METHOD PROVIDING FOR A STORAGE ELEMENT

Abstract

A method for forming a thin film comprising a metal, metal compound, or metal oxide on a substrate, which method comprises forming one or more thin film layers of a metal or metal oxide by a deposition process employing reactant precursors and/or relative amounts thereof which are selected to deposit a thin film layer with a controlled amount of dopant derived from at least one reactant precursor.

Claims

1. A method for forming a thin film comprising a metal oxide, which method comprises forming one or more thin film layers of metal oxide by a chemical vapour deposition or an atomic layer deposition process employing reactant precursors comprising a metal-containing reactant precursor and an oxidant to form a first thin film layer with a controlled amount of dopant and a second thin film layer with a controlled amount of dopant wherein the dopant is derived from at least one of the reactant precursors, the oxidant is selected from the group consisting of O.sub.2, O.sub.3, oxygen plasma species, H.sub.2O, D.sub.2O, H.sub.2O.sub.2, NO, N.sub.2O, CO and CO.sub.2 and mixtures thereof and the forming of the first thin film layer employs an oxidant and/or relative amount of an oxidant which is different to the oxidant and/or relative amount of oxidant for forming the second thin film layer whereby the controlled amount of dopant of the second thin film layer is different to that of the first thin film layer.

2. (canceled)

3. A method according to claim 1, which further comprises forming a third thin film layer with a controlled amount of dopant, wherein the forming of the third thin film layer employs an oxidant and/or relative amount of an oxidant which is different to the oxidant and/or relative amount of oxidant for forming the second thin film layer whereby the controlled amount of dopant of the third film layer is different to that of the second thin film layer.

4. A method according to claim 1, wherein the forming of the first thin film layer employs an oxidant which is selected to be different to the oxidant for the forming of the second thin film layer.

5. A method according to claim 3, wherein the forming of the third film layer employs an oxidant which is selected to be different to the oxidant for the forming of the second thin film layer.

6. A method according to claim 1, wherein the forming of the first thin film layer employs a relative amount of oxidant which is selected to be different to the relative amount of oxidant for forming the second thin film layer.

7. A method according to claim 3, wherein the forming of the third thin film layer employs a relative amount of oxidant which is selected to be different to the relative amount of oxidant for forming the second thin film layer.

8. A method according to claim 1, wherein the forming of each thin film layer employs the same deposition temperature.

9. A method according to claim 1, wherein the reactant precursors comprise a metal halide or an organometallic compound selected from the group consisting of NiCl.sub.4, Ni(AMD), Ni(Cp).sub.2, Ni(thd).sub.2, Ni(acac).sub.2, Ni(CH.sub.3C.sub.5H.sub.4).sub.2, Ni(dmg).sub.2, Ni(apo).sub.2, Ni(dmamb).sub.2, Ni(dmamp).sub.2, Ni(C.sub.5(CH.sub.3).sub.5).sub.2 and Ni(CO).sub.4.

10. (canceled)

11. A method for the manufacture of a storage element, which method comprises forming a thin film of a correlated electron material on a substrate by a chemical vapour deposition or an atomic layer deposition process depositing a first thin film layer comprising a first amount of dopant, a second thin film layer comprising a second amount of dopant and a third thin film layer comprising a third amount of dopant, from reactant precursors comprising a metal-containing reactant precursor and an oxidant selected from the group consisting of O.sub.2, O.sub.3 oxygen plasma species, H.sub.2O, D.sub.2O, H.sub.2O.sub.2, NO, N.sub.2O, CO and CO.sub.2 and mixtures thereof wherein the depositing of the first thin film layer and the third thin film layer employs an oxidant and/or relative amount of an oxidant which is different to the oxidant and/or relative amount of oxidant for depositing the second thin film layer whereby the second amount of dopant is different to the first amount of dopant and the third amount of dopant.

12. A method according to claim 11, wherein the second amount of dopant is greater than the first amount of dopant and the third amount of dopant.

13. A method according to claim 12, wherein the second amount of dopant is less than the first amount of dopant and the third amount of dopant.

14. A method according to claim 11, wherein the first amount of dopant and the third amount of dopant are the same.

15. A method according to claim 11, wherein the correlated electron material is a metal oxide selected from the group consisting of NiO, ZnO, Al.sub.2O.sub.3, Cr.sub.2O.sub.3, Fe.sub.2O.sub.3, YO, TiO.sub.2, MoO.sub.3, V.sub.2O.sub.5, WO.sub.3, CuO, MnO.sub.2, YTiO and CuAlO.sub.2.

16. A method according to claim 15, wherein the dopant is carbon or nitrogen derived from a ligand selected from the group of ligands consisting of carbon containing molecules of the form C.sub.aH.sub.bN.sub.dO.sub.f (in which a≧1, and b, d and f≧0), nitric oxide (NO), and nitrogen dioxide (NO.sub.2), or Fluorine (F), Iodine (I), Bromine (Br); or sulfur (S) derived from a ligand selected from the group of sulfur containing molecules consisting of thioalkyl or thioaryl.

17. A storage device comprising a thin film of a correlated electron material wherein the thin film comprises a first thin film layer comprising a first amount of dopant, a second thin film layer comprising a second amount of dopant and a third thin film layer comprising a third amount of dopant, wherein the second amount of dopant is different to the first amount of dopant and the third amount of dopant.

18. A storage device element according to claim 17, wherein the second amount of dopant is greater than the first amount of dopant and the third amount of dopant.

19. A storage device according to claim 17, wherein the correlated electron material is a metal oxide selected from the group consisting of NiO, ZnO, Al.sub.2O.sub.3, Cr.sub.2O.sub.3, Fe.sub.2O.sub.3, YO, TiO.sub.2, MoO.sub.3, V.sub.2O.sub.5, WO.sub.3, CuO, MnO.sub.2, YTiO and CuAlO.sub.2.

20. A storage device according to claim 18, wherein the dopant is carbon or nitrogen derived from a ligand selected from the group of ligands consisting of carbon containing molecules of the form C.sub.aH.sub.bN.sub.dO.sub.f (in which a≧1, and b, d and f≧0) such as: carbonyl (CO), cyano (CN.sup.−), ethylene diamine (C.sub.2H.sub.8N.sub.2), phen(1,10-phenanthroline) (C.sub.12H.sub.5N.sub.2), bipyridine (C.sub.10,H.sub.8N.sub.2), ethylenediamine ((C.sub.2H.sub.4(NH.sub.2).sub.2), pyridine (C.sub.5H.sub.5N), acetonitrile (CH.sub.3CN), and cyanosulfanides such as thiocyanate (NCS.sup.−); in addition nitric oxide (NO), Nitrogen dioxide (NO.sub.2), halides such as Fluorine (F), Iodine (I), Bromine (Br); and sulfur (S) and other ligands such that result in correlated electron behaviour, control or stabilization.

21. A method according to claim 1, wherein the relative amounts of oxidants are controlled by controlling mass flows of oxidants using a mass flow controller.

22. A method according to claim 11, wherein the relative amounts of oxidants are controlled by controlling mass flows of oxidants using a mass flow controller.

23. A method according to claim 11, wherein the relative amounts of oxidants are controlled by controlling mass flows of oxidants using a mass flow controller.

24. A method according to claim 3, wherein the forming of each thin film layer employs the same deposition temperature.

Description

[0129] The presently disclosed methods and storage element will now be described in more detail with reference to the following implementations and the accompanying drawings in which:

[0130] FIG. 1 A is a schematic illustration of a storage element comprising a correlated electron material providing a correlated electron switch;

[0131] FIG. 1 B is a plot of current density versus voltage for the storage element of FIG. 1 A;

[0132] FIG. 1 C is a representation of a circuit element corresponding to the storage element of FIG. 1 A;

[0133] FIG. 1 D is a truth table for the storage element of FIG. 1A;

[0134] FIG. 2 is a schematic illustration of apparatus for implementing methods for forming the storage element;

[0135] FIG. 3 is a scheme illustrating one method for forming a storage element using the apparatus of FIG. 2; and

[0136] FIG. 4 shows pulse profiles for A atomic layer deposition and B chemical vapour deposition according to the method shown in FIG. 3.

[0137] FIG. 2 shows an apparatus 201 for forming a thin film by atomic layer deposition or by chemical vapour deposition. The apparatus comprises a process chamber 202 connected to up line sources of a metal-containing reactant precursor 203 such as dicylcopentadienyl-nickel Ni(Cp).sub.2, a purge gas N.sub.2 and several reactant precursors 204 comprising oxidants of differing reactivity for the metal-containing reactant precursor, O.sub.2, H.sub.2O and NO. The reactivity of these reactant precursors has the order O.sub.2>H.sub.20>NO.

[0138] The process chamber 202 includes a platform (not shown) providing for the placement of a semiconductor substrate in the middle of the process chamber 202 and equipment (not shown) regulating the pressure, temperature and gas flow within the chamber in combination with a vacuum pump 204 connected to downline of the process chamber 202. The vacuum pump 204 evacuates to an abatement chamber 205 where the reactant precursors and by-products of reaction are made safe before they enter the environment.

[0139] The apparatus includes a plurality of independently operable valves which help regulate the gas flow up line and downline of the process chamber. The up line valves allow the reactant precursors and purge gas to enter the process chamber 202 sequentially and enable a selection of one or other oxidant or a particular combination of oxidants for reaction with dicylcopentadienylnickel and/or the surface of the substrate.

[0140] The equipment regulating the gas flow in the pressure chamber includes a mass flow controller 206 providing very precise and highly repeatable control of the amount of oxidant introduced into the process chamber in a predetermined time period.

[0141] The apparatus is first prepared for use by loading the platform with the semiconductor wafer and evacuating the chamber 202 by operating the vacuum pump 204 and opening the up line valves for the purge gas N.sub.2. During the purging, the process chamber 202 is heated to the temperature which has been selected for the thin film forming process.

[0142] Referring also to FIG. 3, a thin film of nickel oxide 302 is then formed on the semiconductor wafer 301 by atomic vapour deposition employing cycles of the following operations. The semiconductor wafer may have prior films and structures already present.

[0143] First, the up line valves for the purge gas are closed and the up line valves for the dicylcopentadienylnickel are opened. After a predetermined time period in which the semiconductor wafer is exposed to and reacts with dicylcopentadienylnickel, the up line valves for dicylcopentadienyl-nickel are closed and the up line valves for the purge gas are reopened. After a predetermined time period, the up line valves for the purge gas are closed and the up line valves for NO are opened. After a predetermined time period in which the semiconductor wafer is exposed to and reacts with NO, the up line valves for NO are closed and the up line valves for the purge gas are reopened. The number of cycles of these operations is selected to provide a first thin film layer 303 on the semiconductor wafer of a desired thickness on the semiconductor wafer. The initial order may be the oxidizer first. There may be required a certain number of initial “incubation” cycles, where incubation is known to one skilled in the art as a certain number of exposures of a surface to a precursor that is required to cause initial reactivity.

[0144] When the first thin film layer 303 has been formed, a second thin film layer 304 of nickel oxide is formed on the first thin film layer by atomic layer deposition employing cycles of the following operations. First, the up line valves for the purge gas are closed and the up line valves for the dicylcopentadienylnickel are opened. After a predetermined time period in which the first thin film layer is exposed to and reacts with dicylcopentadienylnickel, the up line valves for dicylcopentadienylnickel are closed and the up line valves for the purge gas are reopened. After purging for an appropriate period, the up line valves for the purge gas are closed and the up line valves for oxygen are opened. After a predetermined time period in which the first thin film layer 303 is exposed to and reacts with oxygen, the up line valves for oxygen are closed and the up line valves for the purge gas are reopened. The number of cycles of these operations is selected to provide a second thin film layer 304 of a desired thickness on the first thin film layer 303. The initial order may be the oxidizer first. There may be required a certain number of initial “incubation” cycles, where incubation is known to one skilled in the art as a certain number of exposures of a surface to a precursor that is required to cause initial reactivity.

[0145] When the second thin film layer 304 has been formed, a third thin film layer 305 of nickel oxide is formed on the second thin film layer by atomic layer deposition employing cycles of the following operations. First, the up line valves for the purge gas are closed and the up line valves for the dicylcopentadienylnickel are opened. After a predetermined time period in which the second thin film layer 304 is exposed to and reacts with dicylcopentadienylnickel, the up line valves for dicylcopentadienylnickel are closed and the up line valves for the purge gas are reopened. After a predetermined time period, the up line valves for the purge gas are closed and the up line valves for NO are opened. After a predetermined time period in which the second thin film layer 304 is exposed to and reacts with NO, the up line valves for NO are closed and the up line valves for the purge gas are reopened. The number of cycles of these operations is selected to provide a third thin film layer 305 of a desired thickness on the second thin film layer 304. The initial order may be the oxidizer first. There may be required a certain number of initial “incubation” cycles, where incubation is known to one skilled in the art as a certain number of exposures of a surface to a precursor that is required to cause initial reactivity.

[0146] The time period during which the semiconductor wafer or thin film layer is exposed to oxygen or NO is selected so that the oxygen gas flow during that period results in the desired amount of dopant ligand bonding to or remaining in the layer.

[0147] In that case, the thin film layers will be doped with carbon derived from dicylcopentadienylnickel and the amount of the dopant in the first and third thin film layers 303, 305 will be different than the amount of dopant in the second thin film layer 303.

[0148] The gas flows during this time period can be easily adjusted by the mass flow controller so that they are different. The adjustment enables a fine tuning in the relative amount of dopant in the second thin film layer 304 as compared to the dopant in the first and third thin film layers 303, 305.

[0149] The gas flow of oxygen or steam during this time period can also be adjusted by dilution with steam. The introduction of a controlled amount of steam in either gas flow enables a fine tuning in the amount of dopant in the second thin film layer 304 as compared to the amount in the first and third thin film layers 303, 305.

[0150] The thin film may alternatively be formed on the semiconductor wafer by chemical vapour deposition employing the following operations.

[0151] First, the up line valves for the purge gas are closed and the up line valves for the dicylcopentadienylnickel and oxygen are opened. After a predetermined time period in which the semiconductor wafer is exposed to and reacts with the mixture, the up line valves for oxygen are closed. The predetermined time period is chosen so that the first thin film layer 303 forms with the desired thickness under the selected process conditions.

[0152] When the first thin film layer 303 has been formed, a second thin film layer 304 may be formed on the first thin film layer 303 by chemical vapour deposition employing the following operations. First, the up line valves for oxygen are opened. The gas flow of oxygen to the chamber 202 is adjusted by the mass flow controller 206 so that it is higher than the gas flow used for the first thin film layer 303. After a predetermined time period in which the first thin film layer 303 is exposed to the mixture, the up line valves for oxygen are closed. The predetermined time period is chosen so that the second thin film layer 304 forms with the desired thickness under the selected process conditions.

[0153] When the second thin film layer has been formed, a third thin film layer 305 is formed on the second thin film layer by chemical vapour deposition employing the following operations. First, the up line valves for oxygen are opened. The gas flow of oxygen to the chamber is adjusted by the mass flow controller 206 so that it is the same as the gas flow used for the first thin film layer 303. After a predetermined time period in which the second thin film layer 304 is exposed to and reacts with the mixture, the up line valves for dicylcopentadienylnickel and oxygen are closed and the up line valves for the purge gas are reopened. The predetermined time period is chosen so that the third thin film layer 305 forms with the desired thickness under the selected process conditions.

[0154] In either case, when the third thin film layer 305 has been formed, the final nickel oxide thin film 302 is obtained by an annealing carried out in the process chamber 202 during a predetermined time period in which purging with nitrogen is maintained. The temperature of the process chamber 202 and/or the pressure therein may be maintained or adjusted to a selected value or values during this predetermined time period.

[0155] FIG. 4 shows the gas flows in the apparatus during the formation of the thin film by A atomic layer deposition and B chemical vapour deposition as described above.

[0156] The pulse profile for the chemical vapour deposition shows continuous exposure of the semiconductor wafer to dicylcopenta-dienylnickel and intermittent exposure to a single oxidant wherein the species of oxidant for one exposure is greater than the amount for the other exposures.

[0157] The present disclosure provides a method which enables a storage element to be fabricated as a thin film of an electron correlation material by a continuous process. The method also enables the electrical and switching properties of the element to be tuned so that it provides optimum performance through abrupt switching under normal operation conditions.

[0158] Note the present disclosure refers in detail to a limited number of implementations and that other implementations which are not described here in detail are possible.

[0159] Note also that it is the accompanying claims which particularly point out an invention in the present disclosure and the scope of protection which is sought.

[0160] Note further that a reference to a particular range of values in this disclosure (including the claims) includes the starting and finishing values.