Selective etching by removal of a volatilizable terminal functional group

Abstract

Examples are disclosed that relate to selective etching of materials with similar chemical compositions. One example provides a method of selectively etching a feature in a substrate. The substrate comprises a first silicon-containing material and a second silicon-containing with different concentrations of volatilizable terminal functional groups. The method comprises exposing the substrate to energy sufficient to dissociate at least some terminal functional groups, and exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules to remove silicon from the substrate and thereby etch the substrate. The first silicon-containing material is etched at a higher rate than the second silicon-containing material.

Description

SELECTIVE ETCHING BY REMOVAL OF A VOLATILIZABLE TERMINAL FUNCTIONAL GROUPBACKGROUND

[0001] Semiconductor device fabrication processes can involve many steps of material deposition, patterning, and removal to form integrated circuits on substrates. Various methods can be used to selectively remove material from a substrate. As an example, reactive ion etching (RIE) uses a chemically reactive plasma to remove material from a substrate surface. As another example, atomic layer etching (ALE) can be used to remove substrate material layer-by-layer using etching cycles. In an ALE cycle, a modification step is used to chemically modify a layer of material at a substrate surface. Then, a removal step volatilizes and removes the chemically modified layer.SUMMARY

[0002] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

[0003] Examples are disclosed that relate to the selective etching of materials with similar chemical compositions by removal of a volatilizable terminal functional group from a material being etched. One example provides a method of selectively etching a feature in a substrate. The substrate comprises a first silicon-containing material and a second silicon-containing material with different concentrations of volatilizable terminal functional groups. The method comprises exposing the substrate to energy sufficient to dissociate at least some terminal functional groups, and exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules to remove silicon from the substrate and thereby etch the substrate. The first silicon-containing material is etched at a higher rate than the second silicon-containing material.

[0004] In some such examples, the first silicon-containing material is a low dielectric constant (low k) material, and the functional groups comprise organic functional groups.

[0005] Alternatively or additionally, in some such examples, the low k dielectric material comprises carbon doped silicon oxide (SiOCH), and the organic functional groups comprise methyl groups.

[0006] Alternatively or additionally, in some such examples, the second silicon- containing material comprises an etch stop layer.

[0007] Alternatively or additionally, in some such examples, the etch stop layer comprises oxygen doped silicon carbide.

[0008] Alternatively or additionally, in some such examples, exposing the substrate to energy comprises exposing to a plasma.

[0009] Alternatively or additionally, in some such examples, exposing the substrate to energy comprises exposing the substrate to one or more of particle beam energy or photon energy.

[0010] Alternatively or additionally, in some such examples, the halogencontaining etching agent comprises a fluorine-containing etching agent.

[0011] Alternatively or additionally, in some such examples, the etching cycle further comprises depositing a film layer during the etching cycle.

[0012] Alternatively or additionally, in some such examples, the film layer is deposited after exposing the substrate to the halogen-containing etching agent and before performing a next etching cycle.

[0013] Alternatively or additionally, in some such examples, the film layer is deposited after exposing the substrate to the energy and before exposing the substrate to the halogen-containing etching agent and before performing a next etching cycle.

[0014] Alternatively or additionally, in some such examples, depositing the film layer comprises depositing the film layer using a plasma.

[0015] Alternatively or additionally, in some such examples, depositing the film layer comprises depositing the film layer without using a plasma.

[0016] Another example provides a method of selectively etching a feature in a substrate. The substrate comprises a low dielectric constant material (low k dielectric material) and an etch stop layer. The method comprises performing a plurality of etching cycles to etch a trench in the low k layer. An etching cycle of the plurality of etching cycles comprises exposing the low k dielectric material to a directional plasmato remove a quantity of terminal functional groups from the low k dielectric material, wherein an etch stop layer in a via formed in the low k dielectric material also is exposed to the directional plasma, and wherein the etch stop layer has a lower concentration of the volatilizable terminal functional groups than the low k dielectric material. The method further comprises exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules at locations of removed terminal functional groups to remove silicon from the low k dielectric material, wherein the etch stop layer etches at a lower etch rate than an etch rate of the low k dielectric material.

[0017] In some such examples, the low k dielectric material comprises a carbon doped silicon oxide material, and the etch stop layer comprises oxygen doped silicon carbide.

[0018] Alternatively or additionally, in some such examples each etching cycle further comprises depositing a film layer during the etching cycle.

[0019] Alternatively or additionally, in some such examples the volatilizable terminal functional groups comprise methyl groups.

[0020] Another example provides a processing tool. The processing tool comprises a processing chamber and a substrate holder disposed in the processing chamber. The processing tool further comprises flow control hardware to control processing chemical flows into the processing chamber. The processing tool further comprises an energy source for exposing a substrate positioned in the substrate holder to energy. The processing tool further comprises a controller configured to control the processing tool to perform an etching process comprising a plurality of etching cycles. The controller is configured to, for each etching cycle of the plurality of etching cycles, control the energy source to expose the substrate to the energy sufficient to dissociate at least some terminal functional groups of a first silicon-containing material from the silicon atoms, and control the flow control hardware to expose the substrate to a halogen-containing etching agent to form volatile silicon halide molecules to remove silicon from the substrate and thereby etch the substrate.

[0021] In some such examples, the energy source comprises a plasma source.

[0022] Alternatively or additionally, in some such examples, the energy source comprises one or more of a particle beam energy source or a photon energy source.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIGS. 1A-1C schematically show an etching process with insufficient selectivity relative to an etch stop layer.

[0024] FIG. 2 schematically shows an example ALE process that utilizes an oxygen-containing plasma to remove a volatilizable terminal functional group.

[0025] FIG. 3 shows etch rate data for the etching of SiOCH, ODC, and NDC using an example ALE process in which an oxygen plasma is used to dissociate volatilizable terminal functional groups from the SiOCH.

[0026] FIG. 4 schematically shows an example ALE process that utilizes an inert gas-containing plasma to dissociate volatilizable terminal functional groups.

[0027] FIG. 5 shows etch rate data for the etching of SiOCH, ODC, and NDC using an example ALE process in which an oxygen plasma is used to dissociate volatilizable terminal functional groups from the SiOCH.

[0028] FIG. 6 shows a flow diagram depicting an example method of selectively etching different materials having similar chemical compositions.

[0029] FIGS. 7A-7C schematically show an example etching process performed according to the method of FIG. 6.

[0030] FIGS. 8A-8F schematically show an example process for etching a via and trenches in a low k material layer according to the method of FIG. 6.

[0031] FIG. 9 schematically shows an example processing tool.

[0032] FIG. 10 shows a block diagram of an example computing system.DETAILED DESCRIPTION

[0033] The term “aspect ratio” generally represents a ratio of a depth of a feature to a width of the feature (e.g. an average width).

[0034] The term “atomic layer etching” (ALE) generally represents a process for removing material from a substrate by performing a series of etching cycles. Each etching cycle comprises modifying a surface layer of a substrate material and then volatilizing the modified layer of the substrate material.

[0035] The term “carbon doped silicon oxide” (SiOCH) generally represents a silicon oxide material comprising terminal organic groups (e.g. methyl groups) and terminal hydrogens to decrease a density and dielectric constant of the carbon doped silicon oxide compared to silicon dioxide.

[0036] The term “controller” generally represents a computing system configured to control a machine, such as a processing tool.

[0037] The term “directional energy source” generally represents a source of energy that can be used to dissociate volatilizable terminal functional groups in a film material at a higher rate on surfaces with a first orientation relative to the energy source than surfaces with a second orientation relative to the energy source. For example, a “directional plasma” comprises an ion flux that is greatest in a particular direction.

[0038] The term “dissociate” generally represents the act of separating. For example, a volatile terminal group in a carbon doped silicon oxide can be dissociated from a silicon atom by the application of sufficient energy.

[0039] The term “dissociating energy” generally represents energy useable to dissociate a terminal functional group from a film layer. For example, dissociating energy can be used to dissociate a terminal organic group and / or a terminal hydrogen atom from a carbon doped silicon oxide film.

[0040] The term “energy source” generally represents a device for exposing a substrate in a processing chamber to dissociating energy. Example energy sources include plasma sources, photon (light) sources, and ion beam sources.

[0041] The term “etch” and variants thereof general refer to processes in which materials are removed from a substrate using chemical and / or physical processes.

[0042] The term “etching agent” generally represents a chemical species that can chemically react with a substrate material in an etching process.

[0043] The term “etch stop layer” generally refers generally to a layer of a material on a substrate with a lower etch rate than a material being etched above the etch stop layer.

[0044] The term “feature” generally represents a topological structure on a substrate.

[0045] The term “flow control hardware” generally represents components configured to place one or more chemical sources in fluid connection with a processing chamber. Flow control hardware can comprise one or more mass flow controllers and / or valves, for example.

[0046] The term “low k dielectric material” generally represents a material with a dielectric constant lower than that of silicon dioxide.

[0047] The term “oxygen doped carbide” generally represents a material comprising silicon carbide doped with oxygen atoms.

[0048] The term “particle beam source” refers generally to a device that can output an energized beam of particles. Examples include ion beam sources, electron beam sources, and neutron beam sources.

[0049] The term “photon energy source” generally represents a UV or visible light source.

[0050] The term “plasma” generally represents a gas comprising ions and free electrons. A plasma can be used to generate ions and radical species from a precursor molecule introduced into the plasma. A plasma also can be used to sputter a substrate surface.

[0051] The term “processing chemical” generally represents any chemical introduced into a processing chamber during substrate processing. Examples include reactive chemicals and inert gases.

[0052] The term “processing chamber” generally represents an enclosure in which chemical and / or physical processes are performed on substrates.

[0053] The term “processing tool” generally represents a machine comprising a processing chamber and other hardware configured to enable processing to be carried out on a substrate.

[0054] The terms “purge” and variants thereof generally represent processes in which unwanted species are at least partially removed from a processing chamber.

[0055] The term “reactive ion etching (RIE)” generally represents a process by which a chemically reactive plasma is used to remove material from a substrate surface. RIE uses an electric field to accelerate reactive ions in the plasma towards the substrate surface.

[0056] The term “selectivity” generally represents a ratio of an etch rate of a first material compared to an etch rate of a second material exposed to an etching process.

[0057] The term “substrate” generally represents generally represents any object from which a layer of material can be etched.

[0058] The term “substrate holder” generally represents generally represents any structure for supporting a substrate in a processing chamber.

[0059] The term “terminal functional group” generally represents a functional group bound to one atom, and not bridging two or more atoms. Example functional groups include hydrogen and organic groups (e.g. aliphatic and aryl groups).

[0060] As introduced above, semiconductor device fabrication processes can involve many steps of material deposition, patterning, and removal to form integrated circuits on substrates. As one example, reactive ion etching (RIE) uses a chemically reactive plasma to remove material from a substrate surface. As another example, atomic layer etching (ALE) removes substrate material layer-by-layer using etching cycles. Each etching cycle comprises a modification step in which a surface layer of a substrate material is chemically modified, followed by a volatilization step in which the chemically modified layer is removed from the substrate.

[0061] It is desirable for an etching process to have a high selectivity to a material being etched compared to other materials exposed to the etching process. A relatively higher selectivity allows for a material to be etched with less impact on other materials exposed to the etching process compared to a relatively lower selectivity. For example, an etch stop layer can be used beneath a material being etched. The etch stop layer is selected to have a much lower etch rate for a chosen etching process than the material being etched. When the etching process reaches the etch stop layer, the etch rate of the etching process substantially slows. This can help to prevent the etching process from negatively impacting structures below the etch stop layer. As another example, a patterning mask layer can be used above portions of a material being etched to protect those portions of an underlying material. The patterning mask layer protects covered regions of the material being etched from the etching process, while allowing uncovered regions to be etched. The use of an etching process with a relatively higher selectivity relative to the mask layer allows the use of a thinner mask layer than the use of an etching process with a relatively lower selectivity.

[0062] The efficacy of an etch stop layer or a patterning mask layer is dependent upon a selectivity of the material used. The use of a lower selectivity material for an etch stop layer or a patterning mask material can require the use of a relatively thicker layer of material. This can negatively impact throughput and cost compared to the use of a relatively thinner layer of material.

[0063] Some materials commonly used as an etch stop material for selectivity relative to silicon-containing layers are aluminum oxide and aluminum nitride. Fluorine-based etching chemistries commonly used to etch silicon oxide-based materials are highly selective to the silicon oxide-based materials compared to aluminum oxide or aluminum nitride.

[0064] However, aluminum-containing etch stop layers have relatively higher dielectric constants compared to low dielectric constant (low k) materials that are used in integrated circuits for electrically isolating adjacent conductive lines. Example of a low k dielectric material includes carbon-doped silicon oxide (SiOCH) materials. The relatively higher dielectric constant of aluminum oxide etch stop layer can increase a resistive-capacitive (RC) time constant of conductive lines in the integrated circuit due to a corresponding increase in capacitance, relative to omitting the aluminum oxide etch stop layer. As etch stop layers often remain within the material stack of a completed integrated circuit, this can impact performance of the completed integrated circuit.

[0065] The use of lower dielectric constant etch stop layers than aluminum oxide can achieve a lower RC time constant of a conductive line. This can allow conductive lines to be placed closer together relative to the use of aluminum oxide as an etch stop layer. One example of an etch stop material with a lower dielectric constant than aluminum oxide is oxygen-doped silicon carbide (ODC).

[0066] However, using ODC as an etch stop layer (or patterning mask layer) can pose challenges. For example, SiOCH comprises a silicon oxide network with terminal functional groups bonded to silicon atoms. Example terminal functional groups include organic groups (e.g. methyl groups) and hydrogen atoms. The terminal functional groups reduce an amount of silicon-oxygen-silicon bridging in the material. This decreases a density of the material compared to silicon oxide lacking such terminal functional groups. The decreased density leads to a decreased dielectric constant.

[0067] Such SiOCH low k dielectric materials are compositionally similar to ODC. This is because both materials comprise silicon, oxygen, carbon, and some hydrogen. While ODC comprises a more dense, more connected SiO2 network than SiOCH, both are etched by fluorine-based etching chemistries. Thus, commonly used fluorine-based etching chemistries can have an unsuitably low selectivity for etching a SiOCH layer with an ODC etch stop layer.

[0068] FIGS. 1A-1C illustrate this issue. More particularly, FIGS. 1A-1C shows a substrate 100 comprising a lower layer 102 including a first low k dielectric material region 104 (e.g. SiOCH) and a metal line 106. The substrate 100 also comprises an etch stop layer 108 comprising an aluminum nitride layer 109 and ODC layer 110. The substrate 100 further comprises an upper layer 112 comprising a second low k dielectric material region 114. A hard mask layer 116 is positioned on the second low k dielectric material region 114. The hard mask layer 116 can be formed fromtitanium nitride or tungsten carbide in some examples. In other examples the hard mask can be formed from ODC.

[0069] FIG. 1A shows the substrate 100 after a portion of the second low k dielectric material region 114. The hard mask layer 116 includes an opening defining a location of a recessed feature 118 being etched. The recessed feature 118 can be etched, for example, using reactive ion etching (RIE). As a more particular example, the recessed feature 118 can be etched using a fluorine based RIE process. RIE allows highly directional etching to be performed. Thus, RIE is often used to etch relatively higher aspect ratio features.

[0070] FIG. IB shows the substrate 100 after additional material has been etched from second low k dielectric material region 114. Here, the recessed feature 118 is deeper, but has not yet reached the ODC layer 110. FIG. 1C shows the substrate 100 after the recessed feature 118 has been etched through the depth of the second low k dielectric material region 114. As described above, current fluorine based RIE etching processes can have relatively poor selectivity to SiOCH and ODC. As such, in FIG. 1C, the etching process did not stop at the ODC layer 110. Instead, etching continued into the ODC layer 110. The resulting damage to ODC layer 110 can lead to higher capacitance between a metal later deposited into the recessed feature 118 and metal line 106, and thus can impact circuit performance.

[0071] Etching of the ODC layer 110 can be avoided by including an aluminum oxide or aluminum nitride etch stop layer between the ODC layer 110 and the second low k dielectric material region 114. However, as mentioned above, this can increase the overall dielectric constant of the etch stop layer 108.

[0072] Accordingly, examples are disclosed that relate to selectively etching materials having similar chemical compositions, such as SiOCH and ODC. For example, a substrate comprising SiOCH can be exposed to energy to dissociate volatilizable terminal functional groups that are bonded to silicon atoms in the SiOCH. As described in more detail below, dissociation of the volatilizable terminal functional groups creates reactive sites that can be attacked by a halogen-based etching chemistry. This forms volatile silicon halides, which leave the SiOCH, thereby etching the SiOCH. The SiOCH is etched much more slowly by the same chemistry when the dissociating of the functional groups is omitted. Likewise, ODC can lack any significant concentration of the volatile terminal functional groups of SiOCH. As such, ODC is also etched much more slowly. Thus, dissociation of the volatilizable terminalfunctional groups of an SiOCH followed by exposure of the SiOCH to a halogen-based etching chemistry allows the SiOCH to be selectively etched with respect to ODC, as well as with respect to SiOCH that has not been exposed to the dissociating energy. As described in more detail below, selectivities of greater than 50: 1 can be achieved. Other solid materials with volatilizable terminal functional groups bonded to atoms that otherwise form an interconnected network (e.g. nitrogen-doped silicon oxide) may be etched in a similar manner.

[0073] Any suitable etching process can be used to selectively etch SiOCH. Examples include ALE, tempo pulsing, and RIE. As described above, ALE processes comprise etching cycles to remove substrate material layer-by-layer. Each etching cycle comprises a modification step in which volatilizable terminal functional groups are dissociated, and then a volatilization step in which a halogen-containing etching agent reacts with the modified layer to remove substrate material. ALE can comprise flowing an inert gas and / or purging a processing chamber between processing steps. Tempo pulsing comprises pulsed gas flows. Tempo pulsing is similar to ALE in that substrate material is removed layer-by-layer with volatilization and modification steps. However, in contrast to ALE, processing gas flow may overlap during tempo pulsing.

[0074] Performing etching by removing a volatilizable terminal functional group as disclosed can help to avoid depth loading effects compared to conventional RIE etching of high aspect ratio features. The term “depth loading effects” refers to etch rate variation as a function of feature width. Conventional RIE is a continuous process in which transport rates of reactants into a feature and byproducts out of the feature can vary based upon feature width. Small degrees of feature width variation often occur. This can lead to difficulties in closely controlling etching rates. For example, when performing back-end-of-line (BEOL) fabrication of interconnects, vias and lines, via- over-trench overlay errors can occur. RIE processes often use over-etch landing on a etch stop layer to correct for depth loading effects, which can lead to width variation in etched features. However, the disclosed etching according to the disclosed examples can help to avoid depth loading. Since both the volatilizable functional group dissociation process and the volatile silicon halide removal process involve selflimiting reaction mechanisms, transportation loading of reactants and byproducts do not gate the etch rate. Thus, the disclosed examples may intrinsically equalize etch rates for features having different aspect ratios, particularly in the case of ALE.

[0075] SiOCH can comprise an amorphous network of interconnected atoms. The SiOCH 200 can include many silicon-methyl (Si-CH?) bonds and many siliconhydrogen (Si-H) bonds. The bonds between the methyl and hydrogen functional groups and silicon atoms are terminal. In other words, the methyl and hydrogen functional groups do not bridge between two silicon atoms. Further, methyl groups and hydrogen can form volatile compounds (for example, methane gas (CH4) and hydrogen gas (H2)) when dissociated from silicon atoms. The dissociation of these functional groups modifies the surface layer of the SiOCH. This leaves reactive sites at the silicon atoms that can react with halogen-based etching agents to form volatile silicon halides. The formation of the volatile silicon halides removes material from the substrate, thereby etching the substrate. The modification of the SiOCH layer by dissociation of the volatilizable terminal functional groups, followed by the formation of the volatile silicon halides, can be repeated cyclically to etch the substrate by ALE.

[0076] The disclosed examples also can allow a directionality of an etching process to be controlled. The directionality can be controlled by controlling a directionality of energy used to dissociate the volatile terminal functional groups in material being etched. For example, a relatively less directional energy source can be used to perform relatively more isotropic etching. Examples of relatively less directional energy sources include plasmas with relatively higher pressures and relatively lower energies. Likewise, a relatively more directional energy source can be used to perform relatively more anisotropic etching. As a more specific example, a directional plasma can be used to dissociate volatilizable terminal functional groups of a material layer (e.g. an SiOCH layer) at a higher rate at a bottom of a recessed feature being etched than at sidewalls of the recessed feature being etched. The removal of the volatilizable terminal functional groups at a relatively higher rate at a bottom surface than on sidewalls of a recessed feature being etched provides for a higher concentration of reactive sites at the bottom surface for forming volatile silicon halides. This leads to a higher etching rate at the bottom surface than on the sidewalls. By utilizing a suitably directional energy source (e.g. a directional plasma, directional particle beam, directional photon energy, etc.), relatively high aspect ratio features can be etched using the disclosed example ALE processes.

[0077] FIG. 2 schematically illustrates example chemical reactions that can occur during an example ALE cycle performed on SiOCH. In the example of FIG. 2, an oxygen-containing plasma is used as a dissociating energy source to modify a surfaceof a material being etched. Further, a fluorine-containing plasma is used to implement a fluorine-based etching chemistry to volatilize the modified surface. In other examples, other types of plasmas and / or halogen-based etching chemistries can be used. Examples of other plasmas include inert gas plasmas (e.g. argon plasmas). Examples of other halogen-based etching chemistries can include chlorine-based, bromine-based, iodine- based, and mixed halogen-based etching chemistries. Further, in some examples, other energy sources than a plasma can be used to dissociate volatilizable terminal functional groups. Examples include particle beam (e.g. ion beam, electron beam, or neutron beam) and photon (e.g. gamma, x-ray, ultraviolet, and / or visible) energy.

[0078] First referring to 202 in FIG. 2, SiOCH comprises terminal methyl groups 204 and terminal hydrogen groups 206. When exposed to the oxygen-containing plasma, ions from the plasma can physically and chemically interact with the terminal methyl groups 204 and the terminal hydrogen groups 206 to remove a quantity of terminal methyl groups 204 and terminal hydrogen groups 206. The terminal functional groups can form volatile methane and hydrogen gas, as examples. The oxygencontaining plasma can be formed using any suitable oxygen-containing gas. Example oxygen containing gases include molecular oxygen, ozone, hydrogen peroxide, water vapor, carbon dioxide, sulfur dioxide, and nitrous oxide. The plasma can have a pressure of between 10 mTorr - 1 Torr in some examples. Such pressures can provide for a more directional plasma. In other examples, pressures outside of this range can be used.

[0079] Next referring to 208, the dissociation of the volatilizable terminal functional groups and bonding of oxygen atoms from the oxygen-containing plasma creates reactive silicon sites due to the increased bond polarity compared to siliconmethyl and silicon-hydrogen bonds. The increased polarity is represented by 6+next to Si atoms. Exposure to reactive fluorine species generated in a fluorine-containing plasma results in the fluorination of the active sites. Fluorine can continue to react with silicon atoms, forming volatile silicon tetrafluoride (SiF4), as shown at 210. This removes the silicon from the surface of the SiOCH. A next cycle can then begin by again exposing the SiOCH to an oxygen-containing plasma at 2O2.Example fluorine- containing etching agents that can be used to form a fluorine-containing plasma include hydrogen fluoride (HF), molecular fluorine (F2), nitrogen trifluoride (NF3), boron trifluoride (BF3), hexafluoroethane (C2F6), other partially or fully fluorinated alkyl molecules, and sulfur fluorides such as sulfur hexafluoride (SFe). In other examples, achlorine-containing etching agent, a bromine-containing etching agent, an iodine- containing etching agent, or a mixed halide-containing etching agent, can be used. In further examples, the plasma can comprise a chemical that can generate methyl groups in the plasma, such as methane or methanol. The creation of methyl groups in the plasma can allow the methyl groups to react with the SiOCH after removal of a volatilized surface layer. This can help to mitigate or avoid densifi cation of the surface by the removal of the volatilizable terminal functional groups, and thereby help to mitigate any increase in dielectric constant caused by such densification. Additionally or alternatively, the plasma can be formed using molecular nitrogen (N2). In still further examples, the substrate can be exposed to a methyl-containing plasma and / or a nitrogen-containing plasma in one or more separate plasma treatment steps after the fluorine-containing plasma step.

[0080] As mentioned above, in other examples, any other suitable plasma chemistry can be used to dissociate volatilizable terminal functional groups as disclosed. Examples include inert gases, nitrogen, ammonia, hydrazine, oxygen, methane, hydrogen, and chlorine gases. Additionally, other volatilizable terminal functional groups than hydrogen atoms and methyl groups can be used in other examples. Other suitable terminal functional groups include other alkyl groups (e.g. ethyl, propyl) and volatilizable aryl groups.

[0081] FIG. 3 shows a graph illustrating a selectivity of SiOCH (low k), NDC (nitrogen doped silicon carbide), and ODC when etched according to the etching cycle of FIG. 2. The oxygen-containing plasma utilized a mixture of oxygen and argon at a pressure within a range of 5 - 100 mTorr and a plasma power within a range of 50-600 W. The plasma frequency was within a range 1 MHz and 27 MHz, and a DC bias was applied to the plasma to increase a directionality of the plasma relative to the use of no DC bias. The fluorine-containing plasma comprised a fluorine-containing etchant and argon gas at a pressure within a range of 50-300 mTorr. The substrate was maintained at a temperature within a range of -10 to 80 degrees C through both plasma exposures. The resulting etch rate was 10.5 Angstroms per cycle for the SiOCH, 2.4 Angstroms per cycle for the NDC, and 0.16 Angstroms per cycle for the ODC. As such, the selectivity of the etch was 4 for the SiOCH / NDC pair, and 65 for the SiOCH / ODC pair. It will be understood that the process parameter ranges described above are presented for the purpose of example, and that one or more parameters outside of these ranges also can be used.

[0082] In another experiment, the etch rates of (a) an oxygen-containing plasma alone, (b) fluorine-containing vapor alone, and (c) an ALE process using the example etching cycle of FIG. 4 for SiOCH were compared. It was found that fluorine- containing vapor alone did not successfully etch the SiOCH. Further, the oxygencontaining plasma (which utilized O2 and argon) had an etch rate of 2.6 Angstroms per cycle. In contrast, as mentioned above, the ALE process illustrated in FIG. 4 had an etch rate of 10.5 Angstroms per cycle. Thus, the ALE process of FIG. 2 had a synergy of approximately 70% compared to the use of either sub-step (oxidation and fluorination) of the ALE process alone.

[0083] In some examples, it may be desired to use a plasma that omits oxygen. For example, an inert gas plasma (e.g. an argon plasma) can be less aggressive than an oxygen plasma. This can help to cause less damage to the sidewalls of a feature in a material being etched compared to the use of an oxygen-containing plasma. Other inert gases that can be used in a plasma include helium, neon, krypton, and xenon.

[0084] FIG. 4 schematically illustrates example chemical reactions that occur during an example ALE cycle performed on SiOCH using an argon-only plasma as a dissociating energy source. As with FIG. 2, a fluorine-containing plasma is used to implement a fluorine-based etching chemistry.

[0085] The SiOCH comprises terminal methyl groups 404 and terminal hydrogen groups 406. When exposed to the oxygen-containing plasma at 402, ions from the plasma can physically and chemically interact with the terminal methyl groups 404 and the terminal hydrogen groups 406 to modify the surface of the SiOCH by removing the terminal functional groups. The terminal functional groups can form volatile methane and hydrogen gas, as examples. Next referring to 408, the dissociation of the volatilizable terminal functional groups creates reactive silicon sites due to the increased bond polarity compared to silicon-methyl and silicon-hydrogen bonds. The increased polarity is represented by 6+next to Si atoms. Unlike the example of FIG. 2, however, the reactive sites do not react with oxygen.

[0086] Continuing, exposure to a fluorine-containing plasma results in the fluorination of the active sites. Fluorine can continue to react with silicon atoms, forming volatile silicon tetrafluoride, as shown at 410. This removes the silicon from the surface. A next cycle can then begin by again exposing the SiOCH to the plasma at 402. In other examples, another halogen-containing etching agent, or a mixed halide etching agent, can be used instead of a fluorine-containing etching agent.

[0087] FIG. 5 shows a graph illustrating a selectivity of SiOCH (low k), NDC, and ODC when etched according to the etching cycle of FIG. 6. The oxygen-containing plasma utilized a mixture of oxygen and argon at a pressure within a range of 5 to 100 mTorr and a plasma power within a range of 50-600 W. The plasma frequency was within a range of 1 MHz to 27 MHz, and a DC bias was applied to the plasma to increase a directionality of the plasma relative to the use of no DC bias. The resulting etch rate was 13.6 Angstroms per cycle for the SiOCH, 6.6 Angstroms per cycle for the NDC, and 0.16 Angstroms per cycle for the ODC. As such, the selectivity of the etch was 2.06 for the SiOCH / NDC pair, and 85 for the SiOCH / ODC pair.

[0088] As mentioned above, by using a directional dissociating energy source, such as a directional plasma, the disclosed example ALE processes can be used to etch relatively high aspect features. In some examples, an ALE process according to the present disclosure can be used to etch a recessed feature having an aspect ratio within a range of 5 to 30. In other examples, an ALE process according to the present disclosure can be used to etch a recessed feature having an aspect ratio outside of this range. When using plasma energy, various plasma conditions can be used to favor the formation of a more directional plasma compared to a less directional plasma. Example conditions that can favor a more directional plasma compared to a less directional plasma include a relatively lower pressure (e.g. in a range of 10 mTorr to 1 Torr), a relatively higher RF power, and / or the use of a DC bias in the plasma power.

[0089] FIG. 6 shows a flow diagram illustrating an example method 600 for performing ALE by, for each etching cycle, dissociating volatilizable terminal functional groups in a material being etched, and then reacting the material with a halogen-containing etching agent to remove substrate material. Method 600 can be used to etch SiOCH selectively with respect to ODC, for example. Method 600 can be performed using any suitable processing tool. An example processing tool is described below with reference to FIG. 9.

[0090] Method 600 comprises, at 602, exposing a substrate comprising a first silicon-containing material and a second silicon-containing material to energy from an energy source to dissociate at least some terminal functional groups from silicon atoms. The first and second silicon-containing materials comprise different concentrations of the terminal functional groups. As described above, in some examples, the first silicon- containing material can comprise a low k dielectric material. In such examples, the functional groups can comprise organic functional groups. Example organic functionalgroups include methyl groups. Other example organic functional groups include other aliphatic groups, such as ethyl or propyl groups. In yet other examples, the organic functional groups can comprise an aryl group. Further, in some examples, the first silicon-containing material also can comprise hydrogen functional groups. In more specific examples, the first silicon-containing material can comprise SiOCH, and the organic functional groups can comprise methyl groups. In further examples, the silicon- containing material can comprise another silicon-containing material than SiOCH. In yet further examples, materials other than silicon-containing materials can comprise such volatilizable terminal functional groups.

[0091] As mentioned above, the second silicon-containing material can comprise a lesser concentration of volatilizable terminal functional groups than the first silicon-containing material. In some examples, the second silicon-containing material comprises an etch stop layer. In some examples, the etch stop layer can comprise ODC.

[0092] The energy to which the substrate is exposed can dissociate at least some of the volatilizable terminal functional groups from a surface layer of the first silicon- containing material, thereby modifying the surface layer. The dissociated volatile terminal functional groups can form volatile products, and thereby leave the substrate. Any suitable dissociating energy source can be used. Examples include plasma energy, particle beam energy, and photonic energy. As described above, where a plasma is used, the plasma can comprise reactive species or an inert gas only. Example plasmas include oxygen-containing plasmas and inert gas plasmas. Example oxygen-containing plasmas can be formed using an oxygen-containing gas and an inert gas. Example oxygencontaining gases can comprise molecular oxygen (O2), water vapor (H2O), ozone (O3), nitrous oxide (N2O), carbon dioxide (CO2), sulfur dioxide (SO2), and hydrogen peroxide (H2O2). Example inert gases can comprise helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0093] In some examples, the dissociating energy comprises directional energy. Exposure of the substrate to directional energy can dissociate a higher concentration of volatilizable terminal functional groups on surfaces normal to a direction of the greatest magnitude of the energy (e.g. a bottom surface of a feature that is oriented approximately normal to a peak angular ion flux density of a directional plasma), and a lesser concentration on surfaces of other orientations, such as feature sidewalls. This can provide for a higher etch rate in the vertical direction (e.g. normal to a substrate surface plane) than in a horizontal direction, and thereby allow etching of high aspectratio features. Examples of directional energy sources can comprise one or more of a directional plasma, a particle beam or photonic energy (e.g. a laser or focused light).

[0094] Continuing, after exposing the substrate to dissociating energy, method 600 comprises, at 604, exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules. In some examples, a halogen-containing etching agent can be introduced into a plasma to form reactive halogen species. As a more specific example, a fluorine-containing etching agent can be used. In some such examples, the fluorine-containing etching agent can be introduced into a plasma to form reactive fluorine species (ions and radicals). The reactive fluorine species can react with active sites created by dissociation of the volatilizable terminal functional groups of the first silicon-containing material. Example fluorine-containing etching agents include hydrogen fluoride (HF), molecular fluorine (F2), nitrogen trifluoride (NF3), boron trifluoride (BF3), hexafluoroethane (C2F6), other partially or fully fluorinated alkyl molecules, and sulfur fluorides such as sulfur hexafluoride (SFe). In other examples, a chlorine-containing etching agent, a bromine-containing etching agent, an iodine- containing etching agent, or a mixed halide-containing etching agent, can be used. In some examples, the plasma can further comprise a methyl-generating chemical and / or nitrogen.

[0095] The volatile silicon halide molecules leave the substrate, thereby etching the substrate. Because the second silicon-containing material comprises a lower concentration of volatilizable terminal functional groups than the first silicon- containing material, the first silicon-containing material is etched at a higher rate than the second silicon-containing material.

[0096] In some examples, an energy source used to expose the substrate to the dissociating energy at 602 can cause densification of portions of a material being etched. For example, a plasma used to dissociate methyl and hydrogen functional groups from a SiOCH layer into which a feature is being etched can potentially damage and densify sidewalls of the feature being etched. As such, to protect the sidewalls from the dissociating energy of a next ALE cycle, method 600 can optionally comprise, at 606, depositing a film layer in the feature being etched after exposing the substate to the halogen-containing etching agent and before performing a next ALE cycle. The film layer acts as a protective layer to absorb damage from the plasma that provides dissociating energy. This helps to prevent damage to the sidewalls of the feature being etched. The film layer can be removed by the dissociating energy and the halogen-containing etchant, and thus can be reapplied in each ALE cycle, or in a subset of ALE cycles. Any suitable material can be used as such a film layer. Examples include nitrogen-containing layers deposited using an ammonia plasma, fluorine-containing layers deposited using a fluorine-containing plasma, and hydrogen-containing layers deposited using a hydrogen-containing plasma. More specific examples of materials that can be used to form a passivating layer include C2F6 and other fluorocarbons, NF3, NEE, and SFe. When deposited as a protective layer, the substrate is exposed to a lower concentration of such materials for a shorter time than when these materials are used as etching agents. This allows the materials to react and form a surface coating, without fully forming volatile compounds. Other examples of materials that can be used to deposit film layers during an ALE process include siloxanes such as OMCTS (octamethylcyclotetrasiloxane), and aminosilanes such as dimethylamino trimethylsilane. These and other siloxanes and aminosilanes also can be used for depositing a low k film. In other examples, a film layer alternatively or additionally can be deposited after step 602 and before step 604 of an ALE process. Further, in yet other examples a film layer can be deposited for any other suitable purpose than damage / densification mitigation during an ALE cycle according to the present disclosure. In still further examples, a methyl-generating chemical (such as methane) can be used in a plasma to help repair damage to sidewall surfaces caused by dissociating terminal methyl groups from SiOCH. This can help mitigate or prevent densification of the SiOCH, and thereby mitigate or prevent any increase in dielectric constant from the etching.

[0097] In some examples, the film layer can be deposited using a plasma. In such examples, the precursor compound(s) used to form the film layer can be introduced into the processing chamber while a plasma is ignited. The plasma can create reactive species from the precursor(s) that can react to form the film on the substrate. In other examples, the film layer can be deposited without using a plasma. In some such examples, the reaction to form the film layer can be thermally driven. In other examples, the precursor(s) can adsorb to the substrate without otherwise reacting.

[0098] Continuing, after completing an ALE cycle, method 600 comprises, at 608, determining whether to perform another ALE cycle. Where a feature has not been fully etched, method 600 can return to 602 to begin another ALE cycle. Where a feature has been fully etched, method 600 can terminate. When etching a feature in an SiOCH layer, the selectivity of the SiOCH etch with regard to an ODC etch stop layer can allowthe etch to reach the ODC layer without unduly damaging the ODC layer, even if one or more additional etching cycles are performed after the ODC layer is reached.

[0099] FIGS. 7A-7C schematically illustrates an example implementation of method 700 as performed on a substrate 700. Substrate 700 has a same configuration as substrate 100 of FIGS. 1 A-1C. Substrate 700 comprises a lower layer 702 including a first low k dielectric material region 704 (e.g. SiOCH) and a metal line 706. The substrate 700 also comprises an etch stop layer 708 comprising an aluminum nitride layer 709 and ODC layer 710.

[0100] The substrate 700 further comprises an upper layer 712 comprising a second low k dielectric material region 714. A hard mask layer 716 is positioned on the second low k dielectric material region 714. The hard mask layer 716 includes an opening defining a location of a recessed feature 718 being etched according to method 600 of FIG. 6.

[0101] FIG. 7B shows the substrate 700 after additional material has been etched from second low k dielectric material region 714. Here, the recessed feature 718 is deeper, but has not yet reached the ODC layer 710. FIG. 7C shows the substrate 700 after the recessed feature 718 has been etched through the depth of the second low k dielectric material region 714. As described above, method 600, when used to etch an SiOCH layer having an underlying ODC etch stop layer, is sufficiently selective to essentially stop at the etch stop layer 708. Thus, the etch stop layer 708 is not unsuitably damaged, unlike the etch stop layer 108 of FIG. 1C. This helps to preserve device performance, compared to the damaged etch stop layer 108 of FIG. 1C.

[0102] FIGS. 8A-8F show another example of an ALE process that utilizes the dissociation of a volatilizable terminal leaving group in a material to allow the material to be selectively etched with regard to another material. More particularly, FIGS. 8A- 8F show a schematic sectional view of a substrate 800 that is etched first to form a via, and then etched to form trenches. FIGS. 8A-8F can represent an example back-end-of- line (BEOL) process for forming trenches for metal lines in low k dielectric material layers, and for forming vias for conductively connecting metal lines in different low k dielectric material layers.

[0103] Referring first to FIG. 8A, the substrate 800 comprises a lower layer 802 including a first low k dielectric material region 804 (e.g. SiOCH). The substrate 800 also comprises an etch stop layer 808 comprising an aluminum nitride layer 809 and ODC layer 810.

[0104] The substrate 800 further comprises an upper layer 812 comprising a second low k dielectric material region 814. A hard mask layer 816 is positioned on the second low k dielectric material region 814. The hard mask layer 816 includes an opening 818 defining a location of a via being etched according to method 600 of FIG. 6.

[0105] FIG. 8B shows the substrate 800 after material has been etched from second low k dielectric material region 814. Here, the via 819 has been partially etched, but has not yet reached the ODC layer 810. FIG. 8C shows the substrate 800 after the via 819 has been etched through the depth of the second low k dielectric material region 814. As described above, method 600, when used to etch an SiOCH layer having an underlying ODC etch stop layer, is sufficiently selective to essentially stop at the ODC layer 810 of the etch stop layer 808.

[0106] Continuing, FIGS. 8D-8F illustrate the formation of trenches in the second low k dielectric material region 814. First referring to FIG. 8D, the hard mask 816 has been further patterned to define a plurality of openings 820 that define the locations of trenches to be etched according to method 600 in the second low k dielectric material layer 814. While three openings for defining trenches are shown in FIG. 8A, only one opening 820 is numbered for clarity. However, the openings are collectively referred to as “openings 820”. In some examples, the hard mask layer 816 can be removed after the via etch of FIGS. 8A-8C, and a new hard mask can be deposited for the trench etch of FIGS. 8D-8F.

[0107] FIG. 8E shows the substrate 800 after material has been etched from the second low k dielectric material layer 814 to partially form trenches 821. Only one trench of the three illustrated trenches 821 is numbered for clarity. FIG. 8F shows the substrate 800 after the trenches 821, have been etched through the depth of the second low k dielectric material region 814 to the ODC layer 810.

[0108] While etching the trenches 821 using the ALE process of method 600, the ODC layer 810 at the bottom of the via 819 is exposed to the ALE process. However, as described above, the selectivity of method 600 to the SiOCH second low k material layer 814 compared to the ODC layer 810 allows the trench etch to be performed without etching the ODC layer at the bottom of the via 819 to an unsuitable degree. This allows the via and trench etching process of FIGS. 8A-8F to be performed without using an aluminum-based etch stop layer (e.g. AlOx or AINx). This helps to maintain a lower dielectric constant for the etch stop layer 808 than if an aluminum-based etch stop layer were used. Further, while method 600 describes an implementation of an example ALE process, in other examples, etching by removal of volatilizable terminal functional groups can be performed using tempo pulsing or RIE. Tempo pulsing comprises pulsed gas flows where the flow of processing gases from different steps may overlap.

[0109] FIG. 9 schematically shows an example processing tool 900 that can be used to implement the examples described above. Processing tool 900 comprises a processing chamber 902 and a substrate support 904 within the processing chamber. The substrate support 904 is configured to support a substrate 906 disposed within the processing chamber 902. The substrate support 904 comprises a substrate heater 908. In other examples, a heater can be omitted, or can be located elsewhere within processing chamber 902.

[0110] The processing tool 900 further comprises a showerhead 910 configured for introducing gas into processing chamber 902. In other examples, a processing tool can comprise a nozzle or other apparatus for introducing gas into processing chamber 902, as opposed to or in addition to a showerhead. The processing tool 900 further comprises flow control hardware 912. The flow control hardware 912 connects processing gas source(s) to the processing chamber. In the depicted example, the flow control hardware 912 connects a dissociative plasma gas source 916, a halogencontaining etching agent source 918, and an optional film precursor source 920 to the processing chamber 902. The flow control hardware 912 can include any suitable components. For example, the flow control hardware 912 can comprise one or more conduits and valves controllable to place a selected gas source or selected gas sources in fluid connection with showerhead 910. The flow control hardware 912 also can comprise one or more mass flow controllers or other controllers for controlling a flow rate of one or more processing chemicals.

[0111] The dissociative plasma gas source 916 can comprise any suitable gas that can be ionized in a plasma for dissociating a volatilizable terminal functional group in a film material. Examples include oxygen-containing gases 922. Example oxygen containing gases include molecular oxygen, ozone, hydrogen peroxide, water vapor, carbon dioxide, sulfur dioxide, and nitrous oxide. Other examples include inert gases 924. Example inert gases include helium, neon, argon, krypton, and xenon. Other example dissociative plasma gases can include nitrogen, ammonia, hydrazine, methane, hydrogen, and chlorine.

[0112] The halogen-containing etching agent source 918 comprises any material that includes one or more halogen atoms that can react with an active site created by the removal of a volatilizable terminal functional group from a film material. Examples include fluorine-containing etching agents. Some example fluorine- containing etching agents include hydrogen fluoride (HF), molecular fluorine (F2), nitrogen trifluoride (NF3), boron trifluoride (BF3), hexafluoroethane (C2F6), other partially or fully fluorinated alkyl molecules, and sulfur fluorides such as sulfur hexafluoride (SFe). In other examples, a chlorine-containing etching agent, a brominecontaining etching agent, an iodine-containing etching agent, or a mixed halide- containing etching agent, can be used. The halogen-containing etching agent can be introduced into a plasma to form reactive halogen species (ions and radicals) to react with active sites created by the removal of volatilizable terminal functional groups.

[0113] The optional film precursor source 920 comprises any suitable material that can be used to deposit a film layer in an ALE cycle. A film layer can be deposited after a dissociation step of an ALE cycle, and / or after a volatilization step of an ALE cycle. For example, a film layer can be used to protect sides of a feature from plasma damage during a dissociation process or a volatilization process. As a more specific example, a film layer can be used to at least partially protect a low k dielectric material (e.g. SiOCH) from plasma damage. Examples include nitrogen, ammonia, nitrogen trifluoride, hydrogen, carbon dioxide, oxygen, and methane. Other example film precursors include precursors used to deposit low k films. Examples of such precursors include siloxanes such as OMCTS, and amino silanes such as dimethylamino trimethylsilane.

[0114] The processing tool 900 further comprises an exhaust system 926. The exhaust system 926 is configured to exhaust gases from the processing chamber 902. The exhaust system 926 can comprise any suitable hardware, including one or more low vacuum pumps and one or more high vacuum pumps. Together, flow control hardware 912 and exhaust system 926 can be operated to achieve a selected pressure in processing chamber 902 during substrate processing.

[0115] The processing tool 900 further comprises a radiofrequency power source 928 that is electrically connected to showerhead 910. Radiofrequency power source 928 is configured to form a plasma using a gas mixture. For example, during a modification step, the radiofrequency power source 928 can be operated to form a plasma to dissociate a volatilizable terminal leaving group from a film material. In someexamples, the radiofrequency power source 928 can be controlled to form a directional plasma to enable the etching of relatively high aspect ratio features. Conditions that can be used to form a directional plasma are described below. The substrate support 904 is configured as a grounded opposing electrode in this example. In other examples, the radiofrequency power source 928 can supply radiofrequency power to substrate support 904, or to another suitable electrode structure. Thus, the radiofrequency power source 928 forms a capacitively coupled plasma when operated. In other examples, a processing tool alternatively or additionally can include a particle beam source (not shown) and / or a photonic energy source (not shown) for dissociating volatilizable terminal leaving groups from film materials.

[0116] The processing tool 900 further includes a matching network 930 for impedance matching of the radiofrequency power source 928. The radiofrequency power source 928 can be configured to provide RF energy of any suitable frequency and power. Examples frequencies include 400 kHz, 13.56 MHz, 27 MHz, 60 MHz, and 90 MHz. In some examples, the radiofrequency power source 928 is configured to operate at a plurality of different frequencies and / or powers. For example, a plasma can comprise a LF component and a HF component. Examples of frequencies for the LF component can include frequencies of 3 MHz and below. The LF component can comprise a power of 0 - 6500W in some examples. Examples of frequencies for the HF component can include frequencies of 3 MHz to 300 MHz. The HF component can comprise a power of 50 - 6500W in some examples. In some examples, a DC bias is applied to one or both electrodes of the electrode pair. Applying a DC bias can help increase the directionality of the directional plasma. In further examples, a processing tool can comprise a remote plasma chamber for forming a remote plasma.

[0117] The processing tool 900 further comprises a controller 940 configured to control operation of the processing tool. The controller 940 is operatively coupled to the substrate heater 908, the flow control hardware 912, the exhaust system 926, and the radiofrequency power source 928. The controller 940 is configured to control various functions of processing tool 900 to perform an ALE process as disclosed by example herein, among other possible processes. For example, the controller 940 is configured to operate the substrate heater 908 to heat a substrate to a desired temperature. The controller 940 also is configured to operate the flow control hardware 912 to flow a selected processing chemical or mixture of processing chemicals at a selected rate into the processing chamber 902. The controller 940 is further configuredto operate the exhaust system 926 to remove processing chemicals and byproducts from processing chamber 902. The controller 940 further can control the exhaust system 926 and / or the flow control hardware 912 to purge the processing chamber 902.

[0118] The controller 940 further can operate the flow control hardware 912 and the radiofrequency power source 928 to form a plasma and control a directionality of the plasma. For example, a directionality of a plasma can be increased (i.e. an ion angular distribution made to be more narrowly concentrated about a vertical direction relative to a substrate surface) by using a relatively lower pressure, a relatively higher RF power, including a DC bias, and / or by include both HF and an LF RF energy components. Likewise, a directionality of a plasma can be decreased by using a relatively higher pressure, a relatively lower RF power, and / or omitting an LF RF energy component. Controlling the plasma to be more directional can allow the etching of structures with relatively high aspect ratios using the disclosed example ALE processes. The controller 940 can comprise any suitable computing system. Example computing systems are described below with reference to FIG. 10.

[0119] Thus, the disclosed examples can allow the selective etching of a material that is compositionally similar to another material, but that has a different concentration of volatilizable terminal functional groups than the other material. This can allow, for example, the selective etching of a SiOCH low k layer using an ODC etch stop layer (and potentially an ODC hard mask layer). Other solid materials with volatilizable terminal functional groups bonded to atoms that otherwise form an interconnected network (e.g. nitrogen-doped silicon oxide) may be etched in a similar manner. Further, the disclosed examples help to avoid depth loading effects that are encountered with RIE due to small variations in feature width.

[0120] FIG. 10 schematically shows a non-limiting example of a computing system 1000 that can enact one or more of the methods and processes described above. Computing system 1000 is shown in simplified form. Computing system 1000 can take the form of one or more personal computers, workstations, computers integrated with substrate processing tools, and / or network accessible server computers.

[0121] The computing system 1000 includes a logic subsystem 1002 and a storage subsystem 1004. The computing system 1000 can optionally include a display subsystem 1006, input subsystem 1008, communication subsystem 1010, and / or other components not shown in FIG. 10. The controller 940 is an example of computing system 1000.

[0122] The logic subsystem 1002 includes one or more physical devices configured to execute instructions. For example, the logic subsystem can be configured to execute instructions that are part of one or more applications, services, programs, routines, libraries, objects, components, data structures, or other logical constructs. Such instructions can be implemented to perform a task, implement a data type, transform the state of one or more components, achieve a technical effect, or otherwise arrive at a desired result.

[0123] The logic subsystem 1002 can include one or more processors configured to execute software instructions. Additionally or alternatively, the logic subsystem 1002 can include one or more hardware or firmware logic subsystems configured to execute hardware or firmware instructions. Processors of the logic subsystem 1002 can be single-core or multi-core, and the instructions executed thereon can be configured for sequential, parallel, and / or distributed processing. Individual components of the logic subsystem optionally can be distributed among two or more separate devices, which can be remotely located and / or configured for coordinated processing. Aspects of the logic subsystem 1002 can be virtualized and executed by remotely accessible, networked computing devices configured in a cloud-computing configuration.

[0124] The storage subsystem 1004 includes one or more physical devices configured to hold instructions 1012 executable by the logic subsystem 1002 to implement the methods and processes described herein. When such methods and processes are implemented, the state of the storage subsystem 1004 can be transformed — e.g., to hold different data.

[0125] The storage subsystem 1004 can include removable and / or built-in devices. The storage subsystem 1004 can include optical memory, semiconductor memory, and / or magnetic memory, among others. The storage subsystem 1004 can include volatile, nonvolatile, dynamic, static, read / write, read-only, random-access, sequential-access, location-addressable, file-addressable, and / or content-addressable devices.

[0126] It will be appreciated that the storage subsystem 1004 includes one or more physical devices. However, aspects of the instructions described herein alternatively can be propagated by a communication medium (e.g., an electromagnetic signal, an optical signal, etc.) that is not held by a physical device for a finite duration.

[0127] Aspects of the logic subsystem 1002 and the storage subsystem 1004 can be integrated together into one or more hardware-logic components. Such hardware-logic components can include field-programmable gate arrays (FPGAs), program- and application-specific integrated circuits (PASIC / ASICs), program- and application-specific standard products (PSSP / ASSPs), system-on-a-chip (SOC), and complex programmable logic devices (CPLDs), for example.

[0128] When included, the display subsystem 1006 can be used to present a visual representation of data held by the storage subsystem 1004. This visual representation can take the form of a graphical user interface (GUI). As the herein described methods and processes change the data held by the storage subsystem, and thus transform the state of the storage subsystem, the state of the display subsystem 1006 can likewise be transformed to visually represent changes in the underlying data. The display subsystem 1006 can include one or more display devices utilizing virtually any type of technology. Such display devices can be combined with the logic subsystem 1002 and / or the storage subsystem 1004 in a shared enclosure, or such display devices can be peripheral display devices.

[0129] When included, the input subsystem 1008 can comprise or interface with one or more user-input devices such as a keyboard, mouse, or touch screen. In some examples, the input subsystem can comprise or interface with selected natural user input (NUI) componentry. Such componentry can be integrated or peripheral, and the transduction and / or processing of input actions can be handled on- or off-board. Example NUI componentry can include a microphone for speech and / or voice recognition, and an infrared, color, stereoscopic, and / or depth camera for machine vision and / or gesture recognition.

[0130] When included, the communication subsystem 1010 can be configured to communicatively couple the computing system 1000 with one or more other computing devices. The communication subsystem 1010 can include wired and / or wireless communication devices compatible with one or more different communication protocols. As non-limiting examples, the communication subsystem 1010 can be configured for communication via a wireless telephone network, or a wired or wireless local- or wide-area network. In some examples, the communication subsystem can allow computing system 1000 to send and / or receive messages to and / or from other devices via a network such as the Internet.

[0131] It will be understood that the configurations and / or approaches described herein are exemplary in nature, and that these specific examples or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein can represent one or more of any number of processing strategies. As such, various acts illustrated and / or described can be performed in the sequence illustrated and / or described, in other sequences, in parallel, or omitted. Likewise, the order of the above-described processes can be changed.

[0132] The subject matter of the present disclosure includes all novel and non- obvious combinations and sub-combinations of the various processes, systems and configurations, and other features, functions, acts, and / or properties disclosed herein, as well as any and all equivalents thereof.

Claims

CLAIMS:

1. A method of selectively etching a feature in a substrate comprising a first silicon-containing material and a second silicon based material with different concentrations of volatilizable terminal functional groups, the method comprising: exposing the substrate to energy sufficient to dissociate at least some terminal functional groups; and exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules to remove silicon from the substrate and thereby etch the substrate, wherein the first silicon-containing material is etched at a higher rate than the second silicon-containing material.

2. The method of claim 1, wherein the first silicon-containing material is a low dielectric constant (low k) material, and wherein the functional groups comprise organic functional groups.

3. The method of claim 2, wherein the low k dielectric material comprises carbon doped silicon oxide (SiOCH), and wherein the organic functional groups comprise methyl groups.

4. The method of claim 2, wherein the second silicon-containing material comprises an etch stop layer.

5. The method of claim 4, wherein the etch stop layer comprises oxygen doped silicon carbide.

6. The method of claim 1, wherein exposing the substrate to energy comprises exposing to a plasma.

7. The method of claim 1, wherein exposing the substrate to energy comprises exposing the substrate to one or more of particle beam energy or photon energy.

8. The method of claim 1, wherein the halogen-containing etching agent comprises a fluorine-containing etching agent.

9. The method of claim 1, wherein the exposing the substrate to the energy and the exposing the substrate to the halogen-containing etching agent are performed within an etching cycle, the etching cycle further comprising depositing a film layer in the feature using a deposition step during the etching cycle.

10. The method of claim 9, wherein the film layer is deposited after exposing the substrate to the halogen-containing etching agent and before performing a next etching cycle.

11. The method of claim 9, wherein the film layer is deposited after exposing the substrate to the energy and before exposing the substrate to the halogen-containing etching agent and before performing a next etching cycle.

12. The method of claim 9, wherein depositing the film layer comprises depositing the film layer using a plasma.

13. The method of claim 9, wherein depositing the film layer comprises depositing one or more of an aminosilane precursor or a siloxane precursor without using a plasma.

14. A method of selectively etching a feature in a substrate, the substrate comprising a low dielectric constant material (low k dielectric material) and an etch stop layer, the method comprising; performing a plurality of etching cycles to etch a trench in the low k layer, an etching cycle of the plurality of etching cycles comprising exposing the low k dielectric material to a directional plasma to remove a quantity of terminal functional groups from the low k dielectric material, wherein an etch stop layer in a via formed in the low k dielectric material also is exposed to the directional plasma, and wherein the etch stop layer has a lower concentration of the volatilizable terminal functional groups than the low k dielectric material, and exposing the substrate to a halogen-containing etching agent to form volatile silicon halide molecules at locations of removed terminal functional groups to remove silicon from the low k dielectric material;wherein the etch stop layer etches at a lower etch rate than an etch rate of the low k dielectric material.

15. The method of claim 14, wherein the low k dielectric material comprises a carbon doped silicon oxide material, and wherein the etch stop layer comprises oxygen doped silicon carbide.

16. The method of claim 14, wherein the etching cycle further comprises depositing a film layer.

17. The method of claim 14, wherein the volatilizable terminal functional groups comprise methyl groups.

18. A processing tool, comprising: a processing chamber; a substrate holder disposed in the processing chamber; flow control hardware to control processing chemical flows into the processing chamber; an energy source for exposing a substrate positioned in the substrate holder to energy; and a controller configured to control the processing tool to perform an etching process comprising a plurality of etching cycles, wherein the controller is configured to, for each etching cycle of the plurality of etching cycles: control the energy source to expose the substrate to the energy sufficient to dissociate at least some terminal functional groups of a first silicon- containing material from the silicon atoms, and control the flow control hardware to expose the substrate to a halogencontaining etching agent to form volatile silicon halide molecules to remove silicon from the substrate and thereby etch the substrate.

19. The processing tool of claim 18, wherein the energy source comprises a plasma source.

20. The processing tool of claim 18, wherein the energy source comprises one or more of a particle beam energy source or a photon energy source.

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