Evolutionary optimization of the electron-beam lithography process for gate fabrication of high electron mobility transistors

An electron-beam lithography simulation tool was realized. This tool models the development of multilayered poly(methylmethacrylate) resist structures after exposure with an electron beam. A development front propagates inside the resist stack as a function of time and the local solubility. The local solubility was experimentally measured versus the electron dose for different types of resist. The efficiency of incident and backscattered electrons was determined using doughnut-shaped structures. The ratio of the backscattered to incident electron efficiencies η was found to be 1.35 for an acceleration voltage of 30 kV on InP substrates. We used genetic algorithms to optimize the electron dose necessary for the realization of a given resist profile. This tool was applied to fabricate T-gates and asymmetric gate recesses.