Abstract:
A method of removing a damaged magnetic layer at the sidewall of MTJ edge is provided to form damage-free MRAM cell. In this method, the MTJ film stack outside the Ta hard mask protected area is first etched by high-power magnetic reactive ion etch (RIE) using methanol (CH3OH) or Co &amp; NH3 as etchant gases. Then a very mild chemical vapor trimming (CVT) process is used to remove a damaged layer (by the high power RIE) from the MTJ sidewall followed by an in-situ edge passivation with Si nitride (SiN) layer formed by PECVD. The MRAM cell formed by such method will have higher magnetoresistance with good device performance and better reliability.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a method of patterning magnetic random access memory (MRAM) cells without sidewall damage using two-step etching &amp; trimming processing. 
     2. Description of the Related Art 
     In recent years, magnetic random access memories (hereinafter referred to as MRAMs) using the magnetoresistive effect of a ferromagnetic tunnel junction, also called magnetic tunnel junction (MTJ), have been drawing increasing attention as the next-generation solid-state nonvolatile memories that can cope with high-speed reading and writing, large capacities, and low-power-consumption operations. A ferromagnetic tunnel junction has a three-layer stack structure formed by stacking a recording layer having a changeable magnetization direction, an insulating spacing layer, and a fixed layer that is located on the opposite side from the recording layer and maintains a predetermined magnetization direction. 
     To record information in such magnetoresistive elements, there has been suggested a write method using spin momentum transfers or spin torque transfer (STT) switching technique, or the so-called STT-MRAM. Depending on the direction of magnetic polarization, STT-MRAM is further clarified as in-plane STT-MRAM and perpendicular pSTT-MRAM, among which pSTT-MRAM is preferred. According to this method, the magnetization direction of a recording layer is reversed by applying a spin-polarized current to a magnetoresistive element. Furthermore, as the volume of the magnetic layer forming the recording layer is reduced, the injected spin-polarized current to write or switch can be also smaller. Accordingly, this method is expected to be a write method that can achieve both device miniaturization and currents reduction. 
     Patterning a MTJ cell, in a prior art, is by reactive ion etching using CH3OH or CO &amp; NH3 as etchant gases (see U.S. Pat. No. 7,060,194 and U.S. Pat. No. 7,936,027). Very good junction profile (almost or virtually vertical) can be achieved and the etching process is pretty fast. However, there is a damaged layer surrounding a MTJ cell due to high energy ion beam of bombardment. The magnetic property is severely worsened while still electrically conducting, which results in a lower TMR value. 
     For avoiding such sidewall damages on a MTJ, an alternative way of neutral beam etching was introduced (see U.S. Pat. No. 8,722,543 and ECS Transactions, 35 (4)701-716 (2011) 10.1149/1.3572314 © The Electrochemical Society). However, the entire process is very slow. 
     Recently developed oxygen neutral beam process technology has attracted attention as a way of solving sidewall damages on a MTJ. A neutral beam suppresses the incidence of charged particles and UV photon radiation onto a device in process, and is able to expose the device only to energy controlled neutral beam (neutral beam motion energy can be precisely controlled by ion acceleration energy with the applied electric field before neutralization), resulting in ultra-precise nanoprocessing that can suppress the formation of defects at the atomic layer level and control surface chemical reactions with high precision. Since the energized particles that inhibit the metal complex reactions, such as ultraviolet rays and electrons are completely cut off, the metal complex reaction is possible even at room temperature in a neutral beam process. As a result, the etching shape by oxidation and complex reaction of the transition metal Ta, Ru, or a Pt becomes ideal shape to the mask as the deterioration of the magnetic properties of the magnetic body which is observed in the plasma etching in the magnetic properties and that was also found that it is possible to suppress completely. 
     Device using this technology can be implemented in conventional plasma sources, simply by adding a graphite grit for neutralization. It is that the future, and to promote a great deal of device development practical in advancing the research and development of surface modification-modification techniques that does not stop the processing technology in the MRAM manufacturing, using a neutral particle beam. 
     The above development is found in a publication by X. Gu, Y. Kikuchi, T. Nozawa and S. Samukawa, “A Novel Metallic Complex Reaction Etching for Transition Metal and Magnetic Material by Low-temperature and Damage-free Neutral Beam Process for Non-volatile MRAM Device Applications”, VLSI Technology Symposium, Session 6 Process Technology I, No. 6.5 Jun. 10, 2014 and in US Patent Application No. 2014/0291288. 
     BRIEF SUMMARY OF THE PRESENT INVENTION 
     A method of making a MTJ cell without sidewall damage by removing wear and tear resulted from a patterning process, on surfaces and edges including side walls of a MTJ is provided here. In this method, a MTJ film stack outside the Ta hard mask protected area is first etched by high-power magnetic reactive ion etch (RIE) using methanol (CH3OH) or Co &amp; NH3 as etchant gases. Then a very mild chemical vapor trimming (CVT) process is used to remove the wear and tear resulted from a patterning process, on surfaces and edges including sidewalls of a MTJ (by the high power RIE) followed by an in-situ surface passivation with Si nitride (SiN) layer formed by a process of plasma-enhanced chemical vapor deposition (PECVD). AMTJ or MRAM cell formed by such a method will have higher magnetoresistance with improved device performance and improved reliability. 
     The following detailed descriptions are merely illustrative in nature and are not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a prior art having a photolithography patterning with a patterned photoresist layer (PRL)  150  before hard mask  120  patterning and MTJ  110  etching. 
         FIG. 2  illustrates a prior art having MTJ cells with a damaged layer  125  surrounding the MTJ surfaces and edges including side walls after an etching process using Ta as hard mask  120 . 
         FIG. 3  illustrates a stack film formed in first embodiment of present invention having a Ta/C  120 / 230  hard mask for MRAM patterning before etching. 
         FIG. 4  illustrates first embodiment of present invention having a Ta/C  120 / 230  hard mask for MRAM patterning before etching, where a patterned photoresist layer  150  has been formed. 
         FIG. 5  illustrates first embodiment of present invention having a C mask  230  after etching for transferring a PR mask  150  to a C layer  230 . 
         FIG. 6  illustrates first embodiment of present invention having a Ta mask  120  after etching for transferring a C mask  230  to a Ta hard layer  120 . 
         FIG. 7  illustrates first embodiment of present invention after etching MTJ cells  110  at a high power using Ta as hard mask  120  with, indicating a damaged layer  125  surrounding a MTJ cell  110 . 
         FIG. 8  illustrates the present invention having a chemical vapor trimming (CVT) extraction on patterned MTJ cells  110 . 
         FIG. 9  illustrates a result from removal of wear and tear damage on surfaces and edges including sidewalls of MTJ cells resulted from a patterning process on MTJ cells after CVT. 
         FIG. 10  illustrates the present invention making protection of the MTJ cells by a layer of Si nitride (SiN)  160 . 
         FIG. 11  illustrates second embodiment of present invention having a bi-layer of Ta  120  and an etching enhancement layer (EEL)  335 , Ta/EEL  120 / 335 , hard mask for MRAM patterning before etching, wherein the EEL  335  is made of one or more of Si oxide (SiO2), Si nitride (SiN), Si oxynitride (SiON), and Si carbide (SiC). 
         FIG. 12  illustrates second embodiment of present invention having a Ta/EEL  120 / 335  hard mask for MRAM patterning before etching, wherein the EEL  335  is made of one or more of Si oxide (SiO2), Si nitride (SiN), Si oxynitride (SiON), and Si carbide (SiC). Atop the EEL  335 , an optical planarization layer (OPL)  345  is formed, thus forming a tri-layer photoresist element (PRE) atop a hard mask element (HME) for achieving a better light exposure in the patterned PRL  150 , wherein the OPL  345  may also be formed by spin-on-coating. 
         FIG. 13  illustrates second embodiment of present invention having an EEL  335  after etching for transferring a PRL mask  150  to the EEL mask  335 . 
         FIG. 14  illustrates second embodiment of present invention having the mask of Ta after etching for transferring a mask of EEL  335  to the Ta layer  120 . 
         FIG. 15  illustrates second embodiment of present invention after etching MTJ cells  110  at a high power using Ta as hard mask  120  with, indicating a damaged layer  125  surrounding a MTJ cell  110 . 
         FIG. 16  illustrates second embodiment of present invention having a result from removal of wear and tear damage on surfaces and edges including sidewalls of MTJ cells resulted from a patterning process on MTJ cells after CVT. 
         FIG. 17  illustrates the present invention making protection of the MTJ cells by a layer of Si nitride (SiN)  160 . 
         FIG. 18  illustrates the present invention after filling a layer  170  of SiO2 on top of SiN  160 . 
         FIG. 19  illustrates the present invention making a flat top surface by chemical mechanical polishing (CMP). 
         FIG. 20  illustrates the present invention forming a pair of SiN  160  and SiO2  170  layers after CMP. 
         FIG. 21  illustrates the present invention patterning for making a top electrode via (TEV)  180  connected to MTJ cells. 
         FIG. 22  illustrates the present invention forming a top electrode via (TEV)  180  connected to MTJ cells. 
         FIG. 23  illustrates the present invention forming top electrode (TE)  190  connected to via(s) (TEV)  180 . 
         FIG. 24  illustrates third embodiment of present invention having a Ta/C/EEL  120 / 230 / 335  hard mask for MRAM patterning before etching, wherein the EEL  335  is made of one or more of Si oxide (SiO2), Si nitride (SiN), Si oxynitride (SiON), and Si carbide (SiC). 
         FIG. 25  illustrates third embodiment of present invention having the EEL  335  mask after etching for transferring a PR mask to the EEL layer  335 . 
         FIG. 26  illustrates third embodiment of present invention having the mask of C  230  after etching for transferring an EEL mask  335  to the C layer  230 . 
         FIG. 27  illustrates third embodiment of present invention having the mask of Ta  120  after etching for transferring a mask of C  230  to the Ta layer  120 . 
         FIG. 28  illustrates third embodiment of present invention after etching MTJ cells  110  at a high power using Ta as hard mask  120  with, indicating a damaged magnetic layer  125  surrounding a MTJ cell  110 . 
         FIG. 29  illustrates third embodiment of present invention having a result from removal of wear and tear damage on surfaces and edges, including side walls, of MTJ cells resulted from a patterning process on MTJ cells after CVT. 
         FIG. 30  illustrates the present invention forming top electrode (TE)  190  directly connected to MTJ cells without TEV in fourth embodiment. 
     
    
    
     Table 1 illustrates etching rate for the materials discussed in this invention using CF4 and O2 gas, respectively. 
     Table 2 illustrates the present invention describing chemical vapor trimming having a list of several volatile magnetic metal carbonyls formed most likely during a chemical vapor trimming (CVT) process, thus can be pumped out of a process chamber. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A method of fabricating a magnetic random access memory (MRAM) has steps below, 
     forming a MRAM film element (MRAM-FE); 
     forming a hard mask element (HME) atop the MRAM-FE; 
     forming a photoresist element (PRE) atop the HME; 
     patterning the PRE by photolithography or in-print; 
     patterning the HME; 
     patterning the MRAM-FE; 
     applying a chemical vapor trimming (CVT) process on surfaces and edges, including sidewalls, of the patterned MRAM-FE; and 
     encapsulating the patterned MRAM-FE by a Si nitride (SiN) layer, whereby producing a MJT cell without damage on surfaces and edges including sidewalls. 
     The method in present invention is in general suitable for IC fabrication patterning. However, herein, as an example, it is illustrated in MRAM fabrication patterning. 
     An exemplary embodiment will be described hereinafter with reference to the accompanying drawings. The drawings are schematic or conceptual, and the relationships between the thickness and width of portions, the proportional coefficients of sizes among portions, etc., are not necessarily the same as the actual values thereof. 
     First Embodiment 
     Illustrated in  FIG. 3 - FIG. 7 , this embodiment starts from having an MRAM film element (MRAM-FE)  110  atop a bottom electrode (BE) base layer  100  made first, wherein a set of required films stacked one by one for forming a functional foundation of MRAM before an MRAM circuit is fabricated. The BE is made of an electric conductor, such as a metal or an alloy. A step forming a hard mask element (HME)  120 / 230  starts with forming a metal Ta layer  120  with a thickness between 40-150 nm followed by forming a carbon layer  230  with a thickness between 20-200 nm atop the Ta layer  120 . The Ta layer  120  may be formed by approaches including physical vapor deposition (PVD), or ion-beam deposition (IBD) using Ta as a target. The carbon layer  230  is formed by approaches including one or more of the following methods a). chemical vapor deposition (CVD) using reactants comprising C, H, and O; b). a spin-on-Carbon coating; c). PVD using carbon as a target; and d). IBD using carbon as a target. Then an antireflection layer (ARL)  140  and a photoresist layer (PRL)  150  are formed by spin-coating atop of the carbon layer of HME thus forming a bi-layer photoresist element (PRE) atop the HME  120 / 230 . 
     Next, the PRL  150  is patterned, as shown in  FIG. 4 , either by photolithography with the help of ARL or in-print with a mask mold followed by patterning the ARL  140  with etching. Thus, the bi-layer PRE is patterned. Then using patterned PRE as a mask, the carbon layer  230  of HME is patterned, as shown in  FIG. 5 , by O2, O2+Ar, or O2+CF4+Ar ashing. Then the Ta layer  120  of the HME is patterned, as shown in  FIG. 6 , by reactive ion etching (RIE) with gases comprising CF4 or a mixture of CF4, C, F, and H, using the patterned carbon  230  as a hard mask followed by ashing the remained carbon layer  230  atop the Ta layer  120  of HME by O2. Next, the MRAM film element (MRAM-FE)  110  atop the BE  100  is patterned by etching using gases containing methanol (CH3OH), ethanol (C2H5OH), a mixture of CO and NH4, or Chlorine (Cl) as etchant(s), using the patterned Ta layer  120  as a hard mask. Thus, a patterned MRAM-FE with wear and tear damages  125 , from patterning, on MTJ surfaces and edges including sidewalls are formed, as shown in  FIG. 7 , above the BE  100 . 
     Then, as shown in  FIG. 8  and Table 2 a chemical vapor trimming (CVT) process is applied on surfaces and edges including sidewalls of the patterned MRAM-FE. The CVT process is applied at low power to mildly remove a layer of particles of wear and tear, from patterning, surrounding the post-patterning surfaces and edges including sidewalls for achieving improved device performance. The CVT process uses molecules of at least one of carbon monoxide (CO), alcohols, and carbonyl, wherein alcohols and carbonyl are in one or more of their various forms, preferably ethanol (C2H5OH) and acetic acid (CH3COOH) respectively, for extracting particles of loosen metal or metal oxide wear and tear, from patterning, on exposed surfaces and edges including sidewalls of the patterned MRAM-FE to form volatile metal carbonyls. The CVT process is conducted at a temperature such that the formed metal carbonyls are in their vapor state (volatile) and thus subsequently are pumped out of the process chamber. Thus, a patterned MRAM-FE having magnetically isolated MTJ cells without damage on surface and edge including side walls is formed, as shown in  FIG. 9 , above the BE  100 . 
     Then, as shown in  FIG. 10 , the patterned MRAM-FE is immediately encapsulated by depositing a Si nitride (SiN) layer  160  on it with a plasma-enhanced chemical vapor deposition (PECVD) process for protecting surfaces of MTJ cells or MRAM elements, whereby producing a desired MJT cell without damage on surfaces and edges including sidewalls but with larger magnetoresistance, better performance, and better reliability. 
     Second Embodiment 
     As another example, alternatively illustrating the method in present invention, as shown in  FIG. 11 - FIG. 16 , an MRAM film element (MRAM-FE)  110  atop the BE  100  is made first, wherein a set of required films stacked one by one for forming a functional foundation of MRAM before an MRAM circuit is fabricated. A step forming a hard mask element (HME) starts with forming a metal Ta layer  120  with a preferred thickness between 40-150 nm. The next step is forming an etching enhancement layer (EEL)  335  made of one or more of Si oxide (SiO2), Si nitride (SiN), Si oxynitride (SiON), and Si carbide (SiC), atop the carbon layer  230 , with a preferred thickness of 50-200 nm. The SiO2 layer of the EEL  335  in HME is formed by approaches including one or more of the following: a). CVD using reactants comprising Si, H, and O; b). spin-on-SiO coating; c). PVD using Si or SiO2 as a target with Ar or Ar+O2 gas(es); and d). IBD using SiO2 as a target. The SiN layer of the EEL  335  in the HME is formed by approaches including one or more of the following: a). CVD using reactants comprising Si, N, and H; and b). PVD using Si as a target with Ar+N2 or Ar+NH4 gases. The SiON layer of EEL  335  in the HME is formed by approaches including one or more of the following: a). CVD using reactant(s) comprising Si, O, N, and H; and b). PVD, using Si as a target with gases comprising Ar, O, and N. The SiC layer of the EEL  335  in the HME is formed by approaches including one or more of the following: a). CVD using reactants comprising Si, C, and H; b). PVD using SiC as a target; and c). IBD using SiC as a target. Then as shown in  FIG. 11 , an antireflection layer (ARL)  140  is formed atop of the ELL layer  335  of the HME followed by forming a photoresist layer (PRL)  150  atop the ARL  140 , wherein both the PRL  150  and the ARL  140  may be formed by spin-on-coating. Alternatively, as shown in  FIG. 12 , an optical planarization layer (OPL)  345  is formed atop the EEL  335  thus forming a tri-layer photoresist element (PRE) atop the HME for achieving a better light exposure in the PRL  150 , wherein the OPL  345  may also be formed by spin-on-coating. 
     Next, the PRL  150  is patterned, as shown in  FIG. 11  and  FIG. 12 , either by photolithography or in-print with a mold followed by patterning ARL  140  and OPL  345  by etching using the patterned PRL  150  as a mask. Next steps include a). patterning the EEL  335  of the HME by reactive ion etch (RIE) with reactant gas(es) containing CF4 or a mixture of CF4, C, F, and H, using the patterned PRE as a mask as shown in  FIG. 13 ; b). patterning the Ta layer  120  of the HME by RIE with reactant gas(es) containing CF4 or a mixture of CF4, C, F, and H, using the patterned EEL  335  as a hard mask as shown in  FIG. 14 . Table 1 illustrates etching rate using CF4 gas and ashing rate using O2 gas for each mask material in the present invention. 
     Next, using the Ta layer  120  as a hard mark, the MRAM film element (MRAM-FE) is patterned as shown  FIG. 15  by reactive ion etching (RIE) using reactant gas(es) including one or more of CH3OH, CH5OH, a mixture of CO and NH4, and Chlorine (Cl). 
     Then a chemical vapor trimming (CVT) process similar to the one described in the first embodiment is performed to remove the damaged layer surrounding the etched surface and edges including sidewalls to achieve better device performance. The above CVT process is used for more than one time and, in between a time and its subsequent time of applying the CVT process, a bombardment process using argon ions and oxygen ions is applied for forming a layer of loosen metal oxide on exposed surfaces and edges including sidewalls of the patterned MRAM for better facilitating CVT extractions, whereby a patterned MRAM-FE having magnetically isolated MTJ cells without damage of surfaces and edges including sidewalls is produced, as shown in  FIG. 16 , above the BE  100 . 
     Then, as shown in  FIG. 17 , the patterned MRAM-FE is immediately encapsulated by depositing a Si nitride (SiN) layer  160  on it with a plasma-enhanced chemical vapor deposition (PECVD) process for protecting surfaces including of MTJ cells or MRAM elements, whereby producing a desired MJT cell without damage  125  on surfaces and edges including sidewalls. 
     As shown in  FIG. 18  a thick layer of SiO2  170  is filled atop the SiN layer by PECVD. Thereafter, a CMP process is used for flattening the surfaces of MTJ cells as shown in  FIG. 19 . Then a pair of SiN &amp; SiO2 film stack  160 / 170  is deposited by PECVD on the smooth surfaces and edges of MTJ as shown in  FIG. 20 . As shown in  FIG. 21  and  FIG. 22 , a next step in the present invention forms via(s) (TEV)  180  connected to MTJ cells. Then a next step is to form a top electrode (TE)  190  connected to via(s) (TEV)  180  as shown in  FIG. 23 , thus MRAM cells are made of MTJ cells without damage on side walls and edges but with larger magnetoresistance, better performance, and better reliability. 
     Third Embodiment 
     As another example, alternatively illustrating the method in present invention, as shown in  FIG. 24 - FIG. 29 , an MRAM film element (MRAM-FE)  110  atop the BE  100  is made first, wherein a set of required films stacked one by one for forming a functional foundation of MRAM before an MRAM circuit is fabricated. A step forming a hard mask element (HME) starts with forming a metal Ta layer  120  with a preferred thickness between 50-150 nm followed by forming a carbon  230  with a preferred thickness between 20-200 nm atop the Ta layer  120 , that is formed by approaches including PVD, or IBD using C as a target. The next step is forming an etching enhancement layer (EEL)  335  made of one or more of Si oxide (SiO2), Si nitride (SiN), Si oxynitride (SiON), and Si carbide (SiC), atop the carbon layer  230 , with a preferred thickness of 40-200 nm. The SiO2 layer of the EEL  335  in HME is formed by approaches including one or more of the following: a). PECVD using reactants comprising Si, H, and O; b). spin-on-SiO coating; c). PVD using Si or SiO2 as a target with Ar or Ar+O2 gas(es); and d). IBD using SiO2 as a target. The SiN layer of the EEL  335  in the HME is formed by approaches including one or more of the following: a). PECVD using reactants comprising Si, N, and H; and b). PVD using Si as a target with Ar+N2 or Ar+NH4 gases. The SiON layer of EEL  335  in the HME is formed by approaches including one or more of the following: a). PECVD using reactant(s) comprising Si, O, N, and H; and b). PVD, using Si as a target with gases comprising Ar, O, and N. The SiC layer of the EEL  335  in the HME is formed by approaches including one or more of the following: a). PECVD using reactants comprising Si, C, and H; b). PVD using SiC as a target; and c). IBD using SiC as a target, wherein the OPL  345  may also be formed by spin-on-coating. Then an optical planarization layer (OPL)  345  is formed atop the EEL  335  layer of the HME followed by forming a antireflection layer (ARL)  140  atop the OPL  345  and photoresist layer (PRL)  150  atop the ARL  140 , wherein the OPL, ARL and PR may be formed by spin-on-coating, thus forming a tri-layer photoresist element (PRE) atop the HME for achieving a better light exposure in the PRL  150 . 
     Next, the PRL  150  is patterned, as shown in  FIG. 24 , either by photolithography or in-print with a mold followed by patterning ARL  140  and OPL  345  by etching using the patterned PRL  150  as a mask. Next steps include a). patterning the EEL  335  of the HME by reactive ion etch (RIE) with reactant gas(es) containing CF4 or a mixture of CF4, C, F, and H, using the patterned PRE as a mask, as shown in  FIG. 25 ; b). patterning the carbon layer  230  of HME by O2, or O2+Ar ashing using the patterned EEL  335  as a hard mask, as shown in  FIG. 26 ; c). patterning the Ta layer  120  of the HME by RIE with reactant gas(es) containing CF4 or a mixture of CF4, C, F, and H, using the patterned carbon  230  as a hard mask followed by ashing the remained carbon layer  230  atop the Ta layer  120  of HME by O2 as shown in  FIG. 27 . Table 1 illustrates etching rate using CF4 gas and ashing rate using O2 gas for each targeted material in the present invention. 
     Next, using the Ta layer  120  as a hard mark, the MRAM film element (MRAM-FE) is patterned as shown in  FIG. 28  by reactive ion etching (RIE) using reactant gas(es) including one or more of CH3OH, CH5OH, a mixture of CO and NH4, and Chlorine (Cl). 
     Then a chemical vapor trimming (CVT) process similar to the one described in the first embodiment is performed to remove the damaged layer surrounding the etched surface and edges including sidewalls to achieve better device performance. The above CVT process is used for more than one time and, in between a time and its subsequent time of applying the CVT process, a bombardment process using argon ions and oxygen ions is applied for forming a layer of loosen metal oxide on exposed surfaces and edges including sidewalls of the patterned MRAM for better facilitating CVT extractions, whereby a patterned MRAM-FE having magnetically isolated MTJ cells without damage of surfaces and edges including sidewalls is produced, as shown in  FIG. 29 , above the BE  100 . 
     Then, as shown in  FIG. 17 , the patterned MRAM-FE is immediately encapsulated by depositing a Si nitride (SiN) layer  160  on it with a plasma-enhanced chemical vapor deposition (PECVD) process for protecting surfaces including of MTJ cells or MRAM elements, whereby producing a desired MJT cell without damage  125  on surfaces and edges including. 
     As shown in  FIG. 18  a thick layer of SiO2  170  is filled atop the SiN layer by PECVD. Thereafter, a CMP process is used for flattening the surfaces of MTJ cells as shown in  FIG. 19 . Then a pair of SiN &amp; SiO2 film stack  160 / 170  is deposited by PECVD on the smooth surfaces and edges of MTJ as shown in  FIG. 20 . As shown in  FIG. 21  and  FIG. 22 , a next step in the present invention forms via(s) (TEV)  180  connected to MTJ cells. Then a next step is to form a top electrode (TE)  190  connected to via(s) (TEV)  180  as shown in  FIG. 23 , thus MRAM cells are made of MTJ cells without damage on sidewalls and edges but with larger magnetoresistance, better performance, and better reliability. 
     Fourth Embodiment 
     In this embodiment, patterning processes and CMP process(s) are the same as that in Third Embodiments. Right after the CMP flattening of the MTJ top surface as shown in  FIG. 19 , the process of forming a TEV and a TE in Third Embodiment is replaced by a process of forming a TE directly in contact with the top surface of MTJ without any TEV, as shown in  FIG. 30 . 
     The above detailed descriptions are merely illustrative in nature and are not intended to limit the embodiment of the subject matter or the application and uses of such embodiment. Indeed, the novel embodiment described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.