Noise in scanning capacitance microscopy measurements

Scanning capacitance microscopy (SCM) is a powerful tool for two-dimensiona l (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 source s during SCM measurements are capacitance sensor noise and oxide-semiconduc tor surface induced noise. Fur adequate tip size, the dominant noise in SCM measurements is caused by variations in the quality of surface. On as-poli shed surfaces, nonstationary noise is observed. This noise is likely caused by the variations in the density of oxide traps. Tip induced charging of t hese traps and local variations or fluctuations in discharge time during SC M imaging cause the noise level and noise pattern to be different from imag e co image. Heat treatment under ultra-violet irradiation or in a hydrogen ambient is found to be an effective way to reduce or even eliminate this ty pe of SCM noise. Stationary surface noise is mostly created by the variatio ns in the oxide thickness, This type of noise correlates with topographic r oughness and is very consistent during SCM measurements. By reducing the to pographic roughness, the stationary surface noise may be reduced to the lev el of similar to 10(-2) of the depletion SCM signal for typical experimenta l conditions. It is shown that the capacitance sensor noise depends on the capacitance sensor tuning parameters and under proper conditions can be red uced to a negligible level for standard probe tips used in SCM measurements . (C) 2000 American Vacuum Society. [S0734-211X(00)04403-6].