Non-volatile memory having 3D array of read/write elements with low current structures and methods thereof
View Patent ↗A three-dimensional array read/write (R/W) memory elements is formed across multiple layers of planes positioned at different distances above a semiconductor substrate. It is preferable to operate the R/W elements with low current and high resistive states. The resistance of these resistive states depends also on the dimension of the R/W elements and is predetermined by the process technology. A sheet electrode in series with the R/W element and a method of forming it provide another degree of freedom to adjust the resistance of the R/W memory element. The thickness of the sheet electrode is adjusted to obtain a reduced cross-sectional contact in the circuit path from the word line to the bit line. This allows the R/W memory element to have a much increased resistance and therefore to operate with much reduced currents. The sheet electrode is formed with little increase in cell size.
1. A method of forming a memory having memory elements arranged in a three-dimensional pattern defined by rectangular coordinates having x, y and z-directions and with a plurality of parallel planes stacked in the z-direction, comprising:
providing a semi-conductor substrate;
forming predetermined active elements and metal lines on the semi-conductor substrate;
forming a multi-layer structure on top of the substrate, the multi-layer structure being repeated subsets of layers, each subset of layers comprising a layer for forming a sheet electrode, a dielectric layer and a sacrificial material;
forming a 2-D array in the x-y plane of conductive pillars as bit line pillars elongated in the z-direction through the plurality of planes, each said conductive pillars being formed with a cladding layer of R/W material for of the memory elements, said layer of R/W material for the memory elements being in electrical contact with the layer of sheet electrode when said conductive pillars in the x-z plane and the layer of sheet electrode in the x-y plane intersect at each subset of layers;
exposing a cross section of the multi-layer structure by opening a plurality of trenches in the x-z plane in the multi-layer structure;
etching recesses in the sacrificial layer of the multi-layers to within a predetermined offset from the conductive pillars from each of the trenches, thereby exposing a portion of the layer for forming the sheet electrode; and
forming the word lines on the multiple planes in a lateral direction in the recesses, said word lines being formed over the exposed portion of the layer for forming the sheet electrode and making electrical contact therewith.
2. The method as in claim 1 , wherein:
the conductive pillars are formed from polysilicon.
3. The method as in claim 1 , wherein:
the word lines are formed from a metal.
4. The method as in claim 1 , wherein:
the layer for forming the sheet electrode is a metal.
5. The method as in claim 1 , wherein:
the layer for forming the sheet electrode is TiN.
6. The method as in claim 1 , wherein:
the layer for forming the sheet electrode is carbon.
7. The method as in claim 1 , wherein:
the layer for forming the sheet electrode is also constituted from the R/W material.
8. The method as in claim 7 , wherein:
each said conductive pillars being formed with a cladding layer of R/W material for of the memory elements is optional.
9. The method as in claim 1 , wherein:
said forming a 2-D array in the x-y plane of conductive pillars as bit line pillars elongated in the z-direction through the plurality of planes is by a trench process comprising:
opening a plurality of trenches for forming the conductive pillars in the x-z plane in the multi-layer structure;
forming a layer of R/W material for of the memory elements in the trenches for forming the conductive pillars;
filling the trenches for forming the conductive pillars with a slab of material for forming the conductive pillars;
removing portions of the slab of material for forming the conductive pillars along the x-direction to form individual conductive pillars; and
filling the removed portions of the slab with oxide.
10. The method as in claim 1 , wherein:
said forming a 2-D array in the x-y plane of conductive pillars as bit line pillars elongated in the z-direction through the plurality of planes is by a damascene process comprising:
opening a plurality of trenches for forming the conductive pillars in the x-z plane in the multi-layer structure;
filling the trenches for forming the conductive pillars with a slab of oxide;
removing portions of the slab of oxide along the x-direction;
forming a layer of R/W material for of the memory elements in the removed portions; and
filling the removed portions of the slab with material for forming the conductive pillars to form the conductive pillars.