Patent Document

[0001]    This application is a divisional of U.S. patent application Ser. No. 11/875,222, attorney docket number FIS920070152US1, filed on Oct. 19, 2007, currently pending. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The disclosure relates to fabrication of a metal oxide semiconductor field effect transistor (MOSFET) and the structure thereof. More particularly, the disclosure relates to the fabrication of a gate structure where single-layer or dual-layer nitride liners are used to boost N-channel MOSFET (NFET) and P-channel MOSFET (PFET) performance, respectively. 
         [0004]    2. Related Art 
         [0005]    In the current state of the art, continued scaling of gate structures in complimentary metal oxide semiconductors (CMOS), use gate-spacer integration and strain engineering by one or more selective thin film deposition to enhance carrier mobility. Typically, plasma enhanced chemical vapor deposition (PECVD) is used to deposit a nitride film or films for forming a single or dual-layer nitride integration to boost NFET and PFET performance. With each film deposited as a single layer having uniform properties, the extent of control over conformality and adequate stress is limited. This limitation and the shape of the spacer having a vertical space extending from between the bases of adjacent gates tend to create voids in gate structures. The voids, which are subsequently filled by metal, result in electrical shorted paths at a contact level. This is particularly severe in the second liner deposition process, and more so in the case of PFET liners, which require compressive plasma enhanced nitride for enhancing carrier mobility. 
         [0006]      FIG. 5  illustrates voids  30  formed in the deposition process of fill structure  40  for filing vertical space  25 . Fill structure  40  may include barrier films (not shown) or dual-nitride films (not shown). Such typical fabrication processes use a constant film composition having a constant stress for forming the fill structure  40 . Fill structure  40  is usually formed from a single PECVD film. When dual-layer nitride films are used for forming fill structure  40 , multiple PECVD films are used. Since each layer of PECVD films shares uniform composition and stress properties, conformality variation in fill structure  40  is limited. This in turn compromises the ability for maintaining adequate composite stress. 
         [0007]    Efforts to address the problem of void formation include tapering of spacers, replacing PECVD compressive nitride with high density plasma (HDP) chemical vapor deposition (CVD) nitride or alternating between deposition and reactive-ion-etching (RIE). However, these efforts have their limitations. The tapering of spacers may lead to over-etching of some areas because of the variable pitch of isolated and/or nested features. As to the use of HDP CVD nitride, the significant variable thickness with in a nominal 1000 Å across varied device structures poses a problem for RIE of the compressive nitride because of unavoidable over-etching in some areas. Alternating deposition and RIE is impractical because many cycles are required to prevent void formation. Even with the many cycles, avoidance of void formation is dependent on the profile after each cycle, which is very difficult to control in view of the number of cycles. Therefore the problem of void formation remains. 
         [0008]    In view of the foregoing, it is desirable to develop an alternative method for depositing nitride films over a gate structure to obviate void formation in vertical space between adjacent gates within the gate structure. 
       SUMMARY 
       [0009]    A method of fabricating a gate structure in a metal oxide semiconductor field effect transistor (MOSFET) and the structure thereof is provided. The MOSFET may be n-doped or p-doped. The gate structure, disposed on a substrate, includes a plurality of gates. Each of the plurality of gates is separated by a vertical space from an adjacent gate. The method deposits at least one dual-layer liner over the gate structure filling each vertical space. The dual-layer liner includes at least two thin high density plasma (HDP) films. The deposition of both HDP films occurs in a single HDP chemical vapor deposition (CVD) process. The dual-layer liner has properties conducive for coupling with plasma enhanced chemical vapor deposition (PECVD) films to form tri-layer or quadric-layer film stacks in the gate structure. 
         [0010]    A first aspect of the disclosure provides a gate structure comprising: a plurality of gates disposed on a substrate; and at least one dual-layer liner disposed on the plurality of gates and filling a vertical space between adjacent gates, the at least one dual-layer liner including an intrinsically stressed protective layer and an intrinsically stressed filling layer, the intrinsic stress of each of the intrinsically stressed protective layer and the intrinsically stressed filling layer being variable, and wherein the at least one dual-layer liner is formed of high density plasma (HDP) films. 
         [0011]    A second aspect of the disclosure provides a method of fabricating a gate structure, the method comprising: forming a plurality of gates on a substrate; and depositing at least one dual-layer liner to fill a vertical space between adjacent gates, the at least one dual-layer liner including an intrinsically stressed protective layer and an intrinsically stressed filling layer, the intrinsic stress of each of the intrinsically stressed protective layer and the intrinsically stressed filling layer being variable, and wherein the depositing is a single step deposition of high density plasma (HDP) films. 
         [0012]    A third aspect of the disclosure provides a gate structure comprising: a plurality of gates disposed on a substrate; and at least one tri-layer film stack disposed on the plurality of gates and filling a vertical space between adjacent gates, the at least one tri-layer film stack including at least one dual-layer liner and at least a layer selected from a group consisting of: a capping layer and a base layer, wherein the at least one dual-layer liner includes an intrinsically stressed protective layer and an intrinsically stressed filling layer, the intrinsic stress of each of the intrinsically stressed protective layer and the intrinsically stressed filling layer being variable, and wherein the at least one dual-layer liner is formed of high density plasma (HDP) films. 
         [0013]    A fourth aspect of the disclosure provides a gate structure comprising: a plurality of gates disposed on a substrate; and at least one quadric-layer film stack disposed on the plurality of gates and filling a vertical space between adjacent gates, the at least one quadric-layer film stack including at least one dual-layer liner, a base layer and a capping layer, wherein the at least one dual-layer liner includes an intrinsically stressed protective layer and an intrinsically stressed filling layer, the intrinsic stress of each of the intrinsically stressed protective layer and the intrinsically stressed filling layer being variable, and wherein the protective layer and filling layer is formed of a high density plasma (HDP) film, and wherein the at least one dual-layer liner is between the base layer and the capping layer, wherein each of the protective layer, filling layer, base layer and capping layer include an intrinsic stress. 
         [0014]    The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]    These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which: 
           [0016]      FIG. 1  illustrates a cross-sectional view of an embodiment of a gate structure in a MOSFET. 
           [0017]      FIG. 2  illustrates a cross-sectional view of another embodiment of a gate structure in a MOSFET. 
           [0018]      FIG. 3  illustrates a cross-sectional view of an alternative embodiment of a gate structure in a MOSFET. 
           [0019]      FIG. 4  illustrates a cross-sectional view of yet another embodiment of a gate structure in a MOSFET. 
           [0020]      FIG. 5  illustrates a cross-sectional view of a prior art gate structure in a MOSFET with a barrier layer disposed over the gate structure. 
       
    
    
       [0021]    The accompanying drawings are not to scale, and are incorporated to depict only typical aspects of the disclosure. Therefore, the drawings should not be construed in any manner that would be limiting to the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings. 
       DETAILED DESCRIPTION  
       [0022]    Embodiments depicted in the drawings in  FIGS. 1-4  illustrate the resulting structure of the different aspects of fabricating a gate structure  101  in a metal oxide semiconductor field effect transistor (MOSFET)  100  with the use of high density plasma (HDP). 
         [0023]      FIG. 1  illustrates an exemplary embodiment of a gate structure  101  in a MOSFET  100 . Gate structure  101  includes gates  120  disposed on substrate  110 . Gates  120  are separated by vertical space  125  formed therebetween, which may be of the same depth as gates  120 . Substrate  110  includes channel  112  that divides source-drain region  114 . Each gate  120  includes gate electrode  122  and spacer  124 , and is disposed directly above corresponding channel  112  and source-drain region  114 . 
         [0024]    Also illustrated in  FIG. 1  is a dual-layer liner  130  which includes of a protective layer  132  and a filling layer  134 . Protective layer  132  is a high density plasma (HDP) film deposited at a bias power of, at maximum, approximately 300 W. Protective layer  132  primarily provides protection of gates  120  from damage by high power deposition of high stress films, for example, but is not limited to filling layer  134 . However, the deposition of protective layer  132  also provide bottom-up fill of vertical space  125 . Filling layer  134  is also a HDP film deposited at a high bias power of approximately 1000 W to approximately 2000 W to maximize bottom-up fill of vertical space  125 . 
         [0025]    Typically, the desired thickness of dual-layer liner  130  (i.e., the combined thickness of protective layer  132  and filling layer  134 ) may range from, but is not limited to, for example, approximately 500 Å to approximately  1 300 Å. The thickness of each of protective layer  132  and filling layer  134  may be varied or adjusted to achieve this desired thickness. Protective layer  132  usually has a thickness ranging from approximately 100 Å to approximately 200 Å. Filling layer  134  usually has a thickness of approximately 300 Å to approximately 1200 Å. The HDP films may include, but are not limited to: nitride, oxide, doped nitride or doped oxide or any combination thereof. The nitride may be doped with, but is not limited to, for example, germanium, phosphorous or boron. 
         [0026]    The deposition of dual-layer liner  130  is performed in a single deposition step, where protective layer  132  and filling layer  134  of differing properties and purposes are deposited to provide conformality and stress variation. For example, protective layer  132  may have a density range of approximately 2.80 g/cc to approximately 2.85 g/cc and filling layer  134  may have a density range of approximately 2.5 g/cc or less. Additionally, protective layer  132  may have a reflective index that range from approximately 1.95 to approximately 1.97, while filling layer  134  may have a reflective index of greater than approximately 1.89. Multiple layers  136  of dual-layer liner  130  may be formed with the single deposition step, which occurs after completion of standard processes for the formation of gates  120  following reactive-ion etching (RIE). Dual-layer liner  130  is deposited using HDP chemical vapor deposition (CVD) to fill any vertical space  125  between spacers  124  in a bottom-up manner from the base of gates  120 . The deposition of dual-layer liner  130  levels out the bottom of vertical space  125  and provides for subsequent plasma enhanced chemical vapor deposition (PECVD) of nitride layers. 
         [0027]      FIG. 2  illustrates another exemplary embodiment of gate structure  101  in MOSFET  100  where, in addition to dual-layer liner  130 , a capping layer  140  is disposed over filling layer  134  forming tri-layer film stack  160 . Capping layer  140  is formed from currently known or later developed PECVD techniques. Capping layer  140  is usually deposited at a power ranging from approximately 300 W to approximately 1500 W depending on the desired thickness and the reliability requirement to be met. Capping layer  140  is used to make up the desired thickness of a tri-layer film stack  160 . The desired thickness of tri-layer film stack  160  is the combined thickness of dual-layer liner  130  and capping layer  140 . The desired thickness of tri-layer film stack  160  may range from, but is not limited to, for example, approximately 500 Å to approximately 1300 Å. The thickness of capping layer  140  may vary according to the desired thickness of tri-layer film stack  160  and the thickness of deposited dual-layer liner  130 . Usually, the thickness of capping layer  140  may range from, but is not limited to, for example, approximately 100 Å to approximately 1100 Å. Each of protective layer  132  and filling layer  134  usually has a thickness that range from, but are not limited to, for example, approximately 100 Å to approximately 200 Å. Protective layer  132  is deposited at medium bias (high frequency) power of no greater than approximately 300 W in order to provide a thin HDP nitride film for filling vertical space  125  in a bottom-up manner. Medium bias (high frequency) power is also selected to avoid damage to any low temperature oxide liner (LTO) (not shown) that exist over gate structure  101 . Following the deposition of protective layer  132 , filling layer  134  is deposited at high bias (high frequency) power ranging from approximately 1000 W to approximately 2000 W to maximize bottom-up fill of vertical space  125 . This subsequent very high bias power for depositing filling layer  134  does not damage any LTO in view of the coating formed by protective layer  132 . 
         [0028]    For example, in the case of a PFET, protective layer  132  is a HDP nitride film of a thickness of approximately 150 Å deposited at a bias power of approximately 300 W without damaging topography of any LTO (not shown) that exist as part of gate structure  101 . Filling layer  134  is then deposited at a high bias power of approximately 1750 W. LTO (not shown) is not damaged in view of deposition of protective layer  132  as a coating over the LTO (not shown). Subsequent to the deposition of filling layer  134 , PECVD follows to form capping layer  140 . Dual-layer liner  130  and capping layer  140  forms tri-layer film stack  160  in vertical space  125 . Tri-layer film stack  160  leaves a void-free region and does not pose any difficulty for subsequent processing with RIE and exhibits high uniformity in thickness. HDP nitride film maybe selected as protective layer  132  and filling layer  134  because the deposition of HDP nitride film offers a high compressive nitride with compression ranging from approximately 0.7 GPa to approximately 3.5 GPa. The high compressive nitride facilitates composite stress in tri-layer film stack  160 . Furthermore, the use of HDP easily integrates into the manufacturing process just before the next standard step (i.e., RIE) of the process. The deposition process for forming tri-layer film stack  160  demonstrates high repeatability, where multiple layers of tri-layer film stack  166  or  176  may be formed. 
         [0029]      FIG. 3  illustrates an alternative embodiment of gate structure  101  in MOSFET  100 , where following the formation of gates  120 , deposition of a base layer  150  is performed prior to the single step deposition of dual-layer liner  130  to form a tri-layer film stack  170 . Base layer  150  is a PECVD thin film formed from currently known or later developed PECVD techniques. Base layer  150  usually has a thickness that may range from, but is not limited to, for example, approximately 80 Å to approximately 120 Å. Protective layer  132  has a thickness that may range from, but is not limited to, for example, approximately 100 Å to approximately 200 Å. Filling layer  134  has a thickness that may range from, but is not limited to, for example, approximately 200 Å to approximately 1100 Å. Tri-layer film stack  170  formed in this embodiment is such that a PECVD thin film coats any LTO (not shown) that exists as part of gate structure  101 . The desired thickness of tri-layer film stack  170  (i.e., combined thickness of base layer  150  and dual-layer liner  130 ) may range from, but is not limited to, for example, approximately 500 Å to approximately 1300 Å. As with the previous embodiments, once base layer  150  is formed, thickness of dual-layer liner  130 , especially filling layer  134  therein may vary to make up the thickness of tri-layer film stack  170 . 
         [0030]    In another alternative embodiment shown in  FIG. 4 , gate structure  101  in MOSFET  100  includes base layer  150 , dual-layer liner  130  and capping layer  140 . Base layer  150  and capping layer  140  are both deposited using currently known PECVD or later developed techniques. Dual-layer liner  130  is formed using currently known or later developed HDP CVD deposition of protective layer  132  and filling layer  134  in a single deposition step. The combination of dual-layer liner  130  between base layer  150  and capping layer  140  form a quadric-layer film stack  180 . Thickness of the respective layers so formed is such that base layer  150  has a thickness that may range from but is not limited to, for example, approximately 80 Å to approximately 120 Å. Protective layer  132  has a thickness ranging from, but is not limited to, for example, approximately 0 Å to approximately 100 Å. Filling layer  134  has a thickness that may range from, but is not limited to, for example, approximately 200 Å to approximately 500 Å. Capping layer  140  has a thickness of approximately 0 Å to approximately 500 Å. The desired thickness of quadric-layer film stack  180  (i.e., combined thickness of base layer  150 , dual-layer liner  130  and capping layer  140 ) may range from, but is not limited to, for example, approximately 500 Å to approximately 1300 Å. In order to adhere to the desired thickness, once base layer  150  is deposited, protective layer  132  may be omitted or at most be of a thickness of 100 Å. The thickness of filling layer  134  and capping layer  140  may vary accordingly to make up the thickness of quadric-layer film stack  180 . Multiple layers of quadric-layer  186  may be formed by repeating the same deposition processes. 
         [0031]    According to the fabrication process of the various embodiments of gate structure  101  in MOSFET  100 , illustrated in  FIGS. 1-4 , the bias power applied in the HDP deposition of the nitride film is optimized to allow compatibility with various types of RIE. In addition to avoiding damage to any existing LTO on the gate structure  101 , the optimized bias power also provides substantial bottom-up instead of sidewall deposition unlike the fabrication process of a typical MOSFET  10  ( FIG. 5 ) in the prior art. Currently proposed fabrication process of dual-layer liner  130 , illustrated in  FIGS. 1-4 , provides a more compatible conformality with gate structure  101 , and stress that can be varied to meet channel mobility requirements of a given technology. The inclusion of base layer  150  and/or capping layer  140 , illustrated in  FIGS. 2-4 , enhance conformality and mitigate thin sidewall deposition. Furthermore, the combination of base layer  150  and/or capping layer  140  with dual-layer liner  130  form tri-layer film stack  160  and  170  or quadric-layer film stack  180 . PECVD base layer  150  and/or capping layer  140  in tri-layer film stack  160  and  170  or quadric-layer film stack  180  form a barrier against mobile ions, which may otherwise diffuse through any LTO (not shown) disposed on gate structure  101  and impede performance. 
         [0032]    Each of protective layer  132 , filling layer  134 , within dual-layer liner  130 , capping layer  140  and base layer  150  for forming tri-layer film stack  160 ,  170  and/or quadric-layer  180 , may be intrinsically stressed. Typically, protective layer  132  may have an intrinsic compressive stress ranging from approximately 300 MPa to approximately 3300 MPa. While filling layer  134  may have an intrinsic compressive stress ranging from approximately 2000 MPa to approximately 3300 MPa. The intrinsic compressive stress of protective layer  132  and filing layer  134  may be varied such that a desired resultant composite compressive stress of the dual-layer liner  130  is achieved. The intrinsic stress may be varied to achieve desired net composite stress/strain in a multilayer film stack over a device channel through adjustment of thickness ratio between the individual layers. A multilayer film stack may include but is not limited to, for example, dual-layer liner  130 , tri-layer film stack  160 , 170 , quadric-layer film stack  180 , multiple layers of dual-layer liner  136 , multiple layers of trip-layer film stack  166 , 176  and multiple layers of quadric-layer film stack  186 . 
         [0033]    The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the scope of the invention to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of the invention as defined by the accompanying claims.

Technology Category: 5