Memory device containing composition-controlled ferroelectric memory elements and method of making the same
A semiconductor memory device includes an alternating stack of insulating layers and electrically conductive layers, a memory opening vertically extending through the alternating stack, and a memory opening fill structure located in the memory opening and including a vertical stack of discrete ferroelectric material portions and a vertical semiconductor channel. In one embodiment, the discrete ferroelectric material portions include a ferroelectric alloy material of a first dielectric metal oxide material and a second dielectric metal oxide material. In another embodiment, each of the discrete ferroelectric material portions is oxygen-deficient.
1. A semiconductor memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers;
a memory opening vertically extending through the alternating stack; and
a memory opening fill structure located in the memory opening and comprising a vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions and a vertical semiconductor channel,
wherein:
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions are vertically spaced apart from each other;
each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions is in direct contact with a sidewall of a respective oxygen-gettering liner; and
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have a formula selected from:
HfO 2-x , where x >0, or
ZrO 2-y , where y >0, or
AlO 1.5-z , where z >0.
2. The semiconductor memory device of claim 1 , wherein each of the electrically conductive layers comprises the respective oxygen-gettering liner comprising a first conductive material and conductive fill material layer comprising a second conductive material that is different from the first conductive material.
3. The semiconductor memory device of claim 2 , wherein the first conductive material comprises TaN or TiN.
4. The semiconductor memory device of claim 2 , wherein the first conductive material comprises an elemental metal that is selected from platinum, titanium, tantalum, hafnium, or aluminum.
5. The semiconductor memory device of claim 2 , wherein the oxygen-gettering liner of each of the electrically conductive layers is in direct contact with a respective pair of insulating layers of the insulating layers of the alternating stack.
6. The semiconductor memory device of claim 1 , wherein each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions has a radial oxygen concentration gradient such that an atomic percentage of oxygen atoms decreases with a radial distance from a vertical axis passing through a geometrical center of the memory opening fill structure.
7. The semiconductor memory device of claim 1 , wherein the memory opening fill structure further comprises a vertical stack of discrete spacer material portions that is interlaced with the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions along a vertical direction.
8. The semiconductor memory device of claim 7 , wherein the discrete spacer material portions comprise a ferroelectric material having a material composition that differs from a material composition of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions by a reduced density of oxygen vacancies.
9. The semiconductor memory device of claim 7 , wherein:
outer sidewalls of the vertical stack of discrete spacer material portions are vertically coincident with outer sidewalls of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions; and
inner sidewalls of the vertical stack of discrete spacer material portions are vertically coincident with inner sidewalls of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions.
10. The semiconductor memory device of claim 1 , wherein:
the vertical semiconductor channel is in direct contact with sidewalls of the insulating layers within the alternating stack; and
each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions comprises a respective top surface that contacts a bottom surface of a respective overlying insulating layer of the insulating layers, and a respective bottom surface that contacts a top surface of a respective underlying insulating layer of the insulating layers.
11. The semiconductor memory device of claim 1 , wherein the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have the formula HfO 2-x , where x>0.
12. The semiconductor memory device of claim 1 , wherein the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have the formula ZrO 2-y , where y >0.
13. The semiconductor memory device of claim 1 , wherein the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have the formula AlO 1.5-z , where z>0.
14. A method of forming a semiconductor structure, comprising:
forming an alternating stack of insulating layers and sacrificial material layers over a substrate;
forming a memory opening through the alternating stack;
forming an in-process memory opening fill structure in the memory opening, wherein the in-process memory opening fill structure comprises metal oxide tubular portions located at levels of the sacrificial material layers and a vertical semiconductor channel that is formed over the metal oxide tubular portions;
forming backside recesses by removing the sacrificial material layers selective to the insulating layers and the metal oxide tubular portions;
forming an oxygen-gettering liner in each of the backside recesses and directly on an outer sidewall of a respective one of the metal oxide tubular portions; and
gettering oxygen atoms from the metal oxide tubular portions to convert them into a vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions;
wherein:
the oxygen-gettering liner comprises platinum, titanium, tantalum, hafnium, aluminum, TaN or TiN;
the metal oxide tubular portions comprise stoichiometric hafnium oxide, stoichiometric zirconium oxide or stoichiometric aluminum oxide; and
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have a formula selected from HfO 2-x , ZrO 2-x , or AlO 1.5-x , where x >0.
15. The method of claim 14 , further comprising forming a conductive fill material layer comprising a second conductive material on the oxygen-gettering liners in each remaining volume of the backside recesses to form word lines, wherein the oxygen-gettering liners comprise a conductive material.
16. The method of claim 14 , further comprising forming a metal oxide layer on a sidewall of the memory opening, wherein the metal oxide tubular portions comprise portions of the metal oxide layer that are located at the levels of the sacrificial material layers.
17. The method of claim 16 , wherein:
portions the metal oxide layer located at levels of the insulating layers comprise ferroelectric dielectric spacer material portions after formation of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions;
the discrete spacer material portions have a first average density of oxygen vacancies; and
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have a second average density of oxygen vacancies which is greater than the first average density.
18. The method of claim 14 , further comprising:
laterally recessing sidewalls of the sacrificial material layers around the memory opening to form annular recesses at levels of the sacrificial material layers around the memory opening;
conformally depositing a metal oxide layer the annular recesses; and
removing portions of the metal oxide layer located outside the annular recesses by anisotropically etching the metal oxide layer to leave the metal oxide tubular portions in the annular recesses.
19. The method of claim 18 , wherein the vertical semiconductor channel is formed by depositing a semiconductor channel material directly on inner sidewalls of the metal oxide tubular portions and directly on sidewalls of the insulating layers around the memory opening.
20. A method of forming a semiconductor structure, comprising:
forming an alternating stack of insulating layers and sacrificial material layers over a substrate;
forming a memory opening through the alternating stack;
forming an in-process memory opening fill structure in the memory opening, wherein the in-process memory opening fill structure comprises metal oxide tubular portions located at levels of the sacrificial material layers and a vertical semiconductor channel that is formed over the metal oxide tubular portions;
forming backside recesses by removing the sacrificial material layers selective to the insulating layers and the metal oxide tubular portions;
forming an oxygen-gettering liner in each of the backside recesses and directly on an outer sidewall of a respective one of the metal oxide tubular portions;
gettering oxygen atoms from the metal oxide tubular portions to convert them into a vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions; and
forming a metal oxide layer on a sidewall of the memory opening, wherein the metal oxide tubular portions comprise portions of the metal oxide layer that are located at the levels of the sacrificial material layers;
wherein:
portions the metal oxide layer located at levels of the insulating layers comprise ferroelectric dielectric spacer material portions after formation of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions;
the discrete spacer material portions have a first average density of oxygen vacancies; and
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions have a second average density of oxygen vacancies which is greater than the first average density.
21. A semiconductor memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers;
a memory opening vertically extending through the alternating stack; and
a memory opening fill structure located in the memory opening and comprising a vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions and a vertical semiconductor channel,
wherein:
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions are vertically spaced apart from each other;
each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions is in direct contact with a sidewall of a respective oxygen-gettering liner; and
each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions has a radial oxygen concentration gradient such that an atomic percentage of oxygen atoms decreases with a radial distance from a vertical axis passing through a geometrical center of the memory opening fill structure.
22. A semiconductor memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers;
a memory opening vertically extending through the alternating stack; and
a memory opening fill structure located in the memory opening and comprising a vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions and a vertical semiconductor channel,
wherein:
the discrete non-stoichiometric oxygen-deficient ferroelectric material portions are vertically spaced apart from each other;
each of the discrete non-stoichiometric oxygen-deficient ferroelectric material portions is in direct contact with a sidewall of a respective oxygen-gettering liner;
the memory opening fill structure further comprises a vertical stack of discrete spacer material portions that is interlaced with the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions along a vertical direction;
outer sidewalls of the vertical stack of discrete spacer material portions are vertically coincident with outer sidewalls of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions; and
inner sidewalls of the vertical stack of discrete spacer material portions are vertically coincident with inner sidewalls of the vertical stack of discrete non-stoichiometric oxygen-deficient ferroelectric material portions.