Quantitative measurement of outgas products from EUV photoresists

Abstract

The photon-stimulated emission of organic molecules from the photoresist during exposure is a serious problem for extreme-ultraviolet lithography (EUVL) because the adsorption of the outgassing products on the EUV optics can lead to carbonization and subsequent reflectivity loss. In order to accurately quantify the total amount of outgassing for a given resist during an exposure, we have constructed a compact, portable chamber that is instrumented with a spinning rotor gauge and a capacitance diaphragm gauge that, unlike the more commonly used ionization gauge or quadrupole mass spectrometer, provides a direct and accurate measurement of the total pressure that is largely independent of the composition of the outgas products. We have also developed a method to perform compositional analysis on the outgas products and, more generally, on any contaminants that might be present in the stepper vacuum. The method involves collecting the vacuum contaminants in a trap cooled to liquid-nitrogen temperature. Once collected, the products from the trap are transferred to a system for analysis with gas chromatography with mass spectrometry. We will describe the workings of the instruments in detail as well as results of initial tests.