Device for detecting an attack in an integrated circuit chip
An integrated circuit chip including a plurality of parallel wells of alternated conductivity types formed in the upper portion of a semiconductor substrate of a first conductivity type, and a device of protection against attacks including: between the wells, trenches with insulated walls filled with a conductive material, said trenches extending from the upper surface of the wells to the substrate; and a circuit capable of detecting a modification of the stray capacitance formed between said conductive material and a region of the chip.
1. An integrated circuit chip, comprising:
first and second wells, of first and second conductivity types, respectively, formed in an upper portion of a semiconductor substrate of the first conductivity type; and
a protection device configured to protect the integrated circuit chip against attacks and including:
between the wells, a trench with insulated walls and filled with a conductive material, the trench extending from upper surfaces of the wells to a lower portion of the substrate below the wells; and
a stray capacitance modification detector configured to detect a modification of a stray capacitance between said conductive material and a region of the chip.
2. The chip of claim 1 , wherein said region is configured so that the stray capacitance is modified when the substrate is locally etched from a back side of the substrate.
3. The chip of claim 1 , further comprising a layer of the second conductivity type, extending under said plurality of wells, between the wells and the lower portion of the substrate.
4. The chip of claim 1 , wherein the trench has a depth greater than 2 μm.
5. The chip of claim 1 , wherein the conductive material is polysilicon.
6. The chip of claim 1 , wherein said stray capacitance modification detector comprises an oscillator having a resonance frequency depending on a value of said stray capacitance, and a comparator configured to compare said resonance frequency with a reference value.
7. The chip of claim 1 , wherein said region is the lower portion of the substrate.
8. The chip of claim 1 , wherein said region is a bias contact region of the first well.
9. The chip of claim 1 , comprising:
a first plurality of MOS transistors each having a channel of the second conductivity type formed in the first well; and
a second plurality of MOS transistors each having a channel of the first conductivity type formed in the second well, the MOS transistors of second plurality being inverter-connected with corresponding MOS transistors of the first plurality.
10. A method of forming an integrated circuit chip, comprising:
forming first and second wells, of first and second conductivity types, respectively, in an upper portion of a semiconductor substrate of the first conductivity type; and
forming a protection device configured to protect the integrated circuit chip against attacks and including:
forming, between the wells, a trench with insulated walls and filled with a conductive material, the trench extending from upper surfaces of the wells to a lower portion of the substrate below the wells; and
forming a stray capacitance modification detector configured to detect a modification of a stray capacitance between said conductive material and a region of the chip.
11. The method of claim 10 , wherein said region is configured so that the stray capacitance is modified when the substrate is locally etched from a back side of the substrate.
12. The method of claim 10 , further comprising forming a layer of the second conductivity type, extending under said plurality of wells, between the wells and the lower portion of the substrate.
13. The method of claim 10 , wherein forming said stray capacitance modification detector comprises forming an oscillator having a resonance frequency depending on a value of said stray capacitance, and a comparator configured to compare said resonance frequency with a reference value.
14. The method of claim 10 , wherein said region is the lower portion of the substrate.
15. The method of claim 10 , comprising:
forming a first plurality of MOS transistors each having a channel of the second conductivity type formed in the first well; and
forming a second plurality of MOS transistors each having a channel of the first conductivity type formed in the second well, the MOS transistors of second plurality being inverter-connected with corresponding MOS transistors of the first plurality.
16. A method of protecting an integrated circuit chip, comprising:
detecting a modification of a stray capacitance between a conductive material and a region of the chip, the chip including first and second wells, of first and second conductivity types, respectively, in an upper portion of a semiconductor substrate of the first conductivity type; a trench with insulated walls and filled with a conductive material, the trench extending between the wells from upper surfaces of the wells to a lower portion of the substrate below the wells; and
disabling the chip in response to detecting the modification of the stray capacitance.
17. The method of claim 16 , wherein the detecting includes detecting the modification of the stray capacitance in response to the substrate being locally etched from a back side of the substrate.
18. The method of claim 16 , wherein the detecting includes detecting a change in a resonance frequency of an oscillator having a terminal coupled to the conductive material filling the trench, the resonance frequency depending on a value of said stray capacitance.
19. The method of claim 18 , wherein detecting the change in the resonance frequency includes using a counter to detect the resonance frequency, and comparing the resonance frequency detected by the counter to a stored value corresponding to a desired resonance frequency of the oscillator.