Carrier profiling with fast Fourier transform scanning spreading resistance microscopy: A case study for Ge, GaAs, InGaAs, and InP

Quantitative scanning spreading resistance microscopy is currently a powerful method for carrier profiling in scaled nanoelectronic devices. Faced with the further reduction of dimensions and increasing architecture complexity, a force modulation method was developed to address the challenges associated with parasitic series resistances. Called fast Fourier transform scanning spreading resistance microscopy, the method has been shown to increase dynamic range when profiling Si devices and retains the doping contrast even in the presence of a series resistance. In this work we systematically investigate the potential of fast Fourier transform scanning spreading resistance microscopy for Ge, GaAs, InP, and InGaAs, presenting a quantitative comparison with Si as well as a more in-depth understanding of the capabilities and limitations of the method. Our results show that both GaAs and InP greatly benefit, with a significantly larger dynamic range and the ability to filter undesired series resistances. Doping concentration contrast in the presence of a series resistance can also be maintained in Ge but with high noise. For InGaAs there are only minor benefits. These findings prove that fast Fourier transform scanning spreading resistance microscopy is a valuable extension to regular scanning spreading resistance microscopy for more accurate carrier profiling in Si and non-Si materials, especially in architectures where parasitic series resistances are present.

Nanoscale Electrical Degradation of Silicon-Carbon Composite Anode Materials for Lithium-Ion Batteries

High-performance lithium-ion batteries (LIBs) are in increasing demand for a variety of applications in rapidly growing energy-related fields including electric vehicles. To develop high-performance LIBs, it is necessary to comprehensively understand the degradation mechanism of the LIB electrodes. From this viewpoint, it is crucial to investigate how the electrical properties of LIB electrodes change under charging and discharging. Here, we probe the local electrical properties of LIB electrodes with nanoscale resolution by scanning spreading resistance microscopy (SSRM). Via quantitative and comparative SSRM measurements on pristine and degraded LIB anodes of Si-C composites blended with graphite (Gr) particles, the electrical degradation of the LIB anodes is visualized. The electrical conductivity of the Si-C composite particles considerably degraded over 300 cycles of charging and discharging, whereas the Gr particles maintained their conductivity.

Outwitting the series resistance in scanning spreading resistance microscopy

The performance of nanoelectronics devices critically depends on the distribution of active dopants inside these structures. For this reason, dopant profiling has been defined as one of the major metrology challenges by the international technology roadmap of semiconductors. Scanning spreading resistance microscopy (SSRM) has evolved as one of the most viable approaches over the last decade due to its excellent spatial resolution, sensitivity and quantification accuracy. However, in case of advanced device architectures like fins and nanowires a proper measurement of the spreading resistance is often hampered by the increasing impact of parasitic series resistances (e.g. bulk series resistance) arising from the confined nature of the aforementioned structures. In order to overcome this limitation we report in this paper the development and implementation of a novel SSRM mode (fast Fourier transform-SSRM: FFT-SSRM) which essentially decouples the spreading resistance from parasitic series resistance components. We show that this can be achieved by a force modulation (leading to a modulated spreading resistance signal) in combination with a lock-in deconvolution concept. In this paper we first introduce the principle of operation of the technique. We discuss in detail the underlying physical mechanisms as well as the technical implementation on a state-of-the-art atomic force microscope (AFM). We demonstrate the performance of FFT-SSRM and its ability to remove substantial series resistance components in practice. Eventually, the possibility of decoupling the spreading resistance from the intrinsic probe resistance will be demonstrated and discussed.