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Investigation of Various Substrate Dopants and Epitaxial Growth Techniques for Producing Sharp Transition Epitaxial Wafers
Arsenic, antimony, phosphorus, boron, and gallium doped silicon substrates were used for the fabrication of n/n+ or p/p+ epitaxial wafers to study autodoping effects in a horizontal induction heated atmospheric pressure epitaxial reactor. Using the "high‐low" technique which uses a high temperature prebake (without etching) followed by a relatively low temperature and slow growth rate deposition, sharp n/n+ transition on arsenic material was achieved. This method appears to produce an epitaxial layer of more uniform resistivity out to the beginning of the transition region for all of the n‐type substrates used. This is indicative of reduced autodoping effects. Results show that when the epitaxy employs the high‐low technique at a temperature of 1050°C, heavily doped arsenic substrates offer unique transition and defect density advantages over either antimony or phosphorus material. This should enable a reduction in n/n+ epitaxial layer thickness. The high‐low technique did not reduce autodoping for the p‐type substrates. The gallium substrates evaluated during these experiments exhibited unexpected behavior in light of the fact that gallium has a diffusion constant nearly identical to that of boron at 1100°C. However, the gallium wafers showed little difference in transition between any of the deposition conditions tried. Extreme gas phase autodoping is believed to be the cause for these gallium doped substrate results. Source:IOPscience