After being bonded to the device wafer , the cap wafer is thinned from the back surface until {HEAD ~ the back surface} of the cap wafer reaches {TAIL ~ the partially etched cavities}  
reaches
After being bonded to the device wafer , the cap wafer is thinned from the back surface until { HEAD ~ the back surface } of the cap wafer reaches { TAIL ~ the partially etched cavities }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH