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Experimental Investigation of a high-k reticle absorber system for EUV lithography
Author(s): Jo Finders; Frank Timmermans; Robbert de Kruif; Brid Connely; Markus Bender; Takahiro Onoue; Yohei Ikebe; Dave Farrar
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Paper Abstract

EUV lithography is entering High Volume Manufacturing at relative high Rayleigh factor k1 above 0.4. In comparison, ArFi immersion lithography has been pushed to k1 values of 0.3 or below over the last two decades. One of the strong contributors determining the effective usable resolution is the mask absorber stack. The mask stack alters the diffraction by modifying the phase and intensity of the diffracted orders. As a result the mask 3D induced phase leads to contrast loss, which has an adverse effect on the usable resolution in EUV lithography. One known way to improve these mask 3D effects is going to a higher extinction coefficient of the absorber material and lower the absorber film thickness. We considered the impact of the extinction coefficient on the imaging performance for current and future EUV applications. The current extinction coefficient using Ta as base material is 0.03. There are known materials (e.g. Ni) with extinction coefficients up to 0.07. When going to a higher extinction coefficient the thickness of the absorber can be lowered and the phase and intensity effects coming from the mask topography are reduced. This benefits both Critical Dimension related Figures of Merits as well as image placement. We see strong improvements of the imaging performance when increasing the extinction coefficient. For some parameters, the improvement saturates at higher extinction coefficient. This is understood by diffraction analysis and will be explained in this work. Goal of this work is to study the imaging performance gain versus incremental improvement in extinction coefficient, both by means of simulation and experiment. Higher extinction coefficient benefits the imaging. But at the same time the mask manufacturing aspects (cleaning, etch) will become more difficult. A preliminary optimum extinction coefficient of 0.04 has been established based on the trade-off we made of imaging performance gain versus mask manufacturing complexity. A test mask has been manufactured with higher extinction coefficient and lower thickness. We will elaborate on the basic mask material properties, such as EUV reflection, final absorber profile and testing of scanner compatibility under plasma environment. Furthermore we will show imaging results obtained with the test mask when exposing on a 0.33NA EUV scanner and compare them to the results of the POR Ta mask We will focus on the advantages in imaging because of reduced Mask 3D effects and we will discuss the applicability of this type of masks for customer applications at 0.33 and 0.55NA.

Paper Details

Date Published: 14 March 2019
Proc. SPIE 10957, Extreme Ultraviolet (EUV) Lithography X, 1095714 (14 March 2019); doi: 10.1117/12.2515496
Show Author Affiliations
Jo Finders, ASML Netherlands B.V. (Netherlands)
Frank Timmermans, ASML Netherlands B.V. (Netherlands)
Robbert de Kruif, ASML Netherlands B.V. (Netherlands)
Brid Connely, Toppan Photomasks, Inc. (Germany)
Markus Bender, Advanced Mask Technology Ctr. GmbH Co. KG (Germany)
Takahiro Onoue, HOYA Corp. (Japan)
Yohei Ikebe, HOYA Corp. (Japan)
Dave Farrar, HOYA Corp. (Japan)

Published in SPIE Proceedings Vol. 10957:
Extreme Ultraviolet (EUV) Lithography X
Kenneth A. Goldberg, Editor(s)

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