반도체 웨이퍼 製造工程 중 發生混合廢酸으로부터 불산, 질산 및 초산의 각 산 回收에 관한 硏究
Study on Recovery of Separated Hydrofluoric Acid, Nitric Acid and Acetic Acid Respectively from Mixed Waste Acid Produced during Semiconductor Wafer Process
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초록
반도체 웨이퍼 제조 공정 중 발생하는 질산, 불산, 초산으로 구성된 혼합폐산을 재활용하기 위한 연구를 수행하였다. 초기에 NaNO3와 Si powder를 사용하여 불산을 Na2SiF6로 침전시켜 불소화합물을 제조하였고, 이 때 혼산 중 불산의 농도는 초기 127g/L에서 0.5g/L로 낮아져 불산 회수율은 99.5%였다. Na2SiF6 제조 후 남은 혼산의 질산과 초산의 농도는 각각 502g/L, 117g/L였고, 이 혼산에 NaOH를 투입하여 pH=4로 맞춘 후 -440 ㎜Hg, 95℃에서 증발농축을 하여 초산을 분리·회수하였다. 회수된 초산의 농도는 약 15%였고, 회수율은 85.3% 이상이었다. 또한, 농축여액을 20℃까지 냉각하여 NaNO3 결정을 석출시킴으로 질산나트륨을 제조하였고, 그 회수율은 약 93%이상이었다. 제조된 Na2SiF6와 NaNO3를 90℃에서 건조시킨 후, XRD 분석한 결과, 순수 Na2SiF6 와 NaNO3만 합성된 것을 확인하였고, 그 순도는 각각 약 97%, 98%로 시판용과 유사하였다.
Abstract
We researched separation of mixed waste acids with HF, CH3COOH, HNO3 that were produced during a semiconductor wafer process to recycle these acids. At first, we manufactured the fluoride compound in form of Na2SiF6 by precipitating HF using NaNO3 and Si powder. The concentration of HF was reduced from the initial concentration of 127 g/L to 0.5 g/L with an HF recovery ratio of 99.5%. After the manufacture of Na2SiF6, the concentration of HNO3 and CH3COOH demonstrated 502 g/L and 117 g/L respectively. Following these findings we added NaOH in this CH3COOH/HNO3 mixed acid in order to obtain pH=4. Next we separated the CH3COOH and recoverd it through the use of vaccum evaporation at -440 ㎜Hg, 95℃. The concentration of the recovered CH3COOH was approximately 15% and the recovery ratio of CH3COOH was over 85%. We precipitated the NaNO3 by cooling the concentrated solution to 20oC with a HNO3 recovery ratio of over 93%. We confirmed that only Na2SiF6 and NaNO3 were manufactured by XRD analysis after drying these precipitants at 90oC. The precipitants demonstrated a purity of approximately 97% and 98% respectively. Therefore, the purity of the precipitants proved to be similar to that of commercial products.
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