Abstract
The variation of impurity concertation in the ultra-high purity (UHP) gases, delivered from cryogenic storage tanks and transported through long pipes, is a major problem in systems like those used in semiconductor manufacturing facilities. A method is developed for stabilizing the purity and reducing the gas consumption in these systems. This technique uses a dynamically controlled mixing of gases supplied by multiple cryogenic tanks. The control scheme uses software modules that simulate the processes that cause purity variation in both the cryogenic tanks and the transport lines. These processes include vaporization and supply in tanks, various modes of transport in delivery pipes, and the adsorption and desorption on surfaces. The method also includes and corrects for variations caused by transience in gas usage rate as well as ambient conditions.
Highlights
Ultra-high-purity (UHP) gases are widely used in semiconductor fabrication plants, both as reactants in some processes like deposition and etching [1] [2], and as inert gases for purging various parts of the system
The variation of impurity concertation in the ultra-high purity (UHP) gases, delivered from cryogenic storage tanks and transported through long pipes, is a major problem in systems like those used in semiconductor manufacturing facilities
The UHP gases are typically delivered through pipes from gas storage facilities outside the fab to the point of use (POU)
Summary
Ultra-high-purity (UHP) gases are widely used in semiconductor fabrication plants (fabs), both as reactants in some processes like deposition and etching [1] [2], and as inert gases for purging various parts of the system. UHP nitrogen is used in very large quantities in semiconductor fabs as diluent and purge medium. The UHP gases are typically delivered through pipes from gas storage facilities outside the fab to the point of use (POU). UHP gases, such as nitrogen, are usually stored in the cryogenic tanks where gas is produced by controlled vaporization of the stored liquid and transported through delivery. Most semiconductor processes are very sensitive to impurities and require a well-controlled quality [3] [4]. Failure to maintain a stable purity level at the (POU) can lower the performance of process tools and even slow or shut down the processing line [5]
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