Etching process for oxides of alkaline earth metals

Abstract

A method of processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing an oxide, and the oxide contains an alkaline earth metal; flowing a processing gas containing CCl4 into the plasma processing chamber; forming a fluorine-free plasma from the processing gas by applying source power to a source electrode of the plasma processing chamber in the plasma processing chamber; and exposing the substrate to the fluorine-free plasma to etch the oxide on the surface.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the benefit of U.S. Patent Application No. 17 / 746,406, filed on May 17, 2022, which is incorporated herein by reference.

[0002] The present invention generally relates to a method of processing a substrate, and in certain embodiments, to etching oxides of alkaline earth metals.

Background Art

[0003] Generally, semiconductor devices used in electronic devices such as mobile phones, digital cameras, and computers are fabricated by using photolithography and etching to sequentially deposit and pattern layers of dielectric materials, conductive materials, and semiconductor materials on a semiconductor substrate to form structures that function as circuit components (e.g., transistors, resistors, and capacitors) and interconnect elements (e.g., conductive lines, contacts, and vias). Driven by the demand for low - cost electronic devices, the semiconductor industry has reduced the cost of integrated circuits (ICs) by repeatedly shrinking the minimum feature size in semiconductor devices to several nanometers through innovations in lithography (e.g., immersion lithography and multiple patterning) to increase the packing density of components. Further increases in density and cost reduction are achieved by using three - dimensional (3D) structures (e.g., fin - type field - effect transistors (FinFETs)), and in some examples, electronic components such as memory storage elements (e.g., ferroelectric capacitors, magnetic tunnel junctions (MTJs), etc.), and precision passive components (e.g., thin - film resistors (TFRs), and metal - insulator - metal (MIM) capacitors) are stacked within layers between successive interconnect levels.

[0004] Plasma processing technologies, such as reactive ion etching (RIE), plasma enhanced chemical vapor deposition (PECVD), plasma enhanced atomic layer etching and deposition (PEALE and PEALD), sputter etching, physical vapor deposition (PVD), and periodic etching-deposition (e.g., Bosch etching process) have become indispensable in fabricating integrated circuits (ICs). The diversity of materials used in IC fabrication, such as semiconductors, (SiO 2 , Si 3 N 4 , high-k gate dielectrics, and low-k dielectrics) insulators, magnetic films and ferroelectric films, and metals for interconnects and electrodes, pose challenges to the development of plasma processes. Miniaturization to a few nanometers has made this challenge severe. Plasma processes are expected to precisely control nanometer-scale precise dimensions (e.g., linewidth, etching depth, and film thickness) with precisely controlled features, such as conformality, anisotropy, selectivity, surface roughness and line edge roughness, and edge profile, and often provide them uniformly across a large area (e.g., 300 mm) wafer at atomic scale dimensions. Furthermore, the introduction of new materials different from the conventional ones (e.g., high-k dielectrics such as barium titanate) can present new challenges in developing plasma etching and deposition processes compatible with conventional Si IC fabrication. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0005] According to one embodiment of the present invention, a method of processing a substrate includes loading the substrate into a plasma processing chamber, the substrate having a surface containing an oxide, the oxide containing an alkaline earth metal; flowing a processing gas containing CCl 4 into the plasma processing chamber; forming a fluorine-free plasma from the processing gas by applying source power to a source electrode of the plasma processing chamber within the plasma processing chamber; and exposing the substrate to the fluorine-free plasma to etch the oxide on the surface.

[0006] According to one embodiment of the present invention, a method for processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing barium; flowing a processing gas into the plasma processing chamber, wherein the processing gas contains a mixture of Cl 2 and BCl 3 ; forming a fluorine-free plasma from the processing gas by applying source power to a source electrode of the plasma processing chamber within the plasma processing chamber; and exposing the substrate to the fluorine-free plasma to etch barium on the surface.

[0007] According to one embodiment of the present invention, a method for processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing a mixed oxide, and the mixed oxide contains an alkaline earth metal and another metal; performing a plurality of cyclic processes, each of the plurality of cyclic processes comprising exposing the mixed oxide to a first fluorine-free species supplied from a first processing gas to react the mixed oxide with the first species to form a reaction product containing an alkaline earth metal, and exposing the reaction product to a second fluorine-free species supplied from a second processing gas to remove the reaction product from the surface.

[0008] For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0009]

Fig. 1A-1D

Fig. 2A-2B

Fig. 3

Fig. 4

Fig. 5A-5C

[0010] The present application relates to a method of processing a substrate, and more particularly, to etching oxides of alkaline earth metals such as barium perovskite. New materials have been proposed to replace conventional materials for the design and fabrication of advanced logic and memory devices. For example, barium titanate (BaTiO 3)And similar perovskite materials are expected. However, currently, there is no satisfactory etching method for these materials that is compatible with semiconductor fabrication processes. Specifically, the etching of barium titanate using a halogen-based plasma process is problematic due to the low volatility of the expected etching products (e.g., fluorides and chlorides). Embodiments of the present application disclose a chlorine (e.g., boron trichloride or carbon tetrachloride) - based fluorine - free etching method for alkaline earth metal oxides, which advantageously can provide a more thermodynamically favorable reaction pathway and volatile etching products. Density functional theory (DFT) calculations have revealed that some chlorine compounds, such as boron trichloride and / or carbon tetrachloride, can facilitate the cleavage of metal - oxygen bonds in oxides and the formation of volatile etching products containing boron - oxygen bonds or carbon - oxygen bonds. The following description of the present disclosure mainly focuses on barium titanate, but the methods herein can also be applied to other barium oxides and, more generally, to alkaline earth metal oxides, including mixed oxides of alkaline earth metals and other metals. By providing a novel etching chemistry tailored specifically to these metal oxides, the methods of the embodiments can reduce their etching challenges and enable their application as high - k dielectrics in advanced logic devices and memory devices.

[0011] First, exemplary steps of semiconductor fabrication including etching a high - k dielectric such as barium titanate will be described with reference to FIGS. 1A - 1D and FIGS. 2A - 2B according to various embodiments. Next, the expected reaction pathways for etching barium titanate using the calculated reaction energies are presented in FIGS. 3 and 4, and two exemplary conditions, namely, the Cl - only condition (FIG. 3) and the condition with B / C added (FIG. 4), are compared. Exemplary process flow diagrams are shown in FIGS. 5A - 5C. All drawings in the present disclosure are drawn for illustrative purposes only and are not drawn to the correct scale, including the aspect ratios of the features.

[0012] Figures 1A - 1D show cross - sectional views of an exemplary substrate 100 at various stages of a fabrication process including etching a high - k dielectric (HK) layer 110, according to various embodiments. In the illustrated example, a portion of a fabrication process for a metal - oxide - semiconductor field - effect transistor (MOSFET) that uses a high - k material for the gate dielectric is described. However, the methods herein can be applied to any fabrication process that uses etching of alkaline earth metal oxides, including but not limited to transistor, quantum computing, and photonics applications.

[0013] Figure 1A shows an incoming substrate 100 including a high - k dielectric (HK) layer 110.

[0014] In various embodiments, the substrate 100 may be part of a semiconductor device or may include a semiconductor device, and may have gone through several processing steps, for example, after a conventional process. Thus, the substrate 100 may comprise a layer of semiconductor useful in various microelectronics. For example, the semiconductor structure may comprise a substrate 100 in which various device regions are formed.

[0015] In one or more embodiments, the substrate 100 can be a silicon wafer or a silicon - on - insulator (SOI) wafer. In certain embodiments, the substrate 100 can include a silicon - germanium wafer, a silicon - carbide wafer, a gallium - arsenide wafer, a gallium - nitride wafer, or other compound semiconductors. In other embodiments, the substrate 100 comprises hetero - layers such as silicon - germanium - on - silicon, gallium - nitride - on - silicon, silicon - carbon - on - silicon, similar to a silicon - on - silicon layer or an SOI substrate. In various embodiments, the substrate 100 is patterned or embedded into other components of the semiconductor device.

[0016] A high - k dielectric (HK) layer 110 can be formed on the substrate 100. In various embodiments, the HK layer 110 is barium titanate (BaTiO 3) Barium-strontium titanate (Ba x Ti y Sr z O m ), barium stannate (BaSnO 3 ), barium strontium stannate (Ba x Ti y Sr z O m ), and includes but is not limited to any mixture thereof, including barium perovskite. Although their compositions are indicated by chemical formulas, barium perovskite or any other oxide may not be strictly stoichiometric. In alternative embodiments, the HK layer 110 may include another oxide containing an alkaline earth metal. The HK layer 110 is, for example, a layer etched using the methods of the embodiments described in this disclosure to fabricate a gate dielectric for a MOSFET. The HK layer 110 can be deposited on the substrate 100 using suitable deposition techniques including atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), and other plasma processes such as plasma enhanced CVD (PECVD), sputtering, and other processes. In certain embodiments, an optional insulating layer such as a silicon oxide layer may be formed between the substrate 100 and the HK layer 110.

[0017] On the HK layer 110, a polysilicon layer 120 may be formed and patterned. The polysilicon used in the polysilicon layer 120 may include doped polysilicon to have desired material properties including electrical properties. The polysilicon layer 120 can be deposited on the HK layer 110 using suitable deposition techniques including chemical vapor deposition (CVD), physical vapor deposition (PVD), and other plasma processes such as plasma enhanced CVD (PECVD), sputtering, and other processes. In one or more embodiments, the polysilicon layer 120 may have a thickness of about 50 nm to about 500 nm.

[0018] In various embodiments, the polysilicon layer 120 is patterned to form a gate structure or a dummy gate structure for a semiconductor device. Accordingly, the polysilicon layer 120 may be patterned into fins, pillars, or any suitable shape. The patterning of the polysilicon layer 120 may be performed using a plasma dry etching process, such as a reactive ion etching (RIE) process. During such an etching process for the polysilicon layer 120, the hard mask layer 130 may be used as an etching mask.

[0019] Still referring to FIG. 1A, in one embodiment, the hard mask layer 130 may include silicon oxide. In various embodiments, the hard mask layer 130 may include silicon nitride, silicon carbonitride (SiCN), or silicon oxycarbide (SiOC). In alternative embodiments, the hard mask layer 130 may include titanium nitride. In one or more embodiments, the hard mask layer 130 may include other suitable organic materials such as spin-on carbon hard mask (SOH) materials. Further, the hard mask layer 130 may be a stacked hard mask including, for example, two or more layers using two different materials. In some of such embodiments, the first hard mask of the hard mask layer 130 may include a metal-based layer such as titanium nitride, titanium, tantalum nitride, tantalum, tungsten-based compounds, ruthenium-based compounds, or aluminum-based compounds, and the second hard mask material of the hard mask layer 130 may include a dielectric layer such as silicon oxide, silicon nitride, SiCN, SiOC, silicon oxynitride, or silicon carbide. The hard mask layer 130 can be deposited using suitable deposition techniques such as chemical vapor deposition (CVD), vapor deposition including physical vapor deposition (PVD), and other plasma processes such as plasma-enhanced CVD (PECVD), sputtering, and other processes including wet processes. The hard mask layer 130 may have a thickness of about 5 nm to about 50 nm in various embodiments. In one or more embodiments, an additional layer such as a silicon-containing antireflective coating film (SiARC) or other ARC film may be formed on the hard mask layer 130. In further embodiments, photoresist that may have been used to form the hard mask layer 130 by lithography may remain on the hard mask layer 130.

[0020] FIG. 1B shows the substrate 100 after etching the high-k dielectric (HK) layer 110.

[0021] In various embodiments, the etching of the HK layer 110 may be performed using a chlorine-based plasma dry etching process in a plasma processing chamber. In certain embodiments, the etching gas is boron trichloride (BCl3 ) or carbon tetrachloride (CCl 4 ) may be included. In one or more embodiments, the etching gas may include dichlorine (Cl 2 ). In addition to chlorine, the etching gas may further include a noble gas (e.g., Ar, He, Xe, etc.). In one embodiment, for example, the etching gas is Ar / Cl 2 / BCl 3 mixture, or Ar / Cl 2 / CCl 4 mixture. In other embodiments, the etching gas may include other halogens other than fluorine. For example, the etching gas may include BBr 3 , BBr 2 Cl, BBrCl 2 , CBr 4 , CBr 3 Cl, CBr 2 Cl 2 , or CBrCl 3 . In an alternative embodiment, the etching gas may include N 2 , SO 2 , or COS. Further, in one or more embodiments, the etching gas may include any molecule that can react with oxygen from the surface, including but not limited to CO, CO 2 , NO and NO 2 . As will be further described below with reference to FIGS. 3-4, using boron chloride, tetrachloride, or both in the etching gas has unique advantages compared to using dichlorine alone, because such chlorides promote the cleavage of the metal-oxygen bonds of the dielectric material of the HK layer 110, and in addition to other chloride etching products (e.g., BOCl, CO, and COCl 2 ), volatile etching products (e.g., BaCl 2 and TiCl 4This is because it can form 3 and CCl 4 ). Only certain gases (e.g., BCl 2 ), when used alone or in combination with other chlorine-containing gases (e.g., Cl

[0022] ), can improve the etching of such metal oxides due to the ability of boron or carbon in the etching gas to form bonds with the metal atoms of the metal oxide on the surface. 4 ), etc., and can form deposits such as titanium oxide through hydrolysis. Accordingly, in one or more embodiments, to eliminate fluorine and hydrogen from the plasma for etching, fluorocarbons (e.g., CF 4 ) and hydrofluorocarbons (e.g., CHF 3 ) can be avoided as components of the etching gas. Similarly, in certain embodiments, other halogen compounds containing hydrogen, such as chloromethane (CH 3 Cl), dichloromethane (CH 2 Cl 2 ), and chloroform (CHCl 3) can be avoided. In the present disclosure, a fluorine-free plasma and a hydrogen-free plasma refer to a plasma that does not contain fluorine or hydrogen, respectively, or a plasma in which the concentration of fluorine or hydrogen is below any amount that can cause a chemical or physical effect in the process.

[0023] In certain embodiments, the noble gas component of the etching gas provides additional ion bombardment by ions (e.g., argon ions Ar + ) to cause some damage and enhance etching by removing the etching products from the surface of the HK layer 110. Ions in the plasma are accelerated toward the substrate by the vertical electric field in the sheath region. The intensity of the vertical electric field can be adjusted by the bias voltage supplied to the substrate holder. For example, relatively heavy (40 amu) Ar + ions, even though they have too low an energy to cause significant sputtering of the HK layer 110, can collide with the etching products (e.g., BaCl 2 ) formed on the surface and remove the etching products from the surface.

[0024] In an alternative embodiment, the fluorine-free chlorine-based plasma dry etching process for the HK layer 110 can be implemented as an atomic layer etching (ALE), or quasi-ALE, cyclic process. The first step (reaction step) of the cyclic process is to react the surface of the HK layer 110, which may or may not be a monolayer, with one or more chlorine compounds (e.g., Cl 2 and BCl 3 ) as described in the previous embodiments. After the first step, some of the etching products can be directly formed as gaseous products (e.g., BClO), while the etching products (e.g., BaCl 2 , TiCl 4Some of may remain on the surface due to its relatively low volatility. The second step (removal step) of the periodic process is to process the substrate with a plasma optimized to remove these remaining etching products. In various embodiments, the desired plasma conditions for this second step (removal step) may include a high bias power to enable a high ion impact energy (E i ), while the first step (reaction step) may include a low bias power and a low E i . The second step may use the same process gas as the etching gas or a process gas different from the etching gas. In one or more embodiments, the etching gas for the first step is a mixture of Ar / Cl 2 / BCl 3 , or a mixture of Ar / Cl 2 / CCl 4 , while the process gas for the second step may include a noble gas without halogen. In one or more embodiments, the periodic embodiment of the fluorine-free chlorine-based plasma dry etching process further includes an additional step of using or not using a plasma, such as a purge step using an inert gas. For example, a purge step may be inserted between the reaction step and the removal step in each cycle.

[0025] The plasma for etching the HK layer 110 can be generated from an etching gas in the plasma processing chamber by applying source power to the source electrode of the plasma processing chamber. The method of the embodiment can be implemented in a suitable plasma processing chamber equipped with one or more plasma sources such as inductively coupled plasma (ICP), capacitively coupled plasma (CCP), microwave plasma (MW), surface wave plasma (SWP). The process conditions for plasma etching can be selected such that anisotropic selective etching is possible. As a result, as shown in FIG. 1B, the pattern of the polysilicon layer 120 can be transferred to the HK layer 110. For example, the chamber pressure can affect the etching rate by shifting the adsorption equilibrium of the etching products. A relatively low chamber pressure may be preferable for the desorption of the etching products from the surface. In one embodiment, the chamber pressure may be 1000 mTorr or less, and in another embodiment, 20 mTorr or less. In one embodiment, a source power of 20 W or more and a bias voltage of 10 V or more can be used. In one embodiment, the bias voltage can be 5000 V or less. In various embodiments, the source power and the bias voltage may be high enough to enable sufficient ion bombardment on the surface, while the bias voltage also enables anisotropy of etching. In a particular embodiment, when sufficient ion bombardment energy (E i ) is supplied, physical sputtering can contribute to the etching of the HK layer 110. In various embodiments, the substrate temperature can be maintained at any reasonable temperature.

[0026] Although not described herein, the embodiments of the present invention can also be applied to remote plasma systems and batch systems. For example, the substrate holder may be capable of supporting a plurality of wafers that are spun around the central axis as they pass through different plasma zones. The use of a system having a plurality of plasma zones can conveniently enable various periodic embodiments of the etching method.

[0027] In certain embodiments, a chlorine-based plasma dry etching process without fluorine for etching the HK layer 110 may be implemented using two or more plasma conditions, where one condition enables the surface reaction of the HK layer 110 with the chemical species supplied from the plasma, and another condition enables the efficient removal of the etching products from the surface. In one or more embodiments, to enable such conditions, pulsing of the source / bias power, throttling of the chamber pressure and temperature, and / or gas flow rate adjustment may be used. The substrate 100 may be repeatedly processed under these conditions as part of a periodic process to improve the etching rate and selectivity. For example, higher temperature and lower chamber pressure may be advantageous for the removal of the etching products. A relatively high bias voltage may also enhance the effect of ion bombardment on the surface. Further, it is possible to implement an ALE or quasi-ALE process by combining multiple plasma conditions with a change in the etching gas composition as described in the previous embodiments.

[0028] FIG. 1C shows the substrate 100 after spacer material deposition and spacer top hat etching.

[0029] After etching the high-k dielectric (HK) layer 110, subsequent process steps may be implemented to continue the fabrication of the MOSFET. The gate spacer material 140, such as silicon nitride, can be deposited on the substrate 100 using suitable deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and vapor phase growth including atomic layer deposition (ALD), as well as other plasma processes such as plasma enhanced CVD (PECVD), sputtering, and other processes. Subsequently, the upper surface of the gate spacer material 140 can be removed by spacer top hat etching using a plasma dry etching process, such as a reactive ion etching (RIE) process.

[0030] FIG. 1D shows the substrate 100 after source / drain formation.

[0031] In FIG. 1D, the source / drain regions 150 can be formed adjacent to the gate structure by ion implantation into the substrate 100. Ion implantation can inject dopant atoms into the substrate 100 to change the electronic structure and properties of the implanted regions. In the ion implantation process, ions are supplied by an ion source and then electrostatically accelerated to collide onto the substrate 100. For source / drain formation, various dopants including p-type dopants (e.g., boron) and n-type dopants (e.g., phosphorus) can be used. Doping can be achieved by other techniques such as gas cluster ion beam (GCIB) and atomic layer deposition (ALD).

[0032] After source / drain formation, other fabrication process steps such as a metallization process and other middle-of-line (MOL) / backend-of-line (BEOL) processes can be performed. In the example illustrated above, polysilicon is used as the gate material, but in other embodiments, other MOSFET device structures, such as those using non-silicon gate materials, can be fabricated.

[0033] FIGS. 2A - 2B show cross-sectional views of another exemplary substrate 100 with a high-k dielectric (HK) layer 110 during high-k / metal gate (HKMG) fabrication according to an alternative embodiment, where polysilicon is used as a dummy gate and is replaced by a metal gate. In the example shown, the substrate 100 has the same initial structure as the previous embodiment shown in FIG. 1A, and then the same steps as described with reference to FIGS. 1B - 1D follow. Thus, the details of the structure and these steps identical to the previous embodiment are not repeated.

[0034] FIG. 2A shows the substrate after etching of the HK layer 110, spacer material deposition, spacer top hat etching, source / drain formation, dielectric deposition, and removal of the dummy gate.

[0035] In FIG. 2A, a substrate 100 having the same structure as the substrate shown in FIG. 1A is fabricated by the steps described above (i.e., etching of the HK layer 110 in FIG. 1B, spacer material deposition and spacer top hat etching in FIG. 1C, and source / drain formation in FIG. 1D). Following these steps, a low-k dielectric 160 may be deposited on the substrate 100, the polysilicon layer 120 (shown in FIGS. 1A - 1D) may be removed (dummy gate removal), and recesses 165 may be created to fill with a replacement metal gate (RMG) material 170 (e.g., FIG. 2B). The low-k dielectric 160 may include silicon-based dielectric materials having a low dielectric constant (i.e., a low k value), such as organosilicate glass (SiCOH), high-density SiCOH, porous SiCOH, and other porous dielectric materials. The low-k dielectric may be deposited using deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD), as well as other plasma processes such as plasma-enhanced CVD (PECVD), sputtering, and other processes.

[0036] Still referring to FIG. 2A, the polysilicon layer 120 may be removed using a plasma dry etching process that is selective to removing polysilicon, such as a reactive ion etching (RIE) process. In various embodiments, the RIE process for the polysilicon layer 120 may use an etching gas that includes, for example, a halogen gas. In a particular embodiment, the etching gas may include hydrogen bromide (HBr) and dichlorine (Cl 2 )). The etching gas may also include dioxygen (O 2 ) and / or noble gases (e.g., He, Ne, Ar, Kr, etc.). The etching gas and process conditions may be selected such that the first plasma for etching polysilicon has high selectivity and a high polysilicon etching rate.

[0037] FIG. 2B shows the substrate 100 after metal gate formation.

[0038] After dummy gate removal, the recess 165 can be filled with a replacement metal gate (RMG) material 170. In various embodiments, the RMG material 170 can include a combination of multiple layers including a work function metal and a metal filler. The work function metal of the RMG material can include titanium nitride, tantalum nitride, or a metal alloy such as AlC, TiAl, and TiAlC. To select different threshold voltages for different types of FETs, the work function metal of the n-type FET is generally different from that of the p-type FET. Metal deposition continues until the recess 165 is filled with an excessive metal filling material. In some embodiments, the metal filling material can include a low resistance metal such as tungsten (W), copper (Cu), cobalt (Co), or aluminum (Al). In some embodiments, the RMG material 170 can be deposited on the substrate 100 using a highly conformal process such as an atomic layer deposition (ALD) process.

[0039] After filling the recess 165 with the RMG material 170, any excessive metal can be removed by a planarization process (e.g., a chemical mechanical planarization process). The resulting top surface comprises the upper portions of the RMG material 170, the low-k dielectric 160, and the gate spacer material 140. Subsequently, a middle-of-line (MOL) / back-end-of-line (BEOL) process can be performed.

[0040] Hereinafter, with reference to FIGS. 3 and 4, the effect of adding a boron-containing agent and a carbon-containing agent to an etching gas is explained by comparison of the calculated reaction energies.

[0041] FIG. 3 shows the reaction pathway of barium titanate under etching conditions according to one embodiment.

[0042] In FIG. 3, it is assumed that the etching of barium titanate proceeds by reaction with chlorine species from the plasma. Based on density functional theory (DFT) calculations, the reaction energies of three reaction steps are obtained as follows. (1)BaTiO 3 (s)+6Cl(g)=BaCl 2 +TiCl4 (s) + 3O(g); ΔE = 0.857 eV (2a) BaCl 2 = BaCl 2 (g); ΔE = 2.883 eV (2b) TiCl 4 (s) = TiCl 4 (g); ΔE = 0.0054 eV

[0043] Reaction (1), i.e., the surface reaction of solid barium chloride (BaCl 2 ), solid titanium chloride (TiCl 2 ), and oxygen atoms to form barium titanate, is found to exhibit only slight endothermicity (almost thermally neutral) with a reaction energy of 0.857 eV. Furthermore, DFT calculations show that the formation of gaseous BaCl 2 (2a) requires a significant amount of energy (2.883 eV), which means that BaCl 2 has only moderate volatility. In contrast, TiCl 2 has high volatility with a minimum energy difference (0.054 eV) between the solid and gas phases. This result indicates the difficulty of removing the etching products, especially BaCl 2 , to form the surface. In other words, the barium-oxygen bond in BaTiO 3 is very stable and requires a very large amount of energy to break. Accordingly, a fluorine-free chlorine-based plasma etching process that provides only chlorine (e.g., Cl 2 alone) may not be able to effectively etch BaTiO 3 . However, it should be noted that barium and titanium fluoride are even less volatile (i.e., more difficult to remove from the surface), so the chlorine-based plasma etching process can still be advantageous compared to the fluorine-based plasma etching process. Accordingly, in various embodiments, the etching gas includes halogens other than fluorine (e.g., chlorine and bromine).

[0044] Figure 4 shows an alternative reaction pathway of barium titanate under etching conditions containing boron or carbon according to an alternative embodiment.

[0045] In Figure 4, three DFT calculations involving reactions with boron or carbon enable new oxygen-containing etching products, indicating that the difficulty of etching BaTiO 3 can be alleviated. The three additional reactions shown in Figure 4 are reactions of oxygen atoms with (A) boron trichloride (BCl 3 ), (B) carbon, and (C) dichloromethane (CCl 2 ), which produce the oxygen-containing etching products BClO, CO, and COCl 2 , respectively. All the calculated reactions exhibit significant negative reaction energies in the range of approximately -35.1 eV to -23.5 eV, as shown below as (A) - (C), and are presented together with the initial reaction with chlorine (1) as follows. (1) BaTiO 3 (s) + 6Cl(g) = BaCl 2 (g) + TiCl 4 (g) + 3O(g); ΔE = 3.795 eV (A) 3O(g) + 3BCl(g) = 3BClO(g); ΔE = -26.964 eV (B) 3O(g) + 3C(g) = 3CO(g); ΔE = -35.092 eV (C) 3O(g) + 3CCl 2 (g) = 3COCl 2 (g); ΔE = -23.538 eV

[0046] The magnitudes of these values are significantly larger than the moderate positive reaction energy (i.e., 3.795 eV) in the case of the formation of (1) BaCl 3 , TiCl 2 , and oxygen atoms via the reaction of BaTiO 4 with chlorine. Therefore, BaTiO 3By coupling the etching of 3 with one or more of the additional reactions, the overall reaction can be made thermodynamically favorable (i.e., exothermic). In other words, adding boron or carbon to the etching gas breaks the barium-oxygen bond and forms a stable etching product with a boron-oxygen bond or a carbon-oxygen bond, thereby 3 substantially improving the etching of BaTiO 4 . In these etching products, the bond order of these bonds can be any valid value. In other words, in various embodiments, single, double, and / or triple bonds with oxygen can be formed. Thus, to enable these etching products, the etching gas can include boron or carbon in addition to chlorine. In various embodiments, boron trichloride (BCl 2 ) or carbon tetrafluoride (CCl 2 ) can be used alone as the etching gas or as an additive to an etching gas that includes another chlorine source such as dichlorine (Cl 2 ). In certain embodiments, other molecules may also be included in the etching gas to facilitate the breaking of the barium-oxygen bond by providing novel oxygen-containing etching products. Such molecules can include, but are not limited to, N 2 , SO 2 , COS, NO, NO 3 , CO, CO 2 , BBr 2 , BBr 4 Cl, BBrCl 3 , CBr 2 , CBr 2 Cl, CBr 3 Cl

[0047] Figures 5A - 5C show process flowcharts of methods for etching barium titanate or similar oxides according to various embodiments.

[0048] In FIG. 5A, process flow 50 begins with loading a substrate into a plasma processing chamber, and the substrate has a surface containing an oxide of an alkaline earth metal (block 500, FIG. 1A). Next, a process gas containing carbon tetrachloride (CCl 4 ) may be flowed into the plasma processing chamber (block 510), and a fluorine-free plasma may be formed from the process gas by applying source power to the source electrode of the plasma processing chamber (block 520, FIG. 1B). Then, the substrate may be exposed to the plasma to etch the surface oxide (block 530, FIG. 1B).

[0049] In FIG. 5B, process flow 52 begins with loading a substrate into a plasma processing chamber, and the substrate has a surface containing barium, such as barium titanate (block 502, FIG. 1A). Next, a process gas containing a mixture of dichloride (Cl 2 ) and boron chloride (BCl 3 ) may be flowed into the plasma processing chamber (block 512), and a fluorine-free plasma may be formed from the process gas by applying source power to the source electrode of the plasma processing chamber (block 520, FIG. 1B). Then, the substrate may be exposed to the plasma to etch the surface barium (block 532, FIG. 1B).

[0050] In FIG. 5C, process flow 54 begins with loading a substrate into a plasma processing chamber, and the substrate has a surface containing a mixed oxide containing an alkaline earth metal and another metal (block 504, FIG. 1A). Next, a periodic process may be performed. The periodic process may first expose the mixed oxide to a first fluorine-free species supplied from a first process gas to react the mixed oxide with the first species to form a reaction product containing an alkaline earth metal (block 534, FIG. 1B), and subsequently expose the reaction product to a second fluorine-free species supplied from a second process gas to remove the reaction product from the surface (block 536, FIG. 1B).

[0051] Here, exemplary embodiments of the present invention are summarized. Other embodiments can also be understood throughout this specification and from the claims appended hereto.

[0052] Example 1. A method for processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing an oxide, and the oxide contains an alkaline earth metal; flowing a processing gas containing CCl4 into the plasma processing chamber; forming a fluorine-free plasma from the processing gas by applying source power to the source electrode of the plasma processing chamber within the plasma processing chamber; and exposing the substrate to the fluorine-free plasma to etch the oxide on the surface.

[0053] Example 2. The method according to Example 1, wherein the plasma is hydrogen-free.

[0054] Example 3. The method according to Example 1 or 2, further comprising flowing a noble gas into the plasma processing chamber.

[0055] Example 4. The processing gas further contains Cl 2 , BCl 3 , BCl 2 Br, BClBr 2 , or BBr 3 . The method according to any one of Examples 1 to 3.

[0056] Example 5. The processing gas further contains N 2 , NO, NO 2 , CO, CO 2 , SO 2 , or COS. The method according to any one of Examples 1 to 4.

[0057] Example 6. Etching the oxide includes forming a volatile product containing a carbon-oxygen bond. The method according to any one of Examples 1 to 5.

[0058] Example 7. The oxide is barium titanate. The method according to any one of Examples 1 to 6.

[0059] Example 8. The method according to any one of Examples 1 to 7, wherein the oxide is barium strontium titanate.

[0060] Example 9. The method according to any one of Examples 1 to 8, wherein the oxide is barium stannate.

[0061] Example 10. The method according to any one of Examples 1 to 9, wherein the alkaline earth metal is calcium (Ca) or magnesium (Mg), and the oxide is perovskite titanate.

[0062] Example 11. A method for processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing barium; flowing a processing gas into the plasma processing chamber, wherein the processing gas contains a mixture of Cl 2 and BCl 3 forming a fluorine-free plasma from the processing gas by applying source power to a source electrode of the plasma processing chamber in the plasma processing chamber; and exposing the substrate to the fluorine-free plasma to etch the barium on the surface.

[0063] Example 12. The method according to Example 11, wherein the fluorine-free plasma is hydrogen-free.

[0064] Example 13. The method according to Example 11 or 12, further comprising flowing a noble gas into the plasma processing chamber.

[0065] Example 14. The method according to any one of Examples 11 to 13, wherein the surface further contains oxygen, and etching the barium includes forming a volatile product containing a boron-oxygen bond.

[0066] Example 15. A method for processing a substrate, comprising loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing a mixed oxide, and the mixed oxide contains an alkaline earth metal and another metal; and performing a plurality of cyclic processes, each of the plurality of cyclic processes comprising exposing the mixed oxide to a first fluorine-free species supplied from a first processing gas to react the mixed oxide with the first species to form a reaction product containing an alkaline earth metal, and exposing the reaction product to a second fluorine-free species supplied from a second processing gas to remove the reaction product from the surface.

[0067] Example 16. The method according to Example 15, further comprising forming a first plasma to generate the first fluorine-free species.

[0068] Example 17. The method according to Example 15 or 16, wherein the first processing gas contains a halogen other than fluorine.

[0069] Example 18. The first processing gas contains BCl 3 、BCl 2 Br、BClBr 2 、BBr 3 、CCl 4 、CCl 3 Br、CCl 2 Br 2 、CClBr 3 、or CBr 4 and the first processing gas further contains N 2 、NO、NO 2 、CO、CO 2 、SO 2 、or COS. The method according to any one of Examples 15 to 17.

[0070] Example 19. The method according to any one of Examples 15 to 18, further comprising forming a second plasma to generate the second fluorine-free species, and the second processing gas contains a noble gas.

[0071] Example 20. The method according to any one of Examples 15 to 19, wherein each of the plurality of cyclic processes further comprises purging the plasma processing chamber to remove the first chemical species before exposing the reaction product to the second chemical species.

[0072] Although the present invention has been described with reference to exemplary embodiments, this specification is not intended to be construed in a limiting sense. Various modifications and combinations of the exemplary embodiments, as well as other embodiments of the present invention, will be apparent to those skilled in the art upon reference to this specification. Accordingly, the appended claims are intended to cover any such modifications or embodiments.

Claims

1. A method for processing a substrate, the method comprising: loading the substrate into a plasma processing chamber, the substrate having a surface containing an oxide, the oxide containing an alkaline earth metal; A step of introducing a processing gas containing CCl ４ into the plasma processing chamber; forming a fluorine-free plasma from the process gas by applying source power to a source electrode of the plasma processing chamber in the plasma processing chamber; exposing the substrate to the fluorine-free plasma to etch the oxide on the surface; A method comprising.

2. The method according to claim 1, wherein the plasma is hydrogen-free.

3. The method according to claim 1, further comprising flowing a noble gas into the plasma processing chamber.

4. The processing gas further contains Cl ２ , BCl ３ , BCl ２ Br, BClBr ２ , or BBr ３ The method according to claim 1, which contains such components.

5. The treatment gas further contains N ２ , NO, NO ２ , CO, CO ２ , SO ２ , or COS, according to the method of claim 1.

6. The method according to claim 1, wherein the step of etching the oxide comprises forming a volatile product containing a carbon-oxygen bond.

7. The method according to claim 1, wherein the oxide is barium titanate.

8. The method according to claim 1, wherein the oxide is barium strontium titanate.

9. The method according to claim 1, wherein the oxide is barium stannate.

10. The method according to claim 1, wherein the alkaline earth metal is calcium (Ca) or magnesium (Mg), and the oxide is a perovskite titanate.

11. A method for processing a substrate, the method comprising: loading the substrate into a plasma processing chamber, the substrate having a surface containing barium; A step of flowing a processing gas into the plasma processing chamber, wherein the processing gas contains Cl ２ and BCl ３ in a mixture of, step forming a fluorine-free plasma from the process gas by applying source power to a source electrode of the plasma processing chamber in the plasma processing chamber; exposing the substrate to the fluorine-free plasma to etch the barium on the surface; A method comprising.

12. The method according to claim 11, wherein the fluorine-free plasma is hydrogen-free.

13. The method according to claim 11, further comprising flowing a noble gas into the plasma processing chamber.

14. The method according to claim 11, wherein the surface further contains oxygen, and the step of etching the barium comprises forming a volatile product containing a boron-oxygen bond.

15. A method of processing a substrate, the method comprising: loading the substrate into a plasma processing chamber, the substrate having a surface comprising a mixed oxide, the mixed oxide comprising an alkaline earth metal and another metal; performing a plurality of cyclic processes, each of the plurality of cyclic processes comprising: exposing the mixed oxide to a first fluorine-free chemical species supplied from a first process gas, reacting the mixed oxide with the first chemical species to form a reaction product comprising the alkaline earth metal; and exposing the reaction product to a second fluorine-free chemical species supplied from a second process gas and removing the reaction product from the surface ; a method.

16. The method of claim 15, further comprising forming a first plasma to generate the first fluorine-free chemical species.

17. The method of claim 15, wherein the first process gas comprises a halogen other than fluorine.

18. The first processing gas contains BCl ３ , BCl ２ Br, BClBr ２ , BBr ３ , CCl ４ , CCl ３ Br, CCl ２ Br ２ , CClBr ３ , or CBr ４ and The first process gas further contains N ２ , NO, NO ２ , CO, CO ２ , SO ２ , or COS, according to the method of claim 15.

19. The method of claim 15, further comprising forming a second plasma to generate the second fluorine-free chemical species, wherein the second process gas comprises a noble gas.

20. The method of claim 15, wherein each of the plurality of cyclic processes further comprises purging the plasma processing chamber to remove the first chemical species prior to exposing the reaction product to the second chemical species.

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