Low-Temperature Plasma-Enhanced Atomic Layer Deposition of SiO2 Using Carbon Dioxide

Zhen Zhu,Kenichiro Mizohata,Hele Savin,Harri Lipsanen,Saoussen Merdes,Marisa Di Sabatino,Perttu Sippola,Oili M E Ylivaara,Chiara Modanese

doi:10.1186/s11671-019-2889-y

Abstract

In this work, we report the successful growth of high-quality SiO2 films by low-temperature plasma-enhanced atomic layer deposition using an oxidant which is compatible with moisture/oxygen sensitive materials. The SiO2 films were grown at 90 °C using CO2 and Bis(tertiary-butylamino)silane as process precursors. Growth, chemical composition, density, optical properties, and residual stress of SiO2 films were investigated. SiO2 films having a saturated growth-per-cycle of ~ 1.15 Å/cycle showed a density of ~ 2.1 g/cm3, a refractive index of ~ 1.46 at a wavelength of 632 nm, and a low tensile residual stress of ~ 30 MPa. Furthermore, the films showed low impurity levels with bulk concentrations of ~ 2.4 and ~ 0.17 at. % for hydrogen and nitrogen, respectively, whereas the carbon content was found to be below the measurement limit of time-of-flight elastic recoil detection analysis. These results demonstrate that CO2 is a promising oxidizing precursor for moisture/oxygen sensitive materials related plasma-enhanced atomic layer deposition processes.

Highlights

While SiO2 thin films can be grown by several methods such as thermal oxidation, plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD), atomic layer deposition (ALD) offers the exceptional advantage of combining precise film thickness control, high uniformity, and conformality [9–11]
Film Preparation plasma-enhanced atomic layer deposition (PEALD) SiO2 films were grown on Si(100) and sapphire substrates at 90 °C using CO2 (99.5%, Air Products) plasma as oxygen source and bis(tertiary-butylamino)silane (BTBAS) (97%, Strem Chemicals) as Si precursor [22]
Film Growth The dependence of the SiO2 film GPC on the BTBAS pulse and purge time was investigated during the oxidation step with a fixed plasma power of 180 W, a CO2 plasma exposure time of 3 s, and a CO2 plasma purge time of 2 s

Summary

Introduction

SiO2 is a widely used material for applications such as microelectronics [1, 2], microelectromechanical systems [3, 4], photovoltaics [5, 6], and optics [7, 8]. While SiO2 thin films can be grown by several methods such as thermal oxidation, plasma-enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD), atomic layer deposition (ALD) offers the exceptional advantage of combining precise film thickness control, high uniformity, and conformality [9–11]. Many ALD processes, with various Si precursors (chlorosilanes or aminosilanes) and oxidants (H2O, H2O2, or O3), were developed for the growth of SiO2. Those processes usually require relatively high temperatures (> 150 °C) [12– 16]. We report the development of a CO2-based PEALD process for SiO2 films at 90 °C. We report the chemical composition, structural and optical properties, and residual stress analysis of the films

Methods

Results

Conclusion