Analysis of Buried Interfaces for Device Technology by Soft and Hard X-Ray Photoelectron Spectroscopy

X-ray photoelectron spectroscopy (XPS) has long been favored for its precision and reliability in discerning nanometer-thick overcoats on silicon surfaces. However, a challenge arises when using surface sensitive soft X-ray sources, as the areas of interest are often concealed beneath metal electrodes or oxide layers. While higher energy X-ray beams have enabled the detection of photoelectron signals from deeper layers, most of this analysis has been conducted at synchrotron radiation facilities. Recent advancements in lab-based hard X-ray photoelectron spectrometers (HAXPES), such as the PHI <i>Genesis</i>, have opened new accessible avenues for the routine examination of subsurface layers of technologically significant devices.<br/><br/>Angle-resolved or angle-dependent XPS and HAXPES (ADXPS/ADHAXPES) represent a potent, non-destructive method for providing a quantitative chemical composition depth profile for thin film structures, with thicknesses falling within the XPS or HAXPES sampling depth. This depth typically ranges from under 5-10 nanometers for an Al K alpha soft X-ray source to approximately 15-30 nanometers for a Cr K alpha hard X-ray source. Using <i>StrataPHI</i> analysis software, non-destructive XPS/HAXPES depth profiles can be reconstructed from angle-dependent photoelectron spectra. In the latest development of this software package (<i>StrataPHI 2.0</i>), spectra from both hard and soft X-ray sources can be combined. If the layer identity, order, and approximate thicknesses, are known, <i>StrataPHI</i> will recommend the X-ray source and transition to use for angle resolved measurements, reducing the overall data acquisition time.<br/><br/>This poster will highlight current cutting-edge and potential future directions for the integration of HAXPES and XPS in the investigation of semiconductors and nanoelectronics. It will underscore the advantages of utilizing hard X-ray sources in combination with a high-throughput, fully automated spectrometer located in a laboratory setting. These advantages encompass the ability to investigate concealed interfaces, such as electronic layers positioned beneath surface capping layers, and compositional studies within the bulk of materials and interfaces beyond the limited probing depth of soft X-rays.