BACKGROUND OF THE INVENTION 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.

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 FIGURES 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.

FIGURE 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 FIGURE 2 according to the invention.

FIGURE 4 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after encapsulation is applied to the structure of FIGURE 3 according to the invention.

FIGURE 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 FIGURE 4 according to the invention.

FIGURE 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 FIGURE 5 according to the invention.

FIGURE 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 FIGURE 6 according to the invention.

FIGURE 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 FIGURE 7 according to the invention.

FIGURE 9 is a diagrammatic cross-sectional illustration of the MTJ device of FIGURE 8 after a top metal (M3) layer deposition and CMP according to the invention.

FIGURE 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 FIGURE 2.

FIGURE 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 FIGURE 10.

FIGURE 12 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after lift-off of the photoresist layer of FIGURE 11.

FIGURE 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 FIGURE 12.

FIGURE 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 FIGURE 13.

FIGURE 15 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after etching the hardmask of the structure of FIGURE 14 and removing the photoresist layer.

FIGURE 16 is a diagrammatic cross-sectional illustration of a resulting portion of an MTJ device after using the hardmask of FIGURE 15 as a pattern to etch the cap layer, tunnel barrier layer and lower magnetic layer of FIGURE 15.

FIGURE 17 is a diagrammatic cross-sectional illustration of the structure of FIGURE 16 after encapsulation.

FIGURE 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 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.

It should be noted that the layers illustrated in FIGURES 1-18 are provided for explanatory purposes, and their dimensions are not necessarily shown to scale.

FIGURES 1 and 2 illustrate the first deposition step of a wo-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.

As shown in FIGURE 3, the layers deposited in the deposition step of FIGURES 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 FIGURE 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 FIGURE 5.

As shown in FIGURE 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.

Thereafter, as shown in FIGURE 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.

FIGURE 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 FIGURE 6.

As illustrated in FIGURE 9, conventional techniques can be used to deposit the top metal (M3) layer 80 (e. g. , Cu, W, or Al<BR> (Cu) ), followed by conventional CMP.

Referring again to FIGURES 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.

An alternate exemplary approach that employs a lift-off technique using photoresist can also be used as illustrated in FIGUREs 10-18.

Beginning with the structure of FIGURE 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 FIGURE 10.

Thereafter, as shown in FIGURE 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 FIGURE 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.

As shown in FIGURE 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 FIGURE 13, a hardmask 7 is deposited. The hardmask can be, for example, an oxide or a nitride (e. g. , SiN or TaN).

As shown in FIGURE 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 FIGURE 15.

Thereafter, as shown in FIGURE 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 FIGURE 16.

After the MTJ stack of FIGURE 16 is encapsulated with, for example, an oxide encapsulant 9 as shown in FIGURE 17, conventional techniques can be used to produce (as shown in FIGURE 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 (M3) layer 80 in the via 82. Conventional CMP can then be performed, and the result is shown in FIGURE 18.

In some exemplary embodiments, the photoresist layers 5 and 8 of FIGUREs 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 FIGUREs 6 and 7.

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.