Chip protected against back-face attacks
A semiconductor chip includes at least two insulated vias passing through the chip from the front face to the rear face in which, on the side of the rear face, the vias are connected to one and the same conducting strip and, on the side of the front face, each via is separated from a conducting pad by a layer of a dielectric.
1. A semiconductor chip comprising:
a chip substrate having a front face and a rear face opposite the front face, active circuitry being disposed at the front face;
a plurality of insulated vias extending between the front face and the rear face of the chip substrate, wherein, at the rear face, each via is connected to a common conducting strip, and wherein, at the front face, each via comprises a bottom insulated surface and a bottom conducting surface; and
a plurality of capacitors, wherein each capacitor of the plurality of capacitors comprises
a first conductor formed from a conducting pad directly overlying an associated via of the plurality of insulated vias,
a second conductor formed from the bottom conducting surface of the associated insulated via, and
a dielectric formed from the bottom insulated surface of the associated insulated via, the dielectric being disposed directly between the first conductor and the second conductor to form the capacitor.
2. The semiconductor chip according to claim 1 , further comprising a second plurality of insulated vias extending between the front face and the rear face of the chip substrate, wherein, at the rear face, each via of the second plurality of insulated vias is connected to a second common conducting strip and wherein, on the front face, each via of the second plurality of insulated vias is separated from an associated conducting pad by a second associated region of dielectric.
3. The semiconductor chip according to claim 1 , wherein the common conducting strip includes a serpentine portion on rear face.
4. The semiconductor chip according to claim 1 , further comprising decoy conducting pads at the front face.
5. The semiconductor chip according to claim 1 , further comprising decoy conducting vias at the front face.
6. The semiconductor chip according to claim 1 , further comprising an insulating material uniformly covering the rear face of the chip substrate.
7. The semiconductor chip according to claim 1 , wherein each region of dielectric comprises silicon oxide.
8. The semiconductor chip according to claim 1 , wherein the common conducting strip comprises copper, titanium or aluminum.
9. The semiconductor chip according to claim 1 , further comprising a capacimeter coupled between a first conducting pad and a second conducting pad.
10. The semiconductor chip according to claim 9 , wherein the capacimeter comprises:
an inverter with an input and an output that is coupled to the first conducting pad;
a Schmitt-trigger flip-flop with an input coupled to the first conducting pad and an output coupled to the input of the inverter; and
a ground terminal coupled to the second conducting pad.
11. The semiconductor chip according to claim 1 , further comprising circuitry disposed at the front face, the circuitry configured to store or process confidential information.
12. A semiconductor chip comprising:
a chip substrate having a front face and a rear face opposite the front face, active circuitry being disposed at the front face;
a plurality of conducting pads including a first conducting pad and a second conducting pad;
a plurality of insulated vias extending between the front face and the rear face of the chip substrate, wherein, at the rear face, each via is connected to a common conducting strip and wherein, at the front face, each via is separated from an associated one of the conducting pads by a layer of an associated region of dielectric; and
means for measuring a capacitance between the first conducting pad and the second conducting pad, wherein the existence of a hack attempt can be determined when the measured capacitance is higher than a threshold capacitance value and wherein the absence of a hack attempt can be determined when the measured capacitance is lower than the threshold capacitance value.
13. The semiconductor chip according to claim 12 , further comprising circuitry disposed at the front face, the circuitry configured to store or process confidential information.
14. The semiconductor chip according to claim 12 , wherein the means for measuring the capacitance comprises a circuit comprising an inverter with an input and an output that is coupled to the first conducting pad and a Schmitt-trigger flip-flop with an input coupled to the first conducting pad and an output coupled to the input of the inverter.
15. A semiconductor chip comprising:
a chip substrate having a front face and a rear face opposite the front face, active circuitry being disposed at the front face;
a plurality of insulated vias extending between the front face and the rear face of the chip substrate, wherein, at the rear face, each via is connected to a common conducting strip and wherein, at the front face, each via is separated from an associated conducting pad by a layer of an associated region of dielectric; and
a capacimeter coupled between a first conducting pad and a second conducting pad.
16. The semiconductor chip according to claim 15 , wherein the capacimeter comprises:
an inverter with an input and an output that is coupled to the first conducting pad;
a Schmitt-trigger flip-flop with an input coupled to the first conducting pad and an output coupled to the input of the inverter; and
a ground terminal coupled to the second conducting pad.