Mansour Moinpour

Enhanced adhesion of copper to dielectrics via titanium and chromium additions and sacrificial reactions

Abstract Ti and Cr as both interposed layers and alloying components were found to enhance copper adhesion to dielectrics. Films deposited on SiO2, phosphosilicate glass (PSG) and boronphosphosilicate glass (BPSG) were annealed in 95%Ar-5%H2 over the temperature range 400–600 °C. The force required to separate films from substrates was measured by scratch testing. Optical and scanning electron microscopies provided detection of substrate exposure. In the Cu Ti and Cu Cr bilayer systems the force decreases with temperature on all substrates, generally exhibiting better adhesion on SiO2 than on PSG or BPSG. In the Cu(Ti) and Cu(Cr) alloy systems the force increases with temperature with less systematic difference among the three substrates. These results correlate well with tape testing. Ti and Cr segregate out of the Cu layer and react both with the dielectrics and with the ambient gases, as observed by Rutherford backscattering and secondary ion mass spectroscopy. These reactions appear to improve adhesion; however, only a small amount of this reaction is required for the enhancement to occur. We surmise that stress in the copper and/or voiding at the Cu-dielectric interface may play a role as well. We observe a correlation between adhesion and the degree of Cu texturing.

Mechanistic study of plasma damage of low k dielectric surfaces

Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by Ar, O2, N2, N2∕H2, and H2 plasmas in a standard reactive ion etching chamber and the damage was characterized by angle resolved x-ray photoelectron spectroscopy, x-ray reflectivity, Fourier transform infrared spectroscopy, and contact angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to p...

Composite Polymer-Core Silica-Shell Abrasive Particles during Oxide CMP A Defectivity Study

Ceria-based and fumed silica-based systems are compared for oxide chemical mechanical polishing (CMP) in terms of defectivity and removal rate (RR). Ceria-based slurries yield RR ca. threefold that of conventional silica slurries but result in enhanced defectivity. To reduce defectivity, composite structures comprising a 300 nm polymer core coated by 14 nm ceria particles have been investigated. The polymer core shows mechanical properties that are highly tunable by variation of synthesis parameters, while the major advantage of the ceria coating is an enhanced chemical action of the abrasive particles. We report the evolution of RR, root-mean-square roughness, and defects during silica CMP experiments using different abrasive types at pH 3 and 10. Interestingly, the two types of composites, achieved by either silane coupling agents or electrostatic attractive interactions between the core and the coating, exhibit different RR. This is attributed to differences in morphology and surface composition. Overall, the ceria composites result in reduced defectivity after CMP due to the springlike effect coming from the elastic component of the core, compared with conventional slurry material.

Measurements of Slurry Film Thickness and Wafer Drag during CMP

dIntel Corporation, Santa Clara, California 95052-8119, USA Chemical mechanical planarization ~CMP! is a process widely used for the manufacture of silicon integrated circuits. In this work, we measured the thickness of the slurry film between the wafer and the pad during polish while simultaneously measuring the frictional drag. All experiments are performed on a 1:2 scale laboratory tabletop rotary polisher with variable pad speed and wafer downforce control. Dual emission laser-induced fluorescence techniques optically measured the slurry film thickness through a dual-camera imaging system. The resulting data are discussed for wafers polished with a 3.1 wt % abrasive concentration slurry solution on Freudenberg’s FX-9 polishing pads. It was found that the degree of surface curvature of the wafer substrate significantly influences the slurry film thickness and wafer drag, and therefore, the polish. The convex wafer shows the expected behavior of increased downforce reduces the slurry film thickness and increases the coefficient of friction. Further, as the pad speeds up, the slurry thickness increases and the friction decreases. The concave wafer shows no change in slurry film thickness and a decrease in the frictional coefficient with increasing downforce. Both the film thickness and frictional coefficient appear to decrease slightly with increasing pad speed. This difference between the two wafer shapes reflects the different fluid mechanics in each case.

Origin of dielectric loss induced by oxygen plasma on organo-silicate glass low-k dielectrics

This study investigated the origin of dielectric loss induced by O2 plasma on organo-silicate glass low-k dielectrics. The contributions from the polarization components to dielectric constant were delineated by analyzing the results from capacitance-voltage measurement, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy together with the Kramers–Kronig dispersion relation. The dielectric loss was found to be dominated by the dipole contribution, compared with the electronic and ionic polarizations. The origin of the dipole contribution was further investigated by performing quantum chemistry calculations. The physisorbed water molecules were found to be primarily responsible for the dipole moment increase and the dielectric loss.

Composite Polymer Core–Silica Shell Abrasives: The Effect of the Shape of the Silica Particles on Oxide CMP

We use oxide chemical mechanical planarization (CMP) as a convenient test vehicle for comparing the material removal rate and defectivity induced by different silica abrasives. The effect of particle shape is investigated by comparing fumed and colloidal silica. In particular, the effect of a polymer core on the behavior of a composite abrasive is explored. Overall, fewer and shallower scratches are detected for the composites with a colloidal silica shell as compared with colloidal silica, as well as composites with a fumed silica shell. It is difficult to control the shape and dimension of the fumed silica and fumed silica-based composite agglomerates. Both the length and depth of microscratches increase with particle size and irregularity. Under the same pH conditions, fumed silica and fumed silica-coated abrasives lead to a comparable scratch depth. Fumed silica exhibits agglomerates of greater hardness but higher overall particle stability with respect to its composites, which show lower hardness and lower overall particle stability.

Effect of particle interaction on agglomeration of silica-based CMP slurries

Chemical Mechanical Planarization has become a method of choice for planarization of metal and oxide layers in microelectronics industry. A CMP process includes up to 16 variables that need to be controlled to achieve a stable CMP process [1]. One of the major variables in CMP is related to slurry compositions. In particularly, a uniform distribution of the sizes of the abrasive particle in slurry is crucial for a stable CMP performance. The agglomerates can be unstable, since their size depends on addition of chemical additives and shearing during the CMP process. In this work, the authors studied agglomeration of the fumed and colloidal silica-based slurries using dynamic rheometry, zeta potential tests, and an accusizer. Slurry viscosity, determined using a steady state rheometry, was correlated to the particle charge, characterized by zeta potential, and to the particle sizes obtained using the particle size analyzer. Additionally, rheometer was used for slurry shearing to study effect of shear on slurry characteristics. Particle agglomeration due to slurry shearing and storage was observed and corroborated using rheometry, zeta potential, and particle size measurements.

In Situ Investigation of Slurry Flow Fields during CMP

The objective of this work is to obtain in situ slurry fluid flow data during the chemical mechanical planarization (CMP) process. Slurry flow affects the material removal processes, the creation of defects, and consumable use during CMP, and therefore impacts the cost and quality of polishing. Wafer-scale flow visualization using seeded slurry was accomplished for a variable applied load (0.3-2.5 psi downforce), wafer rotation speed (0 and 33 rpm), slurry injection locations, and various pad types (flat, XY grooved, and AC grooved). In situ pad conditioning was employed in all experiments. The data indicated complex slurry flow fields on the pad surface in the wafer vicinity, which are influenced by slurry injection point, pad grooving, downforce, and wafer/conditioner rotation. Injection location and pad type were shown to have the strongest impact on the variation in the fluid flow fields obtained.

In Situ Measurement of Pressure and Friction during CMP of Contoured Wafers

In situ fluid film pressure and interfacial friction measurements during chemical mechanical planarization (CMP) are reported over a range of applied loads (27.6-41.4 kPA or 4-6 psi) and relative pad/wafer velocities (0.35-0.58 m/s). The slurry film pressure beneath contoured test wafers was measured using a novel experimental setup that enables dynamic data collection. The friction data have a repeatability of ∼10%. The uncertainty of the pressure measurements and the computed down forces were ′2.1 kPa(′0.3 psi) and 20%, respectively. The data indicate that wafer shape, specifically global curvature, is a significant factor in determining the lubrication regime during CMP. Full hydrodynamic lubrication, in which the slurry fluid film supports the entire applied load, was not realized for either concave (center high) or convex (center low) wafers. The data for concave wafers show that -6% to 37% of the applied load is supported by the slurry film, where the negative sign indicates suction conditions that were obtained at the lowest applied load condition. CMP of convex wafers is found to operate closer to full hydrodynamic lubrication, with the fluid layer supporting 36% to 64% of the applied downforce. In all cases, the measured friction coefficient decreased as the support of the fluid layer increased (higher positive pressures). CMP of concave wafers is more sensitive to changes in applied downforce, while the convex wafer type was most affected by changes in the wafer/pad rotation speed, which in turn determines effective slurry film velocity beneath the wafer. Overall, the CMP conditions seen in these scaled experiments operate primarily in the partial lubrication regime shifting closer to hydrodynamic lubrication for convex wafers at the high load, high speed conditions.

Interaction Forces Between a Glass Surface and Ceria-Modified PMMA-Based Abrasives for CMP Measured by Colloidal Probe AFM

Interaction forces between a glass surface and two types of ceria-coated polymethyl methacrylate PMMA-based terpolymerabrasive particles were investigated using colloidal probe atomic force microscopy and correlated with relevant chemical me-chanical planarization CMP and post-CMP parameters. The composite particles were achieved by either creating chemical bondsby silane coupling agents compositeA or tuning the pH in order to form electrostatic attractive interactions between the core andshell composite composite B. Based on the average values of the pull-off force vs pH, a qualitative agreement between themeasured adhesion forces and the material removal rate MRR was found. For pH 3, both the MRR and adhesion forces are largerfor composite B with respect to composite A. Interestingly, for pH 10, composite B and ceria give almost the same MRR andsimilar adhesion force values. Nevertheless, in general, the adhesion forces measured at pH 10 are significantly smaller than thosemonitored at pH 3, whereas the MRR is significantly larger for pH 10. This suggests that factors other than adhesion, such as anenhanced silica dissolution rate, dominate and define the MRR at pH 10. The increase in repulsive force with increasing pHcorresponds to a decrease in composite-glass adhesion. For pH between 2 and 7, the electrostatic attractive forces betweenpolymer particles and the silica surface are responsible for high particle counts. To improve the particle removal efficiency afterCMP with the ceria-based slurry, pH values higher than 7 are recommended.© 2008 The Electrochemical Society. DOI: 10.1149/1.2834456 All rights reserved.Manuscript submitted November 19, 2007; revised manuscript received December 20, 2007.Available electronically January 31, 2008.