Adhesion energy and interfacial fracture in semiconductor multilayers are critical to the reliability and performance of advanced electronic devices. The mechanical integrity of interfaces such as SiO2/Si or metal/semiconductor systems directly impacts device longevity, especially in multilayer structures where delamination can lead to catastrophic failure. Understanding and quantifying adhesion energy requires specialized techniques, including blister tests, four-point bending, and mixed-mode delamination analysis. These methods provide insights into the interfacial toughness and failure mechanisms under different loading conditions.

The adhesion energy, or work of adhesion, is defined as the energy required to separate two materials at their interface. It depends on factors such as surface chemistry, roughness, and residual stresses. For semiconductor multilayers, interfacial fracture often occurs under mixed-mode loading, where both normal (Mode I) and shear (Mode II) stresses contribute to delamination. Accurate measurement of adhesion energy is essential for designing robust interfaces in integrated circuits, MEMS, and flexible electronics.

Blister tests are widely used to measure adhesion energy in thin-film systems. In this method, a pressurized fluid or gas is introduced beneath a thin film, causing it to deform and eventually delaminate from the substrate. The critical pressure at which delamination occurs is related to the adhesion energy through mechanical models. For SiO2/Si interfaces, blister tests have revealed adhesion energies in the range of 1-10 J/m², depending on processing conditions and surface treatments. The advantage of blister testing is its ability to apply pure Mode I loading, isolating the normal stress component. However, challenges include precise control of pressure and avoiding plastic deformation in the film.

Four-point bending is another established technique for evaluating interfacial fracture toughness. A multilayer sample is subjected to bending forces, creating a controlled crack at the interface of interest. The strain energy release rate is calculated from the applied load and crack length. This method is particularly useful for studying metal/semiconductor interfaces, where residual stresses can significantly influence adhesion. For example, Cu/Si interfaces exhibit adhesion energies between 5-20 J/m², with variations due to interfacial oxide layers or alloying effects. Four-point bending allows for stable crack propagation and can be adapted for mixed-mode loading by adjusting the loading geometry.

Mixed-mode delamination is a common failure scenario in semiconductor devices, where both tensile and shear stresses act simultaneously. The phase angle, defined as the ratio of Mode II to Mode I loading, determines the failure mechanism. Experimental setups combining blister tests or bending with asymmetric loading can simulate these conditions. For SiO2/Si interfaces, mixed-mode studies show that adhesion energy often decreases as the phase angle increases, indicating shear-induced weakening. Metal/semiconductor interfaces, such as Al/Si, exhibit similar trends but with higher sensitivity to interfacial defects.

Material pairs like SiO2/Si and metal/semiconductor interfaces exhibit distinct failure behaviors. SiO2/Si interfaces typically fail cohesively within the oxide layer near the interface, reflecting strong bonding but limited toughness. In contrast, metal/semiconductor interfaces often fail adhesively at the atomic junction, with adhesion energy heavily influenced by interfacial chemistry. For instance, Au/Si interfaces show lower adhesion energy (0.5-2 J/m²) compared to Ti/Si (5-15 J/m²) due to differences in chemical bonding. Surface treatments such as plasma cleaning or adhesion promoters can enhance interfacial strength by modifying surface energy or introducing covalent bonds.

Residual stresses play a significant role in interfacial fracture. Thin films deposited at high temperatures often develop tensile or compressive stresses upon cooling, altering the effective adhesion energy. For example, compressive stresses in SiO2 films on Si can suppress delamination, while tensile stresses may promote it. Similarly, metal films like Cu or Al on semiconductors exhibit stress-dependent adhesion, with thermal mismatch being a key contributor. Accurate stress measurement via techniques like wafer curvature or X-ray diffraction is essential for interpreting adhesion data.

Environmental factors such as humidity and temperature also affect interfacial fracture. Moisture can penetrate interfaces, reducing adhesion through hydrolytic weakening. For SiO2/Si, humidity exposure has been shown to decrease adhesion energy by up to 50% due to water-assisted bond breaking. High-temperature annealing, however, can improve adhesion by promoting interfacial diffusion or chemical reaction, as seen in Ni/Si systems where silicide formation enhances bonding.

Advanced modeling techniques, including finite element analysis and cohesive zone modeling, complement experimental methods by predicting interfacial failure under complex loading. These models incorporate material properties, residual stresses, and interface characteristics to simulate delamination. Validated against experimental data, they provide valuable insights for optimizing multilayer designs.

In summary, adhesion energy and interfacial fracture in semiconductor multilayers are governed by material properties, loading conditions, and environmental factors. Blister tests, four-point bending, and mixed-mode delamination studies offer quantitative measurements essential for reliability assessment. Interfaces like SiO2/Si and metal/semiconductor systems exhibit distinct behaviors, highlighting the need for tailored characterization approaches. Understanding these mechanisms enables the development of more durable multilayer structures for next-generation semiconductor devices.