Quadruply self-aligned MOS (QSA MOS)—A new short-channel high-speed high-density MOSFET for VLSI

A new device named Quadruply Self-Aligned (QSA) MOS is proposed to overcome speed and density limits of conventional scaled-down MOS VLSI circuits. This device includes four mutually self-aligned areas: narrow poly-Si gate, shallow-source/drains to eliminate short-channel effects, deep junctions for high conductance, and specific contacts to afford efficient metal interconnection. To get these four regions to register, the gate pattern is first defined followed by undercutting of the polysilicon, anisotropic reactive ion etching of the gate oxide, and ion implantation into the source/drain regions. The device has been fabricated and its proper operation has been demonstrated. Because of its short-channel length and small gate-drain overlap capacitance, this device allows the design of high-speed VLSI circuits using high-conductive interconnects. Also, the self-aligned process allows the design of high-density VLSI circuits. It is shown that the design of the ultimate 3F × 2F cell (6 µm²/cell, namely 3 × 2 mm²/1 Mbit in 1-µm rule) and the 4F pitch sense amplifier in dynamic MOS RAM are feasible using this QSA technology. (F is the minimum feature size.)