Method for preparing transition metal-containing films

Abstract

The present invention is in the field of methods for producing transition metal-containing films on substrates, in particular atomic layer deposition methods. The present invention relates to a method for preparing a transition metal-containing membrane on a substrate, the method comprising (a) forming an organic-inorganic hybrid membrane by repeatedly contacting the substrate with a transition metal-containing compound in a gaseous state and an organic acid wherein the organic acid is oxalic acid, glyoxylic acid or glycollic acid, and (b) decomposing the organic-inorganic hybrid membrane into a transition metal-containing membrane by heat treatment.

Description

[0001] The invention belongs to the field of methods for producing transition metal-containing films on substrates, in particular atomic layer deposition methods.

[0002] With the development of miniaturization, for example in the semiconductor industry, the demand for thin films containing transition metals on substrates has increased, while the quality requirements for such films have become more stringent. Thin films containing transition metals have different uses, such as barrier layers, conductive features or capping layers. Several methods for generating transition metal films are known. One of these methods is to deposit film-forming compounds from the gaseous state onto the substrate. In order to make the transition metal atoms gaseous at moderate temperatures, volatile precursors must be provided, for example by complexing the metal or semimetal with a suitable ligand. These precursors need to be sufficiently stable to evaporate, but on the other hand, they need to be sufficiently reactive to react with the deposition surface. In order to obtain a film of a single transition metal, the deposited precursor must be reduced. Typically, a reducing agent is used during or after the deposition.

[0003] US 2019 / 0 249 300 A1 discloses a method for depositing transition metal-containing films, in which formic acid is used as a co-reagent, which is unlikely to be integrated into the film at any time. However, as a result, it is difficult to obtain very thin, uniform, elemental transition metal films using this method.

[0004] WO 2004 / 035 858 A2 discloses a method for depositing metal films of Pd, Rh, Ru, Pt and Ir by using a reducing gas such as hydrogen, glyoxylic acid or oxalic acid. After each deposition step, the transition metal is reduced. Again, it is difficult to obtain very thin, uniform single transition metal films using this method.

[0005] US 2021 / 398 848 A1 discloses a method for selectively depositing metals using formic acid. However, low film growth rates are generally observed.

[0006] The object of the present invention is therefore to provide a process in which very thin, uniform transition metal-containing films, in particular transition metal films, can be obtained. The present invention is directed to a process that results in high film growth rates. The process is directed to being broadly applicable to different transition metals and different substrates. The process should leave as few by-products as possible in the film, thereby resulting in a film with a very low level of contamination by undesired residues.

[0007] These objects are achieved by a method for preparing a transition metal-containing film on a substrate, the method comprising:

[0008] (a) forming an organic-inorganic hybrid film by repeatedly contacting a substrate with a transition metal-containing compound and an organic acid in a gaseous state, wherein the organic acid is formic acid, oxalic acid, glyoxylic acid or glycolic acid, and

[0009] (b) Decomposing the organic-inorganic hybrid membrane into a transition metal-containing membrane by heat treatment.

[0010] According to the invention, a transition metal-containing film is prepared. Transition metals include the elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, La, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg. Preferred transition metals are Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ru, Rh, Pd, Ag, W, Re, Os, Ir, Pt, Au, more preferably Co, Ni, Cu, Nb, Mo, W, in particular Ni or Ru. The transition metal-containing film may contain one transition metal, or it may contain more than one transition metal, for example two or three. In the context of the present invention, transition metal-containing means that the film contains more than trace amounts of transition metals, typically at least 1 wt.-%, such as at least 10 wt.-% or at least 30 wt.-%. The transition metal-containing film may be an inorganic film, such as a film of a metal, a metal nitride, a metal carbide, a metal carbonitride, a metal alloy, an intermetallic compound or a mixture thereof. Preferably, the transition metal-containing film is a transition metal film, i.e. a film containing an elemental transition metal. The transition metal film typically contains at least 90 wt.-%, or at least 95 wt.-%, or at least 99 wt.-% of the transition metal. The transition metal film typically exhibits a high electrical conductivity, typically at least 10 4 S / m, preferably at least 10 5 S / m, especially at least 10 6 S / m.

[0011] The film containing transition metal is on a substrate. The substrate can be any solid material. These include, for example, metals, semimetals, oxides, nitrides and polymers. The substrate can be a homogeneous material, or it can be a mixture of different materials. Examples of metals are aluminum, steel, zinc and copper. Examples of semimetals are silicon, germanium and gallium arsenide. Examples of oxides are silicon dioxide, titanium dioxide and zinc oxide. Examples of nitrides are silicon nitride, aluminum nitride, titanium nitride and gallium nitride. Examples of polymers are polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polyamide.

[0012] The substrate can have any shape. These include thin plates, films, fibers, particles of various sizes, and substrates with grooves or other indentations. The substrate can be of any size. If the substrate has a particle shape, the particle size can range from less than 100 nm to several centimeters, preferably 1 μm to 1 mm. In order to avoid particles or fibers sticking to each other during the film preparation process, it is preferred to keep the particles or fiber substrate in motion during the film preparation process. This can be achieved, for example, by stirring, drum or fluidized bed technology.

[0013] In step (a) of the method of the present invention, an organic-inorganic hybrid film is formed by repeatedly contacting a substrate with a transition metal-containing compound and an organic acid in a gaseous state. This means that a sequence including contacting a substrate with a transition metal-containing compound and an organic acid in a gaseous state is carried out in sequence at least twice, or at least five times, or at least ten times, or at least 50 times. Typically, the sequence is carried out no more than 1000 times. As an example, in order to prepare a thin film, the sequence is carried out two to ten times, or five to 50 times. The sequence can reflect a cycle of an atomic layer deposition method, that is, the sequence includes contacting a substrate with a transition metal-containing compound for a certain period of time, removing any residual transition metal-containing compound from the gas phase (e.g., by purging with an inert gas or by evacuating), then contacting the substrate with an organic acid for a certain period of time, and removing any residual organic acid from the gas phase (e.g., by purging with an inert gas or by evacuating). Purge can be carried out for 0.5s to 1min, preferably 5 to 30s, more preferably 10 to 25s, especially 15 to 20s.

[0014] In this way, on substrate, form organic-inorganic hybrid film, if substrate surface and the compound reaction containing transition metal form thin layer, this thin layer reacts with organic acid subsequently.Therefore, organic-inorganic hybrid film contains transition metal and organic acid or its salt.At least a portion of this organic acid or its salt can be combined or coordinated with transition metal.Diproton organic acid molecule can be combined or coordinated with a transition metal atom or two transition metal atoms.The latter can form polymer structure in whole organic-inorganic hybrid film.

[0015] A wide variety of transition metal-containing compounds can be used. Generally, any transition metal-containing compound that can be converted into a gaseous state is suitable. These compounds include transition metal alkyls, such as dimethyl zinc; transition metal alkoxides, such as triisopropoxy iron; transition metal carbenes, such as tri(neopentyl)neopentylene tantalum or bis-imidazolidinyl ruthenium chloride; transition metal halides, such as tantalum pentachloride, molybdenum pentachloride, tungsten hexachloride; carbon monoxide complexes, such as chromium hexacarbonyl or nickel tetracarbonyl.

[0016] Other suitable transition metal-containing compounds are transition metal complexes in which the ligands are coordinated to the transition metal via oxygen atoms and / or nitrogen atoms. These complexes may contain ligands that are coordinated to the transition metal atom via at least one nitrogen atom, or via at least one oxygen atom, or via at least one nitrogen atom and at least one oxygen atom, or via at least two nitrogen atoms, or via at least two oxygen atoms. These complexes may contain ethylenediamine derivative ligands, such as N,N,N'N'-tetramethylethylenediamine, for example bis(N,N,N'N'-tetramethylethylenediamine)niobium chloride; ethanolamine derivative ligands, such as dimethylamino-2-propanol salts or dimethylamino-tert-butanol salts, for example bis(dimethylamino-2-propanol)nickel (Ni(dmap)2); imino ligands, for example bis(tert-butylimino)bis(dimethylamido)molybdenum or bis(tert-butyl bis(dimethylamido)tungsten; diketonate ligands, such as bis(2,2,6,6-tetramethyl-3,5-heptanedione)manganese; acetylacetonate ligands, such as bis(acetylacetonate)nickel; acetamidine ligands, such as bis(N,N'-diisopropylacetamidine)nickel (Ni(iPrAMD)2); diketoimine ligands, such as penta-2,4-diimine derivatives, such as bis(N,N'-diethylpenta-2,4-diimino)cobalt. The transition metal-containing compound may also contain different ligands, such as two or three different ligands coordinated to the transition metal via oxygen atoms and / or nitrogen atoms, such as bis(acetylacetonate)-N,N,N'N'-tetramethylethylenediamine-nickel (Ni(acac)2(tmeda)).

[0017] Preferably, the compound containing transition metal is a transition metal cyclopentadienyl complex. These can contain one or two, preferably two cyclopentadienyl ligands. These can be identical or different from each other. The transition metal cyclopentadienyl complex can only contain cyclopentadienyl ligands, or it can contain one or two cyclopentadienyl ligands and at least one other ligand. The cyclopentadienyl ligand can be unsubstituted cyclopentadienyl (i.e. C5H5) or substituted cyclopentadienyl--wherein at least one hydrogen is replaced by, for example, alkyl (such as methyl, ethyl, n-propyl or isopropyl), as in ethyl-cyclopentadienyl. The example of the transition metal cyclopentadienyl complex is dicyclopentadienyl nickel, di(ethylcyclopentadienyl) manganese or di(pentamethylcyclopentadienyl) ruthenium.

[0018] The transition metal containing compound preferably has a molecular weight of up to 1000 g / mol, more preferably up to 800 g / mol, especially up to 600 g / mol, such as up to 500 g / mol.

[0019] Preferably, the transition metal-containing compound has a melting point in the range of -80°C to 125°C, preferably -60°C to 80°C, even more preferably -40°C to 50°C, in particular -20°C to 20°C. It is advantageous if the transition metal-containing compound melts to give a clear liquid which remains constant up to the decomposition temperature.

[0020] Preferably, the transition metal-containing compound has a decomposition temperature of at least 80° C., more preferably at least 100° C., in particular at least 120° C., such as at least 150° C. Typically, the decomposition temperature is not higher than 250° C. The transition metal-containing compound has a high vapor pressure. Preferably, the vapor pressure is at least 1 mbar at a temperature of 200° C., more preferably 150° C., in particular 120° C. Typically, the temperature at which the vapor pressure is 1 mbar is at least 50° C.

[0021] The organic acid is formic acid, oxalic acid, glyoxylic acid or glycolic acid. It can be one organic acid or more than one (e.g. two or three) organic acids. If more than one organic acid is selected, it can be used as a mixture, or it can be used in different cycles, for example, one organic acid is selected in one cycle and another acid is selected in the next cycle. Preferably, the organic acid is formic acid or oxalic acid, in particular oxalic acid.

[0022] The transition metal-containing compound or organic acid used in the method according to the invention is used in high purity to achieve the best results. High purity means that the substance used contains at least 90 wt.-%, preferably at least 95 wt.-%, more preferably at least 98 wt.-%, in particular at least 99 wt.-% of transition metal-containing compound or organic acid. The purity can be determined by elemental analysis according to DIN 51721 (Prüfung fester Brennstoffe-Bestimmung des Gehaltes an Kohlenstoff und Wasserstoff-Verfahren nach Radmacher-Hoverath [Testing of solid fuels - Determination of carbon and hydrogen content - Radmacher-Hoverath method], August 2001).

[0023] The transition metal-containing compound or organic acid is brought into contact with the solid substrate from the gaseous state. For example, it can be made gaseous by heating it to a high temperature. In any case, a temperature lower than the decomposition temperature of the transition metal-containing compound or organic acid must be selected. The decomposition temperature is the temperature at which the original transition metal-containing compound or organic acid begins to change its chemical structure and composition. Preferably, the heating temperature ranges from 80°C to 300°C, more preferably from 100°C to 290°C, even more preferably from 160°C to 280°C, and particularly from 180°C to 260°C.

[0024] Another way of making the compound with general formula (I) or (II) gaseous is direct liquid injection (DLI), as described in US2009 / 0 226 612A1, for example. In this method, typically the compound containing transition metal or organic acid is dissolved in a solvent and sprayed in a carrier gas or vacuum. If the vapor pressure and temperature of the compound containing transition metal or organic acid are high enough and the pressure is low enough, the compound containing transition metal or organic acid becomes gaseous. Various solvents can be used, provided that the compound containing transition metal or organic acid shows enough solubility in the solvent, such as at least 1g / l, preferably at least 10g / l, more preferably at least 100g / l. Examples of these solvents are coordination solvents (such as tetrahydrofuran, dioxane, diethoxyethane, pyridine) or non-coordinating solvents (such as hexane, heptane, benzene, toluene or xylene). Solvent mixtures are also suitable.

[0025] Alternatively, the transition metal-containing compound or organic acid can be transformed into a gaseous state by direct liquid evaporation (DLE), as described, for example, by J. Yang et al. (Journal of Materials Chemistry C, Vol. 3 (2015), pp. 12098-12106). In this method, the transition metal-containing compound or organic acid is mixed with a solvent (e.g., a hydrocarbon, such as tetradecane) and heated to a boiling point below the solvent. By evaporating the solvent, the transition metal-containing compound or organic acid is transformed into a gaseous state. This method has the advantage of not forming particulate contaminants on the surface.

[0026] It is preferred to make the transition metal-containing compound or organic acid gaseous under reduced pressure. In this way, the method can usually be carried out at a lower heating temperature, resulting in reduced decomposition of the transition metal-containing compound or organic acid. It is also possible to use increased pressure to push the transition metal-containing compound or organic acid in a gaseous state toward the solid substrate. For this purpose, an inert gas (such as nitrogen or argon) is usually used as a carrier gas. Preferably, the pressure is 10 bar to 10 -7 mbar, more preferably 1 bar to 10 -3 mbar, in particular 1 to 0.01 mbar, such as 0.1 mbar.

[0027] The substrate can be exposed to the transition metal-containing compound or organic acid for a period of milliseconds to several minutes, preferably 0.1 seconds to 1 minute, and particularly 1 to 10 seconds. The longer the substrate is exposed to the transition metal-containing compound or organic acid at a temperature below the decomposition temperature of the transition metal-containing compound or organic acid, the more regular the film formed is and the fewer defects it has.

[0028] Preferably, the temperature of the substrate is 5° C. to 40° C., for example, 20° C. higher than the place where the transition metal-containing compound or the organic acid becomes gaseous. The temperature of the substrate needs to be lower than the decomposition temperature of the organic-inorganic hybrid membrane, and is generally in the range of 100° C. to 300° C., such as 160° C. to 260° C.

[0029] Organic-inorganic hybrid membranes are formed by repeatedly contacting the substrate with a transition metal-containing compound and an organic acid in a gaseous state. The organic-inorganic hybrid membrane contains a transition metal and an organic acid or a salt thereof. Ideally, it contains alternating layers of a transition metal and an organic acid or a salt thereof, wherein the organic acid can be combined with or coordinated to the transition metal. However, in practice, the organic-inorganic hybrid membrane may also contain residues and other defects of ligands contained in the transition metal-containing compound. The organic-inorganic hybrid membrane may contain 10 to 90 wt.-%, such as 30 to 70 wt.-%, of transition, depending on the transition metal and the organic acid. The organic-inorganic hybrid membrane may contain 10 to 90 wt.-%, such as 20 to 60 wt.-% of an organic acid, depending on the transition metal and the organic acid.

[0030] The method according to the present invention further comprises decomposing the organic-inorganic hybrid film into a film containing a transition metal by heat treatment. Heat treatment may mean heating the organic-inorganic hybrid film to a temperature higher than its decomposition temperature. The temperature of the heat treatment may be 250°C to 1000°C, preferably 300°C to 800°C, for example 350°C to 500°C. Typically, the temperature of the heat treatment is higher than the temperature during the formation of the organic-inorganic hybrid film, preferably at least 20°C, more preferably at least 50°C, and in particular at least 100°C higher than the temperature during the formation of the organic-inorganic hybrid film. The heat treatment may be in an inert atmosphere, such as in a vacuum, nitrogen or argon, or in an oxidizing atmosphere, such as in air, oxygen, ozone, or in a reducing atmosphere, such as in hydrogen, hydrazine or carbon monoxide. Alternatively or additionally, the heat treatment may include exposing the substrate to radiation (e.g., exposure to UV radiation) or exposure to plasma (e.g., oxygen plasma). The heat treatment may be performed for varying amounts of time, typically from 1 s to 1 h, such as from 1 min to 30 min, depending on the transition metal-containing film to be obtained.

[0031] The method according to the invention obtains a film containing a transition metal. The film may be just a metal monolayer, or thicker, such as 0.1 nm to 1 μm, preferably 0.5 to 50 nm. The film may contain defects, such as holes. However, these defects usually account for less than half of the surface area covered by the film. The film preferably has a very uniform film thickness, which means that the film thickness at different locations on the substrate varies very little, usually less than 10%, preferably less than 5%. In addition, the film is preferably a conformal film on the surface of the substrate. Suitable methods for determining film thickness and uniformity are XPS or ellipsometry techniques.

[0032] The film obtained by the method according to the present invention can be used for electronic components. The electronic component can have structural features of various sizes, such as 1nm to 100μm, such as 10nm, 14nm or 22nm. The method for forming a film for electronic components is particularly suitable for very fine structures. Therefore, electronic components with a size less than 1μm are preferred. Examples of electronic components are field effect transistors (FETs), charge trapping memory cells, solar cells, light emitting diodes, sensors or capacitors. In optical devices such as light emitting diodes or light sensors, the film obtained by the method according to the present invention is used to increase the refractive index of the layer that reflects light.

[0033] The preferred electronic component is a transistor. Preferably, the film acts as a chemical barrier metal in the transistor. A chemical barrier metal is a material that reduces diffusion of adjacent layers while maintaining electrical connectivity.

[0034] Examples

[0035] Example 1

[0036] In an ALD reactor (Plasma Electronic GmbH), a Si wafer sample with a native SiOx layer was heated to 220°C. It was contacted with Ni(dmap)2 (dmap = dimethylamino-2-propanolate) vapor, purged with argon, then contacted with oxalic acid vapor, subsequently purged with argon. This sequence was performed 300 times. An organic-inorganic hybrid film with a thickness of 158 nm as determined by ellipsometry was obtained. The organic-inorganic hybrid film was subjected to a heat treatment by heating to 400°C for 1 hour under an argon flow. A film with a metallic appearance was obtained, which contained 49 at.-% Ni as determined by X-ray photoemission spectroscopy (XPS) elemental distribution.

[0037] Example 2

[0038] The procedure of Example 1 was repeated, using Ni(iPrAMD)2 (iPrAMD=N,N'-diisopropylacetamidine) as the transition metal-containing compound and deposited at 240°C, and the sequence was performed 600 times. The growth rate monitored by quartz crystal micro-plane in situ was 8.4 Hz / cycle. An organic-inorganic hybrid film with a thickness of 99 nm as determined by ellipsometry was obtained. A film with a metallic appearance was obtained, containing 45 at.-% Ni as determined by X-ray photoemission spectroscopy (XPS) elemental distribution.

[0039] Example 3

[0040] The deposition procedure described in Example 2 was repeated, using formic acid instead of oxalic acid. The reactor temperature was set to 160° C., 200° C., and 240° C., and 100 ALD cycles were performed at each temperature. The growth rate at all temperatures monitored by a quartz crystal micro-plane was 1.8 Hz / cycle or less.

[0041] Example 4

[0042] The procedure of Example 2 was repeated, wherein Ni(EtCp)2 (EtCp=ethylcyclopentadienyl) was used as the transition metal-containing compound. The growth rate monitored by quartz crystal micro-plane in situ was 8.8 Hz / cycle. An organic-inorganic hybrid film with a thickness of 69 nm as determined by ellipsometry was obtained. A film with a metallic appearance was obtained, which contained 39 at.-% Ni as determined by X-ray photoemission spectroscopy (XPS) elemental distribution.

[0043] Example 5

[0044] The deposition procedure described in Example 4 was repeated, using formic acid instead of oxalic acid. The reactor temperature was set to 140°C, 180°C, 220°C, and 260°C, and 100-200 ALD cycles were performed at each temperature. The growth rate at all temperatures monitored by a quartz crystal micro-sky flat plane was 0.2 Hz / cycle or less.

[0045] Example 6

[0046] The procedure of Example 1 was repeated, using Ni(Cp)2 (Cp=cyclopentadienyl) as the transition metal-containing compound and depositing at 220°C, and the sequence was performed 1000 times. An organic-inorganic hybrid film with a thickness of 140 nm as determined by ellipsometry was obtained. The organic-inorganic hybrid film was subjected to a heat treatment by heating to 300°C for 1 hour under a stream of hydrogen. A film with a metallic appearance was obtained, containing 75 at.-% Ni as determined by X-ray photoemission spectroscopy (XPS) elemental distribution.

Claims

1. A method for preparing a transition metal-containing film on a substrate, the method comprising (a) forming an organic-inorganic hybrid film by repeatedly contacting the substrate with a transition metal-containing compound and an organic acid in a gaseous state, wherein the organic acid is oxalic acid, glyoxylic acid or glycolic acid, and (b) Decomposing the organic-inorganic hybrid film into a transition metal-containing film by heat treatment.

2. The method according to claim 1, wherein: The transition metal is Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ru, Rh, Pd, Ag, W, Re, Os, Ir, Pt or Au.

3. The method according to claim 1 or 2, wherein: The transition metal is nickel or ruthenium.

4. The method according to any one of claims 1 to 3, wherein: The transition metal-containing film is a transition metal film.

5. The method according to any one of claims 1 to 4, wherein: The transition metal-containing film has a thickness of 0.5 to 50 nm.

6. The method according to any one of claims 1 to 5, wherein: The transition metal-containing compound is a transition metal cyclopentadienyl complex.

7. The method according to any one of claims 1 to 6, wherein: The organic acid is oxalic acid.

8. The method according to any one of claims 1 to 7, wherein the organic-inorganic hybrid film is formed at a temperature of 160°C to 280°C.

9. The method according to any one of claims 1 to 8, wherein: The formation of the organic-inorganic hybrid film is performed as an atomic layer deposition method, which includes a sequence of multiple times including: contacting the substrate with a transition metal-containing compound, removing residual transition metal-containing compound from the gas phase, contacting the substrate with an organic acid, and removing residual organic acid from the gas phase.

10. The method according to any one of claims 1 to 9, wherein: The heat treatment is performed by heating the organic-inorganic hybrid film to a temperature of 350° C. to 450° C. in an inert atmosphere.

11. The method according to any one of claims 1 to 10, wherein: The organic-inorganic hybrid membrane contains 20 to 60 wt.-% of an organic acid.