Development Of Photoresists Research Articles

Exploring the Development of Photoresists in Lacquer under the Background of Global Carbon Neutrality: A Mini Review

With the establishment of a global carbon-neutral target, green and sustainable design concepts, materials, and processes have become the key to scientific and technological innovation, which highlights the development and utilization of environmentally-friendly materials and renewable energy sources. At present, almost all the raw materials in commercial photoresist are from oil resources. In order to implement the policy of “green chemistry”, there is an urgent need to take the place of petroleum with renewable, biodegradable, and green biomass resources in photoresist production. As a kind of green and natural high polymer material from China, lacquer has excellent physical and chemical properties and has great application potential in the field of electronics. In this paper, the potential connections between photoresist and lacquer, especially in the green development of photoresist, are sorted out. The introduction of lacquer and its derivatives may help to improve the environmentally-friendly production of photoresist and its performance. Therefore, in the context of global carbon neutrality, the study of photoresists in the “lacquer” is of great significance in promoting the application of eco-friendly materials in the field of microelectronics.

XUV Absorption Spectroscopy and Photoconversion of a Tin-Oxo Cage Photoresist.

Extreme ultraviolet lithography has recently been introduced in high-volume production of integrated circuits for manufacturing the smallest features in high-end computer chips. Hybrid organic/inorganic materials are considered as the next generation of photoresists for this technology, but detailed knowledge about the response of such materials to the ionizing radiation used (13.5 nm, 92 eV) is still scarce. In the present work, we use broadband high-harmonic radiation in the energy range 22-70 eV for absorption spectroscopy and photobleaching (that is, the decrease of absorbance) of thin films of an n-butyltin oxo-cage, a representative of the class of metal-based EUV photoresist. The shape of the absorption spectrum in the range 22-92 eV matches well with the spectrum predicted using tabulated atomic cross sections. The photobleaching results are consistent with loss of the butyl side groups due to the breaking of Sn-C bonds following photoionization. Bleaching is strongest in the low-energy range (<40 eV), where the absorption is largely due to the carbon atoms in the organic groups. At higher energies (42-70 eV), absorption is dominated by the tin atoms, and since these remain in the film after photoconversion, the absorption change in this region is smaller. It is estimated that after prolonged irradiation (up to ∼3 J cm-2 in the range 22-40 eV) about 70% of the hydrocarbon groups are removed from the film. The rate of bleaching is high at the beginning of exposure, but it rapidly decreases with increasing conversion. We rationalize this using density functional theory calculations: the first Sn-C bonds are efficiently cleaved (quantum yield Φ ≈ 0.9), because the highest occupied molecular orbitals (HOMOs) (from which an electron is removed after photoionization) are located on Sn-C sigma bonds. In the photoproducts, the HOMO is localized on tin atoms that have lost their hydrocarbon group (formally reduced to the Sn(II) oxidation state), and holes formed on those tin atoms lead to less efficient cleavage reactions. Our results reveal the primary reaction steps following excitation with ionizing radiation of tin-oxo cages. Our methodology represents a systematic approach of studying and quantitatively assessing the performance of new photoresists and as such enables the development of future EUV photoresists.

Photoresist Fabrication for High-NA EUV Lithography: Material and Mechanism

Extreme ultraviolet (EUV) lithography is critical for the semiconductor industry nowadays. However, high-numerical aperture (NA) EUV systems face challenges in many areas, especially in photoresists. This paper reviews requirements and recent progress in EUV photoresists for high-NA EUV lithography. The key needs for photoresists include high resolution, low stochastic defects, minimal pattern collapse, and high sensitivity. Proposed solutions involve new photoresist materials and mechanisms, such as metal-containing photoresists, non-chemically amplified photoresists and tin-oxo cages photoresists. Basic fabrication and processing procedures are also discussed. Other than photoresists, the weak EUV light source also heavily restrains the development of photoresists. In the future, improvements in EUV light sources and patterning techniques will further help high-NA EUV photoresist development. In summary, the realization of high-NA EUV lithography system depends critically on the breakthrough of photoresists, while solutions are emerging to meet demanding requirements from various directions. Overall, these results shed light on guiding further exploration of next generation lithography.

A Critical Review of Lithography Methodologies and Impacts of Topography on 2.5-D/3-D Interposers

This paper analyzes the lithography design rules in package foundry and wafer foundry and reviews the major lithography techniques for package redistribution layer (RDL) fabrication for panel level 2.5D/3D interposers, fan-out packages and heterogeneous integration. The techniques surveyed in this paper are- contact aligners, projection aligners/steppers, laser direct writing (LDW) and laser ablation, capable of resolving routing line and space (L/S) of 0.8-1.5 μm with aspect ratio (AR) ≤ 5 and creating microvia with diameter of 1.5-2.0 μm at via pitch ≤5μm. The biggest challenge of advanced packaging is scaling the critical dimensions (CDs) on package to keep up with the pace of scaling of the bump pitch. In addition, there is a critical need for patterning fine lines-and-spaces with high aspect ratio to have low resistance traces. These high AR ultra-fine lines and ultra-fine pitch vias are crucial for meeting the needs of high-bandwidth die-to-die interconnections at high input/output (I/O) densities. All these challenges are mainly driven by lithography. With the development of advanced photoresists (PRs), the resolution factor K1 in projection lithography reduces from 0.66 to 0.39, improving the resolution by 40% without the negative impacts on the depth-of-focus (DOF). This paper also discusses the specific lithography challenges associated with topography of multi-layer RDL as well as their impacts on the fabrication of fine features. The fine pitch microvias can be a solution for scaling the I/O pitch down to 5-10 μm as a bumpless way to connect copper pads of known-good-dies to known-good- substrates in fan-out packages.

Utilizing the Sensitization Effect for Direct Laser Writing in a Novel Photoresist Based on the Chitin Monomer N‐acetyl‐D‐glucosamine

The great flexibility of direct laser writing (DLW) arises from the possibility to fabricate precise three‐dimensional structures on very small scales as well as the broad range of applicable materials. However, there is still a vast number of promising materials, which are currently inaccessible requiring the continuous development of novel photoresists. Herein, a new bio‐sourced resist is reported that uses the monomeric unit of chitin, N‐acetyl‐D‐glucosamine, paving the way from existing hydrogel resists based on animal carbohydrates to a new class of non‐hydrogel ones. In addition, it is shown that the combined use of two photoinitiators is advantageous over the use of a single one. In this approach, the first photoinitiator is a good two‐photon absorber at the applied wavelength, while the second photoinitiator exhibits poor two‐photon absorbtion abilities, but is better suited for cross‐linking of the monomer. The first photoinitiator absorbs the light acting as a sensitizer and transfers the energy to the second initiator, which subsequently forms a radical and initializes the polymerization. This sensitization effect enables a new route to utilize reactive photointiators with a small two‐photon absorption cross section for DLW without changing their chemical structure.

Silk-based organic photoresists for extreme ultraviolet lithography: a multiscale in silico study

The development of photoresists (PRs) for extreme ultraviolet (EUV) lithography has become increasingly popular in the field of semiconductor nanopatterning.

The Synthesis of the High Resolution i Line Novolak Resist

Semiconductors have continued to grow smaller alongside the development of shorter wavelength exposure sources and the development of photoresists optimized for such exposure wavelengths. For the g-line (436 nm) and i-line (365 nm) exposure wavelengths, novolak resists made of novolak resin have been used for patterning at pattern sizes of 0.5 μm-1 μm. For the exposure wavelength of 248 nm (KrF excimer laser), polyhydroxystyrene (PHS) has been used for patterning at pattern sizes of 0.2 μm-0.35 μm. For the exposure wavelength of 193 nm (ArF excimer laser), acrylic-based resin has been used for patterning at pattern sizes of 30 nm-0.2 μm. With the most advanced current lithography technologies, patterning at pattern sizes finer than 20 nm can be performed using exposure wavelengths of 13.5 nm (EUV). Apparently, then, lithography using novolak resists made of novolak resins is an outdated technology. However, it continues to be employed in LCD processes that involve TFT technology, where the development of higher definition LCDs continues to drive miniaturization. We studied the novolak resist, from synthesis to formulation and to evaluation of its resolution, to reexamine which factors are key to achieving high resolution in novolak resists.

Multiple regression analysis of postdevelop unbiased line width roughness and etch resistance for high-accuracy estimations of postetch pattern roughness

As device scaling continues, development of photoresists with low pattern roughness and high sensitivity has become challenging. One obstacle that delays the material development process is the discrepancy between postdevelop and postetch pattern roughness, where a photoresist with high postdevelop patterning performance shows poor postetch pattern roughness. Herein, we demonstrate that pattern roughness after a nontrim etch process can be accurately estimated by a multiple regression analysis of a power spectral density (PSD) variable of postdevelop roughness and an etch resistance parameter of resins. The nontrim etch process here refers to an etch condition which leads to increased pattern roughness. Unbiased line width roughness (LWR) shows the highest correlation with postetch LWR among postdevelop roughness PSD variables. An etch resistance parameter also correlates well with postetch roughness. A multiple regression analysis reveals that the contributions of postdevelop unbiased LWR and etch resistance to the postetch LWR are 59% and 41%, respectively. Based on the calculated contributions, postetch LWR is estimated with a high accuracy (R2 > 0.93). This estimation method allows for an efficient material screening at a lithography level without assessing postetch patterning performance, thus the process of material development could be accelerated.

Development of Extreme Ultraviolet Photoresists

Development of Extreme Ultraviolet Photoresists

Direct Laser Writing of Four-Dimensional Structural Color Microactuators Using a Photonic Photoresist

With the advent of direct laser writing using two-photon polymerization, the generation of high-resolution three-dimensional microstructures has increased dramatically. However, the development of stimuli-responsive photoresists to create four-dimensional (4D) microstructures remains a challenge. Herein, we present a supramolecular cholesteric liquid crystalline photonic photoresist for the fabrication of 4D photonic microactuators, such as pillars, flowers, and butterflies, with submicron resolution. These micron-sized features display structural color and shape changes triggered by a variation of humidity or temperature. These findings serve as a roadmap for the design and creation of high-resolution 4D photonic microactuators.

Imaging Chemical Kinetics of Radical Polymerization with an Ultrafast Coherent Raman Microscope.

Numerous mechanisms have been proposed for polymerization to provide qualitative and quantitative prediction of how monomers spatially and temporally arrange into the polymeric chains. However, less is known about this process at the molecular level because the ultrafast chemical reaction is inaccessible for any form of microscope so far. Here, to address this unmet challenge, a stimulated Raman scattering microscope based on collinear multiple beams (COMB‐SRS) is demonstrated, which allows label‐free molecular imaging of polymer synthesis in action at speed of 2000 frames per second. The field of view of the developed 2 kHz SRS microscope is 30 × 28 µm2 with 50 × 46 pixels and 7 µs dwell time. By catching up the speed of chemical reaction, COMB‐SRS is able to quantitatively visualize the ultrafast dynamics of molecular vibrations with submicron spatial resolution and sub‐millisecond temporal resolution. The propagating polymer waves driven by reaction rate and persistent UV initiation are observed in situ. This methodology is expected to permit the development of novel functional polymers, controllable photoresists, 3D printing, and other new polymerization technologies.

Two-Photon-Assisted Polymerization and Reduction: Emerging Formulations and Applications.

Two-photon lithography (TPL) is an emerging approach to fabricate complex multifunctional micro/nanostructures. This is because TPL can easily develop various 2D and 3D structures on a variety of surfaces, and there has been a rapidly expanding pool of processable photoresists to create different materials. However, challenges in developing two-photon processable photoresists currently impede progress in TPL. In this review, we critically discuss the importance of photoresist formulation in TPL. We begin by evaluating the commercial photoresists to design micro/nanostructures for promising applications in anti-counterfeiting, superomniphobicity, and micromachines with movable parts. Next, we discuss emerging hydrogel/organogel photoresists, focusing on customizing photoresist formulations to fabricate reconfigurable structures that can respond to changes in local pH, solvent, and temperature. We also review the development of metal salt-based photoresists for direct metal writing, whereby various formulations have been developed to enable applications in online sensing, catalysis, and electronics. Finally, we provide a critical outlook and highlight various outstanding challenges in formulating processable photoresists for TPL.

Ferrocene Bearing Non-ionic Poly-aryl Tosylates: Synthesis, Characterization and Electron Beam Lithography Applications

The development of new organic-inorganic hybrid photoresists with optimal lithographic performances is an extremely important but challenging task. In this regard, we have synthesized a new family of homo- and hybrid-polymer resists based on 4-(tosyloxy)phenyl methacrylate (TPMA) and ferrocene methacrylate (FEMA) monomers for micro-/nano-lithography applications. The homo polymer resist, poly(TPMA), was synthesized by a free radical polymerization of TPMA monomer in ACN/THF (2:1, v/v) solvent system using azobisisobutyronitrile (AIBN) as the radical initiator. The hybrid copolymer resists, 2.0%-&4.0%-poly(FEMA-co-TPMA), containing 2.0 and 4.0 weight percentages of FEMA respectively, were synthesized by reacting FEMA (10 and 20% initial feed ratios respectively) and TPMA (90 and 80% initial feed ratios respectively) under similar reaction conditions. The ferrocene contents of the hybrid copolymers were calculated by proton NMR analysis. The potential of these polymer resists to pattern micro- and nano-features were tested under deep ultraviolet (DUV) and electron beam (e-beam) lithography tools respectively. The thin films formed by 4.0%-poly(FEMA-co-TPMA) exhibited high surface roughness in comparison to those of poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists, probably due to the high ferrocene content of the former. The scanning electron microscopy (SEM) analysis of the e-beam exposed (dose 950 µC/cm2) thin films of poly(TPMA) revealed patterning of 40 nm (L/10S to L/4S), 30 nm (L/10S & L/5S) and 22 nm (L/10S) line features. Similarly, 2.0%-poly(FEMA-co-TPMA) patterned 40 nm (L/5S to L/S), 30 (L/5S to L/S) and 20 nm (L/5S & L/4S) line features under the e-beam exposure (dose 500 µC/cm2). The sensitivity and contrast values were calculated from the normalized remaining thickness (NRT) curve analysis as 270 µC/cm2; 5.2 and 153 µC/cm2; 1.98 respectively for poly(TPMA) and 2.0%-poly(FEMA-co-TPMA) resists. The present study therefore reveals that the incorporation of small amounts of ferrocene into the poly-aryl tosylate based resist formulations helps to enhance its sensitivity and resolution.

Development of Photoresists for ArF Excimer Laser Lithography

Development of Photoresists for ArF Excimer Laser Lithography

Role of the dense amorphous carbon layer in photoresist etching

The development of new photoresists for semiconductor manufacturing applications requires an understanding of the material properties that control the material's plasma etching behavior. Ion bombardment at ion energies of the order 100 s of eV is typical of plasma-based pattern-transfer processes and results in the formation of a dense amorphous carbon (DAC) layer on the surface of a photoresist, such as the PR193-type of photoresist that currently dominates the semiconductor industry. Prior studies have examined the physical properties of the DAC layer, but the correlation between these properties and the photoresist etching behavior had not been established. In this work, the authors studied the real-time evolution of a steady-state DAC layer as it is selectively depleted using an admixture of oxygen into an argon plasma. Observations of the depletion behavior for various DAC layer thicknesses motivate a new model of DAC layer depletion. This model also correlates the impact of the DAC layer thickness with the etch rate of the bulk photoresist. The authors find that up to a 40% depletion of the DAC layer thickness does not have a significant impact on the bulk photoresist etch rate. However, further depletion results in an exponential increase in the etch rate, which can be up to ten times greater at full depletion than for the fully formed DAC layer. Thus, with these trends the authors show that the photoresist etch rate is controlled by the thickness of the DAC layer. Furthermore, thickness loss of the DAC layer in an O2-containing plasma coincides with a chemical modification of the layer into an oxygen-rich surface overlayer with properties that are intermediate between those of the DAC layer and the bulk photoresist. Support for this interpretation was provided via x-ray photoelectron spectroscopy characterization. Atomic force microscopy was used to gauge the impact on surface roughness as the DAC layer is formed and depleted. The trends established in this work will provide a benchmark in our development of new photoresists, which will be suitable for pattern transfer processes that will ultimately be a part of enabling smaller semiconductor device feature sizes and pitches.

1,3,5,7-Tetrasubstituted adamantanes as frameworks in the design of assemblies of porphyrin macrocycles

A new strategy for the synthesis of adamantane-containing polyphenols of a porphyrin series has been suggested on the basis of Suzuki–Miyaura reaction between 1,3,5,7-tetrakis(4'-iodophenyl)adamantane and a monoboryl derivative of substituted porphyrin. The synthesis of this porphyrin assembly on the adamantane core followed by chemical transformations of this compound has provided a possibility to synthesize the corresponding polyphenol derivative. The latter has been used in the development of positive photoresists for nanolithography with exposure to radiation at a wavelength 13.5 nm capable of producing topological structures with a resolution of 16 nm.

Formulating an Ideal Protein Photoresist for Fabricating Dynamic Microstructures with High Aspect Ratios and Uniform Responsiveness.

The physical properties of aqueous-based stimuli-responsive photoresists are crucial in fabricating microstructures with high structural integrity and uniform responsiveness during two-photon lithography. Here, we quantitatively investigate how various components within bovine serum albumin (BSA) photoresists affect our ability to achieve BSA microstructures with consistent stimuli-responsive properties over areas exceeding 10(4) μm(2). We unveil a relationship between BSA concentration and dynamic viscosity, establishing a threshold viscosity to achieve robust BSA microstructures. We also demonstrate the addition of an inert polymer to the photoresist as viscosity enhancer. A set of systematically optimized processing parameters is derived for the construction of dynamic BSA microstructures. The optimized BSA photoresists and processing parameters enable us to extend the two-dimensional (2D) microstructures to three-dimensional (3D) ones, culminating in arrays of micropillars with aspect ratio > 10. Our findings foster the development of liquid stimuli-responsive photoresists to build multifunctional complex 3D geometries for applications such as bioimplantable devices or adaptive photonic systems.

Development of Lift-off Photoresists with Unique Bottom Profile

Development of Lift-off Photoresists with Unique Bottom Profile

Application of Polymers to Photoresist Materials

Demands for high performance chips have been drastically increased along with the development of smart phones, tablet-PCs and so on. Scaling is an ongoing challenge to fabricate a chip with multi-functions in a limited space for semiconductor manufacturers. In accordance with the design rules, critical dimensions (CD) have shrunk in half every two years. Scaling has been realized by making a photolithography pattern finer and finer by implementing a light source that has a shorter wavelength for lithography. In the development of photoresists for each wavelength, such as g-line, i-line, KrF and ArF, it is necessary to select suitable polymer platforms in order to obtain transmittance of the wavelength being used. This report introduces the history of the development of photoresist material and describes future lithography materials such as nano-imprint lithography (NIL) and direct self-assembly (DSA) technology.

Molecular Structure of Advanced Photoresists

This article reviews the development of lithography technology and photoresists as well as their molecular structure for 193 nm and extreme ultravioletlithography(EUVL,the next generation lithography).Especially,we describe the recent research and development of EUV photoresists in detail for the purpose of being conducive to the domestic research on advanced photoresists.