Direct-Liquid-Evaporation Chemical Vapor Deposition of Nanocrystalline Cobalt Metal for Nanoscale Copper Interconnect Encapsulation.

Jun Feng,Xian Gong,Roy G Gordon,Xiabing Lou

doi:10.1021/acsami.7b01327

Abstract

In advanced microelectronics, precise design of liner and capping layers become critical, especially when it comes to the fabrication of Cu interconnects with dimensions lower than its mean free path. Herein, we demonstrate that direct-liquid-evaporation chemical vapor deposition (DLE-CVD) of Co is a promising method to make liner and capping layers for nanoscale Cu interconnects. DLE-CVD makes pure, smooth, nanocrystalline, and highly conformal Co films with highly controllable growth characteristics. This process allows full Co encapsulation of nanoscale Cu interconnects, thus stabilizing Cu against diffusion and electromigration. Electrical measurements and high-resolution elemental imaging studies show that the DLE-CVD Co encapsulation layer can improve the reliability and thermal stability of Cu interconnects. Also, with the high conductivity of Co, the DLE-CVD Co encapsulation layer have the potential to further decrease the power consumption of nanoscale Cu interconnects, paving the way for Cu interconnects with higher efficiency in future high-end microelectronics.

Highlights

Continued progress in the downsizing of microelectronic devices has brought great challenges in many fields, especially interfacial engineering and interconnect fabrication at nanometer scales.[12]
In order to understand the deposition process of direct-liquid-evaporation chemical vapor deposition (DLE-CVD) cobalt metal, we conducted a series of temperature-dependent studies
A lower temperature with a lower flow rate is suitable for nano-scale applications such as local interconnect and nanoscale capping layer, while a higher temperature with higher flow rate is favorable for larger-scale coatings such as intermediate and global interconnects in 3D microelectronics.[7]

Summary

Introduction

Continued progress in the downsizing of microelectronic devices has brought great challenges in many fields, especially interfacial engineering and interconnect fabrication at nanometer scales.[12]. Cobalt (Co) and Co alloys are known as effective capping layers that are capable of suppressing surface electromigration of Cu at macroscopic scales.[15,16] since Co has a high bulk metallic conductivity of 1.60 × 107 S/m and an estimated MFP of only ~16 nm at room temperature, it is emerging as a promising candidate for advanced Cu liner/capping layers.[17,18] Traditionally, Co metal was deposited by PVD methods that do not have the capability of coating inside high-aspect-ratio structures.[19] metal-organic chemical vapor deposition (MOCVD) with cobalt carbonyl precursors [e.g., Co2(CO)8] was introduced for better conformality.[20] cobalt carbonyl precursors have poor thermal stability and narrow useful deposition temperature windows, and usually lead to a rough film with surface roughness rms higher than 2.2 nm.[21] Recently, our group reported novel direct-liquid-evaporation chemical vapor deposition (DLE-CVD) methods for metal and metal nitride thin films, which provided the feasibility to create higher-quality Co films over a wide range of deposition temperatures and low chance of pre-deposition decomposition of precursors.[22,23]. This work provides direct evidence that encapsulating nanoscale Cu interconnects with nanocrystalline DLE-CVD Co can substantially improve its stability and suppress diffusion of Cu atoms, paving the way for improved Cu interconnects in advanced microelectronics

Experimental Section

Results and Discussion

Conclusions