Dielectric breakdown in nano-porous thin films

Abstract

Unknown to most computer users and mobile device enthusiasts, we have finally entered into a critical age of chip manufacturing. January of 2014 marks the official start of the quest by the semiconductor industry to successfully integrate sub 14nm process technology nodes in accordance to the International Technology Roadmap for Semiconductors (ITRS). The manufacturing of nano-scale features represents a major bottleneck of its own. However, a bigger challenge lies in reliably isolating the massive chip interconnect network. The present work is aimed at generating a theoretical and experimental framework to predict dielectric breakdown for thin films used in computer chip components. Here, a set of experimental techniques are presented to assess and study dielectric failure in novel thin films. A theory of dielectric breakdown in thin nano-porous films is proposed to describe combined intrinsic and metal ion catalyzed failure. This theory draws on experimental evidence as well as fundamental concepts from mass and electronic charge transport.

The drift of metal species was found to accelerate intrinsic dielectric failure. The solubility of metals species such as Cu was found to range from 7.0x10^25 ions/m^3 to 1.86x10^26 ions/m^3 in 7% porous SiCOH films. The diffusion coefficient for Cu species was found to span from 4.2x10^-19 m^2/s to 1.86x10^-21 m^2/s. Ramped voltage stress experiments were used to identify intrinsic failure from metal catalyzed failure. Intrinsic breakdown is defined when time to failure against applied field ramp rate results in d(ln(TTF))/d(ln(R)) ≈ -1. Intrinsic failure was studied using Au. Here, d(ln(TTF))/d(ln(R)) ≈ -0.95, which is an experimental best case scenario for intrinsic failure. Au is commonly reluctant to ionize which means that failure occurs in the absence of ionic species. Metal catalyzed failure was investigated using reactive electrodes such as Cu, and Ag. Here, trends for d(ln(TTF))/d(ln(R)) significantly deviated from -1. Cu and Ag were worst case scenarios with d(ln(TTF))/d(ln(R)) equal to -0.86 for Cu and -0.85 for Ag. Plasma processes in 7% porous SiCOH were found to accelerate dielectric breakdown by increasing the interfacial concentration of metal species from 1.1x10^26 ions/m^3 to 2.9x10^26 ions/m^3. In 25% porous SiCOH plasma treatments resulted in interfacial densification of films leading to added resistance to ionic transport.