以矽膠管與吸收瓶採集無塵室無機酸鹼性氣體之方法比較

Abstract

無機酸鹼性氣體皆為無塵室主要之分子狀空氣污染物，過高之無機酸鹼氣體濃度會影響晶圓製品之良率。本研究針對無塵室之無機酸性氣體，以兩種型號之矽膠管(silica gel tube)及吸收瓶(impinger)測試其採樣條件，並比較採樣結果。對於氨氣，則以吸收瓶建議最適合之採樣方式。 由採樣條件測試結果可知，矽膠管在200-300 ml/min流量下，對各無機酸氣有較佳之採集效果，其於無塵室採樣時，採氣量至少需400L以上。而吸收瓶採樣流量需控制在300 ml/min以下，吸收液減少量才能小於5%，建議吸收瓶採集無機酸氣之流率為50 ml/min，NH3氣體則為300 ml/min，採集時間皆為24小時，在此條件下採集效果最佳。若環境中之濃度偏高時，則可適當地增加吸收液體積及縮短採樣時間。 由無塵室實地採樣結果則顯示，兩種型號之矽膠管背景值過高，無法反應出無塵室真實氣體濃度，故不適用於無塵室之採樣。吸收瓶於低濃度之採集效率較矽膠管高，用於無塵室採樣較矽膠管更適合。而由吸收瓶採樣結果顯示，無塵室空氣中之HF、HCl及NH3之濃度在1000 n mole/m3以上，以濃度值而言，此三者為無塵室中主要之無機氣狀污染物。另外NO2-、HNO3與H2SO4之濃度值雖較低，但仍高於濃度管理最高極限值，皆有可能造成晶圓表面之污染低。

Inorganic airborne molecular contaminants are important sources of contamination in cleanroom air that may cause device failure and decrease product yield. In this study, the optimal sampling conditions of two types of silica gel tubes as well as the impinger sampler for measuring acidic contaminants in cleanroom air were investigated. In addition, the optimum sampling condition for measuring ammonia by using the impinger sampler was also studied. The experimental results indicated that silical gel tube has the best collection efficiency under flowrate of 200~300 ml/min and the sample volume must over 400 liter for effective sampling in cleanroom. The impinger sampler had non-obvious decrease in absorbent volume (<5%) when the sampling flowrate was controlled to below 300 ml/min. The optimal sampling condition of impinger for acidic contaminants and ammonia were at sample flowrate of 50 and 300 ml/min, respectively, sample time of 24-hr. The results of actual cleanroom sampling showed that due to high interferences from residue contaminants in silica gel tubes, they were not suitable for low concentration cleanroom sampling. The interference from residue contaminants in silica gel was especially obvious for SUPELCO ORBO-53 sampler. The most suitable sampler for collecting acidic airborne contaminants in cleanroom air was the impinger sampler. It had the high recovery for HF of exceeded 90% in 60 ml absorbent and 100% for other acidic species in 30 ml absorbent. Beside, Impinger has the advantages of negligible interference from blank samples. The sampling results from the impinger sampler showed that the concentrations of HF, HCl and NH3 were exceeded 1,000n mol/m3. So these three species were the major inorganic airborne molecular contaminants in the cleanroom air.