Method for manufacturing a substrate for a front-facing image sensor

A method of fabricating a front-side image sensor, comprising:

• fabricating a substrate for the front-side image sensor, comprising:
• providing a donor substrate comprising a semiconductor layer to be transferred;
• providing a semiconductor carrier substrate;
• bonding the donor substrate to the carrier substrate, an electrically insulating layer being at a bonding interface;
• transferring the semiconductor layer to the carrier substrate;
• implanting gaseous ions into the carrier substrate through the transferred semiconductor layer and the electrically insulating layer;
• and
• after the implantation, heat treating the implanted carrier substrate a temperature suitable for causing cavities to develop from the implanted gaseous ions and epitaxially growing an additional semiconductor layer on top of the transferred semiconductor layer, wherein the heat treatment is carried out during the epitaxial growth of the additional semiconductor layer, and wherein the transferred semiconductor layer and the additional semiconductor layer together form an active layer of the image sensor;
• and
• forming a plurality of electrically isolating trenches extending through the active layer to the electrically insulating layer of the substrate for the front-side image sensor, the plurality of electrically isolating trenches defining a plurality of pixels.