| 摘要 |
A method of performing a nitride strip process step for a plurality of semiconductor wafers includes partially draining the chemical solution within a chemical bath after every nitride strip in which the oxide etch rate is within a specified range. If the oxide etch rate is above the specified range, the partial drain is performed. Once the etch rate falls within the range, the partial drain is performed every time a bath increment signal is received. If the etch rate falls below the specified range, then the bath is completely drained so that the solution may be replaced with fresh chemicals. While it is generally desirable to minimize the amount of field oxide that is removed during the nitride strip process step, the field oxide etch should be maintained at a specified level because, when below that level, the chemical solution silicon content is too high risking the possibility that the silicon will precipitate and cause undesirable effects including coating the wafers being stripped of nitride. The partial drain time is adjusted from a nominal rate according to measured oxide etch rates. For a first bath in a sequential series of baths, the nominal partial drain time is fifteen seconds. For a second bath in the sequential series of baths, the nominal rate is ten seconds.
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