Imaging and analysis of subsurface Cu interconnects by detecting backscattered electrons in the scanning electron microscope

Cu–SiO2–SiNx interconnects that were located 0.65–2.7-μm below the surface of silicon-integrated circuits were imaged in a scanning electron microscope and a transmission electron microscope with a scanning attachment by detecting backscattered electrons (BSEs) with an incident electron-beam energy (Eo) in the range of 30–400keV. BSE images could be used to detect voids in subsurface Cu interconnects, even in regions covered with upper level Cu lines or vias. As Eo was increased from 30to400keV, structures could be seen as a result of atomic number (Z) contrast farther below the surface while structures closer to the surface had reduced Z contrast. The subsurface beam diameter was measured from BSE images as a function of Eo and depth below the surface. For all Eo, the subsurface beam diameter initially rapidly increased with SiO2 overlayer thickness but, for 150keV, a leveling off in the beam spread was seen for depths >1.7μm. Beam broadening affected whether the TaN∕Ta liners that surrounded the Cu cond...

[1]  E. I. Rau,et al.  “Apparatus” electron beam microtomography in SEM† , 1995 .

[2]  L. Reimer,et al.  Fundamental problems of imaging subsurface structures in the backscattered electron mode in scanning electron microscopy , 2006 .

[3]  A Monte Carlo calculation of the backscattering coefficient for a multilayer sample , 1992 .

[4]  R. P. Becker,et al.  Scanning Electron Microscopy/1978 , 1979 .

[5]  O. Wells.  Effects of collector take-off angle and energy filtering on the BSE image in the SEM , 1979 .

[6]  Andras E. Vladar,et al.  Inverse scattering approach to SEM linewidth measurements , 1999, Advanced Lithography.

[7]  H. August,et al.  Theoretical prediction of the electron backscattering coefficient for multilayer structures , 1990 .

[8]  Fumio Mizuno,et al.  Study on irradiation damage to semiconductor devices by 200-keV electrons caused by backscattered electron assisting LSI inspection (BEASTLI) method , 1995, Advanced Lithography.

[9]  Erik H. Anderson,et al.  Dynamical x-ray microscopy investigation of electromigration in passivated inlaid Cu interconnect structures , 2002 .

[10]  Paul A. Flinn,et al.  High Resolution Observation of Void Motion in Passivated Metal Lines Under Electromigration Stress , 1992 .

[11]  E. I. Rau,et al.  Comparison of experimental and Monte Carlo simulated BSE spectra of multilayered structures and `in-depth' measurements in a SEM* , 2002 .

[12]  H. Todokoro,et al.  Observation and measurement of microstructures using a high-energy scanning electron microscope , 1995 .

[13]  E. Anderson,et al.  Electromigration in passivated Cu interconnects studied by transmission x-ray microscopy , 2002 .

[14]  Paul R. Besser,et al.  In situ scanning electron microscopy observation of the dynamic behavior of electromigration voids in passivated aluminum lines , 1992 .

[15]  A. D. Romig,et al.  High-energy backscattered electron imaging of voids in aluminum metallizations , 1991 .

[16]  E. Rau,et al.  Information depth and spatial resolution in BSE microtomography in SEM , 1998 .

[17]  M. Dapor.  Electron-Beam Interactions with Solids , 2003 .

[18]  S. Reed.  The single-scattering model and spatial resolution in X-ray analysis of thin foils , 1982 .

[19]  L. Reimer,et al.  Calculation of energy spectra from layered structures for backscattered electron spectrometry and relations to rutherford backscattering spectrometry by ions , 1991 .

[20]  Ian McNulty,et al.  Tomography of integrated circuit interconnect with an electromigration void , 2000 .

[21]  David G. Seiler,et al.  Characterization and metrology for ULSI technology , 2006 .

[22]  V. Robinson,et al.  An annular toroidal backscattered electron energy analyser for use in scanning electron microscopy , 2006 .

[23]  K. Murata.  Exit angle dependence of penetration depth of backscattered electrons in the scanning electron microscope , 1976 .

[24]  J. Maiz,et al.  In situ observations of dc and ac electromigration in passivated Al lines , 1991 .

[25]  O. Kraft,et al.  3-D focused ion beam mapping of nanoindentation zones in a Cu–Ti multilayered coating , 2002 .

[26]  R. Hull,et al.  Quantitative three-dimensional reconstruction of geometrically complex structures with nanoscale resolution , 2002 .

[27]  L. Reimer,et al.  Scanning Electron Microscopy , 1984 .

[28]  L. Reimer.  Scanning Electron Microscopy: Physics of Image Formation and Microanalysis , 1984 .

[29]  Paul A. Flinn,et al.  A high-voltage scanning electron microscopy system for in situ electromigration testing , 2000 .

[30]  H. Niedrig,et al.  Electron backscattering from thin films , 1982 .

[31]  L. Reimer.  Image Formation in Low-Voltage Scanning Electron Microscopy , 1993 .

[32]  B. A. Young.  Scanning Electron Microscopy/1978/I , 1979 .

[34]  J. Hejna.  A study of BSE signals of double layers on substrates at various detector take-off angles , 1992 .