{HEAD ~ The windows} are etched through {TAIL ~ the glass layer} with BCl2 or CHF3 /CF4 etch gases 
are etched through
{ HEAD ~ The windows } are etched through { TAIL ~ the glass layer } with BCl2 or CHF3 /CF4 etch gases
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH