Abstract:
A field effect transistor device includes a first conductive channel disposed on a substrate, a second conductive channel disposed on the substrate, a first gate stack formed on the first conductive channel, the first gate stack including a metallic layer having a first oxygen content, a second gate stack a formed on the second conductive channel, the second gate stack including a metallic layer having a second oxygen, an ion doped source region connected to the first conductive channel and the second conductive channel, and an ion doped drain region connected to the first conductive channel and the second conductive channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation application of application Ser. No. 12/860,979, filed Aug. 23, 2010, incorporated herein by reference in its entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to semiconductor field effect transistors (FET), and particularly to threshold voltages in FET devices. 
       DESCRIPTION OF RELATED ART 
       [0003]    A FinFET, Tri-Gate, and nanowire devices typically include a non-planar multiple gate transistor device. The device includes a conducting channel disposed on a silicon fin, nanowire, or similar linear structure. 
         [0004]    Complimentary metal oxide semiconductor (CMOS) devices exhibit a threshold voltage (Vt). A voltage applied to the gate of an n-type device (gate voltage) that equals or exceeds the threshold voltage induces a low resistance conductive path between the source and drain regions of the device. While a gate voltage that is below the threshold voltage results in little or no conductive path between the source and drain regions. 
         [0005]    In electronic circuits with CMOS devices, devices with different threshold voltages are used to realize circuit function. Previous methods of fabricating multiple devices with different threshold voltages included implanting different types of substrate dopants for FET devices that result in different threshold voltages. 
       BRIEF SUMMARY 
       [0006]    In one aspect of the present invention, a field effect transistor device includes a first conductive channel disposed on a substrate, a second conductive channel disposed on the substrate, a first gate stack formed on the first conductive channel, the first gate stack including a metallic layer having a first oxygen content, a second gate stack a formed on the second conductive channel, the second gate stack including a metallic layer having a second oxygen, an ion doped source region connected to the first conductive channel and the second conductive channel, and an ion doped drain region connected to the first conductive channel and the second conductive channel. 
         [0007]    In another aspect of the present invention, a field effect transistor device (FET) includes a first conductive channel disposed on a substrate, wherein the first conductive channel includes a fin of a FinFET device, second conductive channel disposed on the substrate, wherein the first conductive channel includes a fin of a FinFET device, a first gate stack formed on the first conductive channel, the first gate stack including a metallic layer having a first oxygen content, a second gate stack a formed on the second conductive channel, the second gate stack including a metallic layer having a second oxygen, an ion doped source region connected to the first conductive channel and the second conductive channel, and an ion doped drain region connected to the first conductive channel and the second conductive channel. 
         [0008]    In yet another aspect of the present invention, a field effect transistor device (FET) includes a first conductive channel disposed on a substrate, wherein the first conductive channel includes a nanowire, a second conductive channel disposed on the substrate, wherein the first conductive channel includes a nanowire, a first gate stack formed on the first conductive channel, the first gate stack including a metallic layer having a first oxygen content, a second gate stack a formed on the second conductive channel, the second gate stack including a metallic layer having a second oxygen, an ion doped source region connected to the first conductive channel and the second conductive channel, and an ion doped drain region connected to the first conductive channel and the second conductive channel. 
         [0009]    Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0011]      FIGS. 1-7  illustrate an exemplary method for fabricating an exemplary embodiment of a FET device, in which: 
           [0012]      FIG. 1  illustrates a perspective view of an exemplary substrate and conducting channels; 
           [0013]      FIGS. 2  illustrates side views along the line  2 - 2  of  FIG. 1 ; 
           [0014]      FIG. 3  illustrates the formation of a layer; 
           [0015]      FIG. 4  illustrates the formation of a layer; 
           [0016]      FIG. 5  illustrates the formation of a masking layer; 
           [0017]      FIG. 6  illustrates the removal of portions of the masking layer; and 
           [0018]      FIG. 7  illustrates the removal of the masking layer. 
           [0019]      FIGS. 8-10  illustrates an alternate exemplary method for fabricating an alternate exemplary embodiment FET device, in which: 
           [0020]      FIG. 8  illustrates a perspective view of a buried oxide layer formed on a substrate; 
           [0021]      FIG. 9  illustrates a side view along the line  9 - 9  of  FIG. 8  including the formation of a masking layer; and 
           [0022]      FIG. 10  illustrates the removal of portions of the masking layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIGS. 1-7  illustrate an exemplary method for fabricating a FET device having a variety of different threshold voltages (Vt). In this regard,  FIG. 1  illustrates a perspective view of a substrate  102  that may include, for example, silicon. A buried oxide (BOX) layer  104  is disposed on the substrate  102 . A plurality of conducting channels  105   a,    105   b,    105   c,  and  105   d  are arranged on the BOX layer  104 . The conducting channels  105  include a layer of silicon  106  formed on the BOX layer  104 , and a layer of silicon nitride  108  formed on the layer of silicon  106 . The layer of silicon  106  may also include SiN. The conducting channels may be formed by, for example, forming a layer of silicon on the BOX layer  104  and forming a layer of silicon nitride on the silicon layer. A lithographic patterning and etching process may be used to remove portions of the silicon and silicon nitride layers to form the conducting channels  105 . Following the patterning of the conducting channels  105  n-type dopants (e.g., phosphorus, arsenic, or antimony) or p-type dopants (e.g., boron or aluminum) may be implanted in portions of the conducting channels  105  to form a source region  110  and a drain region  112  connected to the conducting channels  105  of the device. Alternatively, the devices may be doped following the formation of the gate stacks described below. 
         [0024]    Though the illustrated embodiment describes methods for forming a FinFET device (using conducting channels  105 ), alternate embodiments may use similar methods in forming a nanowire FET device. FIGS. 
         [0025]      FIG. 2  illustrates a side cut-away view of the FET device along the line  2 - 2  of  FIG. 1 . 
         [0026]    Referring to  FIG. 3 , a layer  302  is formed over portions of the conducting channels  105   a,    105   b,    105   c,  and  105   d  and the BOX layer  104 . The layer  302  includes, for example, a high-K material or SiON. The layer  302  may be formed by, for example, a chemical vapor deposition (CVD) or a plasma-enhanced chemical vapor deposition (PECVD) process. 
         [0027]      FIG. 4  illustrates the formation of a layer  402  over the layer  302 . The layer  402  may include, for example, a metallic gate material such as, for example, tungsten, titanium, cobalt, or nickel that may be formed by a CVD or PECVD process. The layers  302  and  402  form the gate stacks  401  of FET devices  405   a,    405   b,    405   c,  and  405   d.    
         [0028]    It may be desirable to fabricate FET devices having different threshold voltages. For example, the FET  405   a  may have a different threshold voltage than the FETs  405   b,    405   c,  and  405   d.    
         [0029]    In this regard, referring to  FIG. 5 , a masking layer  502   a  is deposited over the FETs  405   b,    405   c,  and  405   d,  leaving the FET  405   a  exposed. The masking layer  502   a  may include, for example, a lithographically patterned layer of silicon nitride material. In the illustrated embodiment, the FET that will be formed with the FET  405   a  remains exposed, however alternate embodiments may cover or expose any number of FET similar to  405 . Following the formation of the masking layer  502   a,  the device is annealed to activate the implanted dopants. The annealing process changes the threshold voltage (Vt) of the exposed FET  405   a.  The change in threshold voltage (ΔVt) will depend on the parameters used such as annealing temperature, time, ambient fluid, and dopant type will determine the ΔVt for the annealed device. For example, in the illustrated embodiment the annealing process includes heating the device to approximately 550° C. in ambient water vapor or oxygen. The annealing process may be performed, by example, at temperatures ranging from 350° C. to 800° C.; a partial pressure of oxygen or water vapor of between 1 Torr to 100 Torr; and a process time ranging from 30 seconds to 300 seconds. The annealing process results in the introduction of oxygen into the metal gate stack causing a reduction of oxygen vacancy in the stack. The introduction of oxygen in the annealing process results in a ΔVt of the FET  405   a  of approximately +50 mV (for a nFET device) and approximately −50 mV (for a pFET) device. 
         [0030]      FIG. 6  illustrates the resultant structure following the patterning and removal of portions of the masking layer  502   a  (of  FIG. 5 ) to expose the FET  405   b  resulting in the masking layer  502   b.  Following the exposure of the FET  405   b  the device may be annealed in a similar manner as described above; introducing additional oxygen into the exposed gate stacks. In the illustrated exemplary embodiment, the second annealing process uses similar parameters as discussed above resulting in a similar change in Vt for the FETs  405   a  and  405   b.  The resultant Vt for the devices may be described as Vt=x+ΔVt where x is a baseline threshold voltage of the device and n is the number of similar annealing processes performed on an exposed FET  405 . Thus, the Vt of the FET  405   a  may be defined as Vt a =x+(ΔVt*2) where n=2; while the Vt of the FET  405   b  may be defined as Vt b =x+ΔVt where n=1. 
         [0031]    Though the illustrated embodiment uses similar annealing parameters for each annealing process, resulting in a similar ΔVt, different annealing parameters may be used for one or more of the annealing processes resulting in a different ΔVt. For example, if the FET  405   a  is exposed to a first annealing process resulting in a ΔVt 1  and the FETs  504   a  and  405   b  are exposed to a second annealing process resulting in a ΔVt 2 , the Vt of the FET  405   a  may be defined as Vt a =x+ΔVt 1 +ΔVt 2  while the Vt of the FET  405   b  may be defined as Vt b =x+ΔVt 2 . 
         [0032]      FIG. 7  illustrates the resultant structure following the removal of the masking layer  502   b  (of  FIG. 6 ) to expose the FETs  405   c  and  405   d.  Following the removal of the masking layer, another annealing process may be performed on the devices. For example, following the annealing of the exposed FETs  405   c  and  405   d,  the resultant voltage thresholds for the devices (where the ΔVt is similar for each of the annealing processes) may be defined as Vt a =x+(ΔVt*3) where n=3; Vt b =x+(ΔVt*2) where n=2, and Vt c =Vt d  =x+ΔVt where n=1. 
         [0033]    Though the illustrated exemplary methods above describe forming a FinFET device (using conducting channels  105 ), alternate embodiments may use similar methods in forming other multi-gate devices such as, for example, a nanowire FET device.  FIGS. 8-10  illustrate an alternate exemplary method for forming FET devices with different threshold voltages in a nanowire FET device. 
         [0034]      FIG. 8  illustrates a perspective view of a BOX layer  104  formed on a silicon substrate  102 . A plurality of nanowire FET devices  805   a,    805   b,    805   c,  and  805   d  are formed on the BOX layer  104 . The FET devices  805   a - d  include a nanowire  906  conducting channel (shown in  FIG. 9  below) that may include, for example, a silicon material formed by a patterning and etching process. A gate stack is formed over the nanowire  906  that includes a high-K layer  904  (shown in  FIG. 9  below) that is formed on the nanowire  906 , and a metallic gate layer  802  is formed on the high-K layer  904 . The devices may be doped with ions in a similar manner as described above to form a source region  810  and a drain region  812  of the device. Once the nanowire FET devices  805   a - d  are formed, similar masking and annealing methods as described above may be performed to vary the threshold voltage in the device. 
         [0035]    In this regard,  FIG. 9  illustrates a side cut-away view of the device along the line  9 - 9  (of  FIG. 8 ). In the illustrated embodiment the masking layer  902   a  is formed over the FET devices  805   b,    805   c,  and  805   d.  An annealing process similar to the process described above is performed to increase or decrease the threshold voltage of the FET device  805   a.    
         [0036]      FIG. 10  illustrates the removal of a portion of the masking layer  902   a  resulting in the masking layer  902   b  that exposes the FET device  805   b.  Following the exposure of the FET device  805   b,  a second annealing process may be performed in a similar manner as described above. 
         [0037]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one ore more other features, integers, steps, operations, element components, and/or groups thereof. 
         [0038]    The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated 
         [0039]    The diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
         [0040]    While the preferred embodiment to the invention had been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.