James W. Thackeray

Nanoscopic Cylindrical Dual Concentric and Lengthwise Block Brush Terpolymers as Covalent Preassembled High-Resolution and High-Sensitivity Negative-Tone Photoresist Materials

We describe a high-resolution, high-sensitivity negative-tone photoresist technique that relies on bottom-up preassembly of differential polymer components within cylindrical polymer brush architectures that are designed to align vertically on a substrate and allow for top-down single-molecule line-width imaging. By applying cylindrical diblock brush terpolymers (DBTs) with a high degree of control over the synthetic chemistry, we achieved large areas of vertical alignment of the polymers within thin films without the need for supramolecular assembly processes, as required for linear block copolymer lithography. The specially designed chemical compositions and tuned concentric and lengthwise dimensions of the DBTs enabled high-sensitivity electron-beam lithography of patterns with widths of only a few DBTs (sub-30 nm line-width resolution). The high sensitivity of the brush polymer resists further facilitated the generation of latent images without postexposure baking, providing a practical approach for controlling acid reaction/diffusion processes in photolithography.

Effect of acid diffusion on performance in positive deep ultraviolet resists

Two methods to measure acid diffusion in positive acid catalyzed resists are described. The first method employs a spectrophotometric titration to determine the acid concentration ([H+]) followed by measuring the ion conductivity (σ) of the resist film to determine the diffusion coefficient (D). This method allows the diffusion coefficient of acid in the resist to be determined at different temperatures ranging from room temperature to different post‐exposure bake (PEB) temperatures. The second method is based on the threshold acid density theory of image formation, which assumes that when a critical concentration of acid is reached, the developer solubility of the resist is changed. With this method, a constant level of acid can be followed at different PEB times and the diffusion coefficient determined. A comparison of the two methods to measure the acid diffusion coefficient will be made and the temperature dependence of diffusion for different types of organic acids will be presented. Based on a previ...

Generation of Powerful Tungsten Reductants by Visible Light Excitation

The homoleptic arylisocyanide tungsten complexes, W(CNXy)6 and W(CNIph)6 (Xy = 2,6-dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400-550 nm). MLCT emission (λ(max) ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy)6 and W(CNIph)6 with lifetimes of 17 and 73 ns, respectively. Diffusion-controlled energy transfer from electronically excited W(CNIph)6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bu(n)4N][PF6], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph)6](+) and [anth](•-). ET from *W to benzophenone and cobalticenium also is observed in [Bu(n)4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6](+)/*W couple is -2.8 V vs Cp2Fe(+/0), establishing W(CNIph)6 as one of the most powerful photoreductants that has been generated with visible light.

Stochastic exposure kinetics of extreme ultraviolet photoresists: simulation study

The stochastic nature of extreme ultraviolet (EUV) resist exposure leads to variations in the resulting acid concentration, which leads to line-edge roughness (LER) of the resulting features. Using a stochastic resist simulator, we predicted the mean and standard deviation of the acid concentration for an open-frame exposure and fit the results to analytical expressions. The EUV resist exposure mechanism of the PROLTIH Stochastic Resist Simulator is first order, and an analytical expression for the exposure rate constant C allows prediction of the mean acid concentration of an open-frame exposure to about 1% accuracy over a wide range of parameter values. A second analytical expression for the standard deviation of the acid concentration also matched the output of the simulator to within about 1%. Given the assumptions of the PROLTIH Stochastic Resist Simulator, it is possible to use the results of this paper to predict the stochastic uncertainty in acid concentration for EUV resists, thus allowing optimization of resist processing and formulations and contributing to a comprehensive LER model.

Materials challenges for sub-20-nm lithography

We discuss the future of resist materials for sub-20-nm lithography and believe that polymer-bound PAG-based resists will be used to 16-nm node. There has been enough progress in resolution and sensitivity to justify the use of these materials. Polymer-bound PAG resists have shown that the principal demerit of acid diffusion can be overcome through attachment of the PAG anion to the lithographic polymer. Since the introduction of this chemically amplified resist approach, we have seen steady improvement in resolution, sensitivity, and LWR. We have also seen improvement in OOB response, outgassing, and pattern collapse. There is no doubt that continuous improvement is still required for these resist systems. We believe that increasing the overall resist quantum yield for acid generation substantially improves the shot-noise problem thereby leading to faster high-resolution resist materials. Using a 0.30-NA extreme ultraviolet tool with dipole, we can achieve 22-nm hp resolution, with a 12-mJ dose and a 4.2-nm LWR.

Deep UV ANR Photoresists For 248 nm Excimer Laser Photolithography

This paper describes the development of deep UV resist materials based on chemically amplified crosslinking systems for use in excimer laser photolithography at the KrF lasing wavelength of 248 nm. This work will describe the use of a transparent resin, polyp-vinyl)phenol, which has excellent plasma etch resistance and demonstrates high resolution (sub half-micron line-space pairs for a 1.0 micron thick film) when used in an Advanced Negative Resist (ANR) formulation, XP-8843. Under 140C post-exposure bake conditions, XP-8843 exhibits fast photospeed (15 mJ/cm2), high contrast (4.1), vertical sidewalls, and good process latitude.

Materials challenges for sub-20nm lithography

This paper discusses the future of resist materials for sub-20nm lithography. It is my contention that polymer-bound PAG based resists will be used to 16nm node. There has been enough progress in resolution and sensitivity to justify the use of these materials. PBP resists have shown that the principal demerit of acid diffusion can be overcome through attachment of the PAG anion to the lithographic polymer. Since the introduction of this chemically amplified resist approach, we have seen steady improvement in resolution, sensitivity, and LWR. We have also seen improvement in OOB response, outgassing, and pattern collapse. There is no doubt that continuous improvement is still required for these resist systems. We believe that increasing the overall resist quantum yield for acid generation substantially improves the shot noise problem thereby leading to faster high resolution resist materials. Using a 0.30NA EUV tool with dipole, we can achieve 22nm hp resolution, with 12mJ dose, and 4.2nm LWR.

Directing Self-Assembly of Nanoscopic Cylindrical Diblock Brush Terpolymers into Films with Desired Spatial Orientations: Expansion of Chemical Composition Scope

Diblock brush terpolymers (DBTs) with different fluorinated methacrylate-based block segments are synthesized through sequential ring-opening metathesis polymerizations and are used to prepare polymer thin films with predictable film thicknesses. These DBTs exhibit preferable substrate vertical alignments within the films, induced by the relatively lower surface energy of the fluorinated structural components, together with the overall cylindrical morphology of the brush architecture.

Statistical simulation of resist at EUV and ArF

Requirements of resist modeling strategies for EUV and low-k1 ArF nanolithography continue to become more stringent. Resist designers are consistently faced with the task of reducing exposure dose and line roughness while simultaneously improving exposure latitude, depth-of-focus and ultimate resolution. In this work, we briefly discuss a next-generation resist model for the prediction of statistical resist responses such as line-edge roughness, line-width roughness and CD variability, as well as base lithographic responses such as exposure latitude. The models parameterized fit to experimental data from a state-of-the art polymer-bound PAG resist irradiated at ArF and EUV will be shown. The probabilistic computation of acid generation at ArF and EUV will be discussed. The factors influencing the hypothesized primary cause of resist roughness, acid shot noise, are discussed.

Chemically amplified resists resolving 25 nm 1:1 line: space features with EUV lithography

We have investigated a number of key resist factors using EUV lithography including activation energy of deprotection. Our standard high activation resist material, MET-2D (XP5271F), is capable of robust performance at CDs in 40 nm regime and thicknesses above 100 nm. Below 100 nm film thickness, controlling acid diffusion becomes a difficult challenge. We have also developed a low activation resist (XP6305A) which shows superior process window and exposure latitude at CDs in the 35 nm regime. This resist is optimal for 80 nm film thickness. Lastly, we have demonstrated 25 nm 1:1 resolution capability using a novel chemical amplification resist called XP6627. This is the first EUV resist capable of 25 nm resolution. The LER is also very low, 2.7 nm 3&sgr;, for the 25 nm features. Our first version, XP6627G, has a photospeed of 40 mJ/cm2. Our second version, XP6627Q, has a photospeed of 27 mJ/cm2. Our current focus is on improving the photospeed to less than 20 mJ/cm2. The outstanding resolution and LER of this new resist system raises the possibility of extending chemically amplified resist to the 22 nm node.