The development of lens systems for projection x-ray lithography presents significant challenges associated with the fabrication and testing of ultra precise optical surfaces. Once assembled, these projection lenses must further be dimensionally stable to tolerances determined by the wavelength of the soft x-rays used for illumination, typically between 100Å and 300Å. Lens systems capable of printing over large areas will contain a number of mirrors with reflectivities in the range of 60±10%. For these systems, the first element will be subjected to a significant incident x-ray flux, of which ~40% will be absorbed. This absorbed power causes heating which in turn will cause a distortion of the optical surface. The intent of this study has been to examine the magnitude of these distortions under a variety of conditions.
{"title":"Analysis of Thermally Induced Distortion of Optics for Soft X-ray Projection Lithography","authors":"R. Watson, R. Stulen","doi":"10.1364/sxray.1991.fb4","DOIUrl":"https://doi.org/10.1364/sxray.1991.fb4","url":null,"abstract":"The development of lens systems for projection x-ray lithography presents significant challenges associated with the fabrication and testing of ultra precise optical surfaces. Once assembled, these projection lenses must further be dimensionally stable to tolerances determined by the wavelength of the soft x-rays used for illumination, typically between 100Å and 300Å. Lens systems capable of printing over large areas will contain a number of mirrors with reflectivities in the range of 60±10%. For these systems, the first element will be subjected to a significant incident x-ray flux, of which ~40% will be absorbed. This absorbed power causes heating which in turn will cause a distortion of the optical surface. The intent of this study has been to examine the magnitude of these distortions under a variety of conditions.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131622121","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the scanning transmission x-ray microscope (STXM) the specimen is scanned in a raster by an x-ray probe formed with a Fresnel zone plate. To achieve near diffraction limited resolution it is necessary to have a coherent source, even when forming an incoherent brightfield image by measuring the x-ray intensity transmitted by the object. This has so far been the only imaging mode used in the STXM and for hydrated biological specimens is well suited to soft x-ray wavelengths within the “water window” (2‧33 to 4‧36 nm) where carbon absorbs much more strongly than water. However, by the use of phase contrast rather than amplitude contrast, it is possible to form images at wavelengths where the absorption is low, resulting in lower radiation dose for the same level of contrast. Calculations made by Howells [1] and Rudolph and Schmahl [2] have demonstrated very clearly the advantages of phase contrast imaging at wavelengths outside the water window.
{"title":"Differential Phase Contrast Imaging in the Scanning Transmission X-ray Microscope","authors":"J. R. Palmer, G. Morrison","doi":"10.1364/sxray.1991.wa15","DOIUrl":"https://doi.org/10.1364/sxray.1991.wa15","url":null,"abstract":"In the scanning transmission x-ray microscope (STXM) the specimen is scanned in a raster by an x-ray probe formed with a Fresnel zone plate. To achieve near diffraction limited resolution it is necessary to have a coherent source, even when forming an incoherent brightfield image by measuring the x-ray intensity transmitted by the object. This has so far been the only imaging mode used in the STXM and for hydrated biological specimens is well suited to soft x-ray wavelengths within the “water window” (2‧33 to 4‧36 nm) where carbon absorbs much more strongly than water. However, by the use of phase contrast rather than amplitude contrast, it is possible to form images at wavelengths where the absorption is low, resulting in lower radiation dose for the same level of contrast. Calculations made by Howells [1] and Rudolph and Schmahl [2] have demonstrated very clearly the advantages of phase contrast imaging at wavelengths outside the water window.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115846584","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Kinoshita, K. Kurihara, T. Mizota, T. Haga, Y. Torii
We have conducted the research work on X-ray projection lithography and have already demonstrated a 0.5 µm replicated pattern using a reflection mask. To obtain smaller features, we have designed a Schwarzschild typed demagnifying objective with a numerical aperture size of 0.1 and fabricated a Mo/B4C multilayer very precisely on its optics.
{"title":"Soft X-ray reduction lithography using a reflection mask","authors":"H. Kinoshita, K. Kurihara, T. Mizota, T. Haga, Y. Torii","doi":"10.1364/sxray.1991.wd2","DOIUrl":"https://doi.org/10.1364/sxray.1991.wd2","url":null,"abstract":"We have conducted the research work on X-ray projection lithography and have already demonstrated a 0.5 µm replicated pattern using a reflection mask. To obtain smaller features, we have designed a Schwarzschild typed demagnifying objective with a numerical aperture size of 0.1 and fabricated a Mo/B4C multilayer very precisely on its optics.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130241335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The total overlay budget in semiconductor lithography has many components, including mask dimensional accuracy, tool-to-tool printing distortion, and process bias, but historically alignment registration has been the most critical. Yet progress in alignment has not kept pace with the exponential increases in printing resolution achieved during the last 10 years. In manufacturing, it is difficult to overlay lithography levels better than 200 nm at the 3 σ confidence level. Registration accuracy is limited by the complex interaction of the alignment optics with wafer registration marks at different process levels. Recent experimental and analytical work has led to an understanding of how to design optical alignment systems with reduced sensitivity to mark structure, coatings and processing. However, it is possible that no single alignment system can be optimized .for all process layers encountered in the fabrication of DRAMS or bipolar logic.
{"title":"Optical Alignment for Lithography","authors":"N. Bobroff, A. Rosenbluth","doi":"10.1364/sxray.1991.fc1","DOIUrl":"https://doi.org/10.1364/sxray.1991.fc1","url":null,"abstract":"The total overlay budget in semiconductor lithography has many components, including mask dimensional accuracy, tool-to-tool printing distortion, and process bias, but historically alignment registration has been the most critical. Yet progress in alignment has not kept pace with the exponential increases in printing resolution achieved during the last 10 years. In manufacturing, it is difficult to overlay lithography levels better than 200 nm at the 3 σ confidence level. Registration accuracy is limited by the complex interaction of the alignment optics with wafer registration marks at different process levels. Recent experimental and analytical work has led to an understanding of how to design optical alignment systems with reduced sensitivity to mark structure, coatings and processing. However, it is possible that no single alignment system can be optimized .for all process layers encountered in the fabrication of DRAMS or bipolar logic.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133108650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A recent feasibility study on X-ray projection lithography (XRPL) has demonstrated an extremely high resolution reaching 0.1 µ m1). For practical manufacturing of integrated circuits, however, a high throughput is also necessary. Although the throughput of an XRPL system was already estimated at a wavelength of 4.5nm2), this system is difficult to build owing to low performance of actual multilayers. We discuss the throughput of an XRPL system using 13nm radiation for which good quality multilayers can be fabricated3).
{"title":"Throughput estimate of an X-ray projection lithography system","authors":"Masaaki Itou, T. Terasawa, S. Moriyama","doi":"10.1364/sxray.1991.the2","DOIUrl":"https://doi.org/10.1364/sxray.1991.the2","url":null,"abstract":"A recent feasibility study on X-ray projection lithography (XRPL) has demonstrated an extremely high resolution reaching 0.1 µ m1). For practical manufacturing of integrated circuits, however, a high throughput is also necessary. Although the throughput of an XRPL system was already estimated at a wavelength of 4.5nm2), this system is difficult to build owing to low performance of actual multilayers. We discuss the throughput of an XRPL system using 13nm radiation for which good quality multilayers can be fabricated3).","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130147081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recently, there have been a number of reports where two-mirror inverted Schwarzschild microscopes, which were coated with appropriate multilayers, have been used in soft x-ray projection lithography experiments and have obtained resolutions as small as 50 nm [1-3]. A projection optics design survey [4] reported that the Schwarzschild type optics will have a field of view less than 1 mm with a resolution of 0.1 microns. However, it has been demonstrated [4,5] that four-mirror projection systems can be designed by conventional techniques to have a resolution less than 0.1 micron over a 20 mm field of view with distortion limiting system performance. Canon has disclosed [6] a number of three- and four-mirror projection lithography systems which are reported to yield 0.25 micron resolution over large fields of view.
{"title":"Design and Analysis of Multi-Mirror Soft X-Ray Projection Lithography Systems","authors":"D. Shealy, Cheng Wang","doi":"10.1364/sxray.1991.the3","DOIUrl":"https://doi.org/10.1364/sxray.1991.the3","url":null,"abstract":"Recently, there have been a number of reports where two-mirror inverted Schwarzschild microscopes, which were coated with appropriate multilayers, have been used in soft x-ray projection lithography experiments and have obtained resolutions as small as 50 nm [1-3]. A projection optics design survey [4] reported that the Schwarzschild type optics will have a field of view less than 1 mm with a resolution of 0.1 microns. However, it has been demonstrated [4,5] that four-mirror projection systems can be designed by conventional techniques to have a resolution less than 0.1 micron over a 20 mm field of view with distortion limiting system performance. Canon has disclosed [6] a number of three- and four-mirror projection lithography systems which are reported to yield 0.25 micron resolution over large fields of view.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122472411","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Synchrotrons and laser-produced plasmas (LPPs) are leading candidates for radiation sources for x-ray lithographic systems. Each has its own strengths and weaknesses. Synchrotrons offer higher flux and brightness but are large and expensive. Laser-produced plasmas sources may be cheaper and smaller but have low average power and non-directional output.
{"title":"Source Issues Relevant to X-Ray Lithography","authors":"K. Nguyen, D. Attwood, T. Gustafson","doi":"10.1364/sxray.1991.tha1","DOIUrl":"https://doi.org/10.1364/sxray.1991.tha1","url":null,"abstract":"Synchrotrons and laser-produced plasmas (LPPs) are leading candidates for radiation sources for x-ray lithographic systems. Each has its own strengths and weaknesses. Synchrotrons offer higher flux and brightness but are large and expensive. Laser-produced plasmas sources may be cheaper and smaller but have low average power and non-directional output.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131555477","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Recent advances in multilayer (ML) fabrication and characterization have brought this technology to the verge of satisfying the severe requirements posed by soft x-ray projection lithography (SXPL). To enable a viable production SXPL system, the ML coatings must simultaneously demonstrate (1) high normal incidence reflectivity in the range of 65-70% at λ=130Å, (2) ML period errors of less than 0.5% over the optical surface to maintain diffraction- limited imaging and (3) long term stability under realistic operating conditions. In addition, it is possible that certain optical designs will require laterally graded coatings with similar tolerances for the ML period errors. This set of stringent requirements can only be achieved via a thorough understanding and control of the ML deposition process, ML structure and properties.
{"title":"Multilayer Mirror Technology","authors":"D. Stearns, R. S. Rosen, S. Vernon","doi":"10.1364/sxray.1992.tub1","DOIUrl":"https://doi.org/10.1364/sxray.1992.tub1","url":null,"abstract":"Recent advances in multilayer (ML) fabrication and characterization have brought this technology to the verge of satisfying the severe requirements posed by soft x-ray projection lithography (SXPL). To enable a viable production SXPL system, the ML coatings must simultaneously demonstrate (1) high normal incidence reflectivity in the range of 65-70% at λ=130Å, (2) ML period errors of less than 0.5% over the optical surface to maintain diffraction- limited imaging and (3) long term stability under realistic operating conditions. In addition, it is possible that certain optical designs will require laterally graded coatings with similar tolerances for the ML period errors. This set of stringent requirements can only be achieved via a thorough understanding and control of the ML deposition process, ML structure and properties.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"2015 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1992-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127307369","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
X-ray multilayer structures derive their utility primarily from the specular reflectance at the first order multilayer Bragg peak. Ideal x-ray multilayer structures would have composition modulation only along the direction of the sample normal (z direction) and would be homogeneous in the x-y plane. Ideal structures would thus exhibit only specular reflectance in the region of low scattering vector near the multilayer Bragg peaks. Structural inhomogeneities in the x-y plane within the multilayer (possibly arrising from the substrate) would give rise to diffuse non-specular scattered intensity in this region.
{"title":"Non-Specular X-ray Scattering from Multilayer Structures","authors":"J. Kortright","doi":"10.1063/1.349259","DOIUrl":"https://doi.org/10.1063/1.349259","url":null,"abstract":"X-ray multilayer structures derive their utility primarily from the specular reflectance at the first order multilayer Bragg peak. Ideal x-ray multilayer structures would have composition modulation only along the direction of the sample normal (z direction) and would be homogeneous in the x-y plane. Ideal structures would thus exhibit only specular reflectance in the region of low scattering vector near the multilayer Bragg peaks. Structural inhomogeneities in the x-y plane within the multilayer (possibly arrising from the substrate) would give rise to diffuse non-specular scattered intensity in this region.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"91 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1991-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125744773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The variation of multilayer period, or d-spacing, across the reflecting surfaces of soft x-ray normal-incidence focussing optics is of primary importance in the optical performance of these systems. Focussing necessarily implies a specific optimal variation of period across the surfaces, and the multilayer bandpass sets the tolerance scale for acceptable deviations from this ideal variation.1,2 Mo/Si multilayers for use at wavelengths above 12.4 nm have relatively broad bandpasses, easing these tolerances. Multilayers for use at shorter wavelengths have significantly narrower bandpasses, thus placing significantly greater demands on the control of the period variation. Other design considerations, such as higher magnification systems and larger optics, also place more stringent demands on the control of multilayer period.
{"title":"Controlling short wavelength x-ray multilayer period variation on focussing optics","authors":"J. Kortright, K. Nguyen, P. Denham, D. Windt","doi":"10.1364/sxray.1992.tub2","DOIUrl":"https://doi.org/10.1364/sxray.1992.tub2","url":null,"abstract":"The variation of multilayer period, or d-spacing, across the reflecting surfaces of soft x-ray normal-incidence focussing optics is of primary importance in the optical performance of these systems. Focussing necessarily implies a specific optimal variation of period across the surfaces, and the multilayer bandpass sets the tolerance scale for acceptable deviations from this ideal variation.1,2 Mo/Si multilayers for use at wavelengths above 12.4 nm have relatively broad bandpasses, easing these tolerances. Multilayers for use at shorter wavelengths have significantly narrower bandpasses, thus placing significantly greater demands on the control of the period variation. Other design considerations, such as higher magnification systems and larger optics, also place more stringent demands on the control of multilayer period.","PeriodicalId":409291,"journal":{"name":"Soft-X-Ray Projection Lithography","volume":"514 ","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133910636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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