Atomic Layer Deposition of an Indium Gallium Oxide Thin Film for Thin

Subscriber access provided by EAST TENNESSEE STATE UNIV

Article

Atomic Layer Deposition of Indium Gallium Oxide Thin Film for Thin Film Transistor Applications Jiazhen Sheng, Eun Jung Park, Bonggeun Shong, and Jin-Seong Park ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 23 Jun 2017 Downloaded from http://pubs.acs.org on June 23, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Atomic Layer Deposition of Indium Gallium Oxide Thin Film for Thin Film Transistor Applications

Jiazhen Sheng1, Eun Jung Park2, Bonggeun Shong2*, and Jin-Seong Park1*

1

Division of Materials Science and Engineering, Hanyang University, Seoul, Korea 2

Department of Chemistry, Chungnam National University, Daejeon, Korea

Abstract Indium gallium oxide (IGO) thin films were deposited via atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1) and trimethylgallium (TMGa) as indium and gallium precursors, respectively, and hydrogen peroxide (H2O2) as the reactant. In order to clearly understand the mechanism of multicomponent ALD growth of oxide semiconductor materials, several variations in the precursor-reactant deposition cycles were evaluated. Gallium could be doped into oxide film at 200°C when accompanied by an InCA-1 pulse, and no growth of gallium oxide was observed without the simultaneous deposition of indium oxide. Density functional theory calculations for initial adsorption of the precursors revealed that chemisorption of TMGa was kinetically hindered on hydroxylated SiOx, but was spontaneous on a hydroxylated InOx surface. Moreover, the atomic composition and electrical characteristics, such as carrier concentration and resistivity, of the ALD-IGO film were controllable by adjusting deposition supercycles composed of InO and GaO sub-cycles. Thus, ALD-IGO could be employed to fabricate active layers for thin film transistors (TFTs) in order to realize optimum mobility of 9.45 cm2/(V s), threshold voltage of -1.57 V, and subthreshold slope of 0.26 V/decade.

Keywords: surface reaction mechanism, gallium-doped indium oxide, oxide semiconductor, TFT, ALD 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

I.

Introduction

Oxide semiconductor thin film transistors (TFTs) have been extensively researched in the display industry because of their attractive characteristics, including high performance, low processing temperature, and simple fabrication. Besides, oxide semiconductor TFTs can show outstanding performance required for scalability, because of high mobility and low leakage current attributed to its wide band gap compared to low-temperature polycrystalline silicon (LTPS) or amorphous Si.1 Indium oxide (In2O3) is a well-known transparent conducting oxide material with intrinsic oxygen deficiency that endows the material with high mobility, but also an undesirable negative shift in threshold voltage caused by unexpected increase in oxygen vacancy densities.2-3 Doping of indium oxide has been investigated for improvement of TFT performance by reducing the density of oxygen vacancies, with elements such as gallium, hafnium, and silicon4-6 which have larger dopantoxygen bond dissociation energy than that of In-O (346 kJ/mol)7. Ga has large Ga-O bond dissociation energy (374 kJ/mol)7, and atomic size similar to In, so that the lattice structure and the charge transport properties of InOx would be little affected upon doping.8 Thus, as Jang et al. reported 9, gallium-doped indium oxide, or indium gallium oxide (IGO), can be a potential candidate material for high performance oxide TFT. Indeed, among the well-known indium-based active layer materials, including indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), and indium tin zinc oxide (ITZO), IGO has been utilized in high-mobility backplane devices for next-generation displays such as 4K2K liquid crystal displays and 3-D displays.10 Although sputtering is most widely used for fabrication of oxide semiconductor TFTs, it is difficult to control the elemental ratio of sputter-deposited films without transferring the target, and the presence of high-energy species during deposition can create interfacial 2


Page 2 of 26

Page 3 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


defects, resulting in TFT performance degradation. On the other hand, oxide TFTs fabricated using atomic layer deposition (ALD) showed performance comparable to those of the sputtered TFTs in previous reports, for example, mobility of 20cm2/Vs for ZnO11, 10cm2/Vs for IGZO12 and 42.1cm2/Vs for IZO13. Furthermore, ALD process enables uniform deposition of films with precise control of the thickness and composition over large areas. Therefore, ALD is a promising technology for oxide semiconductor TFTs for large area display devices.11, 13 In addition, ALD provides great benefits for multicomponent growth of binary systems to form ternary materials such as Al2O3/ZnO (aluminum-doped ZnO, AZO), ZnO/SnOx (zinc–tin oxide, ZTO), and In2O3/ZnO (indium–zinc oxide, IZO).14 In previous research on ALD for TFT applications, ZnO doped with Al, Hf, or Mg were investigated, whose elemental compositions could be controlled to optimize the device performance.15-17 However, the mechanisms of ALD growth for multicomponent oxides are often more complex than a simple sum of the growth metrics for constituent binary oxides.13, 18-19

Therefore, current lack of understanding regarding multicomponent ALD growth for

oxide semiconductor materials has limited their applicability as the active layer of TFTs. In this study, IGO thin films were deposited via ALD, with variations in the deposition sequence, wherein a reactant pulse was emitted before and after a metal precursor pulse. Doing so enabled gallium oxide to be successfully incorporated into IGO thin films at 200°C, when accompanied by an [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1)– H2O2 deposition sequence. Conversely, no deposition of pure gallium oxide was observed without indium oxide deposition. Density functional theory calculations showed an increase in the reactivity of TFTs to favor the adsorption of trimethylgallium (TMGa) upon termination of the surface with hydroxylated InOx compared to Si(100). Based on the 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

controllable composition of this ternary deposition system, the experimental IGO thin films were employed as the active layer of oxide TFTs and optimized at a specific composition ratio between In and Ga. Our results revealed that IGO thin films deposited using ALD could be promising components for oxide semiconductor TFTs.

II.

Experimental Procedures

IGO thin films were deposited via ALD (NCD-D100) at 200°C, using InCA-1 as an indium precursor, TMGa as a gallium precursor, and hydrogen peroxide (30 % H2O2 with 70 % H2O, Sigma Aldrich) as the reactant on a Si(100) substrate with a native oxide, after acetone washing. The temperature of the indium precursor was maintained at 40 °C for sufficient vapor pressure and dose, as previously reported.20 Auger electron spectroscopy (AES) (PHI 700Xi) and spectroscopic ellipsometry (SE) (Elli-SE(UV)-FM8) were carried out to analyze the thickness and chemical composition of the thin films. Five different ALD sequences, with variations in the order of metal precursors and reactant pulses, were used, as shown in Figure 1. Hall measurements (Ecopia; AH5TTT5) were carried out to determine electrical characteristics such as resistivity, carrier concentration, and mobility. Analysis of core-level electronic states was conducted using Xray photoelectron spectroscopy (XPS) (XPS-Theta Probe). The crystallinity of indium oxide (bcc phase) and indium gallium oxide (amorphous) thin films was examined via θ–2θ scanning using a Rigaku X-ray diffractometer with Cu Ka radiation at 1.542 Å (Figure S1, Supporting Information). Top-gate, bottom-contact IGO TFTs were fabricated on a glass substrate. First, a 100 nm indium tin oxide (ITO) source/drain and gate layer were deposited via sputtering at room 4


Page 4 of 26

Page 5 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


temperature, on which a 100 nm aluminum oxide gate-insulator layer was grown at 200 °C via ALD, using trimethylaluminum (TMA) and H2O. Then, an IGO active layer with a thickness of 20 nm was deposited at 200°C using the precursors mentioned above, following the InO–GaO sequence. The number of InO sub-cycles changed from 1 to 3. The active region was then patterned by a combination of photolithography and wet etching steps to realize channel width (W) and length (L) of 40 µm and 20 µm, respectively. TFT devices were annealed at 300 °C in an ambient atmosphere for 1 h. The device properties of TFTs were evaluated using a HP 4155A parameter analyzer in air at room temperature. Density functional theory (DFT) calculations were performed using Orca 3.0.3 software.21 Geometry optimization was carried out using B97-D3 functional22 with allelectron def2-TZVP basis set.23 Then, the single-point energy of the optimized structures was obtained with PWPB95-D3 double-hybrid functional24 and def2-TZVPP basis set. All calculations involved D3 atom-pairwise dispersion correction with Becke-Johnson damping.25 The Si surface with hydroxyl functionalities was modeled using a Si15H16 cluster with two dissociatively adsorbed H2O molecules;26 the hydroxyl on the InO-terminated surface were modeled with an –OH group bonded to a trivalent In of a Si15H18O2InOH cluster (Figure S2, Supporting Information). The transition state structures were initially guessed from relaxed potential energy surface scans, and confirmed after optimization to have an imaginary vibrational mode along the suggested reaction coordinate.

III.

Results and Discussion

Table 1 shows the growth rate and chemical composition of the ALD-grown IGO thin films. No growth of gallium oxide was detected in the film produced using the GaO sequence. This result was corroborated by a previous report in which TMGa with H2O2 or H2O could 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 26

not grow gallium oxide via ALD, even at a higher deposition temperature of 350°C.27 On the other hand, a varying Ga composition was observed when an InCA-1 pulse was included in the sequence. Here, only 3.8% Ga was contained in the thin film following an In–Ga (TMGa pulsed immediately after InCA-1) sequence, resulting in a slight decrease in the growth rate (0.77 Å/cycle) compared to that of the pure indium oxide ALD (InO, 0.97 Å/cycle). However, when [(InCA-1)–H2O2] and [TMGa–H2O2] cycles were alternated using an InO–GaO sequence, the concentration of Ga rose to 20.6%. By initiating a TMGa pulse immediately following the H2O2 pulse but before the InCA-1 pulse (Ga–In sequence), the Ga content reached 28.3 %. This increase in the Ga concentration was accompanied by a drop in the film’s growth rate to 0.42 Å/cycle and 0.33 Å/cycle for the InO–GaO and Ga–In sequences, respectively.

Similar

growth

behavior

for

an

AlxSiyOz

ALD

using

an

Al(CH3)3−D2O−Si2(NHEt)6−D2O sequence was reported by Ritala et al., who focused on how

the

reaction

mechanism

affected

the

chemisorption

of

the

Si2(NHEt)6

[(hexakis(ethylamino)disilane)] precursor.28 The oxygen-metal bonding of the thin films was analyzed via XPS, as shown in Figure 2. The chemical concentrations of Ga and In in the IGO films obtained from XPS results corroborated those from AES measurements. In particular, the O 1s region was deconvoluted into sub-peaks. For metal oxides, a lower binding energy at the O 1s sub-peak can generally be attributed to O that is directly bonded to metal cations, while peaks with higher binding energy can be assigned to OH of hydroxides.29 In addition, the O 1s core-level electrons shifted according to the deposition sequence. Therefore, the metal-bound oxygen peak could be further deconvoluted into Ga-O and In-O peaks. In particular, the lower binding energy component (530.2 eV) was ascribed to free oxygen bonded to In, while the higher binding energy component (530.9 eV) was related to Ga-O bonds.30 Conversely, it was difficult to 6


Page 7 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


distinguish the Ga-bound O 1s electrons for the film resulting from the In–Ga sequence, since the Ga content was only 3.8% (Table 1). Nonetheless, the Ga 3d peak (shown in Figure 2(e)) revealed the presence of Ga in the film. Otherwise, the relative fraction of peaks due to O-In, O-Ga, and O impurities (Figure 2(f)) were consistent with AES data (Table 1). To determine the reason behind the dependence of the films’ growth behavior on the precursor exposure sequence, a potential energy diagram for the adsorption of InCA-1 and TMGa precursors was obtained via DFT calculations (Figure 3). Two different surface hydroxyl functional groups, those bound to Si(100) and those on a trivalent indium, were considered to represent the initial adsorption environment on the silica substrate and the functionality created after an InCA–H2O2 sequence. Molecular adsorption of both TMGa and InCA-1 on a hydroxylated Si(100) surface through O-metal dative bonding was spontaneous and did not exhibit an activation barrier (Figure 3(a)). However, the adsorption energy of Odative TMGa (-72.1 kJ/mol) and InCA-1 (-90.6 kJ/mol) would have resulted in lifetimes less than 1 ms at a deposition temperature of 200 °C, assuming a typical pre-exponential factor for desorption of 1013 s-1. Thus, dative bonded molecular precursors could not enable the deposition of metal ions. On the other hand, removing ligands via transfer of hydrogen from the surface hydroxyl groups is irreversible and can leave metal ions deposited on the surface after the precursor pulse. Accordingly, since the removal of [Si(CH3)3]2NH from the InCA-1 precursor involves a small activation barrier of 14.5 kJ/mol, deposition of In with this precursor easily occur. In constrast, the removal of CH4 from both TMGa and InCA-1 (not shown; similar to that of TMGa) on hydroxylatd Si(100) cannot proceed due to activation barriers higher than the desorption energy of the dative bonded precursors. Therefore, while nucleation of indium oxide with InCA-1 is possible, TMGa cannot lead to nucleation of gallium oxide on the silica substrate by itself. 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

On the other hand, the reactivity of the surface to TMGa increased upon deposition of indium oxide. The active surface functionality after an (InCA-1)–H2O2 sequence was modeled using a hydroxylated trivalent indium on the Si(100) surface (abbreviated as InOH)31. On this surface, TMGa spontaneously decomposed into Ga(CH3)2 and CH3, with a significant adsorption energy of -285.3 kJ/mol (Figure 3(b)). Both In and Ga centers became tetravalent after dissociation of Ga-C and formation of In-C bonds. No transition state with energy above that of the entrance channel could be located, despite multiple attempts, thereby suggesting kinetic viability for this process. Subsequently, ligands of the surface-adsorbed Ga(CH3)2 could either react further with the remaining surface hydroxyl to lose CH4, or be oxidized during the H2O2 pulse. Thus, TMGa could be adsorbed on a hydroxylated indium oxide surface. This result accounted for the incorporation of gallium oxide into the thin films, which was enabled by inter-deposition with indium oxide. The variations in the relative amount of Ga and In in IGO films according to the sequence of the precursors can be explained in light of the above-described reactivity of the surfaces toward TMGa after each ALD pulse. The film deposited with InO-GaO sequence, where TMGa is dosed on the hydroxylated InOx surface generated by [InCA-1 - H2O2] pulses, can be directly related to the reactivities of the InOx surface toward TMGa and GaOx surface toward InCA-1 as described above. In this case, both In and Ga precursors would easily adsorb on the hydroxylated surfaces prepared after each H2O2 pulse. As a result, the atomic fractions of In and Ga are similar to each other (ca. 20 %). On the other hand, in In-Ga and Ga-In sequences, there is no H2O2 pulse included between two precursor pulses. In such situations, it can be expected that much of the surface –OH react with the first metal pulse, leaving methylated In or Ga moieties on the surface, which are no longer reactive toward the second precursor. Only a fraction of surface hydroxyl moieties remaining after the first 8


Page 8 of 26

Page 9 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


precursor pulse would then allow the second precursor to adsorb, depositing smaller amount of the second precursor on the surface. As a result, the obtained films from In-Ga and Ga-In sequences are richer with In and Ga, respectively. The properties of the ALD IGO thin films could be systematically varied by adjusting the deposition supercycles, which consisted of InO–GaO sequences. As a proof of concept, IGO films obtained from sub-cycles of 3InO–GaO (three InO cycles + one GaO cycle) and InO–3GaO (one InO cycles + three GaO cycle) were compared with those from InO–GaO (one InO cycles + one GaO cycle) film. The AES depth profiles (Figure 4) indicated a homogeneous composition of In and Ga throughout the films. The compositional and electrical properties (Table 2) of the films demonstrated the dependence of these values on deposition sequence. For instance, an IGO thin film with a larger number of InO cycles (3InO–GaO) exhibited a highest indium content (30.9%) and carrier concentration (1.68×1020 cm-3), whereas, a thin film deposited with a larger number of GaO cycles (InO–3GaO) had a 34.9% Ga concentration, resulting in higher resistivity outside the Hall measurement limit. Accordingly, manipulating both the composition and resulting material properties of thin films by adjusting ALD supercycles can facilitate optimization of IGO thin film properties, thereby enabling these films to be utilized as active layers for TFTs. Putatively, the atomic ratio of In to Ga is an important factor affecting the performance of IGO TFTs.32 As the carrier concentration of the ALD-deposited pure InO thin film exceeded the threshold value—i.e., 8.16×1020 cm-3—for TFT active layers, a GaO sub-cycle was added to decrease it. On the other hand, the film deposited using the InO–GaO sequence contained 20.6% Ga, yielding a carrier concentration of 8.16×1018 cm-3, which was too low for an active layer material. Therefore, the relative proportions of Ga and In in the IGO film were varied by increasing the number of InO sub-cycles during ALD of IGO. Table 2 lists the chemical 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

composition and hall measurement results for the IGO thin films when the number of InO sub-cycles increased from one to three.

According to the AES data in Figure 4, the

proportion of In increased with the number of InO sub-cycles. This process was accompanied by an increase in the carrier concentration (1.68×1020 cm-3) and decrease in the resistivity (1.21×10-3 Ω cm) for 3InO-GaO sequence. The corresponding devices with controlled In/Ga ratios were fabricated via photolithography with a top gate bottom contact structure, as shown in Figure 5(a). The performance criteria of the IGO TFT (shown in Table 3 and Figure 5(b)) indicated systematic dependence on the sequence of supercycles. The TFT resulting from the 3InO– GaO sequence showed enhanced performance parameters, including a negative shift in threshold voltage (Vth) to -1.57 V, a mobility (µsat) of 9.45 cm2/(V s), subthreshold slope (S.S.) of 0.26 V/decade, hysteresis of 0.63 V, and on-off current ratio (Ion/Ioff) of 8×10-8. These values were superior to those from the device fabricated using an InO–GaO sequence (Vth = 3.02V, µsat = 0.17 cm2/(V s), S.S. = 0.42 V/decade, hysteresis = 1.24 V, Ion/off = 8×10-8). These values were comparable or similar to those from previous studies. For instance, a mobility of 10.7 cm2/(V s) was reported by Bae et al.27. Similarly, a mobility of 5.2 cm2/(V s) was reported by Yoon et al.33 These values indicate that composition-adjustable ALD-IGO could be a promising TFT-active-layer candidate material. As mentioned earlier, TFT performance of is expected to be improved when doping with Ga by reducing the oxygen vacancies. Thus, as previously reported 9, Ga dopant acts as a carrier suppressor that decrease the carrier concentration. In our experiments, as the number of InO sub-cycle increased, Ga% decreased, resulting in increased oxygen vacancy and carrier concentration. The on current showed dramatic increment with the fraction of InO sub-cycle, and the threshold voltages also showed negative shift. The origin of subthreshold slop is commonly ascribed to the bulk 10


Page 10 of 26

Page 11 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


defect density of active layer and interface trap states (Nt) between active layer (IGO) and gate insulator layer (Al2O3). Thus, the Nt values of each TFT were calculated using the following equation ܰ௧ = [

݈ܵ‫݃݋‬ሺ݁ሻ ‫ܥ‬௜ − 1] ݇ܶൗ ‫ݍ‬ ‫ݍ‬

where S is the subthreshold slope, and Ci is the gate capacitance per unit area. The calculated Nt values (Table 3) decreases according to increasing In%. It reveals that elemental composition of the active layer can be the dominant reason for different interface density state as well as the subthreshold slope, as reported by Jeong et al.34 Besides, the compositions result in difference in surface characteristics such as hydrophilicity. As shown in figure S3, higher In% thin film shows smaller water contact angle, which is translated as larger hydrophilicity and leading to relatively faster Al2O3 nucleation and denser Al2O3 gate insulator deposition over IGO active layer, and finally affect the interfacial properties between the active layer and gate insulator layer as well. The stability of the optimized device (with IGO deposited using 3InO-GaO supercycle) under positive bias stress (PBS) was measured (shown in Figure S4), applying VGS=20 V for a total stress time of 3600 s. The threshold voltage showed positive shift for about 2.25V with slight degradation in mobility and S.S., which is comparable to the previous reports ( 3.87V by Rim et al.35; 1.5V by Bae et al.32).

Conclusion Indium gallium oxide (IGO) thin films were deposited via ALD, with variations in precursor/reactant pulse sequences. By launching a reactant pulse before and after sequential metal precursor pulses, a clear understanding of the ALD growth mechanism for 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

multicomponent oxide semiconductor materials could be obtained. While gallium oxide alone could not be deposited via ALD, Ga could be doped into IGO at 200 °C when a Ga precursor pulse was accompanied by an InO sub-cycle [(InCA-1)–H2O2)]. In doing so, an atomic composition of over 20% Ga could be obtained. The mechanism behind the switch in the reactivity of the Ga precursor in relation to an InO sub-cycle was explained using DFT calculation results: the reaction between trimethylgallium and the hydroxylated trivalent InOx surface was expected to be spontaneous and irreversible. Adjusting the supercycles of InO could enable control over the atomic composition and electrical characteristics of ALD-IGO and GaO sequences. Such controllability was applied to optimize IGO active layers in TFT devices with the aim to obtain optimal performance metrics such as a mobility of 9.45 cm2/(V s), threshold voltage of -1.57 V, and subthreshold slope of 0.26 V/decade.

Supporting Information The thin film deposited by sequence InO and In-Ga was shown crystal bcc phase attributed to none or low concentration of Ga element, and thin film deposited by sequence Ga-In and InO-GaO was amorphous phase, examined via XRD (Figure S1). The side view of SiOx-OH and InOx-OH surface model cluster for DFT calculation (Figure S2). The image of water droplets used to determine the change in water contact angle on IGO thin film with different number of InO sub-cycle (Figure S3). The stability of IGO TFT (with 3InO-GaO supercycle) under 20V positive bias stress during 3600s (Figure S4).

12


Page 12 of 26

Page 13 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


AUTHOR INFORMATION Corresponding Authors *

E-mail: [email protected] (Jin-Seong Park)

*

E-mail: [email protected] (Bonggeun Shong)

AUTHOR CONTRIBUTIONS J. S, and J. –S. P. designed the InGaO ALD experiments and fabricated the thin film transistor. E. J. P and B. S. performed Density functional theory calculations. The manuscript was written by the contribution of all authors, who have approved the final version of the manuscript.

Acknowledgements J. S. and J. –S. Park were supported by Samsung Display Co. and done by the MOTIE (Ministry of Trade, Industry & Energy (project number 10051403, 10052020, and 10052027) and KDRC (Korea Display Research Corporation). E.J.P. and B.S. were partially supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2016R1C1B2006513). The supercomputing resources including technical support was partially provided by the National Institute of Supercomputing and Network/Korea Institute of Science and Technology Information (KSC-2016-C1-0007).

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Reference 1.

Bak, J. Y.; Yang, S.; Ryu, H.-J.; Park, S. H. K.; Hwang, C. S.; Yoon, S. M. Negative-Bias

Light Stress Instability Mechanisms of the Oxide-Semiconductor Thin-Film Transistors Using In–GaO Channel Layers Deposited With Different Oxygen Partial Pressures. IEEE Trans. Electron Devices 2014, 61 (1), 79-86. 2.

Wager, J. F.; Yeh, B.; Hoffman, R. L.; Keszler, D. A. An Amorphous Oxide Semiconductor

Thin-Film Transistor Route to Oxide Electronics. Curr. Opin. Solid State Mater. Sci. 2014, 18 (2), 5361. 3.

Noh, J. H.; Ryu, S. Y.; Jo, S. J.; Kim, C. S.; Sohn, S.-W.; Rack, P. D.; Kim, D.-J.; Baik, H. K.

Indium Oxide Thin-Film Transistors Fabricated by RF Sputtering at Room Temperature. IEEE Electron Device Lett. 2010, 31 (6), 567-569. 4.

Itagaki, N.; Iwasaki, T.; Kumomi, H.; Den, T.; Nomura, K.; Kamiya, T.; Hosono, H. Zn–In–

O based Thin- Film Transistors: Compositional dependence. Phys. Status Solidi A 2008, 205 (8), 1915-1919. 5.

Iwasaki, T.; Itagaki, N.; Den, T.; Kumomi, H.; Nomura, K.; Kamiya, T.; Hosono, H.

Combinatorial Approach to Thin-Film Transistors using Multicomponent Semiconductor Channels: An Application to Amorphous Oxide Semiconductors in In–Ga–Zn–O System. Appl. Phys. Lett. 2007, 90 (24), 242114. 6.

Kim, C.-J.; Kim, S.; Lee, J.-H.; Park, J.-S.; Kim, S.; Park, J.; Lee, E.; Lee, J.; Park, Y.; Kim,

J. H. Amorphous Hafnium-Indium-Zinc Oxide Semiconductor Thin Film Transistors. Appl. Phys. Lett. 2009, 95 (25), 252103. 7.

Chong, E.; Chun, Y. S.; Lee, S. Y. Amorphous Silicon–Indium–Zinc Oxide Semiconductor

Thin Film Transistors Processed below 150 C. Appl. Phys. Lett. 2010, 97 (10), 102102. 8.

Luo, Y.-R., Comprehensive handbook of chemical bond energies. CRC press: 2007.

9.

Parthiban, S.; Kwon, J.-Y. Role of Dopants as a Carrier Suppressor and Strong Oxygen

Binder in Amorphous Indium-Oxide-Based Field Effect Transistor. J. Mater. Res. 2014, 29 (15), 158514


Page 14 of 26

Page 15 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1596. 10.

Kim, Y. G.; Kim, T.; Avis, C.; Lee, S.-H.; Jang, J. Stable and High-Performance Indium

Oxide Thin-Film Transistor by Ga Doping. IEEE Trans. Electron Devices 2016, 63 (3), 1078-1084. 11.

Lin, Y.-Y.; Hsu, C.-C.; Tseng, M.-H.; Shyue, J.-J.; Tsai, F.-Y. Stable and High-Performance

Flexible ZnO Thin-Film Transistors by Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2015, 7 (40), 22610-22617. 12.

Illiberi, A.; Cobb, B.; Sharma, A.; Grehl, T.; Brongersma, H.; Roozeboom, F.; Gelinck, G.;

Poodt, P. Spatial Atmospheric Atomic Layer Deposition of In x Ga y Zn z O for Thin Film Transistors. ACS Appl. Mater. Interfaces 2015, 7 (6), 3671-3675. 13.

Sheng, J.; Lee, H.-J.; Oh, S.; Park, J.-S. Flexible and High-Performance Amorphous Indium

Zinc Oxide Thin-Film Transistor Using Low-Temperature Atomic Layer Deposition. ACS Appl. Mater. Interfaces 2016, 8 (49), 33821-33828. 14.

Ritala, M.; Niinistö, J. Industrial Applications of Atomic Layer Deposition. ECS Trans. 2009,

25 (8), 641-652. 15.

Chung, Y. J.; Choi, W. J.; Kang, S. G.; Lee, C. W.; Lee, J.-O.; Kong, K.-J.; Lee, Y. K. A

Study on the Influence of Local Doping in Atomic Layer Deposited Al: ZnO Thin Film Transistors. J. Mater. Chem. C 2014, 2 (43), 9274-9282. 16.

Ahn, C. H.; Yun, M. G.; Lee, S. Y.; Cho, H. K. Enhancement of Electrical Stability in Oxide

Thin-Film Transistors using Multilayer Channels Grown by Atomic Layer Deposition. IEEE Trans. Electron Devices 2014, 61 (1), 73-78. 17.

Shaw, A.; Whittles, T.; Mitrovic, I.; Jin, J.; Wrench, J.; Hesp, D.; Dhanak, V.; Chalker, P.;

Hall, S. In Physical and Electrical Characterization of Mg-doped ZnO Thin-Film Transistors. ESSDERC 2003, Proc. Eur. Solid-State Device Res. Conf., 45rd 2015; pp 206-209. 18.

Mackus, A. J.; MacIsaac, C.; Kim, W.-H.; Bent, S. F. Incomplete Elimination of Precursor

ligands During Atomic Layer Deposition of Zinc-Oxide, Tin-Oxide, and Zinc-Tin-Oxide. J. Chem. Phys. 2017, 146 (5), 052802. 19.

Murray, C.; Elliott, S. D. Density Functional Theory Predictions of the Composition of

Atomic Layer Deposition-Grown Ternary Oxides. ACS Appl. Mater. Interfaces 2013, 5 (9), 3704-3715. 20.

Sheng, J.; Choi, D.-w.; Lee, S.-H.; Park, J.; Park, J.-S., Performance Modulation of

Transparent ALD Indium Oxide Films on Flexible Substrates: Transition between Metal-like Conductor and High Performance Semiconductor States. J. Mater. Chem. C 2016, 4 (32), 7571-7576. 21.

Neese, F. The ORCA program system. Wiley Interdiscip. Rev.: Comput. Mol. Sci. 2012, 2 (1),

73-78. 22.

Grimme, S. Semiempirical GGA- type Density Functional Constructed with a Long- Range 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Dispersion Correction. J. Comput. Chem. 2006, 27 (15), 1787-1799. 23.

Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and

Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297-3305. 24.

Goerigk, L.; Grimme, S. Efficient and Accurate Double-Hybrid-Meta-GGA Density

Functionals Evaluation with the Extended GMTKN30 Database for General Main Group Thermochemistry, Kinetics, and Noncovalent Interactions. J. Chem. Theory Comput. 2010, 7 (2), 291309. 25.

Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping Function in Dispersion

Corrected Density Functional Theory. J. Comput. Chem. 2011, 32 (7), 1456-1465. 26.

Dick, D.; Ballard, J. B.; Longo, R. C.; Randall, J. N.; Cho, K.; Chabal, Y. J. Toward Selective

Ultra-High-Vacuum Atomic Layer Deposition of Metal Oxides on Si (100). J. Phys. Chem. C 2016, 120 (42), 24213-24223. 27.

Comstock, D. J.; Elam, J. W. Atomic Layer Deposition of Ga2O3 films using

Trimethylgallium and Ozone. Chem. Mater. 2012, 24 (21), 4011-4018. 28.

Tomczak, Y.; Knapas, K.; Haukka, S.; Kemell, M.; Heikkilä, M.; Ceccato, M.; Leskelä, M.;

Ritala, M. In Situ Reaction Mechanism Studies on Atomic Layer Deposition of Al x Si y O z from Trimethylaluminium, Hexakis (ethylamino) disilane, and Water. Chem. Mater. 2012, 24 (20), 38593867. 29.

Al-Kuhaili, M.; Durrani, S.; Khawaja, E. Optical Properties of Gallium Oxide Films

Deposited by Electron-Beam Evaporation. Appl. Phys. Lett. 2003, 83 (22), 4533-4535. 30.

Hollinger, G.; Skheyta-Kabbani, R.; Gendry, M. Oxides on GaAs and InAs surfaces: An X-

Ray-Photoelectron-Spectroscopy Study of Reference Compounds and Thin Oxide Layers. Phys. Rev. B 1994, 49 (16), 11159-11167. 31.

Dyan, A.; Cenedese, P.; Dubot, P. Physical Properties of γ Alumina Surface Hydroxyls

Revisited Through a Large Scale Periodic Quantum-Chemistry Approach. J. Phys. Chem. B 2006, 110 (20), 10041-10050. 32.

Hwang, Y. H.; Bae, B.-S. Effect of Aluminum and Gallium Doping on the Performance of

Solution-Processed Indium Oxide Thin-Film Transistors. J. Disp. Technol. 2013, 9 (9), 704-709. 33.

Bak, J. Y.; Kang, Y.; Yang, S.; Ryu, H.-J.; Hwang, C.-S.; Han, S.; Yoon, S.-M. Origin of

Degradation Phenomenon under Drain Bias Stress for Oxide Thin Film Transistors using IGZO and IGO Channel Layers. Sci. Rep. 2015, 5, 7884. 34.

Jeong, J. K.; Jeong, J. H.; Yang, H. W.; Park, J.-S.; Mo, Y.-G.; Kim, H. D. High Performance

Thin Film Transistors with Cosputtered Amorphous Indium Gallium Zinc Oxide Channel. Appl. Phys. 16


Page 16 of 26

Page 17 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Lett. 2007, 91 (11), 113505. 35.

Rim, Y. S.; Choi, H.-W.; Kim, K. H.; Kim, H. J. Effects of Structural Modification via High-

Pressure Annealing on Solution-Processed InGaO films and Thin-Film Transistors. J. Phys. D: Appl. Phys. 2016, 49 (7), 075112.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

List of Figure Captions Figure 1. Diagram of different ALD process for GaO, InO, In–Ga, Ga–In, and InO–GaO sequences

Figure 2. (a-d) XPS spectra in the O 1s region and (e) Ga 3d region of ALD-IGO thin films with InO, Ga–In, Ga–In, InO–GaO sequences; (f) areal ratios of the three O 1s peaks (Ga−O, In-O, and −OH) from different sequences.

Figure 3. DFT-calculated energy profiles of chemisorption and optimized structures (top view) of TMGa and InCA-1 on (a) SiOx-OH surface, and (b) InOx-OH surface. Brown = In, green = Ga, yellow = Si, red = O, blue = N, and white = H.

Figure 4. Depth profile of IGO thin films grown via ALD with different sequences: (a)3In– Ga, (b)In–Ga, (c)In–3Ga.

Figure 5. (a) Structure diagram of top gate bottom IGO TFT. (b) Transfer performance of the InO–GaO sequence in different InO sub-cycles.

18


Page 18 of 26

Page 19 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


List of Tables Table 1. The growth rate and atomic composition of thin films grown via ALD with various sequences (growth rate and atomic percentages obtained via SE and AES)

Sequence

Supercycle

Growth rate (Å/cycle)

at% C

at% Ga

at% In

at% O

GaO

(TMGa)–H2O2

-

-

-

-

-

InO

(InCA-1) –H2O2

0.97

0.5

0

42.8

56.7

In–Ga

(InCA-1) – (TMGa) –H2O2

0.77

0.7

3.8

39.6

55.9

Ga–In

(TMGa)–(InCA-1)–H2O2

0.33

0.4

28.3

14.9

56.4

0.6

20.6

22.7

56.2

InO–GaO

(InCA-1)–H2O2–(TMGa)–H2O2

0.42

Table 2. Chemical composition and electrical characteristics of 40nm IGO thin films grown via ALD with different sequences: InO, 3InO–GaO, 2InO–GaO, InO–GaO, and InO–3GaO

Sample

C%

Ga%

In%

O%

Carrier Concentration (cm-3)

Mobility (cm2/(V s))

Resistivity (Ω cm)

InO

0.5

0

42.8

56.7

8.16×1020

20.5

3.73×10-4

3InO–GaO

0.6

11.8

30.9

56.8

1.68×1020

35.8

1.21×10-3

2InO–GaO

0.6

18.6

24.4

56.4

2.14×1019

22.2

9.18×10-2

InO–GaO

0.6

20.6

22.7

56.2

1.62×1018

17.4

2.22×10-1

InO–3GaO

0.5

34.9

5.6

59.0

Out of range

Out of range

Out of range

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 26

Table 3. List of key device parameters of ALD IGO TFT fabricated with the sequence InO– GaO in different InO sub-cycle

Sequence

Vth [V]

µsat S.S. Hysteresis [cm2/(V s)] [V/decade] [V]

InO

-

-

-

-

-

InO–GaO

3.02

0.17

0.42

1.24

3.2×106

2.1×1012

2InO–GaO

2.58

1.21

0.30

1.24

1.8×108

1.4×1012

3InO–GaO

-1.57

9.45

0.26

0.63

8.0×108

1.1×1012

20


ION/IOFF

Nt [cm-2]

Page 21 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2

22


Page 22 of 26

Page 23 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4 24


Page 24 of 26

Page 25 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table of Contents

26


Page 26 of 26

Atomic Layer Deposition of an Indium Gallium Oxide Thin Film for Thin

Recommend Documents