Abstract:
A FinFET device with an independent control gate, including: a silicon-on-insulator substrate; a non-planar multi-gate transistor disposed on the silicon-on-insulator substrate, the transistor comprising a conducting channel wrapped around a thin silicon fin; a source/drain extension region; an independently addressable control gate that is self-aligned to the fin and does not extend beyond the source/drain extension region, the control gate comprising: a thin layer of silicon nitride; and a plurality of spacers.

Description:
FIELD OF THE INVENTION 
     The invention disclosed broadly relates to the field of integrated circuit devices and more particularly relates to the field of control gates. 
     BACKGROUND OF THE INVENTION 
     Scaling of FinFET devices to dimensions relevant to and exceeding ground rule requirements for a 22 nm node requires the formation of one or more silicon (Si) fins on the order of 10-20 nm thick. A FinFET device is a nonplanar, double-gate transistor built on an SOI (silicon-on-insulator) substrate. The definition of this fin can be performed directly using a lithographic technique or an indirect patterning technique such as the sidewall image transfer (SIT) process. Regardless of the method, it is anticipated that control of the final fin width will be a significant issue in the manufacturing of FinFETs. Single nanometer variation in this parameter results in a ˜7% change in the effective body thickness of the channel. As a consequence variability in the threshold voltage, Vt, of the device across the wafer is expected to be a concern. 
     For a 15 nm thick fin, a single nanometer variation results in a ˜7% change in the effective body thickness of the channel. As a consequence, variability in the threshold voltage, Vt, of the device across the wafer is expected to be a concern. Control gates for other thin-body devices have been shown to be an effective way of electrically modulating Vt after completing device fabrication. However, due to the unique structure of a FinFET, integration of a control gate is problematic without compromising the integration density or electrical integrity of the device structure. 
     Therefore, there is a need for a solution to the FinFET shortcomings as described above. 
     SUMMARY OF THE INVENTION 
     Briefly, according to an embodiment of the invention a method comprises steps or acts of performing shallow trench isolation process on a substrate; depositing control gate oxide on the substrate, followed by a control gate material to form the control gate; depositing oxide and nitride layers on the control gate for use as fin and control gate hard-masks, wherein the hard-masks are used to define the control gate and fin; patterning the hard-masks; depositing a sacrifical gate material on the control gate; patterning the sacrifical gate material to produce a dummy gate pattern; depositing a sacrificial oxide layer over the dummy gate pattern, whereby the dummy gate pattern is obscured; planarizing the sacrificial oxide layer to reveal the obscured dummy gate; removing the dummy gate, wherein the removal forms trenches with the hard-mask disposed along the bottom of the control gate; introducing a slight lateral recess into the control gate using an isotropic wet etch; depositing a thin conformal film of SiN over the control gate; patterning the thin conformal film to form a first spacer; depositing a gate stack into the trenches; planarizing the gate stack using a pattern transfer technique; removing the sacrificial oxide; patterning to the gate stack to form a second spacer, wherein the second spacer comprises oxide; patterning the control gate material using the second spacer as a mask; depositing a layer of nitride; patterning the layer to form a third spacer that is needed to prevent the control gate to diffusion shorts during silicide formation; forming the silicide; and contacting the control gate over the shallow trench isolation to avoid control gate to source drain shorting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the foregoing and other exemplary purposes, aspects, and advantages, we use the following detailed description of an exemplary embodiment of the invention with reference to the drawings, in which: 
         FIG. 1   a  through  FIG. 1   p  show illustrative examples of the set of steps of the process according to an embodiment of the present invention; 
         FIG. 2  shows a three-dimensional device simulation of a FinFET according to an embodiment of the invention; and 
         FIG. 3  is a graph of Id-Vg characteristics for a top oxide width of 10 nano-meters; 
         FIG. 4  is a graph of Id-Vg characteristics for a top oxide width of one nano-meter; 
         FIG. 5  is a cross section of a  FIG. 3  is a graph of Id-Vg characteristics for a top oxide width of 10 nano-meters; 
         FIG. 6  is a flow chart of the method steps for producing an independently addressable control gate according to an embodiment of the present invention; and 
         FIG. 7  is a graphical illustration of how the FinFET architecture with shorter and wider fins with thinner top oxide thickness provides an optimized y for a given capacitance penalty, according to an embodiment of the present invention. 
     
    
    
     While the invention as claimed can be modified into alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention. 
     DETAILED DESCRIPTION 
     We discuss a fin-last replacement gate FinFET architecture that features an independently addressable control gate. The control gate can be used to compensate for non-uniformities in the fin thickness, offering a way to reduce variability in operating characteristics, such as threshold voltage (Vt). Similar to the standard fin-last replacement gate FinFET architecture, the gate we describe is self-aligned to the fins and source/drain (S/D) extension region and does not require epitaxial Si growth in the S/D region. The control gate is self-aligned to the individual fins and does not extend over the entire S/D region, minimizing the capacitance typically associated with “back gate” control gate schemes. 
     The control gate is passivated by a thin layer of Si nitride to help minimize active gate to control gate capacitance and alleviate the risk of shorting between the two (gates) electrodes. The control gate can be contacted outside of the source/drain region and should not impact the ability to scale the gate pitch. The gate pitch is primarily limited by the requirement to form three spacers. 
     Assuming a 20 nm gate, 20 nm total spacer thickness (sum of all spacers) and 30 nm contact via, a 100 nm gate pitch can be achieved with a 5 nm contact-to gate-overlay budget. Further reducing the gate length, total spacer thickness or contact size allows scaling to denser pitches. 
     Scaling of FinFET devices to dimensions relevant to and exceeding ground rule requirements for the 22 nm node requires the formation of one or more Si fins on the order of 15 nm thick. The definition of this fin can be performed directly using a lithographic technique or it can use an indirect patterning technique such as the sidewall image transfer (SIT) process. Regardless of the method, it is anticipated that control of the final fin width will be a significant issue in the manufacturing of FinFETs. Single nanometer variation in this parameter results in a ˜7% change in the effective body thickness of the channel. As a consequence variability in the threshold voltage, Vt, of the device across the wafer is expected to be a concern. 
     Control gates for other thin-body devices have been shown to be an effective way of electrically modulating Vt after completing device fabrication. However, due to the unique structure of a FinFET, integration of a control gate is problematic without compromising the integration density or electrical integrity of the device structure. 
     The process begins by using the standard shallow trench isolation (STI) process commonly practiced for SOI devices ( FIG. 1   a ). The control gate oxide is grown or deposited onto the SOI followed by deposition of the control gate material. Lastly, an oxide and nitride layers are deposited for use as the fin and control gate hard-masks ( FIG. 1   b ). The oxide/nitride hard mask stacks are patterned using lithography and reactive ion etching ( FIG. 1   c ). 
     A sacrificial gate material (e.g. polysilicon) is deposited followed by lithography and etching to produce a “dummy-gate” pattern ( FIG. 1   d ). A sacrificial oxide layer is deposited and planarized to reveal the dummy gate ( FIG. 1   e ). At this time the dummy gate is removed forming trenches ( FIG. 1   f ). The oxide/nitride hard mask materials shown in  FIG. 1   c  lie at the bottom of these trenches and are used to define the control gate and fin of the device ( FIG. 1   g ). A slight lateral recess is introduced into the control gate using an isotropic wet etch ( FIG. 1   h ). A thin conformal film of SiN is deposited and reactive ion etching is performed to form a first spacer ( FIG. 1   i ). Beyond acting as a sidewall spacer, the lateral recess of the control gate shown in  FIG. 1   h  enables the SiN layer to act as passivation for the control gate. 
     The gate stack is deposited into the trenches formed by the removal of the dummy gates and planarization is performed using a “damascene-gate” pattern transfer technique ( FIG. 1   j ). The sacrificial oxide is removed ( FIG. 1   k ). A second spacer is formed from a deposited oxide layer using reactive ion etching ( FIG. 1   l ). This layer serves as a self-aligned etch mask for the patterning of the control gate material ( FIG. 1   m ). 
     A third and final spacer is formed by depositing a layer of SiN followed by reactive ion etching ( FIG. 1   n ). This spacer is required to prevent control gate to diffusion shorts during Silicide formation ( FIG. 1   o ). An overview of the contact scheme is shown in  FIG. 1   p . The control gate is contacted over STI to avoid control gate to source/drain shorting concerns. 
     Referring now in specific detail to the drawings, and particularly to the flow chart of  FIG. 6 , the process for producing an independently addressable control gate begins at step  605  by performing the standard shallow trench isolation (STI) process commonly practiced for SOI devices, as illustrated in  FIG. 1   a . A SiO 2  substrate  102  has a Si layer  104  over it and a couple of Nitride strips  106  are included. 
     In  FIG. 1   a  there is shown performing a standard shallow trench isolation process. A substrate  102  is made of SiO 2 ; a Si layer  104  and a pair of Nitride strips are deposited on the substrate  102 . 
       FIG. 1   b  shows growing a control gate oxide, depositing a control gate material, depositing a oxide, and nitride hardmask. This step comprises growing a control gate oxide, depositing a control gate material, and depositing oxide and nitride hardmask. 
       FIG. 1   c  illustrates a step of patterning the fin/control gate hard mask stack (nitride and oxide)  106  into a set of fins. 
       FIG. 1   d  shows a step of depositing sacrificial gate poly  114  and etching. 
       FIG. 1   e  shows a step of depositing sacrificial oxide and planarizing. 
     Next, in step  610 , the control gate oxide is grown or deposited onto the SOI (Silicon on insulator) followed by deposition of the control gate material  108 . In step  615 , oxide  108  and nitride  106  layers are deposited for use as the fin and control gate hard-masks, as illustrated in  FIG. 1   b . Following the deposition of the oxide  108  and nitride  106  layers, in step  620 , the oxide/nitride hard mask stacks are patterned using lithography and reactive ion etching, as illustrated in  FIG. 1   c.    
     The process continues at step  625  with the deposition of a sacrificial gate material (e.g. polysilicon), followed by lithography and etching in step  630  to produce a “dummy-gate” pattern  114 , as illustrated in  FIG. 1   d . In step  635 , a sacrificial oxide layer  116  is deposited and planarized to reveal the dummy gate, as illustrated in  FIG. 1   e.    
     At this time, step  640  proceeds by removing the dummy poly gate  126 , thereby forming trenches, as illustrated in  FIG. 1   f.    
       FIG. 1   g  shows patterning the fin/control gate  128  using the entrained hard mask (HM). 
       FIG. 1   h  shows laterally recessed control gate material  129  with isotropic wet etching. 
       FIG. 1   i  shows depositing a thin conformal nitride and form first spacer. The control gate lateral recess allows the formation of nitride passivation on the control gate sidewall  130 . 
     The oxide/nitride hard-mask materials shown in  FIG. 1   c  lie at the bottom of these trenches and are used to define the control gate and fin of the device ( FIG. 1   g ). The process continues at step  645  where a slight lateral recess  129  is introduced into the control gate using an isotropic wet etch, as illustrated in  FIG. 1   h . Next, in step  650 , a thin conformal film of SiN  130  is deposited and reactive ion etching is performed to form first spacer  130 , as illustrated in  FIG. 1   i . Beyond acting as a sidewall spacer, the lateral recess of the control gate shown in  FIG. 1   h  enables the SiN layer to act as passivation for the control gate. 
     In step  655 , the gate stack is deposited into the trenches formed by the removal of the dummy gates and planarization is performed using a “damascene-gate” pattern transfer technique, as shown in  FIG. 1   j . In step  660 , the sacrificial oxide is removed, as shown in  FIG. 1   k . Following, this, in step  665 , a second spacer  142  is formed from a deposited oxide layer using reactive ion etching (see  FIG. 11 ). This layer  144  serves as a self aligned etch mask for the patterning of the control gate material ( FIG. 1   m ). 
     In step  670 , a third and final spacer  146  is formed by depositing a layer of SiN followed by reactive ion etching, as shown in  FIG. 1   n . This spacer is required to prevent control gate to diffusion shorts during Silicide formation  116  (see  FIG. 1   o ). An overview of the contact scheme is shown in  FIG. 1   p . The control gate  148  is contacted over STI to avoid control gate to source/drain shorting concerns. 
     Referring to  FIG. 2 , a three-dimensional device simulation is shown. A gate  202  is shown coupled with a Nitride structure  204 , a control gate is shown on the Nitride layer  204 , a top oxide  208 , a source region  210  is coupled with the top oxide  208 , and a buried oxide (BOX)  212 . 
       FIG. 3  is a graph of Id-Vg characteristics for a top oxide width of 10 nano-meters.  FIG. 4  is a graph of Id-Vg characteristics for a top oxide width of one nano-meter.  FIG. 5  is a cross section of a FinFET device according to another embodiment of the invention. The FinFET device comprises a gate  502 , a Nitride  504 , a control gate  506 , a top Oxide  508 , a source/drain region, and a BOX  512 . Shorter and wider fin with thinner top oxide gives stronger V th  tuning efficiency. 
       FIG. 7  provides a graphical illustration of how the FinFET architecture with the shorter and wider fin with thinner top oxide thickness provides the optimized y for a given capacitance penalty. 
     Therefore, while there has been described what is presently considered to be the preferred embodiment, it will understood by those skilled in the art that other modifications can be made within the spirit of the invention. The above description(s) of embodiment(s) is not intended to be exhaustive or limiting in scope. The embodiment(s), as described, were chosen in order to explain the principles of the invention, show its practical application, and enable those with ordinary skill in the art to understand how to make and use the invention. It should be understood that the invention is not limited to the embodiment(s) described above, but rather should be interpreted within the full meaning and scope of the appended claims.