Kee-Won Kwon

SOLID-STATE AMORPHIZATION AT TETRAGONAL-TA/CU INTERFACES

This letter describes the formation of a thin amorphous layer at the tetragonal-Ta/Cu interfaces, which appear in copper metallization structures of microelectronic devices. The disordered layer grows up to 4 nm when annealed at between 400 and 600 °C. Since Ta and Cu are immiscible according to thermodynamic data, this is an unusual observation. A mechanism for the amorphous phase formation is proposed using both physical and chemical considerations. A high content of Cu is detected in the Ta layer up to 5 nm from the interface when annealed at 600 °C. Although the adhesion is promoted by the interface reaction, a sufficiently thick Ta underlayer is recommended for efficient blocking of Cu diffusion. Neither solid-state amorphization nor Cu diffusion into Ta is observed at bcc-Ta/Cu interfaces.

Evidence of heteroepitaxial growth of copper on beta-tantalum

Crystallographic orientations between thin-sputtered Cu film and β-Ta adhesion layer have been studied using high resolution electron microscopy and electron diffraction. Tetragonal β-Ta deposited on SiO2 has a strong texture with its closest packed plane (002) parallel to the film surface. On (002) β-Ta, the growth of (111) Cu is preferred. Even though more than 100 β-Ta grains are found under a single Cu grain, the Ta grains under a Cu grain have long range in-plane texture with [330] direction aligned parallel to the [220] direction of Cu. This orientational coincidence is explained by the heteroepitaxial relationship between the hexagonal close-packed atomic array in Cu (111) plane and the pseudohexagonal configuration of β-Ta atoms in (002) plane with a misfit strain of 7.6%.

A Study on the Bonding Process of Cu Bump/Sn/Cu Bump Bonding Structure for 3D Packaging Applications

This study reports the kinetics of the bonding process of a Cu bump/10 μm thick Sn bonding layer/Cu bump bonding structure, popularly adopted for three-dimensional (3D) packaging, and the mechanical properties of the joints. Characterizing the bonding morphologies of the joints using scanning electron microscopy disclosed that a drastic intermetallic phase transformation occurred around the melting temperature of Sn in a manner similar to the wetting process of SnPb solder on Cu. We also delved into the mechanical behavior of the joints using lap-shear testing to illuminate that a unique feature of the joints is a lack of ductility. In addition, the samples exhibited a sensitive dependence of the joint strength on the bonding conditions (temperature and pressure).

Barriers For Copper Interconnections

The integration of Cu interconnections will require sophisticated structures to prevent Cu from coming into contact with devices. The barriers for Cu also must have good adhesion with dielectric and Cu, and yield desirable microstructure of Cu. This paper discusses several critical barrier requirements and compares the properties of Ta and Ti/TiN barrier systems.

Electromigration of submicron Damascene copper interconnects

Summary form only given. This paper compares the microstructure and reliability of submicron Damascene CVD and electroplated Cu interconnects. For CVD Cu, the electromigration lifetime degrades in the deep submicron range due to fine grains constrained by the deposition process. However, electroplated Cu has relatively large grains in trenches, resulting in no degradation of reliability in the deep submicron range. The electromigration performance of electroplated Cu is superior to that of CVD Cu especially for deep submicron Damascene interconnects.

Barrier/seed layer requirements for copper interconnects

The microstructure of electroplated Cu is highly dependent on the characteristics of underlying barrier and seed layers. A smooth and strongly textured Cu seed layer is needed to promote the development of highly textured, large grains in the electroplated Cu film, even in damascene structures. This microstructure is desired for extended reliability.