Direct quantitative analysis of phthalate esters as micro-contaminants in cleanroom air and wafer surfaces by auto-thermal desorption–gas chromatography–mass spectrometry

This study established an analytical method for the trace analyses of two phthalate esters, including diethyl phthalate (DEP) and di-n-butyl phthalate (DBP), known as the major constituents of cleanroom micro-contamination detrimental to the reliability of semiconductor devices. Using thermal desorption coupled with a GC–MS system, standard tubes were prepared by delivering liquid standards pre-vaporized by a quasi-vaporizer into Tenax GR tubes for calibration. This method was capable of achieving detection limits of 0.05μgm−3 for 0.1m3 air samples and 0.03ngcm−2 for 150-mm wafer surface density. Actual samples collected from a semiconductor cleanroom showed that the concentration of DBP in a polypropylene wafer box (0.45μgm−3) was nearly four times higher than that in the cleanroom environment (0.12μgm−3). The surface contamination of DBP was 0.67ngcm−2 for a wafer stored in the wafer box for 24h. Furthermore, among the three types of heat-resistant O-ring materials tested, Kalrez® was found to be particularly suitable for high-temperature processes in semiconductor cleanrooms due to their low emissions of organic vapors. This analytical procedure should serve as an effective monitoring method for the organic micro-contamination in cleanroom environments.

本研究建立了一种对两种邻苯二甲酸酯进行痕量分析的方法，这两种邻苯二甲酸酯包括邻苯二甲酸二乙酯（DEP）和邻苯二甲酸二正丁酯（DBP），它们是洁净室微污染的主要成分，对半导体器件的可靠性有害。利用热脱附与气相色谱 - 质谱联用系统，通过将由准蒸发器预蒸发的液体标准品输送到Tenax GR管中制备标准管用于校准。该方法对于0.1立方米空气样品能够达到0.05微克/立方米的检测限，对于150毫米晶圆表面密度能够达到0.03纳克/平方厘米的检测限。从半导体洁净室采集的实际样品表明，聚丙烯晶圆盒中DBP的浓度（0.45微克/立方米）比洁净室环境中的浓度（0.12微克/立方米）高出近四倍。对于在晶圆盒中存放24小时的晶圆，DBP的表面污染为0.67纳克/平方厘米。此外，在测试的三种耐热O形圈材料中，发现Kalrez®由于其有机蒸汽排放量低，特别适用于半导体洁净室的高温工艺。这种分析程序应作为洁净室环境中有机微污染的一种有效监测方法。