Investigation of Airborne Molecular Contamination in Cleanroom Air Environment through Portable Soft X-Ray Radiolysis Detector

Changhyuk Kim,David Y H Pui,Kyungil Cho

doi:10.3390/app10030978

Abstract

Airborne molecular contamination (AMC) represents a wide range of gaseous contaminants in the cleanroom air environment. It is difficult to monitor AMC in the cleanroom air using conventional methods in real-time due to its ultra-low concentrations, such as part-per-billion or -trillion (ppb or ppt). In this study, AMC in the real university cleanroom air environment was investigated to figure out hot spots through portable soft X-ray radiolysis detector, which converts gaseous AMC into nanoparticles (gas-to-particle conversion) under the soft X-ray irradiation. A soft X-ray was connected to a clean stainless steel chamber to convert the introduced AMC into nanoparticles, and the size distributions of nanoparticles were measured through a scanning mobility particle sizer, which consists of a differential mobility analyzer and a condensation particle counter. By converting the size distribution information into total particle volume concentrations, equivalent AMC concentrations can be calculated using an appropriate calibration curve between AMC and the total particle volume concentration. The volume concentration of nanoparticles were converted into an equivalent sulfur dioxide (SO2, a major acidic AMC in the cleanroom air) concentration by a calibration curve between SO2 and the particle volume concentrations. AMC levels at different locations in the cleanroom at the University of Minnesota were measured by the soft X-ray-assisted AMC detector, and revealed that several tenth-order of pptV (lower than 15 pptV) in terms of the equivalent SO2 concentration existed in the cleanroom air environment.

Highlights

Airborne molecular contamination (AMC) represents a wide range of gaseous contaminants in the cleanroom air environment at part-per-billion or -trillion levels [1,2]
We investigated AMC levels in the cleanroom air environment deploying a portable soft X-ray radiolysis detector, which consists of a soft X-ray radiolysis chamber and a scanning mobility particle sizer (SMPS, a combination of a nano differential mobility analyzer and an ultra- condensation particle sizer (UCPC), Model 3936N76, TSI Inc., Minneapolis, MN, USA)
We investigated the AMC levels at different sub-locations in the cleanroom air environment through a portable AMC detector deploying soft X-ray radiolysis, which consists of 1) soft X-ray chamber for

Summary

Introduction

Airborne molecular contamination (AMC) represents a wide range of gaseous contaminants in the cleanroom air environment at part-per-billion or -trillion (ppb or ppt) levels [1,2]. When AMC is exposed to ultraviolet light sources of lithography tools (e.g., extreme ultraviolet lithography, EUVL), it can form particle and haze contamination on wafers and photomasks during semiconductor manufacturing processes, increasing defects of the products [3,4,5,6]. Detecting and controlling AMC have been big issues for enhancing the product yield in the semiconductor industry. It is difficult to detect due to its extremely low concentration of AMC in the cleanroom air [7,8]. Even though gaseous contaminants generally have been captured using porous media [9,10,11], such as activated carbons, through adsorption, it is difficult to remove AMC totally from the air, and.

Methods

Results

Conclusion