Photolithographic Performance Research Articles

Recent Advances in Metal-Oxide-Based Photoresists for EUV Lithography.

Extreme ultraviolet lithography (EUVL) is a leading technology in semiconductor manufacturing, enabling the creation of high-resolution patterns essential for advanced microelectronics. This review highlights recent progress in inorganic metal-oxide-based photoresists, with a focus on their applications in EUVL. The unique properties of zinc-based, tin-oxygen, and IVB group inorganic photoresists are examined, showcasing their enhanced chemical reactivity and precise patterning capabilities. Key advancements include the development of zinc oxide and tin oxide nanoparticles, which demonstrate significant improvements in photon absorption and solubility under extreme ultraviolet exposure. Additionally, the review delves into the photochemical reactions of tin-oxygen clusters and the influence of various ligands on film density and cross-linking. The findings suggest that these inorganic photoresists not only improve photolithographic performance but also hold potential for broader applications, such as pyroelectric infrared sensors and 3D printing. Future research directions are outlined, including the optimization of process parameters, the exploration of new ligand and metal combinations, and the evaluation of the environmental benefits of inorganic photoresists over traditional organic ones. These advancements are poised to further enhance the resolution and patterning capabilities required for next-generation semiconductor devices.

Synthesis and Characterization of Negative-Tone Photosensitive Polyimides with Low Coefficient of Thermal Expansion for Packaging Applications.

Negative-tone photosensitive polyimides (PSPIs) with a low coefficient of thermal expansion (CTE) were prepared by dissolving polyimide precursor-poly(amide ester) (PAE) resins, photoinitiators, photocrosslinkers and other additives in organic solvents. Using triamine as a monomer and dianhydride and diamine as polycondensates, tri-branched structure PAE resins with different molecular weights named PAE-1~5 were prepared. A series of corresponding PSPI films named PSPI-1~5 were prepared from PAE-1~5 resins with the same formulation, respectively. The PSPI-1~5 films prepared from resins of this structure have excellent mechanical, thermal and electrical properties after being thermally cured at 350 °C/2 h in nitrogen. The PSPI-1~5 films' coating solution also show good photolithographic performance and are able to obtain photolithographic patterns with a resolution of about 10 μm after homogenization, exposure and development. Among the PSPI-1~5 films, PSPI-2 has the most excellent lithographic properties with a weight average molecular weight (Mw) of 2.9 × 104 g/mol, a CTE of 41 ppk/°C, a glass transition temperature (Tg) of 343 °C and a 5% weight loss temperature (Td5) of 520 °C, making it suitable for industrial scale-up. The mechanical properties of elongation at breakage of 42.4%, tensile moduli of 3.4 GPa and tensile strength of 153.7 MPa were also measured.

Low‐temperature‐curable and photo‐patternable benzocyclobutene‐derived aggregation‐induced emission‐active polymer dielectrics

AbstractThe high curing temperatures required for traditional benzocyclobutene (BCB) materials have posed limitations on their applicability in high‐temperature‐sensitive fields. To address this challenge, our work focuses on the synthesis of a novel tetraphenylethylene (TPE)‐functionalized BCB monomer, TPE–BCB, achieved through the introduction of an ether bond onto the BCB's four‐membered ring via Williamson reaction. TPE–BCB demonstrates remarkable low‐temperature curing properties, characterized by a ring‐opening peak temperature of 190°C, representing a reduction of 60°C compared to conventional BCBs. Fully cured TPE–BCB resins exhibit exceptional dielectric and mechanical properties, coupled with minimal water absorption. Additionally, the incorporation of TPE with aggregation‐induced emission characteristics enhances the resins’ luminescence and photolithographic capabilities. Notably, our TPE–BCB resins achieve impressive photolithography performance with a resolution ratio of up to 10 μm. In contrast to conventional BCB‐functionalized resins, TPE–BCB offers the dual advantage of low‐temperature curing and luminescence. This development marks a significant step in the advancement of low‐temperature curing BCB materials and serves as a pioneering example in the realm of multilayer wafer bonding materials.

Novel Mechanism-Based Descriptors for Extreme Ultraviolet-Induced Photoacid Generation: Key Factors Affecting Extreme Ultraviolet Sensitivity.

Predicting photolithography performance in silico for a given materials combination is essential for developing better patterning processes. However, it is still an extremely daunting task because of the entangled chemistry with multiple reactions among many material components. Herein, we investigated the EUV-induced photochemical reaction mechanism of a model photoacid generator (PAG), triphenylsulfonium cation, using atomiC-Scale materials modeling to elucidate that the acid generation yield strongly depends on two main factors: the lowest unoccupied molecular orbital (LUMO) of PAG cation associated with the electron-trap efficiency 'before C-S bond dissociation' and the overall oxidation energy change of rearranged PAG associated with the proton-generation efficiency 'after C-S bond dissociation'. Furthermore, by considering stepwise reactions accordingly, we developed a two-parameter-based prediction model predicting the exposure dose of the resist, which outperformed the traditional LUMO-based prediction model. Our model suggests that one should not focus only on the LUMO energies but also on the energy change during the rearrangement process of the activated triphenylsulfonium (TPS) species. We also believe that the model is well suited for computational materials screening and/or inverse design of novel PAG materials with high lithographic performances.

Negative-tone photosensitive polyimide with high transparency

Negative-tone photosensitive polyimides (n-PSPI) with high transparency at visible wavelength region (400–700 nm) were prepared by dissolving photosensitive polyimide precursor -poly(amide ester)(PAE) resins, photoinitiator, photocrosslinker and other additives in organic solvents. The PAE resins were synthesized by polycondensation of a fluorinated aromatic diamine with an aromatic diester dichloride or its mixture. The n-PSPI coating solutions showed good photolithographic performance with resolution of 8 µm (via) and 7 µm (line) at 5 µm of the thermally cured film thickness. After thermally cured at 350 °C/1h, the typical PSPI film exhibited excellent thermal properties with Tg of 344 °C and Td5 of 525 °C, respectively. The mechanical properties with elongation at breakage of as high as 42.2% and tensile strength of 133.7 MPa were also measured. Additionally, the thermally cured PSPI films exhibited excellent transparency with UV cuttoff wavelength of 362 nm, transmittance of 90.5% at 450 nm, and 95.5% at 550 nm, as well as yellowness indices of less than 6.55. Furthermore, theoretical simulations were used to prove that trifluoromethyl group in the backbone structure of PSPI precursor resin can effectively improve the transparency of PSPI films.

Novel Positive Working Photosensitive Polyimide-Carbon Black (PSPI-CB) Composites Containing Triphenylene Vinyl Ether (TP-VE) Monomers

The first positive working chemically amplified photosensitive polyimide-carbon black (PSPI-CB) composite with 2,2′-bis(4-(2′-(vinyloxy)ethoxy)phenyl)propane (BPA-DEVE) as a crosslinking agent was prepared. In addition, the triphenylene vinyl ether (TP-VE) monomers 2,3-di-[(2-vinyloxy)ethoxy]triphenylene (TP-DEVE) and 2,3,6,7,10,11-hexa-[(2-vinyloxy)ethoxy]triphenylene (TP-HEVE) were used as novel CB dispersing aids as well as crosslinking agents. The photolithographic performance of TP-DEVE and TP-HEVE as crosslinking agents in the positive working PSPI and PSPI-CB composites was similar to that of BPA-DEVE. The CB dispersion ability of the crosslinking agents used in the present study was evaluated on the basis of the shading ability (optical density) and surface roughness of the PSPI-CB films. Given the same amount of crosslinking agent in the formulation of the PSPI-CB composite, the optical density and surface roughness of the corresponding PSPI-CB composite film were 1.4 and 116.0 nm for PSPI-CB-1 with BPA-DEVE, 1.7 and 78.2 nm for PSPI-CB-2 with TP-DEVE, and 1.9 and 58.4 nm for PSPI-CB-3 with TP-HEVE, respectively. The results confirm that the CB dispersion ability of these crosslinking agents decreases in the order TP-HEVE > TP-DEVE > BPA-DEVE.

Programmable pupil correction method for photolithography illumination system

The off-axis illumination (OAI) technology is one of the resolution enhancement technologies, and it used to reduce critical dimension (CD) and increase depth of focus (DOF) which are the important performance parameters of photolithography machine. The performance of illumination modes has great effect on critical dimension uniformity (CDU), H–V bias and overlay accuracy. In order that the pupil characteristic parameters can always meet the requirements for a long time using, it is necessary to adopt the pupil correction technology for photolithography illumination system. Using experiments and photolithography performance simulation, a programmable pupil correction method based on correction fingers is studied. The correction algorithm and its operation process are analyzed in detail. The experimental results show that the energy distribution of corrected pupils is more balanced than the uncorrected ones. Furthermore, the simulation results indicate that the corrected pupil could improve the exposure patterns in different aspects. The proposed method could determine the fingers’ position easily, and could directly reflect the pupil performance requirements.

Photo-sensitive bio-based copolymer containing cholic acids: novel functional materials for 248nm photoresist

Cholic acid is a class of biological compounds that exhibit valuable properties, and have been applied in many fields due to its special chemical structures for many areas. In this study, poly[(methacrylic acid tert-butyl cholate ester)-co-(acetoxy styrene)] [P(MATC-co-AS)] was synthesized from cholic acid, then the final copolymer poly[(methacrylic acid tert-butyl cholate ester)-co-(p-hydrostyrene)] [P(MATC-co-HS)] was obtained after P(MATC-co-AS) was hydrolysized. The structure and properties of the copolymers were determined through nuclear magnetic resonance, gel permeation chromatography, UV spectrometry, thermogravimetric analysis, and differential scanning calorimetry. The ultraviolet spectra of the copolymers indicate that they exhibit excellent optical transmittance at 248 nm. Moreover, the photolithography performance of a positive-tone photoresist based on the copolymers were evaluated using an KrF laser exposure system. The results indicate that a resolution of 0.25 μm could be achieved at a low exposure dose.

Novel Star Polymers as Chemically Amplified Positive-Tone Photoresists for KrF Lithography Applications

Xanthate-mediated reversible addition–fragmentation chain transfer (RAFT) methodologies have been applicable to preparation of branched or star polymers. In this article, novel star copolymers have been synthesized through xanthate-mediated RAFT polymerization with p-acetoxystyrene and tert-butyl acrylate. Fourier transfer infrared, nuclear magnetic resonance spectra, and gas chromatography analyses indicated that the polymerization was successful between both of the monomers and the star RAFT agent. The intrinsic viscosity and Zimm branching factor (g′) were used to confirm the copolymers’ architecture. The ultraviolet absorbance of the copolymer solutions indicated that the copolymer was suitable for use as a krypton fluoride (KrF) laser photoresist. Moreover, the photolithography performance of the positive-tone chemically amplified photoresist was evaluated. The results indicated that the photosensitive based on the star copolymer was higher than the linear one, and the pattern resolution was around 2...

Synthesis of novel copolymer based on precipitation polymerization and its application in positive-tone photoresist

A series of copolymers Poly (TBA-CA-St-ASM)(PTCSA) were synthesized via precipitation polymerization by using tert-Butyl acrylate (TBA), Styrene (St), p-acetoxy styrene (ASM), and cedryl methacrylate (CA) as co-monomer. Then, Poly (TBA-CA-St-HS)(PTCSH) was prepared in the presence of sodium methoxide in methanol. The fourier transfer infrared (FT-IR) spectra and proton nuclear magnetic resonance (1H–NMR) spectra indicated that the synthesis was successful. The molecular weight, glass transition temperature (Tg) and thermal decomposition temperature (T(10%)) of the copolymers increased with the addition of CA. Moreover, a positive-tone chemically amplified Krypton Fluoride (KrF) photoresist was prepared, and the photolithography performance of the photoresist was evaluated using a KrF laser exposure system, the result showed that the resolution could reach the level of 0.25 μm.

In-situ synthesis of thiophene-based multifunctional polymeric networks with tunable conductivity and high photolithographic performance

Design of novel multifunctional polymeric materials combining electrically conducting properties with patterning capability is a significant challenge in materials science. Herein, we report on the synthesis of multifunctional interpenetrating polymer networks (IPN) by the in-situ oxidative polymerization of thiophene-based monomers with Cu(ClO4)2 inside a novolac-based photoresist. The resulting IPNs show conductivities up to 20 S/cm depending on the monomer properties. Among them, 3,3‴-Dihexyl-2,2’:5′,2’’:5″,2‴-quaterthiophene (DH4T) is chosen because it has the largest conjugation length and excellent solubility in organic solvents. Moreover, it renders a low percolation threshold and smooth surface morphology if compared with terthiophene (3T). FTIR and XPS spectroscopy confirm the DH4T polymerization by Cu(ClO4)2 and provide some insights about the doping level of the conducting polymer. We also propose a new photolithographic route based on the DH4T polymerization in novolac after pattern generation by oxidant sorption. This novel fabrication route leads to conducting IPNs with outstanding lithographic performance.

Polystyrene Based Visible Light Responsive Polymer with Donor-Acceptor Stenhouse Adduct Pendants

A polystyrene based visible light responsive polymer bearing donor–acceptor Stenhouse adduct (DASA) pendants is designed and synthesized. Styrene-vinylbenzyl chloride copolymer (PS-co-PCMS) is prepared by free radical polymerization. Then amino-functionalized PS-co-PCMS is obtained by the nucleophilic substitution reaction between the chloromethyl unit and n-butylamine. Finally, the prepared secondary amines of the polymer are reacted with 5-(furan-2-ylmethylene)-2,2-dimethyl-1,3-dioxane-4,6-dione to fully change them into DASA pendants. The final DASA-containing polymer shows a tunable photoswitching property upon irradiation with visible light. A photoinduced contact angle change of water on the spin-coated film of DASA polymer is observed. The DASA polymer film shows excellent photolithographic performance, with well-defined patterns being efficiently photofabricated using a suitable mask.

A novel, organic, UV-sensitive resist ideal for nanoimprint-, photo- and laser lithography in an air atmosphere

A UV-sensitive resist capable of curing in an oxygen atmosphere using single wavelength LED light sources is a niche area many UVnanoimprint lithography resists are incapable of addressing. However, the novel negative tone resist, presently (2015) known as DELOKATIOBOND OM VE 110707 (Delo-Katiobond), from Delo Industrial Adhesives has been designed to be specifically compatible with such conditions within the 320–440 nm wavelength range. The authors acquired some of the resist and evaluated its photolithographic performance under such conditions. Several lithographic methods were evaluated, namely nanoimprint-, photo- and laser lithography. Under the step-and-flash nanoimprint test conditions the Delo-Katiobond outperformed commercial alternatives from AMO and Microresist Technology. Processing and development conditions for photo- and laser lithography are also presented. Different discrete wavelengths were used for curing the resist in these two separate lithography processes, 365 nm and 405 nm respectively. The laser-defined lines in Delo-Katiobond coatings were found to be a fraction of alternative resist Nano SU-8 from MicroChem. The functionality of the Delo-Katiobond resist is also evaluated here. It is demonstrated to be effective for a range of resist functions including metal lift-off, elastomeric polymer casting and as a mask for reactive ion etching of a variety of materials. Open image in new window

The preparation of a novel polymeric sulfonium salt photoacid generator and its application for advanced photoresists

With poly(4-hydroxylstyrene) (PHS) as a raw material, a new type of polymeric photoacid generator (PAG) is synthesized with sulfonium perfluoroalkyl sulfonate groups bonded onto part of the benzene rings. The phenolic hydroxyl groups are esterified to increase the solubilities of the polymeric sulfonium salts in organic solvents. Upon irradiation to 254 nm light, the sulfonium units in the polymer effectively decompose to generate sulfonic acid. The photolysis is confirmed by UV spectroscopy and the generation of sulfonic acids which catalyze the decomposition of the t-BOC protection group of the polymeric PAGs. Making use of the polymeric PAGs, positive-tone chemically amplified 248-nm photoresists can be formed by them and ester acetal polymer with high acidolytic activity. The photolithography performance of the photoresist was evaluated using a KrF laser exposure system with high photosensitivity and resolution. This novel kind of polymeric sulfonium salt PAG is applicable for advanced chemically amplified resist materials.

Novel ester acetal polymers and their application for positive-tone chemically amplified i-line photoresists

Polyaddition reactions of N-hydroxy maleopimarimide with divinyl ether compounds were carried out to give novel polymers with ester acetal linkages in the main chain. The polymers have good solubility in common organic solvents and relatively high Tg temperatures. The number-average molecular weights of the polymers range from 4000 to 5500, with Mw/Mn of 1.7–2.3. The thermal decomposition temperatures of the polymers are above 220 °C. The film of the obtained polymers showed excellent transparency to UV light above 230 nm. The ester acetal linkage of the polymer chain can be cleaved in the presence of strong acid under mild heating. Making use of the high acidolytic activity of the polymers, positive-tone chemically amplified i-line photoresists can be formed from them and 2,1-diazonaphthoquinone-4-sulfonate, in which the well known photoactive compound can also function as a photoacid generator. The photolithographic performance of the photoresists was evaluated using an i-line exposure system with high photosensitivity and resolution.

Oxide nanocrystal based nanocomposites for fabricating photoplastic AFM probes

We report on the synthesis, characterization and application of a novel nanocomposite made of a negative tone epoxy based photoresist modified with organic-capped Fe(2)O(3) nanocrystals (NCs). The mechanical properties of the nanocomposite drastically improve upon incorporation of a suitable concentration of NCs in the polymer, without deteriorating its photolithography performance. High aspect ratio 3D microstructures made of the nanocomposite have been fabricated with a uniform surface morphology and with a resolution down to few micrometres. The embedded organic-capped Fe(2)O(3) NCs drastically increase the stiffness and hardness of the epoxy based photoresist matrix, making the final material extremely interesting for manufacturing miniaturized polymer based mechanical devices and systems. In particular, the nanocomposite has been used as structural material for fabricating photoplastic Atomic Force Microscopy (AFM) probes with integrated tips showing outstanding mechanical response and high resolution imaging performance. The fabricated probes consist of straight cantilevers with low stress-gradient and high quality factors, incorporating sharp polymeric tips. They present considerably improved performance compared to pure epoxy based photoresist AFM probes, and to commercial silicon AFM probes.

Kohonen Neural Network – Based Performance Improvements for Wafer Photolithography Process with CONWIP Control Strategy

Photolithography is usually the bottleneck process with the most expensive equipment in a semiconductor wafer fabrication system. To improve the performances of the photolithography area with dynamic combination rules, a method of Kohonen neural network (KNN)–based performance improvements is proposed. First, a dynamic scheduling framework based on a KNN model and scheduling rules is proposed. A KNN-based sample learning algorithm for improving the performances is presented. Finally, to demonstrate the validity and feasibility of the proposed method, data from a real wafer fabrication system are used to simulate the proposed method. Results of simulation experiments indicate that the proposed method can be used to improve a complex wafer photolithography performance.

New Polyimides Coating Technology for Next Generation Semiconductor Application

In this paper, new polyimide coating technologies will be reported that are useful for next generation semiconductor applications. Traditionally, polyimide materials (PI) have been used as stress buffer and rewiring cover layers to improve semiconductor reliability. However, over recent years, due to process cost reduction, conventional PI has gradually been replaced by photosensitive PI (PSPI). In order to meet the next generation semiconductor applications for stress buffer and packaging, photolithographic performance, Cu compatibility, thicker film thickness formability and low temperature cure are critical process properties that need to be addressed. Development of functional PSPI technologies at HDM to meet each of these needs will be discussed in this paper.

Effect of Photo-active Compound Structure on Photosensitivity of Positive Photosensitive Polyimide

The photo-active compound (PAC) in positive tone photosensitive polyimide (posi PSPI) was investigated in order to obtain good photo lithographic performance (small development loss and good photosensitivity). When the PAC structure was changed posi PSPI showed different levels of photosensitivity and development loss. The development loss and photosensitivity showed a good correlation. The lower development loss posi PSPI showed lower photosensitivity. From the molecular orbital calculation, the PAC in the lower development loss posi PSPI had a lower dipole moment than that in the larger development loss posi PSPI. In addition, dissolution rate measurement (DRM) results suggest that posi PSPI may have two layers from the point of dissolution. The dissolution rate of the surface layer in posi PSPI was shown to be lower than that of a bottom layer. This suggests that PAC using the lower development loss posi PSPI may exist mainly on its surface. These results are quite important for the design of good posi PSPI.

Synthesis and characterization of novel negative-working aqueous base developable photosensitive polyimide precursors

Through molecular designing, three poly(amic esters) (PAEs) have been synthesized from pyromellitic dianhydride (PMDA), 2,2′-bis-(3-amino-4-hydroxyphenyl) hexafluoropropane (BisAPAF), 4,4′-diaminodiphenyl ether (4,4′-ODA) and 2-hydroxyethyl methacrylate (HEMA). Due to the introduction of photosensitive acrylate groups and aqueous base soluble phenolic hydroxyl groups in the backbone, these poly(amic esters) can be used as the precursors of negative-working, aqueous base developable photosensitive polyimides (PSPIs). These poly(amic esters) were prepared by direct polymerization by using phenyl phosphonic dichloride (PPD) as an activator. The inherent viscosities of these polymers were 0.20 (dL/g). Their structures were characterized by Fourier transform infrared spectroscopy (FTIR) and 1H NMR. In order to improve the photolithographic performance of these PSPIs, different photosensitizers, photoinitiators and a crosslinker have been added in the PSPI formulations. Among them, the Michler's ketone (MK)/tribromomethyl phenyl sulfone (TBPS) system gave the best results. Using a 2.38 wt% aqueous TMAH solution as a developer, patterns with a resolution of 10 μm were obtained from these PSPI formulations. In addition, the effects of the molecular structure of the precursors and the concentration of developer on the photosensitivity of the PSPI formulations were also discussed.