Noise in scanning capacitance microscopy measurements

Abstract

Scanning capacitance microscopy (SCM) is a powerful tool for two-dimensional (2D) dopant/carrier profiling. Currently noise limits the accuracy of 2D dopant profiles obtained by SCM. In an effort to reduce noise, a systematic analysis of different SCM noise sources is provided. The main noise sources during SCM measurements are capacitance sensor noise and oxide–semiconductor surface induced noise. For adequate tip size, the dominant noise in SCM measurements is caused by variations in the quality of surface. On as-polished surfaces, nonstationary noise is observed. This noise is likely caused by the variations in the density of oxide traps. Tip induced charging of these traps and local variations or fluctuations in discharge time during SCM imaging cause the noise level and noise pattern to be different from image to image. Heat treatment under ultraviolet irradiation or in a hydrogen ambient is found to be an effective way to reduce or even eliminate this type of SCM noise. Stationary surface noise is mostly created by the variations in the oxide thickness. This type of noise correlates with topographic roughness and is very consistent during SCM measurements. By reducing the topographic roughness, the stationary surface noise may be reduced to the level of ∼10−2 of the depletion SCM signal for typical experimental conditions. It is shown that the capacitance sensor noise depends on the capacitance sensor tuning parameters and under proper conditions can be reduced to a negligible level for standard probe tips used in SCM measurements.