NO343742B1 - Process for the preparation of thin film by gas phase deposition technique - Google Patents

Description

The present invention relates to a method for producing thin films of an organic-inorganic nature.

ALCVD = atomic layer chemical vapor deposition, also known as ALE = atomic layer epitaxy, and ALD = atomic layer deposition is a thin film technique that only utilizes surface reactions, and which is described in known technique, see for example M. Ritala, M. Leskelä, in: H.S. Nalwa (Ed.), Handbook of Thin Film Materials, vol. I, Academic Press, San Diego, CA, 2001, p.103.

It has now surprisingly been found that this technique can be utilized to construct hybrid thin films using different types of precursors. The precursors are sent sequentially as pulses into the reaction chamber where it reacts with all surfaces present, each pulse being followed by a purge time with an inert gas. In this way, gas phase reactions are eliminated and film is formed from precursor units in the order in which they are pulsed. This technique makes it possible to change building units with a monolayer resolution and therefore enables the production of artificial structures of hybrid films with different types of organic and inorganic building elements.

A hybrid material is a material that consists of both inorganic structural elements. This class of materials has recently received much attention due to the fact that it is now possible to synthesize these materials in a more controlled manner. The organic part can provide potential advantages such as good electrical mobility, band gap tuning, mechanical and thermal stability and interesting magnetic or dielectric transitions. Furthermore, the organic part can contribute useful properties such as soft mechanical properties, suitable processing as well as structural and functional diversity. In light of the synthetic flexibility of organic materials, this latter set of possibilities is particularly arresting for the imagination. These advantages are discussed thoroughly in the prior art for example by Z. Xu, in Organic Chemistry, Vol.42, No.6, 2003 or D.B. Mitzi, Progress in Organic Chemistry, 48 (1999) 1-121, and D.B. Mitzi in Chemistry of Materials 13 (2001) 3283-3298. David B. Mitzi has focused his attention on hybrid materials for transistor materials. It is based on perovskite amine type hybrid materials. Known techniques for the production of hybrid materials are: vapor deposition (PVD), spin coating, dip coating. Langmuir film growth, conventional CVD. Other publications in this area are D.B. Mitzi et al., "Organic-inorganic electronics", IBM J. Res. & Dev. Vol.45, no.1, January 2001, pages 21-45. Organic-inorganic hybrid materials and their application are described here. The application of the ALCVD technique to obtain hybrid materials is not described.

In hybrid multilayer films formed by self-assembly of an ordered liquid crystalline array of molecular columns on an ultra-thin metal layer, it has been shown that electrons in the metal interact with the molecular layer above, forming new energy bands that have new electron transport properties. See for example A. Pecchia et al. / Microelectronic Engineering 51-52 (2000) 633-644.

Hybrid films can also have interesting optical properties, for example as described for polysilane-silica hybrid thin films by S. Mimura et al in Journal of Organometallic Chemistry 611 (2000) 40-44.

Due to the large number of possible organic and inorganic building blocks that can be imagined used in hybrid materials, there is an almost unlimited imaginable result in possible interesting properties that can be produced from hybrid materials. Some of these constructions may involve superstructures of different hybrid materials and this should be suitably possible to produce by ALCVD. It is hoped that this area will benefit the next generation of electronics. The motivation for this work has been to demonstrate that hybrid materials can be synthesized in a simple way and with good control by the ALCVD technique. It demonstrates the application of chemical reactions to connect different building elements that together form a hybrid film.

US 6,645,882B1 describes the construction of dielectric material for semiconductor devices using multilayers of materials with varying dielectric constants. All materials considered are to be considered inorganic materials. The resulting stack is sometimes referred to as a composite or a hybrid material since it consists of materials from two different subsets, in this case inorganic materials with varying magnitudes of dielectric constant. The aforementioned patent does not cover any subject of the present invention since the latter focuses on materials containing both inorganic and organic parts and as mentioned the patent focuses only on inorganic materials.

US 2004/0087101 A1 describes the construction of capacitors using multilayers of materials with varying dielectric constant. In the same way as for US 6,645,882B1, this patent uses the formulation artificial hybridites to describe materials with two different subgroups. Also for this patent, both subgroups that are assessed are purely inorganic in nature.

US2004/0118805A1 describes methods for etching/removing the material in the manufacture of electronic devices. The technique uses a combination of ion bombardment on selected areas followed by a wet etching procedure. This combination of two different etching procedures to produce one etching procedure is referred to as a hybrid material removal scheme. The patent is therefore not of significant importance with regard to this invention.

ALCVD technique has now for the first time been used to produce thin films of an inorganic-organic nature also referred to as hybrid film.

According to the present invention, it provides a method for producing a thin film of an organic-inorganic nature on a substrate by a gas phase deposition technique produced by ALCVD, comprising the following steps:

a) contacting the substrate with a pulse of an inorganic precursor selected from the group consisting of metal alkyls and metal halides, wherein the metal is selected from the group consisting of Al, Si, Sn, Zn, Mg, Ti, Zr, V, Mn, Fe , Co, Cr and Pt;

b) reacting the inorganic precursor with at least one surface of the substrate; c) removing unreacted inorganic precursor and reaction byproducts if any; d) contacting the surface of the substrate with a pulse of an organic precursor, wherein the organic precursor is an organic compound substituted with 2-6 substituents selected from the group consisting of –OH, –COOH, –SH, –NH2, –SO4H . the reactive substituents, and where the organic precursor can be brought to gas phase;

e) reacting the organic precursor with the inorganic compound bound to the substrate to form an organic inorganic hybrid layer;

f) removing unreacted organic precursor and reaction by-products if any, g) repeating steps a) to f) until the desired film thickness is achieved.

Steps a) to c) and/or d) to f) can be repeated with independently selected precursors before the procedure continues with respectively steps d) to f) or a) to c).

Other preferred embodiments of the present invention are described in the subclaims.

A thin film comprising hybrid monolayers comprising an organic part and an inorganic part chemically bonded to each other is described.

A substrate comprising a thin film coating containing monolayers comprising an organic part and an inorganic part chemically bonded to each other is also described.

Furthermore, the use of a thin film produced by the method according to the invention or a thin film according to the invention as an optical material, a pressure sensor, a gas sensor, a temperature sensor, a magnetic field sensor, an electric field sensor, a piezoelectric material, a magnetic material, a semiconductor is described -material and as an electrically insulating material.

A pressure sensor characterized by the fact that it comprises a hybrid thin film produced by ALCVD is also described.

It is further described a thin film comprising several hybrid monolayers of organic and inorganic parts chemically bound to each other, where the thin film comprises at least two different organic or inorganic parts.

In the present invention, the term "inorganic precursor" shall be considered to mean any compound comprising an inorganic part which, upon reaction with a surface of a substrate, is bound to the surfaces, thereby connecting the inorganic part to the substrate through a bond or one or more bridging elements elements and where the inorganic part bound to the surface comprises one or more reactive groups for reaction with another precursor. The term "inorganic part" means a part that contains at least one metal atom. For example, it can be a compound that is organometallic, organometallic, a halogen compound, carbonyl, or any other compound capable of transferring the metal to the gas phase.

In the present invention, the term "organic precursor" shall be considered to mean any compound comprising an organic part which, upon reaction with a surface of a substrate, is bound to the surface, thereby connecting the organic part to the substrate through a bond or one or more bridging elements elements and where the organic part bound to the surface comprises one or more reactive groups for reaction with another precursor.

Description of figures

Fig. A The effect of pulse parameters on the growth rate of Al-hydroquinone (Hq) film, calculated on the basis of quartz crystal monitor (QCM) measurements.

Fig. B The effect of pulse parameters on the growth rate of Al-phloroglucinol (Phl) film, calculated on the basis of QCM measurements.

Fig. C Growth rate as a function of temperature for Al-Hq (bottom pair) and Al-Phl (top pair) film calculated on the basis of 80 growth cycles, both for as-deposited and air-treated film.

Fig. D IR absorbance spectra for thin films of (a) Al-Hq, (b) Al-Phl, (c) Al-Hq-Al-Phl, both as deposited and air-treated. The films were grown for 1000 cycles at a reactor temperature of 200°C. The absorbance spectra for pure Hq and Phl are added for reference.

Fig. E The linearity of the growth as measured by QCM with fresh Au electrodes.

Fig. F Growth kinetic analysis obtained by QCM measurements of (a) Al-Hq, (b) Al-Phl, (c) Al-malonic acid, Al-terephthalic acid, Zr-Hq, Ti-Hq, and (d) Thiethylenediamine growth. The data is based on the average of 20 successive pulses.

Fig. G X-ray diffractogram of hybrid thin films grown with a total of 1000

cycles. The upper and lower diffractograms for each pair represent the as-grown and air-treated condition, respectively.

The ALCVD technique can be seen as a control sequential chemical reaction technique. The film builds by allowing a functional group on the gas molecule to react with a suitable site on a surface. The reacting gas molecules must leave a site on the surface that will act as a reactive site for the subsequent type of gas molecule to produce a continuous film.

This type of growth is exemplified by the growth of Al-Hq and Al-Phl films by the fact that methyl groups bonded to aluminum react with hydroxyl groups to form methane and a film of aluminum benzene oxide. Trimethyl aluminum (TMA) does not react with all three of its alkyl groups with the surface due to steric hindrance, but retains at least one group as a reactive site toward a subsequent gas molecule. The Hq gas molecule is a diol type where only one of the hydroxyl groups can react with the surface site due to steric hindrance. This will then leave a hydroxyl-terminated surface for subsequent reactions with TMA.

This type of growth has also been exemplified by the growth of films with the precursor combinations: TMA and malic acid, TMA and terephthalic acid, ZrCl4 and Hq, TiCl4 and Hq, TiCl4 and ethylenediamine. The growth genetics derived from QCM data from these experiments are shown in Fig. F.

The two or more types of functional groups on a gas molecule must not be of the same type, but should leave a reactive site suitable for subsequent growth with another type of gas molecule. Each type of gas molecule must not undergo reactions with itself.

With the method according to the invention, the precursor to each monolayer can be freely chosen from among the compounds that will react with the available functional groups and consequently it is possible to generate films comprising alternating organic and inorganic groups where these groups can be the same or different from the previously deposited groups or they can be selected to form an optional repeating pattern.

Some of the functional groups that can be considered to undergo reactions by the ALCVD principle are described in the following. For all these proposed reaction mechanisms, it is possible that the reaction scheme is somewhat shifted or different and the reaction schemes should not be interpreted as limiting the scope of the invention. The basic principle is that the reaction results in the formation of a film.

Regarding possible reactions between metal-containing precursors and organic molecules with functional groups. Organic molecules with functional groups having some degree of acidity which can donate a proton are preferred. This proton will be used to complement the alkane molecule or the halogen acid molecule from the inorganic precursor and allow the reaction to proceed.

Below are presented some functional groups on the organic precursor that may be involved in the reactions, and examples of the reaction are listed. All the proposed reactions are only illustrations of possible reactions and should not be interpreted as limitations.

Hydroxyl groups

Hydroxyl groups (R-OH) provide an oxygen and hydrogen for a possible reaction. These react easily with electropositive metals, e.g. in the form of alkyls or halides, whereby a metal alkoxide is formed and resp. methyl or hydrohalic acid. This reaction is demonstrated by the production of Al-Hq and Al-Phl films with TMA and Hq or Phl.

The two partial reactions that take place between a diol (HO-R-OH) and TMA ((CH3)3Al) are listed below:

HO-R-OH(g) CH3-Al-| → CH4(g) HO-R-O-Al-|

2HO-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(O-R-|)2

Electropositive metals that are known to easily undergo such reactions are: Al, Mg, Si, Ti, V and most likely several other metals such as Zn, Mn, Fe, Co, Cr among others.

Ether groups

Ether groups (-OR) can react and form adducts to metals in the film. These bonds are quite weak, but still they can be the basis for structure formation for the production of films at low temperatures. An example of such a reaction scheme is:

R'O-R(g) CH3-Mn-| → R’O-R-Mn-|

2R’O-R-| (CH3)3Al(g) → 2R'-CH3(g) CH3-Al-(O-R-|)2

Only a half reaction is presented because it is quite likely that film formed via this reaction pathway will use a different type of functional groups in its structure to form film in the next step. The general idea is to form chelate bonds between the ether and the metal atom.

Ketone groups

Ketones (R=O) can react and form chelate bonds to a metal atom. One such example is the formation of compounds with β-ketones. An example of such a visualized reaction scheme is:

O=R'-R=O (g) Mn-| → R,R'(=O)2-Mn-|

Only half a reaction is presented because it is quite likely that film formed via this reaction pathway will use other types of functional groups in its structure to form film in the next step. The general idea is to form chelate bonds between the ketone and the metal atom.

Carboxyl groups

Carboxyl groups (-COOH) have the same building blocks as hydroxyl (-OH) and ketones (=O), and should therefore undergo the same reactions that these types show.

The two partial reactions that take place between dicarboxylic acid (HOOC-R-COOH) and TMA ((CH3)3Al) are listed below:

HOOC-R-COOH(g) CH3-Al-| → CH4(g) HOOC-R-COO-Al-|

2HOOC-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(COO-R-|)2

There is also a possibility for another reaction scheme with TMA where it will react with both =O and –OH to a carboxylic acid.

Thiol groups

Thiol groups (-SH) should react according to the same pattern as their isoelectronic hydroxyl relatives (-OH). However, the metal affinity towards sulfur is somewhat different from that towards oxygen. This results in elements such as Pb, Au, Pt, Ag, Hg, and several others will readily react and form stable bonds with sulfur.

The two subreactions that take place between a di-thiol (HS-R-SH) and Pt(thd)2 are listed below:

HS-R-SH(g) thd-Pt-| → Hthd(g) HS-R-S-Pt-|

2HS-R-| Pt(thd)2(g) → Hthd(g) thd-Pt-S-R-|

Sulfate groups

Sulphate groups (-SO4H) should react with electropositive metals according to the same reaction pathways as for hydroxyls or ketones.

The two partial reactions that take place between a disulfate (HSO4-R-SO4H) and TMA ((CH3)3Al) are listed below:

HSO4-R-SO4H (g) CH3-Al-| → CH4(g) HSO4-R-SO4-Al-|

2HSO4-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(SO4-R-|)2

Sulfite groups

Sulfite groups (-SO3H) should react according to the same pattern as for sulfate groups.

The two partial reactions that take place between a disulfite (HSO3-R-SO3H) and TMA ((CH3)3Al) are listed below:

HSO3-R-SO3H (g) CH3-Al-| → CH4(g) HSO3-R-SO3-Al-|

2HSO3-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(SO3-R-|)2

Phosphide groups

The two partial reactions that take place between a di-phosphide (H2P-R-PH2) and Ni(thd)2, where thd stands for 2,2,6,6-tetramethyl-3,5-heptanedione, are listed below:

H2P-R-PH2(g) thd-Ni-| → Hthd(g) H2P-R-PH-Ni-|

2H2P-R-| Ni(thd)2(g) → Hthd(g) thd-Ni-PH-R-|

Phosphate groups

The two partial reactions that take place between a diphosphate (HPO4-R-PO4H) and TMA ((CH3)3Al) are listed below:

HPO4-R-PO4H (g) CH3-Al-| → CH4(g) HPO4-R-PO4-Al-|

2HPO4-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(PO4-R-|)2

Amine groups

Amine groups, alkylamines or silated amines or halogenated amines should react with compounds such as SnI2, SnI4, PbI2, PbI4, CuI2, CuI4 or the like to form perovskite related hybrid materials as described by D. B. Mitzi (D. B. Mitzi, Progress in Inorganic Chemistry, 48 (1999 ) 1-121 and D. B. Mitzi in Chemistry of Materials 13 (2001) 3283-3298).

A proposed reaction mechanism is:

SnI4(g)NH4I-R-| → SnI4-NH4I-R-|

SnI4-| NH4I-R-H4NI(g) → NH4I-R-H4NI-SnI4-|

Furthermore, redox reaction with Sn(IV)-Sn(II) and formation of I2(g) may be involved here. Alternatively, using divalent halides is visualized as:

SnI2(g)NH4I-R-| → SnI3-NH4-R-|

SnI3-| NH4I-R-H4NI(g) → NH4I-R-H4N-SnI4-|

Another reaction mechanism with amines is analogous to the hydroxides:

The two partial reactions that take place between a diamine (H2N-R-NH2) and TMA ((CH3)3Al) are listed below:

H2N-R-NH2(g) CH3-Al-| → CH4(g) H2N-R-NH-Al-|

2H2N-R-| (CH3)3Al(g) → 2CH4(g) CH3-Al-(NH-R-|)2

However, it is likely that both H atoms on one of the amines will react with TMA.

The following functional groups will react in a similar way: -OH, -SH, -SeH, -TeH, -NH2, -PH2, -AsH2, -SiH3, -GeH3. -SO4H, -SO3H, -PO4H, -PO3H, SeO3H, SeO4H. In all cases where more than one H is present, the other H may be substituted with an organic group R, where R is straight-chain or branched alkane, cycloalkane, an aryl group, a heteroaryl group or one of the other functional groups.

It should be emphasized that both functional groups of a precursor need not be of the same type. By using different functional groups with different reactivity, it is possible to form a monolayer of organic molecules with a degree of order. This can also be combined with the use of different metal components which will have different affinity to the different groups.

The organic compound that carries the functional groups is not particularly limited but can be any organic molecule that can be brought to gas phase. It is preferred that there is some degree of steric hindrance in the molecule that will prevent it from reacting with both of its reactive groups with the same surface, as there should be some active site left for subsequent reaction. Otherwise, there are no restrictions on what the organic C-C structure looks like. The organic molecule will of course affect the acidity of the protons on the functional groups. The organic compound can be a non-branched alkane, a branched alkane, cycloalkane, alkene, a monocyclic or polycyclic aromatic group, a heterocyclic aromatic group where these compounds, in addition to the functional groups, can be substituted or unsubstituted with other organic groups such as alkyl.

The inorganic precursors that can participate in the method according to the invention are described below. All the suggested reactions are only illustrations of possible reactions and should not be interpreted as limitations.

Metal alkyls

Metal alkyls and metal cycloalkyls are quite reactive and consequently undergo reaction with most organic functional groups. This is exemplified by the production of hybrid thin films with TMA and hydroxides. Examples of possible metal alkyls are: Al(CH3)3, Zn(Et)2, Zn(Me)2, MgCp2;

where Cp stands for cyclopentyl.

Metal halides

Some electropositive metal halides are quite reactive and react with many organic functional groups. Some examples are AlCl3, TiCl4, SiCl4, SnCl4, Si(CH3)2Cl2.

Metal carbonyls

Metal carbonyls are also reactive and some examples are: Fe2(CO)9,Mn(CO)x

Metal chelates

Examples of reactive metal chelates are: VO(thd)2, Mn(HMDS)2, Fe(HMDS)2, TiO(thd)2, Pt(thd)2.

Thd (=2,2,6,6-tetramethyl-3,5-heptanedione) is a chelating compound from which compounds with elements such as Ti, V, and several more can be prepared. HMDS stands for hexamethyl-disilazane.

Other possible chelating compounds are beta-ketones such as acetylacetonates, fluorinated thd compounds and ethylenediaminetetraacetic acid (EDTA).

The metal of the inorganic precursor is selected from the group consisting of Al, Si, Ge, Sn, In, Pb, alkali metals, alkaline earth metals, 3d deposit metals, 4d deposit metals, 5d deposit metals, lanthanides and actanoids. Some of the more interesting metals are Cu, Ni, Co, Fe, Mn and V.

This invention is exemplified in the examples below, where trimethylaluminum (TMA), hydroquinone (Hq) and phloroglucinol (Phl) have been used as precursors to produce thin films of aluminum benzene oxides which construct a hybrid type film. Film is produced using TMA-Phl, TMA-Hq, and a controlled mixture of the type TMA-Phl-TMA-Hq. The growth genetics has been investigated on the basis of quartz crystal monitor (QCM) measurements and the films have been analyzed by Fourier transform infrared spectroscopy (FT-IR) and by X-ray diffraction (XRD). The effect of air treatment on grown films has been noted.

The invention will be described in further detail with reference to the accompanying figures. The effect of pulse parameters on the growth rate was investigated at a reactor temperature of 200 °C by varying one of the parameters and keeping the others at a sufficiently high level.

The relative growth rate was measured with a QCM by applying the slope of the measured resonance frequency over a period of 50 growth cycles and normalizing this to growth per cycle. In this way, the growth rate could be expressed using ∆Hz cycle-1, which is linearly proportional to a growth rate based on mass cycle-1.

The result of this analysis for both hydroquinone and phloroglucinol is shown in fig. A and B respectively. This shows that a self-controlled growth can be achieved for suitably chosen pulse parameters. The results indicate that the reaction of TMA with Phl terminated film occurs on two types of sites. The first type of seats saturates at 0.2 s while a pulse length of 2 s is required to completely saturate the second type. According to the QCM investigations of the pulse parameters (Fig. A, and B) it is possible to grow hybrid films of TMA - Phl and TMA - Hq controlled with ALCVD technique by using pulse parameters of 1.0 s for Phl and Hq pulse followed in both cases by a rinse time of at least 0.5 s, and a pulse period of 1.5, 0.5 s TMA respectively before a rinse of 0.2 s for Phl and Hq containing films. The effect of temperature on the growth rate of TMA-Hq and on TMA-Phl films was measured by X-ray profilometry for films grown for 80 cycles at different reactor temperatures (Fig. C). The thickness measurement was carried out immediately after deposition and also on the same films after treatment in normal atmosphere for at least one week. This revealed that the films are somewhat air sensitive and change thickness over time, however thickness change is different for the two types of film. Films with Phl grow with a typical growth rate of 0.34 nm/cycle and decrease in thickness by 0.25 nm/cycle during air treatment, while films with Hq rather increase in thickness from 0.53 to 0.58 nm/cycle during air treatment. Regardless, it shows that the growth rate is only slightly affected by the growth temperature for both types of film, revealing an ALCVD window of 150–300 and 200–350 °C for respectively. Phl and Hq containing films. The linearity of the growth was also tested by QCM measurements over a total of 1000 pulse cycles with the configuration 1.0-1.0-0.9-0.5 s for Hq/Phl pulse – flushing - TMA pulse – flushing (Fig. E). Both Phl and Hq containing films were found to have a linear thickness depending on the number of pulse cycles, except for the initial weight step (up to about 30 pulses) where a reduced growth rate was found. This behavior may originate from a limited number of nucleating sites on the floor surface of the quartz resonators and preferential subsequent growth on the initial core.

The result of IR analysis of films both as deposited and air-treated after at least one week is shown in fig. 3 together with IR analysis of pure hydroquinone and phloroglucinol pressed in KBr tablets. This reveals that there is a distinct similarity between the pure constituents and the films formed. In addition, some new bands have also formed which are believed to be due to the formation of benzene oxides. The IR signals are slightly changed when the films are air-treated, revealing that a chemical reaction is taking place. For the Phl-Hq mixed films it is possible to identify the pattern from both of the pure types of films. Attempts to map the growth genetics using QCM were made by measuring the growth pattern over 20 fairly long cycles and then taking the arithmetic mean of the results from all these cycles (Fig. F). Figure F shows the growth of the following different hybrid thin films: (a) Al-Hq, (b) Al-Phl, (c) Al-malic acid, Al-terephthalic acid, Zr-Hq, Ti-Hq, and (d) Ti-ethylenediamine .

The most intuitive The most intuitive reaction mechanisms for these processes are presented in the equations below for films containing Phl and Hq respectively. and gives a relative mass change that depends on the released methane stoichiometry for each pulse. The measured relative frequency changes were respectively 3.5 and 1.9 for Phl and Hq containing films. By solving the x parameters based on these values, a final methane stoichiometry of x = 1.87 and 1.25 is calculated for respectively Phl and Hq containing films. However, this cannot be the total truth since it is equally conceivable that an excess of Phl and/or Hq could be introduced leaving unreacted HO-| on the film which is sterically hindered for full reaction with TMA. The apparent two-section shape of the dependence of the growth rate on the TMA pulse time may indicate that the latter case of sterically hindered HO-| groups, is the most likely case in these situations. XRD analysis of the films showed that none of the films were well oriented. As grown the films with Phl gave no diffraction pattern while as grown the films with Hq had a diffraction peak at 2θ = 23.0°. For the air-treated films, a diffraction peak occurred at 2θ = 27.5° on film with Phl. For the same type of films treated with Hq, a smaller peak at 2θ = 18.5° appeared. Rocking curve analysis of the peaks on as grown films with Phl and on both of the aerated films showed that they were all completely randomly oriented. This was also observed for films with both Phl and Hq, as shown in fig. G. The XRD analysis of these films corresponds to those with only Phl.

IR analysis has been carried out on a selection of the exemplified growth systems and a table of the characteristic absorption bands or peaks is given in Table A. It should be taken into account that some of these films have undergone reactions with air while the IR measurements were carried out.

Table A. Characteristic IR absorption bands or peaks for deposited hybrid films.

Inorganic Organic Absorption band / cm–1

precursor precursor

TMA Hq 1507, 1223, 879, 834, 800

TMA Phl 1619, 1516, 1433, 1381, 1247, 1218, 1173, 1020, 946,

905, 845, 668, 574

TMA Terephthalic acid 1596, 1509, 1415, 1312, 1251, 1160, 1103, 879, 812,

755, 573

TMA Malic acid 1620, 1485, 1438, 1376, 1280, 1235, 1180, 1074, 1003,

965, 812, 738, 522

TiCl4Hq 1487, 1198, 886, 832, 817

ZrCl4Hq 1497, 1272, 1203, 884, 832, 804

We have shown the possibility of growing films of a hybrid type by ALCVD technique by growing films with a network of aluminum benzene oxides with hydroquinone and phloroglucinol. We have produced films with aluminum benzene oxide with pure hydroquinone or phloroglucinol and films where these are mixed. In general, we have so far also shown the possibility of growing hybrid-type films by ALCVD technique using precursor pairs such as:

TMA – Hq, thus providing growth of Al and also growth of an aromatic diol.

TMA – Phl, thus providing growth of also an aromatic triol.

TMA – Malonic acid, thus providing growth with a linear di-carboxylic acid. TMA – Terephthalic acid, thus proving prowth with an aromatic di-carboxylic acid.

TiCl4– Hq, thus providing growth with titanium.

ZrCl4– Hq, thus providing growth with zirconium.

TiCl4– Ethylenediamine, thus providing growth of an amine.

Reaction equations:

Principle reaction mechanism:

Phl case:

Al(CH3)3(g) 1.5 HO–| → (CH3)1.5Al-O1.5–| 1.5 CH4(g) ∆m1 = 48.02 u 1.5 C6H4(OH)2(g) (CH3)1.5Al-O1.5–| → (HO–C6H4-O)1.5-Al-O1.5-| 1.5 CH4(g) ∆m2 = 141.10 u

Δm2/Δm1 = 2.94

The mass difference is smaller than measured by QCM and the mechanism should be modified to allow fewer unreacted OH groups in the first step.

Hq case:

Al(CH3)3(g) HO–| → (CH3)2Al-O–| CH4(g) ∆m1 = 56.04 u C6H3(OH)3(g) (CH3)2Al-O–| → HO–C6H3-(O)2-Al-O-| 2 CH4(g)

∆m2 = 94.02 u �

Δm2/Δm1 = 1.68

The mass difference is smaller than measured by QCM and the mechanism should be modified to allow fewer unreacted OH groups in the first step.

The reaction mechanism with varying degrees of reactivity to OH groups:

Phl case:

Al(CH3)3(g) x HO–| → (CH3)3–xAl-Ox–| x CH4(g) ∆m1 = 48.02 u 3-x C6H4(OH)2(g) (CH3)3–xAl-Ox–| → (HO–C6H4-O)3-x–Al-Ox-| (3–x) CH4(g) ∆m2 = 141.10 u x = 1.87

HQ case:

Al(CH3)3(g) x HO–| → (CH3)3-xAl-Ox–| x CH4(g) ∆m1 = 56.04 u C6H3(OH)3(g) (CH3)3–xAl-Ox–| → x ((HO)x–C6H3-(O2)(3-x)/2)3-x-Al-Ox-| (3-x) CH4(g) ∆m2 = 94.02 u x = 1.25

The reaction mechanism with a fixed degree of reactivity to OH groups according to observations with QCM:

Phl case:

Al(CH3)3(g) 1.87 HO–| → (CH3)1.13Al-O1.87–| 1.87 CH4(g) ∆m1 = 42.08 u 1.13 C6H4(OH)2(g) (CH3)1.13Al-O1.87–| → (HO–C6H4-O)1.13-Al-O1.87-| 1.13 CH4(g)

∆m2 = 147.03 u Δm2/ Δm1 = 3.5

Hq case:

Al(CH3)3(g) 1.25 HO–| → (CH3)1.75Al-O1.25–| 1.25 CH4(g) ∆m1 = 52.03 u C6H3(OH)3(g) (CH3)1.75Al-O1.25–| → (HO)1.25–C6H3-(O2)0.875-Al-O1.25-| 1.75 CH4(g) ∆m2 = 98.03 u Δm2/ Δm1 = 1.9

The principle function of this invention is a technique/method or procedure one can use to deposit a film with an organic-inorganic structure. The film is produced by a gas-phase deposition technique utilizing self-inhibiting surface reactions with individual gas-phase precursors. The precursors are produced sequentially, each followed by a purge with an inert gas to avoid gas phase reactions. The procedure has previously been used for pure inorganic materials and is called such names as ALCVD (Atomic Layer Chemical Vapor Deposition, or ALE = Atomic Layer Epitaxy, or ALD = Atomic Layer Deposition).

This invention can be used to produce a type of organic-inorganic material that is built by chemical reactions. The physical properties of the materials are not important in this invention, but rather the method for producing such materials. Accordingly, all types of materials constructed from organic blocks and inorganic blocks with the ALCVD (ALD, ALE) process or similar ways should be within the scope of this invention.

Related methods that are mainly sold as CVD methods but are in principle related to ALCVD should also be included. In this aspect, all methods that allow the ideology to separately introduce different precursors on the substrates are included. This can be done by either moving the substrates between different precursors or moving the precursor lines across the different substrates or a mixture of both.

The films have been deposited using an F-120 Sat (ASM Mirochemistry) reactor using trimethylaluminum, hereafter referred to as TMA, (Crompton, technical grade), hydroquinone (1,4-dihydroxybenzene, hereafter referred to as Hq) (BDH Laboratory Supplies, >99%) and/or phloroglucinol (1,3,5-trihydroxybenzene, hereafter referred to as Phl) (Merck, >99%) as precursors. The temperature of the TMA precursor was maintained at 20 °C during film growth while hydroquinone and phloroglucinol were sublimed at 140 °C and 175 °C.

Nitrogen was produced in-house using a Schmidlin Nitrox 3001 generator (99.999% as N<2>+Ar) and used as purge and carrier gas. The pressure of the reactor during growth was maintained at 1.8 mbar by using an inert gas flow of 300 cm3 min-1.

The pulse and flush parameters of the film growth were investigated using a quartz crystal monitor (QCM), using two 5 MHz gold or silver coated crystal sensors and a Matex MT-400 crystal monitor connected to a computer. This constellation made it possible to test two sensors simultaneously with a 10 Hz acquisition rate.

A Siemens D5000 diffractometer in θ-θ mode, equipped with a Göbel mirror producing parallel Cu Kα radiation was used for X-ray profilometry thickness measurements and for conventional X-ray diffraction analysis.

IR analysis was performed on films deposited on both sides of double-polished Si(100) substrates and using a blank Si(100) substrate as a reference. A Perkin Elmer FT-IR system 2000 was used for this purpose.

The films were deposited on soda lime and Si(100) substrates by sequential pulsing of TMA and either hydroquinone or phloroglucinol. A film was also produced where the organic pulses were alternately changed between hydroquinone and phloroglucinol in an Al-O-Hq-Al-O-Phl manner.

The substrate material is not limited to the types of materials used here, but can be any material reactive towards at least one of the precursors.

Applications of hybrid thin film.

Hybrid materials can have applications in almost any type of field imaginable. Rather, its limitations in application can be imagined as limitations of the films themselves. Since one of the constituents of these films is an organic material, including here biomolecules, the thermal stability of these films will be limited by the stability of these constituents. Another effect that one might imagine at first glance as a limitation is hybrid material stability against natural atmosphere or indeed external chemical environment. This is handled today by the production of organic light-emitting devices, which also have these significant limitations against water and oxygen exposure. However, this can also be used as an advantage if one considers the material as sensors against such exposure.

Some of the areas where hybrid thin film can be used are:

Optical materials

Probably the first application of thin film in general was as an optical material. When using a thin film with a thickness of the order of magnitude of the wavelength of interest, the optical properties of the material will change. This access angle is used in the production of anti-reflection coatings. In the same way, reflective coatings can be produced. More sophisticated wavelength filters can be produced by alternating deposition materials with a high and low reflection index.

The ALCVD technique has only sporadically been demonstrated to be useful for the production of optical materials although it should show a superior ability to produce clear phase transitions. One reason is the slowness of the ALCVD process compared to other longer used techniques. This picture is not necessarily correct for thin films of the hybrid type since the units deposited are much larger in size compared to pure inorganic films. In comparison, deposition of approx. 50 nm of an Al-Phl type hybrid film only involves around 80 pulse sequences, and unoptimized it has a growth rate of approx. 0.18 nm/s = 0.64 μm/h. This can be further increased by using larger types of organic molecules than fluroglucinol.

The reflection index of the different layers of hybrid materials can change with varying types of materials used. Hybrid materials can also be used together with sections of pure inorganic layers to increase versatility.

In this way, films exhibiting properties such as: anti-reflection, increased reflection, cut-on or cut-off filters, narrowband or broadband filters can be produced.

The types of organic or inorganic materials used can be changed with a monolayer solution. This will enable several different types of materials to be used during a film deposition process. This can produce films that look like graded films with respect to changes in reflective index or other physical properties. Such materials are of great interest in thin film optics since a high figure of merit can be achieved.

Optical films can be used for other types of applications than imaging if it is possible to influence the optical properties in some way. Measures that can be imagined are:

- To influence the thickness of the individual layers of the thin films.

- To change the reflection index by changing the chemistry of the material.

Hybrid materials are a class of materials that are highly susceptible to influences that can change the thickness, reflectance index or both. The reason for this is their softness and open structure together with the inorganic materials. This makes the materials ideal as sensor materials with a benefit in changing optical effects, for example changing color.

Applications that utilize these effects will be described below.

Optical hybrid materials as pressure sensors

An immediate effect of constriction of an optical multilayer wavelength filter in materials considered to be soft is of the optical effect is pressure sensitive. By applying a pressure to the film stack, the physical thickness will be somewhat changed, which in turn will affect the optical properties, ie change the wavelength of transmitted light for the wavelength filter.

Optical hybrid materials as gas sensors

Hybrid materials have a crystal structure that depends on the packing efficiency of the organic molecules in the structure. The forces between these molecules are often van der Waals in nature and therefore not too strong. This implies that the size of the crystal unit lattice is susceptible to external effects such as gas molecule absorption between these organic molecules. If an optical thin film material is constructed from such a material, then gas absorption will manifest itself by a change in the physical thickness and again a change in the optical properties in the same way as mentioned for pressure sensors.

It should be possible to construct materials with organic molecules that are more sensitive to some types of gas molecules than others and consequently act as selective gas sensors.

The effect of change in physical thickness with an external gas has already been demonstrated by air treatment of Al-Hq and Al-Phl films. It is interesting in this regard to note that the thickness change upon exposure to normal air results in an increase in thickness for the Al-Phl and a decrease in thickness for the Al-Hq case. Consequently, by combining different types of hybrid materials, many interesting optical effects can be produced.

Optical hybrid materials as temperature sensors

The physical thickness of materials will be affected by temperature, especially when van der Waals interactions take part in the structure or the structure consists of long chains as in the case of many types of hybrid materials. This will in turn manifest itself by a change in the optical properties of optical thin films and thus function as temperature sensors.

Optical hybrid materials as magnetic field sensors

The ability to combine both organic and inorganic materials gives rise to a large number of possibilities. One such possibility is to use magnetically active inorganic material for the production of the hybrid materials. These inorganic parts can interact with external magnetic fields and consequently give rise to a change in the thickness of the material. This in turn will change the optical properties of optical thin films constructed from such materials. The hybrid materials can provide increased properties when deposited under the influence of a relatively strong magnetic field during construction.

There are several possibilities for finding effects that will result in a change in thickness. A not so obvious one is if there are aromatic rings present in the organic molecules. A magnetic field will induce currents in these ring structures which will in turn induce a magnetic field. The result is that these structures will have a driving force to align themselves in a magnetic field. The order of magnitude of this force will be greater for larger structures of aromatic rings.

A more obvious effect is if there are metallic elements with unpaired spins. These spins will be affected by the external magnetic field. This can induce rotation of metal polyhedra in the structure, which in turn will affect the thickness. If some of these metal atoms assume a higher range order then structures that are ferromagnetic or anti-ferromagnetic can occur. Overall, these will be affected by an external field to a higher degree than mentioned above. The entire layer of the film structure can feel contractive or repulsive forces of the magnetic field depending on the orientation of the internal magnetic field. This can actually result in structures where alternating layers in the film structure contract or are pushed apart. This would be an extremely interesting structure from a theoretical point of view.

Optical hybrid materials as electric field sensors

Electric fields will induce forces in dipolar molecules. If a hybrid material is constructed of such molecules as one of its building blocks, then its physical thickness will be affected by external electric fields. Consequently, the material will exhibit piezoelectric effects. It is important that there is an excess of bipolar molecules with a particular orientation in the hybrid material so that a total electrical polarization is produced. This can be increased by depositing these films under electric fields.

Electrical properties

The sensing effects of hybrid materials have been exemplified above on the basis of an optical design, however, in general for all materials, a change in physical size of a material should also affect the electrical properties. This should be measurable as a change in the resistance of the thin film or other electrical effects and consequently also applicable for sensor reading. It has been shown possible to construct hybrid materials with varying degrees of electrical band gap (D. B. Mitzi, Progress in Inorganic Chemistry, 48 (1999) 1-121. and D. B. Mitzi in Chemistry of Materials 13 (2001) 3283-3298).

The size of these band gaps should be influenced by the physical size of the film and consequently give rise to electrically measurable effects.

Based on these effects, it should be possible to produce materials that also exhibit pyroelectricity.

The possibility of producing materials that exhibit piezoelectricity also enables the production of actuators and resonators.

If the properties mentioned above are stabilized in one or more of the affected states, this will produce materials that can be ferroelectric, ferromagnetic and subgroups of these phenomena.

Hybrid materials can be constructed with varying degrees of electrical insulation, depending on both the organic and inorganic molecules used. It should be possible to construct materials that exhibit electrical conduction into the layers, but not normally onto the layers. This is typical for layered structures. Similarly, it may be possible to engineer the opposite case by producing one-dimensional structures of hybrid materials.

Insulating materials can be constructed from organic molecules without aromatic compounds and with only single carbon bonds and from inorganic elements in their highest oxidation state. Both requirements do not necessarily have to be fulfilled at the same time since it has already been demonstrated that Al-Hq and Al-Phl films are insulating even if they contain aromatic organic molecules.

By introducing metallic elements in a lower oxidation state than their highest or by constructing long-range organic bonds, it should be possible to introduce both semiconductor (p- and n-type) and metallic conduction.

One can also imagine that by introducing elements such as Nb or Hg, the materials can be made superconducting at low temperatures. It should also be possible to produce HTc materials by depositing sections with such materials between layers with a pure hybrid structure. The stack should still be considered a hybrid material.

Hybrid thin film is currently used as an electroluminescent material in organic light-emitting diodes. We should aim to produce materials that exhibit such properties with this technique. One such candidate would be the application of TMA and quinoline.

Other types of optically active materials that one should look for are photovoltaic materials. This is in principle the opposite of electroluminescent materials and should be connected to this area.

Light-harvesting materials are typically also of a hybrid nature and can be used as wavelength shift materials. An example is filters converting UV light into visible or near IR light.

An area that generally affects the same areas is photoionic, non-linear optics, chromophoric materials and others.

The summation of these effects is that hybrid films can be used in almost any type of area from flat panel displays and smart windows to the formation of bearings, actuators and sensors.

We have demonstrated that films of Al-Hq and Al-Phl change their physical thickness during air treatment and have thus shown that these materials are potential sensor materials where the physical thickness is monitored in a way.

Claims (11)

Patent claims 1. Method for producing a thin film with an organic-inorganic structure on a substrate by a gas phase deposition technique produced by ALCVD, characterized in that it comprises the following steps: a) - bringing the substrate into contact with a pulse of an inorganic precursor selected from the group consisting of metal alkyls and metal halides, where the metal is selected from the group consisting of Al, Si, Sn, Zn, Mg, Ti, Zr, V, Mn, Fe, Co, Cr, and Pt; b) – reacting the inorganic precursor with at least one surface of the substrate; c) – to remove unreacted inorganic precursor and reaction by-products if any; d) - bringing the surface of said substrate into contact with a pulse of an organic precursor where the organic precursor is an organic compound substituted with with 2-6 substituents selected from the group consisting of –OH, -COOH, -SH, -NH2, - SO4H, -SO3H, -PO4H, and -NH3I, where the organic compound is selected from straight-chain or branched alkanes, cycloalkanes, alkenes, mono- and polycyclic aromatic groups, heterocyclic aromatic groups, where the organic compound may possibly include other substituents than those at least two reactive substituents, and where the organic precursor can be brought to gas phase; e) - reacting the organic precursor with the inorganic compound bound to the substrate to form an organic-inorganic hybrid layer; f) – to remove unreacted organic precursor and reaction by-products if any; g) – to repeat steps a) to f) until the desired film thickness is achieved. 2. Method according to claim 1, characterized in that steps a) to c) are repeated one or more times before steps d) to f) are performed. 3. Method according to claim 1 or 2, characterized in that the method further comprises performing steps d) and f) one or more times before steps a) to g) are performed. 4. Method according to any one of claims 1-3, characterized in that the removal of unreacted precursors and by-products in steps c) and f) is carried out by purging with an inert gas, preferably nitrogen. 5. Method according to any one of claims 1-4, characterized in that the substrate comprises a monolayer of an organic part bound to the surface, before step a) is carried out for the first time. 6. Method according to any one of claims 1-5, characterized in that the pulse in step a) has a duration of 0.1 to 5 s, preferably 0.2 to 2 s. 7. Method according to any one of claims 1-6, characterized in that the flushing in steps c) and f) has a duration of 0.1 to 5 s, preferably 0.2 to 2 s, most preferably 0.5 s. 8. Method according to any one of claims 1-7, characterized in that the pulse of the organic precursor has a duration of 0.1 to 5 s, preferably 0.2 to 2 s. 9. Method according to any one of claims 1-8, characterized in that the inorganic precursor comprises an electropositive metal, preferably Al, Si, Sn, Zn, Mg, Ti, V, Mn, Fe, Co, Cr or Pt and the the organic precursor is an organic compound substituted with 2-6, more preferably 2-3 substituents selected from the group consisting of –OH, –COOH, –SH, –SO4H, –SO3H, –PO4H, –NH2 and –NH3I. 10. Process according to claim 9, characterized in that the organic precursor is benzene substituted with 2-6, more preferably 2-3 hydroxyl groups. 11. Method according to any one of claims 9-10, characterized in that a thin film comprising monolayers of benzene aluminum oxide is produced.