超高精度质谱检出限的测试技术研究

检出限是评价四极质谱仪性能的重要指标,采用集成有高真空腔室、真空泵组、真空计、大气采样阀和待测四极质谱仪等的超高精度质谱检出限测试系统,针对四极质谱仪进行最小可检浓度和最小可检分压的测试技术研究。通过大气采样阀上的金属毛细管直接向四极质谱仪的封闭式离子源中引入新鲜空气,测试空气中极低含量氙气的质谱图。从谱图中可清晰分辨出氙气中除Xe (124)和Xe (126)以外其余各稳定同位素及含量;采用信噪比方法计算获得四极质谱仪的最小可检浓度为0.319×10^-9,最小可检分压为1.46×10^-13Pa。结果表明:该质谱仪的检出限测试方法简单易行,测试结果直观可比;检出限计算结果与仪器标称参数一致,验证了四极质谱仪的超高精度和测试方法的可靠性。

Detection Limit of Ultrahigh Resolution Mass Spectrometer: A Theoretical and Experimental Study

A novel gas detection platform was developed to characterize gas concentration and partial pressure in high vacuum (UHV), required by extreme ultraviolet lithography, to evaluate the detection limit of an ultrahigh resolution mass spectrometer (QMS). The platform comprises the HV chamber, pumping/gauging/controlling units, air sampling valve combined with a metal capillary inlet, and a QMS to be tested. The platform detected the extremely low concentration and partial pressure of xenon in air. The results show that the existing 9 stable Xe-isotopes, except Xe (124) and Xe (126), could be clearly identified in the QMS spectrum and their concentration ratios could be derived. The lowest detectable concentration and partial pressure, analyzed in signal-to-noise ratio (SNR) method, were calculated to be 0. 319×10^-9 and 1. 46×10^-13 Pa, respectively. The evaluation results and QMS specifications were found to be in good agreement.