Steven E. Molis

Property modifications of nanoporous pSiCOH dielectrics to enhance resistance to plasma-induced damage

The resistance to plasma-induced damage of various nanoporous, ultra low-κ porous SiCOH films used as interconnect dielectric materials in integrated circuits was studied. These films are susceptible to damage by plasma processes used during nanofabrication. The dielectric constants and chemical compositions of four dielectric films were correlated with measured amounts of plasma damage. Films deposited with higher carbon content in the form of Si–CH3 and Si(CH3)2 bonding exhibited less plasma damage than similar films with lower carbon content.

Interface engineering for high interfacial strength between SiCOH and porous SiCOH interconnect dielectrics and diffusion caps

The integration of low- and ultralow-k SiCOH dielectrics in the interconnect structures of very large scale integrated chips involves complex stacks with multiple interfaces. Successful fabrication of reliable chips requires strong adhesion between the different layers of the stacks. A critical interface in the dielectric stack is the interface between the SiCNH diffusion cap and the SiCOH inter- and intralevel dielectrics (ILDs). It was observed that, due to the original deposition conditions, the interface layer was weakened both by a low adhesion strength between SiCNH and SiCOH and by the formation of an initial layer of SiCOH with reduced cohesive strength. The manufacturing process has been modified to engineer this interface and obtain interfacial strengths close to the cohesive strengths of the bulk ILDs. This paper discusses the causes for the original low interfacial strength and presents an approach for enhancing it by engineering the interface to the cap for both the dense SiCOH and porous SiC...

Hydrothermal stability of Cr/polyimide interfaces

The hydrothermal stability of both Cr/polyimide and C75Cr2/polyimide interfaces has been studied using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and peel testing. It was found that RF sputter treatment of the polyimide surface prior to metal deposition leads to an enhancement of adhesion through chemical bonding of the metal with polyimide. Owing to the enhanced chemical bonding at the interface, failure always occurs cohesively in the polyimide. The RF sputter treatment of the polyimide surface also simultaneously modifies the polyimide underneath the surface. The adhesion strength of the Cr/polyimide interface is degraded significantly upon exposure to high temperature and high humidity (85°C/81% relative humidity, T/H) environment. It is suggested that this degradation results from the hydrolysis of polyimide. The hydrolysis is facilitated by the presence of unstable modified polyimide near the interface. This degradation of adhesion strength can be minimiz...

Post Copper CMP Hybrid Clean Process for Advanced BEOL Technology

A “hybrid” post Cu CMP cleaning process that combines acidic and basic clean in sequence is developed and implemented. The new process demonstrates the strengths of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic clean process. It also eliminates the circular ring defects that occur intermittently during roller brush cleans. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. As revealed by XRD analysis, surface Cu oxide is dissolved into aqueous solution by the acidic clean chemical. The formation mechanism of circular ring defects and the key to their elimination is discussed.

Evaluation of Direct Cu Electroplating on Ru: Feature Fill, Parametric, and Reliability

Cu films were directly deposited on Ru to check the feasibility of this process for Cu back-end-of-the-line integration beyond 32-nm technology nodes. Feature-fill enhancement was observed from the direct electroplating process as compared to the conventional one with the Cu electroplating performed on a PVD Cu seeding layer. Reasonable parametric yields were demonstrated for the direct electroplating process. The electromigration (EM) resistance of the directly plated Cu lines was degraded relative to that observed on the conventionally plated Cu lines. The observed EM resistance degradation is attributed to a weak interface between Ru/Cu, which can be caused by impurities from the electroplating process.

Robust Ultrathin (20-25 nm)Trilayer Dielectric Low k Cu Damascene Cap for Sub-30 nm Nanoelectric Devices

Robust ultrathin (20 nm) trilayer low k SiNx/SiNy/SiCNH dielectric Cu caps (k ~4.0-4.2) with post ultraviolet (UV) cure compressive stress were developed and integrated into 22nm CMOS Back End Of Line (BEOL) devices. The new cap reduces device’s capacitance (~ 4 %) and enhances stress stability in Cu-Ultra low k structures.

Hybrid clean approach for post-copper CMP defect reduction

A “hybrid” post-Cu CMP cleaning process that combines acidic and basic cleans in sequence is developed and implemented. The new process demonstrates the advantages of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic brush clean process. It also eliminates the circular ring defects that occur intermittently during roller brush clean. TXRF scans confirm the reduction of AlOx defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. Both short and open yields can be improved by using the new clean process. The underlying mechanism of the huge defect reduction benefits is discussed.

Silane Decomposition on Cu Interconnects Inhibited by Ammonia

The rate of copper silicidation by silane was studied in the presence of varying concentrations of ammonia. The presence of ammonia slowed the rate of silicidation, and the effect quickly saturated as the ammonia concentration was increased. Silane is conventionally used for the chemical vapor deposition of silicon nitride and for copper silicide interface modifications in nanoscale copper interconnects. The ability to control the rate of silane decomposition on copper surfaces enables better control of these processes and reduces Si impurities in the copper interconnect lines.

Effect of RF Sputtering on T/H Susceptibility of Cr/Polyimide Adhesion

Effects of RF sputtering on the hydrothermal stability of Cr/polyimide interfaceshave been studied using FTIR, XPS, and peel test. It has been found that RF sputter-treatment of polyimnide surface prior to metal deposition leads to an enhancement of adhesion through chemical bonding of the metal with polyimide resulting in cohesive polyimide failure. The RF sputter treatment of polyimide, however, simultaneously modifies the polyimide underneath its surface. The adhesion strength of the Cr/polyimide interfaceis degraded significantly upon exposure to a temperature/humidity (T/H) environment. It is suggested this degradation results from the hydrolysis of polyimide. The hydrolysis is facilitated by the presence of modified unstable polyimide near the interface. This degradation of adhesion strength can be minimized by converting the unstablemodified polyimide to a more stable state by re-curing the Cr/polyimide interfacebefore exposure to T/H environment.

A plasmaless, photochemical etch process for porous organosilicate glass films

A plasmaless, photochemical etch process using ultraviolet (UV) light in the presence of NH3 or O2 etched porous organosilicate glass films, also called pSiCOH films, in a two-step process. First, a UV/NH3 or UV/O2 treatment removed carbon (mostly methyl groups bonded to silicon) from a pSiCOH film by demethylation to a depth determined by the treatment exposure time. Second, aqueous HF was used to selectively remove the demethylated layer of the pSiCOH film leaving the methylated layer below. UV in the presence of inert gas or H2 did not demethylate the pSiCOH film. The depth of UV/NH3 demethylation followed diffusion limited kinetics and possible mechanisms of demethylation are presented. Unlike reactive plasma processes, which contain ions that can damage surrounding structures during nanofabrication, the photochemical etch contains no damaging ions. Feasibility of the photochemical etching was shown by comparing it to a plasma-based process to remove the pSiCOH dielectric from between Cu interconnect lines, which is a critical step during air gap fabrication. The findings also expand our understanding of UV photon interactions in pSiCOH films that may contribute to plasma-induced damage to pSiCOH films.A plasmaless, photochemical etch process using ultraviolet (UV) light in the presence of NH3 or O2 etched porous organosilicate glass films, also called pSiCOH films, in a two-step process. First, a UV/NH3 or UV/O2 treatment removed carbon (mostly methyl groups bonded to silicon) from a pSiCOH film by demethylation to a depth determined by the treatment exposure time. Second, aqueous HF was used to selectively remove the demethylated layer of the pSiCOH film leaving the methylated layer below. UV in the presence of inert gas or H2 did not demethylate the pSiCOH film. The depth of UV/NH3 demethylation followed diffusion limited kinetics and possible mechanisms of demethylation are presented. Unlike reactive plasma processes, which contain ions that can damage surrounding structures during nanofabrication, the photochemical etch contains no damaging ions. Feasibility of the photochemical etching w...