- Email: [email protected]
Status and critical challenges for 157-nm lithography
Microelectronic Engineering 73–74 (2004) 5–10 www.elsevier.com/locate/mee
Status and critical challenges for 157-nm lithography K. Ronse *, P. De Bisschop, A.M. Goethals, J. Hermans, R. Jonckheere, S. Light 1, U. Okoroanyanwu 2, R. Watso 3, D. McAfferty 3, J. Ivaldi 3, T. Oneil 3, H. Sewell 3 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium Available online 9 March 2004
Abstract In this paper, the status of 157-nm lithography is reviewed. The 157-nm lithography was until recently the prime candidate for printing the critical layers at the 65-nm node, but the progress on 193-nm high-NA lithography has pushed 157-nm to the 45-nm node this year. All potential show-stoppers for 157-nm lithography were removed more than a year ago. In this paper, it is shown that, in the past 12 months, progress has been made in almost all areas (resists, masks, pellicle and exposure tool), except for soft pellicles. Also the most important projects that are planned at IMEC to run on the first 157-nm full-field scanner, are outlined in this paper. Ó 2004 Elsevier B.V. All rights reserved. Keywords: 157-nm lithography; F2; Hard pellicle; VUV cleaning; Full-field scanner
1. Introduction Until 2003, 157-nm lithography was identified on the ITRS roadmap as a number one candidate lithography for printing the critical layers at the 65-nm node [1]. Since 1999 a lot of progress has been made on the various critical issues, identified
*
Corresponding author. E-mail addresses: [email protected], [email protected] (K. Ronse). 1 On assignment from Micron, Boise, USA. 2 On assignment from Advanced Micro Devices, Sunnyvale, USA. 3 ASML Wilton, USA.
for 157-nm lithography. All potential show-stoppers have been removed already, one year ago [2]. In this paper, an update is given on the status of most of these critical issues and their status at mid 2003. Some of these critical issues are being investigated in IMEC and will be reported in Section 3. Other critical issues are being investigated by other groups around the world and are briefly touched in Section 2. An overview of the various critical issues is maintained in the ISMT stop-light chart (Fig. 1). At any major 157-nm meeting, this chart is updated, based on the progress on each issue. Critical issues are classified under masks, exposure tools, resists, metrology and inspection, and timing.
0167-9317/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2004.02.007
6
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
Fig. 1. ISMT Ôstop lightÕ chart illustrating the 157-nm critical issues and their progress over time.
2. 157-nm critical issues: worldwide update
2.2. Exposure tool status
2.1. Resist status
Here also a major milestone was met: the first 157-nm full-field step and scan system has recently been shipped to IMEC and has been installed successfully: the ASML MicraScan VII, equipped with a 4 reduction lens with a maximum numerical aperture of 0.75, interfaced at IMEC to a TEL Clean Track ACT8. This lithocell will be the workhorse of the 157-nm research projects at IMEC and a lot of further learning is expected to take place in the next 12 months that will hopefully turn some yellow lights to green in Fig. 1. At the same 157-nm symposium, a lot of progress was reported on the quality of CaF2 lens material that lately has come available [7]. The levels of stress birefringence that are reported in 2003 are consistently within specification for the h1 1 1i crystal orientations and starts to pass the specification limit also for the more recently developed h1 0 0i orientations that are needed to compensate for the intrinsic birefringence in the CaF2 crystal.
At the fourth International Symposium on 157nm lithography, held end of August 2003 in Yokohama, good progress was shown on 157-nm resist performance [3]. Already last year a few resists started to show absorbances below 1/lm. Now more and more materials are showing this, allowing imaging in 150-nm thick resists. TodayÕs stateof-the-art resists are capable of resolving 60 nm lines and spaces (1:1) on 0.85 NA micro-steppers [4,5]. Resists can be deposited on both organic and inorganic anti-reflective coatings (ARC) with limited footing. Organic bottom ARCs dedicated for 157 nm are starting to appear [5]. Excellent postexposure bake (PEB) sensitivity has been reported by multiple sources (<0.5 nm/°C). All these excellent results have been reported in Yokohama [6]. At the same time, there is still a lot of room for improvements as well, for example in terms of lineedge roughness, post-exposure bake delay stability, and sensitivity.
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
2.3. Soft pellicle The development of soft-pellicle polymers for 157-nm lithography continues to be a worry. The last time progress was reported in mid 2002, the lifetimes of the pellicles were up to 20 J/cm2 , whereas the initial target was set an order of magnitude higher to give a practical lifetime. Currently no major progress in lifetime has been achieved [8], but the focus of the work has shifted more to understanding the failure mechanisms in the polymers [9]. Instead, as a temporary intermediate solution for the 157-nm pellicle problem, hard pellicles (800 lm thick modified fused silica plate) have been proposed. The drawback of this approach is twofold: first of all they are much more expensive to manufacture; and secondly they form an optical element in the light path, so they need to meet very stringent quality specifications in order not to degrade the imaging. The status of hard pellicles will be given in the following section.
3. 157-nm program status at IMEC Now that the ASML MicraScan VII full-field scanner has been accepted at IMEC, several projects can be started in which the real full-field aspects can be taken into consideration or where the real 157-nm wavelength can be applied. Besides projects on resist benchmarking, track integration
7
and critical-layer patterning, a number of projects specific to 157-nm operation have been started, and are described more in detail below. 3.1. MicraScan VII performance at IMEC The ASML MicraScan VII at IMEC is specified for 100-nm equal line-space dimensions and 70 nm isolated-line dimensions. The full-field critical dimension (CD) uniformity is about 10 nm (3 sigma) for the lines and spaces and 15 nm for the isolated lines [10]. In terms of lithographic performance, 100- and 90-nm equal lines and spaces have shown the widest process latitudes when quadrupole illumination is used, whereas dipole illumination further pushed the resolution to 70-nm equal lines and spaces and even 60-nm lines with 75-nm spaces (Fig. 2). All these results are shown in a 150-nm thick F2 resist with an absorption below 1/lm. An important project that will be running on this first full-field scanner will be to monitor the stability over time of the lithographic performance and to try to correlate any degradation with potential molecular contamination detected in the purge gases of the optics. 3.2. Hard-pellicle imaging Hard pellicles have been chosen as an intermediate solution until soft-pellicle materials exhibit
Fig. 2. (a) The 100- and 90-nm equal lines and spaces imaged on the ASML MicraScan VII using quadrupole illumination (0.75 NA), through-focus series. (b) The 70-nm equal lines and spaces and 60 nm lines/75 nm spaces imaged using dipole illumination (0.75 NA), through-focus series.
8
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
sufficient radiation hardness to be useful for 157 nm small-volume manufacturing. However, hard pellicles have a thickness of about 800 lm and contribute significantly to the imaging and overlay budget in a projection exposure system. There are very large focus offsets and high aberration levels if no precautions are taken. Our work, until now done primarily at 193 nm wavelength, has shown that sufficient lens manip-
ulators exist to compensate for these unwanted effects [11]. As a result we can now conclude that all imaging contributions of hard pellicles are understood and that effects on aberrations, focal plane deviation and CD uniformity can be eliminated successfully (Fig. 3). The main still remaining issue is the flatness of the pellicle mounting to the reticle, which is not yet meeting the required specifications; primarily, it
Fig. 3. (a) Focal plane deviation (FPD) and astigmatism (AST) measured across the full scanner field with and without a hard pellicle (1 grey level corresponds to 6 nm for FPD and 10 nm for AST). (b) CD uniformity measured across the full scanner field with and without a hard pellicle (1 grey level corresponds to 1 nm CD).
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
causes distortions at the edge of the field, where the ‘‘local tilt’’ numbers reach their maxima. Pellicle mounting technology improvements are required to meet the specifications, so that the overlay budgets also will not suffer from hard pellicles. Ideas exist how to get there and the work is continuing.
9
the contamination rates (in order to predict the required cleaning frequency). Also other error sources (like transport of a reticle, inspection at a mask shop, reticle storage in the fab) will be investigated and where necessary, cleaning procedures will be established.
3.3. 157-nm VUV reticle cleaning 4. Conclusions It has been reported that organic contamination, which is being deposited as a (few) monolayer(s) onto the 157-nm reticle substrates, will degrade the 157-nm reticle transmission by a few percent [12,13]. Very quick calculations indicate that this will consume a significant portion of the exposure budget for the relevant technology nodes, so this effect cannot be tolerated. It has been reported also that this contamination can be removed by a VUV cleaning process, in which the reticle is illuminated with 172 nm light in the presence of a little oxygen in nitrogen (Fig. 4). This restores the loss in transmission and avoids in situ cleaning while exposing the first dies on the wafer using the 157-nm laser light. At IMEC, quite some work has been spent on setting up a good metrology procedure to measure the effects of such VUV cleaning cycles in a reliable way, i.e., to levels of precision better than 0.2%. Using these procedures, the cleaning processes can be optimised and a detailed look will be taken on
Fig. 4. Blank transmission as function of wavelength, before and after VUV cleaning of the reticle (the interrupted line indicates the actinic exposure wavelength of 157 nm).
The various critical issues for 157-nm lithography have been reviewed in this paper. For almost all of these issues, significant progress has been made or alternative solutions have been suggested and are under way. All potential show-stoppers had already been removed, one year ago. It has been shown that steady progress is being made on the transparency and lithographic quality of 157-nm resists. With respect to line edge roughness reduction, dry-etch resistance, and integration of the total process, the work can really start now using the first full-field scanner, installed at IMEC: the ASML MicraScan VII. No progress has been made on soft pellicles, whereas all the optical effects of hard pellicles have been shown to be understood and manageable. The main remaining issue with hard pellicles is the mounting technology to further reduce the local tilt. In terms of organic contamination of reticles, the work on finding the right handling and cleaning procedures can start using the MSVII. Besides the technical progress on the 157-nm critical features, it is also important to follow the progress on competing technologies. The 193-nm lithography has also made significant progress in the past 2 years, to an extent that almost the complete industry is convinced today that the 65nm node can be done using the newly developed very high-NA 193-nm lenses (NA > 0:85). As a result, the industry does no longer view 157-nm lithography as a technology for the 65-nm node but rather as a 45-nm node technology. As a result, many of the requirements for the 157-nm critical issues have become much more severe. This explains why in August 2003, most of the yellow bullets remained yellow, despite the technical progress that has been demonstrated.
10
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
Acknowledgements The author thank the IMEC lithography department, including the industrial affiliates based at IMEC. Also the dry-etch group is acknowledged for their contributions. The authors also thank the ASML and Zeiss 157 nm development teams. International Sematech (G. Feit, K. Dean and K. Turnquest) and Selete (T. Itani) are acknowledged for providing access to their 157 nm microstepper infrastructure. Walt Trybula (ISMT) is acknowledged for providing the stop light chart on 157 nm. Last but not least, the authors want to thank all the partner companies of the IMEC 157 nm program for their support. Part of this work has been sponsored by International Sematech, Medeaþ (T401 FLUOR) and the European Commission (IST2000-30175 UV2Litho). References [1] International Technology Roadmap for Semiconductors. http://public.itrs.net. [2] Third International Symposium on 157 nm lithography, Antwerp, September, 2002. [3] Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. [4] F. Houlihan, A. Romano, D. Rentkiewicz, R. Sakamuri, R.R. Dammel, W. Conley, G. Rich, D. Miller, L. Rhodes, J. McDaniels, C. Chang, New Fluorinated Resists for Application in 157 nm Lithography Promerus, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. [5] T. Moriya, M. Koh, T. Ishikawa, T. Kodani, T. Araki, M. Toriumi, H. Aoyama, T. Yamashita, T. Hagiwara, T.
[6]
[7]
[8]
[9]
[10]
[11]
[12] [13]
Furukawa, T. Itani, Novel Main-chain-Fluorinated Polymers for 157-nm Photoresists, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. K. Turnquest, K. Dean, V. Graffenberg, S. Patel, D. Miller, G. Rich, Advancements in 157 nm Resist Performance, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. T. Modderman, T. OÕNeill, H. Jasper, H. Sewell, B. Tirri, H. Boom, T. Uiterdijk, S. Dana, M. Brunotte, B. Mecking, W. Kaiser, From Development to Production 157 nm Lithography Exposure Tools in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. A. Tregub, F. Eschbach, J. Powers, F.C. Lo, Development of Fluoropolymer Membranes Transparent and Resistant to 157 nm Exposure, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. V. Liberman, J.H.C. Sedlacek, T.H. Fedynyshyn, R.B. Goodman, R. Sinta, Improved Pellicles for 157 nmLithography – A Nanocomposite Approach, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. Jan Hermans, F. Van Roey, D. Van den Heuvel, R. Gronheid, A.M. Goethals, K. Ronse, S. Light, R. Watso, D. Mc Cafferty, T. OÕNeil, H. Sewell, 157 nm Full Field Imaging, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. P. De Bisschop, R. Bruls, O. Cicilia, T. Uitterdijk, A. Grenville, M. Kocsis, C. Van Peski, Initial Assessment of the Impact of the Use of a Hard Pellicle on Imaging, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. T. Bloomstein, ISMT 157 nm reticle handling meeting, San Diego, 2000. A. Duisterwinkel, W. van Schaik, Molecular Contamination in 157 nm Lithography: Feasibility of Reticle Cleaning, in: Third International Symposium on 157 nm lithography, Antwerp, September 2002.
Status and critical challenges for 157-nm lithography K. Ronse *, P. De Bisschop, A.M. Goethals, J. Hermans, R. Jonckheere, S. Light 1, U. Okoroanyanwu 2, R. Watso 3, D. McAfferty 3, J. Ivaldi 3, T. Oneil 3, H. Sewell 3 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium Available online 9 March 2004
Abstract In this paper, the status of 157-nm lithography is reviewed. The 157-nm lithography was until recently the prime candidate for printing the critical layers at the 65-nm node, but the progress on 193-nm high-NA lithography has pushed 157-nm to the 45-nm node this year. All potential show-stoppers for 157-nm lithography were removed more than a year ago. In this paper, it is shown that, in the past 12 months, progress has been made in almost all areas (resists, masks, pellicle and exposure tool), except for soft pellicles. Also the most important projects that are planned at IMEC to run on the first 157-nm full-field scanner, are outlined in this paper. Ó 2004 Elsevier B.V. All rights reserved. Keywords: 157-nm lithography; F2; Hard pellicle; VUV cleaning; Full-field scanner
1. Introduction Until 2003, 157-nm lithography was identified on the ITRS roadmap as a number one candidate lithography for printing the critical layers at the 65-nm node [1]. Since 1999 a lot of progress has been made on the various critical issues, identified
*
Corresponding author. E-mail addresses: [email protected], [email protected] (K. Ronse). 1 On assignment from Micron, Boise, USA. 2 On assignment from Advanced Micro Devices, Sunnyvale, USA. 3 ASML Wilton, USA.
for 157-nm lithography. All potential show-stoppers have been removed already, one year ago [2]. In this paper, an update is given on the status of most of these critical issues and their status at mid 2003. Some of these critical issues are being investigated in IMEC and will be reported in Section 3. Other critical issues are being investigated by other groups around the world and are briefly touched in Section 2. An overview of the various critical issues is maintained in the ISMT stop-light chart (Fig. 1). At any major 157-nm meeting, this chart is updated, based on the progress on each issue. Critical issues are classified under masks, exposure tools, resists, metrology and inspection, and timing.
0167-9317/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2004.02.007
6
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
Fig. 1. ISMT Ôstop lightÕ chart illustrating the 157-nm critical issues and their progress over time.
2. 157-nm critical issues: worldwide update
2.2. Exposure tool status
2.1. Resist status
Here also a major milestone was met: the first 157-nm full-field step and scan system has recently been shipped to IMEC and has been installed successfully: the ASML MicraScan VII, equipped with a 4 reduction lens with a maximum numerical aperture of 0.75, interfaced at IMEC to a TEL Clean Track ACT8. This lithocell will be the workhorse of the 157-nm research projects at IMEC and a lot of further learning is expected to take place in the next 12 months that will hopefully turn some yellow lights to green in Fig. 1. At the same 157-nm symposium, a lot of progress was reported on the quality of CaF2 lens material that lately has come available [7]. The levels of stress birefringence that are reported in 2003 are consistently within specification for the h1 1 1i crystal orientations and starts to pass the specification limit also for the more recently developed h1 0 0i orientations that are needed to compensate for the intrinsic birefringence in the CaF2 crystal.
At the fourth International Symposium on 157nm lithography, held end of August 2003 in Yokohama, good progress was shown on 157-nm resist performance [3]. Already last year a few resists started to show absorbances below 1/lm. Now more and more materials are showing this, allowing imaging in 150-nm thick resists. TodayÕs stateof-the-art resists are capable of resolving 60 nm lines and spaces (1:1) on 0.85 NA micro-steppers [4,5]. Resists can be deposited on both organic and inorganic anti-reflective coatings (ARC) with limited footing. Organic bottom ARCs dedicated for 157 nm are starting to appear [5]. Excellent postexposure bake (PEB) sensitivity has been reported by multiple sources (<0.5 nm/°C). All these excellent results have been reported in Yokohama [6]. At the same time, there is still a lot of room for improvements as well, for example in terms of lineedge roughness, post-exposure bake delay stability, and sensitivity.
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
2.3. Soft pellicle The development of soft-pellicle polymers for 157-nm lithography continues to be a worry. The last time progress was reported in mid 2002, the lifetimes of the pellicles were up to 20 J/cm2 , whereas the initial target was set an order of magnitude higher to give a practical lifetime. Currently no major progress in lifetime has been achieved [8], but the focus of the work has shifted more to understanding the failure mechanisms in the polymers [9]. Instead, as a temporary intermediate solution for the 157-nm pellicle problem, hard pellicles (800 lm thick modified fused silica plate) have been proposed. The drawback of this approach is twofold: first of all they are much more expensive to manufacture; and secondly they form an optical element in the light path, so they need to meet very stringent quality specifications in order not to degrade the imaging. The status of hard pellicles will be given in the following section.
3. 157-nm program status at IMEC Now that the ASML MicraScan VII full-field scanner has been accepted at IMEC, several projects can be started in which the real full-field aspects can be taken into consideration or where the real 157-nm wavelength can be applied. Besides projects on resist benchmarking, track integration
7
and critical-layer patterning, a number of projects specific to 157-nm operation have been started, and are described more in detail below. 3.1. MicraScan VII performance at IMEC The ASML MicraScan VII at IMEC is specified for 100-nm equal line-space dimensions and 70 nm isolated-line dimensions. The full-field critical dimension (CD) uniformity is about 10 nm (3 sigma) for the lines and spaces and 15 nm for the isolated lines [10]. In terms of lithographic performance, 100- and 90-nm equal lines and spaces have shown the widest process latitudes when quadrupole illumination is used, whereas dipole illumination further pushed the resolution to 70-nm equal lines and spaces and even 60-nm lines with 75-nm spaces (Fig. 2). All these results are shown in a 150-nm thick F2 resist with an absorption below 1/lm. An important project that will be running on this first full-field scanner will be to monitor the stability over time of the lithographic performance and to try to correlate any degradation with potential molecular contamination detected in the purge gases of the optics. 3.2. Hard-pellicle imaging Hard pellicles have been chosen as an intermediate solution until soft-pellicle materials exhibit
Fig. 2. (a) The 100- and 90-nm equal lines and spaces imaged on the ASML MicraScan VII using quadrupole illumination (0.75 NA), through-focus series. (b) The 70-nm equal lines and spaces and 60 nm lines/75 nm spaces imaged using dipole illumination (0.75 NA), through-focus series.
8
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
sufficient radiation hardness to be useful for 157 nm small-volume manufacturing. However, hard pellicles have a thickness of about 800 lm and contribute significantly to the imaging and overlay budget in a projection exposure system. There are very large focus offsets and high aberration levels if no precautions are taken. Our work, until now done primarily at 193 nm wavelength, has shown that sufficient lens manip-
ulators exist to compensate for these unwanted effects [11]. As a result we can now conclude that all imaging contributions of hard pellicles are understood and that effects on aberrations, focal plane deviation and CD uniformity can be eliminated successfully (Fig. 3). The main still remaining issue is the flatness of the pellicle mounting to the reticle, which is not yet meeting the required specifications; primarily, it
Fig. 3. (a) Focal plane deviation (FPD) and astigmatism (AST) measured across the full scanner field with and without a hard pellicle (1 grey level corresponds to 6 nm for FPD and 10 nm for AST). (b) CD uniformity measured across the full scanner field with and without a hard pellicle (1 grey level corresponds to 1 nm CD).
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
causes distortions at the edge of the field, where the ‘‘local tilt’’ numbers reach their maxima. Pellicle mounting technology improvements are required to meet the specifications, so that the overlay budgets also will not suffer from hard pellicles. Ideas exist how to get there and the work is continuing.
9
the contamination rates (in order to predict the required cleaning frequency). Also other error sources (like transport of a reticle, inspection at a mask shop, reticle storage in the fab) will be investigated and where necessary, cleaning procedures will be established.
3.3. 157-nm VUV reticle cleaning 4. Conclusions It has been reported that organic contamination, which is being deposited as a (few) monolayer(s) onto the 157-nm reticle substrates, will degrade the 157-nm reticle transmission by a few percent [12,13]. Very quick calculations indicate that this will consume a significant portion of the exposure budget for the relevant technology nodes, so this effect cannot be tolerated. It has been reported also that this contamination can be removed by a VUV cleaning process, in which the reticle is illuminated with 172 nm light in the presence of a little oxygen in nitrogen (Fig. 4). This restores the loss in transmission and avoids in situ cleaning while exposing the first dies on the wafer using the 157-nm laser light. At IMEC, quite some work has been spent on setting up a good metrology procedure to measure the effects of such VUV cleaning cycles in a reliable way, i.e., to levels of precision better than 0.2%. Using these procedures, the cleaning processes can be optimised and a detailed look will be taken on
Fig. 4. Blank transmission as function of wavelength, before and after VUV cleaning of the reticle (the interrupted line indicates the actinic exposure wavelength of 157 nm).
The various critical issues for 157-nm lithography have been reviewed in this paper. For almost all of these issues, significant progress has been made or alternative solutions have been suggested and are under way. All potential show-stoppers had already been removed, one year ago. It has been shown that steady progress is being made on the transparency and lithographic quality of 157-nm resists. With respect to line edge roughness reduction, dry-etch resistance, and integration of the total process, the work can really start now using the first full-field scanner, installed at IMEC: the ASML MicraScan VII. No progress has been made on soft pellicles, whereas all the optical effects of hard pellicles have been shown to be understood and manageable. The main remaining issue with hard pellicles is the mounting technology to further reduce the local tilt. In terms of organic contamination of reticles, the work on finding the right handling and cleaning procedures can start using the MSVII. Besides the technical progress on the 157-nm critical features, it is also important to follow the progress on competing technologies. The 193-nm lithography has also made significant progress in the past 2 years, to an extent that almost the complete industry is convinced today that the 65nm node can be done using the newly developed very high-NA 193-nm lenses (NA > 0:85). As a result, the industry does no longer view 157-nm lithography as a technology for the 65-nm node but rather as a 45-nm node technology. As a result, many of the requirements for the 157-nm critical issues have become much more severe. This explains why in August 2003, most of the yellow bullets remained yellow, despite the technical progress that has been demonstrated.
10
K. Ronse et al. / Microelectronic Engineering 73–74 (2004) 5–10
Acknowledgements The author thank the IMEC lithography department, including the industrial affiliates based at IMEC. Also the dry-etch group is acknowledged for their contributions. The authors also thank the ASML and Zeiss 157 nm development teams. International Sematech (G. Feit, K. Dean and K. Turnquest) and Selete (T. Itani) are acknowledged for providing access to their 157 nm microstepper infrastructure. Walt Trybula (ISMT) is acknowledged for providing the stop light chart on 157 nm. Last but not least, the authors want to thank all the partner companies of the IMEC 157 nm program for their support. Part of this work has been sponsored by International Sematech, Medeaþ (T401 FLUOR) and the European Commission (IST2000-30175 UV2Litho). References [1] International Technology Roadmap for Semiconductors. http://public.itrs.net. [2] Third International Symposium on 157 nm lithography, Antwerp, September, 2002. [3] Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. [4] F. Houlihan, A. Romano, D. Rentkiewicz, R. Sakamuri, R.R. Dammel, W. Conley, G. Rich, D. Miller, L. Rhodes, J. McDaniels, C. Chang, New Fluorinated Resists for Application in 157 nm Lithography Promerus, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. [5] T. Moriya, M. Koh, T. Ishikawa, T. Kodani, T. Araki, M. Toriumi, H. Aoyama, T. Yamashita, T. Hagiwara, T.
[6]
[7]
[8]
[9]
[10]
[11]
[12] [13]
Furukawa, T. Itani, Novel Main-chain-Fluorinated Polymers for 157-nm Photoresists, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. K. Turnquest, K. Dean, V. Graffenberg, S. Patel, D. Miller, G. Rich, Advancements in 157 nm Resist Performance, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. T. Modderman, T. OÕNeill, H. Jasper, H. Sewell, B. Tirri, H. Boom, T. Uiterdijk, S. Dana, M. Brunotte, B. Mecking, W. Kaiser, From Development to Production 157 nm Lithography Exposure Tools in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. A. Tregub, F. Eschbach, J. Powers, F.C. Lo, Development of Fluoropolymer Membranes Transparent and Resistant to 157 nm Exposure, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. V. Liberman, J.H.C. Sedlacek, T.H. Fedynyshyn, R.B. Goodman, R. Sinta, Improved Pellicles for 157 nmLithography – A Nanocomposite Approach, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. Jan Hermans, F. Van Roey, D. Van den Heuvel, R. Gronheid, A.M. Goethals, K. Ronse, S. Light, R. Watso, D. Mc Cafferty, T. OÕNeil, H. Sewell, 157 nm Full Field Imaging, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. P. De Bisschop, R. Bruls, O. Cicilia, T. Uitterdijk, A. Grenville, M. Kocsis, C. Van Peski, Initial Assessment of the Impact of the Use of a Hard Pellicle on Imaging, in: Fourth International Symposium on 157 nm lithography, Yokohama, August, 2003. T. Bloomstein, ISMT 157 nm reticle handling meeting, San Diego, 2000. A. Duisterwinkel, W. van Schaik, Molecular Contamination in 157 nm Lithography: Feasibility of Reticle Cleaning, in: Third International Symposium on 157 nm lithography, Antwerp, September 2002.