Linewidth Roughness (LWR) remains a difficult challenge in resist materials. In previous work we focused on showing how roughness Power Spectral Density (PSD) parameters were affected by aerial image and basic resist parameters such as diffusion. This highlighted the relationship between PSD(0) and correlation length in optimizing LWR. By measuring the unbiased PSDs with MetroLER we showed LWR measurements could be expressed as a ratio between the roughness PSD parameters. In this paper we show how LWR improvement can be achieved by several strategies that focus on both PSD(0) and correlation length and not a single LWR number.
Linewidth Roughness (LWR) remains a difficult challenge for improvement in all resist materials. In previous work we focused on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software. [1] By measuring the unbiased PSD (with SEM image noise removed), accurate assessment of PSD(0) (the low-frequency limit of the PSD) and correlation length (the length scale of the transition from white to correlated noise) is possible. We showed there was an important relationship between ArF resist frequency components and LWR through lithographic process (before and after a resist trim step) as a function of resist formulation. In this paper we will study how key frequency components such as PSD(0) and correlation length change as we vary basic resist properties such as diffusion. The impact of aerial image on LWR and its frequency components will also be studied with particular attention to how correlation length affects LWR as feature size decreases. We will also look at the impact of diffusion or resist blur on PSD(0) as a function of aerial image Normalized Image Log-Slope (NILS). Understanding the relationship between PSD(0) and correlation length and how to manipulate these variables to minimize LWR for different features is crucial for more rapid LWR improvement at different nodes.
[1] Charlotte Cutler, et al., “Roughness power spectral density as a function of resist parameters and its impact through process,” Proc. SPIE 10587, Optical Microlithography XXXI, 1058707 (23 March 2018).
Linewidth roughness (LWR) remains a difficult challenge for improvement in all resist materials. In this paper, we intend to focus on the impact of key components of LWR by analyzing the Power Spectral Density (PSD) curves which can be obtained using Fractilia’s MetroLER computational software. We will study systematic changes to ArF resist formulations and correlate these changes to the overall PSD curves. In this manner, we can extract LER/LWR 3σ values as well as resist correlation length and the low/high-frequency roughness components. We will also investigate the relationship between PSD and LWR through lithographic/etch processing and demonstrate which components correspond with the largest impact. In order to achieve quality data over low and high frequency ranges we changed our standard metrology setup to capture longer lines. By making systematic changes to the ArF resists, we can determine the key impacts of various controllable resist factors on the PSD. Through systematic analysis, we can deconvolute LWR improvements both after develop and after an etch process.
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