Problem stsetch SNF 2011-10-07 21:07:18: Frequent wafer breakages (amongst several users)

I've noticed that a lot of users (including myself, eszilagy and now ehsans) have had their wafers break inside the etch chamber, on three friday evenings in a row. I'm using the same mask as I've been using the past 2 years and the same type of wafers as well. Something seems wrong with the machine--maybe He pressure or clamping force? (My wafers break even while using the Al holder. In one case, a 1mm thick wafer cracked after having been etched 400um, i.e. there was 600um of material left, which should be still a fair amount of material.) --Thanks, Ben C