An early deposited LPCVD silicon nitride: allowing the possibility of novel cell designs

Abstract

An LPCVD silicon nitride layer deposited in the early stages of cell fabrication has many properties that allow for increased processing flexibility and hence the realisation of novel cell designs. We have shown previously that excellent surface passivation can be achieved provided at least a thin oxide is present under the nitride. Surface passivation is lost once the wafer is heated, due to a loss of hydrogen from the silicon/oxide interface, but can be recovered entirely by re-introducing hydrogen to this interface. The work presented in this paper is concerned with hydrogen re-introduction using a high temperature forming gas anneal. We show that the thermal history of the wafer and the thickness of the silicon nitride layer both affect the time necessary to recover surface passivation.