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Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-Nanoimprint lithography using diluted PDMS material
Microelectronic Engineering 84 (2007) 904–908 www.elsevier.com/locate/mee
Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-Nanoimprint lithography using diluted PDMS material Namil Koo *, Markus Bender, Ulrich Plachetka, Andreas Fuchs, Thorsten Wahlbrink, Jens Bolten, Heinrich Kurz AMO GmbH, AMICA (Advanced Microelectronic Center Aachen), Otto-Blumenthal Strasse 25, D-52074 Aachen, Germany Available online 25 January 2007
Abstract An improved mold fabrication process that utilizes toluene diluted polydimethylsiloxane (PDMS) as flexible mold material was developed. Various toluene concentrations and their implication on the pattern definition using the Soft UV-Nanoimprint process were analyzed and discussed. Dots with a resolution of 50 nm are well replicated and an excellent imprint homogeneity across a 4 in. wafer with one imprint step only is demonstrated. 2007 Elsevier B.V. All rights reserved. Keywords: Soft UV-Nanoimprint; High resolution; Flexible molds; PDMS mold fabrication; Wafer scale imprint; UV-curable resist
1. Introduction The definition of high resolution features on wafer scale at a reasonable cost model is one of the major issues for the existing as well as for future trends in nanotechnology. UVbased nanoimprint techniques have demonstrated their potential to be an attractive low cost method for high resolution nanostructure definition [1,2]. Up to now, the resolution is not limited by the imprint process or the resist material applied but by the mold fabrication process [3]. We have developed the Soft UV-Nanoimprint technique, featuring transparent flexible molds and low viscose UV-curable resist, which enables the definition of high aspect nanostructures on wafer scale with one imprint step only [4,5]. Here, the fabrication of the flexible molds is carried out by a cast moulding process where an appropriate liquid mold material is deposited on a structured master, followed by thermal curing of the material. Polydimethylsiloxane (PDMS) is used as standard mold mate-
*
Corresponding author. Tel.: +49 241 8867 218; fax: +49 241 8867 571. E-mail address: [email protected] (N. Koo).
0167-9317/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.01.017
rial due to its favourable properties concerning flexibility, UV-transparency and low surface energy. The main drawback of PDMS materials is the high viscosity, which is for Sylgard 184 (Dow Corning) 3900 mPa s. As a consequence, the profiles of nanopatterns on the mold are not completely defined, resulting in a loss of pattern height. Thus, the resolution of the mold fabrication process is limited by an inappropriate material flow for pattern geometries within the sub-100 nm regime [6,7]. To overcome this problem other groups have reported the lowering of the viscosity of h-PDMS [6] using triethylamine, toluene and hexane as solvent and demonstrated the imprinting of 75 nm lines with a pitch of 150 nm [8]. However, due to the fragility of h-PDMS the usage for large scale imprint process and the reproducibility seems to be limited. To realise both requirements, definition of nanostructures and wafer scale imprinting within one step we have investigated an improved mold fabrication process using Sylgard 184 diluted with toluene. For a detailed study the PDMS base material was diluted with five concentrations of toluene before the mixture was deposited onto a 6 in. silicon master featuring micro- and nanometerstructures. After curing the quality of the fabricated molds were inves-
N. Koo et al. / Microelectronic Engineering 84 (2007) 904–908
tigated via SEM- and AFM-analysis of the imprinted resist structures. Furthermore, the results obtained were transferred to perform imprinting of high resolution nanostructures on 4 in. wafer scale. The high degree of dimension stability of the mold fabrication process is demonstrated via SEM-analysis of five different fields distributed over an imprinted 4 in. silicon wafer. The excellent homogeneity of the residual resist thickness gives evidence of the uniformity of both, the mold fabrication as well as the imprint process.
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at the resist surface. The main advantage of this material is that no interaction between PDMS-based molds and the resist occurs even for contact times longer than 10 min. In the experiments presented here AMONIL MMS 4 with an initial film thickness of 180 nm was chosen. The imprint process was carried out on the EV 620 imprint tool from EV Group, Austria. As imprint process condition a pressure of 600 mbar and a contact time of 2 min were defined before UV-polymerization of the resist through the transparent mold was carried out. Subsequently the mold was detached from the cured resist.
2. Experimental 3. Results and discussion For the investigation of the mold fabrication process an appropriate 6 in. silicon master for the cast moulding process had to be fabricated. Here, in a first step five fields with nanopatterns containing various geometries and structure sizes from 500 down to 50 nm as well as alignment marks were defined in hydrogensilsesquioxane (HSQ) resist by an EBPG-5000 TFE E-beam writer. Subsequently, the defined HSQ-patterns were transferred into the silicon master via high anisotropic reactive ion etch process, followed by the HSQ mask removal. The definition of micrometer structures with feature sizes from 100 lm down to 1 lm was carried out via contact lithography using the already defined alignment marks. The pattern transfer was carried out with the identical RIE-process guaranteeing a uniform pattern depth of all structures. After the resist mask removal the master was modified with a thin anti-adhesion layer to lower the surface energy and therefore eases the separation of the PDMS molds. To investigate the influence of different concentrations of toluene on the mold fabrication process the material was prepared as follows. The base material, PDMS (Sylgard 184, Dow Corning) was mixed with its curing agent. The mold fabrication process was investigated with the undiluted PDMS basis, as well as diluted mixtures with four different toluene weight concentrations (10%, 20%, 40%, and 60%). These material mixtures were spin coated at 3000 rpm for 30 s onto the silicon master in order to achieve a thin uniform layer. Subsequently, the mixture was degassed and cured at 120 C for 15 min. To guarantee identical mold thicknesses a metal spacer with 3 mm height was placed onto the master and a thick PDMS cushion layer was cast onto the already cured thin layer. Finally a glass carrier with an appropriate primer was placed onto the material stack and the sandwich cured on a hot plate at 120 C for 30 min. The quality of the fabricated molds was investigated by the SEM- and AFManalysis of imprinted resist structures. The imprint resist used for all investigations was AMONIL, a low viscosity UV-curable imprint resist distributed by AMO GmbH. The resist basis is a mixture of inorganic and organic compounds which is modified with a fluorine additive which migrates to the resist free surface during spin coating processes and creates a asymmetric adhesion behaviour with an high adhesion to the substrate and a lower adhesion
The material flow for the PDMS base material as well as for the diluted material is schematically shown in Fig. 1. The viscosity limits the penetration depth of the material into the master cavities, an effect which depends strongly onto the master geometry. Materials with a lower viscosity enable a higher penetration depth thereby the fabrication of molds with a higher aspect ratio is feasible (position E in Fig. 1). The different mold preparation processes and their influence on pattern generation were investigated by SEM- and AFM-analysis of imprinted resist structures. We chose periodic dot arrays with pillar diameters of 50, 100, 250, 500, and 1000 nm and the period of three times the structure diameter to verify the dependency of the master geometry onto the mold fabrication process. The structures were arranged in 100 · 100 lm2 arrays on the master surface. The master depth for all structures was measured to 110 nm. Deformation effects of the flexible mold can be neglected due to the fabrication of molds with a constant thickness and the usage of identical imprint process conditions. The imprinted resist structures were analysed with regard to the lateral and vertical dimensions. It turns out that the lateral dimensions are nearly the same for all mold preparation variations and master geometries. Even structures in the sub-50 nm range match well with the corresponding master structure. In Fig. 2 exemplary SEM pictures of an imprinted 50 nm dot array using different toluene dilutions are shown. The pictures indicate clearly that the pattern quality depends strongly on the concentration of dilution. To verify this phenomena the height of the imprinted dots was analysed via AFM. In Fig. 3 the height of the
Fig. 1. Influence of the material viscosity on the penetration depth into the master cavities for nanostructures.
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Fig. 2. Exemplary SEM pictures of an 50 nm dots array imprinted with diluted PDMS molds prepared with toluene concentration of 10, 20, 40, and 60 wt%.
imprinted resist pattern in dependency of the toluene concentration for five different feature sizes or rather geometries are displayed. One can clearly see that for structures in the lm-range the height of the fabricated structures corresponds well to the master height, whereas for structures with a smaller size the pattern height and therefore the mold depth are significantly lower than the master height. For mold fabrication without any toluene dilution the resist pattern height decreases from 90 nm for 500 nm dots down to 5 nm for 50 nm dots due to the high viscosity which limits the penetration of the material into the cavi-
Fig. 3. Analysis of the resist pattern height in dependency of the toluene concentration for various master geometries. The master depth for all structures was determined to 110 nm.
ties. The analysis of the pattern height for toluene diluted molds show an improvement for the definition of structures especially for toluene concentrations of 60 wt%. Dots with a diameter of 500 nm and 250 nm show a pattern depth increase of only a few nanometers. Yet, a vast improvement for sub-100 nm features is obvious. For the 50 nm dots the pattern height increases from 10 nm up to 70 nm for a toluene concentration of 10 wt% and 60 wt%, respectively. Higher toluene concentration may lead to further improvement of structure definition but dewetting effects
Fig. 4. Photograph of a patterned 4 in. wafer imprinted with a PDMS mold prepared with 60 wt% toluene diluted PDMS. The 5 · 5 matrix marks the measurement points for the analysis of the residual resist thickness.
N. Koo et al. / Microelectronic Engineering 84 (2007) 904–908
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Fig. 5. SEM-analysis of the five imprinted resist fields distributed over an imprinted 4 in. silicon wafer.
during the spin coating process inhibit the fabrication of such molds. As a consequence of these experiments we can estimate that the lowering of the viscosity of the mold material enables a higher penetration depth which results in a higher pattern height. The pattern height was improved by a factor of 15 for 50 nm structures and a factor of 2 for 100 nm structures. These results were transferred to the imprinting of nanostructures on wafer scale. A 4 in. flexible mold with a toluene concentration of 60 wt% was fabricated using the process described in Section 2 . To assess the mold fabrication process further we imprinted 100 mm silicon wafers and determined the homogeneity and the dimensional stability of the resist pattern. In Fig. 4 a photograph of an
imprinted wafer gives evidence of the homogeneity of the imprint process and therefore the mold fabrication process. The residual resist thickness, an essential indicator for the imprint homogeneity, has been measured with an ellipsometer at 25 data points, spread in a 5 · 5 matrix as schematically shown in Fig. 4. The mean value was estimated to 140 nm with a small deviation of less than 1.4 nm. This excellent uniformity demonstrates the high quality of the imprint process on wafer scale and the suitability using toluene diluted mold material for the fabrication of high resolution flexible molds. The dimension stability of the imprint process on wafer scale was investigated by SEM-analysis of the five fields (F1–F5) containing the nanostructures. Exemplary SEM
Fig. 6. (a) SEM picture of an expemplary 45 nm dot array in Field 3 on the silicon master; (b) SEM picture of the corresponding 43 nm resist dot array imprinted with a 60 wt% toluene diluted PDMS mold.
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pictures of the resist structures are shown in Fig. 5. The good quality of the imprinted resist structures demonstrate the capability of imprinting nanostructures in the 50 nm regime on wafer scale using flexible molds. The dimensional stability of the process is exemplary demonstrated by SEM-analysis of the master and the corresponding resist structure of Field 3 in Fig. 6. Taken additional deformation effects of the flexible mold into account the reduction of the dot diameter from 46.1 nm for the silicon master to 43.1 for the resist structure is nearly neglectable.
Acknowledgments
4. Conclusion
References
The definition of high resolution features on wafer scale at a reasonable cost model is one of the major issues for the existing as well as for future trends in nanotechnology. Soft UV-Nanoimprint technology enables the imprint of nanostructure on wafer scale but the resolution is limited by the fabrication processes of the flexible molds. In this paper we present an improved mold fabrication process using toluene diluted PDMS as mold material. We clearly demonstrated the capability of the technique to define patterns with 50 nm resolution over 4 in. with one imprint step only. The excellent homogeneity on wafer scale as well as the high degree of dimensional stability of both, mold fabrication and the imprint process is demonstrated.
[1] J. Haisma, M. Verheijein, K.v.d. Heuvel, J.v.d. Berg, J. Vac. Sci. Technol. B 14 (1996) 4124. [2] M. Bender, M. Otto, B. Hadam, B. Vratzov, B. Spangenberg, H. Kurz, Microelectron. Eng. 53 (2000) 233. [3] M.D. Austin, W. Zhang, H. Ge, D. Wasserman, S.A. Lyon, S.Y. Chou, Nanotechnology 16 (2005) 1058. [4] U. Plachetka, M. Bender, A. Fuchs, B. Vratzov, T. Glinsner, F. Lindner, H. Kurz, Microelectron. Eng. 73–74 (2004) 167. [5] M. Bender, U. Plachetka, J. Ran, A. Fuchs, B. Vratzov and H. Kurz (AMO GmbH) T. Glinsner and F. Lindner (EV Group), J. Vac. Sci. Technol. B 22 (2004) 3229. [6] H. Schmid, B. Michel, Macromolecules 33 (2000) 3042. [7] Y. Hirai, T. Yoschikawa, M. Morimatsu, M. Nakajima, H. Kawata, Microelectron. Eng. 78–79 (2005) 641. [8] H. Kang, j. Lee, J. Park, H. H Lee, Nanotechnology 17 (1) (2006) 97.
The partial support of the EC-funded project NaPa (Contract No. NMP4-CT-2003-500120) and a Grant (06K1401-00210) from Center for Nanoscale Mechatronics and Manufacturing, one of the 21st Century Frontier Research Programs, which are supported by Ministry of Science and Technology, Korea are gratefully acknowledged. The content of this work is the sole responsibility of the authors.
Improved mold fabrication for the definition of high quality nanopatterns by Soft UV-Nanoimprint lithography using diluted PDMS material Namil Koo *, Markus Bender, Ulrich Plachetka, Andreas Fuchs, Thorsten Wahlbrink, Jens Bolten, Heinrich Kurz AMO GmbH, AMICA (Advanced Microelectronic Center Aachen), Otto-Blumenthal Strasse 25, D-52074 Aachen, Germany Available online 25 January 2007
Abstract An improved mold fabrication process that utilizes toluene diluted polydimethylsiloxane (PDMS) as flexible mold material was developed. Various toluene concentrations and their implication on the pattern definition using the Soft UV-Nanoimprint process were analyzed and discussed. Dots with a resolution of 50 nm are well replicated and an excellent imprint homogeneity across a 4 in. wafer with one imprint step only is demonstrated. 2007 Elsevier B.V. All rights reserved. Keywords: Soft UV-Nanoimprint; High resolution; Flexible molds; PDMS mold fabrication; Wafer scale imprint; UV-curable resist
1. Introduction The definition of high resolution features on wafer scale at a reasonable cost model is one of the major issues for the existing as well as for future trends in nanotechnology. UVbased nanoimprint techniques have demonstrated their potential to be an attractive low cost method for high resolution nanostructure definition [1,2]. Up to now, the resolution is not limited by the imprint process or the resist material applied but by the mold fabrication process [3]. We have developed the Soft UV-Nanoimprint technique, featuring transparent flexible molds and low viscose UV-curable resist, which enables the definition of high aspect nanostructures on wafer scale with one imprint step only [4,5]. Here, the fabrication of the flexible molds is carried out by a cast moulding process where an appropriate liquid mold material is deposited on a structured master, followed by thermal curing of the material. Polydimethylsiloxane (PDMS) is used as standard mold mate-
*
Corresponding author. Tel.: +49 241 8867 218; fax: +49 241 8867 571. E-mail address: [email protected] (N. Koo).
0167-9317/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.01.017
rial due to its favourable properties concerning flexibility, UV-transparency and low surface energy. The main drawback of PDMS materials is the high viscosity, which is for Sylgard 184 (Dow Corning) 3900 mPa s. As a consequence, the profiles of nanopatterns on the mold are not completely defined, resulting in a loss of pattern height. Thus, the resolution of the mold fabrication process is limited by an inappropriate material flow for pattern geometries within the sub-100 nm regime [6,7]. To overcome this problem other groups have reported the lowering of the viscosity of h-PDMS [6] using triethylamine, toluene and hexane as solvent and demonstrated the imprinting of 75 nm lines with a pitch of 150 nm [8]. However, due to the fragility of h-PDMS the usage for large scale imprint process and the reproducibility seems to be limited. To realise both requirements, definition of nanostructures and wafer scale imprinting within one step we have investigated an improved mold fabrication process using Sylgard 184 diluted with toluene. For a detailed study the PDMS base material was diluted with five concentrations of toluene before the mixture was deposited onto a 6 in. silicon master featuring micro- and nanometerstructures. After curing the quality of the fabricated molds were inves-
N. Koo et al. / Microelectronic Engineering 84 (2007) 904–908
tigated via SEM- and AFM-analysis of the imprinted resist structures. Furthermore, the results obtained were transferred to perform imprinting of high resolution nanostructures on 4 in. wafer scale. The high degree of dimension stability of the mold fabrication process is demonstrated via SEM-analysis of five different fields distributed over an imprinted 4 in. silicon wafer. The excellent homogeneity of the residual resist thickness gives evidence of the uniformity of both, the mold fabrication as well as the imprint process.
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at the resist surface. The main advantage of this material is that no interaction between PDMS-based molds and the resist occurs even for contact times longer than 10 min. In the experiments presented here AMONIL MMS 4 with an initial film thickness of 180 nm was chosen. The imprint process was carried out on the EV 620 imprint tool from EV Group, Austria. As imprint process condition a pressure of 600 mbar and a contact time of 2 min were defined before UV-polymerization of the resist through the transparent mold was carried out. Subsequently the mold was detached from the cured resist.
2. Experimental 3. Results and discussion For the investigation of the mold fabrication process an appropriate 6 in. silicon master for the cast moulding process had to be fabricated. Here, in a first step five fields with nanopatterns containing various geometries and structure sizes from 500 down to 50 nm as well as alignment marks were defined in hydrogensilsesquioxane (HSQ) resist by an EBPG-5000 TFE E-beam writer. Subsequently, the defined HSQ-patterns were transferred into the silicon master via high anisotropic reactive ion etch process, followed by the HSQ mask removal. The definition of micrometer structures with feature sizes from 100 lm down to 1 lm was carried out via contact lithography using the already defined alignment marks. The pattern transfer was carried out with the identical RIE-process guaranteeing a uniform pattern depth of all structures. After the resist mask removal the master was modified with a thin anti-adhesion layer to lower the surface energy and therefore eases the separation of the PDMS molds. To investigate the influence of different concentrations of toluene on the mold fabrication process the material was prepared as follows. The base material, PDMS (Sylgard 184, Dow Corning) was mixed with its curing agent. The mold fabrication process was investigated with the undiluted PDMS basis, as well as diluted mixtures with four different toluene weight concentrations (10%, 20%, 40%, and 60%). These material mixtures were spin coated at 3000 rpm for 30 s onto the silicon master in order to achieve a thin uniform layer. Subsequently, the mixture was degassed and cured at 120 C for 15 min. To guarantee identical mold thicknesses a metal spacer with 3 mm height was placed onto the master and a thick PDMS cushion layer was cast onto the already cured thin layer. Finally a glass carrier with an appropriate primer was placed onto the material stack and the sandwich cured on a hot plate at 120 C for 30 min. The quality of the fabricated molds was investigated by the SEM- and AFManalysis of imprinted resist structures. The imprint resist used for all investigations was AMONIL, a low viscosity UV-curable imprint resist distributed by AMO GmbH. The resist basis is a mixture of inorganic and organic compounds which is modified with a fluorine additive which migrates to the resist free surface during spin coating processes and creates a asymmetric adhesion behaviour with an high adhesion to the substrate and a lower adhesion
The material flow for the PDMS base material as well as for the diluted material is schematically shown in Fig. 1. The viscosity limits the penetration depth of the material into the master cavities, an effect which depends strongly onto the master geometry. Materials with a lower viscosity enable a higher penetration depth thereby the fabrication of molds with a higher aspect ratio is feasible (position E in Fig. 1). The different mold preparation processes and their influence on pattern generation were investigated by SEM- and AFM-analysis of imprinted resist structures. We chose periodic dot arrays with pillar diameters of 50, 100, 250, 500, and 1000 nm and the period of three times the structure diameter to verify the dependency of the master geometry onto the mold fabrication process. The structures were arranged in 100 · 100 lm2 arrays on the master surface. The master depth for all structures was measured to 110 nm. Deformation effects of the flexible mold can be neglected due to the fabrication of molds with a constant thickness and the usage of identical imprint process conditions. The imprinted resist structures were analysed with regard to the lateral and vertical dimensions. It turns out that the lateral dimensions are nearly the same for all mold preparation variations and master geometries. Even structures in the sub-50 nm range match well with the corresponding master structure. In Fig. 2 exemplary SEM pictures of an imprinted 50 nm dot array using different toluene dilutions are shown. The pictures indicate clearly that the pattern quality depends strongly on the concentration of dilution. To verify this phenomena the height of the imprinted dots was analysed via AFM. In Fig. 3 the height of the
Fig. 1. Influence of the material viscosity on the penetration depth into the master cavities for nanostructures.
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Fig. 2. Exemplary SEM pictures of an 50 nm dots array imprinted with diluted PDMS molds prepared with toluene concentration of 10, 20, 40, and 60 wt%.
imprinted resist pattern in dependency of the toluene concentration for five different feature sizes or rather geometries are displayed. One can clearly see that for structures in the lm-range the height of the fabricated structures corresponds well to the master height, whereas for structures with a smaller size the pattern height and therefore the mold depth are significantly lower than the master height. For mold fabrication without any toluene dilution the resist pattern height decreases from 90 nm for 500 nm dots down to 5 nm for 50 nm dots due to the high viscosity which limits the penetration of the material into the cavi-
Fig. 3. Analysis of the resist pattern height in dependency of the toluene concentration for various master geometries. The master depth for all structures was determined to 110 nm.
ties. The analysis of the pattern height for toluene diluted molds show an improvement for the definition of structures especially for toluene concentrations of 60 wt%. Dots with a diameter of 500 nm and 250 nm show a pattern depth increase of only a few nanometers. Yet, a vast improvement for sub-100 nm features is obvious. For the 50 nm dots the pattern height increases from 10 nm up to 70 nm for a toluene concentration of 10 wt% and 60 wt%, respectively. Higher toluene concentration may lead to further improvement of structure definition but dewetting effects
Fig. 4. Photograph of a patterned 4 in. wafer imprinted with a PDMS mold prepared with 60 wt% toluene diluted PDMS. The 5 · 5 matrix marks the measurement points for the analysis of the residual resist thickness.
N. Koo et al. / Microelectronic Engineering 84 (2007) 904–908
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Fig. 5. SEM-analysis of the five imprinted resist fields distributed over an imprinted 4 in. silicon wafer.
during the spin coating process inhibit the fabrication of such molds. As a consequence of these experiments we can estimate that the lowering of the viscosity of the mold material enables a higher penetration depth which results in a higher pattern height. The pattern height was improved by a factor of 15 for 50 nm structures and a factor of 2 for 100 nm structures. These results were transferred to the imprinting of nanostructures on wafer scale. A 4 in. flexible mold with a toluene concentration of 60 wt% was fabricated using the process described in Section 2 . To assess the mold fabrication process further we imprinted 100 mm silicon wafers and determined the homogeneity and the dimensional stability of the resist pattern. In Fig. 4 a photograph of an
imprinted wafer gives evidence of the homogeneity of the imprint process and therefore the mold fabrication process. The residual resist thickness, an essential indicator for the imprint homogeneity, has been measured with an ellipsometer at 25 data points, spread in a 5 · 5 matrix as schematically shown in Fig. 4. The mean value was estimated to 140 nm with a small deviation of less than 1.4 nm. This excellent uniformity demonstrates the high quality of the imprint process on wafer scale and the suitability using toluene diluted mold material for the fabrication of high resolution flexible molds. The dimension stability of the imprint process on wafer scale was investigated by SEM-analysis of the five fields (F1–F5) containing the nanostructures. Exemplary SEM
Fig. 6. (a) SEM picture of an expemplary 45 nm dot array in Field 3 on the silicon master; (b) SEM picture of the corresponding 43 nm resist dot array imprinted with a 60 wt% toluene diluted PDMS mold.
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pictures of the resist structures are shown in Fig. 5. The good quality of the imprinted resist structures demonstrate the capability of imprinting nanostructures in the 50 nm regime on wafer scale using flexible molds. The dimensional stability of the process is exemplary demonstrated by SEM-analysis of the master and the corresponding resist structure of Field 3 in Fig. 6. Taken additional deformation effects of the flexible mold into account the reduction of the dot diameter from 46.1 nm for the silicon master to 43.1 for the resist structure is nearly neglectable.
Acknowledgments
4. Conclusion
References
The definition of high resolution features on wafer scale at a reasonable cost model is one of the major issues for the existing as well as for future trends in nanotechnology. Soft UV-Nanoimprint technology enables the imprint of nanostructure on wafer scale but the resolution is limited by the fabrication processes of the flexible molds. In this paper we present an improved mold fabrication process using toluene diluted PDMS as mold material. We clearly demonstrated the capability of the technique to define patterns with 50 nm resolution over 4 in. with one imprint step only. The excellent homogeneity on wafer scale as well as the high degree of dimensional stability of both, mold fabrication and the imprint process is demonstrated.
[1] J. Haisma, M. Verheijein, K.v.d. Heuvel, J.v.d. Berg, J. Vac. Sci. Technol. B 14 (1996) 4124. [2] M. Bender, M. Otto, B. Hadam, B. Vratzov, B. Spangenberg, H. Kurz, Microelectron. Eng. 53 (2000) 233. [3] M.D. Austin, W. Zhang, H. Ge, D. Wasserman, S.A. Lyon, S.Y. Chou, Nanotechnology 16 (2005) 1058. [4] U. Plachetka, M. Bender, A. Fuchs, B. Vratzov, T. Glinsner, F. Lindner, H. Kurz, Microelectron. Eng. 73–74 (2004) 167. [5] M. Bender, U. Plachetka, J. Ran, A. Fuchs, B. Vratzov and H. Kurz (AMO GmbH) T. Glinsner and F. Lindner (EV Group), J. Vac. Sci. Technol. B 22 (2004) 3229. [6] H. Schmid, B. Michel, Macromolecules 33 (2000) 3042. [7] Y. Hirai, T. Yoschikawa, M. Morimatsu, M. Nakajima, H. Kawata, Microelectron. Eng. 78–79 (2005) 641. [8] H. Kang, j. Lee, J. Park, H. H Lee, Nanotechnology 17 (1) (2006) 97.
The partial support of the EC-funded project NaPa (Contract No. NMP4-CT-2003-500120) and a Grant (06K1401-00210) from Center for Nanoscale Mechatronics and Manufacturing, one of the 21st Century Frontier Research Programs, which are supported by Ministry of Science and Technology, Korea are gratefully acknowledged. The content of this work is the sole responsibility of the authors.