Apparatus for detection of attacks on a circuit chip

Field of the Invention

p0001The present invention relates to a device for detecting attacks by making contact of an integrated circuit. This type of attack is usually called "intrusion attack" and involves applying conductive tips directly to areas of the integrated circuit to collect signals. In an integrated circuit, the active layers contain processing circuits of information that may be confidential, such as in chip credit cards or access control chips in the pay-TV applications.

Discussion of the prior art

p0002To protect the circuits in the active area of ​​unauthorized intrusion, it is known to use a screen covering the entire surface of the circuit or part thereof. This screen is generally formed of one or more conductive paths formed in one or more upper levels of metallization in the active area to protect.

p0003The purpose of these conductor paths is to detect a break in continuity or change their electrical properties, for example strength and ability. These conductive paths traverse the entire surface or only an area of ​​the circuit to be protected in an irregular and random. If a "hacker" attempts to cross the metallization level containing the path, by introducing one or more points, a detection circuit is supposed to detect a break in the conductive path.

p0004A disadvantage of such a solution is that it does not detect the removal of insulating layers covering the conductor path. Once the conductive path is exposed, a "pirate" could double this conductive path by an outside section to simulate electrical continuity. The conductive path may be interrupted without this being detected.

summary

p0005The invention aims to improve the detection of intrusion attacks on an integrated circuit by detecting the removal of insulating layers covering the integrated circuit.

p0006Thus, one embodiment of the present invention provides an integrated circuit comprising an intrusion attack detection device. The device comprises a single piece made of a conductive material and surrounded by an insulating material and comprising at least one elongated conductive strip under tension or under compression, connected to a movable member, at least a distance of said workpiece conductive portion and a detection circuit of an electrical connection between the part and the conductive portion. This results in a variation of the length of said track, in an attack by removing the insulating material, resulting in a displacement of the movable member to come into contact with the conductive portion.

p0007According to an exemplary embodiment of the invention the solid part comprises a first bar extending along a first direction, a second bar extending along a second direction inclined with respect to the first direction and connected to a first side face of the first bar at a first junction area and a third rod extending in a third direction inclined with respect to the first direction and connected to a second lateral face of the first rod, opposite the first lateral face, to at a second junction region, the first and second junction regions being offset in the first direction. The at least one conductive portion is away from the first, second and third bars and disposed vis-a-vis of the first or second side face. This results in a variation in the length of the second and third bars in the attack by removing the insulating material, resulting in pivoting of the first bar to come into contact with the conductive portion.

p0008According to an exemplary embodiment of the invention, the first bar includes first and second ends. The conductive portion is arranged vis-a-vis of the first side face, at the first end, the circuit comprising a further conductive portion disposed vis-a-vis to the second side face at a distance from the first, second and third bars, at the second end. This results in a variation in the length of the second and third bars in the attack by removing the insulating material, resulting in pivoting of the first bar so that the first end comes into contact with the conductive portion and the second end comes in contact with the additional conductive portion.

p0009According to an exemplary embodiment of the invention, the second bar is extended by a first track of the most important section of conductive material and the third bar is extended by a second track of the most important section of conductive material.

p0010According to an exemplary embodiment of the invention, the second and third bars belong to a conductive path.

p0011According to an exemplary embodiment of the invention, the section of the second bar decreases at the first junction area and the section of the third bar decreases at the second junction area.

p0012According to an exemplary embodiment of the invention, the first bar includes a bevelled face adapted to abut against the conductive portion during pivoting of the first bar.

p0013According to an exemplary embodiment of the invention, the second and third directions are mutually parallel and perpendicular to the first direction.

p0014An exemplary embodiment of the present invention also provides a method of fabricating an integrated circuit including a drive detection device contact, comprising the steps of forming a unitary element made of a conductive material and surrounded by an insulating material and having at least one elongated conductive track connected to a movable member, at least one remote conductive portion of said workpiece and a detection circuit for establishing an electrical connection between the part and the conductive portion and performing annealing. This results in occurrence of tensile stress or compression in said conductive track and a variation of the length of said track during an attack by removing the insulating material, resulting in a displacement of the movable member to come into contact of the conductive portion.

Brief Description of Drawings

p0015These objects, features and advantages, and others will be discussed in detail in the following description of specific embodiments in non-limiting in connection with the accompanying drawings:<ul><li>the <figref idrefs="f0001">figure 1</figref> is intended to show the state of the art;</li><li>the <figref idrefs="f0001">2</figref> is a schematic top view of a device for detecting attacks by making contact of an integrated circuit according to an exemplary embodiment of the invention;</li><li>the <figref idrefs="f0002">3</figref> is a schematic section of the detection device of the <figref idrefs="f0001">2</figref> ; </li><li>the <figref idrefs="f0002">4</figref> is a section similar to <figref idrefs="f0002">3</figref> illustrating the principle of an attack by contact;</li><li>the <figref idrefs="f0002">5</figref> is a view similar to <figref idrefs="f0001">2</figref> illustrating the operation of the detection device according to the present embodiment of the invention during an attack by contact;</li><li>the <figref idrefs="f0003">6</figref> shows the variation of an operating parameter of the detection device of the <figref idrefs="f0001">2</figref> according to a characteristic dimension of the detection device; and</li><li>the <figref idrefs="f0003">Figures 7 and 8</figref> are top views of sensing devices of detail according to other embodiments of the invention.</li></ul>

detailed description

p0016For clarity, the same elements have been designated with the same references in the different drawings and, further, as usual in the representation of integrated circuits, the various drawings are not drawn to scale. In the following description, it is considered an integrated circuit comprising a substrate (e.g. a bulk semiconductor substrate, a substrate of silicon on insulator type (SOI), etc.) coated with a stack of layers of an insulating material at which there are provided metal tracks of different metallization levels. The metal tracks of a given level of metallization may be disposed on the surface of an insulating layer or formed in an insulating layer and flush with the surface thereof. Called metal tracks of the last metallization level, or upper metallization level, the outermost metal tracks of the substrate. The metal tracks of the last metallization level are covered with an insulating layer, generally called passivation layer.

p0017According to an exemplary embodiment of the present invention, a device for detecting the removal of an insulating layer covering the metal tracks of a given level of metallization is formed, at least in part, by metal tracks of the given metallization level. Advantageously, according to an exemplary embodiment of the invention, the metal traces forming the detection device may also belong to a conductive path of a protective screen. An embodiment of the invention is based on the fact that a conventional method of manufacturing an integrated circuit leads to the appearance of tensile stresses in the metal tracks of the various metallization levels. This is due to the fact that annealing is generally carried out once the metal tracks and the insulating layers are formed. Annealing causes grain growth of metal tracks and a decrease in the density of grain boundaries. This results in the occurrence of tensile stresses in the metal tracks as the insulating material surrounding forced to keep their shape. The removal of the insulating material surrounding metal tracks leads to stress relief in these tracks. An embodiment of the invention provides a device for detecting the removal of insulating material during an attack by intrusion. The device comprises a mechanical switch having a movable part which is moved during the release of the constraints to make electrical contact. The establishment of the electrical contact is detected and is representative of the shrinkage of the insulating material.

p0018The <figref idrefs="f0001">figure 1</figref> is a perspective view of an integrated circuit provided in a conventional manner, a protective screen. The circuit includes a substrate S coated with a stack of insulating layers which are associated with different levels of metallization M1 ... Ms. A conductive path L defined by the terminals V and W is formed in one of these levels, for example the upper metallization level Ms. L The conductive path is connected at its ends to a circuit, not shown, adapted to detect an interruption of the conductive path L.

p0019The <figref idrefs="f0001">2</figref> shows a detection device 5 according to an exemplary embodiment of the invention. The device 5 comprises a mechanical switch 10 connected to a detection circuit C (Detection Circuit). More specifically, the<figref idrefs="f0001">2</figref> is a partial and schematic top view of metal tracks of a same metallization level of an integrated circuit forming the switch 10 according to an exemplary embodiment of the invention, the detection circuit C is shown schematically by a block. The switch 10 may be duplicated in multiple locations at a same metallization level. It can further be duplicated in multiple locations in different metallization levels within an integrated circuit.

p0020The switch 10 is formed at a conductive path L comprising first and second metal traces 12, 14. It comprises an arm 16 corresponding to a metal track of length L1, of ℓ1 width and extending along a central axis Δ1 straight. The arm 16 extends the track 12 and a lower section than the section of the track 12. The switch 10 further comprises an arm 18 corresponding to a metal track of length L2, of ℓ2 width and extending along a straight central axis Δ2. The arm 18 extends the track 14 and has a bottom section to the section of the track 14. The Δ1 and Δ2 axes are, for example, parallel. In the present embodiment, arms 16, 18 have a substantially constant section.

p0021Switch 10 further comprises a bar 20 corresponding to a metal track having a length L3, a width ℓ3 and extending according to a rectilinear central axis perpendicular to the Δ3 Δ2 Δ1 and axes. Bar 20 comprises a central portion 22 and two free ends 23, 24. The central portion 22 comprises two side faces 25, 26 opposing. Switch 10 is symmetrical about a plane of symmetry P which corresponds to the plane perpendicular to the axis Δ3 equidistant from ends 23 and 24. We call Y the point of intersection between the plane P and the axis Δ3. We call P the plane perpendicular to axes Δ1 and Δ2 and Δ3 containing the axis. At the opposite end to the track 12, the arm 16 is connected to the face 25 of the central portion 22 at a junction region 27 and at the opposite end to the conductor track 14, the arm 18 is connected to the face 26 of the central portion 22 at a junction region 28. the arms 16, 18 are therefore arranged on either side of the bar 20. in addition, arms 16, 18 are located either side of the plane P. the term ec spacing distance, measured in the direction Δ3, between the middle of the joint zone 27 and the middle of the junction region 28, that is to say, in the present embodiment, between the axes Δ1 and Δ2.

p0022Switch 10 further comprises, metallic tracks 29, 30. The track 29 is disposed on the same side of the bar 20 the arm 16 and extends in vis-a-vis of part of the face 25 the central portion 22 near the end 23. the track 30 is disposed on the same side of the bar 20 the arm 18 and extends in vis-a-vis of part of the face 26 of the portion center 22 of the end side 24. the tracks 29 and 30 are connected to the circuit C which is adapted to detect if these tracks 29, 30 are electrically connected to each other.

p0023In the embodiment shown in <figref idrefs="f0001">2</figref>, Arms 16, 18, slopes 12, 14 and the bar 20 are made in one piece.

p0024The <figref idrefs="f0002">3</figref> represents a partial and schematic section of the switch 10 along line. The switch 10 is made at the level of an integrated circuit 31 comprising a semiconductor substrate 32, for example silicon, covered with a stack of insulating layers at which are disposed metallic tracks of different metallization levels. For example, there is shown the metal tracks 34, 36 of the Ms-1 metallization level flush with the surface of an insulating layer 38. It was further shown an insulating layer 40 covering the insulating layer 38 and the metal tracks 36 and 34. the metal tracks of the metallization level Ms 20, 29 extend on the insulating layer 40. for example, the metal tracks 34, 36 are made of copper and the metal tracks 20, 29 are in Aluminium. An insulating layer 46, called passivation layer, overlies the metal tracks 20, 29 and the insulating layer 40. The layers 40, 46 are made of a same insulating material, for example silicon oxide.

p0025The manufacturing process of the integrated circuit 31 includes an annealing step after formation of the insulating layer 46 covering the metal tracks 20, 29, heating the assembly of the integrated circuit 31 to a temperature, for example of the order of a few hundreds of degrees, for example 400 ° C, for several tens of minutes, for example 50 minutes. The annealing step causes an increase in the size of the metal grains of the metal tracks, in particular of metal grains in the arms 16, 18 by reducing the density of grain boundaries. This increase in grain size leads to the appearance of tensile stresses in the metal grains of the arms 16, 18. These tensile stresses can not loosen due to the presence of the insulating layers 40, 46 surrounding the arms 16 18 and force them to retain their original forms.

p0026The <figref idrefs="f0002">4</figref> is a view similar to <figref idrefs="f0002">3</figref> and illustrates the principle of an attack by contact. Such an attack involves an initial step of etching an opening 50 on the surface of the integrated circuit 31 where one wishes to achieve the leads. The opening 50 is made by etching the insulating layer 46. As the insulating layers 40 and 46 consist of the same insulating material, it is not possible to accurately control the depth of the opening 50. If the attack is formed in the region of the integrated circuit 31 where the switch 10, for example, in order to double the conductive path L, the opening 50 will penetrate at least partially into the insulating layer 40. After completion of the opening 50, the bar 20 is fully open and arms 16 and 18 are at least partially cleared.

p0027Removing the insulating material surrounding the arms 16, 18 results in a relaxation of tension stresses in the arms 16, 18, that is to say a decrease in lengths L1 and L2. As the arms 16, 18 are anchored at one end to the tracks 12, 14, their shortening causes a pivoting of the bar 20 around the center O, the axis Δ3 remaining substantially in a plane perpendicular to the plane P. The pivoting of the bar 20 is sufficient for it contacts metal tracks 29, 30.

p0028The <figref idrefs="f0002">5</figref> is a detail view of the <figref idrefs="f0001">2</figref> which represents the state of the switch 10 after the etching of the opening 50. The arms 16 and 18 not being in the extension of one another, their shortening led to a pivoting bar 20. there may also be a slight deformation of the arms 16, 18 by buckling. deflection called D of the bar 20 the distance between the edge of the end 24 closest to the plane P 'and the plane P' after stress relief.

p0029The detection circuit C connected to the tracks 29, 30 detects the contact of the bar 20 with the metal tracks 29, 30. This can be interpreted as corresponding to a first contact by etching and may cause failure of the operation of IC 31.

p0030The <figref idrefs="f0003">6</figref> shows an example curve 51 of evolution, depending on the spacing ec, the clearance D is observed in the absence of the tracks 29, 30. The curve 51 is obtained for a switch 10 to which lengths L1 , L2 and L3 are equal to 100 microns, where the width ℓ1, ℓ2, ℓ3 are equal to 2 microns and wherein the thickness of the metal tracks of the metallization level Ms is, for example, of the order of 0, 3 microns. It is desirable that the clearance D of bar 20 is as large as possible to ensure that a contact will always be between 20 and bar metal tracks 29, 30 in case of attack. In the example mentioned above, a D displacement of the order of 4.5 .mu.m is obtained for a ec spacing of the order of 4 microns.

p0031In the present embodiment, the switch 10 is formed at a conductive path L belonging to a protective screen. The arms 16, 18 and the bar 20 electrically connect the tracks 12, 14 therebetween. The tracks 12 and 14 are connected to a circuit adapted to detect an interruption of the conductive path L. This provides additional protection in addition to the protection conferred by the switch 10. In an alternative embodiment, only the metal track 29 is present . In this case, a circuit is adapted to detect whether an electrical contact is established between the metal track 29 and one of the tracks 12 or 14. According to another variant, the tracks 29 and 30 may correspond to metal pads. This may be advantageous when several switches 10 are adjacently disposed.

p0032The <figref idrefs="f0003">7</figref> shows a detailed view of a switch 52 according to another embodiment of the invention. The switch 52 has the same structure as the switch 10 with the difference that the arm 16 comprises, at the end connected to the bar 20, a portion 54 whose section decreases such that the junction zone 27 has a reduced cross section, of width ℓ4, relative to the arm 16. Similarly, the arm 18 comprises, at the end connected to the bar 20, a portion 56 whose section decreases such that the junction zone 28 has a reduced cross section, of width ℓ5, relative to the arm 18. the junction areas 27, 28 of the switch 52 are deformed more easily during the pivoting of the bar 20 that the connecting areas 27, 28 of the switch 10 which have a larger cross section. This allows for the same distance D to obtain a larger displacement than when the arms 16, 18 are of constant section. For example, for a switch 52 for which the lengths L1, L2 and L3 are equal to 100 microns, where the width ℓ1, ℓ2, ℓ3 are equal to 2 microns, wherein the thickness of the metal tracks of the level metallization Ms is of the order of 0.3 microns, and wherein the width ℓ4 and ℓ5 are of the order of 0.2 microns, one obtains a displacement D, in the absence of tracks 29, 30, of the order of 10 .mu.m to a ec spacing of the order of 4 microns.

p0033Generally, the shape of the junction areas 27, 28 is determined to allow obtaining the greatest possible clearance D of bar 20 in the absence of the tracks 29, 30 while maintaining sufficient mechanical strength of the switch 10. in one example, each junction zone 27, 28 may have, in a plane perpendicular to the plane P, the shape of a funnel. In another example, each junction area 27, 28 may comprise through openings.

p0034The <figref idrefs="f0003">8</figref> represents a switch 60 according to another embodiment of the invention. The switch 60 comprises, at each end 23 of the bar 20, a bevelled face 62 which is oriented so that, during the pivoting of the bar 20, the bevelled face 62 comes into abutment against the metal track 29. This allows improve the contact between the metal track 20 and 29 bar.

p0035In the examples of embodiments described above, the switch 10, 52, 60 is constituted by portions of conductive material in which appear tensile stresses during the annealing step of the integrated circuit manufacturing process. Alternatively, the switch may be made of pieces of a conductive material in which appear the compressive stresses during the annealing step. This is, for example, a semiconductor material such as polycrystalline silicon. Therefore, upon release of the stresses, the arms 16, 18 of the switch tend to lengthen. In this case, with respect to the switch 10 shown in<figref idrefs="f0001">2</figref>The arm 16 is disposed to the right of the plane P and the arm 18 is disposed to the left of the plane P so that the bar 20 pivots in the right direction when releasing the constraints to ensure the electrical connection between the metal tracks 29, thirty.

p0036particular embodiments of the present invention have been described. Various changes and modifications apparent to those skilled in the art. In particular, in the embodiments described above, the switch 10 has a symmetrical shape. However, this may not be the case. In addition, in the embodiments described above, the arms 16, 18 and the bar 20 have front pivot rectilinear shapes. However, arms 16, 18 and the bar 20 may have, before pivoting, curved shapes.