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Proceedings Paper

Influence of post exposure bake time on EUV photoresist RLS trade-off
Author(s): Yannick Vesters; Danilo De Simone; Stefan De Gendt
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Paper Abstract

To achieve high volume manufacturing, EUV photoresists need to push back the "RLS trade-off" by simultaneously improving Resolution, Line-Width Roughness and Sensitivity (exposure dose). Acid diffusion in chemically amplified resist is known to impact these performances. This work studies the diffusion of acid in chemically amplified resist by varying the post exposure bake duration while monitoring the evolution of CD and LWR for 6 chemically amplified EUV photoresists (CAR).

We observed a first regime where both CD and LWR quickly decrease during the first 30s of post exposure bake (PEB). This can be related to the deprotection reaction taking place in the exposed part of the resist. After 60s the decrease in CD and LWR slows down significantly, likely related to a regime of acid diffusion from exposed to unexposed region, and acid-quencher neutralization at the interface of these two regions.

We tested two resists with different protecting group and the one having lower activation energy shows a faster CD change in the second regime, resulting in a worsening of LWR for longer PEB time. On the contrary, a resist with a high quencher loading shows reduced net diffusion of acid towards the unexposed region and controls the resist edge profile. In other words longer PEB does not degrade LWR, but as it reduces the line CD, sensitivity is impacted. With an appropriate ratio selection of quencher to PAG, an EUV dose reduction of up to 12% can be achieved with a change from a standard 60 second to a 240 second PEB time, while keeping LWR and resolution constant and therefore pushing the RLS performances.

Finally, we confirmed that the observations on positive tone development (PTD) resist could be applied to negative tone development (NTD) resist: with a high quencher NTD resist we observed a dose reduction of 8% for longer PEB time, keeping LWR and resolution constant.

Paper Details

Date Published: 24 March 2017
PDF: 11 pages
Proc. SPIE 10143, Extreme Ultraviolet (EUV) Lithography VIII, 1014324 (24 March 2017); doi: 10.1117/12.2257910
Show Author Affiliations
Yannick Vesters, KU Leuven (Belgium)
IMEC (Belgium)
Danilo De Simone, IMEC (Belgium)
Stefan De Gendt, KU Leuven (Belgium)
IMEC (Belgium)

Published in SPIE Proceedings Vol. 10143:
Extreme Ultraviolet (EUV) Lithography VIII
Eric M. Panning, Editor(s)

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