Depositing ETCH stop layer

Abstract

Examples are disclosed that relate to forming an etch stop layer in a high-aspect ratio gap. One example provides a method comprising, in a first deposition step, depositing a lower-density carbon film in a gap on a substrate. The method further comprises, in an etching step after the first deposition step, etching a portion of the lower-density carbon film to form a carbon shelf within the gap. The method further comprises, in a second deposition step after the etching step, depositing an etch stop layer over the carbon shelf.

Description

DEPOSITING ETCH STOP LAYERBACKGROUND

[0001] Electronic 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 deposit films of materials onto a substrate. As an example, chemical vapor deposition (CVD) involves exposing a substrate to vaporphase precursors under conditions that cause the precursors to form a film on the substrate. Likewise, various methods can be used to selectively remove material from a substrate. Examples include dry etching methods.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 forming an etch stop layer in a high-aspect ratio gap. One example provides a method comprising, in a first deposition step, depositing a lower-density carbon film in a gap on a substrate. The method further comprises, in an etching step after the first deposition step, etching a portion of the lower-density carbon film to form a carbon shelf within the gap. The method further comprises, in a second deposition step after the etching step, depositing an etch stop layer over the carbon shelf.

[0004] In some such examples, the gap comprises an aspect ratio of 5 : 1 to 60: 1.

[0005] Alternatively or additionally, in some such examples, a portion of the gap above the carbon shelf comprises an aspect ratio of 1 :4 to 4: 1.

[0006] Alternatively or additionally, in some such examples, etching the portion of the lower-density carbon film comprises forming a plasma using an etching agent comprising one or more of molecular hydrogen, ammonia, molecular oxygen, carbon dioxide, or nitrous oxide.

[0007] Alternatively or additionally, in some such examples, the lower-density carbon film comprises a density less than 1.5 g / cm3.

[0008] Alternatively or additionally, in some such examples, the etch stop layer comprises a higher-density carbon film comprising a density of 1.5 g / cm3or greater or a densified carbon film.

[0009] Alternatively or additionally, in some such examples, the etch stop layer comprises one of molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, or silicon oxide.

[0010] Alternatively or additionally, in some such examples, depositing the lower-density carbon film comprises forming a plasma using radiofrequency energy comprising a higher-frequency component within a range of 3 MHz to 300 MHz, and omitting radiofrequency energy at frequencies below 3 MHz.

[0011] Alternatively or additionally, in some such examples, depositing the etch stop layer comprises forming a directional plasma using radiofrequency energy comprising the lower-frequency energy and the higher-frequency component.

[0012] Alternatively or additionally, in some such examples, the method further comprises, in a third deposition step after the second deposition step, depositing a second lower-density carbon film over the etch stop layer, and, in a planarization step after the third deposition step, removing the etch stop layer from field regions of the substrate.

[0013] Alternatively or additionally, in some such examples, the method further comprises depositing a plurality of alternating material layers onto the substrate, and cryo-etching through the plurality of alternating material layers to the etch stop layer.

[0014] Alternatively or additionally, in some such examples, the method further comprises, prior to the first deposition step, cooling the substrate and performing a reduced temperature etch to form the gap.

[0015] Another example provides a method of filling a gap on a substrate. The method comprises, in a first deposition step, depositing a lower-density carbon film in the gap. The method further comprises, in an etching step after the first deposition step, etching a portion of the lower-density carbon film to form a carbon shelf in the gap. The method further comprises, in a second deposition step, performing one or more deposition cycles to deposit a densified carbon film over the carbon shelf. Each deposition cycle of the one or more deposition cycles comprises depositing a layer of lower-density carbon film in the gap. Each deposition cycle of the one or moredeposition cycles further comprises forming a plasma using one or more of helium, neon, argon, or nitrogen to densify the layer of lower-density carbon film, thereby forming a layer of densified carbon film.

[0016] In some such examples, a portion of the gap above the carbon shelf comprises an aspect ratio of 1 :4 to 4: 1.

[0017] Alternatively or additionally, in some such examples, the lower-density carbon film comprises a density less than 1.5 g / cm3and the densified carbon film comprises a density of 1.5 g / cm3or greater.

[0018] Alternatively or additionally, in some such examples, depositing the lower-density carbon film comprises forming a plasma using radiofrequency energy comprising a higher-frequency component within a range of 3 MHz to 300 MHz, and omitting radiofrequency energy at frequencies below 3 MHz.

[0019] Another example provides a processing tool for processing a substrate. The processing tool comprises a processing chamber and a substrate support. The processing tool further comprises flow control hardware configured to control processing chemical flow into the processing chamber. The processing tool further comprises a radiofrequency power source configured to provide radiofrequency power to form a plasma in the processing chamber. The processing tool further comprises a controller operatively coupled to the flow control hardware and the radiofrequency power source. The controller is configured to, in a first deposition step, operate the flow control hardware and the radiofrequency power source to deposit a lower-density carbon film in a gap on a substrate. The controller is further configured to, in an etching step after the first deposition step, operate the flow control hardware and the radiofrequency power source to etch a portion of the lower-density carbon film to form a carbon shelf within the gap. The controller is further configured to, in a second deposition step after the etching step, operate the flow control hardware and the radiofrequency power source to deposit an etch stop layer over the carbon shelf.

[0020] In some such examples, the controller is configured to, in the second deposition step, operate the flow control hardware and the radiofrequency power source to form a higher-density carbon film as the etch stop layer.

[0021] Alternatively or additionally, in some such examples, the controller is further configured to, in the second deposition step, operate the flow control hardware and the radiofrequency power source to deposit a layer of lower-density carbon film over the carbon shelf, and form a plasma using helium to densify the layer of lower-density carbon film, thereby forming a layer of densified carbon film as the etch stop layer.

[0022] Alternatively or additionally, in some such examples, the controller is configured to, in the second deposition step, operate the flow control hardware to flow an etch stop film precursor and operate the radiofrequency power source to convert the etch stop film precursor into the etch stop layer, the etch stop layer comprising one of molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, or silicon oxide.

[0023] Another method provides a method of filling a gap on a substrate. The method comprises, in a deposition step, depositing an etch stop layer over a carbon shelf located within the gap. The method further comprises, in a planarization step after the deposition step, removing the etch stop layer from field regions of the substrate.

[0024] In some examples, the method further comprises depositing a lower- density carbon film over the etch stop layer prior to the planarization step.

[0025] Additionally or alternatively, the planarization step comprises sputtering the etch stop layer.

[0026] Additionally or alternatively, the planarization step comprises performing chemical mechanical polishing.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIGS. 1A-1C schematically show a substrate comprising a channel hole etched through a plurality of alternating layers and punching through a lower-density carbon film used as an etch stop layer.

[0028] FIGS. 2A-2B show a flow diagram of an example method for forming a carbon shelf within a gap followed by depositing an etch stop layer onto the carbon shelf.

[0029] FIGS. 3A-3F schematically show example structures formed using the method of FIGS. 2A-2B.

[0030] FIGS. 4A-4C schematically show example structures formed in an example etch stop layer planarization process.

[0031] FIGS. 5A-5B schematically show example structures formed in another example etch stop layer planarization process.

[0032] FIGS. 6A-6B schematically illustrate etching of a channel hole through a second deck of alternating layers of material to an etch stop layer over a carbon shelf of a first deck of alternating layers.

[0033] FIGS. 7A-7B show a flow diagram of an example method for forming a densified carbon layers on a carbon shelf.

[0034] FIGS. 8A-8I schematically show example structures formed using the method of FIGS. 7A-7B.

[0035] FIG. 9 schematically shows an example structure comprising a buried etch stop material that can be used as an etch stop layer.

[0036] FIG. 10 schematically shows a processing tool configured for plasma- enhanced chemical vapor deposition (PECVD) and plasma-based etching.

[0037] FIG. 11 schematically shows a processing tool configured for reduced temperature etching of a substrate.

[0038] FIG. 12 schematically shows a block diagram of an example computing system.DETAILED DESCRIPTION

[0039] The term “aspect ratio” generally represents a ratio between a depth of a feature and an average width of the feature.

[0040] The term “carbon film” generally represents a film comprising one or more forms of elemental carbon. A carbon film can comprise amorphous carbon. The term “lower-density carbon film” generally represents a carbon film comprising a density that is below 1.5 g / cm3. The term “higher-density carbon film” generally represents a carbon film comprising a density that is 1.5 g / cm3or greater.

[0041] The term “carbon-containing film precursor” generally represents any compound that can be introduced into a processing chamber in a gas phase to form a carbon film on a substrate. Example carbon-containing deposition precursors include acetylene (C2H2), ethylene (C2H4), and propylene (CsEL).

[0042] The term “chemical vapor deposition” (CVD) generally represents a process in which a solid phase film is formed on a substrate by directing a continuous flow of one or more precursor gases over the substrate surface under conditions configured to cause the chemical conversion of the precursor gases to the film. The term “plasma-enhanced chemical-vapor deposition” (PECVD) generally represents a CVD process in which a plasma is used to facilitate the chemical conversion of one or moreprecursor gases to a solid phase film on a substrate. Thermal CVD (TCVD) processes utilize thermal energy to facilitate film formation. The terms “growth”, “deposition”, and variants thereof, also can be used to refer to film formation. The term “CVD tool” generally represents a machine comprising a processing chamber and other hardware configured to perform CVD processing.

[0043] The term “etch” and variants thereof generally represent processes by which material is removed from a substrate. An etch using gas phase etchants is referred to as a "dry etch". An etch utilizing etchants in the liquid phase is referred to as a "wet etch". Variables to consider in a dry etch environment include gas mixtures, processing chamber pressure, and process temperature. Reactive ion etching (RIE) is a dry etching process that uses a plasma comprising chemically reactive ions to etch a material. The term “cryogenic etch” (also referred to as “cryo-etch” or “reduced temperature etch”) generally represents a dry etch where the substrate being etched is actively cooled during etching.

[0044] The term “etch stop” generally represents a film layer that is revealed by removal of another material in an etching process and that is more resistant to an etching process than the removed material. The term “etch selectivity” generally represents a ratio of etch rates of the etched film to the etch stop layer.

[0045] The term “etching agent” generally represents a substance that can convert a material into volatile species to facilitate removal of the material from a substrate. Example oxygen-based etching agents include molecular oxygen (O2), carbon dioxide (CO2), and nitrous oxide (N2O). Example hydrogen-based etching agents include molecular hydrogen (H2) and ammonia (NH3).

[0046] The term “flow control hardware” generally represents components configured to place one or more processing 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. Example chemical sources include film precursor sources, inert gas sources, and reactant gas sources such as nitrogen sources and oxidant sources.

[0047] The term “gap” generally represents a recessed structure on a substrate.

[0048] The term “plasma” generally represents a gas comprising ions and free electrons. Energetic ions also can form radical species from gases in a plasma. The term “capacitively coupled plasma” generally represents a plasma formed between capacitive electrode plates. Example capacitive plates can include a showerheadelectrode and a pedestal electrode. The term “inductively coupled plasma” generally represents a plasma formed by an electric field created by an inductive coil.

[0049] The term “processing chamber” generally represents an enclosure in which chemical and / or physical processes are performed on substrates. The pressure, temperature and atmospheric composition within a processing chamber are controllable to perform chemical and / or physical processes.

[0050] The term “processing tool” generally represents a machine comprising a processing chamber. The processing tool is configured for processing one or more substrates at a respective one or more processing stations.

[0051] The term “showerhead” generally represents a processing chemical outlet comprising a plurality of holes distributed across an area.

[0052] The term “sputtering” and variants thereof generally represent processes in which ions in a plasma are accelerated toward a substrate with sufficient kinetic energy to cause at least some material on the substrate to be ejected from the substrate upon collision with the substrate.

[0053] The term “sticking coefficient” generally represents a ratio of a number of gas-phase species that adsorb to a substrate surface compared to a number of the gasphase species that impinge upon the substrate surface.

[0054] The term “3D DRAM” is an acronym for three-dimensional dynamic random-access memory.

[0055] The term “3D NAND” is an acronym for three-dimensional NOT AND memory, and generally represents memory architecture based upon NOT AND logic gates.

[0056] The term “3D NOR” is an acronym for three-dimensional NOT OR memory, and generally represents memory architecture based upon NOT OR logic gates.

[0057] As described above, device fabrication can involve many steps of material deposition, patterning, and removal to form integrated circuits and / or memory structures on substrates. For example, some three-dimensional (3D) integrated circuits, such as 3D NAND memory devices, are fabricated using stacked pairs of materials, with the "active" device layer being one of the pairs and the other being a dielectric for electrical isolation. By stacking these pairs of layers, manufacturers are able to create more active layers. A stack of such alternating layers can be referred to as a mold stack. As a more specific example, alternating silicon oxide and silicon nitride layers can bedeposited to form an ONON (oxide-nitride-oxide-nitride) mold stack in a 3D NAND fabrication process. In some examples, a stack can comprise alternating silicon layers and polysilicon layers to form an OPOP (oxide-polysilicon-oxide-polysilicon) mold stack, where the term polysilicon generally represents polycrystalline silicon. Other examples of 3D integrated circuits include 3D DRAM and 3D NOR memory devices.

[0058] Patterning and device integration in a 3D integrated circuit fabrication process often involves etching holes (e.g. cylindrical holes) through a mold stack. The etching of such holes into a mold stack can be performed using gas phase chemical etchants. An etch step using gas phase etchants is referred to as a "dry etch". An etch utilizing etchants in the liquid phase is referred to as a "wet etch". Variables to consider in a dry etch environment include gas mixtures, processing chamber pressure, and process temperature. Reactive ion etching (RIE) is a dry etching process that uses a plasma comprising chemically reactive ions to etch a material. In some dry etching processes, a material being exposed to the dry etch environment is actively cooled. Such an etching process can be referred to as a cryogenic etch, or reduced temperature etch. Cooling the exposed material removes heat from the substrate as chemical and physical reactions occur between the deposited material and the etchants. Keeping feature sidewalls cold during etching can enable ions in an etching process to move deeper into the gap. As more reactants are at the bottom of the gap, the etch rate can be enhanced. This can have a beneficial impact on relatively longer, deeper etches to keep the surrounding material intact as the etch proceeds in time. As such, cryogenic etching tools can be used for etching features in 3D integrated circuit fabrication processes.

[0059] However, etching of deep, high aspect ratio features, such as channel holes in a 3D NAND mold stack, can be challenging. Thus, the etching of a deep, high aspect ratio feature can be performed in more than one discrete etching process. In the example of a 3D NAND mold stack, a first set of alternating layers (a first “deck” of the mold stack) can be deposited, and then a first hole can be etched through the first deck. Next, the first hole in the first deck can be plugged with a material having sufficiently high selectivity to the etching process to form an etch stop layer. Carbon is one example of an etch stop layer. Plasma enhanced CVD (PECVD) can be used to deposit carbon in the channel hole and on surrounding regions of the substrate. Planarization then can be performed to remove the carbon from the surrounding regions of the substrate, thereby forming a carbon plug in the channel hole. Next, a second deck of alternating material layers can be formed over the first deck, including over thecarbon plug. Then, another etching process can be used to etch a hole through the second deck in a location aligned with the hole in the first deck. The etching process slows when it reaches the carbon plug used as the etch stop layer. This helps to protect the layers of the first deck from the etching chemistry. Then, the carbon plug can be removed (e.g. by ashing - oxidation to volatile carbon dioxide), thereby joining the holes in the first deck and second deck into a single hole through both decks of the mold stack. This process then can be repeated for any additional decks of alternating materials.

[0060] However, some etch stop materials do not always provide adequate etch selectivity to etching of mold stack materials. The problem of etch selectivity can be more pronounced when advanced etching techniques are used, such as cryogenic etching. For example, carbon films can be deposited with different densities by using different deposition conditions. Lower-density carbon films can deposit deeper within a hole in a substrate, and thus form a relatively thicker plug, than higher-density carbon films. In some examples, the term “lower-density carbon film” refers to carbon films comprising densities less than 1.5 g / cm3. The term “higher-density carbon film” refers to carbon films comprising densities of 1.5 g / cm3or higher. In other examples, these terms can refer to other relative densities of carbon layers.

[0061] However, lower-density carbon films can be insufficiently selective for a 3D integrated circuit fabrication process that utilizes cryo-etching. This can allow the cryo-etching to damage material layers of a deck revealed by etching of the plug. FIGS. 1A-1C schematically shows structure formed in a cryo-etching process that utilizes a lower-density carbon film as an etch stop layer. FIG. 1A shows a substrate 100 comprising a first deck 102 and a second deck 104. The first deck 102 and second deck 104 comprise a plurality of alternating material layers including a first material 106 and a second material 108. In some examples, alternating silicon oxide layers and silicon nitride layers are used to form an ONON stack. In some examples, alternating silicon layers and poly silicon layers are used to form an OPOP stack. Further, first deck 102 comprises a lower-density carbon film 110 deposited within a first hole 111 in an earlier etch stop layer deposition process, as described above. First hole 111 comprises a void 112 below the lower-density carbon film 110.

[0062] FIG. IB shows substrate 100 during a cryo-etching process to etch a second hole 114 through the second deck 104, wherein the second hole 114 is aligned with the first hole 111. The cryo-etching process comprises forming a plasma using anetching agent to etch through the alternating material layers of second deck 104. However, due to the unsuitably low selectivity of the lower-density carbon film 110 to the cryo-etching, the cryo-etching removes material from the lower-density carbon film 110, as indicated at 120. This can result in damage to layers of the first deck 102.

[0063] FIG. 1C shows substrate 100 following further cryo-etching to widen second hole 114. Due to the insufficient etch selectivity of the lower density carbon film 110, the cryo-etching punches through the lower-density carbon film 110 to void 112, as indicated at 122. Punch-through exposes sidewalls in lower portions of first deck 104 to the etching agent. As a result, sidewalls of gap 111 are etched laterally, as indicated at 124. Lateral sidewall etching can thin and / or remove the material layers between neighboring gaps. This can lead to device failure.

[0064] To avoid such issues, a different etch stop material can be used to provide higher etch selectivity than lower-density carbon. One example is higher- density carbon, for example comprising a density of 1.5 g / cm3or greater. However, it can be challenging to deposit higher-density carbon in a hole (e.g. in a 3D NAND mold stack) with sufficient thickness to form a robust etch stop layer. As one factor, higher- density carbon can be deposited using plasma conditions that are associated with directional, ion-assisted deposition (e.g., higher radiofrequency power, dual frequency radiofrequency excitation). As a result of the directional deposition, higher-density carbon films can exhibit faster film growth near the top of the gap than deeper within the gap. This can result in a relatively thin plug that potentially can be broken through in a subsequent etching step.

[0065] In contrast, lower-density carbon can be deposited using plasma conditions (e.g., lower power, single high-frequency excitation) associated with radical- assisted deposition. This helps a lower-density carbon film extend into a hole more deeply than higher-density carbon. However, as discussed above, lower-density carbon films can exhibit insufficient etch selectivity for cryo-etching.

[0066] Accordingly, examples are disclosed that relate to forming an etch stop layer in a high aspect ratio gap by forming a carbon shelf with a lower-density carbon film, and then depositing the etch stop layer on the carbon shelf. Briefly, a lower-density carbon film is deposited into a high-aspect ratio gap, such as a channel hole in a 3D NAND process or other feature in a 3D integrated circuit manufacturing process, in a first deposition step. The high-aspect ratio gap can comprise an aspect ratio of 5: 1 to 60: 1, or more, in some examples. As described in more detail below, a plasma can beformed using a carbon-containing precursor to deposit the lower-density carbon film by PECVD. Next, in an etching step, a plasma is formed using an etching agent to etch a portion of the of the lower-density carbon film. This forms a carbon shelf within the gap. The portion of the gap above the carbon shelf has a relatively lower aspect ratio (e.g. l :4 to 4: 1, or less) than the aspect ratio of the gap. Next, in a second deposition step, an etch stop layer is deposited over the carbon shelf. Examples of etch stop layer materials can include higher-density carbon film, molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, and silicon oxide. Such materials can be used to fill a lower aspect ratio gap, such as that formed by the carbon shelf. In this manner, a sufficiently selective etch stop layer can be deposited with sufficient thickness to protect the layers of one deck from the cryo-etching of a next highest deck in a 3D integrated circuit fabrication process.

[0067] The etch stop layer material can be deposited to form an overburden of material, in addition to the material within the gap. The term “overburden” refers to a portion of the etch stop layer on field regions of the substrate and over the etch stop layer material in the gap. The overburden then can be removed by planarization before depositing a next deck of a mold stack. In some examples, deposition of the etch stop material can be highly directional. As the gap is filled with the etch stop material, excess film is deposited on field regions on the surface of the substrate outside the gap. This can result in relatively large variations of film thickness of overburden material on the substrate, sometimes referred to as “pattern loading”. In some examples, pattern loading results in raised structures (e.g., pillars) on a substrate surface that are difficult to planarize by chemical mechanical polishing (CMP).

[0068] Accordingly, examples also are disclosed for planarizing an etch stop layer on a substrate. In some examples, the etch stop layer is first sputtered to remove material from thicker film portions. Sputtering can be optionally followed by a CMP step. In other examples, a lower-density carbon film is deposited onto the etch stop layer to help fill empty space between thicker portions of the overburden of the etch stop layer. Then, a CMP step is performed to remove the lower-density carbon film and the overburden of the etch stop layer and planarize the etch stop layer.

[0069] In some examples, an etch stop layer can be formed from a densified carbon film that is deposited over a carbon shelf. The densified carbon film can be formed in a cyclic process that includes alternating deposition steps and densification steps. As described in more detail below, a layer of lower-density carbon film isdeposited over the carbon shelf. Then, a plasma is formed using helium (He) gas. This can form He ions that can impact the lower-density carbon film. Further, excited He species in the plasma can emit high-energy photons, such as ultraviolet light photons. Photons emitted by excited He species can be absorbed by the lower-density carbon film and cause ejection of hydrogen atoms. This increases sp3hybridization in the carbon film and results in densification. Without wishing to be bound by theory, it is believed that He ion bombardment and photon absorption both contribute to densifying the layer of lower-density carbon film to form a layer of densified carbon film. Further, use of a He-based plasma is less damaging to the carbon film than a relatively heavier inert gas, such as Ar. However, in other examples, a densification plasma other than a helium-containing plasma can be used (e.g. a plasma comprising neon, argon, or nitrogen (N2)). The process can be repeated in a cyclic manner to form an etch stop plug layer-by-layer over the carbon shelf in the gap. Forming a densified carbon film in this manner can help avoid pattern loading. The deposited film then can be planarized, for example, using CMP. More generally, the cyclic process for depositing, and densifying a layer of lower-density carbon film also can be used to deposit carbon films in other applications, including gapfill applications. Examples for depositing densified carbon films are described in more detail below.

[0070] FIGS. 2A-2B show a flow diagram of an example method 200 for forming a carbon shelf within a gap (e.g. a hole formed through a mold stack in a 3D integrated circuit fabrication process), followed by forming an etch stop layer on the carbon shelf. Method 200 is described with reference to FIGS. 3A-6B. At 202, method 200 optionally comprises etching the substrate to form the gap. The etching step at 202 can be performed in-situ or ex-situ in various examples. Here, “in-situ” etching refers to an etching process performed within a same processing chamber as the deposition steps described below. “Ex-situ” refers to an etching process performed in a different processing chamber. Etching the substrate at 202 can be performed using a hardmask, such as an amorphous carbon hardmask. In some such examples, at 203, the method 200 comprises cryo-etching the substrate to form the gap. As described above, cryoetching is a reduced temperature dry etch that can be used to help achieve a faster etch speed for various etch target materials, such as silicon oxide, silicon nitride, and silicon oxynitride. Increasing the etch rate of a silicon-containing film by using cryogenic etching also can help to etch a relatively deep, narrow gap in a substrate. In some examples, slower dry etch rates can lead to bowing (non-uniformity of feature diameteras a function of feature depth) and also a faster etch rate in lateral directions (e.g. growth of a feature diameter) as a function of vertical growth (depth). Further, a slower dry etch rate also can lead to longer process times and greater expense. Thus, the cryogenic etching of a silicon-containing film can help to mitigate such issues compared to dry etching at relatively higher temperatures.

[0071] Cryo-etching at 203 comprises cooling the substrate and / or a substrate support on which the substrate is disposed. In some examples, the substrate is cooled to a temperature of 0° C or below. In some examples, the processing tool can cool the substrate to a substrate temperature within a range of -60 °C to -10 °C. In other examples, substrate temperatures outside this range can be used.

[0072] The cryo-etch step at 203 further comprises forming a plasma using one or more etching agents. In some examples, the etching agent comprises one or more of a phosphorus-containing etching agent, a halogen-containing etching agent, and hydrogen (H2). Examples of etching agents include hydrogen fluoride (HF), nitrogen trifluoride (NF3), perfluoroalkanes, such as carbon tetrafluoride (CF4) and hexafluoroethane (C2F6), and phosphorus halides, such as phosphorus trifluoride (PF3) and phosphorus pentafluoride (PFs). In some more specific examples, a gas mixture comprising a mixture of a phosphorus halide and hydrogen can be used to perform a cryo-etch.

[0073] Further, any suitable plasma conditions can be used for performing the cryo-etch at 203. Example plasma conditions include radiofrequency powers of 50 to 6500 W. Example frequencies for the radiofrequency plasma include frequencies of 400 kHz, 13.56 MHz, 27MHz, 60MHz, and 90MHz. In some examples, the plasma can be pulsed between a first power level and a second power level. The first power level can comprise a radiofrequency power of 50 to 6500 W. Further, the second power level can comprise a power level that is 0% to 20% of the first power level. Any suitable duty cycle can be used for pulsing the plasma. Examples include a duty cycle of 0% to 80%.

[0074] Continuing, at 204, method 200 comprises, in a first deposition step, depositing a lower-density carbon film in the gap. The first deposition step can be performed using PECVD with a carbon-containing film precursor introduced into the plasma. Any suitable carbon-containing film precursor can be used. Examples include alkanes having a general formula CnH2n+2 where n is an integer in a range of 1 to 10 (such as, methane, ethane, etc.), alkenes having a general formula CiJLn where n = 2 to 10 (such as, ethylene, propylene, etc.), and alkynes having a general formula CnH2n-2where n = 2 to 10 (such as, acetylene, propyne, etc.), that are gas-phase under processing conditions. Other examples of carbon-containing film precursors comprise cyclic hydrocarbons including aromatics, nitrogen-containing compounds including alkyl amines, and oxygen-containing compounds including alcohols, ketones, esters, aldehydes, and ethers that are gas-phase under processing conditions, alkanes, alkenes, alkynes, cyclic hydrocarbons, aromatics, alcohols, aldehydes, esters, ethers, ketones, aldehydes, alkyl halides, alkyl amines, and alkyl diamines. In some examples, a carbon- containing film precursor with a suitably low sticking coefficient can be selected (e.g., acetylene). A relatively lower sticking coefficient allows the carbon-containing film precursor to move deeper into the gap compared to a relatively higher sticking coefficient.

[0075] Suitable substrate heater temperatures for PECVD of lower-density carbon films include temperatures of 50 °C to 650 °C. Additionally, suitable pressures include pressures of 1 Torr to 20 Torr. In other examples, temperatures and / or pressures outside these ranges can be used. Unless otherwise stated, ranges described herein are inclusive of the endpoints. In other words, a range from X to Y includes the values X and Y.

[0076] The plasma can be formed using any suitable conditions. Suitable plasma conditions include conditions that favor radical-assisted deposition, as described in more detail below. Example plasma conditions include radiofrequency powers of 50 to 6500 W. Example frequencies for the radiofrequency plasma include frequencies of 400 kHz, 13.56 MHz, 27MHz, 60MHz, and 90MHz. In some examples, the plasma can comprise a higher frequency radiofrequency energy component (“HF component”) and a lower frequency radiofrequency energy component (“LF component”). The HF component can comprise frequencies of 3 MHz to 300 MHz. The LF component can comprise frequencies of 3 MHz and below. In some examples, the plasma can comprise a capacitively coupled plasma (CCP). In other examples, the plasma can comprise an inductively coupled plasma (ICP).

[0077] In some examples, at 206, the plasma is formed using a HF component, and omits radiofrequency energy at frequencies below 3 MHz. Omitting frequencies below 3 MHz (i.e., omitting a LF component) can shift the PECVD process towards more radical-assisted deposition, rather than ion-assisted deposition. This can help deposit lower-density carbon deeper in the gap. Further, use of an HF component with relatively low power also can favor radical-assisted deposition process to help depositthe film deeper in the gap than use of a higher power. In some examples, at 208, forming the plasma comprises using an HF component comprising a power of 100 W to 500 W (for a single processing station). In other examples, a power outside this range can be used. Overall, use of a HF component comprising a relatively lower power and omitting a LF component can provide a more effective gapfill for high aspect ratio gaps than higher power and / or inclusion of a LF component.

[0078] In some examples, the gas mixture used to form the plasma can further comprise one or more of a passivating agent or an etching agent. In some examples, the passivating agent or the etching agent comprises boron trifluoride (BF3), carbon monoxide (CO), carbon dioxide (CO2), carbon oxysulfide (COS), molecular oxygen (O2), nitrogen trifluoride (NF3), sulfur dioxide (SO2), sulfur trifluoride (SF3), sulfur hexafluoride (SFe), a halocarbon gas, a halogen acid (hydrofluoric acid (HF), hydrochloric acid (HC1), hydrobromic acid (HBr), hydroiodic acid (HI)), a halogen gas (F2, Ch, Br2, 12), or a combination of two or more thereof. The passivating agent and / or etching agent can be used to control the profile of a film deposited in a gap. For example, adding hydrogen to the plasma can help etch the carbon film as it is deposited. The hydrogen is consumed mostly at upper surfaces of the gap near the opening of the gap. As such, the hydrogen acts to inhibit film growth at upper portions of the gap. In other words, the inhibition effect is greater on surfaces closer to the opening of the gap than deeper within the gap.

[0079] In some examples, the gas mixture used to form the plasma can further comprise one or more inert gases. Examples of inert gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0080] Thus, a PECVD process using the example conditions described above can help deposit a lower-density carbon film in the gap. In some examples, at 210, the lower-density carbon film comprises a density below 1.5 g / cm3.

[0081] FIGS. 3A-3F show example structures formed using method 200. FIG. 3A shows a substrate 300 prior to etching a gap. In some examples, substrate 300 comprises a plurality of alternating material layers (e.g., ONON or OPOP layers of a deck of a 3D NAND mold stack) (alternating layers not shown).

[0082] FIG. 3B shows substrate 300 after cryo-etching to form a gap 302. As described above, cryo-etching can help to etch a relatively deep, narrow gap in a substrate. Gap 302 can comprise any suitable aspect ratio. Gap 302 can comprise any suitable aspect ratio. Referring briefly to FIG. 2 A, in some examples, at 212, the gapcomprises an aspect ratio within a range of 5: 1 to 60: 1. In other examples gap 302 comprises an aspect ratio outside this range.

[0083] Next, FIG. 3C shows substrate 300 following a first deposition step 204 to deposit a lower-density (LD) carbon film 304 in gap 302. In some examples, the lower-density carbon film also is deposited on field regions 305 of substrate 300. Field regions refer to surfaces of substrate 300 outside of gaps. As shown in FIG. 3C, the lower-density carbon film comprises a void 306 in a lower portion of the gap. In some examples, a lower-density carbon film can be deposited without forming a void.

[0084] Returning to FIG. 2A, at 214, method 200 further comprises, in an etching step after the first deposition step, etching a portion of the lower-density carbon film to form a carbon shelf within the gap. A dry etch can be used at 214 by forming a plasma using an etching agent. Example oxygen-based etching agents include molecular oxygen (O2), carbon dioxide (CO2), and nitrous oxide (N2O). Example hydrogen-based etching agents include molecular hydrogen (EE) and ammonia (NEE). In some examples, at 216, method 200 comprises forming a plasma using an etching agent comprising one or more of hydrogen, ammonia, oxygen, carbon dioxide, or nitrous oxide.

[0085] FIG. 3D shows substrate 300 following etching step 214. As shown, the lower-density carbon film 304 is etched to form a carbon shelf 308. Lower-density carbon film deposited on field regions of substrate 300 also can be etched by etching step 214. The etch reveals a portion of gap 302 comprising a lower aspect ratio than the unfilled gap of FIG. 3B. Referring again to FIG. 2 A, in some examples, at 218, the portion of the gap above the carbon shelf comprises an aspect ratio within a range of l :4 to 4: l.

[0086] Continuing to FIG. 2B, method 200 further comprises performing a second deposition step at 220. The second deposition step 220 comprises depositing an etch stop layer over the carbon shelf. Due to the carbon shelf, the etch stop layer is deposited into a portion of the gap having a lower aspect ratio than the unfilled gap. A relatively lower aspect ratio gap is easier to fill with etch stop material than a high aspect ratio gap. Thus, by etching the lower-density carbon film to form a carbon shelf, method 200 can help achieve a high quality etch stop layer at second deposition step 220. The etch stop layer and the lower-density carbon shelf form a plug in the gap. This can help avoid breaking through the etch stop layer in a subsequent etching step.

[0087] Any suitable material can be used for the etch stop layer. Suitable etch stop materials include materials that have high etch selectivity. In some examples, at 222, the etch stop layer can comprise one or more of molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, or silicon oxide. Alternatively or additionally, in some examples, at 224, the etch stop layer can comprise a higher- density carbon film comprising a density of 1.5 g / cm3or greater. In other examples, any other suitable etch stop layer can be used.

[0088] The etch stop layer can be deposited by PECVD. Examples of etch stop film precursors include molybdenum-containing precursors, aluminum-containing precursors, tungsten-containing film precursors, titanium-containing film precursors, and silicon-containing film precursors. Examples of molybdenum-containing precursors for forming molybdenum films include bis(tert- butylimino)bis(dimethylamino) molybdenum (C12H30M0N4), molybdenum pentachloride (M0CI5), molybdenum dioxide dichloride (MOO2CI2), molybdenum oxytetrachloride (MoOCh), and molybdenum hexacarbonyl (Mo(CO)e). Examples of aluminum-containing precursors for forming aluminum oxide films include aluminum halides (AlXy), aluminum alkoxide (C9H21AIO3), trimethyl aluminum (AIC3H9), aluminum carbonyl (Al(CO)x), and aluminum hydride (AIH3). Examples of tungsten- containing precursors for forming tungsten-containing films include tungsten hexafluoride (WFe), tungsten hexachloride (WCk), bis(tert- butylimino)bis(dimethylamino) tungsten (C12H30N4W), and tungsten hexacarbonyl (W(CO)e). Examples of carbon-containing film precursors for forming carbon- containing films include ethylene, propylene, and acetylene. Examples of titanium- containing precursors for forming titanium-containing films include titanium tetrachloride (TCI4) and titanium isopropoxide (Ti(OCH(CH3)2)4). Examples of nitrogen-containing precursors for forming metal nitride films include ammonia (NH3). Example silicon-containing film precursors include silane and polysilanes, trisilylamine, alkoxysilanes, siloxanes, aminosilanes, and halosilanes. Further examples of silicon-containing film precursors include tetraethyl orthosilicate (TEOS), tetramethoxysilane (TMOS), methylsilane, trimethyl silane (3MS), ethylsilane, butasilanes, pentasilanes, octasilanes, heptasilane, hexasilane, cyclobutasilane, cycloheptasilane, cyclohexasilane, cyclooctasilane, cyclopentasilane, 1,4-dioxa- 2,3,5,6-tetrasilacyclohexane, diethoxymethylsilane (DEMS), diethoxysilane (DES), dimethoxymethylsilane, dimethoxysilane (DMOS), methyl-diethoxysilane (MDES),methyl-dimethoxysilane (MDMS), t-butoxydisilane, triethoxysilane (TES), and trimethoxysilane (TMS or TriMOS). In some examples, the gas mixture used to form the plasma can further comprise one or more inert gases. Examples of inert gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0089] Any suitable plasma conditions can be used for PECVD of the etch stop layer. Example plasma conditions include radiofrequency powers of 50 to 6500 W. Example frequencies for the radiofrequency plasma include frequencies of 400 kHz, 13.56 MHz, 27MHz, 60MHz, and 90MHz. In some examples, at 226, a higher-density carbon film is deposited by forming a directional plasma. The directional plasma can be formed, for example, using radiofrequency power comprising an LF component having a frequency below 3 MHz, and an HF component having a frequency of 3 MHz to 300 MHz. Including an LF component can help favor ion-assisted film deposition. This helps deposit a carbon film comprising a higher-density than the lower-density carbon film deposited at 204. Higher-density carbon films can exhibit better etch selectivity than lower-density carbon films. Additionally, use of relatively higher power also can help favor ion-assisted film deposition than use of lower power. In some examples, the plasma is formed using a HF component comprising a power of 100 W to 5000 W. In some examples, the LF component comprises a power of 100 W to 5000 W. In other examples, a power outside this range can be used. The values listed herein refer to power per station. In examples with processing tools comprising a plurality of stations for processing a respective plurality of substrates, powers can be scaled up based at least upon a number of stations.

[0090] FIG. 3E schematically shows substrate 300 following a second deposition step 220 to deposit an etch stop layer 314 over carbon shelf 308. The etch stop layer 314 also is deposited over field regions 305 of substrate 300, forming an overburden of the material of etch stop layer 314. Etch stop layer 314 can comprise any suitable material. Examples include higher-density carbon film, densified carbon film, molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, and silicon oxide.

[0091] In some examples, the substrate can be planarized to remove etch stop material from the field regions of the substrate. Referring again to FIG. 2B, at 230, method 200 optionally comprises a planarization step. In the optional planarization step at 230, method 200 comprises removing the etch stop layer from field regions of the substrate. This is illustrated in FIG. 3F. In the depicted example, FIG. 3F showssubstrate 300 following a planarization step that uses chemical mechanical polishing (CMP) to remove the overburden of etch stop layer 314 from field regions 305.

[0092] As mentioned above, deposition of the etch stop layer can be highly directional. Excess film deposited on field regions can result in raised structures (e.g., pillars) on the substrate surface that are difficult to planarize by CMP. For example, CMP can cause mechanical stress on raised structures resulting in cracks to the etch stop layer. Thus, method 200 optionally can include a planarization step 230. In some examples, at 232, method 200 comprises sputtering the etch stop layer. Sputtering comprises forming a plasma to accelerate ions in the plasma toward the etch stop layer. The ions are accelerated with sufficient kinetic energy to cause at least some material on the etch stop layer to be ejected from the etch stop layer. In some examples, a plasma is formed using an inert gas to sputter the etch stop layer. In some examples, use of a relatively heavier inert gas (e.g. Ar) can provide for a higher rate of sputtering compared to a relatively lighter inert gas (e.g. He). Sputtering also can be controlled by adjusting pressure, radiofrequency power, duration of applied radiofrequency power, a showerhead temperature, and / or a spacing between the electrodes used to form a capacitively coupled plasma.

[0093] In some examples, at 234, method 200 comprises planarizing the substrate by CMP. In some examples, CMP at 234 can be performed after a sputtering step at 232. FIGS. 4A-4C illustrate such a process. FIG. 4A shows a substrate 400 comprising a gap 402 partially filled with a lower-density carbon film 404 to form a carbon shelf 406. A higher-density carbon film 408 is deposited over the carbon shelf 406. Due to directional deposition, the overburden of higher-density carbon film 408 comprises thicker regions including pillars 410, 412. Next, FIG. 4B shows substrate 400 following a sputtering step (e.g., step 232). The sputtering step helps to remove material preferentially from thicker regions (e.g., pillars 410, 412) of the higher-density carbon film 408. Next, FIG. 4C shows substrate 400 following a CMP step. The CMP step removes material from field regions 414 of substrate 400 outside of gap 402.

[0094] Returning to FIG. 2B, in some examples, at 236, method 200 comprises depositing an additional lower-density carbon film over the high-density carbon film prior to the CMP step 234. Depositing a lower-density carbon film on the substrate can help fill empty space between thicker portions of the higher-density carbon film. The additional lower-density carbon film can be deposited using any suitable method, such as PECVD described above at step 204. Then, a CMP step is performed to remove theadditional lower-density carbon film and planarize the etch stop layer. By filling empty space between thicker portions of the overburden of the etch stop layer with lower- density carbon film, the method helps avoid mechanical stress and damage to the higher-density carbon film during CMP.

[0095] FIGS. 5A-5B schematically illustrate this process. First, FIG. 5A shows a substrate 500 comprising a gap 502 partially filled with a lower-density carbon film 504 to form a carbon shelf 506. A higher-density carbon film 508 is deposited over the carbon shelf 506. Due to directional deposition, the higher-density carbon film 508 comprises thicker regions including pillars 510, 512. An additional lower-density carbon film 520 is deposited onto the higher-density carbon film 508. This fills space between pillars 510, 512. Next, FIG. 5B shows substrate 500 following a CMP step. This removes the additional lower-density carbon film 520 and also removes the overburden of higher-density carbon film 508 from field regions 522 of substrate 500. Due to the additional lower-density carbon film 520, the CMP step does not damage the higher-density carbon film 508.

[0096] Referring again to FIG. 2B, method 200 optionally comprises, at 240, depositing a plurality of alternating material layers onto the substrate. In some examples, the substrate comprises a first deck and step 240 comprises forming a second deck on the first deck. In some examples, method 200 further comprises, at 242, cryoetching a second gap (e.g., a channel hole) through the plurality of alternating material layers to the etch stop layer. Examples of cryo-etching processes are described above. This is illustrated in FIGS. 6A-6B. First, FIG. 6A shows substrate 300 from FIG. 3F, further comprising a second deck 600 deposited onto the substrate 300. Second deck 600 comprises alternating first material layers 602 and second material layers 604. FIG. 6B shows substrate 300 following a cryo-etching step 242 to etch a second gap 606 through the alternating first material layers 602 and second material layers 604 to etch stop layer 314. The second gap 606 is aligned with the first gap 302. In contrast to FIGS. 1B-1C, the etching of second gap 606 does not etch deeper than the target etch depth. This is because etch stop layer 314 comprises a greater etch selectivity than the lower-density carbon film 110. As a result, cryo-etching to form gap 606 does not widen gap 302 or punch-through the etch stop layer 314.

[0097] As mentioned above, in some examples, densified carbon can be used as an etch stop layer. The term “densified carbon” generally represents a carbon layer that is deposited as lower-density carbon and then is densified through one or moresubsequent processes. FIGS. 7A-7B show a flow diagram of an example method 700 for forming a carbon shelf within a gap, and using a helium plasma in deposition cycles to form densified carbon layers on the carbon shelf. Method 700 is described with reference to FIGS. 8A-8I. In some examples, at 702, method 700 optionally comprises etching the substrate to form the gap. The etching step at 702 can be performed in-situ or ex-situ in various examples. Etching the substrate at 702 can be performed using a hardmask, such as an amorphous carbon hardmask. In some such examples, at 704, method 700 comprises cryo-etching the substrate to form the gap. Examples of cryoetching processes are described above (e.g., step 203 of method 200).

[0098] At 706, method 700 comprises, in a first deposition step, depositing a lower-density carbon film in the gap. In some examples, at 708, the gap comprises an aspect ratio of 5: 1 to 60: 1. In other examples, the gap can comprise an aspect ratio outside this range. In some examples, the gap is formed by performing a reduced temperature etch. The first deposition step 706 can utilize PECVD by forming a plasma using a carbon-containing film precursor. Any suitable carbon-containing film precursor can be used. Examples include the carbon precursors listed above. In some examples, a carbon-containing film precursor with a low sticking coefficient can be selected (e.g., acetylene). A low sticking coefficient allows the carbon-containing film precursor to move deeper into the gap.

[0099] Examples of suitable conditions for PECVD of lower-density carbon films include temperatures of 50 °C to 650 °C and pressures of 1 Torr to 20 Torr, or 5 Torr to 14 Torr. Examples of plasma conditions for depositing the lower-density carbon film are described above at step 204 of method 200. In some examples, at 710, plasma conditions are configured to deposit a lower-density carbon film comprising a density less than 1.5 g / cm3. As described above, forming a plasma using relatively lower power and / or omitting LF component can shift the PECVD process towards more radical- assisted deposition. This can help to deposit a lower-density carbon film in a relatively high aspect ratio gap. In some examples, at 712, the plasma is formed using a HF component and omitting radiofrequency energy at frequencies below 3 MHz.

[0100] In some examples, the gas mixture used to form the plasma can further comprise one or more of a passivating agent or an etching agent. In some examples, the passivating agent or the etching agent comprises boron trifluoride (BF3), carbon monoxide (CO), carbon dioxide (CO2), carbon oxysulfide (COS), molecular oxygen (O2), nitrogen trifluoride (NF3), sulfur dioxide (SO2), sulfur trifluoride (SF3), sulfurhexafluoride (SFe), a halocarbon gas, a halogen acid (hydrofluoric acid (HF), hydrochloric acid (HC1), hydrobromic acid (HBr), hydroiodic acid (HI)), a halogen gas (F2, Ch, Br2, I2), or a combination of two or more thereof. As described above, the passivating agent and / or etching agent can be used to control the profile of a film deposited in a gap. In some examples, the gas mixture used to form the plasma can further comprise one or more inert gases. Examples of inert gases include helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).

[0101] FIGS. 8A-8I schematically show example structures formed using method 700. FIG. 8A shows a substrate 800 comprising a gap 802. Substrate 800 can comprise any suitable material, such as silicon, silicon oxide, or silicon nitride. FIG. 8B shows substrate 800 following a first deposition step 706 to deposit a lower-density carbon film 804 into the gap. In some examples, the lower-density carbon film 804 also is deposited on field regions 806 of substrate 800. As shown in FIG. 8B, the lower- density carbon film comprises a void 808. In some examples, a lower-density carbon film can be deposited without forming a void.

[0102] Returning to FIG. 7A, at 714, method 700 further comprises, in an etching step after the first deposition step, etching a portion of the lower-density carbon film to form a carbon shelf within the gap. Etching the lower-density carbon film can comprise forming a plasma using an etching agent. In some examples, the etching agent comprises one or more of hydrogen, ammonia, oxygen, carbon dioxide, or nitrous oxide.

[0103] FIG. 8C shows substrate 800 following step 714 to etch a portion of lower-density carbon film 804. This forms a carbon shelf 810 within gap 802. As such, the portion of gap 802 comprises a lower aspect ratio than the unfilled gap 802 of FIG. 8 A. The portion of gap 802 above carbon shelf 810 can comprise a relatively lower aspect ratio, such as 5: 1 or less. Referring again to FIG. 7 A, in some examples, at 716, the portion of the gap above the carbon shelf comprises an aspect ratio within a range of 1 :4 to 4: 1.

[0104] Continuing to FIG. 7B, method 700 further comprises a second deposition step at 720. The deposition step 720 comprises performing one or more deposition cycles to deposit a densified carbon film over the carbon shelf. Each deposition cycle 720 comprises, at 722, depositing a layer of lower-density carbon film. The layer of lower-density carbon film can be deposited using PECVD according to the conditions described above. However, PECVD at step 722 is performed for a relativelyshorter duration compared to deposition step 706 above. This helps deposit a relatively thin layer of lower-density carbon film, for example, comprising a thickness of 1 nm to 10 nm.

[0105] Next, the deposition cycle 720 comprises, at 724, forming a plasma using helium to densify the layer of lower-density carbon film. The plasma comprises He ions that can impact the lower-density carbon film. Further, excited He species in the plasma can emit high energy photons, such as ultraviolet (UV) photons. He ion bombardment and UV absorption can densify the layer of lower-density carbon film to form a layer of densified carbon film. In some examples, at 726, the layer of densified carbon film comprises a density of 1.5 g / cm3or greater. In other examples, a densification plasma other than a helium-containing plasma can be used (e.g. a plasma comprising neon, argon, or nitrogen (N2)).

[0106] Example processing conditions for forming the He-based plasma include temperatures of 50 °C to 650 °C and pressures of 1 Torr to 20 Torr. In some examples, a densification step can comprise a duration of 5 to 20 seconds. In other examples, a duration outside this range can be used. Any suitable plasma conditions can be used at step 724. Example plasma conditions include radiofrequency powers of 50 to 6500 W. Example frequencies for the radiofrequency plasma include frequencies of 400 kHz, 13.56 MHz, 27MHz, 60MHz, and 90MHz. In some examples, the plasma can be formed using radiofrequency power comprising an LF component and an HF component. Example radiofrequency power for the HF component includes powers of 2000 to 6500 W. Example radiofrequency power for the LF component includes powers of 500 W to 2000 W. In other examples, powers outside these ranges can be used.

[0107] FIGS. 8D to 8H illustrate repeated deposition cycles 720 to deposit a densified carbon film over the carbon shelf 810. First, FIG. 8D shows substrate 800 following step 722 to deposit a layer of lower-density carbon film 812A onto the carbon shelf 810. FIG. 8E shows substrate 800 following step 724 to densify the layer of lower- density carbon film 812A. By using a He-based plasma, the layer of lower-density carbon film 812A is densified to form a layer of densified carbon film 814A.

[0108] As mentioned above, a plurality of deposition cycles 720 can be performed in a cyclic manner to deposit densified carbon film over the carbon shelf. FIG. 8F shows substrate 800 following a second step 722 to deposit a second layer of lower-density carbon film 812B onto the layer of densified carbon film 814A. Next, FIG. 8G shows substrate 800 following a second step 724 to densify the second layerof lower-density carbon film 812B. This forms a second layer of densified carbon film 814B. This process can be repeated any suitable number of times to form a densified carbon film in a layer-by-layer manner over carbon shelf 810. FIG. 8H shows substrate 800 following repeated deposition cycles 720 to form densified carbon 814 over carbon shelf 810 within the gap 802.

[0109] Returning to FIG. 7B, at 730, method 700 optionally comprises performing a planarization step to remove densified carbon film from field regions of the substrate. The planarization step at 730 can comprise sputtering. Alternatively or additionally, the planarization step at 730 can comprise CMP. In some examples, the planarization step at 730 can further comprise depositing an additional lower-density carbon film prior to CMP, as described above at step 236 of FIG. 2. FIG. 81 shows substrate 800 following a planarization step 730. This helps to remove excess densified carbon from field regions 806 of substrate 800.

[0110] In some examples, at 732, method 700 optionally comprises depositing a plurality of alternating material layers (e.g., ONON or OPOP layers of a deck of a 3D NAND mold stack) onto the substrate. In some examples, the substrate comprises a first deck, and step 732 comprises forming a second deck on the first deck. In some examples, at 734, method 700 further comprises cryo-etching a second gap through the plurality of alternating material layers to the etch stop layer. Examples of cryo-etching processes are described above. As the densified carbon film comprises a higher etch selectivity than the lower-density carbon film, the densified carbon film serves as a more effective etch stop layer. This helps to avoid problems discussed above, such as widening the gap in upper layers of a deck or punching through an etch stop layer.

[0111] In some examples, a buried etch stop material can be used as an etch stop layer. FIG. 9 schematically shows a substrate 900 comprising a gap 902. The lower portion of gap 902 is filled with a lower-density carbon film 904 to form a carbon shelf 906 within gap 902. The lower-density carbon film can be deposited and etched using method 200 or method 700, for example. Substrate 900 further comprises a layer of densified carbon film 910 on the carbon shelf 906. The densified carbon film 910 can be formed using one or more deposition cycles 720, for example. Substrate 900 further comprises a second portion of lower-density carbon film 912 formed on the layer of densified carbon film 910. As such, the layer of densified carbon film 910 comprises a buried etch stop layer.

[0112] A buried etch stop layer can offer benefits over other carbon plugs. For example, the buried etch stop layer can be easier to remove than an etch stop layer. This is because the second portion of lower density carbon film 912 can be more easily etched than other etch stop layers. However, the layer of densified carbon film 910 provides higher etch selectivity than a carbon plug comprising only lower-density carbon film. Further, the layer of densified carbon film 910 provides etch resistance in lateral direction. This can help avoid bowing when cryo-etching through a deck (not shown) to the etch stop layer.

[0113] FIG. 10 schematically shows a processing tool configured for plasma- enhanced chemical vapor deposition (PECVD) and plasma-based etching. Processing tool 1000 comprises a processing chamber 1002 and a substrate support 1004 within the processing chamber. The substrate support 1004 is configured to support a substrate 1006 disposed within processing chamber 1002. The substrate support 1004 comprises a substrate heater 1008. In other examples, a heater can be omitted, or can be located elsewhere within processing chamber 1002. The processing tool 1000 further comprises a showerhead 1010 for introducing processing chemicals into the processing chamber. In some examples, the processing tool 1000 comprises a heater configured to heat showerhead 1010.

[0114] The processing tool 1000 further comprises flow control hardware 1014. The flow control hardware 1014 connects processing chemical source(s) to the processing chamber. In the depicted example, the flow control hardware 1014 connects a carbon-containing film precursor source 1016, an optional etch stop layer precursor source 1018, an optional inert gas source 1020, and an etching agent source 1022 to the processing chamber. The flow control hardware 1014 can include any suitable components. Examples include mass flow controllers, valves, and conduits. For example, the flow control hardware 1014 can comprise one or more valves controllable to place a selected gas source or selected gas sources in fluid connection with showerhead 1010. The flow control hardware 1014 also can comprise one or more mass flow controllers or other controllers for controlling a mass flow rate of gas.

[0115] The carbon-containing film precursor source 1016 comprises any suitable precursor compound(s) for forming a lower-density carbon film. In some examples, a same precursor compound also can be used for forming a higher-density carbon film. In some examples, the carbon-containing film precursor source 1016 can further comprise a different precursor compound for forming a higher-density carbonfilm. Examples of carbon-containing film precursors include alkanes having a general formula CnH2n+2 where n is an integer in a range of 1 to 10 (such as, methane, ethane, etc.), alkenes having a general formula CnEEn where n = 2 to 10 (such as, ethylene, propylene, etc.), and alkynes having a general formula CnH2n-2 where n = 2 to 10 (such as, acetylene, propyne, etc.), that are gas-phase under processing conditions. Other examples of carbon-containing film precursors comprise cyclic hydrocarbons including aromatics, nitrogen-containing compounds including alkyl amines, and oxygencontaining compounds including alcohols, ketones, esters, aldehydes, and ethers that are gas-phase under processing conditions, alkanes, alkenes, alkynes, cyclic hydrocarbons, aromatics, alcohols, aldehydes, esters, ethers, ketones, aldehydes, alkyl halides, alkyl amines, and alkyl diamines.

[0116] The optional etch stop layer precursor source 1018 comprises any suitable precursor compound for forming an etch stop layer. Etch stop layer precursor source 1018 is optional, as carbon deposited using carbon-containing film precursor source 1016 optionally can be used to deposit higher-density carbon and / or densified carbon. Examples of etch stop layers include molybdenum, aluminum oxide tungsten, tungsten doped carbon, titanium nitride, and silicon oxide. Examples of etch stop film precursors include molybdenum-containing precursors, aluminum-containing precursors, tungsten-containing film precursors, titanium-containing film precursors, and silicon-containing film precursors. Examples of molybdenum-containing precursors for forming molybdenum films include bis(tert- butylimino)bis(dimethylamino) molybdenum (C12H30M0N4), molybdenum pentachloride (M0CI5), molybdenum dioxide dichloride (MOO2CI2), molybdenum oxytetrachloride (MoOCh), and molybdenum hexacarbonyl (Mo(CO)e). Examples of aluminum-containing precursors for forming aluminum oxide films include aluminum halides (AlXy), aluminum alkoxide (C9H21AIO3), trimethyl aluminum (AIC3H9), aluminum carbonyl (Al(CO)x), and aluminum hydride (AIH3). Examples of tungsten- containing precursors for forming tungsten-containing films include tungsten hexafluoride (WFe), tungsten hexachloride (WCk), bis(tert- butylimino)bis(dimethylamino) tungsten (C12H30N4W), and tungsten hexacarbonyl (W(CO)e). Examples of carbon-containing film precursors for forming tungsten-doped carbon films include those listed above. Examples of titanium-containing precursors for forming titanium-containing films include titanium tetrachloride (TCI4) and titanium isopropoxide (Ti(OCH(CH3)2)4). Examples of nitrogen-containing precursorsfor forming titanium nitride films include nitrogen (N2) and ammonia (NH3). Example silicon-containing film precursors include silane and polysilanes, trisilylamine, alkoxysilanes, siloxanes, aminosilanes, and halosilanes. Further examples of silicon- containing film precursors include tetraethyl orthosilicate (TEOS), tetramethoxysilane (TMOS), methylsilane, trimethylsilane (3MS), ethylsilane, butasilanes, pentasilanes, octasilanes, heptasilane, hexasilane, cyclobutasilane, cycloheptasilane, cyclohexasilane, cyclooctasilane, cyclopentasilane, 1, 4-dioxa-2, 3,5,6- tetrasilacyclohexane, diethoxymethylsilane (DEMS), diethoxysilane (DES), dimethoxymethylsilane, dimethoxysilane (DMOS), methyl-diethoxysilane (MDES), methyl-dimethoxysilane (MDMS), t-butoxydisilane, triethoxysilane (TES), and trimethoxysilane (TMS or TriMOS).

[0117] The optional inert gas source 1020 comprises any suitable inert gas. Examples include argon, helium, neon, krypton, and xenon. In some examples, inert gas source 1020 comprises a helium source 1021 for use in a helium-based densification step. In some examples, inert gas source additionally or alternatively comprises an inert gas for use in sputtering. In some examples, using a heavier inert gas, such as Ar, Kr, or Xe, can help increase a sputtering rate of overburden material of an etch stop layer compared to use of a lighter inert gas, such as He or Ne.

[0118] The etching agent source 1022 can comprise any suitable etching agent gas. Example oxygen-based etching agents include molecular oxygen (O2), carbon dioxide (CO2), and nitrous oxide (N2O). Example hydrogen-based etching agents include molecular hydrogen (H2) and ammonia (NH3).

[0119] The processing tool 1000 further comprises an exhaust system 1032. The exhaust system 1032 is configured to exhaust gases from the processing chamber 1002. The exhaust system 1032 can comprise any suitable hardware, including one or more low vacuum pumps, one or more high vacuum pumps, and one or more valves for controlling an exhaust flow. Together, flow control hardware 1014 and exhaust system 1032 can be operated to achieve a selected pressure in processing chamber 1002 during substrate processing. Example pressures include pressures of 1 Torr to 20 Torr. Further, exhaust system 1032 can be operated to purge processing chamber 1002.

[0120] The processing tool 1000 further comprises a radiofrequency power source 1034 that is electrically connected to showerhead 1010. Radiofrequency power source 1034 is configured to form a plasma using a gas mixture.

[0121] For example, during a deposition step, radiofrequency power source 1034 can be operated to form a plasma using a gas mixture comprising one or more of film precursors to deposit a film (e.g., a lower-density carbon film, a higher-density carbon film, or an etch stop layer). Further, during an etching step, radiofrequency power source 1034 can be operated to form a plasma using an etching agent to etch a portion of a lower-density carbon film. Further, during a densification step, radiofrequency power source 1034 can be operated to form a plasma using helium to densify a layer of lower-density carbon film and form a layer of densified carbon film.

[0122] Radiofrequency power can be supplied to the showerhead electrode or substrate holder electrode in various examples. As shown in FIG. 10, the radiofrequency energy is provided to substrate support 1004, and showerhead 1010 is configured as a grounded opposing electrode. In other examples, the radiofrequency power source 1034 can supply radiofrequency power to showerhead 1010, and substrate support 1004 can be grounded. In the depicted example, a capacitively coupled plasma can be formed in processing chamber 1002 between showerhead 1010 and substrate support 1004. In other examples, an inductively coupled plasma can be used.

[0123] The processing tool 1000 further includes include a matching network 1036 for impedance matching of the radiofrequency power source 1034. The radiofrequency power source 1034 can be configured to provide radiofrequency energy of any suitable frequency and power. Examples frequencies include 400 kHz, 13.56 MHz, 27 MHz, 60 MHz, and 100 MHz. In some examples, the radiofrequency power source 1034 is configured to operate at a plurality of different frequencies and / or powers. For example, as described above, a plasma can comprise a LF component and a HF component. Examples of frequencies for the LF radiofrequency energy component can include frequencies of 3 MHz and below. The LF radiofrequency energy component can comprise a power of 0 to 3000 W, in some examples. Further, the HF radiofrequency energy component can comprise frequencies of 3 MHz to 300 MHz. The HF radiofrequency energy component can comprise a power of 50 W to 6000 W, in some examples.

[0124] The processing tool 1000 further comprises a controller 1050 configured to control operation of the processing tool. The controller 1050 is operatively coupled to the substrate heater 1008, the flow control hardware 1014, the exhaust system 1032, and the radiofrequency power source 1034. The controller 1050 is configured to control various functions of processing tool 1000 to perform deposition steps, etching steps,and densification steps. For example, the controller 1050 is configured to control processing tool 1000 to operate the substrate heater 1008 to heat a substrate to a desired temperature. Examples include temperatures of 50 °C to 650 °C. The controller 1050 also is configured to operate the flow control hardware 1014 to flow a selected gas or mixture of gases at a selected rate into the processing chamber 1002. The controller 1050 is further configured to operate the exhaust system 1032 to remove gases from processing chamber 1002. The controller 1050 can, for example, control the exhaust system 1032 and / or the flow control hardware 1014 to purge the processing chamber 1002. The controller 1050 is configured to operate the radiofrequency power source 1034 to form a plasma, as well as to control any other suitable functions of processing tool 1000.

[0125] FIG. 11 schematically shows an example etching tool 1100 configured to perform cryogenic dry etching processes, also referred to as reduced temperature etching processes herein. Etching tool 1100 comprises a processing chamber 1102 and a substrate support 1104 within the processing chamber. Substrate support 1104 is configured to support a substrate 1106 disposed within processing chamber 1102. Substrate support 1104 can comprise a pedestal, a chuck, and / or any other suitable structure.

[0126] Etching tool 1100 further comprises a gas inlet 1112 and flow control hardware 1114. Flow control hardware 1114 is connected to an etchant agent source 1116 and an inert gas source 1120. Etchant agent source 1116 can comprise any suitable etchant agent. Examples of etching agents include hydrogen fluoride (HF), nitrogen trifluoride (NF3), and perfluoroalkanes, such as carbon tetrafluoride (CF4) and hexafluoroethane (C2F6). In some examples, etchant agent source 1116 comprises a phosphorus halide source 1118. Examples of phosphorus halides include phosphorus trifluoride (PF3) and phosphorus pentafluoride (PFs). Further examples of etching agents include oxygen-based etching agents and hydrogen-based etching agents. Example oxygen-based etching agents include molecular oxygen (O2), carbon dioxide (CO2), and nitrous oxide (N2O). Example hydrogen-based etching agents include molecular hydrogen (H2) and ammonia (NH3). In some examples, a combination of two or more etching agents can be used.

[0127] Inert gas source 1120 can comprise any suitable inert gas, such as one or more of helium, neon, argon, krypton, xenon, or nitrogen.

[0128] Flow control hardware 1114 can be controlled to flow gas from etchant agent source 1116 and inert gas source 1120 into processing chamber 1102 via gas inlet 1112. Flow control hardware 1114 can comprise one or more valves controllable to place a selected gas source in fluid connection with gas inlet 1112.

[0129] Etching tool 1100 further comprises an exhaust system 1124. Exhaust system 1124 is configured to receive gas outflowing from processing chamber 1102. In some examples, exhaust system 1124 is configured to actively remove gas from processing chamber 1102 and / or apply a partial vacuum. Exhaust system 1124 can comprise any suitable hardware, including one or pumps.

[0130] Etching tool 1100 further comprises a radiofrequency power source 1128 that is electrically connected to substrate support 1104. Thus, substrate support 1104 forms a first electrode. Etching tool 1100 further comprises a second electrode 1130. Radiofrequency power source 1128 is configured to form a plasma comprising the etchant gas. Etching tool 1100 can include a matching network 1129 for impedance matching of the radiofrequency power source 1128. The plasma also can comprise an inert diluent gas from inert gas source 1120. Radiofrequency power source 1128 can be configured for any suitable frequency and power. In some examples, radiofrequency power source 1128 is configured to operate at a plurality of different frequencies and / or powers.

[0131] Etching tool 1100 further comprises a chiller 1140 configured to circulate a coolant through substrate support 1104 to cool a substrate for a reduced temperature etching process. In some examples, the substrate is cooled to a temperature of 0° C or below. In some examples, the chiller can cool the substrate to a substrate temperature within a range of -60 °C to -10 °C. In other examples, substrate temperatures outside this range can be used.

[0132] Controller 1150 is operatively coupled to flow control hardware 1114, exhaust system 1124, radiofrequency power source 1128, and chiller 1140. Controller 1150 is configured to control various functions of processing tool 1100, such as operating chiller 1140 to cool to a desired temperature, operating flow control hardware 1114 to flow selected gases into processing chamber 1102, operating exhaust system 1124, and / or operating radiofrequency power source 1128 to form a plasma. Controller 1150 can comprise any suitable computing system, examples of which are described below with reference to FIG. 12.

[0133] FIG. 12 schematically shows a non-limiting example of a computing system 1200 that can enact one or more of the methods and processes described above. Computing system 1200 is shown in simplified form. Computing system 1200 can take the form of one or more personal computers, workstations, computers integrated with substrate processing tools, and / or network accessible server computers.

[0134] Computing system 1200 includes a logic subsystem 1202 and a storage subsystem 1204. Computing system 1200 can optionally include a display subsystem 1206, input subsystem 1208, communication subsystem 1210, and / or other components not shown in FIG. 12. Controller 1050 and controller 1150 is an example of computing system 1200.

[0135] Logic subsystem 1202 includes one or more physical devices configured to execute instructions. For example, the logic machine 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.

[0136] The logic machine can include one or more processors configured to execute software instructions. Additionally or alternatively, the logic machine can include one or more hardware or firmware logic machines configured to execute hardware or firmware instructions. Processors of the logic machine 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 machine 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 machine can be virtualized and executed by remotely accessible, networked computing devices configured in a cloud-computing configuration.

[0137] Storage subsystem 1204 includes one or more physical devices configured to hold instructions 1212 executable by the logic machine to implement the methods and processes described herein. When such methods and processes are implemented, the state of storage subsystem 1204 can be transformed — e.g., to hold different data.

[0138] Storage subsystem 1204 can include removable and / or built-in devices. Storage subsystem 1204 can include optical memory (e.g., CD, DVD, HD-DVD, Blu-Ray Disc, etc.), semiconductor memory (e.g., RAM, EPROM, EEPROM, etc.), and / or magnetic memory (e.g., hard-disk drive, floppy-disk drive, tape drive, MRAM, etc.), among others. Storage subsystem 1204 can include volatile, nonvolatile, dynamic, static, read / write, read-only, random-access, sequential-access, location-addressable, file-addressable, and / or content-addressable devices.

[0139] It will be appreciated that storage subsystem 1204 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.

[0140] Aspects of logic subsystem 1202 and storage subsystem 1204 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 applicationspecific standard products (PSSP / ASSPs), system-on-a-chip (SOC), and complex programmable logic devices (CPLDs), for example.

[0141] When included, display subsystem 1206 can be used to present a visual representation of data held by storage subsystem 1204. 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 machine, and thus transform the state of the storage machine, the state of display subsystem 1206 can likewise be transformed to visually represent changes in the underlying data. Display subsystem 1206 can include one or more display devices utilizing virtually any type of technology. Such display devices can be combined with logic subsystem 1202 and / or storage subsystem 1204 in a shared enclosure, or such display devices can be peripheral display devices.

[0142] When included, input subsystem 1208 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.

[0143] When included, communication subsystem 1210 can be configured to communicatively couple computing system 1200 with one or more other computingdevices. Communication subsystem 1210 can include wired and / or wireless communication devices compatible with one or more different communication protocols. As non-limiting examples, the communication subsystem 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 1200 to send and / or receive messages to and / or from other devices via a network such as the Internet.

[0144] 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.

[0145] 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 filling a gap on a substrate, the method comprising: in a first deposition step, depositing a lower-density carbon film in the gap; in an etching step after the first deposition step, etching a portion of the lower- density carbon film to form a carbon shelf within the gap; and in a second deposition step after the etching step, depositing an etch stop layer over the carbon shelf.

2. The method of claim 1, wherein the gap comprises an aspect ratio of 5: 1 to 60: 1.

3. The method of claim 1, wherein a portion of the gap above the carbon shelf comprises an aspect ratio of 1 :4 to 4: 1.

4. The method of claim 1, wherein etching the portion of the lower-density carbon film comprises forming a plasma using an etching agent comprising one or more of molecular hydrogen, ammonia, molecular oxygen, carbon dioxide, or nitrous oxide.

5. The method of claim 1, wherein the lower-density carbon film comprises a density less than 1.5 g / cm3.

6. The method of claim 1, wherein the etch stop layer comprises a higher-density carbon film comprising a density of 1.5 g / cm3or greater or a densified carbon film.

7. The method of claim 1, wherein the etch stop layer comprises one of molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, or silicon oxide.

8. The method of claim 1, wherein depositing the lower-density carbon film comprises forming a plasma using radiofrequency energy comprising a higher- frequency component within a range of 3 MHz to 300 MHz, and omitting radiofrequency energy at frequencies below 3 MHz.

9. The method of claim 8, wherein depositing the etch stop layer comprises forming a directional plasma using radiofrequency energy comprising a lower-frequency component at a frequency below 3 MHz and the higher-frequency component.

10. The method of claim 1, further comprising, in a third deposition step after the second deposition step, depositing a second lower-density carbon film over the etch stop layer, and, in a planarization step after the third deposition step, removing the etch stop layer from field regions of the substrate.

11. The method of claim 1, further comprising depositing a plurality of alternating material layers onto the substrate, and cryo-etching through the plurality of alternating material layers to the etch stop layer.

12. The method of claim 1, further comprising, prior to the first deposition step, cooling the substrate and performing a reduced temperature etch to form the gap.

13. A method of filling a gap on a substrate, the method comprising: in a first deposition step, depositing a lower-density carbon film in the gap; in an etching step after the first deposition step, etching a portion of the lower- density carbon film to form a carbon shelf in the gap; and in a second deposition step, performing one or more deposition cycles to deposit a densified carbon film over the carbon shelf, each deposition cycle of the one or more deposition cycles comprising: depositing a layer of lower-density carbon film in the gap, and forming a plasma using one or more of helium, neon, argon, or nitrogen to densify the layer of lower-density carbon film, thereby forming a layer of densified carbon film.

14. The method of claim 13, wherein a portion of the gap above the carbon shelf comprises an aspect ratio of 1 :4 to 4: 1.

15. The method of claim 13, wherein the lower-density carbon film comprises a density less than 1.5 g / cm3and the densified carbon film comprises a density of 1.5 g / cm3or greater.

16. The method of claim 13, wherein depositing the lower-density carbon film comprises forming a plasma using radiofrequency energy comprising a higher- frequency component within a range of 3 MHz to 300 MHz, and omitting radiofrequency energy at frequencies below 3 MHz.

17. A processing tool for processing a substrate, the processing tool comprising: a processing chamber; a substrate support; flow control hardware configured to control processing chemical flow into the processing chamber; a radiofrequency power source configured to provide radiofrequency power to form a plasma in the processing chamber; and a controller operatively coupled to the flow control hardware and the radiofrequency power source, the controller being configured to in a first deposition step, operate the flow control hardware and the radiofrequency power source to deposit a lower-density carbon film in a gap on a substrate; in an etching step after the first deposition step, operate the flow control hardware and the radiofrequency power source to etch a portion of the lower-density carbon film to form a carbon shelf within the gap; and in a second deposition step after the etching step, operate the flow control hardware and the radiofrequency power source to deposit an etch stop layer over the carbon shelf.

18. The processing tool of claim 17, wherein the controller is configured to, in the second deposition step, operate the flow control hardware and the radiofrequency power source to form a higher-density carbon film as the etch stop layer.

19. The processing tool of claim 17, wherein the controller is further configured to, in the second deposition step, operate the flow control hardware and the radiofrequency power source to: deposit a layer of lower-density carbon film over the carbon shelf, and form a plasma using helium to densify the layer of lower-density carbon film, thereby forming a layer of densified carbon film as the etch stop layer.

20. The processing tool of claim 17, wherein the controller is configured to, in the second deposition step, operate the flow control hardware to flow an etch stop film precursor and operate the radiofrequency power source to convert the etch stop film precursor into the etch stop layer, the etch stop layer comprising one of molybdenum, aluminum oxide, tungsten, tungsten doped carbon, titanium nitride, or silicon oxide.

21. A method of filling a gap on a substrate, the method comprising: in a deposition step, depositing an etch stop layer over a carbon shelf located within the gap; and in a planarization step after the deposition step, removing the etch stop layer from field regions of the substrate.

22. The method of claim 21, further comprising depositing a lower-density carbon film over the etch stop layer prior to the planarization step.

23. The method of claim 21, wherein the planarization step comprises sputtering the etch stop layer.

24. The method of claim 21, wherein the planarization step comprises performing chemical mechanical polishing.

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