Thermal atomic layer deposition of In2O3 thin films using a homoleptic indium triazenide precursor and water.

Pamburayi Mpofu,Urban Forsberg,Nathan J O'Brien,Henrik Pedersen,Polla Rouf

doi:10.1039/d1dt03748j

Pamburayi Mpofu, Urban Forsberg + Show 3 more

Open Access

https://doi.org/10.1039/d1dt03748j

Copy DOI

Abstract

Indium oxide (In2O3) is an important transparent conducting material widely used in optoelectronic applications. Herein, we study the deposition of In2O3 by thermal atomic layer deposition (ALD) using our recently reported indium(III) triazenide precursor and H2O. A temperature interval with self-limiting growth was found between ∼270 and 385 °C with a growth per cycle of ∼1.0 Å. The deposited films were polycrystalline cubic In2O3 with In : O ratios of 1 : 1.2, and low levels of C and no detectable N impurities. The transmittance of the films was found to be >70% in visible light and the resistivity was found to be 0.2 mΩ cm. The high growth rates, low impurities, high optical transmittance, and low resistivity of these films give promise to this process being used for ALD of In2O3 films for future microelectronic displays.

Highlights

Indium oxide (In2O3) is a material of high interest due to its high electrical conductivity and optical transparency, making it a key material for transparent and optoelectronics[1] e.g. microelectronic displays on touch screens
Determination of band gap was determined using the Tauc plot formalism from data obtained by UV-Vis spectrophotometry based on the Tauc relation:1/y = β where α is the absorption coefficient, β is the band tailing parameter, h is the Planck’s constant, ν is the frequency of incident light, Eg is the energy of the optical band gap and y is the power factor, which depends upon the nature of the transition
The film thickness for films deposited at 290 °C using 300, 500, 800 and 1100 atomic layer deposition (ALD) cycles (Fig. 2c) follows a linear trend line, it shows a significantly slower initial deposition interpreted as a nucleation delay of approximately 49 cycles

Summary

INTRODUCTION

Indium oxide (In2O3) is a material of high interest due to its high electrical conductivity and optical transparency, making it a key material for transparent and optoelectronics[1] e.g. microelectronic displays on touch screens. ALD of In2O3 is especially interesting as it can deposit high quality films with precise thickness, controlled composition, low impurity contents, and excellent conformality on complex substrates has been demonstrated.[10]. Amidinate and guanidinate ligands have been employed to improve the thermal stability of In precursors whilst maintaining sufficient reactivity for surface reactions This has led to the formation of homoleptic hexacoordinated In–N bonded precursors, In(III) trisformamidinate[31] (In(famd)3) 1, amidinate[35] (In(amd)3) 2 and guanidinate[36] (In(guan)3,) 3 (Fig. 1a). A surface chemical model was used to explain the faster kinetics of 1, which was thought to be due to its smaller endocyclic carbon substituent This allowed the exocyclic N-isopropyl groups of the ligand to fold up more, leading to a surface species with less surface repulsion and a more exposed In centre for its subsequent reaction with H2O.31. The deposition process was studied between 150 and 520 °C

Film characterization

Film deposition

SUMMARY AND CONCLUSIONS