Thermal Oxidation of Cu Interconnects Capped with CoWP

Abstract

The thermal oxidation of Cu interconnects, at 350 o C in air, has been studied as a function of thickness of a CoWP capping layer. For thin CoWP layers (25 nm), a thick oxide layer (200 nm) is formed which is mainly composed of Cu 2 O. For thick CoWP layers (50 nm), the oxide layer is much thinner (36 nm) and is mainly composed of CoO. For both CoWP thicknesses, depletion of the underlying Cu is often observed after oxidation and whisker growth is often observed on the surface. The results are consistent with an oxidation mechanism where metal is the dominant diffusing species. For thin CoWP layers, Cu diffuses more quickly to the surface than Co, and therefore mainly Cu oxides are formed. For thick CoWP layers, the Cu diffusion to the surface is greatly reduced, and as a result, mainly Co oxides are formed. These results indicate that CoWP is not a good barrier for thermal oxidation, so high temperature exposure to oxidizing ambients must be minimized during processing of integrated circuits where CoWP is used instead of a dielectric barrier.

Reliability of Copper Interconnects: Stress-Induced Voids

“…High temperature anneals after cap deposition can lead to high rates of stress-induced void formation (Fig. 2), due to either confined grain growth or due to increased stress in the Cu (17,30).…”

Impact of Plasma and Diluted HF on a CoWP Material

“…Self-Aligned Barriers (SAB) are investigated to achieve reliable copper interconnects for the 45 nm technology node and beyond [1] [2]. The integration of this material requires the study of the process impacts: plasma etch and ash, and cleaning process.…”