Four parts per billion (ppb) of moisture almost cost Tiger Optics a major order from a large chipmaker. In the demo phase, Tiger’s new LaserTrace 3 analyzer, boasting the lowest detection limits and greatest sensitivity in its field, showed higher amounts of moisture in oxygen than in the other bulk gases (H2, He, Ar, and N2).
With alarms set at 0.5 ppb, the customer complained that such readings could stall production. So fragile are the fab’s infinitesimal integrated circuits that a mere ppb of moisture can lead to costly, irreparable damage.
Having observed this phenomenon at other fabs around the world, Tiger set out to determine both the true source of the moisture and how best to alleviate its impact. But, first, the instrument maker ensured that its analyzer was operating properly. To begin, internal diagnostics were performed. Using spectroscopic data, the maker verified that the gas actually contained the measured ppbs of H2O.
Next, the gas flow was checked. With its local representative, Tiger created a bypass flow, speeding the gas to the inlet of the analyzer from one liter to five liters per minute. The readings dropped by approximately five-fold, demonstrating that the gas was actually drier than that delivered to the analyzer without the additional bypass. NOTE: If the source gas were truly wet, increased flow would not change the readings. Used to verify the integrity of a gas delivery system, the bypass dilutes moisture due to leaks, dead-legs or, in rare instances, the use of bellows tubing. (At the fab in question, the absence of measurable leaks was previously confirmed.)
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