Abstract:
An integrated semiconductor device includes a resistor and an FET device formed from a stack of layers. The stack of layers includes a dielectric layer formed on a substrate; a metal conductor layer having lower electrical resistance formed on the dielectric layer; and a polysilicon layer formed on the metal conductor layer. A resistor stack is formed by patterning a portion of the original stack of layers into a resistor. An FET stack is formed from another portion of the original stack of layers. The FET stack is doped to form a gate electrode and the resistor stack is doped aside from the resistor portion thereof. Then terminals are formed at distal ends of the resistor in a doped portion of the polysilicon layer. Alternatively, the polysilicon layer is etched away from the resistor stack followed by forming terminals at distal ends of the metal conductor in the resistor stack.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to semiconductor devices and more particularly to a process for fabricating polysilicon resistors for use in integrated circuits including Field Effect Transistor (FET) devices. 
         [0002]    Heretofore, in the case of Complementary Metal Insulator Semiconductor (CMIS) Complementary Metal Oxide Semiconductor (CMOS) (FET) technology, it has been typical for the gate electrode stack of a Metal Oxide (MOS) FET device to comprise a conductor in the form of a doped polysilicon gate electrode formed over a gate dielectric layer composed of a dielectric material such as silicon oxide. A disadvantage of utilizing polysilicon gates is that at inversion, polysilicon gate electrodes generally experience depletion of carriers in the area of the polysilicon gate adjacent to the gate dielectric. Such depletion of carriers, which is referred to in the art as the polysilicon depletion effect, reduces the effective gate capacitance of the Metal Insulator Semiconductor (MIS) device. More recently MIS FET devices have substituted high-K gate dielectric materials for the materials such as silicon oxide of MOS FET devices and metal gates have been substituted for polysilicon or combined therewith. Thus a gate electrode stack may comprise a complex stack of high K dielectric material, a metal layer, a layer of doped polysilicon, and a silicide layer. In CMOS devices including a gate stack comprising a bottom polysilicon portion and a top silicide portion a layer of silicide in such a gate stack contributes to a decrease in the resistance of the gate. The decrease in resistance causes a decrease in the time propagation delay RC of the gate. Although a silicide top gate region may help to decrease the resistance of the transistor, charge is still depleted in the vicinity of the interface formed between the bottom polysilicon gate and gate dielectric, thereby causing a smaller effective gate capacitance. 
         [0003]    Commonly assigned copending U. S. Patent Application No. 2007/0148838 of Doris et al. entitled “Metal Gate CMOS with at Least a Single Gate Metal and Dual Gate Dielectrics” states that in one type of “CMOS device the gate electrode includes at least a metal layer beneath a Si-containing, e.g., polysilicon, gate electrode.” 
         [0004]    Typical resistor processing provides for a doped polysilicon resistor body, where a block layer is employed to exclude the low resistance silicidation from the resistor body. This approach can have drawbacks due to the multiple process steps that influence the resistance value, and thus increase resistor tolerance. 
         [0005]    An alternative to employing a doped polysilicon resistor body, where a block layer is employed to exclude the low resistance silicidation from the resistor body is to utilize a separately processed resistor layer, for instance in the (Back End Of the Line) BEOL processing of the device. This adds significant process costs to the technology due to additional deposition, lithography and etching steps. 
         [0006]    U.S. Pat. No. 6,462,386 of Moriwaki et al. entitled “Semiconductor Device and Method of Manufacturing the Same” describes a semiconductor device comprising a first MOSFET and a second MOSFET. The first MOSFET includes a first gate insulating film formed on a semiconductor substrate and having a relatively large thickness and a first gate electrode composed of a polysilicon film formed on the first gate insulating film. The second MOSFET includes a second gate insulating film formed on the semiconductor substrate with a relatively small thickness and a second gate electrode composed of a metal film made of a refractory metal or a compound of a refractory metal and over on the second gate insulating film. 
         [0007]    U.S. Pat. No. 7,112,535 of Coolbaugh et al. entitled “Precision Polysilicon Resistor Process” which is commonly assigned describes a process for fabricating precision polysilicon resistors which more precisely control the tolerance of the sheet resistivity of the produced polysilicon resistors. The process includes performing an emitter/FET activation Rapid Thermal Anneal (RTA) on a wafer having partially formed polysilicon resistors, followed by steps of depositing a protective dielectric layer on the polysilicon, implanting a dopant through the protective dielectric layer into the polysilicon to define the resistance of the polysilicon resistors, and forming a silicide. The process included forming a first gate insulating film, having a relatively large thickness, on a semiconductor substrate followed by forming thereon a first gate electrode composed of a polysilicon film. A second FET includes a second gate insulating film formed on the semiconductor substrate which has a relatively small thickness; and forming thereon a second gate electrode composed of a metal film, and a barrier metal covering the sides and bottom of the first gate electrode formed in between the second gate insulating film and the second gate electrode. A resistor is composed of a polysilicon film formed in the step of forming the polysilicon film of the first gate electrode. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention utilizes a process of forming both a resistor and an FET from dual layers including a metal layer and a polysilicon layer. The pair of layers can be formed into both a gate electrode stack and a resistor stack by selective processing of different regions of the dual layers. 
         [0009]    An advantage of the method and the resulting structure is that the metal layer thickness is tightly controlled thereby providing an excellent resistor tolerance. The metal layer thickness naturally provides for a suitable resistor sheet resistance value of between 50-300 Ω/square. 
         [0010]    Another advantage is that the resistor formed by the metal layer within the gate electrode stack will be on the same chip as MOSFETs fabricated with HiK metal gate stack and will have no additional cost. 
         [0011]    The invention and objects and features thereof will be more readily apparent from the following detailed description and appended claims when taken with the drawings. 
         [0012]    In accordance with this invention, an integrated semiconductor device is formed on a substrate which includes a Field Effect Transistor (FET) device and a resistor adjacent thereto. A stack of layers is provided comprising a dielectric layer formed on the substrate, a metal conductor layer formed on the dielectric layer, and a polysilicon layer formed on the metal conductor layer. The stack of layers is patterned into the resistor and the FET device. The FET device is composed of a gate electrode stack formed from the dielectric layer, the metal conductor layer and the polysilicon layer with the polysilicon layer in the FET device being doped and conductive. Distal ends of the polysilicon layer of the resistor are doped and conductive, and between the distal ends of the resistor the polysilicon layer is undoped and nonconductive. 
         [0013]    Preferably, conductive electrical terminals are formed on the distal ends of the resistor with one of the conductive terminals being connected to the FET device. Preferably, the dielectric layer comprises a High-K material selected from a hafnium based material and a material selected from the group consisting of hafnium zirconate (HfZrO 4 ), hafnium silicon oxynitride (HfSiON), hafnium dioxide (HfO 2 ) and hafnium silicate (HfSiO), La 2 O 5 , HfLaO, Hf silicates, nitrided Hf silicates, hafnium dioxide (HfO 2 ) with La, N, and Mg, Hf silicates with La, N, Mg, and aluminum oxide. Preferably, the dielectric layer comprises a High-K material and the metal conductor is composed of a material selected from the group consisting of titanium nitride (TiN) and tantalum carbide (TaC,) TaN, Ta, Ru, Ni, NiSi, CoSi 2 , and TiAlN. 
         [0014]    In accordance with another aspect of this invention, a method is provided for forming an integrated semiconductor device on a substrate including an Field Effect Transistor (FET) device adjacent to a resistor. The method comprises the following steps. Form a stack of layers on the substrate including a dielectric layer formed on the substrate, a conductive layer formed on the dielectric layer and an undoped polysilicon layer formed on the conductive layer. Form an FET stack for the FET device and a resistor stack for the resistor by patterning and etching the dielectric layer, the conductive layer, and the polysilicon layer, implant dopant into the FET stack to form doped polysilicon gate electrode for the FET device. Implant dopant into distal ends of the resistor stack without implanting dopant between the distal ends, thereby forming the resistor between the distal ends. Preferably, form resistor terminals connected to the distal ends of the resistor stack, form FET terminals connected to the FET device, and connect one of the resistor terminals to one of the FET terminals. 
         [0015]    Preferably, the dielectric layer comprises a High-K material. Preferably, the dielectric layer comprises a High-K material group consisting of hafnium based materials. Preferably, the dielectric layer comprises a High-K material comprising a material selected from the group consisting of hafnium zirconate (HfZr O 4 ), hafnium silicon oxynitride (HfSiON), hafnium dioxide (HfO 2 ) and hafnium silicate (HfSiO). Preferably, the dielectric layer comprises a High-K material, and the metal conductor is composed of a material selected from the group consisting of titanium nitride (TiN) and tantalum carbide (TaC.) Preferably, the polysilicon in the distal ends comprises doped polysilicon and central regions of the polysilicon between the distal ends is undoped, and the metal conductor is composed of a material selected from the group consisting of titanium nitride (TiN) and tantalum carbide (TaC.) Preferably, the polysilicon layer is thin, and silicide contacts are formed from the polysilicon layer reaching down to the metal conductor layer. 
         [0016]    In accordance with another aspect of this invention, another method is provided for method of forming an integrated semiconductor device on a substrate including an Field Effect Transistor (FET) device adjacent to a resistor comprises the following steps. Form a stack of layers on the substrate including a dielectric layer formed on the substrate, a conductive layer formed on the dielectric layer, and an undoped polysilicon layer on the conductive layer. Form an FET stack and a resistor stack by patterning and etching the dielectric layer, the conductive layer, and the polysilicon layer. Etch away the polysilicon from the resistor stack to form the resistor from the conductive layer, with the resistor having distal ends, and implant dopant into the FET stack to form a doped FET gate electrode for the FET device from the undoped polysilicon layer. 
         [0017]    Preferably, form resistor terminals connected to the distal ends, form FET terminals connected to the FET device, and connect one of the resistor terminals to one of the FET terminals. Preferably, the dielectric layer comprises a High-K material comprising a High-K material group consisting of hafnium based materials or a material selected from the group consisting of hafnium zirconate (HfZr O 4 ), hafnium silicon oxynitride (HfSiON), hafnium dioxide (HfO 2 ) and hafnium silicate (HfSiO). Preferably, the dielectric layer comprises a High-K material, and the metal conductor is composed of a material selected from the group consisting of titanium nitride (TiN) and tantalum carbide (TaC.) 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The foregoing and other aspects and advantages of this invention are explained and described below with reference to the accompanying drawings, in which: 
           [0019]      FIGS. 1A-1O  shows the steps of manufacture in accordance with this invention of a semiconductor device with a resistor formed from a dual layer metal-polysilicon structure. 
           [0020]      FIG. 2  shows a flow chart of the steps of the method of  FIGS. 1A-1O . 
           [0021]      FIG. 3  shows a flow chart with a modification of some steps of the method of  FIGS. 1A-1O . 
           [0022]      FIG. 4  shows a flow chart with other modifications of steps of the method of FIGS.  1 A- 1 N.O 
           [0023]    FIG.  5 F″ shows the device  10  of  FIG. 1E  following Step F″ which is a modification of Step F. 
           [0024]    FIG.  5 M′ shows the device  10  of  FIG. 1E  following step M′ in which the process of Step M is modified slightly. 
           [0025]      FIG. 6  is a flow chart with still other modifications of steps of the method of  FIGS. 1A-1N . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Step A 
         [0027]      FIG. 1A  shows a device  10  in an early stage of manufacture with a silicon semiconductor substrate  11 . The substrate  11  may comprise a Silicon-On-Insulator (SOI) substrate or other known substrates which can support fabrication of integrated circuits. Between the STI regions  12  a source/drain/channel region  13  is defined in the silicon substrate  11 . In order to produce the device  10  of  FIG. 1A , a set of well known conventional processing steps employed in the early stages of fabrication of Complementary Metal Insulator Semiconductor (CMIS) Field Effect Transistor (FET) devices are performed including formation of a pair of Shallow Trench Isolation (STI) regions  12 , formation of N wells and P wells, threshold adjustment implantation, all of which steps are well known by those skilled in the art. 
         [0028]    A blanket insulator layer  14  has been thermally grown or deposited, over the surface of The device  10 . Alternatively, any combination of these materials may be formed as needed for optimization of the electrical properties of a CMIS or CMOS FET device. Deposited films may reside as blanket films across the top of the isolation and the silicon regions. Typical thickness of each material is expected to be in the range of 0.5 nm to 10 nm. The blanket insulator layer  14  is composed of a material suitable for a gate dielectric layer such as silicon dioxide, silicon nitride, silicon oxynitride, or a high dielectric constant material, e.g. a hafnium dioxide (HfO 2 ) or hafnium zirconate (HfZr O 4 ), material or other known high dielectric constant material. Other possible hafnium high-K dielectric compounds include hafnium silicon oxynitride (HfSiON) and hafnium silicate (HfSiO.) Additional High-K materials include La 2 O 5 , HfLaO, Hf silicates, nitrided Hf silicates, hafnium dioxide (HfO 2 ) with La, N, and Mg, Hf silicates with La, N, Mg, and Al 2 O 3 . 
         [0029]    Step B 
         [0030]      FIG. 1B  shows the device  10  of  FIG. 1A  following deposition of a blanket metal layer  15  which is electrically conductive over the blanket insulator layer  14 . While the composition of the metal layer  15  is not critical for this invention, its properties as applied to the embodiment of a transistor formed in the integrated circuit are critical. This metal may be composed of TiN or TaC (other metals: TaN, Ta, Ru, Ni, NiSi, CoSi2, TiAlN) or one any other material with suitable properties for inclusion in the gate electrode of an FET device. For the purpose of this invention, this layer forms a moderate resistivity layer, from 50 to 500 Ohms/square, with thickness expected in the range of 1-7 nm thereby providing adequate electrical conductivity to be used as an electrical resistor and a low enough electrical resistance to be employed in a dual layer gate electrode. Thus the blanket metal layer  15  should be composed of a material suitable to be formed into a gate electrode of a CMOS FET device and to be formed into an electrical resistor juxtaposed with the CMOS FET device. 
         [0031]    Step C 
         [0032]      FIG. 1C  shows the device  10  of  FIG. 1B  following deposition of a blanket, undoped polysilicon layer  16  over the blanket metal layer  15  comprising the complementary layer of the dual layers to be formed into an electrical resistor juxtaposed with a gate electrode of a CMOS FET device. The blanket insulator layer  14 , the blanket metal layer  15 , and the blanket, undoped polysilicon layer  16  comprise a feature blanket  21  which can be patterned into various features. 
         [0033]    Step D 
         [0034]      FIG. 1D  shows the device  10  of  FIG. 1C  following formation of a patterned photoresist mask  18  in accordance with this invention. 
         [0035]    Step E 
         [0036]      FIG. 1E  shows the device  10  of  FIG. 1D  following after a step of anisotropic etching was applied to transfer the pattern of the photoresist mask  18  to the polysilicon layer  16  and the metal layer  15  at least, with the option of also patterning some of the insulator layers  14 , which has been shown in  FIG. 1D  thereby forming perpendicular resistor stacks  21 A and  21 B oriented at right angles to each other with stack  21 A reaching lengthwise back into the page and stack  21 B reaching lengthwise from right to left across the page and a gate electrode stack  21 C. The patterned polysilicon layer  16  has been formed into an undoped polysilicon region  16 C which is to be doped to provide a gate electrode for an FET and the undoped resistor polysilicon layer  16 A and  16 B of the dual layer resistors as shown from two different cross-sections. The patterned metal layer  15  has been formed into two metal resistor elements  15 A and  15 B oriented at right angles to each other with layer  16 A reaching lengthwise back into the page and layer  16 B reaching lengthwise from right to left across the page and a conductive element  15 C which is a portion of the dual gate electrode FET. The patterned polysilicon layer  16  has been formed into undoped resistor polysilicon layers  16 A and  16 B of two resistors in perpendicular cross-sections, an undoped gate electrode polysilicon layer  16 C for an FET. The patterned blanket insulator layer  14  comprises an incidental (i.e. not required for this invention) insulator feature for the resistor stacks  21 A and  21 B, but which comprises a gate dielectric for the gate electrode stack  21 C. Then strip the photoresist layer  18 . 
         [0037]    Step F 
         [0038]      FIG. 1F  shows the device  10  of  FIG. 1E  following removal of photoresist layer  18  and formation of sidewall spacers  19  on the sidewalls of the resistor stacks  21 A and  21 B and gate electrode stack  21 C by conventional deposition of spacer layer followed by anisotropic etching of the spacer layer from planar regions of the devices. Then LDD (Lightly Doped Drain) implantation is performed into the source/drain region  13  for the purpose of defining a working MOSFET, and incidentally into the gate region  16 C and resistor stack  16 A and  16 B. As the present invention pertains to the device and structure of a dual layer metal/polysilicon resistor, the low dosage of these implanted dopant ions into layers  16 A and  16 B will have a small effect on the resistivity of the device, they are not essential steps for the purpose of this invention, and do not harm the intended purpose of this invention. These steps may or may not be performed as needed by the MOSFET, so such description is left for those knowledgeable in MOSFET fabrication to define and implement. The spacers  19  are composed of silicon oxide. 
         [0039]    Step G 
         [0040]      FIG. 1G  shows the device  10  of  FIG. 1F  after formation of an insulating layer such as silicon nitride (Si 3 N 4 ) deposited conformally over the polysilicon and the sidewalls of the polysilicon in addition to all exposed areas of the chip or wafer, which combined with layer  19  provides protective layers  20  (shown as a single layer for convenience of illustration.) This film thickness of the insulating layer is expected to be in the range 5-30 nm. 
         [0041]    Step H 
         [0042]      FIG. 1H  shows the device  10  of  FIG. 1G  after application and patterning of a photoresist mask  22  which covers the middle regions of the a resistor stack, shown partially covering the cross-section  21 B and completely covering the cross-section  21 A, whereas the gate electrode stack  21 C remains exposed. Then ion implantation is performed to form resistor terminals  26 B by doping the distal ends of the resistor stack  21 B while leaving the central region of the resistor polysilicon layer  16 B undoped or lightly doped, thereby forming a resistor stack  21 B with terminals  26 B. In addition the dopant is introduced into the body  16 C of the dual layer gate electrode  16 C/ 15 C forming a gate electrode stack  21 C including the conductive gate electrode body  26 C, the conductive element  15 C and the gate dielectric layer  14  therebelow. At this point the resistor  31  on the left, the resistor  32  in the center and the FET  33  on the right have been formed by the formation of contacts at each end of the resistors  31  and  32  and the doping of the undoped polysilicon region  16 C of the gate electrode stack which is now a doped, conductive gate electrode  26 C. In the resistor stack  21 B this process of ion implantation may employ either N-type or P-type dopant which will form a pair of conductive electrical terminals  26 B at the distal ends of the previously undoped resistor polysilicon layer  16 B. The conductive electrical terminals  26 B are located adjacent to the protective layers  20  on the sides of the resistor polysilicon layer  16 B (now  26 B) and above the bottom metal layer  15 B. The bottom metal layer  15 B will comprise the resistor since the remaining undoped polysilicon  16 B comprises a dielectric layer with much greater value of resistivity. The dopant also dopes the source/drain regions S/D shown in  FIG. 1H . The photoresist mask  22  shown in  FIG. 1H  covers central portions of the resistor stacks to prevent the N or P implant dopant from reaching the polysilicon between the resistor terminals  26 B in order to retain the high resistivity of the undoped polysilicon regions  16 A and  16 B as shown in  FIG. 1H . 
         [0043]    Step I 
         [0044]      FIG. 1I  shows the device  10  of  FIG. 1H  after etching of the exposed portions of the protective layers  20  which are composed of silicon nitride (Si 3 N 4 ) is performed utilizing the photoresist mask  22  that defined the ion implantation in step H. The etch is selective leaving the spacers  19  composed of silicon oxide in place. The order of the just-described step H of ion implantation and the patterning of the protective layers  20  is not critical. The ion implantation step H may be performed either before or after the etching step I. This etched protective layers  20  may remain on the sidewalls of the doped polysilicon gate electrode  26 C of the FET  33  and the resistor polysilicon layer  16 B. The resistor cross-section  16 A illustrates that the spacers  19  remain on the sidewalls of this portion of the resistor  16 A, the same portion as the center region shown  16 B as an alternate cross-section without sidewall. As will be seen—it is critical that the sidewalls of the resistors  31  and  32  remain covered through this and following steps. The planar region and the sidewalls of region  16 A which are blocked from etching will later form a layer that inhibits the formation of a silicide conductive layer. 
         [0045]    Step J 
         [0046]      FIG. 1J  shows the device  10  of  FIG. 1I  after the patterned photoresist mask  22  is removed by either a wet or a dry etch. 
         [0047]    Step K 
         [0048]      FIG. 1K  shows the device  10  of  FIG. 1J  after self-aligned silicide layers are formed where the exterior surfaces of regions of silicon are exposed, including the top regions of the resistor ends  26 B to form low resistance contact regions  36 B and silicide layer  36 C on the top surface of the doped, conductive polysilicon body  26 C of the gate electrode stack  21 C of the MOSFET, and silicide layers  33  on the top surfaces of the source-drain regions S/D. It is important that protective layer  20  blocks formation of silicide on the central, planar portion of device  21 B, and the planar and sidewalls of device  21 A as this would present a parallel low resistance path for conduction and a poorly controlled resistance value for the resistor. 
         [0049]    Step L 
         [0050]      FIG. 1L  shows the device  10  of  FIG. 1K  after an insulator layer  37  and contact holes  38 B are formed over the contact regions  36 B of the resistor stack  21 B and contact holes  38 C are formed over the contact regions  36 C of the source/drains regions S/D as shown in  FIG. 1L . 
         [0051]    Step M 
         [0052]      FIG. 1M  shows the device  10  of  FIG. 1L  after metallization layer  50  has been formed over the insulator layer  37  and filling the contact holes  38 B and  38 C. 
         [0053]    Step N 
         [0054]      FIG. 1N  shows the device  10  of  FIG. 1M  after planarization of the metallization layer  50 . In general Step N can be followed by metal layers (not shown) such as needed to fabricate an integrated circuit. 
         [0055]    Step O 
         [0056]      FIG. 1O  shows the device  10  of  FIG. 1M  after forming metal interconnect  60  between the column  50 A′ which connects to terminal  26 B′ and column  50 B which connects to the source region of the FET in the FET area  21 C thereby connecting one terminal of the resistor  21 B. This connection is shown for illustration that these devices are intended to be connected in some method. Actual connections between devices will depend on the intended function of the integrated circuit, and may employ multiple (stacked) metal layers (not shown here) and multiple devices of varying sizes and implant parameters, as will be well understood by those skilled in the art. 
         [0057]    First Alternative Process 
         [0058]      FIG. 3  shows a flow chart with other modifications of some the steps of the method of  FIGS. 1A-1N  which is the same as  FIG. 2  except for the modified Steps C′ and H′. 
         [0059]    Steps A and B 
         [0060]    Steps A and B are performed in the identical manner described above with respect to  FIGS. 1A-1B . 
         [0061]    Step C′ 
         [0062]      FIG. 1C  shows the device  10  of  FIG. 1B  following deposition of a blanket, undoped polysilicon layer  16  over the blanket metal layer  15  comprising the complementary layer of the dual layers to be formed into an electrical resistor juxtaposed with a gate electrode of a CMOS FET device. The blanket insulator layer  14 , the blanket metal layer  15 , and the blanket, undoped polysilicon layer  16  comprise a feature blanket  21  which can be patterned into various features. Alternatively, the polysilicon layer  16  may be in-situ doped or doped by an implantation step after deposition in step C. 
         [0063]    Steps D-G 
         [0064]    Steps D-G are performed in the identical manner described above with respect to  FIGS. 1D-1G . 
         [0065]    Step H′ 
         [0066]    In the previously mentioned alternate process and embodiment of Step C′, the implantation of the ends of the resistor is optional, as a dopant is defined throughout the resistor polysilicon layer  16 B. 
         [0067]    Steps I-O 
         [0068]    Steps I-O are performed in the identical manner described above with respect to  FIGS. 1I-1O . 
         [0069]    Second Alternative Process 
         [0070]      FIG. 4  is a flow chart with other modifications of some the steps of the method of  FIGS. 1A-1N , which is the same as  FIG. 2  except for the modified Steps C′ and K′ 
         [0071]    Steps A-B 
         [0072]    Steps A-B are performed in the identical manner described above with respect to  FIGS. 1A-1B . 
         [0073]    Step C″ 
         [0074]      FIG. 1C  shows the device  10  of  FIG. 1B  following deposition of a blanket, undoped polysilicon layer  16  over the blanket metal layer  15  comprising the complementary layer of the dual layers to be formed into an electrical resistor juxtaposed with a gate electrode of a CMOS FET device. The blanket insulator layer  14 , the blanket metal layer  15 , and the blanket, undoped polysilicon layer  16  comprise a feature blanket  21  which can be patterned into various features. Alternatively, the polysilicon layer  16  may be in-situ doped or doped by an implantation step after deposition in step C. In this alternate process the polysilicon layer  16  must be deposited as a thin polysilicon layer. 
         [0075]    Steps D-J 
         [0076]    Steps D-J are performed in the identical manner described above with respect to  FIGS. 1D-1J . 
         [0077]    Step K′ 
         [0078]    A third embodiment leaves all intentional dopant out of the resistor layer, including the ends, and relies on connection with Silicide through the body to contact the metal region. In this third embodiment, it is preferred that the low resistance silicide contact region  36 B directly contacts the metal layer  15 B. This is accomplished if polysilicon layer  16  is thin enough such that the silicide layer  26 B consumes the thickness of region  26 B and forms contacts to the bottom metal layer  15 B. This is not an additional step. If thickness of layer  16  is small enough then  26 B will touch the bottom metal layer  15 B. The silicide process consumes some or all of the thickness of layer  16 . This is not allowed in processes without metal-gate because the silicide cannot touch the insulator ( 14 ) without unintended consequence in the FET. With metal gate, the silicide can touch the metal as explained here, without such adverse effects. 
         [0079]    Steps L-O 
         [0080]    Steps L-O are performed in the identical manner described above with respect to  FIGS. 1L-1O . 
         [0081]    Third Alternative Process 
         [0082]      FIG. 5  is a flow chart with still other modifications of some the steps of the method of  FIGS. 1A-1N , with the same steps as those of  FIG. 2  except for the modified Steps F″, H″, and M′ and the omission of Step G which has been added into the modified step F. 
         [0083]    Steps A-E 
         [0084]    Steps A-E are performed in the identical manner described above with respect to  FIGS. 1A-1E . 
         [0085]    Step F″ 
         [0086]    FIG.  5 F″ shows the device  10  of  FIG. 1E  following Step F″ which is a modification of Step F in which a blanket insulating layer  17  is formed over the device  10 . Then a photoresist mask  22 ′ is formed with an opening over the center of the undoped resistor polysilicon layer  16 A and  16 B of the dual layer. The next function in Step F″ is to etch through the exposed portions of the blanket insulating layer  17  to expose top surfaces of the undoped resistor polysilicon layer  16 A and  16 B of the dual layer resistors. Then etching continues through the mask and the undoped resistor polysilicon layer  16 A and  16 B through the top surfaces of the undoped resistor polysilicon layer  16 A and  16 B removing all of the undoped resistor polysilicon layer  16 A and  16 B and exposing the entire top surface of the two metal resistor elements  15 A and  15 B. Then Step F″ ends by stripping away the photoresist mask  22 ′. 
         [0087]    Steps G 
         [0088]    Steps G is performed in the identical manner described above with respect to  FIGS. 1G . 
         [0089]    Step H″ 
         [0090]    FIG.  5 H″ shows the device  10  of  FIG. 1G  following Step H″ form a mask and ion implant dopant into gate electrode  33  and the source region S and the drain region D and then anneal. 
         [0091]    Steps I-L 
         [0092]    Steps I-L are performed in the identical manner described above with respect to  FIGS. 1I-1L . 
         [0093]    Step M′ 
         [0094]    FIG.  5 M′ shows the device  10  of  FIG. 1E  following step M′ in which the process of Step M is modified slightly in that the vias are in direct contact with the two metal resistor elements  15 A and  15 B. 
         [0095]    Step O 
         [0096]    Step O is performed in the identical manner described above with respect to  FIG. 1O . 
         [0097]      FIG. 6  is a flow chart with still other modifications of some the steps of the method of  FIGS. 1A-1N , with the same steps as those of  FIG. 2  except for the modified Steps F″, H″, and M′ and the omission of Step G which has been added into the modified step F. 
         [0098]    While this invention has been described in terms of the above specific embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims, i.e. that changes can be made in form and detail, without departing from the spirit and scope of the invention. Accordingly all such changes come within the purview of the present invention and the invention encompasses the subject matter of the following claims.