Double exposure technology for KrF lithography
2008
The application of Double Exposure Lithography (DEL) would enlarge the capability of 248 nm exposure technique to
smaller pitch. We will use the DEL for the integration of critical layers for dedicated applications requiring resolution
enhancement into 0.13 μm BiCMOS technology. In this paper we present the overlay precision and the focus difference
of 1st and 2nd exposure as critical parameters of the DEL for k 1 ≤ 0.3 lithography (100 nm half pitch) with binary masks
(BIM). The realization of excellent overlay (OVL) accuracy is a main key of double exposure and double patterning
techniques. We show the DEL requires primarily a good mask registration, when the wafer stays in the scanner for both
exposures without alignment between 1st and 2nd exposure. The exposure tool overlay error is more a practical limit for
double patterning lithography (DPL). Hence we prefer the DEL for the resolution enhancement, especially if we use the
KrF high NA lithography tool for 130 nm generation.
Experimental and simulated results show that the critical dimension uniformity (CDU) depends strongly on the overlay
precision. The DEL results show CDU is not only affected by the OVL but also by an optical proximity effect of 1st and
2nd exposure and the mask registration.
The CD uniformity of DEL demands a low focus difference between 1st and 2nd exposure and therefore requires a good
focus repeatability of the exposure tool. The Depth of Focus (DOF) of 490 nm at stable CD of lines was achieved for
DEL. If we change the focus of one of the exposures the CD-focus performance of spaces was reduced with
simultaneous line position changing. CDU vs. focus difference between 1st and 2nd exposure demands a focus
repeatability <100 nm for the exposure tool.
Summary, the results show DEL has the potential to be a practical lithography enhancement method for device
fabrication using high NA KrF tool generation.
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