David L. Rath

Comparison of Cu electromigration lifetime in Cu interconnects coated with various caps

Electromigration in Cu Damascene lines with bamboo-like grain structures, either capped with Ta/TaN, SiNx, SiCxNyHz layers, or without any cap, was investigated. A thin Ta/TaN cap on top of the Cu line surface significantly improves electromigration lifetime when compared with lines without a cap and with lines capped with SiNx or SiCxNyHz. The activation energy for electromigration increased from 0.87 eV for lines without a cap to 1.0–1.1 eV for samples with SiNx or SiCxNyHz caps and to 1.4 eV for Ta/TaN capped samples.

Effects of overlayers on electromigration reliability improvement for Cu/low K interconnects

Electromigration in Cu Damascene lines capped with either a CoWP, Ta/TaN, SiN/sub x/, or SiC/sub x/N/sub y/H/sub z/ layer was reviewed. A thin CoWP or Ta/TaN cap on top of the Cu line surface significantly reduced interface diffusion and improved the electromigration lifetime when compared with lines capped with SiN/sub x/ or SiC/sub x/N/sub y/H/sub z/. Activation energies for electromigration were found to be 2.0 eV, 1.4 eV, and 0.85-1.1 eV for the Cu lines capped with CoWP, Ta/TaN, and SiN/sub x/ or SiC/sub x/N/sub y/H/sub z/, respectively.

Enhancement of Semiconductor Wafer Cleaning by Chelating Agent Addition

To realize environmental and cost benefits it is desirable to reduce the RCA cleaning sequence from its historical SCI + SC2 combination, in which the particle-removing SC1 solution deposits certain metals, necessitating the metal-removing SC2. One approach is to add a chelating agent to the SC1. Extensive testing of SCI solutions with addition of the complexing agent 1,2-cyclohexanediaminetetraacetic acid (CDTA) were performed. CDTA was shown to he more stable than other complexing agents in SC1 solutions, facilitating significant hath life extension. Further, SC1 solutions with CDTA were shown to be capable of removing large quantities of metals from contaminated wafers, comparable to SC2, and preventing deposition of metals. An exception is aluminum, which can deposit from SC1 even with large amounts of added CDTA, but which can he removed by a subsequent dilute (1000:1) H 2 O:HCl step.

Studies of electrode resistance in the electrochemical cell

Abstract With thin metal films used as electrodes, double-layer processes can be tracked and identified by the complimentary technique of electrode resistance monitoring. This is demonstrated with chloride adsorption and lead underpotential deposition on gold electrodes. An example of the latter system with the process of controlled electrode emersion is included where the continuously measured resistance clearly shows that the lead adlayer is removed completely intact with the electrode. A simple model for adionic effects on conduction electron scattering at metal surfaces is proposed and found to correlate well with the experiment. The merits of the electrode resistance measurement for in situ studies are discussed.

CVD-Co/Cu(Mn) integration and reliability for 10 nm node

In studying integrated dual damascene hardware at 10 nm node dimensions, we identified the mechanism for Co liner enhancement of Cu gap-fill to be a wetting improvement of the PVD Cu seed, rather than a local nucleation enhancement for Cu plating. We then show that Co “divot” (top-comer slit void defect) formation can be suppressed by a new wet chemistry, in turn eliminating divot-induced EM degradation. Further, we confirm a relative decrease in Cu-alloy seed proportional resistivity impact compared to scattering at scaled dimensions, and finally we address the incompatibility between the commonly-used carbonyl-based CVD-Co process with Cu-alloy seed EM performance This problem is due to oxidation of Ta(N) barriers at the TaN/CVD-Co interface by carbonyl-based CVD processes, which then consumes alloy atoms before they can segregate at the Cu/cap interface. We show that O-free CVD-Co may solve this problem. The above solutions may then enable CVD-Co/Cu-alloy seed integration in advanced nodes.

Copper-to-dielectric heterogeneous bonding for 3D integration

A novel hybrid bonding process has been developed that achieved a successful copper/SiO2 heterogeneous bonding.

Resistance contributions to copper interconnects

Experimental decomposition of contributions of electron scattering events in deeply scaled interconnects has been complicated by the fact that grain size and line dimensions are generally not varied independently. In this paper, we describe a combination of experiments to examine scattering mechanism independently. The cross section of was changed by recessing individual copper interconnects from the top using wet chemical etching, which was combined with repeated cryogenic resistance measurements. A fit for the grain boundary reflectivity was then obtained. In addition, it was found that the average grain size increase from the bottom to the top of the interconnect. This was confirmed by TEM based grain size measurements. Further, in order to assess surface scattering, magnetoresistance was employed for the first time for interconnects. It is observed to be sensitive to the geometry of the line. The method also allows for independent assessment of sidewall vs. bottom/top surface scattering. Results indicate that sidewall scattering is more severe than top/bottom surface scattering.