BS ISO 13083:2015 pdf download – Surface chemical analysis — Scanning probe microscopy — Standards on the definition and calibration of spatial resolution of electrical scanning probe microscopes (ESPMs) such as SSRM and SCM for 2D-dopant imaging and other purposes
5 General information
5.1 Background information ESPM is a branch of scanning probe microscope that can be used to image an electrical or electronic property of a sample surface using an electrically conducting probe. Since this conductive probe is scanned over the sample surface in the contact mode, its lateral resolution is strongly related to the size and shape of the probe apex. Currently, this can be as small as a few nanometres, enabling sub-10 nanometre spatial resolution to be achieved. Such a high resolution, shown in ESPM images, allows the investigation of the two-dimensional distribution of carriers in nanoscale semiconductor devices.
5.2 Target There are a number of types of ESPM categorized by the methods of electrical characterization. Among these ESPMs, this International Standard is for SCM and SSRM.
5.2.1 Scanning capacitance microscope Scanning capacitance microscopy (SCM) is a modification of scanning probe microscopy in which a conductive probe is in contact with the surface of a sample, with an applied AC bias, and scanned across it. SCM characterizes the change in electrostatic capacitance between the sample and the probe on the surface of the sample. SCM uses an ultra-sharp conducting probe made from etched silicon (often coated with Pt/Ir or Co/Cr alloy) to form a metal-insulator-semiconductor (MIS/MOS) capacitor with a semiconductor sample if a native oxide exists on the sample. When the conducting probe is in contact to the surface under an AC bias, generated capacitance variations on the surface can be detected using a GHz resonant capacitance sensor. The probe is then scanned across the semiconductor’s surface in x- and y-axes while the probe is operated under the contact mode. By applying an alternating bias to the metal-coated probe or the sample, carriers are alternately accumulated and depleted within the semiconductor’s surface layers under the probe, 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). [2]
5.2.2 Scanning spreading resistance microscope A very challenging task as the size of the semiconductor components shrinks towards sub-100 nm level is the development of new tools allowing two-dimensional (2D) carrier profiling with very high spatial resolution. One of the promising new tools is scanning spreading resistance microscopy (SSRM).
SSRM is based on atomic force microscopy (AFM) and has been developed in recent years to probe the 2D resistivity and carrier distribution in semiconductor devices. In SSRM, a very small conductive tip is contacted on the sample surface to be used to measure the local spreading resistance, which is intimately linked to the local resistivity. Scanning a cross section of the sample provides a 2D map of the local spreading resistance with a spatial resolution set by the tip radius (typically 5 nm ~ 15 nm). The main advantages of SSRM lie in its relative robustness, as it is less sensitive to surface preparation than, for instance, scanning capacitance microscopy (SCM) leading to excellent reproducibility. SSRM also benefits from an excellent dynamic range covering the entire dopant range of interest (10 14 ~ 10 20 ) cm −3 with constant sensitivity and from a high spatial resolution (set by the tip radius only) combined with very accurate junction delineation capabilities. [3]
5.3 Measurement method for lateral resolution in SCM and SSRM The spatial resolution is not only influenced by geometric factors of the conductive probe. Other factors that affect spatial resolution include surface roughness of the sample, contrast of the electrical image from difference in carrier density, pixilation, noise and sensitivity of the detector. The spatial resolution of the ESPM instrument or the image has been determined by a few methods: imaging a regular pattern and measuring the smallest feature and imaging across an electrically abrupt interface, etc. It is very difficult to fabricate electrically separated layers with two different carrier density. Also, it is crucial to connect, electrically, each plane of the repetitive pattern or the smallest feature. Therefore, the method chosen here is the sharp-edge method based on consideration of ease of use. This method of resolution definition is widely applied for depth-profiling of micro-beam spectroscopy such as secondary ion mass spectroscopy (SIMS). An electrically abrupt interface is line-scanned perpendicularly across the interface by a conductive probe and the detected profile of electrical characteristics is inspected. In the micro-beam spectroscopy, so called 16 % to 84 % width or some other criterion may be applied as the spatial resolution of SCM or SSRM as shown in Figure 1. [1][4] However, the definition of the resolution as 10 % to 90 % width is adopted as a standard method for SCM and SSRM since it has been well agreed academically.BS ISO 13083 pdf download.