Ichiro Nakao

A practical trench isolation technology with a novel planarization process

We develop a new vertical-trench isolation method that utilizes a thin SiO2film in-between double photoresists for uniform top-resist coating and for an etch-back barrier, a poly-silicon film above active regions for an etch-back buffer and large tilt-angle boron ion implantations into the trench-sidewalls for narrow channel effect control. The Planarization with the Resist / Oxide / Resist and the Poly _Silicon (PRORPS) can isolate the whole surface of a 6 inch-diameter wafer very uniformly with a large process margin. The standard deviation of the threshold voltage of a n-channel MOS-FET (W/L= 10µm/0.8µm) over the whole wafer is 0.38 % at about 0.6 V threshold voltage. The narrow-channel-effect is controlled for FETs down to 0.5 µm channel width. The method is applied to the megabit SCC (Surrounded Capacitor Cell) DRAM developed here and the cells and the peripheral-circuits are isolated at the same time successfully.