Etching process for alkaline earth metal oxides

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 of related applications This application claims the benefits of U.S. Patent Application No. 17 / 746,406, filed on 17 May 2022, which is incorporated herein by reference.

[0002] The present invention generally relates to a method for processing a substrate, and in particular embodiments to etching an alkaline earth metal oxide. [Background technology]

[0003] Generally, semiconductor devices used in electronic devices such as mobile phones, digital cameras, and computers are fabricated by sequentially depositing and patterning layers of dielectric, conductive, and semiconductor materials onto a semiconductor substrate using photolithography and etching to form structures that function as circuit components (e.g., transistors, resistors, and capacitors) and interconnection 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 reducing the minimum feature size in semiconductor devices to a few 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 reductions are achieved by using three-dimensional (3D) structures (e.g., fin-type field-effect transistors (FinFETs)) and, in some examples, by stacking electronic components such as memory 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) in layers between consecutive interconnection 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 essential for IC fabrication. The diversity of materials used in IC fabrication, such as semiconductors, insulators (including SiO2, Si3N4, high-k gate dielectrics, and low-k dielectrics), magnetic and ferroelectric films, and metals for interconnects and electrodes, presents challenges for plasma process development. Miniaturization to a few nanometers makes this challenge particularly demanding. Plasma processes are expected to provide precise dimensions in the nanometer range (e.g., line width, etching depth, and film thickness) uniformly across a wide range of wafers (e.g., 300 mm) at atomic scale dimensions, along with precisely controlled features such as conformality, anisotropy, selectivity, surface roughness, and line edge roughness, as well as edge profiles. Furthermore, the introduction of materials different from conventional ones (for example, high-k dielectrics such as barium titanate) may present new challenges in developing plasma etching and deposition processes that are compatible with conventional Si IC fabrication. [Overview of the project] [Means for solving the problem]

[0005] 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 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 etching the oxide on the surface of the substrate by exposing it to the fluorine-free plasma.

[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 Cl2 and BCl3; 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 etching the barium on the surface of the substrate by exposing it to the fluorine-free plasma.

[0007] According to one embodiment of the present invention, a method for processing a substrate, comprising: loading a substrate into a plasma processing chamber, wherein the substrate has a surface containing a mixed oxide, the mixed oxide containing an alkaline earth metal and another metal; and performing a plurality of periodic processes, each of which includes exposing the mixed oxide to a first fluorine-free chemical species supplied from a first processing gas to react the mixed oxide with the first chemical species to form a reaction product containing an alkaline earth metal, and exposing the reaction product to a second fluorine-free chemical 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, the following description is to be referred to here in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0009] [Figure 1A-1D] The following are exemplary cross-sectional views of a substrate at various stages in a fabrication process involving etching a high-k dielectric (HK) layer according to various embodiments: Figure 1A shows the incoming substrate with the HK layer; Figure 1B shows the substrate after etching the HK layer; Figure 1C shows the substrate after spacer material deposition and spacer top-hat etching; and Figure 1D shows the substrate after source / drain formation. [Figure 2A-2B]Figure 2A shows a cross-sectional view of another exemplary substrate containing a high-k dielectric (HK) layer during the fabrication of a high-k / metal gate (HKMG) according to an alternative embodiment. Figure 2A shows the substrate after HK layer etching, spacer material deposition, spacer top-hat etching, source / drain formation, dielectric deposition, and dummy gate removal, while Figure 2B shows the substrate after metal gate formation. [Figure 3] The reaction pathway of barium titanate under etching conditions according to one embodiment is shown, and the reaction energy is calculated along this pathway. [Figure 4] An alternative reaction pathway for barium titanate under etching conditions containing boron or carbon is shown using the calculated reaction energy according to an alternative embodiment, and the reaction energy is calculated along this pathway. [Figures 5A-5C] Figure 5A shows an exemplary process flow diagram for etching an alkaline earth metal-containing layer, with Figure 5A showing one embodiment, Figure 5B showing an alternative embodiment, and Figure 5C showing yet another embodiment. [Modes for carrying out the invention]

[0010] This application relates to a method for processing substrates, and more specifically, to etching alkaline earth metal oxides such as barium perovskite. Novel materials have been proposed to replace conventional materials for the design and fabrication of advanced logic and memory devices. For example, barium titanate (BaTiO3) and similar perovskite materials are expected to be promising candidates for novel high-k gate dielectric materials. However, currently there is no satisfactory etching method for these materials that is compatible with semiconductor fabrication processes. Specifically, etching barium titanate using halogen-based plasma processes is problematic due to the low volatility of the expected etching products (e.g., fluorides and chlorides). Embodiments of this application disclose a fluorine-free etching method for alkaline earth metal oxides using chlorine (e.g., boron chloride or carbon tetrachloride), which can conveniently provide a thermodynamically more desirable reaction pathway and volatile etching products. Density function theory (DFT) calculations have revealed that several chlorine compounds, such as boron chloride and / or carbon tetrachloride, can promote the cleavage of metal-oxygen bonds in oxides, thereby facilitating the formation of volatile etching products containing boron-oxygen or carbon-oxygen bonds, as demonstrated by the inventors of this application. While the following description of this disclosure is primarily focused on barium titanate, the methods described herein may 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 novel etching chemicals specifically formulated for these metal oxides, the methods of the embodiments can mitigate their etching challenges and become applicable as high-k dielectrics in advanced logic and memory devices.

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

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

[0013] Figure 1A shows the 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 it may include a semiconductor device, and may have undergone several processing steps after a conventional process, for example. Therefore, the substrate 100 may comprise semiconductor layers useful in various microelectronics. For example, a semiconductor structure may comprise the substrate 100 on which various device regions are formed.

[0015] In one or more embodiments, the substrate 100 may be a silicon wafer or a silicon-on-insulator (SOI) wafer. In certain embodiments, the substrate 100 may 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 heterogeneous layers such as silicon-germanium-on-silicon, gallium nitride-on-silicon, or silicon-carbon-on-silicon, as well as silicon-on-silicon layers or SOI substrates. In various embodiments, the substrate 100 is patterned or embedded in other components of a semiconductor device.

[0016] A high-k dielectric (HK) layer 110 can be formed on the substrate 100. In various embodiments, the HK layer 110 may be made of barium titanate (BaTiO3), barium titanate-strontium (BaTiO3), etc. x Ti y Sr z O m ), barium stannate (BaSnO3), barium stannate-strontium (Ba x Ti y Sr z O m The HK layer 110 comprises barium perovskites, including but not limited to ), and any mixture thereof. Their compositions are shown by chemical formulas, but barium perovskites or any other oxides may not be strictly stoichiometric. In alternative embodiments, the HK layer 110 may comprise another oxide containing an alkaline earth metal. The HK layer 110 is a layer etched using the methods of the embodiments described herein, for example, to fabricate a gate dielectric for a MOSFET. The HK layer 110 can be deposited on the substrate 100 using appropriate deposition techniques such as 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] A polysilicon layer 120 may be formed and patterned over the HK layer 110. The polysilicon used in the polysilicon layer 120 may include doped polysilicon so as to have desired material properties including electrical properties. The polysilicon layer 120 can be deposited over the HK layer 110 using suitable deposition techniques such as vapor deposition 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, a 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 laminated hard mask including, for example, two or more layers using two different materials. In some 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 anti-reflective coating film (SiARC) or other ARC film may be formed over the hard mask layer 130. In further embodiments, a 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, etching of the HK layer 110 may be carried out using a chlorine-based plasma dry etching process in a plasma processing chamber. In certain embodiments, the etching gas may include boron chloride (BCl3) or carbon tetrachloride (CCl4). In one or more embodiments, the etching gas may include dichloride (Cl2). In addition to chlorine, the etching gas may further include noble gases (e.g., Ar, He, Xe, etc.). In one embodiment, for example, the etching gas may be a mixture of Ar / Cl2 / BCl3 or a mixture of Ar / Cl2 / CCl4. In other embodiments, the etching gas may include halogens other than fluorine. For example, the etching gas may include BBr3, BBr2Cl, BBrCl2, CBr4, CBr3Cl, CBr2Cl2, or CBrCl3. In alternative embodiments, the etching gas may include N2, SO2, or COS. Furthermore, in one or more embodiments, the etching gas may include, but not limited to, CO, CO2, NO, and NO2, any molecules that can react with oxygen from the surface. As will be further discussed with reference to Figures 3-4, the use of boron chloride, tetrachloride, or both in the etching gas has inherent advantages compared to the use of dichloride alone, because such chlorides promote the cleavage of metal-oxygen bonds in the dielectric material of the HK layer 110, and in addition to other chloride etching products (e.g., BOCl, CO, and COCl2), volatile etching products (e.g., BaCl2 and TiCl4). In various embodiments, the etching gas and the plasma formed from the etching gas may be fluorine-free to avoid the formation of metal fluorides such as barium fluoride, which may have lower volatility than metal chlorides. While chlorine-based plasma processes are commonly used to etch a variety of materials, etching of metal oxides of alkaline earth metals has been difficult, mainly due to the low volatility of the etching products.The inventors of the present application have confirmed that only certain specific gases (e.g., BCl3 and CCl4), when used alone or in combination with other chlorine-containing gases (e.g., Cl2), can potentially 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.

[0022] In certain embodiments, the etching gas and the plasma formed from the etching gas can be substantially hydrogen-free to avoid the formation of water or other hydrogen-containing products. In certain embodiments, water molecules may be undesirable because they can readily react with etching products such as TiCl4 and form deposits such as titanium oxide via hydrolysis. Accordingly, in one or more embodiments, fluorocarbons (e.g., CF4) and hydrofluorocarbons (e.g., CHF3) can be avoided as components of the etching gas to exclude fluorine and hydrogen from the plasma for etching. Similarly, in certain embodiments, other halogen compounds containing hydrogen, such as chloromethane (CH3Cl), dichloromethane (CH2Cl2), and chloroform (CHCl3), 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 causes additional ion bombardment by ions (e.g., argon ions Ar + ) to cause some damage by removing the etching products from the surface of the HK layer 110 and enhance the etching. The ions in the plasma are accelerated towards the substrate by the vertical electric field in the sheath region. The strength of the vertical electric field can be adjusted by the bias voltage supplied to the substrate holder. For example, relatively heavy (40 amu) Ar +Even if the ions have an energy too low to cause significant sputtering of the HK layer 110, they can still collide with etching products (e.g., BaCl2) formed on the surface and remove the etching products from the surface.

[0024] In alternative embodiments, the fluorine-free, chlorine-based plasma dry etching process for the HK layer 110 may be carried out as a periodic process of atomic layer etching (ALE) or a quasi-ALE method. The first step (reaction step) of the periodic process is to react the surface of the HK layer 110, which may be monolayer or none, with one or more chlorine compounds (e.g., Cl2 and BCl3) as described in the previous embodiments. After the first step, some etching products may be formed directly as gaseous products (e.g., BClO), while some etching products (e.g., BaCl2, TiCl4) may remain on the surface due to their relatively low volatility. The second step (removal step) of the periodic process is to treat the substrate with a plasma optimized to remove these residual etching products. In various embodiments, the desired plasma conditions for this second step (removal step) are high ion shock energy (E i The first step (reaction step) may involve high bias power to enable ), while the first step (reaction step) may involve low bias power and low E i This may include the following. The second step may use the same or different process gas as the etching gas. In one or more embodiments, the etching gas for the first step may be a mixture of Ar / Cl2 / BCl3 or Ar / Cl2 / CCl4, while the process gas for the second step may include a halogen-free noble gas. In one or more embodiments, a periodic embodiment of a fluorine-free chlorine-based plasma dry etching process further includes additional steps using or not using plasma, such as a purging step using an inert gas. For example, a purging 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 the 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 carried out 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), and surface wave plasma (SWP). The process conditions for plasma etching can be selected to enable anisotropic selective etching. As a result, the pattern of the polysilicon layer 120 can be transferred to the HK layer 110, as shown in Figure 1B. For example, the chamber pressure can affect the etching rate by shifting the adsorption equilibrium of the etching product. Relatively low chamber pressure may be preferable for the desorption of etching products from the surface. In one embodiment, the chamber pressure may be 1000 mTorr or less, and in another embodiment, it may be 20 mTorr or less. In one embodiment, a source power of 20 W or more and a bias voltage of 10 V or more may be used. In one embodiment, the bias voltage may be 5000 V or less. In various embodiments, the source power and bias voltage may be sufficiently high to allow sufficient ion bombardment on the surface, while the bias voltage also allows for etching anisotropy. In certain embodiments, sufficient ion bombardment energy (E i If a suitable material is supplied, physical sputtering may contribute to etching the HK layer 110. In various embodiments, the substrate temperature can be maintained at any reasonable temperature.

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

[0027] In certain embodiments, a fluorine-free, chlorine-based plasma dry etching process for etching the HK layer 110 may be carried out using two or more plasma conditions, one condition enabling surface reactions of the HK layer 110 to chemical species supplied from the plasma, and another condition enabling efficient removal of etching products from the surface. In one or more embodiments, pulsed source / bias power, throttling of chamber pressure and temperature, and / or gas flow rate adjustment may be used to enable such conditions. The substrate 100 may be repeatedly treated under these conditions as part of a periodic process to improve etching rate and selectivity. For example, higher temperatures and lower chamber pressures may be advantageous for the removal of etching products. Relatively high bias voltages may also enhance the effect of ion bombardment on the surface. Furthermore, multiple plasma conditions can be combined with variations in etching gas composition, as described in previous embodiments, to carry out an ALE or quasi-ALE process.

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

[0029] After etching the high-k dielectric (HK) layer 110, the subsequent process steps may be carried out to continue the fabrication of the MOSFET. The gate spacer material 140, for example, silicon nitride, can be deposited on the substrate 100 using appropriate 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. Subsequently, the top surface of the gate spacer material 140 can be removed by spacer top-hat etching using a plasma dry etching process, for example, a reactive ion etching (RIE) process.

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

[0031] In Figure 1D, the source / drain region 150 can be formed adjacent to the gate structure by ion implantation into the substrate 100. Ion implantation can alter the electronic structure and properties of the implanted region by implanting dopant atoms into the substrate 100. In the ion implantation process, ions are supplied by an ion source and then electrostatically accelerated to collide with the substrate 100. Various dopants, including p-type dopants (e.g., boron) and n-type dopants (e.g., phosphorus), can be used for source / drain formation. Doping can also 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 may be performed, such as a metallization process and other middle-of-line (MOL) / back-end-of-line (BEOL) processes. In the example illustrated above, polysilicon is used as the gate material, but in other embodiments, other MOSFET device structures, such as structures using non-silicon gate materials, may be fabricated.

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

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

[0035] In Figure 2A, a substrate 100 having the same structure as the substrate shown in Figure 1A is fabricated by the steps described above (i.e., etching of the HK layer 110 in Figure 1B, deposition of spacer material and spacer top-hat etching in Figure 1C, and source / drain formation in Figure 1D). Following these steps, a low-k dielectric 160 may be deposited on the substrate 100, and the polysilicon layer 120 (shown in Figures 1A to 1D) may be removed (dummy gate removal) to create a recess 165 for filling with substitution metal gate (RMG) material 170 (e.g., Figure 2B). The low-k dielectric 160 may include silicon-based dielectric materials having a low dielectric constant (i.e., low k value), such as organosilicate glass (SiCOH), high-density SiCOH, porous SiCOH, and other porous dielectric materials. Low-k dielectrics can 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 Figure 2A, the polysilicon layer 120 can be removed using a plasma dry etching process that selectively removes 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 containing, for example, a halogen gas. In certain embodiments, the etching gas may contain hydrogen bromide (HBr) and dichlorine (Cl2). The etching gas may also contain dioxygen (O2) and / or noble gases (e.g., He, Ne, Ar, Kr, etc.). The etching gas and process conditions may be selected so that the first plasma etching the polysilicon has high selectivity and a high polysilicon etching rate.

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

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

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

[0040] In the following, with reference to Figures 3 and 4, the effects of adding boron-containing and carbon-containing agents to the etching gas will be explained by comparing the calculated reaction energies.

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

[0042] In Figure 3, it is assumed that the etching of barium titanate proceeds by a reaction between the plasma and chlorine species. Based on density function theory (DFT) calculations, the reaction energies for the three reaction steps are obtained as follows. (1)BaTiO3(s)+6Cl(g)=BaCl2+TiCl4(s)+3O(g);ΔE=0.857eV (2a)BaCl2=BaCl2(g);ΔE=2.883eV (2b)TiCl4(s)=TiCl4(g);ΔE=0.0054eV

[0043] Reaction (1), namely the surface reaction between solid barium chloride (BaCl2), solid titanium chloride (TiCl2), and barium titanate forming oxygen atoms, is found to exhibit only slight endothermic properties (almost thermodynamically neutral) with a reaction energy of 0.857 eV. Furthermore, DFT calculations show that forming gaseous BaCl2 (2a) requires considerable energy (2.883 eV), meaning that BaCl2 exhibits only moderate volatility. In contrast, TiCl2 has high volatility with a minimal energy difference (0.054 eV) between the solid and gas phases. This result indicates the difficulty of removing etching products, particularly BaCl2, from the surface. In other words, the barium-oxygen bond in BaTiO3 is very stable and requires extremely large energy to break. Accordingly, fluorine-free chlorine-based plasma etching processes that only provide chlorine (e.g., Cl2 alone) may not be able to effectively etch BaTiO3. However, it should be noted that chlorine-based plasma etching processes may still be advantageous compared to fluorine-based plasma etching processes because barium and titanium fluoride are even less volatile (i.e., more difficult to remove from surfaces). 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 for barium titanate under etching conditions containing boron or carbon, according to an alternative embodiment.

[0045] Figure 4 shows that three DFT calculations, including reactions with boron or carbon, can alleviate the difficulty of etching BaTiO3 by enabling novel oxygen-containing etching products. The three additional reactions shown in Figure 4 are reactions of oxygen atoms with (A) boron chloride (BCl3), (B) carbon, and (C) dichloromethylene (CCl2), which produce the oxygen-containing etching products BClO, CO, and COCl2, respectively. All the calculated reactions exhibit substantial negative reaction energies in the range of approximately -35.1 eV to -23.5 eV, as shown below as (A) to (C), along with the initial reaction with chlorine (1). (1)BaTiO3(s)+6Cl(g)=BaCl2(g)+TiCl4(g)+3O(g);ΔE=3.795eV (A)3O(g)+3BCl(g)=3BClO(g);ΔE=-26.964eV (B)3O(g)+3C(g)=3CO(g);ΔE=-35.092eV (C)3O(g)+3CCl2(g)=3COCl2(g);ΔE=-23.538eV

[0046] The magnitude of these values ​​is considerably larger than the moderate positive reaction energy (i.e., 3.795 eV) in the case of (1) the formation of BaCl2, TiCl4 and oxygen atoms via the reaction of BaTiO3 with chlorine. Therefore, the etching of BaTiO3 can be made thermodynamically favorable (i.e., exothermic) by linking it with one or more additional reactions. In other words, adding boron or carbon to the etching gas can substantially improve the etching of BaTiO3 by cleaving the barium-oxygen bond and forming stable etching products having boron-oxygen or carbon-oxygen bonds. In these etching products, the bond order of these bonds may be any reasonable value. In other words, in various embodiments, single, double, and / or triple bonds with oxygen may be formed. Therefore, to enable these etching products, the etching gas may contain boron or carbon in addition to chlorine. In various embodiments, boron chloride (BCl3) or carbon tetrafluoride (CCl4) may be used alone as an etching gas or as an additive to an etching gas containing another chlorine source, such as dichloride (Cl2). In certain embodiments, other molecules may also be included in the etching gas to facilitate the cleavage of the barium-oxygen bond by providing novel oxygen-containing etching products. Such molecules may include, but are not limited to, N2, SO2, COS, NO, NO2, CO, CO2, BBr3, BBr2Cl, BBrCl2, CBr4, CBr3Cl, CBr2Cl2, or CBrCl3.

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

[0048] In Figure 5A, process flow 50 begins with loading a substrate into a plasma processing chamber, the substrate having a surface containing an alkaline earth metal oxide (block 500, Figure 1A). Next, a processing gas containing carbon tetrachloride (CCl4) may be flowed into the plasma processing chamber (block 510), and a fluorine-free plasma may be formed from the processing gas by applying source power to the source electrode of the plasma processing chamber (block 520, Figure 1B). Subsequently, the substrate may be exposed to the plasma to etch the oxide on its surface (block 530, Figure 1B).

[0049] In Figure 5B, process flow 52 begins with loading a substrate into a plasma processing chamber, the substrate having a surface containing barium, such as barium titanate (block 502, Figure 1A). Next, a processing gas containing a mixture of dichloride (Cl2) and boron chloride (BCl3) may be flowed into the plasma processing chamber (block 512), and a fluorine-free plasma may be formed from the processing gas by applying source power to the source electrode of the plasma processing chamber (block 520, Figure 1B). Subsequently, the substrate may be exposed to the plasma to etch the barium on its surface (block 532, Figure 1B).

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

[0051] Herein, exemplary embodiments of the present invention are summarized. Other embodiments may be understood from the entirety of this specification and the claims appended herein.

[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; and etching the oxide on the surface of the substrate by exposing it to the fluorine-free plasma.

[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 a plasma processing chamber.

[0055] Example 4. The method according to any one of Examples 1 to 3, wherein the treatment gas further comprises Cl2, BCl3, BCl2Br, BClBr2, or BBr3.

[0056] Example 5. The method according to any one of Examples 1 to 4, wherein the treatment gas further comprises N2, NO, NO2, CO, CO2, SO2, or COS.

[0057] Example 6. The method according to any one of Examples 1 to 5, wherein etching an oxide comprises forming a volatile product containing a carbon-oxygen bond.

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

[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 a 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 Cl2 and BCl3; forming a fluorine-free plasma from the processing gas by applying source power to the source electrode of the plasma processing chamber; and etching the barium on the surface of the substrate by exposing it to the fluorine-free plasma.

[0063] Example 12. The fluorine-free plasma is hydrogen-free, as described in Example 11.

[0064] Example 13. The method according to Example 11 or 12, further comprising flowing a noble gas into a 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 barium is performed to form volatile products containing boron-oxygen bonds.

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

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

[0069] Example 18. The method according to any one of Examples 15 to 17, wherein the first treatment gas comprises BCl3, BCl2Br, BClBr2, BBr3, CCl4, CCl3Br, CCl2Br2, CClBr3, or CBr4, and the first treatment gas further comprises N2, NO, NO2, CO, CO2, SO2, or COS.

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

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

[0072] While the present invention has been described with reference to exemplary embodiments, this specification is not intended to be constrained. Various modifications and combinations of the exemplary embodiments, as well as other embodiments of the present invention, will become apparent to those skilled in the art by reference to this specification. Accordingly, the appended claims are intended to encompass any such modifications or embodiments.

Claims

1. A method for processing a substrate, the method is The step of loading the substrate into a plasma processing chamber, wherein the substrate is barium titanate (BaTiO ３ ) or barium stannate (BaSnO ３ A step having a surface including, CCL ４ and the step of introducing a treatment gas containing bromine gas, The steps include: forming a fluorine-free plasma from a processing gas by applying source power to a source electrode in the plasma processing chamber, wherein the plasma is hydrogen-free; The substrate is exposed to the hydrogen-free and fluorine-free plasma, and the BaTiO ３ or BasnO ３ The step of etching, A method having

2. The method according to claim 1, further comprising the step of introducing a noble gas into the plasma processing chamber.

3. The aforementioned processing gas is further composed of Cl ２ including, or The bromine-containing gas is BCl ２ Br, BClBr ２ , or BBr ３ The method according to claim 1, which comprises.

4. The aforementioned processing gas is further N ２ No, no ２ CO, CO ２ SO ２ The method according to claim 1, or comprising COS.

5. The aforementioned BaTiO ３ The method according to claim 1, wherein the step of etching comprises the step of forming a volatile product containing a carbon-oxygen bond.

6. The aforementioned BaTiO ３ or BasnO ３ , BaTiO ３ The method according to claim 1.

7. The aforementioned BaTiO ３ or BasnO ３ is BasnO ３ The method according to claim 1.

8. A method for processing a substrate, the method is A step of loading the substrate into a plasma processing chamber, wherein the substrate has a surface containing barium, The step of introducing a processing gas into the plasma processing chamber, wherein the processing gas is Cl ２ , BCl ３ A step comprising a mixture of bromine-containing gases, The plasma processing chamber comprises the step of forming a fluorine-free plasma from the processing gas by applying source power to the source electrode of the plasma processing chamber, The steps include: exposing the substrate to the fluorine-free plasma to etch the barium on the surface; A method having

9. The method according to claim 8, wherein the fluorine-free plasma is hydrogen-free.

10. The method according to claim 8, further comprising the step of introducing a noble gas into the plasma processing chamber.

11. The method according to claim 8, wherein the surface further contains oxygen, and the step of etching the barium comprises the step of forming a volatile product containing a boron-oxygen bond.

12. A method for processing a substrate, the method is The step of loading the substrate into a plasma processing chamber, wherein the substrate is barium titanate (BaTiO ３ ) or barium stannate (BaSnO ３ A step having a surface including, A step of carrying out multiple periodic processes, wherein each of the multiple periodic processes is The first fluorine-free chemical species supplied from the first process gas is subjected to the BaTiO ３ or BasnO ３ Expose the BaTiO ３ or BasnO ３ The steps include reacting with the first fluorine-free chemical species to form a reaction product containing barium, and The step of exposing the reaction product to a second fluorine-free chemical species supplied from a second processing gas to remove the reaction product from the surface, wherein the first processing gas is N ２ No, no ２ CO, CO ２ SO ２ , or steps including COS, Steps having, A method having

13. The method according to claim 12, further comprising the step of forming a first plasma to generate the first fluorine-free chemical species.

14. The method according to claim 12, wherein the first processing gas contains a halogen other than fluorine.

15. The first processing gas is further composed of BCl ３ , BCl ２ Br, BClBr ２ , BBr ３ , CCl ４ , CCl ３ Br, CCl ２ Br ２ , CClBr ３ , or CBr ４ The method according to claim 12, including the method described in claim 12.

16. Furthermore, the process includes the step of forming a second plasma to generate the second fluorine-free chemical species, The method according to claim 12, wherein the second processing gas includes a noble gas.

17. The method according to claim 12, wherein each of the plurality of periodic processes further comprises the step of purging the plasma processing chamber to remove the first fluorine-free chemical species before the step of exposing the reaction product to the second fluorine-free chemical species.

18. Barium titanate (BaTiO) ３ The method according to claim 12, wherein the surface including ) does not contain strontium.

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