Abstract:
Method of forming a magnetic memory device are disclosed. In one embodiment, a first plurality of conductive lines are formed over a semiconductor workpiece. A plurality of magnetic material lines are formed over corresponding ones of the first plurality of conductive lines and a second plurality of conductive lines are formed over the semiconductor workpiece. The second plurality of conductive lines cross over the first conductive lines and the magnetic material lines. These second lines can be used as a mask to while the magnetic material lines are patterned.

Description:
This patent claims the benefit of the filing date of provisionally filed patent application Serial No. 60/263,990, filed Jan. 24, 2001, and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The preferred embodiment of the present invention generally relates to cross-point magnetic memory integrated circuits (ICs). More particularly, the preferred embodiment relates to self-aligned conductive lines for cross-point magnetic memory ICs. 
     BACKGROUND OF THE INVENTION 
     “FIG. 1 a  shows a cross-section of magnetic memory IC  101 . The memory IC comprises a plurality of magnetic memory cells in an array region  103  of the IC. The cells each comprises a magnetic stack  120  sandwiched between upper and lower metal lines  140  and  150 . The upper and lower metal lines run in orthogonal directions embedded in interlevel dielectric (ILD) layers  110   a  and  110   b . The upper and lower metal lines serve as bitlines and wordlines of the memory array. A cell is located at an intersection of a bitline and wordline.” 
     The alignment of the various layers of the memory cells become more critical as ground rules decreases. For example, misalignments among the layers can result in line-to-line and/or level-to-level electrical shorts. 
     SUMMARY OF THE INVENTION 
     As evident from the foregoing discussion, it is desirable to provide a process for forming magnetic memory cells which avoids or reduces misalignments of the various layers used to form the cells. 
     In a first aspect, the present invention provides a method of forming a magnetic memory device. A first plurality of conductive lines (e.g., bitlines or wordlines)are formed over a semiconductor workpiece. A plurality of magnetic material lines are formed over corresponding ones of the first plurality of conductive lines. A second plurality of conductive lines are formed over the semiconductor workpiece. The second plurality of conductive lines cross over the first conductive lines and the magnetic material lines. These second lines, which can serve as either the bitline or wordline, can be used as a mask to while portions of the magnetic material lines are removed. 
     In another aspect, the present invention provides another method of forming an integrated circuit device. This method can be combined with the first method described but does not need to be. In this method, a magnetic material layer is formed over a workpiece and a metallic hard mask is formed over the magnetic material layer. The metallic hard mask is patterned and used as a mask to etch portions of the magnetic material layer. A dielectric layer is formed over remaining portions of the magnetic material layer. A chemical-mechanical polish can then be performed to planarize the dielectric layer. The metallic hard mask can serve as an etch stop for the chemical-mechanical polish. 
     In yet another aspect, the present invention provides another technique that can be combined with either or both of the above-mentioned methods. This method can also be used independently. In this method, an insulating layer is formed over a magnetic material layer. A number of trenches are formed in the insulating layer and filled by a conductive material to form a plurality of conductive lines. Remaining portions of the insulating layer are then removed. Portions of the magnetic material layer can then be removed using the conductive lines as a mask. 
     In its various aspects, the present invention has a number of advantages over prior art methods. Some of these advantages of certain embodiments include avoiding the short between first conductive lines  140  and second conductive lines  150 . The problem that is avoided can be clearly seen in FIG. 1 b  where the misalignment of the second conductive line  150  to magnetic stack  120  results in an electrical short between the first and second conductive lines  140  and  150 . 
     Aspects of the present also have the advantage that additional process steps that are required to prevent M 2  to M 3  shorting, such as a dielectric deposition and planarization to form the isolation in between the magnetic stacks  120  can be avoided. As a result, reductions in cost are achieved. Yield can also be increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features of the present invention will be more clearly understood from consideration of the following descriptions in connection with accompanying drawings in which: 
     “FIGS. 1 a  and  1   b  shows a cross-sectional view of a known magnetic memory device; and”. 
     FIGS. 2 a,b  through  9   a,b  show cross-section views of a magnetic memory device during various stages of fabrication. 
    
    
     DETAILED DESCRIPTION 
     In a CU damascene back-end-of-line structures, magnetic metal stacks are embedded to manufacturing the magnetic random access memory (MRAM) devices. The magnetic stack consists of many different layers of metals and a thin layer of dielectric with total thickness of a few tens of nanometers. For the cross-point MRAM structures, the magnetic stack is located at the intersection of the two metal wiring levels, for example metal  2 (M 2 ) and metal  3  (M 3 ) that are running in the orthogonal directions embedded in inter level dielectrics (ILD). The magnetic stack is contacted at bottom and top to M 2  and M 3  wiring levels, respectively. 
     In various aspects, the present invention provides various techniques to improve the fabrication process for forming a magnetic memory devices. The techniques will be discussed with reference to FIGS. 2-9, which illustrate a preferred embodiment fabrication process. 
     FIGS. 2-9 show a process for fabricating a magnetic memory integrated circuit (IC)  101  in accordance with one embodiment of the invention. Each cross-section is provided in orthogonal views, labeled with an a or b appended to the Figure number. 
     Referring now to FIGS. 2 a  and  2   b , a prepared substrate  205  is provided with an interlevel dielectric (ILD) layer  110   a  is shown. First conductive lines  140  which run in a first direction are formed in the ILD layer. The first conductive lines  140 , for example, are referred to as either wordlines or bitlines of the memory array. The first conductive lines typically are located on a second metal or conductive level (M 2 ) of the IC. A lower metal level (M 1 ) and circuit elements (not shown) are formed below the ILD layer. 
     In one embodiment, each conductive line  140  comprises copper or copper alloy. Other types of conductive material, such as tungsten and aluminum, can also be used to form the conductive lines. The conductive lines can be formed using conventional damascene or reactive ion etch (RIE) techniques. Such techniques are described in, for example, S. Wolf and R. Tauber, Silicon Processing for the VLSI Era, Lattice Press (2000), and the references used therein, which is/are herein incorporated by reference for all purposes. The conductive lines can include a Ta, TaN, TiN, W liner, which promote the adhesion and prevent the diffusion of the metal to the dielectric where the lines embedded in. 
     A magnetic layer  221  is deposited over the dielectric  110   a  and conductive lines  140 . The magnetic layer  221 , in one embodiment, comprises PtMn, CoFe, Ru, Al 2 O 3 , and/or NiFe as examples. Other types of magnetic material, such as Ni, Co, and various ratio of the compounds mentioned above, can also be used. The magnetic layer is deposited by, for example, physical vapor deposition (PVD), evaporation, chemical vapor deposition (CVD) or other suitable techniques. 
     In accordance with the preferred embodiment of the invention, a hard mask layer  225  is deposited over the magnetic layer  221 . In one embodiment, the hard mask layer comprises tantalum, tungsten, or titanium, including their compounds, such as tantalum nitride or titanium nitride. Other types of hard mask materials, such as PECVD silicon oxide, silicon nitride, silicon carbide can also be used. 
     The hard mask layer  225  is deposited by, for example, physical vapor deposition (PVD) or chemical vapor deposition (CVD), including plasma enhanced CVD (PECVD). The thickness of the hard mask layer  225  is sufficient to serve as a hard mask for etching the magnetic layer  221 . In one embodiment, the hard mask layer  221  is about 10-60 nm, e.g., about 20-40-nm. 
     Referring to FIGS. 3 a  and  3   b , a resist layer  370  is formed on the hard mask layer  221  and patterned to form openings therein. Patterning of the resist includes selectively exposing the resist with an exposure source (not shown) through a mask (not shown). The resist  370  is then developed, removing the exposed or unexposed portions of the resist (depending on whether a positive or negative type resist is used) to form the openings. In one embodiment, the pattern of the resist corresponds to the conductive lines  140 . For positive resist applications, in the active device array region a reverse M 2  pattern is used. Alternatively, for negative resist applications, the M 2  mask pattern is used. 
     An etch is then performed to remove portions of the hard mask layer  225  unprotected by the resist layer. The etch, for example, comprises a reactive ion etch (RIE). Other techniques, such as a wet etch or ion milling, can also be used to pattern the metallic layer. After the hard mask layer  225  is patterned, the resist layer  370  is removed. 
     In some applications, an anti-reflective coating (ARC) (not shown) can be formed on the hard mask layer  225  prior to depositing the resist the resist layer  370 . The use of ARC is useful to enhance lithographic resolution by reducing reflection of radiation from the exposure source. If an ARC is used, it is removed along with the resist layer  370  after the hard mask layer  225  is patterned. 
     Referring to FIGS. 4 a  and  4   b , the patterned hard mask layer  225  serves as an etch mask for patterning the magnetic layer  221 . The magnetic layer  221  is patterned by, for example, an RIE to form rows or strips  420  of magnetic stacks contacting conductive lines  140 . Other techniques, such as a wet etch or ion milling, can also be used to pattern the hard mask layer  225 . 
     Referring to FIGS. 5 a  and  5   b , a dielectric layer  528  is deposited on the substrate, filling the spaces between the magnetic stacks  221 . In one embodiment, the dielectric layer  528  comprises silicon nitride (e.g., Si 3 N 4 ). Other types of dielectric layers can alternatively (or also) be used. In the preferred embodiment, a plasma enhanced CVD silicon nitrite film with a thickness of about 30 nm to about 150 nm, preferably about 50 nm to about 70 nm is deposited at a temperature below 350° C. 
     The dielectric layer  528  is planarized with, for example, a chemical mechanical polish (CMP), as shown in FIGS. 6 a  and  6   b . The CMP is selective to the hard mask layer  225  (e.g., etch stop), creating a substantially planar surface which is substantially co-planar with the top of the magnetic stacks. 
     In FIGS. 7 a  and  7   b , second conductive lines  150  are formed over the substrate above the ILD  110   a , isolated by a dielectric layer  712 , such as silicon oxide. Other dielectric layers, such as Silk, porous silk, hydrogen silsesquioxane (HSQ),fluorinated glass, or fluorinated oxide, that can be removed selective to the conductive line  150  can also be used. 
     Typically, the second conductive lines  150  are located in a third metal level (M 3 ). The conductive line  150  can be formed using copper, copper alloy, or other types of conductive material such as W and Al. In one embodiment, the conductive line comprises copper or its alloy. The second conductive lines  150  can be formed from the same or a different material than the first conductive lines  140 . 
     The second conductive lines  150  cross the first conductive lines  140  and are referred to either as bitlines or wordlines. In the preferred embodiment, the second conductive lines  150  run in an orthogonal direction to the first conductive lines. Providing second conductive lines  150  that intersect first conductive lines  140  at angles other than 90° is also useful. 
     In one embodiment, the second conductive lines  150  are formed using conventional damascene techniques. This technique will now be described. The process includes, depositing a dielectric layer  712 , such as silicon oxide (e.g., SiO 2 ), by CVD, as an example. In an alternative embodiment, the dielectric layer  712  comprises silicon nitride to avoid oxidizing the subsequently formed copper lines. Other types of dielectric material can also be used, depending on the application. Other deposition techniques are also useful. 
     The dielectric layer  712  is planarized, if necessary, to provide a planar surface. The dielectric layer  712  is then patterned with a resist mask (not shown) to form trenches. After the trenches are formed, the resist mask is removed. A conductive material, such as copper is deposited to fill the trenches. Optionally, a conductive liner (not shown), such as W and Al, can be deposited to line the trench. A CMP is used to remove excess conductive material and to form a planar surface with the dielectric layer  712 . 
     Optionally, a cobalt phosphide (CoP) or cobalt tungsten phosphide (CoWP) layer is deposited over the conductive material  150  by electroless plating deposition. Such a technique is described in, for example, U.S. Pat. No. 5,695,810 issued to Dubin et al., which is herein incorporated by reference for all purposes. The CoP or CoWP layer advantageously reduces erosion when the conductive lines  150  are used as an etch mask during subsequent processing. 
     Referring to FIGS. 8 a  and  8   b , the dielectric layer  712  is removed, e.g., by means of RIE, leaving conductive lines  150  on the substrate. The conductive lines  150  serve as an etch mask for removing portions of the magnetic stacks  521  exposed by the removal of the dielectric layer  721 . As a result, the etch forms conductive lines  150  over the magnetic stacks  221  which are self-aligned, thus reducing misalignment problems. 
     An alternative approach here is to use Al as metal lines  150  in FIGS. 7 and 8. Instead of damascene process, the Al stack is deposited on the surface of  225  in FIG.  6 . In one embodiment, the Al stack includes a Ti and TiN barrier and/or a TiN cap layer. The deposition of the stack can be done by PVD. The Al stack is then lithographically patterned followed by RIE to transfer pattern to the Al stack as well as magnetic stack in the same process as shown in FIG.  8 . 
     Referring to FIGS. 9 a  and  9   b , a dielectric liner  952  is deposited on the substrate, lining the conductive lines  150 . The liner  952  comprises, for example, silicon nitride. In other embodiments, the dielectric can be a low k dielectric such as HSQ, Silk, porous silk, or formed with air gaps using poor gap filling materials. 
     In one embodiment, the liner layer  952  is deposited by PECVD. Other techniques for depositing the liner layer are also useful. The liner layer prevents oxidation of the copper lines  150  by the subsequently formed silicon oxide ILD layer  110   b . Typically, the liner layer  952  is about 2-30 nm, preferably about 5-15 nm. A nitride liner can be avoided if a silicon nitride ILD layer or conductive materials other than copper are used. 
     While not shown, the process continues to complete processing of the MRAM IC. These additional steps are left out to simplify illustration of the present invention. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.