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Characterization of anti-adhesive self-assembled monolayer for nanoimprint lithography
Applied Surface Science 255 (2008) 2885–2889
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Characterization of anti-adhesive self-assembled monolayer for nanoimprint lithography Weimin Zhou a,b,*, Jing Zhang a, Yanbo Liu a,b, Xiaoli Li a, Xiaomin Niu a, Zhitang Song b, Guoquan Min a, YongZhong Wan a, Liyi Shi a, Songlin Feng b a b
Laboratory of Nanotechnology, Shanghai Nanotechnology Promotion Center (SNPC), Shanghai 200237, China Laboratory of Nanotechnology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 30 April 2008 Received in revised form 11 June 2008 Accepted 16 August 2008 Available online 27 August 2008
In nanoimprint lithography process, resist adhesion to the mold was usually self-assembled and a release agent on the mold surface to detach easily from the imprinted resist. In the paper, the commercially available silane, 1H,1H,2H,2H-perfluorodecyltrichlorosilane (CF3–(CF2)7–(CH2)2–SiCl3 or FDTS) was used to investigate the anti-adhesion for UV-nanoimprint lithography. A water contact angle as high as 113.11 was achieved by self-assembled monolayer (SAM) deposited on the quarter mold by vapor evaporation, which is desirable for a good anti-adhesion agent between the fused silica and the curing resist. The homogeneous monolayer was also evaluated by AFM and XPS. UV-NIL using FDTS-coated fused silica process good pattern transfer fidelity. It is shown that the FDTS is an excellent and promising release agent material for UV-nanoimprint lithography. ß 2008 Elsevier B.V. All rights reserved.
PACS: 81.15.Kk 81.16.Rf 68.37.Ps 81.16.Dn 81.16.C Keywords: Anti-adhesive Self-assembled monolayer FDTS UV-nanoimprint lithography
1. Introduction Nanoimprint lithography (NIL) promising high-throughput patterning of microstructure has attracted much attention in comparison with other conventional techniques such as optical lithography, EBL and focused ion beam lithography. Its capability of nanoimprint lithography makes it a very useful technique in many device applications that require precision patterning of large areas with nanoscale structures, including application in photonics, display, molecular electronics and data storage [1]. For example, 1 kbit A crossbar memory circuits at 30 nm half on both top and bottom electrodes were fabricated by UV-NIL technique combined with metal lift off and Langmuir–Blodgett (LB) film
* Corresponding author at: Laboratory of Nanotechnology, Shanghai Nanotechnology Promotion Center (SNPC), 3/f No. 3 Building, 245 Jiachuan Road, Shanghai 200237, China. E-mail addresses: [email protected], [email protected] (W. Zhou). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.08.045
deposition [2]. Lee et al. reported the result of fabrication of Ge2Sb2Te5-based phase change memory cell device at 60 nm scale by using UV-NIL, which showed on/off resistance ratio up to 3000 [3]. The light extraction of LED can be enhanced greatly by photonic crystal fabricated by NIL [4]. The novel nanoimprint technology would be used intensively for the IC production and related application at the 32 nm node and beyond, and have an enormous prospect in the field of nanofabrication. In the UV-NIL process, a low viscosity and photocurable resist (for example AMONIL, PAK01) was spin-coated on the substrate, and a transparent rigid or flexible mold is applied on the photocurable resist and then cured by the desired pressure and UV exposure. The NIL patterns could be obtained after the separation of the mold and UV-curable resin. However, the features precision of resists would be maintained during the demolding. Usually, the mold should be modified in virtue of self-assembled monolayer (SAM) of a fluorinated silane release agent or other methods. A low surface energy monolayer on mold surface not only helps to enhance nanoimprint qualities, but significantly increase the mold lifetime
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Fig. 1. Schematic of self-assembled monolayer on mold.
by preventing surface contamination. Jaszewski et al. used plasma polymerized CF4/H2 microwave discharge or ion sputtering from CHF3 plasma to form anti-adhesive PTFE-like films for the replication of microstructures [5]. More recently, the researchers from IBM research center indicated that an ion-beam deposited diamond-like carbon (DLC) coating is a useful alternative for fluorosilane layers. Although the DLC layer has higher surface energy, it is possessed of stability in reactive environment and lower adhesion [6,7]. Among these reported papers, many researchers used a commercially available F13-OTCS (tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane) or octadecyltrimethoxysilane (OTMS) to deposite antiadhesive coating on the surface of SiO2 or Si stamp [8–12]. It was also reported that solution phase-based release agent cannot replicate
faithfully with sub-100 nm pitch features [13] and vapor phasebased anti-adhesion is appealing for modification of the imprint mold. In the paper, a SAM of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) is deposited by vapor phase instead of liquid phase. The SAM on the fused silica mold was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and contact angle. The imprinted patterns were fabricated by UV-NIL with a silica mold-coated monolayer of FDTS, and their patterns were analyzed and characterized. 2. Experimental The schematic of vapor phase deposition was presented in Fig. 1. Before vapor deposition, the fused silica was first soaked in a piranha solution at 90 8C for 30 min and thoroughly rinsed with deionized (DI) water and dried with N2. The glove box was flushed with N2 after the mold and FDTS was put in. After it being fully with N2 (ca 2 h), a drop of FDTS is syringed on the Petri dish and the coating is placed on the Petri dish. After 3 h, the hotplate is cooled to room temperature and the excess is washed by anhydrous hexane to prevent FDTS polymerization. The as-deposited fused
Fig. 2. Photos of water droplet on (a) blank mold surface (b) SAM coated mold surface.
Fig. 3. AFM images of the FDTS coated fused Silica surface.
W. Zhou et al. / Applied Surface Science 255 (2008) 2885–2889
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AMONIL-MMS4 (AMO GmbH, Germany) at 3000 rpm/min, then bakes at 100 8C to yield 220 nm thick films. The quality of asimprinted patterns was also characterized by AFM. 3. Result and discussion
Fig. 4. XPS survey spectra of the FDTS deposited quartz mold.
silica was characterized by XPS. The measurement was performed on a Kratos Axis Ultra DLD system with Al Ka X-ray source (1486.6 eV, under operation at 15 KV and 10 mA). Its chamber is remained at 5 109 Torr. The morphologies and roughness of SAM were investigated by atomic force microscope (Vecco, Dimension 3100). And the contact angle was analyzed by measuring on the mold coated with a SAM (OCA20, TBU 80E, Germany). The UV-NIL was performed on an EVG620 (EVG Group, Austria). The nanoimprint pressure is 100 Pa and hold time of UV exposure is 120 s. Before UV-NIL, the Si substrate is spun on UV-curable resin
The photos, recorded with a CCD camera, of water droplet on the blank and SAM-coated quarter mold were shown in Fig. 2 (a) and (b), respectively. The water contact angle for blank mold is 33.018, but the markedly increased values of water contact angle for the FDTS-coated mold are up to 113.118, indicating that the SAM is highly hydrophobic and suitable for nanoimprint lithography. The water repellency of the mold modified with FDTS is close to or better than that of FOTS, which is reported to be 112.978 by our result (not shown here). Fig. 3 presents the surface roughness of the modified blank fused silica with uniform FDTS SAM. A root mean square roughness (RMS) was defined according to the following equation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi PN 2 i¼1 ðZ i Z av Þ RMS ¼ N Where Zav, Zi, and N are the average height for the entire region, the height of individual point i, and the number of points measured within a given area, respectively. The roughness of SAM obtained from AFM image analysis from Fig. 3 is 1.06 nm, which is close to the blank fused silica. It is shown that a dense and uniform nanofilm was deposited on the fused silica. Moreover, in comparison with modification quarter mold by solution methods, the vapor deposition self-assembled nanofilm
Fig. 5. Scheme of the SAM formation mechanism on fused silica surface.
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Fig. 6. AFM image of the imprinted resin pattern.
seems to process better quality [14], which can improve pattern fidelity during UV-NIL. An XPS spectra of the FDTS-coated fused silica is shown in Fig. 4. It can be seen that the F/C ratio of mass is 3.8, the C (1 s) spectra mainly consist of CF3, CF2 and CF, which are centered at binding energies of 295 eV, 292 eV and 291 eV, respectively. The C (1 s) spectra indicated clearly that a thin organic layer successfully was coated on the surface of the fused silica mold. Besides, a broad peak could be seen from the spectra, and responsible for some organic impurities. The SAM is so thinner that the Si peak can be detected from the fused silica mold, as shown in Fig. 4. In vapor deposition process, the SAM was grafted on the fused silica stamp, and a known formation mechanism of SAM for vapor deposition developed in the research could be explained in Fig. 5. Silanes with short chain lengths and high vapor pressures are easily deposited on the silica through vapor phase. Before vapor deposition, the mold is treated with piranha solution and rinsed with DI water to form large number of hydroxyl (OH) groups attached on mold surface as shown in Fig. 5a. Then the silane head groups hydrolyze and form trisilanols (Fig. 5b). The Si(OH)3 groups form covalent bonds with the hydroxyl groups on SiO2 surface, which is grafted to the silica surface(Fig. 5c).Subsequently condensation reaction goes on between neighbor molecules and the Si–O–Si covalent bonds can take place (Fig. 5d). Finally, the networked coating is its ease of formation on the mold surface to lower the surface energy. The AFM image in Fig. 6 shows 23 nm deep imprinted AMONIL resin, and by measuring the dimension of the imprinted resin, no oblivious discrepancy of dimension could be detected from the AFM results, indicating good pattern transfer into curing resin for UV-NIL process with a FDTS-coated fused silica. It was well known that the more contact angle, the less surface energy. From the
aforementioned water contact angle, surface energy of FDTS is much less than that of FOTS. It is noted that the adhesion energy of AMONIL and FDTS, calculated similarly in the Ref. [15], is lower than that of AMONIL and FOTS. Easier of separation from the mold to the curing resin is expected when FDTS is applied on the mold than FOTS did. It can also be confirmed by the AFM image of Fig. 6 without obvious pattern distortion. 4. Conclusion The commercially available FDTS was self-assembled on the fused mold by vapor deposition to show good pattern transfer fidelity into the resist. The self-assembled dense and homogeneous monolayer was characterized by means of contact angle, XPS, and AFM. The formation mechanism of SAM was also proposed. The results show that FDTS is an excellent coating material for the mold of separation from the curing resist. Acknowledgements This work was jointly supported by China Postdoctoral Scientific Foundation Funded Project (20070420105), National 973 Program (2007CB935400), Science and Technology Committee of Shanghai (0652nm052, 0752nm013, 0752nm014), and Shanghai Postdoctoral Scientific Program (07R214204, 08R214211). References [1] [2] [3] [4]
L. Jay Guo, J. Phys. D: Appl. Phys. 37 (2004) R123. W. Wu, Appl. Phys. A 80 (2005) 1173. H. Lee, S.H. Hong, K.Y. Yang, G.Y. Jung, Microelectron. Eng. 84 (2007) 573. S.H. Kim, K.D. Lee, J.Y. Kim, M.K. Kwon, S.J. Park, Nanotechnology 18 (2007) 055306.
W. Zhou et al. / Applied Surface Science 255 (2008) 2885–2889 [5] R.W. Jaszewski, H. Schift, P. Groning, G. Margaritondo, Microelectro. Eng. 35 (1997) 381. [6] F.A. Houle, C.T. Rettner, D.C. Miller, R. Sooriyakumaran, Appl. Phys. Lett. 90 (2007) 213103. [7] L. Tao, S. Ramachandran, C.T. Nelson, M. Lin, L.J. Overzet, M. Goeckner, G. Lee, C.G. Willson, Nanotechnology 19 (2008) 105302. [8] M. Beck, M. Graczyk, I. Maximov, E.L. Sarwe, T.G. ILing, M. Keil, L. Montelius, Microelectron. Eng. 61 (2002) 441. [9] H. Schift, S. Saxer, S. Park, C. Padeste, U. Pieles, J. Gobrecht, Nanotechnology 16 (2005) s171.
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[10] S. Park, H. Schift, C. Padeste, B. Schnyde, R. Kuotz, J. Gobrecht, Microelectron. Eng. 73 (2004) 196. [11] R.W. Jaszewski, H. Schift, B. Schnyder, Appl. Surf. Sci. 143 (1999) 301. [12] L. Ressier, C. Martin, B. Viallet, J. Vac. Sci. Technol. B 25 (2007) 17. [13] G.Y. Jung, Z.Y. Li, W. Wu, Y. Chen, D.L. Olynick, S.Y. Wang, W.M. tong, R.S. Williams, Langmuir 21 (2005) 1158. [14] T. Zhang, B. Kobrin, M. Wanebo, R. Nowak, R. Yi, J. Chinn, M. Bender, A. Fuchs, M. Ott, Proc. SPIE 6151 (2006) 615117. [15] L. Tao, S. Ramachandran, C.T. Nelson, M. Lin, L.J. Overzet, M. goechner, G. Lee, C.G. Willson, W. Wu, W. Hu, Nanotechnology 19 (2008) 105301.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Characterization of anti-adhesive self-assembled monolayer for nanoimprint lithography Weimin Zhou a,b,*, Jing Zhang a, Yanbo Liu a,b, Xiaoli Li a, Xiaomin Niu a, Zhitang Song b, Guoquan Min a, YongZhong Wan a, Liyi Shi a, Songlin Feng b a b
Laboratory of Nanotechnology, Shanghai Nanotechnology Promotion Center (SNPC), Shanghai 200237, China Laboratory of Nanotechnology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 30 April 2008 Received in revised form 11 June 2008 Accepted 16 August 2008 Available online 27 August 2008
In nanoimprint lithography process, resist adhesion to the mold was usually self-assembled and a release agent on the mold surface to detach easily from the imprinted resist. In the paper, the commercially available silane, 1H,1H,2H,2H-perfluorodecyltrichlorosilane (CF3–(CF2)7–(CH2)2–SiCl3 or FDTS) was used to investigate the anti-adhesion for UV-nanoimprint lithography. A water contact angle as high as 113.11 was achieved by self-assembled monolayer (SAM) deposited on the quarter mold by vapor evaporation, which is desirable for a good anti-adhesion agent between the fused silica and the curing resist. The homogeneous monolayer was also evaluated by AFM and XPS. UV-NIL using FDTS-coated fused silica process good pattern transfer fidelity. It is shown that the FDTS is an excellent and promising release agent material for UV-nanoimprint lithography. ß 2008 Elsevier B.V. All rights reserved.
PACS: 81.15.Kk 81.16.Rf 68.37.Ps 81.16.Dn 81.16.C Keywords: Anti-adhesive Self-assembled monolayer FDTS UV-nanoimprint lithography
1. Introduction Nanoimprint lithography (NIL) promising high-throughput patterning of microstructure has attracted much attention in comparison with other conventional techniques such as optical lithography, EBL and focused ion beam lithography. Its capability of nanoimprint lithography makes it a very useful technique in many device applications that require precision patterning of large areas with nanoscale structures, including application in photonics, display, molecular electronics and data storage [1]. For example, 1 kbit A crossbar memory circuits at 30 nm half on both top and bottom electrodes were fabricated by UV-NIL technique combined with metal lift off and Langmuir–Blodgett (LB) film
* Corresponding author at: Laboratory of Nanotechnology, Shanghai Nanotechnology Promotion Center (SNPC), 3/f No. 3 Building, 245 Jiachuan Road, Shanghai 200237, China. E-mail addresses: [email protected], [email protected] (W. Zhou). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.08.045
deposition [2]. Lee et al. reported the result of fabrication of Ge2Sb2Te5-based phase change memory cell device at 60 nm scale by using UV-NIL, which showed on/off resistance ratio up to 3000 [3]. The light extraction of LED can be enhanced greatly by photonic crystal fabricated by NIL [4]. The novel nanoimprint technology would be used intensively for the IC production and related application at the 32 nm node and beyond, and have an enormous prospect in the field of nanofabrication. In the UV-NIL process, a low viscosity and photocurable resist (for example AMONIL, PAK01) was spin-coated on the substrate, and a transparent rigid or flexible mold is applied on the photocurable resist and then cured by the desired pressure and UV exposure. The NIL patterns could be obtained after the separation of the mold and UV-curable resin. However, the features precision of resists would be maintained during the demolding. Usually, the mold should be modified in virtue of self-assembled monolayer (SAM) of a fluorinated silane release agent or other methods. A low surface energy monolayer on mold surface not only helps to enhance nanoimprint qualities, but significantly increase the mold lifetime
2886
W. Zhou et al. / Applied Surface Science 255 (2008) 2885–2889
Fig. 1. Schematic of self-assembled monolayer on mold.
by preventing surface contamination. Jaszewski et al. used plasma polymerized CF4/H2 microwave discharge or ion sputtering from CHF3 plasma to form anti-adhesive PTFE-like films for the replication of microstructures [5]. More recently, the researchers from IBM research center indicated that an ion-beam deposited diamond-like carbon (DLC) coating is a useful alternative for fluorosilane layers. Although the DLC layer has higher surface energy, it is possessed of stability in reactive environment and lower adhesion [6,7]. Among these reported papers, many researchers used a commercially available F13-OTCS (tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane) or octadecyltrimethoxysilane (OTMS) to deposite antiadhesive coating on the surface of SiO2 or Si stamp [8–12]. It was also reported that solution phase-based release agent cannot replicate
faithfully with sub-100 nm pitch features [13] and vapor phasebased anti-adhesion is appealing for modification of the imprint mold. In the paper, a SAM of 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) is deposited by vapor phase instead of liquid phase. The SAM on the fused silica mold was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM) and contact angle. The imprinted patterns were fabricated by UV-NIL with a silica mold-coated monolayer of FDTS, and their patterns were analyzed and characterized. 2. Experimental The schematic of vapor phase deposition was presented in Fig. 1. Before vapor deposition, the fused silica was first soaked in a piranha solution at 90 8C for 30 min and thoroughly rinsed with deionized (DI) water and dried with N2. The glove box was flushed with N2 after the mold and FDTS was put in. After it being fully with N2 (ca 2 h), a drop of FDTS is syringed on the Petri dish and the coating is placed on the Petri dish. After 3 h, the hotplate is cooled to room temperature and the excess is washed by anhydrous hexane to prevent FDTS polymerization. The as-deposited fused
Fig. 2. Photos of water droplet on (a) blank mold surface (b) SAM coated mold surface.
Fig. 3. AFM images of the FDTS coated fused Silica surface.
W. Zhou et al. / Applied Surface Science 255 (2008) 2885–2889
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AMONIL-MMS4 (AMO GmbH, Germany) at 3000 rpm/min, then bakes at 100 8C to yield 220 nm thick films. The quality of asimprinted patterns was also characterized by AFM. 3. Result and discussion
Fig. 4. XPS survey spectra of the FDTS deposited quartz mold.
silica was characterized by XPS. The measurement was performed on a Kratos Axis Ultra DLD system with Al Ka X-ray source (1486.6 eV, under operation at 15 KV and 10 mA). Its chamber is remained at 5 109 Torr. The morphologies and roughness of SAM were investigated by atomic force microscope (Vecco, Dimension 3100). And the contact angle was analyzed by measuring on the mold coated with a SAM (OCA20, TBU 80E, Germany). The UV-NIL was performed on an EVG620 (EVG Group, Austria). The nanoimprint pressure is 100 Pa and hold time of UV exposure is 120 s. Before UV-NIL, the Si substrate is spun on UV-curable resin
The photos, recorded with a CCD camera, of water droplet on the blank and SAM-coated quarter mold were shown in Fig. 2 (a) and (b), respectively. The water contact angle for blank mold is 33.018, but the markedly increased values of water contact angle for the FDTS-coated mold are up to 113.118, indicating that the SAM is highly hydrophobic and suitable for nanoimprint lithography. The water repellency of the mold modified with FDTS is close to or better than that of FOTS, which is reported to be 112.978 by our result (not shown here). Fig. 3 presents the surface roughness of the modified blank fused silica with uniform FDTS SAM. A root mean square roughness (RMS) was defined according to the following equation: sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi PN 2 i¼1 ðZ i Z av Þ RMS ¼ N Where Zav, Zi, and N are the average height for the entire region, the height of individual point i, and the number of points measured within a given area, respectively. The roughness of SAM obtained from AFM image analysis from Fig. 3 is 1.06 nm, which is close to the blank fused silica. It is shown that a dense and uniform nanofilm was deposited on the fused silica. Moreover, in comparison with modification quarter mold by solution methods, the vapor deposition self-assembled nanofilm
Fig. 5. Scheme of the SAM formation mechanism on fused silica surface.
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Fig. 6. AFM image of the imprinted resin pattern.
seems to process better quality [14], which can improve pattern fidelity during UV-NIL. An XPS spectra of the FDTS-coated fused silica is shown in Fig. 4. It can be seen that the F/C ratio of mass is 3.8, the C (1 s) spectra mainly consist of CF3, CF2 and CF, which are centered at binding energies of 295 eV, 292 eV and 291 eV, respectively. The C (1 s) spectra indicated clearly that a thin organic layer successfully was coated on the surface of the fused silica mold. Besides, a broad peak could be seen from the spectra, and responsible for some organic impurities. The SAM is so thinner that the Si peak can be detected from the fused silica mold, as shown in Fig. 4. In vapor deposition process, the SAM was grafted on the fused silica stamp, and a known formation mechanism of SAM for vapor deposition developed in the research could be explained in Fig. 5. Silanes with short chain lengths and high vapor pressures are easily deposited on the silica through vapor phase. Before vapor deposition, the mold is treated with piranha solution and rinsed with DI water to form large number of hydroxyl (OH) groups attached on mold surface as shown in Fig. 5a. Then the silane head groups hydrolyze and form trisilanols (Fig. 5b). The Si(OH)3 groups form covalent bonds with the hydroxyl groups on SiO2 surface, which is grafted to the silica surface(Fig. 5c).Subsequently condensation reaction goes on between neighbor molecules and the Si–O–Si covalent bonds can take place (Fig. 5d). Finally, the networked coating is its ease of formation on the mold surface to lower the surface energy. The AFM image in Fig. 6 shows 23 nm deep imprinted AMONIL resin, and by measuring the dimension of the imprinted resin, no oblivious discrepancy of dimension could be detected from the AFM results, indicating good pattern transfer into curing resin for UV-NIL process with a FDTS-coated fused silica. It was well known that the more contact angle, the less surface energy. From the
aforementioned water contact angle, surface energy of FDTS is much less than that of FOTS. It is noted that the adhesion energy of AMONIL and FDTS, calculated similarly in the Ref. [15], is lower than that of AMONIL and FOTS. Easier of separation from the mold to the curing resin is expected when FDTS is applied on the mold than FOTS did. It can also be confirmed by the AFM image of Fig. 6 without obvious pattern distortion. 4. Conclusion The commercially available FDTS was self-assembled on the fused mold by vapor deposition to show good pattern transfer fidelity into the resist. The self-assembled dense and homogeneous monolayer was characterized by means of contact angle, XPS, and AFM. The formation mechanism of SAM was also proposed. The results show that FDTS is an excellent coating material for the mold of separation from the curing resist. Acknowledgements This work was jointly supported by China Postdoctoral Scientific Foundation Funded Project (20070420105), National 973 Program (2007CB935400), Science and Technology Committee of Shanghai (0652nm052, 0752nm013, 0752nm014), and Shanghai Postdoctoral Scientific Program (07R214204, 08R214211). References [1] [2] [3] [4]
L. Jay Guo, J. Phys. D: Appl. Phys. 37 (2004) R123. W. Wu, Appl. Phys. A 80 (2005) 1173. H. Lee, S.H. Hong, K.Y. Yang, G.Y. Jung, Microelectron. Eng. 84 (2007) 573. S.H. Kim, K.D. Lee, J.Y. Kim, M.K. Kwon, S.J. Park, Nanotechnology 18 (2007) 055306.
W. Zhou et al. / Applied Surface Science 255 (2008) 2885–2889 [5] R.W. Jaszewski, H. Schift, P. Groning, G. Margaritondo, Microelectro. Eng. 35 (1997) 381. [6] F.A. Houle, C.T. Rettner, D.C. Miller, R. Sooriyakumaran, Appl. Phys. Lett. 90 (2007) 213103. [7] L. Tao, S. Ramachandran, C.T. Nelson, M. Lin, L.J. Overzet, M. Goeckner, G. Lee, C.G. Willson, Nanotechnology 19 (2008) 105302. [8] M. Beck, M. Graczyk, I. Maximov, E.L. Sarwe, T.G. ILing, M. Keil, L. Montelius, Microelectron. Eng. 61 (2002) 441. [9] H. Schift, S. Saxer, S. Park, C. Padeste, U. Pieles, J. Gobrecht, Nanotechnology 16 (2005) s171.
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[10] S. Park, H. Schift, C. Padeste, B. Schnyde, R. Kuotz, J. Gobrecht, Microelectron. Eng. 73 (2004) 196. [11] R.W. Jaszewski, H. Schift, B. Schnyder, Appl. Surf. Sci. 143 (1999) 301. [12] L. Ressier, C. Martin, B. Viallet, J. Vac. Sci. Technol. B 25 (2007) 17. [13] G.Y. Jung, Z.Y. Li, W. Wu, Y. Chen, D.L. Olynick, S.Y. Wang, W.M. tong, R.S. Williams, Langmuir 21 (2005) 1158. [14] T. Zhang, B. Kobrin, M. Wanebo, R. Nowak, R. Yi, J. Chinn, M. Bender, A. Fuchs, M. Ott, Proc. SPIE 6151 (2006) 615117. [15] L. Tao, S. Ramachandran, C.T. Nelson, M. Lin, L.J. Overzet, M. goechner, G. Lee, C.G. Willson, W. Wu, W. Hu, Nanotechnology 19 (2008) 105301.