Analysis of Organic Contamination Adsorbed on a Silicon Surface in a Vacuum Chamber in Electron Beam Lithography

Abstract

Organic contaminants adsorbed on the surface of a silicon stencil mask in a high-vacuum chamber in an electron-beam exposure lithography system have been analyzed and identified using thermal-desorption gas chromatography/mass spectrometry (TD-GC/MS), X-ray photoelectron spectrometry (XPS), and electron energy loss spectroscopy (EELS). The major organic compound adsorbed onto the surface of the silicon stencil mask in the high vacuum chamber has been found to be di-2-ethylhexyl phthalate (DOP). The amount of DOP adsorbed onto the silicon surface in high vacuum is much larger than that adsorbed in ambient air. A relatively high molar ratio and long mean free path of organic molecules with a low vapor pressure, such as DOP, in high vacuum is considered to enable them to be easily adsorbed onto the silicon surface in high vacuum. On the other hand, organic volatiles with higher vapor pressure are not adsorbed on the silicon surface in high vacuum. It has been found by XPS and EELS that the organic contaminants adsorbed on the surface of the silicon stencil mask are transformed into graphite-like carbon by electron beam irradiation during the exposure process.