February_EDFA_Digital

edfas.org 1 7 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 24 NO . 1 SIMULTANEOUS LOCAL CAPACITANCE-VOLTAGE PROFILING AND DEEP LEVEL TRANSIENT SPECTROSCOPY USING TIME-RESOLVED SCANNING NONLINEAR DIELECTRIC MICROSCOPY Yasuo Cho Research Institute of Electrical Communication, Tohoku University, Japan yasuocho@riec.tohoku.ac.jp EDFAAO (2022) 1:17-28 1537-0755/$19.00 ©ASM International ® INTRODUCTION Scanning nonlinear dielectric microscopy (SNDM) can be employed to assess the surface distributions of dielectric polarization on various solids as well as the distributions of fixed electric charges and carriers in semiconductor materials and devices with high resolu- tion and good sensitivity. [1-2] This capacitance-based technique provides an exceptionally high sensitivity of 2×10 -22 F/√Hz and allows the examination of dielectric materials exhibiting even extremely weak nonlinear dielectric phenomena. Prior work used SNDM to assess the distributions of ferroelectric polarization, [3] fixed charges within a semiconductor-based flash memory device, [4] and carriers in semiconductors. This technique was also used to investigate depletion layer distribution in p/n junctions. SNDM has additionally been applied to data storage based on next-generation ultrahigh-density ferroelectric systems. [5] Earlier work resulted in a demonstration of higher- order scanning nonlinear dielectric microscopy (HO- SNDM). This process provides improved lateral resolution based on monitoring higher-order nonlinear dielectric constants. [6] This new technique was used, in turn, to devise yet another novel analytical tool, termed noncon- tact scanning nonlinear dielectricmicroscopy (NC-SNDM). Thismethod does not exhibit any loss of resolution result- ing from tip abrasion and has allowed demonstration of the first-ever dielectricmeasurements (based on analyses of atomic dipoles) with atomic-scale resolution. [7] Following this, the group at TohokuUniversity recently devised a new technique referred to as super-higher-order scanning nonlinear dielectric microscopy (SHO-SNDM), capable of accessing seventh-order harmonic nonlinear components. [8] Because SHO-SNDM responds to these higher-order harmonic components (that is, up to seventh- order differential coefficients), this method allows local- ized capacitance-voltage (CV) plots to be obtained from individual pixels. This technique is also the basis of a novel type of local deep level transient spectroscopy (local DLTS) that allows the distribution of interface traps to be visual- ized in two dimensions. [9] In addition, NC-SNDM serves as the basis for a quantitative surface potentiometry tech- nique termed scanning nonlinear dielectric potentiometry (SNDP). [10] This potentiometric method permits the local surface potentials resulting solely from surface dipole moments to be determined. Semiconductors can be evaluated using SNDM-based methods such that the dopant type (that is, p-type or n-type) can be readily determined and the distribution of thedopant canbe visualized in conjunctionwithanexpan- sive dynamic range spanning extremely low to extremely high carrier concentrations. Compound semiconductors that generate signalsmuchweaker than those obtainable from Si can also be analyzed using SNDM. Because this technique permits themeasurement of the dc capacitance component in theabsenceof voltagedifferentiation, errors related to d C /d V signal contrast reversal are avoided. [11-12] Recently, Yamagishi and Cho developed a new digital technique termed time-resolved SNDM (tr-SNDM) that provides additional capabilities. [13] This process takes advantage of advanced high-speed digital processing to provide a wider bandwidth and greater post-processing capabilities than standard SNDM systems based on ana-