Process for fabricating a buried, laterally insulated zone of increased conductivity in a semiconductor substrate

A process for fabricating a buried, laterally insulated zone of increased conductivity in a semiconductor substrate, having the following steps:

• providing a silicon substrate with a buried zone of increased conductivity;
• forming a reference layer on the substrate;
• patterning the reference layer;
• forming a trench with at least one shallow region and at least one deep region in the substrate;
• and
• filling the trench with silicon oxide insulation material and depositing the insulation material on the structure thus produced in an ozone-activated CVD process;
• selecting a material of the reference layer such that a growth rate of the insulation material on the reference layer is at least by a factor of two less than a growth rate of the insulation material on a surface of the trench to be covered, a ratio of a width of the deep region to a step height of the shallow region being approximately equal to 2*α/(α−1), where α corresponds to a ratio of the growth rate of the insulation material on the surface of the trench to be covered to the growth rate of the insulation material on the reference layer.