess of the imprint template has been terminated;
Comparing the total amount of radiation incident on the detector with a threshold set to a level indicating that the flow of the imprintable material into the recess of the imprint template has been completed, wherein the total amount of radiation is the threshold A lithographic apparatus further comprising a controller configured to generate an output when lowered below . A lithographic apparatus comprising:
A template holder configured to hold an imprint template;
A substrate table arranged to hold a substrate provided with imprintable material;
A radiation output section arranged and configured to illuminate a portion of the imprint template;
A detector configured to detect radiation reflected by the substrate;
The radiation reflected by the substrate provides an indication of whether the flow of the imprintable material into the recess of the imprint template has been terminated;
The contrast of the radiation incident on the detector is compared to a threshold set at a level indicating that the flow of the imprintable material into the recess of the imprint template is complete, and the contrast is below the threshold. A lithographic apparatus further comprising a controller configured to generate an output when reduced to . 12. An apparatus according to claim 10 or claim 11 , wherein the detector comprises a charge coupled device (CCD) camera or one or more photodiodes. 12. An apparatus according to claim 10 or claim 11 , wherein the radiation output is configured to direct the UV radiation onto the imprintable material at an angle so that the UV radiation does not enter the detector. 12. An apparatus according to claim 10 or claim 11 , wherein the detector is translatable and can be moved away from the imprint template. 12. An apparatus according to claim 10 or claim 11 , wherein the detector is arranged to produce a plurality of outputs, each output representing a different area of the detector. 12. An apparatus according to claim 10 or claim 11 , wherein the radiation output is configured to provide radiation at a wavelength or band of wavelengths in the range of 400 to 700 nanometers. 12. An apparatus according to claim 10 or claim 11 , wherein the radiation output is configured to direct radiation onto the imprint template such that the radiation is incident substantially perpendicular to the imprint template. 12. An apparatus according to claim 10 or claim 11 , comprising a beam splitter disposed between the detector and the imprint template. 12. An apparatus according to claim 10 or claim 11 , wherein the refractive index of the imprintable material and the refractive index of the imprint template are substantially coincident. The apparatus according to claim 10 or 11 , wherein an antireflection coating that is effective at a wavelength or a band of wavelengths of radiation emitted from the radiation output unit is provided on an uppermost surface of the imprint template. A method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
Detecting radiation scattered by the presence of bubbles at the interface between the imprint template and the imprintable material on the substrate;
Comparing the total amount of detected radiation with a threshold set at a level indicating that a predetermined amount of the bubble has been removed;
Generating an output when the total amount of radiation falls below the threshold;
A method comprising: A method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
Detecting radiation scattered by the presence of bubbles at the interface between the imprint template and the imprintable material on the substrate;
Comparing the detected radiation contrast with a threshold set at a level indicating that a predetermined amount of the bubble has been removed;
Generating an output when the contrast drops below the threshold;
A method comprising: 23. A method according to claim 21 or claim 22 , wherein the refractive index of the imprintable material and the refractive index of the imprint template are substantially matched. A method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
Detecting radiation reflected by the substrate,
The radiation reflected by the substrate provides an indication of whether the flow of the imprintable material into the recess of the imprint template has been terminated;
Comparing the total amount of radiation detected to a threshold set at a level indicating that the flow of the imprintable material into the depression of the imprint template is complete;
Generating an output when the total amount of radiation has risen above the threshold . A method of imprint lithography,
Pressing the imprint template against a layer of imprintable material on the substrate;
Illuminating part of the imprint template with radiation,
Detecting radiation reflected by the substrate,
The radiation reflected by the substrate provides an indication of whether the flow of the imprintable material into the recess of the imprint template has been terminated;
Comparing the detected radiation contrast to a threshold set at a level indicating that the flow of the imprintable material into the depression of the imprint template is complete;
Generating an output when the contrast drops below the threshold . 26. A method according to claim 24 or claim 25 , wherein the refractive index of the imprintable material substantially matches the refractive index of the imprint template.