Method for contacting a buried interconnect rail of an integrated circuit chip from the back side of the IC

A method of producing an integrated circuit chip comprising:

• providing a device substrate comprising a semiconductor material at least on its upper surface;
• producing a front end of line (FEOL) portion of the chip on the semiconductor material of the device substrate, wherein the FEOL portion comprises active devices and interconnect rails, the interconnect rails being at least partially embedded in a shallow trench isolation (STI) dielectric layer;
• producing a back end of line (BEOL) portion on the FEOL portion;
• bonding the device substrate to a landing substrate, with a surface of the BEOL portion being bonded to a surface of the landing substrate, and thereafter:
• thinning the device substrate from the back side, and
• producing a power delivery network (PDN) on the thinned backside of the device substrate, wherein the PDN is connected to the interconnect rails by a plurality of through semiconductor vias (TSV) which are isolated from the semiconductor material of the device substrate by a dielectric liner,
• wherein:
• the TSVs are formed during the production of the FEOL portion on the device substrate, the TSVs extending into the semiconductor material of the device substrate and being formed in a self-aligned manner with respect to the interconnect rails, the TSVs being self-aligned to the interconnect rails in the direction perpendicular to the interconnect rails, with the liner isolating the TSVs laterally and on the bottom of the TSVs,
• thinning the device substrate includes thinning the semiconductor material of the device substrate until the liner at the bottom of the TSVs is exposed, and
• the liner is subsequently removed from the bottom of the TSVs so as to allow the PDN to contact the TSVs,
• and wherein forming the interconnect rails and the TSVs comprises:
• producing a trench through the STI dielectric layer and extending into the semiconductor material of the device substrate,
• providing a first dielectric liner on the bottom and the sidewalls of the trench, and thereafter:
• providing a mask that defines at least one local open area extending across the longitudinal direction of the trench and on both sides of the trench,
• removing the liner from the bottom of the trench in the at least one local open area, and thereafter:
• etching a blind cavity extending underneath the trench, by a self-aligned etch process in the at least one local open area, the etch process being self-aligned to the trench in the direction perpendicular to the longitudinal direction of the trench,
• providing a second dielectric liner on the bottom and the sidewalls of the blind cavity, and thereafter:
• filling the blind cavity and the trench with an electrically conducting material, so as to create a rail having one of the TSVs extending locally and in a self-aligned manner from a bottom of the rail.