Takeshi Momose

Conformal Deposition and Gap-Filling of Copper into Ultranarrow Patterns by Supercritical Fluid Deposition

Supercritical fluid deposition (SCFD) of Cu onto ultranarrow vias (50 to 220 nm and 1 µm depth) was studied with using angled polishing for future ultralarge scale integration metallization. SCFD conformally fabricated a smooth, continuous, and 10-nm-thick Cu film in ultranarrow vias. Excess H2 compared with the precursor as well as surface saturation of the precursor enabled uniform nucleation and conformal deposition. Highest H2 concentration in this study (0.39 mol/L) promoted the nucleation density, resulting in formation of a smooth and continuous film. In conclusion, SCFD successfully achieved complete filling without any voids onto via patterns.

Precursor Evaluation for Cu-Supercritical Fluid Deposition Based on Adhesion Properties and Surface Morphology

Three Cu-precursors [Cu(hfac)2, Cu(DPM)2, and Cu(acac)2] for supercritical fluid deposition (SCFD) were evaluated based on their adhesion strength onto a TiN underlayer for ULSI metallization. Although the fluorinated precursor, Cu(hfac)2, has the highest solubility in supercritical CO2 among these three precursors, the deposited Cu film was hazy and had poor adhesion property due to the fluorine at the interface of Cu and its TiN underlayer. The two non-fluorinated precursors, Cu(DPM)2 and Cu(acac)2, dramatically improved the adhesion property of the deposited Cu film. Although Cu(acac)2 has the lowest solubility among these precursors, it had the lowest nucleation temperature and much smoother surface morphology, which are crucial for ULSI metallization.

Hot-wire-assisted atomic layer deposition of a high quality cobalt film using cobaltocene: Elementary reaction analysis on NHx radical formation

Hot-wire-assisted atomic layer deposition (HW-ALD) has been identified as a successful method to form high quality metallic films using metallocene and NH3. A cobalt film formed by HW-ALD using cobaltocene and NH3 was successfully demonstrated. The authors have elucidated the mechanism of HW-ALD during the precursor feed period and the reducing period. In the case of cobalt, a deposition temperature above 300 °C is needed to avoid an inclusion of carbon impurities. This is because the physisorbed species are involved during the precursor feed period. NH2 radical promotes the dissociation of the carbon–metal bond during the reducing period. This is examined by elucidation of the gas-phase kinetics, estimation of the surface reactions by quantum chemical calculations, and analysis of the exhaust gas using a quadrupole mass spectrometer.

In situ Observation of Initial Nucleation and Growth Processes in Supercritical Fluid Deposition of Copper

The initial nucleation and coalescence of Cu by supercritical fluid deposition (SCFD) were monitored by measuring the surface reflectivity of visible white light. The reflectivity at 770 nm is sensitive to initial nucleation, thus, the nucleation and coalescence temperatures of Cu-SCFD can be easily monitored by this in situ technique. The nucleation temperature of Cu-SCFD was found to be independent of the precursor concentration, which suggests a strong adsorption and surface saturation of the source precursor at high concentration. A high H2 concentration up to 0.39 mol/L with Cu(tmhd)2 as a precursor can decrease the nucleation temperature from 215 to 180 °C. A high H2 concentration is also effective for realizing a smooth surface morphology of the deposited Cu film and for making the film thin at the coalescence stage probably because of the initial nucleation with a high number density. The fabrication of a 10-nm-thick continuous Cu film, which is required as a seed layer in ultralarge scale integration (ULSI), was successfully demonstrated with a high H2 concentration of 0.39 mol/L.

Step Coverage Quality of Cu Films by Supercritical Fluid Deposition Compared with Chemical Vapor Deposition

Feasibility of step coverage (SC) by supercritical fluid deposition (SCFD) of Cu was evaluated using a finite element method (FEM) simulation with experimentally estimated kinetics and transport properties of the precursor. This SC by Cu-SCFD was compared with that by chemical vapor deposition (CVD). SCFD showed superior SC, especially for ultra narrow features less than 1 µm wide, although CVD has a higher diffusion coefficient. This superior SC was due to the non-linear reaction kinetics of SCFD (CVD has linear reaction kinetics), where precursor concentration had negligible effect on growth rate when the precursor concentration was higher than about 1 mol/L.

Deposition of Cu?Ag Alloy Film by Supercritical Fluid Deposition

Cu–Ag alloy films for microelectronics interconnects were deposited by H2 reduction of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) [Cu(tmhd)2] and (1,5-cyclooctadiene) (hexafluoroacetylacetonato)silver(I) [Ag(hfac)(COD)] in supercritical carbon dioxide (scCO2). By varying Ag precursor concentration from 0.001 to 0.003 mol %, while keeping Cu precursor concentration constant, the maximum Ag content in the film can be adjusted from 1.2 to 7.8 at. %. Silver in the films was concentrated near the substrate, because Ag deposition could be initiated first during the deposition process. X-ray diffraction (XRD) analysis showed that a strong Cu(111) texture was formed for all the deposited films including pure Cu film. It was also found that Ag alloying by supercritical fluid deposition (SCFD) would not deteriorate surface quality of Cu film. The electrical resistivity of Cu–Ag film was determined to be between 3.7 and 5.0 µΩcm.

Atomic Layer Deposited Co(W) Film as a Single-Layered Barrier/Liner for Next-Generation Cu-Interconnects

Cobalt film with tungsten addition [Co(W)] has the potential to be an effective single-layered barrier/liner in interconnects awing to its good adhesion with Cu, a lower resistivity than TaN, and an improved barrier property with respect to cobalt films. Our previous study on chemical-vapor-deposited (CVD) Co(W) using carbonyl precursors clarified, however, that WO3 included in the films increased the resistivity. In this current study, to reduce the resistivity of Co(W), oxygen-free Co(W) films were fabricated from two oxygen-free precursors, bis(cyclopentadienyl)cobalt and bis(cyclopentadienyl)tungstendihydride, by atomic layer deposition (ALD) using NH2 radicals generated using a hot filament. Results revealed that (a) W concentration in ALD-Co(W) could be controlled by adjusting the gas-feed sequences, (b) W addition improved the barrier property of ALD-Co(W) against Cu diffusion, (c) diffusion of Cu into ALD-Co(W) had a high activation energy, 2.0 eV, indicating interstitial diffusion, and (d) ALD-Co(W) consisted mainly of an amorphous-like phase, which is consistent with the high activation energy of Cu diffusion.

Ultra-Conformal Metal Coating on High-Aspect-Ratio Three-Dimensional Structures Using Supercritical Fluid: Controlled Selectivity/Non-Selectivity

Underlayer dependence can be controlled for supercritical fluid deposition (SCFD) of Cu. SCFD, which has a remarkable potential for ultra-conformal deposition and gap-filling, has previously required a metallic underlayer to initiate deposition. Here, this constraint has been overcome by depositing a novel catalytic layer, CuMnxOy, onto a semiconducting and insulating substrate. The stoichiometry of CuMnxOy affected both the morphology of CuMnxOy film and the catalytic effect on succeeding SCFD of Cu. By using this technique of depositing CuMnxOy as a catalytic layer, conformal SCFD of Cu was achieved on high-aspect-ratio trenches (aspect ratio 50) whose surfaces were SiO2. In conclusion, a CuMnxOy film with graded stoichiometry in the depth direction might improve the adhesion between Cu and an insulative underlayer.

Precursor-based designs of nano-structures and their processing for Co(W) alloy films as a single layered barrier/liner layer in future Cu-interconnect

The drive to continuously downscale Cu interconnects in ultra-large-scale integrated (ULSI) devices requires strategic improvements in materials and their design processes. For example, development of thinner single-layer barrier/liner materials is desired, because Cu line widths approaching the mean free path greatly increase RC signal delays. We designed Co films with the addition of W [Co(W)] for use as a single-layer barrier/liner material using principles from surface engineering and metallurgy. Dupres equation was used to evaluate the adhesion of metals to Cu, which suggested Co as the main component of our proposed single-layer barrier/liner material. Metallurgical analysis suggested that the addition of W would lead to nanostructural improvements and increased barrier performance in Co films. The Co–W phase diagram suggested that W would segregate at grain boundaries, thereby improving barrier performance due to grain-boundary stuffing. Amidinato, metallocene, and carbonyl Co and W precursors were evaluated in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes for the formation of Co(W) films. Oxygen and halogen inclusions were undesirable, because they were predicted to increase the resistivity and cause deviation from the Co–W binary system. To reduce the prevalence of grain boundaries through formation of an amorphous structure, sequential feeding of Co and W precursors in an ALD process was developed for each set of precursors. Oxygen-free Co(W) CVD and ALD processes were achieved using amidinato and metallocene precursors, both of which led to stuffed grain-boundary structures. ALD-Co(W) films exhibited amorphous structures with sufficient barrier performance and low resistivity, which was consistent with our material and process design.

Kinetic study on hot-wire-assisted atomic layer deposition of nickel thin films

High-purity Ni films were deposited using hot-wire-assisted atomic layer deposition (HW-ALD) at deposition temperatures of 175, 250, and 350 °C. Negligible amount of nitrogen or carbon contamination was detected, even though the authors used NH2 radical as the reducing agent and nickelocene as the precursor. NH2 radicals were generated by the thermal decomposition of NH3 with the assist of HW and used to reduce the adsorbed metal growth precursors. To understand and improve the deposition process, the kinetics of HW-ALD were analyzed using a Langmuir-type model. Unlike remote-plasma-enhanced atomic layer deposition, HW-ALD does not lead to plasma-induced damage. This is a significant advantage, because the authors can supply sufficient NH2 radicals to deposit high-purity metallic films by adjusting the distance between the hot wire and the substrate. NH2 radicals have a short lifetime, and it was important to use a short distance between the radical generation site and substrate. Furthermore, the impurity...