Measurement of substrate impurity fluctuation using CCD image sensor

Abstract

It is well known that saturation signal level of CCD image sensor with VOD (Vertical Overflow Drain) photo diode varies with substrate impurity density. However, analytical results between them are not obtained yet. In this paper, the saturation signal level is calculated using drift-diffusion model as a function of the photo diode structure and operation conditions. Using this method, impurity fluctuations at the peripheral of CZ and MCZ and epitaxial wafer were ±11%, ±16% and ±6%, respective1y and those at the center were ±7% and ±9% and ±6%, respectively. Distinctive features of impurity fluctuation pattern for these wafers were clarified. The minimum detectable impurity fluctuation reaches to ±2%.