Extreme ultraviolet (EUV) lithography at 13.5 nm is the main candidate for patterning integrated circuits and reaching sub-10-nm resolution within the next decade. Should photon-based lithography still be used for patterning smaller feature sizes, beyond EUV (BEUV) lithography at 6.x nm wavelength is an option that could potentially meet the rigid demands of the semiconductor industry. We demonstrate simultaneous characterization of the resolution, line-edge roughness, and sensitivity of distinct photoresists at BEUV and compare their properties when exposed to EUV under the same conditions. By using interference lithography at these wavelengths, we show the possibility for patterning beyond 22 nm resolution and characterize the impact of using higher energy photons on the line-edge roughness and exposure latitude. We observe high sensitivity of the photoresist performance on its chemical content and compare their overall performance using the Z-parameter criterion. Interestingly, inorganic photoresists have much better performance at BEUV, while organic chemically-amplified photoresists would need serious adaptations for being used at such wavelength. Our results have immediate implications for deeper understanding of the radiation chemistry of novel photoresists at the EUV and soft X-ray spectra.

All nanofabrication methods come with an intrinsic resolution limit, set by their governing physical principles and instrumentation. In the case of extreme ultraviolet (EUV) lithography at 13.5 nm wavelength, this limit is set by light diffraction and is ≈3.5 nm. In the semiconductor industry, the feasibility of reaching this limit is not only a key factor for the current developments in lithography technologies, but also is an important factor in deciding whether photon-based lithography will be used for future high-volume manufacturing. Using EUV-interference lithography we show patterning with 7 nm resolution in making dense periodic line-space structures with 14 nm periodicity. Achieving such a cutting-edge resolution has been possible by integrating a high-quality synchrotron beam, precise nanofabrication of masks, very stable exposures instrumentation, and utilizing effective photoresists. We have carried out exposure on silicon- and hafnium-based photoresists and we demonstrated the extraordinary capability of the latter resist to be used as a hard mask for pattern transfer into Si. Our results confirm the capability of EUV lithography in the reproducible fabrication of dense patterns with single-digit resolution. Moreover, it shows the capability of interference lithography, using transmission gratings, in evaluating the resolution limits of photoresists.

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The performance of EUV resists is one of the main challenges for the cost-effectiveness and the introduction of EUV lithography into high-volume manufacturing. The EUV interference lithography (EUV-IL) is a simple and powerful technique to print periodic nanostructures with a resolution beyond the capabilities of other tools. In addition, the welldefined and pitch-independent aerial image of the EUV-IL provides further advantages for the analysis of resist performance. In this paper, we present evaluation of chemically-amplified resists (CAR) and inorganic resists using EUV-IL. We illustrate the performance of the tool through a reproducibility study of a baseline resist over the course of 16 months. A comparative study of the performance of different resists is presented with the aim of resolving patterns with CARs for 16 nm half-pitch (HP) and 11 nm HP. Critical dimension (CD) and line-edge roughness (LER) are evaluated as functions of dose for different process conditions. With a CAR with about 10 mJ/cm 2 sensitivity, 18 nm L/S patterns are obtained with low LER and well-resolved patterns are achieved down to 16 nm HP. With another CAR of about 35 mJ/cm 2 sensitivity, L/S patterns with low LER are demonstrated down to 14 nm HP. Resolved patterns are achieved down to 12 HP, demonstrating the capability of its potential towards 11 nm HP if pattern collapse mitigation can be successfully applied. With EUV-sensitive inorganic resists, patterning down to 8 nm has been realized. In summary, we show that resist platforms with reasonable sensitivities are already available for patterning at 16 nm HP, 11 nm HP, and beyond, although there is still significant progress is needed. We also show that with decreasing HP, pattern collapse becomes a crucial issue limiting the resolution and LER. Therefore resist stability, collapse mitigation, and etch resistance are some of the significant problems to be addressed in the development of resist platforms for future technology nodes.