We introduce an original method capable of quantifying, on micrometer scale dimensions, the maximum tensile strength at interfaces typically found in microelectronic devices’ frontside metallization for power and signal routing. The method has also the potential to fully derive the fracture parameters at such interfaces by measuring the adhesion strength in Mode I and Mode II/III delamination. The structures employed to this end are microcantilevers and pillars processed with routine microelectronics Back-End-of-Line (BEoL) production steps. Such structures can then be prepared for test by employing standard etching procedures without the need of time-consuming preparation by Focused Ion Beam (FIB) which allows to prepare hundreds of units in one single process run.

Small-scale delamination experiments at single copper vias in on-chip interconnect stacks of microelectronic chips are performed using a novel experimental setup for testing of interface properties of single copper interconnect structures. The method is based on in-situ SEM nanoindentation experiments, utilized to test customized copper test structures manufactured in the Dual Damascene process. In this unique way, the test structures resemble product-like length-scales as well as material and interface properties. For the investigation of interface properties, the experimental load-displacement data is reviewed. FIB cross sections are performed to validate the delaminated interface. The results gain information on the critical delamination forces and show a good reproducibility for two investigated interfaces. Future work could focus on resimulating the experimental load- displacement data and thereby gain knowledge of interfacial toughness parameters.

Cu wire bonding is fast coming up as Au wire replacement in semiconductor industry due to its lower price and several expected technological advantages. Cu bond wire reliability on Al pads is an ongoing study of interest and one of the mostly addressed topics is the degradation of Al-Cu intermetallic compounds (IMC) under high temperature or humidity stress conditions. The majority of published studies were carried out on Al-Cu systems in encapsulated packages. Many of them reported the degradation of the wire/pad-interface by cracks which are starting from the ball periphery and are penetrating inwards. Some also report about voids which are forming within IMCs or at interfaces. Questions have been raised about the root cause of the reported physical defects and the associated reliability risks. This paper is a more fundamental research investigating the Al and Cu diffusion reactions and the formation of individual IMC phases at clean and ideal Al/Cu interfaces without potential impacts of bond process and molding compound. It is conducted by using thin film couples of clean sputtered Al and Cu layers, which have been annealed under forming gas atmosphere at different temperatures (150 °C–275 °C) and for various time periods. Two different thin film couples have been used: a) 5000 nm Al followed by several µm copper to simulate an almost infinite Al reservoir and b) 650 nm Al followed by several µm Cu to simulate a typical Al reservoir after bonding. The samples were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Focused Ion Beam (FIB) and X-ray diffraction (XRD).

The growth kinetics of Al-Cu intermetallic compounds (IMC) have been investigated on thin film couples and bonded samples in the range 150°C to 250°C using XRD, SEM/EDX and in-situ interface resistance monitoring. Individual diffusion constants D o and activation energies E a (1.01eV, 0.97eV, 1.23eV, 1.28eV) have been obtained from thin film couples for the main three IMC phases Al 4 Cu 9 , AlCu and Al 2 Cu, and for the total IMC growth, respectively. Two additional phases (Al 3 Cu 2 , Al 0.06 Cu 0.94 ) contribute to the total IMC growth at T ≥ 200°C, but do not form at lower temperatures. Lower activation energies of 1.13eV (thin film) and 1.05eV (bonded samples) have thus been derived for T <; 200°C for the overall IMC growth and are recommended to be used for lifetime predictions in the typical regime of device application temperatures.