Extreme ultra violet (EUV) lithography is one of the most promising next generation lithographic techniques for the production of sub-50 nm feature sizes with applications in the semiconductor industry. Coupling this technique with molecular glass resists is an effective strategy for high resolution lithographic patterning. In this study, a series of tert-butyloxycarbonyl (t-Boc) protected C-4-hydroxyphenyl-calix[4]resorcinarenes derivatives were synthesized and evaluated as positive tone molecular glass resists for EUV lithography. The amorphous nature of these molecules was confirmed using thermal analysis, FTIR and powder X-ray diffraction. Feature sizes as small as 30 nm with low line edge roughness (4.5 nm, 3s) were obtained after patterning and development.
The success of the semiconductor industry is based on the ability to fabricate hundreds of millions of devices on a single chip. In order to fulfill the ever‐shrinking feature sizes, the industry requires new patternable materials in order to operate in the sub‐50 nm regime. Molecular glass (MG) resists are a new type of patterning material that has gained considerable attention over the past few years. This Research News article describes the chemical and structural aspects of MGs as well as important concepts of MG resist design. We also highlight some of the recent advances in high‐resolution patterning capabilities with next‐generation imaging tools.
In this paper, we report the synthesis and characterization of a family of phenolic molecular glasses with variable size and branch architecture. This research is aimed at providing an improved understanding of the relationship between the structural variations of these phenolic photoresist materials and their thermal properties. In particular, the effects of the molecular weight, intermolecular hydrogen bonding, and structural effects on the glass transition temperature are studied in detail to gain a better understanding of their glass forming behavior. A fundamental understanding of such behavior is invaluable to the development of potential molecular photoresists for next generation lithography. Finally, these compounds are evaluated as positive-tone photoresists for lithographic applications for extreme UV (λ = 13.4 nm) lithography.
Abstract. Process-induced overlay errors are a growing problem in meeting the ever-tightening overlay requirements for integrated circuit production. Although uniform process-induced stress is easily corrected, nonuniform stress across the wafer is much more problematic, often resulting in noncorrectable overlay errors. Measurements of the wafer geometry of free, unchucked wafers give a powerful method for characterization of such nonuniform stress-induced wafer distortions. Wafer geometry data can be related to in-plane distortion of the wafer pulled flat by an exposure tool vacuum chuck, which in turn relates to overlay error. This paper will explore the relationship between wafer geometry and overlay error by the use of silicon test wafers with deliberate stress variations, i.e., engineered stress monitor (ESM) wafers. A process will be described that allows the creation of ESM wafers with nonuniform stress and includes many thousands of overlay targets for a detailed characterization of each wafer. Because the spatial character of the stress variation is easily changed, ESM wafers constitute a versatile platform for exploring nonuniform stress. We have fabricated ESM wafers of several different types, e.g., wafers where the center area has much higher stress than the outside area. Wafer geometry is measured with an optical metrology tool. After fabrication of the ESM wafers including alignment marks and first level overlay targets etched into the wafer, we expose a second level resist pattern designed to overlay with the etched targets. After resist patterning, relative overlay error is measured using standard optical methods. An innovative metric from the wafer geometry measurements is able to predict the process-induced overlay error. We conclude that appropriate wafer geometry measurements of in-process wafers have strong potential to characterize and reduce process-induced overlay errors.
Continuous advances in the semiconductor and microfabrication industries are based on formation of increasingly smallscale devices. Photolithography, the process by which small features are patterned into a thin organic film (photoresist) by UV or electron-beam (e-beam) irradiation, is the principle process by which small features are formed. To produce the planned sub-50 nm features required for next-generation devices remains a challenge due to the increased importance of pattern perfection and elimination of problems such as pattern collapse in small, high-aspect-ratio features. At these very small dimensions, conventional development in an aqueous base can cause small, dense lines to collapse inward due to high surface tension. These and other problems will remain significant challenges unless new approaches to lithography are pursued. Supercritical carbon dioxide (scCO 2 ), which is known for its properties of high diffusivity and zero surface tension, is an ideal alternative to aqueous bases as an advanced development solvent and can help to realize the potential of sub-50 nm patterning.Supercritical CO 2 development is a powerful alternative process to aqueous-base or organic-solvent development for high-resolution patterning from both an environmental and practical point of view. In practice, scCO 2 is a single-phase fluid that exists above the critical temperature and pressure of CO 2 (T = 31°C, P = 7.4 MPa). Supercritical CO 2 as a solvent can provide environmental benefits, which result from a reduction in solvent and water waste, and it may also serve as a platform where harmful solutes are easily separated from the solvent in question (via depressurization). scCO 2 has been shown to be an ideal solvent for processing structures on the nanoscale. [1,2] In terms of performance, scCO 2 is a solvent with zero surface tension and high diffusivity. This leads to better development characteristics compared to liquid solvents for dense, high-aspect-ratio features. However, scCO 2 tends to be a very poor solvent for polymers, such as those that current photoresists are comprised of; though certain fluoropolymers and silicones have been shown to be soluble at moderate supercritical conditions. [3,4] This would necessitate the incorporation of groups, such as fluorinated side chains, into photoresist materials to effect scCO 2 solubility. Despite the advantages of scCO 2 development, there are several reasons that make the incorporation of fluorine in scCO 2 developable resists undesirable. Usually the large quantities of fluorine present in scCO 2 -soluble polymers degrade plasma-etch resistance and are undesirably expensive. Also, due to their persistent nature, fluorinated compounds are coming under increased scrutiny [5] and their use needs to be phased out. Finally, although scCO 2 -soluble polymeric resists based on fluoropolymer platforms have been studied in recent years, [6,7] no features smaller than 100 nm have been demonstrated. Regardless of exposure method, these materials have not shown sufficien...
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