Self-powered near field electron lithography

Abstract

Electron beam exposure is the tool of choice for highest resolution lithography but suffers from the low throughput during serial beam writing T. Ito and S. Okazaki, Nature (London) 406, 1027 (2000); R. F. Pease and S. Y. Chou, Proc. IEEE 96, 248 (2008). The authors designed and developed a low-cost self-powered near-field electron lithography (SPEL ) technique, which utilizes the spontaneously emitted energetic electrons from beta-emitting radioisotope thin films. This approach enables massively parallel e-beam lithography, with potentially arbitrarily large concurrently exposed surface area, controlled by the size of the radioactive source. This method potentially eliminates the need for vacuum systems and the electron focusing column as needed in the existing electron beam lithography systems. This will greatly simplify the overall lithographic system and reduce the cost of deep-subnanometer lithography. In SPEL system, emitted electrons are spatially blocked using a nanostenciled micromachined mask that is placed in proximity to an electron sensitive resist on the silicon substrate (Fig. 1). The electrons that are not blocked, impact and enter the e-beam resist, along with secondary electrons generated by primary electrons impacting the sidewalls of the stencil layer. Using three-dimensional 3D Monte Carlo (MC) simulations of electron paths, the authors show that the critical dimension (CD) in the system could be down to 20 nm with 14.9 keV electrons emitted from 63Ni. The 3D MC simulation considered both elastic scattering and inelastic scattering for the high energetic primary electrons as well as the cascade secondary electrons generated. The 20 nm limit is imposed by the secondary emission scattering. In order to prove the concept, experiments were conducted using the safe and low-activity (1 mCi/cm2) beta particle emitting 63Ni thin film source with electrons emitted at an average energy of 14.9 keV. They exposed negative tone resist NEB31A, and a minimum gap between ebeam resist posts or CD of 100 nm was achieved. The secondary electrons generated by the primary electron impact onto mask are also useful for exposure. Compared to traditional electron beam lithography, with serial raster scanning taking days to expose a wafer, the lithography system will enable parallel exposure of large patterns on arbitrarily large wafers in several minutes. SPEL may enable massively parallel top-down approach to realizing nanostructures in bulk quantities. Show more