Metrology plays a crucial role in semiconductor manufacturing by providing accurate and precise measurement and characterization of critical parameters. With the development of high-resolution extreme ultraviolet lithography (EUVL) processes, critical dimensions are shrinking to sub-10 nm. Resist materials encounter the challenge of providing heightened sensitivity and a handle on exacerbating stochastic variations. A comprehensive understanding of the chemical profile of the latent image is pivotal for mitigating stochastic effects and optimizing pattern quality. However, the subtle differences in chemistry between the exposed and unexposed regions of the resists make it extremely challenging to characterize the latent images with sub-nanometer precision. Here, we develop the metrology with critical-dimension resonant soft X-ray scattering (CD-RSoXS) to probe the chemical profiles of latent images stored in resist after exposure. The combination of absorption spectroscopy and enhanced scattering contrast makes it possible to characterize the subtle structural and chemical variations in the latent image. Moreover, the results of the measurements are compared with the simulations with a finite element method–based Maxwell solver to extract a detailed profile of the latent and developed images. We demonstrate that the CD-RSoXS technique can provide valuable insights into the high spatial resolution and local chemical sensitivity simultaneously, which is crucial to understanding the resolution limits and stochastic effects in EUVL processes.
The adoption of EUV lithography has enabled the reduction of device dimensions; however, the commensurate scaling of variability, such as line edge and width roughness (LER/LWR), has remained elusive. Understanding the origins of these effects has proven challenging, as they cannot be detected until after the final dissolution step. In this study, we present our recent findings using critical-dimension resonant soft X-ray scattering (CD-RSoXS) to investigate the scattering behavior of photoresist materials. Our primary objective is to gain insights into the contributions of each process step to the generation of LER/LWR as well as footing/scumming. RSoXS capitalizes on tunable soft X-ray sources to significantly enhance the scattering cross-sections from heterogeneous materials. This enhancement provides valuable insights into sub-nanometer spatial resolution and local chemical sensitivity concurrently. To extract a comprehensive profile of the latent image, we employ simulations involving the form factor and subsequent reconstruction of line shapes.
Extreme ultraviolet (EUV) lithography is growing in demand as device feature sizes shrink. With shrinking sizes, reducing line edge roughness (LER) and line width roughness (LWR) becomes critical. While several processes contribute to the LER/LWR of the final structure, understanding the stochastic effects arising from the discrete interaction of photons with the photo-active components in the EUV resist will aid in designing resists and optimizing processes. Infrared photo-induced force microscopy (IR PiFM) is a technique that combines non-contact AFM and IR spectroscopy to non-destructively analyze local chemical bonds on extremely thin samples (~ 1 nm thick) with sub-5 nm spatial resolution. In addition to local IR spectra with high spectral resolution (~ 3 cm-1), it can also generate absorption maps (PiFM images at different wavenumbers associated with chemical components) for visualizing a chemical interface between the exposed and unexposed regions of a resist, providing an unprecedented opportunity to perform chemical metrology. This paper will present IR PiFM data on metal oxide EUV resists, both patterned and un-patterned, that are exposed at different conditions. PiF-IR spectra acquired on exposed but undeveloped resists clearly follow the chemical changes associated with changing dosage, even on a low dose of 10 mJ/cm2. On patterned samples, LER and LWR on chemical images are calculated for different exposure conditions and compared to the values derived from topographical data. The chemical sensitivity and the mapping capability at ultrahigh resolution afforded by IR PiFM will help greatly in developing and optimizing EUV resist composition and processing steps.
Metrology plays a crucial role in semiconductor manufacturing by providing accurate and precise measurement and characterization of critical parameters. With the development of high-resolution extreme ultraviolet (EUV) lithography processes, critical dimensions are shrinking to sub-10 nanometer. The small differences in chemistry between the exposed and unexposed regions of the resists make it extremely challenging to characterize the latent images with sub-nanometer precision. Here we report on our recent results using critical-dimension resonant soft x-ray scattering (CD-RSoXS) to probe the scattering behavior of latent images at specific energy levels. RSoXS leverages tunable soft x-ray sources in order to dramatically enhance the scattering cross sections from heterogeneous materials, which can provide valuable insights into the sub-nm spatial resolution and local chemical sensitivity simultaneously. Moreover, to extract a detailed profile of the latent image, the simulations of the form factor and subsequent reconstruction of the line shapes are performed under DWBA and RCWA.
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