Failure Mode Analysis in Microsecond UV Laser Annealing of Cu Thin Films

TL;DR

This paper investigates failure modes in microsecond UV laser annealing of copper thin films, focusing on issues like diffusion, oxidation, and intermixing that affect electrical performance in 3D integrated devices.

Contribution

It provides a detailed analysis of failure mechanisms during microsecond UV laser annealing of Cu thin films, a topic not deeply explored before.

Findings

Identified Cu diffusion into SiO2 as a failure mode.

Observed oxygen incorporation into Cu during annealing.

Detected intermixing between Cu and Ta layers.

Abstract

The need of surface-localized thermal processing is strongly increasing especially w.r.t three-dimensionally (3D) integrated electrical devices. UV laser annealing (UV-LA) technology well addresses this challenge. Particularly UV-LA can reduce resistivity by enlarging metallic grains in lines or thin films, irradiating only the interconnects for short timescales. However, the risk of failure in electrical performance must be correctly managed, and that of UV-LA has not been deeply studied yet. In this work microsecond-scale UV-LA is applied on a stack comparable to an interconnect structure (dielectric/Cu/Ta/SiO2/Si) in either melt or sub-melt regime for grain growth. The failure modes such as (i) Cu diffusion into SiO2, (ii) O incorporation into Cu, and (iii) intermixing between Cu and Ta are investigated.