Method for providing electrical isolating material in selected regions of a semiconductive material

A method of fabricating a semiconductor device comprising the steps of:

• forming on the surface of a body of semiconductive material of a first semiconductivity type a layer of second semiconductivity type material, said layer having a high concentration of impurities on a side adjacent the body and a lower concentration on a side opposite said body;
• forming a protective layer on said layer of second semiconductivity type material;
• removing said protective layer from selected regions to expose the semiconductive material;
• forming a porous dielectric material from at least a portion of the semiconductive material in the selected regions by submerging said device in an anodizing solution and applying an anodizing potential to the semiconductive material in the regions so that the exposed semiconductive material becomes an anode and is at least partially anodized to form the porous dielectric insulation in the regions, the porosity of said dielectric material being sufficient to allow the anodizing solution to penetrate the dielectric and react with the unanodized semiconductive material in said regions, whereby the isolation regions may be formed to a desired thickness;
• removing said device from the anodizing solution;
• forming regions of first semiconductivity type material in the layer of second semiconductivity type material;
• and
• forming zones of second type semiconductivity material in said regions of first type semiconductivity material.