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