Trapping-free string select transistors and ground select transistors for Vg-type 3D NAND Flash memory

In SONOS 3D NAND, if the string select transistor (SST) and the ground select transistor (GST) use memory cell's trapping dielectric as their gate dielectrics, they could suffer abnormal Vt shift due to unwanted charge injection during programming/erasing (P/E). To solve this, we remove the blocking oxide and the trapping nitride, and use the BE-SONOS' ONO tunneling dielectric and an additional LPCVD oxide as the gate dielectric of SST and GST. The nitride in the ONO tunnel dielectric is thin (<;30A) so it is trapping-free. After repeatedly programming/erasing the NAND strings for more than 3,000 times, the Vt shifts of the select transistors are less than 200mV. The trapping-free SST and GST can prolong the cycling endurance of SONOS 3D NAND Flash memory.