Abstract:
A method for fabricating a dynamic random access memory capacitor is disclosed. The method may comprise depositing a first titanium nitride (TiN) electrode; creating a first layer of titanium dioxide (TiO 2 ) on the first TiN electrode; depositing a dielectric material on the first layer of titanium dioxide; and depositing a second TiN electrode on the dielectric material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation Application of U.S. patent application Ser. No. 13/051,531, filed on Mar. 18, 2011, which is herein incorporated by reference for all purposes. 
         [0002]    This document relates to the subject matter of a joint research agreement between Intermolecular, Inc. and Elpida Memory, Inc. 
     
    
     TECHNICAL FIELD 
       [0003]    The present invention relates to the field of dynamic random access memory (DRAM) fabrication methods, and particularly to electrode treatments for enhanced DRAM performance. 
       BACKGROUND 
       [0004]    Dynamic Random Access Memory or DRAM uses capacitors to store bits of information within an integrated circuit. Some DRAM devices use Metal-Insulator-Metal or MIM capacitors. MIM capacitors in DRAM applications use insulating materials with a dielectric constant higher than that of SiO 2  (3.9). Such materials are referred to as high-K materials. Dielectric constant, or K value, is a measure of a material&#39;s ability to be polarized; polarization is closely associated with a material&#39;s ability to hold electrical charge. Therefore, the higher the dielectric constant of a material, the more electrical charge the material can hold. A capacitor&#39;s ability to hold electrical charge (capacitance) is a function of the surface area of the capacitor plates A, the distance between the capacitor plates d, and the dielectric constant or K value of the insulator ε. 
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         [0000]    The higher the K value, the smaller is the area of the capacitor needed for the same capacitance. Reducing the size of capacitors is important for reducing the size of integrated circuits. 
         [0005]    As DRAM technologies scale down below 40 nm (referring to the average half-pitch of a memory cell, or half the distance between cells in a DRAM chip), manufacturers must reduce the equivalent oxide thickness of dielectric films in MIM capacitors to increase charge storage capacity. Equivalent oxide thickness (EOT) is inversely related to a dielectric&#39;s capability to store charge, and is expressed for different materials using a normalized measure of silicon dioxide (SiO2) as a reference 
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         [0006]    Where, d represents the physical thickness and ε represents the K value (i.e., dielectric constant) of a material. Thus, the smaller the EOT a dielectric material can achieve, the higher the capability of the dielectric to store charges in associated components, including capacitor, DRAM cell, and so forth. 
         [0007]    Zirconium dioxide (ZrO 2 ), having a high dielectric constant of up to approximately 50, is one of the potential high-K dielectric materials for replacing SiO 2  in numerous applications. For instance, ZrO 2  may be utilized as the insulating dielectric material (i.e., the insulator) in a DRAM MIM capacitor. 
         [0008]    Atomic layer deposition (ALD) is a thin film deposition method that may be utilized for depositing ZrO 2  films on a titanium nitride (TiN) electrode during DRAM MIM capacitor fabrication. ALD may be based on sequential pulsing of two gas phase reactants that are typically referred to as a precursor and an oxidizer. A precursor adsorbs on a substrate surface for a fixed period of time and is then purged. Subsequently, an oxidizer is pulsed onto the substrate for a fixed period of time and is also purged. This process is repeated to obtain a film thickness of interest. Precise thickness control is maintained because the precursor adsorbs in a self-limited fashion so that approximately one monolayer of precursor material reacts with each oxidizer pulse. ZrO 2  films deposited on the TiN electrode utilizing ALD method may require O 3  or H 2 O as oxidizer in order to react with different Zr precursors (e.g., alkylamidos, alkylamido cyclopentadienyls, or other molecules) at a high temperature (200C to 400C). 
         [0009]    To achieve stoichiometric ZrO 2  films, the O 3  or H 2 O oxidizers may need to satisfy certain requirements (e.g. concentration or pulse time), as unsaturated reactions may result in incorrect composition, low dielectric constant and high leakage current (a phenomenon where current passes through an insulator, compromising storage capacity). Reactions between O 3  or H 2 O and the TiN electrode, especially within an initial few nanometers of ZrO 2  deposition, may result in the formation of a TiN x O y  interfacial layer which has an unpredictable, and likely low, dielectric constant. A TiN x O y  interfacial layer (having a low dielectric constant) formed on the initial few nanometers of ZrO 2  deposition may reduce the overall dielectric constant of the insulator. Since the DRAM capacitor&#39;s ability to hold electrical charge is partially based on the dielectric constant (K value) of its insulator, having such a TiN x O y  interfacial layer formed on the insulator may degrade the overall performance of the DRAM capacitor. Therefore, methods/processes are needed to prevent the formation of such TiN x O y  interfacial layers in a DRAM capacitor fabrication process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
           [0011]      FIG. 1  is a flow diagram illustrating a DRAM capacitor fabrication process; 
           [0012]      FIG. 2  is an illustration depicting a DRAM capacitor fabricated in accordance with the DRAM capacitor fabrication process as illustrated in  FIG. 1 ; 
           [0013]      FIG. 3  is an illustration depicting another DRAM capacitor fabricated in accordance with the DRAM capacitor fabrication process as illustrated in  FIG. 1 ; 
           [0014]      FIG. 4  is a flow diagram illustrating another DRAM capacitor fabrication process; 
           [0015]      FIG. 5  is an illustration depicting a DRAM capacitor fabricated in accordance with the DRAM capacitor fabrication process as illustrated in  FIG. 4 ; and 
           [0016]      FIG. 6  is a flow diagram illustrating a method for treating a TiN electrode. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0018]    The present disclosure is directed to a method for treating an electrode, such as a first electrode or a bottom electrode, prior to deposition of the dielectric material in a DRAM capacitor fabrication process. This treatment reduces or prevents the reactions between O 3  or H 2 O ALD oxidizers and the TiN electrode during the dielectric deposition, and therefore reduces or prevents the formation of TiN x O y  interfacial layer which may degrade the overall performance of the DRAM capacitor. 
         [0019]      FIG. 1  shows a flow diagram illustrating steps performed by a DRAM capacitor fabrication process  100 . The fabrication process  100  includes treating a TiN electrode prior to dielectric deposition.  FIG. 2  schematically depicts a simple two-dimensional DRAM Metal-Insulator-Metal (MIM) capacitor  200  fabricated in accordance with the DRAM capacitor fabrication process  100 . The DRAM capacitor  200  having dielectric deposition on the treated TiN electrode may satisfy the equivalent oxide thickness (EOT) and leakage specs for a 40 nm node and/or a high performance 30 nm node that utilizes ZrO 2  for dielectric materials. 
         [0020]    Step  102  may deposit a first TiN electrode  202 . The first TiN electrode  202  may also be referred to as the bottom electrode. The first TiN electrode defines a surface  204  for receiving the deposition of the dielectric materials. Treatment to the first TiN electrode  202  is provided to protect the surface  204  prior to the deposition of the dielectric materials. 
         [0021]    Step  104  may create a first cover layer  206  to cover and protect the surface  204  prior to the deposition of the dielectric materials  208 . Chemical vapor deposition or atomic layer deposition techniques may be utilized to deposit the cover layer on to the surface  204 . In one embodiment, the first cover layer  206  may be a layer of titanium dioxide (TiO 2 ). TiO 2  is selected as a suitable cover layer material for its high-K value. The K value of TiO 2 , in anatase phase, is approximately 40, and the K value of TiO 2  in rutile phase is approximately 90. Furthermore, TiO 2  may template tetragonal ZrO 2  formation which may have a higher K value compared to other phases of ZrO 2 . 
         [0022]    It is contemplated that atomic layer deposition or ALD techniques (as previously described) may be utilized to deposit the TiO 2  cover layer  206  on the surface  204 . Alternatively, ozone (O 3 ) plasma may be utilized to soak the first TiN electrode  202  for a period of time to form the TiO 2  cover layer  206  on the surface  204 . For example, a soak time of between approximately 10 minutes to 60 minutes, with concentration of O 3  between approximately 5 to 20 weight percent, may form a TiO 2  cover layer  206  having a thickness of between approximately 0.1 nm and approximately 1.5 nm. The soak time utilized in a preferred formation process may be approximately 30 minutes. It is noted that the K value of TiO 2  formed utilizing the formation techniques described above is expected to be higher than that of the TiN x O y  interfacial layer, which may result after the deposition of the dielectric materials in step  106 . 
         [0023]    Step  106  may deposit the dielectric materials  208  on to the first cover layer  206 . The dielectric materials may include ZrO 2  films, doped ZrO 2  films (e.g., aluminum-doped ZrO 2  and germanium-doped ZrO 2 ), or a combination of ZrO 2  films and doped ZrO 2  films. For example, atomic layer deposition techniques may be utilized to deposit the dielectric materials on to the first layer of TiO 2    206 . The first layer of TiO 2    206  protects surface  204  of the first TiN electrode  202  and reduces or prevents reactions between O 3  or H 2 O and the first TiN electrode  202  during the dielectric deposition. In this manner, the formation of TiN x O y  interfacial layer may be reduced or prevented. Since the DRAM MIM capacitor&#39;s ability to hold electrical charge relies on the high dielectric constant (K value) of its insulator, reducing or preventing the formation of the TiN x O y  interfacial layer (which has an unpredictable, and likely low, dielectric constant) on the insulator may improve the overall performance of the DRAM capacitor. 
         [0024]    Additional DRAM capacitor fabrication steps may be carried out subsequently. For example, step  110  may deposit a second TiN electrode  210  on the dielectric materials  208  after the dielectric materials  208  have been deposited, forming the DRAM capacitor as illustrated in  FIG. 2 . The second TiN electrode  210  may also be referred to as the top electrode. 
         [0025]    It is contemplated that a second cover layer  212  (shown in  FIG. 3 ) may be utilized to cover and protect the dielectric materials  208 . For example, upon deposition of the dielectric materials, step  108  may introduce a second cover layer  212  to cover the dielectric materials  208 . In one embodiment, the second cover layer  212  may be a second layer of titanium dioxide (TiO 2 ). Step  110  may position the second TiN electrode  210  on top of the TiO 2  covered dielectric material, forming the DRAM capacitor as illustrated in  FIG. 3 . 
         [0026]    Various cover layer thicknesses have been tested under different conditions (e.g., different Zr precursors and pedestal temperatures). Dielectric constant improvement is observed when the surface of the first TiN electrode is protected by the TiO 2  cover layer. Some improvements in current density (J) and equivalent oxide thickness (EOT) curve for a ZrO 2  dielectric layer are also observed when the surface of the first TiN electrode is protected by a TiO 2  cover layer less than 1.5 nm in thickness. In one embodiment, the first layer of TiO 2  may have a first thickness of between approximately 0.1 nm and approximately 1.5 nm, preferably between approximately 0.1 nm and approximately 1.0 nm. The second layer of TiO 2  may have a second thickness of between approximately 0.1 nm and approximately 1.5 nm, preferably between approximately 0.1 nm and approximately 1.0 nm. It is contemplated that the first thickness may or may not be substantially identical to the second thickness. 
         [0027]      FIG. 4  shows a flow diagram illustrating steps performed by an alternative DRAM capacitor fabrication process  400 . The fabrication process  400  also includes treating a first TiN electrode prior to dielectric deposition.  FIG. 5  schematically depicts a simple two-dimensional DRAM MIM capacitor  500  fabricated in accordance with the DRAM capacitor fabrication process  400 . 
         [0028]    Step  402  may deposit a first TiN electrode  502 . The first TiN electrode defines a surface  504  for receiving the deposition of the dielectric materials. Treatment to the first TiN electrode  502  is provided to protect the surface  504  prior to the deposition of the dielectric materials. 
         [0029]    Step  404  may apply a surface treatment to the surface  504 . For example, nitrogen (N 2 ), ammonia (NH 3 ) or nitrogen/hydrogen-mixture (N 2 /H 2 ) plasma treatment of the first TiN electrode  502  may be utilized for hardening or surface modification purposes. In this manner, plasma discharge may be utilized to diffuse nitrogen into the surfaces of the first TiN electrode  502 , hardening the surface  504 . It is contemplated that other surface hardening techniques may also be utilized. For example, nitrogen (N 2 ), ammonia (NH 3 ) or nitrogen/hydrogen-mixture (N 2 /H 2 ) thermal treatment (e.g., thermal annealing) of the first TiN electrode  502  may be utilized without departing from the spirit and scope of the present disclosure. 
         [0030]    Step  406  may deposit the dielectric materials  506  on to the treated surface  504 . The dielectric materials may include ZrO 2  films, doped ZrO 2  films (e.g., aluminum-doped ZrO 2  and germanium-doped ZrO 2 ), or a combination of ZrO 2  films and doped ZrO 2  films. For example, atomic layer deposition techniques may be utilized to deposit the dielectric materials on to the treated surface  504 . Additional DRAM capacitor fabrication steps may be carried out subsequently. For example, step  408  may position the second TiN electrode  508  on the dielectric materials  506  after the dielectric materials  506  have been deposited, forming the DRAM capacitor as illustrated in  FIG. 5 . 
         [0031]    Improvements in leakage reduction are observed when the surface of the first TiN electrode is hardened. The improvements may be significant when N 2 /H 2  plasma treatment or NH 3  thermal treatment is utilized. 
         [0032]    It is understood that while the TiN electrode being treated may be referred to as the bottom electrode contact (BEC) in a DRAM capacitor, the electrode treatment method of the present disclosure is not limited to the BEC. It is contemplated that the electrode treatment method may be utilized for treating electrode in any given orientation without departing from the spirit and scope of the present disclosure. 
         [0033]    It is further contemplated that both the surface treatment and the deposition of one or more cover layers may be utilized for treating a TiN electrode. Referring to  FIG. 6 , a flow diagram illustrating steps performed by a TiN treatment method  600  is shown. The TiN treatment method  600  may be utilized for treating a TiN electrode for a DRAM capacitor. In one embodiment, step  602  may apply a treatment to one or more surfaces of the TiN electrode. For example, nitrogen (N 2 ), ammonia (NH 3 ) or N 2 /H 2  plasma treatment of the TiN electrode may be utilized for hardening treatment purposes. In another example, nitrogen (N 2 ), ammonia (NH 3 ) or N 2 /H 2  thermal treatment (e.g., thermal annealing) of the TiN electrode may be utilized. Step  604  may create a cover layer to cover and protect one or more surfaces of the TiN electrode. In one embodiment, the cover layer may be a layer of titanium dioxide (TiO 2 ). The TiO 2  cover layer may have a thickness of between approximately 0.1 nm and approximately 1.5 nm. 
         [0034]    It is believed that the present invention and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely an explanatory embodiment thereof, it is the intention of the following claims to encompass and include such changes.