(A) Study on the Reliability of VLSI Nano-Interconnections

Abstract

Due to the low manufacturing cost of Al interconnect, the low power application such as mobile CMOS image sensor (CIS) and liquid crystal display (LCD) driver integrated circuits (ICs) prefer the Al interconnect even at the sub-130nm technology. The shrinkage in the thickness and width of Al metal lines is required for reducing chip size and using Al interconnect continuously at the sub-130nm technology. However, as the dimension of metal lines is scaled down, the current density increases, in turn electromigration (EM) becomes more serious. Unfortunately, the investigations on electromigration at a thin Al wire which can be used at sub-130nm technology have not been sufficiently performed yet. Therefore, in this thesis, the reliability of thin Al Interconnect for very large scale integration (VLSI) nano-interconnections were investigated. In Chapter 2, the electromigration (EM) resistance of thin aluminum interconnects for sub-130nm CMOS logic technology was investigated by varying the AlCu underlayers and etched sidewall profiles. Al texture and surface roughness as key parameters were characterized for selecting the AlCu underlayer prior to the EM test. From the results of XRD and AFM analyses, the AlCu film with a Ti or Ti/TiN underlayer was proven to have more dominant (111) orientation and lower surface roughness. In order to evaluate the effect of the etched sidewall profiles of AlCu wire on the EM resistance, we created the different sidewall profiles of AlCu wire by changing the AlCu sidewall passivation gas and process parameters during the metal etching process. From an EM test result, thin AlCu wire with Ti/TiN underlayer and smooth etched sidewall profile is confirmed to have the best EM resistance in terms of the mean-time-to-failure (MTTF) and the failure distribution. Ti/TiN underlayer is believed to lead to a longer MTTF by dramatically reducing the currnet crowding at AlCu layer of thin AlCu wire with a smaller formation of $TiAl_3$ at the TiN...