A method was developed to measure hydrocarbons to 1 part-per-trillion (ppt) concentration levels with a gas chromatograph and flame ionization detector (GC/FID) [1]. This method was used to measure purifier siloxane removal efficiencies from air under both dry and humid conditions. Several media types were examined: activated carbon (AC), bead-shaped activated carbon (BAC), and a proprietary inorganic material (PIM). Under dry conditions, all three materials removed the siloxane challenge to below 1 ppt. The AC material had a removal efficiency of 286 ppt under humid conditions. The BAC and PIM removed the siloxane challenge to below 1 ppt under humid conditions. After media saturation was reached under humid conditions, the materials were regenerated and siloxane removal efficiencies were re-examined. Only the PIM material was regenerable to below 1 ppt efficiency levels.

Introduction

Semiconductor line-widths are shrinking. Airborne molecular contaminants (AMCs) can severely impact integrated circuits (ICs) with line-widths below 0.1 micrometer [2]. Detrimental AMCs include condensable and non-condensable hydrocarbons, inorganic acids and bases, siloxanes, and organic compounds that contain N, S, or P. The negative impacts of AMCs include optics and wafer hazing, degradation of silicon dioxide integrity, etch rate shifts, poisoning of photoresists, and unwanted doping. These factors are forcing semiconductor manufacturers to design significantly cleaner processes, creating a new demand for highly efficient micro-contamination control and gas purification. DUV photolithography tools use purge gases such as compressed air or nitrogen to keep optical surfaces clean and to provide a consistent environment for the laser beam path [3]. Previously published studies have shown that insufficiently purified air or nitrogen purges can be a source of contamination and thus exacerbate the problems caused by AMCs [4]. Even concentrations as low as several hundred parts-per-trillion can be detrimental to some processes. Therefore, leading semiconductor device manufacturers are exploring the use of new purification/chemical filtration materials for environmental purge gases. Gas purifiers that remove AMCs, like siloxanes, can dramatically improve product yields [5]. The purpose of this study is to measure AMCs down to ppt levels in order to establish a cause and effect relationship, to determine potential causes of premature purifier breakthrough, and to investigate the viability of purifier regeneration for several materials. Initial work focused on the development of a concentration method to measure ppt levels of hydrocarbons. An experiment was then designed to determine siloxane removal efficiencies under dry and humid conditions, and to test the media’s ability to regenerate.