Abstract:
A method of comparing micro-electronic devices. The method includes: placing a first micro-electronic device in a sample chamber of a magnetic resonance imaging machine, subjecting the first micro-electronic device to a magnetic field and a radio frequency pulse, turning off or adjusting the magnetic field and detecting a first returned RF pulse from the first micro-electronic device and storing first data relating to the first returned RF pulse; placing a second micro-electronic device in the sample chamber, subjecting the second micro-electronic device to the magnetic field and the radio frequency pulse, turning off or adjusting the magnetic field and detecting a second returned RF pulse from the second micro-electronic device and storing second data relating to the second returned RF pulse; and comparing the first data to the second data and determining if the second micro-electronic device is essentially identical to the first micro-electronic device based on the comparing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of integrated circuits; more specifically, it relates to a system and methods for comparison and validation of integrated circuits using magnetic resonance imaging. 
       BACKGROUND OF THE INVENTION 
       [0002]    Integrated circuits are enormously complex structures which may contain millions of transistors and thousands of circuits. There is always a possibility that unauthorized circuits may have been inserted into integrated circuit chips during manufacture. These unauthorized circuits can, for example, cause circuit malfunctions, cause leakages of confidential data or extrusion of other information that the integrated circuit chip is processing or generating. Because of the complexity noted earlier, it is very difficult to determine if any given integrated circuit chip contains unauthorized circuits. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove. 
       SUMMARY OF THE INVENTION 
       [0003]    A first aspect of the present invention is a method, comprising: (a) placing a first micro-electronic device in a sample chamber of a magnetic resonance imaging machine, subjecting the first micro-electronic device to a static magnetic field and a radio frequency pulse, turning off or adjusting the static magnetic field and then detecting a first returned RF pulse from the first micro-electronic device and storing first data relating to the first returned RF pulse; after (a), (b) placing a second micro-electronic device in the sample chamber of the magnetic resonance imaging machine, subjecting the second micro-electronic device to the static magnetic field and the radio frequency pulse, turning off or adjusting the static magnetic field and then detecting a second returned RF pulse from the second micro-electronic device and storing second data relating to the second returned RF pulse; and (c) comparing the first data to the second data and determining if the second micro-electronic device is essentially identical to the first micro-electronic device based on the comparing. 
         [0004]    A second aspect of the present invention is a system, comprising: a magnetic resonance imaging machine having a magnet unit, a signal processing unit and a computer, the magnet unit including a sample chamber; means for (i) subjecting micro-electronic devices placed in the sample chamber to a static magnetic field and a radio frequency pulse, (ii) turning off or adjusting the magnetic field and then (iii) detecting a returned RF pulses generated by the micro-electronic devices and (iv) storing data relating to the returned RF pulses in the computer; and means for comparing the data from a first micro-electronic device and second micro-electronic device and determining if the second micro-electronic device is essentially identical to the first micro-electronic device based on the comparing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0006]      FIG. 1  a diagram of an exemplary magnetic resonance inspection system according of the present invention; 
           [0007]      FIG. 2  is a cross-section through an exemplary first type of integrated circuit; 
           [0008]      FIG. 3  is a cross-section through an exemplary second type of integrated circuit; 
           [0009]      FIG. 4  is a top view of an exemplary integrated circuit chip for enhanced device comparison according embodiments of the present invention; 
           [0010]      FIG. 5  is a top view of an exemplary integrated circuit chip for preventing unauthorized comparison according embodiments of the present invention; 
           [0011]      FIG. 6A  is a cross-sectional view of an integrated circuit containing devices to flag an unauthorized comparison attempt according embodiments of the present invention; 
           [0012]      FIG. 6B  is a cross-sectional view of the integrated circuit of  FIG. 6A  after an unauthorized comparison attempt according embodiments of the present invention; 
           [0013]      FIG. 7  is a flowchart of methods of comparison according to embodiments of the present invention; 
           [0014]      FIGS. 8A and 8B  illustrate a first method of data analysis for comparison according to embodiments of the present invention; 
           [0015]      FIGS. 9A and 9B  illustrate a second method of data analysis for comparison according to embodiments of the present invention; 
           [0016]      FIGS. 10A ,  10 B and  10 C illustrate a third method of data analysis for comparison according to embodiments of the present invention; and 
           [0017]      FIGS. 11A ,  11 B and  11 C illustrate a fourth method of data analysis for comparison according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The term “integrated circuit” (IC) is defined as an integrated circuit chip and a package or module containing the IC. The term “integrated circuit chip” is defined as the semiconductor (e.g., silicon) die containing devices such as transistors, diodes, capacitors, resisters and inductors and the wiring layers built up on the die that interconnect the devices into circuits. The term micro-electronic device includes an IC or an integrated circuit chip. 
         [0019]    In magnetic resonance imaging (also called nuclear magnetic resonance (NMR) imaging)) a sample is positioned in a static magnetic field and subjected to a pulsed radio frequency (RF) signal to place the sample in an excited state. The magnetic field may be turned off or adjusted and a RF return signal is produced by the sample returning to a normal from the excited state is then recorded. In order to allow spatial encoding, the static magnetic field is superimposed with a gradient magnetic field. 
         [0020]    The term validation means the process by which an unknown micro-electronic device is “imaged” by NMR and the resulting data is compared to data from a known good or trusted micro-electronic that was NMR “imaged” and that the unknown IC micro-electronic device should be essentially identical (i.e., of identical design and within fabrication specification limits) to. Known good micro-electronic devices include those fabricated under secure conditions, those from trusted sources and those thoroughly tested and physically inspected after an NMR signature has been obtained. 
         [0021]      FIG. 1  is a diagram of an exemplary magnetic resonance inspection system according of the present invention. In  FIG. 1 , a magnetic resonance imaging (MRI) system  100  includes a magnet unit  105 , a signal processing unit  110  and a computer  115 . Magnet unit  105  of MRI system  100  includes a gradient magnetic field coil  120 , a transmit coil  125 , a sample chamber  130 , a receive coil and a high gauss magnet  140  (e.g., a permanent magnet, coil magnet or super-conductive magnet). Signal processing unit  110  includes a driving circuit  145 , an RF power amplifier  150 , a preamplifier  155 , a sequence memory  160 , a modulation circuit  165 , an RF oscillator  170 , a phase detector  175  and an analog-to-digital (A/D) converter  180 . Computer  115  includes a display  185 , an input (e.g., a keyboard, mouse, disk drive) and an output (e.g., a display unit, a printer, a disk drive). Gradient magnetic field coil  120 , transmit coil  125 , receive coil  135  and high gauss magnet  140  are disposed so as to substantially surround sample chamber  130 . 
         [0022]    High gauss magnet  140  applies a static magnetic field having a constant strength to a sample in chamber  130 . Gradient magnetic field coil  120  applies gradient magnetic fields selectively to mutually orthogonal x, y and z directions (in imaging parlance, to a slice axis, phase axis and frequency axis). Transmit coil  125  supplies a pulsed RF signal for exciting spins of atomic nuclei within a micro-electronic device  200  in sample chamber  130 . Receive coil  135  detects returned RF signals from the sample in chamber  130  generated when spins of atomic nuclei within micro-electronic device  200  return to a normal state from an exited state. 
         [0023]    Gradient magnetic field coil  120 , transmit coil  125 , and receive coil  135  are operatively associated with driving circuit  145 , an RF power amplifier  150 , and a preamplifier  155 , respectively. Sequence memory  160  operates driving circuit  145  based on a stored pulse sequence in response to instructions from computer  115  to thereby apply gradient fields from gradient magnetic field coil  120  in specific directions. Sequence memory  160  also operates a modulation circuit  165  to modulate a carrier output signal from RF oscillator  170  into a pulsed RF signal of predefined timing and envelope shape. The pulsed RF signal is applied to RF power amplifier  150  and then the amplified pulsed RF signal is applied to transmit coil  125 . Preamplifier  155  amplifies the return RF signal from micro-electronic device  200  in sample chamber  130  detected at receive coil  135 . Preamplifier  155  amplifies the received RF signal and sends an amplified RF signal to phase detector  175 . Phase detector  175  generates an analog phase-detect signal from the amplified RF signal using a carrier output signal from RF oscillator  170  as a reference signal, and supplies the phase-detected signal to A/D converter  180 . A/D converter  180  converts the phase-detected analog signal into a digital signal, which is supplied to the computer  115 . 
         [0024]    Computer  115  reads and/or processes the data from A/D converter  1801 , and includes algorithms in the form of computer instructions which when executed perform various signal analyses and statistical analyses on the stored data as described infra. Results of these analyses may be displayed on output unit  195 . Computer  115  can also be responsible for overall control such as receiving information supplied from input  195  from an operator. 
         [0025]    MRI system  100  includes an optional tester  205 , which is connected between a socket, or probe card (not shown) in sample chamber  130  and computer  185 . This allows voltage bias, analog signals, digital data patterns or combinations thereof to be applied to micro-electronic device  200  during the MRI process. Biasing, applying signals and test patterns serves two purposes. First it results in more complex return RF signals. Second, if the biasing analog signals, digital data patterns are kept secure, it is very difficult for a an unauthorized party to place a masking circuit into an unauthorized micro electronic device, the purpose of the masking circuit being is to mask the presence of the unauthorized circuit and the masking circuit in the unauthorized micro-electronic device by altering the NMR image of the unauthorized micro-electronic device to mimic that of an authorized micro-electronic device. 
         [0026]    MRI system  100  shown in  FIG. 1  is provided as an example, and it will be understood that embodiments of the invention are not limited to MRI system  100  shown in  FIG. 1 . It will be understood that an MRI system  100  according to aspects of the invention can include additional components to those shown in  FIG. 1  or may not include every component shown in  FIG. 1 . 
         [0027]      FIG. 2  is a cross-section through an exemplary first type of integrated circuit. In  FIG. 2 , an IC  200 A includes an integrated circuit chip  210  physically and electrically connected to a module  215  by solder bumps  220 . Wires  225  in module  225  connect solder bumps  220  to solder balls  230 . Module  215  may be organic (e.g., fiberglass) or ceramic and wires  25  may comprise one or more wiring layers. Solder balls  230  are designed for surface mounting IC  200 A directly to a printed circuit board (PCB). Solder balls  230  may be replaced by solder columns. Solder balls  230  may be replaced with pins, which can be used to mount ICs into sockets, which are mounted on a PCB or mounted directly to a PCB. IC  200 A is thus an example of an IC that uses flip-chip (or C4) technology. 
         [0028]      FIG. 3  is a cross-section through an exemplary second type of integrated circuit. In  FIG. 3 , an IC  200 B includes and integrated circuit chip contained within a plastic package  240 . Wire bonds  245  electrically connect integrated circuit chip  235  to leads  250 . Leads  250  are designed for surface mounting IC  200 B directly to a PCB. Leads  250  may be replaced with pins, which can be used to mount ICs into sockets, which are mounted on a PCB or mounted directly to a PCB. The leads on some plastic packages are designed to be mounted in sockets on a PCB. IC  200 B is thus an example of plastic packaging technology. 
         [0029]      FIG. 4  is a top view of an exemplary integrated circuit chip for enhanced comparison according embodiments of the present invention. In  FIG. 4 , an exemplary integrated circuit chip  255  includes regions  260 A,  260 B,  260 C,  260 D,  260 E,  260 F,  260 G,  260 H,  2601 ,  269 J and  260 K. There may be more or less regions than illustrated in  FIG. 4 . These regions often correspond to cores, which are pre-designed circuit functions. For example, a microprocessor may contain multiple processing cores, memory cores, arithmetic cores etc. Formed, by way of example, in cores  260 B,  260 G,  2601  and  260 J are serpentine signal enhancing structures  265  which are not electrically connected to any wire or device (e.g., transistor, diode, resistor, capacitor or inductor) of integrated circuit chip  255 . Signal enhancing structures  265  may comprise an electrical conductor, a magnetic material, or an electrically conductive magnetic material. Signal enhancing structures  265  are designed to interact with the magnetic fields from gradient magnetic field coil  120  and high gauss magnet  140  of MRI system  100  (see  FIG. 1 ) to generate a more complex return RF signal. 
         [0030]      FIG. 5  is a top view of an exemplary integrated circuit chip for preventing or detecting comparison according embodiments of the present invention. In  FIG. 5 , an integrated circuit chip  255 A (similar to integrated circuit chip  255  of  FIG. 4 ) includes s serpentine structure  265 A connected to a destruct circuit  270 . Serpentine structure  265 A acts as an inductor which generates a current when subjected to a varying magnetic field. The current may be used by destruct circuit  270  to program fuses or activate transistors to render integrated circuit  155 A inoperable or to leave a signature that can later be read to indicate if an attempt at NMR imaging has been performed on integrated circuit chip  255 A. In one example, serpentine structure  265 A is designed to not be detectable by X-ray imaging. 
         [0031]      FIG. 6A  is a cross-sectional view of an integrated circuit containing devices to flag an unauthorized comparison attempt according embodiments of the present invention. In  FIG. 6A , an IC  200 C includes an integrated circuit chip  235 A in a plastic package body  240 A. A set (two sets are shown in the example of  FIG. 6A ) of three “horseshoe” magnets  275 A,  275 B and  275 C are placed in body  240 A. They are aligned so respective lines (dashed lines) passing through the poles of each magnet are mutually orthogonal. In  FIG. 6A , the line passing through the poles of magnets  275 A and  275 C are in planes parallel to the top surface  272  of integrated circuit chip  235 A. Other pole orientations are possible. In one example, only a single horseshoe magnet is used. Horseshoe shaped magnets may be replaced by other shaped magnets such as bar magnets and disc magnets. 
         [0032]      FIG. 6B  is a cross-sectional view of the integrated circuit of  FIG. 6A  after an unauthorized comparison attempt according embodiments of the present invention. When magnets  275 A,  275 B and  275 C are subjected to the intense magnetic field generated in an NMR machine, magnets  275 A,  275 B and  275 C are pulled/pushed by that field so strongly that cracks  280  are formed in body  240 A. 
         [0033]      FIG. 7  is a flowchart of methods of comparison according to embodiments of the present invention. The steps of the flowchart of  FIG. 7  are performed first on a known or trusted micro-electronic device and then on an unknown (or suspect) micro-electronic device that and essentially identical to the known micro-electronic device (i.e., identically designed and within fabrication specification limits). For the integrated circuit chip specification limits define allowable variations in material and structure and include, for example, the allowable differences in metal line widths and thickness differences in metal and insulating layers. For the package of the IC specification limits define allowable variations in material and structure and include, for example, package dimensions, size of solder bumps, positions and size of wire bonds, widths and thickness of land in modules. 
         [0034]    In step  300  an IC (or integrated circuit) is placed in the MRI chamber. In step  305  the high gauss magnetic field is turned on. In one example, the high gauss magnetic field has a field strength of between about a 0.5 telsa and about 10 telsa and is applied in the z direction. The method can know follow one of two mutually exclusive paths. The first is the path (1) through steps  310 ,  315 ,  320 ,  325  and  330  to step  335 . The second path (2) is through steps  315 A,  320 A and  325 A to step  335 . The unknown micro-electronic device advantageously follows the same path and is subjected to the same NMR conditions as the known micro-electronic device. 
         [0035]    In step  310 , a direction (x, y or z) is selected. In step  315 , a gradient magnetic field of, for example,  1  telsa is applied in the selected direction and in step  320  a RF pulse is directed to the IC. In step  325  the emitted (returned) RF signal is detected and information describing the return RF signal (which is also a pulse) is stored. The duration and time of reception of the return RF signal will vary. In step  330 , if another direction of the three possible directions (x, y, z) is selected and the method loops back to step  310 . This loop will repeat three times, once for each direction. 
         [0036]    In path (2) in step  31   5 A, gradient magnetic fields are applied in the x, y, and z directions simultaneously. Each gradient field may have a same or a different field strength of between about 0.5 telsa and about 10 telsa. Steps  320 A and  325 A are similar to steps  320  and  325  respectively. 
         [0037]    In steps  315  and  315 A, optional test conditions (i.e., voltage bias, analog signal, digital data pattern or combinations thereof) may be applied to the micro-electronic device. In a first example, optional test conditions are applied only during step  315  (or  315 A). In a second example, optional test conditions are applied the only during steps  315  and  320  (or  315 A and  320 A). In a third example, the optional test conditions are applied the only during steps  305 ,  310 ,  315  and  320  (or  305 ,  315 A and  320 A). In a fourth example, the optional test conditions are applied during steps  305 ,  310 ,  315 ,  320  and  325  (or  305 ,  315 A,  320 A and  325 A). 
         [0038]    In step  335 , the IC is removed from the MRI chamber and it is determined whether the micro-electronic device was a known micro-electronic device or an unknown micro-electronic device. If the micro-electronic device was a known micro-electronic device then in step  340  analyses are performed and the analyses data is stored. If the micro-electronic device was an unknown micro-electronic device then in step  345  analyses are performed and the analyses is compared to analyses previously stored from a known micro-electronic device MRI “images” under the same MRI (and bias/pattern) conditions. If the compare is within predefined limits the unknown micro-electronic device is validated. It does not matter whether the known or unknown micro-electronic device is run first, but the comparison cannot be performed until both known or unknown micro-electronic devices have been run and the respective data analyzed. 
         [0039]      FIGS. 8A and 8B  illustrate a first method of data analysis for comparison according to embodiments of the present invention.  FIG. 8A  is a plot of the transverse component of the returned RF signal for a known micro-electronic device  350  and an unknown micro-electronic device  355  as relative RF strength versus time. Direct comparison or statistical analysis of the difference between curves  350  and  355  is performed to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device. In  FIG. 8A , the difference between curve  355  relative to curve  350  is shown as a positive time shift. The shift may be negative.  FIG. 8B  is a plot of the longitudinal component of the returned RF signal for a known micro-electronic device  360  and an unknown micro-electronic device  365  as relative RF strength versus time. Direct comparison or statistical analysis of the difference between curves  360  and  365  is performed to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device. In  FIG. 8B , the difference of curve  365  relative to curve  360  is shown as a negative time shift. The shift may be positive. 
         [0040]      FIGS. 9A and 9B  illustrate a second method of data analysis for comparison according to embodiments of the present invention.  FIG. 9A  is a plot of a fast Fourier transform of the returned RF signal for a known IC (or integrated circuit) as RF amplitude versus RF frequency. Element  370  is the returned signal and elements  370 A and  370 B are harmonic artifacts of element  370 .  FIG. 9B  is a plot of a fast Fourier transform of the returned RF signal for an unknown IC (or integrated circuit) as RF amplitude versus RF frequency. Element  375  is the returned signal and elements  375 A and  3750 B are harmonic artifacts of element  370 . Element  370  and  375  are statistically compared in terms of amplitude of a given frequency range to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device. In  FIGS. 9A and 9B , the amplitude of the returned RF signal has been transferred from a time domain to a frequency domain. 
         [0041]      FIGS. 10A ,  10 B and  10 C illustrate a third method of data analysis for comparison according to embodiments of the present invention.  FIG. 10A  is a plot of the returned RF signal as relative RF signal strength versus time for a known micro-electronic device. RF signal  380  has a fixed amplitude between times A and B measured from when the RF pulse signal terminated (or other convenient time reference). An unknown micro-electronic device may exhibit a signal that is offset ion amplitude, phase, frequency or combinations thereof. Two simple examples are given in  FIGS. 10B and 10C . 
         [0042]      FIG. 10B  is a plot of the returned RF signal as relative RF signal strength versus time for an unknown micro-electronic device having only a frequency shift. RF signal  385 A has fixed amplitude between times A′ and B′ measured from the same reference as A and B of  FIG. 10A . The shift between A and A′ and B and B′ is statistically to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device. 
         [0043]      FIG. 10C  is a plot of the returned RF signal as relative RF signal strength versus time for an unknown micro-electronic device having only an amplitude shift. RF signal  385 B has a fixed amplitude between times A and B measured from the same reference as A and B of  FIG. 10A . The change in amplitude between curve  380  of  FIG. 10A  and curve  385 B of  FIG. 10C  is statistically to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device. 
         [0044]    It will be appreciated that a complete statistical analysis would compare time, amplitude, frequency and phase differences of the curves described in  FIGS. 10A ,  10 B and  10 C. 
         [0045]      FIGS. 11A ,  11 B and  11 C illustrate a fourth method of data analysis for comparison according to embodiments of the present invention.  FIG. 11A  is a plot of the returned RF signal XY space (at a selected Z) as a function of frequency for a known micro-electronic device. As such  FIG. 11A  is closer to what is may be considered an “image.”  FIG. 11B  is a plot of the returned RF signal XY space (at the selected Z) as a function of frequency for an unknown micro-electronic device.  FIG. 11C  is a plot of the delta between the plot of  FIG. 11A  and that of  FIG. 11B . The amount of structure (and optionally the position of the structures) is statistically analyzed to determine if the unknown micro-electronic device is significantly different from the unknown micro-electronic device.  FIG. 11C  is  FIG. 11A  “subtracted” from  FIG. 11A . 
         [0046]    Thus the embodiments of the present invention allow for relatively quick and inexpensive validation of integrated circuit chips. 
         [0047]    The description of the embodiments of the present invention is given above for the understanding of the present invention. It will be understood that the invention is not limited to the particular embodiments described herein, but is capable of various modifications, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, it is intended that the following claims cover all such modifications and changes as fall within the true spirit and scope of the invention.