For Optical And Microelectronic Applications

Field of the invention

The present invention relates to metal complexes and their use as metal oxide precursors for optical and microelectronic applications. The metal complexes comprise one or more metals M selected from V, Nb and Ta and one or more organic oxime type ligands L. An organic oxime type ligand is an organic ligand comprising an oxime group, which is optionally substituted on the O atom. The metal complexes are particularly suitable as metal oxide precursors for the formation of metal oxides in optical and microelectronic applications such as e.g. in diffractive gratings for augmented reality (AR) and/or virtual reality (VR) devices, or as metal hard mask (MHM) materials in integrated circuit (IC) chip manufacturing. They show improved film-forming and gap-filling properties and allow the formation of highly refractive metal oxide structures on the surface of patterned or non-patterned substrates. The metal complexes of the present invention offer a wide range of different applications and can be used, for example, in formulations together with further metal complexes.

The present invention further relates to a method for preparing a metal oxide on a surface of a substrate, wherein said metal complexes are used as metal oxide precursors. The metal oxide may form various structures such as, for example, layers covering a surface of a non-patterned substrate and/or fillings covering topographical features such as e.g. gaps on the surface of a patterned substrate, thereby providing highly refractive optical layers and/or etch-resistant MHM layers enabling a selective structuring of silicon wafers, silicon wafer dies or semi-finished analogues during manufacturing of integrated circuits (ICs). In particular, the metal complex according to the present invention and the formulations containing the same allow for advanced gap filling with low overburden, thus enabling easy and cost-effective mass production of complex optical and microelectronic devices by avoiding typical problems of layer deposition and gap filling as performed by physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes such as, e.g. incomplete gap filling due to deposition and/or layer growth deposition characteristics including increased deposition and/or growth rates at corners and edges.

The obtained metal oxides (a) allow the formation of layers having favorable optical properties such as, for example, a high refractive index of > 1.7, preferably > 2.0, at wavelengths < 520 nm, a low absorbance and a low degree of haze formation; (b) they show high etch resistance towards wet phase and/or gaseous phase etching agents, thereby enabling selective etching due to different etching rates; (c) they allow formation of dense layers and homogeneous filling of topographical features such as e.g. gaps ; and (d) they can be prepared and structured in an easy and cost-efficient manner using the metal complexes of the present invention as metal oxide precursors.

The metal complexes are therefore particularly suitable for the preparation of metal oxide layers having high refractive index for optical applications such as, for example, in diffractive gratings for augmented reality (AR) and/or virtual reality (VR) devices, or as metal hard mask (MHM) materials for microelectronic applications and devices such as, for example, thin films in integrated circuit (IC) chips.

Hence, there is further provided a metal oxide showing the aforementioned beneficial effects and a device, preferably an optical or microelectronic device, comprising the same. Background of the invention

Leading edge microelectronic and optical devices are typically composed of composites comprising a carrier substrate as well as complex and interlaced patterns, which are derived from manifold different layers or layer stacks. Usually, the creation of such complex patterns demands for structuring processes, which become increasingly challenging with decreasing size of structural dimensions to be prepared. Hard mask (HM) materials and metal hard mask (MHM) materials are particularly used underneath photoresist layers and patterns to allow structuring of parts of integrated circuits by reactive ion etching (RIE) processes. As an underlayer under photoresist and removed in areas, where the photoresist is structured and opened, the MHM layer supports to keep and maintain the dimension of opened areas during RIE etching, which is not achieved by the photoresist layer itself, since the material is too weak to fully withstand aggressive etching conditions. Thus, the MHM layer defines the creation of structures in the material layers underneath the MHM and photoresist on top of it. Similar to that mentioned, MHM materials, in support of structure creation, may be also used as nanometer scaled blocks of materials. The latter, for example, applies to creation of silicon fins during FinFET- manufacturing process. Here, the substrate is homogeneously covered by a layer of sacrificial material such as, for example, a layer of so-called spin-on carbon. This sacrificial layer is structured using conventional photoresist technology, e. g. defining an array of trenches in which, after opening of the photoresist layer, the exposed carbon layer is removed by an oxygen-rich RIE etching process. In the following steps and after removal of the photoresist, a MHM composition is coated on the surface of the substrate allowing to fill the array of lines or trenches in the sacrificial carbon layer as well as forming a dense and homogenous layer completely capping the spun-on carbon. After that, the carbon capping MHM is then removed by selective etching leaving over the carbon layer being completely exposed now as well as the array of lines and trenches being still be filled with the gap filling material. As a next step, the carbon layer is removed by oxygen- rich RIE, followed by a second etching step removing all parts of the substrate material, usually silicon, which was released from the spun-on carbon layer, whereas those areas of the array of lines and former trenches being still composed of the MHM material are not attacked. The MHM possesses a sufficiently low etch rate in order to allow the etching gas mixture to remove the exposed silicon only. As a consequence of this process, an array of upright standing, high aspect ratio rectangular profiles is generated at the top of the substrate being a silicon wafer. These rectangular profiles can later serve as fins for FinFET-devices after the remaining MFIM material has been selectively removed.

WO 2017/174476 A1 relates to a gap filling composition and pattern forming method using low molecular weight compound. The gap filling composition is said to reduce pattern collapse and includes an organic gap filling compound, an organic solvent, and as required, water.

WO 2019/048393 A1 relates to a spin-on inorganic oxide containing composition useful as hard masks and filling materials with improved thermal stability. The composition is used in methods for manufacturing electronic devices through either the formation of patterned films of high K material comprised of a metal oxide on a semiconductor substrate, or through the formation of a patterned metal oxide comprised layer overlaying a semiconductor substrate which may be used to selectively etch the semiconductor substrate with a fluorine plasma.

As leading edge optical devices, however, not limited hereto, one may consider diffractive gratings. In addition to various uses in kinds types of applications such as, for example, in spectrometers or as principle underlying optical memory systems (CD, DVD, etc.), diffractive gratings are the core components of so-called XR-devices, mostly glasses. In this context, R stands for the term reality and X denotes different attributes, as e. g. virtual, augmented, mixed and so forth. Thus, diffractive gratings are the core of the optical engine of augmented reality and mixed reality glasses, however not solely limited hereto. Virtual reality glasses, when built as head mounted display, are often composed to a conventional LC- or OLED-display being embedded in the device, and thus do not necessarily require diffractive gratings. In contrast, augmented and mixed reality glasses are designed that way to enable consumers to obtain visual impressions of their environment, at its best as if they would not wear any glasses at all. However, they also make it possible to provide and serve digital information and also to project it into the field of vision of individuals. Additional digital information is gathered from recognizing and analyzing the environment, the individual inspects or takes a look currently at. In order to convey and project supporting digital information into the eyes of an individual, the augmented or mixed reality glasses are equipped with an information supply unit which is coupled to an optical waveguide system that transports the optically coded supporting information through it directly to the lens of the glasses. Here, the information passes a diffractive grating which couples the incident light into the lens and splits it according to its angular information and its spectral bands by diffraction. After incoupling of the light, the lens serves as waveguide enabling transport of the light to and into the pupil of an individual. The location of light incoupling is independent of any preferred position and thus of the implication of technical needs. The direction of traversal of light within the lenses is determined by the diffractive grating diffracting or splitting the light. At certain positions in the lens, a second and a third diffractive gratings serve for changing the direction of light traversal and enforcing the light to be projected into pupil of the user. The light traversal in the glasses is accomplished by total internal reflections (TIR) of the light, thus bouncing a several times between the glass interfaces until reaching another diffractive grating, which changes the internal TIR direction of the light (see Figure 2). The second and third grating are geometrically aligned in different directions with respect to the first and incoupling grating, e. g. by a certain angular distortion of the longitudinal axis, thus allowing to change the direction of propagation of totally internally reflected light. Needless to say, the lens itself or the material of which lenses are made of shall not be absorbing. Otherwise, the supportive information never reaches the pupil of the user or only with strongly depleted light intensity. The process works regardless of the use of reflection or transmission gratings. Usually, the lenses are equipped with both types to guide the light properly. There are differences in the optical performance of reflection and transmission gratings, which, however, are of no further interest for the current invention. The basic structure of the gratings is very similar, which is more important at this point. Nevertheless, there are different design rules and structures such as surface relief (SR) or volume phase holographic (VPH) gratings to accomplish wave-guiding.

Both types are very similar in appearance. In the simplest case, the gratings are somehow mounted onto the surface of a waveguiding material, here the lens. The grating itself is composed of an array of fine structures, mostly trenches of a first material type Material 01 with a refractive index Rl 01 , however, not limited thereto. The geometrical shape of the trenches may be manifold, from rectangular, over V-shaped trenches, U-shaped and there like. The width, including structures with different widths, the geometrical form of the trenches, their pitch as well as their depth, including different depths, are dedicatedly engineered to influence the diffraction pattern of the incident light to become split. In case of VPH gratings, the trenches or structures of a first material type (Material 01) having a refractive index (Rl 01) are filled by a second material type (Material 02) having a refractive index (Rl 02), wherein Rl 02 is incrementally different from Rl 01 (see Figures 1 and 3). For the sake of completeness, it is mentioned that Material 01 or Material 02 may be composed of a stack of structured layers, each containing a different material composition with different refractive index, stacked on top of each other, thereby forming Material 01 or Material 02 having an effective or graded refractive index Rl 01 or Rl 02, respectively. Incidentally, the (effective or graded) refractive indices Rl 01 and Rl 02 depend on the refractive index of the waveguide or the lens from which the glasses are built. If a glass lens with high refractive index (n03 > 1.46) is used, the (effective or graded) refractive indices of Material 01 and Material 02 are considered to be higher than that of the lens itself, whereby a Rl value of 2.0 can be reached and exceeded. Surface relief (SR) gratings may look similar and may also include a second type of material as a filler for the trenches, but the trenches can also be just air. High performance gratings, especially those of VPH-type, may be manufactured using standard lithography and deposition techniques known from micro-fabrication such as, for example, the manufacturing of integrated circuits. In view of the above-mentioned situation, trenches and structures in an optically active material or material stack need to be filled by a second type of optically active material - this has been already explained in a similar way for the use of MHM materials. Conventional gap filling materials are typically deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes and often suffer from incomplete gap filling due to inconsistent deposition and/or layer growth deposition characteristics, such as, e.g. increased deposition and/or growth rates at corners and edges. Such incomplete gap filling results in the formation of voids within the structures to be filled by the PVD- and CVD-materials. In addition to the formation of voids, the surface of the substrate becomes covered by PVD- and/or CVD-layer being almost closely as thick as the maximum depth of the deepest structure to be filled by the deposited gap filling material (see Figures 4 and 5). In some applications, however, it may be necessary to expose the surface of the substrate so that it is available for further processing. As a consequence, undesired overburden layers from PVD or CVD need to be removed by e. g. chemical mechanical planarization (CMP) without harming the original substrate surface underneath. Although CMP is well established and very mature in the process of manufacturing integrated circuits, CMP is a time consuming and costly process and can be seen as a potential economic show stopper for the mass production of certain electronic and optical devices, especially the mass production of diffraction gratings.

The present invention addresses this aspect and provides a solution for an advanced and cost-effective manufacturing of microelectronic and optical devices involving gap filling without the need for CMP (see Figure 6).

Thus, the present invention addresses various challenges. On the one hand, it provides economically-friendly solutions for delivering material with high etch-resistance and selectivity. On the other hand, it provides a material with a high refractive index for selective trench and gap filling during the manufacturing of diffractive gratings.

Object of the invention

It is an object of the present invention to provide novel metal complexes for the preparation of metal oxides for optical and microelectronic applications. It is an object that said metal oxides (a) allow the formation of layers having favorable optical properties such as, for example, a high refractive index of > 1.7, preferably > 2.0, at wavelengths < 520 nm, a low absorbance and a low degree of haze formation; (b) they show high etch resistance towards wet phase and/or gaseous phase etching agents, thereby enabling selective etching due to different etching rates; (c) they allow formation of dense layers and homogeneous filling of topographical features such as e.g. gaps ; and (d) they can be prepared and structured in an easy and cost-efficient manner.

It is a further object that said metal oxides can be used for various optical and microelectronics applications such as, for example, in diffractive gratings for augmented reality (AR) and/or virtual reality (VR) devices, or as metal hard mask (MHM) materials in integrated circuit (IC) chip manufacturing. It is an object of the present invention that the metal complexes can be used in formulations together with further metal complexes for a wide range of different applications.

It is a further object of the present invention to provide a method for preparing a metal oxide on a surface of a substrate, wherein said method allows an easy and cost-efficient preparation and structuring of dense metal oxide layers on different kinds of substrates, wherein said metal oxide layers (a) have favorable optical properties such as, for example, a high refractive index of > 1.7, preferably > 2.0, at wavelengths < 520 nm, a low absorbance and a low degree of haze formation; (b) show high etch resistance towards wet phase and/or gaseous phase etching agents, thereby enabling selective etching due to different etchings rates; and (c) allow homogeneous filling of topographical features such as e.g. gaps.

It is an object of the present invention to provide a method for preparing a metal oxide on a surface of a substrate as a layer covering a surface of a non-patterned substrate and/or covering the surface and filling topographical features such as e.g. gaps on the surface of a patterned substrate, thereby providing high refractive optical layers and/or etch- resistant MHM layers enabling a selective structuring of silicon wafers, silicon wafer dies or semi-finished analogues during manufacturing of integrated circuits (ICs).

Finally, it is an object of the present invention to provide a metal oxide showing the aforementioned beneficial effects and a device, preferably an optical or microelectronic device, comprising the same. Summary of the invention

The present inventors surprisingly found that the above objects are achieved by a metal complex comprising one or more metals M selected from the list consisting of V, Nb and Ta; and one or more ligands L, wherein L is an organic ligand comprising an oxime group, which is optionally substituted on the O atom.

The metal complex according to the present invention allows the preparation of a metal oxide, which (a) allows the formation of layers having favorable optical properties such as, for example, a high refractive index of > 1.7, preferably > 2.0, at wavelengths < 520 nm, a low absorbance and a low degree of haze formation; (b) shows high etch resistance towards wet phase and/or gaseous phase etching agents, thereby enabling selective etching due to different etching rates; (c) allows formation of dense layers and homogeneous filling of topographical features such as e.g. gaps; and (d) can be prepared and structured in an easy and cost-efficient manner.

The present invention further relates to a formulation comprising one or more metal complexes according to the present invention, and optionally one or more further metal complexes.

The metal complex and formulation according to the present invention can be used for preparing a metal oxide on a surface of a substrate by the following method, which also forms part of the present invention:

Method for preparing a metal oxide on a surface of a substrate, comprising the following steps: (i) providing a formulation comprising one or more metal complexes according to the present invention as metal oxide precursor;

(ii) applying said formulation on a surface of a substrate; and (iii) converting said metal oxide precursor to a metal oxide.

Moreover, a metal oxide is provided, which is obtainable or obtained by the above-mentioned method for preparing a metal oxide on a surface of a substrate.

Finally, a device is provided comprising a metal oxide according to the present invention. Preferred embodiments of the present invention are described hereinafter and in the dependent claims.

Brief description of the figures Fig. 1 : Schematic cross-sectional view of a VPFI grating with a Material 01 and a Material 02, wherein the refractive index IR 01 of Material 01 is incrementally different to the refractive index IR 02 of Material 02.

Fig. 2: Schematic cross-sectional view of a VPFI grating enabling light diffraction (transmissive case) including propagation of diffracted light within waveguide (e.g. lens) by total internal reflection.

Fig. 3: Schematic cross-sectional view of a VPFI grating providing gaps (trenches) to be filled with a high refractive index material (Material 02), wherein the refractive index of Material 02 is incrementally different form the refractive index of Material 01 flanking the gaps (trenches). Fig. 4: Schematic representation of PVD- or CVD-mediated gap filling process and removal of undesired overburden.

Fig. 5: Schematic representation of PVD- or CVD-mediated gap filling process creating and leaving voids within gaps and deposited layers.

Fig. 6: Schematic representation of gap filling process using formulations containing inventive metal complex or formulations thereof being converted to metal oxides. Fig. 7: Dispersion relation of real and complex part of complex refractive index of metal oxide according to Example 4.

Fig. 8: Transmission spectra of quartz wafers coated with metal complex according to Example 1 and cured according to Example 4.

Detailed description

Definitions The term “metal complex” as used herein, refers to a coordination complex consisting of one or more central metal atoms or ions, which form one or more coordination centers, and a surrounding array of bound molecules or ions as ligands, which contain one or more pairs of electrons that can be shared with the metal. In a metal complex, the metal atoms or ions typically act as Lewis acids, whereas the ligands typically act as Lewis bases. Metal complexes can be neutral, positively charged, or negatively charged. Electrically charged metal complexes may be also called complex ions.

The term “metal-organic complex” as used herein, refers to a class of metal complexes that contain metals and organic ligands, which confer solubility in organic solvents or volatility. Compounds with these properties find various applications in materials science for metal organic vapor deposition (MOCVD) or sol-gel processing. The distinct term “metal-organic complex” refers to metal-containing compounds lacking direct metal-carbon bonds, but which contain organic ligands. Metal b-diketonates, alkoxides, dialkyl- amides, and metal phosphine complexes are representative members of this class.

The term “ligand” as used herein, refers to ions or neutral molecules (having one or more functional groups) that bind to a central metal atom or ion to form a metal complex. The bonding with the metal generally involves formal donation of one or more of the ligand’s electron pairs often through Lewis bases. The nature of metal-ligand bonding can range from covalent to ionic. Furthermore, the metal-ligand bond order can range from one to three. Ligands are typically regarded as Lewis bases, although rare cases are known to involve Lewis acids ligands. Ligands are classified as L or X (or a combination thereof), depending on how many electrons they provide for the bond between ligand and central atom. L ligands provide two electrons from a lone electron pair, resulting in a coordinate covalent bond. X ligands provide one electron, with the central atom providing the other electron, thus forming a regular covalent bond.

The term “alkyl” or “alkyl group” as used herein, relates to a linear, branched, cyclic or bridged cyclic alkyl group, which forms part of a structure of a chemical compound and binds via a carbon atom. An alkyl group may contain one or more heteroatoms selected from N, O, S and P. An alkyl group may be unsubstituted or substituted, preferably with one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , - NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = H, C3-C10 aryl or C1 -C10 alkyl, R ^w = H, C3-C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = H, methyl, ethyl, propyl or phenyl, R ^w = H, methyl, ethyl, propyl or phenyl and R ^x = phenyl. An alkyl group may contain one or more functional groups, preferably selected from the list consisting of C=C double bond, CºC triple bond, amide, carbamate, carbonate, carboxylic acid, ester, ether, secondary or tertiary amine, and keto. Alkyl groups that connect two adjacent structural units in a chemical compound are referred to as “alkylene groups”.

The term “aryl” or “aryl group” as used herein, relates to a monocyclic or polycyclic aromatic group, which forms part of a structure of a chemical compound. Polycyclic aromatic groups include two or more connected aromatic ring systems, which are fixed in one plane. An aryl group may be (i) a hydrocarbon aryl group or (ii) a heteroatom containing aryl group, also referred to as heteroaryl group. Hydrocarbon aryl groups contain an aromatic ring structure made of carbon atoms, whereas heteroaryl groups contain an aromatic ring structure, which further comprises one or more heteroatoms selected from N, O, S and P. An aryl group may be unsubstituted or substituted, preferably with one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , -NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = H, C3-C10 aryl or C1 -C10 alkyl, R ^w = H, C3- C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = H, methyl, ethyl, propyl or phenyl, R ^w = H, methyl, ethyl, propyl or phenyl and R ^x = methyl, ethyl, propyl or phenyl.

The term “microelectronic device” as used herein refers to electronic devices of very small electronic designs and components. Usually, but not always, this means micrometer-scale or smaller. These devices typically contain one or more microelectronic components which are made from semiconductor materials and interconnected in a packaged structure to form the microelectronic device. Many electronic components of normal electronic design are available in a microelectronic equivalent. These include transistors, capacitors, inductors, resistors, diodes and naturally insulators and conductors can all be found in microelectronic devices. Unique wiring techniques such as wire bonding are also often used in microelectronics because of the unusually small size of the components, leads and pads.

The term “optical device” as used herein relates to a device containing one or more optical components for forming a light beam including, but not limited to, gratings, lenses, prisms, mirrors, optical windows, filters, polarizing optics, UV and IR optics, and optical coatings. Preferred optical devices in the context of the present invention are augmented reality (AR) glasses and/or virtual reality (VR) glasses. Preferred embodiments

Metal complex The present invention relates to a metal complex, which comprises one or more metals M selected from the list consisting of V, Nb and Ta; and one or more ligands L, wherein L is an organic ligand comprising an oxime group, which is optionally substituted on the O atom.

An oxime group is a functional group, represented wherein represents a binding site.

An oxime group optionally substituted on the O atom is a functional group, represented wherein R is a substituent and represents a binding site.

In a preferred embodiment of the present invention, the ligand L is an organic ligand comprising an oxime group, which is optionally substituted on the O atom, and a carboxylic acid group, which is optionally deprotonated.

A carboxylic acid group is a functional group, represented wherein represents a binding site. It is preferred that the ligand L comprising an oxime group and a carboxylic acid group coordinates (i) via the carboxylic acid group, (ii) via the oxime group, or (iii) via the carboxylic acid group and the oxime group to the one or more metals M.

In a preferred embodiment of the present invention, the ligand L in the metal complex corresponds to a compound represented by Formula (1), which is optionally deprotonated at the carboxylic acid group: Formula (1) wherein: the curved line represents a single bond or an alkylene group having 1 to 10 carbon atoms; R ¹ is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms;

R ² is selected from the list consisting of H, -NHR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 30 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 30 aromatic ring atoms, which may be substituted;

R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 30 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 30 aromatic ring atoms, which may be substituted; and R ^2b is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms. Preferably, the ligand L corresponds to a compound represented by Formula (1), wherein: the curved line represents a single bond or an alkylene group having 1 to 10 carbon atoms; R ¹ is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms;

R ² is selected from the list consisting of H, -NHR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 20 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 20 aromatic ring atoms, which may be substituted;

R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 20 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 20 aromatic ring atoms, which may be substituted; and R ^2b is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms.

More preferably, the ligand L corresponds to a compound represented by Formula (1), wherein: the curved line represents a single bond or an alkylene group having 1 to 3 carbon atoms;

R ¹ is selected from the list consisting of H, alkyl having 1 to 5 carbon atoms, and aryl having 6 to 10 aromatic ring atoms;

R ² is selected from the list consisting of H, -NFIR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 10 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 6 to 10 aromatic ring atoms, which may be substituted;

R ^2a is selected from the list consisting of H, -NFIR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 10 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 6 to 10 aromatic ring atoms, which may be substituted; and R ^2b is selected from the list consisting of H, alkyl having 1 to 5 carbon atoms, and aryl having 6 to 10 aromatic ring atoms.

Most preferably, the ligand L corresponds to a compound represented by Formula (1), wherein: the curved line represents a single bond, a methylene group, an ethylene group or a propylene group;

R ¹ is selected from the list consisting of H, methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl; R ² is selected from the list consisting of H, -NHR ^2a , -NR ^2a R ^2a , -OR ^2a , methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl;

R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl; and

R ^2b is selected from the list consisting of H, methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl.

It is preferred in Formula (1) that substituted alkyl contains one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , -NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = H, C3-C10 aryl or C1-C10 alkyl, R ^w = H, C3-C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = FI, methyl, ethyl, propyl or phenyl, R ^w = FI, methyl, ethyl, propyl or phenyl and R ^x = phenyl.

It is preferred in Formula (1) that alkyl, which contains one or more functional groups, contains one or more functional groups selected from the list consisting of C=C double bond, CºC triple bond, amide, carbamate, carbonate, carboxylic acid, ester, ether, secondary or tertiary amine, and keto. It is preferred in Formula (1 ) that substituted aryl contains one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , -NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = FI, C3-C10 aryl or C1-C10 alkyl, R ^w = H, C3-C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = H, methyl, ethyl, propyl or phenyl, R ^w = H, methyl, ethyl, propyl or phenyl and R ^x = methyl, ethyl, propyl or phenyl. In a more preferred embodiment of the present invention, the ligand L in the metal complex corresponds to a compound represented by Formula (2): Formula (2) wherein:

R ¹ is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms;

R ² is selected from the list consisting of H, -NFIR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 30 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 30 aromatic ring atoms, which may be substituted;

R ^2a is selected from the list consisting of H, -NFIR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 30 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 30 aromatic ring atoms, which may be substituted; and

R ^2b is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms.

Preferably, the ligand L corresponds to a compound represented by Formula (2), wherein:

R ¹ is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms; R ² is selected from the list consisting of H, -NHR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 20 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 20 aromatic ring atoms, which may be substituted; R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 20 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 5 to 20 aromatic ring atoms, which may be substituted; and

R ^2b is selected from the list consisting of H, alkyl having 1 to 10 carbon atoms, and aryl having 5 to 10 aromatic ring atoms.

More preferably, the ligand L corresponds to a compound represented by Formula (2), wherein:

R ¹ is selected from the list consisting of H, alkyl having 1 to 5 carbon atoms, and aryl having 6 to 10 aromatic ring atoms;

R ² is selected from the list consisting of H, -NHR ^2a , -NR ^2a R ^2a , -OR ^2a , alkyl having 1 to 10 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 6 to 10 aromatic ring atoms, which may be substituted; R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , alkyl having 1 to 10 carbon atoms, which may be substituted and/or may contain one or more functional groups, and aryl having 6 to 10 aromatic ring atoms, which may be substituted; and

R ^2b is selected from the list consisting of H, alkyl having 1 to 5 carbon atoms, and aryl having 6 to 10 aromatic ring atoms.

Most preferably, the ligand L corresponds to a compound represented by Formula (2), wherein:

R ¹ is selected from the list consisting of H, methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl;

R ² is selected from the list consisting of H, -NFIR ^2a , -NR ^2a R ^2a , -OR ^2a , methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl; R ^2a is selected from the list consisting of H, -NHR ^2b , -NR ^2b R ^2b , -OR ^2b , methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl; and R ^2b is selected from the list consisting of H, methyl, ethyl, propyl, butyl, pentyl, phenyl and naphthyl.

It is preferred in Formula (2) that substituted alkyl contains one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , -NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = H, C3-C10 aryl or C1-C10 alkyl, R ^w = H, C3-C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = FI, methyl, ethyl, propyl or phenyl, R ^w = FI, methyl, ethyl, propyl or phenyl and R ^x = phenyl.

It is preferred in Formula (2) that alkyl, which contains one or more functional groups, contains one or more functional groups selected from the list consisting of C=C double bond, CºC triple bond, amide, carbamate, carbonate, carboxylic acid, ester, ether, secondary or tertiary amine, and keto.

It is preferred in Formula (2) that substituted aryl contains one or more substituents selected from the list consisting of -C(0)R ^v , -C(0)0R ^v , -NR ^V R ^W , -OR ^v , -R ^x , -CN, -F and -Cl, wherein R ^v = FI, C3-C10 aryl or C1-C10 alkyl, R ^w = H, C3-C10 aryl or C1 -C10 alkyl and R ^x = C3-C10 aryl or C1 -C10 alkyl, preferably R ^v = FI, methyl, ethyl, propyl or phenyl, R ^w = FI, methyl, ethyl, propyl or phenyl and R ^x = methyl, ethyl, propyl or phenyl.

It is preferred that the metal M in the metal complex of the present invention is in an oxidation state selected from the list consisting of +l, +II, +111, +IV and +V, preferably +11, +111, +IV and +V, more preferably +V. In a preferred embodiment of the present invention, the metal complex is represented by the following Formula (3): M _m mL _n nA _a aB _b D Formula (3) wherein:

M is at each occurrence independently from each other a metal selected from the list consisting of V, Nb and Ta;

L is at each occurrence independently from each other an organic ligand comprising an oxime group, which is optionally substituted on the O atom;

A is a bridging ligand selected from m-OFI-, m-F- m-CI-, m-B r or m-I ^_ ;

B is a bridging ligand represented by m-O ^2- ; m is an integer from 1 to 10, preferably 1 to 5, more preferably 1 or 2, and most preferably 1 ; n is an integer from 5 to 50, preferably 5 to 25, more preferably 5 to 10, and most preferably 5; a is an integer from 0 to 20, preferably 0 to 10, more preferably 0 to 4, and most preferably 0; and b is an integer from 0 to 10, preferably 0 to 5, more preferably 0 to 2, and most preferably 0; with the proviso that the following equation is met: n + a + 2 ^* b = S ^* m, wherein S is the value of the oxidation state of M, preferably selected from 1 , 2, 3, 4 and 5, more preferably 2, 3, 4 and 5, most preferably 5.

It is preferred in Formula (3) that the ligand L is an organic ligand comprising an oxime group, which is optionally substituted on the O atom, and a carboxylic acid group, which is optionally deprotonated. Oxime and carboxylic acid groups are described above.

It is further preferred in Formula (3) that the ligand L comprising an oxime group and a carboxylic acid group coordinates (i) via the carboxylic acid group, (ii) via the oxime group, or (iii) via the carboxylic acid group and the oxime group to the one or more metals M. It is preferred in Formula (3) that the ligand L is represented by Formula (1) or (2) as described above.

The metal complex of the present invention can be prepared by any standard synthesis. Usually, the complex is formed from a metal precursor compound, which can be a salt or a complex, and the corresponding ligand(s). For this, known standard reactions can be used.

Formulation

The present invention further relates to a formulation comprising one or more metal complexes according to the present invention as metal oxide precursor(s). Preferably, the formulation according to the present invention comprises one or more solvents. The solvents are selected to improve applicability, wettability, deposition properties, filling properties and/or stability of the formulation. Any solvent can be used as long as it can dissolve or disperse the metal complex according to the present invention. Preferred solvents for the formulation are selected from water, alcohols, organic solvents and mixtures thereof. Preferred organic solvents are esters, ketones, lactones, diketones, carboxylic acids, amides and mixtures thereof. Particularly preferred organic solvents are ethanol, propanol, 1 -butanol, 2-butanol, diacetone alcohol, 1-methoxy-2-propanyl acetate (PGMEA), 1-methoxy-2- propanol (PGME), butyl acetate, amyl acetate, cyclohexyl acetate, 3- methoxybutyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methyl amyl ketone, cyclohexanone, cyclopentanone, ethyl-3-ethoxy propanoate, methyl-3-ethoxy propanoate, methyl-3-methoxy propanoate, methyl acetoacetate, ethyl acetoacetate, methyl pivalate, ethyl pivalate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monomethyl ether propanoate, propylene glycol monoethyl ether propanoate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, 3-methyl-3-methoxybutanol, N-methylpyrrolidone, dimethyl sulfoxide, gamma-butyrolactone, gamma valerolactone, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, methyl lactate, ethyl lactate, propyl lactate, tetramethylene sulfone, propylene glycol dimethyl ether, dipropylene glycol dimethyl ether, ethylene glycol dimethyl ether or diethylene glycol dimethyl ether, N-ethylpyrrolidone, 2-pyrrolidone, 2,2,4-trimethyl-1 ,3-pentandiol monoisobutyrate, terpineol, 3- phenoxytoluene, 4-phenoxytoluene and anisole. These solvents may be used singly or in a mixture of two or more.

Preferably, the mass ratio (w/w) of the metal complex in the formulation according to the present invention is usually not less than 1% and not more than 100%, more preferably not less than 1% and not more than 80%, still more preferably not less than 1 % and not more than 60%, and most preferably not less than 2% and not more than 40%, based on the total mass of the formulation.

In a preferred embodiment of the present invention, the formulation comprises one or more further metal complexes, which may act as further metal oxide precursor(s). In such case, a metal oxide mixture may be formed comprising a metal oxide obtained from the metal oxide precursor and a further metal oxide obtained from the further metal oxide precursor. Preferred further metal complexes comprise one or more trivalent or tetravalent metals M’, preferably selected from the list consisting of Sc, Y, La, Ti, Zr, Hf and Sn, more preferably one or more tetravalent metals M’ selected from the list consisting of Ti, Zr, Hf and Sn. Preferred further metal complexes comprise one or more ligands L, represented by Formula (1) or (2) as described above for the metal complex according to the present invention. In a preferred embodiment of the present invention, the formulation is a binary, ternary or quaternary metal complex mixture comprising a second, third or fourth further metal complex, where preferably each of the second, third and fourth further metal complex contains alkoxides, carboxylates, basic carboxylates, derivatized 1 ,3-diketonates, beta-keto carboxylates and beta-keto carboxylic acid esters, catechol, 2,3-dihydroxybenzoic acid, gallic acid, 1 ,8-dihydroxynaphthalene, 1 ,9-anthracenediol, 1-hydroxy-9-anthrone, 9-hydroxy-1-anthracenone, 1 ,8,9-anthracenetriol, dithranol or derivatives thereof.

Such further metal complexes may be used neatly or prepared in situ by, for example, dissolving and/or dispersing metal oxides, metal hydroxides, metal carbonates and metal alkoxides in a suitable solvent, followed by addition of any kind of acid, preferably a carboxylic acid, however, not limited hereto, to facilitate dissolution, as well as followed by the addition of any kind of alkoxide, carboxylate, basic carboxylate, derivatized 1 ,3- diketonate, beta-keto carboxylate and beta-keto carboxylic acid ester, catechol, 2,3-dihydroxybenzoic acid, gallic acid, 1 ,8-dihydroxynaphthalene, 1,9-anthracenediol, 1-hydroxy-9-anthrone, 9-hydroxy-1-anthracenone,

1 ,8,9-anthracenetriol, dithranol or derivatives thereof.

Such binary, ternary or quaternary metal complex mixtures allow a fine tuning of certain properties of metal oxides prepared therefrom. Such properties may include, for example, material hardness, shrinkage, refractive index, transparency and absorbance, haze suppression as well as etch resistance and selectivity towards RIE, plasma or wet chemical etching and content of carbon residue or non-metal oxide impurity and combinations thereof.

Preferably, the mass ratio (w/w) between the one or more metal complexes and the one or more further metal complexes in the formulation according to the present invention is in the range from 1 :100 to 100:1 , preferably 1 :10 to 10:1 , more preferably 1 :5 to 5:1.

Method for preparing metal oxide

The present invention further provides a method for preparing a metal oxide from one or more metal complexes according to the present invention. In this method the metal complex(es) is/are used as metal oxide precursor(s). The obtained metal oxide is particularly suitable for use in optical and/or microelectronic applications.

The method for preparing a metal oxide according to the present invention comprises the following steps: (i) providing a formulation comprising one or more metal complexes according to the present invention as metal oxide precursor(s);

(ii) applying said formulation to a surface of a substrate; and

(iii) converting said metal oxide precursor to a metal oxide. Preferably, the formulation provided in step (i) is a solution or dispersion comprising one or more solvents. Preferred solvents for the formulation provided in step (i) of the method according to the present invention are the same as described above for the formulation according to the present invention.

Depending on the specific problem to be solved, the metal oxide precursors and their respective metal oxides may be required to become either deposited as a homogenous, dense and thin layer covering the entire surface of the substrate by a coating technique or the metal oxide precursors may be required to be deposited locally in a structured manner, thus requiring for a printing technique. Both, coating and printing of metal oxide precursors require them to be formulated in an adequate manner to comply with the physico-chemical needs of the coating and printing technique chosen as well as to comply with certain needs with respect to the surface of the substrate to be coated or printed. It is preferred that in step (ii) the formulation is applied to the surface of the substrate by a coating process or a printing process, preferably by a spin coating process or an inkjet printing process. Alternative coating or printing processes may be selected from the list consisting of roller coating, spray coating, slot coating, slit coating, screen printing, stencil printing, gravure printing and flexo printing.

Said formulation provides a layer of metal oxide precursors, which are subsequently converted to a metal oxide or a metal oxide mixture in step (in)·

It is preferred that the conversion of the metal oxide precursor in step (iii) takes place by exposure to thermal treatment and/or irradiation treatment.

Preferred thermal treatment includes exposure to elevated temperatures as high as 1200*C, preferably up to 60013, more prefer ably up to 550*C and most preferably up to 500*0. Thermal treatment is n ot limited to any specific thermal treatment methods or times. Depending on the type of substrate and formulation, a person skilled in the art is able to determine suitable thermal treatment methods and times.

Preferred irradiation treatment includes exposure to infrared (IR) light, visible (VIS) light and/or ultraviolet (UV) light. IR light has a wavelength of > 800 nm. VIS light has a wavelength from 400 to 800 nm. UV light has a wavelength of < 400 nm and may include EUV (extreme UV). Irradiation treatment is not limited to any specific irradiation treatment methods or times. Depending on the type of substrate and formulation, a person skilled in the art is able to determine suitable irradiation treatment methods and times.

It is preferred that the conversion of the metal oxide precursor in step (iii) takes place by soft baking at a temperature from 40 to 150Ό, preferably 100Ό; and then curing (sintering or annealing) at a temperature from 150 to 600Ό, preferably 200 to 550Ό, more preferably 250 to 500Ό.

In a preferred embodiment of the method for preparing a metal oxide according to the present invention, the metal oxide forms a coating layer on the surface of the substrate.

In a more preferred embodiment of the method for preparing a metal oxide according to the present invention, the substrate is a patterned substrate comprising topographical features and the metal oxide forms a coating layer covering the surface of the substrate and filling said topographical features. As a result, the topographical features are filled and levelled by the metal oxide.

Preferred topographical features include, for example, gaps, grooves, trenches and vias. Topographical features may be distributed non-uniformly or uniformly over the surface of the substrate. Preferably, they are arranged as an array or a grating on the surface of the substrate. It is preferred that the topographical features have different lengths, widths, diameters as well as different aspect ratios. It is preferred that said topographical features have an aspect ratio of 1 :20 to 20:1 , more preferably 1:10 to 10:1. The aspect ratio is defined as width of structure to its height (or depth). From the viewpoint of dimension, the depth of the topographical features is preferably in the range from 10 nm to 10 pm, more preferably 50 nm to 5 pm, and most preferably 100 nm to 1 pm. It may be also necessary to fill topographical features locally with metal complexes (metal oxide precursors) and their respective metal oxides, either completely or to a certain level, but not to cover adjacent surfaces of the layer stack or of the substrate itself, where no structures to be filled are available.

Hence, it is preferred that the method for preparing a metal oxide further comprises the following step: (iv) removing the portion of said metal oxide coating layer covering the top of the topographical features, thereby producing filled topographical features, wherein the metal oxide coating layer is flush with the top of said topographical features. Step (iv) takes place after steps (i) to (iii). Preferably, removing the portion of the metal oxide coating layer covering the top of the topography in step (iv) is performed by using a chemical stripper or fluorinated plasma etch.

The process of leveling or filling structures can be understood as a gap filling process.

The substrate is preferably a substrate of a microelectronic device or an optical device. Preferred substrates are made of inorganic or organic base materials, preferably inorganic base materials. Preferred inorganic base materials contain materials selected from the list consisting of ceramics, glass, fused silica, sapphire, silicon, germanium, silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN) and transparent polymers or resins. The geometry of the substrate is not specifically limited, however, preferred are sheets or wafers.

In step (ii) of the method for preparing a metal oxide, the formulation is applied on a surface of a substrate, wherein said surface may be either a surface of a base material of the substrate or a surface of a layer of a material being different from the base material of the substrate, wherein such layer has been formed prior to applying said formulation. In this way, sequences of different layers (layer stacks) can be formed on top of one another. Such layer stacks may be also structured, wherein such structures typically have dimensions in the nanometer scale, at least with respect to diameter, width and/or aspect ratio. Metal oxide

The present invention further relates to a metal oxide, which is obtainable or obtained by the method for preparing a metal oxide according to the present invention as described above.

Device

Finally, the present invention relates to a device comprising a metal oxide according to the present invention as described above. The metal oxide is obtainable or obtained by the method for preparing a metal oxide according to the present invention as described above.

It is preferred that the device is a microelectronic device or an optical device. Preferred microelectronics devices are integrated circuit (IC) chips. Preferred optical devices are augmented reality (AR) devices and virtual reality (VR) devices.

The present invention is further illustrated by the examples following herein after which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims. Examples

A Measurement methods

Ellipsometry was used to determine layer thickness, refractive index (n) and absorption index (k) of a metal oxide layer. Measurements were performed using an ellipsometer M2000 from J. A. Woollam and three different angles of incidence (65° 70 °and 75°). The measurement d ata was analyzed with software CompleteEase from J. A. Woolam, assuming either full or almost nearly complete transparent behavior above a wavelength of 600 nm and applying B-spline fitting for obtaining refractive index (n) as well as absorption index (k). Transmission spectra were recorded using UV/Vis/NIR spectrophotometer Cary 5000. Measurements were carried out using dual beam mode using a scan speed of 100 nm/min and a spectral band width of 2 nm. The angle of incidence versus substrate surface was 90 °and the reference beamline was allowed to pass through air.

B Synthesis of metal complex Example 1 A reaction apparatus composed of a three-necked reaction flask equipped by a dripping funnel, a reflux condenser, glass thermometer and a magnetic stir bar was thoroughly flushed by constant stream of Ar. A conventional magnetic lab hotplate was used as heating source as well as magnetically coupled stirrer. 3.68 g of 2-methoxyimino propanoic acid were filled into the flask and dissolved in 17.78 g of THF. In parallel, 2 g of niobium(V) ethoxide became dissolved in 5 g of THF and the resulting solution poured into the dripping funnel. All steps described further below were performed under constant stirring of the reaction mixture. The solution of niobium ethoxide was allowed to drop slowly into the reaction mixture at room temperature. After completion of the addition, the temperature of the reaction mixture was raised to 45 Ό and the mixture was allowed to react overnight. Then, the solvent was removed from the reaction mixture by means of rotary evaporation while the crude product started to precipitate. The product had a creamy-colored appearance and it was dried in vacuum furnace. After drying, it was subjected to elementary, ICP-OES, TGA and ¹ H-NMR-analysis.

TG-analysis was performed in air, starting from room temperature to 950 Ό using a heating rate of 10 K/min. The residue obtained upon analysis amounted to a final solid content of 21.49 % w/w which was found to be in good agreement with the expected value of 19.74 % w/w. Elementary analysis of the product provided 34.4 % w/w (35.67 % w/w) for C, 5.2 % w/w (4.49 % w/w) for H, 8.9 % w/w (10.40 % w/w) for N and 36.6 % w/w (35.64 % w/w) for O, where theoretically expected values are provided as values in brackets. The content of niobium was found to be 15.1 % w/w (13.80 %). ¹ H-NMR (THF-ds) provided at Me-O-N at 3.96 ppm (15 H) and Me-C=N at1.93 ppm (15 H).

The obtained niobium oximate complex was found to best correspond to the mononuclear structure Nb[MeO-N=C(Me)-COO]5.

C Preparation of metal oxide Example 2 The reaction product from Example 1 was used as directly received after the synthesis and dissolved in 1-methoxy-2-propanol to prepare a 40 % w/w solution with respect to the metal oxide precursor. 0.15 ml of the solution was deposited on static 2” <100> Si-wafers (CZ) and spin coated at 2000 rpm for 25 s. After coating, the wafers were soft baked at 100 Ό for 1 min and subsequently cured at 250 Ό as well as a 1300 Ό for 10 minutes each. Layer thickness and refractive index of obtained metal oxide films were determined by ellipsometry as shown in Table 1.

Table 1 : Layer thickness and refractive index of metal oxide obtained in Example 2.

Example 3

The reaction product from Example 1 was used as directly received after the synthesis and dissolved in 1-methoxy-2-propanol to prepare a 40 % w/w solution with respect to the metal oxide precursor. 0.15 ml of the solution was deposited on static squared glass sheets of AF45-glass having an edge length of 5 cm and spin coated at 2000 rpm for 25 s. After coating, the wafers were soft baked at 100 Ό for 1 min and subsequently cured at 250 Ό as well as at 300 Ό for 10 minutes each. La yer thickness and refractive index of obtained metal oxide films were determined by ellipsometry as shown in Table 2.

Table 2: Layer thickness and refractive index of metal oxide obtained in Example 3.

Example 4

The reaction product from Example 1 was used as directly received after the synthesis and dissolved in 1-methoxy-2-propanol to prepare a 20 % w/w solution with respect to the metal oxide precursor. The coating was prepared on 2” quartz-wafers. 0.5 ml of the coating solution was deposited in the center of the static wafers and after depositing, the coating solution was spun off. The coating speeds applied ranged from 1500 rpm to 2500 rpm applying an interval of 500 rpm. After coating, the wafers were cured directly at 500 Ό for 15 minutes. Layer thickness and refractive index of obtained metal oxide films were determined by ellipsometry as shown in Table 3.

Table 3: Layer thickness and refractive index of metal oxide obtained in Example 4.

Figure 7 shows the dispersion relation of real and complex part of complex refractive index of metal oxide as obtained from ellipsometry measurements and according to experimental procedure of Example 4.

Figure 8 shows transmission spectra of quartz wafers coated with metal complex according to Example 1 and cured according to Example 4.

D Conclusion

New metal oxide precursors based on oxime type ligands for group 5 metals, V, Ta and in particular Nb, were described. These compounds can be formulated that way in order to achieve simply to coat and print formulations. The formulation may be used to become deposited onto e. g. inorganic substrates where upon and after thermal activation and decomposition, the formulations and the metal oxide precursors dissolved allow the formation of layers of metal oxides on the coated and printed substrates. The thickness of the metal oxide layer, typically in the range of 1 pm or below, can be adjusted by the concentration of the metal oxide precursors in the solution as well as by the coating and printing parameters to become applied. The refractive index of the metal oxide layers is dependent on the type of central metal in the metal oxide precursor, as well as on the conversion process of the precursor to the oxide and e. g. the maximum temperature as well as respective holding time achieved during the conversion process. It was shown that a refractive index of 2.16 at 520 nm was achieved using a niobium precursor. The metal oxide precursors can be used in course of the manufacturing of optical as well as microelectronic devices, as e. g. diffractive gratings and integrated circuits respectively. During their manufacturing, the metal oxide precursors and correspondingly derived metal oxides may be particularly used as coatable and printable gap filling materials, thus enabling creating structures with different refractive indices at the one hand (e. g. for volume phase holographic gratings), and allowing for high chemical stress resistance on the other hand when being used during manufacturing of integrated circuits.

List of reference signs

1 Material 02 with Rl 02

2 Material 01 with Rl 01 3 Substrate (e.g. glass)

4 Diffraction of incident light represented by broad arrow

5 Total internal reflection of light (TIR)

6 Waveguide

7 Structured layer stack with gaps (trenches) 8 Substrate (e.g. glass or silicon)

9 Overburden of material (e.g. high refractive index material or high etch resistant material)

10 Material (e.g. high refractive index material or high etch resistant material) providing gap fill 11 Voids

12 Formulation (e.g. ink) of high refractive index material (e.g. metal oxide precursor)

13 High refractive index material (e.g. metal oxide) providing gap fill with optional concave geometry 14 Overburden layer (optional)

15 Energy