Method of fabricating a semiconductor device having a top layer and base layer joined by wafer bonding

A method of manufacturing a silicon body having a weakly doped n-type top layer and an adjoining highly doped n-type base layer, comprising the steps of:

• providing a doped first n-type silicon slice with a doping concentration of less than about 10.sup.15 cm.sup.-3, said first silicon slice having a polished surface;
• providing a doped second n-type silicon slice with a doping concentration greater than the doping concentration of the first silicon slice, the second silicon slice having a phosphorous doping as a first doping impurity and either an antimony or arsenic doping as a second doping impurity at a doping concentration greater than the phosphorous doping concentration, said second silicon slice also having a polished surface;
• bringing the polished surfaces of the first and second silicon slices into contact with each other and heating said first and second silicon slices while the polished surfaces are in contact with each other at a temperature and for a time sufficient to bond said polished surfaces, said temperature and time being sufficiently high also to diffuse the phosphorous first doping impurity from the second silicon slice into the first silicon slice to form a boundary layer in the first silicon slice having a doping concentration higher than the doping concentration elsewhere in the first silicon slice, the boundary layer assuring a low contact resistance between the first and second silicon slices, the phosphorous first doping impurity having a doping concentration sufficiently high to overdope any boron diffusion into the boundary layer from boron contamination of the polished surfaces, the second doping impurity diffusing more slowly than phosphorous into the boundary layer to provide a steep doping concentration profile between the first and second silicon slices.