Investigation of the resist outgassing and hydrocarbonaceous contamination induced in multi electron beams lithography tools

摘要

In emerging high-vacuum multi e-beams exposure tools, the release of hydrocarbonaceous species (precursor) by resists outgassing is unavoidable and leads to premature contamination of optics projection systems. In this work, we present an experimental methodology aiming at resist outgassing qualification. A specific experimental setup was designed to monitor the induced outgassing phenomena by irradiating resist coated on 100mm silicon wafer. The wafer can be exposed through specific silicon micromachined membranes (called mimics) that are representative of the optics projection system usually embedded in real multi e-beam exposure tools. A Quadrupole Mass Spectrometer (QMS) is plugged into the vacuum chamber and enables in-situ analysis of the by-products outgassing. Combining this tool with the Thermo Desorption - Gas Chromatography coupled to Mass Spectroscopy (TD-GC-MS) analysis, we could not only determine the outgassing amount of different resists but also identify all the outgassed by-products and their origin. Finally, the Focus Ion Beam combined to Scanning Electron Microscopy (FIB-SEM) and X-ray Photoelectron Spectroscopy (XPS) characterization techniques were used to determine the contamination layer thickness and elementary composition, respectively. A first process oriented conclusion from this work shows that the use of a thin topcoat layer can considerably reduce the resist outgassing amount and, consequently, the hydrocarbonaceous contamination layer induced on the mimics. The outgassing amount as well as the top-coat efficiency was shown to be mainly dependent on the resist chemical properties. The contamination layer growth was shown to be dependent on e-beam current density and hydrocarbon pressure in the vicinity of the mimics.