Abstract:
An electronic component includes a substrate, a capacitor, and a wiring. The capacitor has a multilayer structure including a first electrode film provided on the substrate, a second electrode film of 2 to 4 μm in thickness disposed to face the first electrode film, and a dielectric film interposed between the first and the second electrode film. The wiring includes a joint portion connected to the second electrode film, on the opposite side of the dielectric film.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an electronic component that includes a capacitor provided on a substrate, for example formed by semiconductor processing technology.  
         [0003]     2. Description of the Related Art  
         [0004]     In a radio frequency (RF) system such as a mobile phone or a wireless LAN, signals are subjected to phase-matching for satisfactory transmission among functional devices constituting the system. Accordingly, the input/output (I/O) terminal of each device is provided with a passive element that includes a passive component such as an inductor or a capacitor, and that acts as a phase shifter for controlling the phase of the signals.  
         [0005]     In the RF system, a SAW filter is employed for use as a narrow-band frequency filter. The SAW filter, which includes a piezoelectric element, produces a difference in potential between piezoelectric element electrodes because of a piezoelectric effect, when a physical impact or a thermal effect is applied to the SAW filter or the piezoelectric element thereof during the manufacturing process of the apparatus in which the SAW filter is incorporated. In this case, a predetermined voltage is applied to an electronic component electrically connected to the SAW filter. The capacitor included in the passive element (phase shifter) is usually electrically connected to the SAW filter, and hence the capacitor has to have a high withstanding voltage (e.g. 150 V or higher), to prevent a dielectric breakdown between the capacitor electrodes, which may occur upon application of a voltage accidentally generated by the SAW filter or the piezoelectric element thereof.  
         [0006]     There has been a constant demand for reduction in dimensions of various parts composing RF systems, driven by the increase in number of parts for achieving a higher performance. For making the system smaller in dimensions, an integrated passive device (hereinafter, IPD) manufactured based on a semiconductor processing technology, which includes a plurality of predetermined passive components such as an inductor, a capacitor, a resistor and a filter densely integrated therein, may be employed the passive element (phase shifter). When employing the IPD, the capacitor included therein still has to have a high withstanding voltage, for preventing a dielectric breakdown between the capacitor electrodes, as stated above. Techniques related to the IPD are found, for example, in JP-A-H04-61264 and JP-A-2002-33239.  
         [0007]      FIG. 9  is a schematic cross-sectional view showing a part of a conventional IPD  90 . The IPD  90  includes a substrate  91 , a plurality of passive components each including a capacitor  92 , integrated on the substrate  91 , an wiring  93  and a protecting film  94 . The capacitor  92  has a multilayer structure including an electrode film  92   a  (lower electrode film), an electrode film  92   b  (upper electrode film), and a dielectric film  92   c . The wiring  93  includes a joint portion  93   a  connected to the electrode film  92   b.    
         [0008]     The electrode film  92   b  has a thickness of approximately 1 μm. For forming the electrode film  92   b , a conductor film, which is to subsequently serve as the electrode film  92   b , is formed on the substrate  91  to cover the electrode film  92   a  and the dielectric film  92   c  already formed on the substrate  91 . A resist film given a pattern corresponding to the electrode film  92   b  is then provided on the conductor film, and an ion milling process is performed utilizing the resist film as the mask, thus to shape the conductor film according to the pattern. When performing such subtractive process to form the electrode film  92   b , the thinner the conductor film, or the electrode film  92   b  is, the more accurately the electrode film  92 b can be formed in pattern (hence in area). The precision in area of the electrode film  92   b  affects the precision in static capacitance of the capacitor  92 , which is why the electrode film  92   b  is formed in a thickness of approximately 1 μm in the conventional IPD  90 , for achieving high precision in static capacitance.  
         [0009]     In contrast, the wiring  93  (including the joint portion  93   a ) is formed in a relatively greater thickness. Making the wiring  93  thicker can reduce a resistance thereof, and the reduction in resistance is preferable from the viewpoint of reducing a signal loss through the IPD  90 . Accordingly, the wiring  93  is formed in a thickness of approximately 10 μm for example.  
         [0010]     The capacitor  92  of the conventional IPD  90 , however, often has a withstanding voltage below a practically acceptable level, which has to be addressed. For improving the withstanding voltage of the capacitor  92 , it could be an option to form the dielectric film  92   c  in a greater thickness. Increasing the thickness of the dielectric film  92   c , however, requires increasing the area of the electrode film  92   b , because otherwise the static capacitance of the capacitor  92  cannot be maintained. Therefore, it is not preferable to increase the thickness of the dielectric film  92   c , from the viewpoint of suppressing an increase in dimensions of the capacitor  92 , hence the IPD  90 .  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention has been proposed in the above-described situation. It is an object of the present invention to provide an electronic component including a capacitor that facilitates achieving a high withstanding voltage.  
         [0012]     The present invention provides an electronic component comprising a substrate, a capacitor, and a wiring. The capacitor has a multilayer structure including a first electrode film (lower electrode film) provided on the substrate, a second electrode film (upper electrode film) having a thickness of 2 to 4 μm and disposed to face the first electrode film, and a dielectric film interposed between the first and the second electrode film. The wiring includes a joint portion connected to the second electrode film on the opposite side of the dielectric film. The electronic component according to the present invention encompasses a single capacitor element as well as an integrated electronic component in which a capacitor element and other elements are combined.  
         [0013]     According to studies pursued by the present inventors, it has been discovered that, in the capacitor  92  of the conventional IPD  90 , the dielectric film  92   c  is prone to incur collapse of the film structure at a portion corresponding to a periphery of the joint portion  93   a  of the wiring  93 , once a dielectric breakdown takes place. Stress strain concentrates on a periphery of the joint portion  93   a , which is relatively thick, and the stress strain is considered to propagate to the dielectric film  92   c  via the electrode film  92   b  which is as thin as approximately 1 μm, in the capacitor  92  before emergence of the dielectric breakdown, thereby producing more flaws in the film structure in the portion of the dielectric film  92   c  corresponding to the periphery of the joint portion  93   a , than in the remaining portions thereof. This is considered to be a reason why the dielectric film  92   c  is prone to incur collapse -of the film structure in the portion corresponding to the periphery of the joint portion  93   a , in the capacitor  92 .  
         [0014]     The inventors have also found that employing an upper electrode film of 10 μm in thickness in place of the electrode film  92   b  provokes the collapse of the film structure, upon applying an excessive voltage, in a portion of the dielectric film  92   c  corresponding to the periphery of the upper electrode film, rather than the portion thereof corresponding to the periphery of the joint portion  93   a . Since stress strain concentrates on the periphery of the upper electrode film itself, which is relatively thick, the stress strain is considered to propagate to the dielectric film  92   c  before the emergence of the dielectric breakdown, thereby producing more flaws in the film structure in the portion of the dielectric film  92   c  corresponding to the periphery of the upper electrode film, than in the remaining portions thereof. This is considered to be a reason that the dielectric film  92   c  is prone to incur the collapse of the film structure in the portion corresponding to the periphery of the upper electrode film.  
         [0015]     Based on the foregoing findings, the present inventors have discovered that the thickness of the upper electrode film affects the withstanding voltage of a capacitor element fabricated by, for example, a semiconductor processing technology, thereby accomplishing the present invention.  
         [0016]     In the electronic component according to the present invention, the second electrode film (upper electrode film), interposed between the dielectric film of the capacitor and the joint portion of the wiring, is formed in a thickness of 2 μm or greater. The present inventors have discovered that the second electrode film of 2 μm or more in thickness can significantly suppress propagation of stress strain concentrating in the periphery of the joint portion of the wiring to the dielectric film, even when the joint portion is formed to be relatively thick (for example, 10 μm or more), thereby preventing emergence of a flaw in the film structure of the dielectric film originating from the propagation of the stress strain in the joint portion to the dielectric film. Also, in the electronic component according to the present invention, the second electrode film is formed in a thickness of 4 μm or less. This is because the present inventors have discovered that the second electrode film of 4 μm or less in thickness does not incur therein unduly great stress strain, and hence barely provokes emergence of a flaw due to the stress strain, in the film structure of the dielectric film. The electronic component according to the present invention is provided based on these findings, and includes the capacitor that facilitates suppressing emergence of a flaw in the film structure of the dielectric film, and thus achieving a high withstanding voltage.  
         [0017]     According to the present invention, preferably the joint portion of the wiring may-be thicker than the second electrode film, and more preferably 10 μm or more in thickness. This is because forming the joint portion in a greater thickness can reduce the resistance of the joint portion and the wiring.  
         [0018]     Preferably, the dielectric film of the capacitor may have a thickness of 1 μm or less. The thinner the dielectric film is, the larger static capacitance can be obtained in the capacitor.  
         [0019]     It is preferable that the second electrode film is formed by a plating process. The plating process is appropriate for efficiently forming the second electrode film in a thickness of 2 to 4 μm.  
         [0020]     Preferably, the electronic component according to the present invention may further include a passive component provided on the substrate, and the wiring electrically may connect the passive component and the second electrode film of the capacitor. Under or in place of such structure, the electronic component according to the present invention may further include an electrode pad provided on the substrate, and the wiring electrically may connect the electrode pad and the second electrode film of the capacitor. The electronic component according to the present invention may be an integrated electronic component having such structure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a plan view showing an integrated electronic component according to the present invention;  
         [0022]      FIG. 2  is a cross-sectional view taken along the line II-II of  FIG. 1 ;  
         [0023]      FIG. 3  is a cross-sectional view taken along the line III-III of  FIG. 1 ;  
         [0024]      FIG. 4  is an enlarged fragmentary cross-sectional view taken along the line IV-IV of  FIG. 1 ;  
         [0025]      FIG. 5  is a circuit diagram of the electronic component shown in  FIG. 1 ;  
         [0026]      FIG. 6  shows, in section, a manufacturing process of a portion around a capacitor in the integrated electronic component shown in  FIG. 1 ;  
         [0027]      FIG. 7  shows, in section, manufacturing steps subsequent to those shown in  FIG. 6 ;  
         [0028]      FIG. 8  is a graph showing measurement results of withstanding voltages with respect to preferred examples 1, 2 and comparative examples 1, 2; and  
         [0029]      FIG. 9  is a schematic cross-sectional view showing a part of a conventional IPD. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]     FIGS.  1  to  4  depict an integrated electronic component X according to the present invention.  FIG. 1  is a plan view of the integrated electronic component X.  FIGS. 2 and 3  are cross-sectional views taken along the line II-II and III-III of  FIG. 1 , respectively.  FIG. 4  is an enlarged fragmentary cross-sectional view taken along the line IV-IV of  FIG. 1 .  
         [0031]     The integrated electronic component X includes a substrate S, capacitors  10 A,  10 B, a coil inductor  20 , electrode pads  30 A,  30 B,  30 C,  30 D, a wiring  40 , and a protecting film  50  (not shown in  FIG. 1 ), and has a circuit configuration shown in  FIG. 5 .  
         [0032]     The substrate S may be a semiconductor substrate, a quartz substrate, a glass substrate, a silicon on insulator (SOI) substrate, a silicon on quartz (SOQ) substrate, or a silicon on glass (SOG) substrate. The semiconductor substrate may be made of a silicon material, such as monocrystalline silicon.  
         [0033]     The capacitors  10 A,  10 B respectively have a multilayer structure including electrode films  11 ,  12  and a dielectric film  13 , as explicitly shown in  FIGS. 2 and 4 . The electrode film  11  is a lower electrode film formed in a pattern on the substrate S. The electrode film  11  may be made of Cu, Au, Ag or Al, and may have a multilayer structure including a plurality of conductor films. The electrode film  11  may have a thickness of 0.5 to 2 μm. The electrode film  12  is an upper electrode film formed to face the electrode film  11  via the dielectric film  13 , and may be made of Cu, Au, Ag or Al. The electrode film  12  has a thickness of 2 to 4 μm. The dielectric film  13  may be made of silicon oxide, silicon nitride, aluminum oxide, tantalum oxide or titanium oxide, for example. The dielectric film  13  may have a thickness of 0.1 to 1 μm. Making the dielectric film  13  thinner facilitates granting a larger static capacitance to the capacitors  10 A,  10 B.  
         [0034]     The coil inductor  20  is a flat spiral coil formed in a pattern on the substrate S as shown in  FIGS. 1 and 3 , and has end portions  21 ,  22 . Preferable materials of the coil inductor  20  include Cu, Au, Ag and Al.  
         [0035]     The electrode pads  30 A to  30 D serve for external connection. The electrode pads  30 A,  30 B serve as terminals for ground connection, while the electrode pads  30 C,  30 D serve as I/O terminals for electrical signals. The electrode pads  30 A to  30 D may be made of a Ni body with the upper surface coated with a Au film.  
         [0036]     The wiring  40  serves to electrically connect the components on the substrate S, and includes a joint portion  41  directly connected to the electrode film  12  of the capacitor  10 A,  10 B as shown in  FIGS. 2 and 4 . Preferable materials of the wiring  40  include Cu, Au, Ag and Al. The wiring  40  and the joint portion  41  may have a thickness of 10 μm or greater. Forming the wiring  40  in a greater thickness leads to reduced resistance thereof, and the reduction in resistance is preferable from the viewpoint of reducing a signal loss in the integrated electronic component X.  
         [0037]     Referring to  FIG. 5 , the capacitor  10 A is electrically connected to the electrode pads  30 A,  30 C and the coil inductor  20 . More specifically, the electrode film  11  of the capacitor  10 A is electrically connected to the electrode pad  30 A, and the electrode film  12  of the capacitor  10 A is electrically connected to the electrode pad  30 C and the end portion  21  of the coil inductor  20 . Likewise, the capacitor  10 B is electrically connected to the electrode pads  30 B,  30 D and the coil inductor  20 . More specifically, the electrode film  11  of the capacitor  10 B is electrically connected to the electrode pad  30 B, and the electrode film  12  of the capacitor  10 B is electrically connected to the electrode pad  30 D and the other end portion  22  of the coil inductor  20 .  
         [0038]     The protecting film  50  may be made of a polyimide or benzocyclobutene (BCB), and covers the capacitors  10 A,  10 B, the coil inductor  20  and the wiring  40 , leaving exposed a portion of the electrode pads  30 A to  30 D.  
         [0039]      FIGS. 6 and 7  show a manufacturing process of a portion around the capacitors  10 A,  10 B of the integrated electronic component X. Specifically, FIGS.  6 ( a ) to  7 ( d ) represent the progress of the formation process of a capacitor  10  (corresponding to either of the capacitors  10 A,  10 B) shown in  FIG. 7 ( d ), a joint portion of the wiring  40  with the capacitor  10 , and the protecting film  50  around the capacitor  10 , in cross-sectional drawings covering a similar section to that shown in  FIG. 4 .  
         [0040]     When forming the capacitor  10 , firstly the electrode film  11  is formed on the substrate S as shown in  FIG. 6 ( a ). A sputtering process may be performed to deposit a predetermined metal material on the substrate S, and the metal film may be subjected to a wet or dry etching process to be shaped in a predetermined pattern, for forming the electrode film  11 .  
         [0041]     Proceeding to  FIG. 6 ( b ), the dielectric film  13  is formed on the electrode film  11 . A sputtering process may be performed to deposit a predetermined dielectric material at least on the electrode film  11 , and the dielectric film may be subjected to a wet or dry etching process to be shaped in a predetermined pattern, for forming the dielectric film  13 .  
         [0042]     Then a seed layer (not shown) for electric plating is formed on the substrate S, to cover the electrode film  11  and the dielectric film  13 . The seed layer may be formed by vapor deposition or sputtering.  
         [0043]     Referring to  FIG. 6 ( c ), a resist pattern  61  for forming the electrode film  12  is provided. The resist pattern  61  includes an opening  61   a  defining the pattern shape of the electrode film  12 . For forming the resist pattern  61 , firstly a liquid photoresist is applied to the substrate S from above the electrode film  11  and the dielectric film  13 , and spin coating is performed to produce a film. Then the photoresist film is subjected to exposure and subsequent development, thus to be shaped into the resist pattern  61 .  
         [0044]     The above is followed by an electric plating process to form the electrode film  12  in the opening  61   a  of the resist pattern  61 , as shown in  FIG. 6 ( d ). In this electric plating process, the seed layer is energized. The electric plating process is appropriate for efficiently forming the electrode film  12  in a thickness of 2 to 4 μm.  
         [0045]     Proceeding to  FIG. 7 ( a ), the resist pattern  61  is removed by applying a predetermined stripping solution. And the seed layer (the part at which the electrode film  12  is not formed) is removed (by a dry or wet etching process). Then as shown in  FIG. 7 ( b ), an insulating film  51  is formed, which is to subsequently constitute a part of the protecting film  50 . The insulating film  51  includes an opening  51   a  in which a portion of the electrode film  12  is exposed.  
         [0046]     Referring then to  FIG. 7 ( c ), the wiring  40  is formed. The wiring  40  includes a joint portion  41  that fills in the opening  51   a  of the insulating film  51 , thus to be connected to the electrode film  12 . Specific formation method of the wiring  40  includes forming a seed layer (not shown) for an electric plating process on the insulating film  51  as well as inside the opening  51   a  shown in  FIG. 7 ( b ), providing on the seed layer a resist pattern defining a predetermined opening for forming the wiring  40 , growing a predetermined conductive material by electric plating in the opening of the resist pattern, removing the resist pattern, and removing the seed layer (the part at which the wiring  40  is not formed).  
         [0047]     Then as shown in  FIG. 7 ( d ), an insulating film  52  is formed to cover the wiring  40 . Thus, the capacitor  10  ( 10 A,  10 B) and the peripheral structure can be obtained, in the manufacturing process of the integrated electronic component X.  
         [0048]     As stated earlier regarding the capacitor  92  of the conventional IPD  90 , when undue stress is applied to the dielectric film between the electrode films of the capacitor element manufactured by the semiconductor processing technology, the portion of the dielectric film suffering the stress is prone to incur a flaw in the film structure, and hence prone to collapse when a high voltage is applied. Accordingly, presence of undue stress against the dielectric film impedes achieving a high withstanding voltage of the capacitor. In contrast, the capacitor  10 A,  10 B in the integrated electronic component X according to the present invention allows achieving a high withstanding voltage.  
         [0049]     In the integrated electronic component X, as described above, the wiring  40  and the joint portion  41  thereof are formed to be relatively thick such as 10 μm or more, and the respective electrode films  12  of the capacitors  10 A,  10 B are formed in a thickness of 2 to 4 μm. Although stress strain tends to concentrate on the periphery of the joint portion  41 , which is relatively thick, the propagation of the stress strain to -the dielectric film  13  can be significantly suppressed, because the electrode film  12  has a thickness of 2 μm or more. Such structure, therefore, can prevent emergence of a flow in the film structure of the dielectric film  13  originating from the propagation of the stress strain from the joint portion  41  to the dielectric film  13 . Further, the electrode film  12  itself, which has a thickness of 4 μm or less, does not incur therein unduly great stress strain, and hence barely provokes emergence of a flaw due to the stress strain, in the film structure of the dielectric film  13 . For such reasons, the capacitor  10 A,  10 B allows achieving a high withstanding voltage.  
         [0050]     The inventors produced several capacitor elements and measured their withstanding voltages for comparison. The results are as follows.  
       WORKING EXAMPLE 1  
       [0051]     A capacitor element was fabricated to have the structural features of the capacitor  10 A and its neighborhood shown in  FIG. 4 . Specifically, the substrate S was made of quartz. The electrode film  11  had a multilayer structure consisting of a Ti film (50 nm thick) provided on the substrate S, an Au film (500 nm thick) on the Ti film, an Ni film (50 nm thick) on the Au film, and another Au film (500 nm thick) on the Ni film. The electrode film  12  was an electrically plated Cu film (2 μm thick). The dielectric film  13  was an SiO 2  film (220 nm thick). The wiring  40 , including the joint portion  41 , had a multilayer structure consisting of an electrically plated Ni film (10 μm thick) closer to the capacitor  10 , and an electrically plated Ai film (2 μm thick) formed on the Ni film.  
       WORKING EXAMPLE 2  
       [0052]     A capacitor element of Working Example 2 was fabricated to have a structure identical to that of the above capacitor element (Working Example 1), except that the Cu-plated electrode film  12  had a thickness of 4 μm instead of 2 μm.  
       COMPARATIVE EXAMPLES 1, 2  
       [0053]     Capacitor elements were fabricated to have a structure identical to that of the capacitor element of Working Example 1, except that the upper electrode film (corresponding to the Cu-plated electrode film  12 ) had a thickness of 1 μm (Comparative Example 1) instead of 2 μm, or a thickness of 10 μm (Comparative Example 2).  
         [0054]     &lt;Measurement of Withstanding Voltage&gt; 
         [0055]     The withstanding voltage was measured with respect to the capacitor elements according to Working Examples 1, 2 and Comparative Examples 1, 2. The withstanding voltages of the capacitor elements according to Working Examples 1, 2 were 185 V and 172 V, respectively. The withstanding voltages of the capacitor elements according to Comparative Examples 1, 2 were 130 V and 133 V, respectively. These results are shown in the graph of  FIG. 8 , in which the horizontal axis represents the thickness [μm] of the electrode film  12  (upper electrode film), and the vertical axis represents the withstanding voltage [V]. The measurement results with respect to the capacitor elements according to Working Examples 1, 2 and Comparative Examples 1, 2 are plotted at points indicated by E 1 , E 2 , C 1  and C 2 , respectively.  
         [0056]     &lt;Evaluation&gt; 
         [0057]     As seen from  FIG. 8 , the withstanding voltages of the capacitor elements according to Comparative Examples 1, 2 did not exceed 135 V. The examining of the dielectric film  13  of the capacitor element according to Comparative Example 1 after the dielectric breakdown in the withstanding voltage measurement showed that the collapse of the film structure was observed mainly in a portion of the dielectric film  13  corresponding to the periphery of the joint portion  41  of the wiring  40 . In the capacitor element of Comparative Example 1 prior to the occurrence of a dielectric breakdown, stress strain tends to concentrate on a periphery of the joint portion  41 , which is relatively thick, and the strain propagates to the dielectric film  13  via the upper electrode film, which is as thin as 1 μm. As a result, the film structure in the portion of the dielectric film  13  corresponding to the periphery of the joint portion  41  suffers more flaws than in the other portions of the dielectric film  13 . Thus, the dielectric film  13  is prone to incur the collapse of the film structure in the portion corresponding to the periphery of the joint portion  41 . By examining the dielectric film  13  of the capacitor element according to Comparative Example 2 after the dielectric breakdown in the withstanding voltage measurement, it was found that the collapse of the film structure occurred in a portion of the dielectric film  13  corresponding to the periphery of the upper electrode film. Since stress strain concentrates in the periphery of the upper electrode film of Comparative Example 2, which is relatively thick, the stress strain propagates to the dielectric film  13  in the capacitor element according to the comparative example 2 before the dielectric breakdown occurred. Thus, more flaws were produced in the film structure in the portion of the dielectric film  13  corresponding to the periphery of the upper electrode film, than in the other portions. Accordingly, in the capacitor element according to Comparative Example 2, the dielectric film  13  is prone to incur the collapse of the film structure in the portion corresponding to the periphery of the upper electrode film.  
         [0058]     On the other hand, the withstanding voltages of the capacitor elements according to Working Examples 1, 2 exceeded 170 V and were greater by more than 35 V than those of the capacitor-elements according to Comparative Examples 1, 2. This is probably because the 2 μm-thick electrode film  12  of Working Example 1 and the 4 μm-thick electrode film  12  of Working Example 2 can suppress the propagation of stress strain from the joint portion  41  to the dielectric film  13  more effectively than the upper electrode film in Comparative Example 1, thereby suppressing emergence of flaws in the film structure of the dielectric film  13 . Also, the electrode films  12  of Working Examples 1, 2 merely incur smaller stress strain than the upper electrode film according to Comparative Example 2, which is advantageous to the suppression of the flaws in the dielectric film  13 .