Method for etching a substrate using a hybrid wet atomic layer etching process

Abstract

The present disclosure provides a hybrid atomic layer etching (ALE) process that combines a gas-phase surface modification step with a liquid-phase dissolution step to etch exposed material on a substrate disposed in a process chamber. In the hybrid ALE process disclosed herein, a gas-phase reactant is used to modify the exposed surface of the material to form a surface modification layer, and one or more liquid-phase reactants are used to selectively dissolve the surface modification layer without dissolving the material underlying the surface modification layer. Once the surface modification layer has been selectively dissolved, the substrate may be dried, and the gas-phase surface modification step and the liquid-phase dissolution step may be repeated for one or more ALE cycles until a desired amount of material has been etched.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 151,579, entitled "HYBRID WET ATOMIC LAYER ETCHING," filed February 19, 2021, and U.S. Patent Application No. 17 / 580,879, entitled "METHODS FOR ETCHING A SUBSTRATE USING A HYBRID WET ATOMIC LAYER ETCHING PROCESS," filed January 21, 2022, the disclosures of which are expressly incorporated herein by reference in their entireties.

[0002] The present disclosure relates to processing of substrates. In particular, the present disclosure provides a method for etching a layer on a substrate. [Background technology]

[0003] As substrate feature geometries continue to shrink and the types of structures evolve, the challenges of etching substrates increase. One technique that has been utilized to address these challenges is atomic layer etching (ALE). ALE processes are generally known to involve the sequential removal of thin layers through one or more self-limiting reactions. For example, ALE typically refers to techniques that can etch with atomic precision, i.e., by removing material one or a few monolayers at a time. Generally, ALE processes rely on chemical modification of the surface to be etched and the subsequent selective removal of the modified layer. Therefore, ALE processes improve performance by separating the etching process into sequential steps of surface modification and removal of the modified surface. Such processes often involve a series of layer modification and etching steps that are repeated multiple times, where the modification step modifies the exposed surface and the etching step selectively removes the modified layer. Thus, in some ALE processes, a series of self-limiting reactions may occur, and this cycle may be carried out repeatedly.

[0004] Various ALE processes are known, including plasma ALE, thermal ALE, and wet ALE. In plasma ALE, a target substrate disposed in a process chamber is exposed to reactive precursors, which adsorb and react with the exposed surface of the target substrate to modify the surface in a surface modification step. The exposed surface of the target substrate is then bombarded with low-energy non-reactive ions (e.g., ions from an inert gas) to remove the surface modification layer in a subsequent etching step. Some plasma ALE processes use periodic pulsing of process gases (e.g., reactive precursor gas(es) and inert gas(es)) in one or more ALE cycles (each ALE cycle consisting of at least one surface modification step and an etching step) to remove material from the surface of the target substrate. In plasma ALE, operating variables (e.g., chamber temperature, chamber pressure, process gas flow rate, process gas type, and / or other operating variables) can be adjusted to control the surface modification and etching process steps. In some cases, plasma ALE processes can be performed at relatively high temperatures and / or pressures. In plasma ALE, the process chamber is often purged after each surface modification step and after each etching step to avoid mixing of the reactive precursors and inert gases in the process chamber, which increases cycle time and reduces throughput.

[0005] In thermal ALE, the modified layer is removed by volatilization when the material is brought from the solid phase to the gas phase. This phase change requires additional latent heat and is limited by the vapor pressure of the modified layer. Thermal energy is used to replace the intermolecular interactions that stabilize the modified layer on the surface. In thermal ALE, high temperatures are often required to remove the modified layer.

[0006] In wet ALE, material is removed from a surface in a cyclic process that utilizes self-limiting and selective reactions. The name "wet ALE" indicates that some, if not all, of the reactions occur in the liquid phase. One advantage of wet ALE over thermal or plasma ALE techniques is that the wet ALE process can be performed at ambient temperature and pressure.

[0007] The wet ALE process begins with a self-limiting surface modification step, which can be achieved by oxidation, reduction, ligand binding, or ligand exchange. Ideally, the modified layer is limited to the top monolayer of material and acts as a passivation layer to prevent further modification reactions. The second step in the wet ALE process is the selective dissolution of the modified layer. The process must dissolve the modified layer without removing the underlying unmodified material. This can be achieved by using a different solvent in the second step than used in the first step, changing the pH, or changing the concentration of other components in the first solvent.

[0008] In wet ALE, a purging step is typically performed between the surface modification and selective dissolution steps by washing the surface modification layer with a purging solution to remove excess reactants. The purpose of the purging step is to ensure that no mixing occurs between the solution used for surface modification and the solution used for dissolution. If these two solutions mix, the mixed solution may modify and dissolve the substrate. Once the solutions mix, the modification reaction is no longer self-limiting, resulting in continuous etching. Continuous etching tends to preferentially etch at grain boundaries, resulting in a rough surface after etching.

[0009] As an atomic layer process, wet ALE tends to be time-consuming. Each reaction must be long enough to reach saturation, and each purge step must be long enough to completely separate the surface modification solution from the dissolving solution. This can result in low throughput for high-volume manufacturing (HVM), making wet ALE an expensive process. Summary of the Invention [Means for solving the problem]

[0010] One advantage of wet ALE over thermal or plasma ALE techniques is that the wet ALE process can be carried out at ambient temperature and pressure. Gas-phase reactants, condensates, sprays, or mists can be used in wet ALE processes while maintaining these advantages, as long as the reactants are delivered near room temperature and ambient pressure. In ALE of metals, oxidation is often used as a surface modification step, and many self-limiting oxidation processes are performed on metal surfaces using reactants at room temperature and ambient pressure.

[0011] As further described herein, the present disclosure provides a hybrid wet ALE process that combines a gas-phase surface modification step with a liquid-phase dissolution step to etch a substrate disposed in a process chamber, thereby avoiding the disadvantages of wet ALE (e.g., low throughput, high cost, etc.) while maintaining the advantages of wet ALE (e.g., self-limiting reaction at near ambient pressure and temperature, smoothing of the surface after etching, digital control of the total etching amount, etc.). In the hybrid ALE process described herein, a gas-phase reactant is used to modify the exposed surface of a material to form a surface-modified layer, and one or more liquid-phase reactants are used to selectively dissolve the surface-modified layer without dissolving the material underneath. Once the surface-modified layer has been selectively dissolved, the substrate may be dried, and the gas-phase surface modification step and the liquid-phase dissolution step may be repeated for one or more ALE cycles until the desired amount of material has been etched.

[0012] In some embodiments, the exposed surface of the material can be sequentially exposed to the gas-phase reactant and the liquid-phase reactant(s). In other embodiments, the exposed surface of the material can be exposed to the liquid-phase reactant(s) while the gas-phase reactant is being supplied to the process chamber. When the liquid-phase reactant is supplied in the presence of the gas-phase reactant, the liquid-phase reactant supplied onto the exposed surface of the material displaces the gas-phase reactant from the exposed surface, preventing further surface modification of the exposed surface. When supplied in this manner, the liquid-phase reactant not only dissolves the surface modification layer but also separates the gas-phase surface modification step from the liquid-phase dissolution step. This reduces the cycle time and improves throughput of the hybrid ALE process described herein compared to other ALE techniques by eliminating the need to perform a purge step between the surface modification step and the dissolution step.

[0013] Cycle time and throughput can be further improved in the hybrid ALE process described herein by performing the vapor-phase surface modification step and the liquid-phase dissolving step in the same process chamber. In one exemplary embodiment, both the vapor-phase surface modification step and the liquid-phase dissolving step can be performed in a spin chamber. In some embodiments, the vapor-phase surface modification step and the liquid-phase dissolving step can be performed in the same process chamber at approximately the same temperature and pressure. In one exemplary embodiment, the vapor-phase surface modification step and the liquid-phase dissolving step can be performed at (or near) ambient room pressure. Performing the vapor-phase surface modification step and the liquid-phase dissolving step in the same process chamber at approximately the same temperature and pressure reduces cycle time and improves throughput of the hybrid ALE process described herein by avoiding unnecessary chamber transitions and temperature / pressure changes.

[0014] The hybrid ALE process described herein can be used to etch a wide variety of materials, including polycrystalline, single-crystalline, and amorphous materials. In some embodiments, the hybrid ALE process described herein can be used to etch polycrystalline materials such as transition metals (e.g., molybdenum (Mo)), and a gas-phase oxidizer (e.g., oxygen (O) or ozone (O)) can be used to oxidize the exposed surface of the transition metal to form a self-limiting oxide layer (e.g., MoO). The oxidation of transition metals such as molybdenum is self-limiting at (or near) room temperature. After the exposed surface of the transition metal is exposed to the gas-phase oxidizer and an oxide layer is formed, a liquid-phase reactant can be delivered onto the substrate to selectively dissolve the oxide layer, thereby removing it without etching the underlying polycrystalline material. Several chemistries can be used to selectively dissolve molybdenum oxide (e.g., MoO) without dissolving metallic Mo, and these are described in detail below.

[0015] Exemplary process conditions (e.g., etch chemistries, temperatures, pressures, etc.) for etching transition metals, and more specifically, for etching molybdenum, using the hybrid ALE processes described herein are provided. However, those skilled in the art will recognize that the disclosed processes are not strictly limited to the exemplary process conditions described herein and can be carried out using a wide variety of process conditions depending on the material being etched. Generally, the hybrid ALE processes described herein may use a minimum pressure that is greater than the vapor pressure of the liquid-phase reactant used to remove and / or dissolve the surface modification layer. However, the temperatures used in the hybrid ALE processes described herein may generally range between the melting point and boiling point of the liquid-phase reactant.

[0016] Thus, in some embodiments of the present disclosure, atmospheric pressure and room temperature gas phase reactants (or condensates, sprays, or mist) can be added to a wet ALE process to form a hybrid ALE process, which improves on other ALE techniques by reducing cycle time and increasing throughput while maintaining the advantages of traditional wet ALE.

[0017] Provided herein is a method for etching a substrate using a hybrid atomic layer etching (ALE) process according to a first embodiment of the present disclosure. In the first embodiment, the method includes receiving a substrate, the substrate having exposed material, and selectively etching the material by performing multiple cycles of the hybrid ALE process, each cycle including: a) performing a gas-phase surface modification step to chemically modify the exposed surface of the material and provide a surface-modified layer, the gas-phase surface modification step including exposing the substrate to a gas-phase reactant to chemically modify the exposed surface of the material; and b) performing a liquid-phase dissolution step to selectively dissolve the surface-modified layer of the material, the liquid-phase dissolution step including supplying one or more liquid-phase reactants onto the surface of the substrate to dissolve the surface-modified layer. In the first embodiment, the one or more liquid-phase reactants are supplied onto the surface of the substrate while the substrate is exposed to the gas-phase reactants. In doing so, one or more liquid phase reactants separate the vapor phase surface modification process from the liquid phase dissolution process by displacing the vapor phase reactants from the surface of the substrate.

[0018] In some embodiments, performing the gas-phase surface modification step a) may include exposing the substrate to a gas-phase oxidizing agent to oxidize the exposed surface of the material and form a self-limiting oxidation layer. In such embodiments, performing the liquid-phase dissolution step b) may include supplying a complexing agent dissolved in a first liquid solvent onto the surface of the substrate, where the complexing agent binds to the self-limiting oxidation layer to form a ligand-metal complex. In addition, performing the liquid-phase dissolution step b) may include supplying a second liquid solvent onto the surface of the substrate to dissolve the ligand-metal complex and remove the self-limiting oxidation layer. In some embodiments, the first liquid solvent and the second liquid solvent may be the same solvent. In other embodiments, the first liquid solvent and the second liquid solvent may be different solvents.

[0019] In some embodiments, each cycle of the hybrid ALE process can further include drying the surface of the substrate after a liquid-phase dissolution step is performed that selectively dissolves the surface-modified layer of the material. For example, drying the surface of the substrate can include spin-drying the substrate to rinse one or more liquid-phase reactants from the surface of the substrate and re-exposing the exposed surface of the material to a gas-phase reactant in a subsequent gas-phase surface-modification step.

[0020] Provided herein is another method for etching a substrate using a hybrid atomic layer etching (ALE) process according to a second embodiment of the present disclosure. In the second embodiment, the method includes receiving a substrate, the substrate having exposed polycrystalline material, and selectively etching the polycrystalline material by performing multiple cycles of the hybrid ALE process, each cycle including: a) chemically modifying an exposed surface of the polycrystalline material to provide a surface-modified layer, the exposed surface being chemically modified by oxidizing the polycrystalline material using a gas-phase oxidizing agent; b) attaching a complexing agent to the surface-modified layer of the polycrystalline material to provide a complexed-type surface-modified layer; and c) selectively removing the complexed-type surface-modified layer of the polycrystalline material by exposing the complexed-type surface-modified layer to a liquid solvent, the liquid solvent dissolving the complexed-type surface-modified layer without dissolving the polycrystalline material underlying the complexed-type surface-modified layer. In some embodiments, steps a) through c) may be repeated at least one time.

[0021] Provided herein is yet another method for etching a substrate using a hybrid atomic layer etching (ALE) process according to a third embodiment of the present disclosure. In the third embodiment, the method includes receiving a substrate, the substrate having exposed molybdenum (Mo) metal, and selectively etching the Mo metal by performing multiple cycles of the hybrid ALE process, each cycle including: a) chemically modifying the exposed surface of the Mo metal to provide a surface-modified layer, the exposed surface being chemically modified by oxidation of the Mo metal using a gas-phase oxidizing agent including ozone; b) binding a complexing agent to the Mo metal surface-modified layer to provide a complex-bonded surface-modified layer; and c) selectively removing the complex-bonded surface-modified layer of the Mo metal by exposing the complex-bonded surface-modified layer to a liquid solvent, the liquid solvent dissolving the complex-bonded surface-modified layer without dissolving the Mo metal underlying the complex-bonded surface-modified layer. In some embodiments, steps a) through c) may be repeated at least one time.

[0022] In the methods disclosed in the second and third embodiments, the order and / or timing of steps a) through c) performed in each cycle of the hybrid ALE process may vary. In one embodiment, for example, steps b) and c) may be performed consecutively without overlapping in time in each cycle of the hybrid ALE process. In such an embodiment, the complexing agent may be dissolved in a first liquid solvent that is different from the liquid solvent used to dissolve the complex-bonded surface-modified layer, and the complex-bonded surface-modified layer may be insoluble in the first liquid solvent but soluble in the liquid solvent.

[0023] In other embodiments, two or more of steps a) through c) may be combined in each cycle of the hybrid ALE process. For example, steps b) and c) may be performed with at least partial temporal overlap in each cycle of the hybrid ALE process. In such embodiments, the liquid solvent may include a complexing agent, and the complex-bonded surface-modified layer may be soluble in the liquid solvent.

[0024] In some embodiments, the methods disclosed in the second and third embodiments may further include: d) rinsing the substrate to remove excess liquid solvent and unbound complexing agent; and e) drying the substrate using a gas flow, a spin-drying process, and / or a desiccant. In some embodiments, steps a) through e) may be repeated at least one time.

[0025] The methods disclosed herein can be used to etch a wide variety of materials, including polycrystalline, single-crystalline, and amorphous materials. In some embodiments, the methods disclosed herein can be used to etch polycrystalline metallic materials, such as transition metals. Examples of transition metals that can be etched using the methods disclosed herein include, but are not limited to, molybdenum (Mo), tungsten (W), vanadium (V), niobium (Nb), tantalum (Ta), and chromium (Cr).

[0026] A more complete understanding of the present invention and its advantages can be obtained by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals indicate like features, and in which: It should be noted, however, that the accompanying drawings depict only exemplary embodiments of the disclosed concepts and are therefore not to be considered limiting in scope, as the disclosed concepts may also be susceptible to other equally effective embodiments. [Brief explanation of the drawings]

[0027] [Figure 1] 1 illustrates an example of a cyclic hybrid atomic layer etching (ALE) process according to the present disclosure. [Figure 2A] 1 is a graph showing exemplary etching amounts (shown in nanometers (nm)) that can be achieved over time (shown in minutes (min)) when attempting to etch a molybdenum (Mo) surface using (a) UV ozone oxidation alone and (b) a solution of α-benzoin oxime and DMSO. [Figure 2B] 1 is a graph showing exemplary etch depth (nm) as a function of cycle number that can be achieved when a UV ozone oxidation step, an α-benzoin oxime ligand binding (complexation) step, and a DMSO dissolution step are used to etch a Mo surface using the hybrid ALE process disclosed herein. [Figure 3A] FIG. 1 is a block diagram illustrating one embodiment of a processing system capable of etching material on a surface of a substrate using the hybrid ALE process disclosed herein. [Figure 3B] FIG. 3B is an enlarged view of a portion of the substrate shown in FIG. 3A illustrating how the gas-phase surface modification and liquid-phase dissolution steps are divided within the hybrid ALE process disclosed herein. [Figure 4] FIG. 1 is a flow diagram illustrating one embodiment of a method that utilizes the techniques described herein. [Figure 5] FIG. 10 is a flow diagram illustrating another embodiment of a method utilizing the techniques described herein. [Figure 6]FIG. 10 is a flow diagram illustrating yet another embodiment of a method utilizing the techniques described herein. DETAILED DESCRIPTION OF THE INVENTION

[0028] Chemical reactions on a surface can proceed using gas-phase or liquid-phase reactants in contact with the surface. Wet ALE typically relies on reactions between a surface and a liquid-phase reactant, but gas-phase reactants can also be used to deliver reactants to the surface. Sequential reactions can also be achieved by utilizing reactants in different phases, such as a gas-phase reactant followed by a liquid-phase reactant (or vice versa). The present disclosure utilizes these concepts to provide a hybrid ALE process that maintains the advantages of wet ALE while avoiding its drawbacks.

[0029] In the hybrid ALE process described herein, a gas-phase reactant is used to modify the exposed surface of a material to form a surface-modified layer, and a liquid-phase reactant is used to selectively dissolve the surface-modified layer without dissolving the material underneath. Once the surface-modified layer has been selectively dissolved, the substrate may be dried, and the gas-phase surface modification step and the liquid-phase dissolution step may be repeated for one or more ALE cycles until the desired amount of material has been etched.

[0030] In some embodiments, the exposed surface of the material can be sequentially exposed to a gas-phase reactant and a liquid-phase reactant. In other embodiments, the exposed surface of the material can be exposed to a liquid-phase reactant while a gas-phase reactant is being supplied to the process chamber. When a liquid-phase reactant is supplied in the presence of a gas-phase reactant, the liquid-phase reactant supplied onto the exposed surface of the material displaces the gas-phase reactant from the exposed surface, preventing further surface modification of the exposed surface. When supplied in this manner, the liquid-phase reactant not only dissolves the surface modification layer but also separates the gas-phase surface modification step from the liquid-phase dissolution step. This reduces the cycle time and improves throughput of the hybrid ALE process described herein compared to other ALE techniques by eliminating the need to perform a purge step between the surface modification step and the dissolution step.

[0031] Cycle time and throughput can be further improved in the hybrid ALE process described herein by performing the vapor-phase surface modification step and the liquid-phase dissolving step in the same process chamber. In one exemplary embodiment, both the vapor-phase surface modification step and the liquid-phase dissolving step can be performed in a spin chamber. In some embodiments, the vapor-phase surface modification step and the liquid-phase dissolving step can be performed in the same process chamber at approximately the same temperature and pressure. In one exemplary embodiment, the vapor-phase surface modification step and the liquid-phase dissolving step can be performed at (or near) ambient room pressure. Performing the vapor-phase surface modification step and the liquid-phase dissolving step in the same process chamber at approximately the same temperature and pressure reduces cycle time and improves throughput of the hybrid ALE process described herein by avoiding unnecessary chamber transitions and temperature / pressure changes.

[0032] The techniques described herein offer several advantages over other etching techniques. For example, the techniques described herein provide the benefits of ALE, such as precise control of total etching volume, control of surface roughness, and improved wafer-scale uniformity. The techniques described herein also provide various advantages of wet etching, such as simplified etching chambers, self-limiting reactions at or near ambient etching conditions, and reduced surface roughness. Unlike traditional wet ALE processes, which tend to be time-consuming, the techniques described herein provide a hybrid ALE process that improves cycle time and throughput by combining a gas-phase surface modification step with a liquid-phase dissolution step.

[0033] The techniques described herein can be performed on a wide variety of substrates having a wide variety of layers and features formed thereon. In general, the substrate used in the techniques disclosed herein can be any substrate on which it is desirable to etch a material. For example, the substrate can be a semiconductor substrate having one or more semiconductor processing layers formed thereon (all of which together may comprise the substrate). In one embodiment, the substrate can be a substrate that has undergone multiple semiconductor processing steps (all of which are well known in the substrate processing arts) that result in a wide variety of structures and layers. In one embodiment, the substrate can be a semiconductor wafer that includes various structures and layers formed thereon.

[0034] The techniques described herein can be used to etch a wide variety of materials. Such materials include polycrystalline materials, single-crystalline materials, and amorphous materials. In some embodiments, the techniques described herein can be used to etch metallic materials, such as, but not limited to, transition metals and noble metals. In one exemplary embodiment, the material to be etched can be a polycrystalline transition metal, such as molybdenum (Mo). While the techniques described herein are discussed below with reference to etching molybdenum, those skilled in the art will recognize that such examples are illustrative only and that the techniques described herein can be used to etch a wide variety of other materials. For example, the techniques described herein can be used to etch other transition metals, such as, but not limited to, tungsten (W), vanadium (V), niobium (Nb), tantalum (Ta), and chromium (Cr).

[0035] FIG. 1 illustrates an example of a hybrid ALE process according to the present disclosure. More specifically, FIG. 1 illustrates exemplary steps performed in one cycle of a hybrid ALE process. In the process illustrated in FIG. 1, polycrystalline material 105 surrounded by dielectric material 110 is exposed to gas-phase reactants 115 in a surface modification step 100 that modifies the exposed surface of polycrystalline material 105 and forms surface modification layer 120. In some embodiments, the polycrystalline material 105 being etched can be, for example, a transition metal. In one exemplary embodiment, polycrystalline material 105 can include molybdenum (Mo). In some embodiments, gas-phase reactants 115 can be included in an oxygen-containing gas environment. For example, gas-phase reactants 115 can be, for example, a gas-phase oxidizer including oxygen (O), ozone (O), nitrogen dioxide (NO), and / or a halogen gas. When the exposed surface of the polycrystalline material 105 is exposed to an oxygen-containing gas environment, i.e., the gas-phase oxidizing agent contained therein, the exposed surface is oxidized to form a self-limiting oxide layer (e.g., a molybdenum oxide such as MoO) on the unmodified polycrystalline material.

[0036] Oxidation is often used as a surface modification step in ALE. Many oxidizing agents, such as oxygen (O2) and ozone (O3), are readily available at room temperature and atmospheric pressure. These oxidizing agents form self-limiting oxide layers at room temperature on many materials, such as metals. While not strictly limited to this, these metals can include transition metals, and more specifically, polycrystalline transition metals, such as molybdenum (Mo) metal.

[0037] 1, a chemical reaction (e.g., oxidation) occurs on the exposed surface of the polycrystalline material 105 to form a surface modification layer 120 (e.g., a self-limiting oxide layer such as molybdenum oxide). In some cases, the reaction may be fast and self-limiting, i.e., the reaction products may modify one or more monolayers of the exposed surface of the polycrystalline material 105, but may prevent further reaction between the gas-phase reactants 115 and the underlying polycrystalline material 105.

[0038] In some embodiments, the surface modification layer 120 may be exposed to one or more liquid-phase reactants to selectively dissolve the surface modification layer 120. For example, the surface modification layer 120 may be exposed to a complexing agent 125 dissolved in a liquid solvent 135 (e.g., an aqueous or non-aqueous solution) in a complexing step 130. In the complexing step 130, the complexing agent 125 (e.g., a carboxylate-based ligand) binds to the surface modification layer 120 (e.g., a self-limiting oxidation layer) to form a ligand-metal complex 140. In some embodiments, the complexing agent 125 binds to a higher oxidation state of the polycrystalline material 105 (e.g., Mo 6+ ) and react with the ligand dissolved in the liquid solvent 135 to form a ligand-metal complex 140 that is soluble in a subsequent dissolution step 150. However, as described in more detail below, non-selective ligands may also be used to bind to the surface modification layer 120 and form the ligand-metal complex 140.

[0039] After oxidation and complexation, the polycrystalline material 105 is contacted with a liquid solvent 145 in a dissolution step 150 to selectively dissolve the surface modification layer 120 (e.g., MoO3) without dissolving the underlying polycrystalline material 105 (e.g., metallic Mo). This is achieved by one of two different methodologies: reactive dissolution or ligand binding followed by dissolution.

[0040] In reactive dissolution, the ligand is dissolved in a liquid solvent 135 that can dissolve both the ligand and the ligand-metal complex 140 in a dissolution step 150. This allows for ligand binding and dissolution to be achieved using a single solvent 135 / 145. Thus, in reactive dissolution, the ligand binding and dissolution steps at least partially overlap in time.

[0041] In the reactive dissolution method, the surface modification layer 120 (e.g., MoO3) reacts with the ligand in the liquid solvent 135 / 145 to form a soluble ligand-metal complex 140, which dissolves in the liquid solvent 135 / 145 to remove the surface modification layer 120. Any thickness of the surface modification layer 120 (e.g., MoO3) can be removed using this method. Selectivity is achieved by removing the ligand in a higher oxidation state (e.g., MoO3). 6+ ) polycrystalline material 105 but not to polycrystalline material 105 of a lower oxidation state or to unmodified portions of polycrystalline material 105. Because reactive dissolution is not self-limiting, the oxidation step must be self-limiting to keep the overall process self-limiting.

[0042] In the ligand-binding followed by dissolution method, the ligand binding and dissolution steps do not overlap in time. In this method, the ligand is dissolved in a liquid solvent 135 in which the ligand-metal complex 140 is insoluble. The ligand in the liquid solvent 135 reacts with the surface modification layer 120 (e.g., MoO3) to form an insoluble layer of the ligand-metal complex 140. This layer is dissolved in the dissolution step 150 when the surface is washed with a different liquid solvent 145 in which the ligand-metal complex 140 is soluble. In the ligand-binding followed by dissolution method, removal of the surface modification layer 120 (e.g., MoO3) is limited by the ligand packing density on the surface. Ligand binding in the complexation step 130, and therefore dissolution of the ligand-metal complex 140 in the dissolution step 150, are self-limiting.

[0043] Once the surface modification layer 120 is dissolved, the ALE etching cycle may be completed by drying the surface of the substrate in a drying step 160. In one embodiment, the surface of the substrate may be dried in step 160 by supplying a gas flow of air or nitrogen to the substrate. In another embodiment, the surface of the substrate may be dried in step 160 by performing a spin-drying step. In some embodiments, a drying aid (e.g., isopropyl alcohol (IPA) or the like) may be supplied onto the surface of the substrate (not shown in FIG. 1 ) to further aid in drying the substrate before performing the spin-drying step. Once the surface of the substrate is dry, the surface modification step 100, complexing step 130, dissolving step 150, and drying step 160 shown in FIG. 1 may be repeated for one or more ALE cycles until the desired amount of polycrystalline material 105 is removed.

[0044] As mentioned above, in some embodiments, the hybrid ALE cycle shown in Figure 1 can be used for Mo etching. In this etching scheme, oxidation can be achieved by exposing the Mo surface to a gas-phase oxidizing agent, such as ozone. Ozone is a more oxidizing and reactive agent than molecular oxygen, forming a self-limiting oxide that differs from the layer formed upon exposure to air. In particular, exposure to ozone results in the formation of a self-limiting molybdenum trioxide (MoO) layer on the exposed Mo surface. After oxidation, the self-limiting molybdenum trioxide (MoO) layer can be selectively removed by ligand-assisted dissolution in an appropriate solvent.

[0045] One good choice of ligand for the Mo etching process is α-benzoin oxime. The α-benzoin oxime ligand is Mo 6+Because MoO3 selectively binds ions, it reacts with the ligand to form molybdenum α-benzoin oximate (i.e., a ligand-metal complex), but not with metallic molybdenum. This chemical selectivity allows ligand binding and dissolution to be achieved in a single solvent (e.g., dimethyl sulfoxide (DMSO)). By exposing the MoO3 surface layer to a solution of α-benzoin oxime dissolved in DMSO, the MoO3 surface layer is converted to molybdenum α-benzoin oximate, which is then dissolved in DMSO. In this example, the ligand binding and dissolution steps are self-limiting because metallic molybdenum does not react with α-benzoin oxime. For other non-selective ligands, the self-limiting behavior can be maintained by separating the ligand binding and dissolution steps into consecutive steps using different solutions (i.e., different liquid solvents 135 and 145) for each process step.

[0046] The self-limiting and selective behavior of the individual reaction steps described above is illustrated in FIG. 2A. More specifically, FIG. 2A shows a graph 200 illustrating exemplary etching amounts (in nanometers (nm)) that can be achieved with time (in minutes (min)) when attempting to etch a molybdenum (Mo) surface using (a) UV-ozone oxidation alone and (b) a solution of α-benzoin oxime and DMSO. As shown in FIG. 2A, even after 20 minutes of exposure to ozone in a UV ozone cleaner, the Mo surface is not etched. This indicates that the reaction between Mo and ozone is self-limiting at room temperature. Similarly, the Mo surface is not etched with a solution of α-benzoin oxime in DMSO. No etching is observed even after 20 minutes of exposure. This indicates that α-benzoin oxime does not react with the metal or low oxidation states of Mo.

[0047] Figure 2B shows a graph 250 illustrating exemplary etching depth (nm) as a function of cycle number when UV ozone oxidation, α-benzoin oxime ligand binding (complexation), and DMSO dissolution steps are used to etch a Mo surface using the hybrid ALE process disclosed herein. In the example shown in Figure 2B, one ALE cycle consists of placing the Mo sample in a UV ozone cleaner for 1 minute, followed by a 10-second immersion in a 50 mM α-benzoin oxime solution in DMSO. After removing excess DMSO and unbound α-benzoin oxime (complexing agent) with an acetone wash, the sample was dried using compressed air. Alternatively, a different drying gas, such as nitrogen (N), may be used. The thickness of the Mo layer was calculated from four-probe resistivity measurements performed every five cycles. As shown in Figure 2B, etching is essentially linear with cycle number after the first nanometer of etching. Etching was observed for samples exposed to both UV and ozone during the oxidation step, as well as ozone alone. This indicates that ozone, but not UV irradiation, is required for the hybrid ALE process of Mo. Figures 2A and 2B further demonstrate that exposure to either reactant alone does not remove Mo material (Figure 2A), but the cyclic hybrid ALE process shown in Figure 1 and described herein does remove Mo material (Figure 2B).

[0048] The hybrid ALE process, shown in Figure 1, smooths the etched surface. To observe the etched surface, scanning electron microscope (SEM) images were acquired of the as-deposited Mo film and the Mo film etched using the hybrid ALE scheme described above. No pitting or preferential grain boundary etching was observed in the etched samples. In addition, the thickness of the etched sample calculated from four-probe resistivity measurements was observed to be consistent with the thickness measured on the SEM cross section. Etching using the hybrid ALE process described above did not increase the roughness of the Mo film, but particulate contamination (probably from the acetone washing step) was observed.

[0049] The hybrid ALE process described herein can be used to etch a wide variety of materials, including polycrystalline, single-crystalline, and amorphous materials. In some embodiments, the hybrid ALE process described herein may be used to etch polycrystalline materials, such as transition metals (e.g., molybdenum (Mo)), as described above, and a gas-phase oxidizer (e.g., oxygen (O) or ozone (O)) may be used to oxidize the exposed surface of the transition metal to form a self-limiting oxide layer (e.g., MoO). The oxidation of transition metals, such as molybdenum, is self-limiting when carried out at (or near) room temperature. After the exposed surface of the transition metal is exposed to the gas-phase oxidizer and a self-limiting oxide layer is formed, one or more liquid-phase reactants may be supplied onto the surface of the substrate to selectively dissolve the self-limiting oxide layer, thereby removing the self-limiting oxide layer without etching the underlying polycrystalline material. To selectively dissolve molybdenum oxide (e.g., MoO3) without dissolving metallic Mo, several different chemicals can be used, which are described in more detail below.

[0050] In some embodiments, for example, the MoO3 surface layer can be exposed to a ligand (such as α-benzoin oxime) dissolved in a non-aqueous solution (such as DMSO). Exposure to α-benzoin oxime dissolved in DMSO converts the MoO3 surface layer to molybdenum α-benzoin oximate, which is then dissolved in DMSO. However, in addition to DMSO, α-benzoin oxime is also soluble in water, alcohol, acetone, methyl ethyl ketone (MEK), and other ketones. The α-benzoin oxime ligand can be used to convert the MoO3 containing surface layer to molybdenum α-benzoin oximate. 6+It selectively binds to ions to form Mo-α-benzoin oxime complexes, which are soluble in acetone, DMSO, and other ketones but insoluble in alcohols or water. This chemical selectivity allows for ligand binding and dissolution to be achieved in a single solvent, for example, acetone, DMSO, and other ketones. Alternatively, ligand binding and dissolution can be carried out in sequential, non-overlapping steps, for example, using water or alcohols in the first step and acetone, DMSO, and other ketones in the second step.

[0051] Besides α-benzoin oxime, other ligands have been used to 6+ These ligands can selectively bind to Mo to form alternative ligand-metal complexes without binding to metallic molybdenum (Mo) or lower oxidation states of Mo. Examples of such ligands include, but are not limited to, toluenedithiol, cupferron, and 8-hydroxyquinoline. Similar to α-benzoin oxime, these ligands selectively bind to Mo. 6+ Mo selectively binds to the metal to form a ligand-metal complex that is soluble in non-aqueous solutions. For example, the Mo-toluenedithiol complex is soluble in acetates (e.g., ethyl acetate, butyl acetate, and amyl acetate) and carbon tetrachloride. Toluenedithiol is soluble in aqueous solutions and alcohol, but the Mo complex is insoluble. The Mo-cupferron complex is soluble in chloroform, concentrated nitric acid, or concentrated ammonium hydroxide. Cupferron is soluble in neutral aqueous solutions, but the Mo complex is insoluble. The Mo-8-hydroxyquinoline complex is soluble in concentrated mineral acids. 8-hydroxyquinoline is soluble in ethanol, acetone, chloroform, and benzene, but the Mo complex is insoluble. Any of the above-mentioned ligands can be used in the above-mentioned ligand-binding and dissolution methods to selectively dissolve the MoO surface layer.

[0052] Reactive dissolution of the MoO surface layer can also be achieved in aqueous solutions. For example, concentrated hydrochloric acid (HCl) can be used to selectively dissolve molybdenum oxide over metallic Mo. Measured Mo etch rates for 0.1 M, 1 M, 5 M, and 12 M HCl are below typical detection thresholds (e.g., <0.01 nm / min). HCl at these same concentrations dissolves a monolayer of MoO in less than 2 seconds, providing selectivity ratios of over 800:1. In addition to HCl, other mineral acids (such as sulfuric acid) can be used to dissolve molybdenum oxide. In some cases, sulfuric acid (H2SO4) may be preferred over HCl from a materials compatibility perspective. The availability of HCl and sulfuric acid (and other mineral acids) at high purity and low cost, their use in many other semiconductor processes, and their performance in selectively removing MoO3 may make mineral acids one of the preferred aqueous chemicals used for selective dissolution of MoO3 in the hybrid ALE process described herein. Concentrated ammonium hydroxide (NH4OH) can also be used to dissolve molybdenum oxides, but the selectivity to metallic Mo is not as good with concentrated NH4OH as with HCl.

[0053] The use of aqueous chemistries for the selective dissolution of MoO3 offers several advantages. Water-soluble chemistries use inexpensive, commodity chemicals, are environmentally friendly enough, and do not pose the risk of flammability from organic solvents. However, aqueous solutions of ammonium hydroxide (NH4OH) and concentrated mineral acids (such as HCl) react with many different metals. This can raise selectivity concerns for Mo etching when multiple metals are present on the wafer surface. This leads to the advantage of non-aqueous chemistries, namely, that the ligand-metal complex formation can be highly selective between metals. For example, α-benzoin oxime selectively dissolves Mo over most other metals. 6+α-Benzoin oxime is used to separate Mo from solutions containing many other metal ions in quantitative analysis. However, the selectivity benefits of using these ligands come at the cost of additional chemical costs and flammability risks from using organic solvents.

[0054] While the foregoing discussion focuses on etching Mo, those skilled in the art will readily understand how the hybrid ALE process shown in Figure 1 can be used to etch other transition metals. For example, α-benzoin oxime binds not only molybdenum but also other ions. These include ligand-metal complexes of tungsten, palladium, vanadium, niobium, tantalum, and chromium. There is inherent selectivity for other metals that do not bind with α-benzoin oxime. Selectivity for other metals that form complexes with α-benzoin oxime can still be achieved. While α-benzoin oxime binds the transition metals listed above, the ligand-metal complexes formed with such metals have varying solubilities in different solutions. Selectivity is achieved during the dissolution step because molybdenum oximate is soluble in DMSO, while tungsten oximate, for example, is insoluble. However, both molybdenum and tungsten oximate complexes are soluble in chloroform.

[0055] Room temperature processing is a major advantage of wet hybrid ALE over thermal ALE. This advantage is due to the mechanism by which the modified layer is removed. In thermal ALE, the modified layer is removed by volatilization when the material is brought from the solid phase to the gas phase. This phase change requires additional latent heat and is limited by the vapor pressure of the modified layer. Because thermal energy is used to replace the intermolecular interactions that stabilize the modified layer on the surface, high temperatures are often required to remove the modified layer.

[0056] Unlike thermal ALE, in wet hybrid ALE, the modified layer is dissolved in a solution. This process forms a solvation shell around the molecules as they dissolve. The interactions between the solvent and solute replace the intermolecular interactions found in solids. This solvation energy, rather than thermal energy, drives the dissolution. The fundamental difference between the energy required for dissolution and the energy required for vaporization explains why wet hybrid ALE can be performed at room temperature, whereas thermal ALE cannot. Because solvation energy is highly dependent on the solvent species, an appropriate solvent must be selected to dissolve the modified layer in the hybrid ALE process described herein. For surfaces made of multiple materials, the different solvation energies of different components provide another route to selectivity.

[0057] While the hybrid ALE process described herein can be realized using many different process chambers, tools, and equipment, the processing equipment used to perform the hybrid ALE process is preferably capable of operating at or near room temperature and atmospheric pressure. In one exemplary embodiment, the hybrid ALE process described herein can be performed in a spin chamber. When a spin chamber is utilized, liquid-phase reactants are supplied from a nozzle positioned above the substrate and dispersed by the rotational motion of a spin chuck on which the substrate is positioned. Gas-phase reactants (e.g., gas-phase oxidizers such as oxygen or ozone) can also be supplied from a nozzle that can be moved across the substrate surface so that the entire surface receives an equal amount of gas-phase reactant. Alternatively, the gas-phase reactants can be supplied from a gas inlet that introduces the gas-phase reactants into the spin chamber to form an oxygen-containing gas environment. The use of gas-phase reactants requires that the spinner (also called a spin chuck) be housed in an airtight enclosure equipped with an exhaust port and appropriate exhaust purification equipment, such as an ozone depletion module. In some embodiments, the spinner may be housed in an airtight enclosure that contains gas phase reactants at static pressure.

[0058] FIG. 3A illustrates one embodiment of a processing system 300 capable of etching material on a surface of a substrate 330 using the hybrid ALE techniques described herein. As illustrated in FIG. 3A, the processing system 300 includes a process chamber 310, which in some embodiments may be a pressure-controlled chamber. In the embodiment illustrated in FIG. 3A, the process chamber 310 is a spin chamber having a spinner 320 (or spin chuck) configured to spin or rotate at a controlled rate. A substrate 330 is held on the spinner 320 by, for example, electrostatic force or vacuum pressure. In one example, the substrate 330 may be a semiconductor wafer having a material (e.g., a polycrystalline material) formed on or within the substrate 330.

[0059] The processing system 300 shown in FIG. 3A further includes a nozzle 340 positioned above the substrate 330 to deliver a liquid-phase reactant 342 onto the surface of the substrate 330 and a gas inlet 350 to introduce a gas-phase reactant 352 into the process chamber 310. In some embodiments, the polycrystalline material formed on or within the substrate 330 may be a transition metal (e.g., molybdenum (Mo) or the like), and a gas-phase reactant 352, such as a gas-phase oxidizer (e.g., O or O), may be introduced into the process chamber 310 via the gas inlet 350 to form an oxygen-containing gas environment. The oxygen-containing gas environment oxidizes the exposed surface of the transition metal to form a self-limiting oxide layer (e.g., MoO or the like). After the oxide layer is formed, one or more liquid-phase reactants 342 are delivered via the nozzle 340 onto the surface of the substrate 330 to selectively dissolve the oxide layer, thereby removing it without etching the underlying polycrystalline material. Examples of liquid-phase reactants 342 that can be used to selectively bond with and dissolve the oxide layer are discussed in more detail above.

[0060] The liquid-phase reactant(s) 342 may be stored in a chemical delivery system 346, which may include one or more reservoirs for holding various liquid-phase reactant(s) 342 and a chemical injection manifold fluidly coupled to the process chamber 310 via liquid supply lines 344. In operation, the chemical delivery system 346 may selectively apply desired chemicals to the process chamber 310 via the liquid supply lines 344 and nozzles 340 disposed within the process chamber 310. In this manner, the chemical delivery system 346 may be used to deliver the liquid-phase reactant(s) 342 onto the surface of the substrate 330.

[0061] The gas-phase reactant(s) 352 may be stored in a gas supply system 356, which may include one or more reservoirs for holding various gas-phase reactant(s) 352 and a gas injection manifold coupled to the process chamber 310 via gas supply lines 354. In operation, the gas supply system 356 may selectively apply desired gas-phase reactants to the process chamber 310 via the gas supply lines 354 and gas inlets 350 disposed within the process chamber 310. In this manner, the gas supply system 356 may be used to introduce the gas-phase reactants 352 into the process chamber 310.

[0062] Because a gas-phase reactant 352 is used, the process chamber 310 may comprise an airtight enclosure capable of maintaining a static pressure of the gas-phase reactant. The process chamber 310 may further comprise a gas exhaust 370 for removing the gas-phase reactant 352 and a drain 380 for removing the liquid-phase reactant 342 from the process chamber 310. In some embodiments, the gas exhaust 370 may be coupled to a suitable exhaust cleaning device (not shown), such as an ozone depletion module.

[0063] The components of the processing system 300 may be coupled to and controlled by a controller 360, which may be coupled to corresponding memory storage units and a user interface (not shown). Various processing operations may be performed via the user interface, and various process recipes and operations may be stored in the storage unit. Thus, a given substrate 330 may be processed in the process chamber 310 according to a particular recipe. In some embodiments, a given substrate 330 may be processed in the process chamber 310 according to an etch recipe that utilizes the hybrid ALE techniques described herein.

[0064] The controller 360, shown in block diagram form in FIG. 3A, can be implemented in a wide variety of ways. In one example, the controller 360 can be a computer. In another example, the controller 360 can include one or more programmable integrated circuits programmed to provide the functionality described herein. For example, one or more processors (e.g., microprocessors, microcontrollers, central processing units, etc.), programmable logic devices (e.g., complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), etc.), and / or other programmable integrated circuits can be programmed with software or other programming instructions to implement the functionality of a defined plasma process recipe. It is further noted that the software or other programming instructions can be stored on one or more non-transitory computer-readable media (e.g., memory storage devices, flash memory, dynamic random access memory (DRAM), reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs, etc.), and that the software or other programming instructions, when executed by the programmable integrated circuit, cause the programmable integrated circuit to perform the processes, functions, and / or capabilities described herein. Other variations may also be implemented.

[0065] 3A, a controller 360 may be coupled to receive inputs from and provide outputs to various components of the processing system 300. For example, the controller 360 may be coupled to the process chamber 310 to control the temperature and / or pressure therein, to the spinner 320 to control the rotational speed of the spinner 320, to a chemical delivery system 346 to control various liquid-phase reactants 342 delivered onto the substrate 330, and to a gas delivery system 356 to control various vapor-phase reactants 352 introduced into the process chamber 310.

[0066] In some embodiments, the controller 360 can control various components of the processing system 300 according to an etching recipe that utilizes the hybrid ALE technique described herein. For example, the controller 360 can provide various control signals to the gas supply system 356, causing the gas supply system 356 to introduce gas-phase reactants 352 into the process chamber 310 to form a surface modification layer on the substrate 330. Similarly, the controller 360 can provide various control signals to the chemical delivery system 346, causing the chemical delivery system 346 to deliver one or more liquid-phase reactants 342 onto the surface of the substrate 330 to selectively dissolve the surface modification layer without dissolving the material underlying the surface modification layer. Exemplary gas-phase reactants 352 and liquid-phase reactants 342 for modifying the exposed surface of a polycrystalline molybdenum (Mo) material and for selectively dissolving the Mo surface modification layer are discussed above.

[0067] Once the surface modification layer is selectively dissolved, the substrate 330 may be dried, and the vapor-phase surface modification process and the liquid-phase dissolution process may be repeated for one or more ALE cycles until a desired amount of polycrystalline material is etched. In some embodiments, the controller 360 may provide control signals to the spinner 320 and / or the chemical delivery system 346 to dry the substrate 330. In one example, the controller 360 may control the rotational speed of the spinner 320 to dry the substrate 330 in a spin-dry process. In another example, the control signal provided from the controller 360 to the chemical delivery system 346 may cause a desiccant (e.g., isopropyl alcohol) to be provided onto the surface of the substrate 330 to further help dry the substrate before performing the spin-dry process.

[0068] In some embodiments, the gas-phase surface modification step, the liquid-phase dissolving step, and the spin-drying step of the hybrid ALE process described herein may each be performed at approximately the same temperature and pressure in the same process chamber 310. In one exemplary embodiment, the gas-phase surface modification step, the liquid-phase dissolving step, and the spin-drying step may be performed at (or near) ambient pressure and room temperature. Performing the processing steps in the same process chamber at approximately the same temperature and pressure reduces cycle time and improves throughput of the hybrid ALE process described herein by avoiding unnecessary chamber transitions and temperature / pressure changes.

[0069] However, it should be noted that the embodiments described herein are not strictly limited to atmospheric pressure and room temperature, nor are they limited to any particular process chamber. In other embodiments, one or more processing steps of the hybrid ALE process described herein can be carried out in a pressure vessel above atmospheric pressure or at reduced pressure in a vacuum chamber. Liquid-phase reactants can be supplied in these environments as long as the vapor pressure of the liquid is lower than the chamber pressure. In these embodiments, a spinner with a liquid supply nozzle is located in the pressure vessel or vacuum chamber. The temperature of the supplied liquid can be raised to any temperature below its boiling point at the process pressure. Higher liquid temperatures can increase the rate of dissolution.

[0070] In some embodiments of the hybrid ALE process described herein, the substrate 330 may be sequentially exposed to the gas-phase reactant(s) 352 and the liquid-phase reactant(s) 342. However, in other embodiments, the substrate 330 may be exposed to one or more liquid-phase reactants 342 while the gas-phase reactants 352 are being supplied to the process chamber 310. When the liquid-phase reactants 342 are supplied in the presence of the gas-phase reactants 352, the liquid-phase reactants 342 supplied onto the surface of the substrate 330 displace the gas-phase reactants 352 from the surface, preventing further modification of the surface. When supplied in this manner, the liquid-phase reactants 342 not only dissolve the surface modification layer, but also separate the gas-phase surface modification step from the liquid-phase dissolution step. This is shown schematically in FIG. 3B and improves the cycle time and throughput of the hybrid ALE process described herein compared to other ALE techniques by eliminating the need to perform a purge step between the surface modification step and the dissolution step.

[0071] To illustrate the division between the gas-phase surface modification step and the liquid-phase dissolution step, a close-up view of a portion 390 of a substrate 330 is shown in FIG. 3B. In the hybrid ALE process described herein, gas-phase reactant(s) 352 are introduced into the process chamber 310 to form, for example, an oxygen-containing gas environment. The gas-phase reactant(s) 352 react with the exposed surface of the substrate 330 to form a self-limiting surface modification layer 335. Next, one or more liquid-phase reactants 342 are delivered onto the surface of the substrate 330 in the presence of the gas-phase reactants 352 while the spinner 320 is rotating. As the spinner 320 rotates, the liquid-phase reactant(s) 342 spread outward (in the direction shown in FIG. 3B) and dissolve the surface modification layer 335. The liquid-phase reactant(s) 342 prevent the gas-phase reactants 352 from reaching the surface of the substrate 330, thereby dissolving the surface modification layer 335 while preventing the underlying portions of the substrate 330 from being re-oxidized.

[0072] As the liquid-phase reactant(s) 342 spread outward (in the direction shown in FIG. 3B ), the gas-phase reactant(s) 352 are expelled from the surface of the substrate 330. This expulsion occurs because the liquid-phase reactant(s) 342 form a continuous film on the surface, which makes it difficult or substantially prevents the gas-phase reactant(s) 352 from reaching the surface of the substrate 330. For example, the gas-phase reactant 352 must diffuse through the liquid-phase reactant(s) 342 to reach the surface of the substrate 330. However, if the surface modification layer 335 is dissolved by the liquid-phase reactant(s) 342, the liquid-phase reactant(s) 342 may be washed away from the surface of the substrate 330, re-exposing the surface to the gas-phase reactant(s) 352 and forming a new surface modification layer. Exposure to the gas-phase reactant(s) 352 may, in some embodiments, be accomplished by spin-drying the substrate 330. Because the liquid-phase reactant(s) 342 may be washed off the surface of the substrate 330 at a rate faster than the diffusion timescale of the gas-phase reactant(s) 352 into the liquid, repeated supply of the liquid-phase reactant(s) 342 effectively separates the gas-phase surface modification process from the liquid-phase dissolution process.

[0073] The techniques described herein offer several advantages over other etching techniques. For example, the techniques described herein offer the benefits of ALE, such as precise control of total etching volume, control of surface roughness, and improved wafer-scale uniformity. The techniques described herein also offer various advantages of wet etching, such as simplified etching chambers, self-limiting reactions at or near atmospheric and room temperature etching conditions, and reduced surface roughness.

[0074] Unlike conventional wet ALE processes, which tend to be time-consuming, the techniques described herein provide a hybrid ALE process that improves cycle time and throughput by combining a gas-phase surface modification step with a liquid-phase dissolution step. As noted above, cycle time and throughput are improved in the hybrid ALE process described herein by performing the gas-phase surface modification step and the liquid-phase dissolution step in the same process chamber at approximately the same temperature and pressure. In some embodiments, cycle time and throughput are further improved by delivering liquid-phase reactant(s) onto the surface of the substrate in the presence of gas-phase reactant(s), such that the liquid-phase reactant(s) displace the gas-phase reactant(s) from the surface, thereby separating the gas-phase surface modification step from the liquid-phase dissolution step.

[0075] 4-6 illustrate exemplary methods using the hybrid ALE technique described herein. More specifically, FIGS. 4-6 illustrate various embodiments of methods used to provide a hybrid ALE process that maintains the advantages of wet ALE while avoiding its drawbacks by combining a gas-phase surface modification step with a liquid-phase dissolution step to etch a substrate disposed in a process chamber. It should be understood that the embodiments of FIGS. 4-6 are merely exemplary, and that additional methods may utilize the hybrid ALE technique described herein. Furthermore, additional processing steps may be added to the methods illustrated in FIGS. 4-6, as the described processing steps are not intended to be exclusive. Furthermore, the order of steps is not limited to the order shown in the figures, as different orders may occur and / or various steps may be performed in combination or simultaneously.

[0076] FIG. 4 illustrates one embodiment of a method 400 that can be used to etch a substrate using a hybrid atomic layer etching (ALE) process. The method 400 illustrated in FIG. 4 includes receiving a substrate (at step 410), where the substrate has exposed material. Then, at step 420, the method 400 includes selectively etching the material by performing multiple cycles of the hybrid ALE process, each cycle including: a) performing a gas-phase surface modification step to chemically modify the exposed surface of the material and provide a surface-modified layer, where the gas-phase surface modification step includes exposing the substrate to a gas-phase reactant to chemically modify the exposed surface of the material; and b) performing a liquid-phase dissolution step to selectively dissolve the surface-modified layer of the material, where the liquid-phase dissolution step includes delivering one or more liquid-phase reactants onto the surface of the substrate to dissolve the surface-modified layer. In the method 400 illustrated in FIG. 4, one or more liquid-phase reactants are delivered onto the surface of the substrate while the substrate is exposed to the gas-phase reactants. In such methods, one or more liquid phase reactants drive the gas phase reactants away from the surface of the substrate, thereby separating the gas phase surface modification step from the liquid phase dissolution step.

[0077] 5 illustrates another embodiment of a method 500 that can be used to etch a substrate using a hybrid atomic layer etching (ALE) process. The method 500 illustrated in FIG. 5 includes receiving a substrate (at step 510), where the substrate has exposed polycrystalline material. Then, at step 520, the method 500 includes selectively etching the polycrystalline material by performing multiple cycles of the hybrid ALE process, each cycle including: a) chemically modifying an exposed surface of the polycrystalline material to provide a surface-modified layer, where the exposed surface is chemically modified by oxidizing the polycrystalline material using a gas-phase oxidizing agent; b) attaching a complexing agent to the surface-modified layer of the polycrystalline material to provide a complexed-type surface-modified layer; and c) selectively removing the complexed-type surface-modified layer of the polycrystalline material by exposing the complexed-type surface-modified layer to a liquid solvent, where the liquid solvent dissolves the complexed-type surface-modified layer without dissolving the polycrystalline material underlying the complexed-type surface-modified layer.

[0078] 6 illustrates yet another embodiment of a method 600 that may be used to etch a substrate using a hybrid atomic layer etching (ALE) process. The method 600 illustrated in FIG. 6 includes receiving (at step 610) a substrate, the substrate having exposed molybdenum (Mo) metal. Then, in step 620, the method 600 includes selectively etching the Mo metal by performing multiple cycles of a hybrid ALE process, each cycle including: a) chemically modifying an exposed surface of the Mo metal to provide a surface-modified layer, wherein the exposed surface is chemically modified by oxidation of the Mo metal using a gas-phase oxidizing agent comprising ozone; b) binding a complexing agent to the surface-modified layer of the Mo metal to provide a complex-bonded surface-modified layer; and c) selectively removing the complex-bonded surface-modified layer of the Mo metal by exposing the complex-bonded surface-modified layer to a liquid solvent, wherein the liquid solvent dissolves the complex-bonded surface-modified layer without dissolving the Mo metal underlying the complex-bonded surface-modified layer, and wherein b) and c) at least partially overlap in time.

[0079] It should be noted that throughout this specification, references to "one embodiment" or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention, but do not indicate that it is present in all embodiments. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the invention. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. In other embodiments, various additional layers and / or structures may be included and / or described features may be omitted.

[0080] As used herein, the term "substrate" refers to and includes a base material or structure upon which a material is formed. It should be understood that a substrate can include a single material, multiple layers of different materials, one or more layers having regions of different materials or structures therein, etc. These materials can include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate may be a semiconductor substrate, a base semiconductor layer on a supporting structure, a metal electrode, or a semiconductor substrate having one or more layers, structures, or regions formed thereon. The substrate may be a conventional silicon substrate or other bulk substrate including a layer of semiconducting material. As used herein, the term "bulk substrate" refers to and includes not only silicon wafers, but also silicon-on-insulator ("SOI") substrates such as silicon-on-sapphire ("SOS") substrates and silicon-on-glass ("SOG") substrates, epitaxial layers of silicon on a base semiconductor substrate, and other semiconductor or optoelectronic materials such as silicon germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped.

[0081] Systems and methods for processing a substrate are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, and may be, for example, a base substrate structure such as a semiconductor substrate, or a layer on or overlying the base substrate structure, such as a thin film. Thus, the substrate is not intended to be limited to any particular base structure, underlying layer, or overlying layer, patterned or unpatterned, but rather is intended to include any such layer or base structure, and any combination of layers and / or base structures.

[0082] As will be understood by those skilled in the art, various embodiments may be practiced without one or more of the specific details, or with other alternative and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth to provide a thorough understanding of the invention. However, the invention may be practiced without the specific details. Furthermore, it should be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0083] Further modifications and alternative embodiments of the described systems and methods will be apparent to those skilled in the art upon review of this specification. Accordingly, it is understood that the described systems and methods are not limited by these exemplary configurations. It should be understood that the forms of the systems and methods shown and described herein should be construed as exemplary embodiments. Various modifications can be made to the embodiments. Thus, while the hybrid ALE technique is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present disclosure. Accordingly, the specification and drawings should be regarded in an illustrative rather than a restrictive sense, and such modifications are intended to be included within the scope of the present disclosure. Furthermore, any benefits, advantages, or solutions to problems described herein with respect to particular embodiments are not intended to be construed as any or all critical, necessary, or essential features or elements of the appended claims.

Claims

1. 1. A method of etching a substrate using a hybrid atomic layer etching (ALE) process, the method comprising: receiving the substrate, the substrate having exposed material; Selectively etching the material by performing multiple cycles of the hybrid ALE process, each cycle comprising: a) performing a gas-phase surface modification process to chemically modify an exposed surface of the material and provide a self-limiting surface modification layer on the material, the gas-phase surface modification process comprising exposing the substrate to a gas-phase reactant to chemically modify the exposed surface of the material and form the self-limiting surface modification layer on the material via a self-limiting reaction; b) performing a liquid-phase dissolution process to selectively dissolve the self-limiting surface modification layer of the material, the liquid-phase dissolution process comprising providing one or more liquid-phase reactants on the surface of the substrate to dissolve the self-limiting surface modification layer; Including, the one or more liquid phase reactants are delivered onto the surface of the substrate while the substrate is exposed to the gas phase reactants; the one or more liquid-phase reactants displace the gas-phase reactants from the surface of the substrate, thereby separating the gas-phase surface modification step from the liquid-phase dissolution step; Steps a)-b) are repeated one or more times until a desired amount of the material is removed from the substrate. A method comprising:

2. The method of claim 1 , wherein the material comprises a transition metal.

3. 10. The method of claim 1, wherein said performing a gas-phase surface modification step comprises exposing said substrate to a gas-phase oxidizing agent to oxidize said exposed surface of said material and form a self-limiting oxide layer.

4. 4. The method of claim 3, wherein said performing a liquid phase dissolution step comprises providing a complexing agent dissolved in a first liquid solvent onto the surface of the substrate, wherein said complexing agent binds to the self-limiting oxidation layer to form a ligand-metal complex.

5. 5. The method of claim 4, wherein said performing a liquid phase dissolution step comprises supplying a second liquid solvent onto said surface of said substrate to dissolve said ligand-metal complex and remove said self-limiting oxidation layer.

6. The method of claim 5 , wherein the first liquid solvent and the second liquid solvent are the same.

7. 6. The method of claim 5, wherein the first liquid solvent and the second liquid solvent are different solvents.

8. 10. The method of claim 1, wherein each cycle further comprises drying the surface of the substrate after the liquid phase dissolution process is performed to selectively dissolve the self-limiting surface modification layer of the material.

9. 9. The method of claim 8, wherein said drying the surface of the substrate comprises spin-drying the substrate to rinse the one or more liquid-phase reactants from the surface of the substrate and re-exposing the exposed surface of the material to the gas-phase reactants in a subsequent gas-phase surface modification step.

10. 1. A method of etching a substrate using a hybrid atomic layer etching (ALE) process, comprising: receiving the substrate, the substrate having exposed polycrystalline material; Selectively etching the polycrystalline material by performing multiple cycles of the hybrid ALE process, each cycle comprising: a) chemically modifying an exposed surface of the polycrystalline material to provide a surface modification layer, wherein the exposed surface is chemically modified by oxidizing the polycrystalline material using a gas phase oxidizing agent to form a self-limiting oxidation layer on the polycrystalline material via a self-limiting oxidation reaction; b) binding a complexing agent to the self-limiting oxidation layer formed on the polycrystalline material to provide a complex-bonded surface modification layer; c) selectively removing the complex-bonded surface-modified layer of the polycrystalline material by exposing the complex-bonded surface-modified layer to a liquid solvent, the liquid solvent dissolving the complex-bonded surface-modified layer without dissolving the polycrystalline material underlying the complex-bonded surface-modified layer; Including A method comprising:

11. The method of claim 10 , wherein in each cycle, b) and c) are performed with at least partial overlap in time.

12. The method of claim 11 , wherein the liquid solvent comprises the complexing agent, and the complex-bonded surface-modified layer is soluble in the liquid solvent.

13. 11. The method of claim 10, wherein in each cycle, b) and c) are performed consecutively without overlap in time.

14. 14. The method of claim 13, wherein the complexing agent is dissolved in a first liquid solvent different from the liquid solvent used to dissolve the complex-bonded surface-modified layer, and the complex-bonded surface-modified layer is insoluble in the first liquid solvent and soluble in the liquid solvent.

15. The method of claim 10 , wherein the polycrystalline material comprises a transition metal.

16. The method of claim 10, further comprising repeating steps a) to c) at least once until a desired amount of the polycrystalline material is removed from the substrate.

17. 1. A method of etching a substrate using a hybrid atomic layer etching (ALE) process, comprising: receiving the substrate, the substrate having exposed molybdenum (Mo) metal; Selectively etching the Mo metal by performing multiple cycles of the hybrid ALE process, each cycle comprising: a) chemically modifying an exposed surface of the Mo metal to provide a surface modification layer, wherein the exposed surface is chemically modified by oxidizing the Mo metal using a gas phase oxidizing agent comprising ozone to form a self-limiting molybdenum oxide layer on the Mo metal via a self-limiting oxidation reaction; b) bonding a complexing agent to the self-limiting molybdenum oxide layer formed on the Mo metal to provide a complex-bonded surface modification layer; c) selectively removing the complex-bonded surface-modified layer of the Mo metal by exposing the complex-bonded surface-modified layer to a liquid solvent, wherein the liquid solvent dissolves the complex-bonded surface-modified layer without dissolving the Mo metal underlying the complex-bonded surface-modified layer, and b) and c) at least partially overlap in time; Including A method comprising:

18. The method of claim 17, further comprising repeating steps a) to c) at least once until a desired amount of the Mo metal is removed from the substrate.

19. The method of claim 17 , wherein the liquid solvent comprises the complexing agent, and the complex-bonded surface-modified layer is soluble in the liquid solvent.

20. d) washing the substrate to remove excess liquid solvent and unbound complexing agent; e) drying the substrate using a gas flow, a spin-dry process, and / or a desiccant; 20. The method of claim 17, further comprising:

21. The method of claim 20, further comprising repeating steps a) through e) at least once until a desired amount of the Mo metal is removed from the substrate.

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