PECVD low and ultralow dielectric constant materials: From invention and research to products
This paper is based on the 2015 AVS John A. Thornton Memorial Award Lecture. In 2015, the semiconductor industry celebrated the 50th anniversary of Moore's law, which has been followed by the semiconductor industry, resulting in continuously improved performance and increased density of the semiconductor microprocessors. For 22 years, this progress was accomplished using the same materials, comprising the elements Si, Al, O, and N, and shrinking the dimensions of the devices. However, while the performance of the active devices improved with scaling according to Dennard's law, the RC delay of the interconnect did not scale and, at the 0.25 μm technology node, the RC of the interconnect became the bottleneck to the improvement of the performance of the ultralarge scale integrated circuits. To overcome this obstacle, it was necessary to introduce new materials in the interconnect. Al was replaced with the more conductive Cu in 1997, but it took seven more years and several technology nodes to replace the SiO2 insulator of the interconnect with a material of lower dielectric constant (low-k). The paper reviews the invention, development, and implementation in products of the low-k SiCOH and ultralow-k porous SiCOH (pSiCOH) interconnect dielectrics. It will discuss integration issues related to these materials, which are characterized by reduced mechanical and chemical properties compared to SiO2, and how to address some of these issues. Finally, it will present the current status of the interconnect dielectrics, which enabled the continuation of Moore's law into the nanoscale dimensions, and the continuing efforts to further optimize the ultralow-k pSiCOH dielectrics.