Takeo Katoh

Effects of Abrasive Morphology and Surfactant Concentration on Polishing Rate of Ceria Slurry

To reveal the mechanism behind the high oxide-to-nitride removal selectivity of ceria slurry in shallow trench isolation (STI) chemical mechanical polishing (CMP), we examined the effects of the abrasive morphology and the concentration of surfactant added to control the selectivity. A slurry with small abrasives showed a more drastic drop in the oxide removal rate as the surfactant concentration increased, compared to a slurry with large abrasives. For the nitride removal rate, however, both slurries showed the same trend. These results can be qualitatively explained from the movement of abrasives though the layer of surfactant adsorbed on the film surface.

Influence of the electrokinetic behaviors of abrasive ceria particles and the deposited plasma-enhanced tetraethylorthosilicate and chemically vapor deposited Si 3 N 4 films in an aqueous medium on chemical mechanical planarization for shallow trench isolation

The effects of the electrokinetic behavior of abrasive ceria particles suspended in an aqueous medium and the deposited plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) Si 3 N 4 films onchemical mechanical planarization (CMP) for shallow trench isolation were investigated. The colloidal characteristics of ceria slurries, such as their stability and surface potential, in acidic, neutral, and alkaline suspensions were examined to determine the correlation between the colloidal properties of ceria slurry and CMP performance. The surface potentials of the ceria particles and the PETEOS and CVD Si 3 N 4 films in an aqueous suspending medium were dependent on the pH of the suspending medium. The differences in surface charges of ceria particles and the PETEOS and CVD Si 3 N 4 films have a profound effect on the removal rate and oxide-to-nitride selectivity of CMP performance.

Influence of Physical Characteristics of Ceria Particles on Polishing Rate of Chemical Mechanical Planarization for Shallow Trench Isolation

By considering the physical characteristics of ceria particles, the factors affecting the chemical mechanical planarization (CMP) performance for shallow trench isolation (STI) were investigated. Ceria powders were synthesized by calcination at temperatures of 400, 600, 700, 800, and 900°C. The influence of the calcination temperature on the physical characteristics, such as the crystallinity, grain size, porosity, morphology and high-resolution lattice images of the ceria particles, were investigated, and a correlation between the physical characteristics and the electrokinetic behaviors of the ceria particles in aqueous suspending media was also investigated to identify the relationship with CMP performance. Grain size increased with calcination temperature, as did the removal rate of plasma-enhanced tetraethylorthosilicate (PETEOS) film with slurries including these particles. The results indicate that the grain size of ceria particles is one of the key parameters controlling the removal rate and uniformity of PETEOS film.

Surfactant Effect on Oxide-to-Nitride Removal Selectivity of Nano-abrasive Ceria Slurry for Chemical Mechanical Polishing

Through a chemical mechanical polishing (CMP) test using oxide and nitride blanket film wafers, we investigated the effect of adding an anionic surfactant to a ceria slurry, especially at very dilute concentrations (less than 0.2 wt%). The removal rate trend, which decreases with increasing surfactant concentration, was compared with the variation in the electrokinetic behavior of the ceria abrasives dispersed in the slurry. The removal rate transition did not coincide with the changes in the zeta potential or the secondary particle size distribution of the abrasives. This suggests that the electrostatic effect is not the dominant factor in the removal rate with ceria slurry. It is also found that abrasive size influences removal rate trend versus surfactant concentration, and that oxide removal follows Prestons law but nitride removal shows non-Prestonian behavior. To explain the result qualitatively, we have proposed a hydrodynamic model in which a particle travels through the viscous fluid and approaches the film surface.

Effect of Molecular Weight of Surfactant in Nano Ceria Slurry on Shallow Trench Isolation Chemical Mechanical Polishing (CMP)

We examined the effect of the molecular weight of surfactants in ceria slurry during chemical mechanical polishing (CMP) for shallow trench isolation (STI). We found that for a surfactant with a higher molecular weight, the oxide removal rate decreased drastically as the surfactant concentration increased, but in the case of a lower molecular weight, it only slightly decreased. In addition, slurries whose surfactants had lower molecular weights maintained a higher nitride removal rate with increasing surfactant concentration. The results showed that the molecular weight and surfactant concentration have complex effects on the oxide removal rate and the oxide-to-nitride removal selectivity.

Effects of the physical characteristics of cerium oxide on plasma-enhanced tetraethylorthosiliate removal rate of chemical mechanical polishing for shallow trench isolation

Ceria powders were synthesized by two different methods, solid-state displacement reaction and wet chemical precipitation, and the influence of the physical characteristics of cerium oxide on the removal rate of plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) nitride films in chemical mechanical planarization (CMP) was investigated. The fundamental physicochemical property and electrokinetic behavior of ceria particles in aqueous suspending media were investigated to identify the correlation between the colloidal property of ceria and the CMP performance. The surface potentials of two different ceria particles are found to have different isoelectric point (pHiep) values and differences in physical properties of ceria particles such as porosity and density were found to be the key parameters in CMP of PETEOS films. Ceria powders synthesized by the solid-state displacement reaction method yielded a higher removal rate of PETEOS and higher selectivity than powders synthesized by the wet chemical precipitation method.

The Stability of Nano Fumed Silica Particles and Its Influence on Chemical Mechanical Planarization for Interlayer Dielectrics.

The effects of water-soluble polymer adsorption on the stability of silica particles and its influence on chemical mechanical planarization (CMP) for interlayer dielectrics (ILD) were investigated. This study was focused on the properties of silica slurry with and without surface modification by analyzing dispersion stability and chemical mechanical planarization field evaluation. As a silica slurry for interlayer dielectric chemical mechanical planarization was prepared in the alkaline region to accelerate the chemical corrosion process of plasma enhanced tetraethlyorthosilicate (PETEOS) film, Si ions dissolved the point where it would adversely affect the colloidal stability of the silica particles. As the silica surface was modified with poly vinyl pyrrolidone (PVP) polymer, the decrease of surface potential above pH 9.0 disappears and thus resulted in an increase of the stability of silica particles dispersed in the alkaline region. Modification of the slurry with PVP reduced micro-scratches and remaining silica particles on the wafers with favorable removal rate and better uniformity.

A Reverse Selectivity Ceria Slurry for the Damascene Gate Chemical Mechanical Planarization Process

The reverse selectivity of nanosized ceria slurry for the damascene gate chemical mechanical planarization (CMP) process has been investigated. The relationship between the electrokinetic behaviors of abrasive ceria particles and the plasma-enhanced tetraethylorthosilicate (PETEOS), and CVD Si3N4 films in an aqueous medium were observed to determine the reverse selectivity performance in the CMP process. The surface potentials of abrasive and PETEOS/CVD Si3N4 films were found to have different surface charges in certain pH regions and these differences were found to be key parameters in the selective removal performance of damascene gate CMP process. The ceria slurry with polymeric additives showed reverse selectivity with a low PETEOS removal rate and a high CVD Si3N4 film removal rate.

Spectral Analyses of the Impact of Nanotopography of Silicon Wafers on Oxide Chemical Mechanical Polishing

The purpose of this study is to investigate quantitatively how the height change of silicon wafer surfaces (nanotopography) impacts on the variation of removal rate during oxide chemical mechanical polishing (CMP). We have analyzed the spatial power spectral densities (PSD) of both nanotopography and thickness variation of oxide film after CMP. We defined a transfer function as the ratio of PSD for the oxide film thickness variation to that for nanotopography. The transfer function decreased with increase of the wavelength and this result quantitatively indicates that longer wavelength of nanotopography influence relatively less on the oxide thickness variation after CMP.

Effects of abrasive size and surfactant concentration on the non-prestonian behavior of ceria slurry in shallow trench isolation chemical mechanical polishing

We examined the dependence of a non-Prestonian behavior on surfactant concentrations in ceria slurries that contained abrasives of various sizes by performing chemical mechanical polishing (CMP) tests using blank wafers. We found that both the surfactant concentrations and the slurry abrasive sizes influence the non-Prestonian behavior. In this paper, we explain in detail a factor that can be used to quantify relation on the non-Prestonian behavior of a slurry, βNP. This non-Prestonian factor βNP was determined to be almost independent of the surfactant concentration in slurry A (large abrasive), but increased with the surfactant concentrations in slurries B (medium-sized abrasive) and C (small abrasive).