Abstract:
Methods of fabricating an on-chip capacitor with a variable capacitance, as well as methods of adjusting the capacitance of an on-chip capacitor and design structures for an on-chip capacitor. The method includes forming first and second ports configured to be powered with opposite polarities, first and second electrodes, and first and second voltage-controlled units. The method includes configuring the first voltage-controlled unit to selectively couple the first electrode with the first port, and the second voltage-controlled unit to selectively couple the second electrode with the second port. When the first electrode is coupled by the first voltage-controlled unit with the first port and the second electrode is coupled by the second voltage-controlled unit with the second port, the capacitance of the on-chip capacitor increases.

Description:
BACKGROUND 
       [0001]    The invention relates generally to semiconductor device fabrication and, in particular, to methods for fabricating an on-chip capacitor characterized by a tunable variable capacitance, as well as to methods of tuning an on-chip capacitor and design structures for an on-chip capacitor. 
         [0002]    Capacitors are on-chip passive devices commonly employed in many types of monolithic integrated circuits designed to operate at high frequencies, such as those found in wireless communication devices. In particular, on-chip capacitors are found in radiofrequency integrated circuits (RFICs), which have applications such as Phase-Locked Loop (PLL) transmitters, voltage controlled oscillators (VCOs), impedance matching networks, filters, etc. The integration of on-chip capacitors may be accomplished by introducing these passive devices into one or more of the metallization levels of the back-end-of-line (BEOL) wiring structure. The BEOL wiring structure is used to electrically interconnect the active devices, such as field effect transistors (FETs), of the integrated circuit during front-end-of-line (FEOL) processing. A popular method of forming a BEOL wiring structure is a dual damascene process in which vias and trenches are formed in a dielectric layer and then filled with metal in a single process step. 
         [0003]    A significant problem with conventional BEOL on-chip capacitors is an inability to tune the capacitance during actual circuit operation. This problem is especially acute for on-chip capacitors found in oscillators, which have a natural resonance frequency that is highly dependent on the capacitance. Manufacturing tolerances may cause significant variations in the capacitance of different capacitors on a chip, significant variations in the capacitance among nominally equivalent capacitors on different chips fabricated on a single wafer, and significant variations in the capacitance for nominally equivalent capacitors fabricated on different wafers. These capacitance variations among on-chip capacitors that have been designed to have a nominally identical capacitance can limit the reproducibility of the resonance frequency. 
         [0004]    On-chip capacitors with the ability to actively adjust capacitance may be fabricated by FEOL processes. These on-chip capacitors rely on the capacitance of a p-n junction or the gate capacitance of an FET. However, FEOL on-chip capacitors require extra masks for manufacturing and, therefore, are costly. Because FEOL on-chip capacitors are entirely embedded within the semiconductor substrate, FEOL on-chip capacitors are also more susceptible to substrate noise, in comparison with capacitors sited in the BEOL wiring. 
         [0005]    In summary, improved methods for fabricating an on-chip capacitor, as well as improved methods of tuning an on-chip capacitor, are needed that overcome these and other deficiencies of conventional device fabrication methods for on-chip capacitors and design structures for an on-chip capacitor. 
       BRIEF SUMMARY 
       [0006]    In an embodiment of the invention, a method of fabricating a variable capacitance, on-chip capacitor includes forming first and second ports and first and second electrodes in a dielectric layer. The first and second ports are configured to be powered with opposite polarities. The method further includes forming a first voltage-controlled unit configured to selectively couple the first electrode with the first port, and forming a second voltage-controlled unit configured to selectively couple the second electrode with the second port. When the first electrode is coupled by the first voltage-controlled unit with the first port and the second electrode is coupled by the second voltage-controlled unit with the second port, the capacitance of the on-chip capacitor increases. 
         [0007]    In another embodiment of the invention, a method is provided for tuning an on-chip capacitor during operation of an integrated circuit electrically coupled with the on-chip capacitor. The method includes powering first and second ports of the on-chip capacitor with opposite polarities, selectively connecting a first electrode with the first port using a first voltage signal supplied from the integrated circuit, and selectively connecting a second electrode with the second port using a second voltage signal supplied from the integrated circuit. 
         [0008]    In another embodiment of the invention, a design structure is embodied in a machine readable medium for designing, manufacturing, or testing an integrated circuit. The design structure comprises an on-chip capacitor including first and second ports configured to be powered with opposite polarities, first and second electrodes, and first and second voltage-controlled units. Each of the first and second voltage-controlled units is configured to be switched between a first state in which the first and second electrodes are electrically isolated from the first and second ports and a second state. The first electrode is electrically connected with the first port when the first voltage-controlled unit is switched to the second state. The second electrode electrically is connected with the second port when the second voltage-controlled unit is switched to the second state. The on-chip capacitor has a larger capacitance value when the first and second voltage-controlled units are in the second state than when the first and second voltage-controlled units are in the first state. The design structure may comprise a netlist, may reside on storage medium as a data format used for the exchange of layout data of integrated circuits, or may reside in a programmable gate array. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the embodiments of the invention. 
           [0010]      FIG. 1  is a perspective view of a portion of an on-chip capacitor in accordance with an embodiment of the invention. 
           [0011]      FIG. 2  is a cross-sectional view of a portion of  FIG. 1  in which the ports and the electrodes of the on-chip capacitor, as well as the dielectric layers for the metallization levels in which the ports and electrodes are embedded, are visible. 
           [0012]      FIG. 3  is a schematic view of the on-chip capacitor and switching devices of  FIGS. 1 and 2 . 
           [0013]      FIG. 4  is a perspective view of an on-chip capacitor in accordance with an alternative embodiment of the invention. 
           [0014]      FIG. 5  is a perspective view of an on-chip capacitor in accordance with an alternative embodiment of the invention. 
           [0015]      FIG. 6  is a flow diagram of a design process used in semiconductor design, manufacture, and/or test. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    With reference to  FIGS. 1-3  and in accordance with an embodiment of the invention, a back-end-of-line (BEOL) wiring structure, generally indicated by reference numeral  10 , includes a dielectric layer  12  of a metallization level (M x+1 ), a dielectric layer  14  of a metallization level (M x ) underlying the metallization level (M x+1 ), and an on-chip capacitor  16  embedded in the dielectric layers  12 ,  14 . Additional metallization lower levels (not shown) may exist below the metallization levels (M x , M x+1 ) and/or additional metallization levels may exist above the metallization levels (M x , M x+1 ). Conductive features in the different metallization levels of the BEOL wiring structure  10 , such as the representative feature  18  in metallization level (M x+1 ) and the representative features  19 ,  20  in a metallization level (M x+2 ), interconnect active devices of an integrated circuit and may provide circuit-to-circuit connections, or may establish contacts with input and output terminals of the chip. 
         [0017]    The on-chip capacitor  16  represents a passive device that is associated with an integrated circuit, such as a radiofrequency integrated circuit (RFIC), which also includes active devices fabricated by front-end-of-line (FEOL) processes on a substrate  22 . The device design for such RFICs and the nature of the various FEOL processes used to form the active devices of an RFIC are familiar to a person having ordinary skill in the art. The substrate  22  is typically a chip or die consisting of a piece of a semiconductor wafer composed of a semiconductor material including, but not limited to, silicon (Si), silicon germanium (SiGe), a silicon-on-insulator (SOI) layer, and other like silicon-containing semiconductor materials. The active devices are coupled by contacts  21  and wires (not shown) in a dielectric layer  23  of the local interconnect (M1) metallization level with the overlying metallization levels of the BEOL wiring structure  10  and with each other. 
         [0018]    The on-chip capacitor  16  is structured as a vertical natural capacitor formed in two of the metallization levels (M x , M x+1 ) of the BEOL wiring structure  10 . The on-chip capacitor  16  includes conductive bars or tabs  24 ,  26  and electrodes  28 ,  30  constructed on metallization level (M x+1 ), as well conductive bars or tabs  32 ,  34  and electrodes  36 ,  38  constructed on metallization level (M x ). Conductive tabs  24 ,  26  and electrodes  28 ,  30  are disposed in the same plane of the BEOL wiring structure  10  and are formed from conductor material of a common thickness. Conductive tabs  32 ,  34  and electrodes  36 ,  38  are disposed in a different plane of the BEOL wiring structure  10  underlying the plane containing the conductive tabs  24 ,  26  and electrodes  28 ,  30 . Conductive tabs  32 ,  34  and electrodes  36 ,  38  are formed from conductor material of a common thickness. In certain embodiments, the involved metallization levels (M x ) and (M x+1 ) for the on-chip capacitor  16  may be the M2 and M3 levels, or the M3 and M4 levels, of the BEOL wiring structure  10 . 
         [0019]    Conductive tabs  24 ,  26  have a substantially parallel arrangement and are spaced apart by a distance sufficient to transversely fit the electrodes  28 ,  30  into the space separating them. Conductive tabs  32 ,  34  have a substantially parallel arrangement and are spaced by an amount sufficient to transversely fit the electrodes  36 ,  38  into the space separating them. Interconnect members, in the representative form of a row of spaced-apart vias  40  defined in the dielectric layer  14 , extend vertically between conductive tab  24  in metallization level (M x+1 ) and conductive tab  32  in metallization level (M x ). Interconnect members, in the representative form of a row of spaced-apart vias  42  defined in the dielectric layer  14 , extend vertically between conductive tab  26  in metallization level (M x+1 ) and conductive tab  34  in metallization level (M x ). 
         [0020]    Vias  40  electrically short conductive tabs  24 ,  32  together to define one port, which is generally indicated by reference numeral  25 , of the on-chip capacitor  16 . Vias  42  electrically short conductive tabs  26 ,  34  together to define another port, which is generally indicated by reference numeral  35 , of the on-chip capacitor  16 . Ports  25 ,  35  of the on-chip capacitor  16  are continuously connected to terminals of opposite polarity at a power supply  45 . 
         [0021]    In metallization level (M x+1 ), electrodes  28  and  30  project transversely as a substantially parallel set of fingers in the space separating conductive tabs  24 ,  26 . In metallization level (M x ), electrodes  36  and  38  project transversely as a substantially parallel set of fingers in the space between conductive tabs  32 ,  34 . Electrodes  28 ,  30  and electrodes  36 ,  38  are arranged in respective arrays of rows with one of the electrodes  28  stacked in near vertical alignment above one of the electrodes  36  and one of the electrodes  30  stacked in near vertical alignment above one of the electrodes  38 . Specifically, the lateral sidewalls of the electrodes  28  are approximately aligned, when viewed in a vertical direction, with the lateral sidewalls of the electrodes  36 . Similarly, when viewed in a vertical direction, the lateral sidewalls of the electrodes  30  are approximately aligned with the lateral sidewalls of the electrodes  38 . 
         [0022]    With continued reference to  FIGS. 1-3 , electrodes  28  and  30  have an interleaved arrangement relative to each other that is effective to define a construction in which one of the electrodes  28  is disposed between each adjacent pair of electrodes  30  and one of the electrodes  30  is disposed between each adjacent pair of electrodes  28 . Similarly, electrodes  36  and  38  are interleaved such that one of the electrodes  36  is disposed between each adjacent pair of electrodes  38  and one of the electrodes  38  is disposed between each adjacent pair of electrodes  36 . Slots or spaces between adjacent pairs of the electrodes  28  and  30  and adjacent pairs of electrodes  36  and  38  are filled with portions of the dielectric layers  12 ,  14 , which supply electrical isolation. In addition, the tip of each of the electrodes  28 ,  30 ,  36 ,  38  is separated from the adjacent conductive tabs  24 ,  26 ,  32 ,  34  by a respective small gap, G 1 . The opposite tip of each of the electrodes  28 ,  30 ,  36 ,  38  is separated from the adjacent conductive tabs  24 ,  26 ,  32 ,  34  by a respective small gap, G 2 . Hence, as constructed, the electrodes  28 ,  30 ,  36 ,  38  are electrically floating relative to the conductive tabs  24 ,  26 ,  32 ,  34  and lack any direct physical connection with the conductive tabs  24 ,  26 ,  32 ,  34 . 
         [0023]    Interconnect members, in the representative form of a row of spaced-apart vias  44 , extend vertically in dielectric layer  12  between the electrodes  28  in metallization level (M x+1 ) and the electrodes  36  in metallization level (M x ). Vias  44  electrically connect each individual stacked pair of the electrodes  28  and  36  in parallel. Similarly, interconnect members, in the representative form of a row of spaced-apart vias  46 , extend vertically in dielectric layer  12  between the electrodes  30  in metallization level (M x+1 ) and the electrodes  38  in metallization level (M x ). Vias  46  electrically connect each individual stacked pair of the electrodes  30  and  38  in parallel. 
         [0024]    The on-chip capacitor  16  may have one or more additional rows of interleaved electrodes (not shown) in a metallization level of the BEOL wiring structure  10  either below metallization level (M x ) or above metallization level (M x+1 ) to provide a construction characterized by more than two levels as in the representative embodiment. These additional electrodes are connected by additional rows of vias (not shown) with either electrodes  28 ,  36  or electrodes  30 ,  38  contingent upon vertical alignment. In one specific embodiment of the invention, the involved metallization levels for a three-level capacitor construction of the on-chip capacitor  16  may be the M2, M3, and M4 levels of the BEOL wiring structure  10 . 
         [0025]    The on-chip capacitor  16  features a plurality of capacitance states when different contact combinations are selected. Specifically, field effect transistors  48 ,  49 ,  50 ,  51 ,  52 ,  53 , of which only field effect transistors  48 ,  49 ,  50  are visible in  FIG. 1 , are employed to electrically connect the electrodes  28 ,  30 ,  36 ,  38  in a selective manner with the conductive tabs  24 ,  26 ,  32 ,  34 . The field effect transistors  48 - 53  are among the active devices on the substrate  22  and may be fabricated by complementary metal-oxide-semiconductor (CMOS) processes. Each of the field effect transistors  48 - 53  has a respective gate stack  54  residing on a top surface  56  of the substrate  22  and respective source/drain regions  58 ,  60  defined as heavily doped regions in the semiconductor material of the substrate  22 . A control voltage applied to each gate stack  54  is effective to permit current flow in an underlying channel of the semiconductor material of substrate  22 , which is disposed between the source/drain regions  58 ,  60 . In an alternative embodiment, one or more of the field effect transistors  48 - 53  may be replaced by a different type of voltage-controlled device. 
         [0026]    With the assistance of the field effect transistors  48 - 53 , the capacitance of the on-chip capacitor  16  is configured to be tunable or variable among multiple different incremental capacitance values. During operation of the associated integrated circuit containing the on-chip capacitor  16  and based upon a perceived need to tune the capacitance of the on-chip capacitor  16 , voltage control signals are communicated to the field effect transistors  48 - 53 . The voltage control signals are effective to switch the field effect transistors  48 - 53  to close respective current paths connecting each of the electrodes  28 ,  30 ,  36 ,  38  with one of the ports  25 ,  35 . As a result, the capacitance of the on-chip capacitor  16  can be actively varied while the associated integrated circuit carried on substrate  22  is operating. Therefore, adjustments in the capacitance of the on-chip capacitor  16  are programmable. 
         [0027]    As best shown schematically in  FIG. 3 , each of the field effect transistors  48 - 53  controls whether a particular via-connected pair of the electrodes  28 ,  36  or a particular via-connected pair of the electrodes  30 ,  38  is connected to the on-chip capacitor  16  and, therefore, whether its capacitance contributes to the total capacitance of the on-chip capacitor  16 . Specifically, field effect transistors  48  and  53  are concurrently switched by a control voltage or bit  62  to selectively connect one via-connected pair of electrodes  28 ,  36  in a closed circuit with port  25  and one via-connected pair of electrodes  30 ,  38  in a closed circuit with port  35 . Similarly, field effect transistors  49  and  52  are concurrently switched by a control voltage or bit  64  to selectively connect a different via-connected pair of electrodes  28 ,  36  in a closed circuit with port  25  and a different via-connected pair of electrodes  30 ,  38  in a closed circuit with port  35 . Field effect transistors  50  and  51  are concurrently switched by a control voltage or bit  66  to selectively connect yet another via-connected pair of electrodes  28 ,  36  in a closed circuit with port  25  and yet another via-connected pair of electrodes  30 ,  38  in a closed circuit with port  35 . Because the electrodes  28 ,  36  and the electrodes  30 ,  38  are wired in parallel by vias  44 ,  46 , respectively, each of the field effect transistors  48 - 53  controls whether or not an entire electrode stack is powered. 
         [0028]    The aggregate number of pairs of electrodes  28 ,  36  connected in a closed circuit with port  25  and the aggregate number of pairs of electrodes  30 ,  38  connected in a closed circuit with port  35  determines the capacitance value of the on-chip capacitor  16 . Only one of the control bits  62 ,  64 ,  66  may be selected such that only one via-connected pair of electrodes  28 ,  36  is connected in a closed circuit with port  25  and one via-connected pair of electrodes  30 ,  38  is connected in a closed circuit with port  35 . Of course, all of the control bits  62 ,  64 ,  66  may be concurrently selected so that all pairs of electrodes  28 ,  36  are connected in a closed circuit with port  25  and both pairs of electrodes  30  are connected in a closed circuit with port  35  to provide the maximum value of the capacitance. Only two of the three control bits  62 ,  64 ,  66  may be selected under voltage control, during the operation of the integrated circuit, such that multiple, but less than all, pairs of electrodes  28 ,  36  are connected in a closed circuit with port  25  and multiple, but less than all, pairs of electrodes  30 , are connected in a closed circuit with port  35 . These selections provide capacitance values intermediate between the maximum and minimum capacitance values. Additional electrodes like electrodes  28 ,  30 ,  36 ,  38  may be added within the metallization levels (M x , M x+1 ) of the BEOL wiring structure  10 , in conjunction with additional field effect transistors (not shown) among the active devices on the substrate  22 , to increase the range of tunability for the variable capacitance of the on-chip capacitor  16 . 
         [0029]    Symmetrically arranging and switching the electrodes  28 ,  30 ,  36 ,  38  promotes the ability to predict the total capacitance and the parasitic capacitance for the on-chip capacitor  16 . In an alternative embodiment, additional control bits similar to control bits  62 ,  64 ,  66  can be provided such that each individual field effect transistor  48 - 53  is subject to separate voltage control during operation of the integrated circuit. Each of the via-connected pairs of electrodes  28 ,  36  and each of the via-connected pairs of electrodes  30 ,  38  adds approximately the same nominal incremental capacitance to the total capacitance of the on-chip capacitor  16 . The ability to adjust the total capacitance of the on-chip capacitor  16  in discrete amounts may be useful, for example, to adjust the resonance frequency output by an LC resonator commonly found in an RFIC. 
         [0030]    As a result of the opposite polarity electrical connection with the ports  25 ,  35  and the interleaved arrangement, the stacked pairs of electrodes  28 ,  36 , and the stacked pairs of electrodes  30 ,  38  are electrically connected in a selective manner by the control bits  62 ,  64 ,  66  to the power supply terminals of opposite polarity to generate a capacitance laterally between the different electrodes  28 ,  30  in metallization level (M x+1 ) and laterally between the electrodes  36 ,  38  in metallization level (M x ). 
         [0031]    As mentioned above, the on-chip capacitor  16  is formed by damascene processes conventionally associated with BEOL processing, which is used to form the conductive features in the various different stacked metallization levels of the BEOL wiring structure  10 . Because of this commonality during manufacture (having the same material, thickness, etc.), the conductive features of the on-chip capacitor  16  are concurrently formed with the other conductive features, such as the representative conductive features  18 ,  19 ,  20 , that are used to establish electrical connections with the active devices. 
         [0032]    Specifically and with reference to  FIGS. 1-3 , dielectric layer  14  of metallization level (M x ) is applied by a conventional deposition technique recognized by a person having ordinary skill in the art. A pattern of via openings and trenches is defined in dielectric layer  14  using known lithography and etching techniques characteristic of a damascene process. To that end, a resist layer (not shown) is applied to the top surface of dielectric layer  14 , exposed to radiation to impart a latent image of a trench pattern characteristic of conductive tabs  32 ,  34  and electrodes  36 ,  38 , and developed to transform the latent image of the trench pattern into a final image pattern with laterally dispersed surface areas of dielectric layer  14  unmasked at the future sites of conductive tabs  32 ,  34  and electrodes  36 ,  38 . Unmasked regions of dielectric layer  14  at these sites are removed with an etching process, such as reactive ion etching (RIE), capable of producing substantially vertical sidewalls for the trenches. The resulting trenches are filled using a conventional deposition process with amounts of a representative conductor to define the conductive tabs  32 ,  34  and electrodes  36 ,  38  of metallization level (M x ). Any excess overburden of conductor remaining after the filling step is removed by planarization, such as with a chemical mechanical polishing (CMP) process. The resist layer is removed from the top surface of dielectric layer  14 . 
         [0033]    Dielectric layer  12  of metallization level (M x+1 ) is then applied by a conventional deposition process on dielectric layer  14 . A resist layer (not shown) is applied to the top surface of dielectric layer  12 , exposed to radiation to impart a latent image of a via opening pattern for vias  40 ,  42 ,  44 ,  46  and developed to transform the latent image of the via pattern into a final image pattern with laterally dispersed surface areas of dielectric layer  12  unmasked at the future sites of vias  40 ,  42 ,  44 ,  46 . Unmasked regions of dielectric layer  12  at these sites are removed with an etching process, such as RIE, capable of producing substantially vertical sidewalls for the via openings which extend vertically to intersect the top surfaces of the conductive tabs  32 ,  34  and electrodes  36 ,  38 . The resist layer is removed from the top surface of dielectric layer  12 . 
         [0034]    Another resist layer (not shown) is applied to the top surface of dielectric layer  12 , exposed to radiation to impart a latent image of a trench pattern for conductive tabs  24 ,  26  and electrodes  28 ,  30 , and developed to transform the latent image of the trench pattern into a final image pattern with laterally dispersed surface areas of dielectric layer  12  unmasked at the future sites of conductive tabs  24 ,  26  and electrodes  28 ,  30 . Unmasked regions of dielectric layer  12  at these sites are removed with an etching process, such as RIE, capable of producing substantially vertical sidewalls for the trenches. The resist layer is removed from the top surface of dielectric layer  12 . 
         [0035]    The via openings and trenches in the dielectric layer  12  are filled with a representative conductor to define the tabs  32 ,  34 , electrodes  36 ,  38 , and vias  40 ,  42 ,  44 ,  46  of metallization level (M x+1 ). Any excess overburden of conductor remaining after the filling step is removed from the top surface of the dielectric layer  12  by planarization, such as a CMP process. Metallization level (M x+2 ) is applied in a manner similar to metallization levels (M x , M x+1 ), as are any additional metallization levels (not shown). 
         [0036]    The various resist layers used to form the on-chip capacitor  16  are the resist layers used to form the conventional BEOL metallization contained in metallization level (M x ) and metallization level (M x+1 ). Consequently, the conductive features of the on-chip capacitor  16  represent portions of the BEOL metallization in these different metallization levels and may be formed without additional masks. 
         [0037]    Dielectric layers  12 ,  14  may comprise any organic or inorganic dielectric material recognized by a person having ordinary skill in the art, which may be deposited by any number of well known conventional techniques such as sputtering, spin-on application, chemical vapor deposition (CVD) process or a plasma enhanced CVD (PECVD) process. Candidate inorganic dielectric materials for dielectric layers  12 ,  14  may include, but are not limited to, silicon dioxide, fluorine-doped silicon glass (FSG), and combinations of these dielectric materials. Alternatively, the dielectric material constituting dielectric layers  12 ,  14  may be characterized by a relative permittivity or dielectric constant smaller than the dielectric constant of silicon dioxide, which is about 3.9. Candidate low-k dielectric materials for dielectric layers  12 ,  14  include, but are not limited to, porous and nonporous spin-on organic low-k dielectrics, such as spin-on aromatic thermoset polymer resins, porous and nonporous inorganic low-k dielectrics, such as organosilicate glasses, hydrogen-enriched silicon oxycarbide (SiCOH), and carbon-doped oxides, and combinations of organic and inorganic dielectrics. 
         [0038]    Candidate conductive materials for the on-chip capacitor  16  include, but are not limited to, copper (Cu), aluminum (Al), alloys of these metals, other similar metals like tungsten (W), and metal silicides. These types of metals may be deposited by conventional processes including, but not limited to, CVD processes, electrochemical processes like electroplating or electroless plating, and silicidation processes as each is understood by a person having ordinary skill in the art. 
         [0039]    A relatively thin conductive liner layer (not shown) may respectively clad the metallization of the on-chip capacitor  16  such that the conductor is isolated from the surrounding dielectric material of dielectric layers  12 ,  14  against unwanted diffusion and such that adhesion is enhanced between the conductor and the dielectric material. Representative thin conductive liner layers include, but are not limited to, a bilayer of titanium and titanium nitride or a bilayer of tantalum or tantalum nitride applied to the dielectric material by conventional deposition processes. 
         [0040]    The gate stack  54  for each of the field effect transistors  48 - 53  includes a gate electrode and a gate dielectric layer positioned between the gate electrode and the top surface  56  of the substrate  22 . Each gate stack  54  is formed by conventional fabrication methods that involve the patterning of an appropriate layer stack by techniques understood by a person having ordinary skill in the art. The conductor constituting the gate electrode may be, for example, metal, silicide, polycrystalline silicon (polysilicon), or any other appropriate material(s) deposited by a CVD process, etc. The gate dielectric layer may be composed of any suitable dielectric or insulating material including, but not limited to, silicon dioxide, silicon oxynitride, a high-k dielectric material such as hafnium oxide or hafnium oxynitride, or combinations of these dielectric materials. 
         [0041]    Each gate stack  54  and any spacers (not shown) applied to the sidewalls of the gate stack  54  may act as self-aligned masks for one or more ion implantations that define the respective source/drain regions  58 ,  60  in the semiconductor material of the substrate  22 . Techniques for implanting ions to doped such source/drain regions  58 ,  60  are familiar to persons of ordinary skill in the art. Alternatively, the source/drain regions  58 ,  60  of the field effect transistors  48 - 53  may be formed by dopant diffusion or a combination of dopant diffusion and ion implantation. Shallow trench isolation (STI) regions  68 , which electrically isolate the source/drain regions  58 ,  60  of adjacent field effect transistors  48 - 53 , are formed in the substrate  22  by, for example, a conventional patterning, etch, dielectric fill, and planarization process characteristic of standard bulk CMOS processing. 
         [0042]    The dielectric layer  23  for the local interconnect (M1) metallization level is applied on the top surface  56  of the substrate  22 . Contacts  21 , which are formed in the dielectric layer  23 , are coupled electrically with the gate electrode of the gate stack  54  and the source/drain regions  58 ,  60  of each of the field effect transistors  48 - 53 . Each of the contacts  21  connected with the gate electrode of one of the gate stacks  54  is further coupled with one of the control bits  62 ,  64 ,  66 . One of the contacts  21  connected with one of the source/drain regions  58 ,  60  of each of the field effect transistors  48 - 53  is further coupled with either port  25  or port  35 . Another of the contacts  21  connected with the other of the source/drain regions  58 ,  60  of each of the field effect transistors  48 - 53  is further coupled with one of the pairs of electrodes  28 ,  36  or with one of the pairs of electrodes  30 ,  38 . 
         [0043]    With reference to  FIG. 4  in which like reference numerals refer to like features in  FIGS. 1-3  and in accordance with an alternative embodiment, an on-chip capacitor  16   a , which is otherwise similar to the on-chip capacitor  16 , has a fixed capacitance established as a baseline by a plurality of electrodes  70 ,  72 ,  74 ,  76  that are each continuously and directly connected with one of the ports  25 ,  35 . Specifically, electrodes  70 ,  72  are disposed in the same metallization level (M x+1 ) as electrodes  28 ,  30  and, similar to electrodes  28 ,  30 , project laterally as substantially parallel fingers in the space between conductive tabs  24 ,  26 . Each of the electrodes  70 ,  72  is directly coupled with one of the conductive tabs  24 ,  26 . Similarly, electrodes  74 ,  76  are disposed in the same metallization level (M x ) as electrodes  36 ,  38  and, similar to electrodes  36 ,  38 , project transversely as substantially parallel fingers in the space between conductive tabs  32 ,  34 . Each of the electrodes  74 ,  76  is directly coupled with one of the conductive tabs  32 ,  34 . In other words, each of the electrodes  70 ,  72 ,  74 ,  76  is continuously tied electrically with one of the ports  25 ,  35 , which provides the fixed capacitance. 
         [0044]    Electrodes  70 ,  72 ,  74 ,  76  are fabricated by the same BEOL processes and from the same materials as the electrodes  28 ,  30 ,  36 ,  38  ( FIGS. 1-3 ). Interconnect members, in the representative form of rows of spaced-apart vias  78 , extend vertically in dielectric layer  14  between electrodes  70 ,  74  such that stacked pairs of electrodes  70 ,  74  are electrically connected. Interconnect members, in the representative form of rows of spaced-apart vias  80 , extend vertically in dielectric layer  14  between electrodes  72 ,  76  such that stacked pairs of electrodes  72 ,  76  are electrically connected. 
         [0045]    Electrodes  28 ,  30 ,  36 ,  38  are used to adjust the capacitance of the on-chip capacitor  16   a  relative to the baseline capacitance established by the fixed capacitance from electrodes  70 ,  72 ,  74 ,  76 . Each of the via-connected pairs of electrodes  28 ,  36  and each of the via-connected pairs of electrodes  30 ,  38  adds approximately the same nominal discrete capacitance increment to increase the total capacitance of the on-chip capacitor  16   a  above the baseline value. As a result, the capacitance of the on-chip capacitor  16  can be adjusted to compensate for process variations in the BEOL processes used to fabricate the on-chip capacitor  16 . For example, the on-chip capacitor  16   a  in the BEOL wiring structure  10  on one chip may have a capacitance that is abnormally high, in which case a subset of the electrodes  28 ,  30 ,  36 ,  38  may be connected to the ports  25 ,  35  or, alternatively, disconnected from the ports  25 ,  35 . Alternatively, the on-chip capacitor  16   a  in the BEOL wiring structure  10  on another chip may have a capacitance that is abnormally low, in which instance a different subset of the electrodes  28 ,  30 ,  36 ,  38  may be connected to the ports  25 ,  35  or, alternatively, disconnected from the ports  25 ,  35 . In either embodiment, capacitance variations of the on-chip capacitor  16   a  arising from tolerances in the BEOL fabrication processes can be compensated in a programmed manner while retaining the same hardware and after the chip is fabricated, packaged, and deployed in an RFIC. The impact of the ability to fine tune the capacitance is that a designer may effectively make a near zero tolerance version of the on-chip capacitor  16   a.    
         [0046]    With reference to  FIG. 5  in which like reference numerals refer to like features in  FIG. 2  and in accordance with an alternative embodiment, an on-chip capacitor  82  has a baseline fixed capacitance established by a plurality of electrodes  84  that are each continuously and directly connected with conductive tab  24  and port  25 , and a plurality of electrodes  86  that are each continuously and directly connected with conductive tab  26  and port  35 . Electrodes  84 ,  86 , which are disposed in metallization level (M x+1 ) and are similar to electrodes  70 ,  72  ( FIG. 4 ), project transversely as substantially parallel fingers in the space between conductive tabs  24 ,  26 . Of course, electrodes  84  are electrically isolated by portions of dielectric layer  12  from conductive tab  26  and electrodes  86  are electrically isolated by other portions of dielectric layer  12  from conductive tab  24 . 
         [0047]    Another plurality of electrodes  88 , which are disposed in metallization level (M x ), are each continuously and directly connected with conductive tab  32 . Similarly, another plurality of electrodes  90 , which are disposed in metallization level (M x ), are each continuously and directly connected with conductive tab  34 . Electrodes  88 ,  90 , which are also similar to electrodes  74 ,  76  ( FIG. 4 ), project transversely as substantially parallel fingers in the space between conductive tabs  32 ,  34 . Electrodes  88  are electrically isolated by portions of dielectric layer  12  from conductive tab  34  and other portions of the dielectric layer  12  electrically isolate electrodes  90  from conductive tab  32 . 
         [0048]    The electrodes  84 ,  86 ,  88 ,  90  are fabricated by the same BEOL processes and from the same materials as the electrodes  28 ,  30 ,  36 ,  38  ( FIGS. 1-3 ). However, in contrast to on-chip capacitor  16  ( FIGS. 1-3 ) and on-chip capacitor  16   a  ( FIG. 4 ), the electrodes  84 ,  88  aligned in each individual vertical stack and the electrodes  86 ,  90  aligned in each individual vertical stack are not connected by vertical interconnects in the form of vias. 
         [0049]    The on-chip capacitor  82  features a binary pair of capacitance states that can be selectively established. Specifically, field effect transistors  92 ,  93 , which are constructed and function similar to field effect transistors  48 - 53 , are employed to electrically connect conductive tabs  24 ,  26  in a selective manner with conductive tabs  32 ,  34  when a voltage is applied to a single control bit  94 . Specifically, when the control bit  94  is logically switched to cause the field effect transistors  92 ,  93  to close the respective current paths, conductive tab  24  is electrically connected in an indirect manner through the field effect transistor  92  with conductive tab  32 , and conductive tab  26  is electrically connected in an indirect manner through the field effect transistor  93  with conductive tab  34 . If the control voltage is absent from control bit  94 , conductive tabs  32 ,  34  and electrodes  88 ,  90  are electrically floating. 
         [0050]    During operation of the associated integrated circuit containing the on-chip capacitor  82  and based upon a need to tune the capacitance of the on-chip capacitor  82 , the integrated circuit communicates voltage signals to the field effect transistors  92 ,  93 . With this assistance from the field effect transistors  92 ,  93 , the capacitance of the on-chip capacitor  82  may be coarsely tunable between two significantly different capacitance values. For example, the on-chip capacitor  82  may have a capacitance of about 10 picofarads when only conductive tabs  24 ,  26  are powered and a capacitance of about 20 picofarads when the control bit  94  is activated to connect conductive tabs  32 ,  34  with conductive tabs  24 ,  26 , respectively. The voltage signal on control bit  94  is the stimulus effective to cause the field effect transistors  92 ,  93  to change state and close a current path connecting the conductive tabs  24 ,  26  with the conductive tabs  32 ,  34 . As a result, the capacitance of the on-chip capacitor  82  can be actively tuned, albeit in a coarse binary manner in comparison with on-chip capacitor  16 , while the associated integrated circuit is operating. 
         [0051]    In an alternative embodiment, the construction of capacitor  82  can be combined with the construction of either capacitor  16  ( FIGS. 1-3 ) or capacitor  16   a  ( FIG. 4 ) to provide a device structure in which the resultant capacitor (not shown) can be coarsely tuned using electrodes  84 ,  86 ,  88 ,  90  and control bit  94 , and can be finely tuned using electrodes  28 ,  30 ,  36 ,  38  and control bits  62 ,  64 ,  66 . 
         [0052]      FIG. 6  shows a block diagram of an exemplary design flow  100  used for example, in semiconductor IC logic design, simulation, test, layout, and manufacture. Design flow  100  includes processes and mechanisms for processing design structures or devices to generate logically or otherwise functionally equivalent representations of the design structures and/or devices described above and shown in  FIGS. 1-5 . The design structures processed and/or generated by design flow  100  may be encoded on machine-readable transmission or storage media to include data and/or instructions that when executed or otherwise processed on a data processing system generate a logically, structurally, mechanically, or otherwise functionally equivalent representation of hardware components, circuits, devices, or systems. Design flow  100  may vary depending on the type of representation being designed. For example, a design flow  100  for building an application specific IC (ASIC) may differ from a design flow  100  for designing a standard component or from a design flow  100  for instantiating the design into a programmable array, for example a programmable gate array (PGA) or a field programmable gate array (FPGA) offered by Altera® Inc. or Xilinx® Inc. 
         [0053]      FIG. 6  illustrates multiple such design structures including an input design structure  102  that is preferably processed by a design process  104 . Design structure  102  may be a logical simulation design structure generated and processed by design process  104  to produce a logically equivalent functional representation of a hardware device. Design structure  102  may also or alternatively comprise data and/or program instructions that when processed by design process  104 , generate a functional representation of the physical structure of a hardware device. Whether representing functional and/or structural design features, design structure  102  may be generated using electronic computer-aided design (ECAD) such as implemented by a core developer/designer. When encoded on a machine-readable data transmission, gate array, or storage medium, design structure  102  may be accessed and processed by one or more hardware and/or software modules within design process  104  to simulate or otherwise functionally represent an electronic component, circuit, electronic or logic module, apparatus, device, or system such as those shown in  FIGS. 1-5 . As such, design structure  102  may comprise files or other data structures including human and/or machine-readable source code, compiled structures, and computer-executable code structures that when processed by a design or simulation data processing system, functionally simulate or otherwise represent circuits or other levels of hardware logic design. Such data structures may include hardware-description language (HDL) design entities or other data structures conforming to and/or compatible with lower-level HDL design languages such as Verilog and VHDL, and/or higher-level design languages such as C or C++. 
         [0054]    Design process  104  preferably employs and incorporates hardware and/or software modules for synthesizing, translating, or otherwise processing a design/simulation functional equivalent of the components, circuits, devices, or logic structures shown in  FIGS. 1-5  to generate a netlist  106  which may contain design structures such as design structure  102 . Netlist  106  may comprise, for example, compiled or otherwise processed data structures representing a list of wires, discrete components, logic gates, control circuits, I/O devices, models, etc. that describes the connections to other elements and circuits in an integrated circuit design. Netlist  106  may be synthesized using an iterative process in which netlist  106  is resynthesized one or more times depending on design specifications and parameters for the device. As with other design structure types described herein, netlist  106  may be recorded on a machine-readable data storage medium or programmed into a programmable gate array. The medium may be a non-volatile storage medium such as a magnetic or optical disk drive, a programmable gate array, a compact flash, or other flash memory. Additionally, or in the alternative, the medium may be a system or cache memory, buffer space, or electrically or optically conductive devices and materials on which data packets may be transmitted and intermediately stored via the Internet, or other networking suitable means. 
         [0055]    Design process  104  may include hardware and software modules for processing a variety of input data structure types including netlist  106 . Such data structure types may reside, for example, within library elements  108  and include a set of commonly used elements, circuits, and devices, including models, layouts, and symbolic representations, for a given manufacturing technology (e.g., different technology nodes, 32 nm, 45 nm, 90 nm, etc.). The data structure types may further include design specifications  110 , characterization data  112 , verification data  114 , design rules  116 , and test data files  118  which may include input test patterns, output test results, and other testing information. Design process  104  may further include, for example, standard mechanical design processes such as stress analysis, thermal analysis, mechanical event simulation, process simulation for operations such as casting, molding, and die press forming, etc. One of ordinary skill in the art of mechanical design can appreciate the extent of possible mechanical design tools and applications used in design process  104  without deviating from the scope and spirit of the invention. Design process  104  may also include modules for performing standard circuit design processes such as timing analysis, verification, design rule checking, place and route operations, etc. 
         [0056]    Design process  104  employs and incorporates logic and physical design tools such as HDL compilers and simulation model build tools to process design structure  102  together with some or all of the depicted supporting data structures along with any additional mechanical design or data (if applicable), to generate a second design structure  120 . Design structure  120  resides on a storage medium or programmable gate array in a data format used for the exchange of data of mechanical devices and structures (e.g., information stored in a IGES, DXF, Parasolid XT, JT, DRG, or any other suitable format for storing or rendering such mechanical design structures). Similar to design structure  102 , design structure  120  preferably comprises one or more files, data structures, or other computer-encoded data or instructions that reside on transmission or data storage media and that when processed by an ECAD system generate a logically or otherwise functionally equivalent form of one or more of the embodiments of the invention shown in  FIGS. 1-5 . In one embodiment, design structure  120  may comprise a compiled, executable HDL simulation model that functionally simulates the devices shown in  FIGS. 1-5 . 
         [0057]    Design structure  120  may also employ a data format used for the exchange of layout data of integrated circuits and/or symbolic data format (e.g. information stored in a GDSII (GDS2), GL1, OASIS, map files, or any other suitable format for storing such design data structures). Design structure  120  may comprise information such as, for example, symbolic data, map files, test data files, design content files, manufacturing data, layout parameters, wires, levels of metal, vias, shapes, data for routing through the manufacturing line, and any other data required by a manufacturer or other designer/developer to produce a device or structure as described above and shown in  FIGS. 1-5 . Design structure  120  may then proceed to a stage  122  where, for example, design structure  120 : proceeds to tape-out, is released to manufacturing, is released to a mask house, is sent to another design house, is sent back to the customer, etc. 
         [0058]    References herein to terms such as “vertical”, “horizontal”, etc. are made by way of example, and not by way of limitation, to establish a frame of reference. The term “horizontal” as used herein is defined as a plane parallel to a conventional plane of a semiconductor substrate, regardless of its actual three-dimensional spatial orientation. The term “vertical” refers to a direction perpendicular to the horizontal, as just defined. Terms, such as “on”, “above”, “below”, “side” (as in “sidewall”), “upper”, “lower”, “over”, “beneath”, and “under”, are defined with respect to the horizontal plane. It is understood that various other frames of reference may be employed for describing the invention without departing from the spirit and scope of the invention. It is also understood that features of the invention are not necessarily shown to scale in the drawings. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” 
         [0059]    It will be understood that when an element as a layer, region or substrate is described as being “on” or “over” another element, it can be directly on or over the other element or intervening elements may also be present. In contrast, when an element is described as being “directly on” or “directly over” another element, there are no intervening elements present. It will also be understood that when an element is described as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is described as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
         [0060]    As used herein, the terms “vertical alignment” and “vertically aligned” do not require precise vertical alignment of all edges of vertically aligned objects as some spatial offsets and tolerances are allowed. Objects can overlap, when viewed from a perspective normal to the top surface  56  of the substrate  22 , and retain the vertical alignment attribute. 
         [0061]    The fabrication of the semiconductor structure herein has been described by a specific order of fabrication stages and steps. However, it is understood that the order may differ from that described. For example, the order of two or more fabrication steps may be swapped relative to the order shown. Moreover, two or more fabrication steps may be conducted either concurrently or with partial concurrence. In addition, various fabrication steps may be omitted and other fabrication steps may be added. It is understood that all such variations are within the scope of the present invention. It is also understood that features of the present invention are not necessarily shown to scale in the drawings. 
         [0062]    While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.