Scanning Electron Microscopy

Scanning electron microscopy (SEM) is a high-resolution characterization technique that probes a sample by scanning its surface with a focused electron beam. While scanning, the signals produced by the interaction of the electron beam with the sample are recorded with various detectors. The data is visualized in the form of an image of the scanned sample surface. Depending on the detector used, different properties can be primarily imaged, e.g. the sample’s surface topography or its composition. Advanced characterization techniques can be facilitated by equipping an SEM tool with additional detectors. For example, X-Ray Energy Dispersive Spectroscopy (XEDS) and Electron Backscatter Diffraction (EBSD) allow for characterization of the chemical composition of the sample and its microstructure, respectively. There are two SEM tools at KAI that serve as a means for characterization in different areas of research.

The Thermo Fisher Scientific Apreo 2 S HiVac is a versatile high-resolution SEM. It is equipped with an Everhart-Thornley detector, Trinity Detection System for simultaneous selective collection of backscattered/secondary/low-energy secondary electrons, an insertable segmented backscattered electron detector for energy filtered imaging and increased signal-to-noise, and XEDS and EBSD systems for chemical and microstructural characterization. The large specimen chamber, 1 nm resolution at 10 mm analytical working distance, and 105° stage tilt range allow for a wide range of sample geometries and in-situ experimental stages – such as a 3-probe Electron Beam Induced Current (EBIC) setup for defect analysis and resistance measurements in semiconductors and semiconductor devices, and a high-temperature heating stage for heating experiments and quantitative dopant contrast imaging in semiconductors. The Apreo 2 S is also equipped with a rocking-beam mode that, along with four other microscope modes, enables Electron Channeling Contrast Imaging (ECCI) for defect analyses in a range of materials from polycrystalline to magnetic single crystals.

Poly-heaters are special test chips that are provided with a resistive polycrystalline silicon layer (“poly”) with ohmic behavior, utilized for active heating. Within the materials science group at KAI, poly-heaters are employed as simplified test chips that can replicate the extreme thermal conditions occurring in smart power semiconductors during short-circuit or thermal overload events. By these means, the thermo-mechanical behavior of metallization layers can be investigated during the early development stages of future-generation chips.

The poly-heater experimental setup at KAI, with its in-house designed hard- and software, enables the execution of automated poly-heater fatigue tests. Such tests can optionally be accompanied by automated in-situ characterization, including electrical resistance measurements and/or SEM image acquisitions. With the capability to choose parameters pertaining to the thermal profile of the heat pulses applied for loading, highly comprehensive studies are possible.

Wafer Curvature

The wafer curvature technique is used to investigate the thermo-mechanical behavior of thin films on a substrate (a wafer) by monitoring its curvature while undergoing a thermal treatment. The measured curvature is related to the biaxial stress in the film, and from this, mechanical properties such as elastic modulus and temperature-dependent yield stress can be determined. Furthermore, processes such as recrystallization and stress relaxation can be captured.

The k-Space MOS Thermal Scan wafer curvature tool at KAI utilizes an optical module to measure curvature via an array of laser beams. By means of its rapid thermal processing system and its gas control units, the replication of relevant thermal treatments in terms of thermal profile and atmosphere is enabled. Temperatures are controlled precisely and may range from −55 °C (employing the optional feature of liquid-nitrogen cooling) to +600 °C.

The Allied MultiPrep™ Precision Mechanical Polishing System can be used for grinding and polishing different sample types. It can be used with SiC and diamond polishing papers with a grit sizes between 30 µm and 0.1 µm as well as with different diamond suspensions. The material removal can be monitored to reach a target position of the sample. Both cross-sectional preparation as well as coplanar thinning is possible.