Plasma etch chemistries for high aspect ratio features in dielectrics

Abstract

To provide a method for etching features in a stack beneath a patterned mask in an etch chamber.SOLUTION: A method of forming a semiconductor device on a semiconductor wafer, a stack in a chamber is cooled with a coolant having a coolant temperature below -20°C, an etching gas is flowed into the etching chamber, a plasma is generated from the etching gas, and a feature is etched into the stack selectively with respect to a patterned mask.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 644,095, filed March 16, 2018, which is incorporated herein by reference for all purposes.

[0002] The present disclosure relates to a method for forming a semiconductor device on a semiconductor wafer. [Background technology]

[0003] For example, in the formation of semiconductor devices, etching layers may be etched to form memory holes or lines or other semiconductor features. Some semiconductor devices may be formed by etching a single silicon dioxide (SiO) stack, for example to form a capacitor in a dynamic access random memory (DRAM). Other semiconductor devices may be formed by etching a bilayer (ONON) of alternating silicon dioxide (oxide) and silicon nitride (nitride) or a stack of bilayers of alternating silicon dioxide and polysilicon. Such stacks may be used in memory applications and three-dimensional "not and" gates (3D NAND). The background art description provided herein is intended to provide a general background for the present disclosure. These stacks tend to require relatively high aspect ratio (HAR) etching of the dielectric. For high aspect ratio etches, examples of desirable etching characteristics are high etch selectivity to the mask (such as an amorphous carbon mask), low sidewall etching with a straight profile, and high etch rate at the etch front. The work of the inventors named herein, to the extent described in this Background, along with aspects of the description that would not ordinarily be considered prior art at the time of filing, are not admitted, expressly or impliedly, as prior art to the present disclosure. Summary of the Invention

[0004] To achieve the above and in accordance with the objectives of the present disclosure, a method is provided for etching features in a stack beneath a patterned mask in an etch chamber. The stack is cooled with a coolant having a coolant temperature below -20°C. An etch gas is flowed into the etch chamber. A plasma is generated from the etch gas. Features are etched into the stack selectively to the patterned mask.

[0005] These and other features of the present disclosure are set forth in the detailed description that follows, taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0006] The present disclosure is illustrated by way of example, and not by way of limitation, in the accompanying drawings, in which like elements are numbered like elements and in which:

[0007] [Figure 1] 1 is a high level flow chart of one embodiment.

[0008] [Diagram 2] FIG. 1 is a schematic diagram illustrating an etching chamber that can be used in one embodiment.

[0009] [Diagram 3] FIG. 1 is a schematic diagram illustrating a computer system that can be used to practice one embodiment.

[0010] [Figure 4A] 1A-1C are schematic cross-sectional views of a stack processed according to one embodiment. [Figure 4B] 1A-1C are schematic cross-sectional views of a stack processed according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present disclosure will be described in detail below with reference to some preferred embodiments illustrated in the accompanying drawings. In the following description, numerous specific details are set forth to facilitate a thorough understanding of the present disclosure. However, it will be apparent to those skilled in the art that the present disclosure can be practiced without some or all of these specific details. Additionally, detailed descriptions of well-known process steps and / or structures are omitted to avoid unnecessarily obscuring the present disclosure.

[0012] FIG. 1 is a high level flow chart of one embodiment. In this embodiment, a stack is placed in an etch chamber (step 104). The stack is placed below a patterned mask. The stack has at least one dielectric layer. The stack is cooled by a cryogenic coolant (step 108). An etch gas is provided by flowing the etch gas into the etch chamber (step 112). The etch gas is turned into an etch plasma (step 116). The stack is exposed to the plasma (step 120). A bias is provided to accelerate ions from the plasma towards the stack (step 124). The stack is etched by the etch plasma selectively to the patterned mask (step 128). The stack is removed from the etch chamber (step 132).

[0013] Etching high aspect ratio structures through semiconductor materials, such as silicon dioxide, is also commonly required to fabricate semiconductor devices. High aspect ratio etching requires directional (anisotropic) etching, which is distinct from isotropic etching. Typically, directional etching is accomplished with ions in a plasma that are accelerated perpendicular to the wafer surface. For example, a bias of 10 to 5000 electron volts (eV) is applied to accelerate ions present in the plasma toward the wafer surface. The ions provide the plasma etching.

[0014] In this specification and claims, the term cryogenic refers to a "cold" substrate temperature. The term "cold" in conventional etching means -20°C or below. The history of cryogenic etching dates back to 1988 and has been most extensively studied for silicon materials. In silicon high aspect ratio etching, it is important to control the tendency for sidewall chemical etching to maintain directionality. Chemical etching is a process in which chemicals chemisorb onto a surface and spontaneously form new species with the surface that desorb at hot surface temperatures. For example, fluorine spontaneously reacts with silicon surfaces to form silicon tetrafluoride (SiF4) at room temperature. This is problematic for directional etching because chemical etching is isotropic. In other words, the chemicals in the plasma are isotropic and land on the surface based on line of sight. This chemical etching can cause lateral etching, thus compromising the directionality of the high aspect ratio etch. In silicon high aspect ratio etching, this has been managed using the Bosch process or cryo-etching, but it would inhibit the chemical etching. The most common approach for etching high aspect ratio structures and silicon is to use the Bosch process, which alternates between etch chemistries and deposition chemistries to protect the sidewalls. This type of etch is usually performed at moderate temperatures (typically between -20°C and 100°C). The purpose of the deposition chemistries is to protect the sidewalls.

[0015] The reason for using cryogenic temperatures is that the natural chemical etching of the sidewalls is suppressed, thereby eliminating the need for deposition chemicals used in the Bosch process. Such cryogenic processes have not generally been pursued due to the difficulty of maintaining the substrate surface at cryogenic temperatures during processing.

[0016] In the literature for high aspect ratio etching of silicon, the typical chemistries utilized are sulfur hexafluoride (SF6) and oxygen (O2), where fluorine is the reactant to remove silicon as SiF4 or silicon difluoride (SiF2), and sulfur and oxygen provide some protection of the sidewall that evaporates when the wafer is returned to room temperature. Ion etching is the primary etching process in cryogenic etching. Although fluorocarbons are used in the deposition step of the Bosch process, fluorocarbons are typically not utilized at cryogenic temperatures for silicon because silicon and carbon form very hard silicon carbide that impedes etching. At the etch front, the silicon carbide impedes etching, but is eventually broken by ion bombardment. Another advantage of cryogenic etching of silicon (Si) is that the sidewall protection does not need to be as strong. Cryogenic etching of silicon can help speed up the etch rate by reducing the amount of deposition needed to protect the sidewall.

[0017] Etching dielectrics can be different from etching silicon. For example, silicon tends to be chemically etched, meaning that a chemical reaction occurs spontaneously to desorb silicon by-products (such as SiF4 or SiCl2). Silicon nitride (SiN) can also be chemically etched with nitrogen trifluoride (NF3), but in contrast, silicon dioxide is typically not etched spontaneously. Instead, etching of silicon dioxide is ion-induced with a reactant to accelerate desorption. Additionally, dielectrics such as oxides and nitrides contain silicon and another element (such as oxygen or nitrogen) in the lattice. Silicon is spontaneously etched with halogens (such as fluorine, chlorine, or bromine), but oxygen does not readily form stable volatile species with halogens alone. At room temperature, removal of oxygen in oxides results in the formation of carbon, which forms carbon monoxide (CO) or carbon dioxide (CO2) volatile compounds, or hydrogen (H), which forms water (H2O), or volatile B. x Cl z O yThis is aided by the presence of boron chloride (BCl3) forming a compound or sulfur oxide (SO) forming sulfur dioxide (SO2). In the case of nitrogen (N), fluorine can remove N as NF3 or with H as ammonia (NH3). More specifically: for etching silicon components at cryogenic temperatures, halogens (such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I)) can be used to etch silicon components. For etching oxygen components in silicon oxide at cryogenic temperatures, carbon (C), boron (B), hydrogen (H), sulfur (S), and nitrogen are effective for etching oxygen components. For etching nitrogen components in silicon nitride at cryogenic temperatures, H and F can be used for etching nitrogen components. It has also been found that C, H, oxygen (O), silicon (Si), F, and S can be used as passivation agents at cryogenic temperatures. Therefore, the chemistries required to etch dielectric layers at cryogenic temperatures may be different from those used for silicon.

[0018] In typical chemistries for etching dielectrics at room temperature, fluorocarbons (such as octafluorocyclobutane (C4F8) and / or hexafluoro-2-butyne (C4F6)) are typically utilized. C4F8 and / or C4F6 fragment in the plasma to form fluorocarbon polymers that can passivate the sidewalls and protect the mask. Meanwhile, at the etch front, as long as the polymer is not too dense, ions incident on the etch front will etch the oxide with carbon and fluorine. For example, carbon combines with oxygen to form CO and CO2. Fluorine combines with silicon to form SiF4, SiF2 volatile compounds. The sidewalls are not affected by the incident ions and the polymer still protects the sidewalls. In 3D NAND applications for etching stacks of oxide and nitride layers, typical plasma process chemistries are C4F8, C4F6, O2, and fluoromethane (CH3F). The C4F8 and C4F6 gases fragment in the plasma to produce polymerized fluorocarbons. The carbon and fluorine at the etch front are reactants. O2 is added as an effective knob to adjust and control the polymer to maintain the top of the feature opening. CH3F assists in the nitride etch by providing a H source and a fluorocarbon. Thus, compared to room temperature silicon etching, for dielectric etching there is typically not only a halogen source utilized as a reactant, but also a carbon and hydrogen source.

[0019] However, etching at room temperature requires a trade-off between etch rate and selectivity and / or sidewall profile. If the etch rate is high with lean fluorocarbon polymer deposition, the sidewalls and mask may not be sufficiently protected, resulting in bowing on the sidewalls. On the other hand, if the fluorocarbon polymer deposition is increased to protect the sidewalls and mask, the etch rate is hindered and slowed. Pinch-off of deposition at the top of the feature may also occur. Cryogenic etching offers an opportunity to break some of this trade-off in dielectric etching.

[0020] Despite the vast amount of research on high aspect ratio etching of silicon at cryogenic temperatures, comparatively little research has been done on high aspect ratio etching of dielectrics. As the surface temperature decreases, there are four main principles that provide various embodiments with different chemistries for etching dielectrics at cryogenic temperatures:

[0021] First principle: Similar to high aspect ratio silicon etching, spontaneous chemical etching of dielectrics can also be suppressed. However, this principle is different for oxide etching compared to silicon etching. This difference is because oxide etching does not tend to be chemically etched. Instead, oxide etching is known to be an ion-induced process since it requires ion energy for desorption to proceed. Etching with ion energy can provide vertical etching by deflection of ions that reach the sidewall. However, nitrogen is rather close to silicon and can be chemically etched. Cryogenic temperatures preferably help to reduce lateral etching of SiN. Thus, cryogenic temperatures can help to reduce chemical etching in dielectric high aspect ratio etches. However, unlike the silicon case, reduced chemical etching is not the most important principle of cryogenic etching. The extent to which cryogenic temperatures are important for high aspect ratio dielectric etches is due to the following: For polymer sidewall passivation, leaner fluorocarbon or fluorohydrocarbon (or combination of fluorocarbon and hydrogen) etch chemistries are possible due to the reduced amount of passivation required. Lean etch chemistries have a low percentage of polymeric components such as carbon. For example, in non-cryogenic etch processes, C4F6 and C4F8 may be used in the etch gas as passivators. At cryogenic temperatures, carbon tetrafluoride (CF4) is used as a passivator. Other examples of lean chemistries are fluoromethane (CHF3), CH3F, carbon tetrachloride (CCl4), trifluoroiodomethane (CF3I), dibromodifluoromethane (CBr2F2), pentafluoroethane (C2HF5), and C2F5Br. These chemistries may be combined with each other or may be supplemented with one or more of hydrogen (H2) or O2, or H2O, hydrogen peroxide (H2O2). In addition to C-containing chemistries that etch dielectrics, other non-C-containing chemistries are also known to passivate and may be effective at cryogenic temperatures since the passivation does not need to be strong. BCl3 may be included as it has passivating properties and can be effective at cryogenic temperatures.BCl3 is not a conventional etchant for oxides at room temperature because boron trioxide (B2O3) blocks the etch. It is believed that BCl3 may function as an etchant component at cryogenic temperatures because there may be less blocking at cryogenic temperatures. Other passivating components may be chromyl chloride (CrO2Cl2), silicon tetrachloride (SiCl4), thionyl chloride (SOCl2), titanium dichloride (TiCl2), titanium trichloride (TiCl3), and phosgene (CoCl2). The lean chemistry in this example has a low carbon to fluorine ratio.

[0022] Second principle: As the surface temperature is reduced, the sticking coefficient increases. The sticking coefficient is a measure of how long a molecule will physisorb to a surface before re-entering the gas phase. In other words, at lower temperatures, molecules will stick to the surface longer, following the Arrhenius law, such that the sticking time is inversely proportional to the surface temperature. This temperature dependence will have an even more pronounced effect at cryogenic temperatures. The consequences of this temperature dependence of the sticking coefficient are very important in determining where and how much reactants and inhibitors (i.e., deposits) will occur at various locations on a feature. In particular, the deposition rate of fluorocarbon polymers is strongly dependent on the sticking coefficient. Fluorocarbon polymer deposition is driven by the presence of C in the plasma, which tends to crosslink. x F y This is driven by the seeds. Roughly speaking, the larger the seeds and the higher the carbon content in them, the more likely they are to form polymers. Among the fragments formed by the C4F6 gas in the plasma, C4F6, C4F5, trifluoroarene (C3F4), 1,2,3,3,3-pentafluoroprop-1-ene (C3F5), trifluorovinyl (C2F3), and C3F2 tend to crosslink and form polymers. The lower the temperature, the longer these molecules will attach to the surface, increasing the deposition rate. Also, the lower temperature means that most of the deposition will occur at the top of the feature. The polymer will accumulate in the opening and cannot move down along the sidewalls at the very low temperatures.

[0023] One consequence of the second principle is that gases for cryogenic etching of dielectrics are selected to be less polymerizing. In one embodiment, the gas mixture includes carbon. For carbon-containing gases, this principle presents CF4 as an example. CF4 is not a typical gas for dielectric etching at high aspect ratios. However, at cryogenic temperatures, CF4 may work well because it has a leaner C:F ratio and is less likely to block the top of the feature. At the same time, the use of CF4 is preferable to provide some protection to the sidewalls. Another example of a leaner chemistry is the use of CHF3 for oxide etching or CHF3 and N2 for nitride etching. Another example may include CF4 and N2 for nitride etching. Also, CH2F2 and CH3F and CCL4 and carbonyl sulfide (COS), CO, CO2, methylene chloride (CH2Cl2), methane (CH4), CF3I, chloroform (CHCl3) may be used as etchants. Other gases may be added or combined with these gas mixtures to facilitate etching with nitrides, such as N-containing gases (such as NH3), hydrogen sulfide (H2S), silane (SiH4), disilane (SiH6), propene (C3H6), nitric oxide (N2O), H2O2, nitric acid (HNO3), and O2 to adjust the deposition that occurs. Thus, for example, some possible gas mixture recipes may be a mixture of CF4, O2, and N2, or a mixture of CF4, CHF3, and O2, or a mixture of CF4, COS, and N2, or a mixture of CF4 and CO, or a mixture of CF4 and CH4, and all other permutations. Thus, since both oxygen and nitrogen may be desired, it may also be possible to use non-traditional reactants for etching dielectrics, such as H2O in a combination of CF4 and H2O. Since HO is not normally a gas at room temperature, some hardware modifications may be required to accommodate the input of HO. None of these combinations mentioned above can typically be used to etch high aspect ratio dielectric structures, as they do not polymerize sufficiently at room temperature.However, at cryogenic temperatures, even these lean chemistries may provide some protection to the sidewalls, as they are more likely to condense on the surface at cryogenic temperatures, and therefore such chemistries that are normally considered etchants may also deposit or passivate the sidewalls at cryogenic temperatures.

[0024] Further, regarding the second principle: in the previous paragraph, we focused on leaner chemistries that contain carbon. However, at cryogenic temperatures, there is another group of chemistries that are available for sidewall passivation that are not typically used at room temperature, since at cryogenic temperatures, the gas is more likely to protect the sidewall, even if the gas does not contain carbon as a passivation. Since not much deposition is required, silicon with oxygen and / or nitrogen may be etched using the following halogen-containing chemical mixtures: BCl3 with chlorine (Cl2) or HBr, or Cl2 with N2 or CF4 or Br2 or COS or SiH4 as the H source for silicon nitride etching. In some embodiments, iodine may be used as the halogen. BCl3 is not typically used to etch dielectrics at room temperature, since it does not readily etch oxides at room temperature, since it forms a surface film of SiOBCl that blocks the etch. However, it has been found that at low temperatures, BCl3 deposition actually decreases at low temperatures. In this case, the BCl3 etch is caused by a slower reaction, not an increase in the sticking coefficient. As a result, BCl3 is normally deposited at room temperature but can be etched at cryogenic temperatures to produce volatile B x Cl y O z This is another example of a chemistry that may be suitable for etching at cryogenic temperatures but not at room temperature. Other chemistries in the BCl3 family may include MgCl2, PdCl2, and TiCl3.

[0025] The second principle provides another result. We mentioned above about the increase in the sticking coefficient at low temperatures. This means that molecules tend to stick to the top of the feature or to the etch front of the feature before going down the sidewall. However, if the molecule is small enough or does not deposit, it can reach the bottom of the feature. Specifically, for fluorocarbon deposition, it is known that the etching species (ions or molecules) tend to be F, fluorocarbon (CF), difluoromethane (CF2). These species are small enough not to polymerize and instead are more likely to etch if they reach the surface. In the inverse reactive ion etching (RIE) lag phenomenon, where high aspect ratio features etch faster and faster than low aspect ratio features, it is known that the high aspect ratio acts as a kind of filter for small particles. Inverse RIE is caused by only small particles reaching the bottom of the feature. Inverse RIE can be useful to select both to increase the etch rate at the bottom by depositing less and to protect the mask at the top where the deposition of larger species occurs and forms the deposited film.

[0026] Implications of the second principle indicate that utilizing gases with high fluorine sources is advantageous for high aspect ratio dielectric etching. C4F6 and C4F8, typically used at room temperature, are not good F sources because very low concentrations of these gases fragment into small particles of F, CF, or CF2. Instead, at cryogenic temperatures, the larger species in C4F6 and C4F8 are likely to deposit at the top of the feature and block the etch without allowing any reactants to reach the bottom. Types of gases that fragment into F (radical) sources include those readily available in the laboratory: CF4, SF6, NF3, XeF2, tungsten hexafluoride (WF6), SiF4, tantalum pentafluoride (TaF5), iodine heptafluoride (IF7), hydrogen fluoride (HF) (either vapor or indirectly generated in the plasma). More commonly, metals charged to +5 or higher (such as metal halides) are more volatile and can be delivered to the surface via the plasma. Therefore, many pentafluorides tend to be gases and may be good candidates for F-generating plasmas. This class of pentafluoride gases further includes chlorine pentafluoride (ClF5), bromine pentafluoride (BrF5), arsenic pentafluoride (AsF5), nitrogen pentafluoride (NF5), phosphorus pentafluoride (PF5), niobium pentafluoride (NbF5), bismuth pentafluoride (BiF5), and uranium pentafluoride (UF5). The advantage of some of these (BiF5) is that they also form a polymer that can protect the sidewalls. This approach may also work with chlorine-containing species for the same reasons. Other options include SiCl2, CrO2Cl2, SiCl4, tantalum tetrachloride (TaCl4), hafnium tetrachloride (HfCl4), titanium chloride (TiCl3(l)), titanium tetrachloride (TiCl4(l)), and cobalt chloride (CoCl2(l)).

[0027] Some of these gases mentioned above are readily available but are rarely used in dielectric or any etching platforms as they are more commonly found in deposition platforms such as WF6, TiCl3 and TiCl2. In fact, some of them are known in etching as by-products rather than etching species. For example, WF6 is a by-product of etching tungsten (W) in SF6 or CF4 plasma. TiCl4, TaCl4 and HfCl4 are by-products of etching titanium (Ti), tantalum (Ta), titanium nitride (TiN) and tantalum nitride (TaN) or hafnium (Hf) in Cl2 or BCl3 plasma. Various embodiments use such gases as CF4, SF6, NF3, XeF2, WF6, SiF4, TaF5, IF7, HF, ClF5, BrF5, AsF5, NF5, PF5, NbF5, BiF5, UF5, WF6, TiCl3, and TiCl2 to provide high F or Cl species for dielectric etching. Cl species may be less effective. In particular, WF6, TaCl4, and HfCl4 may provide additional benefits since W, Ta, Hf, niobium (Nb), and rhenium (Re) are refractory metals known to be very hard. As mentioned above, the mask tends to be C. If a hard species is doped into the C, the mask can be strengthened. Thus, for example, W-doped C is harder than amorphous C. Therefore, if the etching process uses WF6, TaCl4, or HfCl4, W, Ta, or Hf is implanted into the mask. The implantation is preferred because it has the added advantage of hardening the mask and increasing the selectivity. F can be more effective than Cl or Br. The preferred etching gas is WF6 or TaF5. WF6 or TaF are both gases at room temperature and easy to insert into the plasma. In addition to the refractory metals, both B and C are also very hard and can harden or reharden the amorphous carbon mask. Therefore, CF4, boron trifluoride (BF3), and boron tribromide (BBr3) may be used as etchant component gases in various embodiments.For fluoride-generating etching gases, the preferred etching gases provide F radicals and are fairly large molecules. Therefore, hexafluorine is preferred over tetrafluorine. For example, WF6 and TaF5 are preferred over SiCl2. If these gases can remove O, they can be combined with C or H containing gases.

[0028] As mentioned above, some of these gases are used in deposition processes. These gases may deposit on the top of the feature, but not on the etch front at the bottom of the feature. In one embodiment, etching may be further enhanced by intentionally depositing on the top of the feature. For example, using etching gases of WF6 or TiCl4 or TaF5, metals can be deposited (rather than implanted / doped) on the mask on the top of the feature, as is done in ALD, for example, with chemistry of WF6 and H2 or chemistry of WF6 and SiH4. It is believed that the deposits will adhere to and deposit on the top of the feature, while only F and H will reach and etch the bottom of the feature. This is also a way to provide H as H2O or NH3, which can help etch O and N. In another example, Ta is deposited using TaF5. Ta is a very hard material, so it can be used to harden the mask. Ti may be deposited using TiCl4 with appropriate precursors.

[0029] The third principle is as follows: SiO2 etching at room temperature usually does not work with F alone, but also requires C, B, or H, but one embodiment etches SiO2 with F alone at cryogenic temperatures without the need for C, B, or H. The reason that F requires C, B, or H to etch SiO2 at room temperature is that fluoronium diolate (FO2) is volatile at room temperature (boiling point is -144°C). Oxygen difluoride (OF2) decomposes via a radical mechanism into oxygen and fluorine. In a plasma, this can happen even more rapidly. Thus, OF2 is not stable. One embodiment uses cryogenic temperatures to provide a stable OF2 vapor. Then, at cryogenic temperatures, SiO2 is etched with an F-containing gas without the addition of C, B, or H additives. It is also known that underexposure of plasma O2 is preferentially sputtered. Thus, the surface becomes more metallic. Thus, one embodiment etches SiO2 with a composition that includes a fluorine-containing etching gas (such as SF6) at cryogenic temperatures, but typically such gases are intended for silicon only and cannot etch SiO2.

[0030] The fourth principle is as follows: In another approach, it has been found that a non-cryogenic etchant has been unexpectedly found to be a passivator at cryogenic temperatures. For example, SF6 is used as an etchant in non-cryogenic processes. However, SF6 has been found to function like a passivator at cryogenic temperatures, rather than an etchant. Other molecules that do not provide passivation at non-cryogenic temperatures provide passivation at cryogenic temperatures. For example, as discussed above, water can be a passivating component at cryogenic temperatures. Amines and SO2 can also be utilized as passivators at cryogenic temperatures. CO2 has been found to be utilized as a passivator at cryogenic temperatures. CO2 can be a desirable passivator because it is less likely to form crystals and instead takes on more of a slurry form. Other passivators at cryogenic temperatures can be COS, CO, S from SF6, or SiF4.

[0031] Another embodiment provides for atomic layer etching (ALE) or atomic layer deposition (ALD) at cryogenic temperatures. In one embodiment of cryogenic ALE, a chemical reactant is provided as an atomic layer etch gas in step A, where step B provides thermal or ionic energy or another type of energy to desorb by-products. Specifically, cryogenic temperatures are used in step A of ALE to suppress any etching, since any etching that occurs in step A is non-ideal and undesirable. Many reactants then may adsorb but not etch at room temperature. There are quite a few reactants that will spontaneously etch at room temperature. The most well-known case of this is silicon in the presence of fluorine, which spontaneously forms SiF4 at room temperature. By using cryogenic temperatures, this reaction is suppressed. Various embodiments extend this approach. In one embodiment, tin oxide (SnO) spontaneously etches with H2 at room temperature, making it very difficult to convert this to an ALE process at room temperature. However, it is believed that by going to cryogenic temperatures, estimated at -70°C, this reaction is suppressed and the ALE process can be successful.

[0032] ALE can be advantageous for HAR, where in one embodiment the second step provides only argon. It is known that argon alone can actually strengthen an amorphous carbon film to be more diamond-like. Thus, the intermittent use of an argon-only plasma to strengthen the mask can be used in high aspect ratio etch processes. Such processes may be used in ALD in one embodiment.

[0033] Furthermore, it has been found that harder materials are more easily etched with ALE. By performing ALE at cryogenic temperatures, the cryogenic temperature effectively makes the material harder to etch without changing the surface bond energy of the material. This provides easier ALE onto the material. In one embodiment, the chemical reaction step A is performed at cryogenic temperatures to provide a modified layer, and the use of ionic energy for activation in step B is also performed at cryogenic temperatures to activate the modified layer. In another embodiment, the chemical reaction step A is performed at cryogenic temperatures and the activation step B is performed at higher temperatures (with ions) or even thermally, where heat is utilized as the energy source. In one embodiment, the substrate is moved between two different chambers for each step, such that step A is performed in a cryogenic chamber and step B is performed in a non-cryogenic chamber. In another embodiment, step A is performed at cryogenic temperatures and activation step B is performed under a heat lamp, where the heat lamp provides heat energy to the small space where heat energy is required.

[0034] In embodiments where cryogenic temperatures are used for ALD, a first precursor may be delivered as an atomic layer deposition gas and deposited at cryogenic temperatures during step A, and a second precursor may be deposited at cryogenic temperatures during step B. Typically, this is not done at cryogenic temperatures, since precursor adsorption usually requires elevated temperatures. However, if a plasma is used to increase the reactivity of the precursor, cryogenic temperatures can be used to avoid other thermally activated surface reactions. Potential condensation of the precursor on the substrate becomes an issue. Condensation is not self-limiting. Thus, the temperature range may or may not be compatible with cryogenic temperatures. The likelihood that the range is compatible with cryogenic temperatures increases when a plasma is used.

[0035] example 2 is a schematic diagram illustrating an etch reactor 200 that can be used in one embodiment. In one or more embodiments, the etch reactor 200 includes a gas distribution plate 206 that provides a gas inlet into an etch chamber 209 surrounded by a chamber wall 252, and an electrostatic chuck (ESC) 208. Within the etch chamber 209, a stack 204 is disposed on the ESC 208. The ESC 208 can be provided with a bias from an ESC source 248. An etch gas source 210 is connected to the etch chamber 209 through the gas distribution plate 206. An ESC temperature controller 250 is connected to a chiller 214 that cools a coolant 215. In this embodiment, the chiller 214 provides the coolant 215 to a flow passage 217 in or near the ESC 208. A radio frequency (RF) source 230 provides RF power to a lower electrode and / or an upper electrode, which in this embodiment are the ESC 208 and the gas distribution plate 206, respectively. In an exemplary embodiment, 400 kilohertz (kHz), 60 megahertz (MHz), and optionally 2 MHz, 27 MHz power sources constitute the RF source 230 and the ESC source 248. In this embodiment, the upper electrode is grounded. In this embodiment, one generator is provided for each frequency. In another embodiment, multiple generators may be in separate RF sources, or separate RF generators may be connected to different electrodes. For example, the upper electrode may have inner and outer electrodes connected to different RF sources. Other configurations of RF sources and electrodes may be used in other embodiments. A controller 235 is controllably connected to the RF source 230, the ESC source 248, the exhaust pump 220, and the etching gas source 210. An example of such an etching chamber is the Flex™ Etch System manufactured by Lam Research, Fremont, Calif. The processing chamber may be a CCP (capacitively coupled plasma) reactor or an ICP (inductively coupled plasma) reactor.

[0036] 3 is a high-level block diagram illustrating a computer system 300 suitable for implementing the controller 235 used in the embodiments. The computer system 300 may take many physical forms, from integrated circuits, printed circuit boards, and small handheld devices to large supercomputers. The computer system 300 includes one or more processors 302 and may further include an electronic display device 304 (for displaying images, text, and other data), a main memory 306 (e.g., random access memory (RAM)), a storage device 308 (e.g., a hard disk drive), a removable storage device 310 (e.g., an optical disk drive), a user interface device 312 (e.g., a keyboard, touch screen, keypad, mouse, or other pointing device, etc.), and a communication interface 314 (e.g., a wireless network interface). The communication interface 314 allows software and data to be transferred between the computer system 300 and external devices over a link. The system may further comprise a communication infrastructure 316 (eg, a communication bus, crossover bar, or network) to which the above-mentioned devices / modules are connected.

[0037] Information transferred through communications interface 314 may be in the form of signals, such as electronic, electromagnetic, optical, or other signals that may be received by communications interface 314 over a communications link carrying the signals, which may be implemented using wires or cables, fiber optics, telephone lines, cellular phone links, radio frequency links, and / or communications channels. It is contemplated that using such communications interface 314, one or more processors 302 may receive information from a network or output information to a network when performing the method steps described above. Additionally, method embodiments may be performed solely by the processor or may be performed over a network, such as the Internet, in cooperation with a remote processor that shares some of the processing.

[0038] The term "non-transitory computer-readable medium" is generally used to refer to media such as main memory, secondary memory, removable storage, and storage devices (such as hard disks, flash memory, disk drive memory, CD-ROMs, and other forms of persistent memory), and should not be construed to encompass transitory objects, such as carrier waves or signals. Examples of computer code include machine code, such as code produced by a compiler, and files containing high-level language code that are executed by a computer using an interpreter. A computer-readable medium may also be computer code conveyed by a computer data signal embodied in a carrier wave and representing a sequence of instructions executable by a processor.

[0039] In an exemplary embodiment, the stack is placed in an etch chamber (step 104). FIG. 4A is a schematic cross-sectional view of the stack 204. In this embodiment, the stack 204 comprises a substrate 408 beneath a plurality of bilayers 412 disposed beneath a patterned mask 416. In this example, one or more layers may be disposed between the substrate 408 and the plurality of bilayers 412 or between the plurality of bilayers 412 and the patterned mask 416. In this example, the patterned mask 416 is a carbon-containing patterned mask, such as amorphous carbon. This embodiment does not have a silicon-containing mask above the plurality of bilayers 412 or above the patterned mask 416. In this example, the pattern of the patterned mask provides a mask feature 420 for a high aspect ratio contact. In some embodiments, the mask feature 420 is formed before the stack 204 is placed in the etch chamber 209. In another embodiment, the mask feature 420 is formed while the stack 204 is in the etch chamber 209. In this embodiment, each bilayer 412 is a bilayer of a silicon oxide layer 424 and a silicon nitride layer 428 .

[0040] After the stack 204 is placed in the etching chamber 209, the stack 204 is cooled with a coolant at a coolant temperature below -20°C (step 108). An etching gas is flowed into the etching chamber 209 (step 112). In this example, the etching gas is CF4. In this example, a pressure of 5 to 60 mTorr is provided. The etching gas is turned into an etching plasma (step 116). This may be accomplished by providing excitation RF at a frequency of 60 MHz at 200 to 8000 watts. The stack 204 is exposed to the plasma (step 120). A bias of at least about 400 volts magnitude is provided (step 124). In this embodiment, the high bias is provided by providing RF having a frequency of 400 kHz at 2 kW to 18 kW to the ESC 208 by the ESC source 248. The bias accelerates ions towards the stack 204, causing selective etching of high aspect ratio etch features in the plurality of bilayers 412 relative to the carbon-containing patterned mask 416 (step 128). The plasma is maintained for 180 to 3600 seconds. The etch may etch both the silicon oxide layer 424 and the silicon nitride layer 428. After the etch is completed, another process may be performed on the stack 204. The stack 204 is then removed from the etch chamber 209 (step 132).

[0041] FIG. 4B is a cross-sectional view of stack 204 after contact 432 is etched. Contact 432 is a high aspect ratio contact. Preferably, high aspect ratio contact 432 has a height to critical dimension (CD) width aspect ratio greater than 20:1, where in this embodiment, CD is measured at the top of the feature. In another embodiment, the height to width aspect ratio may be greater than 50:1. The etch process can selectively etch silicon oxide layer 424 and silicon nitride layer 428 relative to amorphous carbon with a selectivity ratio greater than 5:1 during etching of high aspect ratio features. The resulting features also have reduced bowing, striations, distortion, capping, and tapering. Additionally, this embodiment allows for the use of a carbon-containing patterned mask, such as amorphous carbon, without the need for a silicon-containing mask, such as polysilicon. Eliminating the need for a silicon-containing mask reduces costs and defects.

[0042] Previous processes using etching relied on fluorocarbon chemistries where the stack was processed at temperatures above -20°C to etch and provide sidewall protection. Such processes resulted in etch selectivity ratios of mask to silicon oxide and silicon nitride of less than 5:1. Sidewall protection for previous processes was provided by polymer deposition. Polymer deposition was controlled by carbon concentration, with higher carbon increasing sidewall deposition, and by oxygen, with higher oxygen consuming the deposited polymer. Higher oxygen also increases mask consumption. Some previous processes utilized silicon-containing masks. The above embodiments increase etch rates and improve contact profile / striations compared to conventional approaches.

[0043] In some embodiments, the coolant is cooled to a coolant temperature of less than -60°C to provide the stack 204 with a coolant 215 having a coolant temperature of less than -20°C. In another embodiment, the coolant 215 is cooled to a coolant temperature of between -30°C and -200°C. In another embodiment, the coolant 215 is cooled to a coolant temperature of between about -40°C and about -200°C. In some embodiments, the stack is cooled to a temperature of between -30°C and -200°C. In the specification and claims, performing an etch at a cryogenic temperature is defined as performing an etch with a coolant at a temperature of less than -20°C. More preferably, the cryogenic temperature utilizes a coolant at a temperature of between -20°C and -150°C. More preferably, the cryogenic temperature utilizes a coolant at a temperature of less than -60°C. In general, performing an etch at a cryogenic temperature has one of the coolants in the above range. In some embodiments, the cryogenic operation cools the stack 204 to a temperature of less than -20°C at some point during the operation. In another embodiment, cryogenic operation maintains the stack 204 at a temperature below −20° C. throughout operation.

[0044] In some embodiments, the etching gas further comprises one or more of a free fluorine-providing component, a hydrogen-containing component, a hydrocarbon-containing component, a fluorocarbon-containing component, and an iodine-containing component. A free fluorine-providing component is defined as a component that typically decomposes in the plasma to provide free fluorine, such as NF3 and sulfur hexafluoride (SF6). The hydrogen-containing components are preferably H2, CH3F, and difluoromethane (CH2F2).

[0045] The ONON stack may be etched to form features (such as contact holes, lines, or trenches) in the fabrication of 3D NAND memory devices. In another embodiment, contact holes used in M0C and M0A may be etched, which are the first metal contacts used to control the 3D NAND junction. Another embodiment may be utilized in dynamic random access memory (DRAM) capacitor etching. Another embodiment may be used to etch silicon oxide and polysilicon bilayers (OPOPs). An embodiment provides an etch depth greater than 20 microns. In another embodiment, the etch depth is greater than 3 microns. Such an embodiment allows etching of at least 48 bilayers of silicon oxide and silicon nitride in a single etch step using a single amorphous carbon mask less than 1 micron thick. Additionally, the contacts preferably have an aspect ratio of etch depth to neck greater than 30:1.

[0046] In some embodiments, the stack may be a single layer of silicon oxide or silicon nitride, while in other embodiments, the stack may be a single layer or multiple layers of other silicon-containing materials.

[0047] The above embodiment utilizes a bias magnitude of at least 400 volts. A bias magnitude of at least 1000 volts has been found to improve etching. A bias magnitude of at least 2000 volts is believed to further improve etching. Without being bound by theory, it is believed that the higher bias allows for higher aspect ratio etching while utilizing other features, allows for the utilization of amorphous carbon masks, and reduces striations and bowing.

[0048] In some embodiments, liquid nitrogen is utilized as a coolant that is flowed over the chuck or lower electrode to provide cooling. In another embodiment, Vertel Sinera™ from DuPont of Wilmington, Delaware may be utilized as a coolant.

[0049] Bowing is typically an issue in contact etching, where the features are cylindrical and may have a circular cross section. Thus, in various embodiments, the features are contacts with a circular cross section. In other embodiments, the features may have other cross sections, such as ovals, squares, and other polygons. By reducing bowing, the etch features have a more cylindrical shape. In other embodiments, the features may be lines, steps, or other shapes. Other embodiments may include one or more of a silicon-containing mask or a metal-containing mask. The halogen in various embodiments is preferably fluorine, bromine, or iodine.

[0050] Although the present disclosure has been described with reference to certain preferred embodiments, there are numerous alternatives, modifications, permutations, and equivalents within the scope of the present disclosure. It should also be noted that there are numerous other ways of implementing the method and apparatus of the present disclosure. Therefore, the appended claims should be interpreted as covering all such alternatives, modifications, permutations, and equivalents that fall within the true spirit and scope of the present disclosure. [Application Example 1] A method for etching features in a stack below a patterned mask in an etch chamber, comprising: a) cooling the stack with a coolant, the coolant temperature being less than -20°C; b) flowing an etching gas into the etching chamber; c) generating a plasma from the etching gas; d) selectively etching features in the stack relative to the patterned mask; A method comprising: [Application Example 2] The method according to Application Example 1, further comprising supplying a bias of at least 400 volts. [Application Example 3] The method according to Application Example 1, wherein the etching gas does not contain oxygen. [Application Example 4] The method according to Application Example 1, wherein the etching gas contains an etchant component, and the etchant component is CF 4 ,SCIENCE FICTION 6 , N.F. 3 , XeF 2 , W.F. 6 , SiF 4 , TaF 5 , IF 7 , HF, ClF 5 ,BrF 5 , AsF 5 , N.F. 5 , P.F. 5 , NbF 5 , BiF 5 , U.F. 5 , SiCl 2 , CrO 2 Cl 2 , SiCl 4 , TaCl 4 , HfCl 4 , TiCl 3 (l) TiCl 4 (l) CoCl 2 (l) TiCl 3 , and TiCl 2 , a method comprising at least one of the following: [Application Example 5] The method according to Application Example 1, wherein the etching gas contains a passivation component, and the passivation component is CF 4 , CHF 3 , C.H. 3 F, CCl 4 , C.F. 3 I, CBr 2 F 2 、C 2 HF 5 、C 2 F 5 Br, H 2 、O 2 、H 2 O, H 2 O 2 , BCl 3 , N.H. 3 , C.O.S., C.O., S.F. 6 , and SiF 4 , a method comprising at least one of the following: [Application Example 6] The method according to Application Example 1, wherein the etching gas contains a passivation component, and the passivation component is CrO 2 Cl 2 , SiCl 4 , SOCl 2 , TiCl 2 , TiCl 3 , and CoCl 2 , a method comprising at least one of the following: [Application Example 7] The method according to Application Example 1, wherein the stack is cooled to a temperature below -20°C. [Application Example 8] The method according to Application Example 1, wherein the stack is cooled to a temperature below -60°C. [Application Example 9] The method according to Application Example 1, wherein the etching gas is an atomic layer etching gas or an atomic layer deposition gas, and the plasma from the etching gas modifies a layer of the stack to provide a modified layer; The method further comprises: e) ceasing the generation of the plasma; f) activating the modified layer of the stack after ceasing generation of the plasma; A method comprising: [Application Example 10] The method described in Application Example 9, wherein steps b) to f) are repeated multiple times. [Application Example 11] A method as described in Application Example 10, wherein activating the modified layer of the stack includes at least one of heating the modified layer, irradiating the modified layer, or flowing a gas to chemically react with the modified layer. [Application Example 12] The method of Application Example 1, further comprising supplying a bias of at least 1000 volts. [Application Example 13] The method described in Application Example 1, wherein the etching gas includes at least one of a fluorine supplying component, a hydrogen-containing component, a hydrocarbon-containing component, a fluorocarbon-containing component, and an iodine-containing component. [Application Example 14] The method described in Application Example 1, wherein the feature has a height-to-width aspect ratio of greater than 20:1. [Application Example 15] The method according to Application Example 1, wherein the etching gas includes a metal halide gas. [Application Example 16] The method described in Application Example 1, wherein the stack includes a dielectric layer. [Application Example 17] The method described in Application Example 1, wherein the stack comprises at least one layer of silicon nitride, silicon carbide, or silicon oxide.

Claims

1. 1. A method for etching features in a stack below a patterned mask in an etch chamber, comprising: a) cooling the stack with a coolant, the coolant temperature being less than −20° C.; b) flowing an etching gas into the etching chamber, the etching gas comprising an etchant component comprising at least one of NF3, XeF2, WF6, SiF4, TaF5, IF7, HF, ClF5, BrF5, AsF5, NF5, PF5, NbF5, BiF5, UF5, SiCl2, CrO2Cl2, SiCl4, TaCl4, HfCl4, TiCl3(l), TiCl4(l), CoCl2(l), TiCl3, and TiCl2, the etching gas being an atomic layer etching gas or an atomic layer deposition gas; c) generating a plasma from the etching gas; d) providing a bias of at least 400 volts such that the plasma from the etching gas modifies a layer of the stack to provide a modified layer; e) ceasing the generation of the plasma; f) activating the modified layer of the stack after ceasing generation of the plasma, the activating of the modified layer of the stack including heating the modified layer, and steps b) to f) are repeated multiple times; g) selectively etching features in the stack relative to the patterned mask; A method comprising:

2. 10. The method of claim 1, wherein the etching gas is oxygen-free.

3. 10. The method of claim 1, wherein the etching gas includes a passivation component, the passivation component being CF ４ , C.H.F. ３ , C.H. ３ F, CCl ４ , C.F. ３ I, CBr ２ F ２ , C ２ H.F. ５ , C ２ F ５ Br, H ２ , O ２ , H ２ O, H ２ O ２ , BCl ３ , N.H. ３ , COS, CO, SF ６ , and SiF ４ , the method comprising at least one of:

4. 2. The method of claim 1, wherein the etching gas comprises a passivating component, the passivating component being CrO ２ C ２ , SiCl ４ , SOCl ２ , TiCl ２ , TiCl ３ , and CoCl ２ , the method comprising at least one of:

5. The method of claim 1, wherein the stack is cooled to a temperature below -20°C.

6. The method of claim 1 , wherein the stack is cooled to a temperature below −60° C.

7. 10. The method of claim 1, further comprising providing a bias of a magnitude of at least 1000 volts.

8. 10. The method of claim 1, wherein the etching gas comprises at least one of a fluorine-providing component, a hydrogen-containing component, a hydrocarbon-containing component, a fluorocarbon-containing component, and an iodine-containing component.

9. The method of claim 1 , wherein the feature has a height-to-width aspect ratio of greater than 20:

1.

10. 2. The method of claim 1, wherein the etching gas comprises a metal halide gas.

11. The method of claim 1 , wherein the stack comprises a dielectric layer.

12. 10. The method of claim 1, wherein the stack comprises at least one layer of silicon nitride, silicon carbide, or silicon oxide.

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