Proceedings Article | 18 March 2009
Proc. SPIE. 7271, Alternative Lithographic Technologies
KEYWORDS: Lithography, Optical lithography, Metals, Scanners, Photography, Photomasks, Extreme ultraviolet, Extreme ultraviolet lithography, Optical proximity correction, Semiconducting wafers
Since the k1 factor is much larger in extreme-ultraviolet lithography (EUVL) than in optical lithography, optical
proximity correction (OPC) should be much simpler for patterns on EUVL masks than for those on advanced
photomasks. This will facilitate the fabrication of complex device patterns with EUVL. In this study, static
random-access memory (SRAM) cell patterns for the half-pitch (hp) 32- and 45-nm nodes were fabricated using two
EUV exposure tools (SFET, EUV1), and their fidelity was evaluated. The levels of SRAM patterns were isolation, gate,
contact, and metal. The size of the SRAM unit cell was 0.191 μm2 for the hp 45-nm and 0.097 μm2 for the hp 32-nm
patterns. Most of the experiments employed SSR2, a high-resolution EUV resist. The high performance of the SFET and
SSR2 enabled hp 45-nm SRAM patterns to be fabricated faithfully. However, some of the hp 32-nm patterns deviated
from the mask patterns. To determine the causes of this degradation, we made a simulation analysis using the Sentaurus
Lithography simulator. The main cause of the degradation was found to be resist blur. When we used MET-2D resist,
which has a relatively large resist blur, the degradation became quite severe. Although the resist blur for SSR2 is about
10 nm, it is not small enough for the hp 32-nm SRAM patterns, especially for the gate and metal levels. It is necessary to
reduce resist blur to improve the fidelity for this pattern size. Simulation results indicated that resist blur should be
reduced to about 5 nm for hp 22-nm node device patterns.
