Trench storage capacitors for high density DRAMs

The authors have demonstrated trench capacitors with openings down to 0.25 mu m 0.25 mu m and aspect ratios as high as 40, and with a capacitance of 31 fF for 8 nm equivalent ONO (oxide/nitride/oxide) thickness. The projected trench dimensions for a 256 Mb DRAM are 0.25 mu m 0.40 mu m 4 mu m, yielding a capacitance of 30 fF when a 5 nm thick oxide dielectric is used. A capacitance of about 50 fF has been obtained using 8 nm oxide-equivalent ONO dielectric with trench dimensions of 0.25 mu m 0.4 mu m 11.5 mu m.