Plasma-enhanced chemical vapor deposition of silicon dioxide : optimizing dielectric films through plasma characterization
Boogaard, Arjen (2011) Plasma-enhanced chemical vapor deposition of silicon dioxide : optimizing dielectric films through plasma characterization. thesis.
|Abstract:||Our first objective was to contribute to PECVD technology by exploring its capability to fabricate high‐quality silicon dioxide gate dielectrics at low substrate temperatures. Our second objective was to contribute to a more exact understanding of PECVD technology by demonstrating that an accurate description of plasma parameters and chemistry can help researchers find optimal process conditions.
We built a remote ICPECVD system to deposit thin SiO2 dielectric films. The plasma state was determined using a Langmuir probe and optical emission spectroscopy. The EEDF of Ar plasma in the reactor could largely be described by the Maxwell‐Boltzmann distribution function, but it also contained a fraction (~10‐3) of electrons which were much faster (20‐50 eV). We demonstrated that ignoring this tail would result in significant modeling and interpretation errors.
We modeled the composition of an Ar‐SiH4‐N2O ICPECVD system. We used our simulations to predict the influence of the SiH4/N2O gas‐flow ratio and total gas pressure on the film’s electrical properties. We deposited silicon dioxide films in plasma conditions similar to those in the model. It appeared that the predictions we made through the model could be verified experimentally.
Optimization led to the deposition of films with a high dielectric quality at a deposition temperature of only 150°C. The films exhibited low leakage currents and a low midgap‐Dit. We showed the apllicability of our silicon dioxide films to low‐temperature TFTs by demonstrating their competitive mobility values and low off‐currents.
The charge of our ICPECVD oxides appeared to be negative and a function of layer thickness. We demonstrated that two mechanisms contributed to the film growth and charge formation, namely plasma oxidation of the silicon substrate and chemical vapor deposition. We suggest that the first nm‐range of oxide thickness is formed by plasma oxidation that added a negative charge to the interfacial oxide layer, while the CVD component added a positive charge to the bulk oxide.
We conclude that measuring actual plasma parameters in combination with an accurate description of plasma chemistry can help researchers reach optimal process conditions. The described method enables the fabrication of high‐quality silicon dioxide gate dielectrics using ICPECVD technology.
Electrical Engineering, Mathematics and Computer Science (EEMCS)
|Link to this item:||http://purl.utwente.nl/publications/75577|
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