Abstract:
A method includes forming a gate structure by growing an interfacial layer on a substrate, depositing a High K layer on the interfacial layer, depositing a TiN Cap on the High K layer and forming a thin barrier layer on the TiN Cap. The gate structure is annealed.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to semiconductor devices and methods of fabricating semiconductor devices, and more particularly, to methods of fabricating gate structures for semiconductor devices. 
     BACKGROUND OF THE INVENTION 
     A finished gate structure (such as a finished gate or transistor gate) is the transistor terminal that modulates channel conductivity. Two principle approaches for forming high-k metal gate CMOS semiconductor device gate structures are the gate-first and gate-last process approaches. 
       FIG. 1  depicts a conventional gate structure having a substrate  10 , an oxide layer  20  and a polysilicon layer  30 . Substrate  10  includes a source  40  and a drain  50 .  FIG. 2  depicts a Gate-last High K metal gate which includes a substrate  110 , an interfacial layer  120 , a high dielectric constant (High K) layer  125 , and metal gate  130 . Substrate  110  also includes a source  140  and a drain  150 . 
     During the formation of such gate structures, a titanium nitride (TiN) cap may be applied between the high K layer and the metal gate. An amorphous silicon cap may be applied to the TiN cap followed by a post cap reliability anneal and an amorphous silicon cap strip. The strip of the Si cap may result in an increase in TiN surface roughness and to portions thereof being lost, thereby leading to metal work function shift and a degradation in gate stack reliability. 
     Accordingly, a need exists for improved systems and methods for forming semiconductor device gate structures. 
     BRIEF SUMMARY 
     The shortcomings of the prior art are overcome and advantages are provided through the provision, in one aspect, of a method which includes forming a gate structure by growing an interfacial layer on a substrate, depositing a High K layer on the interfacial layer, depositing a TiN Cap on the High K layer and forming a barrier layer on the TiN Cap. The gate structure is annealed. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       One or more aspects of the present invention are particularly pointed out and distinctly claimed as examples in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side cross-sectional view of a prior art gate structure; 
         FIG. 2  is a side cross-sectional view of another prior art gate structure; 
         FIG. 3  is a flow chart for forming a gate structure in accordance with the present invention; 
         FIG. 4  is a side cross-sectional view of a gate structure in accordance with the present invention; 
         FIG. 5  is a flowchart for forming the gate structure of  FIG. 4 ; 
         FIG. 6  is a chart indicating the work function results of the adjustment of an annealing process; 
         FIG. 7  is a chart indicating nFET and pFET mobility; and 
         FIG. 8  is a chart indicating nFET and pFET BTI reliability. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting embodiments illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as to not unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions, and/or arrangements within the spirit and/or scope of the underlying inventive concepts will be apparent to those skilled in the art from this disclosure. 
     Referring to  FIG. 3 , a flow chart is depicted for the formation of a High K metal gate for a semiconductor device. As described above and referring to  FIGS. 3 and 4 , a substrate (e.g., silicon) may have an interfacial layer  220  and high-K layer  230  applied thereto in step  300 . A TiN cap may be deposited in step  310 . A treatment of inert gas (e.g., nitrogen or argon)  240  may be performed in step  320  as part of a plasma or thermal annealing process of an intermediate gate structure  200  which includes the substrate having the interfacial layer and high K layer applied thereto. 
     The treatment (e.g., nitrogen or argon) described above relative to the annealing step includes an inert gas which minimizes a thickness increase in the interfacial layer due to the function of a thin barrier layer caused by the treatment to inhibit migration of oxygen into the high-K layer. Optimized process could provide sufficient thermal budget required for gate stack reliability and thus may minimize or eliminate a need to deposit the amorphous silicon dummy cap, conduct reliability anneal and then strip the amorphous silicon dummy cap. The stripping of the silicon cap may result in an increase in TiN roughness and to portions thereof being lost, thereby leading to metal work function shift and a degradation in gate stack reliability. The barrier layer also inhibits migration of the oxygen into and past the interfacial layer into the substrate. The thickness increase of the interfacial layer is thus minimized or suppressed. 
     The annealing described above may also modulate film properties of the TiN cap and interface property between high-k and TiN cap, and result in a reduction in the NMOS metal work function. 
     As indicated in steps  360  to  390  in  FIG. 3 , the remainder of the gate structure may be formed. In step  360 , a TaN etch stop layer dep may be performed followed by a P-type metal oxide semiconductor (PMOS) work function metal deposit in  FIG. 370 . The patterning of N/P work function metals may be done in step  380  followed by a N-type metal oxide semiconductor (NMOS) work function metal deposit in step  390 . 
     As depicted in  FIG. 5 , steps  330 - 350  listed in  FIG. 4  may be eliminated with the rest of the steps remaining and therefore resulting in increased reliability and better work function due to the lack of damage to the TiN cap caused by the stripping of the amorphous silicon dummy cap with the attendant roughness increase of the TiN cap. 
     Further, the work function of the gate structure may be tuned by varying an amount of nitrogen and manipulating the annealing temperature (e.g., at 700-1000 C, and/or soaking or spiking) As depicted in  FIG. 6 , for example, at about 80 mV work function tuning may be achieved by adjusting the annealing conditions. As depicted in  FIG. 7 , the annealing step may yield comparable or improved carrier mobility for both nFET and pFET with reliability improving with treatment temperature. Further, this supports the inert gas element (e.g., nitrogen) remaining in the HK layer and not in the interfacial layer/silicon layer interface which is desirable. 
     As depicted in  FIG. 9 , the annealing step also results in a wide range of reliability improvement, as compared to having a baseline without such treatments. 
     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 “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises”, “has”, “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements. Likewise, a step of a method or an element of a device that “comprises”, “has”, “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below, if any, 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 one or more aspects of the invention and the practical application, and to enable others of ordinary skill in the art to understand one or more aspects of the invention for various embodiments with various modifications as are suited to the particular use contemplated.