Abstract:
A CMOS device is provided in a substrate. A magnetic tunnel junction (MTJ) is provided over the CMOS device and connected to the CMOS device by a metal ring contact wherein a dielectric or other filling material forms the center of the metal ring contact and wherein a bottom of the metal ring contact underlying said filling material is metal.

Description:
TECHNICAL FIELD 
     This disclosure is related to Magnetic Devices, and more particularly, to methods of integrating Magnetic Devices with semiconductor devices. 
     BACKGROUND 
     Magnetoresistive random access memory (MRAM) is now a proven nonvolatile memory technology with many advantages over other commercialized memory types in areas such as write/read speed, power consumption, lifetime, etc. However, conventional MRAM has a fundamental limitation of scalability. In a newer design of MRAM, a spin transfer switching technique (STT) can be used to manipulate the memory element as well. This new design will allow better packing and shrinkage of individual magnetic tunneling junction (MTJ) devices on the wafer, effectively increasing the overall density of the MRAM memory elements. STT MRAM not only possesses the major benefits of conventional MRAM but also has tremendous potential for scalability. Unlike conventional MRAM that requires a separated word line in addition to a BIT line to switch the magnetization direction of the free layer (FL), STT MRAM relies on only a current passing through a MTJ junction to rotate the magnetization direction of the free layer (FL). In order for STT MRAM to switch a bit, however, the current density passing through the MTJ device should be larger than a critical switching current density (Jc). Since current density is inversely proportional to device physical size given a fixed amount of current, the switching efficiency increases as the critical dimension (CD) size of MTJ junction decreases. Thus, CD is normally very small for STT MRAM (typically &lt;100 nm). In our previous disclosures (U.S. Pat. No. 7,884,433, U.S. Pat. No. 8,133,745, and U.S. patent application Ser. No. 12/586,900), all incorporated herein in their entirety, we revealed our methods to address many challenges for STT memory device fabrication. 
     MRAM devices are often combined with complementary metal-oxide-semiconductor (CMOS) devices. Process integration involves connection between MRAM and CMOS elements without causing any defect related issues. 
     U.S. Patent Application 2007/0069296 to Park et al describes a deep via contact from CMOS to MRAM. U.S. Pat. No. 7,999,246 to Iwayama and U.S. Patent Application 2008/0089118 to Kajiyima show ring-shaped magnetic junction elements. 
     SUMMARY 
     It is the primary objective of the present disclosure to provide a new integration method to connect a magnetic tunneling junction to a transistor that provides improved magnetic performance. 
     It is another objective of the present disclosure to provide an improved method for process integration of MRAM and CMOS devices that provides improved magnetic performance, including better thermal stability and lower offset magnetic field (H 0 ). 
     It is a further objective to provide an improved method for fabricating MRAM and CMOS devices connected by a contact ring. 
     It is a yet further objective to provide a magnetic device connected to a CMOS transistor by a contact ring. 
     In accordance with the objectives of the present disclosure, a method of fabricating an integrated spin-torque-transfer magnetic random access memory and CMOS device is achieved. A metal contact to a CMOS device is provided in a substrate. The metal contact is covered with a dielectric layer. A via is opened in the dielectric layer thereby exposing the metal contact. A metal ring contact is formed in the via wherein a filling layer is formed in a center of the metal ring and wherein a bottom of the metal ring contact underlying the filling layer is metal. A magnetic tunnel junction (MTJ) structure is provided over the metal ring contact and a bit line is formed over the MTJ. 
     Also in accordance with the objectives of the present disclosure, a spin-torque-transfer magnetic random access memory device having excellent thermal stability is achieved. A CMOS device is provided in a substrate. A magnetic tunnel junction (MTJ) is provided over the CMOS device and connected to the CMOS device by a metal ring contact wherein a dielectric or other filling material forms the center of the metal ring contact and wherein a bottom of the metal ring contact underlying the filling material is metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings forming a material part of this description, there is shown: 
         FIGS. 1-10  are cross-sectional representations of steps in a preferred embodiment of the present disclosure. 
         FIG. 11  is a completed device of the present disclosure. 
         FIG. 12  is a top view of the cross-section A-A′ in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure is a process integration method of fabricating MRAM devices and especially, high-density spin-transfer torque MRAM (STT MRAM) devices, connected to CMOS transistors. A ring-contact is created for connection between a CMOS transistor and a magnetic junction. This method allows one to build a magnetic device on top of a dielectric material or other special materials with benefits to magnetic performance. This method particularly provides a high thermal stability and a lower offset magnetic field (H 0 ). H 0  equals zero when the magnetic field to switch a magnetic layer from the parallel state to the anti-parallel state equals the magnetic field required to switch the same layer from the anti-parallel state to the parallel state 
     Referring now more particularly to  FIGS. 1-10 , the method of the present disclosure will be described in detail.  FIG. 1  illustrates a substrate  10 . CMOS devices (not shown) are formed within the substrate. The topmost metal level  12  of one CMOS device structure is shown, surrounded by dielectric layer  11 . The metal layer  12  may be copper, for example. The metal layer will serve as a metal landing pad  12  for a magnetic tunnel junction (MTJ). It will be understood that many CMOS devices and MRAM devices may be formed, but only one will be shown in the drawings. 
     Now, the magnetic RAM layers will be formed over the CMOS layers. A dielectric layer  14  is coated over the CMOS metal pad  12 . A contact metal via  16  is created to the landing pad  12 , for example, by a single Cu damascene method. 
     Referring now to  FIG. 2 , a double dielectric layer is deposited over the contact via  16 . For example, a first dielectric layer  18  may be a silicon nitride layer having a thickness of between about 300 and 500 Angstroms. A second dielectric layer  20  may be a silicon dioxide layer having a thickness of between about 1000 and 3000 Angstroms. Copper is usually used as the interconnect metal  16 . Layer  18  normally serves as an etch stop for layer  20  and as a copper diffusion barrier. If layer  16  is not copper, layers  18  and  20  could instead be a single dielectric layer. 
     Referring to  FIG. 3 , a via is now patterned into the double dielectric layer to provide an opening  23  to the contact via  16 . The size of the opening  23  will be determined by the size of the MTJ  38  in  FIG. 8 . It is preferred that the opening  23  is larger than the size of the MTJ  38 . 
     Now, a single or multi-layer metal film is deposited into the opening  23 . The thickness of the deposited metal film or film stack should be thinner than the total dielectric film thickness of layers  18  and  20 . The thickness difference is preferred to be larger than 1000 Angstroms for the later chemical mechanical polishing (CMP) process window. For example,  FIG. 4  illustrates a three-layer metal film stack with a tantalum layer  24 , copper-layer  26  and tantalum layer  28 . 
     Next, as shown in  FIG. 5 , another dielectric film  30  is deposited over the topmost metal film  28 . Preferably, the thickness of the film  30  will be between about 450 and 550 Angstroms. It is preferred that the top surface of  30  inside the filled via is equal to or higher than dielectric layer  20 . Film  30  can be chemical vapor deposited (CVD) dielectric materials or spin-on dielectric, metal, or alloy materials. The requirements for the selection of this material are: 1) Good fillability inside the via, and 2) good CMP capability. 
     Now, a CMP process is performed to polish the dielectric layer  30  and the metal films  24 / 26 / 28 . As shown in  FIG. 6 , the CMP endpoint should be after the metal films on the wafer are fully removed except inside the via opening  23 , but before touching the metal films on the bottom of the via. After this CMP step, a ring-shaped contact is formed.  FIG. 12  shows the top view of the ring-shaped contact comprised of the metals  24 / 26 / 28  with the film  30  filling the center of the ring.  FIG. 6  is the cross-section A-A′ of  FIG. 12 . 
     Now, the wafer is ready for the deposition of the MTJ stack of layers, as illustrated in  FIG. 7 . The present disclosure encompasses a variety of configurations including bottom spin valve, top spin valve, and dual spin valve structures, and so on. Preferably, the MTJ stack has an uppermost capping layer comprised of a hard mask. In one embodiment, for example, the MTJ stack has a bottom spin valve configuration in which seed/buffer layer  34 , pinned layer or layers  36 , barrier layer  38 , free layer  40 , and cap and hard mask layers  42  are sequentially formed on the contact ring  32 . 
     The MTJ stack is patterned by a process that includes at least one photolithography step and one etching step to form a MTJ element. In one embodiment, when two lithography processes are employed to define the MTJ element, a top portion of the MTJ may have a narrower width and smaller area size from a top view than a bottom portion of the MTJ. For example,  FIG. 8  shows a first step of patterning the MTJ free layer where the etch is stopped at or before the pinned layer  36 . 
     Then, in  FIG. 9 , a protective dielectric layer  44  is deposited over the MTJ stack. Next, the pinned layer is patterned, as shown in  FIG. 10 . The size of the pinned layer pattern must be large enough to create conduction between the pinned layer metal  34  and the contact ring  32 . 
       FIG. 11  illustrates a completed device having bit line  50  contacting the top of MTJ element  46 . Dielectric layer  48  surrounds MTJ element  46  and contact ring  32 . MTJ element  46  electrically contacts the metal ring  24 / 26 / 28  of the contact ring  32 . The contact ring  32  provides electrical connection between the CMOS device  12  and the MTJ device  46 . 
     The present disclosure provides a new process integration for spin torque MRAM products. The method allows one to build a magnetic device on top of a dielectric material or other special materials in the center of a contact ring, which benefits magnetic performance. The advantages of the present disclosure include improved thermal stability (higher Hc) and lower offset magnetic field (lower H 0 ). 
     Although the preferred embodiment of the present disclosure has been illustrated, and that form has been described in detail, it will be readily understood by those skilled in the art that various modifications may be made therein without departing from the spirit of the disclosure or from the scope of the appended claims.