A portion of the control gate could extend into a trench formed into the substrate, wherein {TAIL ~ the drain region} is formed underneath {HEAD ~ the trench}, and the channel region has a first portion extending along the trench sidewall and a second portion extending along the substrate surface 
A portion of the control gate could extend into a trench formed into the substrate , wherein { TAIL ~ the drain region } is formed underneath { HEAD ~ the trench } , and the channel region has a first portion extending along the trench sidewall and a second portion extending along the substrate surface
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH