The continued miniaturization of electronic devices containing dielectric materials has increased the impact of nanoscale permittivity distributions on device characteristics. As a result, more precise control of process damage is required to ensure the fabrication of reliable highly integrated devices, and the nanoscale analysis of permittivity has become important. Permittivity assessments over nanoscale regions require the measurement of capacitance with sufficiently high sensitivity. Various techniques for the measurement of local capacitance based on scanning probe microscopy (SPM) have been proposed to date, including scanning capacitance microscopy (SCM), scanning microwave microscopy (SMM), microwave impedance microscopy (MIM) and scanning nonlinear dielectric microscopy (SNDM). SNDM is an especially useful technique as it is highly sensitive to variations in capacitance on the order of 10−22 F/√Hz. As a result, SNDM can detect capacitance variations even when employing extremely sharp probe tips, and so is a very effective means of obtaining improved spatial resolution.
Conventional SNDM is typically used to determine nonlinear dielectric permittivity and to visualize dielectric anisotropy in ferroelectrics and semiconductors. In contrast, there have been only a few reports concerning linear permittivity imaging using SNDM. Herein, we propose a novel method for linear permittivity imaging, termed ∂C/∂z -mode SNDM (∂C/∂z-SNDM), that substantially reduces the effects of stray capacitance and enables quantitative imaging with high spatial resolution.
∂C/∂z-SNDM technique employs probe-height modulation to suppress disturbances originating from stray capacitance and to improve measurement stability. This method allows local permittivity distributions to be examined with extremely low noise levels (approximately 0.01 aF) by virtue of the highly sensitive probe. A cross-section of a multilayer oxide film was visualized using ∂C/∂z-SNDM as a demonstration, and numerical simulations of the response signals were conducted. Moreover, the beneficial aspects of higher-harmonic response imaging are discussed herein, taking into account assessments of spatial resolution and quantitation.
