Removing metal precipitates from semiconductor devices
AssigneeDelco Electronics Corporation
InventorDouglas R. Sparks
Life of this patent
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Abstract
Rapid thermal annealing, involving rapid heating to a temperature of between 550 degrees C. and 750 degree C. for between 30 and 90 seconds and rapid cooling, is used to dissolve the precipitates of transition metals which tend to occur in a silicon wafer and to keep such metals in solution after cooling. Such annealing can be used in the manufacture of bipolar transistors to limit the emitter-collector shorting caused by metallic precipitates. It is also useful more generally to improve the leakage current of p-n junctions either in diodes or as parts of bipolar or field-effect transistors.
Claims9
A process of making a silicon wafer of a silicon device essentially free of transition metal precipitates which comprises the steps of heating the wafer rapidly to a temperature of between 550-750 degrees C., maintaining such temperatures for between 30-90 seconds, rapidly cooling the wafer for quenching the transition metal atoms in solution, and thereafter avoiding conditions in the further processing under which the metal atoms can reform into precipitates.
In the manufacture of a diffused base silicon junction transistor which involves successive base and emitter diffusion steps into a silicon wafer, the improvement which comprises a first rapid thermal annealing step before the emitter diffusion step to dissolve metal precipitates in the silicon wafer, a second rapid thermal annealing step after the emitter diffusion step, and subsequently avoiding heating the wafer under conditions apt to lead to the reformation of the metal precipitates in the silicon wafer.
Dependencies are inferred from the claim text.