Production from week 5.12.2008
Wafers 525 & 527 have a 1000 Å dry thermal oxide mask with all three films on the frontside sputtered. Both these wafers had a high density of pinholes. The pores are also irregular in shape and seem to have material “hanging” off the edges of the pores. Could this be a consequence of depositing at a higher base pressure. Because the relative humidity has been creeping up in the last few weeks (from %10 to %30) we have had to deposit at a higher vacuum pressure (from 7e-7 torr to 2e-6 torr). Because of the increased water vapor in the chamber, we may be depositing a silicon film with a higher concentration of oxygen. This in turn may be what’s causing the irregular pore shapes and “cornflake” texture. Recall that we were battling this morphology last summer as well…
I should note that we’ve only observed this cornflake texture on wafers with a thermal oxide mask. I’ve never seen it on TEOS wafers. This week will show whether the morphology is affected by the different masking material.
Talks are underway on how to deal with this issue…