A Self Aligned Contact Process with Improved Surface Planarization

A new self aligned contact technology has been introduced into a 4Mbit DRAM process. The contact hole is overlapping gate and field oxide. A thin nitride/thin poly-Si/oxide multilayer allows a contact hole etch, which does not significantly affect the oxide isolation of the gate and the field oxide. After acting as etch stop, the poly-Si is changed into oxide by selective oxidation. The new process offers an improved reflow of isolation oxide and contact hole rounding.