The two processes in combination etch the upper layer of {TAIL ~ a wafer} by {HEAD ~ chemical and mechanical action} which removes high points much faster than the low points on the wafer surface 
The two processes in combination etch the upper layer of { TAIL ~ a wafer } by { HEAD ~ chemical and mechanical action } which removes high points much faster than the low points on the wafer surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH