Connection pad structure for an image sensor on a thinned substrate
The invention relates to the fabrication of electronic circuits on a thinned semiconductor substrate. To produce a connection pad on the back side of the thinned substrate, the procedure is as follows: an integrated circuit is produced on an unthinned substrate, in which a portion of a polycrystalline silicon layer ( 18 ) dedicated for the connection of the pad is provided. The circuit is transferred onto a transfer substrate ( 30 ) and then its back side is thinned. A via is opened in the thinned semiconductor layer ( 12 ) in order to gain access to the polycrystalline silicon; aluminum ( 80 ) is deposited and this layer is etched so as to define a pad which is in contact with the internal interconnects of the integrated circuit by way of the polycrystalline silicon.
1. A method for producing a connection pad on an electronic component, comprising the following steps:
producing an integrated circuitry on a first substrate, said circuitry comprising at least one internal conductive connection and a portion of a polycrystalline silicon layer dedicated for the connection of the pad, said portion of polycrystalline silicon layer being in contact with said internal conductive connection of the integrated circuitry;
transferring a front side of said first substrate onto a transfer substrate and then thinning said first substrate from a back side thereof;
opening an aperture in the thinned back side and baring said portion of polycrystalline silicon in said aperture; and
depositing a metal layer on said thinned back side and in the aperture, and etching said metal layer so as to define said pad which is in electrical contact with the internal connection of the integrated circuitry by way of said polycrystalline silicon layer.
2. The method as claimed in claim 1 , wherein:
said first substrate comprises on its front side a surface semiconductor layer having a front side and a back side, and
the step of producing the integrated circuitry comprises the formation, on the front side of the semiconductor layer, of an insulating layer, then the formation of the portion of polycrystalline silicon layer on said insulating layer, and then the deposition and etching of an alternation of insulating layers and metal layers with interconnects between the various metal layers and interconnects between said polycrystalline silicon layer and at least one of the metal layers;
the step of thinning said first substrate comprises retaining only a semiconductor layer about 2 to 30 microns in thickness;
the step of opening the aperture comprises locally etching the back side of the semiconductor layer, through the entire thickness of the semiconductor layer on top of a portion of said insulating layer area covered with polycrystalline silicon; and
removing the insulating layer at a bottom of the aperture so as to bare the polycrystalline.
3. The method as claimed in claim 2 , wherein, during the operation of locally etching the semiconductor layer, through the entire thickness thereof, a peripheral trench is etched that completely surrounds both the pad and the aperture formed in the semiconductor layer.
4. The method as claimed in claim 3 , wherein the transfer substrate is an integrated circuit chip.
5. The method as claimed in claim 3 , wherein the metal deposited on the back side is an aluminum-based metal.
6. The method as claimed in claim 2 , wherein the metal deposited on the back side is an aluminum-based metal.
7. The method as claimed in claim 6 , wherein the transfer substrate is an integrated circuit chip.
8. The method as claimed in claim 2 , wherein the transfer substrate is an integrated circuit chip.
9. An electronic component comprising an integrated circuit produced on the front side of a thinned first silicon substrate, the thinned substrate comprising a thin semiconductor layer about 2 to 30 microns in thickness, the first substrate being mounted via its front side on a transfer substrate, wherein the component includes, on the accessible back side of the semiconductor layer, at least one external connection pad formed by a portion of the metal layer deposited on the semiconductor layer, the metal layer being in direct contact, through an aperture formed in the semiconductor layer, with a polycrystalline silicon layer formed on the front side of the thinned first substrate, the polycrystalline silicon layer itself being in contact with a metal layer formed on the front side of the thinned silicon substrate.
10. The component as claimed in claim 9 , wherein the aperture formed in the semiconductor layer is formed in a semiconductor layer island that is entirely isolated electrically, by a trench surrounding this island, from the rest of the semiconductor layer.
11. The electronic component as claimed in claim 10 , wherein the transfer substrate is an integrated-circuit chip.
12. The electronic component as claimed in claim 9 , wherein the transfer substrate is an integrated-circuit chip.