Microstrain and Residual Stress in Thin-Films Made from Silver Nanoparticles Deposited by Inkjet-Printing Technology

Romain Cauchois,Patrice Gergaud,Karim Inal,András Borbély,Mohamed Saadaoui

doi:10.4028/www.scientific.net/amr.996.930

Abstract

Colloidal suspensions of nanoparticles are increasingly employed in the fabrication process of electronic devices using inkjet-printing technology and a consecutive thermal treatment. The evolution of internal stresses during the conversion of silver nanoparticle-based ink into a metallic thin-film by a thermal sintering process has been investigated by in-situ XRD using the sin2ψ method. Despite the CTE mismatch at the film/substrate interface, the residual stress in silver films (below 70 MPa) remains lower than in conventional PVD thin-films, as a result of the remaining porosity. A Warren-Averbach analysis further showed that the crystallite growth is associated with a minimization of the twin fault density and the elastic microstrain energy above 150°C. A stabilization of the microstructure and internal stress is observed above 300°C. Inkjet-printing technology thus appears as a good alternative to conventional metallization techniques and offers significant opportunities asset for interconnect and electronic packaging.

Highlights

Analysis of residual stress in thin films is of utmost importance because of its crucial influence on product reliability, as well as on induced local properties
Several non-destructive methods have been suggested to characterize the residual stress in thin films, which ranges from common techniques such as curvature measurement (Stoney) [1] or X-ray diffraction (XRD) [2], to more specific approaches such as Raman scattering [3]
Strain can be locally further accommodated due to the free surfaces related to porosity. Bolstered by these in-situ measurements performed on a specific sintering condition at 550°C, the behavior of the internal stress during the thermal cycle attests that the final temperature determines the resultant microstructure and the associated residual stress

Summary

Introduction

Analysis of residual stress in thin films is of utmost importance because of its crucial influence on product reliability, as well as on induced local properties. The evolution of internal stress during the conversion of silver nanoparticle-based ink into a metallic thin film has been investigated by insitu XRD using the sin2ψ method [11,12], which relates the evolution of interplanar spacing to XRD peaks shift and to the underlying stress. The microstructure of such thin films has been further studied by analyzing the broadening of high-resolution X-ray peaks and correlating peak breadth to average crystallite size and lattice microstrain using a Warren-Averbach analysis [13]. The particle size, the planar fault density and the microstrain were determined according to the Warren-Averbach analysis using the 111/222 and 200/400 reflection-pairs

Results and discussions

Residual Stresses IX

Conclusion