oxygen flash process may be performed with the following parameters o2fl time 0 15 min pressure 45 mtorr high frequency power 1500 whf low frequency power 500 wlf gas flows 80 sccm o2 500 sccm ar center flow ratio cfr 60 helium backside pressure hebs 45 20 in situ polymer strip the silicon nitride cover layer 5 may be removed from the bottom of the second opening 8 with the following process time 2 00 min pressure 20 mtorr high frequency power 1500 w low frequency power 500 wlf gas flows 20 sccm o2 30 sccm ch3f 200 sccm co center flow ratio cfr 70 hebs 45 20 the first and or the second opening 4 8 are formed in a silicon oxide first and or second layer in a further embodiment with the following process parameters temperature 10 u00b0 c 60 u00b0 c time 3 10 min pressure 10 50 mtorr high frequency power 1500 3000 whf low frequency power 1500 4000 wlf gas flows 10 70 sccm o2 10 70 sccm c4f6 600 1500 sccm ar 0 35 sccm c3f8 0 35 sccm ch2f2 o2fl time 0 10 0 30 min pressure 45 mtorr high frequency power 500 1500 whf low frequency power 0 500 wlf gas flows 20 400 sccm o2 0 800 sccm ar insitu polymer strip in a further embodiment the cover layer 5 made of silicon nitride may be etched using the following parameters temperature 10 60 u00b0 c time 1 3 min pressure 10.