Shallow-trench isolation with raised-field-oxide structure

This paper describes a novel shallow-trench isolation (STI) structure to su ppress the corner metal-oxide semiconductor field-effect transistor (MOSFET ) inherent to trench isolation. A gate oxide and a thin polysilicon layer a re first processed, and are then followed by the STI process. With this rai sed-field-oxide structure, the anomalous subthreshold conduction of the sha llow-trench isolated MOSFETs due to electric-field crowding at the active e dge has been successfully eliminated. No inverse-narrow-width effect is obs erved as the device width has been scaled down to 0.3 mu m. The raised-fiel d-oxide structure provides a larger process margin for planarization, and g ood device characteristics were achieved by this novel STI structure.