Jin Onuki1 and Masateru Suwa1
1Hitach Research Laboratory, Hitachi Ltd., Hitachi
When a n+-type surface of a diode is bonded to a tungsten or molybdenum electrode using aluminum solder, a thin p-type regrowth layer is formed on the n+-type silicon after bonding. This layer formation generates a considerable forward voltage drop (FVD) in the regrowth layer.
In order to clarify the role of phosphorous in brazing between n+-type silicon and aluminum, effects of P concentration on the thickness and the electrical property of regrowth layer have been investigated.
The P concentrations in n+-type silicon of diodes were 1×1020 cm-3, 4×1020 cm-3 and 2×1021 cm-3. Brazing atmospheres used were N2, air and vacuum. In the case of brazing in N2 atmosphere, the thickness of regrowth layer is increased with increasing P concentration in n+-type silicon. Difference in the thickness and the morphology of regrowth layer between n+-type silicon with high P concentration and that with low P concentration, becomes more remarkable by brazing in air. On the other hand, in the case of brazing in vacuum, the thickness of regrowth layer is nearly the same independent of P concentration. These results indicate that cleaning action in the interface between molten aluminum and n+-type silicon is greatly promoted by the presence of P. It is also found that in n+-type silicon with high P concentration, the junction formed between regrowth layer and n+-type silicon is more imperfect than that of n+-type silicon with low P concentration.
forward voltage drop, aluminum, n+-type silicon, phosphorous concentration, thickness of regrowth layer, brazing atmosphere, current-voltage characteristics of pn junction
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