Thermal atomic layer etching using refluorination

Abstract

Provided herein are methods of atomic layer etching (ALE) of a variety of materials using a HF source fort etching, in which the HF is recycled through repeated introduction of a volatilizing agent. The present method allows for continuous re-use of HF in the system.

Description

[0001] TITLE OF THE INVENTION

[0002] Thermal Atomic Layer Etching Using Refluorination

[0003] CROSS-REFERENCE TO RELATED APPLICATION

[0004] This application claims priority to U.S. Provisional Application No. 63 / 678,318 entitled "THERMAL ATOMIC LAYER ETCHING USING REFLUORINATION," filed August I, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0005] BACKGROUND

[0006] Thermal ALE (atomic layer etching) is typically defined by two sequential surface reactions with two reactants: one reactant modifies the surface and the second reactant volatilizes the modified surface layer. Hydrofluoric acid (HF) is a frequently used etching agent, how ever its high reactivity and toxicity make it challenging to use and handle. It would be desirable to develop an ALE process where etching agent is effectively recycled such one of the reaction products from the volatilization reaction yields the reactant for the surface modification. Under these circumstances, the etching can continue nearly indefinitely by repeating the exposure of the volatilization reactant.

[0007] There is a need in the art for novel methods of performing ALE on a surface. These methods should feature recyclable etching agents and demonstrate etch enhancement. The present invention solves this unmet need.

[0008] BRIEF DESCRIPTION OF THE FIGURES

[0009] The drawings illustrate generally, by w ay of example, but not by way of limitation, various embodiments of the present application.

[0010] FIGs. 1 A-1B depict a mechanism for etching as described herein, in accordance with various embodiments. FIG. 1A shows formation of an aluminum fluoride layer after exposure of a substrate coated with AI2O3 to HF. FIG. IB shows etching (removal) of the AIF3 layer after exposure to an volatilizing reactant (Hacac).

[0011] FIG. 2 shows a proposed mechanism of volatilizing an AIF3 layer with Hacac, in accordance with various embodiments.

[0012] FIG. 3 show s a mechanistic scheme for etching with and reusing HF, in accordance with various embodiments.

[0013] FIG. 4 is a graph of mass loss vs. ALE cycle number for etching an AIF3 layer with Hacac, in accordance with various embodiments. FIG. 5 is a graph of mass loss vs. ALE cycle number for etching an AIF3 layer with Hacac with an enlarged scale to show the mass loss in greater detail, in accordance with various embodiments.

[0014] FIG. 6 is is a graph of mass loss vs. time for etching an AIF3 layer with Hacac at 250 °C over 10 ALE cycles, in accordance with various embodiments.

[0015] FIGs. 7A-7B is a graph of mass loss vs. ALE cycle number for etching an AIF3 layer with Hacac. FIG. 7A shows mass loss as a function of ALE cycle number for 10 cycles. FIG. 7B shows the cumulative mass loss over the ALE cycles in FIG. 7A, in accordance with various embodiments.

[0016] FIGs. 8A-8D show quantitative mass spectrometry (QMS) measurements illustrating the AI2O3 etch enhancement resulting from refluorination by product HF during the Hacac reaction, in accordance with various embodiments.

[0017] FIGs. 9A-9E show time dependent QMS data for Hacac+(FIG. 9 A), HF+(FIG. 9B), H2O+(FIG. 9C), Al(acac)2+(FIG. 9D), and Al(acac)3+(FIG. 9E) ion intensities for 50 consecutive Hacac mini-doses after an initial HF exposure, in accordance with various embodiments.

[0018] FIG. 10 shows mean ion intensities as a function of the number of Hacac mini-doses, in accordance with various embodiments.

[0019] FIG. 11 shows mass change as a function of temperature between 160 - 300 °C, in accordance with various embodiments.

[0020] FIG. 12 shows an Arrhenius plot for the data in FIG. 1 1 , in accordance with various embodiments.

[0021] FIG. 13 shows the sum of the mass changes for 10 Hacac mini-doses for experiments conducted between 160 and 290 °C, in accordance with various embodiments.

[0022] DETAILED DESCRIPTION OF THE INVENTION

[0023] Reference will now be made in detail to certain embodiments of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0024] Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example. a range of "about 0. 1% to about 5%" or "about 0.1% to 5%" should be interpreted to include notjust about 0.1% to about 5%, but also the individual values (e.g, 1%. 2%, 3%, and 4%) and the sub-ranges (e.g, 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise.

[0025] In this document, the terms "a." "an." or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. The statement "at least one of A and B" or "at least one of A or B" has the same meaning as "A, B, or A and B." In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0026] In the methods described herein, the acts can be carried out in any order, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0027] Definitions

[0028] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0029] The term "substantially" as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. The term "substantially free of' as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that the composition is about 0 wt% to about 5 wt% of the material, or about 0 wt% to about 1 wt%, or about 5 wt% or less, or less than, equal to, or greater than about 4.5 wt%, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8. 0.7, 0.6, 0.5, 0.4. 0.3, 0.2, 0.1, 0.01, or about 0.001 wt% or less. The term "substantially free of' can mean having a trivial amount of, such that a composition is about 0 wt% to about 5 vrt.% of the material, or about 0 wt% to about 1 wt%, or about 5 wt% or less, or less than, equal to, or greater than about 4.5 wt%, 4, 3.5, 3. 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt% or less, or about 0 wt%.

[0030] The term "solvent" as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Non-limiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

[0031] The term "independently selected from" as used herein refers to referenced groups being the same, different, or a mixture thereof, unless the context clearly indicates otherwise. Thus, under this definition, the phrase "X1, X2, and X3are independently selected from noble gases" would include the scenario where, for example, X1, X2, and X3are all the same, where X1. X2. and X3are all different, where X1and X2are the same but X3is different, and other analogous permutations.

[0032] The term "room temperature" as used herein refers to a temperature of about 15 °C to 28 °C.

[0033] The term "standard temperature and pressure" as used herein refers to 20 °C and 101 kPa.

[0034] The term "substituted" as used herein in conjunction with a molecule or an organic group as defined herein refers to the state in which one or more hydrogen atoms contained therein are replaced by one or more non-hydrogen atoms. The substitution can be direct substitution, whereby the hydrogen atom is replaced by a functional group or substituent, or an indirect substitution, whereby an intervening linker group replaces the hydrogen atom, and the substituent or functional group is bonded to the intervening linker group. A non-limiting example of direct substitution is: RR-H RR-C1, wherein RR is an organic moiety / fragment / molecule. A non-limiting example of indirect substitution is: RR-H RR- (LL)zz-Cl, wherein RR is an organic moiety / fragment / molecule, LL is an intervening linker group, and 'zz' is an integer from 0 to 100 inclusive. When zz is 0, LL is absent, and direct substitution results. The intervening linker group LL is at each occurrence independently selected from the group consisting of -H, -O-, -OR, -S-, -S(=O)-, -S(=O)2-, -SR, -N(R)-, - NR2, -CR=, -CA, -CH2-, -CHR-, -CR2-, -CH3, -C(=O)-, -C(=NR)-, and combinations thereof. (LL)zz can be linear, branched, cyclic, acyclic, and combinations thereof.

[0035] The term "functional group" or "substituent" as used herein refers to a group that can be or is substituted onto a molecule or onto an organic group. Examples of substituents or functional groups include, but are not limited to, a halogen (e.g, F, Cl, Br, and I); an oxygen atom in groups such as hydroxy groups, alkoxy groups, aryloxy groups, aralkyloxy groups, oxo(carbonyl) groups, carboxyl groups including carboxylic acids, carboxylates, and carboxylate esters; a sulfur atom in groups such as thiol groups, alkyl and aryl sulfide groups, sulfoxide groups, sulfone groups, sulfonyl groups, and sulfonamide groups; a nitrogen atom in groups such as amines, hydroxyamines, nitriles, nitro groups, N-oxides, hydrazides, azides, and enamines; and other heteroatoms in various other groups. Non-limiting examples of substituents that can be bonded to a substituted carbon (or other) atom include F. CL Br, I. OR, OC(O)N(R)2, CN, NO, NO2, ONO2, azido, CF3, OCF3, R, O (oxo), S (thiono), C(O), S(O), methylenedioxy, ethylenedioxy, N(R)2, SR, SOR, SO2R, SO2N(R)2, SOsR, C(O)R, C(O)C(O)R, C(O)CH2C(O)R, C(S)R, C(O)OR, OC(O)R, C(0)N(R)2, 0C(0)N(R)2, C(S)N(R)2. (CH2)O-2N(R)C(0)R. (CH2)O-2N(R)N(R)2, N(R)N(R)C(O)R, N(R)N(R)C(O)OR, N(R)N(R)C0N(R)2, N(R)SO2R, N(R)SO2N(R)2, N(R)C(O)OR, N(R)C(O)R, N(R)C(S)R, N(R)C(0)N(R)2, N(R)C(S)N(R)2, N(COR)COR, N(OR)R, C(=NH)N(R)2, C(O)N(OR)R, and C(=NOR)R, wherein R can be hydrogen or a carbon-based moiety; for example, R can be hydrogen, (Ci-Cioo)hydrocarbyl. alkyl, acyl, cycloalkyl, aryl, aralk l, heterocyclyl. heteroaryl, or heteroarylalkyl; or wherein two R groups bonded to a nitrogen atom or to adjacent nitrogen atoms can together with the nitrogen atom or atoms form a heterocyclyl.

[0036] The term "alkyl" as used herein refers to straight chain and branched alkyl groups and cycloalkyl groups having from 1 to 40 carbon atoms, 1 to about 20 carbon atoms, 1 to 12 carbons or. in some embodiments, from 1 to 8 carbon atoms. Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n- butyl, n-pentyl, n-hexyl, n-hept l. and n-oct l groups. Examples of branched alkyd groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, t-butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups. As used herein, the term "alkyl" encompasses n-alkyl, isoalkyl, and anteisoalkyl groups as well as other branched chain forms of alkyl. Representative substituted alkyl groups can be substituted one or more times with any of the groups listed herein, for example, amino, hydroxy, cyano, carboxy, nitro, thio, alkoxy, and halogen groups.

[0037] The term "aryl" as used herein refers to cyclic aromatic hydrocarbon groups that do not contain heteroatoms in the ring. Thus aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl. biphenylenyl, anthracenyl, and naphthyl groups. In some embodiments, aryl groups contain about 6 to about 14 carbons in the ring portions of the groups. Aryl groups can be unsubstituted or substituted, as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as, but not limited to, a phenyl group substituted at any one or more of 2-, 3-, 4-. 5-, or 6-positions of the phenyl ring, or a naphthyl group substituted at any one or more of 2- to 8-positions thereof.

[0038] The term "aralkyl" as used herein refers to alky l groups as defined herein in which a hydrogen or carbon bond of an alkyl group is replaced with a bond to an aryl group as defined herein. Representative aralkyl groups include benzyl and phenylethyl groups and fused (cycloalkylaryl)alkyl groups such as 4-ethyl-indanyl. Aralkenyl groups are alkenyl groups as defined herein in which a hydrogen or carbon bond of an alkyd group is replaced with a bond to an ary l group as defined herein.

[0039] The term "cycloalkyl" as used herein refers to cyclic alkyl groups such as, but not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. In some embodiments, the cycloalkyl group can have 3 to about 8-12 ring members, whereas in other embodiments the number of ring carbon atoms range from 3 to 4, 5, 6, or 7. Cycloalkyl groups further include polycyclic cycloalkyl groups such as, but not limited to, norbomyl, adamantyl, bornyl, camphenyl. isocamphenyL and carenyl groups, and fused rings such as, but not limited to, decalinyl, and the like. Cycloalkyl groups also include rings that are substituted with straight or branched chain alkyl groups as defined herein. Representative substituted cycloalkyl groups can be mono-substituted or substituted more than once, such as, but not limited to, 2,2-, 2,3-. 2,4- 2,5- or 2,6-disubstituted cyclohexyl groups or mono-, di- or tri-substituted norbomyl or cycloheptyl groups, which can be substituted with, for example, amino, hydroxy, cyano, carboxy, nitro, thio, alkoxy, and halogen groups. The term "cycloalkenyl" alone or in combination denotes a cyclic alkenyl group.

[0040] Methods of Thermal Atomic Layer Etching (ALE) and Refluorination

[0041] Thermal atomic layer etching (ALE) is typically comprised of two sequential, selflimiting reactions: surface modification and the volatilization of the modified surface layer. The reactants for the surface modification and volatilization reactions are usually different than the reaction products from the surface modification and volatilization reactions. However, it has surprisingly been discovered that a process where one of the reaction products from the volatilization reaction yields the reactant for the surface modification reaction can achieve etch enhancement that is not otherwise possible using conventional methods that do not reuse / recycle a surface modification reactant. Substrates

[0042] In various embodiments, the ALE methods describe herein etch solid substrates, surfaces of a solid substrate, or portions of a surface of a solid substrate. The substrate can be a cleaned substrate (i.e., a substrate from which impurities are at least partially removed) obtained, for example, according to the methods described herein. The solid substrate can be a porous substrate or a high-aspect-ratio structure obtained according to the methods described herein. Solid substrates can also include 3D structures with reduced feature sizes obtained, for example, according to the methods of the invention. The substrate can also be a patterned solid substrate or a smoothened solid substrate obtained, for example, according to the methods described herein. Substrates with the described morphologies and / or characteristics produced by art recognized methods can also be used.

[0043] In certain embodiments, the solid substrate comprises at least one material such as Si, SiN, SiNxOy, SixGey, SiC, SiBs, SiP, SiAs, SiSe, or SiTe, and the like, or mixtures thereof, where x is an integer from 1 to 6 and y is an integer from 1 to 6. In other embodiments, the solid substrate comprises at least one material such as RuSi, TixSiy, TiCz. VxSiy, NbxSiy, MoxSiy, TaxSiy, RexSiy, or WxSiy, or mixtures thereof, and the like, where x is an integer from 1 to 6, y is an integer from 1 to 6, and z is from about 0.3 to about 1. In various embodiments, z is about 0.50, 0.625, 0.75, 0.85, 0.90, or about 1.0. In various embodiments, z is 1.

[0044] In certain embodiments, prior to conducting ALE as described herein, the solid substrate is first treated such that at least a portion of the surface of the solid substrate becomes coated (including conformally coated) with a metal compound that includes one or more of a metal oxide, metal nitride, metal phosphide, metal sulfide, metal arsenide, metal fluoride, metal silicide, metal boride, metal carbide, metal selenide, metal telluride, elemental metal, metal alloy, and hybrid organic-inorganic material. The metal can be any metal that is suitable for or compatible with the methods described herein, and can be Al, Hf, Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr, Si, Ti, Sc, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Nb, Cd or Sn, and combinations of any of the preceding metals and / or metal compounds. When the compound is an elemental metal, the elemental metal can be converted to a metal oxide by adding an oxidation step to the ALE process, for example prior to exposing the elemental metal to HF. This type of oxidation can be accomplished by, for example, using thermal O2 or O3 oxidation. Likewise, this oxidation can be accomplished with an O2 plasma.

[0045] In various embodiments, the solid substrate includes one or more of the substrate materials described herein and one or more of the metal compounds described here. In various embodiments, the solid substrate includes one or more of the substrate materials described herein and one or more of the metal oxides described here. For example, in one non-limiting embodiment, the solid substrate is a mixture of TiCz and AI2O3 (commonly referred to as “AlTiC”).

[0046] Non-limiting Etching Methods

[0047] In various embodiments, a method of thermal atomic layer etching (ALE) is provided. The method includes: i) contacting, in a reaction chamber, a substrate containing a metal compound layer with a surface modification reactant comprising hydrogen fluoride (HF) to form a metal fluoride on at least one portion of the metal compound layer; ii) contacting the metal fluoride with a dose of a volatilization reactant containing a compound of Formula (I), or a tautomer thereof, to etch the at least one portion of the metal compound layer: Formula (I), wherein R and R' are each independently selected from the group consisting of C1-6 alky l, Ce-io aryl, and C4-10 cycloalkyl, each optionally substituted by at least one substituent selected from the group consisting of F, Cl, CN. OC1-4 alkyl, NO2, and Ci-4 alkyl; and iii) repeating step ii) at least once; wherein exposing the metal fluoride to the compound of Formula (I) regenerates HF in the reaction chamber.

[0048] In various embodiments, the metal compound is a metal oxide of a metal selected from the group consisting of AL Hf, Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr, Si, Ti, Sc, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Nb, Cd and Sn. In various embodiments, the metal is Al. In various embodiments, the metal compound is the metal oxide AI2O3. In various embodiments, the metal compound forms a layer on at least a portion of the substrate, such as at least about 5, 10, 20, 30, 40. 50. 60. 70. 80. 90, 95, 96, 97, 98, 99, or 100% of the surface area of the substrate is covered by the metal compound layer. The layer of the metal compound can be a conformal layer. The thickness of the layer of the metal compound depends on the intended uses of the substrate, and can be at least, equal to, or greater than about 1, 2, 3. 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19. 20. 21. 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89. 90. 91. 92, 93, 94, 95, 96, 97, 98, 99, or about 100 A.

[0049] The reaction chamber can be under a vacuum, whereby a vacuum pump operably attached to the reaction chamber continuously maintains a certain vacuum level in the reaction chamber. The reaction chamber can also be under static pressure. Under static pressure the chamber is not actively pumped on and there is no purge gas (Ar, N2, etc.). The pressure in the chamber during static processing could be anywhere from vacuum to the vapor pressure of the precures and products.

[0050] In various embodiments, the methods described herein are performed at a temperature of about 150 to about 350 °C. In various embodiments, the methods described herein are performed at a temperature of equal to, less than, or greater than about 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 200, 205, 210, 215, 220, 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, 275, 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, 330, 335, 340, 345, or about 350 °C.

[0051] The HF can be introduced into the reaction chamber by any suitable means that enable introduction of a controlled amount of HF, and from any suitable source without limitation. For example, the HF can be introduced as pure gaseous HF or mixed with an inert carrier gas such nitrogen, argon, air, and the like. Or, for the example, the HF can be dissolved in solution, such as in an HF / pyridine solution, where the source of HF is the partial pressure of HF above the solution. Or, for example, the HF can be produced from thermal fluorination sources such as XeF2 or SF4 or from plasma sources such as NF3 or SFe plasmas. The dose (amount) of HF introduced into the reaction chamber depends on the composition and thickness of the metal compound layer on the substrate, as well as the ultimate desired amount of etch per cycle in the method. In various embodiments, the dose of HF introduced into the reaction chamber is about 0.05 to about 3 Torr s. In various embodiments, the dose of HF introduced into the reaction chamber is equal to, less than, or greater than about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3. 0.35. 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85. 0.9, 0.95, 1, 1.2. 1.4. 1.6, 1.8, 2. 2.2. 2.4, 2.6, 2.8. or about 3 Torr s. In various embodiments, the HF is introduced via a manifold. In various embodiments, the manifold includes operably connected in series: a) a precursor source (e.g., HF / pyridine), b) a diaphragm valve, c) a fill volume with pressure sensor, d) a diaphragm valve e) a flow reducing needle valve, and 1) a particle bed.

[0052] The manifold can contain additional components that facilitate introduction of HF into the reaction chamber or for other reasons that enhance or facilitate the etching process, including for commercial reasons. The diaphragm valve between the precursor source and the fill volume can be controlled on a feedback loop using the fill volume pressure sensor. The pressure in the fill volume can be maintained at any pressure between the vacuum and the vapor pressure of the precursor. In various embodiments, the control loop can maintain the pressure in the fill volume at a constant pressure of about 1, 2, 3, 4, 5. 6, 7, 8. 9, 10, 11, 12. 13. 14. 15, 16, 17, 18, 19, 20, 25, 30, 35, 40. 45. 50. 55. 60. 65, 70, 75, 80, 85, 90, 95, or about 100 Torr.

[0053] In the compound of Formula (I), R and R' can be the same or different. In various embodiments, R and R' are the same. In various embodiments, R and R' are different. Formula (I).

[0054] In various embodiments, R and R' are the same and each is Ci-6 alky l. In various embodiments, R and R' are the same and each is Ci-6 perfluoroalkyl. In various embodiments, R and R' are the same and each is Ce aryl. In various embodiments. R and R' are the same and each is CsHs. In various embodiments, R and R' are the same and each is CeFs. In various embodiments, R is CFs and R' is CF3. In various embodiments, R is CHs and R' is CH3, and the compound of Formula (I) has the structure:

[0055] Compounds of Formula (I) can form tautomers due to keto-enol tautomerism. Thus, for example, the enol form (tautomer of the diketo form) of Hacac has the structure:

[0056] O OH H3C^X<^'CH3

[0057] Without being bound by theory, the keto, enol, or both forms of the compound of Formula (I) can undergo the reactions and etching described herein.

[0058] The amount of compound of Formula (I) introduced into the reaction chamber depends on the composition and thickness of the metal compound layer on the substrate, as well as the ultimate desired amount of etch per cycle in the method. In various embodiments, the amount of compound of Formula (I) introduced into the reaction chamber is about 0.05 to about 3 Torr s. In various embodiments, the amount of compound of Formula (I) introduced into the reaction chamber is equal to, less than, or greater than about 0.05, 0.06, 0.07, 0.08. 0.09. 0.1. 0.15. 0.2, 0.25. 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6. 0.65. 0.7. 0.75. 0.8, 0.85. 0.9, 0.95, 1. 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, or about 3 Torr s. In various embodiments, the compound of Formula (I) is introduced via a manifold. In various embodiments, the manifold includes operably connected in series: a) a precursor source (i. e. , compound of Formula (I)), b) a diaphragm valve, c) a fill volume with pressure sensor, d) a diaphragm valve e) a flow reducing needle valve, and f) a particle bed. The diaphragm valve between the precursor source and the fill volume can be controlled on a feedback loop using the fill volume pressure sensor. The pressure in the fill volume can be maintained at any pressure between the vacuum and the vapor pressure of the precursor. In various embodiments, the control loop can maintain the pressure in the fill volume at a constant pressure of about 1, 2, 3, 4, 5, 6. 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35. 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or about 100 Torr. In various embodiments, the control loop can maintain the pressure in the fill volume at a constant pressure that is equal to the partial pressure of HF in the fill volume.

[0059] In various embodiments, the compound of Formula (I) is introduced into the reaction at least 2, 3, 4, 5. 6, 7, 8, 9, 10. 11. 12. 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26. 27. 28. 29. 30. 31, 32, 33, 34, 35, 36, 37, 38, 39. 40. 41. 42. 43. 44. 45, 46, 47, 48, 49, 50, 51,

[0060] 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76,

[0061] 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 times, or more. Each introduction of the compound of Formula (I) results in the regeneration

[0062] (recycling) of HF via reaction with a metal fluoride and subsequent etching as described herein. The only limit to the number of times the compound of Formula (I) can be introduced is determined by whether there is sufficient HF in the reaction chamber to etch the desired amount of material. In various embodiments, no other additional HF or HF precursor is introduced into the reaction chamber after the first introduction of HF as described in the method herein.

[0063] Surprisingly and unexpectedly, the use of multiple injections of a compound of Formula (I), such as Hacac, results in a greatly enhanced amount of material etched on each introduction of the compound of Formula (I). Each introduction of a compound of Formula (I) is a cycle. In various embodiments the etch per cycle (EPC) resulting from a single introduction (dose) of a compound of Formula (I) is at least or equal to about 2, 3, 4, 5, 6, 7, 8, 9, 10, 50, 100, 500, 1000, or 10000 times lower than the etch per cycle (EPC) resulting from at least ten, 50, 100, 500, 1000, or 10000 injections (doses) of the compound of Formula (I).

[0064] Also provided are a method of smoothing the surface of a solid substrate, w herein the solid substrate comprises a first metal compound. Smoothing of surfaces is of interest in the semiconductor industry. Smoothing may be used to obtain damage-free layers. Sputtering can be used to remove some materials, but can leave a rough, damaged surface. ALE can be used to remove the damaged layer and smooth the surface to produce a “damage-free surface.” Surface smoothing can serve as a means to “clean” surfaces or portions of a surface that may have undesired deposits on them.

[0065] Surface smoothing can also be used to obtain very high-quality ultrathin films. For example, high quality ultrathin films can be produced by a “deposit / etch back” strategy by depositing a thicker film and then etching back to a thinner film. In a non-limiting embodiment, nucleation effects can lead to roughness in the ultrathin deposited film; once a continuous and pinhole-free thicker film is formed, ALE can etch this film back and obtain a smoother surface than would have been produced by growing to this ultrathin thickness.

[0066] Due to the low temperatures under which the methods described herein can perform etching, such as below 300 °C, the methods are of particular use in etching surfaces in nanoscale devices, such as, for example, sensitive semiconductor devices that would otherwise we damaged by high temperature etching techniques. Nanoscale devices, in one embodiment, are devices that include at least one feature having at least one dimension measuring at least, equal to, or less than 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35. 30, 25, 20, 15 10, 9, 8 7, 6, 5, 4, 3, 2, or 1 nm. Nanoscale devices, in one embodiment, are devices that include at least one feature having at least two dimensions measuring at least, equal to, or less than 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 10, 9, 8 7, 6, 5, 4, 3, 2, or 1 nm. Nanoscale devices, in one embodiment, are devices that include at least one feature having three dimensions measuring at least, equal to, or less than 1000, 900, 800, 700, 600, 500, 400, 300, 200, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15 10, 9, 8 7, 6, 5, 4, 3, 2, or 1 nm.

[0067] Additionally, due to the low temperatures under which the methods described herein can perform etching, such as below 300 °C, the methods can be used in etching conditions where a substrate to be etched also contains features or structures that are sensitive to higher temperatures, such as temperatures above 300 °C, but are not themselves etched. For example, the magnetic reader stack in hard disk drives can be located on or adjacent to a substrate being etched without being damaged.

[0068] Non-limiting Example With AI2O3 In one embodiment, in AI2O3 ALE using HF and A1(CI L)? as the reactants, HF fluorinates AI2O3 to produce AIF3 and H2O. A1(CH3)3 then undergoes ligand-exchange with AIF3 to produce primarily A1F(CH3)2-A1F(CH3)2 dimers and A1F(CH3)2-A1(CH3)3 dimers. However, under the conditions described herein, a product from one reaction could become a reactant for the second reaction. Under these circumstances, there can be perpetual / effectively continuous etching by application of only one reactant. Multiple doses of the one reactant would then lead to a large etch enhancement.

[0069] Thermal AI2O3 ALE using HF and Hacac as the reactants is another possible chemistry for AI2O3 ALE. Moreover, thermal AI2O3 ALE using HF and Hacac is an ALE system that displays an etch enhancement because the HF reaction product can be recycled and returns as a reactant. The HF / Hacac etch process follows the mechanism shown in FIG. 1. In the A-step, the AI2O3 surface is first fluorinated by HF. This fluorination step results in a surface AIF3 layer. In the B-step, Hacac then reacts with the surface AIF3 layer to form the volatile reaction product Al(acac)s and HF. The rection equations for these two steps are:

[0070] (A) AI2O3 + 6HF 2A1F3+ 3H2O (Eq. 1 )

[0071] (B) 3Hacac + A1F3Al(acac)3+ 3HF (Eq. 2)

[0072] FIG. 2 shows a mechanistic view of the ligand-substitution hydrogen-transfer reaction that is described in Equation 2. The result of this Hacac reaction is the replacement of F ligands on AIF3 with acetylacetonate ligands on Al(acac)3and the formation of product HF. The Hacac reaction is unique because a product of the Hacac + AIF3 reaction is HF. The HF generated as a result of the Hacac dose can either be purged from the reactor or fluorinate the underlying AI2O3.

[0073] The refluorination of AI2O3 by the HF reaction product is shown schematically in FIG. 3.

[0074] A. QCM Measurements

[0075] Thermal ALE of AI2O3 using sequential exposures of HF and Hacac was monitored with QCM. Initial experiments used both a single exposure of HF and a single exposure of Hacac. At 250 °C, these single exposure experiments resulted in an AI2O3 etch rate of 0.2 A / cycle. This low etch rate is believed to result from the inefficient use of Hacac. Additional exposures of Hacac were used to increase the etch rate.

[0076] In most experiments, ten mini -doses of Hacac were used for every HF dose. The results of an experiment at 250 °C using a HF / 10xHacac pulse sequence are displayed in FIG. 4. The mass loss is a linear versus the number of ALE cycles. An etch per cycle (EPC) of EPC = -37.9 ± 0.02 ng / (cm2- cycle) is determined from the slope of the line. Using the density for AI2O3 ALD films of pALCh = 3.0 g em'2, this EPC equates to an AI2O3 etch rate of 1.3 A / cycle.

[0077] FIG. 5 is obtained from the same experiment as FIG. 2 and is enlarged to show the detail of each individual HF and Hacac dose. The HF dose results in a small but rapid mass increase that is followed by a slow mass loss. The net response to the HF dose at 250 °C is - 2.3 ± 0.76 ng / cm2The conversion of AI2O3 (50.98 g / mol Al) to AIF3 (83.98 g / mol Al) by HF should result in a mass gain. The net mass loss from the HF dose at 250 °C indicates that, in addition to fluorinating the AI2O3, the HF is participating in the removal of residual Hacac on the surface. The mass loss from the loss of surface Hacac is significant enough to result in a net negative mass change during the HF dose.

[0078] Each of Hacac mini-doses shown FIG5 is very similar. There is an initial positive mass transient followed by a mass loss. The initial mass transient is believed to be the adsorption and subsequent desorption of Hacac and etch products from the fluorinated AI2O3 surface. The net result of each Hacac mini-doses is a mass loss. Each subsequent Hacac mini -doses is less effective than the previous Hacac mini-doses at removing AIF3 from the surface. The first Hacac mini-doses removes the most mass. The 10thHacac mini-doses removes the least mass.

[0079] The diminishing returns of the Hacac mini-doses are shown clearly in FIG. 6. To prepare the results in FIG. 6, each Hacac mini-dose was treated separately. The mini-doses were moved to a common origin at t = 0 and mass change = 0. Then the average of nthminidose was computed for al 100 ALE cycles. For example, there were 100 1stmini-doses during this 100 cycle experiment. The average of those 100 1stmini-doses is shown in FIG. 6. The diminishing effect of each Hacac mini-dose can be identified by observing the intersection of the curve with right y-axis. The first Hacac mini-dose removes the most AIF3 with a mass loss of -11.1 ng / ( cm2- cycle). The 10thHacac mini-dose removes the least AIF3 with a mass loss of -1.5 ng / (cm2cycle).

[0080] As showm in FIG. 3, the HF produced by the reaction of Hacac with fluorinated AI2O3 can produce AKacacL and HF as reaction products. The HF reaction product can refluorinate AI2O3 and produce additional H2O. The refluorinated AI2O3 can again react with Hacac and produce AKacacL and HF as reaction products. This process could continue indefinitely if all the HF reaction product was used to refluorinate AI2O3. Alternatively, this process could lead to progressively smaller mass losses with consecutive Hacac mini-doses because some HF reaction product could escape and not refluorinate AI2O3.

[0081] The continual mass loss with each Hacac mini-dose is believed to reflect the continual refluorination of AI2O3 by the product HF during the Hacac mini-doses. FIG. 7 shows the mass changes for each Hacac mini-dose during the 10 consecutive Hacac exposures. As quantified from the results in FIG. 6, the individual mass changes in FIG. 7A decrease with each Hacac mini-dose during the first six Hacac mini-doses. Subsequently, the mass loss is nearly consistent at -1.72 ± 0.29 ng / cm2for the last four Hacac mini-doses. In addition, the sum of the individual mass changes increases during the 10 consecutive Hacac mini-doses in FIG. 7B. The change of the sum of the individual mass changes is nearly linear with Hacac mini-doses number for the last four Hacac mini-doses.

[0082] The results in FIG. 7A and FIG. 7B are well modeled by a simple exponential of the form mass loss = a exp[-n / b] + c, where n is the number of cycles and a, b, and c are fitting parameters. The scaling factor, b, is a measure of how quickly the reaction proceeds with respect to each Hacac mini-dose. Physically, b represents the efficiency of the reaction and the degree of refluorination. Asymptotically, this mass loss function approaches the value of c. If c = 0, the etch will process will stop after the consumption of the AIF3 on the surface.

[0083] A non-zero value of c indicates a steady state between the amount of AIF3 removed during a Hacac mini-dose and the amount of refluorination. With a non-zero value of c, the etch process will continue with additional Hacac mini-doses until the consumption of the entire AI2O3 film. The value of c in FIG. 7A is c = -1.72 ± 0.29 ng / cm2. This result indicates that a steady state has been achieved where nearly all the HF reaction product refluorinates the AI2O3 film. Under these conditions, the AI2O3 etching can proceed almost indefinitely with Hacac mini-doses without additional HF doses until the AI2O3 film is completely removed by etching.

[0084] The ability of the HF reaction product to refluorinate the AI2O3 film may depend on the thickness of the AIF3 layer on the AI2O3 film. After the HF reactant exposure prior to the first Hacac mini-dose, there is a thick AIF3 surface layer. This thick AIF3 layer acts as an effective HF diffusion barrier and the underlying AI2O3 is more inert to additional HF fluorination. The AlFs layer is then thinned resulting from consecutive Hacac

[0085] The thinner AIF3 layer will become less effective as an HF diffusion barrier and the underlying AI2O3 will then be more susceptible to refluorination by HF reaction product. The AIF3 layer may become thin enough that nearly all the HF reaction product refluorinates the underlying AI2O3. This situation may explain the constant mass changes during the last four HF mini-doses in FIG. 7A and the linear increase in the sum of mass changes during the last four HF mini-doses in FIG. 7B.

[0086] Additional experiments were performed where a single HF fluorination exposure was followed by 50 Hacac mini-doses. This experiment was conducted for 25 cycles using the pulse sequence (1 - 30 - 50 x [2 - 30]) for each cycle. The results were consistent with the 10 Hacac mini-dose experiment. The AI2O3 continued to be etched through all 50 Hacac mini-doses.

[0087] The c value in this experiment with 50 Hacac mini-doses was cso = -0.85 ± 0.49 ng / cm2This c value is in reasonable agreement with cio = -1.72 ± 0.29 ng / cm2determined from the 10 Hacac mini -dose experiment. The cio value is less than the cso value because a small amount of HF is lost to the gas phase for every Hacac mini-dose. However, the error on the cso value is less suggesting that the amount of refluorination is more consistent for smaller AIF3 layer thicknesses.

[0088] B. QMS (Quantitative Mass Specrometry) Measurements

[0089] QMS measurements were able to monitor the AI2O3 etch enhancement resulting from refluorination by product HF during the Hacac reaction. QMS analysis of the reactant and products during an Hacac exposure after HF reactant fluorination at 250°C is shown in FIG. 8A for 1-400 amu. For m / z > 110 the spectrum was enlarged *250. At this scale, three prominent species are identified in the spectrum: (1 ) Al(acac)3 - etch product from AI2O3 with parent at m / z 324 AMU; (2) Hacac - reactant with parent at m / z 100; and (3) Fe(acac)s - etch product from the stainless-steel reactor walls with parent at m / z 353. The parent peaks and their cracking fragments are labeled on FIG. 8A. Present, but not visible at the scale of FIG. 8A, are HF at m / z 20 and H2O at m / z 18.

[0090] FIG. 8B shows the enlarged regions around m / z 100 AMU for the Hacac+, the molecular ion of Hacac. FIG. 8C displays the enlarged regions around m / z 225 AMU for the Al(acac)2+, the primary crack of Al(acac)3. FIG. 8C shows the enlarged regions around m / z 324 AMU for Al(acac)3+. the molecular ion of Al(acac)3. The calculated spectrum based on the natural abundance of the isotopes is also shown in FIGs. 8B-8D. There is excellent agreement between the QMS results and the calculated isotope distribution.

[0091] The QMS analysis can also monitor the effect of refluorination of AI2O3 by HF reaction products during multiple Hacac doses following an initial HF reactant exposure. FIG. 9 shows time dependent QMS data for Hacac+, HF+, H2O+, Al(acac)2+, and AKacacf ion intensities for 50 consecutive Hacac mini-doses after an initial HF exposure. FIG. 9 shows a subset of the results for cycles 4 - 26. The Hacac+ion intensities in FIG. 9A are constant for consecutive cycles.

[0092] The HF+ion intensities in FIG. 9B and the H2O+ion intensities in FIG. 9C are observed during every Hacac mini-dose. HF is first produced by the reaction of Hacac with AlFs: 3Hacac + AIF3 Al(acac)s + 3HF. The HF reaction product then can refluorinate the underlying AI2O3 to produce H2O according to: AI2O3 + 6HF — > 2AIF3 + 3H2O. The observation of H2O+is evidence for the refluorination process. The HF+and H2O+ion intensities progressively decrease with each Hacac mini-dose from cycles 4-20. Subsequently, HF+and H2O ion intensities are approximately constant with each Hacac mini-dose from cycles 21 -26.

[0093] The HF+ion intensities provide evidence that some HF reaction product is able to escape the surface and enter the gas phase. The remainder of the HF reaction product is consumed by refluorination of AI2O3. The reduction of the HF+ion intensity with number of Hacac mini-doses could result from the depletion of the AIF3 layer from the AI2O3 surface. Another explanation for the HF reduction is that the AIF3 layer becomes thinner resulting from the release of the Al(acac)s etch product. As the AIF3 layer becomes thinner, the thinner AIF3 layer can allow for more fluorination of the underlying AI2O3 film. Both the depletion of the AIF3 layer and more fluorination of the AI2O3 film would lead to less HF+ion intensity observed by QMS.

[0094] A close inspection of FIG. 9B and FIG. 9C also reveals that the HF+ion intensities are decreased more than the H2O+ion intensities versus Hacac mini-doses. This behavior is expected because H2O can be produced even if no HF reaction product appears in the gas phase. In this case, all the HF reaction product would be consumed by refluorination of the underlying AI2O3 film. However, there is still measurable HF+ion intensity during the 50thHacac mini-dose. Reaching the limit where all the HF reaction product is consumed by refluorination would require more than 50 Hacac mini-doses.

[0095] The Al(acac)2+ion intensities are shown in FIG. 9D and the Al(acac)s+ion intensities are displayed in FIG. 9E. The Al(acac)2+and Al(acac)s+ion intensities also progressively decrease with each Hacac mini-dose from cycles 4-20. However, the decrease is not as large as the decrease observed for the HF+and H2O+ion intensities. The Al(acac)2+and Al(acac)3+ion intensities are then approximately constant with each Hacac mini-dose from cycles 21-26.

[0096] The mean ion intensities during the Hacac mini-doses were computed for all the ion intensities show n in FIG. 9. These mean intensities are shown in FIG. 10 as a function of the number of Hacac mini-doses for Hacac mini-doses 4 - 50. The HF+, FLO and Al(acac)2+ion intensities were modeled according to an exponential decay (I = a exp[-b / n] + c)), similar to the mass changes during the QCM measurements. The model is in excellent agreement with the data. The b parameter is a measure of the number of Hacac doses required to reduce the given QMS ion intensity by a factor of 1 / e. The values for the b parameter are 7.6. 10.6 and 18.7 for HF+. H2O+and Al(acac)2+ion intensities, respectively.

[0097] C. Temperature Dependence of AI2O3 ALE

[0098] The temperature dependence of AI2O3 ALE using HF and Hacac was investigated using QCM analysis. The AI2O3 ALE used the same reaction pulse sequence with one HF exposure followed by 10 Hacac mini-doses. FIG. 11 shows the mass change as a function of temperature between 160 - 300 °C. The dotted line show-s a mass change of zero. Data points below the line indicate mass loss and data points above the line indicate mass gains. The blue squares depict the etch rate derived from 100 cycles of HF / Hacac ALE. The data for the point at 250 °C is shown in FIG. 4. Similar experiments to the one shown in FIG. 4 w ere conducted at each temperature. The etch rate increases with increasing temperature. The maximum etch rate of 91. 1 ± 0.26 ng / (cm2cycle) was obtained at 290°C. The etch rate began to decrease at 300 °C.

[0099] FIG. 11 also show the mass changes from the HF dose (purple diamonds) and the sum of the mass changes from the 10 Hacac mini -doses (yellow circles) as a function of temperature. The mass changes from the Hacac mini-doses follow the same trend as the etch rate. At low temperatures T < 180 °C. the Hacac mini-doses result in a slight mass gain. The reason for this small mass increase is attributed to Hacac adsorption with very little mass loss from etching. At low temperatures < 250 °C, HF doses result in a mass loss. This mass loss is attributed to displacement of surface Hacac molecules. The loss of surface Hacac molecules at low temperatures offsets the mass gain expected for the HF fluorination of AI2O3.

[0100] At higher temperatures T > 260 °C, the mass change from the HF dose is positive. The mass gain expected from fluorination is observable at these higher temperatures because there is little surface Hacac to be displaced during the HF dose. The orange triangles show' the sum of the mass changes from the HF dose (purple diamonds) with the sum of the mass changes from the 10 Hacac mini-doses (yellow circles). This sum represent an alternative method of calculating the overall etch. This sum agrees well with the etch rate calculated from the slope of the QCM trace.

[0101] The etch rates in FIG. 11 (blue squares), can also be displayed on the Arrhenius plot shown in FIG. 12. The trend is linear with the exception of the data points at T = 300 °C. The slope of the line yields an activation energy of Ea= 0.72 eV. This activation energy could be related to the desorption activation energy of Altacac)? or one of the activation barriers during the ligand-substitution hydrogen transfer reaction between Hacac and AIF3.

[0102] FIG. 13 shows the sum of the mass changes for the 10 Hacac mini-dose for experiments conducted between 160 and 290 °C. The data for 250 °C was presented independently earlier in FIG. 7B. In addition to the data points, FIG. 13 also shows curves displaying fits of the same model used in FIG. 7B where sum of mass loss = a exp[-n / b] + g x + d. The fit parameter b remained nominally constant at b= 1.25 ± 0.45 for T > 200 °C. The value of g varies linearly, inversely proportional to temperature, g is thought to be representative of the degree of refluorination.

[0103] D. Applications

[0104] There are implications for the refluormation of AI2O3 by product HF during the Hacac reactions. One possibility is that refluorination by HF reaction product could lead to perpetual AI2O3 etching in a closed system. If the HF reaction product can not escape, the HF reaction product could return indefinitely to fluorinate AI2O3. The Hacac volatilization reaction could then continuously etch AI2O3. The AI2O3 etching would continue as long as there was sufficient Hacac reactant.

[0105] One possible application for the thermal AI2O3 ALE using HF and Hacac reactions is AI2O3 cleaning from vacuum chambers. The initial AI2O3 surface area could be florinated by HF. Subsequently an abundance of Hacac could be injected to the vacuum chamber thant is closed to any pumping. The fluorinated AI2O3 should all be converted to Al(acac)s and H2O. This procedure would greatly reduce the amount of fluorine reactant required for AI2O3 etching.

[0106] Thermal ALE of AI2O3 using HF and Hacac can be accomplished using fluorination and ligand exchange hydrogen transfer reactions. This study examined the reaction with QCM, AES, and QMS at 250 °C. Temperature dependence was investigated with QCM and QMS over the range 160 - 300 °C. ALE was observed at all temperatures, with the highest etch rate observed at 290 °C.

[0107] Auto-fluorination, where HF generated as a byproduct from the ligand exchange hydrogen transfer reaction between AIF and Hacac converts AI2O3 to AIF3, is a significant contributor to the behavior of this ALE process. The auto-fluorination reaction was confirmed by the presence of H2O in response to Hacac mini-doses in the QMS. The autofluorination process is dependent on the amount of HF present in the gas phase and the thickness of the existing AIF3. Thick AIF3 films will produce proportionally large quantities of HF in response to Hacac mini-dose. However, thick AIF3 films serve as a protective layer, preventing further fluorination of the underlying AI2O3.

[0108] Modeling of the QCM and QMS data with exponential provided high quality fits to the data and qualitative insights into the chemistr}’. Continued Hacac cycles, up to 50 minidoses, resulted in etch. These results indicate the possibility of an equilibrium condition where HF is recycled with 100% efficiency and the etch process continues indefinitely. This result seems untenable as it is expected that some amount of HF will always be lost to the pump.

[0109] AES experiments provided additional confirmation of the ALE of AI2O3 using HF and Hacac. Additionally, AES demonstrated the effectiveness of this ALE process to clean the film-substrate interface.

[0110] ALE reactions using auto-fluorination may provide unique behaviors if used in a static vacuum environment. In a static vacuum environment, no HF will be lost. A stoichiometric dose of Hacac, equivalent to the amount of material to be removed, can be used as the limiting reagent. In addition to application in wafer processing, this static chemistry could be used for chamber cleaning.

[0111] Examples

[0112] Various embodiments of the present application can be better understood by reference to the following Examples which are offered by way of illustration. The scope of the present application is not limited to the Examples given herein.

[0113] A. In situ QCM Measurements

[0114] ALE of AI2O3 using HF and Hacac was performed on a QCM in a hot walled viscous flow reactor. Ultrahigh purity nitrogen was used as a carrier gas (Airgas. 99.999%). The flow of nitrogen was controlled with mass flow controller (GM50, MKS Instruments). The deposition chamber was held at the process temperature using ceramic heaters controlled by a proportional-integral-derivative (PID) temperature controller (Nanodac, Eurotherm). The controller maintained the set point temperature to within ±0. 1 °C. Precursors entered the deposition chamber through progressively heated lines from the precursor source to the reactor. Precursors lines were heated with heat tapes maintained at a fixed voltage. The reactor pressure was measured using a capacitance manometer (Baratron 121A, MKS Instruments). The base pressure was maintained at ~ 1 Ton using a 200 SCCM flow of nitrogen. The reactor was pumped by an oil sealed, rotary vane, mechanical pump (2010 Cl, Alcatel / Adixen).

[0115] Quartz crystals (polished, RC cut, 6 MHz, Phillip Technologies) were sealed into a sensor head (Inficon) using a high temperature silver epoxy (Epo-Tek H21D, Epoxy Technology Inc.). The cry stal electrodes were gold. Prior to each HF / Hacac etch experiment, fresh AI2O3 was deposited throughout the reactor, including the QCM sensor. AI2O3 was grow n via ALD using trimethylaluminum (TMA, Sigma Aldrich, 97%) and H2O (HPLC grade, Sigma Aldrich).

[0116] AI2O3 was typically grown at the process temperature for the subsequent etch experiment. Frequency fluctuations during the HF / Hacac etch process w ere recorded using a QCM monitor (SQM- 160, Inficon). These frequency changes were converted to mass changes using the Sauerbrey equation. The QCM was also used to monitor the AI2O3 deposition process. The behavior of AI2O3 ALD was used as a metric to evaluate QCM health.

[0117] B. Reactant Exposures for QCM Measurements

[0118] The reactants for thermal AI2O3 ALE were HF and Hacac. HF -pyridine (70% wt. HF, Sigma Aldrich) was used without further purification. Acetylacetone (Hacac, >99%, Sigma Aldrich) underwent 3 cycles of freeze-pump-thaw to remove dissolved gases prior to being used as a reagent. Both reactants were dosed directly into the reactor through a series of valves: reactant source - diaphragm valve - needle valve - diaphragm valve - reactor.

[0119] For the HF, the diaphragm valves were opened for 1 s. A typical total dose under these conditions w as 0.35 ± 0. 12 Torr s. The peak of the pressure transient during the HF dose was PHF = 0. 13 ± 0.008 Torr. For the Hacac. the diaphragm valves were opened for 2 s. This resulted in a typical total dose of 0.63 ± 0.06 Torr s. The peak of the pressure transient during the Hacac dose was Pnacac = 0.214 ± 0.012 Torr. After each exposure, the reactor was purged under nitrogen for 30 s. A ty pical cycle of the HF / Hacac chemistry was one HF exposure followed by ten Hacac exposures (1 - 30 - 10 x [2 - 30]).

[0120] C. Quadrupole Mass Spectrometry Experiments

[0121] Quadrupole mass spectrometry (QMS) studies were performed in a separate reactor that has been described previously. The precursors were flowed through a packed powder bed of AI2O3 nanoparticles (Amorphous, 93wt% AI2O3. 6-7wt% H2O, US-Nano). The typical mass of AI2O3 particles at the start of an experiment was 30-50 mg. The nanoparticles had an average diameter of 50 nm as measured by US-Nano.

[0122] After passing through the particle bed, the gas stream was sampled via an aperture (0.3 mm, Lenox Laser).

[0123] Gases passing through the aperture were expanded into a molecular beam in a differentially-pumped vacuum low pressure region. The molecular beam was transported through a parabolic skimmer that separated the differentially -pumped chamber from the vacuum chamber that housed the QMS. After passing through the skimmer, the molecular beam entered the ionizer of the QMS (MAX-QMS Flange Mounted System, Extrel).

[0124] A constant stream of N2 was flowed through the particle bed. The N2 was metered by a mass flow controller (GM50, MKS Instruments). The flow rate of N2 was 0.8 seem. This flow rate resulted in a pressure upstream of the particle bed of 2.63 Torr. Pressure was measured with capacitance manometers (Baratron 121 A, MKS Instruments) that were located upstream and downstream of the particle bed and on the gas manifold.

[0125] The HF and Hacac reactants were dosed from a custom manifold. The manifold consisted of the precursor source - diaphragm valve - fill volume with pressure sensor - diaphragm valve - flow reducing needle valve - particle bed. The diaphragm valve between the source and the fill volume was controlled on a feedback loop using a fill volume pressure sensor. The control loop maintained the pressure in the fill volume at a constant pressure of 8 Torr.

[0126] Precursor w as dosed into the particle bed by opening the diaphragm valve between the fill volume and the particle bed. The flow rate of the precursor was modulated with the needle valve. The precursors used on the QMS experiment w ere identical to those used on the AES and QCM experiments. A typical precursor dose consisted of a 120 s exposure, followed by a 300 s purge. During the dose, the capacitance manometer upstream of the pressure bed observed a pressure of 3.59 Torr. The temperature of the powder bed was controlled via a proportional loop operated in LabVIEW.

[0127] The precursor gas flows and QMS electron multiplier were each adjusted at the start of each QMS experiment. The precursor gas flow w as adjusted to reach a total pressure of ~3.6 Torr using a needle valve on the precursor line. The electron multiplier was adjusted to achieve the greatest signal without saturating the QMS detector. These adjustments made the data from the initial cycles inconsistent with the remainder of the data set. Consequently, only cycles 4 - 50 are presented in this study.

[0128] The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present application. Thus, it should be understood that although the present application describes specific embodiments and optional features, modification and variation of the compositions, methods, and concepts herein disclosed may be resorted to by those of or inary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present application.

[0129] Enumerated Embodiments

[0130] The following enumerated embodiments are provided, the numbering of which is not to be construed as designating levels of importance:

[0131] Embodiment 1 provides a method of performing thermal atomic layer etching (ALE), the method comprising: i) contacting, in a reaction chamber, a substrate comprising a metal compound layer with a surface modification reactant comprising hydrogen fluoride (HF) to form a metal fluoride on at least one portion of the metal compound layer; ii) contacting the metal fluoride with a volatilization reactant comprising a compound of Formula (I), or a tautomer thereof, to etch the at least one portion of the metal compound layer: wherein R and R' are each independently selected from the group consisting of Ci-6 alkyd, Ce-io ai 4, and C4-10 cycloalkyl, each optionally substituted by at least one substituent selected from the group consisting of F, Cl, CN. OC1-4 alkyl, NO2, and C1-4 alkyl; and iii) repeating step ii) at least once, wherein exposing the metal fluoride to the volatilization reactant regenerates HF in the reaction chamber.

[0132] Embodiment 2 provides the method of embodiment 1 , wherein the substrate comprises a material selected from the group consisting of Si, SiN, S1O2. SiNxOy, SixGey, SiC, S1B3, SiP, SiAs, SiSe, SiTe, RuSi, TixSiy, TiCz, TiC, VxSiy, NbxSiy, MoxSiy, TaxSiy, RexSiy, and WxSiy, wherein: each occurrence of x is independently an integer from 1 to 6; each occurrence of y is independently an integer from 1 to 6; and z is from about 0.3 to about 1.

[0133] Embodiment 3 provides the method of any one of embodiments 1-2, wherein the metal in the metal compound layer is selected from the group consisting of AL Hf. Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr, Si, Ti, Sc, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Nb, Cd and Sn, and combinations thereof.

[0134] Embodiment 4 provides the method of any one of embodiments 1-3, wherein the metal compound is selected from the group consisting of a metal oxide, metal nitride, metal phosphide, metal sulfide, metal arsenide, metal fluoride, metal silicide, metal boride, metal carbide, metal selenide, metal telluride, elemental metal, metal alloy, and hybrid organic- inorganic material.

[0135] Embodiment 5 provides the method of any one of embodiments 1-4, wherein the metal compound is a metal oxide.

[0136] Embodiment 6 provides the method of any one of embodiments 1-5, wherein the metal in the metal compound layer is Al.

[0137] Embodiment 7 provides the method of any one of embodiments 1-6, wherein the metal compound layer comprises AI2O3.

[0138] Embodiment 8 provides the method of any one of embodiments 1-7, wherein the metal compound layer is about 1 to about 100 A thick.

[0139] Embodiment 9 provides the method of any one of embodiments 1-8, wherein no additional HF is added to the reaction chamber after step i).

[0140] Embodiment 10 provides the method of any one of embodiments 1-9, wherein the HF is provided in a dose of about 0.05 to about 3 Torr s.

[0141] Embodiment 11 provides the method of any one of embodiments 1-10, wherein the compound of Formula (I) is provided in a dose of about 0.05 to about 3 Torr s.

[0142] Embodiment 12 provides the method of any one of embodiments 1-11, wherein the thermal ALE is performed at a temperature of about 150 to about 350 °C.

[0143] Embodiment 13 provides the method of any one of embodiments 1-12, wherein the compound of Formula (I) is or a tautomer thereof.

[0144] Embodiment 14 provides the method of any one of embodiments 1-13, wherein the compound of Formula (I) is or a tautomer thereof.

[0145] Embodiment 15 provides the method of any one of embodiments 1-14, wherein R and R' are each perfluorinated.

[0146] Embodiment 16 provides the method of any one of embodiments 1-15, wherein step ii) is repeated continuously until no further etching as a result of exposing the metal fluoride to the volatilization reactant is observed.

Claims

CLAIMSWhat is claimed is:

1. A method of performing thermal atomic layer etching (ALE), the method comprising: i) contacting, in a reaction chamber, a substrate comprising a metal compound layer with a surface modification reactant comprising hydrogen fluoride (HF) to form a metal fluoride on at least one portion of the metal compound layer; ii) contacting the metal fluoride with a volatilization reactant comprising a compound of Formula (I), or a tautomer thereof, to etch the at least one portion of the metal compound layer:O O R^^R' (I), wherein R and R' are each independently selected from the group consisting of Ci-6 alkyl, Ce-io aryl, and C4-10 cycloalkyl, each optionally substituted by at least one substituent selected from the group consisting of F. Cl, CN. OC1-4 alkyl, NO2, and Ci-4 alkyl; and iii) repeating step ii) at least once, wherein exposing the metal fluoride to the volatilization reactant regenerates HF in the reaction chamber.

2. The method of claim 1 , wherein the substrate comprises a material selected from the group consisting of Si, SiN, SiCh, SiNxOy, SixGey, SiC, SiEL, SiP, SiAs, SiSe, SiTe, RuSi, TixSiy, TiCz, TiC, VxSiy, NbxSiy, MoxSiy, TaxSiy, RexSiy, and VxSiy, wherein: each occurrence of x is independently an integer from 1 to 6; each occurrence of y is independently an integer from 1 to 6; and z is from about 0.3 to about 1.

3. The method of claim 1, wherein the metal in the metal compound layer is selected from the group consisting of Al, Hf, Zr, Fe, Ni, Co, Mn, Mg, Rh, Ru, Cr, Si, Ti, Sc, Ga, In, Zn, Pb, Ge, Ta, Cu, W, Mo, Pt, Nb, Cd and Sn, and combinations thereof.

4. The method of claim 1 , wherein the metal compound is selected from the group consisting of a metal oxide, metal nitride, metal phosphide, metal sulfide, metal arsenide, metal fluoride, metal silicide, metal boride, metal carbide, metal selenide, metal telluride,elemental metal, metal alloy, and hybrid organic-inorganic material.

5. The method of claim 1, wherein the metal compound is a metal oxide.

6. The method of claim 1, wherein the metal in the metal compound layer is Al.

7. The method of claim 1, wherein the metal compound layer comprises AI2O3.

8. The method of claim 1, wherein the metal compound layer is about 1 to about 100 A thick.

9. The method of claim 1, wherein no additional HF is added to the reaction chamber after step i).

10. The method of claim 1 , wherein the HF is provided in a dose of about 0.05 to about 3 Torr s.

11. The method of claim 1, wherein the compound of Formula (I) is provided in a dose of about 0.05 to about 3 Torr s.

12. The method of claim 1, wherein the thermal ALE is performed at a temperature of about 150 to about 350 °C.

13. The method of claim 1, wherein the compound of Formula (I) isor a tautomer thereof.

14. The method of claim 1, wherein the compound of Formula (I) isO O F3C^^CF3or a tautomer thereof.

15. The method of claim 1, wherein R and R' are each perfluorinated.

16. The method of claim 1, wherein step ii) is repeated continuously until no further etching as a result of exposing the metal fluoride to the volatilization reactant is observed.

Images