Low pressure microwave plasma process from Zr and Ti metalorganicprecursors: A comparative study of metal oxide and metal/oxide/silica films
Résumé
In this work, metal oxide and metal oxide/silica « composite » thin films were obtained byPECV in multi-dipolar ECR Plasma reactor from gas mixture composed of oxygen gas and metalorganicprecursors. [Zirconium (IV) tert-Butoxide (ZTB, ZrO4C16H36) and Titanium (IV) Isopropoxide (TTIP,TiO4C12H28)]. To investigate the plasma behavior, OES, FTIR and MS have been employed while thecharacteristics of the deposited thin films have been examined by FTIR, XPS, SEM, AFM, X-rayreflectivity (XRR) and ellipsometry porosimetry (EP).In the first part of the work, the study focuses on thin film characteristics as a function ofO2/precursor ratio. As O2/precursor ratio increased, analyzed properties evolve similarly in bothzirconium and titanium oxide films. Composition of the films progresses from organic to almostinorganic with the addition of oxygen to plasma gas mixture. The growth mode evolves fromhomogeneous to columnar in highly oxidized plasma. From a fundamental point of view, columnsobtained experimentally in ZTB and TTIP were compared with those obtained by theoretical simulation(Monte Carlo method) in order to understand the observed morphological differences (column width).Further, we investigated the influence of the total gas pressure of plasma gas mixture composedof O2 (95%)/metalorganic precursor (5%) on thin film growth. Chemical composition of the films doesnot change drastically with the increase in pressure. In the case of ZTB, total gas pressure has a stronginfluence on the morphological characteristics: columnar growth disappears at pressures above 8 mTorr.This phenomenon was not observed in films deposited in TTIP plasma.In the third part of this work we have demonstrated the possibility of synthesizing ZrSiwOxCyHzand TiSiwOxCyHz homogeneous thin composite films by simultaneously introducing a metalorganicprecursor and an organosilicon precursor [Hexamethyldisiloxane (HMDSO, OSi2C6H18)] into thereactor. Increase in the fraction of HMDSO in the plasma gas mixture induces a change in growth modefrom columnar growth mode (low HMDSO content) to uniform growth mode (higher HMDSO content).This work has highlighted the various possibilities of obtaining a large panel of thin film properties interms of density, optical index and porosity.
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