Plasmon Interference Lithography Research Articles

Plasmonic interference lithography based on the second-order diffracted wave of grating and hyperbolic multilayer graphene

Surface plasmon interference lithography (SPIL), which can break the diffraction limit to achieve a large area deep subwavelength resolution, has great application potential in the field of micro-nano manufacturing. However, considering the characteristics of the intensity of each order diffraction wave and the rapid attenuation of surface plasmon polariton (SPP) intensity, most of the current work uses the first order diffraction wave of grating to stimulate SPP. According to the matching conditions, the half-pitch resolution of the interference pattern is 1/4 of the grating period, which makes the method still have high requirements for the mask period. In addition, the intimate contact relationship between each layer limits the reuse of the mask, which ultimately limits the development of SPIL. To address these issues, plasmonic interference lithography based on the second-order diffracted wave of grating and hyperbolic multilayer graphene is proposed. Simulation results show that structures with air gaps can obtain interference patterns with a half-pitch resolution of 1/8 of the grating period and 1/6.7 of incident wavelength, as well as maintaining the characteristic of the insensitive to photoresist (PR) thickness.

Theoretical fabrication of subwavelength structures by surface plasmon interference based on complementary grating

This paper presents a surface plasmon interference lithography technique based on the complementary grating, which comprises silicon gratings and complementary aluminum grating masks, for fabricating subwavelength structures. In this theoretical study, the optimal parameters of the complementary grating structure were determined using the reflectance spectrum. The optical field distributions of one- and two-dimensional subwavelength structures were obtained using the finite-difference time-domain method and rotation-related formulas. The results of numerical evaluations show that a one-dimensional periodic structure with a half-pitch resolution of 60.5 nm (approximately [Formula: see text]/6.7) can be fabricated. In addition, subwavelength structures can be diversified using different rotation methods to expose the photolithography samples, such as square dot arrays and quasi-hexagonal closely packed structures. The proposed method combines surface plasmon interference with sample rotation, thereby enabling fabrication of abundant subwavelength structures.

Theoretical investigation of two-dimensional sub-wavelength structures fabricated by multi-beam surface plasmon interference lithography

In this study, multi-beam surface plasmon (SP) interference lithography was theoretically proposed and demonstrated to fabricate periodic two-dimensional sub-wavelength structures. The lithography structures were based on an attenuated total reflection prism used to excite the SPs using a 442 nm laser. Circular lattices with periods of 166 and 288 nm were successfully obtained via three- and six-beam SP interference lithography, respectively; these lattices exhibited an identical feature size of 96 nm. Square dot arrays with a 177 nm period and 88.5 nm spot size were obtained by four-beam SP interference lithography. The proposed lithography technology has a simple structure and is economical; further, it may provide an effective method for the fabrication of two-dimensional sub-wavelength structures.

Directional excitation of surface plasmon using multi-mode interference in an aperture

Plasmonics is a promising technology that can find many applications in nanophotonics and biosensing. Local excitation of surface plasmons with high directionality is required for many of these applications. We demonstrate that by controlling the interference of light in a metal slot with the adjustment of the angle of incidence, it is possible to achieve highly directional surface plasmon excitation. Our numerical analysis of the structure showing a strong directionality of excited surface plasmon is confirmed by near field scanning measurements. The proposed structure can be useful for many applications including excitation of plasmonic waveguides, nanolithography, and optical sensing. To illustrate its usefulness, we experimentally demonstrate that it can be used for highly directional excitation of a dielectric loaded plasmonic waveguide. We also propose a simple structure for surface plasmon interference lithography capable of providing high image contrast using this scheme.

Plasmonic interference lithography by coupling the bulk plasmon polariton mode and the waveguide mode

Plasmonic lithography based on surface plasmon polariton has been proven to breaking the diffraction limit and deliver the super-resolution patterns. However, most previously reported studies suffer from the low energy efficiency and subwavelength excitation grating that obstructs the application in nanofabrication. In this work, a special plasmonic lithography prototype is proposed based on the coupling of the bulk plasmon polariton mode squeezed through the hyperbolic metamaterial (HMM) and the waveguide mode supported in the coupling layer/HMM/photoresist sandwich structure. The results demonstrate that periodic patterns with strong lithography light intensity (>220%) over the whole photoresist layer compared with incident optical intensity, high aspect ratios (1.5:1) and a half-pitch of 57.5 nm can be generated, under the interference of the fourth-order diffracted light of grating. The lithography linewidth can reach 1/16 of the mask period of 920 nm and ~1/8 of the wavelength of the 436 nm illumination light. This design of period reduction makes the device fabrication much easier, costless and even exhibits good tolerance to the roughness of the multilayer. In addition, theoretical analyses performed are widely applicable to systems working at other ultraviolet wavelengths including 248, 365 and 405 nm.

Highly Uniform Plasmonic Interference Lithography Assisted by Hyperbolic Multilayer Graphene

Plasmonic interference lithography (PIL) is able to break the diffraction limit, realizing deep-subwavelength resolution in a large area. However, because the energy of surface plasmon polariton (SPP) wave is mainly confined on the surface of the metallic layer, the interference patterns in the photoresist layer often suffer from shallowness and nonuniformity. In this work, a PIL structure with highly uniform patterns is proposed, working in the wavelength of 193 nm. The structure consists of a silicon substrate and a photoresist sandwiched by two multilayer graphene films. Due to the hyperbolic property of the multilayer graphene, a slot SPP mode which is weakly dependent on the photoresist thickness is stimulated through volume plasmon polaritons in the hyperbolic multilayer graphene. A uniform periodic pattern with a half-pitch resolution of 29 nm (λ/6.7) maintains even the photoresist thickness that is larger than 80 nm. Our findings may provide a new method to realize robust PIL patterns.

Theoretical study of subwavelength circular grating fabrication based on continuously exposed surface plasmon interference lithography

A surface plasmon interference lithography technique to fabricate subwavelength circular grating by continuous rotating and exposing lithography sample is theoretically demonstrated. Based on the theory of surface plasmon interference lithography in combination with coordinate transformation, the period and contrast of the subwavelength circular grating are analyzed by simulating the corresponding magnetic field intensity distribution. It is believed that this technique can be applied to practical experiments, which provides an interesting alternative for the fabrication of subwavelength circular grating.

Plasmonic Interference Lithography for Low-Cost Fabrication of Dense Lines with Sub-50 nm Half-Pitch

Limited by the cost and complexity, a sub-50 nm lithography node is hard to achieve through the traditional interference lithography. In this paper, the dense lines with half-pitch of 32 nm (∼λ/11) and 22 nm (∼λ/16) are first achieved at the wavelength of 365 nm by simple plasmonic interference lithography. Through selecting the high spatial frequency plasmonic modes in Al/Photoresist (Pr)/Al waveguide and allowing interference with each other, the deep subwavelength plasmonic interference field could be obtained in Pr film. Moreover, the lithography structure is separated from the mask, so etch transfer process from Pr to substrate after lithography is easy to attain, and the mask with high cost could be used multiple times. Meanwhile, a near-field lithography setup was developed, and we experimentally realized the comparatively distinct lithography fringes with the half-pitch of 32 and 22 nm when there is an air gap smaller than ∼20 nm between mask and the lithography films. Compared with the imaging li...

Theoretical investigation of subwavelength structure fabrication based on multi-exposure surface plasmon interference lithography

Abstract We propose a method of fabricating subwavelength structures based on multi-exposure surface plasmon interference lithography. This new nanolithography technique fabricates various subwavelength structures breaking the diffraction limit, which differs from the common method of writing various micro structures by using a two-laser-beam interference with sample rotation. Analysis of the optical field distributions obtained using the proposed nanolithography technique, which was performed using the theory of surface plasmon interference lithography in combination with coordinate matrix transformation, is also provided. Various special subwavelength structures are demonstrated by presenting simulated optical field distributions corresponding to different sample rotations, including two-dimensional lattice structures and periodic quasi-hexagonal structures. These structures are potentially useful in micro- and nano-optics applications.

Large-Area High Aspect Ratio Plasmonic Interference Lithography Utilizing a Single High-k Mode.

Plasmonic lithography, which utilizes subwavelength confinement of surface plasmon polartion (SPP) waves, has the capability of breaking the diffraction limit and delivering high resolution. However, all previously reported results suffer from critical issues, such as shallow pattern depth and pattern nonuniformity even over small exposure areas, which limit the application of the technology. In this work, periodic patterns with high aspect ratios and a half-pitch of about 1/6 of the wavelength were achieved with pattern uniformity in square centimeter areas. This was accomplished by designing a special mask and photoresist (PR) system to select a single high spatial frequency mode and incorporating the PR into a waveguide configuration to ensure uniform light exposure over the entire depth of the photoresist layer. In addition to the experimental progress toward large-scale applications of plasmonic interference lithography, the general criteria of designing such an exposure system is also discussed, which can be used for nanoscale fabrication in this fashion for various applications with different requirements for wavelength, pitch, aspect ratio, and structure.

Pattern Distortion Analysis of Surface Plasmon Interference Lithography Using Line Grating Structure on Photoresist

Photolithography has a resolution limit of the incident wavelength that is generated by the diffraction of light. Surface plasmon (SP) is a recently proposed nanolithography technology that overcomes this diffraction limit. In this paper, we focus on the fabrication process in order to utilize SP with a direct grating structure, and we compare the simulation and fabrication results: the pitch of the expected patterns is 120 nm in the simulation results and 121.5 nm in the calculation results. Therefore, the fabrication results establish that the period of the patterns is 115 nm. These results demonstrate that it is possible for photolithography to use SP. Furthermore, the random horizontal patterns in the fabrication results are analyzed, and it is found that the patterns result from the mask side distortion. Therefore, reducing the mask side distortion using other techniques could enable clearer line patterns in surface plasmon interference lithography.

Surface Plasmon Interference Lithography Assisted by a Fabry–Perot Cavity Composed of Subwavelength Metal Grating and Thin Metal Film**Supported by the Natural Science Foundation of Hebei Province under Grant Nos A2013402069 and A2013402081.

A surface plasmon interference lithography assisted by a Fabry–Perot (F-P) cavity composed of subwavelength metal gratings and a thin metal film is proposed to fabricate high-quality nanopatterns. The calculated results indicate that uniform straight interference fringes with high contrast and high electric-field intensity are formed in the resist under the F-P cavity. The analyses of spatial frequency spectra illuminate the physical mechanism of the formation for the interference fringes. The influence of the F-P cavity spacing is discussed in detail. Moreover, the error analyses reveal that all parameters except the metal grating period in this scheme can bear large tolerances for the device fabrication.

Enhanced surface plasmon interference lithography from cavity resonance in the grating slits**Project supported by the National Basic Research Program of China (Grant No. 2013CBA01702) and the National Natural Science Foundation of China (Grant Nos. 61377016, 61308017, and 61307072).

Surface plasmon interference lithography based on grating diffraction has been studied both theoretically and experimentally in recent years. In this paper, we demonstrate that the cavity resonance in the grating slits can improve the subwavelength interference, not only the intensity but also the uniformity of the pattern. Both the typical lithography structure which merely consists of periodic metallic gratings and the modified structure equipped with a reflection layer are studied. The finite element method has been performed to study the interference pattern. Numerical simulations show that the property of the interference pattern is the optimum when cavity resonance happens. This enhancement can be applied to all the lithography structures which are based on the grating diffraction.

Pushing the resolution of photolithography down to 15nm by surface plasmon interference.

A deep ultraviolet plasmonic structure is designed and a surface plasmon interference lithography method using the structure is proposed to generate large-area periodic nanopatterns. By exciting the anti-symmetric coupled surface plasmon polaritons in the structure, ultrahigh resolution periodic patterns can be formed in a photoresist. The resolution of the generated patterns can be tuned by changing the refractive index and thickness of the photoresist. We demonstrate numerically that one-dimensional and two-dimensional patterns with a half-pitch resolution of 14.6 nm can be generated in a 25 nm-thick photoresist by using the structure under 193 nm illumination. Furthermore, the half-pitch resolution of the generated patterns can be down to 13 nm if high refractive index photoresists are used. Our findings open up an avenue to push the half-pitch resolution of photolithography towards 10 nm.

Enhanced Kretschmann structure for maskless surface plasmon interference lithography

Mask less surface plasmon interference lithography provides potential to obtain nanoscale feature size with large area at low cost. In this paper, we present a novel structure for mask less surface plasmon interference lithography. It is an enhanced Kretschmann structure in which a dielectric layer with low refractive index is added between the prism and metal layer. Numerical results show that the additional dielectric layer eliminates the inherent limit in classic Kretschmann structure that requires use of a prism with high refractive index for lithography purpose. Also, the structure exhibits more flexibility in tuning the spatial resolutions than classic Kretschmann structure. Both advantages lead to the structure more practical in real use.

Surface plasmon interference lithography with a surface relief metal grating

A surface plasmon interference lithography method with a surface relief metal grating is proposed. The interference of the surface plasmon waves produced by a surface relief metal grating with a large feature size at the interface between the surface relief metal grating and a photoresist layer is studied by the finite element method. Numerical results show that the minimum feature size of interference patterns produced by a surface relief AI grating with the minimum feature size of 225.2nm is smaller than 29nm under the condition of 248nm light illumination. Furthermore, the influence of some grating parameters on the intensity of the electric field of surface plasmon interference patterns has been discussed. It is found that the intensity of the electric field of surface plasmon interference patterns obtains its maximum when the groove width of the surface relief metal grating is about an integer multiple of the wavelength of the surface plasmon waves, which can be applied to optimizing the parameter of the surface relief Al grating.

Tuning Metamaterials for Applications at DUV Wavelengths

The unique properties of metamaterials, namely, their negative refractive index, permittivity, or permeability, have gained much recent attention. Research into these materials has led to the realization of a host of applications that may be useful to enhance optical nanolithography. A selection of materials has been examined both experimentally and theoretically to verify their support of surface plasmons, or lack thereof, in the DUV spectrum via the attenuated total reflection (ATR) method using the Kretschmann configuration. At DUV wavelengths, materials that were previously useful at mid-UV and longer wavelengths no longer act as metamaterials. Structured materials comprised of alternating layers of aluminum and aluminum oxide (Al2O3), as well as some other absorption-free dielectrics, exhibit metamaterial behavior, as do some elemental materials such as aluminum. These elemental and structured materials exhibit the best properties for use in plasmonic nanolithographic applications. Therefore, a simulator was created to examine material and thickness combinations to generate a tunable metamaterial for use in the DUV. A method for performing plasmonic interference lithography with this metamaterial has been proposed, with calculations showing the potential for half-pitch imaging resolution of 25 nm.

Coupled surface plasmon interference lithography based on a metal-bounded dielectric structure

We propose a coupled surface plasmon (SP) interference lithography based on a metal-bounded dielectric structure. The long and short range SP interferences at different dielectric thicknesses in the structure are analyzed. The interference in Kretschmann structure under the same conditions is also compared. Numerical results show the coupled SP interference offers better lithography performance as compared with the Kretschmann SP interference. This proposed technique provides potential for fabrication of periodic nanostructures.

Breaking the feature sizes down to sub-22 nm by plasmonic interference lithography using dielectric-metal multilayer

We have developed the plasmonic interference lithography technique to achieve the feature sizes theoretically down to sub-22 nm even to 16.5 nm by using dielectric-metal multilayer (DMM) with diffraction-limited masks at the wavelength of 193 nm with p-polarization. An 8 pairs of GaN (10 nm)/Al (12 nm) multilayer is designed as a filter allowing only a part of high wavevector k (evanescent waves) to pass through for interference lithography. The analysis of the influence by the number of DMM layers is presented. 4 pairs of the proposed multilayer can be competent for pattern the minimal feature size down to 21.5 nm at the visibility about 0.4 to satisfy the minimum visibility required with positive resist. Finite-difference time-domain analysis method is used to demonstrate the validity of the theory.

Plasmonic interference nanolithography with a double-layer planar silver lens structure

We present here a surface plasmon interference lithography method with double-layer planar silver lens. This kind of lithography method provides interference patterns with sufficient contrast for lithography process and simple structure for the convenience of fabrication. Rigorous coupled wave analysis method has been performed with practical parameters to testify this lithography scheme. Furthermore, some key factors influencing the pattern quality have been discussed. It is pointed out that three factors mainly determine the resolution of the interference patterns, and therefore we give a theoretical resolution limit of about 1/12 wavelength to the surface plasmon interference lithography method.