Process for forming two MOS structures with different juxtaposed dielectrics and different dopings

Claim 1

A process for forming two MOS structures with different juxtaposed dielectrics and different dopings on a semiconductor substrate, for isolating in different ways the regions of the substrate where the channel is situated on the surface and those where the channel is situated in the mass comprising the steps of forming on a surface of the substrate a first silicon oxide layer then a second silicon nitride layer above the first layer, etching the second silicon nitride layer by photolithography so as to form a first window and define the isolating regions, causing a thick isolating oxide self-aligned with the double oxide and nitride layer to grow inside the window, replacing the double silicon oxide and nitride layer by a third silicon oxide layer forming the first dielectric, depositing a fourth layer of a material formed by doped silicon, etching in the fourth layer a second window for defining a channel region in the mass by means of the mask thus formed, baring the surface of the substrate defined by the second window and by the thick oxide, doping the substrate through the second window, oxidizing then depositing a double silicon dioxide and silicon nitride layer above the doped silicon layer and the bared portion of the sustrate, removing the double silicon dioxide and silicon nitride layer above the fourth doped silicon layer which served as mask for obtaining the second window, and depositing a fifth silicon layer above the fourth doped silicon layer and the remaining double silicon dioxide and silicon nitride layer covering the second window and etching the fifth doped silicon layer as well as the silicon layer for forming a gate.