Patent Publication Number: US-9406776-B2

Title: High temperature gate replacement process

Description:
PRIORITY DATA 
     This application is a continuation application of U.S. application Ser. No. 12/643,279, filed Dec. 21, 2009, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The semiconductor integrated circuit (IC) industry has experienced rapid growth. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. 
     The continuing decrease in technology nodes has lead to a desire to replace a conventional polysilicon gate electrode with a metal gate electrode to improve device performance. One process for forming a metal gate structure (i.e., having a metal gate electrode) is referred to as a “gate last” process, where a final gate stack is fabricated last. This reduces the number of subsequent processes, including high temperature processing, that must be performed after formation of the gate structure. However, there are challenges to implementing such features and processes in conventional fabrication. As the gate length and spacing between devices decreases, these problems are exacerbated. For example, conventional gate replacement processes have limited thermal budgets, which limits flexibility in metal gate work function tuning. The limited thermal budgets can arise because contact features (e.g., silicide regions of source/drain regions) are formed prior to the gate replacement process. The contact features have low thermal budgets. Consequently, if the gate replacement processes employ temperatures exceeding the contact features&#39; thermal budget, such as a high temperature annealing process, the contact features are damaged. Accordingly, what is needed is an improved method for fabricating an IC device. 
     SUMMARY 
     The present disclosure provides for many different embodiments. An exemplary method for fabricating an integrated circuit device comprises performing a gate replacement process to form a gate structure, wherein the gate replacement process includes an annealing process; after the annealing process, removing portions of a dielectric material layer to form a contact opening, wherein a portion of the substrate is exposed; forming a silicide feature on the exposed portion of the substrate through the contact opening; and filling the contact opening to form a contact to the exposed portion of the substrate. 
     Yet another exemplary method comprises providing a substrate having a gate structure disposed thereover; replacing a dummy gate of the gate structure with a metal gate; performing a high temperature annealing process to adjust a threshold voltage of the metal gate; and forming a silicide region in the substrate after the high temperature annealing process. 
     Yet another exemplary method comprises providing a substrate; forming a gate structure over the substrate, wherein the gate structure includes a gate stack having a dummy gate; forming a doped region in the substrate; forming a dielectric material layer over the substrate; removing the dummy gate of the gate structure, thereby forming a trench; and forming a gate in the trench. An annealing process is performed. Thereafter, the method further comprises removing portions of the dielectric material layer to form a contact opening, wherein the doped region in the substrate is exposed; performing a salicidiation process, wherein a contact feature is formed in the doped region through the contact opening; and filling the contact opening to form a contact to the doped region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a flow chart of a method for fabricating an integrated circuit device according to aspects of the present disclosure; and 
         FIGS. 2A-2H  are various cross-sectional views of embodiments of an integrated circuit device during various fabrication stages according to the method of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to methods for manufacturing integrated circuit devices, and more particularly, to gate replacement processes (or methods). 
     It is understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     With reference to  FIGS. 1 and 2A-2H , method  100  and semiconductor device  200  are collectively described below. The semiconductor device  200  illustrates an integrated circuit, or portion thereof, that can comprise memory cells and/or logic circuits. The semiconductor device  200  can include passive components such as resistors, capacitors, inductors, and/or fuses; and active components, such as P-channel field effect transistors (PFETs), N-channel field effect transistors (NFETs), metal-oxide-semiconductor field effect transistors (MOSFETs), complementary metal-oxide-semiconductor transistors (CMOSs), high voltage transistors, and/or high frequency transistors; other suitable components; and/or combinations thereof. It is understood that additional steps can be provided before, during, and after the method  100 , and some of the steps described below can be replaced or eliminated for additional embodiments of the method. It is further understood that additional features can be added in the semiconductor device  200 , and some of the features described below can be replaced or eliminated for additional embodiments of the semiconductor device  200 . 
       FIG. 1  is a flow chart of one embodiment of the method  100  for fabricating the semiconductor device  200  in a “gate last” process. In the gate last process, a dummy poly gate structure is formed first and then the dummy poly gate structure may be removed and replaced with a metal gate structure.  FIGS. 2A-2F  are various cross-sectional views of the semiconductor device  200  according to one embodiment, in portion or entirety, during various fabrication stages of the method  100 . The semiconductor device  200  may be formed by CMOS technology processing, and thus some processes are not described in detail herein. 
     Conventional gate replacement processes form silicide features in source/drain regions, before performing a gate replacement process. The silicide features present thermal budget limitations for subsequent processing. More particularly, the silicide features have a low thermal budget, sometimes only able to withstand temperatures less than 500° C. Higher temperatures can damage silicide features, which negatively effects device performance. The low thermal budget limitations constrain subsequent processing, such as the gate replacement process. For example, the low thermal budget limitations limit a temperature of an annealing process used during the gate replacement process. Limiting the annealing temperatures reduces work function tuning of the gate structures. 
     Accordingly, the method  100  implements a gate replacement process before forming silicide features in contact regions of a substrate, such as silicide in the source/drain regions. Since the gate replacement process and the associated annealing are performed first, the silicide features are formed through a contact opening (i.e., a hole/trench provided to form a contact to the substrate). Performing the gate replacement process first can increase a thermal budget for the annealing processes, which increases the flexibility of using the annealing processes to tune a work function of the gate structure, and accordingly adjust a threshold voltage of the gate structure. Thus, the gate replacement process is not limited by silicide thermal budget limitations. It is understood that different embodiments may have different advantages, and that no particular advantage is necessarily required of any embodiment. 
     Referring to  FIGS. 1 and 2A , at block  102  of the method  100 , a substrate  202  is provided. In the present embodiment, the substrate  202  is a semiconductor substrate comprising silicon. Alternatively, the substrate  202  comprises an elementary semiconductor including silicon and/or germanium in crystal; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. The alloy semiconductor substrate may have a gradient SiGe feature in which the Si and Ge composition change from one ratio at one location to another ratio at another location of the gradient SiGe feature. The alloy SiGe may be formed over a silicon substrate. The SiGe substrate may be strained. Furthermore, the semiconductor substrate may be a semiconductor on insulator (SOI). In some examples, the semiconductor substrate may include a doped epi layer. In other examples, the silicon substrate may include a multilayer compound semiconductor structure. 
     The substrate  202  may include various doped regions depending on design requirements as known in the art (e.g., p-type wells or n-type wells). The doped regions are doped with p-type dopants, such as boron or BF 2 ; n-type dopants, such as phosphorus or arsenic; or combinations thereof. The doped regions may be formed directly on the substrate  202 , in a P-well structure, in a N-well structure, in a dual-well structure, or using a raised structure. The semiconductor substrate  202  may further include various active regions, such as regions configured for an N-type metal-oxide-semiconductor transistor device (referred to as an NMOS device) and regions configured for a P-type metal-oxide-semiconductor transistor device (referred to as a PMOS device). 
     The substrate  202  may include an isolation region to isolate various regions (e.g., NMOS and PMOS device regions) of the substrate  202 . The isolation region is formed by any suitable process. The isolation region utilizes isolation technology, such as local oxidation of silicon (LOCOS) or shallow trench isolation (STI), to define and electrically isolate the various regions. The isolation region can comprise silicon oxide, silicon nitride, silicon oxynitride, other suitable materials, or combinations thereof. 
     One or more gate structures are formed over the substrate  202  by any suitable process. In the present example, a gate structure including a gate stack having a dummy gate  204  and spacers  208  is formed over the substrate  202 . The gate structure is formed by deposition, photolithography patterning, and etching processes. The deposition processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD), metal organic CVD (MOCVD), remote plasma CVD (RPCVD), plasma enhanced CVD (PECVD), plating, other suitable methods, and/or combinations thereof. The photolithography patterning processes include photoresist coating (e.g., spin-on coating), soft baking, mask aligning, exposure, post-exposure baking, developing the photoresist, rinsing, drying (e.g., hard baking), other suitable processes, and/or combinations thereof. Alternatively, the photolithography exposing process is implemented or replaced by other proper methods such as maskless photolithography, electron-beam writing, or ion-beam writing. The etching processes include dry etching, wet etching, and/or other etching methods. 
     At block  104 , the gate stack including dummy gate  204  is formed over the substrate  202  by any suitable process. The gate stack may include gate dielectric layers, capping layers, conductive layers, other suitable layers, and/or combinations thereof. The dummy gate  204  comprises any suitable material. In the present example, the dummy gate  204  comprises silicon oxide, high k dielectric layer and polysilicon. In another example, the dummy gate  204  may comprises silicon oxide and polysilicon on the silicon oxide. In this case, a high k dielectric material is incorporated into the gate in the gate replacement process. 
     At block  106 , a first doped region  206  is formed in the substrate  202 . The first doped region  206  is a lightly doped source/drain (LDD) region. The LDD region  206  is formed by one or more ion implantation processes, photolithography processes, diffusion processes, and/or other suitable processes. The LDD region  206  is doped with suitable doping species depending on the type of device being fabricated. The doping species include p-type dopants, such as boron or BF 2 ; n-type dopants, such as phosphorus or arsenic; and/or combinations thereof. 
     At block  108 , the spacers  208  are formed on the sidewalls of the gate stack including the dummy gate  204  by any suitable process. The gate spacers  208  are positioned on each side of the gate stack. The gate spacers  208  comprise a dielectric material, such as silicon nitride, silicon carbide, silicon oxynitride, other suitable materials, and/or combinations thereof. The gate spacers  208  may be used to offset subsequently formed doped regions, such as heavily doped source/drain regions. Forming the spacers  208  may further include forming other features, such as a sealing layer and/or spacer liner. 
     At block  110 , a second doped region  210  is formed in the substrate  202 . The second doped region  210  is a source/drain (S/D) region (also referred to as heavily doped S/D (HDD) region). The HDD region  210  is formed by one or more ion implantation processes, photolithography processes, diffusion processes, and/or other suitable processes. The HDD region  210  is doped with suitable doping species depending on the type of device being fabricated. The doping species include p-type dopants, such as boron or BF 2 ; n-type dopants, such as phosphorus or arsenic; and/or combinations thereof. In the present example, the HDD region  210  is aligned with an outer edge of the spacers  208  following the one or more implantation processes. An annealing process, such as a rapid thermal annealing (RTA) and/or laser annealing process, may be performed to activate the LDD region  206  and/or HDD region  210 . 
     In some examples, the HDD region  210  includes raised source and drain regions. Raised S/D regions may be formed by one or more epitaxy processes, such that SiGe or Si features can be formed in a crystalline state in the substrate  202 . The epitaxy processes include CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/or other suitable processes. The epitaxy process may use gaseous and/or liquid precursors, which interact with the composition of the substrate  202  (e.g., silicon). 
     Referring to  FIG. 2B , a dielectric material layer is formed over the substrate  202  by any suitable process to any suitable thickness, including over the gate structure. The dielectric material layer may include one or more layers. For example, the dielectric material layer can comprise an etch stop layer (ESL)  212  and a first dielectric layer  214 . The ESL  212  comprises silicon nitride, silicon oxynitride, and/or other suitable materials. The composition of the ESL  212  is selected based upon etching selectivity to one or more additional features of the semiconductor device  200 . In the present example, ESL  212  is a contact etch stop layer (CESL). 
     At block  112 , the first dielectric layer  214 , such as an interlayer (or inter-level) dielectric (ILD) layer, is formed over the substrate  202 . The first dielectric layer  214  comprises any suitable dielectric material, such as silicon oxide, silicon nitride, silicon oxynitride, TEOS oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), low-k dielectric materials, other suitable dielectric materials, and/or combinations thereof. Exemplary low-k dielectric materials include fluorinated silica glass (FSG), carbon doped silicon oxide, Black Diamond® (Applied Materials of Santa Clara, Calif.), Xerogel, Aerogel, amorphous fluorinated carbon, Parylene, BCB (bis-benzocyclobutenes), SiLK (Dow Chemical, Midland, Mich.), polyimide, other proper materials, and/or combinations thereof. The first dielectric layer  214  may include a multilayer structure comprising multiple dielectric materials. 
     Subsequent to the deposition of the first dielectric layer  214 , at block  114 , a chemical mechanical polishing (CMP) process may be performed. For example, a CMP process is performed until a top portion of the gate structure, particularly a top portion of the gate stack including the dummy gate  204 , is exposed as illustrated in  FIG. 2C . 
     At blocks  116  and  118 , a gate replacement process is performed, where the dummy gate  204  is replaced with a gate, such as a metal gate. Referring to  FIGS. 2D and 2E , the dummy gate stack is removed, thereby forming a trench (opening)  215  in the gate structure, and a gate  216  is formed in the trench (opening)  215 . The dummy gate is removed from the gate structure by any suitable process, such as a dry etching and/or wet etching process. The gate  216  includes gate dielectric  216 A and gate electrode  216 B. In one example, the gate  216  includes interfacial layers, high k dielectric layer, capping layers, a material layer with a proper work function, conductive layers, other suitable layers, and/or combinations thereof. 
     The gate dielectric layer  216 A comprises a dielectric material, such as silicon oxide, silicon oxynitride, high-k dielectric material, other suitable dielectric material, and/or combinations thereof. Examples of high-k dielectric material include HfO 2 , HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconium oxide, aluminum oxide, hafnium dioxide-alumina (HfO 2 —Al 2 O 3 ) alloy, and/or combinations thereof. In one example, the gate dielectric layer  216 A includes an interfacial layer such as silicon oxide, and a high k dielectric layer formed on the interfacial layer. The gate dielectric layer can be formed in the dummy gate  204  and remains in the gate  216 . Alternatively, the gate dielectric layer can be formed in the gate replacement process. 
     The gate electrode  216 B is formed over the gate dielectric layer  216 A by any suitable process. The gate electrode  216 B may include a conductive layer having a proper work function or tuned to the proper work function (therefore also referred to as a work function layer). In various examples, the work function layer includes tantalum, tantalum nitride, nickel silicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, other suitable material, or combination thereof. The gate electrode  216 B further comprises a conductive material layer formed on the work function layer using a suitable conductive material, such as aluminum, tungsten, or copper. The conductive material layer may additionally or collectively include polysilicon, titanium, tantulum, metal alloys, other suitable materials, and/or combinations thereof. 
     At block  120 , an annealing process, such as a rapid thermal annealing (RTA), is performed for any suitable time. The annealing process is a high temperature annealing process. For example, the annealing process employs a temperature greater than or equal to 550° C. In an example, the temperature ranges from about 550° C. to about 800° C. The annealing process can be used to adjust a threshold voltage of the gate structure and/or tune a work function of the gate structure. As noted herein, because a silicide feature for the S/D regions (e.g., HDD region  210 ) will be formed after the annealing process, the annealing process is not limited by silicide thermal budget limitations. High temperature annealing processes can be utilized without concern about damaging or negatively affecting the contact feature (or silicide), providing a wider replacement gate process window, particularly expanding the ability to tune various work functions. Thus, the annealing process parameters may be selected depending on the work function (or threshold voltage) desired. 
     At block  122 , a second dielectric layer  218 , such as an interlayer (or inter-level) dielectric (ILD) layer, is disposed over the substrate  202 . In the present example, the second dielectric layer  218  is formed over the first dielectric layer  214 . The second dielectric layer  218  comprises any suitable dielectric material and may be similar to the first dielectric layer  214 . It is understood that the second dielectric layer  218  may be considered a part of the dielectric material layer, and thus, in the present example, the dielectric material layer comprises the ESL  212 , first dielectric layer  214 , and second dielectric layer  218 . 
     Referring to  FIG. 2F , portions of the material layer are removed to form a contact opening that exposes a portion of the substrate  202 . In the present example, at block  124 , portions of the ESL  212  and dielectric layers (e.g., first and second dielectric layers  214 ,  218 ) are removed to form a contact opening  220 . As illustrated, the contact opening exposes the substrate  202 , particularly, a portion of the HDD doped region  210  (S/D region). Removing the dielectric material layer comprises any suitable process. For example, various etching processes, such as dry and/or wet etching processes may be utilized. Removing dielectric material layer also includes a lithography patterning process to form a patterned resist layer defining the contact opening. 
     Then, at block  126 , a salicidation process is performed. The salicidation process forms a silicide (contact) feature  222  through the contact opening  220  as illustrated in  FIG. 2G . In the present example, the silicide feature  222  is formed in the substrate  202 , coupled to the HDD region  210 . In one embodiment, the contact feature  222  comprises nickel silicide (NiSi). In furtherance of the embodiment, if the annealing process applied to the NiSi is beyond a thermal budget, the NiSi can be turned into a higher resistivity phase, which degrades the performance of the device. The silicide material may alternatively include NiSi, nickel-platinum silicide (NiPtSi), nickel-platinum-germanium silicide (NiPtGeSi), nickel-germanium silicide (NiGeSi), ytterbium silicide (YbSi), platinum silicide (PtSi), iridium silicide (IrSi), erbium silicide (ErSi), cobalt silicide (CoSi), other suitable silicide materials, and/or combinations thereof. 
     The contact feature  222  is formed by any suitable process, such as a salicide (self-aligned silicide) process. For example, a metal material may be deposited over the substrate, including over the doped regions. After deposition, the salicidation process may continue with a reaction between the deposited metal material and the silicon regions at an elevated temperature. The elevated temperature may be selected based on the specific metal material or materials. This is also referred to as annealing, which may be a RTA process. The unreacted metal material is removed thereafter. The reacted silicide may require additional thermal process to reduce the resistance of the silicide. 
     Referring to  FIG. 2H , at block  128 , a contact  224  is formed in the contact opening  220  by any suitable process. Contact  224  provides contact to the HDD region  210  (via the contact feature/silicide region  222 ). In the present example, the contact  224  is formed by filling the contact opening  220  with a conductive material. The conductive material comprises any suitable material, such as tungsten, aluminum, copper, tungsten, titanium, tantulum, titanium nitride, tantalum nitride, nickel silicide, cobalt silicide, other suitable materials, and/or combinations thereof. 
     Subsequently, the semiconductor device  200  may undergo further CMOS technology processing to form various features known in the art. Subsequent processing may form additional contacts, various vias/lines, and multilayer interconnect features (e.g., metal layers and interlayer dielectrics) over the substrate  202 , configured to connect the various features or structures of the semiconductor device  200 . The additional features may provide electrical interconnection to the device including the formed metal gate structure. For example, a multilayer interconnection includes vertical interconnects, such as conventional vias or contacts, and horizontal interconnects, such as metal lines. The various interconnection features may implement various conductive materials including copper, tungsten, and/or silicide. In one example a damascene, such as a dual damascene process, is used to form a copper related multilayer interconnection structure over the substrate  202 . 
     In summary, a high temperature gate replacement process is provided. The high temperature gate replacement process implements an annealing process before formation of contact features, such as silicide regions of the source/drain regions. Instead of forming the silicide features prior to the gate replacement process, the contact features are formed through a contact opening, which are formed after the gate replacement process to provide contact to the substrate and devices formed therein/thereon. Consequently, the annealing process of the gate replacement process is not limited by contact feature (silicide) thermal budget limitations. The gate replacement process window is increased, allowing high annealing temperatures for work function tuning. Accordingly, annealing temperatures greater than about 550° C. can be utilized for adjusting a threshold voltage (or work function) of the gate structures. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.