Youbo Lin

Nucleation and Adhesion of ALD Copper on Cobalt Adhesion Layers and Tungsten Nitride Diffusion Barriers

Microprocessor technology now relies on copper for most of its electrical interconnections. Because of the high diffusivity of copper, diffusion barriers are needed to keep the copper from diffusing into the insulators and silicon semiconductors, in which copper would degrade or destroy performance. Sputtered tantalum nitride sTaNxd generally serves as the copper diffusion barrier. Another problem with copper is that it has weak adhesion to most other materials, including TaNx. Thus an adhesion-enhancing layer of sputtered tantalum metal ~Ta! is placed between the TaNx and the copper. A thin layer of sputtered copper serves as the seed for electroplating of the bulk of the copper interconnections. The sputtering technology for depositing seed layers of copper is experiencing difficulty in placing the copper within increasingly narrow trenches and vias. 1 If the copper seed layer has any gaps in its continuity, then a void may remain after the electrochemical filling of the conductor. Such a void may cause high resistance or even an open circuit. This problem arises because of the limited step coverage that can be achieved using sputtering. Atomic layer deposition ~ALD! 2 is able to deposit films that are

Selective Chemical Vapor Deposition of Manganese Self-Aligned Capping Layer for Cu Interconnections in Microelectronics

In modern Cu interconnections in microelectronics, weak adhesion between the chemical-mechanical polished copper surface and the dielectric capping material can lead to rapid electromigration of Cu and early failure of the wiring. A self-aligned chemical vapor deposition (CVD) Mn capping process is introduced to strengthen the interface between Cu and dielectric insulators without increasing the resistivity of Cu. In this CVD process, a vapor mixture of Mn precursor and molecular hydrogen deposits Mn selectively on copper and not at all on the adjacent, previously deactivated surfaces of insulators. Deactivation of the insulator surfaces is accomplished by exposure to vapors containing reactive alkylsilyl groups. The presence of Mn at the Cu/insulator interface greatly increases the strength of the bonding between Cu and the insulator. The debonding energy increases approximately linearly with the amount of Mn at the interface, up to values so large that the interface could not be broken apart. This Mn-enhanced binding strength of Cu to insulators is observed for all insulators tested, including plasma-enhanced chemical vapor deposited Si 3 N 4 , SiCNOH, SiO 2 , and low-k SiCOH, as well as thermal SiO 2 and atomic-layer-deposited SiO 2 . This selective CVD Mn capping process should increase the lifetime of advanced copper interconnections.

Filling Narrow Trenches by Iodine-Catalyzed CVD of Copper and Manganese on Manganese Nitride Barrier/Adhesion Layers

We present a process for the void-free filling of sub-100 nm trenches with copper or copper-manganese alloy by chemical vapor deposition (CVD). Conformally deposited manganese nitride serves as an underlayer that initially chemisorbs iodine. CVD of copper or copper-manganese alloy releases the adsorbed iodine atoms from the surface of the manganese nitride, allowing iodine to act as a surfactant catalyst floating on the surface of the growing copper layer. The iodine increases the growth rate of the copper and manganese by an order of magnitude. As the iodine concentrates near the narrowing bottoms of features, void-free, bottom-up filling of CVD of pure copper or copper-manganese alloy is achieved in trenches narrower than 30 nm with aspect ratios up to at least 5:1. The manganese nitride films also show barrier properties against copper diffusion and enhance adhesion between copper and dielectric insulators. During post-deposition annealing, manganese in the alloy diffuses out from copper through the grain boundaries and forms a self-aligned layer that further improves adhesion and barrier properties at the copper/insulator interface. This process provides nanoscale interconnects for microelectronic devices with higher speeds and longer lifetimes.

Octamethylcyclotetrasiloxane-Based, Low-Permittivity Organosilicate Coatings Composition, Structure, and Polarizability

bTexas Instruments, Incorporated, Silicon Technology Development, Dallas, Texas 75243, USA Organosilicate glass OSG coatings with a range of compositions have been deposited using O2, He, and octamethylcyclotetrasiloxane as a precursor in a plasma-enhanced chemical vapor deposition process. Rutherford backscattering spectrometry and forward recoil spectrometry were used to determine the composition of the coatings. The measurements show that addition of carbon and hydrogen lowers the density of the coatings, effectively reducing the concentration of the polarizing species. The dielectric constant is further lowered by a reduction of the ionic and orientation polarizabilities. Fourier transform infrared measurements show that as more C and H are incorporated, the siloxane network is more frequently interrupted by terminal methyl CH3– and H groups. Based on the experimental results a quantitative model for the OSG structure is proposed and the inverse infrared absorption cross sections of various absorption bands are determined, some of which for the first time. The structural model also makes it possible to calculate the average electronic polarizability of the various bond configurations in the OSG.

The Effect of Porogen Loading on the Stiffness and Fracture Energy of Brittle Organosilicates

Integrating porous low-permittivity dielectrics into Cu metallization is one of the strategies to reduce power consumption, signal propagation delays, and crosstalk between interconnects for the next generation of integrated circuits. The porosity and pore structure of these low- k dielectric materials, however, also affect other important material properties in addition to the dielectric constant. In this paper, we investigate the impact of porogen loading on the stiffness and cohesive fracture energy of a series of porous organosilicate glass (OSG) thin films using nanoindentation and the double-cantilever beam (DCB) technique. The OSG films were deposited by plasma-enhanced chemical vapor deposition (PECVD) and had a porosity in the range of 7−45%. We show that the degree of porogen loading during the deposition process changes both the network structure and the porosity of the dielectric, and we resolve the contributions of both effects to the stiffness and fracture energy of the films. The experimental results for stiffness are compared with micromechanical models and finite element calculations. It is demonstrated that the stiffness of the OSG films depends sensitively on their porosity and that considerable improvements in stiffness may be obtained through further optimization of the pore microstructure. The cohesive fracture energy of the films decreases linearly with increasing porosity, consistent with a simple planar through-pore fracture mechanism.

Adhesion Degradation and Water Diffusion in Nanoporous Organosilicate Glass Thin Film Stacks

The diffusion of water in nanoporous organosilicate glass (NPOSG) film stacks causes significant adhesion degradation of the capping layer on top of the NPOSG. We have used this adhesion degradation to estimate the diffusivity of water in an NPOSG film stack. The effective diffusivity is 1.0 × 10- 9 m 2 /s, nearly 2 orders of magnitude larger than in previous generations of dense organosilicate glass film stacks. This result is consistent with the diffusion coefficient measured using secondary-ion mass spectroscopy and a deuterium oxide tracer. An optical microscopy study yields similar results for the diffusion of toluene in NPOSG film stacks, but the optical technique is not suitable for measuring the diffusion coefficient of water.