# Patent

## Title
Method for producing highly conformal transparent conducting oxides

## Abstract

A method for forming a transparent conducting oxide product layer. The method includes use of precursors, such as tetrakis-(dimethylamino) tin and trimethyl indium, and selected use of dopants, such as SnO and ZnO for obtaining desired optical, electrical and structural properties for a highly conformal layer coating on a substrate. Ozone was also input as a reactive gas which enabled rapid production of the desired product layer.

## Background
STATEMENT OF GOVERNMENT INTEREST
The United States Government claims certain rights in this invention pursuant to Contract No. W-31-109-ENG-38 between the United States Government and the University of Chicago and/or pursuant to DE-AC02-06CH11357 between the Untied States Government and UChicago Argonne, LLC representing Argonne National Laboratory.


FIELD OF THE INVENTION
This invention relates to a method and system for producing transparent conducting oxides. More particularly the invention relates to methods and systems for producing a variety of highly conformal transparent conducting oxides, such as, indium oxide, indium tin oxide, indium zinc oxide and tin zinc oxide.
BACKGROUND OF THE INVENTION
Transparent conducting oxides (“TCOs”) are important components for many applications, such as but not limited to: photovoltaic cells, flat panel displays, touch screens and architectural glass. Current methods of deposition, such as sputtering, are typically used; but production costs are in need of reduction; and quality of the product films need to be improved for various applications and also for providing layer uniformity over large areas. Previously, In2O3 deposition by ALD has been accomplished using InCl3 with either H2O or H2O2 as the oxygen source. Although useful for coating planar surfaces, this method suffers from several limitations. First, the InCl3 chemistry requires high growth temperatures of 300° C. to 500° C., and yields a low growth rate of only 0.25-0.40 Å/cycle. In addition, the InCl3 has a very low vapor pressure and must be heated to 285° C. just to saturate a planar surface. Furthermore, the corrosive HCl by-product can damage the deposition equipment. But the greatest limitation of the InCl3/H2O method, especially for coating nanoporous materials, is that InCl3 can etch the deposited In2O3. Consequently, nanoporous materials require very long precursor exposures that are likely to completely remove the In2O3 from the outer portions of the nanoporous substrate.
An improved ALD process for In2O3 has also been sought for many years and a number of alternate precursors have been investigated including β-diketonates (In(hfac)3 (hfac=hexafluoropentadionate), In(thd)3 (thd=2,2,6,6-teramethyl-3,5-heptanedioneate), and In(acac)3 (acac=2,4-pentanedionate)) and trimethyl indium (In(CH3)3). Unfortunately, these efforts were unsuccessful. No growth was observed using β-diketonates with water or hydrogen peroxide, while trimethyl indium did not yield self-limiting growth.
SUMMARY OF THE INVENTION
An improved method and system for producing indium oxide (In2O3) and other transparent conducting oxides is provided by the instant invention. In2O3 can also be doped with tin to form indium tin oxide (“ITO”) with improved electrical conductivity, high optical transparency and good chemical stability. Deposition of such materials is accomplished by using atomic layer deposition (“ALD”) to deposit ITO (and other such transparent conducting oxides) over large areas with high uniformity to address selected commercial applications. The ALD method is used in conjunction with particular precursor materials, such as trimethyl indium (TMIn”) due to its high vapor pressure, low cost and availability as a commodity. The ALD method is used with TMIn and O3(ozone). In addition to ITO, other transparent conducting oxides can be prepared including, for example without limitation, doped ITO and tin zinc oxide. These and other features of the invention will be described in more detail hereinafter with reference to the figures described below.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a flow diagram of ALD;
FIG. 1B illustrates a gas pulsing cycle during ALD; and
FIG. 1C illustrates one cycle of an ALD process;
FIG. 2 illustrates an ALD reactor system;
FIG. 3 illustrates schematically the ALD process temperature window;
FIG. 4A shows deposition data of In2O3 by use of TMIn and H2O;
FIG. 4B shows deposition data of In2O3 by use of TMIn and H2O2;
FIG. 4C shows deposition data of In2O3 by use of TMIn and O2;
FIG. 4D shows deposition data of TMIn and O3 (ozone); and
FIG. 4E shows deposition data of TMIn and O3 for two ALD cycles (magnified image of FIG. 4D);
FIGS. 5A(1)-5A(5) shows process cycle conditions and
FIG. 5B show comparative growth for In2O3 by TMIn with H2O and O3;
FIG. 6 show comparative growth for In2O3 by TMIn with dosing O3 or O2;
FIG. 7A(1)-7A(4) illustrates deposition data of ALD In2O3 using TMIn and O3 self limiting behavior growth;
FIG. 8A shows ALD In2O3 growth saturation data using TMIn and
FIG. 8B shows ALD growth saturation data using O3;
FIG. 9A shows In2O3 thickness versus number of ALD cycles;
FIG. 9B shows index of refraction versus In2O3 thickness; and
FIG. 9C shows In2O3 thickness across a deposition surface;
FIG. 10A shows In2O3 growth rate versus deposition temperature and
FIG. 10B shows index of refraction of In2O3 versus deposition temperatures;
FIG. 11A shows an X-ray diffraction pattern for as deposited In2O3 at 150° C.;
FIG. 11B shows the layer of FIG. 11A annealed at 400 C for 6 h;
FIG. 12A shows transmission percent as a function of wavelength for In2O3 layers at various ALD cycles and annealed; and
FIG. 12B shows transmission percent for various as deposited cycles of ALD;
FIG. 13A shows In2O3 resistivity as a function of layer thickness;
FIG. 13B shows carrier concentration as a function of layer thickness; and
FIG. 13C shows Hall mobility as a function of layer thickness;
FIG. 14A shows an X-ray diffraction pattern for as deposited ALD layers of In2O3 deposited at selected temperatures; and
FIG. 14B shows these same layers after annealing at 400° C. for 6 h;
FIG. 15A shows resistivity for In2O3 before and after annealing;
FIG. 15B shows carrier concentration for In2O3 before and after annealing; and
FIG. 15C shows Hall mobility before and after annealing;
FIG. 16A shows percent transmittance for In2O3 layers deposited at various temperatures; and
FIG. 16B shows transmittance after being annealed;
FIG. 17A Tauc plot calculated from FIG. 16A for In2O3 layers as deposited at various temperatures and
FIG. 17B Tauc plot calculated for In2O3 layers as deposited at various number of ALD cycles;
FIG. 18 shows full range XPS scan of In2O3 after Ar sputter;
FIG. 19 shows deposition of SnO2 using TDMASn and H2O2;
FIGS. 20A-20F show the ALD process for TDMASn with H2O2 and TMIn with O3;
FIG. 21 shows a growth curve for alternate growth of TDMASn with H2O2 and TMIn with O3;
FIG. 22 shows deposition of SnO2 using TDMASn and O3;
FIG. 23A shows a growth curve over time for TDMASn with In2O3 and SnO2 cycles of three;
FIG. 23B shows alternate growth of In2O3 and SnO2 for use of alternate growth cycles;
FIG. 24A shows X-ray diffraction patterns for ITO (10% Sn-90% In2O3) for different oxidizing environments and as deposited as well as annealed;
FIG. 24B shows percent transmittance for as deposited and annealed Sn2O3 deposited with Sn:O3;
FIG. 24C shows percent transmittance for as deposited and annealed Sn2O3 deposited with Sn:H2O2;
FIG. 24D shows electrical resistivity for Sn:H2O2 and Sn:O3;
FIG. 24E shows carrier concentration for SN:H2O2 and Sn:O3;
FIG. 24F shows Hall mobility for Sn:H2O2 and Sn:O3;
FIG. 25A shows X-ray diffraction patterns for as deposited ITO with various % Sn content;
FIG. 25B shows the ITO after annealing;
FIG. 25C shows percent transmittance for various % Sn deposited ITO;
FIG. 25D shows the layers of FIG. 25C after various annealing treatments;
FIG. 25E shows resistivity for various % SnO ALD cycles in In2O3;
FIG. 25F shows carrier concentration for the various % SnO ALD cycles;
FIG. 25G shows Hall mobility for the various of % SnO ALD cycles;
FIG. 26 shows layer thickness versus % doping in In2O3;
FIG. 27 shows XRF analysis of ITO for various amounts of Sn;
FIG. 28 shows after Ar sputter full scan XPS for as deposited 10% Sn ALD cycles in In2O3;
FIG. 29A show an X-ray diffraction pattern of ITO deposited on sapphire and
FIG. 29B shows ITO on fused silica;
FIGS. 30A-30F show process cycle conditions for deposition of ZnO—In2O3 layers using H2O and O3 with TMIn;
FIGS. 31A-31E show process cycle conditions for deposition of ZnO—In2O3 layers using O3;
FIG. 32A shows the X-ray diffraction patterns for as deposited ZnO—In2O3 layers for various percentages of In2O3; FIG. 32B shows X-ray diffraction patterns for after annealed ZnO—In2O3 layers for various percentages of In2O3;
FIG. 33 shows optical transmittance for the as deposited layers of FIG. 32A; and
FIG. 34A shows electrical resistivity for the various layers of FIG. 33;
FIG. 34B shows carrier concentration for the various layers of FIG. 33; and
FIG. 34C shows Hall mobility for the various layers of FIG. 33.



DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS
In one form of the invention a system 10 is shown in FIG. 1A which illustrates a flow diagram of an atomic layer deposition (“ALD”) process used to form layers of transparent conducting oxides. In the system, 10 various gas sources are provided, such as for example, precursor sources 20 and inert gas 30 which are selectively output to reaction chamber 40. Vacuum pump 50 enables control of the vacuum level and/or pressure level of gases input to the reaction chamber 40. FIG. 1B illustrates an example of a cycle of gas level pulses during an ALD deposition cycle. FIG. 1C shows schematically one ALD cycle of gas pulsing and purges of the reaction chamber 40.
FIG. 2 illustrates further detail of a preferred form of an ALD system 60. The fundamentals of an ALD system are described in U.S. Pat. No. 4,058,430 which is incorporated by referenced herein. In the system 60 a reaction chamber 70 includes heaters 80, a flow tube 90 within which are disposed samples 100. Various precursor sources 110, 120 and 130 provide reactants and purge gases to the reaction chamber 70. The sources 110 can include, for example, trimethyl indium (“TMIn”), ozone (O3), tin oxide (“SnO2”) and zinc oxide (“ZnO”). The purge gases of the sources 120 and 130 include for example Ar, N2 and other non-reactive gases. The system 60 further includes various valving systems 140 for processing deposition of selected transparent conducting oxides. In FIG. 3 is shown a schematic of an ALD process temperature window with areas of active ALD as well as condensation, incomplete reaction, decomposition and desorption regions of reaction. Consequently, proper ALD deposition is dependent on a particular temperature window for a growth precursor and desired oxide deposition. In various preferred embodiments described hereinafter, TMIn is applied to produce an In2O3 layer growth along with doping of In2O3 by Sn and Zn. Various temperatures were determined to provide productive ALD along with use of O3. In addition, SnO—ZnO layer growth is described hereinafter.
In a preferred embodiment, In2O3 was deposited using the system 60 by use of the precursors TMIn and O3, and was compared to unproductive uses of H2O, H2O2 and O2. This point is further amplified by reference to FIGS. 4A through 8B showing In2O3 growth rates under various conditions. The resulting In2O3 layers have highly desirable optical, electrical and mechanical/structural properties; and various properties are shown in FIGS. 9A through 18B, including for example, refractive index, optical transmittance, resistivity (with and without annealing step), carrier concentration, Hall mobility and X-ray diffraction patterns are illustrative of crystalline/amorphous structures (with and without annealing). FIG. 18 shows the various molecular orbital levels of the deposited In2O3 layers from an XPS scan.
In order to illustrate further the effectiveness of the use of O3 to produce Sn2O3 deposition along with In2O3, FIGS. 19 through 29B illustrate growth curves for a variety of conditions, including co-deposition of In2O3, and data indicating achievement of Sn2O3 containing layers with desirable optical and electrical properties.
Other transparent conducting oxides can be deposited very effectively using O3, such as Zn—In2O3, using the system 60 with precursors ZnO and TMIn to produce doped In2O3 layers. In FIGS. 30A through 32B are shown growth curves, again showing the effectiveness of the use of O3 with precursors, to provide layers of In2O3 doped with ZnO. The resulting layers have excellent optical and electrical properties as shown by FIGS. 33 through 34C.
The preferred embodiments described hereinafter illustrate the advantageous features of forming transparent conducting oxides, such as In2O3 (doped and undoped) by use of TMIn and TDMASn tetrakis-(dimethylamino) tin and O3 to produce layers with excellent optical, electrical and structural properties, contrary to conventional teachings. These layers enable application to a wide variety of commercial applications and produceable with greatly reduced cost and simplified system requirements.
The foregoing description of embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the present invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the present invention. The embodiments were chosen and described in order to explain the principles of the present invention and its practical application to enable one skilled in the art to utilize the present invention in various embodiments, and with various modifications, as are suited to the particular use contemplated.

## Claims

1. A method of forming a transparent conducting oxide layer having a desired set of properties, comprising the steps of:
providing an atomic layer deposition system;
providing a substrate disposed in the atomic layer deposition system;
inputting a precursor consisting essentially of trimethyl indium to the atomic layer deposition system;
inputting ozone to the atomic layer deposition system;
depositing In2O3;
depositing a dopant using a precursor selected from the group consisting of tetrakis-(dimethylamino) tin and diethyl zinc; and
forming a deposited layer on the substrate comprising In2O3 and the dopant, wherein the deposited layer has the desired set of properties;
where temperature is controlled during deposition in a temperature range between 100° C. to 150° C. and the deposited layer is formed at a growth rate greater than 0.4 Å/cycle.

2. The method as defined in claim 1 wherein the precursor and the ozone are input in a pulsed manner.

3. The method as defined in claim 2 further including pulses of a gas in a purging step.

4. The method as defined in claim 1 wherein the dopant is selected from the group of SnO and ZnO.

5. The method as defined in claim 4 wherein depositing the dopant comprises inputting tetrakis-(dimethylamino) tin and inputting ozone to the atomic layer deposition system for depositing the dopant.

6. The method as defined in claim 1 wherein the deposited layer has a structure selected from the group of amorphous, crystalline and mixtures thereof.