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# Spectroellipsometric detection of silicon substrate damage caused by radiofrequency sputtering of niobium oxide

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## Abstract

Substrate surface damage induced by deposition of metal atoms by radiofrequency (rf) sputtering or ion beam sputtering onto single-crystalline silicon (c-Si) surface has been characterized earlier by electrical measurements. The question arises whether it is possible to characterize surface damage using spectroscopic ellipsometry (SE). In our experiments niobium oxide layers were deposited by rf sputtering on c-Si substrates in gas mixture of oxygen and argon. Multiple angle of incidence spectroscopic ellipsometry measurements were performed, a four-layer optical model (surface roughness layer, niobium oxide layer, native silicon oxide layer and ion implantation-amorphized silicon [i-a-Si] layer on a c-Si substrate) was created in order to evaluate the spectra. The evaluations yielded thicknesses of several nm for the i-a-Si layer. Better agreement could be achieved between the measured and the generated spectra by inserting a mixed layer (with components of c-Si and i-a-Si applying the effective medium approximation) between the silicon oxide layer and the c-Si substrate. High depth resolution Rutherford backscattering (RBS) measurements were performed to investigate the interface disorder between the deposited niobium oxide layer and the c-Si substrate. Atomic resolution cross-sectional transmission electron microscopy investigation was applied to visualize the details of the damaged subsurface region of the substrate.

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... The inset shows the extracted charge profile as a function of depth, (e) TLM measurements performed pre and post deposition of high-k dielectric showing the increase in sheet resistance and contact resistance.Device CharacteristicsCapacitance-voltage (C-V) and transfer length measurements (TLM) were performed to estimate the effect of sputtering the high-k gate dielectric at high temperature (670 ℃) on the channel charge density, mobility and contact resistance by comparing these measurements pre and post deposition. Sputtering involves deposition using high energy atomic species and can cause significant damage to the semiconductor surface35,36 . C-V measurements performed pre dielectric deposition show a total charge density of 1.8 ×10 13 cm -2 in the channel as shown inFigure 3(c). ...
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