Kurt Rubin and Yongliang Yang 1
Region 1 Location Carrier
3.4. Additional Examples
sMIM is a relatively new nanoscale electrical property characterization technique and continues to evolve and be applied to a growing set of materials, devices and applications.
In addition to being used to characterize dielectric constants and doping concentrations it is also being used to understand 2D material systems such as dichalcogenides: MoS2 [13], WSe2 [14], Phosphorene[15] and graphene [16] for electronic applications. Ferroelectric materials are also a material class that is gaining interest for use in next generation microelectronics and memory systems [17, 18]. Fig. 3.16 shows an example of spontaneously induced domains written using an sMIM probe with an applied bias and then being imaged simultaneously with piezo-force microscopy and sMIM [19].
Fig. 3.16. sMIM reveals that spontaneous and recorded domain walls in thin films of lead zirconate and bismuth ferrite exhibit large conductance at microwave frequencies despite being insulating at d.c. Same tip was used for both writing the domains and measuring the electrical properties of domains and domain walls.
Fig. 3.17 shows a case utilizing the ability of sMIM to image subsurface features that are isolated towards development of quantum computing devices [20]. STM lithography was used to write 10 nm features onto a flash cleaned silicon substrate then the sample was encapsulated with polysilicon. Individual structures are isolated from each other. sMIM is a method that can image and resolve the features and enable researchers to connect the subsystems to construct working devices.
sMIM has also been integrated into extreme environments such as cryogenic systems with high magnetic field [21-25]. There are now turnkey commercial systems where researchers can purchase a system and image below 2 K and up to 12 T. Fig. 3.18 shows
an experiment measuring the quantum Hall edge conduction in a graphene film at cryogenic temperatures and high magnetic field [23]. The device structure is fabricated as a FET that can be excited using the backgate electrode or using the sMIM probe.
Fig. 3.17. (a) Cross-sectional view of the donor structure and imaging sMIM tip, (b) top-down sMIM capacitive image of a buried phosphine device showing the fan out to microscale bond pads and (c) zoom on the nanoscale donor wire in (b) in the dashed square. The STM patterned structure is overlaid on (c) in white. The white arrow indicates the smallest gap in the structure [20].
Fig. 3.18. (a) cross-sectional view of the donor structure and imaging sMIM tip, (b) top-down sMIM capacitive image of a buried phosphine device showing the fan out to microscale bond pads and (c) zoom on the nanoscale donor wire in (b) in the dashed square. The STM patterned structure is overlaid on (c) in white. The white arrow indicates the smallest gap in the structure [23].
As continued interest on extreme environments for investigating fundamental physics on systems where traditional transport methods are not applicable, sMIM has been shown to be a valuable method for further investigation of these materials systems.
3.5. Conclusion
Scanning microwave impedance microscopy is a non-destructive technique to image, measure and characterize electrical properties spatially resolved at the nanoscale as well as at large feature sizes. By leveraging near-field imaging it achieves nanometer-scale lateral resolutions that are orders of magnitude smaller than the operating wavelength and with high sensitivity. It is being used in a broad and expanding range of commercial and scientific applications. Being a probe-based technique, it is well matched to investigate failures of semiconductor devices. There is growing use of sMIM to characterize 3D, 2D and 1D materials and devices at room and cryogenic temperatures. It can measure structures that are of interest to both classical and quantum devices. It can characterize surface, buried and bulk structures.
In this article we have illustrated how sMIM can be used to learn about dielectric and semiconductor properties. Combining measurements with simulations, we have illustrated how one can characterize dielectric constant and dielectric thickness variations. The technique is viable for a wide range of dielectric properties including conventional oxides and nitrides and low-k and high-k material; as well as exploratory materials. We have also illustrated a way to characterize doping structures and concentrations over many orders of magnitude of doping concentration together with determining polarity in semiconductor materials and devices. The sample in this example was silicon, but the technique is applicable to wide band-gap materials, such as those of interest to energy and lighting applications. Leveraging the small geometry of the probe, the technique is applicable to both bulk materials and device geometries.
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