Sealing the backside of a semiconductor wafer prevents evaporation of the dopant (typically boron) when an epitaxial layer is grown on the front (active) side, thereby preventing autodoping of the epitaxial layer with excess dopant. The present technique deposits an oxide layer during the ramp-up of the furnace that also deposits the nitride cap, thereby avoiding an extra process step. Il also avoids the higher temperatures required for the prior-art technique of growing the oxide layer, resulting in lower oxygen precipitation due to the capping process and a greater yield of usable wafers.