Comment lampoly SNF 2009-06-18 18:03:04: Resist burning

mtang at mtang at
Thu Jun 18 18:03:04 PDT 2009

Resist is burning around most of the wafer, except for a bit of the middle and leading out to the left side relative to the flat.
Checked chamber rate of rise:  0.23 mt/min
Check gas flows -- all well within +/-5% of full range of MFS'c.
Wafer rotation relative to the chamber clamp looks good.  Chiller and lower electrode temperatures look good (setpoint 67, actual chiller 66.8, electrode 58.5C.)
When running wafers, the backside He controls well (once system is warm) to 6.3 torr (set point 6.0) with He flow of 11-12 sccm.  Normally, this is 8-9 sccm.
Purged the system and opened the chamber with Cesar.  It looks very clean, although there was a little dot on the electrode (left/above the flat).  Cesar scotch-brited it down, did IPA wipe and closed up.
Ran the purge and cycled wafers in.  Backside He is now 6.2 torr -- and 14 sccm!!!
Will leave this down for now.  This is probably OK for non-critical etches, but will burn resist and no doubt yield terrible profiles for critical etches.
By the way, I wonder if the annoying He backside stablization problem (frequent alarms with the first few wafers until it stabilizes) is due to the bleed/bypass (supposed to evacuate excess He pressure) not working.  This is probably not related to the current problem, but worth looking into some time soon.

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