Demonstration of pattern transfer into sub-100 nm polysilicon line/space features patterned with extreme ultraviolet lithography

In two separate experiments, we have successfully demonstrated the transfer of dense- and loose-pitch line/space (L/S) photoresist features, patterned with extreme ultraviolet (EUV) lithography, into an underlying hard mask material. In both experiments, a deep-UV photoresist (similar to 90 nm thick) was spin cast in bilayer format onto ii hard mask (50-90 nm thick) and was subsequently exposed to EW radiation using a 10 x reduction EUV exposure system. The EUV reticle was fabricated at Motorola (Tempe, AZ) using a subtractive process with Ta-based absorbers on Mo/Si multilayer mask blanks. Tn the first set of experiments, following the EUV exposures, the L/S patterns were transferred first into a SiO2 hard mask (60 nm thick) using a reactive ion etch (RIE), and then into polysilicon (350 nm thick) using a triode-coupled plasma RTE etcher at the University of California, Berkeley, microfabrication facilities. The latter etch process, which produced steep (>85 degrees) sidewalls, employed a HBr/Cl chemistry with a large (>10:1) etch selectivity of polysilicon to silicon dioxide. In the second set of experiments, hard mask films of SiON (50 nm thick) and SiO2 (87 nn thick) were used. A RIE was performed at Motorola using a halogen gas chemistry that resulted in a hard mask-to-photoresist etch selectivity >3:1 and sidewall profile angles greater than or equal to 85 degrees. Line edge roughness (LER) and linewidth critical dimension (CD) measurements were performed using Sandia's GORA(R) CD digital image analysis software. Low LER values (6-9 nm, 3 sigma, one side) and good CD linearity (better than 10%) were demonstrated for the final patttern-transferred dense polysilicon L/S features from 80 to 175 nm. In addition, pattern transfer (into polysilicon) of loose-pitch (1:2) L/S features with CDs greater than or equal to 60 nm was demonstrated. (C) 1999 American Vacuum Society. [S0734-211X(99)14906-0].