MO/Ti bilayer metallization for a self-aligned TiSi2 process

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Abstract
During the TiSi2 formation from Ti/Si couples, Ti is often found to oxidize appreciably by reacting with residual oxygen in annealing ambients. A bilayer of Mo/Ti replacing a single layer of Ti has been evaluated for application to a self-aligned process. Due to the presence of the thin overlayer Mo, a reduced internal oxidation of Ti increased the overall oxidation resistance during the silicide-formation cycle. We also found that the Mo/Ti bilayer was incorporating an appreciable amount of nitrogen along with the formation of TiSi2 layer in a flowing nitrogen forming-gas (N2+8–10% H2) ambient when the structure was subjected to heat treatment at 590 °C±10 °C. The thin-film rections of Mo/Ti/Si structures will be discussed and compared with that of Ti/Si couples. Due to the uniform TiSi2 formation with minimized oxidation, a very homogeneous etching across a wafer resulted during an excess-metal etch step. This bilayer was applied to fabricate MOSFET’s giving 3–4 Ω/⧠ of sheet resistance with good reproducibility.

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