Abstract:
Various embodiments of the present invention are directed to a method for fabricating a memory cell comprising performing a passivation step on a cell structure and cell source lines prior to exhuming a masking layer to prevent oxidation of the cell structure and source lines.

Description:
FIELD 
       [0001]    Certain embodiments of the disclosure relate to a method for a dry exhumation without oxidation of the cell and source line. 
       BACKGROUND 
       [0002]    Multi-metallic films are being actively pursued as alternative memory technologies. Copper-containing CBRAM (Conductive Bridge Random Access Memory) cells are being developed using both subtractive and damascene process flows. The CBRAM damascene flow utilizes patterning of carbon, deposition of the CBRAM cell and copper source line, followed by a chemical-mechanical planarization (CMP) process and carbon exhumation. During conventional carbon exhumation processes, the copper surface in the cell and source line is exposed to oxygen plasma, and is therefore heavily oxidized, corrupting the structure of the copper lines. In some instances, oxidation is prevented by the use of a capping material or alternative metal source lines. However, this increases the resistivity of the source line and requires a more complicated and expensive structural and process integration scheme. Similarly high aspect ratio contacts landing on copper film require a blanket Barrier Low-k (BLOK) dielectric punch after a mask strip to protect the copper from oxidation during a conventional O 2  strip. This BLOK punch increases the top critical dimension (CD) significantly and is a critical impediment for scaling in cases where the contact CD is very small. 
         [0003]    Therefore, there is a need in the art for a method to perform a dry exhume without oxidizing the copper source lines or copper cell, and without increasing the resistivity of the source lines in accordance with exemplary embodiments of the present invention. 
       SUMMARY 
       [0004]    A method is provided for a dry exhumation without oxidation of copper substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
         [0005]    These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1-6  depict a process for exhuming carbon without oxidizing the cell and the source line in a damascene flow. 
           [0007]      FIG. 1  illustrates a first step in exhuming process in accordance with exemplary embodiments of the present invention; 
           [0008]      FIG. 2  illustrates a second step in the exhuming process in accordance with exemplary embodiments of the present invention; 
           [0009]      FIG. 3  illustrates a third step in the exhuming process in accordance with exemplary embodiments of the present invention; 
           [0010]      FIG. 4  illustrates a fourth step in the exhuming process in accordance with exemplary embodiments of the present invention; 
           [0011]      FIG. 5  illustrates a fifth step in the exhuming process in accordance with exemplary embodiments of the present invention; and 
           [0012]      FIG. 6  illustrates a sixth step in the exhuming process in accordance with exemplary embodiments of the present invention; 
           [0013]      FIGS. 7-11  depict a process for etching a via without contact critical dimension (CD) blowout in high aspect ratio contact etching in accordance with the exemplary embodiments of the present invention; 
           [0014]      FIG. 7  illustrates a first step in exhuming process in accordance with exemplary embodiments of the present invention; 
           [0015]      FIG. 8  illustrates a second step in exhuming process in accordance with exemplary embodiments of the present invention; 
           [0016]      FIG. 9  illustrates a third step in exhuming process in accordance with exemplary embodiments of the present invention; 
           [0017]      FIG. 10  illustrates a fourth step in exhuming process in accordance with exemplary embodiments of the present invention; and 
           [0018]      FIG. 11  illustrates a fifth step in the etching process in accordance with exemplary embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Exemplary embodiments of the present invention are related to a method for dry exhumation without oxidation of a cell and source line. According to one embodiment, a typical damascene flow is enhanced with a fluorine-based plasma step applied in the dry exhume process. The fluorine reacts with the cell and source line (e.g., copper cell and copper source line) material to form a thin copper fluoride (CuF x ) film. The copper-fluoride film protects the copper cell and copper source line material from oxidation during the oxygen-plasma based carbon exhume process. 
         [0020]    In a typical damascene processing technique, the dielectric layer which is typically an oxide, commonly referred to as an intermetal dielectric (IMD) is deposited over the semiconductor surface. The oxide layer is polished so as to obtain a planar upper surface. A series of well-known process steps are then performed in order to form interconnects between various metal layers. The damascene process allows for the formation of small; closely spaced interconnects and contacts 
         [0021]      FIGS. 1-6  depict a process for exhuming carbon without oxidizing cell and source lines in a damascene flow. 
         [0022]      FIG. 1  illustrates a first step in the exhuming process in accordance with exemplary embodiments of the present invention. A device  100  is shown which comprises a substrate  108  with metal contact  110  built into the device  100  using standard processes. A Carbon or underlayer (UL) dielectric layer  106  deposited atop the substrate  108 . A masking layer  104  is deposited on the dielectric layer  106 , and a photoresist layer  102  is deposited on the masking layer  104  and the photoresist layer  102  is patterned to form opening  105 . Those of ordinary skill in the art will recognize that layer  106  may be something other than carbon, which can be exhumed and is not reactive to fluorine. 
         [0023]      FIG. 2  illustrates a second step in the exhuming process in accordance with exemplary embodiments of the present invention. The masking layer  104  is etched using the patterned photoresist layer  102  to form a trench  200  in the dielectric layer  106 . The trench  200  exposes the metal contact  110  and the substrate  108 . 
         [0024]      FIG. 3  illustrates a third step in the exhuming process in accordance with exemplary embodiments of the present invention. A barrier liner layer  301  is deposited in the trench  200 . The barrier layer  301  may comprise, but is not limited to, CVD/ALD (Chemical Vapor Deposition/Atomic Layer Deposition) oxide and nitride in some embodiments. Subsequently, in some embodiments, copper (Cu) cell materials is deposited into the trench  200  to form the cell  300  and another conducting barrier metal (e.g., electromigration barrier metal) layer  302  is deposited on the cell  300  followed by another deposition of copper to form the source line  310 . The barrier layer  301  and the barrier layer  302 , the cell  300  and source line  310  have overburden above the plane of the dielectric layer  106 . 
         [0025]      FIG. 4  illustrates a fourth step in the exhuming process in accordance with exemplary embodiments of the present invention. The overburden is planarized using a chemical-mechanical planarization (CMP) process, leaving the copper surface of the cell  300  and the source line  310  exposed. 
         [0026]      FIG. 5  illustrates a fifth step in the exhuming process in accordance with exemplary embodiments of the present invention. After CMP the exposed cell  300  and source line  310  are reacted with a fluorine based etchant in a passivation step. The in-situ fluorine reaction can be performed in a plasma-based process chamber of reactive sputtering type prior to exhume or strip processing. According to some embodiments, the fluorine based etchant may be CF4, SF6, NF3, CHF3, CH2F2 or any fluorine based compound which passivates copper. In this embodiment, the passivation gas is diluted with Ar (He) gas in a flow ratio of 1:2 with a total flow of 150 sccm at 40 mTorr. The plasma was created in a 13.56 MHz inductively coupled dry etch chamber at RF power of 500 W. According to this embodiment, the copper cell  300  and source line  310  are exposed to the fluorine based plasma for 25 seconds, though those of ordinary skill in the art recognize that different etchants and timings may be used as appropriate. The exposure of the copper to the fluorine results in the formation of a protective film  400  for the cell  300  and source line  310 , the protective film  400  being composed of CuF x , for example. The protective film  400  acts as a barrier that protects the cell  300  and source line  310  against oxidation. The dielectric layer  106  is also exposed to the Fluorine but Fluorine is not reactive with the material of the dielectric layer  106 , e.g., carbon or UL. 
         [0027]      FIG. 6  illustrates a sixth step in the exhuming process in accordance with exemplary embodiments of the present invention. A dry exhume is performed, where an oxygen based plasma is used to exhume the dielectric layer  106  where protective film  400  protecting the cell  300  and source line  310  from oxidation. Normally, the oxygen plasma based exhume would cause the cell  300  and source line  310  to oxidize. However, the protective film  400  is impermeable by oxygen, thereby protecting the cell  300  and source line  310  from oxidation. The barrier layer  301  protects the side of the cell  300  from the oxygen plasma during exhumation. 
         [0028]    After exhumation, the protective film  400  on the cell material  400  landing surface is sputtered clean using an in-situ H2, H2-Ar plasma, according to one embodiment. This step is optionally performed after the exhumation process when there is a concern regarding the fluorine interacting with substances applied to the device  100 . 
         [0029]      FIGS. 7-11  depict a process for etching a via without contact critical dimension (CD) blowout in high aspect ratio contact etching in accordance with the exemplary embodiments of the present invention. 
         [0030]      FIG. 7  illustrates a first step in the etching process in accordance with exemplary embodiments of the present invention. The initial damascene process yields a device  700  comprising a copper film  702 , a barrier dielectric film  704 , a dielectric layer  706 , masking layers  708  and  710  with a patterned photo resist layer  712 . According to one embodiment, the film  704  is a Barrier low-k (BLOK) film (e.g., silicon carbide/silicon nitride) and the dielectric layer  706  is an oxide or nitride film. In this embodiment, the masking layer  708  is a carbon mask such as a carbon polymer or an under-layer (UL) mask and the masking layer  710  can be hard mask (HM) or Dielectric Anti-Reflection Coating (DARC) consisting of standard silicon oxynitride. 
         [0031]      FIG. 8  illustrates a second step in the etching process in accordance with exemplary embodiments of the present invention. Vias  800  are etched into the masking layer  708 , the dielectric layer  706  and barrier dielectric film  704  exposing the copper film  702 . 
         [0032]      FIG. 9  illustrates a third step in the etching process. Copper passivation is performed by applying fluorine-based plasmas to portions of the exposed copper film  702 . As described in  FIGS. 1-6 , the fluorine based compound reacts with the copper film  702  to create a protective film  900  formed of a copper-fluoride (CuFx) compound that acts as a passivation layer for the copper film  702 . The fluorine based etchant may be CF4, SF6, NF3, CHF3, CH2F2, or any fluorine based compound which passivates copper. The fluorine passivation reaction is performed in a process chamber prior to exhume or strip processing. In some embodiments, the BLOK etch and the passivation step are combined, where the BLOK etching performed using a fluorine-based etch passivates the copper film  702 . 
         [0033]      FIG. 10  illustrates a fourth step in the etching process in accordance with exemplary embodiments of the present invention. The masking layer  708  is exhumed using an oxygen plasma based exhume process, removing the masking layer  708  and stopping at the dielectric layer  706 . The protective film  900  prevents the copper film  702  from oxidation during the exhumation of masking layer  708 . Since this process allows etching of barrier layer (BLOK) in the presence of selective mask, the integrity of contact top CD is maintained. In contrast, existing art mandates the exhumation of mask in the presence of barrier layer to prevent copper oxidation, followed by a blanket (without mask) BLOK punch to expose the copper layer resulting in contact top CD blow out. 
         [0034]      FIG. 11  illustrates a fifth step in the etching process in accordance with exemplary embodiments of the present invention. The protective film  900  is optionally removed using an in-situ H2, H2-Ar plasma based sputter clean after the masking layer  708  is exhumed to prevent future interaction between the fluorine and other compounds. 
         [0035]    While the present disclosure has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed, but that the present disclosure will include all embodiments falling within the scope of the appended claims.