Three Dimensional Stress Mapping of Silicon Surrounded by Copper Filled through Silicon Vias Using Polychromator-Based Multi-Wavelength Micro Raman Spectroscopy

Abstract

Three dimensional (3D) stress distributions in Si, surrounded by copper (Cu) filled through silicon vias (TSVs) with various dimensions and pitches, are non-destructively characterized and stress contour maps generated at different depths using a long focal length, polychromator-based, multi-wavelength micro-Raman spectroscopy system. It was found that stress and crystallinity in Si (in both planar and depth directions) was strongly influenced by the proximity to a TSV, as well as, the dimensions of the TSV. In addition to characterizing semiconductor materials, Multi-wavelength micro-Raman spectroscopy was extremely effective for characterizing process-induced variations in crystalline stress and quality where 3D interconnects and packaging technology is introduced.

Multiwavelength Raman characterization of silicon stress near through-silicon vias and its inline monitoring applications

“…33 A micro-Raman system with spectral resolution, measurement repeatability, and measurement stability better than 0.1 cm −1 before curve fitting is strongly desired for resolving ∼50 MPa of stress in Si near TSVs, which may result in electrical performance variations of devices. [27][28][29]33 The reasoning for this stringent requirement is best given with measurement examples in a later subsection.…”

“…For virtual stress depth profiling, multiwavelength excitation measurement capability without system calibration between wavelength switching is also essential. [27][28][29]33 For inline device wafer characterization, pattern recognition and automated navigation are required.…”

“…[25][26][27][28][29][30][31][32] Micro-Raman spectroscopy is more suitable from a practical point of view. Since the probing depth of Raman spectroscopy is dependent on the excitation wavelength, choice of proper excitation wavelength is very important.…”

“…As TSVs typically have very high-aspect ratios (ARs) with depths of more than tens of micrometers, it is necessary to characterize the stress distribution three dimensionally in both planar and depth directions. [27][28][29] There are few Si stress characterization studies using multiwavelength micro-Raman spectroscopy, which demonstrates the presence of stress variations in the depth direction near TSVs, an important capability of 3-D stress characterizations. [27][28][29] Most studies on stress-induced device performance variations near TSVs are based either on pure simulation or typical stress characterization results from a very limited, and not very well established, dataset without considering potential stress variations within wafer and wafer-to-wafer in production fabs.…”

“…[27][28][29] There are few Si stress characterization studies using multiwavelength micro-Raman spectroscopy, which demonstrates the presence of stress variations in the depth direction near TSVs, an important capability of 3-D stress characterizations. [27][28][29] Most studies on stress-induced device performance variations near TSVs are based either on pure simulation or typical stress characterization results from a very limited, and not very well established, dataset without considering potential stress variations within wafer and wafer-to-wafer in production fabs. 23,35 More attention should be paid to practical issues in TSV process steps for better understanding of the origin of Si stress, which will lead to proper stress management and TSV process control in device manufacturing.…”