Problem amtetcher SNF 2012-07-23 20:41:36: Residue in chamber and on wafers

Helo everyone,
I have used the AMT today for my regular etch of nano-holes, using NF3 (15 sccm, 40 mtorr, -390 V).
I have noticed that there was a brown residue on the window, but could not find Elmer to check it out before starting. The seasoning and first calibration runs were OK, with normal etch rates of 350 Ang./min for SiNx wafers as previous runs. However, after the etch, there was also a residue on my wafers. I will check later the performance of the etch in SEM, but it may have also deposited on the side walls of the nano-holes I made.
I did not see this before. Can it happen from not doing a proper process 2 descum before I started ?
Ofer