Antimony(V) carboxylate photoresists incorporating polymerizable olefins have demonstrated high photospeeds. The work of Passarelli et al. reported a sensitivity hypothesis, polymerizable olefin loading (POL), in which an increase in photospeed correlates to an increase in the number of olefins per molecular weight of resist.1 Utilizing this sensitivity trend, a photoresist of higher molecular weight, triphenylantimony(V) bis(4-vinylbenzoate) (JP-30), was developed exhibiting moderate photospeed at the cost of improved pattern fidelity.
Herein we report three approaches for improving the lithographic performance of polymerizable olefin antimony carboxylate photoresists. Approach 1 increased the number of olefins per molecule through functionalization of the R-group. Tristyreneantimony(V) dicarboxylate photoresists were lithographically evaluated exhibiting high photospeeds and improved resolution capabilities (Figure 1). Approach 2 examined the benefits of blending two antimony carboxylate photoresists with high and low POL values and observing the changes in photospeed. Approach 3 increased the POL relative to JP-30 through reduction in molecular weight of the R-groups by the synthesis and lithographic evaluation of trimethylantimony(V) bis(4-vinylbenzoate).
The EUV photoproducts of antimony carboxylate photoresists [R3Sb(O2CR′)2] are used to evaluate a possible free radical exposure mechanism by studying the change in molecular weight distribution with dose. We demonstrate the redistribution of carboxylate ligands across the metal centers in solution and use this property to create a statistical mono-olefin resist system with blended solutions of olefinic and non-olefinic antimony compounds that limit crosslinking and improve solubility of the photoproducts. Through gel permeation chromatography (GPC) analysis, we demonstrate the formation of high molecular weight oligomers with exposure dose and provide further support for the free-radical polymerization mechanism.
Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is used to evaluate the composition of nonvolatile photoproducts created by EUV photolysis of antimony carboxylate photoresists [R3Sb(O2CR′)2]. Dozens of potential photoproduct ions were identified using exact mass and 121Sb/123Sb isotopic ratios. Several oxygen-rich antimony ions were found to increase in abundance with exposure. Two methods were employed to identify photoproducts which create solubility contrast. First, samples were analyzed pre- and post-development to examine the effects of EUV exposure and developer solvent on secondary ion intensity. Secondly, changes in intensity of select ions were compared to dissolution contrast over a range of doses. Through these studies, ion intensities were found to correlate with dissolution contrast for several fragments, indicating their active role in creating negative-tone response.
We have developed inorganic oxalate compounds [PPh3(CH2Ph)][M(2,2′-bipyridine)n(oxalate)(3-n)] (n=1, 2, 3; M = Co, Fe, Cr) capable of acting as negative-tone extreme ultraviolet (EUV) resists. Two important trends are observed: (1) sensitivity increases with the number of oxalate ligands; (2) Cobalt and iron complexes exhibit greater sensitivity than analogous chromium complexes. Lithographic studies of the most successful compound, [PPh3(CH2Ph)][Co(2,2′-bipyridine)(oxalate)2], show that it can consistently achieve 20 nm h/p lines at doses approaching 30 mJ/cm2. Infrared, paramagnetic nuclear magnetic resonance, and cyclic voltammetric studies of this compound show that the reaction products of the EUV photochemistry are Co(II)(2,2′-bipyridine)(oxalate) and [PPh3(CH2Ph)]2(oxalate) formed from the decomposition of one of the oxalate ligands into two equivalents each of carbon dioxide and electrons.
This paper describes the photoreactivity of six organometallic complexes of the type PhnMX2 containing bismuth, antimony and tellurium, where n = 3 for bismuth and antimony and n = 2 for tellurium, and where X = acetate (O2CCH3) or pivalate (O2CC(CH3)3). These compounds were exposed to EUV light to monitor photodecomposition via in situ mass spectral analysis of the primary outgassing products of CO2, benzene and phenol. This paper explores the effect of metal center and carboxylate ligand on the EUV reactivity of these EUV photoresists.
We have investigated the mechanism of photodecomposition of antimony carboxylate complexes of the type Ph3Sb(O2CR′)2 by means of EUV outgassing in combination with isotopic labelling. A series of photoresists were examined to determine the mechanistic pathways by which volatile photoproducts are generated during EUV exposure. A primary volatile photoproduct from triphenylantimony complexes is benzene. However, the source of hydrogen needed to convert the phenyl groups to benzene (Ph-H) is not obvious. We concluded that the primary source of hydrogen to create benzene is external to the film. Additionally, we have prepared isotopically-labelled versions of Ph3Sb(O2CCH(CH3)2)2 in which the hydrogens in the isobutyrate ligand were replaced with 0, 1, 6 and 7 deuteriums, to provide information about the relative reactivity of these protons during EUV exposure as analyzed by mass spectrometry. High reaction selectivity was identified within the carboxylate dictated by hydrogen location relative to the carbonyl for both benzene and phenol generation. Lastly, the results of these studies were used to propose a series of reaction pathways to generate the aforementioned reaction byproducts.
The photo-mechanism of EUV exposures in chemically amplified photoresists are much different than that of previous lithographic wavelengths. Electrons generated during EUV exposure are demonstrated to be a source of acid production through a process referred to as electron trapping. Density functional theory modeling indicates that it is energetically favorable for the PAG molecule to decompose if an electron is trapped. Low-energy electrons unlikely to produce holes and secondary electrons generate acid indicating electron-PAG interactions are capable to induce decomposition. Additionally, a more easily reduced PAG (i.e. higher likelihood of trapping an electron) produces a higher acid yield supporting electron trapping as a process of acid production. An acid indicator, Coumarin 6, was used to determine the number of acids generated per absorbed EUV photon. The results of these measurements indicate that electron-PAG interactions are a source of acid production through electron trapping; thus, increasing the number of electron-hole pairs available to induce chemical reactions would improve sensitivity. It is expected that lower band gap materials produce more electron-hole pairs after an absorption event. Subsequently, these measurements show that lower band gap polymers generate higher acid yields.
Pure thin-films of unimolecular organometallic photoresists were lithographically evaluated using extreme ultraviolet light (EUV, λ = 13.5 nm) and developed using solutions containing carboxylic acids. Optimization of development solutions used with a cobalt-oxalate EUV resist (NP1, 2) led to a switch in lithographic tone from negative to positive. Additional optimization led to an improvement in top loss (35 to 7%) with development in cyclohexanone and 2-butanone, respectively. We saw a drastic improvement in photo-speed (Emax = 5 mJ/cm2) and contrast of the negative-tone imaging with development in certain acidic solutions. Additionally, carboxylic acid solutions provide excellent development conditions for resists that we, in the past, have been unable to successfully develop.
We have developed a method to study the photomechanism of our antimony carboxylate platform R3Sb(COOR')2. A series of mechanistic studies followed the production of reaction byproducts by mass spectrometer, as they left the film during exposure to EUV photons and 80 eV electrons. We identified several prominent outgassing fragments and their rates of production as a function of ligand structure. The degree of outgassing appears to be well-correlated with the bond dissociation energy of the carboxylate ligand R’ group. Furthermore, a deuterium labeling study was conducted to determine from which ligand hydrogen is abstracted to form benzene and phenol during exposure. Benzene and phenol were found to abstract hydrogen from opposing sites within the film, and with greater than 95% isotopic purity. Using the results of the outgassing studies alongside established mechanisms for electron-induced reactions; a series of reaction pathways were proposed to generate the aforementioned outgassing species and a possible nonvolatile negative-tone photoproduct.
the microelectronics industry. Traditional EUV photoresists have been composed of organic compounds which are moderately transparent to EUV. Resist stochastics and sensitivity can be improved by increasing the number of photons absorbed. Molecular organometallic resists are a type of metal containing resist aimed at improving EUV absorption. This work focuses on studying the role of the metal center (Metal = Co, Fe, Cr) in an oxalate complex by comparing the number of absorbed photons and the photoelectron reactivity in each compound. In the study presented here, the EUV absorption coefficients are determined experimentally by measuring the transmission through a resist coated on a silicon nitride membrane using an Energetiq EQ-10M xenon plasma EUV source. Additionally, the photochemistry is evaluated by monitoring outgassing reaction products. This particular resist platform eliminates oxalate ligands when exposed to electrons or EUV photons resulting in a solubility difference between the exposed and unexposed regions. In the process, carbon dioxide is produced and is monitored using mass spectrometry, where quantitative values are obtained using a calibration technique. For the metal oxalate complexes studied, the absorption of EUV changed minimally due to the low concentrations of metal atoms. However, EUV and electron reactivity greatly changed between the three compounds likely due to the reducibility of the metal center. A correlation is shown between Esize and the reducibility of each photoresist.
Extreme ultraviolet (EUV, ~13.5 nm) lithography is the prospective technology for high volume manufacturing by the microelectronics industry. Significant strides towards achieving adequate EUV source power and availability have been made recently, but a limited rate of improvement in photoresist performance still delays the implementation of EUV. Many fundamental questions remain to be answered about the exposure mechanisms of even the relatively well understood chemically amplified EUV photoresists. Moreover, several groups around the world are developing revolutionary metal-based resists whose EUV exposure mechanisms are even less understood. Here, we describe several evaluation techniques to help elucidate mechanistic details of EUV exposure mechanisms of chemically amplified and metal-based resists. EUV absorption coefficients are determined experimentally by measuring the transmission through a resist coated on a silicon nitride membrane. Photochemistry can be evaluated by monitoring small outgassing reaction products to provide insight into photoacid generator or metal-based resist reactivity. Spectroscopic techniques such as thin-film Fourier transform infrared (FTIR) spectroscopy can measure the chemical state of a photoresist system pre- and post-EUV exposure. Additionally, electrolysis can be used to study the interaction between photoresist components and low energy electrons. Collectively, these techniques improve our current understanding of photomechanisms for several EUV photoresist systems, which is needed to develop new, better performing materials needed for high volume manufacturing.
Here, we present platinum and palladium mononuclear complexes with EUV photosensitivity and lithographic performance. Many platinum and palladium complexes show little or no EUV sensitivity; however, we have found that metal carbonates and metal oxalates (L2M(CO3) and L2M(C2O4); M=Pt or Pd) are sensitive to EUV. The metal carbonates give negative-tone behavior. The most interesting result is that the metal oxalates give the first positive-tone EUV resists based on mononuclear organometallic compounds. In particular, (dppm)Pd(C2O4) (dppm=1,1-bis(diphenylphosphino)methane) (23) prints 30-nm dense lines with Esize of 50 mJ/cm2. Derivatives of (23) were synthesized to explore the relationship between the core metal and the resist sensitivity. The study showed that palladium-based resists are more sensitive than platinum-based resists. The photoreaction has been investigated for two of our most promising resists, (dppm)Pd(C2O4) (23) and (Ph2EtP)2PdC2O4 (27). Our experiments suggest the loss of CO2 and the formation of a zerovalent L4Pd complex upon exposure to light. We have identified dppm2Pd(δ(P)23.6) as the main photoproduct for (23) and (Ph2EtP)4Pd (δ(P)32.7) as the main photoproduct for (27).
We have developed organometallic carboxylate compounds [RnM(O2CR′)2] capable of acting as negative-tone extreme ultraviolet (EUV) resists. The most sensitive of these resists contain antimony, three R-groups and two carboxylate groups, and carboxylate groups with polymerizable olefins (e.g., acrylate, methacrylate, or styrenecarboxylate). Evidence suggests that high sensitivity is achieved through the polymerization of olefins in the exposed region. We have performed a systematic sensitivity study of the molecules of the type RnM(O2CR′)2 where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O2CR′). The sensitivity of these resists was evaluated using Emax or dose to maximum resist thickness after exposure and development. We found that the greatest predictor of sensitivity of the RnSb(O2CR′)2 resists is their level of polymerizable olefins. We mathematically define the polymerizable olefin loading (POL) as the ratio of the number of olefins versus the number of nonhydrogen atoms. Linear and log plots of Emax versus POL for a variety of molecules of the type R3Sb(O2CR′)2 lend insight into the behavior of these resists.
We have developed organometallic carboxylate compounds [RnM(O2CR’)2] capable of acting as negativetone EUV resists. Overall, the best and fastest resists contain antimony, are pentavalent and the carboxylate group contains a polymerizable olefin (e.g. acrylate, methacrylate or styrenecarboxylate). Evidence suggests that high sensitivity is achieved through the polymerization of olefins in the exposed region. We have performed a systematic sensitivity study of molecules of the type RnM(O2CR’)2 where we have studied seven R groups, four main group metals (M), and three polymerizable carboxylate groups (O2CR’). We found that the greatest predictor of sensitivity of the RnSb(O2CR’)2 resists is their level of polymerizable olefins. We mathematically define the polymerizable olefin loading (POL) as the ratio of the number of olefins vs. the number of non-hydrogen atoms. Linear and log plots of Emaxvs. POL for a variety of molecules of the type R3Sb(O2CR’)2 lend insight into the behaviour of these resists.
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