Large area scanning probe microscope in ultra-high vacuum demonstrated for electrostatic force measurements on high-voltage devices

Abstract

Summary Background: The resolution in electrostatic force microscopy (EFM), a descendant of atomic force microscopy (AFM), has reached nanometre dimensions, necessary to investigate integrated circuits in modern electronic devices. However, the characterization of conducting or semiconducting power devices with EFM methods requires an accurate and reliable technique from the nanometre up to the micrometre scale. For high force sensitivity it is indispensable to operate the microscope under high to ultra-high vacuum (UHV) conditions to suppress viscous damping of the sensor. Furthermore, UHV environment allows for the analysis of clean surfaces under controlled environmental conditions. Because of these requirements we built a large area scanning probe microscope operating under UHV conditions at room temperature allowing to perform various electrical measurements, such as Kelvin probe force microscopy, scanning capacitance force microscopy, scanning spreading resistance microscopy, and also electrostatic force microscopy at higher harmonics. The instrument incorporates beside a standard beam deflection detection system a closed loop scanner with a scan range of 100 μm in lateral and 25 μm in vertical direction as well as an additional fibre optics. This enables the illumination of the tip–sample interface for optically excited measurements such as local surface photo voltage detection. Results: We present Kelvin probe force microscopy (KPFM) measurements before and after sputtering of a copper alloy with chromium grains used as electrical contact surface in ultra-high power switches. In addition, we discuss KPFM measurements on cross sections of cleaved silicon carbide structures: a calibration layer sample and a power rectifier. To demonstrate the benefit of surface photo voltage measurements, we analysed the contact potential difference of a silicon carbide p/n-junction under illumination.

Dopant imaging of power semiconductor device cross sections

“…It is found that Secondary Ion Mass Spectroscopy (SIMS) is difficult to be applied in case of power semiconductor devices because of the low dopant concentrations (as low as 10 14 cm -3 ) and narrow dimensions in the µm range. In this contribution, a dedicated Scanning Probe Microscope (SPM) [1], operated under ultra-high vacuum conditions, is applied for this purpose. An image of the scanning probe microscope instrument is shown in Fig.…”

“…(a) AFM with a 100x100 µm 2 closed loop scanner operating in UHV conditions with full optical access[1]. KPFM images of a silicon test structure (b) without and (c) with irradiation (about 20mW, =475-525nm) by sub-bandgap photons, respectively.…”

Water Vapor and Alcohol Vapor Induced Healing of the Nanostructured KBr Surface

“…All AFM measurements were performed by using a custom-built AFM operating under UHV and controlled gas pressures at RT. Our AFM is similar to the design in ref ( 23 ), however with a regular piezo-tube scanner instead of a closed-loop scanner. Commercially available Si cantilevers (Budget Sensors Tap150Al-G, k c ∼ 5 N m –1 ) were used as force sensors, which were annealed at 150 °C for 30 min in UHV prior to measurements.…”

Quantitative characterization of built-in potential profile across GaAs p–n junctions using Kelvin probe force microscopy with qPlus sensor AFM

“…Since its invention, KPFM has been used to evaluate various electronic [3,[5][6][7][8][9][10][11][12][13] and ionic devices [14][15][16][17][18][19]. In particular, several reports have focused on the characterization of the built-in potential profiles in p-n junctions [5,8,9,11,12,[20][21][22], which are the key components of semiconductor devices. However, the magnitudes of the measured built-in potentials are smaller than those expected from the actual band structure.…”