A polycrystalline silicon film is formed on {HEAD ~ a surface} of a trench and on a surface of {TAIL ~ a silicon nitride film} 
A polycrystalline silicon film is formed on { HEAD ~ a surface } of a trench and on a surface of { TAIL ~ a silicon nitride film }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL