Abstract:
Magnetic tunnel junction devices can be fabricated using a two-step deposition process wherein respective portions of the magnetic tunnel junction stack are defined independently of one another.

Description:
[0001]    This application claims the priority under 35 U.S.C. 119(e)(1) of copending U.S. Provisional Application No. 60/422,200, filed on Oct. 30, 2002 and incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates generally to magnetic tunnel junction devices and, more particularly, to the fabrication of magnetic tunnel junction devices.  
         BACKGROUND OF THE INVENTION  
         [0003]    Magnetic tunnel junction devices and their uses are well-known in the art. Conventional magnetic tunnel junction (MTJ) devices typically include a bottom contact electrode, a bottom magnetic layer, an oxidized Al barrier layer, a top magnetic layer and a top contact electrode. These devices are typically fabricated using a single deposition step that deposits all of the constituent layers as a complete stack. The complete stack is subsequently patterned to define the magnetic tunnel junction devices. MTJ devices fabricated in this manner can exhibit shorting through the barrier layer and magnetic coupling between the two magnetic electrodes.  
           [0004]    It is therefore desirable to reduce the incidence of the aforementioned shorting and magnetic coupling phenomena. The present invention can reduce the incidence of these phenomena by using a two-step deposition process to deposit the MTJ stack, wherein respective portions of the MTJ stack are defined independently of one another.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIGS. 1 and 2 are diagrammatic cross-sectional illustrations of a portion of an MTJ device stack produced by a first deposition step according to the invention.  
         [0006]    [0006]FIG. 3 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after patterning and etching are applied to the structure of FIG. 2 according to the invention.  
         [0007]    [0007]FIG. 4 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after encapsulation is applied to the structure of FIG. 3 according to the invention.  
         [0008]    [0008]FIG. 5 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after inter-level dielectric (ILD) deposition and chemical-mechanical polishing (CMP) are applied to the structure of FIG. 4 according to the invention.  
         [0009]    [0009]FIG. 6 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after a contact etch is applied to the structure of FIG. 5 according to the invention.  
         [0010]    [0010]FIG. 7 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after the cap layer is removed from the structure of FIG. 6 according to the invention.  
         [0011]    [0011]FIG. 8 is a diagrammatic cross-sectional illustration of an MTJ device resulting from deposition of a top magnetic layer and contact electrode onto the structure of FIG. 7 according to the invention.  
         [0012]    [0012]FIG. 9 is a diagrammatic cross-sectional illustration of the MTJ device of FIG. 8 after a top metal (M 3 ) layer deposition and CMP according to the invention.  
         [0013]    [0013]FIG. 10 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after a photoresist layer is patterned onto the structure of FIG. 2.  
         [0014]    [0014]FIG. 11 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after removal of the cap layer and deposition of a top magnetic layer and contact electrode relative to the structure of FIG. 10.  
         [0015]    [0015]FIG. 12 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after lift-off of the photoresist layer of FIG. 11.  
         [0016]    [0016]FIG. 13 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after deposition of a hardmask layer onto the structure of FIG. 12.  
         [0017]    [0017]FIG. 14 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after application of a photoresist layer to the structure of FIG. 13.  
         [0018]    [0018]FIG. 15 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after etching the hardmask of the structure of FIG. 14 and removing the photoresist layer.  
         [0019]    [0019]FIG. 16 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after using the hardmask of FIG. 15 as a pattern to etch the cap layer, tunnel barrier layer and lower magnetic layer of FIG. 15.  
         [0020]    [0020]FIG. 17 is a diagrammatic cross-sectional illustration of the structure of FIG. 16 after encapsulation.  
         [0021]    [0021]FIG. 18 is a diagrammatic cross-sectional illustration of an MTJ device that results from forming a via through the encapsulant and hardmask, and depositing a metal layer in the via.  
     
    
     DETAILED DESCRIPTION  
       [0022]    According to exemplary embodiments of the invention, MTJ devices can be fabricated using a two-step deposition process where a bottom portion of the stack, up to the tunnel barrier layer, is deposited in a first deposition step, which first step can also include deposition of a sacrificial cap layer over the tunnel barrier layer. Patterning and etching are then applied to the deposited portion of the stack, after which the top magnetic layer and top contact electrode are deposited in a second deposition step. Such fabrication of an MTJ device using two deposition steps with patterning and etching steps therebetween can reduce the incidence of shorting through the barrier and magnetic coupling between the magnetic electrodes. The sacrificial cap layer protects the integrity of the barrier layer during the patterning and etching steps which occur between the two aforementioned deposition steps. Because the second deposition occurs after patterning and associated etching, the upper magnetic layer and the upper contact electrode of the MTJ device can be designed to have a smaller cross-sectional area than the remaining, lower layers of the MTJ stack, which can help further to reduce shorting through the barrier layer and magnetic coupling between the magnetic electrodes.  
         [0023]    It should be noted that the layers illustrated in FIGS.  1 - 18  are provided for explanatory purposes, and their dimensions are not necessarily shown to scale.  
         [0024]    [0024]FIGS. 1 and 2 illustrate the first deposition step of a two-step deposition process for producing an MTJ device according to exemplary embodiments of the invention. In this first step, the following layers are deposited on a substrate  10 : the bottom contact electrode and bottom magnetic layer, illustrated generally at  20 ; the oxidized tunnel barrier (e.g., Ta/TaN/PtMn/CoFe/Al (ox)) layer, illustrated generally at  30 ; and a thin cap layer, illustrated generally at  40 . The cap layer  40 , in some embodiments, is deposited as a part of the process of the first step deposition, without breaking vacuum. The cap layer  40  is provided to help prevent degradation of the barrier layer  30  after air-exposure and during subsequent processing. The cap layer  40  is thus a sacrificial layer, and can be easily removed under mild etch conditions, prior to deposition of the top magnetic layer, without affecting the properties of the barrier layer  30 . Exemplary materials for use in the cap layer  40  include Ru and diamond-like-carbon (DLC) of, for example, approximately 50-100 angstroms thickness. Such a cap layer can be easily etched in an oxygen plasma without leaving any residue and without damaging the oxide tunnel barrier  30 . In some embodiments, DLC is preferred for the cap layer, in order to avoid any shorting at the edges.  
         [0025]    As shown in FIG. 3, the layers deposited in the deposition step of FIGS. 1 and 2 can be patterned and etched in conventional fashion to define the bottom stack portion of the MTJ device. Thereafter, as illustrated in FIG. 4, a conventional encapsulation step can be performed to provide an encapsulation layer  50  (e.g., SiN) to protect the edges. The encapsulation step is followed by conventional ILD deposition and CMP. The resulting ILD layer is illustrated generally at  60  in FIG. 5.  
         [0026]    As shown in FIG. 6, conventional techniques can be used to etch a contact opening through the ILD layer  60  and the encapsulation layer  50 , to reach the cap layer  40 .  
         [0027]    Thereafter, as shown in FIG. 7, conventional techniques can be used to perform an in situ etch removal of a portion of the cap layer  40  to produce an opening through the cap layer.  
         [0028]    [0028]FIG. 8 illustrates the second deposition step of the two-step MTJ deposition process according to exemplary embodiments of the invention. In this deposition step, the upper magnetic and contact layers (e.g., NiFe/TaN), illustrated generally at  70 , are deposited to define the upper portion of the MTJ stack within the openings in layers  40  and  60 . In some exemplary embodiments, a directional deposition process is used to deposit the upper magnetic and contact layers, in order to prevent buildup on the side walls ( 61 ,  62 ) produced by the etch step of FIG. 6.  
         [0029]    As illustrated in FIG. 9, conventional techniques can be used to deposit the top metal (M 3 ) layer  80  (e.g., Cu, W, or Al (Cu)), followed by conventional CMP.  
         [0030]    Referring again to FIGS.  6 - 8 , the use of a second deposition step for the upper portion of the MTJ stack permits the upper stack portion (e.g., the layers at  70 ) to be designed in some exemplary embodiments with a smaller cross-sectional area than the adjacent lower stack portion (e.g. at  20 ,  30 ), in the plane  81  where the upper stack portion generally adjoins the lower stack portion. This can further reduce shorting through the barrier layer  30 , and can also further reduce magnetic coupling between the two magnetic electrodes. As an example, the offset distance  63  can be approximately 100-1000 nm, and the contact opening dimension  64  can be approximately 100-500 nm.  
         [0031]    An alternate exemplary approach that employs a lift-off technique using photoresist can also be used as illustrated in FIGS.  10 - 18 .  
         [0032]    Beginning with the structure of FIG. 2, a photoresist layer  5  can be patterned onto the cap layer  40  with an opening therein (using conventional techniques) to aid in defining the upper portion of the MTJ stack, as shown in FIG. 10. Thereafter, as shown in FIG. 11, conventional techniques can be used to perform an in situ etch removal of a portion of the cap layer  40  to produce an opening through the cap layer. Thereafter, and also as shown in FIG. 11, a second deposition step is performed. In this deposition step, the upper magnetic and contact layers (e.g., NiFe/TaN), illustrated generally at  70 , are deposited to define the upper portion of the MTJ stack within the openings in photoresist layer  5  and cap layer  40 . In some exemplary embodiments, a conventional directional deposition process is used to deposit the upper magnetic and contact layers  70 .  
         [0033]    As shown in FIG. 12, the photoresist layer  5  and corresponding overlying portions of the upper magnetic and contact layer  70  can be removed using, for example, a conventional wet etch lift-off technique. Thereafter, as shown in FIG. 13, a hardmask  7  is deposited. The hardmask can be, for example, an oxide or a nitride (e.g., SiN or TaN).  
         [0034]    As shown in FIG. 14, a photoresist layer  8  is used to pattern the lower portion ( 20  and  30 ) of the MTJ stack. Conventional techniques can then be used to etch the hardmask  7  and thereafter remove the photoresist layer  8 . The result is illustrated in FIG. 15.  
         [0035]    Thereafter, as shown in FIG. 16, the hardmask  7  is used as a pattern to etch the layers  20 ,  30  and  40  to thereby define the lower portion  20 ,  30  of the MTJ stack. In the illustrated embodiments, the hardmask  7  is larger than the upper stack portion  70 , so the upper stack portion has a smaller cross-sectional area than the adjacent lower stack portion at  20  and  30 , as illustrated in FIG. 16.  
         [0036]    After the MTJ stack of FIG. 16 is encapsulated with, for example, an oxide encapsulant  9  as shown in FIG. 17, conventional techniques can be used to produce (as shown in FIG. 18) a via  82  through the encapsulant  9  and the hardmask  7  to the upper stack portion at  70 , and to deposit the top metal (M 3 ) layer  80  in the via  82 . Conventional CMP can then be performed, and the result is shown in FIG. 18.  
         [0037]    In some exemplary embodiments, the photoresist layers  5  and  8  of FIGS. 10 and 14, respectively, can be appropriately patterned such that the relationship between the cross-sectional areas of the upper ( 70 ) and lower ( 20 ,  30 ) MTJ stack portions is governed by the same dimensions  63  and  64  described above with respect to FIGS. 6 and 7.  
         [0038]    Although exemplary embodiments of the invention have been described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.