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Novel transparent hybrid polymer working stamp for UV-imprinting
Microelectronic Engineering 86 (2009) 697–699
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Novel transparent hybrid polymer working stamp for UV-imprinting Anna Klukowska a,*, Anett Kolander a, Iris Bergmair b, Michael Mühlberger b, Hannes Leichtfried b, Freimut Reuther a, Gabi Grützner a, Rainer Schöftner b a b
Micro Resist Technology GmbH, Koepenicker Str. 325, 12555 Berlin, Germany Profactor GmbH, Im Stadtgut A2, 4407 Steyr, Austria
a r t i c l e
i n f o
Article history: Received 29 September 2008 Received in revised form 22 December 2008 Accepted 23 December 2008 Available online 17 January 2009 Keywords: Nanoimprint Nano-stamp Hybrid polymer Working stamps durability
a b s t r a c t Transparent stamps are an integral and crucial part of the UV-imprinting. Time consuming fabrication of quartz stamps increases the price of the technology. In the presented work a thermally stable transparent imprint stamp made of a novel hybrid polymer system is demonstrated. As a low-cost and highly efficient alternative the hybrid polymer stamp contributes to the acceptance and application of the nanoimprint technology. By using the UV-patternable inorganic–organic hybrid polymer quartz stamps might become superfluous in the UV-imprint process entirely, because transparent working stamps can be manufactured also with use of opaque silicon master stamps. Ó 2009 Elsevier B.V. All rights reserved.
1. Motivation Thermal and UV-based imprint techniques have gained importance in the electronics and optics industrial sectors within the last decade. For UV-based nanoimprint processes stamps with a high UV-transparency are essential, since the UV-range is the characteristic wavelength range for the majority of photo initiators used in photoresist materials. The common quartz stamp is still a significant cost factor among the consumables for the users of the UV-imprint techniques. Another known material for transparent imprint stamps is poly(dimethylsiloxan) (PDMS), the softness of which is a drawback for imprinting of nano-structures [1]. A material with well-tailored properties is needed as a successful nanoimprint stamp material. Easy material processing and high pattern transfer fidelity regarding the master stamp are crucial factors for nanoimprinting. The working stamp shall be of reasonable durability. Only an excellent pattern transfer from the working stamp on the nano-scale can be accepted for the application of nanoimprint technique. We have focused our research on well-established inorganic–organic hybrid polymers. The sol–gel process derived materials are of high thermal and chemical stability and exhibit excellent optical properties due to the presence of inorganic domains within the network. The organic part of the network, often bearing various func-
* Corresponding author. E-mail address: [email protected] (A. Klukowska). 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.12.088
tional groups, contributes to the easy handling, e.g., UVpatternability, and gives multiple possibilities for variation of the material’s physical properties, e.g., surface polarity. The materials have already found application in a variety of industry branches [2]. 2. Experimental results 2.1. Properties of the stamp material A great challenge in the UV-imprint process is the high transparency of the stamp material in the UV-range, which is the characteristic wavelength range for the majority of photo initiators used in photoresist materials. The novel stamp material system based on a UV-curable inorganic–organic hybrid polymer – Ormostamp – offers high UV-transparency even after thermal exposure at 270 °C. In this case 90% transparency remains at 350 nm (Fig. 1). The data was gathered for a 200 lm layer on a glass substrate. An excellent thermal stability was also confirmed in differential thermal analysis and thermal gravimetry analysis (DTA–TG) measurements (DTA–TG) (Fig. 2). The method shows changes in the material composition (by weight detection) during a well-defined heating process. First signs of thermal degradation can be detected for Ormostamp at approximately 300–320 °C with a heating rate of 2 K/min. Both the transparency and the thermal stability are principal material properties for the planned application in nanoimprint processes. The mechanical properties of Ormostamp are defined by its chemical composition. As hybrid polymer it contains –SiOSi–
698
A. Klukowska et al. / Microelectronic Engineering 86 (2009) 697–699
100
Table 1 Physical properties of Ormostamp.
a b c
80
T [%]
60
Liquid Viscosity Refractive index at 25 °C and 589 nm
0.75 Pa s 1.526
Solid Modulus of elasticity Hardness
0.650 GPa 0.036 GPa
40
a) after fabrication o b) after 5 min at 270 C o c) after 10 min at 270 C
20
glass/quartz adhesion promoter
A. Ormostamp deposition
Ormostamp
0 300
400
500 λ [nm]
600
master stamp
700 UV-light
Fig. 1. Ormostamp transparency, (a) UV-cured and hard baked, (b) after 5 min and (c) after 10 min at 270 °C.
B. Ormostamp processing
domains (network) connected covalently to organic backbone. The radical driven polymerisation of the active organic groups will occur under UV exposure. The elasticity and hardness of the stamp material are critical factors for the transfer of nano-structures. The materials used up to now for fabrication of nanoimprint working stamps were too soft, as PDMS [1], or too brittle, as older generation hybrid polymers, to give an acceptable performance. The values of Ormocomp modulus of elasticity and hardness are sufficient for patterning both nano- and micro-structures (Table 1) without any cracks and fractures (too brittle material) or deformations (too soft material).
C. Anti sticking layer deposition anti sticking layer
ready-to-use working stamp
2.2. Stamp fabrication
Fig. 3. Stamp fabrication process.
Ormostamp working stamps can be fabricated in a one-step or a two-steps process, which was shown previously for different hybrid polymers in [3]. The stamps may be processed on a glass or quartz substrate (transparent) or without a substrate. In our present work we have focused on the replication of stamps with a transparent substrate in a one-step process from a silicon master stamp (Fig. 3). The common size of the working stamps was 1.5 cm 1.5 cm. Also bigger stamps up to 4 in. have been fabricated. The relatively low viscosity of Ormostamp is important for efficient filling of the master stamp cavities and allows various deposition techniques, which make the material handling and further processing easier (Table 1).
Table 2 Roughness (root-mean-squared) of Ormostamp surface during the imprint process, determined by AFM measurements on the same top area of the stamp. Imprints
Roughness rms (Å)
1 10 19 29
25.75 25.8 24.9 33.23
The process of stamp fabrication is shown in Fig. 3. After dispensing (Fig. 3 A) of a certain amount of Ormostamp on a master
Fig. 2. Thermal stability of Ormostamp UV-cured and hard baked.
A. Klukowska et al. / Microelectronic Engineering 86 (2009) 697–699
a) 100 nm lines/ 200 nm spaces imprinted in mrUVCur06
b) 200 nm lines/ 100 nm spaces imprinted in mr-NIL 6000
699
c) 51st imprint in mrUVCur06
Fig. 4. Examples of UV and thermal imprints with an Ormostamp working stamp in mr-UVCur06 and mr-NIL 6000.
stamp, the material drop is covered with a clean, transparent substrate (Fig. 3 B). An anti-sticking treatment from a gas phase (as described below) was applied to the master stamp prior to Ormostamp deposition. The glass or quartz plate should be coated with adhesion promoter Ormoprime08 (micro resist technology GmbH). The transferred structures are stable after Ormostamp UV-curing (broadband exposure 1000 mJ/cm2 measured at 365 nm) and final thermal post exposure treatment at 130 °C for 30 min. An anti-sticking treatment (Fig. 3C) with F13TCS from the gas phase [4] is carried out at 150 °C. The stability of the readyto-use working stamps under the considerable thermal stress during the anti-sticking layer deposition proves the integrity of the stamp stock. Furthermore, an experimental liquid anti-sticking treatment (Profactor GmbH) could successfully be applied to the stamp surface. The liquid anti-adhesive agent was spin coated on the stamp surface. The performance of both anti-sticking layers was comparable. Adhesion promoter and anti-sticking layer have a direct influence on the durability of the working stamps. The life time of the working stamp could be increased by use of an adhesion promoter. Besides good adhesion of the stamp material to the glass substrate (GT 0, DIN EN ISO 2409), an easy release of the resist material from the working stamp after the imprint process is guaranteed after anti-sticking treatment. Low surface roughness of Ormostamp, which does not change during the UV-imprint process (Table 2), has a positive impact on the pattern transfer fidelity. The pattern transfer fidelity during the Ormostamp stamp fabrication is highly satisfying and was proven in UV and thermal nanoimprinting tests with different polymers.
needed for patterning process of mr-NIL6000 (110 °C) is an additional stress factor for the stamp stock. UV-irradiation stability of the Ormostamp material is high: after 2 h irradiation with UV light (broadband, I = 15 mW/cm, intensity value measured at line 365 nm) the transparency changed by approximately 8% and the transparency was still above 90%. It may be easily calculated that this insignificant decrease of the working stamp transparency will happen after 360 imprints in mr-NIL6000.
2.3. Ormostamp for thermal and UV-based imprinting
This work was partially funded by the German Bundesministerium für Wirtschaft und Technologie, Contract Number IW060321.
The Ormostamp-made imprint stamps were used in an Obducat NanoImprinter 2.5 in. for patterning two different resists of micro resist technology GmbH: a UV-NIL polymer, mr-UVCur06 (Fig. 4 a) [5] and a photochemically curing resist for thermal NIL, mrNIL6000 (Fig. 4 b) [5]. Nanometer size structures, lines and spaces, were transferred free from defects and with high fidelity in over 50 UV-imprints (Fig. 4 c) from one and the same working stamp. As the surface roughness of Ormostamp stayed almost unchanged from the first to the last imprint, the limitation factor for imprint smoothness is the roughness of the master stamp. During the imprint process the working stamps were exposed to a mechanical pressure of 30 bar for 2–3 min. The temperature
3. Conclusions The presented work has shown that the materials fabricated by a sol–gel process are an excellent choice to fulfil the high expectations regarding the nanoimprint stamp materials. Ormostamp, a new organic–inorganic hybrid polymer system, can be successfully used for the fabrication of nanoimprint working stamps. High transparency and thermal and UV stability are essential for nanoimprinting of polymers. Up to now, only quartz stamps exhibited all these features. A reasonable number of imprints could be achieved using an adequate tailored adhesion promoter Ormoprime08 and an antisticking layer. Excellent pattern transfer fidelity was demonstrated for 100 nm structures. The cost saving working stamps lead to a multiplication of the life cycle of the stamp master. Further on, the expensive quartz master stamps supposedly can be replaced with cheaper silicon master stamps. Acknowledgment
References [1] M. Bender, U. Plachetka, J. Ran, A. Fuchs, B. Vratzov, H. Kurz, T. Glinsner, F. Lindner, J. Vac. Sci. Technol. B 22 (2004) 3229–3232. [2] C. Sanchez, B. Julián, P. Belleville, M. Popall, J. Mater. Chem. 15 (2005) 3559– 3592. [3] A. Klukowska, M. Vogler, A. Kolander, F. Reuther, G. Gruetzner, M. Muehlberger, I. Bergmair, R. Schoeftner, in: Uwe F. Behringer (Ed.), SPIE Proceedings, 24th European Mask and Lithography Conference, vol. 6792, p. 67920J. [4] M. Beck, M. Graczyk, I. Maximov, E.-L. Sarwe, T.G.I. Ling, M. Keil, L. Montelius, Microelectron. Eng. 61–62 (2002) 441–448. [5].
Contents lists available at ScienceDirect
Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee
Novel transparent hybrid polymer working stamp for UV-imprinting Anna Klukowska a,*, Anett Kolander a, Iris Bergmair b, Michael Mühlberger b, Hannes Leichtfried b, Freimut Reuther a, Gabi Grützner a, Rainer Schöftner b a b
Micro Resist Technology GmbH, Koepenicker Str. 325, 12555 Berlin, Germany Profactor GmbH, Im Stadtgut A2, 4407 Steyr, Austria
a r t i c l e
i n f o
Article history: Received 29 September 2008 Received in revised form 22 December 2008 Accepted 23 December 2008 Available online 17 January 2009 Keywords: Nanoimprint Nano-stamp Hybrid polymer Working stamps durability
a b s t r a c t Transparent stamps are an integral and crucial part of the UV-imprinting. Time consuming fabrication of quartz stamps increases the price of the technology. In the presented work a thermally stable transparent imprint stamp made of a novel hybrid polymer system is demonstrated. As a low-cost and highly efficient alternative the hybrid polymer stamp contributes to the acceptance and application of the nanoimprint technology. By using the UV-patternable inorganic–organic hybrid polymer quartz stamps might become superfluous in the UV-imprint process entirely, because transparent working stamps can be manufactured also with use of opaque silicon master stamps. Ó 2009 Elsevier B.V. All rights reserved.
1. Motivation Thermal and UV-based imprint techniques have gained importance in the electronics and optics industrial sectors within the last decade. For UV-based nanoimprint processes stamps with a high UV-transparency are essential, since the UV-range is the characteristic wavelength range for the majority of photo initiators used in photoresist materials. The common quartz stamp is still a significant cost factor among the consumables for the users of the UV-imprint techniques. Another known material for transparent imprint stamps is poly(dimethylsiloxan) (PDMS), the softness of which is a drawback for imprinting of nano-structures [1]. A material with well-tailored properties is needed as a successful nanoimprint stamp material. Easy material processing and high pattern transfer fidelity regarding the master stamp are crucial factors for nanoimprinting. The working stamp shall be of reasonable durability. Only an excellent pattern transfer from the working stamp on the nano-scale can be accepted for the application of nanoimprint technique. We have focused our research on well-established inorganic–organic hybrid polymers. The sol–gel process derived materials are of high thermal and chemical stability and exhibit excellent optical properties due to the presence of inorganic domains within the network. The organic part of the network, often bearing various func-
* Corresponding author. E-mail address: [email protected] (A. Klukowska). 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.12.088
tional groups, contributes to the easy handling, e.g., UVpatternability, and gives multiple possibilities for variation of the material’s physical properties, e.g., surface polarity. The materials have already found application in a variety of industry branches [2]. 2. Experimental results 2.1. Properties of the stamp material A great challenge in the UV-imprint process is the high transparency of the stamp material in the UV-range, which is the characteristic wavelength range for the majority of photo initiators used in photoresist materials. The novel stamp material system based on a UV-curable inorganic–organic hybrid polymer – Ormostamp – offers high UV-transparency even after thermal exposure at 270 °C. In this case 90% transparency remains at 350 nm (Fig. 1). The data was gathered for a 200 lm layer on a glass substrate. An excellent thermal stability was also confirmed in differential thermal analysis and thermal gravimetry analysis (DTA–TG) measurements (DTA–TG) (Fig. 2). The method shows changes in the material composition (by weight detection) during a well-defined heating process. First signs of thermal degradation can be detected for Ormostamp at approximately 300–320 °C with a heating rate of 2 K/min. Both the transparency and the thermal stability are principal material properties for the planned application in nanoimprint processes. The mechanical properties of Ormostamp are defined by its chemical composition. As hybrid polymer it contains –SiOSi–
698
A. Klukowska et al. / Microelectronic Engineering 86 (2009) 697–699
100
Table 1 Physical properties of Ormostamp.
a b c
80
T [%]
60
Liquid Viscosity Refractive index at 25 °C and 589 nm
0.75 Pa s 1.526
Solid Modulus of elasticity Hardness
0.650 GPa 0.036 GPa
40
a) after fabrication o b) after 5 min at 270 C o c) after 10 min at 270 C
20
glass/quartz adhesion promoter
A. Ormostamp deposition
Ormostamp
0 300
400
500 λ [nm]
600
master stamp
700 UV-light
Fig. 1. Ormostamp transparency, (a) UV-cured and hard baked, (b) after 5 min and (c) after 10 min at 270 °C.
B. Ormostamp processing
domains (network) connected covalently to organic backbone. The radical driven polymerisation of the active organic groups will occur under UV exposure. The elasticity and hardness of the stamp material are critical factors for the transfer of nano-structures. The materials used up to now for fabrication of nanoimprint working stamps were too soft, as PDMS [1], or too brittle, as older generation hybrid polymers, to give an acceptable performance. The values of Ormocomp modulus of elasticity and hardness are sufficient for patterning both nano- and micro-structures (Table 1) without any cracks and fractures (too brittle material) or deformations (too soft material).
C. Anti sticking layer deposition anti sticking layer
ready-to-use working stamp
2.2. Stamp fabrication
Fig. 3. Stamp fabrication process.
Ormostamp working stamps can be fabricated in a one-step or a two-steps process, which was shown previously for different hybrid polymers in [3]. The stamps may be processed on a glass or quartz substrate (transparent) or without a substrate. In our present work we have focused on the replication of stamps with a transparent substrate in a one-step process from a silicon master stamp (Fig. 3). The common size of the working stamps was 1.5 cm 1.5 cm. Also bigger stamps up to 4 in. have been fabricated. The relatively low viscosity of Ormostamp is important for efficient filling of the master stamp cavities and allows various deposition techniques, which make the material handling and further processing easier (Table 1).
Table 2 Roughness (root-mean-squared) of Ormostamp surface during the imprint process, determined by AFM measurements on the same top area of the stamp. Imprints
Roughness rms (Å)
1 10 19 29
25.75 25.8 24.9 33.23
The process of stamp fabrication is shown in Fig. 3. After dispensing (Fig. 3 A) of a certain amount of Ormostamp on a master
Fig. 2. Thermal stability of Ormostamp UV-cured and hard baked.
A. Klukowska et al. / Microelectronic Engineering 86 (2009) 697–699
a) 100 nm lines/ 200 nm spaces imprinted in mrUVCur06
b) 200 nm lines/ 100 nm spaces imprinted in mr-NIL 6000
699
c) 51st imprint in mrUVCur06
Fig. 4. Examples of UV and thermal imprints with an Ormostamp working stamp in mr-UVCur06 and mr-NIL 6000.
stamp, the material drop is covered with a clean, transparent substrate (Fig. 3 B). An anti-sticking treatment from a gas phase (as described below) was applied to the master stamp prior to Ormostamp deposition. The glass or quartz plate should be coated with adhesion promoter Ormoprime08 (micro resist technology GmbH). The transferred structures are stable after Ormostamp UV-curing (broadband exposure 1000 mJ/cm2 measured at 365 nm) and final thermal post exposure treatment at 130 °C for 30 min. An anti-sticking treatment (Fig. 3C) with F13TCS from the gas phase [4] is carried out at 150 °C. The stability of the readyto-use working stamps under the considerable thermal stress during the anti-sticking layer deposition proves the integrity of the stamp stock. Furthermore, an experimental liquid anti-sticking treatment (Profactor GmbH) could successfully be applied to the stamp surface. The liquid anti-adhesive agent was spin coated on the stamp surface. The performance of both anti-sticking layers was comparable. Adhesion promoter and anti-sticking layer have a direct influence on the durability of the working stamps. The life time of the working stamp could be increased by use of an adhesion promoter. Besides good adhesion of the stamp material to the glass substrate (GT 0, DIN EN ISO 2409), an easy release of the resist material from the working stamp after the imprint process is guaranteed after anti-sticking treatment. Low surface roughness of Ormostamp, which does not change during the UV-imprint process (Table 2), has a positive impact on the pattern transfer fidelity. The pattern transfer fidelity during the Ormostamp stamp fabrication is highly satisfying and was proven in UV and thermal nanoimprinting tests with different polymers.
needed for patterning process of mr-NIL6000 (110 °C) is an additional stress factor for the stamp stock. UV-irradiation stability of the Ormostamp material is high: after 2 h irradiation with UV light (broadband, I = 15 mW/cm, intensity value measured at line 365 nm) the transparency changed by approximately 8% and the transparency was still above 90%. It may be easily calculated that this insignificant decrease of the working stamp transparency will happen after 360 imprints in mr-NIL6000.
2.3. Ormostamp for thermal and UV-based imprinting
This work was partially funded by the German Bundesministerium für Wirtschaft und Technologie, Contract Number IW060321.
The Ormostamp-made imprint stamps were used in an Obducat NanoImprinter 2.5 in. for patterning two different resists of micro resist technology GmbH: a UV-NIL polymer, mr-UVCur06 (Fig. 4 a) [5] and a photochemically curing resist for thermal NIL, mrNIL6000 (Fig. 4 b) [5]. Nanometer size structures, lines and spaces, were transferred free from defects and with high fidelity in over 50 UV-imprints (Fig. 4 c) from one and the same working stamp. As the surface roughness of Ormostamp stayed almost unchanged from the first to the last imprint, the limitation factor for imprint smoothness is the roughness of the master stamp. During the imprint process the working stamps were exposed to a mechanical pressure of 30 bar for 2–3 min. The temperature
3. Conclusions The presented work has shown that the materials fabricated by a sol–gel process are an excellent choice to fulfil the high expectations regarding the nanoimprint stamp materials. Ormostamp, a new organic–inorganic hybrid polymer system, can be successfully used for the fabrication of nanoimprint working stamps. High transparency and thermal and UV stability are essential for nanoimprinting of polymers. Up to now, only quartz stamps exhibited all these features. A reasonable number of imprints could be achieved using an adequate tailored adhesion promoter Ormoprime08 and an antisticking layer. Excellent pattern transfer fidelity was demonstrated for 100 nm structures. The cost saving working stamps lead to a multiplication of the life cycle of the stamp master. Further on, the expensive quartz master stamps supposedly can be replaced with cheaper silicon master stamps. Acknowledgment
References [1] M. Bender, U. Plachetka, J. Ran, A. Fuchs, B. Vratzov, H. Kurz, T. Glinsner, F. Lindner, J. Vac. Sci. Technol. B 22 (2004) 3229–3232. [2] C. Sanchez, B. Julián, P. Belleville, M. Popall, J. Mater. Chem. 15 (2005) 3559– 3592. [3] A. Klukowska, M. Vogler, A. Kolander, F. Reuther, G. Gruetzner, M. Muehlberger, I. Bergmair, R. Schoeftner, in: Uwe F. Behringer (Ed.), SPIE Proceedings, 24th European Mask and Lithography Conference, vol. 6792, p. 67920J. [4] M. Beck, M. Graczyk, I. Maximov, E.-L. Sarwe, T.G.I. Ling, M. Keil, L. Montelius, Microelectron. Eng. 61–62 (2002) 441–448. [5]