Lithography using ultrathin resist films

Abstract

The industry trend toward higher numerical apertures and lower k1 factors is severely constraining the manufacturing process margin for current and future lithography technologies. Ultrathin resist (UTR) films and other thin layer imaging techniques offer the promise of improved process margin as compared to conventional single layer resist schemes. In this study, an UTR over hard mask process was used to pattern the transistor gates of a high performance microprocessor using 248 nm lithography while focusing on four key areas of concern for UTR films: resist film defectivity, response of thin resist to device topography, quality of pattern transfer on device wafers, and device yield comparable to a baseline process. The intrinsic defectivity of resist films as thin as 65 nm is found to be no greater than that of a >500 nm resist film on flat silicon wafers. No pinhole defects are observed during scanning electronic microscopy review of defects on as-coated UTR films. As expected, the UTR process is sensitive to device topography, but the effects are manageable for the conditions used here. Robust pattern transfer with defect levels comparable to the baseline single layer resist process is demonstrated using UTR films as thin as 150 nm and a hardmask. Finally, device yield data confirms that the UTR process is as manufacturable as a conventional single layer resist process.