Interaction, transformation and toxicity assessment of particles and additives used in the semiconducting industry

Chemical mechanical planarization (CMP) is a widely used technique for the manufacturing of integrated circuit chips in the semiconductor industry. The process generates large amounts of waste containing engineered particles, chemical additives, and chemo-mechanically removed compounds. The environmental and health effects associated with the release of CMP materials are largely unknown and have recently become of significant concern. Using a zebrafish embryo assay, we established toxicity profiles of individual CMP particle abrasives (SiO₂ and CeO₂), chemical additives (hydrogen peroxide, proline, glycine, nicotinic acid, and benzotriazole), as well as three model representative slurries and their resulting waste. These materials were characterized before and after use in a typical CMP process in order to assess changes that may affect their toxicological profile and alter their surface chemistry due to polishing. Toxicity outcome in zebrafish is discussed in relation with the physicochemical characteristics of the abrasive particles and with the type and concentration profile of the slurry components pre and post-polishing, as well as the interactions between particle abrasives and additives. This work provides toxicological information of realistic CMP slurries and their polishing waste, and can be used as a guideline to predict the impact of these materials in the environment.

Functional Paper-Based Platform for Rapid Capture and Detection of CeO2 Nanoparticles

Development of systems for capture, sequestration, and tracking of nanoparticles (NPs) is becoming a significant focus in many aspects of nanotechnology and environmental research. These systems enable a broad range of applications for evaluating concentration, distribution, and effects of NPs for environmental, clinical, epidemiological, and occupational exposure studies. Herein, we describe the first example of a ligand-graft multifunctional platform for capture and detection of cerium oxide (CeO₂ or ceria) NPs. The approach involves the use of redox-active ligands containing o-dihydroxy functionality, enabling multivalent binding, surface retention, and formation of charge transfer complexes between the grafted ligand and the NPs. Using this strategy, paper-based and microarray-printed platforms with NP-capture ability involving either catechol or ascorbic acid as ligands were successfully fabricated. Surface modification was determined by infrared spectroscopy, electron microscopy, X-ray spectroscopy, and thermogravimetric analysis. Functionality was demonstrated for the rapid assessment of NPs in chemical mechanical planarization (CMP) slurries and CMP wastewaters. This novel approach can enable further development of devices and separation technologies including platforms for retention and separation of NPs and measurement tools for detection of NPs in various environments.

Observation of the formation of anisotropic silver microstructures by evanescent wave and electron microscopy

Using a well-known galvanic displacement reaction, ∼25-40 μm long silver ribbons grown after mixing ∼50 nm copper particles with AgNO3 solution were observed as a function of Ag(+) concentration and their growth was characterized in real-time and in situ by evanescent wave (EW) microscopy. At low Ag(+) concentration, chain-like structures consisting of both Ag and Cu were observed. When the sequence of mixing these two reactants was reversed, different Ag microstructures (platelets and dendrites) were formed and were also characterized by EW microscopy. Dependence of the morphology of all these microstructures on silver ion concentration was determined by EW microscopy in conjunction with scanning and transmission electron microscopy.

Real time imaging of the growth of silver ribbons by evanescent wave microscopy

Real time visualization of the in situ growth of ∼40 μm long silver ribbons, synthesized by template-free galvanic displacement using ∼100 nm Cu particles and Ag ions in aqueous conditions, is demonstrated using evanescent wave microscopy.

Charge density and pH effects on polycation adsorption on poly-Si, SiO2, and Si3N4 films and impact on removal during chemical mechanical polishing

The pH-dependent interactions of five aqueous abrasive-free polycationic solutions, all at a concentration of 250 ppm, with poly-Si, SiO(2), and Si(3)N(4) films and IC1000 polishing pads used in chemical mechanical polishing have been investigated and compared with the interaction of poly(diallyldimethyl ammonium chloride) (PDADMAC) that was investigated recently. Three of the polycationic solutions, poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), poly(allylamine), and poly(ethylene imine) (PEI) enhance poly-Si removal rates (RRs) to the range of about 500 to 600 nm/min at pH 10. In contrast, poly(acrylamide) (PAA) suppressed poly-Si RRs to about 50 nm/min, whereas with a copolymer of PAA and PDADMAC, the RRs were lower than those obtained with PDADMAC but higher than those obtained with PAA. For all the polycationic solutions, the RRs of both SiO(2), and Si(3)N(4) films were ~0 nm/min. These solutions offer a low-defect option for the processing of emerging FinFET devices. The variation in the RR magnitude and dependence on pH among the different polycations is related to the relative charge density of the polycations as well as the films being polished, consistent with ζ potential data. Based on the ζ potential data and earlier published reports, it is suggested that the strong polycation-mediated bridging interactions between the polarized and weakened Si-Si bonds of the poly-Si surface and the polyurethane IC 1000 pad are responsible for the high poly-Si RRs.

Role of poly(diallyldimethylammonium chloride) in selective polishing of polysilicon over silicon dioxide and silicon nitride films

A cationic polymer, poly(diallyldimethylammonium chloride), or PDADMAC (MW ≈ 200,000), at a concentration of 250 ppm was used to enhance polysilicon removal rates (RRs) to ∼600 nm/min while simultaneously suppressing both silicon dioxide and silicon nitride RRs to <1 nm/min, both in the absence or in the presence of ceria or silica abrasives during chemical mechanical polishing (CMP). These results suggest that aqueous abrasive-free solutions of PDADMAC are very attractive candidates for several front-end-of-line (FEOL) CMP processes. Possible mechanisms for the enhancement of poly-Si RR and the suppression of oxide and nitride RRs are proposed on the basis of the RRs, contact angle data on poly-Si films, zeta potentials of polishing pads, polysilicon films, silicon nitride particles, and silica and ceria abrasives, thermogravimetric analysis, and UV-vis spectroscopy data.

Effect Of pH On Chemical-Mechanical Polishing Of Copper And Tantalum

pH has a strong effect on the polish rates of copper (Cu) and tantalum (Ta) [1]. In this paper, removal rates of Cu and Ta using aqueous slurries containing alumina and silica abrasives in H2O2-glycine solution are studied at varying pH values. It is observed that variation in the Cu and Ta removal rates is a direct result of the change in surface characteristics of the films. Surface characteristics such as presence/absence of a passivating layer and hardness of such layer vary with pH and hence result in removal rate variation. It is also shown that a favorable Cu/Ta polish rate selectivity can be obtained by adjusting the pH of the slurry.

Novel phosphate-functionalized silica-based dispersions for selectively polishing silicon nitride over silicon dioxide and polysilicon films

We prepared and characterized novel phosphate-functionalized silica particles, and showed that, by using them during chemical mechanical polishing, both silicon dioxide and polysilicon removal rates can be suppressed while simultaneously enhancing silicon nitride removal rates. We achieved a silicon nitride:silicon dioxide:polysilicon removal rate selectivity of (>20):1:1. The measured removal rates of silicon dioxide, silicon nitride, and polysilicon are related to the electrostatic interactions and chemical reactivity between these films and the modified-silica abrasives.

Particle adhesion studies relevant to chemical mechanical polishing

This study describes particle adhesion experiments carried out to elucidate interactions between particles in slurries used for polishing of wafers and disks. For this purpose the packed column technique was employed, which simulated chemical mechanical polishing of copper with silica and alumina, as well as of silicic oxide with ceria. The model systems consisted of uniform copper and glass beads as collectors, representing the wafers, and colloidal dispersions of silica, alumia, and silica coated with nanosize ceria, all of well-defined properties that are used as abrasives. It was shown that a strong correlation exists between deposition and detachment results of the adhesion studies and the polish rates measured using actual substrates with the same or similar slurries.

The use of monodispersed colloids in the polishing of copper and tantalum

The properties of abrasive particles play a significant role in chemical mechanical polishing (CMP) of metal and dielectric films in semiconductor device manufacturing. This study investigates the effects of the particle size, shape, and hardness of abrasives on the polishing of copper and tantalum films in the presence of different slurry chemistries. Well-defined dispersions of uniform particles, including spherical silica of varying diameters, hematite of different shapes, and hematite cores coated with silica of different thicknesses, were prepared and used to polish blanket films of Cu and Ta. It was shown that the total surface area of the solids in the slurry controlled the rate of material removal by pure silica for both Cu and Ta, while the surface quality of the polished films was better when higher silica content was used. The shape or the aspect ratio of hematite particles had a minor effect on the removal rate. In contrast, when hematite particles coated with silica were employed in the polishing of Cu and Ta, the polish rate decreased with increasing thickness of the shell.

Type 1 phosphatase inhibitors reduce the restoration of guanine nucleotide exchange activity of eukaryotic initiation factor 2B inhibited reticulocyte lysates rescued by hemin

In heme-deficient reticulocyte lysates, the alpha-subunit of eukaryotic initiation factor-2 (eIF-2alpha) is phosphorylated due to the activation of the heme-regulated eIF-2alpha kinase (HRI). Phosphorylation of eIF-2alpha impairs the guanine nucleotide exchange activity of eIF-2B and thereby inhibits or shuts off protein synthesis. Delayed addition of hemin to shut-off lysates inhibits the eIF-2alpha kinase activity of HRI and restores protein synthesis; under those conditions, the endogenous phosphatase of the lysate dephosphorylates phosphorylated eIF-2alpha and restores eIF-2B activity. In this report we present evidence that the restoration of eIF-2B activity is dependent on the concentration of added hemin and is related to HRI activity in lysates. The recovery of eIF-2B activity is not affected by protein synthesis inhibitors such as cycloheximide, pactamycin and puromycin, which do not affect the eIF-2alpha phosphorylation. Also, the functional eIF-2B activity that is available in hemin-supplemented lysates is not affected by phosphatase inhibitors such as okadaic acid and heat-stable inhibitor-2. However, the recovery of eIF-2B activity that is observed by the delayed addition of hemin to inhibited heme-deficient lysates is reduced by inhibitor-2 and high concentrations of okadaic acid. These findings suggest that a type 1 phosphatase is involved in the recovery of eIF-2B activity and protein synthesis upon delayed addition of hemin to heme-deficient lysates.

A Comparative Study of the Photoablation of Polyimide-Doped Poly(Tetrafluoroethylene) at 308 NM and 248 NM

Experimental data on the 248 nm and 308 nm wavelength excimer laser ablation of poly(tetrafluoroethylene) (PTFE) doped with polyimide (PI) are reported for a range of fluences and dopant concentrations. Threshold fluences were determined and correlated with the dopant concentrations. The threshold fluences and the limiting etch rates measured at high fluences decreased with increasing dopant concentration and there is a minimum absorption coefficient below which there is no ablation at both the wavelengths. The etch rates have been modeled using a two parameter Arrhenius thermal model to describe the etching process.

Two-step regression procedure for the optical characterization of thin films

A diode array rapid scan spectrometer is used for measuring the intensity of polychromatic light in the 300-420-nm range reflected from a diamondlike carbon film as a function of wavelength. With a fixed grating setting, the wavelength range of 120 nm can be covered in 23 ms. From the reflected intensity, a new two-step regression procedure is utilized to determine refractive index, bandgap, slope of the absorption edge, and film thickness. The calculated parameters are independent of the starting set and the sequence of parameter estimation. The accuracy of the regression procedure is verified by comparison to the envelope method. It is shown using simulated data that, for strongly absorbing films, the new regression procedure is more accurate than the envelope method. The new regression method can handle very noisy reflectance spectra also.