Abstract:
An electronic device includes a semiconductor body and a dielectric layer extending over the semiconductor body. A galvanic isolation module includes a first metal region extending in the dielectric layer at a first height and a second metal region extending in the dielectric layer at a second height greater than the first height. The first and second metal regions are capacitively or magnetically coupleable together. The second metal region includes a side wall and a bottom wall coupled to one another through rounded surface portions.

Description:
BACKGROUND 
       [0001]    Technical Field 
         [0002]    The present disclosure relates to an electronic device including a galvanic isolation module and to a manufacturing method of the same. 
         [0003]    Description of the Related Art 
         [0004]    In the field of galvanic isolation, for safety reasons, many power applications directly connected to high-voltage lines, such as systems for driving industrial machinery or household appliances, or control systems for motors and battery packs of electric vehicles, require decoupling between the power stage and the user control panel. Traditionally, in these applications, galvanic isolation has been obtained by optical couplers with isolation classes of several kilovolts and bandwidths of hundreds of kilohertz, or by coreless transformers on printed-circuit boards (PCBs). 
         [0005]    In the field of integrated transformers for signal transmission, in order to obtain large bandwidths and reduce the size and costs, there have been recently introduced integrated coreless transformers. Design of transformers of this type requires the need to take into consideration numerous parameters, such as the breakdown voltage (also known as “dielectric rigidity”), the bandwidth, the time derivative of the voltage dV/dt, and the immunity to external fields. 
         [0006]    In the field of integrated transformers for power transmission, in order to supply the driving system connected to the high-voltage power MOS transistor, it is desirable to use a power transmission line between the low-voltage (LV) portion and the high-voltage (HV) portion. In order to reduce the power losses and increase the efficiency of the system, it is important to reduce the resistance of the winding and the value of parasitic capacitance that is set up with the substrate. Currently, windings of a material with low resistance (typically, gold) and dedicated high-resistance substrates are used. This solution may not be employed in integrated circuits of a “smart power” type, with consequent increase in costs and loss of efficiency of the system as a whole. 
         [0007]    There is hence felt the need for an integrated transformer that will overcome the drawbacks of the known art and in particular will make it possible to improve the isolation voltage class, will enable decoupling (galvanic isolation) between a low-voltage operating region and high-voltage operating region of the integrated circuit, will enable power transfer between the low-voltage operating region and the high-voltage operating region, and will, in general, enable a reduction of the costs and an improvement in performance. 
       BRIEF SUMMARY 
       [0008]    Embodiments of the present disclosure provide an electronic device with galvanic isolation and a manufacturing method of the same that achieve the aforementioned purposes and that overcomes at least some of the disadvantages of the known art. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    For a better understanding of the present disclosure, some embodiments thereof will now be described, purely by way of non-limiting example and with reference to the attached drawings, wherein: 
           [0010]      FIG. 1  shows a system that comprises a galvanically isolated coupling module, in particular a transformer; 
           [0011]      FIG. 2  illustrates, in lateral sectional view, a device including a micro-integrated transformer according to one embodiment of the present disclosure; 
           [0012]      FIG. 3  shows an enlarged detail of a portion of a turn of the top winding of the micro-transformer of  FIG. 2 ; 
           [0013]      FIGS. 4-10  illustrate, in lateral sectional view, steps of manufacture of the device of  FIG. 2 ; 
           [0014]      FIG. 11  shows, in top plan view, the device of  FIG. 2 , according to one embodiment; and 
           [0015]      FIG. 12  is a schematic representation of a system that comprises a galvanically isolated coupling module, in particular a capacitor, according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  is a schematic illustration of a system for transceiving an electrical signal based upon inductive coupling and configured in such a way that a transmitter TX is galvanically isolated from a receiver RX by a transformer, in particular a micro-transformer,  2 . In this context, the term “micro-transformer” indicates a transformer manufactured according to the technology for the production of integrated circuits. 
         [0017]    The system of  FIG. 1  may be used for the transmission of electrical signals (e.g., data signals, signals of an impulsive type, etc.) from the transmitter TX to the receiver RX. Moreover, it is possible to transfer power through the transformer  2 , or use the transformer  2  for translation of a signal between two different voltage levels. In industrial applications, the system of  FIG. 1  may moreover be used for high-voltage driving circuits, for communication and control systems, measurement systems, and testing systems. Since the signals, of whatever kind they may be, are transmitted through the galvanic isolation, any conductive path type between the transmitter TX and the receiver RX that is to be isolated is eliminated. 
         [0018]    In use, the transmitter TX receives an input signal (to be transmitted) from a control circuitry, and supplies the input signal to a primary winding  2   a;  the receiver RX is coupled for receiving from the secondary winding  2   b  a signal corresponding to the input signal supplied to the primary winding  2   a  and generates an output signal comprising a reconstructed input signal. 
         [0019]    With reference to  FIG. 2 , illustrated in lateral sectional view and in a triaxial reference system X, Y, Z is an electronic device, or chip,  1  including the micro-transformer  2 , of an integrated type, and a signal-transmission unit TX, according to one embodiment of the present disclosure. The transformer  2  includes a bottom winding  2   a  (primary winding) and a top winding  2   b  (secondary winding), which are here represented by way of example as each having three turns designated by the references  21  and  23 , respectively. According to the present disclosure, the transmitter TX and the receiver RX, as likewise the primary and secondary windings, may be swapped round. Moreover, the transmitter TX and the receiver RX may both be transceiver modules, configured to function in transmission or reception according to the need. It is, however, evident that the number of turns may be other than three, and chosen according to the need, for example in a number comprised between 2 and 30. The bottom winding  2   a  and top winding  2   b  extend at a distance from one another along the axis Z, separated by one or more layers of dielectric material (e.g., silicon oxide). An electrical-contact region  3 , of metal material, extends on the same metal level as that of the top winding  2   b,  inside the turns  21  thereof and electrically coupled to the turns  21  of the top winding, and is thus electrically coupled to the top winding  2   b.  The electrical-contact region  3  is moreover electrically coupled to a bonding wire  9  by a bonding region  10  and a coupling-interface region  11  for transferring an electrical signal to the receiver RX external to the device  1 . Since, according to one aspect of the present disclosure, the electrical-contact region  3  is of copper, the coupling-interface region  11  (made, for example, of aluminum) has the function of preventing direct exposure of the copper to the external environment during the manufacturing steps. One or more dielectric layers  15  (just one of which is shown in the figure), made, for example, of silicon oxide and/or silicon nitride, cover the top winding  2   b,  protecting it and isolating it electrically. 
         [0020]    The micro-transformer  2  functions as galvanic isolation module and as power-transfer interface between the transmitter TX, integrated in a semiconductor body  6  of the device  1 , and the receiver RX, which is external to the device  1 , or vice versa. 
         [0021]    The transmitter TX includes, in a per se known manner and on the basis of the signal that is to be transmitted, electronic components/circuits designated as a whole by the reference numbers 4 and 5, which function at voltages ranging between 1 V and 40 V. The transmitter TX is operatively coupled to the bottom winding  2   a,  for supplying to the bottom winding  2   a  the signal to be transferred to the receiver RX. The electrical components and/or circuits  4  may be located in the region underlying the micro-transformer, as shown in the figure, or else staggered with respect to the micro-transformer. 
         [0022]    The semiconductor body  6  (for example, including silicon) is, in particular, obtained in BCD (Bipolar-CMOS-DMOS) technology; i.e., it integrates three different technologies: bipolar technology for precise analog functions, CMOS (Complementary Metal Oxide Semiconductor) technology for digital circuits, and DMOS (Double Diffused Metal Oxide Semiconductor) technology for power and high-voltage components. 
         [0023]    Extending on the substrate  6  are one or more metal levels. In the embodiment of  FIG. 2 , four metal levels M 1 -M 4  are illustrated, each including respective metal regions  14   a - 14   d.  The fourth metal level M 4  moreover includes the bottom winding  2   a.  A fifth metal level M 5  includes the electrical-contact region  3  and the top winding  2   b.  Moreover, as illustrated in  FIG. 2 , the metal levels M 1 -M 4  may include further metal regions, designated by the references  12   a - 12   d.    
         [0024]    According to one aspect of the present disclosure, in the dielectric region that extends between the bottom winding  2   a  and the substrate  6 , electronic circuits and components may, at least in part, be formed. In this case, said region comprised between the bottom winding  2   a  and the substrate  6  is an active-area region of the device  1 . 
         [0025]    According to a different embodiment, the dielectric region that extends between the bottom winding  2   a  and the substrate  6  does not comprise electronic circuits or components. In this case, the micro-transformer  2  is formed alongside the active-area region of the device  1 . 
         [0026]    Extending between the fourth metal level M 4  and the fifth metal level M 5  is a thick dielectric layer  13 , having a thickness, along Z, comprised between 1 μm and 30 μm, for example 15 μm. The thick dielectric layer  13  is the layer that separates the bottom winding  2   a  from the top winding  2   b  of the transformer  2 , and its thickness is chosen as a function of, and such as to guarantee, the voltage class required of the galvanic isolation. 
         [0027]    In order to expose the metal regions  12   d,    14   d  of the fourth metal level M 4  (in order to contact them electrically), trenches  24 ,  26  extend from a front side  1 a of the device  1  in depth along Z, through the thick dielectric layer  13 . The trench  24  exposes the metal region  14   d,  and the trench  26  exposes the metal region  12   d.  The metal region  14   d  of the metal level M 4  forms one or more electrical-contact pads. In particular, the metal region  14   d  is electrically coupled to a bonding wire  16  by a bonding region  19 . The bonding wire  16  and the bonding region  19  are of conductive metal material, for example gold. The metal region  12   d  has, instead, the function of guaranteeing an electrical contact with the material of the package (resin) of the chip and preventing accumulation of electric charge at the interfaces with the region  14 . 
         [0028]    In particular, as illustrated more clearly in  FIG. 11 , the metal region  12   d  (and hence also the trench  26 ) forms, in top plan view in the plane XY, a curvilinear path, in particular an annular path, and surrounds (completely or partially, according to respective embodiments) the bottom winding  2   a  of the transformer  2 . 
         [0029]    Each metal level M 2 -M 4  is electrically coupled to the metal level M 1 -M 3  below it by via levels L 1 -L 3 , which include conductive vias  17   a - 17   c,    18   a - 18   c.  The conductive vias  17   a - 17   c,    18   a - 18   c  are made, for example, of metal material. Dielectric layers  20   a - 20   c,  which are made, for example, of silicon oxide, extend between one metal level M 1 -M 3  and the next metal level and alongside each metal region belonging to a same metal level M 1 -M 4 . 
         [0030]    The substrate  6  may integrate several electrical and electronic components/circuits  5 , which have specific functions and are not described in detail herein in so far as they do not form the subject of the present disclosure. Irrespective of the functions of said electronic circuits  5 , conduction terminals thereof are electrically coupled with the outside of the device  1  via the metal regions  14   a - 14   d  and the conductive vias  17   a - 17   c,  for transmission/reception of electrical control signals for control thereof. 
         [0031]    A layer of resin  30  (for example, epoxy resin) covers the device  1  and forms part of the package (not shown in its entirety) of the device  1 . The layer of resin  30  penetrates into the trenches  24 ,  26  as far as the metal regions  12   d,    14   d.    
         [0032]    According to an aspect of the present disclosure, the turns of the top winding  2   b  of the transformer  2  and, optionally, the electrical-contact region  3 , are U-shaped in lateral sectional view. In greater detail, as shown in  FIG. 3  (here a single turn  21  is illustrated), each turn  21  extends between an own top side  21   a  and an own bottom side  21   b,  which are parallel to one another and to the plane XY. The distance d s  (along Z) between the top side  21   a  and the bottom side  21   b  is between 2 μm and 6 μm, for example 3 μm. The width I s , along X, of each turn  21  is between 5 μm and 100 μm, for example 20 μm. Each turn  21  has, on the bottom side  21   b,  a rounded profile; i.e., it has rounded corners  21   c  that radius the bottom side  21   b  with a lateral surface  21   d  (parallel to the plane YZ) of the turn  21 . The corners  21   c  have a radius of curvature r c  of a value comprised between 1 μm and 6 μm, for example 3 μm. 
         [0033]    The present applicant has found that, in use, the equipotential field lines in an area corresponding to the turns  21  follow the profile of the turns  21  and, hence, are curved at the rounded corners  21   c  following the radius of curvature thereof. The greater the radius of curvature of the rounded corners  21   c,  the smaller the value of electrical field at the corners  21   c  themselves. In fact, the electrical field has higher values in the proximity of the conductors on which there is greater density of equipotential lines, namely, in the proximity of the edges, tips, or areas with small radius of curvature. An excessive electrical field in these regions may cause damage to the device, such as early breakdown of the dielectric. Hence, the embodiment of  FIGS. 2 and 3  overcomes this drawback by increasing the radius of curvature of the corners  21   c  of the turns  21 . In particular, when a certain threshold is overstepped, the electrical field causes breakdown of the dielectric; however, even for not excessively high values, applied for prolonged times, the electrical field is at the basis of the mechanisms of degradation of the dielectric layer. Accurate calculations show that with a radius of curvature of 3 μm, for example, it is possible to reduce the edge electrical field by approximately three times as compared to a practically zero radius of curvature. For this reason, as the radius of curvature increases, the possibility of breakdown of the dielectric is reduced, and simultaneously the service life of the device increases. 
         [0034]      FIGS. 4-10  illustrate, in lateral sectional view, steps for manufacturing the device  1  of  FIG. 2 , according to one aspect of the present disclosure. 
         [0035]      FIG. 4  illustrates the device  1  in an initial manufacturing step, in which the substrate  6  has already been processed for integrating all the electrical and electronic functions required by the specific application, using any available micromachining technology. Extending over of the substrate, in a per se known manner, are the metallizations of the metal levels M 1 -M 4 , including the turns  23  of the bottom winding  2   a  of the transformer  2  (in the metal level M 4 ). 
         [0036]    With reference to  FIG. 5 , the next step is formation of one or more dielectric layers  31  on the device  1 , i.e., above the fourth metal level M 4 . For example, the dielectric layer  31  is a deposited oxide (TEOS oxide). The dielectric layer  31  is deposited between the turns  23  of the bottom winding  2   a,  and over, and between, the metal regions  12   d,    14   d  . The dielectric layer  31  has a thickness of a few micrometers, for example 10-15 μm or more. The dielectric layer  31  is, for example, silicon oxide (SiO 2 ). 
         [0037]    Then ( FIG. 6 ), a step of etching of the dielectric layer  31  is carried out in order to form recesses in surface regions of the dielectric layer  31 , in which it is desired to provide the top winding  2   b  and the electrical-contact region  3 . 
         [0038]    In particular, a recess  34  is formed, aligned (or substantially aligned), along Z, with the turns  23  of the bottom winding  2   a,  and a recess  36  is likewise formed extending inside or outside the region delimited by the recess  34 . The recess  34  and the recess  36  are in fluid communication with one another. In subsequent manufacturing steps, the recess  34  will house the metallization of the turns  21 , and the recess  36  will house the metallization of the electrical-contact region  3 . The number and size of the turns  21  may be the same as or else different from the number and size of the turns  23 . 
         [0039]    Etching of the dielectric layer  31  is carried out using the wet-etching technique. Possibly, a dry etch may precede the wet etch, as described in what follows. Irrespective of the etching technique adopted, the recesses  34  and  36  are formed in such a way that they will have, in lateral sectional view, a U-shaped profile, i.e., with rounded corners at the bottom side, in a way similar (mutatis mutandis) to what has been described with reference to  FIG. 3 . 
         [0040]    A profile of this type may be obtained by appropriately adjusting etching of the dielectric layer  31 , according to what is specified hereinafter. 
         [0041]    In the case of wet etching, an etching mask is used, formed over the dielectric layer  31 , for example according to known lithography and etching steps. In this case, the etching chemistry used is of an isotropic type, i.e., such that the dielectric layer  31  is removed at the same etching rate in all etching directions. For this purpose, a BOE (Buffered Oxide Etch) solution is, for example, used, with a concentration NH 4 F:HF of 18:1, with an etching rate of some tens of nanometers per minute (e.g., 250 nm/min). With an etch of this sort, having a duration of approximately 12 min, recesses  34 ,  36  are obtained having a depth of 3 μm and having rounded corners, with a radius of curvature of approximately 3 μm. The recesses  34 ,  36  thus formed hence have, in lateral sectional view, rounded corners as envisaged by the present disclosure (see, for example,  FIG. 3 ). 
         [0042]    According to a different embodiment for obtaining recesses  34 ,  36 , an approach is used that envisages anisotropic etching, e.g., dry etching, after isotropic etching, e.g., wet etching, for obtaining recesses  34 ,  36  with non-rounded lateral surfaces thanks to anisotropic etching, but guaranteeing in any case the radius of curvature required for the corners at the bottom of the recesses  34 ,  36  thanks to the isotropic etch. For this purpose, after an appropriate etching mask has been provided on the surface of the dielectric layer  31 , an operation of pre-digging is carried out by dry anisotropic etching (e.g., to a depth of a few micrometers, in particular 1-2 μm), and this is followed by wet isotropic etching (e.g., to a depth of a few micrometers, in particular 1-2 μm). Anisotropic etching of the dielectric layer  31  may be carried out using, for example, a chemical/physical etch with chemistry CF 4 /O 2 ; isotropic etching may be conducted using BOE or HF. 
         [0043]    Then ( FIG. 7 ), the recesses  34 ,  36  are filled using a metal material, for example copper. 
         [0044]    According to one aspect of the present disclosure, this step may be carried out by depositing a seed layer of copper, followed by electrochemical growth of copper, in a per se known manner. Removal of the copper grown outside the recesses  34  and  36  is carried out using a CMP (Chemical-Mechanical Polishing) technique. The process used for filling the recesses  34  is moreover known as “damascene”. 
         [0045]    There is thus formed the top winding  2   b  of the transformer  2 , including the metal turns  21  and the electrical-contact region  3 , electrically coupled to the turns  21 . 
         [0046]    Next ( FIG. 8 ), a step of passivation of the exposed surface of the device  1  (formation of the passivation layer  38 ) is carried out, and then, the passivation layer is removed only in an area corresponding to the electrical-contact region  3 , and a step of deposition of an interface metal layer (e.g., of aluminum or of an alloy including aluminum, or of nickel-palladium, etc.) is carried out. The interface metal layer is selectively etched in such a way that it is removed from the surface of the device  1  except for the portion thereof in which the electrical-contact region  3  extends. The coupling interface  11  is thus formed. 
         [0047]    Then, a step of formation of the protective dielectric layer  15  is carried out, depositing, for example, silicon oxide and/or silicon nitride and etching the dielectric layer thus deposited for opening a contact at the coupling interface  11 . 
         [0048]    Next ( FIG. 9 ), the protective dielectric layer  15 , the passivation layer  38 , and the dielectric layer  31  are etched to form deep trenches  42 ,  43  that extend until surface portions of the metal regions  14   d  and  12   d,  respectively, are exposed. 
         [0049]    Next ( FIG. 10 ), coupling steps are carried out by wire bonding, electrically coupling the bonding wire  16  with the metal region  14   d,  through the bonding region  19 , and electrically coupling the bonding wire  9  with the electrical-contact region  3 , through the bonding region  10 . 
         [0050]    Finally, a step of pouring of a resin, for example epoxy resin, makes it possible to provide the layer of resin  30 , thus obtaining the device  1  of  FIG. 2 . 
         [0051]      FIG. 11  shows the device  1  in top plan view, according to one embodiment. The cross-sectional view of  FIG. 2  is taken along the line of section II-II in  FIG. 11 ; however, for simplicity of representation, the device  1  of  FIG. 11  does not comprise the bonding wires  9  and  16  and the layer of resin  30 . As may be noted, the device  1  comprises a plurality of metal pads  50  (including the metal region  14   d  ), for electrical wire bonding (not shown in  FIG. 11 ). The metal region  12   d  in  FIG. 2  belongs to an annular path that surrounds the inductor  2 , with the advantage of preventing the resin that covers the chip from accumulating electric charges that might disturb operation of the underlying devices  4  and  5 . The annular path of the metal region  12   d  may, for example, be interrupted in one or more points to prevent onset of parasitic currents induced by the magnetic field generated by the windings of the transformer. 
         [0052]    In this embodiment, the inductor  2 , has two opposed windings, a right-handed one and a left-handed one, electrically connected together. The electrical-contact region  3  and a further electrical-contact region  3 ′ form electrical connection terminals coupled to respective ends of the opposed windings. 
         [0053]    From what has been described above, the advantages of the present disclosure as illustrated in the various embodiments are evident. 
         [0054]    In particular, rounding of the corners of the top winding  2   b  enables reduction of the curvature and density of the equipotential lines and consequently reduction of the electrical field. For this reason, as the radius of curvature increases, the likelihood of breakdown of the dielectric is reduced and simultaneously the service life of the device increases. 
         [0055]    Finally, it is evident that modifications and variations may be made to the disclosure described herein, without thereby departing from the scope of the present disclosure. 
         [0056]    In particular, the present disclosure applies to electrical components other than the micro-inductor described. For example, the inductor  2  may be replaced by a capacitor  60  with plane and parallel faces to provide a coupling of a capacitive type, as shown by way of example in  FIG. 12 . The bottom and top plates  60   a,    60   b  of the capacitor  60  (integrated in a device, or chip,  1 ′) are of metal material and are obtained according to manufacturing steps similar to those described previously for obtaining the top and bottom windings  2   b  and  2   a  of the transformer  2 . In particular, the top plate  2   b  has the same conformation of the corners as already described with reference to the turns  21 , i.e., a shape with rounded edges, in order to achieve the same advantages described previously. 
         [0057]    In the embodiments of  FIGS. 2 and 12 , the transmitter TX is shown integrated in the device  1 ,  1 ′. It is, however, evident that, according to alternative embodiments, part of the transmitter circuit TX, or the entire transmitter circuit TX, may be provided outside the device  1 ,  1 ′, and operatively connected to it (and, in particular, to the transformer  2  or to the capacitor according to the respective embodiments) by connections of a known type (for example, by solder bumps provided on the front of the device  1 ,  1 ′), or wire bonding, or some other electrical connection still. 
         [0058]    The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.