Accurate Measurement of Porous Low-k Thin-Films by Nanoindentation: Densification Scaling versus Substrate Effects

Abstract

Historically, the integration of insulators with decreasing dielectric constants, k, has been critical in improving devices performance. The most efficient approach to decrease k is by introducing porosity. Since porosity directly impacts the Young's modulus, the accurate determination of the mechanical properties of porous dielectrics is essential in enabling their implementation into state-of-the-art devices. Currently, nanoindentation is the technique of choice, but as technology relevant thicknesses of dielectrics keep decreasing, substrate effects are unavoidably encountered. These issues have so far been circumvented by measuring bulk materials instead of their thin-film counterparts. This approach is, however, less than ideal as physical properties can be size-dependent. Moreover, pores densification also occurs, potentially leading to overestimated Young's modulus values. In this paper, we define a novel protocol based on ultra-low load, quasi-static nanoindentation to measure mechanical properties of porous thin-films as a function of porosity (0-60%) and thickness (150-700 nm). We could isolate materials densification from substrate effect, and we demonstrated that the former can be accounted for, while the latter does not happen until indentation depths are remarkably higher than the traditionally accepted indentation limit of 10% of the film thickness. Consequently, extremely accurate mechanical characterization of porous low-k thin-films is now possible.

Review—Beyond the Highs and Lows: A Perspective on the Future of Dielectrics Research for Nanoelectronic Devices

“…It is also important to point out that while there is currently not a strong drive to implement new high-k gate oxide and low-k ILD materials with increasing or decreasing values of dielectric permittivity, these materials will remain and likely continue to be reused in multiple future single digit nanoelectronic technologies. Thus, there will be a continued need for improved understanding of the electrical, [176][177][178][179][180][181] thermal, 7,[182][183][184][185][186][187][188][189][190] and mechanical 7,[191][192][193][194][195][196] reliability of these materials as they are scaled to increasingly smaller dimensions. As such, research into such reliability issues will continue to be relevant and a constant focus until they are replaced with higher or lower dielectric permittivity materials.…”

Enhanced Mechanical Stability and Scratch Resistance of Mesoporous Aluminosilicate Thin Films

“…However, there are concerns about over-estimating the film hardness due to the contribution of the substrate, especially in films of thickness in the range of hundreds of nanometers. [56][57][58][59] To this end, surface acoustic wave spectroscopy (SAWS), [60,61] Brillouin light scattering (BLS), [62] and X-ray reflectivity [28] were developed as alternatives to NI methods. While these techniques have demonstrated effectiveness for non-destructive E measurement, disadvantages include requirements for X-rays, specialised substrates, [63] and high-resolution interferometry instrumentation.…”

Enhanced Mechanical Stability and Scratch Resistance of Mesoporous Aluminosilicate Thin Films

“…The aforementioned techniques are prevalent when reporting the film modulus and hardness. However, there are concerns about overestimating the film hardness due to the contribution of the substrate, especially in films of thickness in the range of hundreds of nanometers [56][57][58][59]. To this end, surface acoustic wave spectroscopy (SAWS) [60,61], Brillouin light scattering (BLS) [62], and X-ray reflectivity [28] were developed as alternatives to NI methods.…”