Patent Application
20250146128
The ever-shrinking critical dimensions in semiconductor devices require the use of steadily increasing numbers of masks and complex fabrication processes. By contrast, reducing the number of masks and processing steps is sought-after for managing edge placement errors (EPEs) and material and processing budgets. Complementary bottom-up manufacturing methods (sometimes referred to as scaling boosters) are therefore gaining increasing importance for cutting such Gordian Knot.
Deep UV photolithography using 193 nm light has been highly reliable and economically robust, even when critical device dimensions are at the sub-10 nm scale. Achieving these feature sizes in manufacturing relies on litho-etch-litho-etch (LELE) multi-patterning, wherein more than one exposure step is used in a single patterning layer to produce features with size and pitch that are much smaller than those imaged by a single mask.
However, for critical device dimensions at 5 nm or less, new problems have been encountered with photolithography, including the high cost associated with transitioning from deep UV (DUV) light sources to extreme UV (EUV) 13.5 nm light sources and resists, and those associated with the fundamentals of statistical variability. These problems have led to a push to find new reliable bottom-up methods for patterning. Area-selective deposition is one such bottom-up “chemical patterning” method that holds promise to allow molecular-scale chemical sensitivity and reaction design to augment traditional “top-down” patterning methods.
Fully self-aligned vias represent an example of how bottom-up fabrication methods, such as area-selective deposition (ASD), can bolster top-down manufacturing ones. In short, ASD is employed to alleviate the EPE when landing a metal connect to the functional device layer underneath by providing an additional dielectric layer that prevents interconnects from being too close to each other. Other examples are contact-over-gate structures, bottom-up filling, selective hardmask layers, and etch-stop layers, which have been detailed, for example, in Parsons and Clark (2020) Chem. Mater. 32(12), 4920-4953.
In ASD, bottom-up structures may be deposited by inhibiting heterogeneous surface reactions only on predefined surfaces of a patterned substrate that consists of growth surfaces (GSs, on which deposition is desired) and nongrowth surfaces (NGSs, on which deposition is not desired). Such control is often exerted through selective manipulation of surface functional groups to either allow (on the GS) or inhibit (on the NGS) the deposition chemistry.
Atomic layer deposition (ALD) is a layer-by-layer deposition method that allows for atomic-level thickness control and layer conformality on 3D structures over large substrate areas. In its most simple expression, ALD relies on the cyclic and alternating exposures of a substrate to a precursor and a co-reactant that undergo self-limiting surface reactions. ALD can offer the optimal conditions to control each individual surface (half-)reaction at the atomic level, during the precursor or the co-reactant steps. If sufficiently large differences in thermodynamics or kinetics of surface reactions exist on growth vs. nongrowth surfaces, selective deposition can be naturally obtained, referred to as inherently selective ALD.
Often, the NGS needs to be selectively modified so that thermodynamic or kinetic control can be achieved. An overview can be found, for example, in Mameli and Teplyakov (2023) Acc. Chem. Res. 56(15), 2084-2095.
Area-selective ALD (AS-ALD) processes have been developed, yet the selective deposition of hardmask materials on SiN as GS with respect to SiO2 as NGS has been an extremely challenging target to achieve. AS-ALD of TIN, TiO2, and other typical hardmask materials on SiN vs. SiO2 materials that are ubiquitous in almost every device patterning step, could dramatically expand the processing window of several patterning processes employed in semiconductor manufacturing. In turn, this would allow better control of edge placement errors and reduce the number of mask steps required during device fabrication.
So far, only one example of AS-ALD on SiN vs. SiO2 has been reported (Xu et al. (2022) J. Vac. Sci. Technol. A 40(1), 012403). This process allows for depositing ˜2.7 nm of Al2O3 on SiNx vs. SiO2 using sequential exposures of small molecule inhibitors, i.e., bis-(dimethylamino) dimethylsilane (BDMADMS) and (dimethylamino) trimethylsilane (DMATMS) on blanket SiN and SiO2 layers, and dimethylaluminum isopropoxide (DMAI) as an Al precursor and H2O as a co-reactant. While this example represents a milestone in understanding how to chemically differentiate between SiN and SiO2 surfaces, its applicability in industry may be limited. Selective deposition needs to be achieved on half-processed patterns where SiO2 and SiN layers coexist on the surface; thus, for industrially relevant processes, such manipulation of a freshly deposited SiN surface is not a viable option.
In that multiple patterning is crucial to enabling continuous downscaling and ever-shrinking critical dimensions in semiconductor devices, stringent overlay requirements have to be mitigated in order to broaden the processing window. This can currently be achieved by advanced patterning technologies such as self-aligned multiple patterning (SAMP) and self-aligned block (SAB) patterning. However, such technologies increase the number of processing steps needed for functional patterning. Accordingly, there remains a need for improved selective deposition schemes that can selectively deposit hardmask materials on, for example SiN vs. SiO2 are sought that enable more efficient self-aligned patterning fabrication schemes.
Aspects of the inventive concept include methods and tools for simplifying patterning technologies by selective deposition of hardmask materials. Methods of the inventive concept include applications of an SAB patterning technology.
Aspects of the methods of the inventive concept enable high selectivity for deposition between SiN and SiO2 by exploiting differences in surface fluorination, etch-rate, reactivity with aminosilane inhibitors and in the case of halide precursor electrostatic repulsion to further enhance selectivity.
Aspects of the tools of the inventive concept provide a reduced surface to wall ratio and are less prone to process drifts during plasma etching.
Aspects of the methods of the inventive concept and applications thereof provide a reduction in the number of steps required and a pattern-transfer of denser features over conventional SAB methods and applications.
In an aspect of the inventive concept, provided is a method of selectively depositing a metal oxide or metal oxynitride on a substrate, the substrate comprising a surface, the surface comprising: an oxide layer portion comprising hydroxyl groups on SiO2 and a nitride layer portion, the method comprising: pretreating the surface with a plasma, wherein the plasma removes a native oxide layer on the nitride layer portion; and functionalizing the surface of the substrate with at least one cycle of exposing the surface to an aminosilane small molecule inhibitor, followed by at least one cycle of: exposing the surface to a metal precursor; and exposing the surface to a co-reactant, to provide a metal oxide or metal oxynitride layer selectively deposited on the nitride layer portion of the substrate over the oxide layer portion of the substrate.
In another aspect of the inventive concept, provided is a method of selectively depositing a metal oxide or metal oxynitride on a substrate, the substrate comprising a surface, the surface comprising: an oxide layer portion comprising hydroxyl groups on SiO2 and a nitride layer portion, the method comprising: pretreating the surface with a plasma, wherein the plasma removes a native oxide layer on the nitride layer portion; and at least one cycle of: functionalizing the surface of the substrate by exposing the surface to an aminosilane small molecule inhibitor; exposing the surface to a metal precursor; and exposing the surface to a co-reactant, to provide a metal oxide or metal oxynitride layer selectively deposited on the nitride layer portion of the substrate over the oxide layer portion of the substrate.
Further aspects of the inventive concept include tools and devices for performing the methods as described herein, patterned layers prepared by the methods as described herein, and semiconductor devices including patterned layers prepared by the methods as described herein.
The foregoing and other aspects of the present inventive concept will now be described in more detail with respect to other embodiments described herein. It should be appreciated that the inventive concept can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art.
The terminology used in the description of the inventive concept herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive concept. As used in the description of the inventive concept and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Additionally, as used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items and may be abbreviated as “/”.
The term “comprise,” as used herein, in addition to its regular meaning, may also include, and, in some embodiments, may specifically refer to the expressions “consist essentially of” and/or “consist of.” Thus, the expression “comprise” can also refer to, in some embodiments, the specifically listed elements of that which is claimed and does not include further elements, as well as embodiments in which the specifically listed elements of that which is claimed may and/or does encompass further elements, or embodiments in which the specifically listed elements of that which is claimed may encompass further elements that do not materially affect the basic and novel characteristic(s) of that which is claimed. For example, that which is claimed, such as a composition, formulation, method, system, etc. “comprising” listed elements also encompasses, for example, a composition, formulation, method, system, etc. “consisting of,” i.e., wherein that which is claimed does not include further elements, and a composition, formulation, method, system, etc. “consisting essentially of,” i.e., wherein that which is claimed may include further elements that do not materially affect the basic and novel characteristic(s) of that which is claimed.
The term “about” generally refers to a range of numeric values that one of skill in the art would consider equivalent to the recited numeric value or having the same function or result. For example, “about” may refer to a range that is within ±1%, ±2%, ±5%, ±7%, ±10%, ±15%, or even ±20% of the indicated value, depending upon the numeric values that one of skill in the art would consider equivalent to the recited numeric value or having the same function or result. Furthermore, in some embodiments, a numeric value modified by the term “about” may also include a numeric value that is “exactly” the recited numeric value. In addition, any numeric value presented without modification will be appreciated to include numeric values “about” the recited numeric value, as well as include “exactly” the recited numeric value. Similarly, the term “substantially” means largely, but not wholly, the same form, manner or degree and the particular element will have a range of configurations as a person of ordinary skill in the art would consider as having the same function or result. When a particular element is expressed as an approximation by use of the term “substantially,” it will be understood that the particular element forms another embodiment.
The term “substrate,” as used herein, can broadly refer to any layer and/or surface upon which processing is desired. Thus, for example, a native oxide film on the surface of a silicon or silicon nitride substrate may itself be considered a substrate for the purposes of this discussion. Likewise, layers deposited on silicon, silicon nitride, or on other base substrates may likewise be considered substrates in some embodiments. For example, in some embodiments, a multi-layer stack may be formed, and then atomic layer deposition may be performed on the top layer, or a surface of the top layer, of the stack. In such a case, the top layer may be considered the substrate. In general, the layer or layers upon which the chemical precursor is deposited and/or which reacts with the chemical precursor can be considered the substrate layer(s). The material for the substrate may be any that may be appreciated by one of skill in the art in the field of electronics and/or semiconductors.
It will be understood that when an element is referred to as being “on” another element, layer, or substrate, etc., it can be directly on the other element, layer, or substrate, etc., or intervening elements, layers, or substrates, etc. may also be present. In contrast, when an element is referred to as being “directly on” another element, layer, or substrate, etc., there are no intervening elements present.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive concept belongs.
The term atomic layer deposition, or ALD, as used herein, can broadly refer to the level of layer dimensional control in a deposition process, that can be achieved at the angstrom (Å) or sub-angstrom level. Thus, deposition of or growth of a layer through atomic layer deposition, or a cycle thereof, may generally correspond to the size of atoms and/or molecules. The average added layer thickness per cycle of ALD can be less than 1 Å (0.1 nm) per deposition cycle, for example, less than about 0.1 Å, about 0.1 Å, about 0.2 Å, about 0.3 Å, about 0.4 Å, about 0.5 Å, about 0.6 Å, about 0.7 Å, about 0.8 Å, or about 0.9 Å per cycle, or more than 1 Å per cycle, for example, about 1Å, about 1.1 Å, about 1.2 Å, about 1.3 Å, about 1.4 Å, about 1.5 Å, about 1.6 Å, about 1.7 Å, about 1.8 Å, about 2 Å, about 3 Å, about 4 Å, about 5 Å, about 6 Å, about 7 Å, about 8 Å, about 9 Å, about 10 Å (1 nm), about 11 Å, about 12 Å, about 13 Å, about 14 Å, about 15 Å, about 16 Å, about 17 Å, about 18 Å, about 19 Å, or about 20 Å (2 nm) per cycle, or any number between about 0.1-30 Å per deposition cycle. In some embodiments, the average added layer thickness per cycle is between about 0.1-2 Å, about 0.2-2 Å per deposition cycle, about 0.3-2 Å, about 0.4-2 Å per deposition cycle, about 0.5-2 Å per deposition cycle, about 0.6-4 Å per deposition cycle, or about 0.1-4 Å per deposition cycle.
The layer prepared by the methods of the inventive concept may have a thickness of greater than or equal to 1 nm, greater than or equal to 2 nm, greater than or equal to 3 nm, greater than or equal to 4 nm, greater than or equal to 5 nm, greater than or equal to 6 nm, greater than or equal to 7 nm, greater than or equal to 8 nm, greater than or equal to 9 nm, greater than or equal to 10 nm, greater than or equal to 11 nm, greater than or equal to 13 nm, greater than or equal to 14 nm, greater than or equal to 15 nm, greater than or equal to 16 nm, greater than or equal to 18 nm, greater than or equal to 20 nm, in a range of greater than or equal to about 3 nm to about 20 nm, in a range of greater than or equal to about 5 nm to about 20 nm, or in a range of greater than or equal to about 5 nm to about 15 nm.
The choice of chemical precursor or precursors to deposit the metal, metal oxide, metal nitride, or metal oxynitride films according to methods of the inventive concept are not particularly limited, and may be any that may be appreciated by one of skill in the art. In some embodiments, the chemical precursor may include, for example, silicon (Si), titanium (Ti), hafnium (Hf), tantalum (Ta), tin (Sn), molybdenum (Mo), or aluminum (Al). In some embodiments, the chemical precursor includes titanium (Ti), for example, TiCl4, titanium tetraisopropoxide (TTIP), or tetrakis (dimethylamino) titanium (TDMAT). In some embodiments, the chemical precursor may be a metal halide, for example, SiCl4, Si2Cl6, SiH2Cl2, AlCl3, Al2Cl6, FeCl3, HfCl4, MoO2Cl2, MoF6, MoCl5, TaF5, TaCl5, Tal5, WF6, WCl6, or ZrCl4. In some embodiments, the chemical precursor may be TiCl4. In some embodiments, the chemical precursor may be a silane, e.g., a trihalo-alkysilane, such as but not limited to trichloro (octadecyl) silane, a trimethoxy-alkylsilane or a trimethoxy-aminosilane, such as 3-aminopropyltrimethoxysilane. Similarly, the deposition process is not particularly limited. In some embodiments, the deposition may be a thermal deposition process. In some embodiments, the deposition may be or include a plasma deposition process.
In addition, the co-reactant, or co-reactants, to deposit the metal, metal oxide, metal nitride, metal oxynitride, metal oxycarbide, metal carbonitride, metal carbide, metal sulfide, or metal oxysulfide, or metal (oxy) selenide films according to methods of the inventive concept are not particularly limited, and may be any that may be appreciated by one of skill in the art, for example, H2O, H2O2/H2O mixtures, O2, O3, NH3, or N2H4, or H2S, or H2Se, or a hydrocarbon, e.g., CH4, or a halogenated hydrocarbon, e.g., CHX3, CH2X2, etc. In some embodiments, wherein the deposition is a thermal deposition process, the co-reactant may be H2O, such as in thermal titanium oxide (t-TiO2) deposition. In some embodiments, wherein the deposition is a plasma deposition process, the co-reactant may include a gas, for example, N2, H2, Ar, O2, or H2S, or H2Se or a mixture of gases, for example, N2/H2, H2/Ar, or N2/Ar. In some embodiments, the co-reactant may be a N2/H2 plasma, such as in plasma titanium oxynitride (p-TiON) deposition. In some embodiments, the plasma deposition may include an NH3 plasma.
The number of ALD or deposition cycles performed in the methods of the present inventive concept is not particularly limited, and may be any number of cycles that would be appreciated by one of skill in the art. For example, the number of deposition cycles in the process may be between 1 and about 1,000 cycles. In some embodiments, the number of deposition cycles may be between about 1-600 cycles, for example, 1 cycle, about 5 cycles, about 10 cycles, about 20 cycles, about 30 cycles, about 40 cycles, about 50 cycles, about 60 cycles, about 70 cycles, about 80 cycles about 100 cycles, about 150 cycles, about 200 cycles, about 250 cycles, about 300 cycles, about 350 cycles, about 400 cycles, about 450 cycles, about 500 cycles, about 550 cycles, or about 600 cycles, or any number of deposition cycles between and including 1 deposition cycle and about 1,000 deposition cycles. Each deposition cycle may include exposing the substrate to alternating pulses/doses of a chemical precursor and a co-reactant. In some embodiments, the deposition cycle may include exposing the substrate to a pulse/dose, or more than one pulse/dose, for example, 2, 3, 4, 5, 6 pulses/doses, etc. of a chemical precursor, and a pulse/dose, or more than one pulse/dose, for example, 2, 3, 4, 5, 6 pulses/doses, etc. of a co-reactant. Prior to the deposition cycle(s), the surface on which deposition is to take place may be: precleaned, for example, with a plasma/plasma etching step, such as exposure to, or multiple exposures/“cycles” to a CF4/N2 plasma, to remove, for example, a native oxide film that may be present on the surface; and/or functionalized, for example, through exposure to, or multiple exposures/“cycles” to a small molecule inhibitor (SMI), for example, an aminosilane, such as bis (N,N-dimethylamino) dimethylsilane (BDMADMS) or (N,N-dimethylamino) trimethysilane (DMATMS). In some embodiments, the aminosilane/SMI may be hexamethyldisilazane (HMDS) or a silatrane, e.g., methylsilatrane, or related compounds. In some embodiments, the SMI may be DMATMS. In some embodiments, functionalization of the surface may selectively passivate remaining exposed hydroxyl groups on the nongrowth surface of the substrate, for example, an oxide layer, such as an SiO2 layer or portion of a substrate, thus forming an effective inhibition layer for subsequent ALD. Accordingly, any compound/SMI capable of selectively passivating remaining exposed hydroxyl groups on the nongrowth surface of the substrate may be used/envisioned without departing from the scope of the inventive concept.
Accordingly, in some embodiments, a substrate, on which deposition is to take place, may be: precleaned, for example, with a plasma etching step; functionalized, for example, by exposure to an SMI; and followed by at least one deposition cycle including exposure to a precursor and a co-reactant, to provide a layer selectively deposited on a GS vs. an NGS.
In other embodiments, the deposition cycle may include exposure of a surface on which deposition of a film/layer is to take place, for example a surface of a substrate, to an SMI, followed by exposure of the surface to a precursor, and exposure of the surface to a co-reactant. Accordingly, the substrate, on which deposition is to take place, may be precleaned, followed by at least one deposition cycle including: functionalizing the surface, for example, by exposure to an SMI; exposing the surface to a precursor; and exposing the surface to a co-reactant, to provide a layer selectively deposited on a GS vs. an NGS.
In some embodiments, the methods of the inventive concept may include a back-etching step with, for example, exposure to a plasma after the at least one deposition cycle(s). In some embodiments, the chemistry of the back-etching plasma is the same plasma employed for pre-deposition etching/cleaning to limit cross-contamination issues. For example, the precleaning/pre-deposition plasma and the back-etching plasma may both be a mixture, for example, a CF4/N2 plasma, but is not limited thereto. In some embodiments, the mixture may include, CF4, CHF3, and/or CxHyFz with H2, O2, N2, and/or Ar. In some embodiments, the back-etching plasma may include Cl2, and/or mixtures thereof with H2, N2, O2, and/or Ar. In some embodiments, the back-etching plasma may include NH3, and/or mixtures thereof with N2 and/or H2. The exposure of the layer or layers deposited on a substrate to the back-etching plasma may include, for example, a single exposure, or may include multiple exposures/“cycles” to the back-etching plasma.
The exposure of the substrate to a plasma to preclean the substrate prior to deposition, and the exposure of the substrate to a plasma to back-etch following deposition, may include a single plasma exposure or “cycle” on a rotating workpiece/rotary spatial ALD reactor, as opposed to an ALD deposition cycle, or may include multiple plasma exposures/“cycles” on the ALD reactor. The number of plasma exposures/“cycles” prior to deposition and/or postdeposition back-etching is not particularly limited. This number may be anywhere from 1 to about 100 exposures/“cycles.” In some embodiments, the number of pre-deposition plasma exposures/“cycles” may be between about and including 50 to about 100 exposures/“cycles of precleaning plasma prior to ALD. In some embodiments, the number of post-deposition back-etching plasma exposures/“cycles” may be about and including 20 to about 80 exposures/“cycles” of back-etching plasma following ALD.
In some embodiments, when functionalizing the substrate on which deposition is to take place by exposure to an aminosilane SMI prior to ALD, the exposure of the substrate to the functionalizing SMI may include a single exposure or “cycle” on a rotating workpiece/rotary spatial ALD reactor, or exposure of the substrate to the functionalizing SMI may include multiple plasma exposures/“cycles” on the ALD reactor. For example, the number may be anywhere from 1 to about 10 exposures/“cycles,” for example, the number of exposures/“cycles” may be about 5 exposures/“cycles” when functionalizing the substrate prior to ALD.
The temperature and/or pressure at which the methods of the present inventive concept are performed are not particularly limited. Nevertheless, in some embodiments, the temperature at which the ALD methods are performed between and including about 100° C. and about 300° C. In some embodiments, the temperature is between and including about 100° C. and about 250° C. In some embodiments, the temperature is between and including about 100° C. and about 200° C. In some embodiments, the pressure at which the ALD methods are performed at atmospheric or ambient pressures.
The present inventive concept overcomes the limitations and disadvantages of prior techniques. The inventive concept provides ALD techniques, which enable the selective deposition of metals, metal oxides and metal oxynitrides on a surface or substrate. According to embodiments of the present inventive concept, selective deposition may refer to deposition of, for example, a material, such as a metal or a material including a metal, on a first portion of a surface or substrate, such as a GS, with no detectable deposition, with minimal deposition, or with significantly less or reduced deposition, of the material on a second portion of the substrate or surface, such as an NGS. The first and second portions of the surface or substrate may be of differing materials or composition. For example, in some embodiments, the first portion of the surface may be a nitride layer, for example, a silicon nitride (SiN) layer, a carbon-doped silicon nitride (silicon carbon nitride, SiCN) layer, or a metal nitride layer such as HIN, TiN, and/or ZrN, i.e., exemplary nitrides of group-IV metals/elements, or SnN, or nitride layers that may include germanium (Ge) or lead (Pb), and the second portion of the surface may be an oxide layer including hydroxyl groups from SiO2, such as a silicon oxide (SiO2) layer, a carbon-doped silicon oxide (C: SiO2) layer, or a silicon carbide (SiC) layer. In some embodiments, the first portion of the surface may be crystalline silicon (c-Si).
“Selective deposition,” “area selective deposition” (ASD), and “area selective atomic layer deposition” (AS-ALD) refer to processes that lead to deposition of materials on only desired area of, for example, a patterned substrate. The patterned substrate may include areas or portions, and deposition is desired on one area or portion but not the other. Accordingly, selective deposition may include deposition of, for example, a material, such as a metal or a material including a metal, on a first portion (GS) of a surface or substrate, with no deposition, with minimal deposition, or with significantly less or reduced deposition, of the material on a second portion (NGS) of the substrate or surface. The first and second portions/areas of the surface or substrate may be of differing materials or composition.
In some embodiments, the selectivity of deposition may be defined, for example, as discussed in Gladfelter (1993) Chem. Mater. 5 (10), 1372-1388, and as set forth by Equation (1):
wherein XGS and XNGS are measurements of the amount of material deposited (thickness or area coverage) on the growth surface (GS) and on the nongrowth surface (NGS). S may have a value between 0 and 1, wherein S=0 is indicative of no selectivity of deposition on the GS and the NGS, and wherein S=1 is indicative of complete (100%) selectivity of deposition on the GS and the NGS. In some embodiments, the methods of the inventive concept may have a selectivity of deposition S of ≥0.80, ≥0.85, ≥0.88, ≥0.90, ≥0.91, ≥0.92, ≥0.93, ≥0.94, ≥0.95, ≥0.96, ≥0.97, ≥0.98, or ≥0.99, or even S=1.00, wherein no detectible deposition takes place/is observed on the NGS.
In some embodiments, tools of the inventive concept include a carousel-type reactor for performing pre-treatments and deposition steps without exposing the workpiece to a different atmosphere. In some embodiments, the carousel-type reactor may contain a plurality of plasma etching zone(s), inhibitor, precursor, and co-reactant etching zones.
A semiconductor device may be formed on the workpiece. The semiconductor device may comprise SiN and SiO2 patterned areas/layers, for example, including an SiN core and SiO2 spacers.
The plasma zone is equipped to perform plasma chemistries that enable etching of SiO2 (and SiN) e.g. (CF4, H2, CF4 H2 mixtures, and general fluorocarbon chemistries CxHyFz) to reveal fresh SiN surfaces and thus provide enough chemical contrast for carrying out selective deposition processes. Alternatively, other etching methods such as thermal or plasma atomic layer etching may be used for the same purpose. The dosing from the multitude of zones is computer programmable such that N cycles of plasma etching can be performed with a rotation speed comprised between 0.5 and 200 RPM. Upon plasma etching in particular a partially fluorinated SiN and SiO2 surface is formed. Silane-based inhibitors such as (N,N-dimethylamino) trimethylsilane (DMATMS) can then be dosed with appropriate rotation speed between 0.5 and 200 RPM. In some embodiments, the total dose (vapor pressure x exposure time) is adjusted so that only one exposure is needed, and the atomic layer deposition process can be performed immediately thereafter. Alternatively, multiple rotations/“cycles” of the workpiece are performed to functionalize the surface before the chemistry is switched to deposition. DMATMS selectively passivates the remaining exposed hydroxyl on the partially fluorinated SiO2 thus forming an effective inhibition layer for subsequent ALD. TiO2 TiN, TiOxNy, TiC, HfO2, HfN, HfON, Ta2O5, TaN, TaOxNy SiN, Al2O3 can be selectively deposited on the partially fluorinated SiN in presence of fluorinated and silylated SiO2. Amino-based precursors and halide-based precursors (halides may be used to enhance the electrostatic repulsions) may be employed as ALD precursors. H2O, O3 H2O2 or oxidizing plasma chemistries (CO2, CO, O2, H2O) are employed to selectively grow oxides, while NH3, N2H4 or N2 H2 or N2/H2 mixtures are employed to selectively deposit nitrides and/or oxynitrides materials thermally or by plasma. The silane-based inhibitor may be applied as a pretreatment step, prior to and not as part of the ALD cycle (BC-type cycles for ALD), in which only chemical precursor and co-reactant dosing are included in the ALD step, or the silane-based inhibitor may be applied as part of the ALD cycle (ABC-type cycles for ALD), wherein inhibitor, chemical precursor, and co-reactant dosing are included in the ALD step. In cases of plasma-based deposition processes, the inhibitor may be re-applied after every m (with m>1) cycle(s), for example, every 2, 3, 4, 5, etc. cycles, in order to refresh the inhibition layer, as opposed to as a pretreatment step with BC-type cycles for ALD, with every cycle (m=1) with ABC-type cycles for ALD.
One or multiple plasma (or thermal) etching zones can be employed for correction steps in cases where the selectivity is limited. Unwanted material can then be removed by selected etch-back chemistries. In some embodiments, the chemistry of the back-etching is the same as that employed for pre-deposition etching in order to limit cross-contamination issues.
Alternatively, in some embodiments, a cluster tool is employed with separate chambers dedicated to etching and deposition. A timely and under inert atmosphere transfer is needed in order to prevent surface oxidation of the freshly etched SiN pattern.
Current SAB approaches make use of and require several pattering steps and spin-on coating steps for patterning.
A standard SAB process flow may include steps of: (1) core lithography; (2) core etch; (3) spacer deposition; (4) spacer RIE; (5) core cut lithography; (6) core cut etch; (7) spin on block coating; (8) spin on block etch back; (9) spacer side cut lithography; (10) spacer side cut etch; (11) spin on block coat; (12) spin on block etch back; (13) core pull; and (14) metal hardmask etch, for example, as depicted in
In contrast, the SAB with an ASD hardmask deposition according to embodiments of the inventive concept, for example, as depicted in
The SAB process flow of the inventive concept, including an ASD hardmask deposition, reduces the number of steps required for pattern-transferring, and permits the transfer of denser features in the SAB process. It further enables selective deposition on SiN vs. SiO2 with high-throughput, and provides an option for back-etching, all within the same tool which can be critical for such a challenging selective deposition process.
Chemistries that provide enough deposition selectivity between SiN and SiO2 are not obvious and very few examples have been provided in the literature. Pre-treatments are crucial for enabling such selectivity between SiN and SiO2. The carousel-type reactor design of the inventive concept has several advantages for this purpose: short timelapse between SiN surface revealing step and inhibitor dose. This is crucial to limit SiN surface oxidation and hence degradation of selectivity. The preferred use of halide-based precursors enables low-temperature and low-carbon content selective hardmask materials to be deposited and enhanced the attainable selectivity by electrostatic repulsion with the partially fluorinated surfaces.
Having described various aspects of the present inventive concept, the same will be explained in further detail in the following examples, which are included herein for illustration purposes only, and which are not intended to be limiting to the inventive concept.
Herein, an industrially compatible route for AS-ALD of both TiO2 and TiON on SiN vs. SiO2 using both thermal and plasma processes is demonstrated. The process makes use of CF4 plasma chemistry to remove the native oxide(s) from SiN surfaces, followed by a DMATMS functionalization step. AS-ALD of thermal TiO2 (t-TiO2) and plasma TiON (p-TiON), using titanium tetrachloride (TiCl4) as the Ti-precursor, was demonstrated by scanning and transmission electron microscopy (SEM and TEM, respectively). Virtually perfect selectivity for t-TiO2 is demonstrated at both 100 and 200° C. in combination with plasma back-etching correction steps, leading to ˜8 and ˜7 nm-thick selective deposition. For p-TiON, high selectivity was achieved for ˜5 nm-thick selective deposition. By coincidence, the same process was found to be selective also on Si vs. SiO2, thus revealing a broader scope. The effect of several process parameters (deposition temperature, precursor chemistry, recipe strategies) has also been investigated. Lastly, considerations on the underlying surface chemistry enabling the selectivity of these processes are drawn on the basis of these results.
ALD Processes. Depositions were carried out in a home-built rotary spatial ALD reactor. The reactor consists of a rotating substrate holder that can accommodate 150 mm wafers and an injector head with several slots for gas-phase reactant delivery, separated by inert N2 curtains. The reactor is enclosed in a convective oven for temperature control and under atmospheric pressure. The exposure to each reactant is set by the partial pressure of the reactant and the rotation speed expressed in rotations-per-minute (RPM). The injector head is equipped with a dielectric barrier discharge (DBD) plasma source. For the selective deposition of t-TiO2 and p-TiON, commercially available DMATMS (Gelest) was used without further purification and tested as a small molecule inhibitor. A glass bubbler was filled in a glovebox and kept at room temperature with an Ar bubbling flow of 100 sccm, further diluted with 250 sccm of Ar. DMATMS pretreatments were carried out using 5 substrate rotations underneath the injector head (referred to as 5 “cycles”) at a rotation speed of 50 rpm. Titanium tetrachloride, TiCl4, was used as the titanium precursor and deionized H2O as the co-reactant for thermal TiO2. For plasma TiON, a mixture of N2 (9900 sccm) and H2 (100 sccm) was used as a co-reactant, and the plasma was ignited with a dielectric barrier discharge (DBD) plasma source. TiCl4 was stored in a stainless-steel bubbler and kept at room temperature (vapor pressure 9.6 Torr at 20° C.). An Ar bubbling flow of 25 sccm at a rotation speed of 25 rpm was used to carry the vapor to the injector head. This corresponds to exposure times of ˜100 ms and thus a total exposure of ˜0.03 Torrs. The flow was further diluted with Ar to a total of 1000 sccm before it reached the reactor. Although no oxygen was intentionally added to the plasma-feeding mixtures, background impurities resulted in the incorporation of oxygen. In an earlier study, similar results for SiN that was deposited likewise in the same spatial ALD reactor were reported. Other reports exist on the difficulty of removal of O- and C-impurities from ALD-grown nitride films. In a control experiment, TDMAT was employed as the Ti-precursor and stored in a stainless-steel bubbler and heated to 40° C. (vapor pressure 0.5 Torr at 40° C.). An Ar bubbling flow of 120 sccm at a rotation speed of 25 rpm was used to carry the vapor to the injector head. This corresponds to exposure times of ˜100 ms and a total exposure of ˜0.01 Torrs. H2O was kept in a glass bubbler at room temperature. An Ar bubbling flow of 250 sccm was further diluted with 750 sccm of Ar, corresponding to total exposure times of ˜0.25 Torrs.
For p-TiON, 100 sccm of H2 and 9900 sccm of N2 were supplied to the DBD plasma source which was actuated with a supply voltage of 100 V at a frequency of 75 KHz.
Plasma Etching Process. All etching experiments were performed in the same spatial ALD rotary laboratory-scale reactor. CF4 and N2 were transported through separate gas lines to the plasma source from a centralized gas supply and merged only about 50 cm upstream of the plasma source. For the back-etching processes, a flow of 100 sccm was employed for CF4 and 9900 sccm for N2 in order to ensure gentle back-etching conditions.
Substrate and Pattern Preparation. ˜80 nm SiN and ˜150 nm SiO2 layers were deposited on 150 mm c-Si wafers using a PECVD reactor from Elettrorava. The patterned substrates were prepared in a state-of-the-art 300 mm semiconductor fabrication laboratory using lithography, etching, and chemical mechanical polishing to fabricate SiN and SiO2 line and space patterns.
Analytical Methods. An ex situ Horiba Uvisel 2 spectroscopic ellipsometer was used to measure the thickness of the spatial ALD deposited layers and of the SiO2 layers before and after each etching experiment. Ellipsometric data were acquired in the range from 1.5 to 3.5 eV with steps of 0.1 eV and 500 ms integration time, and at an incidence angle of 70°, a spot size of 2030×705 μm2 and a modulator-analyzer configuration of 0-45°. XPS measurements were performed using a ThermoFisher K-alpha system with a monochromatic Al Kα-radiation and a takeoff angle of 45°. When discussing peak positions, the data were calibrated by referring all spectra to C 1s at 248.8 eV.
Cross-sectional SEM was performed using a Hitachi SU 9000 microscope with an accelerating voltage of 0.5-30 kV, 0.4 nm resolution, and high-quality elemental analysis (EDS).
Cross-sectional TEM was performed in high-angle annular dark-field (HAADF) scanning mode (STEM) and in bright-field TEM modes using a probe-corrected TEM system (JEOL JEM ARM 200F) equipped with a 100 mm2 Centurio SDD energy-dispersive X-ray spectroscopy (EDX) detector for chemical analysis. The selectivity, S, from SEM and TEM images was calculated as shown in Equation (1)
wherein XGS and XNGS are measurements of the amount of material deposited on the GS and on the nongrowth surface NGS; for the selectivity in terms of coverage, the area coverage of TiO2 and TiON islands is calculated for the NGS, while for the selectivity in terms of thickness, the thickness was calculated from the TEM images on NGS and GS.
Selectivity on Blanket Substrates. The challenging aspect in developing selective deposition processes on SiN as the GS vs. SiO2 as the NGS is that both materials have similar surface chemistry. This is particularly the case when considering the inevitably present native oxide on the SiN surface, especially when dealing with industrially relevant processes, i.e., half-fabricates consisting of processed-patterned wafers. To this end, an in situ plasma etching step was devised to preclean the SiN from its native oxide and thus achieve a suitable starting surface for further processing.
As illustrated in
An atmospheric-pressure dielectric barrier discharge (DBD) plasma process with CF4/N2 plasma chemistry was employed as a preconditioning treatment. More details on the plasma etching can be found in Karasulu et al. (2023) Adv. Mater. 35(25), 2301204. 3×3 cm2 c-Si substrate coupons with plasma-enhanced chemical vapor deposition (PECVD) SiN and SiO2 atop were loaded together on a 6 in. stainless-steel substrate holder and subjected to the same processing steps. The resulting samples were analyzed by X-ray photoelectron spectroscopy (XPS) to investigate the nucleation and growth behavior of the respective materials on both the SiO2 and SiN surfaces. t-TiO2 was investigated at processing temperatures of 100 and 200° C., respectively, and p-TiON was investigated only at 200° C.
When DMATMS is employed as a pretreatment step only, and not as part of the ALD recipe, are referred to as BC-type cycles, indicating that only TiCl4 and H2O are dosed in the ALD step. Conversely, when DMATMS is dosed also as part of the ALD cycle, are referred to as ABC-type cycles.
It was noted that, after 100 t-TiO2 and 250 p-TiON cycles on the SiN substrate, the Si 2p region shows two features: one at ˜102.0 eV, which is consistent with SiN, and one at 103.5 eV which points toward surface oxidation and SiO2 formation. It is speculated that such oxidation is marginally due to the H2O dosing and largely due to the fact that the TiO2 layer is not yet fully closed; thus, postprocess oxidation can easily take place. Using the thickogram method for measuring film thickness (which makes use of the ratio of overlayer and substrate XPS peak intensities together with electron escape depth and sensitivity factors), a nominal TiO2 thickness of ˜0.7 nm was estimated after 100 cycles on SiN. Based on the growth per cycle (GPC) measurements for the t-TiO2 process at 100° C. on c-Si substrates, a thickness of ˜7 nm was expected after 100 cycles (see FIG. 7). This observation suggests a significant nucleation delay also on the GS, SiN. Assuming an equal GPC of the standard t-TiO2 process on c-Si, it is estimated that there is a nucleation delay of ˜70 cycles on the SiN surface. After 250 cycles, a nominal thickness of ˜0.3 nm was calculated from XPS data on the SiO2 substrate, which indicates a nucleation delay of more than 200 cycles on the NGS.
A consistent behavior was observed also at a deposition temperature of 200° C. for t-TiO2 as shown in
For the case of p-TiON, the water co-reactant was replaced by a remote DBD N2/H2 plasma. Two different approaches were tested right after the initial 100 “cycles” CF4/N2 plasma etching step, followed by 5 “cycles” of DMATMS surface functionalization (A):
For both ABC-and BC-ALD cycles, preferential deposition of p-TiON on SiN vs. SiO2 blanket substrates was confirmed by XPS measurements. Compared to the t-TiO2 case and considering the different GPC values, the obtained selectivity is lower. This is not surprising since selective deposition using plasma-based processes is typically more difficult to achieve because of the high reactivity of plasmas. Based on the thickogram method, after 450 ALD cycles, TiON thicknesses of 7.0 and 7.4 nm were calculated on SiN substrates and ˜1.5 and ˜2.4 nm on SiO2 were found using ABC- or BC-type recipes, respectively. By considering the uncertainties associated with the thickogram method, it can be concluded that a similar selectivity can be obtained with both ABC-and BC-type methods.
Role of DMATMS on t-TiO2 and p-TiON Selectivity. To elucidate the influence of DMATMS on the selectivity of BC-type deposition processes, t-TiO2 and p-TiON deposition runs without DMATMS were carried out, and the resulting samples were analyzed by XPS.
The CF4/N2 etching pretreatment can, therefore, already confer enough chemical contrast when using TiCl4 as precursor, while DMATMS intensifies such chemical contrast, thereby leading to increased selectivity.
Selectivity on Patterned Substrates. Effect of Plasma Etching on t-TiO2. When translating the selective deposition of TiO2 from blanket layers to patterned substrates, it is crucial to understand and control the CF4/N2 pre-deposition etching process. Ideally one needs to remove only the native oxide from the SiN layer.
To gain insights into the plasma etching step, 4 different etching pretreatment “cycles” were tested: 25, 50, 100, and 150 CF4/N2 “cycles”. The rest of the process was kept the same, i.e. five “cycles” of DMATMS, followed by 250 cycles of t-TiO2 ALD at 100° C.
Strategies for Improving the Selectivity of t-TiO2. Several strategies were tested for improving the selectivity of t-TiO2:
For all cases, the number of precleaning plasma etching “cycles” prior to deposition was fixed at 50, in order to limit material removal.
As shown in
Fine-tuning either the number of ALD cycles and/or the back-etching “cycles” can potentially lead to larger deposited thicknesses with comparably high selectivity.
AS-ALD of p-TiON. For p-TiON, 380 BC-type ALD cycles without DMATMS functionalization were selected for tests on patterned substrates since the effect of DMATMS is not so dramatic for the plasma-based process.
It was noted that an unexpected result was also obtained here: because of the severe lateral overetching of SiN during the pre-deposition plasma etching process c-Si areas became without DMATMS pre-functionalization step and also in line with the XPS observations. Virtually perfect p-TiON selectivity could be obtained when employing back-etching correction steps as shown in
Considerations on Underlying Surface Chemistry and Precursor Effect. XPS data were also employed to gain insights into the surface chemistry underpinning the selective deposition process. The C 1s signal was deconvoluted in three components at 284.8, 286.6, and 288.7 eV. No signals related to CF2 or CF3 were detected (see
Regarding the formation of an interfacial TiOF layer, it is possible that TiCl4 chemisorbs on exposed NHx and OH sites and subsequently forms a bond with neighboring fluorine atoms that are still present at the surface. Here, is where it is believed that DMATMS plays an important role in further improving the selectivity. DMATMS is known to be reactive toward OH-groups. Therefore, it is indicated that DMATMS can passivate exposed OH-groups that are left behind after the plasma etching step and can delay even more the onset of TiCl4 chemisorption. This is achieved by deactivating exposed OH-groups and forming O—Si (CH3)3 surface groups that are nonreactive toward TiCl4 and H2O, and possibly by providing an additional steric hindrance.
Effect of Precursor. To further test the hypothesis on the underlying mechanism, similar deposition experiments were performed using tetrakis (dimethylamino) titanium, TDMAT, in place of TiCl4. From XPS data, some degree of preferential deposition was observed also when employing TOMAT as the Ti-precursor, suggesting a broader applicability of the selective deposition method. However, the selectivity is only marginal compared to the CI-based precursor process, which indicates that electrostatic repulsion between the fluorinated surface and the chlorinated precursor is the underlying chemical principle for excellent selectivity.
Testing the same approach with TOMAT as for the titanium precursor provided a few additional insights.
Table 2 provides an overview of layer composition from XPS surface scans, together with processing conditions. Whilst it is currently not possible to rule out the presence of CF species at the interface, it is noted that a comparable level of C at. % is found on SiN and for a standard ALD process on c-Si. Without plasma pre-treatment and inhibitor a C percentage of 14 at. % is found after 250 cycles on c-Si both at 100 and 200° C. This is likely due to adventitious carbon. For CF4 plasma-treated SiN, followed by 250 ALD cycles of TiO2 at 200° C., both with and without additional inhibitor functionalization, similar carbon percentages of 16.2 and 10.7 at. % were found. Furthermore, only a minor F at. % is measured on these samples. These results therefore suggest similar C-content levels on c-Si and SiN. On the other hand, the same experimental conditions on SiO2 lead to a much lower carbon content. However, almost no Ti is present on these surfaces, and it is therefore likely that the fluorine at the surface affects the carbon uptake from the atmosphere.
At 100° C., an unexpectedly high carbon content was found on SiN, 28.1 at. %, while only 9.7% was found on SiO2. It therefore can be concluded that at low processing temperatures CF species may play a mediating role in the selectivity of TiO2 growth on SiN vs. SiO2.
ASD of TiO2 and TiON on SiN vs. SiO2 has been demonstrated for the first time by using atmospheric-pressure spatial ALD on industrially processed patterns. The process exploits the chemical affinity contrast provided by a pre-deposition CF4/N2 etching step and the electrostatic repulsion between TiCl4 and the partially fluorinated SiN and SiO2 surfaces. Such a chemical contrast can be further enhanced by adding an additional DMATMS functionalization step. Through SEM inspection, AS-ALD of ˜8 and ˜7 nm-thick TiO2 on SiN vs. SiO2 with a selectivity of 0.99 and 1.00 for 190 ALD cycles at processing temperatures of 100 and 200° C., and AS-ALD of ˜5 nm TiON on SiN vs. SiO2 with a selectivity of 0.99 at processing temperatures of 200° C. have been seen.
The selectivity can further be improved by increasing the number of ALD cycles and combining it with back-etching steps to remove unwanted defects. The latter approach resulted in virtually perfect selectivity, i.e., no observable spurious particles on the SiO2 patterns.
A few considerations about the possible mechanistic aspects of the selective process can be derived from these results. The different fluorine binding configurations on SiN vs. SiO2 stand out as the possible main driver for the selectivity of the process. TDMAT was tested as an alternative titanium precursor, and it was determined that for TDMAT a much lower selectivity (<5 nm) was obtained. While the difference between TDMAT and TiCl4 may be due to differences in size, reactivity, and available reaction pathways, the comparison supports the concept of electrostatic repulsion as a mechanism behind the high selectivity obtained with TiCl4. The underlying chemistry underpinning the selectivity may lead to novel precursors and process designs for achieving ASD targeting SiN vs. SiO2 surfaces.
The results presented herein add to the fundamental understanding of and lead to new concepts and approaches for ASD applications.
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Although the foregoing subject matter has been described in some detail by way of illustrations and examples for purposes of clarity of understanding, it will be understood by those skilled in the art that certain changes and modifications can be practiced within the scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 63/595,877, filed on Nov. 3, 2023, the entire content of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63595877 | Nov 2023 | US |
