Electrically erasable and programmable read only memory with trench structure

Claim 1

An Electrically Erasable and Programmable Read Only Memory (EEPROM) cell, which comprises: a first semiconductor layer of a first conductivity type and having a high doping level; a second semiconductor layer of said first conductivity type on said first layer and having a lower doping level than that of said first layer, said first and second layers together forming a source region of said EEPROM cell; a third semiconductor layer of a second conductivity type opposite to that of said first type on said second layer and extending to a surface of said EEPROM cell; A fourth surface-adjoining highly-doped semiconductor layer of said first conductivity type provided locally in said third layer and forming a drain region of said EEPROM cell; a trench extending through said third and fourth layers and partially into but not through said second layer; a channel region located in a portion of said third layer adjacent the sidewall portion of said trench and extending from said second region to said fourth region; a gate dielectric covering a sidewall and floor of said trench; a floating gate on said gate dielectric and extending adjacent the sidewall and floor of said trench; an intergate dielectric covering at least an inner sidewall and floor of said floating gate; a control gate located on said intergate dielectric and separated from said channel region by said floating gate; means for causing a localized high electric field density during an erase portion of an operating cycle of said cell across a corner region of said gate dielectric in the area adjacent the intersection of said trench sidewall and floor.