Per- and polyfluoroalkyl substances (PFAS) have been identified by various regulatory bodies as substances of concern. In line with the objective of safer and sustainable by design, a comprehensive program has been initiated to address these concerns. Part of this program includes the development of non -fluorinated photoacid generators (PAGs) without introducing new chemicals with unintended consequences. Using computational chemistry and synthetic organic chemistry , several scaffolds amenable to PAG library design have been realized. These novel PAGs offer facile tunability and advantages in many critical design parameters such as pKa, diffusion, absorption, shelf-life stability, and scalability. These early generation non-fluorinated PAGs show competitive and similar lithographic performance compared to fluorinated PAGs in i-line, krypton fluoride (KrF) laser, argon fluoride (ArF) laser and extreme ultraviolet (EUV) lithography.

Sequential infiltration synthesis (SIS) is becoming an important tool for resist hardening and formation of unique nanostructures. SIS is a variant of atomic layer deposition (ALD), in which the organometallic precursors are allowed to diffuse into the polymeric substrate before condensation. In contrast to ALD, the extended diffusion time in SIS potentially allows for extensive penetration into the substrate. An important parameter in SIS is the affinity of the precursor with the polymer substrate. Differences in affinity can be exploited, for e.g., for generation of patterned structures within block copolymers. To date, the interactions between the precursor molecules, for example trimethyl aluminium (TMA) have been inferred from in situ or ex situ vibrational spectroscopy. Potentially much richer information can be gained from NMR and transmission FTIR spectroscopy of solutions of precursor and polymer. Fundamental studies of PMMA and TMA allow identification and screening of novel polymer substrates for SIS. Previous studies have provided broad design rules for SIS; e.g., highly-polar and strongly basic structures enhance uptake of precursors. The precursor molecules such as TMA are Lewis acids and hence will associate with functional groups having base character. We have investigated SIS polymers that incorporate a stronger Lewis base group, sulfinyl, in poly((2-methylsulfinyl) ethyl methacrylate) (PMSEMA). Details of the interactions between TMA and PMSEMA in solution, and as films, and comparison with a range of other materials, provide information on potential of these materials for SIS.

Conventional chemically amplified resists for extreme ultraviolet (EUV) lithography are comprised of three fundamental components: a photoreactive, acid-generating species (PAG), an acid reactive polymer for solubility switching, and a basic component for acid diffusion control. The PAG component is typically derived from an organic onium salt, wherein the cation's capacity to capture secondary electrons generated upon EUV irradiation of the resist underscores their reactivity in lithographic applications. Thus, effective rational design of these materials is critical for controlling both sensitivity of the resist and feature regularity. Herein, we describe a robust method for in silico prediction of fundamental properties of onium cations including electron affinity, LUMO energy, and relative charge distribution. We correlate these theoretical values to experimental measurements and further to the influence of PAG cation properties on resist performance under EUV exposure. In addition to the reactive properties of these cations, we analyze these lithographic data in the context of the physicochemical properties of the cations, particularly polarity. In all, the results of this study suggest that while electron affinity of the PAG cation may drive reactivity in response to EUV exposure, multiple factors must be considered in the design of cations for optimal overall resist performance.

Block copolymer (BCP) self-assembly has emerged over the past two decades as a promising method for generation of features for manufacture of integrated circuits and memory devices. Low-molecular-weight BCPs with blocks that are highly immiscible can generate features of dimensions below 10 nm. However, it is often challenging to select a common good solvent for high-x BCPs to allow spin coating. In addition, controlling the alignment of phase separated morphologies with respect to the wafer and at the air interface may be challenging. Here, we prepare a series BCPs of polystyrene (PS) and poly-6-O-methacryloyl-D- galactopyranose (PMAGal), where the polar galactose has been protected with more hydrophobic acetonides. The acetonide protecting groups could be deprotected with trifluoroacetic acid to yield the more polar galactose repeat units to increase the incompatibility of the sugar-containing block with the PS blocks. The bulk morphology of the protected and deprotected versions was studied using small-angle X-ray scattering, where the morphology could be switched from disordered for the protected BCP to either cylindrical or lamellar for the deprotected version or between two ordered phases. Finally, we demonstrate phase separation on the wafer via solvent vapor annealing with H2O/THF, resulting in lamellar patterning with domains as small as 14 nm.

The development of Chemically Amplified Resists (CARs) for Extreme Ultra-Violet Lithography (EUVL) requires unique molecular and macromolecular design considerations. The combination of photon-induced variation effect coupled with material and processing variabilities makes stochastic consequences in EUV resist significantly more severe than that in ArF resist. Among the other factors, conversion of the scarce number of absorbed EUV photons into imaging events is directly modulated by acid generation quantum yield. In this study, we measure the EUV acid generation efficiency of different Photoacid Generators (PAGs). Our results show that in addition to PAG electronic properties, other structural-driven PAG properties can have a significant impact on resist sensitivity. In a complementary part of this study, we have measured PAG acid generation efficiency under EUV exposure in newly designed polymer matrixes. Such polymers comprise high absorption EUV elements and EUV-specific sensitizers. Insights into the effect of the polymer matrix on EUV acid generation quantum yield are presented.

The continued miniaturization of integrated circuit features has been made possible through multilayer patterning processes where different etch steps transfer the patterned photoresist image through various hardmasks and ultimately to the underlying substrate. Spin-on carbons (SOCs) are a type of a solution-dispensable carbon hardmask that can offer excellent resistance to various etch gases for good pattern transfer fidelity, while simultaneously conferring desirable gap fill and planarization properties onto the underlying substrate. We recently reported on the development of a new SOC platform with excellent etch resistance, having a relative reactive ion etch (RIE) rate of 1.08 compared to amorphous carbon. However, one drawback we observed for this polymer was its relatively high absorbance between 400-700 nm which can complicate lithographic alignment. Here we report our work on reducing the absorbance of our SOC platform while maintaining its excellent etch resistance. We identify that the origin of high absorbance is from side reactions that occur during curing and discuss the various polymer modifications or additives that prevent these unwanted processes. We additionally look at any trade-offs that are observed between decreasing absorbance and etch resistance and optimize the SOC’s composition to minimize absorbance while having a minimal effect on its etch resistance.

Photoresponsive polymers capable of luminescence switching are attracting significant interest due to their potential application in fluorescence patterning, bioimaging, optical data storage, and anti-counterfeiting. In this work, we have developed aqueous-soluble copolymers of 1-naphthyl methacrylate and oligo(ethylene glycol) methyl ether methacrylate [P(1-NMA-co-OEGMA)] that undergo a significant shift in fluorescence emission wavelength after UV irradiation. Irradiation of the 1-naphthyl methacrylate moieties results in the photo-Fries rearrangement to form hydroxy aryl ketones, which exhibit strong emission at 475 nm through excited-state intramolecular proton transfer (ESIPT) and excited-state proton transfer (ESPT). The resultant shift in fluorescence emission maximum from 338 to 475 nm after rearrangement can potentially be exploited for fluorescence patterning. Furthermore, the copolymers are thermally sensitive in aqueous solutions. The lower critical solution temperature (LCST) of the copolymers depends on the content of hydrophobic 1-naphthyl methacrylate units; the photo-Fries rearrangement results in a more polar structure, shifting the LCST to a higher temperature. Of note, the temperature-triggered volume phase transition of copolymer hydrogels selectively ″switches off″ fluorescence arising from the ESPT mechanism, while the ESIPT emission is unaffected. We also demonstrate that films formed by coating the copolymers onto various substrates can be selectively patterned to form gradients in fluorescence intensity. These versatile P(1-NMA-co-OEGMA) copolymers are simple to prepare at low cost, demonstrate effective photoswitching, and have excellent water solubility, thus ensuring potential applications in a number of important areas.

Photo-directed orientation control of block copolymer (BCP) domains is a powerful method for generating distinct regions of perpendicular and parallel-aligned lamella in a single film layer. In this study we demonstrate the versatility of aromatic methacrylate polymer films for tuning the wetting behaviour of PS-b-PMMA films on UV exposure. Poly(aryl methacrylate) films with excellent thermal and solvent stability were obtained by thermal crosslinking of spin-coated films. Upon exposure to UV light (254 nm), the surface polarity of the films changed as a result of the photo-Fries rearrangement of the aromatic ester groups. Following UV exposure to appropriate doses, the irradiated poly(aryl methacrylate) films can induce a change in the orientation of the domains of an overlayer of PS-b-PMMA from parallel to perpendicular lamellar structures. Patterning with a photomask enables generation of high fidelity BCP microdomain regions with targeted orientation. It is worth noting that the UV dose required to induce lamellar orientation in a wide range of BCP films can be tailored by rational selection of the poly(aryl methacrylate), suggesting outstanding flexibility in controlling BCP wetting behaviour. This simple, rapid, cost-effective and flexible approach to controlling BCP orientation makes poly(aryl methacrylate)s extremely promising for block copolymer self-assembly applications.

Photo-directed orientation control of block copolymer (BCP) domains is a powerful method for generating distinct regions of perpendicular and parallel-aligned lamella in a single film layer. In this study we demonstrate the versatility of Poly(aryl methacrylate) films for controlling the wetting behaviour of PS-b-PMMA films after UV irradiation. Upon exposure to UV light (254 nm), the surface polarity of Poly(aryl methacrylate) films changed due to the photo-Fries rearrangement of the aromatic ester groups. The switch of PS-b-PMMA alignment from parallel to perpendicular lamellar structures was demonstrated after UV exposure to appropriate doses of poly(aryl methacrylate) films. The UV dose required to switch alignment and orientation in a wide range of BCP films can be tailored by rational structural design of the poly(aryl methacrylate). This simple, rapid, cost-effective and flexible approach to controlling BCP orientation makes this photo-directing chemoepitaxy approach promising for block copolymer self-assembly applications.

The products from the 193 nm irradiation of triphenylsulfonium nonaflate (TPS) embedded in a poly(methyl methacrylate) (PMMA) film have been characterized. The analysis of the photoproduct formation was performed using chromatographic techniques including HPLC, GPC and GC-MS as well as UV-vis and NMR spectroscopic methods. Two previously unreported TPS photoproducts, triphenylene and dibenzothiophene, were detected; additionally, GPC and DOSY-NMR spectroscopic analyses after irradiation suggested that TPS fragments had been incorporated into the polymer film. The irradiation of acetonitrile solutions containing 10% w/v PMMA and 1% w/v TPS in a 1 cm-path-length cuvette showed only a trace amount of triphenylene or dibenzothiophene, indicating that topochemical factors were important for the formation of these molecules. The accumulated evidence indicates that both products were formed by in-cage, secondary photochemical reactions: 2-(phenylthio)biphenyl to triphenylene, and diphenylsulfide to dibenzothiophene.

A new class of acid labile poly(aryl acetal) polymers has been developed that can be used in photoresist formulations for next-generation microlithography techniques including extreme ultraviolet (EUV) or electron beam lithography. Example polymers have been synthesized by an optimized Suzuki polycondensation protocol. They are soluble in common photoresist solvents but are insoluble in water or aqueous bases that are used to develop positive photoresists. The structural design includes further elements that are aimed at improving photoresist resolution, stability, and etch resistance. Upon acid exposure, the acetal linkages are cleaved, and the polymers degrade into phenolic terphenyl fragments, which are readily soluble in a photoresist developer. Polymer degradation has been studied by NMR and LC-MS. Lithographic formulations have been developed and tested in line-and-space patterning experiments using EUV photolithography. Optimized resist formulations achieved 22 nm resolution with line width roughness values of 5.7 nm.

Underpinning the Electronic Revolution over the last 50 years is the development of sophisticated patterning materials which have enabled the elegant semiconductor chip design. Of central importance is the photoresist material which has been custom designed for shrinking exposure wavelengths. Polymer chemistry, synthetic organic chemistry, and photochemistry have all played important roles in the design and development of photoresist materials. Ancillary lithographic materials have also been implemented to solve critical lithographic issues such as antireflection control, leaching and outgassing, and pattern transfer. It can be safely stated that without the creative inventions of lithographic materials by chemists and engineers the Electronic Revolution would not happen. This presentation will introduce the critical chemistry and engineering solutions that led to the development of these enabling lithographic materials.

We report the rates of electron transfer (ET) reactions of electronically excited [Ir(COD)(μ-Me2pz)]2 with onium salt photoacid generators (PAGs). The reduction potentials of the PAGs span a large electrochemical window that allows determination of the driving force dependence of the ET reactions. Rate constants of ET from electronically excited [Ir(COD)(μ-Me2pz)]2 to onium PAGs are determined by the reaction driving force until the diffusion limit in acetonitrile is reached.

Multiple patterning is the defacto manufacturing technology for today's advanced semiconductor devices. However, this technology is becoming limited by technical challenges including cost, resolution, overlay and defectivity. To address these challenges there is growing interest in post lithographic processes which can reduce the pattern feature size thereby effectively enabling increased resolution corresponding to low k1 imaging which is not available by single exposure schemes. In addition to increased resolution, these processes can also improve Process Window (PW), Line Width Roughness (LWR) and Critical Dimension Uniformity (CDU).In this paper, we describe our technical approaches to reducing the Critical Dimension (CD) of resist patterns especially on the most challenging layers. In the area of Bright Field (BF) imaging, we have successfully developed a Positive Tone Develop Trim (PTDT) material which effectively reduces the CD of 193nm immersion line/space (L/S) features generated by a conventional PTD process. To enable CD shrink of Dark Field (DF) features [trenches and contact holes (C/H)] as generated by a 193nm immersion Negative Tone Develop (NTD) process, we have developed a NTD Shrink (NTDS) material. Both PTDT and NTDS approaches are low cost spin on track based processes and are competitive with other approaches in terms of cost, controlled shrink amount, post shrink PW and pattern fidelity.

We have shown that the dissolution properties can be successfully modified to improve the line/space profile and LWR of a low diffusion EUV CA resist. The surface roughness is a function of hot spots in the nominally unexposed regions of the resist material. We conjecture that the photoacid hot spots are formed due to DC flare present in the optical train of the exposure system. We also have shown that the PAGs can be further improved for out-of-band radiation (OOB) response. The improvement can be as much as 557% for 193nm exposure, and 838% by 248nm exposure. The improved OOB response leads to better contact hole performance. We also shared our continued improvement in resist witness plate performance with the majority of our resists passing for carbon growth, and all samples passing for non-cleanables. There does appear to be a site-to-site bias which we attribute to differences between e-beam and EUV exposure and/or substrate working distance from the source. Lastly, we show outstanding lithographic process window for 24 nm contact arrays on an NXE 3300 stepper as well as 15 nm half pitch lines and spaces on the PSI interferometric tool.

Implementation of EUV Lithography (EUVL) for device high volume manufacturing (HVM) requires advanced photoresists capable of meeting the criteria of advanced logic and memory design rules. To achieve the level of performance required, resists must show excellent performance in terms of resolution, LWR (or CDU) and sensitivity. In addition, resists must meet the outgassing criteria required for HVM on the NXE toolset. Lastly, it is anticipated that resists with low OOB sensitivity will also be required.In this paper, we describe our progress in all of these areas. Based on our results, we believe we are on track to deliver production worthy resists for the EUVL era.