Negative Charge in Plasma Oxidized SiO2 Layers
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|Abstract:||Silicon dioxide (SiO2) gate dielectric layers (4-60 nm thick) were deposited (0.6 nm/min) on n-type Si by inductively-coupled plasmaenhanced chemical vapor deposition (ICPECVD) in strongly diluted silane plasmas at 150°C . In contrast to the well-accepted positive charge for thermally grown SiO2, the net oxide charge was negative and a function of the layer thickness. Our experiments suggested that the negative charge was created due to unavoidable oxidation of the silicon surface by plasma species, and the CVD component adding a positive space charge to the deposited oxide. The net charge was negative under process conditions where plasma oxidation played a major role. Such conditions included low deposition rates and relatively thin grown layers. Additional measurements showed that the negative charge in SiO2 also persisted on p-type substrates. We suggest that plasma oxidation of the silicon surface results in SiO2 layers with a surplus of oxygen.
This surplus of oxygen is able to accumulate a negative charge. This assumption is addressed in this paper by a review of earlier work on silicon oxidation, and by a first series of experiments wherein oxygen is implanted into thermal SiO2. It is shown that the implantation can result in a negative charge to the bulk oxide layer. The effect of the negative charge on the flatband voltage can be described by the implantation profile.
|Copyright:||© 2011 The Electrochemical Society|
Electrical Engineering, Mathematics and Computer Science (EEMCS)
|Link to this item:||http://purl.utwente.nl/publications/77760|
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