# Patent

## Title
Method for detecting a particle in a nanoimprint lithography system

## Abstract

A method for detecting a particle between a nanoimprint mold assembly and a substrate in a nanoimprint lithography system.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority to U.S. Provisional Application No. 60/793,857, filed on Apr. 21, 2006, entitled “In-Situ Particle Detection Methods for Imprint Lithography Tools,” which is incorporated herein by reference.


BACKGROUND INFORMATION
Nano-fabrication involves the fabrication of very small structures, e.g., having features on the order of nanometers or smaller. One area in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like.
An exemplary nano-fabrication technique is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as United States patent application publication 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; United States patent application publication 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; and U.S. Pat. No. 6,936,194, entitled “Functional Patterning Material for Imprint Lithography Processes,” all of which are assigned to the assignee of the present invention.
The imprint lithography technique disclosed in each of the aforementioned United States patent application publications and United States patent includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be positioned upon a stage to obtain a desired position to facilitate patterning thereof. To that end, a mold is employed spaced-apart from the substrate with a formable liquid present between the mold and the substrate. The liquid is solidified to form a patterned layer that has a pattern recorded therein that is conforming to a shape of the surface of the mold in contact with the liquid. The mold is then separated from the patterned layer such that the mold and the substrate are spaced-apart. The substrate and the patterned layer are then subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the patterned layer.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified side view of a lithographic system having a mold spaced-apart from a substrate;
FIG. 2 is a top down view of the substrate shown in FIG. 1, having a patterned layer thereon;
FIG. 3 is a side view of the lithographic system shown in FIG. 1, with a particle positioned between the mold and the substrate;
FIG. 4 is a side view of the substrate and patterned layer both shown in FIG. 2, the patterned layer having a conformal layer positioned thereon with a particle;
FIG. 5 is a top down view of the conformal layer and the particle, both shown in FIG. 4;
FIG. 6 is a flow chart of a method of detecting a particle in a nanoimprint lithography system, in a first embodiment;
FIG. 7 is a side view of the lithographic system shown in FIG. 1, the substrate and the mold being spaced-apart a distance;
FIG. 8 is a flow chart of a method of detecting a particle in a nanoimprint lithography system, in a second embodiment;
FIG. 9 is a side view of the lithographic system shown in FIG. 1, with a force being applied to the template to separate the mold from the substrate;
FIG. 10 is a flow chart of a method of detecting a particle in a nanoimprint lithography system, in a third embodiment;
FIG. 11 is a simplified side view of the lithographic system shown in FIG. 1, with the system further comprising a detection system in accordance with a further embodiment of the present invention;
FIG. 12 is a flow chart of a method of detecting a particle in a nanoimprint lithography system, in a fourth embodiment; and
FIG. 13 is a simplified side view of the lithographic system shown in FIG. 1, with the system further comprising a detection system in accordance with a further embodiment of the present invention.



DETAILED DESCRIPTION
Referring to FIG. 1, a system 10 to form a relief pattern on a substrate 12 is shown. In an example, substrate 12 may be a double sided polished 200 mm silicon wafer having thickness variations less than 500 nm. Substrate 12 may be coupled to a substrate chuck 14, described further below. Substrate 12 and substrate chuck 14 may be supported upon a stage 16. Further, stage 16, substrate 12, and substrate chuck 14 may be positioned on a base (not shown). Stage 16 may provide motion about the x and y axes.
Spaced-apart from substrate 12 is a template 18 having a mesa 20 extending therefrom towards substrate 12 with a patterning surface 22 thereon. Further, mesa 20 may be referred to as a mold 20. Mesa 20 may also be referred to as a nanoimprint mold 20. In a further embodiment, template 18 may be substantially absent of mold 20. Template 18 and/or mold 20 may be formed from such materials including, but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, and hardened sapphire. As shown, patterning surface 22 comprises features defined by a plurality of spaced-apart recesses 24 and protrusions 26. However, in a further embodiment, patterning surface 22 may be substantially smooth and/or planar. Patterning surface 22 may define an original pattern that forms the basis of a pattern to be formed on substrate 12. Template 18 may be coupled to a template chuck 28, template chuck 28 being any chuck including, but not limited to, vacuum, pin-type, groove-type, or electromagnetic, as described in U.S. Pat. No. 6,873,087 entitled “High-Precision Orientation Alignment and Gap Control Stages for Imprint Lithography Processes” which is incorporated herein by reference. Further, template chuck 28 may be coupled to an imprint head 30 to facilitate movement of template 18, and therefore, mold 20.
System 10 further comprises a fluid dispense system 32. Fluid dispense system 32 may be in fluid communication with substrate 12 so as to deposit polymeric material 34 thereon. System 10 may comprise any number of fluid dispensers, and fluid dispense system 32 may comprise a plurality of dispensing units therein. Polymeric material 34 may be positioned upon substrate 12 using any known technique, e.g., drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and the like. Typically, polymeric material 34 is disposed upon substrate 12 before the desired volume is defined between mold 20 and substrate 12. However, polymeric material 34 may fill the volume after the desired volume has been obtained.
Referring to FIGS. 1 and 2, system 10 further comprises a source 38 of energy 40 coupled to direct energy 40 along a path 42. Imprint head 30 and stage 16 are configured to arrange mold 20 and substrate 12, respectively, to be in superimposition and disposed in path 42. Either imprint head 30, stage 16, or both vary a distance between mold 20 and substrate 12 to define a desired volume therebetween that is filled by polymeric material 34. In an example, imprint head 30 may apply a force of less than 10 Newtons to template 18 such that mold 20 contacts polymeric material 34. After the desired volume is filled with polymeric material 34, source 38 produces energy 40, e.g., broadband ultraviolet radiation that causes polymeric material 34 to solidify and/or cross-link conforming to the shape of a surface 44 of substrate 12 and patterning surface 22, defining a patterned layer 46 on substrate 12. Patterned layer 46 may comprise a residual layer 48 and a plurality of features shown as protrusions 50 and recessions 52, with protrusions 50 having a thickness t1 and residual layer having a thickness t2, with thickness t1 being greater than thickness t2. System 10 may be regulated by a processor 54 that is in data communication with stage 16, imprint head 30, fluid dispense system 32, and source 38, operating on a computer readable program stored in memory 56.
Referring to FIGS. 1-4, during the aforementioned patterning process, a particle 60 may become positioned between substrate 12 and mold 20, which may be undesirable. In a first example, particle 60 may be positioned upon surface 44 of substrate 12; however, in a further example, particle 60 may be positioned within patterned layer 46. In a further embodiment, a plurality of particles 60 may be positioned between substrate 12 and mold 20. Particle 60 may have a thickness t3, with thickness t3 being greater than thickness t1 and thickness t2. In an example, thickness t3 may be in a range of 25 nm to 2 μm. To that end, the presence of particle 60 between substrate 12 and mold 20 frustrates control of the thickness of subsequently disposed layers upon substrate 12. This is shown by formation of multi-layered structure 61 resulting from the deposition of a conformal layer 63 upon patterned layer 46. In the present example, conformal layer 63 may be formed employing spin-on techniques as discussed in U.S. Pat. No. 7,122,079, entitled “Composition for an Etching Mask Comprising a Silicon-Containing Material,” which is incorporated herein by reference. The presence of particle 60 reduces the planarity of a surface 65 of conformal layer 63. The presence of particle 60 may result in deleterious artifacts, inter alia, thickness variations in conformal layer 63. These deleterious artifacts may be present as protrusions in surface 65 and may be referred to as comets 67, shown in FIG. 5. As a result, surface 65 is provided with a roughness that frustrates patterning of features thereon. Similar roughness problems in subsequently formed surfaces arise in the presence of artifacts generated by particle 60. To that end, a method of detecting a presence of particle 60 between substrate 12 and mold 20 is described further below.
The combined height variations of substrate 12 and substrate chuck 14 typically have low spatial frequencies and low amplitudes. Height variations on double side polished 200 mm silicon wafers are much less than 500 nm. Imprint head 38 (shown in FIG. 1) in an imprinter typically has a very fine resolution and an accuracy that is equal to or better than the absolute height variations present in substrate 12 and substrate chuck 14. The imprint process brings template 18 into liquid contact with a very small applied force. This force is usually less than 10 N. In the event that a particle is between template 18 and substrate 12 during the imprint, the low-force nature of the imprint process leaves template 18 resting on the particle. The resulting imprint position, as measure by imprint head 38, is then smaller than what would be expected because template 18 has not moved down as far as was expected. The delta between the actual imprint position and the expected position can be used as a discriminator to determine whether a particle is present.
If only large particle detection is required (e.g., greater than 10 microns), then a simple comparison between the actual and expected values can be sufficient. However, if sensitivity to smaller particles is required, then an adaptive algorithm provides better results. There are several sources of noise in the system such as encoder accuracy, thermal drift, wafer height and wafer chuck height variations. These noise sources typically vary slowly with time or slowly with location of substrate 12. An adaptive filter, such as a Kalman filter, can be tuned for rapid convergence to a desired sensitivity level while also tracking low frequency changes to a mean value. The ability to track these changes results in a detection system that is capable of sensing smaller particles. As the tool imprints, position signals of imprint head 38 are used to update the filter which gradually converges to a tighter error bound. Simultaneously, the predicted value adapts to the low frequency curvature on substrate chuck 14.
Referring to FIGS. 3 and 6, a method of detecting particle 60 between substrate 12 and mold 20 is shown. This process is applied after fluid has spread but prior to UV exposure. More specifically, at step 100, as mentioned above, polymeric material 34 may be positioned on substrate 12. In a further embodiment, polymeric material 34 may be positioned on mold 20. At step 102, a desired spatial relationship may be obtained between mold 20 and substrate 12 such that polymeric material 34 may fill the desired volume between mold 20 and substrate 12. More specifically, imprint head 30 and stage 16 may arrange mold 20 and substrate 12, respectively, such that mold 20 and substrate 12 are spaced-apart a distance d, with the distance having an expected value stored in memory 56.
Referring to FIGS. 6 and 7, at step 104, the distance d defined between mold 20 and substrate 12 may be measured, defining a measured value of the distance d. The distance d may be measured employing encoder signals produced by imprint head 30 and transmitted to processor 54, operating on a computer readable program stored in memory 56.
At step 106, a magnitude of the expected value and the measured value of the distance d may be compared by processor 54, operating on a computer readable program stored in memory 56, defining a difference 62 stored in memory 56. Difference 62 may be determined by processor 54 employing a signal processing algorithm, the algorithm being a 1D filter and either adaptive or non-adaptive. At step 108, based on a magnitude of difference 62, processor 54 may determine if particle 60 is present between substrate 12 and mold 20. To that end, at step 110, particle 60 may be detected. In an example, were particle 60 positioned between substrate 12 and mold 20, the measured value of distance d may be greater than the expected value of distance d. However, if there is not a particle 60 detected, at step 112, polymeric material 34 positioned on substrate 12 may be solidified and/or cross-linked, defining patterned layer 46, and mold 20 may be separated from patterned layer 46.
Further, thickness t3 of particle 60 may be less than 50 nm. However, there may be a plurality of sources of noise within system 10 to frustrate detection of particle 60 having a thickness of 50 nm. Such sources of noise include, but are not limited to, encoder signal accuracy, thermal drift of system 10, thickness variations of substrate 12, and thickness variations of substrate chuck 14. To that end, an adaptive filter, such as a Kalman filter may be employed. The Kalman filter may be tuned for rapid convergence to a desired sensitivity level while concurrently tracking low frequency changes to a mean value.
Referring to FIGS. 8 and 9, a further embodiment of detecting particle 60 between substrate 12 and mold 20 is shown. More specifically, at step 200, as mentioned above, polymeric material 34 may be positioned on substrate 12. In a further embodiment, polymeric material 34 may be positioned on mold 20. At step 202, a desired spatial relationship may be obtained between mold 20 and substrate 12 such that polymeric material 34 may fill the desired volume between mold 20 and substrate 12. At step 204, polymeric material 34 positioned on substrate 12 may be solidified and/or cross-linked, defining patterned layer 46.
At step 206, mold 20 may be separated from patterned layer 46 on substrate 12. More specifically, separation of mold 20 from patterned layer 46 is achieved by application of a force F to template 18 by imprint head 30, with the force F having an expected value stored in memory 56. At step 208, the force F applied to template 18 may be measured, with the force having a measured value. The force F may be measured from encoder signals produced by imprint head 30 and transmitted to processor 54, operating on a computer readable program stored in memory 56. Further, the force F may depend upon, inter alia, an area of mold 20.
At step 210, a magnitude of the expected value and the measured value of the force F may be may be compared by processor 54, operating on a computer readable program stored in memory 56, defining a difference 64 stored in memory 56. Difference 64 may be determined by processor 54 employing a thresholding function algorithm, the algorithm being either adaptive or non-adaptive. To that end, at step 212, based on a magnitude of difference 62, processor 54 may determine if particle 60 is present between substrate 12 and mold 20. In an example, were particle 60 positioned between substrate 12 and mold 20, the measured value of force F may be less than the expected value of force F. To that end, at step 214, particle 60 may be detected. However, if there is not a particle 60 detected, at step 216, the aforementioned patterning of substrate 12 has been completed.
Referring to FIGS. 10 and 11, a third embodiment of detecting particle 60 between substrate 12 and mold 20 is shown, and more specifically, color variations of polymeric material 34 may be employed to detect particle 60. To that end, system 10 may further comprise a detection system that includes a CCD sensor 70 and wave shaping optics 72. The detection system is configured with wave shaping optics 72 positioned between CCD sensor 70 and a mirror 74. CCD sensor 70 and wave shaping optics 72 may be in data communication with processor 54, operating on a computer readable program stored in memory 56, to control an operation thereof.
At step 300, as mentioned above, polymeric material 34 may be positioned on substrate 12. In a further embodiment, polymeric material 34 may be positioned on mold 20. At step 302, a desired spatial relationship may be obtained between mold 20 and substrate 12 such that polymeric material 34 may fill the desired volume between mold 20 and substrate 12.
At step 304, an image of polymeric material 34 may be sensed by CCD sensor 70. At step 306, CCD sensor 70 may produce data corresponding to the image of polymeric material 34. Processor 54 receives the data, and processes differences in color of polymeric material 34, defining a variation 66 stored in memory 56. At step 308, based on variation 66, processor 54 may determine if particle 60 is present between substrate 12 and mold 20. To that end, at step 310, particle 60 may be detected. However, if there is not a particle 60 detected, at step 112, polymeric material 34 positioned on substrate 12 may be solidified and/or cross-linked, defining patterned layer 46, and mold 20 may be separated from patterned layer 46.
In the above mentioned embodiment, a spatial location 55 of variation 64 with respect to substrate 12 may be determined by processor 54, and stored in memory 56. Further, after patterning two or more of substrates 12 in the above-mentioned process, processor 54 may query memory 56 to locate possible particle 60 in spatial location 55. To that end, variations 64 at location 55 may indicate contamination of substrate 12.
Referring to FIGS. 12 and 13, in fourth embodiment, a method of detecting particle 60 between substrate 12 and substrate chuck 14 is shown. More specifically, at step 400, as mentioned above, polymeric material 34 may be positioned on substrate 12. In a further embodiment, polymeric material 34 may be positioned on mold 20. At step 402, a desired spatial relationship may be obtained between mold 20 and substrate 12 such that polymeric material 34 may fill the desired volume between mold 20 and substrate 12. At step 404, polymeric material 34 positioned on substrate 12 may be solidified and/or cross-linked, defining patterned layer 46.
At step 406, an image of polymeric material 34 may be sensed by CCD sensor 70. At step 408, CCD sensor 70 may produce data corresponding to the image of polymeric material 34. Processor 54 receives the data, and processes a difference in color of polymeric material 34, defining a variation 68 stored in memory 56. At step 410, based on variation 68, processor 54 may determined if particle 60 is present between substrate 12 and mold 20. To that end, at step 412, particle 60 may be detected. However, if there is not a particle 60 detected, at step 414, the aforementioned patterning of substrate 12 has been completed.
In the above mentioned embodiment, a spatial location 57 of variation 68 with respect to substrate 12 may be determined by processor 54, and stored in memory 56. Further, after patterning two or more of substrates 12 in the above-mentioned process, processor 54 may query memory 56 to locate possible particle 60 in spatial locations 57. To that end, variation 68 at location 57 may indicate contamination of substrate chuck 14.
Further, any combination of the above mentioned embodiments may be employed concurrently.
The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

## Claims

1. A method for detecting a particle between a nanoimprint mold assembly and a substrate in a nanoimprint lithography system, said method comprising:
positioning said nanoimprint mold assembly and said substrate in a desired spatial relationship using an imprint head and a stage, said nanoimprint mold assembly and said substrate being spaced-apart to define a desired distance and desired volume therebetween, said distance having an expected value and said volume substantially filled by polymerizable material;
measuring said distance between said nanoimprint mold assembly and said substrate employing encoder signals produced by said imprint head, defining a measured value of said distance, wherein measuring occurs after fluid has filled the volume between said nanoimprint mold assembly and said substrate;
comparing said measured value of said distance with said expected value of said distance, defining a difference between said measured value and said expected value; and
determining a presence of said particle between said nanoimprint mold assembly and said substrate based on said difference.

2. The method as recited in claim 1 wherein said measured value of said distance is greater than said expected value of said distance.

3. The method as recited in claim 1 further including the step of positioning a nanoimprint material between said mold and said substrate.

4. The method as recited in claim 3 further including the step of impinging actinic radiation upon said nanoimprint material.

5. The method as recited in claim 4 wherein comparing occurs prior to impinging said actinic radiation.

6. The method as recited in claim 1 wherein the step of comparing further comprises comparing said measured value of said distance with said expected value of said distance employing an algorithm.

7. The method as recited in claim 1 wherein the step of comparing further comprises comparing said measured value of said distance with said expected value of said distance employing a filter.

8. The method as recited in claim 1 wherein the step of comparing further comprises comparing said measured value of said distance with said expected value of said distance employing an adaptive filter.

9. The method as recited in claim 1 further including the step of filtering noise in said nanoimprint lithography system.

10. The method as recited in claim 9 wherein filtering further comprises applying a Kalman filter.

11. The method as recited in claim 9 wherein filtering further comprises applying an adaptive filter.