(Invited) Electron Channeling Contrast Imaging: Potential for Future Metrology in Semiconductor Industry

Abstract

For future scaling of CMOS technology beyond the 10 nm node it is necessary to integrate high mobility semiconductors including (Si)Ge and III/V compounds on silicon substrates. The lattice mismatch between these materials and the Silicon platform can lead to the formation of defects which will cause a degradation of the final device performance. Therefore, a metrology technique is needed to monitor the presence and density of defects in blanket layer as well as in patterned structures such as fins. There are several techniques for defect metrology including optical methods, X-ray diffraction or transmission electron microscopy, however, expected defect densities (<105 cm-2) make them ineffective for this task. Electron channeling contrast imaging (ECCI) is scanning electron microscopy (SEM) technique used for the visualization and characterization of crystalline defects including dislocations or stacking faults. Distortions of the crystal lattice of a material due to the presence of such defects cause the variation of the backscattered electron intensity allowing for the visualization of the defects. Application of ECCI proved to be a consistent method for assessing the density and Burgers vector of different defect types in various materials with reliability comparable to that of transmission electron microscopy (TEM). Moreover, TEM limitations related to the destructive sample preparation necessity, limited viewed area accessible for each sample and possible difference in the behavior of thin samples compared to bulk ones brings SEM based ECCI as excellent candidate for non-destructive investigation of large sample areas with low defect densities. For such an analysis, areas exceeding 105 μm2 in size need to be examined to ensure proper statistics. Therefore, automated acquisition of a set of tiles that can be stitched into a single image with a resolution allowing for the detection of single threading dislocations is required. Important parameter for high contrast ECCI of crystalline defects is the sample orientation with respect to the electron beam. The sample should be oriented close to the Bragg condition. This is facilitated by the acquisition of Electron Channeling Patterns and simultaneous sample tilting and/or rotation. For the majority of samples based on silicon wafers only require a couple of degrees tilt from the zone axis. Hence, the technique can be applied to 300 mm wafers easily.The presented technique allows the visualizing and analyzing the density and distribution of threading dislocations in blanket SiGe layers of different defect densities, strain relaxed buffers as well as on (Si)Ge and III/V fin structures. Therefore we are able to demonstrate that automated image acquisition of ECCI has big potential as possible metrology tool for future semiconductor devices process.