Sub 100 nm proton beam micromachining: theoretical calculations on resolution limits

Proton beam micromachining is a novel direct-write process for the producti on of three-dimensional (3D) microstructures. A focused beam of MeV protons is scanned in a pre-determined pattern over a suitable resist material (e. g. PMMA or SU-8) and the latent image formed is subsequently developed chem ically, In this paper calculations on theoretical resolution limits of prot on beam micromachined three-dimensional microstructures are presented. Negl ecting the finite beam size, a Monte Carlo ion transport code was used in c ombination with a theoretical model describing the delta-ray (delta-ray) en ergy deposition to determine the lateral energy deposition distribution in PMMA resist material. The energy deposition distribution of ion induced sec ondary electrons (delta-rays) has been parameterized using analytical model s. It is assumed that the attainable resolution is limited by a convolution of the spread of the ion beam and energy deposition of the delta-rays. (C) 2000 Elsevier Science B.V. All rights reserved.