Reliability Evalution for Copper/Low-k-Structures Based on Experimental and Numerical Methods

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Bump shear is widely used to characterize the interfacial strength of Cu/low-<formula formulatype="inline"> <tex Notation="TeX">$k$</tex></formula> structures. In this paper, the blanket low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex> </formula> structure was used to evaluate the reliability and strength of Cu/low-<formula formulatype="inline"><tex Notation="TeX"> $k$</tex></formula> structures based on experiment and finite-element modeling technique. The objectives of this paper are to determine the critical stress parameters for low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> interfaces with different low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structures, to understand the failure mechanism, and to improve low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structure reliability by optimizing some parameters. In this paper, a comprehensive parametric study was carried out. Such parameters include the effect of three different low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structures, high-Pb solder bump versus Pb-free solder bump, different underbump metallization (UBM) thicknesses, barrier-layer material elastic modulus, and shear ram height on low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structure reliability. The simulation findings can be summarized as follows. The critical stress decreases with the number of layers of low-<formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structure. An Sn–Ag solder bump results in a higher shear force and stress than a high-Pb solder bump. Reducing the UBM thickness can help improve the low- <formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula> structure reliability. </para>