Method of Non-Isothermal Wet Atomic Layer Etching

Abstract

The present disclosure provides a non-isothermal wet atomic layer etching (ALE) process for etching polycrystalline materials such as metals, metal oxides, and silicon-based materials formed on a substrate. More specifically, the present disclosure provides various embodiments of a method for individually optimizing the reaction temperature utilized within the individual processing steps of a wet ALE process by utilizing the thermal cycle in the wet ALE process. Similar to conventional wet ALE processes, the wet ALE process described herein is a cyclic process that includes multiple cycles of surface modification and dissolution steps. However, unlike conventional wet ALE processes, the wet ALE process described herein is a non-isothermal process that performs the surface modification and dissolution steps at different temperatures. This allows the surface modification and dissolution reactions to be optimized independently.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of the filing date and priority of U.S. Patent Application No. 17 / 835,065, filed on June 8, 2022. The above - mentioned application is a Continuation - in - Part (CIP) of U.S. Patent Application No. 17 / 674,579, titled "Methods for Wet Atomic Layer Etching of Ruthenium", filed on February 17, 2022, which claims the priority of U.S. Provisional Patent Application No. 63 / 257,226, titled "METHOD FOR WET ATOMIC LAYER ETCHING OF RUTHENIUM", filed on October 19, 2021, and the entire disclosure of which is hereby expressly incorporated by reference herein.

[0002] This application is related to U.S. Patent Application No. 17 / 725,072, titled "Methods for Wet Atomic Layer Etching of Ruthenium", filed on April 20, 2022, by the same owner and having the same filing date, and the entire disclosure of which is hereby expressly incorporated by reference herein.

[0003] The present disclosure relates to the manufacture of semiconductor devices, and more specifically, to the removal and etching of polycrystalline materials, such as metals, formed on a substrate. More specifically, the present disclosure relates to the process of wet atomic layer etching (ALE) of polycrystalline materials.

Background Art

[0004] During normal semiconductor manufacturing, various metals formed on a substrate can be removed by patterned etching, chemical mechanical polishing, and other techniques. Various techniques for etching layers on a substrate are known, including plasma-based or vapor-phase etching (referred to as dry etching) and liquid-based etching (referred to as wet etching). Wet etching generally involves dispensing a chemical solution over the surface of the substrate or immersing the substrate in a chemical solution. The chemical solution often contains a solvent, a chemical designed to react with the material on the substrate surface, and a chemical to facilitate the dissolution of the reaction products. When the substrate surface is exposed to the etchant, material is removed from the substrate. By controlling the composition and temperature of the etchant, the etching rate, specificity, and residual material on the substrate surface after etching can be controlled.

[0005] Both thermodynamics and kinetics play a role in the preparation of the etchant. For etching to be successful, the desired reaction needs to be favorable both thermodynamically and kinetically. When etching polycrystalline materials, the requirements for success are much more stringent. In the case of these materials, regardless of the crystallite form or environment, it is desirable for the removal rates for each individual crystallite face and grain boundary geometry to be substantially the same. In the interfacial quality and electrical properties of nanoscale features, surface roughness plays an important role. When etching nanoscale polycrystalline materials, if the etching rate at grain boundaries is different compared to different crystal faces, it causes roughening of the surface during etching. Furthermore, the material removal rate should be uniform at both the macroscopic and microscopic levels and occur at a rate compatible with mass production. Macroscopic uniformity can be addressed by careful operation, but microscopic uniformity depends on the chemical phenomena of the etching itself.

[0006] As the geometry of substrate structures continues to shrink and the types of structures evolve, the challenges of substrate etching are increasing. One technique that has been used to address these challenges is atomic layer etching (ALE). ALE is a process of continuously removing thin layers through one or more self-limiting reactions. For example, ALE typically refers to a technique that can etch with atomic precision, i.e., removing one or a few monolayers of material at a time. Generally, the ALE process relies on the chemical modification of the surface to be etched and the subsequent selective removal of the modified surface layer. Therefore, the ALE process improves performance by separating the etching process into successive steps of surface modification and selective removal of the modified surface. In some embodiments, the ALE process may include a plurality of cyclic series of surface modification and etching steps, where the layer modification step modifies the exposed surface and the etching step selectively removes the modified surface layer. In such a process, a series of self-limiting reactions can occur, and the cycle can be repeatedly executed until the desired or specified etching amount is achieved. In other embodiments, the ALE process may use only one cycle.

[0007] Various ALE processes, including plasma ALE technology, thermal ALE technology, and wet ALE technology, are known in the art. Similar to all other ALE processes, wet ALE is generally a cyclic process that uses successive self-limiting reactions to chemically modify the exposed surface of a material to form a modified surface layer and selectively remove that modified surface layer from the surface. However, unlike thermal and plasma ALE technologies, the reactions used in wet ALE occur primarily in the liquid phase.

[0008] For example, a wet ALE process can generally be started with a surface modification step, which exposes the material to be etched to a first solution to form a self-limiting modified surface layer. The modified surface layer can be formed by oxidation, reduction, ligand binding, or ligand exchange. Ideally, the modified surface layer is limited to the topmost monolayer of the material and functions as a passivation layer to prevent further progress of the modification reaction. After the modified surface layer is formed, the wet ALE process can then expose the modified surface layer to a second solution in a subsequent dissolution step to selectively dissolve the modified surface layer. Ideally, the dissolution step will selectively dissolve the modified surface layer without removing any of the underlying unmodified material. This selectivity can be achieved by using a solvent different from that used in the surface modification step, changing the pH, or changing the concentration of other components in the first solvent. The wet ALE cycle can be repeated until the desired or specified amount of etching is achieved.

Summary of the Invention

Problems to be Solved by the Invention

[0009] In conventional ALE processes, the surface modification step and the etching step are usually performed at the same temperature, resulting in an isothermal etching process. In conventional wet ALE processes, for example, the surface modification step and the dissolution step are often performed at room temperature (or a temperature close to room temperature). This is usually considered an advantage of wet ALE over other ALE techniques. In plasma and thermal ALE processes, the surface modification and etching steps are often performed at a higher temperature than that commonly used in wet ALE. However, plasma and thermal ALE, like wet ALE, are usually isothermal processes. Since it takes a very long time to adjust and reach thermal equilibrium in each cycle, plasma and thermal ALE processes must be performed isothermally to meet the throughput requirements of mass production.

Means for Solving the Problems

[0010] The present disclosure provides a non-isothermal wet atomic layer etching (ALE) process for etching polycrystalline materials such as metals, metal oxides, and silicon-based materials formed on a substrate. More specifically, the present disclosure provides various embodiments of a method for individually optimizing the reaction temperatures utilized within the individual processing steps of a wet ALE process by utilizing the thermal cycles in the wet ALE process. Similar to conventional wet ALE processes, the wet ALE processes described herein are cyclic processes that include multiple cycles of surface modification and dissolution steps. However, unlike conventional wet ALE processes, the wet ALE processes described herein are non-isothermal processes that perform the surface modification and dissolution steps at different temperatures. This allows for independent optimization of the surface modification and dissolution reactions.

[0011] The non-isothermal wet ALE processes described herein generally include multiple ALE cycles, each ALE cycle including a surface modification step, a first purge step, a dissolution step, and a second purge step, with one or more of these processing steps being performed at different temperatures. In some embodiments, a thermal cycle can be introduced as part of the wet ALE processes described herein by supplying a liquid solution used in one or more of the processing steps at different temperatures. By combining the high heat capacity of the liquid solution with a high convective heat transfer coefficient, the substrate surface can quickly reach thermal equilibrium, thereby allowing the temperature of the substrate to be varied within the time frame of a single ALE cycle.

[0012] In some embodiments, the non-isothermal wet ALE process described herein may supply a surface modification solution to the surface of the substrate at a first temperature and then supply a dissolution solution to the surface of the substrate at a second temperature different from the first temperature. The first temperature and the second temperature may be selected to optimize the reactions occurring during the surface modification step and the dissolution step, respectively. In some embodiments, for example, the surface modification solution may be supplied at a first temperature below room temperature (e.g., 25°C or less). However, to optimize the kinetics of the dissolution reaction, the dissolution solution may be supplied at a second temperature higher than room temperature (e.g., 40°C or more). In the wet ALE process described herein, by utilizing liquid solutions having substantially different temperatures, a cyclic non-isothermal etching process is provided that repeatedly adjusts the reaction temperatures of the surface modification and dissolution steps to optimize the surface modification and dissolution reactions, respectively.

[0013] Between each ALE cycle, a purge solution may be supplied to the substrate surface between the surface modification step and the dissolution step to remove the surface modification solution and the dissolution solution from the substrate surface. In some embodiments, the purge solution may be utilized to preheat or precool the substrate before performing the next processing step. For example, after performing the surface modification step and before performing the next dissolution step, a heated purge solution may be supplied to the surface of the substrate to bring the temperature of the substrate closer to the second temperature (i.e., the desired dissolution reaction temperature). After performing the dissolution step and before performing the next surface modification step, a room temperature (or cooled) purge solution may be supplied to the surface of the substrate to bring the temperature of the substrate closer to the first temperature (i.e., the desired surface modification reaction temperature). By utilizing the temperature and heat capacity of the purge solution, the wet ALE process described herein can rapidly adjust the surface of the substrate to the next process temperature.

[0014] Accordingly, a cyclic non-isothermal wet ALE process for etching polycrystalline materials is disclosed herein. By utilizing a heated (and / or cooled) liquid solution, the cyclic non-isothermal wet ALE process described herein can rapidly adjust the reaction temperature of the surface modification and dissolution steps within the time frame of a single ALE cycle and optimize the surface modification and dissolution reactions individually. The disclosed non-isothermal wet ALE process can change the substrate temperature during processing much more easily and rapidly than can be achieved with the vapor-phase processes used in plasma and thermal ALE. Accordingly, the disclosed non-isothermal wet ALE process is suitable for mass production.

[0015] As described above and further explained herein, the present disclosure provides various embodiments of a method of utilizing thermal cycling in a wet ALE process to individually optimize the reaction temperature utilized within the individual processing steps of the wet ALE process. Of course, the order of the description of the various steps described herein is presented for ease of explanation. Generally, these steps can be performed in any suitable order. Further, although each of the various features, techniques, configurations, etc. described herein may be described in separate places in the present disclosure, each concept is to be construed as capable of being performed independently of one another or in combination with one another. Accordingly, the present invention can be embodied and contemplated in many different ways.

[0016] According to one embodiment, a method for etching a polycrystalline material using a non-isothermal wet atomic layer etching (ALE) process is provided herein. Generally, this method involves receiving a substrate having a polycrystalline material formed thereon with the surface of the polycrystalline material exposed on the surface of the substrate, and supplying a surface modification solution to the surface of the substrate at a first temperature, where the surface modification solution chemically modifies the surface of the polycrystalline material to form a passivation layer on the surface of the polycrystalline material. Next, after forming the passivation layer, the method may include removing the surface modification solution from the surface of the substrate, and supplying a dissolution solution to the surface of the substrate at a second temperature different from the first temperature, where the dissolution solution selectively removes the passivation layer from the surface of the polycrystalline material. Next, the method may include removing the dissolution solution from the surface of the substrate, and repeating the steps of supplying the surface modification solution, removing the surface modification solution, supplying the dissolution solution, and removing the dissolution solution over a number of ALE cycles until a predetermined amount of the polycrystalline material is removed from the substrate.

[0017] As described above, the first temperature and the second temperature may be selected to individually optimize the reactions occurring during the surface modification step and the dissolution step of the non-isothermal wet ALE process described herein. In some embodiments, the surface modification solution may be supplied within a first temperature range having a lower limit set by the freezing point of the surface modification solution and an upper limit of approximately room temperature (e.g., a temperature in the range of 20°C to 25°C). In one example embodiment, the surface modification solution may be supplied at approximately room temperature (e.g., a temperature in the range of 20°C to 25°C). In some embodiments, the dissolution solution may be supplied at a second temperature higher than the first temperature to optimize the kinetics of the dissolution reaction. For example, the dissolution solution may be supplied within a second temperature range having a lower limit of 40°C and an upper limit set by the boiling point of the dissolution etching solution. In one example embodiment, the dissolution solution may be supplied within a second temperature range of 40°C to 337°C.

[0018] In some embodiments, the removal of the surface modification solution may include supplying a first purge solution to the surface of the substrate to remove the surface modification solution from the surface of the substrate before supplying the dissolution solution. In some embodiments, depending on the temperature of the first purge solution, the temperature of the substrate may be near a second temperature before supplying the dissolution solution. In some embodiments, the temperature of the first purge solution may be within 10% of the second temperature.

[0019] In some embodiments, the removal of the dissolution solution may include supplying a second purge solution to the surface of the substrate to remove the dissolution solution from the surface of the substrate before re-supplying the surface modification solution during a subsequent ALE cycle. In some embodiments, depending on the temperature of the second purge solution, the temperature of the substrate may be near a first temperature before re-supplying the surface modification solution during a subsequent ALE cycle. In some embodiments, the temperature of the second purge solution may be within 10% of the first temperature.

[0020] For etching a variety of polycrystalline materials, such as metals, metal oxides, and silicon-based materials, various etching chemistries can be used in surface modification solutions and dissolution solutions. Examples of metals that can be etched using the methods disclosed herein include, but are not limited to, ruthenium (Ru), cobalt (Co), copper (Cu), molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), iridium (Ir), and other transition metals. Examples of metal oxides that can be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (Al2O3), hafnium oxide (HfO2). In some embodiments, the methods disclosed herein can also be used to etch silicon-based materials such as, but not limited to, silicon (Si), silicon oxides (e.g., SiO and SiO2), and silicon nitrides (e.g., Si3N4). Although various examples are provided herein, those skilled in the art will recognize that the methods disclosed herein can be used to etch other metals, metal oxides, and silicon-based materials. Examples of etching chemistries for etching ruthenium and molybdenum using the non-isothermal wet ALE technique disclosed herein are described in more detail below.

[0021] In some embodiments, the methods disclosed herein may be used for etching a ruthenium (Ru) surface. When the methods disclosed herein are utilized for etching a ruthenium surface, the surface modification solution may include a halogenating agent (e.g., a chlorinating agent, a fluorinating agent, or a brominating agent) dissolved in a first solvent, and the dissolution solution may include a ligand dissolved in a second solvent. The halogenating agent included in the surface modification solution chemically modifies the ruthenium surface to form a ruthenium halide passivation layer. The ligand included in the dissolution solution reacts with and binds to the ruthenium halide passivation layer to form soluble species, which dissolve in the second solvent to selectively remove the ruthenium halide passivation layer from the ruthenium surface. In some embodiments, the surface modification solution may be supplied at a first temperature in the range of 20 °C to 25 °C, and the dissolution solution may be supplied at a second temperature in the range of 40 °C to 100 °C.

[0022] In other embodiments, the methods disclosed herein may be used for etching a molybdenum (Mo) surface. When the methods disclosed herein are utilized for etching a molybdenum surface, the surface modification solution may include an oxidizing agent and a first ligand dissolved in a first solvent, and the dissolution solution may include a second ligand dissolved in a second solvent. The oxidizing agent oxidizes the molybdenum surface to form a molybdenum oxide passivation layer. The first ligand included in the surface modification solution reacts with and binds to the molybdenum oxide passivation layer to form a ligand-metal complex that is insoluble in the first solvent. When exposed to the dissolution solution, the first ligand in the ligand-metal complex is exchanged with the second ligand included in the dissolution solution through a ligand exchange process to form soluble species, which dissolve in the second solvent to selectively remove the molybdenum oxide passivation layer from the molybdenum surface. In some embodiments, the surface modification solution may be supplied at a first temperature of 20 °C to 25 °C, and the dissolution solution may be supplied at a second temperature of 40 °C to 337 °C.

[0023] According to another embodiment, a method of etching a substrate using a non-isothermal wet atomic layer etching (ALE) process is provided herein. The method generally includes: a) receiving a substrate having a ruthenium surface exposed; b) exposing the ruthenium surface to a first etching solution containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer, wherein the first etching solution is supplied to the surface of the substrate at a first temperature; c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate; d) exposing the ruthenium halide passivation layer to a second etching solution to selectively remove the ruthenium halide passivation layer without removing the surface of the ruthenium underlying the ruthenium halide passivation layer, wherein the second etching solution is supplied to the surface of the substrate at a second temperature higher than the first temperature; e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate; and f) repeating steps b) to e) for one or more cycles.

[0024] In some embodiments, the first etching solution may be supplied to the surface of the substrate at a first temperature below or approximately equal to room temperature. In one example, the first temperature may be selected from a first temperature range of 20°C to 25°C. Although the examples provided herein are within the range of room temperature, the first temperature is not strictly limited to such a temperature. Instead, it may be in the range between an upper limit of 25°C and a lower limit set by the freezing point of the first etching solution. As described above, in order to optimize the kinetics of the dissolution reaction, the second etching solution may be supplied to the surface of the substrate at a second temperature higher than the first temperature. In one example, the second temperature may be selected from a second temperature range of 40°C to 100°C. However, the second temperature, like the first temperature, is not strictly limited to such a temperature range. It may be higher than room temperature and may include any high temperature lower than the boiling point of the second etching solution. For example, the second temperature may be in the range between a lower limit of 40°C and an upper limit set by the boiling point of the second etching solution.

[0025] In some embodiments, the first etching solution may include a chlorinating agent dissolved in a first solvent. In such embodiments, the chlorinating agent may react with the ruthenium surface to form a ruthenium chloride passivation layer that is insoluble in the first solvent. For example, the chlorinating agent may include trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent may include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon.

[0026] In some embodiments, the second etching solution may include a ligand dissolved in a second solvent. In such embodiments, the ligand may react and bond with the ruthenium chloride passivation layer to form a soluble chemical species that dissolves in the second solvent. For example, the ligand may include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent may include a base.

[0027] Note that this summary section does not specify all embodiments and / or stepwise novel aspects of the present disclosure or the claimed invention. Rather, this summary provides only preliminary considerations regarding points corresponding to novelty over various embodiments and the prior art. For additional details and / or contemplated aspects of the present invention and embodiments, the reader is referred to the detailed description section of the present disclosure and the corresponding figures as further discussed below.

Brief Description of the Drawings

[0028] The present invention and its advantages will be more fully understood by reference to the following description in conjunction with the accompanying drawings, in which like reference numerals indicate like features. However, it should be noted that the accompanying drawings merely illustrate multiple exemplary embodiments of the disclosed concept, and the disclosed concept may also encompass multiple other equally valid embodiments, and thus do not limit the scope of the present invention.

[0029]

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[0030] As described above, conventional methods for etching polycrystalline materials are typically implemented as isothermal processes. For example, most wet ALE processes developed to date are implemented isothermally at room temperature. Plasma and thermal ALE processes can be implemented at temperatures higher than those typically used in wet ALE, but plasma and thermal ALE processes must be implemented isothermally to meet the throughput requirements of high-volume production.

[0031] The inventors recognized that in some ALE processes, advantages can be obtained by performing one of the reaction steps at a higher temperature. For example, the inventors recognized that when etching some materials, the kinetics of dissolution can be improved by increasing the temperature of the dissolution reaction, which may increase the etching rate. However, the inventors noted that a beneficial temperature increase for one reaction may be harmful for a second reaction. Therefore, the inventors of the present application recognized that it is not always desirable to perform the entire process at a high temperature, and developed a non-isothermal etching process that improves upon conventional etching processes that are performed isothermally.

[0032] In the present disclosure, a non-isothermal wet atomic layer etching (ALE) process for etching polycrystalline materials such as metals, metal oxides, and silicon-based materials formed on a substrate is provided. More specifically, the present disclosure provides various embodiments of a method for individually optimizing the reaction temperature utilized within each processing step of a wet ALE process by utilizing the thermal cycle within the wet ALE process. Similar to conventional wet ALE processes, the wet ALE processes described herein are cyclic processes that include multiple cycles of surface modification and dissolution steps. However, unlike conventional wet ALE processes, the wet ALE processes described herein are non-isothermal processes that perform the surface modification and dissolution steps at different temperatures. This allows the surface modification and dissolution reactions to be optimized independently.

[0033] The non-isothermal wet ALE process described in this specification generally includes a plurality of ALE cycles, and each ALE cycle includes a surface modification step, a first purge step, a dissolution step, and a second purge step, and one or more of these processing steps are performed at different temperatures. In some embodiments, a thermal cycle can be introduced as part of the wet ALE process described herein by supplying a liquid solution used in one or more of the processing steps at different temperatures. By combining the high heat capacity of the liquid solution with a high convective heat transfer coefficient, the substrate surface can quickly reach thermal equilibrium, thereby allowing the temperature of the substrate to be changed within the time frame of a single ALE cycle.

[0034] In some embodiments, the non-isothermal wet ALE process described herein may supply a surface modification solution to the surface of the substrate at a first temperature and then supply a dissolution solution to the surface of the substrate at a second temperature different from the first temperature. The first temperature and the second temperature may be selected to optimize the reactions occurring during the surface modification step and the dissolution step, respectively. In some embodiments, for example, the surface modification solution may be supplied at a first temperature below room temperature (e.g., 25 °C or below). However, to optimize the kinetics of the dissolution reaction, the dissolution solution may be supplied at a second temperature higher than room temperature (e.g., 40 °C or above). In the wet ALE process described herein, by utilizing liquid solutions having substantially different temperatures, a cyclic non-isothermal etching process is provided that repeatedly adjusts the reaction temperatures of the surface modification and dissolution steps to optimize the surface modification and dissolution reactions, respectively.

[0035] Between each ALE cycle, a purge solution may be supplied to the substrate surface between the surface modification step and the dissolution step to remove the surface modification solution and the dissolution solution from the substrate surface. In some embodiments, the purge solution may be utilized to preheat or precool the substrate prior to performing the next processing step. For example, after performing the surface modification step and prior to performing the next dissolution step, a heated purge solution may be supplied to the surface of the substrate to bring the temperature of the substrate closer to a second temperature (i.e., the desired dissolution reaction temperature). After performing the dissolution step and prior to performing the next surface modification step, a room temperature (or cooled) purge solution may be supplied to the surface of the substrate to bring the temperature of the substrate closer to a first temperature (i.e., the desired surface modification reaction temperature). By utilizing the temperature and heat capacity of the purge solution, the wet ALE process described herein can rapidly adjust the surface of the substrate to the next process temperature.

[0036] The technology described herein provides a number of advantages over conventional methods by providing a cyclic non-isothermal wet ALE process for the etching of polycrystalline materials such as metals. As described above, in the wet ALE process described herein, a thermal cycle is used to individually optimize the reaction temperatures used in the surface modification and dissolution steps of the wet ALE process. In particular, the thermal cycle is provided by utilizing a heated (and / or cooled) liquid solution. Thereby, within the time frame of a single ALE cycle, the reaction temperatures of the surface modification and dissolution steps are rapidly adjusted and the surface modification and dissolution reactions are individually optimized. The cyclic non-isothermal wet ALE process described herein is suitable for mass production because, unlike some conventional etching processes, the substrate temperature can be rapidly changed during the process.

[0037] The techniques described herein can be used for etching a variety of polycrystalline materials such as metals, metal oxides, and silicon-based materials. Examples of metals that can be etched using the methods disclosed herein include, but are not limited to, ruthenium (Ru), cobalt (Co), copper (Cu), molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), iridium (Ir), and other transition metals. Examples of metal oxides that can be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (Al2O3), hafnium oxide (HfO2). In some embodiments, the methods disclosed herein can also be used for etching silicon-based materials such as, but not limited to, silicon (Si), silicon oxides (e.g., SiO and SiO2), and silicon nitrides (e.g., Si3N4). Although various examples are provided herein, those skilled in the art will recognize that the methods disclosed herein can be used for etching other metals, metal oxides, and silicon-based materials. Examples of etching processes and etching chemistries for etching ruthenium and molybdenum are discussed in more detail below.

[0038] FIG. 1 shows an example of a cyclic non-isothermal wet ALE process according to the present disclosure. More specifically, FIG. 1 shows exemplary steps performed during one cycle of a non-isothermal wet ALE process used for etching a polycrystalline material 105 such as ruthenium (Ru). In the process shown in FIG. 1, the polycrystalline material 105 surrounded by the dielectric material 110 is contacted with a surface modification solution 115 during a surface modification step 100 to modify the exposed surface of the polycrystalline material 105. In one embodiment, the polycrystalline material 105 to be etched may be ruthenium (Ru). When etching ruthenium, the surface modification solution 115 may include a halogenating agent 120. For example, the surface modification solution 115 may include a first solvent containing a chlorinating agent, a fluorinating agent, or a brominating agent.

[0039] As shown in FIG. 1, in the surface modification process 100, a chemical reaction occurs on the exposed surface of the polycrystalline material 105 to form a passivation layer 125 (e.g., a surface layer modified with ruthenium halide, ruthenium oxyhalide, or ruthenium salt). Optionally, the chemical reaction for forming the passivation layer 125 can be fast and self-limiting. In other words, the reaction product can modify one or more monolayers of the exposed surface of the polycrystalline material 105, but may prevent further reaction between the surface modification solution 115 and its substrate surface. Naturally, both the etched polycrystalline material 105 and the passivation layer 125 may not be soluble in the surface modification solution 115. Optionally, the surface modification process 100 shown in FIG. 1 can continue until the surface reaction saturates.

[0040] After the passivation layer 125 is formed, the substrate can be rinsed with a first purge solution 135 to remove excess reactants from the surface of the substrate in the first purge step 130. The purge solution 135 should not react with the reagents present in the passivation layer 125 or the surface modification solution 115. In some embodiments, the first purge solution 135 used in the first purge step 130 can use the same solvent as that previously used in the surface modification process 100. In other embodiments, a different solvent can be used for the first purge solution 135. In some embodiments, the first purge step 130 can be long enough to completely remove all excess reactants from the substrate surface.

[0041] After rinsing, a dissolution step 140 is performed to selectively remove the passivation layer 125 from the base surface of the polycrystalline material 105. In the dissolution step 140, the passivation layer 125 is exposed to a dissolution solution 145 to selectively remove or dissolve the passivation layer 125 without removing the unmodified polycrystalline material 105 underlying the passivation layer 125. The passivation layer 125 must be soluble in the dissolution solution 145, while the unmodified polycrystalline material 105 underlying the passivation layer 125 must be insoluble. By virtue of the solubility of the passivation layer 125, the modified surface layer 125 can be removed through dissolution in the bulk dissolution solution 145. In some embodiments, the dissolution step 140 may continue until the passivation layer 125 is completely dissolved.

[0042] Depending on the surface modification solution 115 used during the surface modification step 100 and / or the passivation layer 125 formed, various different dissolution solutions 145 may be used in the dissolution step. In some embodiments, for example, the dissolution solution 145 may be an aqueous solution containing a ligand 150 that aids in the dissolution process. For example, the dissolution solution 145 may contain a ligand 150 dissolved in an aqueous solution containing a second solvent. The ligand 150 contained within the dissolution solution 145 may react or bind with the passivation layer 125 to form soluble species that dissolve within the second solvent, selectively removing the passivation layer 125 from the base surface of the polycrystalline material 105. In some embodiments, the second solvent contained within the dissolution solution 145 may be different from the first solvent contained within the surface modification solution 115.

[0043] When the passivation layer 125 dissolves, the ALE etching cycle shown in FIG. 1 can be completed by performing a second purge step 160. The second purge step 160 can be performed by rinsing the surface of the substrate with a second purge solution 165 that can be the same as or different from the first purge solution 135. In some embodiments, the second purge solution 165 can use the same solvent (i.e., the second solvent) as that used in the dissolution solution 145. The second purge step 160 can generally continue until the dissolution solution 145 and / or the reactants contained in the dissolution solution 145 are completely removed from the surface of the substrate.

[0044] In wet ALE of ruthenium, it is necessary to form self-limiting passivation on the ruthenium surface. The formation of this passivation layer is achieved by exposing the ruthenium surface to a first etching solution (i.e., the surface modification solution 115) that enables or causes a chemical reaction between the chemical species in the solution and the ruthenium surface. This passivation layer must be insoluble in the solution used for its formation but must be freely soluble in the second etching solution (i.e., the dissolution solution 145) used for its dissolution.

[0045] Many chemicals can be used for the etching of ruthenium. However, due to the polycrystalline nature of ruthenium, pitting corrosion is likely to occur when the etching solution preferentially attacks the grain boundaries. The chemical properties of the etching solution should at least not make the surface rougher than before, and ideally should improve the surface roughness during etching. An acceptable surface morphology can be achieved through the formation of a self-limiting passivation layer that is selectively removed in a cyclic wet ALE process.

[0046] The present disclosure contemplates a wide variety of etching chemistries that can be used in the surface modification solution 115 and the dissolution solution 145 when etching ruthenium using the wet ALE process shown in FIG. 1. Examples of etching chemistries are described in more detail below. Mixing these solutions leads to a continuous etching process, resulting in a loss of etching control, a rough surface after etching, and all of these undermine the advantages of wet ALE. Therefore, the purge steps 130 and 160 are performed in the wet ALE process shown in FIG. 1 to prevent direct contact between the surface modification solution 115 and the dissolution solution 145 on the substrate surface.

[0047] According to one embodiment, the ruthenium surface can be exposed to a surface modification solution 115 containing a first solvent that chemically modifies the ruthenium surface to form a ruthenium chloride passivation layer and contains a chlorinating agent. In an example of the embodiment, ruthenium trichloride (RuCl3) can be used as the passivation layer. For example, the RuCl3 passivation layer can be formed when the ruthenium surface is exposed to a solution of trichloroisocyanuric acid (TCCA) dissolved in ethyl acetate (EA). In this embodiment, TCCA can act as both an oxidizing agent and a chlorine source in the reaction. TCCA chemically oxidizes the ruthenium surface to form a ruthenium trichloride (RuCl3) passivation layer on the ruthenium surface, but no metal oxide is formed in this reaction. This is different from conventional ruthenium etching chemistries that use an oxidizing agent (e.g., a strong oxidant) to form a ruthenium metal oxide passivation layer.

[0048] The chlorine chemistry of ruthenium is very complex. RuCl3 exists in two different crystal phases. α-RuCl3 is almost completely insoluble, while β-RuCl3 is hygroscopic and freely soluble in water, alcohol, and many organic solvents. In addition, in the presence of oxygen or water during chlorination, mixed oxychlorides may be formed. These oxychlorides tend to have high solubility. Based on this chemistry, in some embodiments, the α-phase of RuCl3 is considered the preferred passivation layer herein. However, the formation of the phase is controlled by the reaction conditions.

[0049] The self-limiting passivation layer formed during surface modification step 100 must be removed after its formation for each cycle. To selectively dissolve this passivation layer, a second solution is used in dissolution step 140. When TCCA dissolved in EA is used in surface modification solution 115 to form α-RuCl3 on the ruthenium surface, a pure solvent does not function well in dissolution step 140 because it is difficult to dissolve α-RuCl3. However, using reactive dissolution can effectively remove the ruthenium chloride passivation layer. In reactive dissolution, the ligand 150 dissolved in the second solvent reacts with the surface to form soluble chemical species that dissolve in dissolution solution 145. Many different ligand chemical species can be used for the reactive dissolution of the RuCl3 passivation layer. In one embodiment, ethylenediaminetetraacetic acid (EDTA) can be used as the ligand chemical species for reactive dissolution. EDTA reacts with RuCl3 to form a Ru-EDTA complex soluble in aqueous solution. Since this reaction is base-catalyzed, dissolution solution 145 needs to contain EDTA and a strong base. Mixing the TCCA-containing surface modification solution 115 and the EDTA-containing dissolution solution 145 leads to a continuous etching process, loss of control of etching, and roughening of the surface. Therefore, a solvent rinse step (i.e., purge steps 130 and 160) is necessary to prevent direct contact between the two etching solutions on the ruthenium metal surface.

[0050] In the above etching chemicals, the reactant used for chlorination of the ruthenium surface is TCCA, but many chlorinating agents function in this process. Alternative chlorinating agents include, but are not strictly limited to, oxalyl chloride, thionyl chloride, and N-chlorosuccinimide. This is not a complete list of all possible chlorinating agents that can be used in surface modification step 100. In addition, other ruthenium halides can also be used as the passivation layer. For example, in addition to RuCl3, ruthenium fluoride and ruthenium bromide can be used respectively. These ruthenium halides can be formed using fluorinating agents or brominating agents such as, but not limited to, 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate, N-fluorobenzenesulfonimide, N-bromosuccinimide, or dibromoisocyanuric acid.

[0051] In the above etching chemistry, the first solvent used in the surface modification solution 115 for the chlorination reaction is EA. However, other solvents such as acetone, acetonitrile, and chlorocarbons can also be used. Again, this is not a complete list of solvents that can be used in surface modification step 100.

[0052] In the above etching chemical, the dissolution solution 145 is an aqueous solution of EDTA as the ligand 150 and tetramethylammonium hydroxide ((CH3)4NOH) as the base. Alternative ligands for dissolution include, but are not limited to, iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), and acetylacetone (ACAC). EDTA, IDA, and DTPA can be used in aqueous solutions, and ACAC can be used in aqueous solutions, ethanol, dimethyl sulfoxide (DMSO), or other organic solvents. Any strong base can be used in the dissolution solution 145. Since it is only necessary to deprotonate the ligand 150 to enable binding to the ruthenium surface, a base such as potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium hydroxide (NH4OH), tetramethylammonium hydroxide (CH3)4NOH), or any other strong base can be used in the dissolution solution 145.

[0053] The above ruthenium wet ALE process shown in FIG. 1 forms a self-limiting ruthenium chloride (RuCl3) passivation layer using a trichloroisocyanuric acid (TCCA) solution in ethyl acetate (EA). The ruthenium chloride passivation layer is then dissolved in an aqueous solution of ethylenediaminetetraacetic acid (EDTA) at high pH. The dissolution occurs through a ligand exchange process in which EDTA replaces the chloride as a ligand around the ruthenium metal center. Although this dissolution process is slow at room temperature, the kinetics can be improved by dissolving the ruthenium chloride passivation layer at high temperature. In some embodiments, as shown in FIG. 2, by performing the dissolution at 100° C., the amount of etching per cycle can be increased.

[0054] The etching experiments were carried out on coupons cut from 300 mm silicon wafers with chemical vapor deposition (CVD) ruthenium of various thicknesses deposited on one side. The etching recipe used for ruthenium etching included multiple wet ALE cycles, and each cycle included a 1-minute immersion in 5% TCC dissolved in EA, followed by a rinse with EA, a 30-second immersion in 50 mM EDTA and 1 M KOH aqueous solution in H2O (or deionized water), a rinse with 1 M KOH (or a rinse with deionized water) and a rinse with isopropyl alcohol (IPA) and blow drying. The wet ALE process was repeated over several ALE cycles under different process conditions: hot water dissolution, room temperature (RT) reactive dissolution, and thermal reactive dissolution. The thermal dissolution was carried out at 100 °C.

[0055] The total etching amount (nm) as a function of the number of cycles for the various etching conditions described above is shown in graph 200 shown in Figure 2. By reactive dissolution at room temperature (RT), an etching rate of 0.07 nm / cycle is obtained. This is much smaller than a complete monolayer of ruthenium, indicating that the dissolution rate may be slow at room temperature. When the dissolution solution is heated, the etching amount per cycle increases significantly (e.g., 0.26 nm / cycle), and it is confirmed that the dissolution reaction is kinetically limited. The etching rate decreases with the number of cycles and finally stops when the experiment is carried out using deionized water for dissolution instead of the solution of EDTA and KOH. This behavior can be explained when the passivation layer contains a mixture of α-RuCl3, β-RuCl3 and various ruthenium oxychlorides (RuO x Cl y ). β-RuCl3 and RuO x Cl y are water-soluble, but α-RuCl3 remains on the surface. The amount of α-RuCl3 on the surface increases with each cycle until the entire surface is passivated with insoluble α-RuCl3, and etching can no longer continue. This behavior indicates that the ligand 150 in the dissolution solution 145 is beneficial for the etching operation without problems.

[0056] As shown in FIG. 2, by heating the dissolution solution 145 to a high temperature exceeding room temperature, the dissolution reaction can be optimized and the etching rate can be increased (for example, from 0.07 nm / cycle to 0.26 nm / cycle). The experimental results shown in FIG. 2 were obtained by heating the dissolution solution 145 to 100° C., but the dissolution solution 145 may be heated to any temperature that optimizes the dissolution reaction and / or produces a desirable etching rate within a range that does not exceed the boiling point of the dissolution solution 145. When using an aqueous solution, the temperature of the dissolution solution 145 is limited to 100° C. (the boiling point of water). However, when using a non-aqueous solution, the maximum temperature of the dissolution solution 145 can be quite high. For example, when etching ruthenium using a ligand dissolved in DMSO, the maximum temperature of the dissolution solution 145 can be limited to 190° C. (the boiling point of DMSO). Other temperatures may be used for the dissolution solution 145 depending on the polycrystalline material to be etched and the etching chemistry utilized within the dissolution solution 145. Regardless of the specific etching chemistry used, the amount of etching per cycle is expected to increase monotonically with increasing temperature until the entire passivation layer 125 is removed or the boiling point of the solvent is reached.

[0057] Increasing the temperature of the dissolution solution 145 is beneficial for the dissolution reaction, but in the surface modification process, an increase in temperature may not be desirable. In some cases, the etching chemicals used in the surface modification solution 115 need to be carried out at a substantially low temperature in the surface modification process 100. For example, ethyl acetate (EA) boils at 77 °C. When EA is used in the surface modification solution 115, the surface modification solution 115 must be supplied to the substrate at a temperature lower than the boiling point of EA. Otherwise, the solute may precipitate on the surface due to the evaporation of the solvent. In some embodiments, the surface modification solution 115 shown in FIG. 1 may be supplied to the substrate at room temperature (e.g., a temperature in the range of 20 °C to 25 °C) (or at a temperature close to room temperature). Depending on the polycrystalline material to be etched and the etching chemicals, other temperatures may be used for the surface modification solution 115. In some embodiments, the surface modification solution 115 may be supplied to the substrate at a temperature below room temperature. For example, the surface modification solution 115 may be supplied to the substrate within a temperature range having a lower limit set by the freezing point of the surface modification solution 115 and an upper limit of 25 °C.

[0058] The data shown in FIG. 2 were collected using a wet ALE cycle in which the chlorination step was carried out at room temperature and the dissolution step was carried out at 100 °C. In this case, the desired reaction temperature for the dissolution of the RuCl3 passivation layer is higher than the boiling point of ethyl acetate. Therefore, the wet ALE cycle must be carried out non-isothermally or the etching rate must be reduced by lowering the temperature of the dissolution step. In some cases, it may be beneficial to carry out the chlorination step at room temperature. For example, the volatilization of ethyl acetate at high temperatures can lead to the precipitation of TCCA on the substrate surface during processing, and when the solid TCCA remaining on the surface is mixed with the ligand exchange aqueous solution, it can lead to uncontrollable etching. For these reasons, ruthenium wet ALE benefits from being carried out as a non-isothermal process.

[0059] In a preferred embodiment of the present disclosure, the wet ALE process shown in FIG. 1 is implemented as a non-isothermal process. As described above and as shown in FIG. 1, the wet ALE process described herein may generally include a plurality of ALE cycles, and each ALE cycle includes a surface modification step 100, a first purge step 130, a dissolution step 140, and a second purge step 160. In the present disclosure, one or more of these processing steps 100, 130, 140, 160 may be performed at different temperatures.

[0060] In the present disclosure, a thermal cycle is introduced as part of the wet ALE process shown in FIG. 1 by supplying a liquid solution used in one or more of the processing steps 100, 130, 140, 160 at different temperatures. By combining the high heat capacity of the liquid solution with a high convective heat transfer coefficient, the substrate surface can quickly reach thermal equilibrium, thereby allowing the temperature of the substrate to be changed within the time frame of a single ALE cycle.

[0061] In some embodiments, the wet ALE process shown in FIG. 1 may supply a surface modification solution 115 to the surface of the substrate at a first temperature (T1) and a dissolution solution 145 to the surface of the substrate at a second temperature (T2) different from the first temperature as shown in graph 300 shown in FIG. 3. The first and second temperatures may be selected to optimize the reactions occurring during the surface modification step 100 and the dissolution step 140, respectively. In some embodiments, for example, the surface modification solution may be supplied at approximately room temperature (e.g., a temperature in the range of 20°C to 25°C). However, the dissolution solution may be supplied at a high temperature (e.g., a temperature in the range of 40°C to 190°C) to optimize the kinetics of the dissolution reaction. By utilizing liquid solutions having substantially different temperatures, the wet ALE process shown in FIG. 1 provides a cyclic non-isothermal etching process that repeatedly adjusts the reaction temperatures of the surface modification step and the dissolution step to independently optimize the surface modification and dissolution reactions.

[0062] As shown in FIG. 1, purge solutions 135 and 165 may be supplied to the surface of the substrate between the surface modification step 100 and the dissolution step 140 to remove the surface modification solution and the dissolution solution from the surface of the substrate. In some embodiments, the purge solutions 135 and 165 may be used to preheat or precool the substrate before performing the next processing step. For example, after performing the surface modification step 100, the heated purge solution 135 may be supplied onto the surface of the substrate. The heated purge solution may be used to adjust or approach the temperature of the substrate to a second temperature (T2, i.e., the desired dissolution reaction temperature) before performing the next dissolution step, as shown in FIG. 3. After the dissolution step 140 is executed, the room temperature (or cooled) purge solution 165 may be supplied to the surface of the substrate. The room temperature (or cooled) purge solution 165 may be used to adjust or approach the temperature of the substrate to a first temperature (T1, i.e., the desired surface modification reaction temperature) before performing the next surface modification step. By using the temperature and heat capacity of the purge solutions 135 and 165, the wet ALE process described herein can rapidly adjust the surface of the substrate to the next process temperature.

[0063] According to one embodiment, the cyclic non-isothermal wet ALE process for etching the ruthenium surface shown in FIG. 1 is as follows: a) exposing the ruthenium surface to a surface modification solution 115 containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer 125, where the surface modification solution 115 is supplied to the surface of the substrate at a first temperature, a surface modification step 100; b) rinsing the substrate with a first purge solution 135 to remove the surface modification solution 115 from the surface of the substrate, a first purge step 130; c) exposing the ruthenium halide passivation layer to a dissolution solution 145 to selectively remove the ruthenium halide passivation layer 125 without removing the ruthenium surface underlying the ruthenium halide passivation layer 125, where a second etching solution is supplied to the surface of the substrate at a second temperature different from the first temperature, a dissolution step 140, d) the substrate may be rinsed with a second purge solution 165 and a second purge step 160 in which the dissolution solution 145 is removed from the surface of the substrate. In some embodiments, steps a)-d) may be repeated in one or more ALE cycles until a desired amount of ruthenium material is removed. It is recognized that the cyclic non-isothermal wet ALE process shown in FIG. 1 is merely an example of a non-isothermal etching process that can be used to etch polycrystalline materials 105 such as ruthenium.

[0064] The ruthenium wet ALE process described above and shown in FIG. 1 relies on both the surface modification and the dissolution reaction being self-limiting. Self-limiting means that only a limited thickness of ruthenium on the surface is altered or removed, regardless of the length of time a given etching solution is in contact with the ruthenium surface. The self-limiting reaction can be limited to one or more monolayers of the reaction or a partial monolayer of the reaction.

[0065] The ruthenium wet ALE process described above and shown in FIG. 1 can be implemented using various techniques. For example, the ruthenium wet ALE process disclosed above can be performed by immersing a ruthenium sample in a beaker of each etching solution. In this case, the purge can be carried out by rinsing the sample or immersing it in a suitable solvent bath. The ruthenium wet ALE process can also be performed on a spinner. For example, the ruthenium sample can be rotated while the etching solution is dispensed from a nozzle placed on top of the sample. Due to the rotational movement of the sample, the solution is distributed across the surface. After the set exposure time, the nozzle starts dispensing the next solution in the etching recipe. This process continues throughout the etching cycle, and the cycle is repeated as many times as necessary to remove the desired amount of metal. In some embodiments, to assist with temperature control, the solution can also be supplied to the back side of the wafer. Deionized (DI) water can be used for this purpose. For example, hot DI water can be supplied to the back side of the wafer during the dissolution step, and room temperature DI water can be supplied to the back side of the wafer during the surface modification step. For high-volume manufacturing, the dispensing of the etching solution and the rinse can be carried out using conventional tools such as wet etching tools and rinse tools.

[0066] FIG. 4 shows an example of a cyclic non-isothermal wet ALE process according to the present disclosure. More specifically, FIG. 4 shows exemplary steps performed during one cycle of a non-isothermal wet ALE process used for etching a polycrystalline material 405 such as molybdenum (Mo). In the process shown in FIG. 4, the polycrystalline material 405 surrounded by the dielectric material 410 is contacted with the surface modification solution 415 during the surface modification step 400 to modify the exposed surface of the polycrystalline material 405. In one embodiment, the polycrystalline material 405 to be etched is molybdenum (Mo). When etching molybdenum, the surface modification solution 415 can include an oxidizing agent 420 dissolved in a first solvent and a first ligand 425.

[0067] As shown in FIG. 4, the oxidant 420 oxidizes the exposed surface of the polycrystalline material 405 in the surface modification process 400 to form a passivation layer 430 (e.g., a molybdenum oxide passivation layer). Optionally, the chemical reaction to form the passivation layer 430 can be fast and self-limiting. In other words, the reaction product can modify one or more monolayers of the exposed surface of the polycrystalline material 405, but may prevent further reaction between the surface modification solution 415 and its substrate surface. The first ligand 425 contained in the surface modification solution 415 reacts to bind to the passivation layer 430, forming a ligand-metal complex 432 that is insoluble in the first solvent. Optionally, the surface modification process 400 shown in FIG. 4 can continue until the surface reaction saturates.

[0068] After the ligand-metal complex 432 is formed, the substrate can be rinsed with a first purge solution 435 to remove excess reactants from the surface of the substrate in the first purge step 440. The purge solution 435 should not react with the ligand-metal complex 432 or the reagents present in the surface modification solution 415. In some embodiments, the first purge solution 435 used in the first purge step 440 can use the same solvent as that previously used in the surface modification process 400. In other embodiments, a different solvent can be used for the first purge solution 435. In some embodiments, the first purge step 440 can be long enough to completely remove all excess reactants from the substrate surface.

[0069] After rinsing, in dissolution step 450, dissolution solution 445 is supplied to the substrate, and passivation layer 430 is selectively removed from the basal surface of polycrystalline material 105. In one embodiment, dissolution solution 445 may include a second ligand 455 dissolved in a second solvent. When exposed to dissolution solution 445, the first ligand 425 within ligand-metal complex 432 is exchanged with the second ligand 455 contained within dissolution solution 445 by a ligand exchange process, forming a soluble species. This soluble species dissolves within the second solvent and selectively removes passivation layer 430 without removing the unmodified polycrystalline material 105 underlying passivation layer 430. After ligand exchange, passivation layer 430 becomes soluble in dissolution solution 445 and can be removed by dissolution into bulk dissolution solution 445. However, the unmodified polycrystalline material 105 underlying passivation layer 430 must be insoluble in dissolution solution 445. In some embodiments, dissolution step 450 may continue until passivation layer 430 is completely dissolved.

[0070] When passivation layer 430 has dissolved, the ALE etching cycle shown in FIG. 4 can be completed by performing a second purge step 460. Second purge step 460 can be performed by rinsing the surface of the substrate with a second purge solution 465, which may be the same as or different from the first purge solution 435. In some embodiments, second purge solution 465 can use the same solvent (i.e., the first solvent) as that used in surface modification solution 415. Second purge step 460 can generally continue until dissolution solution 445 and / or reactants contained within dissolution solution 445 are completely removed from the surface of the substrate.

[0071] This disclosure contemplates a wide variety of etching chemistries that can be used in the surface modification solution 415 and the dissolution solution 445 when etching molybdenum using the wet ALE process shown in FIG. 4. Examples of etching chemistries are described in more detail below. Mixing these solutions leads to a continuous etching process, resulting in a loss of etching control, a roughened etched surface, all of which undermine the advantages of wet ALE. Therefore, purge steps 440 and 460 are performed in the wet ALE process shown in FIG. 4 to prevent direct contact between the surface modification solution 415 and the dissolution solution 445 on the substrate surface.

[0072] In some embodiments, the surface modification solution 415 used for etching the molybdenum surface may include an oxidizing agent 420 (e.g., hydrogen peroxide (H2O2), ammonium persulfate ((NH4)2S2O8), potassium persulfate (K2S2O8), permanganate salts, cerium (IV) salts, and dissolved gases such as nitrogen dioxide (NO2) and ozone (O3)), and a first ligand 425 (e.g., a carboxylate-based ligand such as oxalic acid, mandelic acid, malic acid, maleic acid, fumaric acid, etc.) dissolved in an organic solvent (e.g., isopropyl alcohol (IPA) or other alcohols, diethyl ether ((C2H5)2O), acetonitrile, dimethyl sulfoxide (C2H6OS), ketones or acetic acid). In one example embodiment, the molybdenum surface may be exposed to a surface modification solution 415 containing H2O2 and oxalic acid dissolved in IPA. In such an embodiment, hydrogen peroxide (H2O2) oxidizes the molybdenum surface to form a passivation layer of molybdenum oxide (MoO3), which then forms a complex with oxalic acid in the surface modification solution 415 to form a ligand-metal complex 432 (e.g., an oxymolybdenum oxalate complex) that is insoluble in the organic solvent.

[0073] In some embodiments, the dissolution solution 445 used for etching the molybdenum surface may contain a second ligand 455 (e.g., ascorbic acid) dissolved in a high-pH aqueous solution (e.g., an aqueous solution of hydrogen chloride (HCl), sulfuric acid (H2SO4), or another strong acid). Oxymolybdenum oxalate is insoluble in HCl water, but ascorbate dissolves. When exposed to the dissolution solution 445 containing ascorbic acid dissolved in HCl water, the oxalic acid of the oxymolybdenum oxalate complex is exchanged with the ascorbic acid contained in the dissolution solution by a ligand exchange mechanism to form oxymolybdenum ascorbate, which dissolves in HCl water and selectively removes the molybdenum oxide passivation layer on the molybdenum surface.

[0074] According to one embodiment, as shown in FIG. 4, the molybdenum wet ALE process described above uses a solution of hydrogen peroxide (H2O2) and oxalic acid in IPA to form a self-limiting oxymolybdenum oxalate passivation layer. The oxymolybdenum oxalate passivation layer is then dissolved in an aqueous solution of a high-concentration acid (e.g., HCl, H2SO4, or other strong acids) containing ascorbic acid. This dissolution is carried out through a ligand exchange process, where ascorbic acid replaces oxalic acid and an oxymolybdenum ascorbate passivation layer is formed. Although this dissolution process is slow at room temperature, the kinetics can be improved by dissolving the oxymolybdenum ascorbate passivation layer at a high temperature. In some embodiments, as shown in FIG. 6, by performing the dissolution at 43° C., the etching amount per cycle can be increased.

[0075] The etching experiments were carried out on coupons cut from 300 mm silicon wafers with chemical vapor deposition (CVD) molybdenum of various thicknesses deposited on one side. The etching recipe used for etching molybdenum included multiple wet ALE cycles, and each cycle included dipping in a solution of 0.1% hydrogen peroxide (H2O2) + 50 mM oxalic acid dissolved in isopropyl alcohol (IPA) for 10 seconds, then rinsing with IPA, dipping in an aqueous solution of 50 M HCl + 100 mM ascorbic acid for 10 seconds, and rinsing with IPA. The wet ALE process was repeated over a number of ALE cycles under different process conditions as shown in FIGS. 5 and 6.

[0076] Graph 500 shown in FIG. 5 shows the total etching amount (nm) as a function of time (minutes) for various surface modification conditions. To obtain the results shown in FIG. 5, molybdenum coupons were immersed in (a) a surface modification solution containing 0.1% H2O2 + 50 mM oxalic acid in IPA at room temperature, (b) a surface modification solution containing 0.1% H2O2 + 50 mM oxalic acid in IPA at 43°C, and (c) a surface modification solution containing 0.05% H2O2 + 50 mM oxalic acid in IPA at 43°C. As shown in FIG. 5, the molybdenum oxalate formation process is self-limiting at room temperature but not at high temperatures (e.g., the continuous etching process reappears at 43°C). Therefore, the maximum temperature of the surface modification step 400 is limited. In some embodiments, the surface modification step 400 may be carried out at room temperature (or below) to avoid the continuous etching process.

[0077] The thermal activation of hydrogen peroxide radical-initiated polymerization depends on the cleavage of peroxide bonds by UV or thermal energy. Graph 500 shown in FIG. 5 further shows that the activity of hydrogen peroxide can be suppressed at lower peroxide concentrations (e.g., 0.05% H2O2). Therefore, in some embodiments, it is possible to carry out the surface modification step 400 at a temperature higher than room temperature.

[0078] Graph 600 shown in FIG. 6 shows the total etching amount (nm) as a function of the number of cycles for various dissolution conditions. To obtain the results shown in FIG. 6, molybdenum coupons were immersed in (a) 5M HCL at room temperature, (b) 5M HCL + 100 mM ascorbic acid at room temperature, and (c) 5M HCL + 100 mM ascorbic acid at 43°C. Graph 600 shown in FIG. 6 shows that oxymolybdenum oxalate is insoluble in HCL, but ascorbate is soluble. When the molybdenum coupon is exposed to a dissolution solution containing 5M HCL + 100 mM ascorbic acid, the oxalic acid in the oxymolybdenum oxalate complex is exchanged with the ascorbic acid contained in the dissolution solution by a ligand exchange mechanism, forming oxymolybdenum ascorbate, which dissolves in the aqueous HCl solution. Therefore, the dissolution of oxymolybdenum oxalate can be achieved by ligand exchange in which oxymolybdenum ascorbate is a soluble species.

[0079] Reactive dissolution in 5M HCl + 100 mM ascorbic acid at room temperature (RT) gives an etching rate of 0.05 nm / cycle. This is much smaller than a complete monolayer of molybdenum, indicating that the dissolution rate may be slow at room temperature. When the dissolution solution is heated (e.g., 43°C), the etching amount per cycle increases (e.g., 0.13 nm / cycle), confirming that the dissolution is kinetically limited. The etching rate decreases with the number of cycles and eventually stops when the experiment is carried out using only HCl for dissolution instead of a solution of HCl and ascorbic acid.

[0080] As shown in FIG. 6, by heating the dissolution solution 445 to a high temperature exceeding room temperature, the dissolution reaction can be optimized and the etching rate can be increased (for example, from 0.05 nm / cycle to 0.13 nm / cycle). The experimental results shown in FIG. 6 were obtained by heating the dissolution solution 445 to 43° C., but the dissolution solution 445 may be heated to any temperature that optimizes the dissolution reaction and / or produces a desirable etching rate within a range not exceeding the boiling point of the dissolution solution 445. In some embodiments, when using a dissolution solution 445 containing 5M HCL + 100 mM ascorbic acid to etch molybdenum, the dissolution solution 445 shown in FIG. 4 may be heated to a temperature in the range of about 40° C. to 107° C. However, when other acidic solutions are used to etch molybdenum, the dissolution solution 445 may be heated to different temperature ranges. For example, when using pure sulfuric acid (H2SO4) to etch molybdenum, the dissolution solution 445 may be heated to a temperature in the range of 40° C. to 337° C., and when using a 1M sulfuric acid solution, the dissolution solution 445 may be heated to a temperature in the range of 40° C. to 100° C. Other temperatures may be used for the dissolution solution 445 depending on the polycrystalline material to be etched and the etching chemistry utilized within the dissolution solution 445. Regardless of the specific etching chemistry used, the amount of etching per cycle is expected to increase monotonically with increasing temperature until the entire passivation layer 430 is removed or the boiling point of the solvent is reached.

[0081] Similar to the ruthenium wet ALE process described above and shown in FIG. 1, the molybdenum wet ALE process shown in FIG. 4 relies on both the surface modification and the dissolution reaction being self-limiting. Self-limiting means that only a limited thickness of molybdenum on the surface is modified or removed regardless of the length of time the given etching solution is in contact with the molybdenum surface. A self-limiting reaction can be limited to a reaction of one or more monolayers or a partial monolayer reaction.

[0082] In some embodiments, the molybdenum wet ALE process described above and shown in FIG. 4 may require oxidation at low temperature and dissolution at high temperature. Therefore, it is necessary to compromise in the optimization of individual reaction steps or to perform the process as a non-isothermal process to enable independent optimization of surface modification and dissolution reactions.

[0083] The molybdenum wet ALE process described above and shown in FIG. 4 can be realized using various techniques. For example, the molybdenum wet ALE process disclosed above can be performed by immersing a molybdenum sample in a beaker of each etching solution. In this case, the purge can be performed by rinsing the sample or immersing it in a suitable solvent bath. The molybdenum wet ALE process can also be performed on a spinner. For example, the molybdenum sample can be rotated while the etching solution is dispensed from a nozzle placed on the sample. Due to the rotational movement of the sample, the solution is distributed across the surface. After the set exposure time, the nozzle starts dispensing the next solution in the etching recipe. This process is continued throughout the etching cycle, and the cycle is repeated as many times as necessary to remove the desired amount of metal. In some embodiments, to assist with temperature control, the solution can also be supplied to the back side of the wafer. Deionized (DI) water can be used for this purpose. For example, hot DI water can be supplied to the back side of the wafer during the dissolution step, and room temperature DI water can be supplied to the back side of the wafer during the surface modification step. For mass production, the dispensing of the etching solution and rinse can be performed using conventional tools such as wet etching tools and rinse tools.

[0084] FIG. 7 shows one embodiment of a processing system 700 that can etch polycrystalline materials such as ruthenium and molybdenum on the surface of a substrate 730 using the techniques described herein. As shown in FIG. 7, the processing system 700 includes a process chamber 710, which in some embodiments can be a pressure control chamber. In the embodiment shown in FIG. 7, the process chamber 710 is a spin chamber having a spinner 720 (or spin chuck), and the spinner 720 (or spin chuck) is configured to spin or rotate at a constant rotational speed. The substrate 730 is held on the spinner 720, for example, by electrostatic force or vacuum pressure. In one example, the substrate 730 can be a semiconductor wafer having a polycrystalline material such as ruthenium or molybdenum formed on or within the substrate 730.

[0085] The processing system 700 shown in FIG. 7 further includes a liquid nozzle 740, which is disposed above the substrate 730 for dispensing various etching solutions 742 onto the substrate surface 730. The etching solution 742 supplied to the surface of the substrate 730 generally includes a surface modification solution for chemically modifying the exposed surface of the polycrystalline material to form a passivation layer (e.g., a ruthenium halide passivation layer or an oxymolybdenum oxalate passivation layer), and a dissolution solution for selectively removing the passivation layer from the surface of the polycrystalline material. A purge solution can also be dispensed onto the surface of the substrate 730 between the surface modification step and the dissolution step to separate the surface modification solution and the dissolution solution. Examples of the surface modification, dissolution, and purge solutions are described above.

[0086] As shown in FIG. 7, the etching solution 742 can be stored in a chemical supply system 746 that may include a chemical injection manifold fluidly coupled to the process chamber 710 via one or more reservoirs and liquid supply lines 744 for holding various etching solutions 742. In operation, the chemical supply system 746 can selectively apply a desired chemical to the process chamber 710 via a liquid supply line 744 and a liquid nozzle 740 disposed within the process chamber 710. Thus, the chemical supply system 746 can be used to dispense the etching solution 742 onto the surface of the substrate 730. The chemical supply system 746, the liquid supply line 744, and / or the liquid nozzle 740 may be configured to supply a heated (and / or cooled) etching solution 742 to the substrate. The process chamber 710 may further include a drain 750 for removing the etching solution 742 from the process chamber 710.

[0087] The components of the processing system 700 can be coupled to and controlled by a controller 760, which can then be coupled to a corresponding memory storage unit and a user interface (not shown). Various processing operations can be performed via the user interface, and various processing recipes and operations can be stored within the memory storage unit. Thus, a given substrate 730 can be processed within the process chamber 710 according to a particular recipe. In some embodiments, a given substrate 730 can be processed within the process chamber 710 according to an etching recipe that utilizes the non-isothermal wet ALE technique described herein.

[0088] In FIG. 7, the controller 760 shown in block diagram form can be implemented in a variety of ways. In one example, the controller 760 can be a computer. In another example, the controller 760 can include one or more programmable integrated circuits programmed to provide the functions 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 functions of a prescribed plasma process recipe. It should be 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 can also be implemented.

[0089] As shown in FIG. 7, the controller 760 can be coupled to various components of the processing system 700 to receive inputs from and supply outputs to the components. For example, the controller 760 can be coupled to the process chamber 710 to control the temperature and / or pressure within the process chamber 710; to the spinner 720 to control the rotational speed of the spinner 720; and to the chemical supply system 746 to control the various etching solutions 742 supplied onto the substrate 730 and / or the temperature of the etching solutions 742. The controller 760 can control other processing system components not shown in FIG. 7, as is known in the art.

[0090] In some embodiments, the controller 760 may control various components of the processing system 700 according to an etching recipe that utilizes the non-isothermal wet ALE technique described herein. For example, the controller 760 may supply various control signals to the chemical supply system 746, and the control signals may cause the chemical supply system 746 to: a) supply a surface modification solution to the surface of the substrate 730 to chemically modify the exposed surface of the polycrystalline material and form a passivation layer (e.g., a ruthenium halide passivation layer or an oxymolybdenum oxalate passivation layer) on the substrate 730; b) rinse the substrate 730 with a first purge solution to remove excess reactants from the surface; c) dispense a dissolution solution onto the surface of the substrate 730 to selectively remove or dissolve the passivation layer; and d) rinse the substrate with a second purge solution to remove the dissolution solution from the surface of the substrate 730. In some embodiments, the controller 760 may supply control signals to the chemical supply system 746 in a periodic manner such that steps a)-d) are repeated over one or more ALE cycles until a desired amount of the polycrystalline material is removed.

[0091] The controller 760 can also supply control signals to other processing system components. In some embodiments, for example, the controller 760 can supply control signals to the spinner 720 and / or the chemical supply system 746 to dry the substrate 730 after the second purge step is performed. In one example, the controller 760 may control the rotation speed of the spinner 720 to dry the substrate 730 in a spin drying process. In another example, the control signal supplied from the controller 760 to the chemical supply system 746 may cause a drying agent (e.g., isopropyl alcohol, etc.) to be dispensed onto the surface of the substrate 730 to further assist in drying the substrate before the spin drying process is performed.

[0092] In some embodiments, the controller 760 can control the temperature of the etching solution 742 supplied to the substrate. The etching solution can be dispensed at various temperatures as long as the vapor pressure of the liquid is lower than the chamber pressure. In these embodiments, a spinner having a liquid dispensing nozzle is disposed within a pressure vessel or vacuum chamber. The temperature of the dispensed liquid can be raised to any temperature below the boiling point at the pressure of the process. In some embodiments, the surface modification solution is supplied to the surface of the substrate 730 at a temperature below room temperature (e.g., 25° C. or less), and the dissolution solution can be supplied to the surface of the substrate 730 at a high temperature (e.g., higher than 40° C. and below the boiling point of the dissolution solution). As described above, a higher liquid temperature can result in a faster dissolution rate. In some embodiments, as shown in FIG. 3, the substrate may be preheated or precooled using a purge solution before performing the next processing step.

[0093] FIGS. 8-9 illustrate an exemplary method that utilizes the non-isothermal wet atomic layer etching (ALE) techniques described herein for etching various polycrystalline materials formed on a substrate. It will be understood that the embodiments of FIGS. 8-9 are merely illustrative, and additional methods may utilize the techniques described herein. Further, since the described processing steps are not intended to be exclusive, additional steps can be added to the method shown in FIGS. 8-9. Moreover, the order of the steps is not limited to that shown in the drawings since different orders may occur and / or various steps may be combined or even performed simultaneously.

[0094] FIG. 8 shows an embodiment of an etching method 800 for a polycrystalline material using a non-isothermal wet atomic layer etching (ALE) process according to the present disclosure. The method 800 shown in FIG. 8 generally includes receiving a substrate on which a polycrystalline material is formed with the surface of the polycrystalline material exposed on the surface of the substrate (step 810), and supplying a surface modification solution onto the surface of the substrate at a first temperature, the surface modification solution chemically modifying the surface of the polycrystalline material to form a passivation layer on the surface of the polycrystalline material (step 820). The passivation layer is self-limiting and insoluble in the surface modification solution. Next, the method 800 may include removing the surface modification solution from the surface of the substrate after forming the passivation layer (step 830), and supplying a dissolution solution onto the surface of the substrate at a second temperature different from the first temperature (step 840). The dissolution solution selectively removes the passivation layer from the surface of the polycrystalline material in step 840. Next, the method 800 may include removing the dissolution solution from the surface of the substrate (step 850), and repeating the steps of supplying the surface modification solution, removing the surface modification solution, supplying the dissolution solution, and removing the dissolution solution over a number of ALE cycles until a predetermined amount of the polycrystalline material is removed from the substrate (step 860).

[0095] When using method 800 shown in FIG. 8, the first temperature and the second temperature can be selected to optimize the reactions occurring during the surface modification step and the dissolution step of the non-isothermal wet ALE process, respectively. In some embodiments, for example, the surface modification solution can be supplied (at step 820) at a first temperature below or approximately equal to room temperature. In one example, the first temperature can be selected from a first temperature range including 20°C and 25°C. However, the first temperature is not strictly limited to such values and can instead be selected from a first temperature range having an upper limit of about 25°C and a lower limit set by the freezing point of the surface modification solution. In some embodiments, the dissolution solution can be supplied (at step 840) at a second temperature higher than the first temperature to optimize the kinetics of the dissolution reaction. For example, the dissolution solution can be supplied at step 840 within a second temperature range having a lower limit of 40°C and an upper limit set by the boiling point of the dissolution solution.

[0096] In some embodiments, the removal of the surface modification solution (step 830) can include supplying a first purge solution onto the surface of the substrate to remove the surface modification solution from the surface of the substrate before the supply of the dissolution solution (step 840). In some embodiments, the temperature of the substrate may be near the second temperature due to the temperature of the first purge solution before the dissolution solution is supplied (step 840). In some embodiments, the temperature of the first purge solution may be within 10% of the second temperature.

[0097] In some embodiments, the removal of the dissolution solution (step 850) can include supplying a second purge solution onto the surface of the substrate to remove the dissolution solution from the surface of the substrate before re-supplying the surface modification solution during a subsequent ALE cycle. In some embodiments, the temperature of the substrate can be near the first temperature before re-supplying the surface modification solution during a subsequent ALE cycle due to the temperature of the second purge solution. In some embodiments, the temperature of the second purge solution may be within 10% of the first temperature.

[0098] When using the method 800 shown in FIG. 8, various etching chemistries may be used in the surface modification and dissolution solution to etch a variety of polycrystalline materials such as metals, metal oxides, and silicon-based materials. Examples of metals that can be etched using the methods disclosed herein include, but are not limited to, ruthenium (Ru), cobalt (Co), copper (Cu), molybdenum (Mo), tungsten (W), gold (Au), platinum (Pt), iridium (Ir), and other transition metals. Examples of metal oxides that can be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (Al2O3), hafnium oxide (HfO2). In some embodiments, the methods disclosed herein can also be used to etch silicon-based materials such as, but not limited to, silicon (Si), silicon oxide (e.g., SiO and SiO2), and silicon nitride (e.g., Si3N4). Although various examples are provided herein, those skilled in the art will recognize that the methods disclosed herein can be used to etch other metals, metal oxides, and silicon-based materials. Examples of etching chemistries for etching ruthenium and molybdenum using the non-isothermal wet ALE techniques disclosed herein are described in more detail below.

[0099] In some embodiments, method 800 shown in FIG. 8 can be used for etching a ruthenium (Ru) surface. When method 800 is utilized for etching a ruthenium surface, the surface modification solution supplied in step 820 includes a halogenating agent (e.g., a chlorinating agent, a fluorinating agent, or a brominating agent) dissolved in a first solvent, and the dissolution solution supplied in step 840 can include a ligand dissolved in a second solvent. The halogenating agent included in the surface modification solution chemically modifies the ruthenium surface to form a ruthenium halide passivation layer. The ligand included in the dissolution solution reacts with and binds to the ruthenium halide passivation layer, forming soluble species that dissolve in the second solvent to selectively remove the ruthenium halide passivation layer from the ruthenium surface. In some embodiments, the surface modification solution can be supplied at a first temperature in the range of 20° C. to 25° C. in step 820. In some embodiments, the dissolution solution can be supplied at an elevated temperature (e.g., a temperature of 40° C. or higher) in step 840 to optimize the kinetics of the dissolution reaction. For example, when a water-soluble dissolution solution is used for etching ruthenium, in step 840, the dissolution solution can be supplied at about 40° C. to 100° C.

[0100] In other embodiments, the method 800 shown in FIG. 8 can be used for etching a molybdenum (Mo) surface. When the method disclosed herein is utilized for etching a molybdenum surface, the surface modification solution supplied in step 820 may include an oxidizing agent and a first ligand dissolved in a first solvent, and the dissolution solution supplied in step 840 may include a second ligand dissolved in a second solvent. The oxidizing agent oxidizes the molybdenum surface to form a molybdenum oxide passivation layer. The first ligand included in the surface modification solution reacts with and binds to the molybdenum oxide passivation layer to form a ligand-metal complex that is insoluble in the first solvent. When the ligand-metal complex is exposed to the dissolution solution in step 840, the first ligand in the ligand-metal complex is exchanged with the second ligand included in the dissolution solution by a ligand exchange process to form a soluble species, and this soluble species is dissolved in the second solvent to selectively remove the molybdenum oxide passivation layer from the molybdenum surface. In some embodiments, the surface modification solution may be supplied at a first temperature in the range of 20°C to 25°C in step 820. In some embodiments, the dissolution solution may be supplied at an elevated temperature (e.g., a temperature of 40°C or higher) in step 840 to optimize the kinetics of the dissolution reaction. For example, the dissolution solution may be supplied at about 40°C to about 337°C in step 840 depending on the acidic solution used for etching molybdenum. However, in other embodiments, the surface modification solution and the dissolution solution may each be supplied at approximately room temperature.

[0101] FIG. 9 shows one embodiment of a method 900 that can be used on a substrate using a non-isothermal wet atomic layer etching (ALE) process according to the present disclosure. The method 900 shown in FIG. 10 generally includes: a) receiving a substrate having a ruthenium surface exposed (step 910); b) exposing the ruthenium surface to a first etching solution containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer, wherein the first etching solution is supplied onto the surface of the substrate at a first temperature (step 920); c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate (step 930); d) exposing the ruthenium halide passivation layer to a second etching solution to selectively remove the ruthenium halide passivation layer without removing the ruthenium surface underlying the ruthenium halide passivation layer, wherein the second etching solution is supplied onto the surface of the substrate at a second temperature higher than the first temperature (step 940); e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate (step 950); and f) repeating steps b) - e) for one or more cycles (step 960).

[0102] In some embodiments, the ruthenium surface can be exposed to the first etching solution (step 920) by supplying the first etching solution onto the surface of the substrate at a first temperature at or near room temperature. For example, the first temperature can be selected from a first temperature range including 20°C to 25°C. In some embodiments, the ruthenium halide passivation layer may be exposed to the second etching solution by supplying the second etching solution onto the surface of the substrate at a second temperature higher than the first temperature (step 940). For example, the second temperature can be selected from a second temperature range including 40°C to 100°C to optimize the kinetics of the dissolution reaction.

[0103] In some embodiments of method 900 shown in FIG. 9, the first etching solution may include a chlorinating agent dissolved in a first solvent. In such embodiments, the chlorinating agent may react with the ruthenium surface to form a ruthenium chloride passivation layer that is insoluble in the first solvent. For example, the chlorinating agent may include trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent may include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon.

[0104] In some embodiments of method 900 shown in FIG. 9, the second etching solution may include a ligand dissolved in a second solvent. In such embodiments, the ligand may react and bind with the ruthenium chloride passivation layer to form a soluble chemical species that dissolves in the second solvent. For example, the ligand may include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent may include a base.

[0105] Note that references throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not mean that they are present in all embodiments. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Further, the 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 the features described may be omitted.

[0106] As used herein, the term "substrate" means and includes a base material or structure on which materials are formed. It will be understood that the substrate may include a single material, multiple layers of different materials, or one or more layers having regions of different materials or different structures inside. These materials may include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate may be a semiconductor substrate, a base semiconductor layer on a support structure, a metal electrode, or a semiconductor substrate having one or more layers, structures or regions formed thereon. The substrate may also be a conventional silicon substrate or other bulk substrate including a layer of a semiconductive material. The term "bulk substrate" as used herein means 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 semiconductors or optoelectronic materials such as silicon germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide, and includes these. The substrate may or may not be doped.

[0107] Systems and methods for processing substrates are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, for example, a base substrate structure such as a semiconductor substrate, or a layer on or covering a 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 upper layer, whether patterned or unpatterned, but rather is intended to include any such layer or base structure, as well as any combination of layers and / or base structures.

[0108] Those skilled in the art will understand that 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 details of operations have not been shown or described in order to avoid obscuring aspects of various embodiments of the present invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are described to provide a thorough understanding of the present invention. Nevertheless, the present invention may be practiced without specific details. Further, it should be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0109] Upon review of this specification, further modifications and alternative embodiments of the described systems and methods will be apparent to those skilled in the art. Accordingly, it will be understood that the described systems and methods are not limited by these illustrative configurations. It should be understood that the forms of the systems and methods illustrated and described herein are to be construed as illustrative embodiments. Various changes may be made in implementation. Thus, while the ruthenium wet ALE technology is described herein with reference to specific embodiments, various modifications and variations can be made without departing from the scope of the present disclosure. Accordingly, this specification and the figures are to be regarded in an illustrative rather than a limiting sense, and such modifications are intended to be included within the scope of the present disclosure. Further, no solution to any benefit, advantage, or problem described herein with respect to a specific embodiment is intended to be construed as a critical, required, or essential feature or element of any or all of the claims.

Claims

1. A method for etching a polycrystalline material using a non-isothermal atomic layer etching (ALE) process, Receiving the substrate having the polycrystalline material formed thereon, with the surface of the polycrystalline material exposed on the surface of the substrate; A surface modification solution is supplied to the surface of the substrate at a first temperature, and the surface modification solution chemically modifies the surface of the polycrystalline material, thereby forming a passivation layer on the surface of the polycrystalline material; After forming the passivation layer, the surface modification solution is removed from the surface of the substrate; Before supplying the dissolving solution to the surface of the substrate, the dissolving solution is heated to a second temperature higher than the first temperature; The dissolving solution heated to the second temperature is supplied to the surface of the substrate, and the dissolving solution selectively removes the passivation layer from the surface of the polycrystalline material; To remove the dissolved solution from the surface of the substrate; The process of supplying the surface modification solution, removing the surface modification solution, supplying the dissolving solution, and removing the dissolving solution is repeated over a number of ALE cycles until a predetermined amount of the polycrystalline material is removed from the substrate. Methods that include...

2. The method according to claim 1, wherein the first temperature is selected from a first temperature range having a lower limit set by the freezing point of the surface modification solution and an upper limit of 25°C.

3. The method according to claim 1, wherein the first temperature is selected from a first temperature range including 20°C to 25°C.

4. The method according to claim 1, wherein the second temperature is selected from a second temperature range having a lower limit of 40°C and an upper limit set by the boiling point of the dissolved solution.

5. The method according to claim 1, wherein the second temperature is selected from a second temperature range including 40°C to 337°C.

6. The method according to claim 1, wherein the polycrystalline material comprises a transition metal, a transition metal oxide, or a silicon-based material.

7. The method according to claim 1, wherein the removal of the surface modification solution includes supplying a first purging solution to the surface of the substrate in order to remove the surface modification solution from the surface of the substrate before supplying the dissolving solution, and the temperature of the substrate approaches the second temperature due to the temperature of the first purging solution before supplying the dissolving solution.

8. The method according to claim 7, wherein the temperature of the first purge solution is within 10% of the second temperature.

9. The method according to claim 1, wherein the removal of the dissolving solution includes supplying a second purging solution to the surface of the substrate to remove the dissolving solution from the surface of the substrate before resupplying the surface modification solution between subsequent ALE cycles, and the temperature of the substrate approaches the first temperature due to the temperature of the second purging solution before resupplying the surface modification solution between subsequent ALE cycles.

10. The method according to claim 9, wherein the temperature of the second purge solution is within 10% of the temperature of the first solution.

11. The method according to claim 1, wherein the polycrystalline material includes a ruthenium surface, the supply of the surface modification solution includes supplying a halogenating agent dissolved in a first solvent onto the surface of the substrate at a first temperature in the range of 20°C to 25°C, and the halogenating agent chemically modifies the ruthenium surface to form a ruthenium halide passivation layer.

12. The method according to claim 11, wherein the supply of the dissolving solution includes supplying a ligand dissolved in a second solvent onto the surface of the substrate at a second temperature in the range of 40°C to 100°C, and the ligand reacts with and binds to the ruthenium halide passivation layer to form a soluble species that dissolves in the second solvent, and the ruthenium halide passivation layer is selectively removed from the ruthenium surface.

13. The method according to claim 1, wherein the polycrystalline material includes a molybdenum surface, and the supply of the surface modification solution includes supplying an oxidizing agent and a first ligand dissolved in a first solvent to the surface of the substrate at a first temperature in the range of 20°C to 25°C, wherein the oxidizing agent oxidizes the molybdenum surface to form a molybdenum oxide passivation layer, and the first ligand reacts with and binds to the molybdenum oxide passivation layer to form a ligand-metal complex insoluble in the first solvent.

14. The method according to claim 13, wherein the supply of the dissolution solution includes supplying a second ligand dissolved in a second solvent onto the surface of the substrate at a second temperature in the range of 40°C to 337°C, and when the ligand-metal complex is exposed to the dissolution solution, a ligand exchange process occurs in which the first ligand in the ligand-metal complex is exchanged with the second ligand contained in the dissolution solution to form a soluble species, and this soluble species is dissolved in the second solvent to selectively remove the molybdenum oxide passivation layer from the molybdenum surface.

15. A method for etching a substrate using a non-isothermal atomic layer etching (ALE) process, a) receiving the substrate having a ruthenium surface exposed thereon; b) Exposing the ruthenium surface to a first etching solution containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer, wherein the first etching solution is supplied to the surface of the substrate at a first temperature; c) Rinsing the substrate with the first purging solution to remove the first etching solution from the surface of the substrate; d) selectively removing the ruthenium halide passivation layer without removing the ruthenium surface beneath the ruthenium halide passivation layer by exposing the ruthenium halide passivation layer to a second etching solution, wherein the second etching solution is heated to a second temperature higher than the first temperature before being supplied to the surface of the substrate at a second temperature; e) Rinsing the substrate with a second purging solution to remove the second etching solution from the surface of the substrate; f) Repeating steps b) to e) for one or more cycles. A method that includes this.

16. The method according to claim 15, wherein the first temperature is selected from a temperature range including 20°C to 25°C.

17. The method according to claim 15, wherein the second temperature is selected from a temperature range including 40°C to 100°C.

18. The method according to claim 15, wherein the first etching solution contains a chlorinating agent dissolved in a first solvent, and the chlorinating agent reacts with the ruthenium surface to form a ruthenium chloride passivation layer insoluble in the first solvent.

19. The method according to claim 18, wherein the chlorinating agent comprises trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent comprises ethyl acetate (EA), acetone, acetonitrile, or chlorocarbon.

20. The method according to claim 18, wherein the second etching solution comprises a ligand dissolved in a second solvent, the ligand reacts with and binds to the ruthenium chloride passivation layer to form a soluble species that dissolves in the second solvent.

21. The method according to claim 20, wherein the ligand comprises ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent comprises a base.

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