Use of a Pi-Phase Shifting X-ray Mask to Increase the Intensity Slope at Feature Edges

摘要

In x ray lithography at deep submicron and sub-100-nm linewidths, the effects of diffraction are not negligible. The possibility of improving the slope of the irradiance profile at features edges are investigated by using an absorber that produces a pi-phase shift in addition to about 10 dB attenuation. Both numerical simulation and experimental modeling at a longer wavelength (365 nm) were used. These show that the irradiance profile at the edge of features is steeper when using a pi-phase shifting mask. For gold, the condition of pi-phase shift and 10 dB attenuation occurs when the wavelength is 1.15 nm and the thickness is 290 nm; and for tungsten at a wavelength of 1.3 nm and a thickness of 275 nm. X ray masks made with the proper phase-shift and attenuation yield an increased slope at feature edges which should result in improved process latitude. The phase shifting scheme introduced here differs from those previously described, and applies to patterns of arbitrary geometry, including isolated lines and spaces. Reprints. (jhd)