Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P50/00—Etching of wafers, substrates or parts of devices
  • H10P50/60—Wet etching
  • H10P50/66—Wet etching of conductive or resistive materials
  • H10P50/663—Wet etching of conductive or resistive materials by chemical means only
  • H10P50/667—Wet etching of conductive or resistive materials by chemical means only by liquid etching only
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
  • C23C22/58—Treatment of other metallic material
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/16—Acidic compositions
  • C23F1/26—Acidic compositions for etching refractory metals
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/16—Acidic compositions
  • C23F1/30—Acidic compositions for etching other metallic material

Definitions

• This disclosure relates to semiconductor device manufacturing, and, in particular, to the removal and etching of polycrystalline materials, such as metals, formed on a substrate. More specifically, the disclosure relates to the process of wet atomic layer etching (ALE) of polycrystalline materials.
• ALE wet atomic layer etching
• etching layers on a substrate may be removed by patterned etching, chemical-mechanical polishing, as well as other techniques.
• a variety of techniques are known for etching layers on a substrate, including plasma-based or vapor phase etching (otherwise referred to as dry etching) and liquid based etching (otherwise referred to as wet etching).
• Wet etching generally involves dispensing a chemical solution over the surface of a substrate or immersing the substrate in the chemical solution.
• the chemical solution often contains a solvent, chemicals designed to react with materials on the substrate surface and chemicals to promote dissolution of the reaction products. As a result of exposure of the substrate surface to the etchant, material is removed from the substrate.
• Etchant composition and temperature may be controlled to control the etch rate, specificity, and residual material on the surface of the substrate post-etch.
• Thermodynamics and kinetics both play roles in etchant formulation.
• the desired reactions need to be both thermodynamically and kinetically favorable for a successful etch.
• the requirements for success become much more stringent for etching polycrystalline materials.
• Surface roughness plays an important role in interface quality and electrical properties of nanoscale features. When etching nanoscale polycrystalline materials, differing etch rates at grain boundaries compared to the different crystal facets leads to roughening of the surface during etching.
• the material removal rate should be uniform at the macroscopic and microscopic levels and occurs at a rate that is compatible with high volume manufacturing. Macroscopic uniformity can be addressed with careful engineering, but microscopic uniformity depends on the chemistry of the etch itself.
• ALE atomic layer etching
• ALE is a process that removes thin layers sequentially through one or more self-limiting reactions.
• ALE typically refers to techniques that can etch with atomic precision, /. ⁇ ., by removing material one or a few monolayers of material at a time.
• ALE processes generally rely on a chemical modification of the surface to be etched followed by selective removal of the modified surface layer.
• ALE processes offer improved performance by decoupling the etch process into sequential steps of surface modification and selective removal of the modified surface layer.
• an ALE process may include multiple cyclic series of surface modification and etch steps, where the modification step modifies the exposed surfaces and the etch step selectively removes the modified surface layer. In such processes, a series of self-limiting reactions may occur and the cycle may be repeatedly performed until a desired or specified etch amount is achieved. In other embodiments, an ALE process may use just one cycle.
• ALE processes are known in the art, including plasma ALE, thermal ALE and wet ALE techniques.
• wet ALE is typically a cyclic process that uses sequential, self-limiting reactions to chemically modify an exposed surface of a material to form a modified surface layer and selectively remove the modified surface layer from the surface.
• thermal and plasma ALE techniques the reactions used in wet ALE primarily take place in the liquid phase.
• a wet ALE process may generally begin with a surface modification step, which exposes a material to be etched to a first solution to create a selflimiting modified surface layer.
• the modified surface layer may be created through oxidation, reduction, ligand binding, or ligand exchange.
• the modified surface layer is confined to the top monolayer of the material and acts as a passivation layer to prevent the modification reaction from progressing any further.
• the wet ALE process may expose the modified surface layer to a second solution to selectively dissolve the modified surface layer in a subsequent dissolution step.
• the dissolution step will selectively dissolve the modified surface layer without removing any of the underlying unmodified material. This selectivity can be accomplished by using a different solvent in the dissolution step than was 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 a desired or specified etch amount is achieved.
• the surface modification and etch steps are usually performed at the same temperature, resulting in an isothermal etch process.
• the surface modification and dissolution steps are often performed at (or near) room temperature. This is usually considered to be an advantage of wet ALE over other ALE techniques.
• the surface modification and etch steps are often performed at a higher temperature than is typically used for wet ALE.
• plasma and thermal ALE are typically isothermal processes. Because adjusting and reaching thermal equilibrium at each cycle is too timeconsuming, plasma and thermal ALE processes must be conducted isothermally to meet the throughput requirements of high volume manufacturing.
• the present disclosure provides a non-isothermal wet atomic layer etch (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 methods that utilize thermal cycling in a wet ALE process to independently optimize the reaction temperatures utilized within individual processing steps of the wet ALE process. Like conventional wet ALE processes, the wet ALE process described herein is a cyclic process that includes multiple cycles of surface modification and dissolution steps. Unlike conventional wet ALE processes, however, the wet ALE process described herein is a non-isothermal process that performs the surface modification and dissolution steps at different temperatures. This allows independent optimization of the surface modification and dissolution reactions.
• ALE wet atomic layer etch
• the non-isothermal wet ALE process described herein may generally include multiple ALE cycles, where each ALE cycle includes a surface modification step, a first purge step, a dissolution step and a second purge step, and where one or more of these processing steps is performed at a different temperature.
• thermal cycling can be introduced as part of the wet ALE process described herein by dispensing liquid solutions utilized within one or more of the processing steps at a different temperature.
• the high heat capacity of the liquid solutions combined with their high convective heat transfer coefficients, allows the substrate surface to reach thermal equilibration quickly, thus allowing the temperature of the substrate to be changed within the timescale of a single ALE cycle.
• the non-isothermal wet ALE process described herein may dispense a surface modification solution onto a surface of a substrate at a first temperature, and may subsequently dispense a dissolution solution onto the surface of the substrate at a second temperature, which is different from the first temperature.
• the first temperature and the second temperature may be selected to independently optimize the reactions that occur during the surface modification and dissolution steps.
• the surface modification solution may be dispensed at a first temperature, which is less than or equal to room temperature (e.g., a temperature less than or equal to 25°C).
• the dissolution solution may be dispensed at a second temperature, which is greater than room temperature (e.g., a temperature greater than or equal to 40°C) to optimize the kinetics of the dissolution reaction.
• room temperature e.g., a temperature greater than or equal to 40°C
• the wet ALE process described herein provides a cyclic, non-isothermal etch process, which repeatedly adjusts the reaction temperatures of the surface modification and dissolution steps to independently optimize the surface modification and dissolution reactions.
• purge solutions may be dispensed onto the surface of the substrate between the surface modification and dissolution steps to remove the surface modification and dissolution solutions from the surface of the substrate.
• the purge solutions may be utilized to pre-heat or pre-cool the substrate prior to performing the next processing step.
• a heated purge solution may be dispensed onto the surface of the substrate to bring the temperature of the substrate closer to the second temperature (i.e., the desired dissolution reaction temperature) prior to performing the next dissolution step.
• a room temperature (or cooled) purge solution may be dispensed onto 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) prior to performing the next surface modification step.
• the wet ALE process described herein is able to quickly adjust the surface of the substrate to the next process temperature.
• a cyclic, non-isothermal wet ALE process for etching polycrystalline materials.
• the cyclic, non-isothermal wet ALE process described herein quickly adjusts the reaction temperatures of the surface modification and dissolution steps within the timescale of a single ALE cycle to independently optimize the surface modification and dissolution reactions.
• the disclosed non-isothermal wet ALE process is able to change the substrate temperature, during processing, much easier and faster than can be achieved in the gas-phase processing used in plasma and thermal ALE. Accordingly, the disclosed non-isothermal wet ALE process is suitable for high volume manufacturing.
• the present disclosure provides various embodiments of methods that utilize thermal cycling in a wet ALE process to independently optimize the reaction temperatures utilized within the individual processing steps of the wet ALE process.
• the order of discussion of the different steps as described herein has been presented for clarity sake. In general, these steps can be performed in any suitable order.
• each of the different features, techniques, configurations, etc. herein may be discussed in different places of this disclosure, it is intended that each of the concepts can be executed independently of each other or in combination with each other. Accordingly, the present invention can be embodied and viewed in many different ways.
• a method for etching a polycrystalline material using a non-isothermal wet atomic layer etching (ALE) process.
• the method may generally include receiving a substrate having a polycrystalline material formed thereon, wherein a surface of the polycrystalline material is exposed on a surface of the substrate, and dispensing a surface modification solution onto the surface of the substrate at a first temperature, wherein the surface modification solution chemically modifies the surface of the polycrystalline material to form a passivation layer on the surface of the polycrystalline material.
• ALE non-isothermal wet atomic layer etching
• the method may include removing the surface modification solution from the surface of the substrate subsequent to forming the passivation layer, and dispensing a dissolution solution onto the surface of the substrate at a second temperature, which is different from the first temperature, wherein the dissolution solution selectively removes the passivation layer from the surface of the poly crystalline material.
• the method may include removing the dissolution solution from the surface of the substrate, and repeating the steps of dispensing the surface modification solution, removing the surface modification solution, dispensing the dissolution solution, and removing the dissolution solution a number of ALE cycles until a predetermined amount of the polycrystalline material is removed from the substrate.
• the first temperature and the second temperature may be selected so as to independently optimize the reactions that occur during the surface modification and dissolution steps of the non-isothermal wet ALE process described herein.
• the surface modification solution may be dispensed within a first temperature range having a lower limit that is set by the freezing point of the surface modification solution and an upper limit of approximately room temperature (e.g., a temperature ranging between 20°C and 25 °C).
• the surface modification solution may be dispensed at approximately room temperature (e.g., a temperature ranging between 20°C and 25°C).
• the dissolution solution may be dispensed at a second temperature, which is greater than the first temperature to optimize the kinetics of the dissolution reaction.
• the dissolution solution may be dispensed within a second temperature range having a lower limit of 40°C and an upper limit that is set by the boiling point of the dissolution etch solution.
• the dissolution solution may be dispensed within a second temperature range comprising 40°C to 337°C.
• said removing the surface modification solution may include dispensing a first purge solution onto the surface of the substrate to remove the surface modification solution from the surface of the substrate prior to dispensing the dissolution solution.
• a temperature of the first purge solution may bring a temperature of the substrate closer to the second temperature before the dissolution solution is dispensed.
• the temperature of the first purge solution may be within 10% of the second temperature.
• said removing the dissolution solution may include dispensing a second purge solution onto the surface of the substrate to remove the dissolution solution from the surface of the substrate before re-dispensing the surface modification solution during a subsequent ALE cycle.
• a temperature of the second purge solution may bring a temperature of the substrate closer to the first temperature before the surface modification solution is re-dispensed during the subsequent ALE cycle.
• the temperature of the second purge solution may be within 10% of the first temperature.
• etch chemistries may be used within the surface modification and the dissolution solutions for etching a wide variety of polycrystalline materials, such as metals, metal oxides silicon-based materials.
• metals that may 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.
• metal oxides that may be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (AI2O3), hafnium oxide (HfCh).
• the methods disclosed herein may also be used to etch silicon-based materials, such as but not limited to, silicon (Si), silicon oxides (e.g., SiO and SiCh) and silicon nitrides (e.g., SisNf).
• silicon Si
• silicon oxides e.g., SiO and SiCh
• silicon nitrides e.g., SisNf
• Example etch chemistries for etching ruthenium and molybdenum using the nonisothermal wet ALE techniques disclosed herein are discussed in more detail below.
• the method disclosed herein may be used for etching a ruthenium (Ru) surface.
• the surface modification solution may include a halogenation agent e.g., a chlorination 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 halogenation agent included within the surface modification solution chemically modifies the ruthenium surface to form a halogenated ruthenium passivation layer.
• the ligand included within the dissolution solution reacts with and binds to the halogenated ruthenium passivation layer to form a soluble species, which is dissolved within the second solvent to selectively remove the halogenated ruthenium passivation layer from the ruthenium surface.
• the surface modification solution may be dispensed at a first temperature ranging between 20°C and 25°C, and the dissolution solution may be dispensed at a second temperature ranging between 40°C and 100°C.
• the method disclosed herein may be used for etching a molybdenum (Mo) surface.
• the surface modification solution may include an oxidation agent and a first ligand dissolved in a first solvent
• the dissolution solution may include a second ligand dissolved in a second solvent.
• the oxidation agent oxidizes the molybdenum surface to form a molybdenum oxide passivation layer.
• the first ligand included within the surface modification solution reacts with and binds to the molybdenum oxide passivation layer to form a ligandmetal complex, which is insoluble in the first solvent.
• a ligand exchange process exchanges the first ligand in the ligand-metal complex with the second ligand included within the dissolution solution to form a soluble species, which is dissolved within the second solvent to selectively remove the molybdenum oxide passivation layer from the molybdenum surface.
• the surface modification solution may be dispensed at a first temperature ranging between 20°C and 25°C, and the dissolution solution may be dispensed at a second temperature ranging between 40°C and 337°C.
• a method for etching a substrate using a non-isothermal wet atomic layer etching (ALE) process.
• the method may generally include: a) receiving the substrate, the substrate having a ruthenium surface exposed thereon; b) exposing the ruthenium surface to a first etch solution containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer, wherein the first etch solution is dispensed onto a surface of the substrate at a first temperature; c) rinsing the substrate with a first purge solution to remove the first etch solution from the surface of the substrate; d) exposing the ruthenium halide passivation layer to a second etch solution to selectively remove the ruthenium halide passivation layer without removing the ruthenium surface underlying the ruthenium halide passivation layer, wherein the second etch solution is dispense
• the first etch solution may be dispensed onto the surface of the substrate at a first temperature, which is less than or approximately equal to room temperature.
• the first temperature may be selected from a first temperature range comprising 20°C to 25°C.
• the first temperature is not strictly limited to such, and may alternatively range between an upper limit of 25°C and a lower limit that is set by the freezing point of the first etch solution.
• the second etch solution may be dispensed onto the surface of the substrate at a second temperature, which is greater than the first temperature to optimize the kinetics of the dissolution reaction.
• the second temperature may be selected from a second temperature range comprising 40°C to 100°C. Like the first temperature, however, the second temperature is not strictly limited to such a temperature range, and may comprise any elevated temperature that is greater than room temperature and less than the boiling point of the second etch solution. For example, the second temperature may range between a lower limit of 40°C and an upper limit that is set by the boiling point of the second etch solution.
• the first etch solution may include a chlorination agent dissolved in a first solvent.
• the chlorination agent may react with the ruthenium surface to form a ruthenium chloride passivation layer, which is insoluble in the first solvent.
• the chlorination agent may include trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride or N-chlorosuccinimide
• the first solvent may include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon.
• the second etch solution may include a ligand dissolved in a second solvent.
• the ligand may react with and bind to the ruthenium chloride passivation layer to form a soluble species that dissolves within the second solvent.
• the ligand may include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTP A) or acetylacetone (ACAC), and the second solvent may include a base.
• FIG. 1 illustrates one example of a cyclic, non-isothermal wet atomic layer etching (ALE) process that can be used to etch ruthenium in accordance with the present disclosure.
• ALE wet atomic layer etching
• FIG. 2 is a graph depicting exemplary etch amounts (expressed in nanometers, nm) that may be achieved as a function of cycle number when attempting to etch ruthenium using various etch conditions.
• FIG. 4 illustrates one example of a cyclic, non-isothermal wet atomic layer etching (ALE) process that can be used to etch molybdenum in accordance with the present disclosure.
• ALE wet atomic layer etching
• FIG. 5 is a graph illustrating how the oxidation of the molybdenum surface using hydrogen peroxide (H2O2) and oxalic acid in isopropyl alcohol (IPA) to form oxymolybdenum oxalate is self-limiting at room temperature, but not self-limiting at elevated temperatures.
• FIG. 6 is a graph depicting exemplary etch amounts (expressed in nanometers, nm) that may be achieved as a function of cycle number when attempting to etch molybdenum using various etch conditions.
• FIG. 7 is a block diagram of an example processing system that can use the techniques described herein to etch a polycrystalline material, such as ruthenium.
• FIG. 8 is a flowchart diagram illustrating one embodiment of a method utilizing the techniques described herein.
• FIG. 9 is a flowchart diagram illustrating another embodiment of a method utilizing the techniques described herein.
• the present inventors recognized that, in some ALE processes, one of the reaction steps may benefit from being run at a higher temperature. For example, the present inventors recognized that increasing the temperature of the dissolution reaction may improve the kinetics of dissolution and increase the etch rate when etching some materials. However, the present inventors noted that raising the temperature for the benefit of one reaction is sometimes detrimental to the second reaction. As such, the present inventors recognized that it is not always desirable to run the entire process at an elevated temperature, and developed a non-isothermal etch process that improves upon conventional etch processes run isothermally.
• a non-isothermal wet atomic layer etch (ALE) process is provided 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 methods that utilize thermal cycling in a wet ALE process to independently optimize the reaction temperatures utilized within individual processing steps of the wet ALE process.
• the wet ALE process described herein is a cyclic process that includes multiple cycles of surface modification and dissolution steps.
• the wet ALE process described herein is a non-isothermal process that performs the surface modification and dissolution steps at different temperatures. This allows independent optimization of the surface modification and dissolution reactions.
• the non-isothermal wet ALE process described herein may generally include multiple ALE cycles, where each ALE cycle includes a surface modification step, a first purge step, a dissolution step and a second purge step, and where one or more of these processing steps is performed at a different temperature.
• thermal cycling can be introduced as part of the wet ALE process described herein by dispensing liquid solutions utilized within one or more of the processing steps at a different temperature.
• the high heat capacity of the liquid solutions combined with their high convective heat transfer coefficients, allows the substrate surface to reach thermal equilibration quickly, thus allowing the temperature of the substrate to be changed within the timescale of a single ALE cycle.
• the non-isothermal wet ALE process described herein may dispense a surface modification solution onto a surface of a substrate at a first temperature, and may subsequently dispense a dissolution solution onto the surface of the substrate at a second temperature, which is different from the first temperature.
• the first temperature and the second temperature may be selected to independently optimize the reactions that occur during the surface modification and dissolution steps.
• the surface modification solution may be dispensed at a first temperature, which is less than or equal to room temperature (e.g., a temperature less than or equal to 25°C).
• the dissolution solution may be dispensed at a second temperature, which is greater than room temperature (e.g., a temperature greater than or equal to 40°C) to optimize the kinetics of the dissolution reaction.
• room temperature e.g., a temperature greater than or equal to 40°C
• the wet ALE process described herein provides a cyclic, non-isothermal etch process, which repeatedly adjusts the reaction temperatures of the surface modification and dissolution steps to independently optimize the surface modification and dissolution reactions.
• purge solutions may be dispensed onto the surface of the substrate between the surface modification and dissolution steps to remove the surface modification and dissolution solutions from the surface of the substrate.
• the purge solutions may be utilized to pre-heat or pre-cool the substrate prior to performing the next processing step.
• a heated purge solution may be dispensed onto the surface of the substrate to bring the temperature of the substrate closer to the second temperature (i.e., the desired dissolution reaction temperature) prior to performing the next dissolution step.
• a room temperature (or cooled) purge solution may be dispensed onto 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) prior to performing the next surface modification step.
• thermal cycling is used in the wet ALE process described herein to independently optimize the reaction temperatures utilized within the surface modification and dissolution steps of the wet ALE process.
• thermal cycling is provided by utilizing heated (and/or cooled) liquid solutions, which quickly adjusts the reaction temperatures of the surface modification and dissolution steps within the timescale of a single ALE cycle to independently optimize the surface modification and dissolution reactions.
• the cyclic, non-isothermal wet ALE process described herein is able to quickly change the substrate temperature during processing, and thus, is suitable for high volume manufacturing.
• metals such as metals, metal oxides and silicon-based materials.
• metals that may 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.
• metal oxides that may be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (AI2O3), hafnium oxide (HfCh).
• the methods disclosed herein may also be used to etch silicon-based materials, such as but not limited to, silicon (Si), silicon oxides (e.g., SiO and SiCh) and silicon nitrides (e.g., Si3N4).
• silicon Si
• silicon oxides e.g., SiO and SiCh
• silicon nitrides e.g., Si3N4
• Example etch processes and etch chemistries for etching ruthenium and molybdenum are discussed in more detail below.
• FIG. 1 illustrates one example of a cyclic, non-isothermal wet ALE process in accordance with the present disclosure. More specifically, FIG. 1 illustrates exemplary steps performed during one cycle of a non-isothermal wet ALE process used for etching a poly crystalline material 105, such as ruthenium (Ru).
• a poly crystalline material 105 surrounded by a dielectric material 110 is brought in contact with a surface modification solution 115 during a surface modification step 100 to modify exposed surfaces of the poly crystalline material 105.
• the poly crystalline material 105 to be etched may be ruthenium (Ru).
• the surface modification solution 115 may contain a halogenation agent 120.
• the surface modification solution 115 may include a first solvent containing a chlorination agent, a fluorinating agent or a brominating agent.
• the substrate may be rinsed with a first purge solution 135 to remove excess reactants from the surface of the substrate in a first purge step 130.
• the purge solution 135 should not react with the passivation layer 125 or with the reagents present in the surface modification solution 115.
• the first purge solution 135 used in the first purge step 130 may use the same solvent previously used in the surface modification step 100. In other embodiments, a different solvent may be used in the first purge solution 135. In some embodiments, the first purge step 130 may be long enough to completely remove all excess reactants from the substrate surface.
• a dissolution step 140 is performed to selectively remove the passivation layer 125 from the underlying surface of the poly crystalline material 105.
• the passivation layer 125 is exposed to a dissolution solution 145 to selectively remove or dissolve passivation layer 125 without removing the unmodified poly crystalline 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.
• the solubility of the passivation layer 125 allows its removal through dissolution into the bulk dissolution solution 145.
• the dissolution step 140 may continue until the passivation layer 125 is completely dissolved.
• the ALE etch cycle shown in FIG. 1 may be completed by performing a second purge step 160.
• the second purge step 160 may be performed by rinsing the surface of the substrate with a second purge solution 165, which may be the same or different than the first purge solution 135.
• second purge solution 165 may use the same solvent (i.e., the second solvent), which was used in the dissolution solution 145.
• the second purge step 160 may generally continue until the dissolution solution 145 and/or the reactants contained with the dissolution solution 145 are completely removed from the surface of the substrate.
• Wet ALE of ruthenium requires the formation of a self-limiting passivation layer on the ruthenium surface.
• the formation of this passivation layer is accomplished by exposure of the ruthenium surface to a first etch solution (i.e., surface modification solution 115) that enables or causes a chemical reaction between the species in solution and the ruthenium surface.
• This passivation layer must be insoluble in the solution used for its formation, but freely soluble in the second etch solution (i.e., dissolution solution 145) used for its dissolution.
• Etchant chemistry should, at a minimum, leave the surface no rougher than it was initially and ideally improve the surface roughness during etching. Acceptable surface morphology can be accomplished through the formation of a self-limiting passivation layer that is selectively removed in a cyclic wet ALE process.
• the present disclosure contemplates a wide variety of etch chemistries that may 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.
• Example etch chemistries are discussed in more detail below. Mixing of these solutions leads to a continuous etch process, loss of control of the etch and roughening of the pos-etch surface, all of which undermines the benefits of wet ALE.
• 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.
• the ruthenium surface may be exposed to a surface modification solution 115 including a first solvent containing a chlorination agent, which chemically modifies the ruthenium surface to form a ruthenium chloride passivation layer.
• a ruthenium trichloride (RuCh) may be used as the passivation layer.
• a RuCh passivation layer may be formed when the ruthenium surface is exposed to a solution of trichloroisocyanuric acid (TCCA) dissolved in ethyl acetate (EA).
• TCCA trichloroisocyanuric acid
• EA ethyl acetate
• the TCCA may act as both the oxidizer and the chlorine source in the reaction.
• TCCA oxidizes the ruthenium surface in the chemical sense to form a ruthenium trichloride (RuCh) passivation layer on the ruthenium surface
• RuCh ruthenium trichloride
• the chlorine chemistry of ruthenium is very complicated. There are two distinct crystalline phases of RuCk. a-RuCk is almost completely insoluble, while P-RuCk is hygroscopic and freely soluble in water, alcohol, and many organic solvents. Additionally, mixed oxychlorides can be formed when oxygen or water are present during chlorination. These oxychlorides tend to be highly soluble. Based on this chemistry, the a-phase of RuCk is considered herein as a preferred passivation layer, in some embodiments. Phase formation, however, is controlled by the reaction conditions.
• the reactant used for the chlorination of the ruthenium surface is TCCA; however, many chlorination agents will work for this step.
• Alternative chlorination agents include, but are not strictly limited to, oxalyl chloride, thionyl chloride and N-chlorosuccinimide. This is not an exhaustive list of all possible chlorination agents that may be used in the surface modification step 100.
• other ruthenium halides can also be used as a passivation layer. For example, ruthenium fluoride and ruthenium bromide can each be used, in addition to RuCh.
• ruthenium halides can be formed using fluorinating agents or brominating agents, such as but not limited to, l-Fluoro-2,4,6- trimethylpyridinium tetrafluoroborate, N-fluorobenzenesulfonimide, N-bromosuccinimide, or dibromoisocyanuric acid.
• fluorinating agents or brominating agents such as but not limited to, l-Fluoro-2,4,6- trimethylpyridinium tetrafluoroborate, N-fluorobenzenesulfonimide, N-bromosuccinimide, or dibromoisocyanuric acid.
• 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 (DTP A), and acetylacetone (ACAC).
• IDA iminodiacetic acid
• DTP A diethylenetriaminepentaacetic acid
• ACAC acetylacetone
• EDTA, IDA, and DTPA can be used in aqueous solution, while ACAC can be used in aqueous solution, ethanol, dimethyl sulfoxide (DMSO) or other organic solvents. Any strong base can be used in the dissolution solution 145.
• bases 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 as it is just needed to deprotonate the ligand 150 to allow binding with the ruthenium surface.
• KOH potassium hydroxide
• NaOH sodium hydroxide
• NH4OH ammonium hydroxide
• (CH3)4NOH) Tetramethylammonium hydroxide
• a larger etch amount per cycle can be achieved by running the dissolution at 100°C, as shown in FIG. 2.
• Etching experiments were conducted on coupons cut from a 300mm silicon wafer with various thicknesses of chemical vapor deposition (CVD) ruthenium deposited on one side.
• the etch recipe used to etch the ruthenium includes multiple wet ALE cycles, where each cycle includes a one minute dip in 5% TCCA dissolved in EA, followed by an EA rinse, a 30 second dip in an aqueous solution of 50mM EDTA and 1 M KOH in H2O (or deionized water), a 1 M KOH rinse (or deionized water rinse) and an isopropyl alcohol (IP A) rinse and blow dry.
• the wet ALE process was repeated for a number of ALE cycles under different process conditions: a hot water dissolution, a room temperature (RT) reactive dissolution and a hot reactive dissolution. The hot dissolutions were performed at 100°C.
• the total etch amount (nm) as a function of cycle number for the various etch conditions described above is illustrated in the graph 200 shown in FIG. 2.
• Reactive dissolution at room temperature (RT) gives an etch rate of 0.07nm/cycle. This is much less than a full monolayer of ruthenium and indicates that the dissolution kinetics may be slow at room temperature.
• the etch amount per cycle increases substantially (e.g., 0.26nm/cycle) when the dissolution solution is heated, confirming that the dissolution reaction is kinetically limited.
• the etch rate decreased with cycle number and eventually stopped when the experiment was run using deionized water for dissolution, rather than a solution of EDTA and KOH.
• the passivation layer contains a mixture of a-RuCh, P-RuCh, and various ruthenium oxychlorides (RuOxCly).
• the P-RuCh and RuOxCly will be water-soluble while the a-RuCh will remain on the surface.
• the amount of a-RuCh on the surface will increase, cycle after cycle, until the entire surface is passivated with insoluble a-RuCh and the etch cannot continue. This behavior indicates that ligands 150 in the dissolution solution 145 are beneficial to successful etch behavior.
• the dissolution reaction can be optimized and the etch rate can be increased e.g., from 0.07nm/cycle to 0.26nm/cycle) by heating the dissolution solution 145 to an elevated temperature above room temperature.
• the experimental results shown in FIG. 2 were obtained by heating the dissolution solution 145 to 100°C, the dissolution solution 145 may be heated to any temperature that optimizes the dissolution reaction and/or produces a desirable etch rate without exceeding the boiling point of the dissolution solution 145.
• the temperature of the dissolution solution 145 is limited to 100°C (the boiling point of water). However, when non-aqueous solutions are used, the maximum temperature of the dissolution solution 145 may be significantly higher.
• the data shown in FIG. 2 was collected using a wet ALE cycle where the chlorination step was performed at room temperature and the dissolution step was performed at 100°C.
• the desired reaction temperature for the dissolution of the RuCh passivation layer is above the boiling point of ethyl acetate. Because of this, the wet ALE cycle must be run non-isothermally, or the etch rate must be reduced by reducing the temperature of the dissolution step. In some cases, it may be beneficial to run the chlorination step at room temperature.
• the wet ALE process described herein may generally include multiple ALE cycles, where each ALE cycle includes a surface modification step 100, a first purge step 130, a dissolution step 140 and a second purge step 160.
• each ALE cycle includes a surface modification step 100, a first purge step 130, a dissolution step 140 and a second purge step 160.
• one or more of these processing steps 100, 130, 140 and 160 may be performed at a different temperature.
• thermal cycling is introduced as part of the wet ALE process shown in FIG. 1 by dispensing the liquid solutions utilized within one or more of the processing steps 100, 130, 140 and 160 at a different temperature.
• the high heat capacity of the liquid solutions combined with their high convective heat transfer coefficients, allows the substrate surface to reach thermal equilibration quickly, thus allowing the temperature of the substrate to be changed within the timescale of a single ALE cycle.
• the wet ALE process shown in FIG. 1 may dispense the surface modification solution 115 onto a surface of a substrate at a first temperature (Ti), and may dispense the dissolution solution 145 onto the surface of the substrate at a second temperature (T2), which is different from the first temperature, as depicted in the graph 300 shown in FIG. 3.
• the first and second temperatures may be selected to independently optimize the reactions that occur during the surface modification step 100 and the dissolution step 140.
• the surface modification solution may be dispensed at approximately room temperature (e.g., a temperature ranging between 20°C and 25°C).
• the dissolution solution may be dispensed at an elevated temperature (e.g., a temperature ranging between 40°C and 190°C) to optimize the kinetics of the dissolution reaction.
• an elevated temperature e.g., a temperature ranging between 40°C and 190°C
• the wet ALE process shown in FIG. 1 provides a cyclic, non-isothermal etch process, which repeatedly adjusts the reaction temperatures of the surface modification and dissolution steps to independently optimize the surface modification and dissolution reactions.
• purge solutions 135 and 165 may be dispensed onto the surface of the substrate between the surface modification step 100 and the dissolution step 140 to remove the surface modification and dissolution solutions from the surface of the substrate.
• the purge solutions 135 and 165 may be utilized to pre-heat or pre-cool the substrate prior to performing the next processing step.
• a heated purge solution 135 may be dispensed onto the surface of the substrate.
• the heated purge solution may be used to adjust or bring the temperature of the substrate closer to the second temperature (T2, z.e., the desired dissolution reaction temperature) prior to performing the next dissolution step, as shown in FIG. 3.
• a room temperature (or cooled) purge solution 165 may be dispensed onto the surface of the substrate.
• the room temperature (or cooled) purge solution 165 may be used to adjust or bring the temperature of the substrate closer to the first temperature (Ti, z.e., the desired surface modification reaction temperature) prior to performing the next surface modification step.
• the wet ALE process described herein is able to quickly adjust the surface of the substrate to the next process temperature.
• the cyclic, non-isothermal wet ALE process shown in FIG. 1 for etching a ruthenium surface may include: a) a surface modification step 100 in which the ruthenium surface is exposed to a surface modification solution 115 containing a halogenating agent to chemically modify the ruthenium surface and form a ruthenium halide passivation layer 125, wherein the surface modification solution 115 is dispensed onto a surface of the substrate at a first temperature; b) a first purge step 130 in which the substrate is rinsed with a first purge solution 135 to remove the surface modification solution 115 from the surface of the substrate; c) a dissolution step 140 in which the ruthenium halide passivation layer is exposed 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, wherein the second
• the steps a) - d) may be repeated for one or more ALE cycles, until a desired amount of the ruthenium material has been removed. It is recognized that the cyclic, nonisothermal wet ALE process shown in FIG. 1 is merely one example of a non-isothermal etch process that may be used to etch a poly crystalline material 105, such as ruthenium.
• the ruthenium wet ALE process described above and shown in FIG. 1 relies on both the surface modification and dissolution reactions being self-limiting.
• Self-limiting means that only a limited thickness of the ruthenium at the surface is modified or removed, regardless of how long a given etch solution is in contact with the ruthenium surface.
• the self-limiting reaction can be limited to one or more monolayers of reaction, or a partial monolayer of reaction.
• the ruthenium wet ALE process described above and shown in FIG. 1 can be accomplished using a variety of techniques.
• the ruthenium wet ALE process disclosed above may be performed by dipping the ruthenium sample in beakers of each etch solution. In this case, purging can be accomplished by either rinsing or dipping the sample in an appropriate solvent bath.
• the ruthenium wet ALE process can also be accomplished on a spinner.
• the ruthenium sample may be rotated while the etchant solutions are dispensed from a nozzle positioned above the sample. The rotational motion of the sample distributes the solution over the surface. After the set exposure time, the nozzle begins dispensing the next solution in the etch recipe.
• solution can also be dispensed onto the backside of the wafer to help control temperature.
• DI Deionized
• hot DI water can be dispensed onto the backside of the wafer during the dissolution step and room temperature DI water can be dispensed onto the backside of the wafer during the surface modification step.
• dispensing of etch solutions and rinses can be executed using conventional tools, such as wet etching tools and rinse tools.
• FIG. 4 illustrates another example of a cyclic, non-isothermal wet ALE process in accordance with the present disclosure. More specifically, FIG. 4 illustrates exemplary steps performed during one cycle of a non-isothermal wet ALE process used for etching a polycrystalline material 405, such as molybdenum (Mo).
• a poly crystalline material 405 surrounded by a dielectric material 410 is brought in contact with a surface modification solution 415 during a surface modification step 400 to modify exposed surfaces of the poly crystalline material 405.
• the poly crystalline material 405 to be etched is molybdenum (Mo).
• the surface modification solution 415 can contain an oxidation agent 420 and a first ligand 425 dissolved in a first solvent.
• the oxidation agent 420 oxidizes an exposed surface of the polycrystalline material 405 to form a passivation layer 430 (e.g., a molybdenum oxide passivation layer) in the surface modification step 400.
• the chemical reaction to form the passivation layer 430 may be fast and self-limiting.
• the reaction product may modify one or more monolayers of the exposed surface of the polycrystalline material 405, but may prevent any further reaction between the surface modification solution 415 and the underlying surface.
• the first ligand 425 included within the surface modification solution 415 reacts with and binds to the passivation layer 430 to form a ligand-metal complex 432, which is insoluble in the first solvent.
• the surface modification step 400 shown in FIG. 4 may continue until the surface reaction is driven to saturation.
• the substrate may be rinsed with a first purge solution 435 to remove excess reactants from the surface of the substrate in a first purge step 440.
• the purge solution 435 should not react with the ligand-metal complex 432 or with the reagents present in the surface modification solution 415.
• the first purge solution 435 used in the first purge step 440 may use the same solvent previously used in the surface modification step 400. In other embodiments, a different solvent may be used in the first purge solution 435.
• the first purge step 440 may be long enough to completely remove all excess reactants from the substrate surface.
• a dissolution solution 445 is supplied to the substrate to selectively remove the passivation layer 430 from the underlying surface of the poly crystalline material 105 in a dissolution step 450.
• the dissolution solution 445 may include a second ligand 455 dissolved in a second solvent.
• a ligand exchange process exchanges the first ligand 425 in the ligand-metal complex 432 with the second ligand 455 included within the dissolution solution 445 to form a soluble species, which is dissolved within the second solvent to selectively remove the passivation layer 430 without removing the unmodified poly crystalline material 105 underlying the passivation layer 430.
• the passivation layer 430 becomes soluble in the dissolution solution 445, which allows for its removal through dissolution into the bulk dissolution solution 445.
• the unmodified poly crystalline material 105 underlying the passivation layer 430 must be insoluble in the dissolution solution 445.
• the dissolution step 450 may continue until the passivation layer 430 is completely dissolved.
• the ALE etch cycle shown in FIG. 4 may be completed by performing a second purge step 460.
• the second purge step 460 may be performed by rinsing the surface of the substrate with a second purge solution 465, which may be the same or different than the first purge solution 435.
• the second purge solution 465 may use the same solvent (i.e., the first solvent), which was used in the surface modification solution 415.
• the second purge step 460 may generally continue until the dissolution solution 445 and/or the reactants contained with the dissolution solution 445 are completely removed from the surface of the substrate.
• etch chemistries that may 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.
• Example etch chemistries are discussed in more detail below. Mixing of these solutions leads to a continuous etch process, loss of control of the etch and roughening of the pos-etch surface, all of which undermines the benefits of wet ALE.
• 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.
• the surface modification solution 415 used for etching the molybdenum surface may include an oxidation agent 420 (such as, e.g., hydrogen peroxide (H2O2), ammonium persulfate ((NH4)2S2Os), 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 or fumaric acid) dissolved in an organic solvent (such as isopropyl alcohol (IP A) or another alcohol, diethyl ether ((C2H5)2O), acetonitrile (C2H3N), dimethyl sulfoxide (C2H6OS), a ketone or an acetate).
• an oxidation agent 420 such as,
• the molybdenum surface may be exposed to a surface modification solution 415 containing H2O2 and oxalic acid dissolved in IPA.
• the hydrogen peroxide (H2O2) oxidizes the molybdenum surface to form a molybdenum oxide (MoOs) passivation layer, which then complexes with the oxalic acid within the surface modification solution 415 to form a ligandmetal complex 432 (e.g., an oxymolybdenum oxalate complex), which is insoluble in the organic solvent.
• H2O2 hydrogen peroxide
• MoOs molybdenum oxide
• the dissolution solution 445 used for etching the molybdenum surface may include a second ligand 455 (e.g., ascorbic acid) dissolved in aqueous solution at high pH (such as, e.g., aqueous hydrochloric acid (HC1), sulfuric acid (H2SO4) or another strong acid).
• a second ligand 455 e.g., ascorbic acid
• HC1 aqueous hydrochloric acid
• H2SO4 sulfuric acid
• Oxymolybdenum oxalate is not soluble in aqueous HC1, but the ascorbate is.
• a ligand-exchange mechanism When exposed to a dissolution solution 445 containing ascorbic acid dissolved in aqueous HC1, a ligand-exchange mechanism exchanges the oxalic acid in the oxymolybdenum oxalate complex with the ascorbic acid included within the dissolution solution to form an oxymolybdenum ascorbate, which is dissolved within the aqueous HC1 to selectively remove the molybdenum oxide passivation layer from the molybdenum surface.
• the molybdenum wet ALE process shown in FIG. 4 and 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 concentrated acid (e.g., HC1, H2SO4, other strong acid) containing ascorbic acid.
• a concentrated acid e.g., HC1, H2SO4, other strong acid
• a larger etch amount per cycle can be achieved by running the dissolution at 43°C, as shown in FIG. 6.
• Etching experiments were conducted on coupons cut from a 300mm silicon wafer with various thicknesses of chemical vapor deposition (CVD) molybdenum deposited on one side.
• the etch recipe used to etch the molybdenum includes multiple wet ALE cycles, where each cycle includes a 10 second dip in 0.1% hydrogen peroxide (H2O2) + 50mM oxalic acid dissolved in isopropyl alcohol (IPA), followed by an IPA rinse, a 10 second dip in an aqueous solution of 50M HC1 + lOOmM ascorbic acid and an IPA rinse.
• H2O2 hydrogen peroxide
• IPA isopropyl alcohol
• the wet ALE process was repeated for a number of ALE cycles under different process conditions, as shown in FIGS. 5 and 6.
• the graph 500 shown in FIG. 5 illustrates the total etch amount (nm) as a function of time (minutes) for various surface modification conditions.
• the molybdenum coupon was soaked in: (a) a surface modification solution containing 0.1% H2O2 + 50mM oxalic acid in IPA at room temperature, (b) a surface modification solution containing 0.1% H2O2 + 50mM oxalic acid in IPA at 43°C and (c) a surface modification solution containing 0.05% H2O2 + 50mM oxalic acid in IPA at 43°C.
• FIG. 1 As shown in FIG.
• the oxymolybdenum oxalate formation process is self-limiting at room temperature, but is not self-limiting at elevated temperatures (e.g., continuous etch process reappears at 43°C). This limits the maximum temperature for the surface modification step 400.
• the surface modification step 400 may be performed at room temperature (or lower) to avoid a continuous etch process.
• the thermal activation of hydrogen peroxide-radical initiated polymerization relies on the cleaving of peroxide bonds with UV or thermal energy.
• the graph 500 shown in FIG. 5 further shows that the activity of hydrogen peroxide may be suppressed with lower peroxide concentration (e.g., 0.05% H2O2).
• the graph 600 shown in FIG. 6 illustrates the total etch amount (nm) as a function of cycle number for various dissolution conditions.
• the molybdenum coupon was soaked in: (a) 5M HCL at room temperature, (b) 5M HCL + lOOmM ascorbic acid at room temperature and (c) 5M HCL + lOOmM ascorbic acid at 43°C.
• the graph 600 shown in FIG. 6 shows that oxymolybdenum oxalate is not soluble in HCL, however, the ascorbate is.
• a ligand-exchange mechanism exchanges the oxalic acid in the oxymolybdenum oxalate complex with the ascorbic acid included within the dissolution solution to form an oxymolybdenum ascorbate, which is dissolved within the aqueous HC1.
• the dissolution of the oxymolybdenum oxalate can be accomplished through ligand exchange where oxymolybdenum ascorbate is the soluble species.
• Reactive dissolution in 5M HC1 + lOOmM ascorbic acid at room temperature (RT) gives an etch rate of 0.05nm/cycle. This is much less than a full monolayer of molybdenum and indicates that the dissolution kinetics may be slow at room temperature.
• the etch amount per cycle increases (e.g., 0.13nm/cycle) when the dissolution solution is heated (e.g., to 43°C), confirming that the dissolution reaction is kinetically limited.
• the etch rate decreased with cycle number and eventually stopped when the experiment was run using only HC1 for dissolution, rather than a solution of HC1 and ascorbic acid.
• the dissolution reaction can be optimized and the etch rate can be increased (e.g., from 0.05nm/cycle to 0.13nm/cycle) by heating the dissolution solution 445 to an elevated temperature above room temperature.
• the experimental results shown in FIG. 6 were obtained by heating the dissolution solution 445 to 43°C, the dissolution solution 445 may be heated to any temperature that optimizes the dissolution reaction and/or produces a desirable etch rate without exceeding the boiling point of the dissolution solution 445.
• the dissolution solution 445 may be heated to a temperature ranging between approximately 40°C and 107°C when using a dissolution solution 445 containing 5M HCL + lOOmM ascorbic acid to etch molybdenum.
• the dissolution solution 445 may be heated to different temperature ranges when other acidic solutions are used to etch molybdenum.
• the dissolution solution 445 may be heated to a temperature ranging between 40°C-337°C when using pure sulfuric acid (H2SO4) or 40°C-100°C when using a IM sulfuric acid solution to etch molybdenum.
• Other temperatures may be used for the dissolution solution 445 depending on the polycrystalline material being etched and the etch chemistry utilized within the dissolution solution 445. Regardless of the particular etch chemistry used, the etch amount per cycle is expected to increase monotonically with increasing temperature until the entire passivation layer 430 is removed or the solvent boiling point is reached - whichever happens at a lower temperature.
• the molybdenum wet ALE process described above and shown in FIG. 4 relies on both the surface modification and dissolution reactions being self-limiting.
• Self-limiting means that only a limited thickness of the molybdenum at the surface is modified or removed, regardless of how long a given etch solution is in contact with the molybdenum surface.
• the self-limiting reaction can be limited to one or more monolayers of reaction, or a partial monolayer of reaction.
• the molybdenum wet ALE process described above and shown in FIG. 4 may require oxidation at low temperature and dissolution at high temperature. This requires a compromise in the optimization of the individual reaction steps, or running as a non-isothermal process to allow for the independent optimization of the surface modification and dissolution reactions.
• the molybdenum wet ALE process described above and shown in FIG. 4 can be accomplished using a variety of techniques.
• the molybdenum wet ALE process disclosed above may be performed by dipping the molybdenum sample in beakers of each etch solution. In this case, purging can be accomplished by either rinsing or dipping the sample in an appropriate solvent bath.
• the molybdenum wet ALE process can also be accomplished on a spinner.
• the molybdenum sample may be rotated while the etchant solutions are dispensed from a nozzle positioned above the sample. The rotational motion of the sample distributes the solution over the surface.
• solution can also be dispensed onto the backside of the wafer to help control temperature.
• DI Deionized
• hot DI water can be dispensed onto the backside of the wafer during the dissolution step and room temperature DI water can be dispensed onto the backside of the wafer during the surface modification step.
• dispensing of etch solutions and rinses can be executed using conventional tools, such as wet etching tools and rinse tools.
• FIG. 7 illustrates one embodiment of a processing system 700 that may use the techniques described herein to etch a poly crystalline material, such as ruthenium, molybdenum, etc., on a surface of a substrate 730.
• the processing system 700 includes a process chamber 710, which in some embodiments, may be a pressure controlled chamber.
• the process chamber 710 is a spin chamber having a spinner 720 (or spin chuck), which is configured to spin or rotate at a rotational speed.
• a substrate 730 is held on the spinner 720, for example, via electrostatic force or vacuum pressure.
• the substrate 730 may be a semiconductor wafer having a polycrystalline material, such as ruthenium or molybdenum, formed on or within the substrate 730.
• the processing system 700 shown in FIG. 7 further includes a liquid nozzle 740, which is positioned over the substrate 730 for dispensing various etch solutions 742 onto a surface of the substrate 730.
• the etch solutions 742 dispensed onto the surface of the substrate 730 may generally include a surface modification solution to chemically modify an exposed surface of the polycrystalline material and form a passivation layer (e.g., a ruthenium halide passivation layer or an oxymolybdenum oxalate passivation layer), and a dissolution solution to selectively remove the passivation layer from the surface of the poly crystalline material.
• Purge solutions may also be dispensed onto the surface of the substrate 730 between surface modification and dissolution steps to separate the surface modification and dissolution solutions. Examples of surface modification, dissolution and purge solutions are discussed above.
• the etch solutions 742 may be stored within a chemical supply system 746, which may include one or more reservoirs for holding the various etch solutions 742 and a chemical injection manifold, which is fluidly coupled to the process chamber 710 via a liquid supply line 744.
• the chemical supply system 746 may selectively apply desired chemicals to the process chamber 710 via the liquid supply line 744 and the liquid nozzle 740 positioned within the process chamber 710.
• the chemical supply system 746 can be used to dispense the etch solutions 742 onto the surface of the substrate 730.
• the chemical supply system 746, liquid supply line 744 and/or liquid nozzle 740 may be configured to provide heated (and/or cooled) etch solutions 742 to the substrate.
• the process chamber 710 may further include a drain 750 for removing the etch solutions 742 from the process chamber 710.
• Components of the processing system 700 can be coupled to, and controlled by, a controller 760, which in turn, can be coupled to a corresponding memory storage unit and user interface (not shown).
• Various processing operations can be executed via the user interface, and various processing recipes and operations can be stored in the memory storage unit.
• a given substrate 730 can be processed within the process chamber 710 in accordance with a particular recipe.
• a given substrate 730 can be processed within the process chamber 710 in accordance with an etch recipe that utilizes the non-isothermal wet ALE techniques described herein.
• the controller 760 shown in block diagram form in FIG. 7 can be implemented in a wide variety of manners.
• the controller 760 may be a computer.
• the controller 760 may include one or more programmable integrated circuits that are programmed to provide the functionality described herein.
• one or more processors e.g., microprocessor, microcontroller, central processing unit, etc.
• programmable logic devices e.g., complex programmable logic device (CPLD), field programmable gate array (FPGA), efc.
• CPLD complex programmable logic device
• FPGA field programmable gate array
• the software or other programming instructions can be stored in one or more non-transitory computer-readable mediums (e.g., memory storage devices, flash memory, dynamic random access memory (DRAM), reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs, efc.), and the software or other programming instructions when executed by the programmable integrated circuits cause the programmable integrated circuits to perform the processes, functions, and/or capabilities described herein. Other variations could also be implemented.
• non-transitory computer-readable mediums e.g., memory storage devices, flash memory, dynamic random access memory (DRAM), reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs, efc.
• the controller 760 may be coupled to various components of the processing system 700 to receive inputs from, and provide outputs to, the components.
• the controller 760 may be coupled to: the process chamber 710 for controlling the temperature and/or pressure within the process chamber 710; the spinner 720 for controlling the rotational speed of the spinner 720; and the chemical supply system 746 for controlling the various etch solutions 742 dispensed onto the substrate 730 and/or the temperature of the etch solutions 742.
• the controller 760 may control other processing system components not shown in FIG. 7, as is known in the art.
• the controller 760 may control the various components of the processing system 700 in accordance with an etch recipe that utilizes the non-isothermal wet ALE techniques described herein.
• the controller 760 may supply various control signals to the chemical supply system 746, which cause the chemical supply system 746 to: a) dispense a surface modification solution onto the surface of the substrate 730 to chemically modify exposed surfaces of the polycrystalline material and create 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.
• a passivation layer e.g., a ruthen
• the controller 760 may supply the control signals to the chemical supply system 746 in a cyclic manner, such that the steps a) - d) are repeated for one or more ALE cycles, until a desired amount of the polycrystalline material has been removed.
• the controller 760 may control the temperature of the etch solutions 742 dispensed onto the substrate.
• Etch solutions can be dispensed at various temperatures as long as the vapor pressure of the liquid is lower than the chamber pressure.
• a spinner with a liquid dispensing nozzle would be placed in a pressure vessel or a vacuum chamber. The temperature of the liquid being dispensed can be elevated to any temperature below its boiling point at the pressure of the process.
• a surface modification solution may be dispensed onto the surface of the substrate 730 at a temperature less than or equal to room temperature (e.g., a temperature less than or equal to 25°C), and a dissolution solution may be dispensed onto the surface of the substrate 730 at an elevated temperature e.g., a temperature greater than 40°C and less than a boiling point of the dissolution solution).
• room temperature e.g., a temperature less than or equal to 25°C
• a dissolution solution may be dispensed onto the surface of the substrate 730 at an elevated temperature e.g., a temperature greater than 40°C and less than a boiling point of the dissolution solution.
• purge solutions may also be utilized to pre-heat or pre-cool the substrate prior to performing the next processing step, as shown in FIG. 3.
• FIGS. 8-9 illustrate exemplary methods that utilize the non-isothermal wet atomic layer etching (ALE) techniques described herein for etching various polycrystalline materials formed on a substrate. It will be recognized that the embodiments of FIGS. 8-9 are merely exemplary and additional methods may utilize the techniques described herein. Further, additional processing steps may be added to the methods shown in the FIGS. 8-9 as the steps described are not intended to be exclusive. Moreover, the order of the steps is not limited to the order shown in the figures as different orders may occur and/or various steps may be performed in combination or at the same time.
• ALE non-isothermal wet atomic layer etching
• FIG. 8 illustrates one embodiment of a method 800 of etching a polycrystalline material using a non-isothermal wet atomic layer etching (ALE) process in accordance with the present disclosure.
• the method 800 shown in FIG. 8 may generally include receiving a substrate having a polycrystalline material formed thereon, wherein a surface of the poly crystalline material is exposed on a surface of the substrate (in step 810), and dispensing a surface modification solution onto the surface of the substrate at a first temperature, wherein the surface modification solution chemically modifies the surface of the polycrystalline material to form a passivation layer on the surface of the polycrystalline material (in step 820).
• the passivation layer is self-limited and insoluble to the surface modification solution.
• the method 800 may include removing the surface modification solution from the surface of the substrate subsequent to forming the passivation layer (in step 830) and dispensing a dissolution solution onto the surface of the substrate at a second temperature, which is different from the first temperature (in step 840).
• the dissolution solution selectively removes the passivation layer from the surface of the polycrystalline material in step 840.
• the method 800 may include removing the dissolution solution from the surface of the substrate (in step 850) and repeating the steps of dispensing the surface modification solution, removing the surface modification solution, dispensing the dissolution solution, and removing the dissolution solution a number of ALE cycles until a predetermined amount of the polycrystalline material is removed from the substrate (in step 860).
• the first temperature and the second temperature may be selected so as to independently optimize the reactions that occur during the surface modification and dissolution steps of the non-isothermal wet ALE process.
• the surface modification solution may be dispensed (in step 820) at a first temperature, which is less than or approximately equal to room temperature.
• the first temperature may be selected from a first temperature range comprising 20°C and 25°C.
• the first temperature is not strictly limited to such, and may alternatively be selected from a first temperature range having an upper limit of approximately 25°C and a lower limit that is set by the freezing point of the surface modification solution.
• the dissolution solution may be dispensed (in step 840) at a second temperature, which is greater than the first temperature to optimize the kinetics of the dissolution reaction.
• the dissolution solution may be dispensed in step 840 within a second temperature range having a lower limit of 40°C and an upper limit that is set by the boiling point of the dissolution solution.
• removing the surface modification solution may include dispensing a first purge solution onto the surface of the substrate to remove the surface modification solution from the surface of the substrate prior to dispensing the dissolution solution (in step 840).
• a temperature of the first purge solution may bring a temperature of the substrate closer to the second temperature before the dissolution solution is dispensed (in step 840).
• the temperature of the first purge solution may be within 10% of the second temperature.
• removing the dissolution solution may include dispensing a second purge solution onto the surface of the substrate to remove the dissolution solution from the surface of the substrate before re-dispensing the surface modification solution during a subsequent ALE cycle.
• a temperature of the second purge solution may bring a temperature of the substrate closer to the first temperature before the surface modification solution is re-dispensed during the subsequent ALE cycle.
• the temperature of the second purge solution may be within 10% of the first temperature.
• etch chemistries may be used within the surface modification and the dissolution solutions for etching a wide variety of polycrystalline materials, such as metals, metal oxides and silicon-based materials.
• metals that may 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.
• metal oxides that may be etched using the methods disclosed herein include, but are not limited to, aluminum oxide (AI2O3), hafnium oxide (HfCh).
• the methods disclosed herein may also be used to etch silicon-based materials, such as but not limited to, silicon (Si), silicon oxides (e.g., SiO and SiCh) and silicon nitrides (e.g., SisNF).
• silicon Si
• silicon oxides e.g., SiO and SiCh
• silicon nitrides e.g., SisNF
• Example etch chemistries for etching ruthenium and molybdenum using the non-isothermal wet ALE techniques disclosed herein are discussed in more detail below.
• the method 800 shown in FIG. 8 may be used for etching a ruthenium (Ru) surface.
• the surface modification solution dispensed in step 820 may include a halogenation agent (e.g., a chlorination agent, a fluorinating agent or a brominating agent) dissolved in a first solvent
• the dissolution solution dispensed in step 840 may include a ligand dissolved in a second solvent.
• the halogenation agent included within the surface modification solution chemically modifies the ruthenium surface to form a halogenated ruthenium passivation layer.
• the surface modification solution may be dispensed in step 820 at a first temperature ranging between 20°C and 25°C.
• the dissolution solution may be dispensed in step 840 at an elevated temperature (e.g., a temperature greater than or equal to 40°C) to optimize the kinetics of the dissolution reaction.
• the dissolution solution may be dispensed in step 840 at approximately 40°C-100°C when aqueous dissolution solutions are used to etch ruthenium.
• the method 800 shown in FIG. 8 may be used for etching a molybdenum (Mo) surface.
• the surface modification solution dispensed in step 820 may include an oxidation agent and a first ligand dissolved in a first solvent
• the dissolution solution dispensed in step 840 may include a second ligand dissolved in a second solvent.
• the oxidation agent oxidizes the molybdenum surface to form a molybdenum oxide passivation layer.
• the first ligand included within the surface modification solution reacts with and binds to the molybdenum oxide passivation layer to form a ligand-metal complex, which is insoluble in the first solvent.
• a ligand exchange process exchanges the first ligand in the ligand-metal complex with the second ligand included within the dissolution solution to form a soluble species, which is dissolved within the second solvent to selectively remove the molybdenum oxide passivation layer from the molybdenum surface.
• the surface modification solution may be dispensed in step 820 at a first temperature ranging between 20°C and 25°C.
• the ruthenium surface may be exposed to the first etch solution (in step 920) by dispensing the first etch solution onto a surface of the substrate at a first temperature, which is at or near room temperature.
• the first temperature may be selected from a first temperature range comprising 20°C to 25°C.
• the ruthenium halide passivation layer may be exposed to the second etch solution (in step 940) by dispensing the second etch solution onto the surface of the substrate at a second temperature, which is greater than the first temperature.
• the second temperature may be selected from a second temperature range comprising 40°C to 100°C to optimize the kinetics of the dissolution reaction.
• the second etch solution may include a ligand dissolved in a second solvent.
• the ligand may react with and bind to the ruthenium chloride passivation layer to form a soluble species that dissolves within the second solvent.
• the ligand may include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTP A) or acetylacetone (ACAC), and the second solvent may include a base.
• the substrate may include any material portion or structure of a device, particularly a semiconductor or other electronics device, and may, for example, be a base substrate structure, such as a semiconductor substrate or a layer on or overlying a base substrate structure such as a thin film.
• substrate is not intended to be limited to any particular base structure, underlying layer or overlying layer, patterned or unpatterned, but rather, is contemplated to include any such layer or base structure, and any combination of layers and/or base structures.

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