A process for fabricating a substrate that includes a buried oxide layer for the production of electronic components or the like. The process includes depositing an oxide layer or a nitride layer on either of a donor or receiver substrate, and bringing the donor and receiver substrates into contact; conducting at least a first heat treatment of the oxide or nitride layer before bonding the substrates, and conducting a second heat treatment of the fabricated substrate of the receiver substrate, the oxide layer and all or part of the donor substrate at a temperature equal to or higher than the temperature applied in the first heat treatment. Substrates that have an oxide or nitride layer deposited thereon wherein the oxide or nitride layer is degassed and has a refractive index smaller than the refractive index of an oxide or nitride layer of the same composition formed by thermal growth.