Explanation of LER using the concept of gel layer in chemically amplified photoresists

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Abstract
Photolithography is the driving technology and key enabler for the fabrication of integrated circuits with continuously decreasing feature sizes. Currently, state-of-the-art photolithography materials and processes can fabricate sub-100nm features, but significant technical hurdles remain in making sub-100nm features. These challenges include the understanding of LER (Line Edge Roughness) that will have a broad industrial impact. The 193nm resist has a thin gel layer at the interface of the developed resist and the developer, and resist patterns are formed by random detachment of this gel layer during development in the developer. Since the detachment of gel layer occurs randomly within the gel zone, LER increases in the case of higher gel layer thickness. This gel layer thickness can be determined by gel layer development model which consider two simultaneous reactions at the front and back of gel layer during dissolution of gel layer in the developer. This study attempts to explain LER using the concept of gel layer of which thickness is determined by hydrophilic and hydrophobic balance depending on the formulations of chemically amplified photoresists. LER can be minimized if we control the hydrophilic and hydrophobic balance by tuning the structure of polymer backbone in chemically amplified photoresists and minimize the gel layer thickness.

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