Patent Application
20240240317
A barrier metal is a material used in integrated circuits to chemically isolate semiconductors from metal interconnects, while maintaining an electrical connection between them. Ideally, the thickness of a diffusion barrier metal should be minimized, so as to allow additional space for a metal conductor. Thicker metal conductors enable higher conductivity and typically have low resistor-capacitor (RC) time constants, which are important for fast processing speeds.
Accordingly, titanium nitride (TiN) is an important material for semiconductor fabrication, as this material can be used as a diffusion barrier to prevent diffusion of copper and/or other conducting metals into surrounding materials having a low dielectric constant (k) in backend interconnects and vias. Additionally, the low resistivity of TiN films further contribute to the conductivity of the conducting line and lowers the RC time constant. Thus, a TiN film that nucleates rapidly, thereby permitting formation of ultrathin continuous TiN, would provide an optimum diffusion barrier.
Thus, there is a need in the art for methods of preparing a TiN film that nucleates rapidly and devices prepared by same. The present disclosure addresses this need.
In one aspect, the present invention provides a method of promoting nucleation and/or growth of a conductive film on a solid substrate.
In certain embodiments, the method comprises contacting at least a portion of the surface of the solid substrate with a volatile metal precursor in the presence of a background gas, wherein the volatile metal precursor is chemisorbed or physisorbed to at least a portion of the surface of the solid substrate to provide a metal precursor-adsorbed substrate surface.
In certain embodiments, the method comprises contacting at least a portion of the metal precursor-adsorbed substrate surface with an electron beam in the presence of the background gas.
In another aspect, the present invention provides a microdevice or nanodevice comprising a conductive film prepared according to the methods described herein.
The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments of the present application.
Ultrathin metal diffusion barriers in backend interconnects are needed to provide as much space as possible for conducting lines in vias. To achieve such continuous ultrathin barriers, fabrication methods which provide rapid nucleation are required. Accordingly, in one aspect, the present disclosure relates to the discovery of a fabrication method utilizing electron-enhanced atomic layer deposition (EE-ALD) to achieve rapid nucleation of TiN barrier films.
EE-ALD uses sequential exposure of precursors and low energy electrons to deposit thin films on a substrate. The precursor molecular first adsorbs on the substrate (i.e., step (a)), then low energy electrons desorb the ligands from the precursor via electron-stimulated desorption (ESD) (i.e., step (b)). The process of ligand desorption leaves behind open sites for further precursor adsorption. Repeating the precursor and low energy electron sequential exposures produces the EE-ALD film growth.
The present disclosure further relates to EE-ALD methods utilizing a reactive background gas (e.g., NH3) concurrently with EE-ALD. The use of a reactive background gas in EE-ALD is enabled by the use of a hollow cathode plasma electron source (HC-PES), as described in Sobell et al. (J. Vac. Sci. Technol. A 2021, 39:042403), as the HC-PES can operate with reactor pressures in the mTorr range. Previously described EE-ALD methods utilized an electron gun as the electron source which necessarily comprises a high temperature filament, thereby precluding the use of reactive background gases.
The EE-ALD methods described herein may be performed at lower temperatures (i.e., temperatures of less than about 100° C.) to produce films with lower resistivity than films prepared by alternative techniques. In certain embodiments, the presence of a reactive background gas can improve the purity of the EE-ALD film. In certain embodiments, the background gas can tune the composition of the EE-ALD film.
In one aspect, the present disclosure describes preparation of TiN films, using EE-ALD, from tetrakis(dimethylamido)titanium (TDMAT) as the titanium precursor and NH3 as the background gas at a continuous pressure of about 1 mTorr. Films described herein have been fabricated on a number of substrate surfaces, including but not limited to silicon nitride (Si3N4), crystalline silicon (i.e., silicon wafer or Si), and thermal silicon oxide (i.e., SiO2). Without wishing to be bound by theory, it has been proposed that exposure of NH3 to the electron beam generates H and N radicals, wherein the N radicals facilitate Ti nitridation and the H radicals facilitate removal of carbon as CH4. An illustration of the effect of the NH3 reactive background gas on Ti EE-ALD is shown in
Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.
Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of “about 0.1% to about 5%” or “about 0.1% to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.
In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. The statement “at least one of A and B” or “at least one of A or B” has the same meaning as “A, B, or A and B.” In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section. All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference.
In the methods described herein, the acts can be carried out in any order, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.
As used herein, unless defined otherwise, all technical and scientific terms generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Generally, the nomenclature used herein and the laboratory procedures in surface chemistry are those well-known and commonly employed in the art.
The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range.
As used herein, the term “ALD” refers to atomic layer deposition, which is a thin film deposition method. In certain embodiments, the term “thin” refers to a range of thickness from about 0.1 nm to about 300 nm. ALD uses a self-limiting reaction sequence that deposits films in discrete steps limited by surface site chemical reactions. It produces continuous films with atomically controlled thicknesses, high conformality, and typically pinhole-free and atomically smooth surfaces. These are essential properties as design constraints push device technologies to ever smaller sizes.
The term “chemisorb” as used herein refers to a type of adsorption which involves a chemical reaction between a substrate surface and an adsorbate (i.e., material adsorbed to the substrate surface). In certain embodiments, chemical bonds are formed between the adsorbate and the substrate surface.
The term “electron beam” as used herein refers to a stream of electrons in a gas or vacuum. Contact of a substrate with an electron beam necessarily comprises contact of the substrate with one or more electrons. The properties of the electron beam (e.g., energy, current, and duration, inter alia) of the electron beam may vary between electron sources and/or experimental conditions.
The terms “halo,” “halogen,” or “halide” group, as used herein, by themselves or as part of another substituent, mean, unless otherwise stated, a fluorine, chlorine, bromine, or iodine atom.
As used herein, the term “μm” is the abbreviation for “micron” or “micrometer”, and it is understood that 1 μm=0.001 mm=10−6 m=1 millionth of a meter.
As used herein, the term “nanodevice” refers to a device that has at least one component with at least one spatial dimension less than 1 micron.
As used herein, the term “nm” is the abbreviation for “nanometer” and it is understood that 1 nm=1 nanometer=10−9 m=1 billionth of a meter.
The term “nucleation” as used herein refers to initial formation of either a thermodynamic phase or structure (e.g., particle, crystal, and/or film) on the surface of a substrate which has been subjected to atomic layer deposition.
The term “organic group” as used herein refers to any carbon-containing functional group. Examples can include an oxygen-containing group such as an alkoxy group, aryloxy group, aralkyloxy group, oxo(carbonyl) group; a carboxyl group including a carboxylic acid, carboxylate, and a carboxylate ester; a sulfur-containing group such as an alkyl and aryl sulfide group; and other heteroatom-containing groups. Non-limiting examples of organic groups include OR, OOR, OC(O)N(R)2, CN, CF3, OCF3, R, C(O), methylenedioxy, ethylenedioxy, N(R)2, SR, SOR, SO2R, SO2N(R)2, SO3R, C(O)R, C(O)C(O)R, C(O)CH2C(O)R, C(S)R, C(O)OR, OC(O)R, C(O)N(R)2, OC(O)N(R)2, C(S)N(R)2, (CH2)0-2N(R)C(O)R, (CH2)0-2N(R)N(R)2, N(R)N(R)C(O)R, N(R)N(R)C(O)OR, N(R)N(R)CON(R)2, N(R)SO2R, N(R)SO2N(R)2, N(R)C(O)OR, N(R)C(O)R, N(R)C(S)R, N(R)C(O)N(R)2, N(R)C(S)N(R)2, N(COR)COR, N(OR)R, C(═NH)N(R)2, C(O)N(OR)R, C(═NOR)R, and substituted or unsubstituted (C1-C100)hydrocarbyl, wherein R can be hydrogen (in examples that include other carbon atoms) or a carbon-based moiety, and wherein the carbon-based moiety can be substituted or unsubstituted.
The term “physisorbed” as used herein refers to a type of adsorption which comprises a physical attraction between a substrate surface and an adsorbate (i.e., material adsorbed to the substrate surface). In certain embodiments, the physical attraction may comprise dispersion and/or van der Waals interactions between the adsorbate and the substrate surface.
The term “resistivity” as used herein refers to electrical resistivity, commonly represented by the Greek letter “p”, a fundamental property of a material that measures how strongly said material resists electrical current.
The term “room temperature” as used herein refers to a temperature of about 15° C. to 28° C.
The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or 100%. The term “substantially free of” as used herein can mean having none or having a trivial amount of, such that the amount of material present does not affect the material properties of the composition including the material, such that the composition is about 0 wt % to about 5 wt % of the material, or about 0 wt % to about 1 wt %, or about 5 wt % or less, or less than, equal to, or greater than about 4.5 wt %, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt % or less. The term “substantially free of” can mean having a trivial amount of, such that a composition is about 0 wt % to about 5 wt % of the material, or about 0 wt % to about 1 wt %, or about 5 wt % or less, or less than, equal to, or greater than about 4.5 wt %, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.01, or about 0.001 wt % or less, or about 0 wt %.
In one aspect, the invention provides a method of promoting nucleation and/or growth of a conductive film on a solid substrate.
In certain embodiments, the method includes contacting at least a portion of the surface of the solid substrate with a volatile metal precursor in the presence of a background gas, wherein the volatile metal precursor is chemisorbed or physisorbed to at least a portion of the surface of the solid substrate to provide a metal precursor-adsorbed substrate surface (i.e., step (a)).
In certain embodiments, the method includes contacting at least a portion of the metal precursor-adsorbed substrate surface with an electron beam in the presence of the background gas (i.e., step (b)).
In certain embodiments, the volatile metal precursor comprises a metal. In certain embodiments, the volatile metal precursor includes a metal-halogen complex. In certain embodiments, the volatile metal precursor includes a metal-organic complex. In certain embodiments, the volatile metal precursor includes a mixture of any of a metal, metal-halogen, complex, and metal-organic complex.
In certain embodiments, the volatile metal precursor is an amide or imide of Be, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Si, Ga, Ge, As, Se, Y, Zr, Nb, Mo, Sn, Sb, Te, La, Hf, Ta, W, Pb, or Bi. In certain embodiments, the volatile metal precursor is a halide of B, C, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, Zr, Hb, Mo, Cd, In, Sn, Sb, Hf, Ta, W, or Pb. In certain embodiments, the volatile metal precursor is an alkyl of B, Al, Si, Zn, Ga, Ge, Cd, In, Sn, Sb, Te, Hg, or Bi. In certain embodiments, the volatile metal precursor is an alkoxide of B, Al, Si, Ti, V, Ni, Ge, Zr, Nb, Hf, Ta, or Gd. In certain embodiments, the volatile metal precursor is a cyclopentadienyl of Mg, Ca, Sc, Ti, Mn, Ge, Co, Ni, Sr, Y, Zr, Ru, In, Ba, La, Hf, or Pt. In certain embodiments, the volatile metal precursor comprises a beta-diketonate or amidinate.
In certain embodiments, the metal is selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, and Al. In certain embodiments, the metal-halogen complex includes a metal selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, or Al. In certain embodiments, the metal-organic complex includes a metal selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, and Al.
In certain embodiments, the volatile metal precursor is tetrakis(dimethylamino)titanium (TDMAT).
In certain embodiments, the background gas has a pressure of about 1 mTorr to about 2 mTorr.
In certain embodiments, the background gas comprises at least one selected from the group consisting of a hydride gas, an oxide gas, a nitride gas, a sulfide gas, and a halide or halogen gas. In certain embodiments, the hydride gas is at least one selected from the group consisting of ammonia (NH3), CH4, H2O, HF, HCl, SiH4, PH3, H2S, GeH4, AsH3, and H2Se. In certain embodiments, the oxide gas is at least one selected from the group consisting of O2, O3, H2O2, and H2O. In certain embodiments, the nitride gas is at least one selected from the group consisting of N2 and NH3. In certain embodiments, the sulfide gas is at least one selected from the group consisting of S8 and H2S. In certain embodiments, the halide or halogen gas is at least one selected from the group consisting of F2, HF, SF6, NF3, BF3, Cl2, HCl, BCl3, HBr, Br2, BBr3, HI, and I2.
In certain embodiments, the background gas is ammonia.
In certain embodiments, the background gas comprises a mixture of two or more distinct chemical species. In certain embodiments, the use of a background gas comprising a mixture of gases permits the deposition of ternary, quaternary, or more diverse alloy metals.
In certain embodiments, the solid substrate includes a semiconductor. In certain embodiments, the solid substrate includes a ceramic. In certain embodiments, the solid substrate includes a metal. In certain embodiments, the solid substrate includes a polymer. In certain embodiments, the solid substrate includes a metal-oxide. In certain embodiments, the solid substrate includes a mixture of any of a semiconductor, ceramic, metal, and metal-oxide.
In certain embodiments, the semiconductor includes silicon. In certain embodiments, the semiconductor is silicon nitride (Si3N4). In certain embodiments, the semiconductor is silicon dioxide (SiO2). In certain embodiments, the semiconductor is crystalline silicon.
In certain embodiments, the contacting of the volatile metal precursor and the solid substrate occurs for a period of about 0.1 to 10 seconds. In certain embodiments, the contacting of the volatile metal precursor and the solid substrate occurs for a period of more than about 0.1 to 10 seconds. In certain embodiments, the contacting of the volatile metal precursor and the solid substrate occurs for a period of less than about 0.1 to 10 seconds.
In certain embodiments, the contacting of the volatile metal precursor and the solid substrate occurs for a period of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or about 4.0 seconds.
In certain embodiments, the contacting of the metal precursor-adsorbed substrate surface and the electron beam occurs for a period of about 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or about 40 seconds. In certain embodiments, the contacting of the metal precursor-adsorbed substrate surface and the electron beam occurs for a period of less than about 10 seconds. In certain embodiments, the contacting of the metal precursor-adsorbed substrate surface and the electron beam occurs for a period of more than about 40 seconds.
In certain embodiments, the contacting of the metal precursor-adsorbed substrate surface and the electron beam occurs for a period of about 20 seconds.
In certain embodiments, the electron beam has a current selected from the group consisting of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and about 100 mA. In certain embodiments, the electron beam has a current less than about 0.1 mA. In certain embodiments, the electron beam has a current which is greater than about 100 mA. In certain embodiments, the electron beam has an energy selected from the group consisting of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, and about 150 eV. In certain embodiments, the electron beam has an energy of less than about 1 eV. In certain embodiments, the electron beam has an energy which is greater than about 150 eV. In certain embodiments, the electron beam is generated using a hollow cathode plasma electron source (HC-PES).
In certain embodiments, steps (a) and (b) occur at a temperature selected from the group consisting of about 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, and about 150° C.
In certain embodiments, steps (a) and (b) occur at a temperature of less than about 18° C. In certain embodiments, steps (a) and (b) occur at a temperature which is greater than about 150° C.
In certain embodiments, nucleation occurs by performing 5 cycles of steps (a)-(b). In certain embodiments, nucleation occurs by performing 6 cycles of steps (a)-(b). In certain embodiments, nucleation occurs by performing 7 cycles of steps (a)-(b). In certain embodiments, nucleation occurs by performing 8 cycles of steps (a)-(b). In certain embodiments, nucleation occurs by performing 9 cycles of steps (a)-(b). In certain embodiments, nucleation occurs by performing 10 cycles of steps (a)-(b).
In certain embodiments, steps (a)-(b) are repeated one or more times, wherein each cycle of steps (a)-(b) increases the thickness of the conductive film by an amount selected from the group consisting of about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and about 2.0 Å.
In certain embodiments, the conductive film comprises titanium nitride (TiN).
In certain embodiments, the TiN film comprises 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% Ti and N.
In certain embodiments, TiN film has a Ti:N ratio selected from the group consisting of about 2.7:4, 2.8:4, 2.9:4, 3:4, 3.1:4, 3.2:4, 3.3:4, 3.4:4, 3.5:4, 3.6:4, 3.7:4, 3.8:4, 3.9:4, and 4:4.
In certain embodiments, the conductive film is prepared by performing about 150 cycles of steps (a)-(b). In certain embodiments, the conductive film is prepared by performing more than about 150 cycles of steps (a)-(b). In certain embodiments, the conductive film is prepared by performing less than about 150 cycles of steps (a)-(b).
In certain embodiments, the conductive film has a thickness selected from the group consisting of about 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, and about 70 Å. In certain embodiments, the conductive film has a thickness less than about 60 Å. In certain embodiments, the conductive film has a thickness which is greater than about 70 Å.
In certain embodiments, the conductive film has a resistivity of about 110, 115, 120, 125, 130, 135, 145, 150, 155, and about 160 μΩ·cm. In certain embodiments, the conductive film has a resistivity less than about 110 μΩ·cm. In certain embodiments, the conductive film has a resistivity which is greater than about 160 μΩ·cm.
In certain embodiments, the conductive film is prepared by performing about 200 cycles of steps (a)-(b). In certain embodiments, the conductive film is prepared by performing less than about 200 cycles of steps (a)-(b). In certain embodiments, the conductive film is prepared by performing more than about 200 cycles of steps (a)-(b).
In certain embodiments, the conductive film has a thickness of about 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, and about 135 Å. In certain embodiments, the conductive film has a thickness of less than about 125 Å. In certain embodiments, the conductive film has a thickness of more than about 135 Å.
In certain embodiments, the conductive film has a resistivity of about 120, 125, 130, 135, 140, 145, and about 150 μΩ·cm. In certain embodiments, the conductive film has a resistivity of less than about 120 μΩ·cm. In certain embodiments, the conductive film has a resistivity which is greater than about 150 μΩ·cm.
The disclosure provides a method of promoting nucleation and/or growth of a conductive film on a solid substrate.
In certain embodiments, the method comprises contacting at least a portion of a surface of the solid substrate with a volatile metal precursor in the presence of a background gas.
In certain embodiments, the volatile metal precursor is chemisorbed or physisorbed to at least a portion of the surface of the solid substrate to provide a metal precursor-adsorbed substrate surface.
In certain embodiments, the contacting occurs with simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam.
In certain embodiments, the volatile metal precursor is an amide or imide of Be, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Si, Ga, Ge, As, Se, Y, Zr, Nb, Mo, Sn, Sb, Te, La, Hf, Ta, W, Pb, or Bi. In certain embodiments, the volatile metal precursor is a halide of B, C, Al, Si, P, Ti, V, Cr, Mn, Cu, Zn, Ga, Ge, Zr, Hb, Mo, Cd, In, Sn, Sb, Hf, Ta, W, or Pb. In certain embodiments, the volatile metal precursor is an alkyl of B, Al, Si, Zn, Ga, Ge, Cd, In, Sn, Sb, Te, Hg, or Bi. In certain embodiments, the volatile metal precursor is an alkoxide of B, Al, Si, Ti, V, Ni, Ge, Zr, Nb, Hf, Ta, or Gd. In certain embodiments, the volatile metal precursor is a cyclopentadienyl of Mg, Ca, Sc, Ti, Mn, Ge, Co, Ni, Sr, Y, Zr, Ru, In, Ba, La, Hf, or Pt. In certain embodiments, the volatile metal precursor comprises a beta-diketonate or amidinate.
In certain embodiments, the metal is selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, and Al. In certain embodiments, the metal-halogen complex includes a metal selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, or Al. In certain embodiments, the metal-organic complex includes a metal selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, and Al.
In certain embodiments, the volatile metal precursor is tetrakis(dimethylamino)titanium (TDMAT).
In certain embodiments, the background gas has a pressure of about 1 mTorr to about 2 mTorr.
In certain embodiments, the background gas comprises at least one selected from the group consisting of a hydride gas, an oxide gas, a nitride gas, a sulfide gas, and a halide or halogen gas. In certain embodiments, the hydride gas is at least one selected from the group consisting of ammonia (NH3), CH4, H2O, HF, HCl, SiH4, PH3, H2S, GeH4, AsH3, and H2Se. In certain embodiments, the oxide gas is at least one selected from the group consisting of O2, O3, H2O2, and H2O. In certain embodiments, the nitride gas is at least one selected from the group consisting of N2 and NH3. In certain embodiments, the sulfide gas is at least one selected from the group consisting of S8 and H2S. In certain embodiments, the halide or halogen gas is at least one selected from the group consisting of F2, HF, SF6, NF3, BF3, C12, HCl, BCl3, HBr, Br2, BBr3, HI, and I2.
In certain embodiments, the background gas is ammonia.
In certain embodiments, the background gas comprises a mixture of two or more distinct chemical species. In certain embodiments, the use of a background gas comprising a mixture of gases permits the deposition of ternary, quaternary, or more diverse alloy metals.
In certain embodiments, the solid substrate includes a semiconductor. In certain embodiments, the solid substrate includes a ceramic. In certain embodiments, the solid substrate includes a metal. In certain embodiments, the solid substrate includes a polymer. In certain embodiments, the solid substrate includes a metal-oxide. In certain embodiments, the solid substrate includes a mixture of any of a semiconductor, ceramic, metal, and metal-oxide.
In certain embodiments, the semiconductor includes silicon. In certain embodiments, the semiconductor is silicon nitride (Si3N4). In certain embodiments, the semiconductor is silicon dioxide (SiO2). In certain embodiments, the semiconductor is crystalline silicon.
In certain embodiments, the electron beam has a current selected from the group consisting of about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, and about 100 mA. In certain embodiments, the electron beam has a current less than about 0.1 mA. In certain embodiments, the electron beam has a current which is greater than about 100 mA.
In certain embodiments, the electron beam has an energy selected from the group consisting of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, and about 150 eV. In certain embodiments, the electron beam is generated using a hollow cathode plasma electron source (HC-PES).
In certain embodiments, the simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam occurs at a temperature selected from the group consisting of about 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, and about 150° C. In certain embodiments, the simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam occurs at a temperature of less than about 18° C. In certain embodiments, the simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam steps occurs at a temperature which is greater than about 150° C.
In certain embodiments, the conductive film comprises titanium nitride (TiN).
In certain embodiments, the TiN film comprises 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% Ti and N.
In certain embodiments, the TiN film has a Ti:N ratio selected from the group consisting of about 2.7:4, 2.8:4, 2.9:4, 3:4, 3.1:4, 3.2:4, 3.3:4, 3.4:4, 3.5:4, 3.6:4, 3.7:4, 3.8:4, 3.9:4, and 4:4.
In certain embodiments, the conductive film is prepared by performing a series of about 150 simultaneous exposures of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam. In certain embodiments, the conductive film is prepared by performing a series of more than about 150 simultaneous exposures of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam. In certain embodiments, the conductive film is prepared by performing a series of less than about 150 simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam.
In certain embodiments, the conductive film has a thickness selected from the group consisting of about 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, and about 70 Å. In certain embodiments, the conductive film has a thickness less than about 60 Å. In certain embodiments, the conductive film has a thickness which is greater than about 70 Å.
In certain embodiments, the conductive film has a resistivity of about 110, 115, 120, 125, 130, 135, 145, 150, 155, and about 160 μΩ·cm. In certain embodiments, the conductive film has a resistivity less than about 110 μΩ·cm. In certain embodiments, the conductive film has a resistivity which is greater than about 160 μΩ·cm.
In certain embodiments, the conductive film is prepared by performing a series of about 200 simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam. In certain embodiments, the conductive film is prepared by performing a series of less than about 200 simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam. In certain embodiments, the conductive film is prepared by performing a series of more than about 200 simultaneous exposure of the volatile metal precursor, background gas, and/or volatile metal precursor-adsorbed substrate surface to an electron beam.
In certain embodiments, the conductive film has a thickness of about 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, and about 135 Å. In certain embodiments, the conductive film has a thickness of less than about 125 Å. In certain embodiments, the conductive film has a thickness of more than about 135 Å.
In certain embodiments, the conductive film has a resistivity of about 120, 125, 130, 135, 140, 145, and about 150 μΩ·cm. In certain embodiments, the conductive film has a resistivity of less than about 120 μΩ·cm. In certain embodiments, the conductive film has a resistivity which is greater than about 150 μΩ·cm.
In certain embodiments, the film deposited by EE-ALD is a metallic film.
In another aspect, the present invention provides a microdevice or nanodevice comprising a conductive film prepared according to the methods described herein.
In certain embodiments, the microdevice or nanodevice is selected from the group consisting of a diffusion barrier, liner, transistor, channel materials, via, conduit, and any other electrical circuit components, Josephson junction, superconducting device, electrical conductor, photovoltaic, transistor, diode, waveguide, electrical transmission line, light emitting diode, thermocouple, mirror, absorber for photons, photon emitter, radiation shield, and radiation detector.
In certain embodiments, the microdevice or nanodevice is selected from the group consisting of a bolometer, transducer, temperature sensor, heater, thermistor, microbolometer, microphone, speaker, ultrasonic transducer, resistor, inductor, spiral inductor, mechanical actuator, flagellum, flagellum motor, freestanding nanodevice, freestanding microdevice, Bragg reflector, Bragg filter, antenna, terahertz detector, electromagnetic transformer, and electrical system.
In certain embodiments, the microdevice or nanodevice is selected from the group consisting of a nanotube, nanowire, coaxial wire, hollow tube with nanoscale diameters, periodic structure, or metamaterial.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures, embodiments, claims, and examples described herein. Such equivalents were considered to be within the scope of this invention and covered by the claims appended hereto. For example, it should be understood, that modifications in reaction conditions, including but not limited to reaction times, reaction size/volume, and experimental reagents, such as solvents, catalysts, pressures, atmospheric conditions, e.g., nitrogen atmosphere, and reducing/oxidizing agents, with art-recognized alternatives and using no more than routine experimentation, are within the scope of the present application. In general the terms and phrases used herein have their art-recognized meaning, which can be found by reference to standard texts, journal references and contexts known to those skilled in the art. Any preceding definitions are provided to clarify their specific use in the context of the invention.
The invention is now described with reference to the following Examples. These Examples are provided for the purpose of illustration only, and the invention is not limited to these Examples, but rather encompasses all variations that are evident as a result of the teachings provided herein.
TiN EE-ALD films were grown in a vacuum chamber that has been described previously. The main UHV chamber had a base pressure of 2×10−9 Torr. This chamber was equipped with a load lock that allowed samples to be introduced without breaking vacuum. The main chamber also contained an in situ ellipsometer (Filmsensel) and mass spectrometer (PrismaPlus QMG 220, Pfeiffer Vacuum). The chamber was also equipped with a cold cathode gauge (MKS) to measure pressure. In addition, a pico-ammeter (Keithley) was attached to the sample stage to measure the incident electron current from the electron source.
TiN EE-ALD growth was conducted using a pulse sequence consisting of: (1) TDMAT dose; (2) pump time; (3) electron beam exposure; and (4) pump time before the next TDMAT dose. The timing for this pulsing sequence can be characterized by (t1, t2, t3, t4). For deposition on the silicon native oxide and the SiO2 thermal oxide, the TDMAT precursor was maintained at P=0.3 Torr behind a micropulse valve. The valve was actuated for t1=1 s. The valve opening led to a transient pressure in the main chamber of 4×10−7 Torr as measured by the cold cathode gauge. The pressure at the sample was higher because the micropulse valve was connected to a ¼″ diameter tube that led to the sample and ended ˜5 cm from the sample. For deposition on the in situ deposited Si3N4, the valve was actuated for 2 s. The TDMAT pressure was 0.2 Torr behind the micropulse valve. These conditions yielded a transient pressure of 6×10−7 Torr.
Pumping was then performed for a total of t2=2 s. Subsequently, the electron exposure was performed with a grid bias of 100 V for t3=20 s, with an electron current measured at the sample stage of −25 mA. The next TDMAT adsorption was then conducted after a pump time of t4=1 s. The timing for this pulsing sequence was (1, 2, 20, 1). The sum of these steps produced a reaction cycle time of ˜24 seconds. The NH3 (Matheson, 99.9992%) RBG was flowed into the chamber though a leak valve and produced an increase in the reactor pressure of −1 mTorr as measured by the cold cathode pressure gauge (MKS) for the entirety of the experiment
The electron source was a hollow cathode plasma electron source (HC-PES) that has been previously described. An argon (Airgas, 99.999%) plasma was sparked in the hollow cathode body. Low energy electrons were extracted with a biased grid. The electrons exited the HC through an aperture. Argon gas also leaked through this aperture and produced a pressure of ˜1 mTorr in the reactor. All the work in this study used an applied voltage of 100 V to the biased grid. This applied voltage accelerated the electrons leaving the aperture. The electrons were separated from any sputtered material from the HC-PES using electron optics. An analysis chamber containing an in vacuo Auger electron spectroscopy (AES) spectrometer (RBD, microCMA) was also attached to the main chamber.
An NH3 RBG (Matheson, 99.9992%) was present continuously during the TiN EE-ALD. The NH3 RBG pressure was ˜1 mTorr. The recommended total cross section for electron scattering in NH3 is 6=8.57×10−16 cm2 for electron energies of 100 eV. In addition, the Ar pressure was ˜1 mTorr. The total cross section for electron scattering in Ar is σ˜8×10−16 cm2 for electron energies of 100 eV. The mean free path for electrons traveling through gas is λe=1/ρσ where ρ is the gas number density and 6 is the cross section for electron scattering from the gas. The gas number density is 6=3.2×1013 molecules/cm3 at a pressure of 1 mTorr for both Ar and NH3. Therefore, the electron mean free path is λe=18 cm using σ˜8×10−16 cm2 for the Ar and NH3 total cross sections. Electron scattering by the Ar and NH3 RBG does not seriously affect the electron transport over the 25 cm distance between the HC-PES and the sample.
TiN EE-ALD can be performed using any of a number of substrates, non-limiting examples including silicon coupons and silicon nitride. For example, substrates may include silicon coupons containing a native oxide, an SiO2 thermal oxide, and in situ deposited silicon nitride. The Si wafer coupons (Silicon Valley Microelectronics, boron-doped) contained a native oxide on the silicon surface. The SiO2 thermal oxide had a thickness of 400 nm on a Si wafer. Prior to insertion into the vacuum apparatus, the coupons were washed sequentially in methanol, acetone, and DI water, then blown dry with ultra-high purity nitrogen. The coupons were then loaded into the load lock chamber following procedures that have been previously described.
Si3N4 substrates have also been employed using the methods described herein. In situ deposited Si3N4 films were grown using pulsed electron-enhanced chemical vapor deposition (EE-CVD). For this Si3N4 pulsed EE-CVD, an NH3 RBG was flowed through the chamber during continuous electron beam irradiation of the sample. Throughout this continuous electron beam and NH3 exposure, Si2H6 was pulsed into the chamber every 5 seconds. In situ ellipsometry measurements observed that the Si3N4 films nucleated on the first Si2H6 pulse and grew linearly versus number of Si2H6 exposures. The Si3N4 pulsed EE-CVD films were grown to a thickness of ˜10 nm. The Si3N4 pulsed EE-CVD films had high purity as measured by in vacuo AES. The films displayed a nearly stoichiometric 3:4 Si:N ratio with C and O impurities <2 at %. In addition, the Si3N4 pulsed EE-CVD films were smooth as measured by ex situ AFM with an RMS roughness of <2 Å.
In situ ellipsometry measurements were collected every second throughout the deposition. The in situ ellipsometer uses four wavelengths of light. The precision of the in situ ellipsometry measurements of film thickness was within ±0.03 Å. The in situ ellipsometer used a Drude-Lorentz model to model the TiN films. The Filmsense software was able to extrapolate resistivity from the model. Ex situ spectroscopic ellipsometry (Model M-2000, J.A. Woollam Co., Inc.) was also performed to measure the film thickness of some samples after taking them from the reactor. The data was fit using a Drude-Lorentz model with a Drude oscillator (119 μΩ·cm resistivity, 0.952 fs scattering time) and one Lorentzian oscillator (energy: 5.385 eV, amplitude: 6.519, broadening: 3.980 eV).
A four-point probe (Signatone, QP2-MB8) was used for ex situ resistivity measurements. The probe spacing was 1 mm. The geometric correction factor was chosen based on the ratio of the probe spacing to the diameter of the largest inset circle possible on the wafer coupon. A typical geometric correction factor was 0.92. AFM measurements were used to monitor ex situ film roughness. The AFM measurements were performed with a Park NX10 AFM instrument using non-contact mode. The scan rate was 0.3-0.8 Hz for a 1×1 m area using an Olympus micro cantilever probe (OMCL-AC160TS).
X-ray reflectivity (XRR) was used to determine film thickness and density. Grazing incidence x-ray diffraction (GI-XRD) determined crystallinity of the films. Both GI-XRD and XRR scans were performed using a Bede D1 from Jordan Valley Semiconductors with radiation from Cu Kα (λ=1.540 Å). The X-ray tube filament voltage was 40 kV and the current was 35 mA. The incident angle used for GI-XRD was 0.3°. The XRR scan range was 300 to 6000 arcsec with a 5 arcsec step size. The modeling software for the XRR scans was REFS by Jordan Valley Semiconductors.
TiN films were grown on various substrates, including silicon nitride (Si3N4) and Si wafer coupons, wherein the silicon coupons contained the native oxide on the surface. In certain embodiments, the substrates were washed with isopropyl alcohol, acetone, rinsed in deionized water, and blown dry with ultrahigh purity N2 gas. Once dried, the substrates were subsequently loaded into the load lock chamber.
Each cycle of TiN EE-ALD nucleation and/or growth was conducted using a pulse sequence comprising: (1) TDMAT; (2) pump; (3) electron beam exposure; and (4) pump.
Tables 1-2 of the present disclosure provide parameters for EE-ALD, according to various embodiments.
In certain embodiments, TiN EE-ALD films were prepared, by alternate dosing of step (a) and step (b) on a silicon nitride substrate, wherein thickness was monitored by ellipsometry (
In situ ellipsometry measurements indicated that the Si3N4 films nucleated on the first Si2H6 pulse and grew linearly versus number of Si2H6 exposures. The Si3N4 pulsed EE-CVD films were grown to a thickness of ˜10 nm. The Si3N4 pulsed EE-CVD films had high purity as measured by in vacuo AES. The films displayed a nearly stoichiometric 3:4 Si:N ratio with C and O impurities at <2%. In addition, the Si3N4 pulsed EE-CVD films were smooth, as measured by ex situ AFM with an RMS roughness of <2 Å.
Linear TiN EE-ALD film growth was observed on the Si3N4 substrate after approximately 7 EE-ALD cycles with a growth rate of 1.8/cycle. The TiN film described herein was analyzed by Auger electron spectroscopy (AES), wherein a high purity of TiN was observed (i.e., approximately 92% Ti+N) (
A high purity was also observed with analysis of the TiN flm by x-ray photoelectron spectroscopy (XPS) (
Ten separate TiN EE-ALD films were prepared, by alternate dosing of step (a) and step (b) on a silicon wafer substrate, wherein the number of EE-ALD cycles were varied (i.e., 0, 5, 10, 15, 20, 30, and 50 cycles). Both the ellipsometry (
Film roughness for these samples was measured by AFM as a function of number of EE-ALD cycles. The films were measured after exposure to the first electron beam and then again after various numbers of EE-ALD cycles up to 50 cycles. The RMS roughness increased slightly and then leveled out at an RMS roughness of ˜3.5 Å. It was further observed that the roughness of the initial sample was high (i.e., ˜4 Å) prior to a 5 min exposure of the electron beam with a ˜1 mTorr NH3 background. Without wishing to be bound by theory, the decrease in roughness may be a result of cleaning of the initial Si native oxide by the interaction of the electron beam with the NH3 RBG to produce radicals which desorb adventitious surface carbon.
TiN EE-ALD films were prepared, by alternate dosing of step (a) and step (b) on a Si thermal oxide substrate. The TiN films described herein were subject to various analyses, including ellipsometry, x-ray reflectometry (XRR), resistivity measurements, and x-ray diffraction (Tables 3-5,
In certain embodiments, the TiN films described here demonstrate superior resistivity (i.e., low resistivity) over other films described in the literature, including thin films prepared by thermal ALD, including Wolf et al. (Applied Surface Science 2018, 462:1029-1035), Stevens et al. (Chem. Mater. 2018, 30:3223-3232), Lee et al. (doi:10.1021/acsaelm.0c01079), J. W. Elam et al. (Thin Solid Films 2003, 436:145-156), Wang et al. (ECS Transactions 2009, 22(1):167-173), and Kuo et al. (doi:10.1109/IITC51362.2021.9537463), or by plasma-enhanced ALD, including Chen et al. (doi:10.1051/matecconf/20163901010) and Musschoot et al. (doi:10.1016/j.mee.2008.09.036), which would not have been expected by one skilled in the art (
The TiN EE-ALD films grown in the presence of the NH3 RBG nucleated rapidly on the Si native oxide, thermal SiO2 and the in situ deposited Si3N4 EE-CVD films.
Additional experiments determined that the TiN EE-ALD growth rates were dependent on the TDMAT precursor exposures. At higher TDMAT precursor exposures, the GPCs could reach >5 Å/cycle. These larger GPCs could be explained by larger TDMAT coverages adsorbed on the growing TiN surface after higher TDMAT exposures. Earlier experiments have confirmed that TDMAT adsorbs with a coverage-dependent sticking coefficient on TiN surfaces. The adsorbed TDMAT then slowly desorbs with a coverage-dependent desorption rate.
There also may be partial decomposition of TDMAT on electron-activated substrates through a mechanism like autocatalytic deposition. This mechanism could lead to the buildup of thick films with partially decomposed TDMAT precursors. To avoid these larger GPCs and higher carbon impurities in the TiN EE-ALD film, the results described herein were obtained with shorter TDMAT precursor exposures of 1 s with TDMAT pressures of 0.30 Torr behind the micropulse valve. These TDMAT exposures produced a pressure transient of 4×10−7 Torr in an empty reactor.
The TiN EE-ALD films grown using the NH3 RBG also nucleated rapidly on the Si native oxide.
The nucleation of TiN EE-ALD on Si native oxide was also explored using in vacuo AES after various numbers of EE-ALD cycles. These AES results are for the same set of samples as shown in
The roughness of the TiN EE-ALD films in the initial nucleation region on the Si native oxide was also studied by ex situ AFM measurements. Surface roughnesses were obtained for separate samples coated with 5, 10, 15, 20, 30, and 50 cycles of TiN EE-ALD.
The change in the surface roughness of the Si native oxide resulting from the initial 5-minute electron exposure with NH3 RBG motivated a study of the change in surface composition using in vacuo AES. One Si native oxide sample was loaded and irradiated with the electron beam and exposed to the NH3 RBG for 5 minutes with an electron sample current of 20 mA as a control. This control sample showed ˜40 at % N on the surface by in vacuo AES. This N AES signal likely results from surface nitridation by •NH2 species from the electron beam interaction with the NH3 RBG. In addition, the oxygen and carbon AES signals decreased by factors of 2.7 and 2.3, respectively, relative to initial Si native oxide samples that were not subjected to the electron exposures with NH3 RBG. These experiments suggest that surface cleaning and smoothing results from the electron exposures with NH3 RBG.
In situ ellipsometry was used to monitor the TiN EE-ALD in the steady state growth regime using sequential exposures of TDMAT and electrons with a NH3 RBG in the chamber as shown in
Initially the thickness decreases quickly during the electron exposure. Subsequently, there is a slow decrease of the thickness. This slow decrease may be the additional loss of dimethylamine ligands or removal of fragmented dimethylamino ligands by the NH3 RBG. An electron exposure of 20 s was chosen because shorter electron exposures led to a higher C content in the films. The effect of the electron beam exposure time had a dramatic effect on the purity of the TiN film.
In vacuo AES measurements also confirmed that the TiN EE-ALD films deposited with larger TDMAT precursor exposures contained more carbon. With the electron exposure held constant, the carbon content in the film increased for these larger TDMAT precursor exposures. Carbon compositions of >30 at % were observed when the TiN EE-ALD growth per cycle was 7 Å/cycle. These larger carbon contents were obtained with a TDMAT precursor exposure of 1 s with TDMAT pressure behind the micropulse valve of >0.60 Torr.
Grazing incidence x-ray diffraction (GI-XRD) was used to determine the crystallinity of the TiN EE-ALD films. Despite low growth temperatures <70° C., the TiN films display crystallinity. The GI-XRD results are displayed in
X-ray reflectometry (XRR) was also used to measure the density of the TiN EE-ALD films. The average density of the films was 5.3 g/cm3. This density is 98.5±0.5% of theoretical TiN bulk density of 5.4 g/cm3. Without wishing to be bound by theory, this high density suggests that these TiN films will be resistant to oxidation. This oxidation resistance has been confirmed by the depth profile XPS measurements where there is minimal O diffusion into the TiN films. This behavior is in contrast to thermal TiN ALD films that display high porosity leading to facile oxidation.
The TiN EE-ALD grown with the NH3 RBG at <70° C. have high purity, high density, and crystallinity. The NH3 RBG is facilitating the growth of these films. An illustration of TiN EE-ALD using TDMAT and low energy electrons in the presence of a continuous NH3 RBG is shown in
In addition to dissociating NH3 in the gas phase, the electrons can also desorb H from —NH2 species on the surface. This H ESD produces additional empty sites on the TiN surface. The TDMAT precursor can then adsorb onto these empty sites to add more Ti to the TiN surface. The electrons may also crack dimethylamino ligands on the surface and produce carbon fragments. However, the continuous flux of •NH2 and •H radicals from NH3 dissociation may be able to remove this surface carbon as CH4 or CH3NH2. The •H radicals may also provide a pathway for the removal of oxygen impurities as H2O.
The primary motivation for introducing the NH3 RBG was to ensure the complete nitridation of the TiN film. The effect of the NH3 RBG on the film purity was an unexpected result that is attributed to the cleaning effect of the •NH2 and •H radicals. In addition, the possibility of introducing various RBGs offers a new parameter to tune the composition of EE-ALD films. Different films can be deposited from a single metal precursor, such as TDMAT, by changing the RBG. For example, the dissociation or adsorption of NH3, Si2H6, CH4, or B2H6 RBGs should form nitrides, silicides, carbides, or borides, respectively, with the metal precursor. The single RBG can also be extended to two or three RBGs to deposit ternary or quaternary EE-ALD films.
The resistivity of the TiN EE-ALD films was characterized using in situ 4 wavelength and ex situ spectroscopic ellipsometry. To confirm that the TiN EE-ALD films were comparable with other TiN films,
The in situ ellipsometry results for the thickness and resistivity of a TiN EE-ALD film is shown in
The film resistivity drops rapidly in the nucleation regime during the first 12-13 cycles. These resistivities are artificially low for film thicknesses <4 nm resulting from the inability of ellipsometry to fully account for electron scattering at grain boundaries and interfaces. The film resistivity continues to decrease progressively and reaches a resistivity of ˜130 μΩ·cm after 50 cycles at a film thickness of ˜4 nm. The resistivity continues to decrease slowly as the film thickness increases to ˜185 Å where the resistivity is ˜110 μΩ·cm after 250 cycles.
The EE-ALD is stopped after 250 cycles. Without the electron current impinging on the sample, the film begins to cool slightly from −65° C. over the next ˜10 minutes. This cooling results in a decrease in the model film thickness of ˜16 Å and a corresponding decrease in resistivity to 104 μΩ·cm. The decrease in the model film thickness is associated with the temperature change of the film. The electronic properties change with temperature. The ellipsometry model interprets this temperature change as a change in film thickness.
The TiN EE-ALD film after 250 cycles in
Four-point probe measurements were also employed to corroborate the resistivity measurements from ellipsometry. A geometric correction factor of 0.92 was applied to the raw resistivity data to account for the small coupon size. A resistivity of 131 μΩ·cm was obtained from 10 locations at the center of substrate immediately after removal from the deposition chamber. This resistivity is also in good agreement with the resistivity from the ellipsometry measurements. There was a negligible increase in resistivity from the four-point probe measurement over a 24 hour period after removing the film from vacuum. No increase in resistivity after prolonged air exposure suggests a dense TiN film that is resistant to oxidation.
Additional experiments were conducted on a 400 nm Si thermal oxide with 150 and 200 TiN EE-ALD cycles. These experiments were performed using the same reactions as employed for the 250 TiN EE-ALD cycles shown in
The TiN EE-ALD deposits on insulating as well as on conducting samples. Electron currents on an insulating substrate might be expected to charge the substrate negatively. This negative charge would then repel additional electron current. Without wishing to be bound by theory, it is believed that if the secondary electron yield is greater than unity, then the sample would charge positive. This positive charge could then pull back secondary electrons to maintain charge neutrality. Secondary electron yields greater than unity have been measured for SiO2 and Si3N4 for primary electron energies from −100-1000 eV. A wide range of insulating materials, such as Al2O3, also have secondary electron yields greater than unity. These high secondary electron yields should allow EE-ALD to be performed on insulating substrates.
The following exemplary embodiments are provided, the numbering of which is not to be construed as designating levels of importance:
Embodiment 1 provides a method of promoting nucleation and/or growth of a conductive film on a solid substrate, the method comprising:
Embodiment 2 provides the method of Embodiment 1, wherein the volatile metal precursor comprises at least one selected from the group consisting of a metal, a metal-halogen complex, and a metal-organic complex, and mixtures thereof.
Embodiment 3 provides the method of Embodiment 2, wherein the metal, metal-halogen complex, metal-organic complex, or any mixture thereof, comprises a metal selected from the group consisting of Ti, Ta, W, Mo, Zr, Hf, Zn, Sc, Nb, Cu, Ni, Pt, Ru, Ni, and Al.
Embodiment 4 provides the method of any one of Embodiments 1-3, wherein at least one of the following applies:
Embodiment 5 provides the method of any one of Embodiments 1-4, wherein the background gas has a pressure of about 1 mTorr to about 2 mTorr.
Embodiment 6 provides the method of any one of Embodiments 1-5, wherein the background gas comprises at least one selected from the group consisting of a hydride gas, an oxide gas, a nitride gas, a sulfide gas, and a halide or halogen gas.
Embodiment 7 provides the method of Embodiment 6, wherein at least one of the following applies:
Embodiment 8 provides the method of any one of Embodiments 1-7, wherein the solid substrate comprises at least one selected from the group consisting of a semiconductor, ceramic, metal, polymer, and metal-oxide, and mixtures thereof.
Embodiment 9 provides the method of Embodiment 8, wherein the semiconductor comprises silicon.
Embodiment 10 provides the method of Embodiment 8 or 9, wherein the semiconductor is selected from the group consisting of silicon nitride (Si3N4), silicon dioxide (SiO2), and crystalline silicon.
Embodiment 11 provides the method of any one of Embodiments 1-10, wherein the contacting of the volatile metal precursor and the solid substrate occurs for a period of about 0.1 to about 4 seconds.
Embodiment 12 provides the method of any one of Embodiments 1-11, wherein the contacting of the metal precursor-adsorbed substrate surface and the electron beam occurs for a period of about 20 seconds.
Embodiment 13 provides the method of any one of Embodiments 1-12, wherein the electron beam has a current of about 0.1 mA to about 100 mA.
Embodiment 14 provides the method of any one of Embodiments 1-13, wherein the electron beam has an energy of about 1 eV to about 500 eV.
Embodiment 15 provides the method of any one of Embodiments 1-14, wherein the electron beam is generated using a hollow cathode plasma electron source (HC-PES).
Embodiment 16 provides the method of any one of Embodiments 1-15, wherein steps (a) and (b) occur at a temperature of less than 150° C.
Embodiment 17 provides the method of Embodiment 16, wherein steps (a) and (b) occur at a temperature of about 70° C.
Embodiment 18 provides the method of any one of Embodiments 1-19, wherein nucleation occurs by performing about 7 cycles of steps (a)-(b).
Embodiment 19 provides the method of any one of Embodiments 1-18, wherein steps (a)-(b) are repeated one or more times, wherein each cycle of steps (a)-(b) increases conductive film thickness by about 0.5 Å to about 2.0 Å.
Embodiment 20 provides the method of any one of Embodiments 1-19, wherein the conductive film comprises titanium nitride (TiN).
Embodiment 21 provides the method of Embodiment 20, wherein the TiN film comprises at least 91% Ti and N.
Embodiment 22 provides the method of Embodiment 20 or 21, wherein the TiN film has a Ti:N ratio of about 3:4.
Embodiment 23 provides the method of any one of Embodiments 1-22, wherein the conductive film is prepared by performing about 150 cycles of steps (a)-(b).
Embodiment 24 provides the method of any one of Embodiments 1-23, wherein the conductive film has a thickness of about 60 Å to about 70 Å.
Embodiment 25 provides the method of any one of Embodiments 1-24, wherein the conductive film has a resistivity of about 110 μΩ·cm to about 160 μΩ·cm.
Embodiment 26 provides the method of any one of Embodiments 1-22, wherein the conductive film is prepared by performing about 200 cycles of steps (a)-(b).
Embodiment 27 provides the method of any one of Embodiments 1-22 and 26, wherein the conductive film has a thickness of about 125 Å to 135 Å.
Embodiment 28 provides the method of any one of Embodiments 1-22 and 27, wherein the conductive film has a resistivity of about 120 μΩ·cm to about 150 μΩ·cm.
Embodiment 29 provides a microdevice or nanodevice comprising a conductive film prepared according to the method of any one of Embodiments 1-28.
Embodiment 30 provides the microdevice or nanodevice of Embodiment 29, which is selected from the group consisting of a diffusion barrier, liner, transistor, channel materials, via, conduit, and any other electrical circuit components, Josephson junction, superconducting device, electrical conductor, photovoltaic, transistor, diode, waveguide, electrical transmission line, light emitting diode, thermocouple, mirror, absorber for photons, photon emitter, radiation shield, and radiation detector.
Embodiment 31 provides the microdevice or nanodevice of Embodiment 29 or 30, which is selected from the group consisting of a bolometer, transducer, temperature sensor, heater, thermistor, microbolometer, microphone, speaker, ultrasonic transducer, resistor, inductor, spiral inductor, mechanical actuator, flagellum, flagellum motor, freestanding nanodevice, freestanding microdevice, Bragg reflector, Bragg filter, antenna, terahertz detector, electromagnetic transformer, and electrical system.
Embodiment 32 provides the microdevice or nanodevice of any one of Embodiments 29-31, which is selected from the group consisting of a nanotube, nanowire, coaxial wire, hollow tube with nanoscale diameters, periodic structure, or metamaterial.
The terms and expressions employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the embodiments of the present application. Thus, it should be understood that although the present application describes specific embodiments and optional features, modification and variation of the compositions, methods, and concepts herein disclosed may be resorted to by those of ordinary skill in the art, and that such modifications and variations are considered to be within the scope of embodiments of the present application.
