In situ characterization of nano-scale pattern roughness during resist dissolution process

• Utilized in situ resist dissolution analysis using high speed AFM.
• Established analysis method for edge roughness analysis during resist dissolution.
• Defined edge roughness trend during resist dissolution.
• Understood optimal dissolution conditions for improved edge roughness.

Advancements in the resist process is viewed as one effective way in meeting the challenge of obtaining high quality, narrow patterns (low line edge roughness/line width roughness or LER/LWR) for leading edge lithographic technologies such as extreme ultraviolet (EUV) lithography, λ = 13.5 nm. Among these processes, resist dissolution, also referred to as resist development, is considered an important process step as this is the first instance where resist patterns are formed from resist film state. This work focuses on a fundamental approach in understanding this resist pattern formation through a visual and in situ characterization of the resist dissolution process. This was done using a high speed atomic force microscope (HS-AFM). Specifically, this paper presents the first successful demonstration of the quantification of resist pattern LER during resist dissolution in the typical alkali (2.38wt% tetramethyl ammonium hydroxide or TMAH)-based developer solution. Based on these results, a number of fundamental information were understood/confirmed regarding resist pattern formation behavior during dissolution; (1) Larger pattern LER can be observed at pattern side-walls nearer the line pattern surface, in comparison to those near the line bottom. Moreover, it was also understood that (2) a reduction of LER occurs in the early stages of pattern formation during dissolution. This trend in decreasing LER was also existent even at longer dissolution times, but was in smaller variations. Lastly, it was also found that (3) at longer dissolution times, partial dissolution of pattern top surface, resulting in line-pinching occurs. This in effect increases LER, especially for measurements taken in pattern side-walls near the line surface.

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