We present fundamentals and representative examples of fast non-contact full wafer characterization of oxide and silicon defects induced by plasma and thermal processing steps. Parametric and distribution results are obtained using the recently introduced 'COCOS' and surface doping methodologies that enhance contact potential difference and surface photovoltage methods. The measured parameters include flatband voltage, interface trap density, soft breakdown, oxide surface potential and recovery lifetime. We studied the effects of plasma metal etching and ashing, thermal oxidation, anneal ambients and nitridation methods.
Recent developments in SiO2 diagnostics have opened a possibility for measuring the mobile charge in oxide without the expensive and time consuming preparation and analysis of MOS test structures. A key element of the new approach is that corona charge is deposited directly onto the SiO2, over the entire wafer surface, to create an electric field needed for ion drift. Mobile charge density is determined by mapping of the oxide voltage change after temperature stress. As a result, whole-wafer mobile charge maps with over 6000 points may be acquired in about ten minutes at a sensitivity below 1010 c-2 for 100 nm oxides. A distinctive feature of the new technique is that the measurement of oxide voltage shift is done under strong inversion or accumulation and is insensitive to interface traps and oxide fixed charge. In other methods based on the flat band voltage shift these charges near the SiO2-Si interface are a major limitation.
We discuss the determination of oxide charge from simultaneous noncontact measurement of the surface potential barrier, Vs, (via surface photovoltage) and the voltage drop across the oxide, Vox, (via contact potential vibrating probe). These two measurements enable us to separate the contributions from total charge and oxide charge. In combination with corona charging and low temperature stress, this approach can be used for wafer-scale determination of the mobile Na+ concentration. The principles of the approach are presented and typical results are given which contrast the effects of ion drift and charge injection in the oxide. Experimental results also illustrate the noncontact, wafer-scale mapping of the mobile ion distribution.
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