In-situ doped polysilicon using vapor dopant for high density DRAMs

A highly conformal LPCVD (low-pressure chemical vapor deposition) in-situ doped (ISD) polysilicon process, using a low-toxicity vapor dopant source, t-butylphosphine (TBP), is developed in a standard automated horizontal LPCVD furnace for prototyping 16-Mb DRAMs (dynamic RAMs). The dopant incorporation is found to increase with increasing TBP concentration and decreasing deposition temperature. However, the conformality of the ISD polysilicon decreases with increasing dopant incorporation. A 700 degrees C anneal is sufficient to activate the dopant. An optimized condition gives uniform deposition over a 75-wafer load with a resistivity less than 1.0 m Omega -cm and a side/top step coverage better than 97%. It can fill 10- mu m-deep, 0.8- by 1.5- mu m-wide trenches without forming any voids.<
>