Silicon/silicon dioxide interface roughness studies

The correlation between interface roughness and charges was examined in the first part of this study. Atomic force microscopy (AFM) and a newly developed area roughness function, A(RMS,D_F), which couples two roughness parameters, root-mean-square (RMS) and fractal dimension (D _F), are used to reliably and accurately characterize surface roughness. Interface charges in terms of interface trapped charge density (D_it) and fixed oxide charge (Q_f) are measured using high frequency and quasistatic capacitance-voltage methods. The results are divided into three parts where smooth, purposely roughened, and purposely smoothened Si substrates are used to make metal-oxide-semiconductor (MOS) capacitors for measurements. We report that the increases of D_it and Q_f with Si roughness are due entirely to the area increase and orientation changes resulting from roughness.; The changes effected by oxidation on purposely roughened and initially smooth Si surfaces are followed in the second part of this study via AFM and spectroscopic ellipsometry (SE) and a new technique called spectroscopic immersion ellipsometry (SIE). Initially rough and smooth Si surfaces yield opposite roughening trends upon thermal oxidation. Rough surfaces become smoother, and smooth surfaces become rougher ultimately yielding a limiting roughness of about 0.3nm RMS. A consideration of the distribution of surface roughness features phis the thermodynamics of small features are used to explain these trends. It is also reported that the changes of interface roughness are primarily the result of the oxidation reaction and not from the high temperatures.; A decrease in the amplitude of Fowler-Nordheim current oscillations (FN-CO) due to interface roughness is observed in the third part of this study for thin film (∼4nm) MOS devices, only when the interface has high spatial complexity. Previous studies using lower spatial complexity roughness have shown no measurable changes in FN-CO's resulting from the oxidation of purposely roughened Si surfaces. AFM was used to measure the interface topography, and D_F was used to describe the surface complexity while RMS roughness was used for obtaining vertical roughness information. It was found that the oscillation amplitude decreases substantially with increasing D_F but has no dependence on RMS.