We extend our recent 2D trajectory (x–y plane) and diffusion coefficient data of ceria particles near a glass surface obtained at pH 3, 5, and 7 using evanescent wave microscopy and video imaging to 3D trajectories by analyzing the separation distance between the particles and the glass surface in the vertical z-direction. Mean squared displacement (MSD3D) of ceria particles was calculated to quantify 3D trajectories. Three-dimensional diffusion coefficients were obtained from the MSD3D curves and were compared with two-dimensional diffusion coefficients. By analyzing the MSD curves, we found that ceria particles exhibited only confined motion at pH 3 and 5, while both confined and Brownian motion were showed at pH 7. We also evaluated the cleaning ability of DI water adjusted to pH 10 and 12 to remove ceria particles from glass surfaces and related the results to the calculated trajectory, diffusion coefficient, and interaction potential data.

Aluminum (Al) gate fill has been implemented in Replacement Metal Gate (RMG) due to its low resistivity. Titanium (Ti) has been widely used as wetting layer for Al to fill the gates. For low resistance gate fill in structures with small feature size and high aspect ratio, Ti-Al metal fill becomes increasingly more challenging as we move from 20nm into 14nm FinFET and 3D type structures.

Cobalt (Co) is a good wetting film for Al with better fill performance and lower resistance than Ti-Al based process. However, due to the difference in corrosion potential between Al and Co, Chemical Mechanical Planarization (CMP) creates pitting type defects on Al-Co film that increases resistance variability across pattern density. CMP induced corrosion is separated in two parts; first is the static Co corrosion happened in the acidic chemical environment in the Al slurry. Second is the galvanic corrosion from Co-Al metal boundary due to high metal electrical potential. Static corrosion can be resolved by adding a Co corrosion inhibitor in the slurry formulation1. Galvanic corrosion can be minimized by controlling Co thickness deposition and formation of complete intermetallic phase. By controlling the removal rate with respect to corrosion rate we were able to suppress corrosion significantly.

We looked into compositions where the corrosion potential (Ecorr) gap between Al and Co is reduced to ≤10mV leading to reduced galvanic currents. Stabilization of the corrosion currents in both Al and Co was observed using potentiodynamic scans. The effect of pH, several oxidizers and additives on the open circuit potentials (Eoc) of Al and Co was investigated and it was found that solutions of KMnO4, saccharides and sulfonate group containing compounds help reduce the Ecorr gap in between Al and Co to ∼10 mV.

Controlling the Al gate height across pattern densities and gate lengths to within few nm is another challenge for Al CMP. The industry widely used approach is to clear all Al using a slurry with high selectivity to dielectric, followed by a CMP step using a non-selective Al-to-oxide slurry. Both polishing steps need to be optimized in parallel in order to remove the incoming spacer SiN divot, minimize Al loss on gates with high pattern density or long gate length, minimize oxide loss on large open areas while maintaining low defectivity.

In this paper we are presenting an innovate Al CMP process that demonstrated low gate resistance with tight distribution up to 80% pattern density. This work has been supported by the independent Bulk CMOS and SOI technology development projects at the IBM Microelectronics Division Semiconductor Research & Development Center, Hopewell Junction, NY 12533.

An important component of the slurries used in chemical mechanical planarization (CMP) is an appropriately chosen corrosion/dissolution inhibitor, which facilitates selective material removal from protrusions while protecting recessed regions of the surface. The present work demonstrates the utility of two environmentally benign anionic surfactants, sodium dodecyl sulfate (SDS) and ammonium dodecyl sulfate (ADS) as dissolution inhibitors. Using a standard slurry (1 wt% glycine with 5 wt% H2O2 at pH = 4.0) typically used for Cu CMP and combining measurements of open circuit potentials and contact angles with those of Cu removal rates, we show that both SDS and ADS suppress chemical dissolution and polish rates of Cu. The dissolution inhibition efficiencies of ADS and SDS measured in these experiments are found to be superior to those of benzotriazole (BTA), a traditional inhibiting agent used for copper CMP.

Slurries containing molybdenum oxide abrasives (MoO2, isoelectric point ∼pH 2) with potassium iodate (KIO3) as the oxidizing agent were used to polish copper disks and films, yielding relatively high removal rates. The relatively high copper removal rates observed were due to the in situ generation of I2 by the reaction between KIO3 and MoO2. The surface quality of the polished Cu films, however, was very poor with surface roughness values as high as 140 nm. A second polishing step using a dilute colloidal silica suspension containing H2O2, benzotriazole, and glycine at pH 4 improved the post-polish surface quality, final surface having surface roughness values as low as 0.35 nm.

The role of the molecular structure - different functional groups, the length of the carbon chain and the relative positions of different functional groups – of several complexing/chelating agents (acetic acid, glycine, ethylene diamine, succinic acid, alanine and amino butyric acid (ABA)) in controlling copper (Cu) removal rates was investigated. The results are consistent with the known activity of –COOH groups at acidic conditions and that of –NH2 groups in an alkaline environment. In comparison with glycine, it was also observed that an increase in the carbon chain length increased the removal rates at acidic pH values and decreased the removal rates at alkaline pH values. Also, Cu removal rates decreased with an increase in the distance between the –NH2 and –COOH groups in an amino acid at all pH values except at 4.

In this study, the interaction between several kinds of surfactants and copper surface was examined to control the dissolution of copper during CMP. Among those surfactants, sodium dodecylsulfate (SDS), one of the conventional anionic surfactants, showed effective interaction with copper and significantly suppressed the dissolution of the copper at acidic and neutral pH ranges in a model copper CMP slurry system consisting of 3 wt% fumed silica, 1 wt% glycine, and 5 wt% hydrogen peroxide in deionized water. The inhibition performance of copper dissolution by SDS is better than that of Benzotriazole (BTA), a conventional inhibiting agent of copper dissolution in a copper CMP slurry.

The polishing pad is one of the prime components in a typical Chemical Mechanical Polishing (CMP) process. The structure and transport properties of a polishing pad are critical in determining the particle and chemical utilization in a conventional CMP process. Our earlier paper investigated the particle retention and transport on two different polishing pads, IC-1400 and Suba-500, during copper polishing. In this paper, the results of chemical retention and transport of IC-1400 and Suba-500 pads during copper polishing are presented. The polish rate results from slurry-step-flow experiments with H2O2-glycine based slurries, where the concentrations of chemicals in the slurry are altered in steps during polishing, are correlated to the chemical retention and transport characteristics of these pads. It is found that IC-1400 has a higher chemical transport capability than Suba-500 pad, which is shown to affect the polish rates of copper.

Two complexing agents, glycine and citric acid, in hydrogen peroxide based slurries for planarizing copper have been compared. Copper dissolution and polish rates and in situ electrochemical experimental results at various slurry pH values and hydroxyl radical concentrations at pH=8.4 are presented. It was observed that the pH of the slurry has a strong influence on copper dissolution and polish rates. While high copper removal rates were observed with citric acid-peroxide solutions at low pH values, glycineperoxide system yielded high Cu removal rates at alkaline pH values. Copper dissolution rates in both the systems at pH 4 and 8 were consistent with the electrochemical measurements. The concentration of hydroxyl radicals generated in citric acid-peroxide system was less than that of those generated in glycine peroxide system at pH=8.4 indicating low copper removal rates at alkaline conditions in the former system.

The process of copper chemical-mechanical planarization (CMP) can be considered as an erosion corrosion process. Such a process can be efficiently studied by in situ and ex situ electrochemical techniques, such as potentiodynamic scan and electrochemical impedance spectroscopy (EIS). Using a copper disk as the working electrode in an electrochemical cell, slurries with different oxidizer concentrations have been investigated with the aforementioned techniques. Corresponding dissolution tests were also studied and compared. It is shown that changing the oxidizer concentration leads to the formation of surface films with different structure and composition on the copper surface during CMP process. The nature of these films controls the rate of copper corrosion. These results could be used to explain the change of copper removal rate in different oxidizer concentration, as well as to understand the copper CMP mechanism.

The properties of abrasive particles, and their interactions with surface films to be polished, play a key role in chemical mechanical polishing (CMP). This study applies the packed column technique for the investigation of the adhesion phenomena at the particle/film interface as a function of different slurry chemistries relevant to polishing processes. Well-defined dispersions, including uniform spherical silica and silica cores coated with nanosized ceria, as well as calcined alumina were used to represent slurry abrasives, and copper or glass beads to simulate wafers or discs. It was shown that the pH and slurry flow rate had significant effects on particle attachment and removal. The results of deposition of silica particles on copper beads in the presence of various concentrations of H2O2 and of detachment from copper beads of alumina particles, loaded at different pH values, had strong correlations to the polish rates of the metal.

We investigated pattern density effects during chemical mechanical planarization (CMP) for shallow trench isolation (STI) applications using fixed abrasive pads to better control the fixed abrasive polishing process. We observed that the polishing characteristics of higher pattern density features are strongly dependent on the presence of lower pattern density features on the same die in the wafer. This has been attributed to the aggressive action of lower pattern density features on the fixed abrasive pad which results in a more effective activation of the pad by them. Thus even the 100% pattern density features are initially polished at a very high rate when lower density features are present.

Mixed abrasive slurries (MAS) containing alumina/silica and alumina/ceria abrasives were evaluated for CMP of metal and dielectric films, respectively. MAS with 0.5wt% calcined alumina and 2.5wt% silica (fumed and colloidal) abrasives were highly selective to tantalum polishing over copper and oxide. Similarly, MAS containing 1.5wt% calcined alumina and 3wt% colloidal ceria particles offered a polish rate selectivity between silicon dioxide and silicon nitride films of more than 30, without any additives, without compromising finished surface quality. This improved performance appears to be a result of modified surface morphology as well as synergistic interactions between the chemical activity of silica or ceria and the hardness of the alumina.

Experimental results on chemical mechanical polishing of copper and tantalum in the presence of different chemicals, such as Fe(NO3)3, H2O2 and glycine, using both silica and alumina abrasive particles are presented. The polish rates with alumina slurries vary in accordance with the hardness of the material being polished, suggesting a dominant role for a wear mechanism. However, polish rates with silica slurries do not relate directly to the hardness of the film, indicating a more complex removal mechanism.

Planarization of dielectric films, silicon dioxide, silicon nitride, etc. by Chemical- Mechanical Polishing (CMP) is regulated and moderated by the interaction of the abrasive particles and chemicals in solution with the film surface through complex chemical and physical processes. Changes in the slurry properties have a profound effect on the polishing chemistry and relative removal rates of dielectric films. Common slurry properties include pH, temperature, abrasive particle composition, its size and shape, degree of agglomeration, and weight percent, and chemical composition. While the slurry vendor has control over most slurry properties, the pH and temperature can be controlled during the polishing process by the user and can have a strong influence. Data are presented highlighting the influence of pH and temperature on the CMP of both blanket and patterned silicon dioxide and silicon nitride films.

Nanoindentation techniques were used to determine the hardness of Cu, Ta & W metal discs and thin films on silicon substrates as a function of load or indentation depth. Cu films exposed to oxidizing solutions containing H202 exhibited a higher hardness at the surface while no such change was observed for W exposed to ferric nitrate. The implication of these measurements and their relationship to chemical-mechanical polishing rates are discussed.

Hydroxyl radical generation has been observed during Cu CMP using hydrogen peroxide-glycine based slurries. While the Cu dissolution/polish rates increased with increasing glycine concentration, the copper dissolution rate decreased with increasing peroxide concentration indicating the occurrence of both dissolution and passive film formation during CMP. This is further confirmed by both in situ and ex situ electrochemical experiments.

The effect of pressure and velocity on the polish rates of copper was determined in DI water and in the presence of ferric nitrate, H202/glycine, and NH4OH with alumina particles as the abrasives. The polish rate shows a stronger dependence on velocity than that predicted by the Preston equation in the case of ferric nitrate, a highly reactive chemical. The velocity dependence is weaker for the other two less reactive chemicals, and is the same as that predicted by Preston equation for DI water. Our earlier empirical model, R = KPV + BV + Rc, where K, B, and Rc are constants, describes all the polish rate data satisfactorily.

0.25 μm thick, single crystal, n-type, silicon carbide (β-SiC) films thermally grown on p-type Si(100) were doped with boron by using KrF excimer laser radiation and a spin-on dopant with a boron concentration of 1020/cm3. The threshold fluence for the doping to occur was approximately 0.08 J/cm2. Similarly, p-SiC/n-SiC diodes were fabricated by laser-induced doping of single-crystal β-SiC (n-type, 6 μm thick) films on n-type Si(100). The diodes obtained at 0.25 J/cm2 showed good rectifying characteristics. The threshold fluence for surface modification and/or ablation was approximately 0.3 J/cm2, indicating that doping and diode formation have to be accomplished within the fluence window of 0.08 J/cm2-0.3 J/cm2 for these films.

Amorphous silicon germanium (a-SiGe) films, deposited on silicon substrates at room temperature in a molecular beam epitaxy system, were transformed into a single-crystal film and doped with phosphorus by exposure to KrF laser pulses. Electron channeling patterns showed that laser exposure resulted in crystallization of the undoped a-SiGe films. The SiGe films were doped by laser irradiation, using a phosphorus spin-on-dopant. The sheet resistance of the doped films decreased with increasing numbers of pulses, reaching a value of about ∼ 5 × 104 ohms/□ after 15 pulses. I-V data from mesa-type n-SiGe/p-Si diode devices were used to determine the effect of laser processing on the quality of the SiGe films.