Mechanical characterization of low-K dielectric materials

Abstract

The implementation of materials in device interconnect structure is being driven by shrinking device geometries. In order to meet customer demands for increasing electrical performance, the industry is adopting a solution that provides both lower resistance and lower capacitance. Lower resistance is accomplished by switching from Al(Cu) to Cu interconnect and the capacitance is reduced by replacing SiO2 in the inter-level and inter-metal dielectric layers with lower dielectric constant materials (low-K materials) [1,2]. A change in materials in a process as complex as IC manufacturing is inherently accompanied by an increase in reliability risk. A thorough understanding of the low-K dielectric candidates is necessary for selection of the best candidate that has sufficient mechanical integrity to survive thermal stresses, CMP, packaging, and test, as well as allows for maximum extendibility to next generation devices. Towards this end, the industry has adopted methods and tools to measure mechanical properties and adhesion energies associated with low-K films. It is expected that porosity will significantly deteriorate the mechanical strength of ILD films compared to non-porous films and the effect on mechanical strength may be markedly different if the pores percolate together to form channels rather than remain isolated. Understanding the mechanical properties of these thin films and choice of appropriate mechanical performance metrics is necessary for successful full-scale integration into a reliable packaged product.