Control of the sidewall angle of an absorber stack using the Faradaycage system for the change of pattern printability in EUVL

摘要

A patterned TaN substrate, which is candidate for a mask absorber in extreme ultra-violet lithography (EUVL), wasetched to have inclined sidewalls by using a Faraday cage system under the condition of a 2-step process that allowed thehigh etch selectivity of TaN over the resist. The sidewall angle (SWA) of the patterned substrate, which was in the shapeof a parallelogram after etching, could be controlled by changing the slope of a substrate holder that was placed in theFaraday cage. The performance of an EUV mask, which contained the TaN absorber of an oblique pattern over themolybdenum/silicon multi-layer, was simulated for different cases of SWA. The results indicated that the opticalproperties, such as the critical dimension (CD), an offset in the CD bias between horizontal and vertical patterns (H-Vbias), and a shift in the image position on the wafer, could be controlled by changing the SWA of the absorber stack. Thesimulation result showed that the effect of the SWA on the optical properties became more significant at largerthicknesses of the absorber and smaller sizes of the target CD. Nevertheless, the contrast of the aerial images was notsignificantly decreased because the shadow effect caused by either sidewall of the patterned substrate cancelled witheach other.