Raymond Nicholas Vrtis

Kinetics of copper drift in low-/spl kappa/ polymer interlevel dielectrics

This paper addresses the drift of copper ions (Cu/sup +/) in various low-permittivity (low-/spl kappa/) polymer dielectrics to identify copper barrier requirements for reliable interconnect integration in future ULSI. Stressing at temperatures of 150-275/spl deg/C and electric fields up to 1.5 MV/cm was conducted on copper-insulator-silicon capacitors to investigate the penetration of Cu/sup +/ into the polymers. The drift properties of Cu/sup +/ in six industrially relevant low-/spl kappa/ organic polymer insulators-parylene-F, benzocyclobutene, fluorinated polyimide, an aromatic hydrocarbon, and two varieties of poly(arylene ether)-were evaluated and compared by capacitance-voltage, current-time, current-voltage, and dielectric time-to-failure measurements. Our study shows that Cu/sup +/ drifts readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. Among these polymers, the copper drift barrier property appears to be improved by increased polymer crosslinking and degraded by polar functional groups in the polymers. A thin nitride cap layer can stop the drift. A physical model has been developed to explain the kinetics of Cu/sup +/ drift.

EVALUATION OF COPPER PENETRATION IN LOW- κ POLYMER DIELECTRICS BY BIAS-TEMPERATURE STRESS

The industry is strongly interested in integrating low- κ dielectrics with Damascene copper. Otherwise, with conventional materials, interconnects cannot continue to scale without limiting circuit performance. Integration of copper wiring with silicon dioxide (oxide) requires barrier encapsulation since copper drifts readily in oxide. An important aspect of integrating copper wiring with low- κ dielectrics is the drift behavior of copper ions in these dielectrics, which will directly impact the barrier requirements and hence integration complexity. This work evaluates and compares the copper drift properties in six low- κ organic polymer dielectrics: parylene-F; benzocyclobutene; fluorinated polyimide; an aromatic hydrocarbon; and two varieties of poly(arylene ether). Copper/oxide/polymer/oxide/silicon capacitors are subjected to bias-temperature stress to accelerate penetration of copper from the gate electrode into the polymer. The oxide-sandwiched dielectric stack is used to overcome interface instabilities occurring when a low- κ dielectric is in direct contact with either the gate metal or silicon substrate. The copper drift rates in the various polymers are estimated by electrical techniques, including capacitance-voltage, current-voltage, and current-time measurements. Results correlate well with timeto-breakdown obtained by stressing the capacitor dielectrics. Our study shows that copper ions drift readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. A qualitative comparison of the chemical structures of the polymers suggests that copper drift in these polymers may possibly be retarded by increased crosslinking and enhanced by polarity in the polymer.

Impact of Pore Size and Morphology of Porous Organosilicate Glasses on Integrated Circuit Manufacturing

Porous organosilicate materials produced by plasma enhanced chemical vapor deposition are the leading candidates for back-end-of-line dielectric insulators for IC manufacturing at 45nm design features and beyond. The properties of porous organosilicate glass films of dielectric constant k=2.50 ± 0.05 formed using diethoxymethylsilane and five different porogen precursors with an ultraviolet post treatment are reported. By varying the porogen precursor type pore sizes of 1-2 nm (equivalent spherical diameter) and porosities in the range of 24-31% were measured. While there were no observable trends in pore size with the molecular volume or plasma reactivity of the porogen precursor, modulus values ranged from 6.6 to 10.8 GPa. Porous films with the highest mechanical properties were found to have the highest matrix dielectric constant, highest network connectivity (lowest methyl content), and highest density. Within this process space, maximizing the network connectivity of the film was found to be more important to mechanical properties than lowering the total porosity. In effect, the choice of porogen precursor dictates the film morphology through its impact on the organosilicate glass matrix and pore size.

Electrical Reliability of Cu and Low- K Dielectric Integration

The recent demonstrations of manufacturable multilevel Cu metallization have heightened interest to integrate Cu and low- K dielectrics for future integrated circuits. For reliable integration of both materials, Cu may need to be encapsulated by barrier materials since Cu ions (Cu + ) might drift through low- K dielectrics to degrade interconnect and device integrity. This paper addresses the use of electrical testing techniques to evaluate the Cu + drift behavior of low- K polymer dielectrics. Specifically, bias-temperature stress and capacitance-voltage measurements are employed as their high sensitivities are well-suited for examining charge instabilities in dielectrics. Charge instabilities other than Cu + drift also exist. For example, when low- K polymers come into direct contact with either a metal or Si, interface-related instabilities attributed to electron/hole injection are observed. To overcome these issues, a planar Cu/oxide/polymer/oxide/Si capacitor test structure is developed for Cu + drift evaluation. Our study shows that Cu + ions drift readily into poly(arylene ether) and fluorinated polyimide, but much more slowly into benzocyclobutene. A thin nitride cap layer can prevent the penetration.

Plasma Enhanced Chemical Vapor Deposition of Porous Organosilicate Glass ILD Films With k ≤ 2.4.

We report on our work to develop a process for depositing nanoporous organosilicate (OSG) films via plasma enhanced chemical vapor deposition (PECVD). This approach entails codepositing an OSG material with a plasma polymerizable hydrocarbon, followed by thermal annealing of the material to remove the porogen, leaving an OSG matrix with nano-sized voids. The dielectric constant of the final film is controlled by varying the ratio of porogen precursor to OSG precursor in the delivery gas. Because of the need to maintain the mechanical strength of the final material, diethoxymethylsilane (DEMS) is utilized as the OSG precursor. Utilizing this route we are able to deposit films with a dielectric constant of 2.55 to 2.20 and hardness of 0.7 to 0.3 GPa, respectively.

Optimized Materials Properties for Organosilicate Glasses Produced by Plasma-Enhanced Chemical Vapor Deposition

In this paper we examine the relationship between precursor structure and material properties for films produced from several leading organosilicon precursors on a common processing platform. Results from our study indicate that for the precursors tested the nature of the precursor has little effect upon film composition but significant impact on film structure and properties. Introduction There are a variety of materials being considered for the next generation interlayer dielectric (ILD) materials. The leading candidates for the 90nm generation are organosilicate glasses produced by Plasma-Enhanced Chemical Vapor Deposition (PECVD). Providing materials with extendibility beyond a single generation solution requires the optimization of both electrical and mechanical properties. These are competing goals since concomitant with reducing the dielectric constant (k) is, in general, a decrease in the mechanical strength of a material. The goal of this work is to build a better understanding of the structure of low k dielectric films deposited from a PECVD process. In attempts to elucidate structureproperty relationships for OSG precursors we assessed a variety of chemicals including those used in various commercial product offerings. Experimental All experiments were performed on an Applied Materials Precision 5000 fitted with a 200mm DxZ chamber. Every attempt was made to optimize process regimes for each precursor to provide the best mechanical properties at a given dielectric constant (k). Films were analyzed for refractive index and thickness with a SCI FilmTek 2000 reflectometer calibrated daily. Electrical tests were performed on low resistivity wafers ( 20 ohm-cm) using a Thermo Nicolet 750 at 4 cm resolution, nitrogen purged cell and background corrected with Si. Selected samples were analyzed using Carbon-13 and Silicon-29 Nuclear Magnetic Resonance (NMR). Density Molecule Si–CH3:Si Si–O:Si Si–H:Si Structure

MOCVD-TiN Barrier Layers for ULSI Applications

Material properties are reported of high quality TiN thin films, deposited by a low temperature (400 – 450 C) and low pressure (10 Torr) metalorganic chemical vapor deposition process using tetrakis(diethylamino)Ti and ammonia. Layer resistivities of less than 200 μΩ cm are achieved in 300 to 500 A thick films. The carbon and oxygen content in the films is found to be low ( Integration of the MOCVD-TiN films in a Ti/TiN/Al-alloy metallization scheme is also reported. The diffusion barrier performance of the MOCVD-TiN layers is found to exceed that of PVD-TiN layers.

Porous low k structural design to meet next generation interconnect needs

As porous low k films are integrated for 45nm/32nm and extend into 22nm/16nm technology nodes, there is a need for more rigorous structural design of porous low k films to meet the integration challenges. This paper demonstrates the ability to tune porous low k films and discusses the impact of these choices to subsequent integration steps such as etch, ash and wet clean processes. Balancing carbon content in the film to minimize damage needs to be coupled with improving mechanical properties for packaging compatibility. By tuning the porous low k deposition process, these properties can be balanced.