Local deep level transient spectroscopy using super-higher-order scanning nonlinear dielectric microscopy and its application to imaging two-dimensional distribution of SiO2/SiC interface traps

Abstract

We propose a new technique called local deep level transient spectroscopy (local-DLTS), which utilizes scanning nonlinear dielectric microscopy to analyze oxide/semiconductor interface traps, and validate the method by investigating thermally oxidized silicon carbide wafers. Measurements of C-t curves demonstrate the capability of distinguishing sample-to-sample differences in the trap density. Furthermore, the DC bias dependence of the time constant and the local-DLTS signal intensity are investigated, and the results agree to characteristic of interface traps. In addition, the Dit values for the examined samples are estimated from the local-DLTS signals and compared with results obtained using the conventional high-low method. The comparison reveals that the Dit values obtained by the two methods are of the same order of magnitude. Finally, two-dimensional (2D) distributions of local-DLTS signals are obtained, which show substantial intensity variations resulting in random 2D patterns. The 2D distribution of the local-DLTS signal depends on the time constant, which may be due to the coexistence of multiple types of traps with different capture cross sections.

Simultaneous Interface Defect Density and Differential Capacitance Imaging by Time-Resolved Scanning Nonlinear Dielectric Microscopy

“…In this setup, only one particular frequency component corresponding to the modulation frequency is extracted and physical information included in the sensor signal are largely omitted. Therefore, an improved setup called super-higher-order SNDM has been proposed to obtain rich information by utilizing multiple higher harmonic components and actually permitted various extended measurement techniques [8]. However, because of limited frequency bandwidth and complicated frequency characteristics of the analog setup, these frequency domain approaches basically suffer from narrow measurement bandwidth and signal distortion.…”

“…In order to give the microscopic insights on these problems, scanning nonlinear dielectric microscopy (SNDM) [4][5][6] has recently been applied for the investigation of the SiO 2 /SiC interfaces [7][8][9][10][11]. SNDM is a microwave based scanning probe microscopy method with remarkably high sensitivity to the variation in the tip-sample capacitance.…”

“…For better understanding the relationship between the dC/dV images and interface quality, here we investigate the cross-correlation between dC/dV and D it images. Nanoscale D it imaging has recently become possible by local deep level transient spectroscopy (local DLTS) based on SNDM [8,9]. Here, we use time-resolved SNDM (tr-SNDM) for the simultaneous local DLTS and dC/dV imaging.…”

Two-dimensional defect mapping of the SiO2/4H−SiC interface

“…Local-DLTS measurements were performed using a commercial contact-mode AFM (Bruker Icon) with a home-built scanning nonlinear dielectric microscopy (SNDM) probe oscillating at a frequency of 1 GHz [see Fig. 6(a)] [25,26]. The radius of the Pt-coated probing tip forming a capacitor with the SiO 2 /SiC stack was 150 nm and the scan size was 1 μm × 1 μm.…”

“…In order to obtain quantitative information on the defects related to the surface morphology of off-axially grown 4H-C, a newly developed modification of the conventional DLTS technique was employed which allows the spatial mapping of interface defect densities with a sub-μm resolution [25]. The working principle of local-DLTS is schematically depicted in Fig.…”