Studies of Silicon Oxynitride Films Produced by Radio-Frequency Plasma Assisted Electron Cyclotron Resonance
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Studies of Silicon Oxynitride Films Produced by Radio-Frequency Plasma Assisted Electron Cyclotron Resonance J.D. Brewer, A. Raveh, and E.A. Irene Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290 ABSTRACT Single crystal silicon wafers were treated by direct oxynitridation using electron cyclotron resonance (ECR) and radio-frequency (rf) plasma with separate N2 and O2 gas sources. Fabricated layers were characterized by ex situ spectroscopic ellipsometry (SE), Auger electron spectroscopy (AES), and atomic force microscopy (AFM). The thickness and nitride/oxide ratio of silicon oxynitride layers were found to be dependent on the main process variables, namely gas pressure, bias voltage, and N2/O2 flow rate ratio. It was also observed that ECR/rf plasma is more efficient for the formation of layers with higher nitrogen content at relatively low pressure (≤ 200 mTorr) and bias voltage (-40 V) when compared to that of rf plasma alone. SE modeling provided good fitting to experimental data, while AES and AFM analyses supported SE results. The effects of fabrication conditions on the thickness and composition of the layers will be presented. INTRODUCTION Silicon oxynitride (SiOxNy) is a candidate to replace silicon dioxide (SiO2) as a gate dielectric due to its good insulating properties [1, 2], resistance against oxidation [3], and diffusion barrier properties against dopants and impurities [4]. A wide variety of techniques exist for production of SiOxNy layers, however the ability to tailor design film properties such as; nitrogen depth profile, interstitial nitrogen concentration, Si-SiO2 interfacial nitrogen concentration, and film morphology has yet to be achieved. Electrical performance of the dielectric layer is highly dependent on these film properties, thus requiring further investigation into production of SiOxNy films. Formation of SiOxNy by direct reaction with Si (rather than by CVD) is believed to proceed through NO species, however it is known that nitride formation proceeds through N+ species, while O- ions are responsible for oxidation. In order to separately control the formation of N/O ions or radicals, we have used N2 and O2 as gas sources for the formation of SiOxNy layers. The use of N2 and O2 instead of NO or N2O allows control of the concentration and form of N+ and O- species by varying substrate voltage to form a particular nitride/oxide ratio. To this end, electron cyclotron resonance/radiofrequency (ECR/rf) plasma was used to separately control homogeneous and heterogeneous reactions in the gas phase and on the Si surface. In previous studies [5, 6] it was shown that dual frequency plasma is an appropriate technique to control the amount of nitrogen on the surface and at the Si-SiO2 interface of nitrided SiO2. In addition, a large amount of bonded nitrogen was incorporated into the SiO2 network of the SiOxNy layer. The present work reports the P6.2.1
effect of plasma process parameters (gas pressure, N2/O2 flow rate ratio, and different process m
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