The role of secondary electrons in electron-beam-induced-deposition spatial resolution

Electron-beam-induced-deposition (EBID) is a versatile direct writing technique occasionally used in micro-and nanofabrication. We focus in our study on the EBID spatial resolution, defined as the lateral size of the smallest deposited structure. The lateral size of dot structures always exceeds the diameter of the electron probe. Many authors have argued that this is due to the secondary electrons emitted as a result of primary electron bombardment, but it has never been modeled quantitatively. We developed a model based on Monte Carlo methods that simulates the role of secondary electrons in the spatial evolution of EBID dots. The results show that the secondary electrons are indeed responsible for the shapes and sizes observed during EBID. The secondary electrons generated inside the substrate by a pin-point primary beam produce initially a very small structure broadening, of about one nanometer. Then using a dynamic Monte Carlo profile simulator which includes the electron scattering in the already grown tip structure, we show for the first time that the laterally emerging secondary electrons are continuously enlarging the tip diameter, up to saturation values of 20-30 nm, in agreement with experiments (C) 2002 Elsevier Science B.V. All rights reserved.