Wet atomic layer etching method for ruthenium

Abstract

The present disclosure provides a new wet atomic layer etching (ALE) process for etching ruthenium. More specifically, the present disclosure provides various embodiments of methods that utilize new etching chemistries for etching ruthenium in a wet ALE process. Unlike conventional etching processes for ruthenium, the wet ALE process described herein for etching ruthenium is metal-free, cost-effective, and improves surface roughness during etching.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 257,226, entitled "METHOD FOR WET ATOMIC LAYER ETCHING OF RUTHENIUM," filed October 19, 2021, U.S. Non-Provisional Patent Application No. 17 / 674,579, entitled "METHOD FOR WET ATOMIC LAYER ETCHING OF RUTHENIUM," filed February 17, 2022, and U.S. Non-Provisional Patent Application No. 17 / 674,593, entitled "RUTHENIUM CMP CHEMISTRY BASED ON HALOGENATION," filed February 17, 2022, the disclosures of which are expressly incorporated herein by reference in their entireties.

[0002] The present disclosure relates to the fabrication of semiconductor devices, and in particular to the removal and etching of polycrystalline materials such as metals. During typical semiconductor fabrication, various metals formed on a substrate can be removed by patterned etching, chemical-mechanical polishing, and other techniques. Various techniques are known for etching layers in a substrate, including plasma-based or gas-phase etching (also called dry etching) and liquid-based etching (also called wet etching). Wet etching generally involves dispensing a chemical solution across the surface of the substrate or immersing the substrate in the chemical solution. The chemical solution often contains a solvent, chemicals designed to react with the material on the substrate surface, and chemicals that promote dissolution of the reaction products. When the substrate surface is exposed to the etching solution, material is removed from the substrate. The composition and temperature of the etching solution can be controlled to control the etching rate, specificity, and residual material on the substrate surface after etching. [Background technology]

[0003] Both thermodynamics and kinetics play a role in formulating an etchant. For successful etching, the desired reaction must be favorable both thermodynamically and kinetically. Etching polycrystalline materials presents much more stringent requirements for success. For these materials, it is desirable for the removal rate for each individual crystallite face and grain boundary geometry to be substantially similar, regardless of the crystallite morphology or environment. Surface roughness plays an important role in the interface quality and electrical properties of nanoscale features. When etching nanoscale polycrystalline materials, the different etch rates at grain boundaries compared to different crystallite faces cause surface roughening during etching. Furthermore, material removal rates should be uniform at both macroscopic and microscopic levels and desirably occur at rates compatible with mass production. While macroscopic uniformity can be addressed through careful manipulation, microscopic uniformity depends on the chemistry of the etch itself.

[0004] As substrate feature geometries continue to shrink and the types of structures evolve, the challenges of etching substrates increase. One technique that has been utilized to address these challenges is atomic layer etching (ALE). ALE is a process that sequentially removes thin layers through one or more self-limiting reactions. For example, ALE typically refers to techniques that can etch with atomic precision, i.e., remove one or a few monolayers of material at a time. Generally, ALE processes rely on chemical modification of the surface to be etched and subsequent selective removal of the modified layer. Thus, ALE processes provide improved performance by separating the etching process into sequential steps of surface modification and removal of the modified surface. In some embodiments, ALE processes can include multiple, cyclical series of layer modification and etching steps, where the layer modification step modifies the exposed surface and the etching step selectively removes the modified layer. In such processes, a series of self-limiting reactions can occur, and cycles can be performed repeatedly until a desired or specified amount of etching is achieved. In other embodiments, the ALE process can use only one cycle.

[0005] Various ALE processes are known, including plasma ALE, thermal ALE, and wet ALE. Like all ALE processes, wet ALE is typically a cyclical process that selectively removes material from a surface using sequential, self-limiting reactions. However, unlike thermal and plasma ALE, the reactions used in wet ALE occur primarily in the liquid phase. Compared to other ALE processes, wet ALE is often desirable because it can be performed at (or near) room temperature and atmospheric pressure. Additionally, the self-limiting nature of the wet ALE process results in a smooth surface during etching, rather than the surface roughness commonly observed in other etching processes.

[0006] The wet ALE process typically begins with a surface modification step in which the material is exposed to a first solution to produce a self-limiting modified surface layer. The modified surface layer can be produced by oxidation, reduction, ligand binding, or ligand exchange. Ideally, the modified surface layer is limited to the top monolayer of the material and acts as a passivation layer to prevent further modification reactions. After the modified surface layer is formed, the wet ALE process can then proceed to a subsequent dissolution step in which the modified surface layer is exposed to a second solution to selectively dissolve the modified surface layer. The dissolution step must selectively dissolve the modified surface layer without removing the underlying unmodified material. This selectivity can be achieved by using a different solvent in the dissolution step than that used in the surface modification step, by changing the pH, or by changing the concentration of other components in the first solvent. The wet ALE cycle can be repeated until the desired or specified etching amount is achieved.

[0007] Ruthenium (Ru) is a noble metal currently being considered as a copper replacement for back-end metallization, as well as front-end functions such as buried power rails (power rails located under active devices). However, due to its noble nature, etching Ru is difficult. Various etching processes can be used to etch Ru. For example, co-pending U.S. Patent Application Publication No. 17 / 580,936, entitled "Dynamically Adjusted Purge Timing in Wet Atomic Layer Etching," filed January 21, 2022, describes a wet ALE process for etching various transition metals, including ruthenium. In this co-pending application, a modified surface layer is formed by exposing the Ru metal surface to an oxidizing agent. While a ruthenium dioxide (RuO) surface layer can be easily formed using a chemical solution containing dissolved oxygen or another oxidizing agent, the stability and insolubility of this surface oxide make it difficult to process in an etching process. Therefore, conventional etching processes typically use strong oxidizing agents to generate soluble or volatile ruthenium compounds.

[0008] Some commercially available ruthenium etchants contain strong oxidizing agents, such as sodium hypochlorite, cerium ammonium nitrate, and periodic acid, which oxidize ruthenium to form ruthenium tetroxide (RuO4). Of these chemicals, the most effective etchants, cerium ammonium nitrate and sodium hypochlorite, are problematic because they pose a risk of metal contamination in the resulting device. For example, the incorporation of trace amounts of sodium or cerium into the front end can significantly degrade transistor performance. Periodic acid, on the other hand, is expensive and cannot be used to provide a cost-effective ruthenium etching process. Additionally, conventional etching processes often result in rough ruthenium surfaces after etching. This is because ruthenium grain boundaries tend to be much more reactive than grain surfaces, resulting in preferential etching at the grain boundaries compared to the grain surfaces. Summary of the Invention [Problem to be solved by the invention]

[0009] The combination of poor post-etch surface morphology, risk of metal contamination and chemical cost demonstrates the need for the development of better ruthenium etch chemistries. [Means for solving the problem]

[0010] The present disclosure provides a new wet atomic layer etching (ALE) process for etching ruthenium. More specifically, the present disclosure provides various embodiments of methods that utilize new etching chemistries for etching ruthenium in a wet ALE process. Unlike conventional etching processes for ruthenium, the wet ALE process described herein for etching ruthenium is metal-free, cost-effective, and improves surface roughness during etching.

[0011] Novel metal-free etchants are desirable for etching ruthenium to avoid the risk of contaminating semiconductor devices. Surface morphology is also important for some etching applications, such as etchback in self-aligned vias. The polycrystalline nature of ruthenium makes it susceptible to pitting corrosion when the etchant preferentially attacks grain boundaries. Etchant chemistry should at least not roughen the surface from its initial roughness, and ideally improve the surface roughness during etching. Acceptable surface morphology can be achieved through the formation of a self-limiting passivation layer that is selectively removed in a cyclical wet ALE process.

[0012] In some embodiments, the present disclosure provides a cyclical wet ALE process that begins with forming an insoluble ruthenium halide or ruthenium oxyhalide layer on a metal surface. For example, ruthenium metal can be exposed to a halogenating agent in a self-limiting surface modification step to chemically modify the exposed surface of the ruthenium metal and form a modified surface layer. The modified surface layer can be a ruthenium halide, such as, but not limited to, ruthenium chloride, ruthenium fluoride, or ruthenium bromide. The modified surface layer can also be a ruthenium oxyhalide, such as, but not limited to, ruthenium oxychloride or ruthenium oxyfluoride. A dissolution step can then be performed to selectively remove the modified surface layer. For example, the modified surface layer can be exposed to a dissolution solution to selectively dissolve the modified surface layer without removing the ruthenium metal underlying the modified surface layer. The dissolution process is selective to the modified layer over the ruthenium metal and uses ligand-assisted dissolution to draw the modified layer of ruthenium halide or oxyhalide into solution.

[0013] Thus, disclosed herein is a wet ALE process for etching ruthenium that is metal-free, leaves the etched ruthenium surface smoother than the as-received surface, and can be accomplished using commercially available chemistries. The etching chemistry described above differs from conventional wet ruthenium etching chemistries in that it primarily uses halide, rather than oxidation, based on forming ruthenium species on the ruthenium surface that are soluble in the dissolution solution. Using the techniques described herein, a passivating layer of insoluble metal halide or oxyhalide is formed during the surface modification step, as opposed to the metal oxide layer typically formed when using conventional wet ALE chemistries.

[0014] In another embodiment, the present disclosure provides a cyclical wet ALE process that begins with the formation of a ruthenium salt passivation layer. For example, the exposed surface of ruthenium metal can be exposed to an oxidizing solution containing hydrochloric acid (HCl) to form an insoluble, self-limiting ruthenium salt passivation layer over the ruthenium metal. The ruthenium species formed on the exposed surface of the ruthenium metal can be controlled by the HCl concentration, and the solubility of the ruthenium salt formed can then be controlled by the HCl concentration and the cationic species present in the oxidizing solution. The ruthenium salt passivation layer can then be removed in one of two ways: (a) by dissolving the ruthenium salt passivation layer in a different solvent, or (b) by using ion exchange to improve the solubility of the ruthenium salt passivation layer in the first solvent. Similar to the previously disclosed embodiment, this embodiment provides a metal-free ruthenium etching process using general-purpose chemistry that reduces the surface roughness of the ruthenium during etching. Additionally, the wet ALE process described in this embodiment may offer the further advantage of allowing isotropic or anisotropic etching by changing the oxidizing agent used in the surface modification step.

[0015] As mentioned above and further described herein, the present disclosure provides various embodiments of methods utilizing new etching chemistries for etching ruthenium in a wet ALE process. It should be understood that the order of description of the different steps described herein is presented for clarity of explanation. Generally, these steps may be performed in any suitable order. In addition, although different features, techniques, configurations, etc. herein may each be referred to in different parts of the present disclosure, it is intended that each concept may be performed independently of each other or in combination with each other. Accordingly, the present invention may be embodied and viewed in many different ways.

[0016] According to one embodiment, an etching method for etching ruthenium is provided herein. The method may generally include receiving a substrate having ruthenium formed thereon, wherein a ruthenium surface is exposed at the surface of the substrate, and exposing the surface of the substrate to a first etching solution such that the first etching solution contacts the ruthenium surface. The first etching solution may include one or more chemical species that cause a passivation layer to form on the ruthenium surface, the passivation layer being self-limiting and insoluble in the first etching solution. The method may then include, following the formation of the passivation layer, removing the first etching solution from the surface of the substrate, and exposing the surface of the substrate to a second etching solution comprising a reactant and a solvent, wherein the reactant reacts with the passivation layer to form a soluble chemical species that is dissolved by the solvent. The method may then include removing the second etching solution and the soluble chemical species from the substrate.

[0017] In some embodiments, the method may further include repeating the steps of exposing the surface of the substrate to a first etching solution, removing the first etching solution, exposing the surface of the substrate to a second etching solution, and removing the second etching solution for several cycles until a predetermined amount of ruthenium is removed from the substrate.

[0018] A variety of different etching chemistries can be used for the first and second etching solutions. In some embodiments, one or more chemical species in the first etching solution can include a halogenating agent dissolved in a first solvent. For example, the halogenating agent can include a chlorinating agent, a fluorinating agent, or a brominating agent. The halogenating agent chemically modifies the ruthenium surface to form a ruthenium halide passivation layer. In some embodiments, the first etching solution can include a chlorinating agent such as trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent can include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon. In some embodiments, the ruthenium halide passivation layer can include ruthenium trichloride (RuCl).

[0019] In some embodiments, the reactant in the second etching solution can be a ligand species that reacts and bonds with the ruthenium halide passivation layer to form a soluble species that is dissolved by the solvent. In some embodiments, the ligand species can include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the solvent in the second etching solution can include a base.

[0020] In other embodiments, the one or more chemical species in the first etching solution may include an oxidizing agent, a cation, and a chlorine source that reacts with ruthenium. In such embodiments, the passivation layer formed on the ruthenium surface may include ruthenate or perruthenate. In one embodiment, the chlorine source may include hydrochloric acid (HCl). In such embodiments, the amount of oxidation of the passivation layer may be controlled by the concentration of hydrochloric acid in the first etching solution.

[0021] According to another embodiment, provided herein is a method for etching a substrate using a wet atomic layer etching (ALE) process. The method may generally include: a) receiving a substrate having a ruthenium (Ru) layer thereon; b) exposing the Ru layer to a first etching solution containing a halogenating agent to form a chemically modified Ru surface layer containing a ruthenium halide or oxyhalide; c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate; d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer; 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) through e) for one or more cycles.

[0022] In some embodiments, the first etching solution used in step b) can include a chlorinating agent dissolved in a first solvent. For example, the chlorinating agent can include trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent can include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon. In such embodiments, the chlorinating agent can react with the Ru layer to form ruthenium chloride.

[0023] In some embodiments, the second etching solution used in step d) can include a ligand dissolved in a second solvent. For example, the ligand can include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent can include a base. In such embodiments, the ligand can react and bond with the chemically modified Ru surface layer to form a soluble species that dissolves in the second solvent.

[0024] According to yet another embodiment, provided herein is another method for etching a substrate using a wet atomic layer etching (ALE) process. The method generally includes: a) receiving a substrate having a ruthenium (Ru) layer thereon; b) exposing the Ru layer to a first etching solution containing an oxidant, a cation, and a chlorine source reactive with the Ru layer to form a chemically modified Ru surface layer containing a ruthenium salt; c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate; d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer; 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) through e) one or more cycles.

[0025] In some embodiments, the chlorine source in the first etching solution can include hydrochloric acid (HCl). In some embodiments, the oxidizer in the first etching solution can include ammonium persulfate (APS) or tetrabutylammonium peroxymonosulfate (TBAPMS). In some embodiments, the cation in the first etching solution can include tetramethylammonium (TMA), tetraalkylammonium, phosphonium, pyridinium, pyrrolidinium, or sulfonium ions. In some embodiments, the first etching solution can further include a salt, wherein the salt includes tetramethylammonium chloride (TMAC) or 1-butyl-3-methylimidazolium chloride.

[0026] In some embodiments, the chemically modified Ru surface layer can be insoluble in the first etching solution and soluble in the second etching solution, in such embodiments, the second etching solution can include trichlorobenzene.

[0027] In some embodiments, the chemically modified Ru surface layer may be insoluble in the first etching solution, and the method may further include using ion exchange to increase the solubility of the chemically modified Ru surface layer. In such embodiments, the second etching solution may include potassium chloride (KCl) and potassium hydroxide (KOH).

[0028] It should be noted that this Summary section does not specify every embodiment and / or inherently novel aspect of the invention described in this disclosure or claimed herein. Instead, this Summary provides only a preliminary discussion of various embodiments and corresponding points of novelty over the prior art. For additional details and / or anticipated aspects of the invention and embodiments, the reader is referred to the Detailed Description section and corresponding figures of the present disclosure as further discussed below.

[0029] A more detailed understanding of the present invention and its advantages will be obtained by referring to the following description in conjunction with the accompanying drawings, in which like reference numerals indicate like features, and in which it is to be noted, however, that the accompanying drawings illustrate only exemplary embodiments of the disclosed concepts and are not intended to limit the scope of the present invention, as the disclosed concepts may encompass other embodiments that are equally effective. [Brief explanation of the drawings]

[0030] [Figure 1] 1 illustrates an example of a cyclic wet atomic layer etching (ALE) process that can be used to etch ruthenium in accordance with the present disclosure. [Figure 2] 1 is a graph showing exemplary etch amounts (expressed in nanometers, nm) that may be achieved as a function of cycle number when attempting to etch ruthenium (Ru) using various etching conditions. [Figure 3A] 1 is a graph illustrating exemplary etch rates (expressed in nm / cycle) that may be achieved as a function of surface modification solution immersion time (expressed in seconds). [Figure 3B]1 is a graph illustrating exemplary etch rates (expressed in nm / cycle) that may be achieved as a function of dissolution solution immersion time (expressed in seconds). [Figure 4] 1 shows scanning electron microscope (SEM) images of as-deposited and etched ruthenium for various etching conditions. [Figure 5] 1 illustrates an example of a salt-mediated wet ALE process that may be used to etch ruthenium in accordance with the present disclosure. [Figure 6A] 1 is a graph of quartz crystal microbalance (QCM) data from a salt-mediated wet ALE process experiment showing the etching behavior of ruthenium for various oxidant concentrations. [Figure 6B] 1 is a graph of QCM data from a salt-mediated wet ALE process experiment showing the etching behavior of ruthenium with and without a chloride salt (e.g., TBAC). [Figure 6C] 1 is a graph of QCM data obtained from a salt-mediated wet ALE process experiment, the data showing the etching behavior of ruthenium for various HCl concentrations. [Figure 6D] 1 is a graph of QCM data obtained from a salt-mediated wet ALE process experiment, the data showing the effect of cationic species on the etching behavior of ruthenium. [Figure 7] 1 is a graph of QCM data obtained from a salt-mediated wet ALE process experiment showing the etching behavior of ruthenium using various dissolution solution compositions. [Figure 8] FIG. 1 is a block diagram of an exemplary processing system in which the techniques described herein can be used to etch polycrystalline materials such as ruthenium. [Figure 9] FIG. 1 is a flow chart diagram illustrating one embodiment of a method utilizing the techniques described herein. [Figure 10] FIG. 10 is a flow chart diagram illustrating another embodiment of a method utilizing the techniques described herein. [Figure 11]FIG. 10 is a flow chart diagram illustrating yet another embodiment of a method utilizing the techniques described herein. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present disclosure provides a new wet atomic layer etching (ALE) process for etching ruthenium. More specifically, the present disclosure provides various embodiments of methods utilizing new etching chemistries for etching ruthenium in a wet ALE process. In some embodiments, the wet ALE process described herein can use halogenation, rather than oxidation, to form an insoluble ruthenium halide or ruthenium oxyhalide passivation layer over unmodified ruthenium metal in the surface modification step of the wet ALE process. The ruthenium halide or ruthenium oxyhalide passivation layer can then be dissolved in a dissolution solution, which uses ligand-assisted dissolution to pull the ruthenium halide or ruthenium oxyhalide passivation layer into solution. In other embodiments, the wet ALE process described herein can form an insoluble ruthenium salt passivation layer over unmodified ruthenium metal by exposing the ruthenium metal to an oxidizing solution containing concentrated hydrochloric acid (HCl). The ruthenium salt passivation layer can then be removed by (a) dissolving the ruthenium salt passivation layer in a different solvent, or (b) using ion exchange to increase the solubility of the ruthenium salt passivation layer in the first solvent.

[0032] The techniques described herein can generally be used to etch ruthenium, a polycrystalline precious metal. While many chemistries can be used to etch ruthenium, the polycrystalline nature of ruthenium makes it susceptible to pitting corrosion when the etchant preferentially attacks grain boundaries. The etchant chemistry must at least not initially roughen the surface, and ideally improve the surface roughness during etching. Acceptable surface morphology can be achieved through the formation of a self-limiting passivation layer that is selectively removed in a cyclical wet ALE process.

[0033] As noted above, conventional methods for etching ruthenium often use an oxidizing agent (or oxidant) to form a ruthenium metal oxide passivation layer on the ruthenium surface. This ruthenium metal oxide passivation layer can be an insoluble ruthenium dioxide (RuO2) surface layer or a soluble ruthenium tetroxide (RuO4) surface layer on the exposed surface of the ruthenium. The oxidizing agents used in these methods either (a) result in an insoluble modified surface layer (such as RuO2) that is difficult to treat in the etching process, or (b) are expensive and / or pose a risk of metal contamination.

[0034] The techniques described herein offer several advantages over other conventional methods used to etch ruthenium. For example, the wet ALE process described herein utilizes etching chemistries that are metal-free, cost-effective, and improve surface roughness during etching. In addition to the advantages provided by the new etching chemistries disclosed herein, the techniques described herein offer the advantages of ALE (e.g., precise control of total etch volume, control of surface roughness, and improved wafer-scale uniformity) and wet etching (e.g., simplicity of the etch chamber, ambient temperature and pressure etching conditions, etc.). Thus, the techniques described herein offer a unique method for etching ruthenium.

[0035] Generally, the wet ALE process described herein can be used to etch ruthenium by performing one or more wet ALE cycles, each cycle including a surface modification step and a dissolution step. In the surface modification step, the exposed surface of the ruthenium can be exposed to a surface modification solution to chemically modify the exposed surface of the ruthenium and form a modified surface layer (e.g., a ruthenium halide, ruthenium oxyhalide, or ruthenium salt passivation layer). In the dissolution step, the modified surface layer can be exposed to a dissolution solution to selectively remove the modified surface layer by dissolving it. A purge step can be performed between the surface modification and dissolution steps to prevent the surface modification and dissolution solutions from mixing, and the process can be cyclically repeated until the desired amount of etching is achieved.

[0036] FIG. 1 illustrates an example of a wet ALE process according to the present disclosure. More specifically, FIG. 1 illustrates exemplary steps performed during one cycle of the wet ALE process. In the process illustrated in FIG. 1, a polycrystalline material 105 surrounded by a 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 being etched can be a noble metal, such as, but not limited to, ruthenium (Ru). In some embodiments, the surface modification solution 115 can include a halogenating agent 120. For example, the surface modification solution 115 can include a first solvent containing a chlorinating agent, a fluorinating agent, or a brominating agent. In other embodiments, the surface modification solution 115 can include an oxidizing agent and a chloride salt in concentrated hydrochloric acid (HCl).

[0037] 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 modified surface layer 125 (e.g., a ruthenium halide, ruthenium oxyhalide, or ruthenium salt-modified surface layer). In some cases, the chemical reaction to form the modified surface layer 125 can be fast and self-limiting. In other words, the reaction products 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 the underlying surface. Of course, neither the polycrystalline material 105 to be etched nor the modified surface layer 125 may be soluble in the surface modification solution 115. In some cases, the surface modification process 100 shown in FIG. 1 can continue until the surface reaction is saturated.

[0038] After the modified surface layer 125 is formed, 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 modified surface layer 125 or the reagents present in the surface modification solution 115. In some embodiments, the first purge solution 135 used in the first purge step 130 may use the same solvent as that previously used in the surface modification step 100. In other embodiments, a different solvent may be used for 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.

[0039] After rinsing, a dissolution step 140 is performed to selectively remove the modified surface layer 125. In the dissolution step 140, the modified surface layer 125 is exposed to a dissolution solution 145 to selectively remove or dissolve the modified surface layer 125 without removing the unmodified polycrystalline material 105 underlying the modified surface layer 125. The modified surface layer 125 must be soluble in the dissolution solution 145, while the unmodified polycrystalline material 105 underlying the modified surface layer 125 must be insoluble. The solubility of the modified surface layer 125 allows it to be removed through dissolution in the bulk dissolution solution 145. In some embodiments, the dissolution step 140 can continue until the modified surface layer 125 is completely dissolved.

[0040] Depending on the surface modification solution 115 used during the surface modification process 100 and / or the modified surface layer 125 formed, a variety of different dissolution solutions 145 can be used in the dissolution process. In some embodiments, for example, the dissolution solution 145 can be an aqueous solution containing ligands 150 that aid in the dissolution process. For example, the ligands 150 can react or bond with the modified surface layer 125 to form a soluble species that dissolves in the dissolution solution 145. In other embodiments, the dissolution solution 145 can be a second solvent that is different from the first solvent used in the surface modification solution 115. In other embodiments, the dissolution solution 145 can include alkali metal ions in a basic solution. In such embodiments, ion exchange can be used to improve the solubility of the modified surface layer 125 in aqueous solutions.

[0041] 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 as or different from the first purge solution 135. In some embodiments, the second purge solution 165 may use the same solvent as used in the dissolution solution 145. The second purge step 160 may generally continue until the dissolution solution 145 and / or reactants contained in the dissolution solution 145 are completely removed from the surface of the substrate.

[0042] 1 includes: a) a first surface modification step 100, in which the exposed surface of the polycrystalline material 105 is chemically modified by exposing the exposed surface of the polycrystalline material 105 to a surface modification solution 115 to form a modified surface layer 125; b) a first purge step 130, in which the substrate is rinsed with a first purge solution 135 to remove excess reactants from the surface; c) a dissolution step 140, in which the modified surface layer is selectively removed or dissolved by exposing the modified surface layer to a dissolution solution 145 to selectively remove the modified surface layer; and d) a second purge step 160, in which the substrate is rinsed with a second purge solution 165 to replace the dissolution solution 145 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 polycrystalline material 105 is removed. The cyclical wet ALE process shown in FIG. 1 is just one example of an etching process that can be used to etch a polycrystalline material 105 such as ruthenium.

[0043] Wet ALE of ruthenium requires the formation of a self-limiting passivation layer on the ruthenium surface. Formation of this passivation layer is achieved by exposing the ruthenium surface to a first etching solution (i.e., surface modification solution 115) that allows or initiates a chemical reaction between chemical species in the solution and the ruthenium surface. This passivation layer must be insoluble in the solution used to form it, but freely soluble in the second etching solution (i.e., dissolution solution 145) used to dissolve it.

[0044] The present disclosure contemplates a wide variety of etching chemistries that can be used for the surface modification solution 115 and the dissolving solution 145 when etching ruthenium using the wet ALE process shown in FIG. 1. Example etching chemistries are described in more detail below. Mixing these solutions can lead to sequential etching processes, loss of etching control, and a rough post-etch surface, all of which negate the benefits of wet ALE. Therefore, 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 dissolving solution 145 on the substrate surface.

[0045] According to one embodiment, the ruthenium surface can be exposed to a surface modification solution 115 comprising a first solvent containing a chlorinating agent that chemically modifies the ruthenium surface to form a ruthenium chloride passivation layer. In one embodiment, ruthenium trichloride (RuCl) can be used as the passivation layer. For example, a RuCl 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 the oxidizing agent and the chlorine source in the reaction. TCCA chemically oxidizes the ruthenium surface to form a ruthenium trichloride (RuCl) passivation layer on the ruthenium surface, but no metal oxide is formed in the reaction. This differs from conventional ruthenium etching chemistries, which utilize an oxidizing agent (or oxidant) to form a ruthenium metal oxide passivation layer.

[0046] The chlorine chemistry of ruthenium is quite complex. Two distinct crystalline phases of RuCl3 exist. α-RuCl3 is almost completely insoluble, while β-RuCl3 is hygroscopic and freely soluble in water, alcohol, and many organic solvents. Additionally, the presence of oxygen or water during chlorination can lead to the formation of mixed oxychlorides. These oxychlorides tend to be highly soluble. Based on this chemistry, in some embodiments, the α-phase of RuCl3 is considered the preferred passivation layer herein. However, phase formation is controlled by the reaction conditions.

[0047] The self-limiting passivation layer formed during the surface modification process 100 must be removed after each cycle. A second solution is used in the dissolution process 140 to selectively dissolve this modified layer. When TCCA dissolved in EA is used in the surface modification solution 115 to form α-RuCl on the ruthenium surface, pure solvents do not work well in the dissolution process 140 because it is difficult to dissolve α-RuCl. However, reactive dissolution can be used to effectively remove the ruthenium chloride layer. In reactive dissolution, ligands dissolved in the second solvent react with the surface to form soluble species that dissolve in the dissolution solution 145. Many different ligand species can be used for reactive dissolution of the RuCl passivation layer. In one embodiment, ethylenediaminetetraacetic acid (EDTA) can be used as the ligand species for reactive dissolution. EDTA reacts with RuCl to form a Ru-EDTA complex that is soluble in aqueous solution. This reaction is base-catalyzed, so the dissolution solution must contain EDTA and a strong base. Mixing of the TCCA-containing surface modification solution 115 and the EDTA-containing dissolution solution 145 leads to sequential etching processes, loss of etching control, and surface roughening. Therefore, solvent rinse steps (i.e., purging steps 130 and 160) are required to prevent direct contact between the two etching solutions on the Ru metal surface.

[0048] In the etching chemistry described above, the reactant used to chlorinate the ruthenium surface is TCCA, although many chlorinating agents will work in this process. Alternative chlorinating agents include, but are not 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 the surface modification process 100. In addition, other ruthenium halides can also be used as the passivation layer. For example, in addition to RuCl, ruthenium fluoride and ruthenium bromide can be used, respectively. These ruthenium halides can be formed using fluorinating or brominating agents such as, but not limited to, 1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate, N-fluorobenzenesulfonimide, N-bromosuccinimide, or dibromoisocyanuric acid.

[0049] In the etching chemistry described above, the first solvent used in the chlorination reaction is EA, although other solvents such as acetone, acetonitrile, and chlorocarbons may also be used. Again, this is not an exhaustive list of solvents that may be used in the surface modification step 100.

[0050] In the etching chemistry described above, the dissolving solution 145 is an aqueous solution of EDTA as the ligand 150 and tetramethylammonium hydroxide ((CH3)4NOH) as the base. Alternative ligands for dissolving 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 dissolving 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 dissolving solution 145, as they are only needed to deprotonate the ligand 150 to enable bonding with the ruthenium surface.

[0051] Etching experiments were performed on coupons cut from 300 mm silicon wafers with various thicknesses of chemical vapor deposition (CVD) ruthenium deposited on one side. The etching recipe used for ruthenium etching included multiple wet ALE cycles, each consisting of a 1-minute immersion in 5% TCC dissolved in EA, followed by an EA rinse, a 30-second immersion in a 50 mM EDTA and 1 M KOH solution in HO (or deionized water), a 1 M KOH rinse (or deionized water rinse), and an isopropyl alcohol (IPA) rinse followed by 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. Thermal dissolution was performed at 100 °C.

[0052] The total amount etched (nm) as a function of cycle number for the various etching conditions described above is shown in graph 200 in Figure 2. Reactive dissolution at room temperature (RT) results in an etch rate of 0.07 nm / cycle. This is much less than a complete monolayer of ruthenium, indicating that the dissolution rate may be slow at room temperature. When the dissolution solution is heated, the amount etched per cycle increases significantly (e.g., 0.26 nm / cycle), confirming that the dissolution is kinetically limited. The etch rate decreases with the number of cycles and eventually stops when experiments are performed using deionized water for dissolution rather than EDTA and KOH solutions. This behavior is observed when the passivation layer is treated with α-RuCl, β-RuCl, and various ruthenium oxychlorides (RuO). x Cl y ) can be explained when it contains a mixture of β-RuCl3 and RuO x Cl y Although α-RuCl is water-soluble, α-RuCl remains on the surface. The amount of α-RuCl on the surface increases with each cycle until the entire surface is passivated with insoluble α-RuCl, making etching unsustainable. This behavior demonstrates that the ligand 150 in the dissolution solution 145 is beneficial for problem-free etching.

[0053] The wet ALE process described above relies on both the surface modification and dissolution reactions being self-limiting. Self-limiting means that only a limited thickness of ruthenium at the surface is modified or removed, regardless of the length of time a given etching solution is in contact with the ruthenium surface. A self-limiting reaction can be limited to one or more monolayers of reaction or a partial monolayer of reaction. The self-limiting behavior of the ruthenium etch chemistry and etching recipe described above is illustrated in graphs 300 and 350 shown in Figures 3A and 3B. In Figure 3A, a coupon with CVD ruthenium is etched by immersing the coupon in 5% TCCA dissolved in EA for X seconds, rinsing the coupon in EA, immersing the coupon in 200 mM (NH4)2EDTA and 1 M KOH aqueous solution at 100 °C for 10 seconds, rinsing the coupon in deionized water, followed by rinsing with IPA and blow drying. In Figure 3B, the etching recipe is modified by immersing the coupon in 5% TCCA dissolved in EA for 10 seconds and then immersing the coupon in 200 mM (NH4)2EDTA and 1 M KOH aqueous solution at 100 °C for X seconds.

[0054] Graph 300 in Figure 3A shows that when the TCCA immersion time is doubled from 5 seconds to 10 seconds, the chlorination reaction is self-limiting—the amount etched per cycle remains unchanged. Graph 350 in Figure 3B shows that the dissolution reaction is also self-limiting. When the dissolution time is doubled from 10 seconds to 20 seconds, the amount etched per cycle remains unchanged. The amount etched per cycle in Figures 3A and 3B is greater than that shown in Figure 2 due to different experimental conditions. For example, a higher ligand concentration is used in the dissolution solution in Figures 3A and 3B, and a diammonium salt of EDTA is used instead of EDTA. In these experiments, approximately two monolayers of ruthenium are removed with each etching cycle.

[0055] The wet ALE process described above results in a smooth etched surface. To observe the etched surface, scanning electron microscope (SEM) images of as-deposited ruthenium (400) and etched ruthenium (410, 420) were acquired under various etching conditions. The SEM images shown in Figure 4 demonstrate that the ruthenium metal surface is smoothed during the etching process. Figure 4 shows two sets of post-etch SEM images. In the first set of post-etch SEM images 410, a coupon is etched using 50 mM EDTA in the dissolution solution. Using this etching solution, approximately 4 nm of etching was achieved after 20 cycles. The second set of post-etch SEM images 420 shows a coupon etched using 100 mM diammonium EDTA in the dissolution solution. This coupon was etched approximately 9 nm after 25 cycles. In both cases, the etching volume calculated from the four-point probe resistivity measurements of the ruthenium film and the etching volume measured from the SEM cross section are in good agreement. Top and oblique views of post-etch SEM images 410 and 420 show that the roughness of the ruthenium surface appears to have been reduced during the etching process.

[0056] The ruthenium wet ALE process described above and illustrated in FIGS. 1-4 can be realized using a variety of 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, purging can be performed by rinsing the sample or by immersing it in an appropriate solvent bath. The ruthenium wet ALE process can also be performed using a spinner. For example, the ruthenium sample can be rotated while the etching solution is dispensed from a nozzle positioned above the sample. The rotational motion of the sample distributes the solution across the surface. After a set exposure time, the nozzle begins dispensing the next solution in the etching recipe. This process continues throughout the entire etching cycle, and the cycle is repeated as needed to remove the desired amount of metal. For mass production, conventional tools such as wet etching and rinsing tools can be used to dispense the etching and rinsing solutions.

[0057] Ruthenium chloride (RuCl) and other ruthenium halides and oxyhalides provide self-limiting modified surface layers that work well for ruthenium wet ALE, but they are not the only options available for producing self-limiting passivation layers on ruthenium surfaces. Alternative chemistries to ruthenium wet ALE can be used to form self-limiting modified surface layers (or passivation layers) composed of ruthenates or perruthenates. In some embodiments, ruthenates or perruthenates can be formed during the surface modification step 100 by exposing the ruthenium surface to an oxidizing solution containing an oxidizing agent, a suitable cation, and a chlorine source that reacts with ruthenium, such as concentrated hydrochloric acid (HCl). Oxidation of ruthenium in the HCl solution produces RuO. x Cl y z- A ruthenium salt passivation layer containing polyanions is formed. HCl acts as a mild reducing agent, limiting the final oxidation state of ruthenium. Therefore, the ruthenium species formed on the surface can be controlled by the concentration of HCl in the oxidizing solution. In addition, the solubility of the ruthenium salt can be controlled by the counterions coordinated to the ruthenium polyanions in the salt. Therefore, the solubility of the ruthenium salt passivation layer can be controlled by the HCl concentration and the cations present in the oxidizing solution.

[0058] After the insoluble ruthenium salt passivation layer is formed on the ruthenium surface, it can be removed in one of two ways, e.g., via solvent exchange or ion exchange, in a subsequent dissolution step 140. For example, the insoluble salt can be dissolved in a pure solvent in a dissolution step utilizing solvent exchange, or the insoluble salt can be removed through a salt metathesis reaction that exchanges cations to improve the solubility of the ruthenium salt in aqueous solution (e.g., ion exchange). A diagram of this salt-mediated wet ALE process is shown in Figure 5.

[0059] In an example of a salt-mediated wet ALE process 500 shown in Figure 5, a ruthenium surface is exposed to an aqueous solution containing ammonium persulfate (APS) or tetrabutylammonium peroxymonosulfate (TBAPMS) as an oxidant in a concentrated HCl solution. In addition, salts such as tetramethylammonium chloride (TMAC) or 1-butyl-3-methylimidazolium chloride are present in the aqueous solution to provide the cations necessary for the formation of ruthenium salts. The stability of the ruthenium salt passivation layer generally depends on the HCl concentration and the cation species. In one example experiment, a stable passivation layer was formed at a 6M HCl concentration using TMAC as the salt species.

[0060] After the insoluble ruthenium salt passivation layer is formed on the ruthenium surface, it can be removed by solvent exchange or ion exchange. In the solvent exchange dissolution method, the insoluble ruthenium salt passivation layer can be dissolved in a pure solvent. In the example process 500 shown in FIG. 5, the insoluble salt is dissolved in trichlorobenzene. Other solvents can also be used. In the ion exchange dissolution method, the insoluble ruthenium salt passivation layer can be removed by using ion exchange to improve the solubility of the ruthenium salt passivation layer in the aqueous solution used to form the ruthenium salt passivation layer. In the example process 500 shown in FIG. 5, for example, the ruthenium salt passivation layer can be removed from the ruthenium surface by exchanging MeN cations with K cations. This ion exchange improves the solubility of the ruthenium salt passivation layer, allowing it to dissolve in the aqueous solution.

[0061] Figures 6A-6D show quartz crystal microbalance (QCM) data obtained from a ruthenium wet ALE experiment in which the ruthenium surface was oxidized using an aqueous solution of APS, HCl, and a chloride salt (e.g., tetrabutylammonium chloride, TBAC) to form a ruthenium salt passivation layer, which was then dissolved in an aqueous solution of KOH and KCl. The graphs shown in Figures 6A-6D show the etching behavior of ruthenium for various oxidant concentrations, HCl concentrations, and cation species during the etching process.

[0062] Graph 600 shown in FIG. 6A illustrates the etching behavior at various APS concentrations (e.g., 0.1% APS, 0.5% APS, 1% APS, and 2% APS). The etching cycle includes oxidation in an aqueous solution containing APS, 6 M HCl, and 200 mM TBAC, followed by purging with 6 M HCl and 200 mM TBAC, dissolution in 1 M KCl and 100 mM KOH, and a second purging with 6 M HCl and 200 mM TBAC solution for 1 minute per step. As shown in graph 600, etching is relatively slow at 0.1% APS and no longer self-limiting at 2% APS, but exhibits moderately self-limiting etching behavior at intermediate APS concentrations.

[0063] Graph 610 shown in Figure 6B illustrates the effect of including and omitting TBAC from the etching solution. As shown in graph 610, without the tetrabutylammonium cation (TBA+), the oxidation is not self-limiting. This is likely due to the increased solubility of the acid species compared to the ammonium salt.

[0064] Graph 620 shown in FIG. 6C illustrates the etching behavior at various HCl concentrations (e.g., 1M, 6M, and 9M HCl). As shown in graph 620, no etching occurs at 1M HCl, a well-behaved cyclical etch occurs at 6M HCl, and continuous oxidation occurs at 9M HCl. The literature on chlorination chemistry for ruthenium indicates that RuO4 is oxidized to RuO2Cl4 in 1M HCl. 2- reduced to RuCl6 in 6M HCl. 2- reduced to RuCl6 in 9M HCl. 3- The difference in etching behavior with HCl concentration is probably due to the difference in the solubility properties of these ruthenium polyanions.

[0065] Graph 630 shown in Figure 6D illustrates the effect of different cation species on etching behavior when used in aqueous solutions to form a ruthenium salt passivation layer. As shown in graph 630, when TBA+ is used in aqueous solutions, oxidation is only semi-self-limiting, whereas when tetramethylammonium (TMA+) is used, oxidation becomes completely self-limiting. When 1-butyl-3-ethylimidazolium (BMIM+) is used in aqueous solutions, oxidation leads to continuous etching. The difference in solubility of the ruthenium salts formed with these three cations may explain the observed difference in etching behavior. While TMA+ was found to be self-limiting, it is not the only possible organic cation that can be used in this process. Other cations, such as other tetraalkylammonium, phosphonium, pyridinium, pyrrolidinium, or sulfonium ions, can also be used.

[0066] Dissolving the ruthenium salts formed by APS oxidation in aqueous solutions (e.g., containing 6 M HCl and 200 mM TMAC) requires K+ ion exchange in a basic solution. A study of etching behavior using different dissolution solution compositions (e.g., dissolution of KCl and HCl, dissolution of KCl, dissolution of KCl and KOH, and dissolution of NH4OH) is shown in Figure 7. As shown in graph 700 in Figure 7, the solution containing KCl and HCl contains K+ ions but does not etch because it has a low pH. The KCl solution contains K+ ions but has a neutral pH and does not etch. The ammonium hydroxide (NH4OH) solution has a high pH but does not contain K+ ions, so it does not etch. As shown in graph 700, the only dissolution solution that resulted in etching contained both KCl and KOH. This solution contains K+ ions at a high pH, ​​indicating that both of these properties are necessary to solubilize the ruthenium salts formed during the oxidation process. In addition to K+ ions, other alkali metal ions such as Li+, Na+, or Rb+ may also be used in the dissolution solution.

[0067] The etching chemistry described above causes anisotropic etching due to sulfate ions adsorbing to the C-plane of the ruthenium crystal lattice. Sulfate adsorbs strongly to this crystal plane but not to the m-plane of ruthenium. The adsorbed sulfate ions prevent further etching along the C-axis. TBAPMS, sold under the trade name OXONE, is an oxidizing agent containing a high concentration of sulfate. APS is another oxidizing agent that forms sulfate as a reaction product. Both of these oxidizing agents cause anisotropic etching of the ruthenium surface. In some embodiments, APS or TBAPMS used in this etching chemistry can be replaced with a sulfate-free oxidizing agent, which should enable isotropic etching of the ruthenium surface. However, the oxidizing agent must be compatible with concentrated HCl.

[0068] The ruthenium etch chemistry data described above and shown in Figures 5, 6A-6D, and 7 were collected using a QCM flow cell. However, the etch chemistry can be performed using several different techniques, such as dispensing the etchant solution in a spinner or sequentially immersing the sample to be etched in the etchant solution. The only important consideration when performing this etch chemistry is the temporal separation of the chemical exposures. That is, the oxidizing and dissolving solutions must be kept separate and prevented from mixing at the wafer surface. Mixing these two solutions can lead to sequential etching processes and increased surface roughness.

[0069] New etching chemistries for etching ruthenium in a wet ALE process have been described above. As noted above, the ruthenium etching chemistries disclosed herein either (a) use primarily halide to form an insoluble ruthenium halide or ruthenium oxyhalide passivation layer, which is selectively removed by ligand-assisted dissolution, or (b) use oxidation in concentrated HCl solutions containing chloride salts to form an insoluble ruthenium salt passivation layer, which is selectively removed by solvent or ion exchange. Unlike conventional etching chemistries, the etching chemistries described herein for etching ruthenium are metal-free, cost-effective, and improve surface roughness during etching.

[0070] The ruthenium wet ALE process described herein can be performed in a variety of semiconductor processing systems. While the ruthenium wet ALE process described herein can be achieved using many different process chambers, tools, and equipment, the processing equipment used to perform the ruthenium wet ALE process is preferably capable of operating at (or near) room temperature and atmospheric pressure (or near atmospheric pressure). In one implementation, the ruthenium wet ALE process described herein can be performed in a spin chamber. When a spin chamber is utilized, the etching solution is dispensed from a nozzle positioned over the substrate, and the substrate is dispensed by the rotational motion of a spin chuck positioned thereon.

[0071] FIG. 8 illustrates one embodiment of a processing system 800 capable of etching a polycrystalline material, such as ruthenium, on a surface of a substrate 830 using the techniques described herein. As shown in FIG. 8, the processing system 800 includes a process chamber 810, which in some embodiments may be a pressure-controlled chamber. In the embodiment shown in FIG. 8, the process chamber 810 is a spin chamber having a spinner 820 (or spin chuck) configured to spin or rotate at a rotational speed. The substrate 830 is held on the spinner 820 by, for example, electrostatic forces or vacuum pressure. In one example, the substrate 830 may be a semiconductor wafer having a polycrystalline material, such as ruthenium, formed on or within the substrate 830.

[0072] 8 further includes a liquid nozzle 840 positioned over the substrate 830 to dispense various etching solutions 842 onto the surface of the substrate 830. The etching solutions 842 dispensed onto the surface of the substrate 830 may generally include a surface modification solution for chemically modifying the ruthenium surface and forming a modified surface layer (e.g., a ruthenium halide, ruthenium oxyhalide, or ruthenium salt passivation layer) and a dissolution solution for selectively removing the modified surface layer from the ruthenium surface. A purge solution may also be dispensed onto the surface of the substrate 830 between the surface modification and dissolution steps to separate the surface modification solution and the dissolution solution. Examples of surface modification, dissolution, and purge solutions are described above.

[0073] 8 , the etching solution 842 may be stored in a chemical delivery system 846, which may include one or more reservoirs for holding various etching solutions 842 and a chemical injection manifold fluidly coupled to the process chamber 810 via liquid supply lines 844. In operation, the chemical delivery system 846 can selectively apply desired chemicals to the process chamber 810 via the liquid supply lines 844 and liquid nozzles 840 disposed within the process chamber 810. Thus, the chemical delivery system 846 can be used to distribute the etching solution 842 over the surface of the substrate 830. The process chamber 810 may further include a drain 850 for removing the etching solution 842 from the process chamber 810.

[0074] The components of processing system 800 may therefore be coupled to and controlled by controller 860, which may be coupled to corresponding memory storage units and a user interface (not shown). Various processing operations may be performed via the user interface, and various process recipes and operations may be stored in the memory storage unit. Accordingly, a given substrate 830 may be processed in process chamber 810 according to a particular recipe. In some embodiments, a given substrate 830 may be processed in process chamber 810 according to an etch recipe that utilizes the wet ALE techniques described herein to etch ruthenium.

[0075] The controller 860, shown in block diagram form in FIG. 8, can be implemented in a variety of ways. In one example, the controller 860 can be a computer. In another example, the controller 860 can include one or more programmable integrated circuits programmed to provide the functionality described herein. For example, one or more processors (e.g., microprocessors, microcontrollers, central processing units, etc.), programmable logic devices (e.g., complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), etc.), and / or other programmable integrated circuits can be programmed with software or other programming instructions to perform the functions of a predetermined plasma process recipe. It is further noted that the software or other programming instructions can be stored on one or more non-transitory computer-readable media (e.g., memory storage devices, flash memory, dynamic random access memory (DRAM), reprogrammable storage devices, hard drives, floppy disks, DVDs, CD-ROMs, etc.), and that the software or other programming instructions, when executed by the programmable integrated circuit, cause the programmable integrated circuit to perform the processes, functions, and / or capabilities described herein. Other variations can also be implemented.

[0076] 8, a controller 860 may be coupled to receive inputs from and provide outputs to various components of the processing system 800. For example, the controller 860 may be connected to the process chamber 810 to control the temperature and / or pressure within the process chamber 810, the spinner 820 to control the rotational speed of the spinner 820, and the chemical delivery system 846 to control the various etching solutions 842 dispensed onto the substrate 830. The controller 860 may control other processing system components not shown in FIG. 8, as is known in the art.

[0077] In some embodiments, the controller 860 can control various components of the processing system 800 according to an etching recipe that utilizes the wet ALE techniques described herein to etch ruthenium. For example, the controller 860 can provide various control signals to the chemical delivery system 846, causing the chemical delivery system 846 to: a) dispense a surface modification solution onto the surface of the substrate 830 to chemically modify the exposed surface of the ruthenium and produce a modified surface layer (e.g., a ruthenium halide, ruthenium oxyhalide, or ruthenium salt passivation layer) on the substrate 830, b) rinse the substrate 830 with a first purge solution to remove excess reactants from the surface, c) dispense a dissolving solution onto the surface of the substrate 830 to selectively remove or dissolve the modified surface layer, and d) rinse the substrate with a second purge solution to remove the dissolving solution from the surface of the substrate 830. In some embodiments, the controller 860 can cyclically provide control signals to the chemical delivery system 846 such that steps a) through d) are repeated in one or more ALE cycles until a desired amount of ruthenium is removed.

[0078] The controller 860 can also provide control signals to other processing system components. In some embodiments, for example, the controller 860 can provide control signals to the spinner 820 and / or the chemical delivery system 846 to dry the substrate 830 after the second purge step is performed. In one example, the controller 860 can control the rotation speed of the spinner 820 to dry the substrate 830 in a spin-dry step. In another example, the control signal provided from the controller 860 to the chemical delivery system 846 can cause a desiccant (e.g., isopropyl alcohol) to be dispensed onto the surface of the substrate 830 to further assist in drying the substrate before performing the spin-dry step.

[0079] In some embodiments, the controller 860 can control the temperature and / or pressure within the process chamber 810. In some embodiments, the surface modification, dissolution, and purging steps of the ruthenium wet ALE process described herein can be performed at approximately the same temperature and pressure. In one example implementation, the surface modification, dissolution, and purging steps can be performed at atmospheric pressure (or near atmospheric pressure) and room temperature, respectively. Performing the processing steps at approximately the same temperature and pressure in the same process chamber reduces cycle time and improves throughput of the wet ALE process described herein by avoiding unnecessary chamber transitions and temperature / pressure changes.

[0080] However, it should be noted that the embodiments described herein are not strictly limited to atmospheric pressure and room temperature, nor are they limited to any particular process chamber. In other embodiments, one or more of the surface modification, dissolution, and purging steps can be performed at pressures above atmospheric pressure in a pressure vessel or at reduced pressure in a vacuum chamber. The etching solution can also be dispensed in these environments as long as the vapor pressure of the liquid is lower than the chamber pressure. In these implementations, a spinner with a liquid dispensing nozzle is placed in the pressure vessel or vacuum chamber. The temperature of the dispensed liquid can be elevated to any temperature below its boiling point at the process pressure. In one implementation, the dissolution step can be performed at 100°C, as shown in Figures 3A and 3B. As noted above, higher liquid temperatures can increase the dissolution rate.

[0081] 9-11 illustrate exemplary methods utilizing the ruthenium etch chemistries described herein to etch ruthenium in a wet ALE process. It should be understood that the embodiments of FIGS. 9-11 are merely exemplary, and that additional methods may utilize the techniques described herein. Furthermore, the described process steps are not intended to be exclusive, and additional process steps may be added to the methods shown in FIGS. 9-11. Furthermore, the order of steps is not limited to the order shown in the figures, as different orders may occur and / or various steps may be performed in combination or simultaneously.

[0082] FIG. 9 illustrates one embodiment of an etching method 900. Method 900 illustrated in FIG. 9 may generally include receiving a substrate having ruthenium formed thereon, wherein a ruthenium surface is exposed at the surface of the substrate (in step 910), and exposing the surface of the substrate to a first etching solution (in step 920) such that the first etching solution contacts the ruthenium surface. The first etching solution may generally include one or more chemical species that cause a passivation layer to form on the ruthenium surface in step 920. The passivation layer is self-limiting and insoluble in the first etching solution. Next, method 900 may include removing the first etching solution from the surface of the substrate following the formation of the passivation layer (in step 930) and exposing the surface of the substrate to a second etching solution comprising a reactant and a solvent (in step 940). The reactant reacts with the passivation layer and forms soluble species that are dissolved by the solvent in step 940. Next, the method 900 may include removing the second etching solution and the soluble species from the substrate (in step 950).

[0083] In some embodiments, method 900 may further include repeating the steps of exposing the surface of the substrate to a first etching solution (in step 920), removing the first etching solution (in step 930), exposing the surface of the substrate to a second etching solution (in step 940), and removing the second etching solution (in step 950) for several cycles until a predetermined amount of ruthenium is removed from the substrate.

[0084] A variety of different etching chemistries can be used for the first and second etching solutions. In some embodiments, one or more chemical species in the first etching solution can include a halogenating agent dissolved in a first solvent. For example, the halogenating agent can include a chlorinating agent, a fluorinating agent, or a brominating agent. The halogenating agent chemically modifies the ruthenium surface to form a ruthenium halide passivation layer. In some embodiments, the first etching solution can include a chlorinating agent such as trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent can include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon. In some embodiments, the ruthenium halide passivation layer can include ruthenium trichloride (RuCl).

[0085] In some embodiments, the reactant in the second etching solution can be a ligand species that reacts and bonds with the ruthenium halide passivation layer to form a soluble species that is dissolved by the solvent. In some embodiments, the ligand species can include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the solvent in the second etching solution can include a base.

[0086] In other embodiments, the one or more chemical species in the first etching solution can include an oxidizing agent, a cation, and a chlorine source to react with ruthenium. In such embodiments, the passivation layer formed on the ruthenium surface in step 920 can include ruthenate or perruthenate. In one embodiment, the chlorine source can include hydrochloric acid (HCl). In such embodiments, the amount of oxidation of the passivation layer formed in step 920 can be controlled by the concentration of hydrochloric acid in the first etching solution.

[0087] FIG. 10 illustrates one embodiment of a method 1000 that may be used to etch a substrate using a wet atomic layer etching (ALE) process. The method 1000 shown in FIG. 10 may generally include: a) receiving a substrate having a ruthenium (Ru) layer thereon (in step 1010); b) exposing the Ru layer to a first etching solution containing a halogenating agent to form a chemically modified Ru surface layer containing a ruthenium halide or ruthenium oxyhalide (in step 1020); c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate (in step 1030); d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer (in step 1040); e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate (in step 1050); and f) repeating steps b) through e) for one or more cycles (in step 1060).

[0088] In some embodiments, the first etching solution used in step 1020 can include a chlorinating agent dissolved in a first solvent. For example, the chlorinating agent can include trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide, and the first solvent can include ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon. In such embodiments, the chlorinating agent can react with the Ru layer to form ruthenium chloride.

[0089] In some embodiments, the second etching solution used in step 1040 can include a ligand dissolved in a second solvent. For example, the ligand can include ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent can include a base. In such embodiments, the ligand can react and bond with the chemically modified Ru surface layer to form a soluble species that dissolves in the second solvent.

[0090] FIG. 11 illustrates one embodiment of a method 1100 that may be used to etch a substrate using a wet atomic layer etching (ALE) process. The method 1100 shown in FIG. 11 may generally include: a) receiving a substrate having a ruthenium (Ru) layer thereon (in step 1110); b) exposing the Ru layer to a first etching solution containing an oxidant, a cation, and a chlorine source that reacts with the Ru layer to form a chemically modified Ru surface layer containing a ruthenium salt (in step 1120); c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate (in step 1130); d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer (in step 1140); e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate (in step 1150); and f) repeating steps b) through e) for one or more cycles (in step 1160).

[0091] In some embodiments, the chlorine source in the first etching solution can include hydrochloric acid (HCl). In some embodiments, the oxidizer in the first etching solution can include ammonium persulfate (APS) or tetrabutylammonium peroxymonosulfate (TBAPMS). In some embodiments, the cation in the first etching solution can include tetramethylammonium (TMA), tetraalkylammonium, phosphonium, pyridinium, pyrrolidinium, or sulfonium ions. In some embodiments, the first etching solution can further include a salt, the salt including tetramethylammonium chloride (TMAC) or 1-butyl-3-methylimidazolium chloride.

[0092] In some embodiments, the chemically modified Ru surface layer can be insoluble in the first etching solution and soluble in the second etching solution, in such embodiments, the second etching solution can include trichlorobenzene.

[0093] In some embodiments, the chemically modified Ru surface layer may be insoluble in the first etching solution, and the method 1100 may further include using ion exchange to increase the solubility of the chemically modified Ru surface layer. In such embodiments, the second etching solution may include potassium chloride (KCl) and potassium hydroxide (KOH).

[0094] It should be noted that throughout this specification, the reference to "one embodiment" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention, but does not mean that it is present in all embodiments. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the present invention. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. In other embodiments, various additional layers and / or structures may be included and / or described features may be omitted.

[0095] As used herein, the term "substrate" refers to and includes a base material or structure upon which a material is formed. It will be understood that a substrate can include a single material, multiple layers of different materials, or one or more layers having regions of different materials or structures therein. These materials can include semiconductors, insulators, conductors, or combinations thereof. For example, a substrate can 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. A substrate can be a conventional silicon substrate or other bulk substrate containing a layer of semiconducting material. As used herein, the term "bulk substrate" refers to and includes not only silicon wafers, but also silicon-on-insulator ("SOI") substrates such as silicon-on-sapphire ("SOS") substrates and silicon-on-glass ("SOG") substrates, epitaxial layers of silicon on a base semiconductor substrate, and other semiconductor or optoelectronic materials such as silicon germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. A substrate can be doped or undoped.

[0096] Systems and methods for processing a substrate are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, and may be a basic substrate structure such as a semiconductor substrate, or a layer on or overlying the basic substrate structure, such as a thin film. Thus, the substrate is not intended to be limited to any particular basic structure, underlying layer, or overlying layer, patterned or unpatterned, but rather is intended to include any such layer or basic structure and any combination of layers and / or basic structures.

[0097] Those skilled in the art will recognize that various embodiments can be practiced without one or more of the specific details, or with other alternative and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth to provide a thorough understanding of the invention. Nevertheless, the invention can be practiced without the specific details. Furthermore, it should be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0098] Further variations and alternative embodiments of the above-described systems and methods will be apparent to those skilled in the art from this specification. Accordingly, it will be appreciated that the above-described systems and methods are not limited to these exemplary configurations. It should be understood that the forms of the systems and methods shown and described herein are to be construed as exemplary embodiments. Various modifications may be made in practice. Thus, while the ruthenium wet ALE technology is described herein with reference to specific embodiments, various modifications and variations may be made without departing from the scope of the present disclosure. Accordingly, the specification and figures should 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. Furthermore, any benefits, advantages, or solutions to problems described herein with respect to specific embodiments are not intended to be construed as critical, necessary, or essential features or elements of any or all of the claims.

Claims

1. 1. A method of etching, said method comprising: receiving a substrate having ruthenium formed thereon, the ruthenium surface being exposed at a surface of the substrate; exposing the surface of the substrate to a first etching solution such that the first etching solution contacts the ruthenium surface, the first etching solution comprising a halogenating agent dissolved in a first solvent, the halogenating agent chemically modifying the ruthenium surface to form a ruthenium halide passivation layer on the ruthenium surface, the ruthenium halide passivation layer being self-limiting and insoluble in the first etching solution; subsequent to the formation of the ruthenium halide passivation layer, removing the first etching solution from the surface of the substrate; exposing the surface of the substrate to a second etching solution comprising a reactive agent and a second solvent, the reactive agent being a ligand species that reacts with and bonds with the ruthenium halide passivation layer to form a soluble species that is dissolved by the second solvent; removing the second etching solution and the soluble species from the substrate; A method comprising:

2. 10. The method of claim 1, wherein the halogenating agent comprises a chlorinating agent, a fluorinating agent, or a brominating agent.

3. 10. The method of claim 1, wherein the first etching solution comprises a chlorinating agent comprising trichloroisocyanuric acid (TCCA), oxalyl chloride, thionyl chloride, or N-chlorosuccinimide.

4. 10. The method of claim 1, wherein the first solvent comprises ethyl acetate (EA), acetone, acetonitrile, or a chlorocarbon.

5. The ruthenium halide passivation layer is ruthenium trichloride (RuCl ３ 10. The method of claim 1, comprising:

6. The method of claim 1 , wherein the second solvent in the second etching solution comprises a base.

7. 10. The method of claim 1, wherein the ligand species comprises ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent in the second etching solution comprises a base.

8. A method of etching, said method comprising: receiving a substrate having ruthenium formed thereon, the ruthenium surface being exposed at a surface of the substrate; exposing the surface of the substrate to a first etching solution such that the first etching solution contacts the ruthenium surface, the first etching solution comprising one or more chemical species that cause the formation of a passivation layer on the ruthenium surface, the passivation layer being self-limiting and insoluble in the first etching solution, the one or more chemical species in the first etching solution comprising an oxidant, a cation, and a chlorine source that react with the ruthenium; subsequent to forming the passivation layer, removing the first etching solution from the surface of the substrate; exposing the surface of the substrate to a second etching solution comprising a reactive agent and a solvent, wherein the reactive agent reacts with the passivation layer and forms a soluble species that is dissolved by the solvent; removing the second etching solution and the soluble species from the substrate; A method comprising:

9. The method of claim 8 , wherein the passivation layer comprises ruthenate or perruthenate.

10. 9. The method of claim 8, wherein the chlorine source comprises hydrochloric acid, and the amount of oxidation of the passivation layer is controlled by the concentration of the hydrochloric acid in the first etching solution.

11. 9. The method of claim 8, further comprising repeating the steps of exposing the surface of the substrate to the first etching solution, removing the first etching solution, exposing the surface of the substrate to the second etching solution, and removing the second etching solution for several cycles until a predetermined amount of the ruthenium is removed from the substrate.

12. 1. A method of etching a substrate using a wet atomic layer etching (ALE) process, comprising: a) receiving the substrate having a ruthenium (Ru) layer thereon; b) exposing the Ru layer to a first etching solution containing a halogenating agent to form a chemically modified Ru surface layer containing a ruthenium halide or oxyhalide; c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate; d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer, the second etching solution comprising ligands dissolved in a second solvent, the ligands reacting and bonding with the chemically modified Ru surface layer to form soluble species that dissolve in the second solvent; e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate; f) repeating steps b) through e) for one or more cycles; A method comprising:

13. 13. The method of claim 12, wherein the first etching solution comprises a chlorinating agent dissolved in a first solvent, the chlorinating agent reacting with the Ru layer to form ruthenium chloride.

14. 14. The method of claim 13, 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 a chlorocarbon.

15. 14. The method of claim 13, wherein the ligand comprises ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), diethylenetriaminepentaacetic acid (DTPA), or acetylacetone (ACAC), and the second solvent comprises a base.

16. 1. A method of etching a substrate using a wet atomic layer etching (ALE) process, comprising: a) receiving the substrate having a ruthenium (Ru) layer thereon; b) exposing the Ru layer to a first etching solution containing an oxidizing agent, a cation, and a chlorine source that reacts with the Ru layer to form a chemically modified Ru surface layer containing a ruthenium salt; c) rinsing the substrate with a first purge solution to remove the first etching solution from the surface of the substrate; d) exposing the chemically modified Ru surface layer to a second etching solution to dissolve the chemically modified Ru surface layer; e) rinsing the substrate with a second purge solution to remove the second etching solution from the surface of the substrate; f) repeating steps b) through e) for one or more cycles; A method comprising:

17. 17. The method of claim 16, wherein the chlorine source in the first etching solution comprises hydrochloric acid (HCl).

18. 17. The method of claim 16, wherein the oxidizer in the first etching solution comprises ammonium persulfate (APS) or tetrabutylammonium peroxymonosulfate (TBAPMS), and the cations in the first etching solution comprise tetramethylammonium (TMA), tetraalkylammonium, phosphonium, pyridinium, pyrrolidinium, or sulfonium ions.

19. 17. The method of claim 16, wherein the first etching solution further comprises a salt, the salt comprising tetramethylammonium chloride (TMAC) or 1-butyl-3-methylimidazolium chloride.

20. 17. The method of claim 16, wherein the chemically modified Ru surface layer is insoluble in the first etching solution and soluble in the second etching solution.

21. 21. The method of claim 20, wherein the second etching solution comprises trichlorobenzene.

22. 17. The method of claim 16, wherein the chemically modified Ru surface layer is insoluble in the first etching solution, the method further comprising using ion exchange to increase the solubility of the chemically modified Ru surface layer.

23. 23. The method of claim 22, wherein the second etching solution comprises potassium chloride (KCl) and potassium hydroxide (KOH).

24. The method of claim 1, further comprising repeating the steps of exposing the surface of the substrate to the first etching solution, removing the first etching solution, exposing the surface of the substrate to the second etching solution, and removing the second etching solution over several cycles until a predetermined amount of the ruthenium is removed from the substrate.

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