Local dose distribution and changing resist cross-sectional shapes in electron beam lithography

In order to apply resist patterns fabricated by electron beam lithography to nanoimprint molds, it is necessary to consider not only line widths and hole diameters observed two-dimensionally from the exposure top surface, but also three-dimensionally including resist cross-sectional shapes. In this study, we focus on the dose distribution inside the pattern and the development time, and investigate the effects of these on the cross-sectional shape of the resist. An exposure method was employed to produce a resist pattern with a line width 100 nm, in which the total dose within a line is the same, but the electron beam scanning position and number of times within a line are changed. The results of a comparison between the dose distribution analyzed by electron scattering simulation and the sidewall shape of the pattern after resolution showed that the dose distribution and the actual resist shape agreed with each other within ±5 nm accuracy under certain conditions. The results showed that the actual shape of the resist sidewalls can be changed by local dose distribution in the resist depending on the scan position and number of scans, even if the average dose is the same for the entire pattern. Furthermore, we investigated the resolution mechanism of the resist by observing the development process of the resist after exposure at different development times. The results showed that the difference in the development speed caused by the difference in the dose inside the pattern affects the cross-sectional shape of the resist. The results of this study indicate that the resist cross-sectional shape is significantly affected by the dose distribution inside the resist and the difference in development speed caused by it, and that these parameters can be expected to be applied to the fabrication of the desired cross-sectional shape in the future.