Method for direct bonding two silicon wafers for minimising interfacial oxide and stresses at the bond interface, and an SOI structure

摘要

A semiconductor substrate (1) comprises first and second silicon wafers (2,3) directly bonded together with interfacial oxide and interfacial stresses minimised along a bond interface (5), which is defined by bond faces (7) of the first and second wafers (2,3). Interfacial oxide is minimised by selecting the first and second wafers (2,3) to be of relatively low oxygen content, well below the limit of solid solubility of oxygen in the wafers. In order to minimise interfacial stresses, the first and second wafers are selected to have respective different crystal plane orientations. The bond faces (7) of the first and second wafers (2,3) are polished and cleaned, and are subsequently dried in a nitrogen atmosphere. Immediately upon being dried, the bond faces (7) of the first and second wafers (2,3) are abutted together and the wafers (2,3) are subjected to a preliminary anneal at a temperature of at least 400° C. for a time period of a few hours. As soon as possible after the preliminary anneal, and preferably, within forty-eight hours of the preliminary anneal, the first and second wafers (2,3) are fusion bonded at a bond anneal temperature of approximately 1,150° C. for a time period of approximately three hours. The preliminary anneal may be omitted if fusion bonding at the bond anneal temperature is carried out within approximately six hours of the wafers (2,3) being abutted together. An SOI structure (50) may subsequently be prepared from the semiconductor structure (1) which forms a substrate layer (52) supported on a handle layer (55) with a buried insulating layer (57) between the substrate layer (52) and the handle layer (55).