Phosphites as precursors in atomic layer deposition thin film synthesis

Kristian B Kvamme,Timo Sajavaara,Ola Nilsen,Amund Ruud,Kristian Weibye

doi:10.1116/6.0000844

Abstract

We here demonstrate a new route for deposition of phosphorous based materials by atomic layer deposition (ALD) using the phosphites Me3PO3 or Et3PO3 as precursors. These contain phosphorous in the oxidation state (III) and are open for deposition of reduced phases by ALD. We have investigated their applicability for the synthesis of LiPO and AlPO materials and characterized their growth by means of in situ quartz crystal microbalance. Phosphites are good alternatives to the established phosphate-based synthesis routes as they have high vapor pressure and are compatible with water as a coreactant during deposition. The deposited materials have been characterized using XPS, x-ray fluorescence, and ion beam analysis for composition analysis, spectroscopic ellipsometry for thickness, and FTIR for local structure.

Highlights

Phosphate materials have the ability to form redox inactive polymeric structures of polyanions with lithium as a charge compensating cation
We have investigated their applicability for the synthesis of lithium phosphite (LiPO) and Aluminum phosphite (AlPO) materials and characterized their growth by means of in situ quartz crystal microbalance
Et3PO3 seems to reach saturation around the end of the pulse, while the Me3PO3 pulse has a high mass change throughout the pulse followed by a large mass loss during the following purge. This may be an indication of reaction with absorbed water into the bulk of the film from the water pulse, as reported for LiOH deposited by atomic layer deposition (ALD).[19]

Summary

Introduction

Phosphate materials have the ability to form redox inactive polymeric structures of polyanions with lithium as a charge compensating cation. When combined with aluminum in a near equal ratio, they can form complex porous structures resembling zeolites, known as AlPO materials.[1] Similar structures may be formed from polyanions such as silicates, sulfates, borates, and even transition element polyanions such as vanadates, molybdates, niobates, and many more.[2] The interactions between the polyanion and the charge compensating cation, Li in LiPON or Fe in FePO4, will be affected by the covalent character of the polyanion itself This can be controlled by the choice of central atom, here phosphorus, and its coordinates. Three of the vertices in the phosphite bond to electronegative elements such as oxygen, while the remaining may bond directly to hydrogen, such as in phosphite acid, or occupy nonbonding electrons, such as for the phosphite precursors used in this study

Results

Discussion

Conclusion