Atomic Layer Etching of Metal Oxides

Abstract

In one example, a method of processing a substrate includes loading a substrate into a process chamber, the substrate including a metal oxide-containing film to be etched. The method further includes performing an atomic layer etch including a plurality of cyclical processes, each of the plurality of cyclical processes including exposing the metal oxide-containing film to a first gas flow including boron trichloride (BCl3) and exposing the metal oxide-containing film to a second gas flow including a borane, amine, alcohol, carboxylic acid, carboxamide, or β-diketone reagent.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 17 / 194,421, filed March 8, 2021, which is incorporated by reference in its entirety.

[0002] The present invention relates generally to semiconductor manufacturing, and in a particular embodiment to a method for atomic layer etching of metal oxides. [Background technology]

[0003] An integrated circuit (IC) is a set of electronic circuits that includes components such as transistors, resistors, and capacitors on a small chip of semiconductor material. ICs are found in essentially every modern electronic device, and fabrication techniques for IC devices are of paramount importance in commercial manufacturing processes. Etching, the process of removing a thin film or part of a substrate, is one of the key processes in the fabrication of such semiconductor devices. In the modern semiconductor industry, etching is usually performed by wet etching using an etchant or by dry etching such as reactive ion etching.

[0004] As IC critical dimensions and feature sizes shrink to below 10 nm, the semiconductor industry demands improved precision of dimensions (e.g., line width, etch depth, and film thickness) during the etching process. For example, atomic scale controllability below 0.5 nm may be required, but is difficult to achieve with conventional etching techniques. For this reason, alternative etching techniques that meet such requirements are highly desirable.

[0005] Atomic layer etching (ALE) is an emerging technology that may provide such atomic-scale control and is currently under development. ALE removes thin film or substrate material using successive self-limiting half-reactions to achieve precise control of etch depth from the surface. A typical ALE process consists of one or more cycles of two self-limiting half-reactions: (1) surface modification by adsorption of a precursor vapor to form a thin layer as an intermediate, and (2) removal of at least a portion of the formed layer as a gaseous product. In other words, the ALE process chemically converts a solid material layer-by-layer into the gas phase to produce highly volatile products that can be removed. These reactions are considered "self-limiting" because the surface reaction is limited to a moderate layer thickness by diffusion, by sparseness of new reactive sites, by the amount of modified surface material, or by other means, so that the reaction stops when the available reactive surface species are exhausted, modified, or removed.

[0006] Due to its atomic-scale controllability, ALE technology offers great potential in applications such as microelectronics, optoelectronics, microelectromechanical systems (MEMS), and other semiconductor devices. However, ALE is still in the early stages of development compared to conventional etching and atomic layer deposition techniques. Effective ALE precursors and surface chemistries for each process step need to be further developed along with a better understanding of the reaction mechanisms. In addition, conventional ALE processes result in slow etch rates, long cycle times, low throughput, and higher costs that hinder their adoption in industrial applications. Summary of the Invention [Means for solving the problem]

[0007] A method of processing a substrate includes loading a substrate into a process chamber, the substrate including a metal oxide-containing film to be etched, the method further includes performing an atomic layer etch including a plurality of cyclical processes, each of the plurality of cyclical processes including exposing the metal oxide-containing film to a first gas flow including boron trichloride (BCl3) and exposing the metal oxide-containing film to a second gas flow including a borane reagent or an amine reagent.

[0008] The atomic layer etching (ALE) method includes loading a substrate including a metal oxide-containing film to be etched into a process chamber, the method further including exposing the substrate to a first gas flow including boron trichloride (BCl3) in the gas phase and exposing the substrate to a second gas flow including an alcohol, a carboxylic acid, a carboxamide, or a β-diketone reagent.

[0009] A method for treating a substrate includes loading a substrate including a metal oxide-containing film to be etched into a process chamber, the method further including performing a continuous etching process including a plurality of self-limiting cyclical processes, each of which includes converting a layer of the metal oxide-containing film to a metal mixed anion compound including chlorine, and liberating the metal mixed anion compound from a remaining portion of the metal oxide-containing film to remove the metal oxide layer, the liberating comprising exposing the metal mixed anion compound to a first gas flow including an adduct of aluminum hydride with a nitrogen-containing additional ligand, a borane reagent, an amine reagent, a β-diketone reagent, an alcohol, or a carboxylic acid. [Brief description of the drawings]

[0010] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0011] [Figure 1A] 1A-1C are schematic cross-sectional views of a substrate at different stages during a thermal ALE process according to an embodiment, with FIG. 1A showing the substrate before the ALE process; [Figure 1B]1A-1C are schematic cross-sectional views of a substrate at different stages during a thermal ALE process according to an embodiment, with FIG. 1B showing the substrate during a surface modification step; [Figure 1C] 1A-1C are schematic cross-sectional views of a substrate at different stages during a thermal ALE process according to an embodiment, with FIG. 1C showing the substrate during a removal step; [Diagram 2] 1 illustrates the change in surface chemistry and removal of volatile products in an example of ALE etching of aluminum oxide (Al2O3) using boron trichloride (BCl3) in a surface modification step and a borane reagent in a removal step, according to an embodiment. [Diagram 3] 1 illustrates the change in surface chemistry and removal of volatile products in an example of ALE etching of aluminum oxide (Al2O3) using boron trichloride (BCl3) in the surface modification step and an amine reagent in the removal step, according to an embodiment. [Figure 4] 1 illustrates the change in surface chemistry and removal of volatile products in an example of ALE etching of aluminum oxide (Al2O3) using boron trichloride (BCl3) in the surface modification step and alcohol in the removal step, according to an embodiment. [Diagram 5] 1 is a flowchart illustrating an example process flow for a thermal ALE process on a substrate, in accordance with an embodiment. [Figure 6] 1 illustrates an ALE processing tool according to an embodiment of the present application. [Figure 7] 1 illustrates a rotating susceptor for ALE processing according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] With each successive technology node, the semiconductor industry has increased the packing density of IC components. Following this increase, there is an urgent demand for precise atomic-scale control in the etching process. Atomic Layer Etching (ALE) is a leading candidate to provide sub-nm precise atomic control. ALE is a film etching technique consisting of successive self-limiting reactions. The first step is the surface modification by adsorption of a precursor vapor to form a thin layer. The second step is the removal of at least a part of the formed layer. The concept of ALE is similar to atomic layer deposition (ALD). The difference is that material is removed during the second step of ALE, rather than added as in ALD. Each step is self-limiting, and only a thin layer is removed by one cycle of the ALE process. To achieve the desired amount of etching, the steps are usually repeated, and therefore the ALE process generally refers to a continuous cycle of such steps.

[0013] There are various techniques to perform these steps. For example, one or both steps can be performed using a plasma process (plasma ALE) that substantially energizes particles interacting with the surface. By using energized particles, plasma ALE generally induces sputtering. This sputtering in plasma ALE allows anisotropic etching, which is a major advantage of plasma ALE. If no plasma is used in either step, it is called thermal ALE. Thermal ALE is characterized by its conformal and isotropic etching and little or no damage to the underlying film.

[0014] The embodiments described in this disclosure provide an isotropic thermal ALE process for substrates including metal oxides, however, in certain embodiments, plasma may also be used to increase the efficiency of the ALE process.

[0015] ALE has been demonstrated in studies on etching different materials such as Si, W, metal oxides (e.g., Al2O3, HfO2, ZrO2, ZnO, TiO2, SiO2, and WO3), metal nitrides (e.g., Si3N4, GaN, TiN, AlN), and metal fluorides (e.g., AlF3). The inventors of the present application confirmed that these prior art techniques are based on fluorination chemistry. HF is mainly used in known ALE techniques, while other reagents such as SF4, F2, WF6, and XeF2 have been proposed as alternative, stronger fluorination reagents. In these prior art techniques, in a first step, metal species are first fluorinated to form metal fluorides and the like (e.g., oxyfluorides), which are then removed in a second step of the ALE process based on a ligand exchange reaction. However, most metal fluorides are relatively less volatile, which may result in a slower etch rate. In addition, this requires the use of higher temperatures and gaseous fluoride-containing species during the process, which often adversely affect or damage other materials to which they are exposed.

[0016] Therefore, existing ALE techniques using fluorinated chemistries may not be desirable for selective etching of metal oxides, especially non-silicon materials that are less reactive with fluorine compared to silicon. Furthermore, in the semiconductor industry, new wiring and contact schemes may introduce films that are sensitive to fluorine-based chemicals. The embodiments of the present application describe ALE techniques that overcome the above problems without relying on fluorination.

[0017] Additionally, new processes are increasingly being introduced into manufacturing flows that may require etching of various non-silicon metal oxides. For example, high-k dielectric materials, including metal oxides such as aluminum oxide, hafnium oxide, zirconium oxide, etc., may need to be precisely etched.

[0018] Various embodiments described herein may be applied to the fabrication of novel field effect transistor (FET) architectures, such as self-aligned contact (SAC), ultra-thin gate dielectric, ultra-thin channel, Fin Field Effect Transistor (FinFET) and gate-all-around transistors, which require near-atomic scale etch control and selectivity.

[0019] More specifically, embodiments of the present disclosure describe an atomic layer etching process based on chlorination rather than fluorination. In various embodiments, BCl3 is used as a precursor to convert a metal oxide layer on the surface of a substrate to an oxychloride layer by partially removing oxygen from the metal oxide to the gas phase. In a subsequent removal step, the oxychloride layer is exposed to a ligand exchange reagent, and at least a portion of the oxychloride layer is converted to volatile products that escape to the gas phase.

[0020] The chlorination-based ALE methods described in various embodiments of the present disclosure can be advantageous in that they result in faster etch rates of target materials while preventing undesired etching of other materials. For example, embodiments of the ALE method can be used in the selective etching of aluminum oxide over silicon, where the aluminum oxide is removed without damaging the silicon surface.

[0021] Additionally, the ALE methods described in various embodiments of the present disclosure recite the use of various ligand exchange reagents that are different from and typically more volatile than conventional reagents, such as tin(II) acetylacetonate (Sn(acac)2) and trimethylaluminum (TMA). The ligand exchange reagents, described in more detail below, can include borane reagents, amine reagents, alcohol reagents, carboxylic acids, carboxamides, β-diketones, or adducts of aluminum hydrides with nitrogen-containing additional ligands.

[0022] In various embodiments, the method includes a set or cycle of processing steps including a surface modification step and a surface removal step. The surface modification step includes exposing the metal oxide-containing film to a first gas flow including boron trichloride (BCl3). The surface removal step includes exposing the metal oxide-containing film to a second gas flow including a ligand exchange reagent. Although BCl3 is the primary reagent in the surface modification step, various ligand exchange reagents can be used according to various embodiments of the present disclosure. Exemplary methods and systems of the present disclosure are described in more detail below in various embodiments.

[0023] In the following, an ALE process according to an embodiment of the present disclosure is first described in Figures 1A-1C, followed by various examples of embodiments using different ligand exchange reagents shown in Figures 2-4. Then, a process flow of a general embodiment of the ALE process is described in Figure 5. Furthermore, an embodiment of an ALE processing tool is described in Figures 6 and 7.

[0024] 1A-1C show cross-sectional views of a metal oxide-containing substrate at different stages during an atomic layer etching (ALE) process according to an embodiment of the present disclosure.

[0025] 1A shows a substrate 102 prior to the ALE process. The substrate 102 may include bulk silicon wafers, silicon-on-insulator (SOI) wafers, silicon carbide, and other substrate materials, and may include layers of semiconductors useful in various nanodevices, including epitaxial silicon, silicon germanium, silicon carbon, gallium nitride, gallium arsenide, indium phosphide, gallium phosphide, indium antimonide, etc. At this stage, in certain embodiments, the substrate 102 may have already undergone various steps of semiconductor fabrication, including the formation of active and isolation regions.

[0026] 1A, the substrate 102 includes a metal oxide-containing film 100 to be etched. In various embodiments, the metal oxide-containing film 100 can be any film that includes a metal oxide. In various embodiments, the metal oxide-containing film 100 can include aluminum oxide, titanium oxide, hafnium oxide, zirconium oxide, yttrium oxide, lanthanum oxide, lutetium oxide, tantalum oxide, copper oxide, ruthenium oxide, cobalt oxide, niobium oxide, tungsten oxide, molybdenum oxide, scandium oxide, and combinations thereof.

[0027] In various embodiments, the metal oxide-containing film 100 may protrude from or be flush with the major surface of the substrate 102. In various embodiments, the metal oxide-containing film 100 may have a thickness of about 1 nm to 10 nm, and in different embodiments, a thickness of 10 nm to 100 nm. In various embodiments, the metal oxide-containing film 100 may cover substantially all of the major surface of the substrate 102. In certain embodiments, the metal oxide-containing film 100 may be patterned and may cover only a portion of the major surface of the substrate 102. In such embodiments, the patterned metal oxide-containing film 100 may include a number of island regions spaced apart in a portion of the substrate 102.

[0028] Prior to the start of the cyclic etching process, the surface may be prepared by a pre-cleaning treatment to remove contaminants such as hydrocarbons and other particles, or metal or salt impurities from the surface. For example, this process may include wet chemistry-based techniques in which the substrate is exposed to deionized water and then to various solutions including chemicals such as hydrochloric acid, hydrogen peroxide, aqueous ammonia, and piranha solution. These chemicals are thoroughly rinsed with water, and the substrate may be dried by various procedures. Despite the pre-cleaning treatment, hydroxyl groups may generally be present on the treated surface of the metal oxide.

[0029] Additionally, in certain embodiments, the process chamber may be purged or evacuated to remove contaminants or other materials that may contaminate the surfaces being cleaned or consume the reactants being introduced.

[0030] In various embodiments, the substrate 102 can be heated so that the metal oxide-containing film 100 is at a temperature suitable for etching. The temperature can be resistively controlled using a proportional-integral-derivative (PID) controller. In certain embodiments, thermal equilibrium can be reached prior to the first step of the ALE process by flowing an inert carrier gas, such as helium (He), argon (Ar), or nitrogen (N2), for 30 minutes or more. In various embodiments, the peak heating temperature can be between 25°C and 600°C. In certain embodiments, the peak heating temperature can be between 100°C and 400°C, or between 100°C and 250°C.

[0031] In certain embodiments, the individual steps of the ALE process may be performed under reduced pressure. In other words, the process chamber may be maintained at a reduced pressure. For example, the pressure may be kept between 10 Torr and 40 Torr. In further examples, the pressure in the process chamber may be between 0.1 Torr and 20 Torr, or between 10 -5 Torr to 1 Torr.

[0032] 1B and 1C show steps of the ALE process, specifically, FIG 1B shows the substrate 102 after a first step of the ALE process, and FIG 1C shows the substrate 102 after a second step of the ALE process.

[0033] Referring to FIG. 1B, in the first step, the substrate 102 is first exposed to a gas flow containing BCl3 vapor 104. This first step may also be referred to as a surface modification step. In certain embodiments, the gas flow may further include an inert carrier flow gas, such as helium (He), argon (Ar), and nitrogen (N2), in any ratio. In various embodiments, the chamber may first be filled with a flow of inert gas, and then the reagent containing BCl3 may be pulsed into the inert carrier flow. In one embodiment, the pulse sequence of reagent and inert gas may be in a ratio of about 1:1 to about 1:5, such as 1:3 in one embodiment, where the reagent containing BCl3 is pulsed for 1 second every 3 seconds, resulting in a ratio of 1:3. In certain embodiments, the duration of exposure to the reagent containing BCl3 in a pulse or step may be about 0.1 to 600 seconds. In certain embodiments, the gas flow may further include an oxidizing gas, such as oxygen and ozone, mixed in any ratio in the flow. This addition may be beneficial in the case of etching non-oxide materials (e.g., W) where the target material may be partially oxidized to an oxide that may be more easily etched in the second step compared to the initial state. In other embodiments, a separate oxidation step involving exposing the substrate to a gas flow containing an oxidizing gas may be performed as a pretreatment step prior to exposure to the first gas flow.

[0034] Exposure to the BCl3-containing vapor 104 induces a chlorination reaction on the surface, forming a thin layer of metal oxychloride 108 on the surface along with volatile by-products including boron oxychloride 106 that are removed from the surface simultaneously or during subsequent processing, such as during a subsequent purge / evacuation step or an optional plasma treatment step, as described below. While not intended to be limiting in any way, this figure illustrates an example of an embodiment in which the gas introduced by exposure 104 selectively reacts with the metal oxide-containing film 100 but not with the non-metal oxide portions of the substrate 102.

[0035] In certain embodiments, after exposure to the BCl3-containing vapor 104, the process chamber holding the substrate 102 may be purged with an inert gas. In the purging process, the substrate 102 may be exposed to a flow of an inert gas, such as helium (He), argon (Ar), or nitrogen (N2), to remove the BCl3-containing vapor 104. In some embodiments, the process chamber may be evacuated instead of purged. In more specific embodiments, both purging and evacuating may be performed. This prevents the resumption of the chlorination process until the next cycle of the ALE process. In addition, the purge / evacuation process may remove volatile by-products 106, including boron oxychloride. In certain embodiments, the duration of the purge / evacuation process may be between 0.5 seconds and 300 seconds.

[0036] In certain embodiments, an optional treatment with plasma may be performed as part of the ALE process after exposure to the vapor 104 containing BCl3 104 to dissociate surface species from the substrate by ion bombardment. The plasma treatment involves exposing the substrate to a plasma-containing gas, which may include ionized inert gas molecules of helium (He), argon (Ar), or nitrogen (N2). The system may be heated or cooled during the plasma treatment step. Plasma treatment may also be performed at pressures between 10 Torr and 40 Torr, between 0.1 Torr and 20 Torr, or between 10 Torr and 20 Torr. -5 The process may be carried out under reduced pressure, which may be kept at Torr to 1 Torr.

[0037] Next, FIG. 1C shows the surface during the removal step where the substrate 102 is exposed to a gas flow 110 containing a reagent to induce a ligand exchange reaction. In certain embodiments, the gas flow may further include an inert carrier gas, such as helium (He), argon (Ar), and nitrogen (N2), in any ratio. In various embodiments, the chamber is first filled with a flow of inert gas, and then the reagents for the ligand exchange reaction may be sequentially delivered as pulses to the inert carrier flow. In one embodiment, the pulse sequence may be at a ratio of 1 / 3 seconds, where the reagents are delivered for 1 second every 3 seconds in a pulsed manner. In certain embodiments, the duration of exposure to the reagents in a pulse or step may be 0.1 to 600 seconds.

[0038] In certain embodiments, the substrate 102 is heated while being exposed to the reagent-containing gas flow 110. This may be a continuation of the heating process described above. In certain embodiments, targeted heating pulses may be provided, for example from lamps. This may be done to control the process temperature, which controls the reaction rate and thus the efficiency of the etching process. In various embodiments, the temperature at the substrate 102 is targeted to be between 25°C and 600°C, and in certain embodiments, between 100°C and 400°C, or between 150°C and 300°C.

[0039] In certain embodiments, the exposure to the reagent-containing gas flow 110 may be performed under reduced pressure. In other words, the process chamber may be maintained at a reduced pressure. For example, the pressure may be between 10 Torr and 40 Torr, and in certain embodiments, between 0.1 Torr and 20 Torr, or between 10 Torr and 40 Torr. -5 Torr can be kept at 1 Torr.

[0040] The ligand exchange reaction in this removal step converts at least a portion of the metal oxychloride 108 layer formed during the surface modification step into more volatile products 112. The volatile products 112 thus formed may desorb from the surface. In various embodiments, the volatile products may be removed during the removal step, a subsequent purge / evacuation step, or an optional plasma treatment step, as described below. While not intended to be limiting in any way, this diagram illustrates an example of an embodiment in which a gas introduced by exposure to the reagent 110 selectively reacts with the layer containing the metal oxychloride 108 but not with the non-metal oxide portions of the metal oxide-containing film 100 or substrate 102.

[0041] After exposure to the vapor 110, the process chamber holding the substrate 102 may be purged with an inert gas. In the purging process, the substrate 102 may be exposed to a flow of an inert gas, such as helium (He), argon (Ar), or nitrogen (N2). In some embodiments, the process chamber may be evacuated instead of purged. Moreover, in certain embodiments, both purging and evacuation may be performed together or sequentially. This purging / evacuation process may remove residual vapor 110 and volatile by-products 112.

[0042] In certain embodiments, an optional treatment with plasma may be performed as part of the ALE process after exposing the substrate 102 to the vapor 110. This treatment may cause surface species to dissociate from the substrate by ion bombardment. The plasma treatment involves exposing the substrate to a plasma-containing gas, which may include ionized inert gas molecules of helium (He), argon (Ar), or nitrogen (N2). The system may be heated or cooled during the plasma treatment step. Plasma treatment may also be performed at pressures between 10 Torr and 40 Torr, between 0.1 Torr and 20 Torr, or between 10 Torr and 40 Torr. -5 The process may be carried out under reduced pressure, which may be kept at Torr to 1 Torr.

[0043] Once the layer containing metal oxychloride 408 is removed, a new layer of metal oxide-containing film 100 is exposed at the surface, which is ready for the next etching cycle. Thus, successive cycles of surface modification and removal steps as described above can be performed to further etch the material. In principle, without wishing to be bound by any theory, each step is expected to be self-limiting, with each cycle removing only a single or few layers of material, providing the ability to achieve atomic-scale etching control. Subsequent cycles can be repeated until the target thickness of metal oxide-containing film 100 is removed. In other words, the steps of Figures 1B and 1C can be repeated multiple cycles.

[0044] In certain embodiments, sequential steps of the ALE process may be separated in time within the same region of the chamber, or in space within different regions of the same chamber, and system embodiments implementing these different separation methods are described in more detail in later sections.

[0045] A variety of non-fluorine-containing ligand exchange reagents may be used in the removal step. In certain embodiments, the ligand exchange reagent is a boron-containing reagent. In some other embodiments, the ligand exchange reagent is a nitrogen-containing reagent. In yet some embodiments, the ligand exchange reagent is an alcohol, a carboxylic acid, a carboxamide, or a β-diketone. In yet some embodiments, the ligand exchange reagent is an adduct of aluminum hydride with a nitrogen-containing additional ligand. Further details of examples using different ligand exchange reagents are provided in later sections.

[0046] In certain embodiments, the ligand exchange reagent is a borane reagent. The borane reagent comprises a first ligand, a second ligand, and a third ligand, the first ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the second ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, and the third ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand. In other words, the borane reagent may have a general formula of BL1L2L3, where Lx (x=1, 2, or 3) is a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand. In the present disclosure, a dialkylamide ligand is defined as a ligand having a general formula of NR1R2, where Rx (x=1 or 2) is an alkyl ligand. When L1, L2, and L3 are equal to each other, the borane reagent is homoleptic (i.e., all ligands are the same), and examples of such homoleptic reagents are borane (BH3), trialkylboranes such as trimethylborane and triethylborane, tri(amino)borane complexes such as tris(dimethylamino)borane, tris(ethylmethylamino)borane, and tris(diethylamino)borane. The borane reagent may be heteroleptic, having at least one ligand that is different from another ligand. Examples of such heteroleptic reagents are ethyl(methyl)borane, ethyl(dimethyl)borane, and ethyl(isopropyl)methylborane.

[0047] In certain embodiments, the ligand exchange reagent is an adduct of a borane reagent with a nitrogen-containing additional ligand. In addition to the additional ligand, the borane reagent includes a first ligand, a second ligand, and a third ligand, the first ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the second ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, and the third ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand. In other words, the borane reagent can have a general formula of ABL1L2L3, where A is a neutral nitrogen-containing additional ligand such as trimethylamine, ammonia, pyridine, and Lx (x=1, 2, or 3) is a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand. The neutral nitrogen-containing attachment ligands can facilitate the removal of hydrochloric acid from the surface, which can be formed as a by-product.

[0048] In certain embodiments, the ALE steps described in Figures 1B-1C may be separated in time or space. Separation may be achieved by purging, evacuation, substrate transfer, or a combination thereof. In certain embodiments, the ALE steps described in Figures 1B-1C may be only partially separated and may partially overlap.

[0049] FIG. 2 shows the change in surface chemical composition in an example of selective aluminum oxide (Al2O3) etching according to an embodiment of the present disclosure. According to an embodiment, a gas containing BCl3 is used in the surface modification step, and a gas containing homoleptic borane reagent BL3 (wherein L is an alkyl or dialkylamide ligand) is used in the removal step. In this example, the substrate further includes a silicon (Si) wafer, and a portion of the Si wafer is also exposed on the surface, as shown in FIG. 2. Upon exposure to the gas containing BCl3, chlorination proceeds in the surface layer of Al2O3. This reaction results in the formation of aluminum oxychloride AlO x Cl y A thin layer of BO is formed on the surface. b Cl a Volatile by-products are produced, including: The Si wafer remains essentially pristine.

[0050] Here, it should be noted that in the actual process, the degree of chlorination is expected to vary depending on many factors such as the position on the surface, impurities on the surface, process parameters, and the reactivity of the reagents (i.e., for AlO x Cl y , 0 < x < 1.5, 0 < y < 3). Therefore, the consideration of the stoichiometric composition is only an example.

[0051] In the next removal step, when the substrate 102 is exposed to the second gas containing BL3, a ligand exchange reaction is carried out, and the layer of AlO x Cl y is converted to a more volatile species. Assuming that all of the oxygen (O), which is a divalent anion in the layer, can be replaced by two monovalent ligands (L) and no ligand exchange with chlorine occurs, the aluminum species can be represented as AlL 2x Cl y . The examples of possible stoichiometric compositions that can occur during the process are by no means intended to be limiting and are presented below only for the purpose of illustration. In this example, x = 0.5, y = 2, a = b = 1, and the stoichiometric numbers are shown in the equation. Other by-products such as water and hydrochloric acid can be formed by reacting with the surface OH groups remaining on the surface. (1) Al2O3 + 2BCl3(g) → Al2OCl4 + 2BOCl(g) (2) Al2OCl4 + 2BL3(g) → 2AlLCl2(g) + 2BO 0.5 L2(g) Overall (1) + (2): Al2O3 + 2BCl3(g) + 2BL3(g) → 2AlLCl2(g) + 2BOCl(g) + 2BO 0.5 L2(g)

[0052] In a particular embodiment, the ligand exchange reagent is an amine reagent. The reagent can have the general formula NH2R1 or NHR1R2, where Rx (x = 1 or 2) is alkyl. Examples of amine reagents are methylamine, dimethylamine, diethylamine, ethylmethylamine, and ethylamine.

[0053] 3 shows reactions in an example of selectively etching aluminum oxide (Al2O3) according to an embodiment of the present disclosure. According to an embodiment, a gas containing BCl3 is used in the surface modification step, and a gas containing the amine reagent NHR1R2 is used in the removal step. In this example, the substrate further includes a silicon (Si) wafer, and a portion of the Si wafer is also exposed on the surface, as shown in FIG. 3. The surface modification step includes the addition of AlO x Cl y In the next removal step, upon exposure of the substrate to a second gas containing NHR1R2, a ligand exchange reaction is carried out to form AlO x Cl y The layer of NR1 is converted to more volatile species. 2- , NR2 2- , N.H. 2- , NR1R2 - , NHR1 - , and NHR2 - There are various ligands that may allow for ligand exchange in some cases, such as: - Assuming that only Al(NR1R2) is used for ligand exchange, the aluminum species is Al(NR1R2) 2x Cl z Other by-products such as water and hydrochloric acid may be formed.

[0054] In certain embodiments, the ligand exchange reagent is an alcohol reagent. The reagent may have the general formula ROH. Examples of alcohol reagents are methanol, ethanol, tert-butanol, isopropanol, trifluoromethanol, perfluoroethanol, perfluoroisopropanol, and perfluoro-tert-butanol. The acidic OH group in the alcohol reagent reacts with the chlorinated metal oxide surface to allow ligand exchange.

[0055] 4 shows reactions in an example of selectively etching aluminum oxide (Al2O3) according to an embodiment of the present disclosure. According to an embodiment, a gas containing BCl3 is used in the surface modification step, and a gas containing the alcohol reagent ROH is used in the removal step. In this example, the substrate further includes a silicon (Si) wafer, and a portion of the Si wafer is also exposed on the surface, as shown in FIG. 4. The surface modification step includes the addition of AlO x Cl y In the next removal step, a ligand exchange reaction is carried out upon exposure of the substrate to a second gas containing ROH, resulting in the formation of an AlO x Cl y The layer of ligand OR is converted to a more volatile species. - is available for exchange, the aluminum species is Al(OR) 2x Cl z Other by-products such as water and hydrochloric acid may also be formed.

[0056] In certain embodiments, the ligand exchange reagent is a carboxylic acid reagent. The reagent may have the general formula RCOOH. Examples of carboxylic acid reagents are acetic acid, ethanoic acid, and trifluoroacetic acid. As with the alcohol embodiment, the acidic OH group in the carboxylic acid reagent can react with the chlorinated metal oxide surface to allow for ligand exchange.

[0057] In certain embodiments, the ligand exchange reagent is a carboxamide reagent. The reagent may have the general formula R1C(O)NR2R3, where Rx (x=1, 2, or 3) is hydrogen or alkyl. Examples of carboxamide reagents are acetamide or dimethylformamide.

[0058] In certain embodiments, the ligand exchange reagent is a β-diketone reagent. The reagent may have the general formula of R1C(O)CR2R3C(O)R4, where R1 is an alkyl, R2 is hydrogen or an alkyl, R3 is hydrogen or an alkyl, and R4 is an alkyl. An example of a β-diketone is acetylacetone or hexafluoroacetylacetone. β-diketones can exist in keto and enol forms due to tautomerism. The OH group exists in the enol form of the β-diketone. Thus, similar to the embodiments using alcohols and carboxylic acids, the acidic OH group in the β-diketone reagent can react with the chlorinated metal oxide surface to enable ligand exchange. Other by-products such as water and hydrochloric acid may also be formed.

[0059] In certain embodiments, the ligand exchange reagent is an adduct of aluminum hydride with a nitrogen-containing additional ligand. One example is (Me3N)AlH3.

[0060] In certain embodiments, during the surface removal step using a gas flow containing an amine reagent, an alcohol reagent, a carboxylic acid reagent, a carboxamide reagent, a β-diketone reagent, or an adduct of aluminum hydride with a nitrogen-containing additional ligand, a neutral nitrogen-containing reagent, such as trimethylamine, ammonia, and pyridine, may be optionally added to the second gas to facilitate removal of hydrochloric acid from the surface that may be formed as a by-product. Alternatively, in certain embodiments, exposure to the neutral nitrogen-containing reagent may be performed in a separate step. The neutral nitrogen-containing reagent may be pulsed at a constant rate into the inert gas flow.

[0061] Compared to common techniques that use fluorine-containing precursors as the main reagent, the use of BCl3 in the first step may be advantageous for several reasons, without wishing to be bound by any theory. First, the oxidophilicity of boron may help it to bind with the oxygen of metal oxides, which may be problematic with other reagents. Second, most metal chlorides tend to be more volatile than the corresponding fluorides. Therefore, approaches based on chlorination may achieve faster etching rates of metal oxide species. Furthermore, fluorine-containing reagents may have high reactivity with silicon species and the like. ALE techniques that rely primarily on fluorination may be problematic in complex systems that may require selective etching of materials without causing serious damage to fluorine-sensitive materials, such as silicon species. The embodiments of the present application advantageously allow the use of fluorine-sensitive materials without damaging these fluorine-sensitive materials or the surfaces of the fluorine-sensitive materials.

[0062] 5 shows an ALE process flow diagram 500 for processing a substrate according to an embodiment. In one embodiment, the process flow 500 includes loading a substrate including a metal oxide-containing film to be etched into a process chamber (block 502). For example, the substrate 102 is described in FIG. 1A.

[0063] The process flow 500 further includes performing an etching process, such as an atomic layer etch, including a plurality of cyclic processes (block 504). Each of the plurality of cyclic processes includes exposing the metal oxide-containing film to a first gas flow including boron trichloride (BCl3) (block 506) and exposing the metal oxide-containing film to a second gas flow including a ligand exchange reagent (block 510), for example, as described with respect to FIG. 1B and FIG. 1C. In certain embodiments, the second gas can include a borane or amine reagent (block 510A), for example, as described with respect to FIG. 2 and FIG. 3, respectively. In some embodiments, the second gas can include an alcohol, a carboxylic acid, a carboxamide, or a β-diketone reagent (block 510B), for example, as described with respect to FIG. 4. In further embodiments, the second gas can include an adduct of aluminum hydride with a nitrogen-containing additional ligand (block 510C).

[0064] In certain embodiments, each of the multiple cyclical processes further includes a purge / evacuation step (blocks 508A and 512A) in which purging with an inert gas flow, evacuation, or both are performed, which may occur after exposure to the first gas (block 506), exposure to the second gas (block 510), or both.

[0065] In certain embodiments, each of the multiple cyclical processes further includes exposing the substrate to a plasma (blocks 508B and 512B). This plasma treatment step may be performed after a first step of purging / evacuating (block 508A), a second step of purging / evacuating (block 512A), or both. Furthermore, in some embodiments, the purging and plasma treatment may be performed together as a single step under the same process conditions (i.e., combining blocks 508A and 508B, and blocks 512A and 512B, respectively).

[0066] The multiple cyclic processes (block 504) may be repeated to achieve a desired level of etching, and the process may be completed (block 514). Conditions for each of the multiple cyclic processes, including but not limited to temperature, pressure, exposure time, reagent type, and gas composition, may be varied from step to step.

[0067] In certain embodiments, each of the multiple cyclical processes may not begin with exposure to a first gas (block 506), but rather with exposure to a second gas in a second step (block 510) or purging / evacuating.

[0068] In certain embodiments, a separate oxidation step (not shown) may be performed as a pretreatment step prior to exposure to the first gas flow (block 506). This oxidation step may include exposing the substrate to a gas flow including an oxidizing gas. In some embodiments, the oxidizing gas includes oxygen or ozone. This additional step may be beneficial during etching of non-oxide materials (e.g., W), where the target elements may first be partially oxidized on the surface to become oxides that may be more easily etched in the second step compared to the initial state.

[0069] 6 shows an ALE processing tool 100 that includes a processing chamber 620 connected to a gas supply system 630 and a vacuum pumping system 640. Gases may be introduced to the processing chamber 620 through the gas supply system 630. The gas supply system 630 may have multiple gas inlets (although only one inlet is shown diagrammatically) that allow for the gas mixture to be introduced symmetrically, for example, around the periphery of the processing chamber 620.

[0070] A substrate 610, e.g., a semiconductor wafer to be processed, may be mounted on a substrate holder 650 in the processing chamber 620. In one or more embodiments, the substrate 610 includes one or more metal oxide layers. The substrate holder 650 may be a circular electrostatic chuck and may have the ability to rotate the substrate 610. Optionally, the substrate 610 may be maintained at a desired process temperature, e.g., by a temperature controller 660 coupled to the substrate holder 650. The processing chamber 620 may include other apparatus and devices, e.g., optional lamps or heating elements for heating the substrate 610. Alternatively, one or more gases may be preheated during introduction into the processing chamber 620.

[0071] The ALE processing tool may further include a quartz crystal microbalance (QCM) (not shown) for accurately measuring mass changes on the surface during processing.

[0072] The configurations of the ALE processing system 100 described above are merely exemplary. In certain embodiments, the processing chamber 620 may be configured to accommodate multiple substrates and process multiple substrates vertically or horizontally in a single operation. In alternative embodiments, various alternative configurations may be used, including plasma processing equipment. For example, an inductively coupled plasma (ICP) tool, a capacitively coupled plasma (CCP), or a helical resonator may be used where some steps of the ALE process are performed without a plasma.

[0073] FIG. 7 is a schematic diagram illustrating a rotating susceptor for ALE processing that may be used to achieve spatial separation of the ALE steps in methods according to embodiments.

[0074] The susceptor has multiple stages 700 to hold multiple substrates. One or more exhaust ports 710 and gas inlets 740 are located between and above some of the stages 700, respectively. This design allows multiple processing regions (e.g., 720 and 730) in the same chamber. In such a configuration, different processing steps can be performed in different regions in the chamber, while spatial separation between the regions is achieved by exhausting via exhaust ports 710 or purging via inlets 740. By rotating the susceptor at a controlled speed, each stage is exposed to successive steps of the ALE process according to the embodiment. In certain embodiments, one portion of the susceptor (e.g., 720) can be used to perform a surface modification step and another portion (e.g., 730) can be used to perform a removal step. The exhausting or purging can prevent contamination between the regions. The duration of the steps of the ALE process can be controlled by adjusting the size of the processing regions and controlling the rotation speed. This mode of operation allows the ALE process to continue without purging or evacuating the entire process chamber.The rotating susceptor configurations described above are merely examples.

[0075] Exemplary embodiments of the present invention are summarized here. Other embodiments can be seen throughout the specification and claims appended hereto. EXAMPLES

[0076] Example 1. A method of processing a substrate includes loading a substrate into a process chamber, the substrate including a metal oxide-containing film to be etched. The method further includes performing an atomic layer etch including a plurality of cyclical processes, each of the plurality of cyclical processes including exposing the metal oxide-containing film to a first gas flow including boron trichloride (BCl3) and exposing the metal oxide-containing film to a second gas flow including a borane reagent or an amine reagent.

[0077] Example 2. The method of example 1, further comprising removing the first gas flow from the process chamber prior to exposing the metal oxide-containing film to the second gas flow.

[0078] Example 3. The method of any one of Examples 1 or 2, further comprising removing the second gas flow from the process chamber prior to beginning a next cycle of the multiple cyclic processes.

[0079] Example 4. The method of any one of Examples 1-3, wherein the process chamber includes a first region containing a first gas flow and a second region containing a second gas flow, and the method further includes transferring the substrate from the first region to the second region after exposing the metal oxide-containing film to the first gas flow.

[0080] Example 5. The method of any one of Examples 1-4, further comprising a purge region located between the first region and the second region, the purge region comprising a third gas flow comprising an inert gas.

[0081] Example 6. The method of any one of Examples 1-5, wherein the borane reagent comprises a first ligand, a second ligand, and a third ligand, the first ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the second ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the third ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, and the second gas stream comprises the borane reagent without any amine reagent.

[0082] Example 7. The method of any one of Examples 1-6, wherein the borane reagent is a trialkylborane reagent.

[0083] Example 8. The method of any one of Examples 1 to 7, wherein the borane reagent is trimethylborane or triethylborane.

[0084] Example 9. The method of any one of Examples 1-8, wherein the borane reagent comprises tris(dimethylamino)borane, tris(ethylmethylamino)borane, or tris(diethylamino)borane.

[0085] Example 10. The method of any one of Examples 1-9, wherein the borane reagent further comprises a neutral nitrogen-containing additional ligand.

[0086] Example 11. The method of any one of Examples 1-10, wherein the amine reagent comprises hydrogen, nitrogen, a first ligand, and a second ligand, the first ligand being a hydrogen ligand or an alkyl ligand, the second ligand being an alkyl ligand, and the second gas stream comprises the amine reagent without any borane reagent.

[0087] Example 12. The method of any one of Examples 1 to 11, wherein the amine reagent is a dialkylamine.

[0088] Example 13. The method of any one of Examples 1 to 12, wherein the amine reagent is dimethylamine, diethylamine, or ethylmethylamine.

[0089] Example 14. The method of any one of Examples 1-13, further comprising exposing the metal oxide-containing film to a gas stream comprising a neutral nitrogen-containing reagent.

[0090] Example 15. An atomic layer etching (ALE) method includes loading a substrate containing a metal oxide-containing film to be etched into a process chamber. The method further includes exposing the substrate to a first gas flow containing boron trichloride (BCl3) in the gas phase and exposing the substrate to a second gas flow containing an alcohol, a carboxylic acid, a carboxamide, or a β-diketone reagent.

[0091] Example 16. The method of example 15, wherein the alcohol comprises methanol, ethanol, tert-butanol, isopropanol, trifluoromethanol, perfluoroethanol, perfluoroisopropanol, or perfluoro-tert-butanol.

[0092] Example 17. The method of example 15 or 16, wherein the carboxylic acid comprises acetic acid, ethanoic acid, or trifluoroacetic acid.

[0093] Example 18. The method of any one of Examples 15-17, wherein the carboxamide comprises acetamide or dimethylformamide.

[0094] Example 19. The method of any one of Examples 15-18, wherein the β-diketone comprises acetylacetone or hexafluoroacetylacetone.

[0095] Example 20. The method of any one of examples 15-19, further comprising exposing the metal oxide-containing film to a gas stream comprising a neutral nitrogen-containing reagent.

[0096] Example 21. A method of treating a substrate includes loading a substrate containing a metal oxide-containing film to be etched into a process chamber. The method further includes performing a continuous etching process including a plurality of self-limiting cyclical processes, each of which includes converting a layer of the metal oxide-containing film to a metal mixed anion compound containing chlorine, and liberating the metal mixed anion compound from a remaining portion of the metal oxide-containing film to remove the metal oxide layer, the liberating comprising exposing the metal mixed anion compound to a first gas flow including an adduct of aluminum hydride with a nitrogen-containing additional ligand, a borane reagent, an amine reagent, a β-diketone reagent, an alcohol, or a carboxylic acid.

[0097] Although the present invention has been described with reference to exemplary embodiments, this specification is not intended to be construed in a limiting sense. Various modifications and combinations of those exemplary embodiments, as well as other embodiments of the present invention, will become apparent to those skilled in the art upon reference to this specification. Therefore, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. 1. A method of processing a substrate, the method comprising: loading the substrate containing the metal oxide-containing film to be etched into a process chamber; performing isotropic thermal atomic layer etching including a plurality of cyclic processes; each of the plurality of cyclical processes comprises: Boron trichloride (BCl ３ exposing the metal oxide-containing film to a first gas stream comprising a first gas flow comprising a first metal oxide-containing gas and a second gas flow comprising a second metal oxide-containing gas flow comprising a second gas flow comprising a first gas flow comprising a second metal oxide-containing gas and a second gas flow comprising ... exposing the modified metal oxide-containing outer surface of the metal oxide-containing film to a second gas stream comprising a borane reagent or an amine reagent to remove the modified metal oxide-containing outer surface and expose a new metal oxide-containing outer surface of the metal oxide-containing film. A method comprising:

2. 10. The method of claim 1, further comprising removing the first gas flow from the process chamber prior to exposing the metal oxide-containing outer surface of the metal oxide-containing film to the second gas flow.

3. 10. The method of claim 1, further comprising removing the second gas flow from the process chamber prior to beginning a next cycle of the multiple cyclic processes.

4. 2. The method of claim 1 , wherein the process chamber comprises a first region containing the first gas flow and a second region containing the second gas flow, the method further comprising transferring the substrate from the first region to the second region after exposing the metal oxide-containing film to the first gas flow.

5. The method of claim 4, wherein the process chamber further includes a purge region located between the first region and the second region, the purge region including a third gas flow including an inert gas, and the method further includes purging the substrate with the third gas flow in the purge region.

6. 2. The method of claim 1, wherein the borane reagent comprises a first ligand, a second ligand, and a third ligand, the first ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the second ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, the third ligand being a hydrogen ligand, an alkyl ligand, or a dialkylamide ligand, and the second gas stream comprises the borane reagent without any of the amine reagent.

7. The method of claim 6 , wherein the borane reagent is a trialkylborane reagent.

8. 7. The method of claim 6, wherein the borane reagent comprises tris(dimethylamino)borane, tris(ethylmethylamino)borane, or tris(diethylamino)borane.

9. The method of claim 6 , wherein the borane reagent further comprises a neutral nitrogen-containing additional ligand.

10. 2. The method of claim 1, wherein the amine reagent comprises hydrogen, nitrogen, a first ligand, and a second ligand, the first ligand being a hydrogen ligand or an alkyl ligand, the second ligand being an alkyl ligand, and the second gas stream comprises the amine reagent without any of the borane reagent.

11. The method of claim 10, wherein the amine reagent is a dialkylamine.

12. The method of claim 10, further comprising exposing the metal oxide-containing film to a gas stream comprising a neutral nitrogen-containing reagent.

13. 1. An atomic layer etching (ALE) method, comprising: Loading a substrate including a metal oxide-containing film to be etched into a process chamber; performing an isotropic thermal etch, heating the substrate to a process temperature for the isotropic thermal etch; Boron trichloride (BCl) in the gas phase ３ exposing the heated substrate to a first gas flow comprising: exposing the heated substrate to a second gas flow comprising an alcohol, a carboxylic acid, a carboxamide, or a β-diketone reagent to remove the modified metal oxide-containing outer surface and expose a new metal oxide-containing outer surface of the metal oxide-containing film; A method comprising:

14. 14. The method of claim 13, wherein the alcohol comprises methanol, ethanol, tert-butanol, isopropanol, trifluoromethanol, perfluoroethanol, perfluoroisopropanol, or perfluoro-tert-butanol.

15. 14. The method of claim 13, wherein the carboxylic acid comprises acetic acid, ethanoic acid, or trifluoroacetic acid.

16. 14. The method of claim 13, wherein the carboxamide comprises acetamide or dimethylformamide.

17. The method of claim 13, wherein the β-diketone reagent comprises acetylacetone or hexafluoroacetylacetone.

18. The method of claim 13 , further comprising exposing the metal oxide-containing film to a gas stream comprising a neutral nitrogen-containing reagent.

19. 1. A method of processing a substrate, the method comprising: loading the substrate containing the metal oxide-containing film to be etched into a process chamber; performing an isotropic thermal atomic layer etching (ALE) process that includes a plurality of self-limiting cyclic processes; each of the plurality of self-limiting cyclic processes comprises: converting the metal oxide-containing film layer to a chlorine-containing metal mixed anion compound; liberating the metal mixed anion compound from a remainder of the metal oxide-containing film to remove the layer of the metal oxide-containing film, the liberating comprising exposing the metal mixed anion compound to a first gas stream comprising an adduct of aluminum hydride with a nitrogen-containing additional ligand, a borane reagent, an amine reagent, a β-diketone reagent, an alcohol, or a carboxylic acid; A method comprising:

20. The method of claim 1, wherein the first gas stream or the second gas stream is essentially free of fluorine.

21. The method of claim 1, further comprising exposing the modified metal oxide-containing outer surface of the metal oxide-containing film to a plasma generated from a third gas flow comprising dinitrogen (N2), argon (Ar), or helium (He).

Images