Chemical analysis of thin films in electronic devices by analytical transmission electron microscopy methodologies

Abstract

The continuous scaling in semiconductor technology has made characterization of transistor components more challenging. One of the main difficulties is to combine high spatial resolution with high enough sensitivity to perform accurate and precise quantitative analysis. In this project, methodologies for the characterization of thin films in electronic devices are developed, based on analytical transmission electron microscopy (TEM) techniques such as energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The problems which are addressed are the quantification methods and their accuracy, the artifacts induced by specimen preparation, and the combination of quantification and spatial resolution. In the first part of the project, quantification methodologies are developed by studying a series of nickel silicide phases with different crystallographic structures and compositions. The methodologies are generic enough to characterize other materials as well. The analyses are performed in STEM mode where a nanometer sized electron probe is directed onto the specimen. To separate the quantification problem from the spatial resolution problem, the quantification methodologies are developed on specimens with a nickel silicide layer thickness of about 100 nm. The influence of the specimen thickness on the quantification results is investigated by studying wedge shaped specimens. In the second part of the project, artifacts induced by the specimen preparation method are examined on the different nickel silicide phases. Focused ion beam (FIB) is commonly used for preparation of TEM specimens of devices, but induces a damaged layer in the specimen during the milling procedure. The formation of surface damage and the difference in milling rate between the silicide layer and the silicon substrate are studied as a function of the silicide phase. It is demonstrated that sample preparation with FIB influences both the quantification accuracy and spatial resolution that can be obtained. Methodologies to reduce damage induced by the milling procedure are investigated. In the third part of the project, the developed methodologies are validated on thin film specimens, where spatial resolution becomes important. The obtainable spatial resolution is examined by performing line scan experiments over a sharp interface. The combination of quantification and spatial resolution is then explored by a few case studies. These case studies allow evaluating the advantages and limitations of the quantitative methodologies. In addition, it is examined if the signals obtained from the different techniques can be combined into a single experiment. The methodologies are compared on the basis of spatial resolution versus analytical sensitivity, quantification accuracy and precision, specimen requirements, ease of use and information content.status: publishe