Abstract:
An integrated circuit device is disclosed. The device includes an active film having a semiconducting material and an integrated circuit disposed on an active face of the active film. The integrated circuit includes a plurality of circuit elements. In addition, the device includes an additional film fixed to the active face of the active film, the additional film at least partially covering said integrated circuit, and an anti-fraud mechanism disposed within the additional film, the anti-fraud mechanism being positioned to align with one of the plurality of circuit elements. In some aspects, the additional film includes a protective sub-film and a sealing sub-film, wherein the protective sub-film is sealed to the active face of the active film by the sealing sub-film.

Description:
FIELD OF THE INVENTION 
     The present invention concerns integrated circuit devices comprising an active layer and an additional layer fixed to one active face of said active layer. The present invention further concerns cards provided with these devices, sections of a semiconducting material provided with a plurality of these devices, as well as methods for producing these devices. 
     BACKGROUND OF THE INVENTION 
     The above-mentioned integrated circuit devices are specifically described in the international applications published under the numbers WO-96/16378, WO-97/11442 and WO-99/12204. Other devices are described in the patent applications filed in France under the numbers FR-98/081305, FR-98/13029 and FR-99/00858 which have not been made available to the public on the date of priority of the present application. 
     These devices are intended to process or store confidential data so as to carrying out, for example, electronic transactions in the various fields, such as those concerning health, pre-paid television, telephone applications or banking. 
     To this effect, the devices include volatile and non-volatile memories of the ROM, RAM, EEPROM, Flash PROM or Ferromagnetic RAM type, as well as a central processing unit or CPU, which manages and distributes said confidential data by means of address and data buses. 
     In practice, the devices are integrated inside an electronic module and mounted inside a card body as defined in the standards ISO 7816 and 14443 or GSM 11.11 and 11.14. Moreover, contact blocks of the devices are connected to contact areas flush with the surface of the card body, or else to the contact terminals of an antenna embedded in the card body, which enables the cards to communicate with the outside world. Depending on their mode of operation, the cards are known as contact, non-contact or mixed cards. 
     By means of the devices of the invention, the protection of data stored or processed in the cards is improved. In fact, physical attacks tending to disassociate the additional layer and the active layer to obtain a non-destructive access to the integrated circuit are no longer possible. The same applies for certain embodiments of said devices concerning attacks known as attacks in light in which a focussed electromagnetic radiation disturbs the protective functioning of the chip. 
     However, other attacks may be used with some success against known devices. These are physical attacks carried out by the controlled destruction of the additional layer and in particular attacks by polishing or etching said layer. Owing to these attacks, fraudulent persons could. access the active face of an integrated circuit device without damaging said circuit, and then learn about the architecture of the circuit and possibly implement the previously prohibited attacks, such as attacks in light, so as to access the confidential data. 
     In the case of attacks by polishing, a rotating polishing plate is brought parallel to the plane of the additional layer. This plate erodes this layer in a controlled way until the level of the active face is reached. 
     In attacks by etching, various known methods can be implemented. This is in particular the case with the RIE method (Reactive Ion Etching) which is carried out by a dry process. According to this method, reactive chemical compound preparations are created inside an electrically neutral plasma then absorbed on the surface of the additional layer of a device where they form a molecular layer of chemical complexes. Ions highly accelerated in an electrostatic field are then directed perpendicular to the additional layer of the device and destroy the molecular chemical complex layer. The additional layer, or more specifically a portion of this layer, not including the openings intended to allow an electric connection to the contact blocks, is thus finally destroyed layer by layer up to the level of the active face. 
     SUMMARY OF THE INVENTION 
     Having regard to the foregoing, the invention seeks to resolve one particular problem, namely to protect the integrated circuit devices comprising one active layer including a semiconducting material, a circuit integrated with one active face of said active layer, said integrated circuit comprising circuit elements and at least one contact block flush with said active face, and an additional layer fixed to said active face, said additional layer covering at least partially said integrated circuit of said active face against attacks via a controlled destruction of said additional face. 
     With regard to the above-mentioned problem, the solution of the invention aims to provide a device characterised in that a hole is provided in the additional layer, said hole being situated plumb with at least one circuit element. 
     Thus, destruction of the additional layer can no longer be controlled and the circuit element situated plumb with the hole is destroyed. 
     In addition, the object of the invention is also to produce a card body equipped with a device conforming to the invention, a section of a semiconducting material fitted with a plurality of devices according to the invention, as well as a method for producing said device. 
     The following description, which is in no way restrictive, shall make it possible to understand how the invention can be put into practice. This description is given with reference to the accompanying drawings on which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a device conforming to the invention whose connection blocks are connected to conducting wires; 
     FIG. 2 shows an exploded cross sectional view of a first embodiment variant of a device according to the invention; 
     FIG. 3 shows an exploded cross sectional view of a second embodiment variant of device according to the invention; 
     FIG. 4 shows an exploded cross sectional view of a third embodiment variant of a device according to the invention; 
     FIG. 5 shows an exploded cross sectional view of a fourth embodiment variant of a device of the invention; 
     FIG. 6 shows an exploded cross sectional view of a fifth embodiment variant of a device of the invention; 
     FIG. 7 shows an exploded cross sectional view of a sixth embodiment variant of a device according to the invention; 
     FIG. 8 shows an exploded cross sectional view of a seventh embodiment variant of a device according to the invention, and 
     FIG. 9 shows a perspective view of the production of a semiconductor wafer fitted with a plurality of devices according to the invention. 
    
    
     DETAILED DESCRIPTION 
     As shown on FIG. 1, an integrated circuit device  1  conforming to the invention comprises an active layer  2  and an additional layer  3 , said layers  2  and  3  being superimposed. Said device  1  is approximately a parallelepiped and rectangle with a thickness of about 200 μm and a side dimension of 2 mm. 
     The active layer  2  is advantageously thinned and has an approximately constant thickness of between 10 and 80 μm, for example about 50 μm. It comprises a base sub-layer formed of a semiconducting material, particularly silicon, and an active sub-layer integrated with a circuit. The surface of the active sub-layer constitutes the active face  4  of the device. This active face  4  shows contact blocks  5 , for example five in number. It also shows various circuit elements and in particular volatile and non-volatile RAM, ROM, EEPROM, Flash PROM or ferromagnetic RAM memories, a central processing unit CPU, as well as address and data bus lines. As regards the present invention, the contact blocks  5  are not circuit elements. 
     The additional layer  3  has an approximately constant thickness of about 150 μm. It is comprised of a sealing sub-layer  6  and a protective sub-layer  7 . 
     The sealing sub-layer  6  is formed of an insulating material, for example a polyimide, for sealing the protective sub-layer  7  onto the active face  4  of the active layer  2 . The thickness of this sub-layer  6  is approximately constant and about 10 μm. 
     The protective sub-layer  7  is formed of a semiconducting material, for example a monocrystalline silicon, and possibly comprises active elements, such as a capacitor, or passive elements, such as chemical particles used to prevent attacks in light, regardless of the wavelength used. The thickness of this sub-layer  7  is approximately constant and about 140 μm. 
     Moreover, the additional layer  3  is pierced with openings  8  opening plumb with contact blocks  5 . These openings  8  are used to allow the electrical connection of the blocks  5  to antenna terminals and/or to contact areas of an electronic device and in particular a microchip card intended to receive the device. FIG. 1 shows the connection means by wires  9 . 
     According to the invention, the additional layer  3  further comprises one or several holes  20 ,  21 ,  22 ,  23 . These holes are plumb with one or several circuit elements. They are advantageously non-opening in the sense that they do not constitute traversing openings in the additional layer  3 . Because of this, a fraudulent person cannot carry out an attack in light directed onto the circuit elements plumb with the hole. In certain embodiments methods of the invention, the non-opening holes are dummy holes in the sense that open onto one of the faces of the additional layer. In other embodiments of the invention, the non-opening holes are not dummy holes and thus form a cavity in the additional layer  3 . The configuration of the holes can be any, for example cylindrical, with a rectangular or square section or conical with a rectangular or square section and possibly with a truncated base. Their section at the level of the top face of the additional layer  3  defines an area of about 100 μm2 and their depth is greater than or equal to the thickness of the sealing layer  6 , that is greater than or equal to a value of 10 μm. 
     FIGS. 2 to  8  show various embodiments of a device conforming to the invention in which for reasons of simplicity for visualising the holes the active  2  and additional  3  [films] layers are severed. 
     In the embodiment of FIG. 2, a straight cylindrical hole  20  is fitted in the sealing sub-layer  6 . This hole  20  is non-opening and dummy in the additional layer  3 . However, it traverses the sealing sub-layer  6  and is associated on the active face  4  of the active layer  2 . 
     In the embodiment of FIG. 3, a pyramidal hole  21  is fitted in the protective sub-layer  7 . This hole  21  is non-opening and dummy in said sub-layer  7  and a fortiori in the additional layer  3 . It opens on the face of the additional layer  3  opposite the active face  4  of the active layer  2 . 
     In the embodiment of FIG. 4, a hole  21  of the type shown on FIG. 3 is fitted in the protective sub-layer  7 . This hole  21  is situated plumb with a hole  20  similar to the one shown on FIG.  2  and in correspondence with said hole  21 . 
     In the embodiment of FIG. 5, a pyramidal hole  22  is fitted in the protective sub-layer  7 . This hole  22  is non-opening and forms a cavity in the additional layer  3 . This cavity is formed in the protective layer  7 . It is limited by the sealing sub-layer  6 . 
     In the embodiment shown on FIG. 6, a hole  22  similar to the one shown on FIG. 5 is situated plumb and in correspondence with a hole  20  fitted in the sealing sub-layer  6  and similar to the hole shown on FIG.  2 . All the holes  20 ,  22  form a dummy non-opening hole in the additional layer  3 . 
     In the embodiment of FIG. 7, a non-opening hole  23  is fitted in the additional sub-layer  7 . This hole  23  is conical and is truncated at its base. It defines a cavity housing a particle  24  with a hardness advantageously greater than or equal to the hardness of the active sub-layer of the active layer  2 . This particle  24  may be a spherical micro-ball whose dimensions are adjusted so that the walls of the hole  23  block said particle  24 . 
     In the embodiment of FIG. 8, a hole  23  of the type shown on FIG. 7 is situated plumb and in correspondence with a hole  20  similar to the one shown on FIG.  2 . The set of holes  20  and  23  forms a non-opening dummy hole in the additional layer  3  whose opening opens on the active face of the active layer  2 . In this case, the particle  24  advantageously more voluminous than the particle  24  shown on FIG.  7 . In fact, in the embodiment shown on FIG. 8, the particle  24  in this instance is directly in contact with the circuit element above which it projects. 
     Thus, should a fraudulent person try for example to access the integrated circuit of a device conforming to the invention and of the type shown on FIG. 2 by means of a RIE attack, the circuit elements situated plumb with the hole  20  would be destroyed. In fact, the RIE attack proceeds molecular layer by molecular layer and parallel to a plane, namely the plane of the additional layer  3 . Also, when the level of the sealing sub-layer  6  is reached, chemical complexes are formed at the level of the hole  20  with the circuit elements. These complexes are also destroyed by ionic bombardment without a fraudulent person being able to stop this destruction. Finally, it is not possible to obtain secrets kept in the circuit. 
     However, it shall be noted that, when a device  1  conforming to the invention is fitted with holes of the type  20 ,  22  or  23 , that is non-visible on the surface of the additional layer  3 , the fraudulent person does not initially know if the device comprises a hole and where it is situated and thus unable to avoid the circuit elements being destroyed. 
     On the other hand, it shall be noted that, should the hole comprise a particle similar to the particle  24  and should the fraudulent person start polishing, the polishing rotating plate pushes the micro-particle back against the active face and this micro-particle, whose hardness is greater than or equal to that of the active sub-layer, destroys the circuit element above which it projects, namely the active layer  2  rendering the circuit unusable for obtaining the secrets it contains. 
     Moreover, so as to produce devices  1  conforming to the invention, sections of semi-conducting material know as wafers are used. 
     The top portion of FIG. 9 shows a conventional wafer  30  equipped with a several hundreds or indeed thousands of integrated circuits  31 . The lower portion of said figure shows a silicon section  32 . This silicon section  32  is intended to be sealed to the wafer  30  by a polyimide thickness represented in the form of an intermediate section  33  between the wafer  30  and the section  32 . 
     In practice, the section  32  is etched with a large number of non-opening openings not visible on the drawings for forming the openings  8  of the devices  1  and non-opening holes conforming to the invention. 
     On the other hand, a polyimide precursor thickness in a non-polymerized form is applied to the surface of the integrated circuits  31  of the conventional wafer  30  previously coated with an adherence promoter. The wafer  30  and the superimposed polyimide precursor thickness  33  are heated to a temperature of about 80° C. so that the polyimide precursor adheres sufficiently to the wafer. Holes similar to said holes  20 , as well as openings permitting an electrical connection of the blocks are then fitted by etching in the precursor thickness  33 . 
     It then suffices to mount said wafer and said polyimide precursor thickness on the section  32  and subject these new elements to pressure and temperature cycles so that the polyimide is polymerised with sealing of these elements so as to obtain a semiconducting material fitted with a plurality of devices  1  conforming to the invention. 
     In the case where particles  24  are added in the holes  23 , said particles  24  are for example deposited on the section  32  kept approximately horizontal. These particles then fall by gravity into the holes  23 . The set formed by the conventional wafer and the precursor is then vertically mounted on the section  32  in the way shown on FIG.  9 . 
     Once sealed, the set is thinned by micro-machining and the devices  1  of the invention are cut and successively detached and mounted inside a known type of module of the prior art, this module being inserted into a card body so as to obtain a protected microchip card conforming to the invention or a portable object of the microchip card type. 
     It shall be noted that the holes are advantageously placed at locations differing from one integrated circuit to another of a given semiconducting section and are advantageously large in number and of different types so that a fraudulent person cannot know in advance their number and localisation.