Perspectives and tradeoffs of absorber materials for high NA EUV lithography

A method for fabricating filters for fiber optic sensors is presented. The interference filter's construction is laid on it's side to allow for the use of air as the low refractive index material. Bandpass filters tuned to the absorption line of a trace gas can then be used as a sensitive means of detecting gas concentration. Complex filter designs can be fabricated in a single patterned layer. A Cl O LCe 4 gas sensor is presented as a design example. Keywords: fiber optic sensors, patterned filters, interference filter design 1: Introduction Optical filtersI passive optical switches and polarizing elements are used extensively in a wide range of sensors 1IOIP and sensing technologies for medicalI environmental and threat detection. The design of a complex optical interference filter used to detect a specific chemical can involve 100 or more discrete alternating layers of high and low index materials. The cost of these filters can be quite high owing to long deposition times and limited yield. te are developing an approach which will allow these filters to be deposited as a singleI printable layer for use in fiber optic and wave guide based sensor systems. rsing emerging 3D printing techniquesI extremely low costI high volume fiber optic sensors can be fabricated. Complex visible through far infrared filters consisting of hundreds of discrete layers can be printed in a single layer deposition. The corresponding low index material can be airI or a second deposition, or both with some layers left as air while other layers are added to provide for other design considerations such as ultra-narrowI high optical density reflection notches and stable performance over a wide range of incidence angle. There are several advantages to using air as the low index layer. crom a design perspectiveI air is non-dispersive and offers the highest index contrast with the material chosen for the high index layers. By designing the filter to pass or reflect at a specific trace gas absorption bandI the transmission or reflection of the open air filter design is a sensitive function of the gas absorption. This paper presents filter construction and a study of design trade-offs for these open air printed (OAP) filters. Optical interference filters consist of multiple groups of high and low refractive index materials. By precisely controlling the thickness of each layerI reflected light from each interface can constructively or destructively interfere to produce unique spectral performance as a function of wavelength

As minimum feature size shrinks to a metal pitch of 21 nm, the current extreme ultra violet (EUV) lithographic tool with a numeric aperture (NA) of 0.33 will face resolution limit for some critical layers. High NA (0.55) EUV with anamorphic optics or EUV double patterning (DP) at 0.33 NA are being considered for the next generation of lithographic technology. Both the high NA EUV system and EUV DP will enhance resolution relative to current EUV single patterning (SP). Nevertheless, in order to be able to compare EUV DP and High NA EUV processes, important lithographic factors including image contrast, mask three dimension (M3D) effects, process variation band, stochastic effects and local critical dimension uniformity need to be investigated to understand their contributions to process variations. This study was carried out using rigorous lithographic model simulations in Sentaurus Lithography, where strong M3D effects in EUVL are computed physically. We have simulated patterns with both isomorphic and anamorphic optical proximity corrections (OPC) using the rigorous model. The study focuses on 3nm node Via layer designs. These vias need to connect to metal features which have pitches of 21 nm. Simulation results using 0.33 NA SP, 0.33 NA DP, and 0.55 NA anamorphic SP are presented. The benefit of using an alternative mask absorber and a thinner resist as well as the impact of stochastic effects have also been explored. Although a 0.55 NA EUV is expected to produce a superior image to 0.33 NA EUV and to have less impact from overlay errors and stochastic effects, an analysis of process margins of 0.33 NA EUV SD and DP versus 0.55 NA anamorphic systems helps to better understand the benefits, challenges and optimal insertion point for introducing High-NA EUV.

Although the investigation on photonic band gap materials has been done more than two decades, it is still a big challenge to fabricate three-dimensional photonic crystal (PC) possessing wide band gaps in visible range. In this article, we have reviewed recent progresses on fabricating the PC with low refractive index material in visible range. In contrast to the material with large refractive index, it is cheap to use low refractive index material in fabricating the PC and will be greatly beneficial for future industrial productions. The holographic method to fabricate such a PC has been introduced, applying it to the design of the microlaser has also been discussed.

As we know, if we consider Extreme Ultra-Violet (EUV) stochastics induced defectivity, the minimum pitch for the line/space is around 36~ 40 nm and 48 ~ 50 nm for the contact holes and vias in 0.33 NA EUV lithography. From the current roadmap, the ultimate minimum pitch of the metal layer in EUV lithography is 14 nm, which will be realized by double patterning with high NA EUV tool. After some studies, we believe that the optimum pitch for the line/space is believed to be around 28 nm and 38 ~ 40 nm for the contact holes and vias with 0.55 NA EUV lithography. We have done a simulation study for some typical patterns with the anchoring metal pitch of 28 nm in high NA EUV lithography with self-developed program. Generally speaking, critical structures in advanced logic technologies nodes are Tip-to- Tip structures, the minimum area structures, etc. For these patterns, we have briefly studied the influence of Source Optimization (SO) on and the impact from coma Y to the process window and we have found that the contribution of SO is not significant (<5%) and we have determined the specification on the optical aberration based on our understanding in the requirement from process window. Due to the high kl nature of EUV lithography, we have also done a study on a 45° local interconnect pattern in a 3 nm CFET SRAM with both low NA and high NA EUV processes.

Complete and absolute photonic bandgaps in highly symmetric photonic quasicrystals embedded in low refractive index materials

Laser induced damage thresholds, measured using N-on-1 and R-on-1 testing, of single layer high index zirconia and hafnia coatings, derived from nitric or acetic acid stabilized sol-gel processing, are reported. Single layer acetic acid, nitric acid and base catalyzed silica sol-gel coatings have also been tested. The sol-gels were dip coated onto fused silica substrates at a rate of 3mm/s. The refractive index of the materials were measured using transmission spectra of multiple pairs of high and low refractive index materials. Absorption in the UV region was similarly measured with multiple layers of the same material and fitting to a Beer's law behavior. The high index materials used were zirconia or hafnia, the low index material was silica. The compatibility of the various combinations of high and low index materials for physical stacking without cracking, achieving high reflectivity and high damage thresholds are discussed and compared.

As low refractive index materials in visible wavelength SiO2, MgF2, and Na3AlF6 have been used in the optical thin film coatings. While MgF2 and Na3AlF6 films have lower refractive index than SiO2 films, their mechanical properties are not as good as SiO2 films. On the other hand, in the semiconductor industry fluorine-doped SiO2 (SiOxFy) films prepared by the CVD method have been developed as an inorganic low-dielectric constant material.[1] In this study, we fabricated SiOxFy films by ion beam assisted deposition (IBAD) to utilize them in the optical coatings as a low index material with a better mechanical property and investigated the optical, mechanical, chemical properties of SiOxFy films.

Optical multilayer interference coatings rely on the refractive index differences and specific thicknesses of the low and high refractive index materials used in optical multilayer structures. An accurate control of important parameters such as film thicknesses, uniformities, and refractive indexes is demanding. Atomic layer deposition (ALD) inherently possesses many characteristics beneficial for obtaining fully conformal and uniform films of specific thicknesses with excellent repeatability. Additionally, the layer-by-layer deposition of the films allows tuning of the film stack properties, such as refractive index, which is an advantage when designing optical filters. By now, has been most often used as a low refractive index material in ALD made interference filters because of a lack of suitable ALD processes. To lower the refractive index from that of , we have developed and examined various ALD processes of aluminum silicate thin films. We concentrate on reporting the refractive indexes, growth rates, and compositions of the films as these parameters are vital for screening suitable ALD processes for optical applications. By varying the amount of silicon in the thin films, the refractive indexes between 1.47 and 1.59 were obtained in this study.

Slot waveguides are very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper we have carried out a detailed analysis of mode confinement properties in slot waveguides realized in very low refractive index materials. We show that the sensitivity of a slot waveguide is not directly related to the refractive index contrast of high and low materials forming the waveguide. Thus, a careful design of the structures allows the realization of high sensitivity devices even in very low refractive index materials (e.g., polymers) to be achieved. Advantages of low index dielectrics in terms of cost, functionalization and ease of fabrication are discussed while keeping both CMOS compatibility and integrable design schemes. Finally, applications of low index slot waveguides as substitute of bulky fiber capillary sensors or in ring resonator architectures are addressed. Theoretical results of this work are relevant to well established polymer technologies.

We have developed a new low refractive index material “SiOC”, which enables high deposition rates for the rewritable HD DVD media. The SiOC film is formed using the SiC target with Ar and O2 gas mixture by the sputter deposition method using RF or DC power supply. The resultant deposition rate per sputter power is about three times higher than the rate of the deposition using a SiO2 target. The obtained thin film consists of substantial amount of carbon (C) as well as silicon (Si) and oxygen (O). However, the film shows almost the same optical characteristics as SiO2. We demonstrated that the single-layer type HD DVD rewritable media with 20 GB using SiOC film had good recording characteristics similar to the disc using a SiO2 film. We believe that this media can be manufactured at a cost similar to conventional rewritable DVDs in mass production. Keywords: rewritable HD DVD media, Low-to-High signal polarity, low refractive index material,

Extreme ultraviolet (EUV) lithography is considered as the leading patterning technology beyond the ArF-based optical lithography, addressing the need for transistor densification to meet Moore's Law. Theoretically, EUV lithography at 13.5nm wavelength meets the resolution requirements for 1xnm technology nodes. However, there are several major challenges in the development of EUV lithography for mass production of advanced CMOS devices. These include the development of high power EUV light sources, EUV optics, EUV masks, EUV resists, overlay accuracy, and metrology and inspection capabilities. In particular, it is necessary to ensure that effective defect control schemes will be made available to reduce the EUV lithography defectivity to acceptable levels. This paper presents a study on the wafer defectivity and characterization of patterned EUV resists, with the objective of providing a quantitative comparison between the defectivity of different resist materials and different stacks. Patterned wafers were printed using the ASML® EUV full-field Alpha-Demo Tool (ADT 0.25 NA) at imec. The EUV resist patterns were 32nm line/spaces. Several advanced resist types were screened experimentally. The different resist types and stacks were inspected using a DUV laser based brightfield inspection tool, followed by a SEM defect review and CD metrology measurements. The patterns were characterized in terms of defect types and defect density. We identified the major defect types and discuss factors that affect the defectivity level and pattern quality, such as resist type, exposure dose and focus. Defect scattering analysis of DUV polarized light at different polarizations was performed, to indicate on the inspection performance trends for a variety of defect types and sizes of the different resists and stacks. The scattering analysis shows that higher defect scattering is induced using polarized light.

EUV (extreme ultraviolet) lithography has been introduced in high volume manufacturing in 2019 and continuous improvements have allowed to push the lithographic performance to the limits of 0.33 NA single exposure. However, stochastic failures, pattern roughness and local critical dimension uniformity (LCDU) are still major challenges that need to be addressed to maintain node shrinkage and improve yield. Together with pitch downscaling, photoresist thickness is decreasing to prevent pattern collapse. A lower depth of focus is also expected with high NA EUV which might even thin further down the resist layer. Being able to transfer the patterns with good fidelity is therefore getting very challenging because the resist “etch budget” is becoming too small to prevent pattern break during plasma etch transfer. A co-optimization of lithography processes, underlayers coating and etch processes is essential to further support the EUV patterning extension. In this report, recently developed hardware and process solutions to stretch the limits of EUV patterning will be presented. The latest performance for both chemically amplified resists (CAR) and metal oxide resists (MOR) will be introduced, with a focus on defect mitigation, dose reduction strategies and CD stability.

Microelectromechanical systems (MEMS) currently see a trend towards inclusion of optical functionalities, i.e., towards microoptoelectromechanical systems (MOEMS). However, typical MEMS materials such as silicon, silicon oxide and silicon nitride limit the choice of available refractive indices and spectral operating regions. Particularly, a low refractive index material is highly desirable which is usable in conjunction with high refractive index silicon, e.g., in distributed Bragg reflectors (DBRs) and which is not etched in an HF release step for releasing movable structures. Furthermore, MEMS applications typically need a careful control of the residual mechanical stress in free-standing structures. For this purpose, we present hydrogenated amorphous silicon carbonitride (a-SiCN:H) thin-films deposited by plasma-enhanced chemical vapour deposition (PECVD) from SiH 4 , CH 4 and NH 3 and show its beneficial properties for optical layers in mOeMS.

Based on the idea of multiple photonic bandgap (PBG) overlapping for a one-dimensional photonic crystal heterostructure, a novel hybrid quasiperiodic heterostructure is proposed to enlarge the omnidirectional photonic bandgap (OPBG). The heterostructure is formed by combining Fibonacci and Thue-Morse quasiperiodic structure. The results show that the OPBG of the heterostructure is enlarged obviously, which increases about three times compared with that of Fibonacci quasiperiodic structure, and twelve times compared with that of Thue-Morse quasiperiodic structure. The influences of structural parameters, such as period number and generation number, on PBGs of Fibonacci and Thue-Morse quasiperiodic structure are studied respectively. The results show that the parameters have little effects on PBG widths of the two quasiperiodic structures. The influences of the refractive indexes and thickness values of the high and low refractive index materials on OPBG of the heterostructure are also investigated. The results show that the OPBG of the heterostructure can be further broadened by increasing the refractive index ratios and thickness values of the high and low refractive index materials. The reason why the quasiperiodic structure can easily realize the multiple band gap overlapping is analyzed by comparing the bandgap properties of periodic structure. The number of PBGs of the quasiperiodic structure in the same wavelength range is more than that of the periodic structure. Moreover, with the increase of generation number of the quasiperiodic structure, due to the occurrence of PBG split, the number of PBGs increases obviously, and each PBG width is less than that of the periodic structure. Owing to this kind of PBG characteristic of the quasiperiodic structure, the heterostructure formed by cascading the two quasiperiodic structures is more prone to realizing the multiple PBG overlapping than other heterostructures, thus more easily achieving the expansion of OPBG. These results lay the design foundation for the compensation and broadening of the more complex bandgap structure.

In this paper, we present the design and fabrication of a 11-layer notch filter for photovoltaic applications. Thickness modulation has been done on a starting quarter-wave design to obtain a 11-layer final structure. For our design parameters, we considered materials with indices of 2.09 and 1.51 as high and low refractive index materials, respectively. Since this filter aims for photovoltaic applications, we defined the substrate as silicon. The design shows a reflection peak of around 73% from 350 to 467 nm with a FWHM of 79 nm along with less than 10% reflection for longer wavelengths of the remaining high transmission region of 300–1200 nm. For fabrication, we used silicon nitride and silicon oxynitride as alternating high and low refractive index materials on a silicon substrate. Layers of silicon nitride and oxynitride were deposited with an electron cyclotron resonance plasma-enhanced chemical vapor deposition reactor and characterized with variable angle spectroscopic ellipsometry and spectrophotometry.