Dynamically adjusted purge timing in wet atomic layer etching

Abstract

The present disclosure provides various embodiments of an improved wet atomic layer etching (ALE) process. More specifically, the present disclosure provides various embodiments of a method for improving a wet ALE process by providing a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness. As described in more detail below, the methods disclosed herein can adjust purge timing between ALE cycles and / or between individual surface modification and selective dissolution steps to provide a desired throughput, etch rate, and / or post-etch surface roughness in a wet ALE process.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 148,563, entitled "Dynamic Dispense Timing in Wet Atomic Layer Etching," filed February 11, 2021, the disclosure of which is expressly incorporated herein by reference in its entirety.

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

[0003] In processing substrates, various techniques are known for etching various layers on the substrate. Plasma etching and wet etching are two well-known techniques. Wet etching involves dispensing a chemical solution onto the surface of the substrate or immersing the substrate in the chemical solution. Often, the chemical solution contains a solvent, chemicals designed to react with the material on the substrate surface, and chemicals to promote dissolution of the reaction products. Exposing the substrate surface to the etchant results in the removal of material from the substrate. The composition and temperature of the etchant can control the etch rate, specificity, and remaining material on the substrate surface after etching.

[0004] Both thermodynamics and kinetics play a role in formulating an etchant. For successful etching, both thermodynamics and kinetics must favor the desired reaction. For etching polycrystalline materials, the requirements for success are much more stringent. 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 difference in etch rates at grain boundaries compared to different crystallographic faces leads to 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 engineering, microscopic uniformity depends on the chemistry of the etch itself.

[0005] As substrate feature geometries continue to shrink and the types of structures evolve, the challenges of etching substrates increase. One technique that has been utilized to address these challenges is atomic layer etching (ALE). ALE processes are generally known to involve the sequential removal of thin layers through one or more self-limiting reactions. For example, ALE typically refers to techniques that can etch with atomic precision, i.e., by removing material one or several monolayers at a time. Generally, ALE processes rely on chemical modification of the surface to be etched and the subsequent selective removal of the modified layer. Therefore, ALE processes improve performance by separating the etching process into sequential steps of surface modification and removal of the modified surface. Such processes often involve a series of layer modification and etching steps that are repeated multiple times, where the modification step modifies the exposed surface and the etching step selectively removes the modified layer. Thus, in some ALE processes, a series of self-limiting reactions may occur, and this cycle may be performed repeatedly. In other embodiments, the ALE process may use only one cycle.

[0006] Various ALE processes are known, including plasma ALE, thermal ALE, and wet ALE. In wet ALE, material is removed from a surface in a repeatable process utilizing self-limiting and selective reactions. The name "wet ALE" indicates that some, if not all, of the reactions occur in the liquid phase. The wet ALE process begins with a self-limiting surface modification step, which can be achieved by oxidation, reduction, ligand binding, or ligand exchange. Ideally, the modified layer is limited to the top monolayer of material and acts as a passivation layer to prevent further modification reactions. The second step in the wet ALE process is the selective dissolution of the modified layer. The process must dissolve the modified layer without removing the underlying unmodified material. This can be achieved by using a different solvent in the second step than in the first step, changing the pH, or changing the concentration of other components in the first solvent.

[0007] In wet ALE, a purging step is typically performed between the surface modification and selective dissolution steps by rinsing the surface modification layer with a purging solution to remove excess reactants. The purpose of the purging step is to ensure that no mixing occurs between the solution used for surface modification and the solution used for dissolution. If these two solutions were to mix, the mixed solution could potentially modify and dissolve the substrate. If the solutions were to mix, the modification reaction would no longer be self-limiting, resulting in continuous etching. Continuous etching tends to preferentially etch at grain boundaries, resulting in a rough surface after etching.

[0008] As an atomic layer process, wet ALE tends to be time-consuming. Each reaction must be long enough to reach saturation, and each purge step must be long enough to completely separate the surface modification solution from the dissolving solution. This can result in low throughput for high-volume manufacturing (HVM), making wet ALE an expensive process. Summary of the Invention [Means for solving the problem]

[0009] The present disclosure provides various embodiments of improved wet atomic layer etching (ALE) processes. More particularly, the present disclosure provides various embodiments of methods for improving wet ALE processes by providing a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness. As described in more detail below, the methods disclosed herein can adjust purge timing between ALE cycles and / or between individual surface modification and selective dissolution steps to provide a desired throughput, etch rate, and / or post-etch surface roughness in a wet ALE process.

[0010] For example, the throughput of a wet ALE process can be improved by shortening the time allotted to each process, but this comes at a cost. Reducing the time allotted to the surface modification or dissolution steps can reduce the amount etched per ALE cycle if the reaction no longer reaches saturation. On the other hand, the purge time between the surface modification and dissolution steps can be shortened to increase the amount etched per ALE cycle by allowing the surface modification solution to mix with the dissolution solution, thereby introducing a degree of continuous etching into the process. While the self-limiting nature of wet ALE results in surface smoothing during etching, continuous etching tends to roughen polycrystalline surfaces due to the high reactivity at grain boundaries. Thus, improving throughput by shortening purge times typically comes at the cost of surface roughness after etching.

[0011] Embodiments of the present disclosure improve upon known wet ALE processes by providing a dynamic ALE cycle timing schedule that balances throughput and overall etch rate requirements with the need for low post-etch surface roughness. In some embodiments, purge times can be dynamically adjusted to (a) increase the etch rate in the early stages of the wet ALE process and (b) decrease the etch rate in the final stages of the wet ALE process. For example, purge times can be relatively short (or eliminated entirely) in one or more cycles performed at the beginning of the wet ALE process to promote fast etch rates, thereby shortening cycle times in the early stages. The purge times can then be increased as the etch progresses in subsequent cycles to reduce post-etch surface roughness in the final stages of the wet ALE process. In some embodiments, the purge times used in intermediate stages of the wet ALE process can be adjusted to balance the etch rate and surface roughness needs. Such embodiments can simultaneously improve throughput while maintaining an acceptable level of post-etch surface roughness for wet ALE processing.

[0012] In other embodiments, the purge time can be dynamically adjusted to compensate for the diffusion-controlled aspect ratio dependence of the etching process. For example, if a wet ALE is used as a recess etch, the purge time can be dynamically adjusted as the etch progresses to compensate for changes in aspect ratio. For example, at the beginning of the etch process, the aspect ratio of the etch profile is zero. As material is removed from the exposed surface, the aspect ratio of the recess (or other feature) increases and reaches a maximum as the etch endpoint is reached. Because solutions are less likely to mix in low aspect ratio features, the purge time can be shortened at the beginning of the etch process to increase the etch rate. As the etch progresses and the aspect ratio increases, the purge time between the surface modification and dissolution steps can be dynamically increased to maintain proper separation of the etching solutions and improve surface roughness by avoiding continuous etching in the later stages of the etch.

[0013] Provided herein is a method for etching a substrate using a wet atomic layer etching (ALE) process according to a first embodiment. In a first embodiment, the method includes receiving a substrate, the substrate having exposed material, and selectively etching the material by performing multiple cycles of a wet ALE process, each cycle including: a) performing one or more surface modification steps to chemically modify an exposed surface of the material and provide a surface-modified layer, the one or more surface modification steps including exposing the exposed surface of the material to at least one surface modification solution to chemically modify the exposed surface of the material; b) performing a first purging step after the one or more surface modification steps, the first purging step including rinsing the substrate with a solvent; c) performing a dissolving step after the first purging step to selectively remove a surface-modified layer of the material, the dissolving step including exposing the surface-modified layer to a dissolving solution to dissolve the surface-modified layer; and d) performing a second purging step after the dissolving step, the second purging step including rinsing the substrate with a solvent or performing a spin-drying step. The method described in the first embodiment may also include adjusting the purge time of the first purge step and / or the purge time of the second purge step in one or more cycles of the wet ALE process to provide a desired throughput, etch rate, and / or post-etch surface roughness in the wet ALE process.

[0014] In some embodiments, performing the one or more surface modification steps a) may include exposing the exposed surface of the material to an oxidizing agent in a first surface modification step to chemically modify the exposed surface of the material and provide a surface modification layer, and exposing the surface modification layer to a complexing agent in a second surface modification step to bond the complexing agent to the surface modification layer and provide a complex-bonded surface modification layer. In such embodiments, performing the dissolution step c) may include exposing the complex-bonded surface modification layer to a dissolution solution to selectively remove the complex-bonded surface modification layer of the material by dissolving the complex-bonded surface modification layer. In some embodiments, exposing the complex-bonded surface modification layer to a dissolution solution may dissolve the complex-bonded surface modification layer and reform the surface modification layer on a new exposed surface of the material.

[0015] In some embodiments, adjusting the purge time of the first purge step and / or the purge time of the second purge step can include increasing the purge time of the first purge step and / or the purge time of the second purge step as the wet ALE process progresses.

[0016] In other embodiments, adjusting the purge time of the first purge step and / or the second purge step may include shortening the purge time of the first purge step and / or the second purge step in one or more first cycles of the wet ALE process to increase the etch rate achieved in the one or more first cycles, and increasing the purge time of the first purge step and / or the second purge step in one or more second cycles of the wet ALE process to reduce the post-etch surface roughness achieved in the one or more second cycles. In such embodiments, one or more second cycles may be performed after one or more first cycles.

[0017] In other embodiments, adjusting the purge time of the first purge step and / or the purge time of the second purge step may include shortening the purge time of the first purge step and omitting the second purge step in each cycle of the wet ALE process to increase the etch rate and improve throughput.

[0018] In another embodiment, adjusting the purge time of the first purge step and / or the purge time of the second purge step includes omitting the first purge step and / or the second purge step in one or more first cycles of the wet ALE process and performing the first purge step and / or the second purge step in one or more second cycles of the wet ALE process, wherein the one or more second cycles are performed after the one or more first cycles, and adjusting the purge time of the first purge step and / or the second purge step in the one or more second cycles. a purge time of the second purge step being insufficient to prevent mixing between the at least one surface modification solution and the dissolving liquid; and performing the first purge step and / or the second purge step in one or more third cycles of the wet ALE process, wherein the one or more third cycles are performed after the one or more second cycles, and a purge time of the first purge step and / or the second purge step performed in the one or more third cycles prevents mixing between the at least one surface modification solution and the dissolving liquid.

[0019] Provided herein is another method for etching a substrate using a wet atomic layer etching (ALE) process according to a second embodiment. In the second embodiment, the method includes receiving a substrate, the substrate having exposed material, and selectively etching the material by performing multiple cycles of the wet ALE process, each cycle including: a) chemically modifying an exposed surface of the material to provide a surface-modified layer, the exposed surface being chemically modified by oxidizing the material using an oxidizing agent; b) binding a complexing agent to the surface-modified layer of the material to provide a complexed-type surface-modified layer; c) rinsing the substrate with a solvent; and d) selectively removing the complexed-type surface-modified layer of the material by exposing the complexed-type surface-modified layer to a dissolving solution to dissolve the complexed-type surface-modified layer. In a second embodiment, the cleaning of the substrate may be performed for a first period of time in one or more first cycles of a wet ALE process, and the cleaning of the substrate may be performed for a second period of time in one or more second cycles of a wet ALE process, the one or more second cycles being performed after the one or more first cycles, and the second period of time being longer than the first period of time.

[0020] Provided herein is yet another method for etching a substrate using a wet atomic layer etching (ALE) process according to a third embodiment. In the third embodiment, the method includes receiving a substrate having exposed material, the material including a polycrystalline material, and selectively etching the polycrystalline material by performing multiple cycles of the wet ALE process, each cycle including: a) chemically modifying an exposed surface of the polycrystalline material to provide a surface-modified layer, the exposed surface being chemically modified by oxidizing the polycrystalline material using an oxidizing agent; b) binding a complexing agent to the surface-modified layer of the polycrystalline material to provide a complex-bonded surface-modified layer; c) rinsing the substrate with a solvent; and d) selectively removing the complex-bonded surface-modified layer of the polycrystalline material by exposing the complex-bonded surface-modified layer to a dissolving solution to dissolve the complex-bonded surface-modified layer. In the third embodiment, the rinsing of the substrate can be performed for increasing periods of time during the performing multiple cycles of the wet ALE process.

[0021] In the second and third embodiments, the order and / or timing of steps a) through d) performed in each cycle of the wet ALE process may vary. In some embodiments, steps a) through d) may be performed consecutively without overlap in time in each cycle of the wet ALE process. In other embodiments, one or more of the steps may be performed substantially simultaneously. For example, in some embodiments, steps a) and b) may be performed with at least partial overlap in time in each cycle of the wet ALE process. In other embodiments, steps b) and d) may be performed with at least partial overlap in time in each cycle of the wet ALE process.

[0022] The methods described herein can be used to etch a wide variety of materials, including polycrystalline, single-crystalline, and amorphous materials. In some embodiments, the methods described herein can be used to etch polycrystalline metallic materials, such as transition metals. Examples of transition metals that can be etched using the methods disclosed herein include, but are not limited to, copper (Cu), ruthenium (Ru), and cobalt (Co).

[0023] The methods described herein offer several advantages over other etching techniques. For example, the methods described herein provide the benefits of ALE, such as precise control of total etch volume, control of surface roughness, and improved wafer-scale uniformity. The methods described herein also provide various advantages of wet etching, such as simplified etch chambers, ambient temperature and pressure etching conditions, and reduced surface roughness. Unlike traditional wet ALE processes, which tend to be time-consuming, the methods described herein provide a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness.

[0024] In some embodiments, the methods disclosed herein can reduce surface roughness after etching. For example, the exposed surface of a material can have a surface roughness characterized by a first surface roughness value after one or more first cycles of a wet ALE process are performed. After one or more second cycles of a wet ALE process are performed, the surface roughness of the exposed surface of the material can be reduced to a second surface roughness that is less than the first surface roughness.

[0025] A more complete understanding of the present invention and its advantages can be obtained by reference to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features, and in which: It should be noted, however, that the accompanying drawings depict only exemplary embodiments of the disclosed concepts and are therefore not to be considered limiting in scope, as the disclosed concepts may also be susceptible to other equally effective embodiments. [Brief explanation of the drawings]

[0026] [Figures 1A-1E] 1 illustrates an example of a cyclic wet atomic layer etching (ALE) process according to the present disclosure. [Figure 2A] 1 illustrates a metal feature recessed in a surrounding dielectric layer, the metal feature being etched by exposing the surface of the metal feature to a surface modification solution, followed by a purge solution and a dissolving solution, and the diffusive mixing that occurs when the dissolving solution is introduced before the surface modification solution has been completely removed from the surface of the metal feature. [Figure 2B] 2B is a graph illustrating how interdiffusion of the surface modification solution and the dissolution liquid in FIG. 2A causes continuous etching. [Figure 3A] A metal feature recessed into a surrounding dielectric layer is shown, the metal feature being etched by exposing the surface of the metal feature to a surface modification solution, followed by a purge solution and a dissolving solution, the purge time between the surface modification and dissolving steps being long enough to completely remove the surface modification solution before introducing the dissolving solution. [Figure 3B] 3B is a graph showing how interdiffusion intermixing can be eliminated and continuous etching can be prevented if the purge time is sufficient as shown in FIG. 3A. [Figure 4A-4B] 1 is a scanning electron microscope (SEM) image of patterned metal features etched using a wet ALE process according to the present disclosure. [Figure 5A] 1 illustrates the relationship between etch time, aspect ratio, and diffusion timescale when a wet ALE process according to the present disclosure is used to etch a feature in a substrate. [Figure 5B] 1 is a graph showing relative diffusion time versus aspect ratio. [Figure 6A]FIG. 10 is a timing diagram illustrating one embodiment of a dynamic wet ALE cycle timing schedule that dynamically adjusts purge time to increase the etch rate in the early stages of the wet ALE process and decrease the etch rate in the later stages of the wet ALE process to balance throughput and etch rate with post-etch surface roughness. [Figure 6B] 6B is a graph showing the expected etching amount per cycle for the different purge conditions shown in FIG. 6A. [Figure 6C] 1 is a graph illustrating exemplary etch depth (nm) that may be achieved with no purge, full purge, and dynamic purge as a function of cycle number. [Figure 6D] 1 is a graph illustrating exemplary etch depth (nm) as a function of process time that may be achieved with no purge, full purge, and dynamic purge. [Figure 6E] As shown schematically in FIG. 6A, the root mean square (RMS) roughness (nm) of the post-etch surface etched using no purge, full purge, and dynamic purge is shown. [Figures 7A-7B] 1 shows a transmission electron microscope (TEM) image of cobalt features etched using the wet ALE process conditions detailed in Table 1. [Figure 8] FIG. 1 is a flow diagram illustrating one embodiment of a method that utilizes the techniques described herein. [Figure 9] FIG. 10 is a flow diagram illustrating another embodiment of a method utilizing the techniques described herein. [Figure 10] FIG. 10 is a flow diagram illustrating another embodiment of a method utilizing the techniques described herein. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present disclosure provides various embodiments of improved wet atomic layer etching (ALE) processes. More particularly, the present disclosure provides various embodiments of methods for improving wet ALE processes by providing a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness. As described in more detail below, the methods disclosed herein can adjust purge timing between ALE cycles and / or between individual surface modification and selective dissolution steps to provide a desired throughput, etch rate, and / or post-etch surface roughness in a wet ALE process.

[0028] In some embodiments, the purge time can be dynamically adjusted to (a) increase the etch rate in the early stages of the wet ALE process and (b) decrease the etch rate in the final stages of the wet ALE process. For example, the purge time can be relatively short (or eliminated entirely) in one or more cycles performed at the beginning of the wet ALE process to promote a fast etch rate, thereby shortening the cycle time in the early stages. The purge time can then be increased as the etch progresses in subsequent cycles to help reduce post-etch surface roughness in the final stages of the wet ALE process. In some embodiments, the purge time used in the intermediate stages of the wet ALE process can be adjusted to balance the need for etch rate and the need for surface roughness. Such embodiments can simultaneously improve throughput while maintaining an acceptable level of post-etch surface roughness for wet ALE processing.

[0029] In other embodiments, the purge time can be dynamically adjusted to compensate for the diffusion-controlled aspect ratio dependence of the etching process. For example, if a wet ALE is used as a recess etch, the purge time can be dynamically adjusted as the etch progresses to compensate for changes in aspect ratio. For example, at the beginning of the etch process, the aspect ratio of the etch profile is zero. As material is removed from the exposed surface, the aspect ratio of the recess (or other feature) increases and reaches a maximum as the etch endpoint is reached. Because solutions are less likely to mix in low aspect ratio features, the purge time can be shortened at the beginning of the etch process to increase the etch rate. As the etch progresses and the aspect ratio increases, the purge time between the surface modification and dissolution steps can be dynamically increased to maintain proper separation of the etching solutions and improve surface roughness by avoiding continuous etching in the later stages of the etch.

[0030] The techniques described herein offer several advantages over other etching techniques. For example, the techniques described herein provide the benefits of ALE, such as precise control of total etch volume, control of surface roughness, and improved wafer-scale uniformity. The techniques described herein also provide various benefits of wet etching, such as simplified etch chambers, ambient temperature and pressure etching conditions, and reduced surface roughness. Unlike traditional wet ALE processes, which tend to be time-consuming, the techniques described herein provide a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness.

[0031] The techniques described herein can be performed on a wide variety of substrates having a wide variety of layers and features formed thereon. In general, the substrate used in the techniques disclosed herein can be any substrate on which it is desirable to etch a material. For example, the substrate can be a semiconductor substrate having one or more semiconductor processing layers formed thereon (all of which together can comprise the substrate). In one embodiment, the substrate can be a substrate that has undergone multiple semiconductor processing steps (all of which are well known in the substrate processing arts) that result in a wide variety of structures and layers. In one embodiment, the substrate can be a semiconductor wafer that includes various structures and layers formed thereon.

[0032] The techniques described herein can also be used to etch a wide variety of materials. Such materials include polycrystalline materials, single-crystalline materials, and amorphous materials. In some embodiments, the techniques described herein can be used to etch polycrystalline metal materials, such as, but not limited to, transition metals and noble metals. In one exemplary embodiment, the material to be etched can be a polycrystalline cobalt material. While the techniques described herein will be discussed below with respect to etching a polycrystalline cobalt material, those skilled in the art will recognize that such examples are illustrative only and that the techniques described herein may be used to etch other materials.

[0033] Although many chemicals can be used to etch polycrystalline cobalt, it is difficult to control surface roughness during etching. In particular, pitting and preferential etching at grain boundaries are difficult to prevent when etching polycrystalline cobalt. Because zero-valent cobalt is generally insoluble, the exposed surface of the polycrystalline cobalt material must first be modified before dissolving it in solution. In one exemplary wet ALE process, the exposed surface of the polycrystalline cobalt material is oxidized in a surface modification step, and the oxidized species can be dissolved in solution in a subsequent dissolution step. A purging step can be performed between the surface modification step and the dissolution step, and the process can be repeated periodically until the desired amount of etching is achieved.

[0034] 1A-1E illustrate an example of a repeatable wet ALE process. More specifically, FIGS. 1A-1E illustrate one cycle of a wet ALE process for etching a material, such as, but not limited to, a polycrystalline material 105. As shown in FIG. 1A, a polycrystalline material 105 surrounded by a dielectric material 110 is contacted with a surface modification solution 115 in a first surface modification step 100 that modifies the exposed surface of the polycrystalline material 105. In one embodiment, the polycrystalline material 105 being etched can be, for example, a transition metal. In one exemplary embodiment, the polycrystalline material 105 can include copper (Cu), ruthenium (Ru), or cobalt (Co) metal. In some embodiments, the surface modification solution 115 shown in FIG. 1A can include an oxidizing agent 120. In one embodiment, the surface modification solution 115 can include a chemical solution containing dissolved oxygen or another oxidizing agent, or a solvent (such as water) that directly participates in oxidizing the surface. In another embodiment, the surface modification solution 115 can be an oxygen-saturated chemical solution containing oxygen dissolved in water, alcohol, or a ketone (such as acetone).

[0035] As shown in FIG. 1A, a chemical reaction occurs at the exposed surface of the polycrystalline material 105 to form a modified surface layer 125 (e.g., a native oxide layer such as cobalt oxide). This surface modification layer 125 can be oxidation products, reduction products, ligand-bound surface atoms, or surface atoms that have exchanged ligands with ligands present in the solution. In some cases, the reaction can be fast and self-limiting (i.e., the reaction products can modify one or more monolayers of the exposed surface of the polycrystalline material 105), but can prevent further reaction between the surface modification solution 115 and the underlying surface. Of course, neither the polycrystalline material 105 being etched nor the surface modification layer 125 is soluble in the surface modification solution 115. In some cases, the surface modification process 100 shown in FIG. 1A can continue until the surface reaction is saturated.

[0036] In some embodiments, the surface modification layer 125 shown in FIG. 1A can be exposed to a complexing agent 130 dissolved in a non-aqueous solution 135 in a second surface modification step 140, as shown in FIG. 1B. In FIG. 1B, the exposed surface of the polycrystalline material 105 is further modified when the complexing agent 130 (e.g., a carboxylate-based ligand) binds to the surface modification layer 125 (e.g., a native oxide layer) to form a metal-ligand complex 145. In one example, the complexing agent 130 can include a mono- or polycarboxylate, such as a citrate or oxalate. Carboxylate salts are derivatives of the corresponding carboxylic acid; that is, salts, esters, and polyatomic anions present in solution. In one example, the second surface modification step 140 shown in FIG. 1B can be performed in a non-aqueous solution 135, such as isopropyl alcohol or acetone, in which the ligand is soluble but the metal-ligand complex 145 is not.

[0037] As shown in FIG. 1C, a first purge step 150 is performed after the surface modification step shown in FIGS. 1A and 1B. In the first purge step 150, the polycrystalline material 105 having the surface modification layer 125 is washed with a purge solution 155 to remove excess reactants. The purge solution 155 should not react with the surface modification layer 125 or the reagents present in the non-aqueous solution 135. In some embodiments, the first purge step 150 is performed using a pure solvent (e.g., the purge solution 155 can be pure isopropyl alcohol or acetone) to remove free carboxylic acid ligands from the non-aqueous solution 135, after which a dissolving solution 165 is used in a subsequent dissolution step 160 (shown in FIG. 1D) to dissolve the metal-ligand complexes 145. In some embodiments, the first purge step 150 can be long enough to completely remove all excess reactants from the wafer surface.

[0038] After cleaning, the polycrystalline material 105 is contacted with a dissolving solution 165 in a dissolving step 160 to dissolve or remove the surface modification layer 125, as shown in FIG. 1D. The surface modification layer 125 must be soluble in the dissolving solution 165, while the unmodified polycrystalline material 105 underneath must be insoluble. The solubility of the surface modification layer 125 allows it to be removed by dissolving in the bulk dissolving solution 165. In one embodiment, a water rinse (e.g., deionized water) may be used as the dissolving solution 165. In such an embodiment, the dissolving solution 165 shown in FIG. 1D may be used to both dissolve the metal-ligand complexes 145 and reform a new surface modification layer 125 (e.g., a native oxide layer such as cobalt oxide) on the exposed surface of the polycrystalline material 105. The dissolving step 160 may continue until the surface modification layer 125 is completely dissolved and renewed.

[0039] Once the surface modification layer is dissolved and reformed, the ALE etching cycle is terminated in FIG. 1E by performing a second purge step 170, for example, using a pure solvent or a spin-dry step. In some embodiments, the second purge step 170 may be performed by rinsing the surface with a second purge solution (not shown in FIG. 1E) having the same properties as those listed above for the first purge solution 155. In some embodiments, the second purge step 170 may be continued until the dissolving liquid 165 is completely removed from the surface.

[0040] The first purging step 150 and the second purging step 170 are typically used to prevent mixing between the surface modification solution and the dissolving solution. Often, the mixture of these two solutions can both modify the material surface and dissolve the modified material. This creates a continuous etching process that negates the benefits of wet ALE.

[0041] It should be appreciated that the cyclic wet ALE process illustrated in Figures 1A-1E is but one example of an etching process that may be used to etch polycrystalline material in accordance with the techniques described herein. As noted above, the cyclic wet ALE process described above includes a) a first surface modification step 100 (see Figure 1A) in which the exposed surface of the polycrystalline material 105 is chemically modified (e.g., by oxidation of the polycrystalline material using an oxidizing agent) to provide a surface modification layer 125; b) a second surface modification step 140 (see Figure 1B) in which a complexing agent 130 is attached to the surface modification layer 125 to form a complex-bonded surface modification layer (e.g., metal-ligand complex 145); and c) a second surface modification step 140 (see Figure 1B) in which the substrate is partitioned. 1C), a first purge step 150 (see FIG. 1C) of washing with a dissolving solution 155 (e.g., a solvent) to remove excess reactants; d) a dissolving step 160 (see FIG. 1D) of dissolving or removing the complex-bonded surface-modified layer by exposing the complex-bonded surface-modified layer to a dissolving solution 165 to dissolve the complex-bonded surface-modified layer; and e) a second purge step 170 (see FIG. 1E) of washing the substrate with a second purge solution to remove the dissolving solution 165 from the surface of the substrate.

[0042] In some embodiments, steps a) through e) may be performed sequentially in each cycle of the repeated wet ALE process, as shown in FIGS. 1A-1E and described above. In other embodiments, one or more of the steps may be performed substantially simultaneously. In some embodiments, for example, steps a) and b) may be performed with at least partial overlap in time in each cycle of the repeated wet ALE process. Alternatively, steps b) and d) may be performed with at least partial overlap in time in each cycle of the repeated wet ALE process. Thus, the order of the steps performed in each cycle of the repeated wet ALE process described herein is not strictly limited to the order shown in FIGS. 1A-1E.

[0043] The time it takes to complete the steps in the cyclic wet ALE process shown in Figures 1A-1E, combined with the fact that each cycle removes one or more monolayers of material, makes wet ALE a slow process. Running each step slowly to saturation achieves many benefits. First, the process is self-limiting, resulting in excellent within-wafer uniformity. Second, the self-limiting nature of the process results in smoothing of the surface during etching. This smoothing is particularly important for metal etch-back, where increased surface roughness can adversely affect the metal's resistivity. Third, the digital nature of the process allows for full control of the total etch volume by varying the number of ALE cycles rather than the exact etch time.

[0044] The repeated wet ALE process shown in Figures 1A-1E smooths the etched surface. While the as-etched surface roughness is reduced during the etching process, the amount of smoothing achieved by the repeated wet ALE process eventually reaches a terminal value. Etching beyond this point does not further improve the surface roughness. In one exemplary process, the root-mean-square (RMS) roughness of an unetched polycrystalline cobalt material can be approximately 1.5 nm in the as-deposited state. The surface roughness of a polycrystalline cobalt material can be reduced to approximately 0.6 nm after removing 10 nm of cobalt using the wet ALE process described above. Even after 30 nm of cobalt is removed, the RMS roughness remains approximately 0.6 nm upon further etching. Thus, for the polycrystalline cobalt material described in the exemplary ALE process above, a final roughness value can be observed after etching 10 nm. Additional etching cycles do not further improve the roughness. These roughness results for cobalt are representative of wet ALE processes in general.

[0045] In high volume manufacturing (HVM), throughput, and therefore process cost, are always important. Economic pressure to reduce cycle time in wet ALE processes leads to situations where the reaction time is only long enough to bring the reaction to near saturation, and the purge time is only long enough to remove most of the excess reactants. These compromises result in improved throughput at the expense of uniformity and roughness.

[0046] As described above, throughput can be improved not only by shortening the ALE cycle time but also by increasing the etch rate per ALE cycle. In the present disclosure, the etch rate per ALE cycle can be increased by shortening the purge time in the early stages of the wet ALE process. The shortened purge time allows the components of the surface modification solution and the dissolving solution to mix, allowing for small amounts of continuous etching during a transient time window in the etching cycle. This continuous etching increases the etch rate in the early stages of the wet ALE process, at the expense of surface roughness. Surface roughness can then be improved in the later stages of the wet ALE process by increasing the purge time used in subsequent cycles of the wet ALE process. Dynamically adjusting the purge time as the etch progresses is particularly useful when etching nanoscale features.

[0047] Schematic illustrations of how mixing of solutions affects etching of nanoscale features are shown in FIGS. 2A-2B and 3A-3B. When etching nanoscale features, diffusion becomes the dominant mass transport phenomenon. The physical dimensions of the features being etched are too small to allow for convective transport. In the example shown in FIGS. 2A-2B and 3A-3B, a metal feature 200 (e.g., a cobalt feature) recessed in a surrounding dielectric layer 205 is etched by exposing the surface of the metal feature 200 to a surface modification solution 210 (e.g., citric acid in isopropyl alcohol (IPA)), followed by a purging solution 220 (e.g., IPA) and a dissolving solution 215 (e.g., deionized water, HO).

[0048] As shown in the example of FIG. 2A, if the dissolving solution 215 is introduced before the surface modification solution 210 is completely removed from the surface of the metal feature 200, interdiffusion of the two solutions (e.g., interdiffusion of citric acid and HO in IPA) creates conditions that allow for a continuous etching process, as shown in FIG. 2B. On the other hand, FIGS. 3A-3B show that if the purge time between the surface modification and dissolving steps is long enough to completely remove the previous etching solution, interdiffusional mixing is eliminated, preventing continuous etching. Because mass transport is diffusion-limited in nanoscale features, deeper features require longer purge times to ensure complete separation of the surface modification solution and the dissolving solution. Dynamically increasing the purge time as etching progresses to maintain effective purging is an aspect of the embodiments described herein.

[0049] If the purge time is insufficient (see, for example, FIGS. 2A-2B), the mixing of the surface modification solution 210 and the dissolving solution 215 results in transient, continuous etching. In addition to increasing the amount of material removed in each etching cycle, continuous etching also increases the roughness of the etched surface. An example of this is shown in FIGS. 4A-4B.

[0050] Figures 4A and 4B are scanning electron microscope (SEM) images of patterned cobalt features etched using a wet ALE process. In the SEM image shown in Figure 4A, sufficient purging time was used between the surface modification and dissolution steps to prevent mixing of the surface modification solution and the dissolution solution and avoid consecutive etching. In this case, the etch volume per cycle is approximately 0.4 nm. Figure 4B shows similar conditions, but with a shortened or insufficient purging time that does not prevent mixing of the surface modification solution and the dissolution solution. In the SEM image shown in Figure 4B, the etch volume per cycle has increased to 0.6 nm, and the surface roughness has clearly deteriorated. Comparing the two SEM images shows how purging time can affect the etch volume per cycle and surface roughness. An intermediate purging time can also be used to balance the need for etch rate with the need for surface roughness.

[0051] The techniques described herein improve upon conventional wet ALE processes by providing a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness. In some embodiments, the purge time can be dynamically adjusted to compensate for the diffusion-controlled aspect ratio dependence of the etch process. For example, when wet ALE is used as a recess etch, the purge time can be adjusted according to the etch process to compensate for changes in aspect ratio. At the beginning of the etch process, the aspect ratio of the etch profile is zero. As metal is removed from the exposed surface, the aspect ratio of the recess (or other feature) increases and reaches a maximum as the etch endpoint is reached. Because solutions are less likely to mix in low aspect ratio features, the purge time can be shortened at the beginning of the etch process to increase the etch rate. As the etch progresses and the aspect ratio increases, the purge time between the surface modification and dissolution steps can be dynamically increased to maintain proper separation of the etch solutions and improve surface roughness by avoiding continuous etching in the final stages of the etch. This dynamic purge timing variation is another aspect of the embodiments described herein.

[0052] 5A and 5B show details of the relationship between etch time, aspect ratio, and diffusion timescale. The diffusion length (d) can be defined as the depth of the feature 500 being etched (e.g., a polycrystalline metal feature). Because convective transport dominates above the wafer surface, diffusion is only important in nanoscale features between this convective zone and the metal surface. As the depth of these features increases, the diffusion length (d) also increases. The increase in the diffusion length (d) as the etching process progresses is shown in FIG. 5A.

[0053] Figure 5B is a graph showing relative diffusion time versus aspect ratio. As shown in Figure 5B, the diffusion timescale increases proportionally to the square of the aspect ratio or diffusion length (d). For typical liquid phase diffusion coefficients and typical semiconductor length scales, the diffusion timescale is less than one second. However, to completely remove all reactants, purge times several times longer than the diffusion timescale are required. Nevertheless, the required purge times are compatible with semiconductor HVM requirements.

[0054] In some embodiments, the purge time can be dynamically adjusted to increase the etch rate in the early stages of the wet ALE process and decrease the etch rate in the final stages of the wet ALE process. For example, the purge time can be relatively short (or eliminated entirely) at the beginning of the etching process or throughout the entire process, depending on the post-etch surface roughness requirements. Reducing the purge timing in the early stages of the wet ALE process allows some mixing of the surface modification solution and the dissolving solution on the wafer surface. This mixing results in a transient, continuous etch, which increases the etch rate and the amount etched per etch cycle. However, as noted above, continuous etching also increases surface roughness. As the etch progresses, the purge timing can be increased in the middle and / or final stages of the wet ALE process to decrease the etch rate and the amount etched per cycle while simultaneously improving the roughness of the etched surface. A schematic diagram of this dynamic purge timing is shown in FIG. 6A, and the results of such timing are shown in FIGS. 6B-6E.

[0055] The feed timing for different purge conditions (e.g., no purge, reduced purge, and full purge) is shown schematically in FIG. 6A. As shown in FIG. 6A, the cycle time increases significantly as the purge time increases. Increasing the purge time (and thus the cycle time) improves surface roughness by reducing the likelihood of continuous etching, but at the expense of throughput. FIG. 6B shows the expected etch volume per cycle (nm / cycle) for the different purge conditions shown in FIG. 6A. As shown in FIG. 6B, the etch volume per cycle (and etch rate) increases as the purge time decreases and decreases as the purge time increases. Increasing the etch volume per cycle (and etch rate) improves throughput, but at the expense of surface roughness.

[0056] In some embodiments, dynamic purging can be used to balance throughput and etch rate with post-etch surface roughness. FIG. 6A illustrates one embodiment of a dynamic wet ALE cycle timing schedule that uses “dynamic purging” (i.e., dynamically varying purge timing) to balance throughput and etch rate with post-etch surface roughness within a single etch. In the embodiment illustrated in FIG. 6A, the etch process begins without purging between the surface modification and dissolution steps to prioritize a fast etch rate, and the purge time increases as the etch progresses to prioritize a smoother post-etch surface as the etch nears completion. More specifically, in the embodiment illustrated in FIG. 6A, the purging between the surface modification and dissolution steps is omitted in the early stages of the etch process (“no purge”), shortened in the middle stages of the etch process (“shortened purge”), and complete in the final stages of the etch process (“full purge”). Each stage illustrated in FIG. 6A can generally include one or more ALE cycles.

[0057] 6C and 6D show simulated etch results that may be achieved with different purge conditions, including no purge, full purge, and dynamic purge, as described above and shown in FIG. 6A. In particular, FIGS. 6C and 6D show exemplary etch depths (nm) that may be achieved with no purge, full purge, and dynamic purge as a function of cycle number ( FIG. 6C ) and process time ( FIG. 6D ). Thus, FIGS. 6C and 6D demonstrate that dynamically varying purge conditions may be used to improve etch productivity using the techniques described herein.

[0058] FIG. 6E shows the RMS roughness (nm) of post-etch surfaces etched using no purge, full purge, and dynamic purge, as shown schematically in FIG. 6A. As shown in FIG. 6E, omitting the purge step between the surface modification and dissolution steps ("no purge") significantly increases the etch rate and etch productivity, but at the expense of surface roughness. On the other hand, FIG. 6E also shows that full purge minimizes surface roughness, but at the expense of etch rate and throughput. For example, as shown in FIG. 6A, by dynamically varying the purge time, the etch rate is faster at the beginning of the etch process (e.g., in the early stages of the etch process) and slows as the etch process endpoint approaches. This "dynamic purge" increases surface roughness at the beginning of the etch and improves it as the purge time increases in the middle and final stages of the etch process. While an example recipe is shown in FIG. 6A, the specific recipe for how the purge time varies as the etch progresses can be experimentally determined to balance the competing needs of a smooth post-etch surface and high process throughput.

[0059] The following is an example of how the dynamic purge timing techniques described herein can be applied to metal recess etching. For a metal recess etching process with constant purge timing, the degree of diffusive mixing is expected to increase as the etch progresses. The increased diffusive mixing occurs because the diffusion length (d) increases without a corresponding increase in purge time. This favors grain boundary etching and results in greater surface roughness at the end of the etch. It also leads to an increased amount etched per cycle near the end of the etch.

[0060] The dynamic supply timing (i.e., dynamic purge timing) technique described herein can be used in alternative etching regimes to improve post-etch surface roughness without increasing process time. For example, if the diffusion length (d) is short, the dynamic purge timing technique described herein can be used to shorten the purge time at the beginning of the etching process. In some cases, aggressively reducing the purge time can cause continuous etching, which increases the amount of etching per cycle and generates some roughness. The purge time can be increased as the etching progresses. This prevents continuous etching and improves surface roughness near the etching process. The etching regime starts with a faster etching rate, which can generate roughness, and ends with a slower rate and conditions that favor surface smoothing. Thus, the dynamic purge timing technique described herein can be used to improve post-etch roughness without increasing the etching time.

[0061] The dynamic purge timing techniques described herein can generally be used to etch a wide variety of materials and features using a wide variety of wet ALE process conditions. One application of the dynamic purge timing techniques described herein can be for etching metal surfaces in a recess etch for fully self-aligned vias. For example, the techniques described herein can be used to etch metal-filled trenches in dielectric materials. In one exemplary application, the trenches can be filled with a polycrystalline cobalt material or another transition metal. When etching metal-filled trenches in dielectric materials, it is necessary to selectively etch the exposed surface of the metal without increasing the surface roughness of the metal. It will be recognized that such applications are merely exemplary, and that the techniques described herein can be used in many other applications.

[0062] In some embodiments, the wet ALE process described herein can be performed in a spin chamber, where the substrate rotates while the etching solution is dispensed onto the substrate surface. The substrate motion evenly distributes the etching solution across the substrate surface. The dispense time of each etching solution (e.g., each surface modification solution and dissolution solution) must be long enough to achieve a self-limiting reaction thickness across the substrate surface. The dispensed chemicals may be switched between etching components to achieve the desired etching. In some embodiments, a purge solution may be dispensed between the surface modification solution and the dissolution solution for a sufficient amount of purge time to prevent spontaneous etching of the metal surface due to transient mixing of the surface modification solution and the dissolution solution. In other embodiments, the purge time between the surface modification and dissolution steps may be shortened, omitted, or dynamically adjusted as the etching progresses to provide the desired throughput, etch rate, and / or post-etch surface roughness in the wet ALE process. A single etching cycle defined by surface modification (e.g., oxidation / complexation) followed by dissolution of the surface modification layer can be repeated until the appropriate amount of material is removed.

[0063] Table 1 shows exemplary wet ALE process conditions that may be used to etch the cobalt features shown in FIGS. 7A and 7B using a spin chamber. It should be appreciated that the use of a spin chamber is merely one embodiment, and that a wide variety of different process tools may be used to implement the techniques described herein. As one alternative, for example, the substrate may be immersed in a chemical bath containing an etchant. In some cases, the substrate may be successively immersed in each etchant bath in sequence, with intermediate rinse baths to prevent chemical cross-contamination. This process may be repeated until an appropriate amount of material is removed. In yet another embodiment, the process may be utilized with an aerosol spray, fog, or mist of each reactant. It should also be appreciated that a combination of the various described tools may be used to apply the reactants, even within one process cycle.

[0064] As shown in Table 1, the wet ALE process used to etch the cobalt features shown in FIGS. 7A and 7B may generally begin by exposing the surface of the cobalt features to isopropyl alcohol (IPA) and a complexing agent (e.g., a carboxylate-based ligand) in a surface modification step. The wet ALE process may then perform a first purge ("Purge 1"), expose the surface of the cobalt features to deionized water in a dissolution step, and perform a second purge ("Purge 2"). The surface modification step, first purge, dissolution step, and second purge may be performed using a wide variety of tool settings, including, but not limited to, spin speed, flow rate, number of cycles, cycle time, etc. In Table 1, the surface modification step and the first purge are performed at a spin speed of 1000 rpm and a flow rate of 300 ml / min, the dissolution step is performed at a spin speed of 1000 rpm and a flow rate of 1500 ml / min, and the second purge is performed at a spin speed of 1000 rpm and a flow rate of 0 ml / min (i.e., the second purge is a dry purge). In the wet ALE process shown in Table 1, the surface modification step, the first purge, the dissolution step, and the second purge are repeated 30 cycles.

[0065] [Table 1]

[0066] In addition to the exemplary process conditions described above, Table 1 compares the total etch time ("Total Time") achieved when etching the cobalt features shown in FIGS. 7A and 7B using a full purge ("Baseline Purge") and a dynamically adjusted purge ("Reduced Purge"). In the case of a full purge ("Baseline Purge"), the first and second purge steps ("Purge 1" and "Purge 2") are each performed for 10 seconds to prevent mixing of the surface modification solution with the dissolving solution. In the case of a dynamically adjusted purge ("Reduced Purge"), in each cycle of the wet ALE process, the first purge step ("Purge 1") is reduced by 50% (i.e., 5 seconds) compared to a full purge ("Baseline Purge"), and the second purge step ("Purge 2") is omitted. Table 1 shows that going from a full purge ("Baseline Purge") to a dynamically adjusted purge ("Reduced Purge") reduces the time per cycle by over 50%. This results in a faster wet ALE process, but it is the faster cycle time combined with a 25% increase in etch volume per cycle that results in a total 3x improvement in etch productivity.

[0067] 7A and 7B show transmission electron microscope (TEM) images of cobalt features etched using the wet ALE process conditions detailed in Table 1. FIG. 7A shows the case of a full purge ("baseline purge") where the surface modification solution and the dissolving solution are completely separated. As shown in Table 1, the etch depth per cycle using a full purge is approximately 0.45 nm, and the etch rate is 0.83 nm / min. As shown in Table 1 for the case of a dynamically adjusted purge ("shortened purge"), when the first purge step is shortened and the second purge step is omitted, the etch depth per cycle increases to 0.57 nm, and the etch rate increases to 2.6 nm / min. This represents a three-fold improvement in the etch rate compared to the case of a full purge ("baseline purge"). In the example shown in Figures 7A and 7B, the surface roughness is good for both the full purge ("baseline purge") and the dynamically adjusted purge ("shortened purge"), so there is no need to dynamically change the purge timing as the etch progresses.

[0068] Dynamically adjusting purge timing during etching provides another tool for optimizing wet etch performance. When surface roughness is not a priority, skipping the purge step entirely can be used to significantly improve throughput. When minimizing surface roughness is a priority, a dynamic purge timing strategy can be used to increase purge time as the etch progresses. In this scenario, etch rate is prioritized at the beginning of the etch, while smoothness is prioritized at the end of the etch. Using this strategy, throughput can be improved while maintaining good post-etch surface roughness. Thus, the embodiments described herein provide a new tool for increasing overall etch productivity while balancing post-etch surface roughness needs. Reducing etch time also reduces chemical consumption, thereby improving the total cost of ownership of the process.

[0069] 8-10 illustrate exemplary methods using the processing techniques described herein. More specifically, FIGS. 8-10 illustrate various embodiments of methods for improving a wet ALE process by providing a dynamic ALE cycle timing schedule that balances throughput and etch rate with post-etch surface roughness. As described in more detail below, the methods illustrated in FIGS. 8-10 can adjust purge timing between ALE cycles and / or between individual surface modification and selective dissolution steps to provide a desired throughput, etch rate, and / or post-etch surface roughness in an improved wet ALE process.

[0070] It should be understood that the embodiments of Figures 8-10 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 steps may be added to the methods shown in Figures 8-10. 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.

[0071] 8 illustrates one embodiment of a method 800 that may be used to etch a substrate using a wet atomic layer etching (ALE) process. The method 800 illustrated in FIG. 8 includes receiving a substrate (at step 810), the substrate having exposed material. Then, in step 820, the method 800 includes selectively etching the material by performing multiple cycles of the wet ALE process, each cycle including: a) performing one or more surface modification steps to chemically modify an exposed surface of the material and provide a surface modification layer, the one or more surface modification steps including exposing the exposed surface of the material to at least one surface modification solution to chemically modify the exposed surface of the material; b) performing a first purging step after the one or more surface modification steps, the first purging step including rinsing the substrate with a solvent; c) performing a dissolution step after the first purging step to selectively remove the surface modification layer of the material, the dissolution step including exposing the surface modification layer to a dissolving solution to dissolve the surface modification layer; and d) performing a second purging step after the dissolution step, the second purging step including rinsing the substrate with a solvent or performing a spin-drying step. In step 830, the method 800 includes adjusting the purge time of the first purge step and / or the purge time of the second purge step in one or more cycles of the wet ALE process to provide a desired throughput, etch rate, and / or post-etch surface roughness in the wet ALE process.

[0072] 9 illustrates another embodiment of a method 900 that can be used to etch a substrate. The method 900 illustrated in FIG. 9 includes receiving a substrate (at step 910), where the substrate has exposed material. Then, at step 920, the method 900 includes selectively etching the material by performing multiple cycles of a wet ALE process, each cycle including: a) chemically modifying an exposed surface of the material to provide a surface-modified layer, where the exposed surface is chemically modified by oxidizing the material using an oxidizing agent; b) binding a complexing agent to the surface-modified layer of the material to provide a complexed-type surface-modified layer; c) rinsing the substrate with a solvent; and d) selectively removing the complexed-type surface-modified layer of the material by exposing the complexed-type surface-modified layer to a dissolving solution to dissolve the complexed-type surface-modified layer. In the method 900 shown in FIG. 9, the cleaning step (c) is performed for a first period of time in one or more first cycles of the wet ALE process, and for a second period of time in one or more second cycles of the wet ALE process, with the one or more second cycles being performed after the one or more first cycles, and the second period of time being longer than the first period of time.

[0073] 10 illustrates another embodiment of a method 1000 that can be used to etch a substrate. The method 1000 illustrated in FIG. 10 includes receiving (at step 1010) a substrate having exposed material, the material including a polycrystalline material. Then, at step 1020, the method 1000 includes selectively etching the polycrystalline material by performing multiple cycles of a wet ALE process, each cycle including: a) chemically modifying an exposed surface of the polycrystalline material to provide a surface-modified layer, the exposed surface being chemically modified by oxidizing the polycrystalline material using an oxidizing agent; b) binding a complexing agent to the surface-modified layer of the polycrystalline material to provide a complexed-type surface-modified layer; c) rinsing the substrate with a solvent; and d) selectively removing the complexed-type surface-modified layer of the polycrystalline material by exposing the complexed-type surface-modified layer to a dissolving solution to dissolve the complexed-type surface-modified layer. In the method 1000 shown in FIG. 10, the washing step (c) is carried out for an increasing period of time during said carrying out multiple cycles of the wet ALE process.

[0074] It should be noted that throughout this specification, references to "one embodiment" or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention, but do not indicate that it is present in all embodiments. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment of the invention. Furthermore, particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments. In alternative embodiments, various additional layers and / or structures may be included and / or described features may be omitted.

[0075] As used herein, the term "substrate" refers to and includes a base material or structure upon which a material is formed. It should be understood that a substrate can include a single material, multiple layers of different materials, one or more layers having regions of different materials or structures therein, etc. These materials can include semiconductors, insulators, conductors, or combinations thereof. For example, the substrate can be a semiconductor substrate, a base semiconductor layer on a supporting structure, a metal electrode, or a semiconductor substrate having one or more layers, structures, or regions formed thereon. The substrate can be a conventional silicon substrate or other bulk substrate including a layer of semiconducting material. As used herein, the term "bulk substrate" refers to and includes not only silicon wafers, but also silicon-on-insulator ("SOI") substrates such as silicon-on-sapphire ("SOS") substrates and silicon-on-glass ("SOG") substrates, epitaxial layers of silicon on a base semiconductor substrate, and other semiconductor or optoelectronic materials, such as silicon germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped.

[0076] Systems and methods for processing a substrate are described in various embodiments. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, and may be, for example, a base substrate structure such as a semiconductor substrate, or a layer on or overlying the base substrate structure, such as a thin film. Thus, the substrate is not intended to be limited to any particular base structure, underlying layer, or overlying layer, patterned or unpatterned, but rather is intended to include any such layer or base structure, and any combination of layers and / or base structures.

[0077] As will be understood by those skilled in the art, various embodiments may be practiced without one or more of the specific details, or with other alternative and / or additional methods, materials, or components. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without the specific details. Furthermore, it should be understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0078] Further modifications and alternative embodiments of the described systems and methods will be apparent to those skilled in the art upon review of this specification. Accordingly, it is understood that the described systems and methods are not limited by these exemplary configurations. It should be understood that the forms of the systems and methods shown and described herein should be construed as exemplary embodiments. Various changes can be made to the implementation. Thus, while the wet ALE technique is described herein with reference to specific embodiments, various modifications and changes can be made without departing from the scope of the present disclosure. Accordingly, the specification and drawings should be regarded in an illustrative rather than a restrictive sense, and such modifications are intended to be included within the scope of the present disclosure. Furthermore, any benefits, advantages, or solutions to problems described herein with respect to particular embodiments are not intended to be construed as any or all critical, necessary, or essential features or elements of the claims.

Claims

1. 1. A method of etching a substrate using a wet atomic layer etching (ALE) process, the method comprising: receiving a substrate, the substrate having exposed material; Selectively etching the material by performing multiple cycles of the wet ALE process, Each cycle is a) performing one or more surface modification processes to chemically modify an exposed surface of the material to provide a modified surface layer, the one or more surface modification processes comprising exposing the exposed surface of the material to at least one surface modification solution to chemically modify the exposed surface of the material; b) performing a first purging step after the one or more surface modification steps, the first purging step comprising rinsing the substrate with a solvent; c) performing a dissolving step after the first purging step to selectively remove the modified surface layer of the material, the dissolving step comprising exposing the modified surface layer to a dissolving liquid to dissolve the modified surface layer; and d) performing a second purge step after the dissolving step, the second purge step comprising rinsing the substrate with a solvent or performing a spin-dry step; and adjusting a purge time of the first purge step and / or a purge time of the second purge step during one or more cycles of the wet ALE process to provide a desired throughput, etch rate, and / or post-etch surface roughness in the wet ALE process; A method comprising:

2. The step of performing one or more surface modification processes includes: in a first surface modification step, exposing the exposed surface of the material to an oxidizing agent to chemically modify the exposed surface of the material to provide the modified surface layer; a second surface modification step of exposing the modified surface layer to a complexing agent, causing the complexing agent to bind to the modified surface layer and provide a complexed modified surface layer; and 2. The method of claim 1, wherein performing the dissolving step comprises selectively removing the complex-bonded modified surface layer of the material by exposing the complex-bonded modified surface layer to the dissolving solution, thereby dissolving the complex-bonded modified surface layer.

3. 3. The method of claim 2, wherein exposing the complex-bonded modified surface layer to the dissolution solution dissolves the complex-bonded modified surface layer and reforms a modified surface layer on the newly exposed surface of the material.

4. 2. The method of claim 1, wherein adjusting the purge time of the first purge step and / or the purge time of the second purge step comprises increasing the purge time of the first purge step and / or the purge time of the second purge step as the wet ALE process progresses.

5. The step of adjusting the purge time of the first purge step and / or the purge time of the second purge step includes: shortening the purge time of the first purge step and / or the purge time of the second purge step during one or more first cycles of the wet ALE process to increase the etch rate achieved in the one or more first cycles; increasing the purge time of the first purge step and / or the purge time of the second purge step during one or more second cycles of the wet ALE process to reduce the post-etch surface roughness obtained during the one or more second cycles, wherein the one or more second cycles are performed after the one or more first cycles; 2. The method of claim 1, comprising:

6. 2. The method of claim 1, wherein adjusting the purge time of the first purge step and / or the purge time of the second purge step comprises shortening the purge time of the first purge step and omitting the second purge step during each cycle of the wet ALE process to increase the etch rate and improve the throughput.

7. The step of adjusting the purge time of the first purge step and / or the purge time of the second purge step includes: omitting the first purge step and / or the second purge step during one or more first cycles of the wet ALE process; performing the first purge step and / or the second purge step during one or more second cycles of the wet ALE process, the one or more second cycles being performed after the one or more first cycles, and the purge time of the first purge step and / or the purge time of the second purge step performed during the one or more second cycles being insufficient to prevent mixing between the at least one surface modification solution and the dissolving liquid; performing the first purge step and / or the second purge step during one or more third cycles of the wet ALE process, the one or more third cycles being performed after the one or more second cycles, and the purge time of the first purge step and / or the purge time of the second purge step performed during the one or more third cycles preventing mixing between the at least one surface modification solution and the dissolving liquid; 2. The method of claim 1, comprising:

8. 1. A method of etching a substrate using a wet atomic layer etching (ALE) process, the method comprising: receiving a substrate, the substrate having exposed material; Selectively etching the material by performing multiple cycles of the wet ALE process, each cycle comprising: a) chemically modifying an exposed surface of the material to provide a modified surface layer, the exposed surface being chemically modified by oxidation of the material using an oxidizing agent; b) attaching a complexing agent to the modified surface layer of the material to provide a complexed modified surface layer; c) rinsing the substrate with a solvent; and d) selectively removing the complex-bonded modified surface layer of the material by exposing the complex-bonded modified surface layer to a dissolving solution to dissolve the complex-bonded modified surface layer; and and rinsing the substrate is performed for a first period of time during one or more first cycles of the wet ALE process; rinsing the substrate is performed for a second period of time during one or more second cycles of the wet ALE process; The method, wherein the one or more second cycles are performed after the one or more first cycles, and the second period of time is longer than the first period of time.

9. 9. The method of claim 8, wherein during each cycle, a) and b) are performed with at least partial overlap in time.

10. 9. The method of claim 8, wherein during each cycle, a) and b) are performed consecutively without overlap in time.

11. 9. The method of claim 8, wherein during each cycle, b) and d) are performed with at least partial overlap in time.

12. the exposed surface of the material has a surface roughness characterized by a first surface roughness value after the one or more first cycles; The method of claim 8 , wherein the surface roughness is reduced to a second surface roughness after the one or more second cycles.

13. The method of claim 8 , wherein the material is a transition metal.

14. The method of claim 8 , wherein the material comprises copper (Cu), ruthenium (Ru), or cobalt (Co).

15. 1. A method of etching a substrate using a wet atomic layer etching (ALE) process, the method comprising: receiving a substrate, the substrate having exposed material, the material comprising a polycrystalline material; Selectively etching the polycrystalline material by performing multiple cycles of the wet ALE process, each cycle comprising: a) chemically modifying an exposed surface of the polycrystalline material to provide a modified surface layer, the exposed surface being chemically modified by oxidation of the polycrystalline material with an oxidizing agent; b) attaching a complexing agent to the modified surface layer of the polycrystalline material to provide a complexed modified surface layer; c) rinsing the substrate with a solvent; and d) selectively removing the complex-bonded modified surface layer of the polycrystalline material by exposing the complex-bonded modified surface layer to a dissolving solution to dissolve the complex-bonded modified surface layer; and and The method, wherein rinsing the substrate is performed for an increasing period of time between performing the multiple cycles of the wet ALE process.

16. 16. The method of claim 15, wherein during each cycle, a) and b) are performed with at least partial overlap in time.

17. 16. The method of claim 15, wherein during each cycle, a) and b) are performed consecutively with no overlap in time.

18. 16. The method of claim 15, wherein during each cycle, b) and d) are performed with at least partial overlap in time.

19. the exposed surface of the polycrystalline material has a surface roughness characterized by a first surface roughness value after one or more first cycles of the wet ALE process are performed; the surface roughness is reduced to a second surface roughness after one or more second cycles of the wet ALE process are performed; 16. The method of claim 15, wherein the one or more second cycles are performed after the one or more first cycles.

20. The method of claim 15 , wherein the polycrystalline material is a transition metal.

21. 16. The method of claim 15, wherein the polycrystalline material comprises copper (Cu), ruthenium (Ru), or cobalt (Co).

Images