stephane durant - Academia.edu (original) (raw)
Papers by stephane durant
Journal of vacuum science & technology, Nov 1, 2004
The development of a nanolithography technique utilizing ultrashort wavelength of surface plasmon... more The development of a nanolithography technique utilizing ultrashort wavelength of surface plasmons (SPs) is presented in this article. The mask consists of silver thin film perforated with two-dimensional hole arrays exhibiting superior confinement due to SPs with a wavelength equal to 1 4 of that of the illuminating light (365 nm). This short wavelength of SPs can confine the field on an area much smaller compared to the excitation light wavelength, leading to the higher resolution lithography than conventional photolithography methods. Finite-difference time-domain simulations show significantly enhanced electric field and tight confinement of the near-field profile obtained from silver plasmonic masks, where features as small as 30 nm can be resolved. Furthermore, the lithography experiments have been performed with demonstration of sub-100 nm spatial resolution.
Journal of the Optical Society of America, 2007
We address the problem of the modeling of the extinction coefficient into an absorbing medium, in... more We address the problem of the modeling of the extinction coefficient into an absorbing medium, including a random distribution of identical scatterers of arbitrary size. We show that the extinction coefficient, including losses in the host medium, can be derived from a diagrammatic expansion arising from the rigorous multiple-scattering theory of electromagnetic waves in random media. While in previous approaches the contribution to the extinction coefficient due to the absorption in the host medium and due to the absorption and scattering by the particles were evaluated separately and heuristically, our approach is based on a derivation from first principles.
de r efraction d epend par exemple de la longueur d'onde, la lumi ere blanche peut se d ecomposer... more de r efraction d epend par exemple de la longueur d'onde, la lumi ere blanche peut se d ecomposer du violet au rouge en passant pour toutes les couleurs de l'arc en ciel
Journal of Physical Chemistry B, Feb 7, 2006
We have developed a novel technique to precisely determine the Raman enhancement factor in single... more We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1 (0.3) × 10 10 , with the highest enhancement factor being achieved by using an individual nanoparticle. By using nanofabrication techniques, we eliminate the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods. TNPRs produce very controllable and repeatable SERS signals at the desired locations and, thus, make an ideal candidate for device integration.
Proceedings of SPIE, Mar 26, 2013
ABSTRACT As design rule shrinks, it is essential that the capability to detect smaller and smalle... more ABSTRACT As design rule shrinks, it is essential that the capability to detect smaller and smaller defects should improve. There is considerable effort going on in the industry to enhance Immersion Lithography using DSA for 14 nm design node and below. While the process feasibility is demonstrated with DSA, material issues as well as process control requirements are not fully characterized. The chemical epitaxy process is currently the most-preferred process option for frequency multiplication and it involves new materials at extremely small thickness. The image contrast of the lamellar Line/Space pattern at such small layer thickness is a new challenge for optical inspection tools. In this investigation, the focus is on the capability for optical inspection systems to capture DSA unique defects such as dislocations and disclination clusters over the system and wafer noise. The study is also extended to investigate wafer level data at multiple process steps and determining contribution from each process step and materials using `Defect Source Analysis' methodology. The added defect pareto and spatial distributions of added defects at each process step are discussed.
Proceedings of SPIE, Mar 28, 2014
Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generati... more Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.), the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces very little defect scattering signal. These defects, termed as “dislocation” and “disclination” have unique shapes and have very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous Coupled-Wave Analysis (RCWA) method for solving Maxwell’s equations to simulate the DSA unique defects and calculate inspection parameters. Controllable inspection parameters include various illumination and collection apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA simulation, we compared SNR between “Post-SiN etch” and “Post-SiN+Si-substrate etch” steps. The study is also extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA unique defect types.
Nano Letters, May 8, 2004
We report experimental and theoretical studies on the plasmon resonances of finite one-dimensiona... more We report experimental and theoretical studies on the plasmon resonances of finite one-dimensional chains of Au nanoparticles excited by evanescent light waves with polarization parallel to the chains. The experimental results show that the plasmon resonance peak wavelengths of these finite 1D chains are significantly red-shifted in comparison to that of single Au nanoparticle. Contrary to previous findings, the peak wavelengths are observed to be a nonmonotonic function of particle numbers in the chain. This phenomenon is reproduced in the theoretical results obtained by using the transfer-matrix method and is shown to occur only for larger particles where phase retardation effects are important in plasmon coupling.
Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-dis... more Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-disk position to study the effect of symmetry breaking in pentamers. It is found that while planar symmetric oligomers can exhibit a single Fano Resonance (FR), an offset of the central nano-disk at a controlled gap of 3 nm from the nearest neighbor nano-disk, gives rise to the appearance of an additional dark mode that can potentially be used in localized surface plasmon resonance sensing. It is shown that this mode leads to the appearance of the second FR in the same spectrum. The simulation results are in a good agreement with experimental data. Furthermore, it is found that unique near-field energy distribution in the asymmetric pentamers can be well tuned to be localized at one, two or three of the four subwavelength gaps of the pentamer selectively by only changing the polarization orientation of a single light source.
Journal of the Optical Society of America, 2007
We address the problem of the modeling of the extinction coefficient into an absorbing medium, in... more We address the problem of the modeling of the extinction coefficient into an absorbing medium, including a random distribution of identical scatterers of arbitrary size. We show that the extinction coefficient, including losses in the host medium, can be derived from a diagrammatic expansion arising from the rigorous multiple-scattering theory of electromagnetic waves in random media. While in previous approaches the contribution to the extinction coefficient due to the absorption in the host medium and due to the absorption and scattering by the particles were evaluated separately and heuristically, our approach is based on a derivation from first principles.
L'invention porte sur un procede d'inspection des defauts de plaquettes qui peut comprend... more L'invention porte sur un procede d'inspection des defauts de plaquettes qui peut comprendre, mais sans y etre limite : la fourniture d'une cible a inspecter; l'application d'au moins un composant d'amelioration d'inspection de defauts a la cible a inspecter; l'eclairement de la cible a inspecter comprenant l'au moins un composant d'amelioration d'inspection pour generer un ou plusieurs signaux d'inspection associes a une ou plusieurs caracteristiques de la cible a inspecter; la detection des signaux d'inspection; et la generation d'un ou plusieurs parametres d'inspection a partir des signaux d'inspection. Une cible a inspecter peut comprendre, mais sans y etre limitee : au moins une couche d'inspection; et au moins une couche d'amelioration d'inspection.
Wafer inspection system includes a laser droplet plasma (LDP) light source for generating light h... more Wafer inspection system includes a laser droplet plasma (LDP) light source for generating light having a sufficient radiation intensity to allow 40 nanometers or less (down-to) at a wavelength of bright field (bright field) test. Light generated by the LDP is directed to the wafer, the light from the illuminated wafer is collected by the high NA objective lens having a total reflection element. Detector, for further image processing, and detects the object to be collected light. LDP source includes a droplet generator for discharging liquid droplets of feed material. Excitation light generated by the laser is focused on the droplets of the feed material. Interaction between the excitation light and the droplet produces a plasma that emits an illumination light having a radiation intensity of at least 10 W / mm 2
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2005
The development of a near-field optical lithography is presented in this paper. By accessing shor... more The development of a near-field optical lithography is presented in this paper. By accessing short modal wavelengths of localized surface plasmon modes on a planar metallic mask, the resolution can be significantly increased while using conventional UV light source. Taking into account the real material properties, numerical studies indicate that the ultimate lithographic resolution at 20nm is achievable through a silver mask by using 365nm wavelength light. The surface quality of the silver mask is improved by adding an adhesion layer of titanium during the mask fabrication. Using a two-dimensional hole array silver mask, we experimentally demonstrated nanolithography with half-pitch resolution down to 60nm, far beyond the resolution limit of conventional lithography using I-line (365nm) wavelength.
We demonstrated an enhanced near-field optical Moir'e effect by inserting a silver slab betwe... more We demonstrated an enhanced near-field optical Moir'e effect by inserting a silver slab between two subwavelength gratings. The evanescent fields can be greatly enhanced by the surface plasmon excitation supported by the silver slab, which leads to a remarkable contrast improvement in the Moir'e fringes. The crucial role of surface plasmon excitation was elucidated by numerical simulation. Experimental enhanced near-field
Optics Express, 2007
A far-field optical superlens, which is able to form subdiffraction-limited images in the far fie... more A far-field optical superlens, which is able to form subdiffraction-limited images in the far field at UV wavelength, was recently demonstrated. In current work we present two methods to tune the working wavelength from UV to visible by tuning either the permittivity of the surrounding medium or that of the metal. A practical design is provided for each method. The tunable far-field superlens enables possible applications of the far-field superlens in sub-diffraction-limited imaging and sensing over a wide range of wavelength.
Optics Express, 2007
Contrary to the conventional near-field superlensing, subwavelength superlens imaging is experime... more Contrary to the conventional near-field superlensing, subwavelength superlens imaging is experimentally demonstrated in the far-field. The key element is termed as a Far-field SuperLens (FSL) which consists of a conventional superlens and a nanoscale coupler. The evanescent fields from the object are enhanced and then converted into propagating fields by the FSL. By only measuring the propagating field in the far-field, the object image can be reconstructed with subwavelength resolution. As an example of this concept, we design and fabricate a silver structured one dimensional FSL. Experimental results show that feature resolution of better than 50nm is possible using current FSL design.
MRS Proceedings, 2006
Conventional optical imaging systems cannot resolve the features smaller than approximately half ... more Conventional optical imaging systems cannot resolve the features smaller than approximately half the size of the working wavelength, called the diffraction limit. The superlens theory predicts that a flat lens made of an ideal material with negative permittivity and/or permeability is able to resolve features much smaller than working wavelength through the restoration of evanescent waves. We experimentally demonstrated the superlens concept for the first time using a thin silver slab in a quasi-static regime; a 60nm half-pitch object was imaged with 365nm illumination wavelength, λ/6 resolution, and the imaging of 50nm half-pitch object under the same light source, λ/7, was also reported. Here, we present mainly experimental studies of near-field optical superlens imaging.
SPIE Proceedings, 2014
Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generati... more Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.), the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces very little defect scattering signal. These defects, termed as “dislocation” and “disclination” have unique shapes and have very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous Coupled-Wave Analysis (RCWA) method for solving Maxwell’s equations to simulate the DSA unique defects and calculate inspection parameters. Controllable inspection parameters include various illumination and collection apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA simulation, we compared SNR between “Post-SiN etch” and “Post-SiN+Si-substrate etch” steps. The study is also extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA unique defect types.
Conference on Electromagnetic and Light Scattering, 2007
ABSTRACT We report a theoretical and numerical investigation of the light scattering in an absorb... more ABSTRACT We report a theoretical and numerical investigation of the light scattering in an absorbing medium with randomly distributed scatterers. The extinction coefficient is derived from the imaginary part of the effective index derived using a diagrammatic approach. The accuracy of the result is assessed by comparison with a numerical solution of Maxwell's equations that fully accounts for multiple scattering.
The Journal of Physical Chemistry B, 2006
We have developed a novel technique to precisely determine the Raman enhancement factor in single... more We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1 (0.3) × 10 10 , with the highest enhancement factor being achieved by using an individual nanoparticle. By using nanofabrication techniques, we eliminate the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods. TNPRs produce very controllable and repeatable SERS signals at the desired locations and, thus, make an ideal candidate for device integration.
Journal of vacuum science & technology, Nov 1, 2004
The development of a nanolithography technique utilizing ultrashort wavelength of surface plasmon... more The development of a nanolithography technique utilizing ultrashort wavelength of surface plasmons (SPs) is presented in this article. The mask consists of silver thin film perforated with two-dimensional hole arrays exhibiting superior confinement due to SPs with a wavelength equal to 1 4 of that of the illuminating light (365 nm). This short wavelength of SPs can confine the field on an area much smaller compared to the excitation light wavelength, leading to the higher resolution lithography than conventional photolithography methods. Finite-difference time-domain simulations show significantly enhanced electric field and tight confinement of the near-field profile obtained from silver plasmonic masks, where features as small as 30 nm can be resolved. Furthermore, the lithography experiments have been performed with demonstration of sub-100 nm spatial resolution.
Journal of the Optical Society of America, 2007
We address the problem of the modeling of the extinction coefficient into an absorbing medium, in... more We address the problem of the modeling of the extinction coefficient into an absorbing medium, including a random distribution of identical scatterers of arbitrary size. We show that the extinction coefficient, including losses in the host medium, can be derived from a diagrammatic expansion arising from the rigorous multiple-scattering theory of electromagnetic waves in random media. While in previous approaches the contribution to the extinction coefficient due to the absorption in the host medium and due to the absorption and scattering by the particles were evaluated separately and heuristically, our approach is based on a derivation from first principles.
de r efraction d epend par exemple de la longueur d'onde, la lumi ere blanche peut se d ecomposer... more de r efraction d epend par exemple de la longueur d'onde, la lumi ere blanche peut se d ecomposer du violet au rouge en passant pour toutes les couleurs de l'arc en ciel
Journal of Physical Chemistry B, Feb 7, 2006
We have developed a novel technique to precisely determine the Raman enhancement factor in single... more We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1 (0.3) × 10 10 , with the highest enhancement factor being achieved by using an individual nanoparticle. By using nanofabrication techniques, we eliminate the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods. TNPRs produce very controllable and repeatable SERS signals at the desired locations and, thus, make an ideal candidate for device integration.
Proceedings of SPIE, Mar 26, 2013
ABSTRACT As design rule shrinks, it is essential that the capability to detect smaller and smalle... more ABSTRACT As design rule shrinks, it is essential that the capability to detect smaller and smaller defects should improve. There is considerable effort going on in the industry to enhance Immersion Lithography using DSA for 14 nm design node and below. While the process feasibility is demonstrated with DSA, material issues as well as process control requirements are not fully characterized. The chemical epitaxy process is currently the most-preferred process option for frequency multiplication and it involves new materials at extremely small thickness. The image contrast of the lamellar Line/Space pattern at such small layer thickness is a new challenge for optical inspection tools. In this investigation, the focus is on the capability for optical inspection systems to capture DSA unique defects such as dislocations and disclination clusters over the system and wafer noise. The study is also extended to investigate wafer level data at multiple process steps and determining contribution from each process step and materials using `Defect Source Analysis' methodology. The added defect pareto and spatial distributions of added defects at each process step are discussed.
Proceedings of SPIE, Mar 28, 2014
Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generati... more Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.), the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces very little defect scattering signal. These defects, termed as “dislocation” and “disclination” have unique shapes and have very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous Coupled-Wave Analysis (RCWA) method for solving Maxwell’s equations to simulate the DSA unique defects and calculate inspection parameters. Controllable inspection parameters include various illumination and collection apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA simulation, we compared SNR between “Post-SiN etch” and “Post-SiN+Si-substrate etch” steps. The study is also extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA unique defect types.
Nano Letters, May 8, 2004
We report experimental and theoretical studies on the plasmon resonances of finite one-dimensiona... more We report experimental and theoretical studies on the plasmon resonances of finite one-dimensional chains of Au nanoparticles excited by evanescent light waves with polarization parallel to the chains. The experimental results show that the plasmon resonance peak wavelengths of these finite 1D chains are significantly red-shifted in comparison to that of single Au nanoparticle. Contrary to previous findings, the peak wavelengths are observed to be a nonmonotonic function of particle numbers in the chain. This phenomenon is reproduced in the theoretical results obtained by using the transfer-matrix method and is shown to occur only for larger particles where phase retardation effects are important in plasmon coupling.
Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-dis... more Arrays of asymmetric pentamers are designed and fabricated with an offset of the central nano-disk position to study the effect of symmetry breaking in pentamers. It is found that while planar symmetric oligomers can exhibit a single Fano Resonance (FR), an offset of the central nano-disk at a controlled gap of 3 nm from the nearest neighbor nano-disk, gives rise to the appearance of an additional dark mode that can potentially be used in localized surface plasmon resonance sensing. It is shown that this mode leads to the appearance of the second FR in the same spectrum. The simulation results are in a good agreement with experimental data. Furthermore, it is found that unique near-field energy distribution in the asymmetric pentamers can be well tuned to be localized at one, two or three of the four subwavelength gaps of the pentamer selectively by only changing the polarization orientation of a single light source.
Journal of the Optical Society of America, 2007
We address the problem of the modeling of the extinction coefficient into an absorbing medium, in... more We address the problem of the modeling of the extinction coefficient into an absorbing medium, including a random distribution of identical scatterers of arbitrary size. We show that the extinction coefficient, including losses in the host medium, can be derived from a diagrammatic expansion arising from the rigorous multiple-scattering theory of electromagnetic waves in random media. While in previous approaches the contribution to the extinction coefficient due to the absorption in the host medium and due to the absorption and scattering by the particles were evaluated separately and heuristically, our approach is based on a derivation from first principles.
L'invention porte sur un procede d'inspection des defauts de plaquettes qui peut comprend... more L'invention porte sur un procede d'inspection des defauts de plaquettes qui peut comprendre, mais sans y etre limite : la fourniture d'une cible a inspecter; l'application d'au moins un composant d'amelioration d'inspection de defauts a la cible a inspecter; l'eclairement de la cible a inspecter comprenant l'au moins un composant d'amelioration d'inspection pour generer un ou plusieurs signaux d'inspection associes a une ou plusieurs caracteristiques de la cible a inspecter; la detection des signaux d'inspection; et la generation d'un ou plusieurs parametres d'inspection a partir des signaux d'inspection. Une cible a inspecter peut comprendre, mais sans y etre limitee : au moins une couche d'inspection; et au moins une couche d'amelioration d'inspection.
Wafer inspection system includes a laser droplet plasma (LDP) light source for generating light h... more Wafer inspection system includes a laser droplet plasma (LDP) light source for generating light having a sufficient radiation intensity to allow 40 nanometers or less (down-to) at a wavelength of bright field (bright field) test. Light generated by the LDP is directed to the wafer, the light from the illuminated wafer is collected by the high NA objective lens having a total reflection element. Detector, for further image processing, and detects the object to be collected light. LDP source includes a droplet generator for discharging liquid droplets of feed material. Excitation light generated by the laser is focused on the droplets of the feed material. Interaction between the excitation light and the droplet produces a plasma that emits an illumination light having a radiation intensity of at least 10 W / mm 2
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2005
The development of a near-field optical lithography is presented in this paper. By accessing shor... more The development of a near-field optical lithography is presented in this paper. By accessing short modal wavelengths of localized surface plasmon modes on a planar metallic mask, the resolution can be significantly increased while using conventional UV light source. Taking into account the real material properties, numerical studies indicate that the ultimate lithographic resolution at 20nm is achievable through a silver mask by using 365nm wavelength light. The surface quality of the silver mask is improved by adding an adhesion layer of titanium during the mask fabrication. Using a two-dimensional hole array silver mask, we experimentally demonstrated nanolithography with half-pitch resolution down to 60nm, far beyond the resolution limit of conventional lithography using I-line (365nm) wavelength.
We demonstrated an enhanced near-field optical Moir'e effect by inserting a silver slab betwe... more We demonstrated an enhanced near-field optical Moir'e effect by inserting a silver slab between two subwavelength gratings. The evanescent fields can be greatly enhanced by the surface plasmon excitation supported by the silver slab, which leads to a remarkable contrast improvement in the Moir'e fringes. The crucial role of surface plasmon excitation was elucidated by numerical simulation. Experimental enhanced near-field
Optics Express, 2007
A far-field optical superlens, which is able to form subdiffraction-limited images in the far fie... more A far-field optical superlens, which is able to form subdiffraction-limited images in the far field at UV wavelength, was recently demonstrated. In current work we present two methods to tune the working wavelength from UV to visible by tuning either the permittivity of the surrounding medium or that of the metal. A practical design is provided for each method. The tunable far-field superlens enables possible applications of the far-field superlens in sub-diffraction-limited imaging and sensing over a wide range of wavelength.
Optics Express, 2007
Contrary to the conventional near-field superlensing, subwavelength superlens imaging is experime... more Contrary to the conventional near-field superlensing, subwavelength superlens imaging is experimentally demonstrated in the far-field. The key element is termed as a Far-field SuperLens (FSL) which consists of a conventional superlens and a nanoscale coupler. The evanescent fields from the object are enhanced and then converted into propagating fields by the FSL. By only measuring the propagating field in the far-field, the object image can be reconstructed with subwavelength resolution. As an example of this concept, we design and fabricate a silver structured one dimensional FSL. Experimental results show that feature resolution of better than 50nm is possible using current FSL design.
MRS Proceedings, 2006
Conventional optical imaging systems cannot resolve the features smaller than approximately half ... more Conventional optical imaging systems cannot resolve the features smaller than approximately half the size of the working wavelength, called the diffraction limit. The superlens theory predicts that a flat lens made of an ideal material with negative permittivity and/or permeability is able to resolve features much smaller than working wavelength through the restoration of evanescent waves. We experimentally demonstrated the superlens concept for the first time using a thin silver slab in a quasi-static regime; a 60nm half-pitch object was imaged with 365nm illumination wavelength, λ/6 resolution, and the imaging of 50nm half-pitch object under the same light source, λ/7, was also reported. Here, we present mainly experimental studies of near-field optical superlens imaging.
SPIE Proceedings, 2014
Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generati... more Directed Self-Assembly (DSA) is considered as a potential patterning solution for future generation devices. One of the most critical challenges for translating DSA into high volume manufacturing is to achieve low defect density in the DSA patterning process. The defect inspection capability is fundamental to defect reduction in any process, particularly the DSA process, as it provides engineers with information on the numbers and types of defects. While the challenges of other candidates of new generation lithography are well known (for example, smaller size, noise level due to LER etc.), the DSA process causes certain defects that are unique. These defects are nearly planar and in a material which produces very little defect scattering signal. These defects, termed as “dislocation” and “disclination” have unique shapes and have very little material contrast. While large clusters of these unique defects are easy to detect, single dislocation and disclination defects offer considerable challenge during inspection. In this investigation, etching the DSA pattern into a silicon (Si) substrate structure to enhance defect signal and Signal-to-Noise Ratio (SNR) is studied. We used a Rigorous Coupled-Wave Analysis (RCWA) method for solving Maxwell’s equations to simulate the DSA unique defects and calculate inspection parameters. Controllable inspection parameters include various illumination and collection apertures, wavelength band, polarization, noise filtering, focus, pixel size, and signal processing. From the RCWA simulation, we compared SNR between “Post-SiN etch” and “Post-SiN+Si-substrate etch” steps. The study is also extended to investigate wafer-level data at post etch inspection. Both the simulations and inspection tool results showed dramatic signal and SNR improvements when the pattern was etched into the SiN+Si substrate allowing capture of DSA unique defect types.
Conference on Electromagnetic and Light Scattering, 2007
ABSTRACT We report a theoretical and numerical investigation of the light scattering in an absorb... more ABSTRACT We report a theoretical and numerical investigation of the light scattering in an absorbing medium with randomly distributed scatterers. The extinction coefficient is derived from the imaginary part of the effective index derived using a diagrammatic approach. The accuracy of the result is assessed by comparison with a numerical solution of Maxwell's equations that fully accounts for multiple scattering.
The Journal of Physical Chemistry B, 2006
We have developed a novel technique to precisely determine the Raman enhancement factor in single... more We have developed a novel technique to precisely determine the Raman enhancement factor in single nanoplasmonic resonators (TNPRs). TNPRs are lithographically defined metallodielectric nanoparticles composed of two silver disks stacked vertically, separated by a silica layer. At resonance, the local electromagnetic fields are enhanced at the TNPR surface, making it an ideal surface-enhanced Raman scattering (SERS) active substrate. The ability to control the dimensions of the metallic and dielectric layers offers the unique advantage of fine-tuning the plasmon resonance frequency to maximize the enhancement of the Raman signal. Furthermore, by selective shielding of the outer surface of the metallic structure, the efficiency can be further enhanced by guiding the molecular assembly to the locations that exhibit strong electromagnetic fields. We experimentally demonstrate SERS enhancement factors of (6.1 (0.3) × 10 10 , with the highest enhancement factor being achieved by using an individual nanoparticle. By using nanofabrication techniques, we eliminate the issues such as large size variations, cluster aggregation, and interparticle effects common in preparing SERS substrates using conventional chemical synthesis or batch fabrication methods. TNPRs produce very controllable and repeatable SERS signals at the desired locations and, thus, make an ideal candidate for device integration.