Method for manufacturing a laterally limited, single-crystal region on a substrate and the employment thereof for the manufacture of an MOS transistor and a bipolar transistor

A method for manufacturing a laterally limited, single-crystal region on a substrate, comprising the steps of:

• a) providing a substrate made of a single-crystal material;
• b) forming a first layer on a surface of the substrate, said first layer being selectively etchable with respect to the substrate and comprising SiO.sub.2 ;
• c) forming a second layer on the first layer, the second layer being selectively etchable with respect to the first layer and comprising polycrystalline silicon;
• d) providing an opening in the first and second layers so as to expose an area on the surface of the substrate;
• e) covering surfaces and side walls of the second layer with a third layer;
• f) selectively etching the first layer with respect to the substrate and the second layer so as to provide an undercut between the second layer and the surface of the substrate, the third layer resisting the etchings of the first layer;
• and
• g) forming a single-crystal region on the exposed surface of the substrate by selective epitaxy, no nucleation occurring at the surface of the third layer in the selective epitaxy step.