A model for the lateral variation of autodoping in epitaxial films

A model is presented that accounts for the variation of autodoping in epitaxial films grown by the chemical vapor deposition technique over substrates containing buried layers. This model is based on the dopant distribution that exists in the epitaxial reactor during growth. It is shown that the lateral variation of autodoping can be described by the following equation: where Cautodopingis the dopant concentration at the epitaxy-substrate interface at a distance from the buried layer, is the projection of onto the direction of gas flow in the reactor, is the linear velocity of the gas flow, Dgis the diffusivity of the dopant vapor in the gas stream, and is a constant. Based on this model, calculations of the lateral variation of autodoping were also made for arrays of buried layers normally encountered in VLSI circuitry. Results show that for high-density arrays with interburied layer distance µm, the autodoping concentration varies approximately as , where is the number of buried-layer elements in the wafer. It was also found that the autodoping variation between buried layers is less than 5 percent for , regardless of the spacing between buried layers.