Photoresist Shrinkage Research Articles

Fabrication of silicon sharp nanocones using dry etch with periodic oxygen plasma shrinking and wet etch

Silicon (Si) nanocones have a wide range of applications in microelectromechanical systems and nanoelectromechanical systems. There is an increasing demand for precise control over the size and shape of nanocones. This paper proposed a novel method combining Si dry etch with periodic oxygen plasma shrinking, wet etch, and oxidation sharpening to achieve well-defined sharp Si nanocones. First, the standard Bosch process was employed to create the base part of nanocones. Second, two alternating steps of etching with sulfur hexafluoride/octafluorocyclobutane plasma and photoresist shrinkage with oxygen plasma were used to form the cone-shaped structures on top of the cylindrical bases. Third, to obtain a sharp tip, wet etching was carried out in either potassium hydroxide or a nitric acid/hydrofluoric (HF) acid mixture. To further sharpen the Si tips, thermal oxidation and HF dipping were conducted and the apex of nanocones can be down to 20 nm. This technique provides a cost-effective way to manufacture nanocones for various applications.

Stochastic Multi-Molecular Modeling Method of Organic-Modified Ceramics in Two-Photon Induced Photopolymerization.

Organic-modified ceramics (Ormocer) are an outstanding class of hybrid materials due to the fact of their various excellent properties, and they have been successfully used in two-photon polymerization microfabrication fields. A series of functional devices has been fabricated and widely used in aerospace, information science, biomedicine, and other fields. However, quantization of intermolecular energy during the fabrication process is still a difficult problem. A stochastic multi-molecular modeling method is proposed in this paper. The detailed molecular-interaction energies during the photon polymerization of Ormocer were obtained by molecular dynamics analysis. The established molecular model was verified by comparing the simulated shrinkage results with commercial calibrated ones. This work is expected to provide a reference for optimizing the fabrication of organically modified ceramics and reducing photoresist shrinkage in two-photon polymerization.

Precise Cross-Sectional Measurement of Photoresist Shrinkage Caused by Electron Beam Irradiation

A mechanism of the photoresist shrinkage induced by electron-beam (EB) irradiation was studied in detail. A precise cross-sectional profile of a photoresist pattern is obtained by a scanning transmission electron microscope (STEM) after HfO2 atomic layer deposition on a sample. Photoresist lines and spaces formed on either of bottom anti-reflective coating (BARC) layer or spin-on-glass (SOG) layer were exposed to EB at a much higher dose than a practical dose (to accelerate shrinkage intentionally). The obtained STEM images of the patterns before and after EB irradiation showed that EB irradiation causes necking of the pattern profile as well as linewidth slimming. In addition, it was suggested that the BARC layer shrinkage results in the elastic deformation of the pattern profile, whereas the SOG layer does not shrink. Furthermore, EB irradiation only to the lines or spaces was performed. The EB irradiation to spaces caused sidewall shrinkage and necking of the pattern profile, although no electron was irradiated directly into the pattern. This result is considered to be due to the electrons scattered from the spaces to the pattern sidewall. Finally, a Monte Carlo simulation showed that the distribution of the deposited energy on the pattern surface corresponds to the change of the pattern shape. Consequently, our study clarifies the importance of the effect of elastic shape change and the impact of the electrons scattered from the underlying layer to the sidewall on photoresist shrinkage.

Time-dependent electron-beam-induced photoresist shrinkage effects

We explore how photoresist shrinkage behavior due to e-beam measurement by critical dimension-scanning electron microscope (CD-SEM) depends on various time-related factors. This will include an investigation of how the photoresist critical dimension (CD) and CD shrinkage varies with photoresist age and the differences in shrinkage trends between load/unload and static and dynamic repeatability cases, where time between measurements is a key variable. The results for this typical immersion argon flouride photoresist process will show that resist CD and shrinkage variation due to resist age and vacuum-cycling is insignificant, yet the shrinkage is strongly linked to time between consecutive measurements, with a well-defined, high-certainty logarithmic decay with time. These experiments identify a key difference between the shrinkage seen in static versus dynamic measurements, which will be shown to have far-reaching implications for the shrinkage phenomenon in general and for the best-known methods for executing CD-SEM metrology with photoresist samples.

Photoresist Shrinkage Caused by Single-Line Scan of Electron Beam

Shrinkage behavior caused by a single-line scan of an electron beam over a photoresist line was observed, including shrinkage distribution in the photoresist-line direction. A new method for evaluating the minute amount shrinkage and the shrinkage distribution caused by a single-line scan was developed. According to the results of evaluations with this method, the shrinkage of an about 50-nm-wide photoresist line caused by a single-line scan is less than 0.1 nm under landing energies of 200, 300, and 500 eV and probe current of 8 pA. This shrinkage is more than ten times smaller than the typical amount of shrinkage caused by a standard two-dimensional scan. This result indicates the possibility of a significant reduction of photoresist shrinkage during scanning-electron-microscope measurements. The evaluation method also yielded the first observation of the shrinkage distribution in the photoresist-line direction. The results show that the shrinkage caused by a single-line scan distributes more than 30 nm, which is wider than the calculated electron-scattering range. This result suggests that there likely to be an additional mechanism involved in photoresist shrinkage other than the microscopic interaction between incident electrons and photoresist molecules. An elastic-relaxation effect and a contribution of back-scattered electrons are plausible additional mechanisms for photoresist shrinkage.

Photoresist Shrinkage Caused by Single-Line Scan of Electron Beam

Photoresist Shrinkage Caused by Single-Line Scan of Electron Beam

Holographic Design and Fabrication of Diamond Symmetry Photonic Crystals Via Dual‐Beam Quadruple Exposure

Diamond symmetry structures (space group No. 227) with tunable lattice size are fabricated from epoxy-functionalized cyclohexyl polyhedral oligomeric silsesquioxane (POSS) by holographic lithography using dual-beam quadruple exposure configuration with careful consideration of the relative phase shift, wobble effect, and pre-compensation of the photoresist shrinkage. Calculation suggests that Si photonic crystals templated from the POSS structures, both directly converted and its inverse structure, offer the same and maximum complete PBGs in comparison to other holographically patterned diamond lattices. Holographic Design and Fabrication of Diamond Symmetry Photonic Crystals Via Dual-Beam Quadruple Exposure Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Analytical model for ArF photoresist shrinkage under scanning electron microscopy inspection

Linewidth slimming is a phenomenon occurring specifically in photolithography of 193 nm wavelength (ArF) radiation. Photoresists for this wavelength appear to lose volume when exposed to electron-beam radiation, as when scanned in scanning electron microscopy for critical dimension (linewidth) measurement. This work is an attempt to understand this “shrinkage” from a polymer physics point of view. More specifically, the authors try to check the applicability of free volume theory in polymer systems by calculating some relevant physical properties, assuming that the exposure to e-beam creates an external hardened shell for the material bulk, and continued exposure will deliver heat into the polymer enclosed in a confined space. The authors’ main conclusion is that the free volume loss (annealing) shows qualitative resemblance to experiment, but this effect exclusively is not a sufficient quantitative explanation for the observed shrinkage. A possible explanation for this discrepancy is that their model is limited due to unknown material parameters, or that the annealing is coupled with other effects such as “wringing” solvent out.

Shrinkage Precompensation of Holographic Three‐Dimensional Photonic‐Crystal Templates

Holographic lithography is an established technique for fabricating three-dimensional photonic-crystal templates. [1–12] The principle of holographic lithography is to expose a photoresist layer to an interference pattern. After processing, a porous polymer–air structure results. In order to achieve a desirable complete photonic bandgap (PBG), these templates have to be replicated with silicon [13] or other high-index materials. Theory predicts complete PBGs for certain crystal symmetries and crystallographic motifs. [5,8–12] In all these proposals it is tacitly assumed that the surface of the resulting polymer template coincides with an isodose surface of the exposing interference pattern. However, many deviations resulting from various steps in the fabrication process may be present. [14] Based on our studies we find that shrinkage is the most prominent deviation. Photoresist shrinkage can be anisotropic and in some cases reduces the size of the template by up to 50%, which significantly affects the PBG and, therefore, can not be neglected. By quantifying and precompensating the anisotropic shrinkage, we solve this problem for the first time for the most common photoresist system in holographic lithography, namely SU-8 from MicroChem. A lateral shrinkage has previously been discussed [15] for a different resist and