CoFeB based magnetic tunnel junction device with boron encapsulation layer
One or more magnetic tunneling junction (MTJ) pillars are disposed on a substrate. The pillars have one or more magnetic reference layers and one or more magnetic free layers. The magnetic free layers have one or more external surfaces and are made of a magnetic free layer material containing atomic percentage amount of boron. A boron-containing encapsulation layer encapsulates the MTJ pillar(s) and is in direct contact with the magnetic free layer external surfaces. The boron-containing encapsulation layer contains an atomic percentage amount of boron greater than the magnetic free layer atomic percentage amount of boron. Embodiments of the boron-containing encapsulation layer contain at least 95 percent pure boron and are between 1 and 3 nanometers thick. Accordingly, the boron-containing encapsulation layer controls and limits the amount of boron diffusing out of the magnetic free layer across a boron diffusion interface formed between the magnetic free layer external surfaces and the boron-containing encapsulation layer. Alternative embodiments of boron-containing encapsulation layers and methods of making MTJ devices are disclosed.
1 . A magnetic tunneling junction (MTJ) pillar disposed on a substrate, wherein the MTJ pillar has one or more MTJ pillar surfaces/sidewalls that are perpendicular to the substrate, and wherein the MTJ pillar comprises:
one or more magnetic reference layers, the magnetic reference layers having a first magnetic orientation, the first magnetic orientation being a fixed magnetic orientation, the magnetic reference layers disposed on the substrate;
one or more magnetic free layers, the magnetic free layers having a second magnetic orientation the second magnetic orientation being switchable to one of a parallel and an anti-parallel alignment with the first magnetic orientation, the magnetic free layers having one or more magnetic free layer external surfaces and one or more internal magnetic free layer interfaces, the magnetic free layers external surfaces being colinear with the MTJ pillar surfaces/sidewalls, the magnetic free layers containing a first atomic percentage amount of boron greater than zero;
a tunnel barrier layer with a tunnel barrier layer thickness, the tunnel barrier layer being sandwiched between the magnetic reference layer and the magnetic free layer; and
a boron-containing encapsulation layer encapsulating and in direct contact with the magnetic free layers external surfaces, the boron-containing encapsulation layer containing a dielectric material with a second atomic percentage amount of boron greater than the first atomic percentage amount of boron in the magnetic free layers.
2 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is made of substantially pure boron.
3 . The MTJ pillar, as in claim 2 , where the boron-containing encapsulation layer is between 1 and 3 nanometers (nm) thick.
4 . The MTJ pillar, as in claim 2 , where the boron-containing encapsulation layer remains on the MTJ pillar surfaces/sidewalls without decomposing.
5 . The MTJ pillar, as in claim 2 , where the boron-containing encapsulation layer further contains hydrogen.
6 . The MTJ pillar, as in claim 2 , where diffusion of the boron from the boron-containing encapsulation layer into the magnetic free layers is limited by a solubility of boron in the magnetic free layers.
7 . The MTJ pillar, as in claim 2 , where the boron-containing encapsulation layer encapsulates all the MTJ pillar surfaces/sidewalls.
8 . The MTJ pillar, as in claim 2 , where the boron-containing encapsulation layer is encapsulated by a dielectric spacer.
9 . The MTJ pillar, as in claim 8 , where the dielectric spacer is made from one of the following: SiBCN, SIN, SiOCN, SiBN, SiON, and SiOC.
10 . The MTJ pillar, as in claim 1 , where the magnetic free layers include at least one material selected from the group consisting of: a magnetic material, a ferromagnetic material, cobalt, iron, alloys of cobalt-iron, nickel, alloys of nickel-iron, alloys of cobalt-iron-boron, and cobalt-iron-boron (CoFeB) alloys.
11 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is a dielectric encapsulation layer made of a boron-containing dielectric material.
12 . The MTJ pillar, as in claim 11 , where the boron-containing dielectric material has a boron content of 40% or more atomic percent.
13 . The MTJ pillar, as in claim 11 , where the boron-containing dielectric material is boron nitride (BN).
14 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is a boron-containing dielectric encapsulation layer made of a boron-containing dielectric material that is encompassed by a second dielectric spacer layer.
15 . The MTJ pillar, as in claim 14 , where the second dielectric spacer layer is made from one of SiN, SiOCN, or SiBCN.
16 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is a dielectric encapsulation layer additionally implanted with boron.
17 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is made of 95% boron.
18 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is made of at least 99% boron.
19 . The MTJ pillar, as in claim 1 , where the boron-containing encapsulation layer is pure boron.
20 . A structure comprising:
a boron-containing encapsulation layer encapsulating and in direct contact with a surface of a magnetic free layer containing a first atomic percentage amount of boron greater than zero, the boron-containing encapsulation layer containing a dielectric material with a second atomic percentage amount of boron greater than the first atomic percentage amount of boron in the magnetic free layer.
21 . The structure, as in claim 20 , wherein the structure is a magnetic tunnel junction.
22 . A MRAM circuit comprising:
a substrate;
at least one of a front-end-of-the-line (FEOL) layer or a back-end-of-the-line BEOL) layer disposed on the substrate;
one or more MTJ pillars disposed on the at least one of the FEOL layer or the BEOL layer, each of the MTJ pillars comprising: one or more MTJ pillar surfaces/sidewalls, the MTJ pillar surfaces/sidewalls being perpendicular to the substrate and the at least one of the FEOL layer or the BEOL layer;
one or more magnetic reference layers disposed on the at least one of the FEOL layer or the BEOL layer and in electrical contact with one or more BEOL connections in the at least one of the FEOL layer or the BEOL layer, the magnetic reference layers having a first magnetic orientation;
one or more magnetic free layers, the magnetic free layers having a second magnetic orientation, the second magnetic orientation being switchable to one of a parallel and an anti-parallel alignment with the first magnetic orientation, the magnetic free layers having one or more magnetic free layer external surfaces, the magnetic free layers external surfaces being colinear with the MTJ pillar surfaces/sidewalls, the magnetic free layers containing a first atomic percentage amount of boron greater than zero;
a capping layer made of a conductive metal, the capping layer in electrical contact with the magnetic free layers and in electrical contact with one or more capping contacts in the at least one of the FEOL layer or the BEOL layer;
a tunnel barrier layer with a tunnel barrier layer thickness, the tunnel barrier layer being sandwiched between the magnetic reference layers and the magnetic free layers;
and a boron-containing encapsulation layer encapsulating and in direct contact with the magnetic free layers external surfaces, the boron-containing encapsulation layer containing a dielectric material with a second atomic percentage amount of at least 95 percent pure boron and being between 1 and 3 nanometers thick, the second atomic percentage amount of boron of the boron-containing encapsulation layer being greater than the first atomic percentage amount of boron in the magnetic free layers.
23 . A method of making a magnetic tunneling junction (MTJ) pillar, comprising the steps of:
forming the MTJ pillar, wherein forming the MTJ pillar comprises:
forming one or more magnetic reference layers, wherein the one or more magnetic reference layers have a first magnetic orientation that is a fixed magnetic orientation;
forming one or more magnetic free layers, wherein the one or more magnetic free layers have a second magnetic orientation that is switchable to one of a parallel and an anti-parallel alignment with the first magnetic orientation, the one or more magnetic free layers having one or more magnetic free layer external surfaces and one or more internal magnetic free layer interfaces, the one or more magnetic free layer external surfaces being colinear with sidewalls of the MTJ pillar, the one or more magnetic free layers containing a first atomic percentage amount of boron greater than zero; and
forming a tunnel barrier layer with a tunnel barrier layer thickness, the tunnel barrier layer being sandwiched between the one or more magnetic reference layers and the one or more magnetic free layers; and
encapsulating the MTJ pillar with a boron-containing encapsulation layer that encapsulates and is in direct contact with the one or more magnetic free layer external surfaces, the boron-containing encapsulation layer containing a dielectric material with a second atomic percentage amount of boron greater than the first atomic percentage amount of boron in the one or more magnetic free layers.
24 . The method, as in claim 23 , where the encapsulating step is performed by the steps of:
exposing the MTJ pillar to a borane gas at a temperature of between 250 and 400 Celsius (C) at a pressure of 0.1-10 torr for between 100 and 1000 seconds until one or more higher boranes are formed and deposited on the sidewalls of the MTJ pillar; and
decomposing the one or more higher boranes on the sidewalls of the MTJ pillar into the boron-containing encapsulation layer.
25 . The method, as in claim 23 , where the decomposing step is performed by the steps of:
over the sidewalls of the MTJ pillar, flowing a 26 standard liter per minute (slm) hydrogen flow with a borane concentration partial pressure at 5×10 −4 to 1×10 −2 mtorr with a flow of 0.2-3 standard cubic centimeter per minute (sccm) of 1% diborane diluted in hydrogen.
26 . The method, as in claim 25 , where the slm hydrogen flow is equivalent to a 0.08-1.14 ppm pure B2 H6 in the gas mixture.