Deposition process

Abstract

A process for depositing an inorganic material on a substrate, the process comprising, providing a substrate having a surface, providing a precursor mixture comprising a metal sulfonate, and delivering the precursor mixture to the surface of the substrate, wherein the surface of the substrate is at a substrate temperature of above 450 C. and is sufficient to effect decomposition of the metal sulfonate. The inorganic material may include a metal or a metal oxide. The preferred metal sulfonate is metal triflate.

Claims

1. A process for depositing a metal and/or a metal oxide on a glass substrate, the process comprising, providing a glass substrate having a surface, providing a precursor mixture comprising a metal sulfonate, at least partially atomizing the precursor mixture, and delivering the at least partially atomized precursor mixture to the surface of the glass substrate, wherein the surface of the glass substrate is at a substrate temperature above 500 C. at the time the precursor mixture is delivered to the surface and is sufficient to effect decomposition of the metal sulfonate.

2. The process as claimed in claim 1, wherein the metal, M, is selected from Zn, Mg, Al, Sb, Cu, Ag, Sn, and In.

3. The process as claimed in claim 1, wherein the metal sulfonate comprises a species of formula M(O.sub.3SR).sub.m, wherein M is a metal, R is a C.sub.1 to C.sub.7 fluorinated or non-fluorinated hydrocarbyl group and m depends upon the oxidation state of M.

4. The process as claimed in claim 3, wherein R is CF.sub.3, optionally wherein M is Zn or Mg and R is CF.sub.3.

5. The process as claimed in claim 1, wherein the precursor mixture further comprises a carrier gas.

6. The process as claimed in claim 1, wherein the precursor mixture further comprises a solvent.

7. The process as claimed in claim 6, wherein the solvent comprises an oxygenated solvent.

8. The process as claimed in claim 7, wherein the solvent comprises a C.sub.1 to C.sub.4 alcohol.

9. The process as claimed in claim 1, wherein the precursor mixture further comprises an additional source of oxygen.

10. The process as claimed in claim 1, wherein the precursor mixture further comprises a source of a second metal.

11. The process as claimed in claim 10, wherein the source of a second metal comprises a source of aluminium, optionally wherein the source of a second metal comprises aluminium acetylacetonate.

12. The process as claimed in claim 10, wherein the molar ratio of the second metal to the metal of the metal sulfonate is in the range 0.01-0.2.

13. The process as claimed in claim 1, wherein the substrate temperature is in the range 500 C. to 700 C. at the time the precursor mixture is delivered to the surface.

14. The process as claimed in claim 1, wherein the metal oxide is deposited to a thickness in the range 400 nm to 700 nm.

15. The process as claimed in claim 1, wherein the substrate comprises soda lime silica glass.

16. The process as claimed in claim 15, wherein the substrate comprises a continuous ribbon of glass.

17. The process as claimed in claim 15, wherein the surface of the glass substrate comprises a layer comprising silicon oxide and the metal and/or metal oxide is deposited on the layer comprising silicon oxide.

18. A process for depositing a coating comprising an inorganic material selected from the group consisting of zinc oxide, aluminium oxide, copper oxide, copper metal, indium oxide, and silver metal on a glass substrate, the process comprising, providing a glass substrate having a surface, providing a precursor mixture comprising a metal trifluoromethanesulfonate, wherein the metal is selected from the group consisting of zinc, aluminium, copper, indium, and silver, and delivering the precursor mixture to the surface of the substrate, wherein the surface of the substrate is at a substrate temperature above 500 C. at the time the precursor mixture is delivered to the surface to effect decomposition of the metal trifluoromethanesulfonate.

19. The process as claimed in claim 7, wherein the solvent comprises methanol.

20. The process as claimed in claim 1, wherein the substrate temperature is in the range 500 C. to 700 C. at the time the precursor mixture is delivered to the surface.

21. The process as claimed in claim 1, wherein the metal oxide is deposited to a thickness in the range 450 nm to 600 nm.

22. The process as claimed in claim 15, wherein the substrate comprises a continuous ribbon of glass undergoing the float glass production process.

23. The process as claimed in claim 1, wherein the substrate temperature is above 550 C. at the time the precursor mixture is delivered to the surface.

24. The process as claimed in claim 18, wherein the substrate temperature is above 550 C. at the time the precursor mixture is delivered to the surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be described by way of example only, and with reference to, the accompanying drawings, in which:

(2) FIG. 1 is a graph showing Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) for Zn(OTf).sub.2.

(3) FIG. 2 is a graph showing Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) for Mg(OTf).sub.2.

(4) FIG. 3 shows the glancing angle X-ray diffraction (XRD) pattern of the deposited ZnO and aluminium-doped ZnO (AZO) thin films (Examples 1 and 2) according to the invention deposited at 600 C. by aerosol assisted chemical vapour deposition (AACVD) using Zn(OTf).sub.2 in methanol.

(5) FIG. 4 shows plane views (A-C) and cross section views (D-F) of scanning electron micrographs (SEM images) of (A) ZnO and (B-F) AZO films according to the invention (Examples 1 and 2) deposited at 600 C. by AACVD from Zn(OTf).sub.2 in methanol.

(6) FIG. 5 is an XPS depth profile for an AZO thin film according to the invention (Example 2) deposited at 600 C. by AACVD from Zn(OTf).sub.2 in methanol.

(7) FIG. 6 is the transmission spectrum for ZnO and AZO films (Examples 1 and 2) according to the invention deposited at 600 C. by AACVD from Zn(OTf).sub.2 in methanol recorded between 250 and 1400 nm. Inset: Tauc plots for the ZnO and AZO films.

(8) FIG. 7 shows the glancing angle X-ray diffraction (XRD) pattern of the deposited In.sub.2O.sub.3 according to the invention (see Example 3) deposited at 550 C. by aerosol assisted chemical vapour deposition (AACVD) using In(OTf).sub.3 in methanol.

(9) FIG. 8 shows the glancing angle X-ray diffraction (XRD) pattern of the deposited copper/copper oxide film according to the invention (see Example 4) deposited at 550 C. by aerosol assisted chemical vapour deposition (AACVD) using Cu(OTf).sub.2 in methanol.

(10) FIG. 9 shows the glancing angle X-ray diffraction (XRD) pattern of the deposited Ag film according to the invention (see Example 6) deposited at 550 C. by aerosol assisted chemical vapour deposition (AACVD) using Ag(OTf) in methanol.

DETAILED DESCRIPTION OF THE INVENTION

(11) The invention is further illustrated, but not limited, by the following Examples.

EXAMPLES

(12) General Procedures

(13) Nitrogen (99.99%) was obtained from BOC and used as supplied. Metal trifluoromethanesulfonates (M(OTf).sub.n) were obtained from Sigma-Aldrich and aluminium acetylacetonate from Merck Millipore and used as supplied. Methanol was dried over magnesium methoxide and distilled under nitrogen. Precursor solutions were formed in glass bubblers and stirred for 10 minutes. A Liquifog piezo ultrasonic atomizer was used to vaporise the precursor solution. A homogeneous aerosol of the precursor solution was formed when the concentration of the ultrasonic waves ejected small droplets of precursor solution from the surface of the solution. N.sub.2 carrier gas was employed to deliver the aerosol mist from the bubbler, though a brass baffle into the cold-walled, horizontal-bed CVD reactor contained within a quartz tube. Thus, samples were deposited using aerosol assisted chemical vapour deposition (AACVD). The reactor was fitted with a graphite block containing a Whatman cartridge heater, used to heat the glass substrate, the temperature of which was controlled and monitored using a Platinum-Rhodium thermocouple. Films were deposited onto float-glass substrates (145 mm45 mm4 mm) (obtained from NSG) having a pre-deposited 25 nm barrier layer of crystalline SiO.sub.2. A second glass plate was held 6 mm above the glass substrate in order to reduce any air turbulence and aid in producing a laminar gas flow. Prior to deposition the glass substrate was cleaned using isopropyl alcohol and acetone. After deposition, the glass substrates were allowed to cool under flowing nitrogen to below 100 C. before being removed from the apparatus. After initial investigations the optimal flow rate of N.sub.2 and substrate temperature were determined to be 1.21 min.sup.1 and 550 C. or 600 C. respectively. Deposition times varied between 30 and 35 minutes.

(14) Film Analysis Methods

(15) Thermal gravimetric analysis (TGA) and differential scanning Calorimetry (DSC) were carried out from room temperature to 600 C. under helium in open aluminum pans using a Netzsch STA 449 C Jupiter Thermo-microbalance.

(16) X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Discover X-ray diffractometer using monochromatic Cu K.sub.1 and Cu K.sub.2 radiation of wavelengths 0.154056 and 0.154439 nm respectively, emitted with a voltage of 40 kV and a current of 40 mA in an intensity ratio of 2:1.

(17) Scanning electron microscopy (SEM) was performed using a Philips XL30 FEG operating in plan and cross section mode at varying instrument magnifications from 10,000 to 50,000. Film thickness was estimated using a Filmetrics, Inc. F20 thin film measurement system.

(18) X-ray photoelectron spectroscopy (XPS) surface and depth profiling was performed using a ThermoScientific K-Alpha XPS system using monochromatic Al K radiation at 1486.6 eV as X-ray source. Etching was achieved using an Ar ion etch beam at 1 keV with a current of 1.55 A. 180 levels of 30 second etching were performed. CasaXPS software was used to analyse the data with binding energies referenced to an adventitious C 1s peak at 284.8 eV.

(19) UV/Vis/NIR transmission spectra were recorded using a PerkinElmer Lambda 950 spectrometer in the range of 250-1400 nm with an air background.

(20) Sheet resistance measurements were recorded using the Van der Pauw method and Hall Effect measurements made to determine the mobility and free carrier concentrations of the deposited films.

Examples 1 and 2

(21) ZnO thin films were deposited from a precursor solution of Zn(OTf).sub.2 (0.5 g) dissolved in dry methanol (30 ml). Aluminium doping was achieved by the addition of aluminium acetylacetonate (Al(acac).sub.3) (0.022 g) to Zn(OTf).sub.2 (0.5 g) in methanol (30 ml).

(22) In Example 1, transparent films of ZnO were deposited by AACVD using Zn(OTf).sub.2 in methanol at 600 C. on SiO.sub.2 coated float-glass substrates, according to Scheme 1 (below).

(23) In Example 2, Al(acac).sub.3 was added to the precursor solution and aluminium-doped ZnO (AZO) films were deposited also using AACVD. The level of Al dopant introduced was investigated by adding Al(acac).sub.3 in varying ratios to Zn(OTf).sub.2 of between 0.02-0.2 molar ratio. The best functional properties were observed for AZO films deposited when Al was added in an Al:Zn ratio of 0.05:1. The aluminium doping of these films was found to be 7 at %.

(24) ##STR00001##
For each reaction, film deposition was observed to occur on the glass substrate. The deposited films were adherent to the glass substrate, passing the Tape Test (could not be removed by applying and removing adhesive tape, e.g. ASTM D3359) but were removed upon scratching with a steel stylus. The films also exhibited good uniformity and coverage of the substrate. Solubility testing of the films indicated that the films were insoluble in organic solvents including THF, ethanol, methanol and toluene but decomposed when in nitric acid.
Precursor Studies

(25) TGA and DSC (FIG. 1) was performed on the Zn(OTf).sub.2 precursor (17 mg) between room temperature (23 C.) and 600 C. under helium. After loss of mass attributed to moisture, the mass is stable until the onset of the decomposition of Zn(OTf).sub.2 occurring at 500 C. A clean decomposition in a single step is observed, predominantly between 520-565 C. The calculated residual mass for ZnO from Zn(OTf).sub.2 is 22.4%. The observed residual mass, accounting for the initial mass loss resulting from residues is 22.7%. This is a strong indication of decomposition to ZnO. From the TGA profile it can be seen that decomposition occurs in a clean one step process to ZnO, showing the suitability of Zn(OTf).sub.2 as a Zn precursor.

(26) TGA and DSC (FIG. 2) was performed on Mg(OTf).sub.2 precursor between room temperature and 600 C. under helium. A clean decomposition in a single step is observed, predominantly between 450-470 C., at a lower temperature that for zinc triflate. As for zinc triflate, it can be seen from FIG. 2 that decomposition occurs in a clean one step process showing the suitability of Mg(OTf).sub.2 as a Mg precursor.

(27) X-Ray Diffraction

(28) Glancing-angle X-ray diffraction (XRD) patterns of the as-deposited films were recorded and are shown in FIG. 3. The reflections for the ZnO film confirm the formation of the hexagonal wurtzite crystal structure of ZnO. Significant preferred orientation was observed along the (002) plane resulting from the packing of the crystallites along the c-axis direction, perpendicular to the underlying substrate. The same crystal structure is also observed for the AZO film. However, upon doping of Al into the ZnO matrix there is a small (up to 0.1) but observable shifting of the 2 peak values to a higher value. This shift in 2 is consistent with all peaks in the pattern and is indicative of Al doping, consistent with EDX and XPS analyses reported below.

(29) Scanning Electron Microscopy

(30) Scanning electron microscopy (SEM) was used to determine surface morphology and height profiles of the deposited films. FIGS. 4(A) and (B) are plane view images at 10,000 magnification of ZnO and AZO respectively. The images show a film structure of rounded agglomerated particles which is indicative of a Volmer-Weber type island growth mechanism. FIG. 4(C), a plane view image of the AZO film at 50,000 magnification shows in greater detail the particle cluster growth of the film. The surface morphology of the ZnO films appears not to change upon doping with Al. Cross section images of the films were also taken. FIGS. 4(D) and (E) are cross section images at an 80 tilt at 10,000 magnification and 50,000 magnification respectively. These images show the coatings consist of larger agglomerates of particles with smaller groupings of particles between these larger agglomerates. The particle clusters are quite pronounced with noticeable height differences, as shown in FIG. 4(F), a cross section image at 90 tilt at 50,000 magnification. The lowest thickness of film was 250 nm with the highest cluster point being 655 nm. Film thickness was also measured using a Filmetrics analyzer system and for the AZO films a thickness range of 470-500 nm was recorded. The ZnO films were thicker, 550-570 nm, but had the same pattern of varying heights of agglomerate clusters.

(31) X-Ray Photoelectron Spectroscopy

(32) XPS of the ZnO films deposited from Zn(OTf).sub.2 at 600 C. confirmed the prescence of Zn and O and were consistent with XRD that solely ZnO had been deposited. Peaks were observed for the Zn 2p.sub.1/2 and 2p.sub.3/2 states at 1045.3 and 1022.2 eV binding energy respectively, as expected with an intensity ratio of 1:2 and an energy gap of 23.1 eV. The O 1s peak in the XPS data can be fitted by a Gaussian distribution and centered at 532.0 eV as expected.

(33) For films doped with Al, the Al 2p.sub.1/2 and 2p.sub.3/2 peaks are observed at 75.1 and 74.7 eV respectively. These appear in a 1:2 ratio of intensity with an energy gap of 0.41 eV consistent with the value for Al.sup.3+ incorporation. The peaks at 1045.7 and 1022.6 eV correspond to Zn 2p.sub.1/2 and 2p.sub.3/2, respectively, again in the 1:2 ratio, with an energy gap of 23.1 eV.

(34) Depth Profiling

(35) Using scan mode, a depth profile for the ZnO and AZO samples were obtained. The argon ion etch beam was operated at 1 keV producing a beam current of 1.55 A. A 30 second etch time per level was used with 180 levels of total etching. The spectral regions for Zn 2p, O 1s, Al 2p and C 1s were scanned as well as a survey spectrum to detect any additional elements.

(36) The depth profile for AZO films deposited from Zn(OTf).sub.2 and Al(acac).sub.3 at 600 C., shown in FIG. 5 reveals the sample to be predominantly zinc oxide with an average stoichiometry of ZnO.sub.1.2. The coating was aluminium doped with an average concentration of 7 at % Al.

(37) Optical Properties

(38) The transmission characteristics of the ZnO and AZO films were investigated using UV/vis/near IR spectrometry, recorded between 250 and 1400 nm. The absorption edge of each deposited film shifts to higher wavelength relative to the float glass substrate, as shown in FIG. 6. The ZnO film has an average transparency of 79%, peaking at 80%. The AZO film was found to have a slightly higher average transparency at 83%, peaking at 85%. The AZO film has a transparency greater than the 80% in the visible light region, a value often quoted for films described as highly transparent.

(39) The band gap of the ZnO and AZO films were determined from the Tauc plot (inset in FIG. 6) to be 3.7 and 3.9 eV respectively.

(40) Electrical Properties

(41) Four-point probe measurements were taken of the ZnO and AZO films deposited at 600 C. The films were conductive with sheet resistances of 70 /sq. for ZnO, decreasing to 15 /sq. for the AZO film doped with 7 at % of Al. The ZnO films had a carrier concentration of 2.2410.sup.20 cm.sup.3, mobility value of 9.3 cm.sup.2 (V s).sup.1 and resistivity of 2.8610.sup.3 cm. The doped AZO films had an increased carrier concentration and mobility of 3.0310.sup.20 cm.sup.3 and 10.5 cm.sup.2 (V s).sup.1 respectively resulting in a decrease in the observed resistivity to 1.9610.sup.3 cm.

Example 3

(42) Indium (III) triflate was used to deposit indium oxide thin films. Indium oxide films were deposited from [In(OTf).sub.3] (0.25 g) in methanol (20 mL) by AACVD at a deposition temperature of 550 C. in a N2 carrier gas (0.6 Lmin.sup.1). Deposition of In.sub.2O.sub.3 was confirmed using XRD, as shown in FIG. 7. The films were visually transparent and had strong adhesion.

Example 4

(43) Copper (II) Triflate was used to deposit films. AACVD of [Cu(OTf).sub.2] (0.5 g) in methanol (30 mL) at a deposition temperature of 550 C. in an N.sub.2 carrier gas (1 Lmin.sup.1) resulted in the deposition of a mixture of Cu.sub.2O and Cu metal, as confirmed by XRD shown in FIG. 8. The deposition of Cu.sub.2O and Cu is dependent on the deposition and post-deposition conditions employed, including presence of oxidant, amounts of oxidant and precursor in the precursor mixture and substrate temperature. The films exhibited good adhesion to the substrate and were deep green/orange in colour.

Example 5

(44) Aluminium triflate was used to deposit films of alumina. AACVD of [Al(OTf).sub.3] (0.5 g) in methanol (30 mL) at a deposition temperature of 550 and 600 C. in N.sub.2 carrier gas (1 Lmin.sup.1) resulted in the deposition of amorphous white but transparent thin films.

(45) XPS analysis of the deposited films confirmed the prescence of Al and O and were consistent with films of Al.sub.2O.sub.3 having been deposited. Peaks were observed for Al.sup.3+ (Al.sub.2O.sub.3) at 75 eV and for Al.sup.3+ (Al.sub.2O.sub.3/Al) at 77.2 eV and 80 eV binding energy respectively. The O.sup.2 peak attributable to Al.sub.2O.sub.3 is centered at around 532 eV.

Example 6

(46) Silver triflate was used to deposit films. AACVD of [AgOTf] (0.5 g) in methanol (30 mL) at a deposition temperature of 550 C. in an N.sub.2 carrier gas (1 Lmin.sup.1) resulted in the deposition of Ag thin films with a reflective metallic appearance. The metallic nature of the films was confirmed by XRD, as shown in FIG. 9.