Quantitative ultra shallow dopant profile measurement by scanning capacitance microscope

Abstract

This paper compares scanning capacitance microscope (SCM) signals of an n-MOS transistor implanted with arsenic ions at an energy as low as 5 keV with a vertical secondary ion mass spectroscopy (SIMS) profile of the same device. Then, it describes SCM measurement by the application of a DC voltage sufficient to compensate for the flat band shift caused by the interaction between the probe of a conductive scanning probe microscope (SPM) and a silicon surface. To acquire the exact impurity distribution beneath a silicon surface, the SIMS measurement was carried out at a primary ion energy of less than 1 keV. As a result, the calibration of SCM signals using SIMS data was accomplished in the ultra shallow region near the silicon surface. It was also confirmed that the formalism based on the depletion approximation applies in this region. Using this formalism, we show that, at concentrations around 10 1 8 cm - 3 , SCM enables quantitative two-dimensional dopant profiling near the source/drain extension at a resolution of better than 10 nm. Moreover, by optimizing the sample preparation and measurement conditions, it is also possible to analyze a sub-μm gate transistor with a 60 nm channel length and investigate the complex dopant distribution in the source/drain region, including the edge of the shallow trench isolation.