I report the results of an experimental study of the line edge roughness (LER) for resist patterned with next generation lithography tools such as extreme ultraviolet (EUV), electron beam (EPL), and x-ray (XRL). Aerial Image Contrast (AIC) has been adjusted using double exposure technique to create rough line edges for different resists and exposure tools. Since the AIC is significantly worse in the sub-100 nm Critical Dimension (CD) ranges, it is possible to model the LER behavior of smaller CDs by manipulating the AIC at larger CDs. The characterization has been performed using an Atomic Force Microscope (AFM) with carbon nanotube tips and a high resolution Scanning Electron Microscope (SEM). Experimental results generally support that higher aerial image contrast leads to lower line edge roughness, while differences exist among the lithographies and resists. For the UV6 resist case, which is the chemically amplified resist used for these particular experiments, LERs are in the order of XRL, EUV, and EPL. For example, given an AIC of 27%, 3σ LER of XRL is 36.3 nm, while that of EUV and EPL are 27.9 nm, and 16.8 nm respectively. XRL shows the highest LER, as expected, due to the shot noise contributions. In the poly (methylmethacrylate) (PMMA) case, however, LERs are not that sensitive to AIC as in the case for UV6.; High resolution AFM scan using carbon nanotube tip provides detailed information on the inside trenches. One of the advantages of using this special tip is to measure resist sidewall angles without breaking wafers to see the cross sections of resist patterns. It is observed from AFM scan that LER depends on the analysis height of the resist when the AIC is poor; i.e. LER is higher at the top of resist, and lower at the bottom of resist. According to the experimental results of UV6, exposed by EPL with an AIC of 17%, 3σ LER increases from 15 nm to 22 nm as resist height increases.
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