Atomic layer deposition of sodium and potassium oxides: evaluation of precursors and deposition of thin films.

E Østreng,H H Sønsteby,S Øien,H Fjellvåg,O Nilsen

doi:10.1039/c4dt01930j

E Østreng, H H Sønsteby + Show 3 more

Open Access

https://doi.org/10.1039/c4dt01930j

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Abstract

Thin films of sodium and potassium oxides have for the first time been deposited using atomic layer deposition. Sodium and potassium complexes of tert-butanol, trimethylsilanol and hexamethyldisilazide have been evaluated as precursors by characterising their thermal properties as well as tested in applications for thin film depositions. Out of these, sodium and potassium tert-butoxide and sodium trimethylsilanolate and hexamethyldisilazide were further tested as precursors together with the Al(CH3)3 + H2O/O3 process to form aluminates and together with ozone to form silicates. Sodium and potassium tert-butoxide and sodium trimethylsilanolate showed self-limiting growth and proved useable at deposition temperatures from 225 to 375 or 300 °C, respectively. The crystal structures of NaO(t)Bu and KO(t)Bu were determined by single crystal diffraction revealing hexamer- and tetramer structures, respectively. The current work demonstrates the suitability of the ALD technique to deposit thin films containing alkaline elements even at 8'' wafer scale.

Highlights

Thin films of sodium and potassium oxides have for the first time been deposited using atomic layer deposition
Atomic layer deposition (ALD) is a versatile thin film deposition technique shown to be useable for most elements in the periodic table.[1]
Alkali metal compounds have previously been deposited as thin films by techniques such as pulsed layer deposition, chemical vapour deposition (CVD) and chemical solution deposition, in addition to the present examples of using ALD.[20,21,22,23,24,25]

Summary

Introduction

Atomic layer deposition (ALD) is a versatile thin film deposition technique shown to be useable for most elements in the periodic table.[1]. Sodium and potassium are constituents in numerous alternative functional materials with high technological potential, such as thermoelectrics (e.g. NaxCoO2), superconductors (e.g. NaxCoO2·H2O), dielectrics (e.g. NaNbO3) and piezoelectrics (K1−xNaxNbO3).[13,14,15,16,17] Recently, sodium has received attention in less expensive sodium ion batteries as alternatives to lithium ion batteries.[18,19] Alkali metal compounds have previously been deposited as thin films by techniques such as pulsed layer deposition, chemical vapour deposition (CVD) and chemical solution deposition, in addition to the present examples of using ALD.[20,21,22,23,24,25] The reported span in precursors for deposition of sodium and potassium oxides is somewhat limited. Silicates were chosen as the trimethyl silanolates and hexamethyldisilazides could potentially be used as single source precursors with ozone for both the alkali metal and silicon

Experimental

Evaluation of precursors

Conclusions