The ac electromigration of multilayered interconnect systems, consisting of TiW/AlSiCu and CVD-W/AlSiCu, is studied under stress of repetitive dual-pulse current waveforms at 2 MHz. By using a general ac waveform in which the peak current density of the first pulse jl is fixed and the second is varied from +jl to -j1, we obtain a continuous electromigration spectrum from dc through pulsed dc to pure ac conditions. Although an average current model fits the data well, there is a singularity in the median time-tofailure at pure-ac conditions. To avoid this singularity, a novel modification of the average current model, called the Average Current Recovery (ACR) model, is developed. It heuristically accounts for the degree of damage recovery during oppositepolarity pulses through a single recovery parameter.

This paper reports on the dramatically enhanced effect rapid thermal anneal (RTA) treatment has on the aluminum (Al) diffusion barrier integrity of reactively sputtered low density titanium nitride (TIN). This low density as sputtered TiN is shown to be superior to high density as sputtered TiN after both films have undergone an identical RTA treatment. The superior integrity of the low density TIN is attributed to enhanced oxygen gettering during RTA treatment at the Ti/TIN interface. This oxygen gettering has been shown to create a titanium oxynitnde (TiON) layer between the Ti and TiN which accounts for the greatly enhanced barrier integrity.Reactively sputtered TiN is commonly used as a contact diffusion barrier for submicron Al talliza1 Because of the high aspect ratio contacts used in the submicron process, the TIN barrier coverage at the bottom of the contact is often greatly reduced.2 This reduced coverage makes the barrier integrity extremely critical for the prevention of Al junction spiking in the submicron process, if conventional (i.e. non-collimating,2'4) sputtering technology is used. Previous reports on TiN barrier enhancement 28 fell into two general categories: 1) barrier enhancement by the manipulation and control of deposition parameters such as substrate temperature 3-4, deposition pressure 2,5, and substrate bias voltage6 to deposit a more densifled (or ciystallized) TiN film, and 2) barrier enhancement through the use of post deposition treatments such as air exposure 7 or RTA 8 prior to Al deposition to block fast diffusion pathways by stuffing the TiN film with oxygen. Many studies have used one of these two approaches to report on TiN barrier enhancement. However, there are few reports that have coupled the effects of controlling the deposition parameters and post deposition treatments to develop an improved TiN difflision barrier. In this study we have investigated the effect process parameters have on the density of reactively sputtered TIN films and, in turn, how the TiN density influences the effect post deposition RTA treatment has on barrier integrity. With the development of this relationship we have proposed a mechanism whereby oxygen gettering at the Ti/TiN interface forms a TiON layer that provIdes for a dramatically enhanced diffi.ision barrier. O-8194-1668-1/941$6.OO SPIE Vol. 2335 / 177 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/30/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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