Deep UV Lithography Research Articles

Global search algorithms in automated design of starting points for deep-UV lithography objective

Global search algorithms in automated design of starting points for deep-UV lithography objective

Sulfate Derivatives with Heteroleptic Tetrahedra: New Deep-Ultraviolet Birefringent Materials in which Weak Interactions Modulate Functional Module Ordering.

Deep-ultraviolet (UV) birefringent materials are urgently needed to facilitate light polarization in deep-UV lithography. Maximizing anisotropy by regulating the alignment of functional modules is essential for improving the linear optical performance of birefringent materials. In this work, we proposed a strategy to design deep-UV birefringent materials that achieve functional module ordering via weak interactions. Following this strategy, four compounds CN4H7SO3CF3, CN4H7SO3CH3, C(NH2)3SO3CH3, and C(NH2)3SO3CF3 were identified as high-performance candidates for deep-UV birefringent materials. The millimeter-sized crystals of CN4H7SO3CF3, CN4H7SO3CH3, and C(NH2)3SO3CH3 were grown, and the transmittance spectra show that their cutoff edges are below 200 nm. CN4H7SO3CF3 exhibits the largest birefringence (0.149 @ 546 nm, 0.395 @ 200 nm) in the deep-UV region among reported sulfates and sulfate derivatives. It reveals that the hydrogen bond can modulate the module ordering of the heteroleptic tetrahedra and planar π-conjugated cations, thus greatly enhancing the birefringence. Our study not only discovers new deep-UV birefringent materials but also provides an upgraded strategy for optimizing optical anisotropy to achieve efficient birefringence.

Synthesis of micro-crosslinked adamantane-containing matrix resins designed for deep-UV lithography resists and their application in nanoimprint lithography.

A certain type of photoresist used for deep-UV lithography (DUVL) can also be used for other types of photolithography. Thus, to meet the requirements of two or more lithography technologies simultaneously, it is necessary to design a variety of corresponding functional groups in the molecules of materials and obtain the required properties. Herein, we designed four matrix resins based on acrylate for DUVL, employing alkyl sulfide, adamantane, methyladamantane, and hydroxyl as dangling groups and a microcrosslinking network by adding a small amount of crosslinker. These polymers were used in the thermal nanoimprint lithography (NIL) process, and distinct patterns with a resolution of 100 nm were observed. The acrylate copolymers designed for DUVL in this work can be used as thermal NIL resists and to obtain good patterns. It was found that ethylene dimethacrylate (EDMA) and adamantane endowed the matrix resins with good thermal stability and that PMMHM demonstrated the best patterning performance among the four resins. These polymers can be applied in the manufacturing of high-density integrated circuits, nano-transistors, optoelectronic devices and other components in the future.

Nanophotonic integrated active-passive InP membrane devices and circuits fabricated using ArF scanner lithography

We present a novel fabrication approach to an integrated nanophotonic platform, based on a III-V membrane bonded to a Si substrate with benzocyclobutene (BCB). The process incorporates a hybrid lithography strategy combining deep-UV and electron-beam lithography on the same wafer. We report for the first time the usage of deep-UV scanner lithography for the fabrication of the active-passive tapers and sub-micron waveguides on the same wafer, which enables better critical dimension control, uniformity, and reproducibility. The platform uses an active-passive butt-joint interface and includes components such as distributed feedback (DFB) and distributed Bragg reflector (DBR) lasers, electro-optical (EO) and electro-absorption (EA) modulators, and sub-micron ultra-confined passive waveguides, all monolithically integrated into a single membrane layer. The active devices have a heat sink achieved by ultra-thin BCB bonding. Lasers demonstrate up to 26 mW of optical power in the waveguide and a direct modulation bandwidth of up to 21 GHz. The modulators show static extinction up to 28.8 dB.

Low temperature PECVD processes for the fabrication of integrated symmetrical resonant UV210 organic/semiconductor structures

The resonant structures used as sensors for investigating specific dark and opaque substances may pose difficulties due to their potential aggressiveness towards photonic chips and the risk of destruction upon contact. To avoid it, this study presents a detailed description of a novel symmetrical waveguide structure with UV210 enclosed between Si/SiO2 bi-layers implemented for integrated photonics. The fabrication process is thoroughly explained, accompanied by various analyses conducted for characterizations purposes. The structure is composed of an organic UV210 material developed using deep UV lithography at 248 nm and fabricated onto an oxidized silicon layer, resulting in a Si/SiO2 bi-layer configuration. This process enables the fabrication of µm-scale access waveguides and racetrack Micro-Resonators (MRs) with a 400-nanometers gap. Several multilayer families have been produced using various low-temperature PECVD processes to obtain symmetrical Si/SiO2/UV210/Si/SiO2 structures and then properly characterized using non-destructive analyses and imaging techniques. The advantage of structural symmetry is primarily related to the electromagnetism and guidance equations, which eliminate the requirement for a cut-off thickness (or frequency), enabling significant miniaturization. Additionally, the upper cladding composed of a Si/SiO2 bi-layer offers protection against potentially aggressive substances directly in contact with the organic waveguide core and MRs. Different bi-layer upper cladding families, produced under various PECVD conditions, were characterized using XPS to understand the bonding mechanism between the silicon and UV210 organic. In addition, ellipsometric analyses were conducted to determine the real and imaginary components of the refractive index of the global structure and the upper cladding bi-layer. Structure imaging were obtained by Raman analyses and optical statistical measurements were conducted on four different types of heterostructures, with silica temperatures ranging from 120°C to 150°C during the second PECVD process. The resonance analysis, performed through Free Spectral Range (FSR) measurements, allowed us to draw conclusions regarding the stability and reproducibility of the fabrication process, as well as the impact of PECVD processes conditions on the optical measurements. Such optoelectronic resonant elements and hybrid heterostructures enable the investigation of aggressive substances in direct contact.

Deep learning-driven forward and inverse design of nanophotonic nanohole arrays: streamlining design for tailored optical functionalities and enhancing accessibility.

In nanophotonics, nanohole arrays (NHAs) are periodic arrangements of nanoscale apertures in thin films that provide diverse optical functionalities essential for various applications. Fully studying NHAs' optical properties and optimizing performance demands understanding both materials and geometric parameters, which presents a computational challenge due to numerous potential combinations. Efficient computational modeling is critical for overcoming this challenge and optimizing NHA-based device performance. Traditional approaches rely on time-consuming numerical simulation processes for device design and optimization. However, using a deep learning approach offers an efficient solution for NHAs design. In this work, a deep neural network within the forward modeling framework accurately predicts the optical properties of NHAs by using device structure data such as periodicity and hole radius as model inputs. We also compare three deep learning-based inverse modeling approaches-fully connected neural network, convolutional neural network, and tandem neural network-to provide approximate solutions for NHA structures based on their optical responses. Once trained, the DNN accurately predicts the desired result in milliseconds, enabling repeated use without wasting computational resources. The models are trained using over 6000 samples from a dataset obtained by finite-difference time-domain (FDTD) simulations. The forward model accurately predicts transmission spectra, while the inverse model reliably infers material attributes, lattice geometries, and structural parameters from the spectra. The forward model accurately predicts transmission spectra, with an average Mean Squared Error (MSE) of 2.44 × 10-4. In most cases, the inverse design demonstrates high accuracy with deviations of less than 1.5 nm for critical geometrical parameters. For experimental verification, gold nanohole arrays are fabricated using deep UV lithography. Validation against experimental data demonstrates the models' robustness and precision. These findings show that the trained DNN models offer accurate predictions about the optical behavior of NHAs.

Direct deep UV lithography to micropattern PMMA for stem cell culture.

Microengineering is increasingly being used for controlling the microenvironment of stem cells. Here, a novel method for fabricating structures with subcellular dimensions in commonly available thermoplastic poly(methyl methacrylate) (PMMA) is shown. Microstructures are produced in PMMA substrates using Deep Ultraviolet lithography, and the effect of different developers is described. Microgrooves fabricated in PMMA are used for the neuronal differentiation of mouse embryonic stem cells (mESCs) directly on the polymer. The fabrication of 3D, curvilinear patterned surfaces is also highlighted. A 3D multilayered microfluidic chip is fabricated using this method, which includes a porous polycarbonate (PC) membrane as cell culture substrate. Besides directly manufacturing PMMA-based microfluidic devices, an application of the novel approach is shown where a reusable PMMA master is created for replicating microstructures with polydimethylsiloxane (PDMS). As an application example, microchannels fabricated in PDMS are used to selectively expose mESCs to soluble factors in a localized manner. The described microfabrication process offers a remarkably simple method to fabricate for example multifunctional topographical or microfluidic culture substrates outside cleanrooms, thereby using inexpensive and widely accessible equipment. The versatility of the underlying process could find various applications also in optical systems and surface modification of biomedical implants.

C- and O-Band Dual-Polarization Fiber-to-Chip Grating Couplers for Silicon Nitride Photonics.

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

Deep Subwavelength Anti-Slot Photonic Crystals Fabricated in Monolithic Silicon Photonics Technology

We report the scalable fabrication and characterization of photonic crystal (PhC) nanobeam waveguides incorporating subwavelength-scale dielectric anti-slot unit cells. These anti-slot PhCs were fabricated using deep UV lithography on a monolithic silicon photonics technology. The dielectric band edge mode is characterized by strong field localization in the anti-slot region where the minimum dielectric feature size is approximately 70 nm. This demonstration opens the door to further investigation of subwavelength engineered photonic structures fabricated using commercial foundry processes for integrated photonics applications that benefit from enhanced light-matter interaction.

Optical and thermal properties of polymethyl methacrylate (PMMA) bearing phenyl and adamantyl substituents

Polymethyl methacrylate (PMMA) is a widely used optical polymer due to its excellent transparency and durability. However, the sole methyl group shows pure PMMA low refractive index and low UV absorbility, and poor thermal stability. In this work, two comonomers phenyl methacrylate (PhMA) and adamantyl methacrylate (AdMA) were used for copolymerization with methyl methacrylate (MMA), and three copolymers P(AdMA-co-MMA), P(PhMA-co-MMA) and P(AdMA-co-PhMA-co-MMA) were prepared. They were characterised by FTIR, 1H NMR, UV-Vis, ellipsometer, DSC, TG, and TG-MS, and the effects of phenyl and adamantyl substituents on the optical and thermal properties of PMMA were studied. It was found that phenyl played an important role in increasing the absorption and refraction of PMMA in the deep UV region (190–260 nm), while the glass transition temperature and thermal stability of PMMA were more affected by adamantyl than by phenyl. Introduction of phenyl and adamantyl substituents provided a method to tune the optical and thermal properties of PMMA as photoresist or antireflective coating for deep UV lithography.

Patterning Gold Nanorod Assemblies by Deep-UV Lithography

Patterning Gold Nanorod Assemblies by Deep-UV Lithography

Atomic layer deposition of GdF3 thin films

Gadolinium fluoride is an attractive optical material with applications in, e.g., deep-UV lithography, solar cells, and medical imaging. Despite the interest toward this material, no atomic layer deposition (ALD) process has been published. In this article, an ALD process for GdF3 using Gd(thd)3 and NH4F as precursors is presented. The deposition was studied at temperatures 275–375 °C, but 285–375 °C produce the purest films. The saturation of the growth per cycle (GPC) with respect to precursor pulses and purges was proved at 300 °C. The GPC value at this temperature is ∼0.26 Å, and the deposition temperature has very little effect on the GPC. According to x-ray diffraction, all the films consist of orthorhombic GdF3. The impurity contents, evaluated by time-of-flight elastic recoil detection analysis, is low, and the films are close to stoichiometric. The nitrogen content is less than <0.04 at. %. The antireflection properties were qualitatively evaluated by UV-vis spectrometry in a transmission mode at a 190–1100 nm range: on sapphire substrates, GdF3 serves as an antireflective coating. Dielectric properties of the films were studied, and for example, a permittivity value of 9.3 was measured for a ∼64 nm film deposited at 300 °C.

Vertical Fibre Interfacing Interleaved Angled MMI for Thermal-Tuning-Free Wavelength Division (de)Multiplexing and Low-Cost Fibre Packaging

We propose and experimentally demonstrate a vertical fibre interfacing interleaved angled MMI (AMMI) for wavelength division (de)multiplexing (WDM) near 1550 nm. This 6-channel WDM device is composed of two 1 × 3 AMMIs and a Mach-Zehnder interferometer (MZI) with an apodized bidirectional grating acting as both vertical optical coupler and 3-dB power splitter. By thoroughly design the bidirectional gratings, a high coupling efficiency of 72.5% and low return loss of −34 dB is obtained by simulation. The AMMI couplers are designed and optimized using the Eigenmode expansion method. For wavelength matching between the MZI and AMMIs, the circuit simulation model of the interleaved AMMI is built by importing the S-parameter matrices of all the optical components extracted from the physical-level simulations. The device was fabricated using the standard CMOS technology and the feature size is compatible with the 193 nm deep-UV lithography. Experimental results obtained without thermal tuning are in good agreement with the simulation results, the device exhibits a small insertion loss (IL) varies between 3.3 and 4.58 dB (including the grating coupling loss), channel spacing of 6 nm, crosstalk (XT) below −20 dB. To investigate the fabrication tolerance, devices on two different chips are measured individually. The results show good consistency in device performance. Also, the fibre misalignment tolerance of the device is experimentally investigated.

High-Efficiency Two-Dimensional Perfectly Vertical Grating Coupler With Ultra-Low Polarization Dependent Loss and Large Fibre Misalignment Tolerance

A two-dimensional grating coupler (2D GC) with four access waveguides is proposed and demonstrated for polarization independent and perfectly vertical coupling. Benefitting from the perfectly vertical coupling and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times 4$ </tex-math></inline-formula> power splitting/combing scheme, broadband polarization independent operation can be achieved. Through grating apodization with etched square holes, a simulated coupling efficiency (CE) of 65% (−1.87 dB) is obtained with a minimum feature size of 180nm which is compatible with the 193-nm deep UV lithography technology. To characterize the device performance, a back-to-back configuration of this 2D GC was fabricated, where phase-delay lines with similar patterns are introduced to ensure the phase equality between different waveguide arms. A CE of 49% (−3.1 dB) was experimentally measured, with a 1-dB bandwidth of 42 nm and PDL below 0.2 dB across the wavelength range from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5~\mu \text{m}$ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6~\mu \text{m}$ </tex-math></inline-formula> . The fibre misalignment tolerance of this device was also investigated by measurement. The excess coupling loss and PDL caused by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm 2~\mu \text{m}$ </tex-math></inline-formula> fibre misalignment are lower than 1 dB and 0.8 dB respectively, and the maximum excess coupling loss and PDL caused by ±2° fibre angle error is 1 dB and 0.7 dB respectively. Finally, optical modulation using this device is preliminarily demonstrated by the embedded thermal-optic functions.

Dual-Wavelength-Band Grating Coupler on 220-nm Silicon-on-Insulator With High Numerical Aperture Fiber Placed Perfectly Vertically

We propose and design a novel dual-wavelength-band grating coupler on 220-nm-thick silicon-on-insulator and experimentally investigate its capability to couple two wavelength bands simultaneously under surface-normal fiber placement. Such dual-wavelength-band operation take advantage of a dual-etch grating design not only with increased directionality but also with unique diffraction angle dispersion characteristics for the two targeted wavelength bands. The role of high numerical aperture fiber is theoretically investigated, leading to reduced angular sensitivity in general and subsequently increased coupling efficiency for our proposed dual-wavelength-band operation scheme. Our device is further fabricated using 248-nm deep-UV lithography on an 8-inch wafer for verification. The peak coupling efficiency is measured to be –5.0 dB at 1275 nm and –5.9 dB at 1519 nm for O-band and S/C-band respectively.

High-efficiency dual-band-multiplexing three-port grating coupler on 220-nm silicon-on-insulator with 248-nm deep-UV lithography.

We experimentally demonstrate a novel, to the best of our knowledge, three-port grating coupler (TPGC) for dual-wavelength-band operation. The TPGC can couple light to/from two ports for S/C-band with polarization diversity and a third port for O-band. Such a coupling scheme could be applied in an integrated wavelength-division-multiplexing passive optical network (PON) unit, benefiting a polarization-diverse receiver for downstream S/C-band and transmitter for upstream O-band. The device is fabricated on a multi-project wafer, with peak coupling efficiency measured to be -3.8dB and -5.4dB for O-band and S/C-band, respectively. We also present a proof-of-concept demonstration for 10-Gb/s PON transmission based on the TPGC.

Optimizing interferences of DUV lithography on SOI substrates for the rapid fabrication of sub-wavelength features

Scalable fabrication of Si nanowires with a critical dimension of about 100 nm is essential to a variety of applications. Current techniques used to reach these dimensions often involve e-beam lithography or deep-UV (DUV) lithography combined with resolution enhancement techniques. In this study, we report the fabrication of <150 nm Si nanowires from SOI substrates using DUV lithography (λ = 248 nm) by adjusting the exposure dose. Irregular resist profiles generated by in-plane interference under masking patterns of width 800 nm were optimized to split the resulting features into twin Si nanowires. However, masking patterns of micrometre size or more on the same photomask does not generate split features. The resulting resist profiles are verified by optical lithography computer simulation based on Huygens−Fresnel diffraction theory. Photolithography simulation results validate that the key factors in the fabrication of subwavelength nanostructures are the air gap value and the photoresist thickness. This enables the parallel top-down fabrication of Si nanowires and nanoribbons in a single DUV lithography step as a rapid and inexpensive alternative to conventional e-beam techniques.

Dual-band fiber-chip grating coupler in a 300 mm silicon-on-insulator platform and 193 nm deep-UV lithography.

Surface grating couplers are fundamental building blocks for coupling the light between optical fibers and integrated photonic devices. However, the operational bandwidth of conventional grating couplers is intrinsically limited by their wavelength-dependent radiation angle. The few dual-band grating couplers that have been experimentally demonstrated exhibit low coupling efficiencies and rely on complex fabrication processes. Here we demonstrate for the first time, to the best of our knowledge, the realization of an efficient dual-band grating coupler fabricated using 193 nm deep-ultraviolet lithography for 10 Gbit symmetric passive optical networks. The footprint of the device is 17×10µm2. We measured coupling efficiencies of -4.9 and -5.2dB with a 3-dB bandwidth of 27 and 56 nm at the wavelengths of 1270 and 1577 nm, corresponding to the upstream and downstream channels, respectively.

Large plasmonic color metasurfaces fabricated by super resolution deep UV lithography.

In this paper, we demonstrate plasmonic color metasurfaces as large as ∼60 cm2 fabricated by deep UV projection lithography employing an innovative combination of resolution enhancement techniques. Briefly, in addition to the established off-axis dipole illumination, double- and cross-exposure resolution enhancement of lithography, we introduce a novel element, the inclusion of transparent assist features to the mask layout. With this approach, we demonstrate the fabrication of relief arrays having critical dimensions such as 159 nm nanopillars or 210 nm nanoholes with 300 nm pitches, which is near the theoretical resolution limit expressed by the Rayleigh criterion for the 248 nm lithography tool used in this work. The type of surface structure, i.e. nanopillar or nanohole, and their diameters can be tailored simply by changing the width of the assist features included in the mask layout. By coating the obtained nanopatterns with thin layers of either Au or Al, we observe color spectra originating from the phenomenon known as localized surface plasmon resonance (LSPR). We demonstrate the generation of color palettes representing a broad spectral range of colors, and we employ finite element modelling to corroborate the measured LSPR fingerprint spectra. Most importantly, the ∼60 cm2 nanostructure arrays can be written in only a few minutes, which is a tremendous improvement compared to the more established techniques employed for fabricating similar structures.

CORNERSTONE’s Silicon Photonics Rapid Prototyping Platforms: Current Status and Future Outlook

The field of silicon photonics has experienced widespread adoption in the datacoms industry over the past decade, with a plethora of other applications emerging more recently such as light detection and ranging (LIDAR), sensing, quantum photonics, programmable photonics and artificial intelligence. As a result of this, many commercial complementary metal oxide semiconductor (CMOS) foundries have developed open access silicon photonics process lines, enabling the mass production of silicon photonics systems. On the other side of the spectrum, several research labs, typically within universities, have opened up their facilities for small scale prototyping, commonly exploiting e-beam lithography for wafer patterning. Within this ecosystem, there remains a challenge for early stage researchers to progress their novel and innovate designs from the research lab to the commercial foundries because of the lack of compatibility of the processing technologies (e-beam lithography is not an industry tool). The CORNERSTONE rapid-prototyping capability bridges this gap between research and industry by providing a rapid prototyping fabrication line based on deep-UV lithography to enable seamless scaling up of production volumes, whilst also retaining the ability for device level innovation, crucial for researchers, by offering flexibility in its process flows. This review article presents a summary of the current CORNERSTONE capabilities and an outlook for the future.