HEPA air reduction in off-hours

Dick Crane rcrane at snf.stanford.edu
Thu Oct 6 13:54:49 PDT 2005

Fab users,

HEPA air flow will be reduced during off-hours starting 10/17/05.

I wish to announce a change in facilities operation concerning air flow 
through the HEPA filters during off-hours as an energy cost reduction 
measure. We followed a similar procedure during the '80s and 90's. About 
eight years ago changes in the control system caused us to stop the 
reductions. The plan is to reduce HEPA air flow by 50% from 2300 to 0700 
MTWThF and all day Saturday and Sunday. Exhaust air flow will not be 
affected. This change will implemented starting Monday evening, 10/17/05.

Discussion:  Even though this procedure has been followed in the past, 
we have recently measured particle counts at full HEPA air flow during 
the day and at 50% flow during the night. The particle counts were very 
similar throughout the cleanroom. In both cases the cleanroom qualified 
as a class 100 facility in litho, etch, and diffusion aisles as 
expected. The thin film and epi aisles qualified as class 1000 as 
expected. What will change is the cleanroom's ability to recover quickly 
from a particle assault. Given the low number of fab users during these 
off-hours, this should be a not a problem. Energy cost saving is 
projected to be $7k-$10k/year.

Thanks for your cooperation,


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