Charging and discharging of electron beam resist films

Abstract

Pattern placement imprecision due to charging of the workpiece is believed to be a significant contribution to the total positional error in electron beam lithography. In an earlier work, Liu et al. [J. Vac. Sci. Technol. B 13, 1979 (1995)] reported that the surface potential of exposed resist could be negative or positive according to the resist thickness and the electron energy. In that work the authors were constrained to use a flood beam. In this study, we report a new independent approach using a Kelvin probe electrometer to measure the surface potential after exposure by a focused beam. There is a qualitative agreement with the earlier work in that the surface potential tends to be less positive at lower electron energies and for thicker resists. We observed positive surface potentials at 10 and 20 keV beam irradiation. This positive charging is much more evident in polybutene sulfone than in UV5.

Charge induced pattern distortion in low energy electron beam lithography

“…Further, Liu et al 12 observed a positive surface potential at electron beam energies greater than 6 kV and a negative surface potential at electron beam energies smaller than 6 kV for a 0.4 m thick polybutene sulfone ͑PBS͒ and SAL601 resists coated on Cr/glass substrate. Recently, Bai et al 19 reported an increase in the positive surface potential with an increase in the beam energy and decrease in the resist thickness for PBS and UV5 resists on silicon substrate. According to these reports, when the resist thickness is smaller than the electron penetration depth, the trapped negative charge is negligible as the conducting substrate gives rise to image charges.…”

The surface potential of insulating thin films negatively charged by a low-energy focused electron beam

“…Experiments were performed to measure surface potentials (Liu et al, 1995;Bai et al, 1999;Mizuhara et al, 2002). The profile and value of surface potential were also simulated by electron scattering (Zhang et al, 2003) and a one-dimensional model (Yasuda et al, 2008), respectively.…”

Calculation of surface potential and beam deflection due to charging effects in electron beam lithography

“…Figure 5͑a͒ compares the dependencies on varying PBS thicknesses for 10 keV energy, a PBS/Si substrate and focused beam exposure. 8 Figure 5͑b͒ shows the results for varying beam energies, SAL601 ͑0.4 m͒/Cr͑0.085 m͒/glass substrate and flood beam exposure. 9 Figures 5͑a͒ and 5͑b͒ show the similar shapes between them.…”

“…Pease's a͒ Author to whom correspondence should be addressed; electronic mail: lyj@mintlab.snu.ac.kr group at Stanford University experimentally confirmed this theory. 8,9 We have assumed the amount of charge as fully constant ͑steady state͒ after a ''critical or relaxation time ͑͒.'' is given by…”