CONTAMINATION CONTROL FOR GAS DELIVERY FROM A LIQUID SOURCE IN SEMICONDUCTOR MANUFACTURING

Gas delivery from a liquid source, common in semiconductor manufacturi ng, raises contamination control concerns not only due to impurity lev els in the source. In addition, the lower vapor pressure of impurity s pecies compared to that of the host (source) species causes impurity c oncentrations in delivered gas to increase as the source is used up, A physics-based dynamic simulator to describe the time-dependent variat ion of impurity level in such a gas delivery system has been developed and applied to the important case of CHCIF2 impurities in host CHF3 l iquid, as routinely used for dry etching processes, For a cylinder of CHF3 liquid with 100 ppm of CHClF2 at 21.1 degrees C (70 degrees F), t he concentration of CHClF2 in the delivered gas is initially similar t o 21 ppm, and rises slowly to similar to 100 ppm with similar to 25% o f the initial material remaining, With further usage, the CHCIF2 level increases quickly to similar to 350 ppm when similar to 15% of the in itial source material is left; at this point, the source has reached t he liquid-dry point, i.e., all the remaining source material is gaseou s, and the impurity concentration in delivered gas remains constant at 350 ppm until all material is gone. The time-dependence of CHClF2 imp urity concentration is also dependent on the operating temperature of the liquid source: for higher temperatures, the fast rise in impurity concentration and the liquid-dry point occur earlier, while the final impurity level after this point is lower, The dynamic simulator repres ents a useful tool for avoiding contamination problems with liquid del ivery systems and for optimizing materials usage (for cost and environ mental benefits) by structuring source usage procedures consistent wit h contamination-sensitivity of the process. The results also suggest b enefits in materials usage if specific source temperatures (different from room temperature) were imposed. The physical basis of the dynamic simulator allows more general application to other systems.