Scanning capacitance microscopy

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Scanning capacitance microscopy (SCM) is a variety of scanning probe microscopy in which a narrow probe electrode is positioned in contact or close proximity of a sample's surface and scanned. SCM characterizes the surface of the sample using information obtained from the change in electrostatic capacitance between the surface and the probe.

Contents

History

The name Scanning Capacitance Microscopy was first used to describe a quality control tool for the RCA/CED (Capacitance Electronic Disc), [1] a video disk technology that was a predecessor of the DVD. It has since been adapted for use in combination with scanned probe microscopes for measuring other systems and materials with semiconductor doping profiling being the most prevalent.

SCM applied to semiconductors uses an ultra-sharp conducting probe (often Pt/Ir or Co/Cr thin film metal coating applied to an etched silicon probe) to form a metal-insulator-semiconductor (MIS/MOS) capacitor with a semiconductor sample if a native oxide is present. When no oxide is present, a Schottky capacitor is formed. With the probe and surface in contact, a bias applied between the tip and sample will generate capacitance variations between the tip and sample. The capacitance microscopy method developed by Williams et al. used the RCA video disk capacitance sensor connected to the probe to detect the tiny changes in semiconductor surface capacitance (attofarads to femptofarads). The tip is then scanned across the semiconductor's surface in while the tip's height is controlled by conventional contact force feedback.

By applying an alternating bias to the metal-coated probe, carriers are alternately accumulated and depleted within the semiconductor's surface layers, changing the tip-sample capacitance. The magnitude of this change in capacitance with the applied voltage gives information about the concentration of carriers (SCM amplitude data), whereas the difference in phase between the capacitance change and the applied, alternating bias carries information about the sign of the charge carriers (SCM phase data). Because SCM functions even through an insulating layer, a finite conductivity is not required to measure the electrical properties.

Resolution

On the conducting surfaces, the resolution limit is estimated as 2 nm. [2] For the high resolution, the quick analysis of capacitance of a capacitor with rough electrode is required. [3] [4] This SCM resolution is an order of magnitude better than that estimated for the atomic nanoscope; however, as other kinds of the probe microscopy, SCM requires careful preparation of the analyzed surface, which is supposed to be almost flat.

Applications

Owing to the high spatial resolution of SCM, [2] it is a useful nanospectroscopy characterization tool. Some applications of the SCM technique involve mapping the dopant profile in a semiconductor device on a 10 nm scale, [5] quantification of the local dielectric properties in hafnium-based high-k dielectric films grown by an atomic layer deposition method [6] and the study of the room temperature resonant electronic structure of individual germanium quantum dot with different shapes. [7] The high sensitivity of dynamical scanning capacitance microscopy, [8] in which the capacitance signal is modulated periodically by the tip motion of the atomic force microscope (AFM), was used to image compressible and incompressible strips in a two-dimensional electron gas (2DEG) buried 50 nm below an insulating layer in a large magnetic field and at cryogenic temperatures. [9]

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Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.

Scanning probe microscopy (SPM) is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded in 1981, with the invention of the scanning tunneling microscope, an instrument for imaging surfaces at the atomic level. The first successful scanning tunneling microscope experiment was done by Gerd Binnig and Heinrich Rohrer. The key to their success was using a feedback loop to regulate gap distance between the sample and the probe.

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Near-field scanning optical microscope

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Conductive atomic force microscopy

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NanoWorld

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Non-contact atomic force microscopy

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A probe tip is an instrument used in scanning probe microscopes (SPM) to scan the surface of a sample and make nano-scale images of surfaces and structures. The probe tip is mounted on the end of a cantilever and can be as sharp as a single atom. In microscopy, probe tip geometry and the composition of both the tip and the surface being probed directly affect resolution and imaging quality. Tip size and shape are extremely important in monitoring and detecting interactions between surfaces. SPMs can precisely measure electrostatic forces, magnetic forces, chemical bonding, Van der Waals forces, and capillary forces. SPMs can also reveal the morphology and topography of a surface.

Multi-tip scanning tunneling microscopy

Multi-tip scanning tunneling microscopy extends scanning tunneling microscopy (STM) from imaging to dedicated electrical measurements at the nanoscale like a ″multimeter at the nanoscale″. In materials science, nanoscience, and nanotechnology, it is desirable to measure electrical properties at a particular position of the sample. For this purpose, multi-tip STMs in which several tips are operated independently have been developed. Apart from imaging the sample, the tips of a multi-tip STM are used to form contacts to the sample at desired locations and to perform local electrical measurements.

References

  1. ↑ Matey, JR; J Blanc (1985). "Scanning Capacitance Microscopy". Journal of Applied Physics. 57 (5): 1437–1444. Bibcode:1985JAP....57.1437M. doi:10.1063/1.334506.
  2. 1 2 Lanyi S; Hruskovic M (2003). "The resolution limit of scanning capacitance microscopes". Journal of Physics D. 36 (5): 598–602. doi:10.1088/0022-3727/36/5/326.
  3. ↑ N.C.Bruce; A.Garcia-Valenzuela, D.Kouznetsov (2000). "The lateral resolution limit for imaging periodic conducting surfaces in capacitive microscopy". Journal of Physics D. 33 (22): 2890–2898. Bibcode:2000JPhD...33.2890B. doi:10.1088/0022-3727/33/22/305.
  4. ↑ N.C.Bruce; A.Garcia-Valenzuela, D.Kouznetsov (1999). "Rough-surface capacitor: approximations of the capacitance with elementary functions". Journal of Physics D. 32 (20): 2692–2702. Bibcode:1999JPhD...32.2692B. doi:10.1088/0022-3727/32/20/317.
  5. ↑ C.C. Williams (1999). "Two-dimensional dopant profiling by scanning capacitance microscopy". Annual Review of Materials Research . 29: 471–504. Bibcode:1999AnRMS..29..471W. doi:10.1146/annurev.matsci.29.1.471.
  6. ↑ Y. Naitou; A. Ando; H. Ogiso; S. Kamiyama; Y. Nara; K. Nakamura (2005). "Spatial fluctuation of dielectric properties in Hf-based high-k gate films studied by scanning capacitance microscopy". Applied Physics Letters . 87 (25): 252908–1 to 252908–3. Bibcode:2005ApPhL..87y2908N. doi:10.1063/1.2149222.
  7. ↑ Kin Mun Wong (2009). "Study of the electronic structure of individual free-standing germanium nanodots using spectroscopic scanning capacitance microscopy". Japanese Journal of Applied Physics . 48 (8): 085002–1 to 085002–12. Bibcode:2009JaJAP..48h5002W. doi: 10.1143/JJAP.48.085002 .
  8. ↑ A. Baumgartner; M.E. Suddards & C.J. Mellor (2009). "Low-temperature and high magnetic field dynamic scanning capacitance microscope". Review of Scientific Instruments. 80 (1): 013704. arXiv: 0812.4146 . Bibcode:2009RScI...80a3704B. doi:10.1063/1.3069289. PMID   19191438.
  9. ↑ M.E. Suddards, A. Baumgartner, M. Henini and C.J. Mellor (2012). "Scanning capacitance imaging of compressible and incompressible quantum Hall effect edge strips". New Journal of Physics. 14: 083015. arXiv: 1202.3315 . Bibcode:2012NJPh...14h3015S. doi:10.1088/1367-2630/14/8/083015.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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