Trench Isolation Chemical Mechanical Polishing Research Articles

Effects of Gas-Dissolved Water for Ceria Nanoparticles on the SiO2 Film Surface in Post-CMP Cleaning

As a trend of using colloidal and smaller ceria nanoparticles (CNPs) at the shallow trench isolation (STI) chemical mechanical polishing (CMP) in semiconductor manufacturing, post-CMP cleaning challenges in the removal of residual CNPs on the SiO2 film surface became much more challenging. We investigated the reduction/oxidation of ceria nanoparticles (CNPs) by hydrogen gas-dissolved water (H2 GDW), carbon dioxide gas-dissolved water (CO2 GDW), and oxygen gas-dissolved water (O2 GDW). The concentration of Ce3+ on the CNPs changed from 18.64% to 19.48%, 20.31% to 21.94%, and 21.27% to 19.22%, respectively, after immersion in H2 GDW, CO2 GDW, and O2 GDW for 3 to 12 h. Following the Ce3+ concentration of the CNP surface, adhesion energies between CNPs immersed in H2 GDW, CO2 GDW, and O2 GDW for 6 h with SiO2 surface were 6.06E-16 J, 6.18E-16 J, and 4.83E-16 J. Cleaning experiments under megasonic conditions revealed the efficacy of H2 GDW and O2 GDW in removing residual CNPs from SiO2 surfaces. The residual cerium (Ce) ion concentrations remaining on the SiO2 film surface after cleaning, were 0.06, 0.41, and 0.10 ppb for H2 GDW, CO2 GDW, and O2 GDW, respectively.

Enhancing ceria slurry performance for shallow trench isolation chemical mechanical polishing through non-ionic surfactant addition

Enhancing ceria slurry performance for shallow trench isolation chemical mechanical polishing through non-ionic surfactant addition

Cleaning Nanoceria Particles by Diluted HNO3 with H2O2 Mixture (NPM) Solution at Different Temperatures

It is difficult to remove nanoceria abrasives from the SiO2 substrate after the shallow trench isolation (STI) chemical mechanical polishing process. In this work, we studied the cleaning behavior of ceria particles by using an acidic cleaning solution instead of normal sulfuric acid and hydrogen peroxide mixture solution (SPM) at high temperatures (above 85 °C) and low temperatures (below 30 °C). The solution, named as NPM, consists of HNO3 (1–2 vol%), H2O2 (5–10 vol%), and deionized water (DIW). It is found that NPM can dissolve nanoceria particles at high temperatures with higher cleaning efficiency (CE) than that of SPM. NPM can clean the A90 (90 nm ceria) particles under ultrasonic/megasonic at low temperatures, while SPM has poor CE at 20 °C. The redox reaction of NPM and its effect on cleaning mechanism were systematically studied.

Effect of lanthanum doping in ceria abrasives on chemical mechanical polishing selectivity for shallow trench isolation

Amino acids, when used with ceria based slurries, yield high selectivity in shallow trench isolation chemical mechanical polishing (CMP). However, the presence of impurities in the abrasives also plays a role in determining the selectivity. Experiments were performed with two different ceria abrasives, one with high purity and the other with controlled lanthanum doping. Various amino acids were evaluated in order to identify the nature of interaction between the additives and the abrasives. The abrasives were further characterized using transmission electron microscopy, X-ray diffraction and X-ray photo-electron spectroscopy. The removal rate results show that glycine and proline are sensitive to the La doping in the ceria abrasive whereas the other amino acids studied suppress the nitride removal irrespective of the purity of the abrasives. Thermo-gravimetric analysis shows that the extent of adsorption of glycine or proline on ceria depends on the presence of La doping, whereas the other amino acids adsorb equally well on ceria abrasives with or without La doping.

Development of a Nonperiodic Boundary Practical Simulator for Oxide and Shallow Trench Isolation Chemical Mechanical Polishing Processes

We developed a fast simulator for the chemical mechanical polishing (CMP) process that works in nonperiodic boundary conditions. Since periodic boundary conditions are not used, it can calculate anywhere on a wafer, such as the wafer’s edge. Additionally, we enhanced the simulator to calculate the shallow trench isolation (STI)-CMP process. In the STI-CMP simulation method, additionally required simulation parameters are only one, under the assumption that dishing reaches steady state in enough short time relative to total polishing time. We found that the simulation results could match experimental film thicknesses with an error range of about and that the calculation time was reduced to relative to when the acceleration method was not introduced.

Mechanism of high selectivity in ceria based shallow trench isolation chemical mechanical polishing slurries

dl-aspartic acid as a removal rate selectivity enhancer for shallow trench isolation chemical mechanical polishing slurries was investigated over a pH range. The effects of downward pressure, rotational speed of the turntable as well as the ceria abrasive loading were also examined. The selectivity is very sensitive to changes in the pressure but not to changes in the rotational speed. Select experiments were also conducted with other types of abrasives with and without the additive. A comparison of the pK a values of the amino acid with the variation of the selectivity with pH indicates that the form of amino acid plays a vital role in determining the polishing behavior and the selectivity. Further, the results corroborate the hypothesis that chemically active sites on the abrasive may be blocked by certain forms of the amino acids, leading to changes in the selectivity.

Selectivity Enhancement in the Removal of SiO2 and Si3N4 Films with Addition of Triethanolamine in a Ceria Slurry during Shallow Trench Isolation Chemical Mechanical Polishing

Selectivity Enhancement in the Removal of SiO2 and Si3N4 Films with Addition of Triethanolamine in a Ceria Slurry during Shallow Trench Isolation Chemical Mechanical Polishing

Enhancement of Selectivity of Oxide-to-Nitride Films on Organic Additive in Nano-ceria Slurry for Shallow Trench Isolation Chemical Mechanical Polishing

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Effects of Calcination and Milling Process Conditions for Ceria Slurry on Shallow-Trench-Isolation Chemical–Mechanical Polishing Performance

To improve the performance of shallow trench isolation chemical–mechanical polishing (STI-CMP) in terms of the removal selectivity of oxide and nitride films and the formation of surface defects, we investigated the effects of the calcination and milling process conditions during ceria slurry synthesis. We have focused on the effects of particle size distribution, the large-particle size, and the dispersion stability in a ceria slurry. We determined the optimum bead size for milling and appropriate calcination temperatures in order to obtain a reasonable particle distribution, with lower numbers of fine primary particles and large, agglomerated particles, in ceria slurry. This was achieved by reducing the quantity of aggregated particles during milling and two-step calcination process generating higher-density particles. These results can be qualitatively explained by abrasive collisions occurring between the milling beads and the decarbonation of cerium carbonate through diffusion during the manufacturing process used for the ceria slurry.

Adsorption behavior of anionic polyelectrolyte for chemical mechanical polishing (CMP)

In this work, we investigated the adsorption characteristics of anionic polyelectrolytes, which are used in shallow trench isolation chemical mechanical polishing with ceria abrasives. Specifically, the adsorption isotherms and chain conformation of anionic polyelectrolytes were studied in order to elucidate the difference in removal rates of silicon dioxide (SiO 2) and silicon nitride (Si 3N 4) layers and the high selectivity characteristics of ceria slurry. Adsorption isotherms, FT-IR spectroscopy and contact angle measurements revealed that the anionic polyelectrolyte additives had much better adsorption affinities for the Si 3N 4 surface than for the SiO 2 surface. Moreover, blanket wafer polishing results were successfully correlated with the adsorption isotherms of polyelectrolytes on the oxide particle suspensions.

Nanotopography Impact of Surfactant Concentration and Molecular Weight of Nano-ceria Slurry on Remaining Oxide Thickness Variation after Shallow Trench Isolation Chemical Mechanical Polishing

It has been reported that wafer nanotopography has a substantial impact on oxide film thickness variation after chemical mechanical polishing (CMP). Currently, shallow trench isolation (STI) is the preferred isolation scheme for device manufacturing, where STI CMP has become an essential process. Studies on nanotopography effects when using fumed silica slurries have been reported. This research examines the impact of nanotopography on the remaining oxide film thickness variation with varying surfactant concentrations in and molecular weights of the nano-ceria slurries used in STI CMP. Higher surfactant concentration and molecular weight lead to higher remaining oxide film thickness variation induced by wafer nanotopography.

Dependence of Nanotopography Impact on Fumed Silica and Ceria Slurry Added with Surfactant for Shallow Trench Isolation Chemical Mechanical Polishing

【The purpose of this study is to investigate the difference of the wafer nanotopography impact on the oxide-film thickness variation between the STI CMP using ceria slurry and STI CMP using fumed silica slurry. The nanotopography impact on the oxide-film thickness variation after STI CMP using ceria slurry is 2.8 times higher than that after STI CMP using fumed silica slurry. It is attributed that the STI CMP using ceria slurry follows non-Prestonian polishing behavior while that using fumed silica slurry follows Prestonian polishing behavior.】

Dependence of Non-Prestonian Behavior of Ceria Slurry with Anionic Surfactant on Abrasive Concentration and Size in Shallow Trench Isolation Chemical Mechanical Polishing

The dependencies of the non-Prestonian behavior of ceria slurry with anionic surfactant on the size and concentration of abrasive particles were investigated by performing chemical mechanical polishing (CMP) experiments using blanket wafers. We found that not only the abrasive size but also the abrasive concentration with surfactant addition influences the non-Prestonian behavior. Such behavior is clearly exhibited with small abrasive sizes and a higher concentrations of abrasives with surfactant addition, because the abrasive particles can locally contact the film surface more effectively with applied pressure. We introduce a factor to quantify these relations with the non-Prestonian behavior of a slurry. For ceria slurry, this non-Prestonian factor, βNP, was determined to be almost independent of the abrasive concentration for a larger size and a smaller weight conentration of abrasive particles, but it increased with the surfactant concentration for a smaller size and a higher concentration of abrasives with surfactant addition.

The Effect of Cerium Precursor Agglomeration on the Synthesis of Ceria Particles and Its Influence on Shallow Trench Isolation Chemical Mechanical Polishing Performance

The level of agglomeration in the cerium precursor and its effect on the physicochemical properties of the synthesized ceria particles and how these properties influence shallow trench isolation chemical mechanical polishing (STI CMP) performance were investigated. Two different types of ceria particles were synthesized from cerium precursors of different degrees of agglomeration. The crystallinity and particle size distribution of the synthesized ceria particles were markedly different between these two types of particles. The ceria particles synthesized from agglomerated cerium precursors had a smaller crystallite size than the other particles due to the incomplete decarbonation reaction, which resulted in large agglomerations of particles. The different physical characteristics of the ceria particles resulted in remarkable discrepancies between the STI CMP performances of the ceria slurries, such as the oxide removal rate, the selectivity and the uniformity.

Agglomerated Large Particles under Various Slurry Preparation Conditions and Their Influence on Shallow Trench Isolation Chemical Mechanical Polishing

The effects of various slurry manufacturing conditions, such as suspension pH, abrasive contents, and the calcination temperature of abrasive ceramic particles on the formation of agglomerated large particles of ceria slurry were investigated. The agglomerated large particles in slurry have much influence on the micro-scratches on the wafer surface in shallow trench isolation chemical mechanical polishing (STI CMP). The formation of large agglomerated particles is affected by the conformation of the organic additives in the slurry as a function of the suspension pH and the specific surface area of the abrasive particle. Regarding the solid content, abrasive particles are more easily dispersed at lower solid loading, which prevents additional agglomeration even under acidic conditions. The influence of agglomerated large particles on STI CMP was investigated through a polishing experiment with plasma-enhanced tetra-ethyl-ortho-silicate (PETEOS) and a low-pressure chemical vapor deposition (LPCVD) nitride layer.

Dependence of pH, Molecular Weight, and Concentration of Surfactant in Ceria Slurry on Saturated Nitride Removal Rate in Shallow Trench Isolation Chemical Mechanical Polishing

We have investigated how controlling the pH, molecular weight, and concentration of the surfactant in ceria slurry affects the nitride film loss and oxide-to-nitride selectivity in the shallow trench isolation (STI) chemical mechanical polishing (CMP) process. We found that for a surfactant with a higher molecular weight, the oxide removal rate markedly decreased as the surfactant concentration increased, but in the case of a lower molecular weight, the removal rate only slightly decreased. In addition, with increasing surfactant concentration and addition of surfactant with the same molecular weight, the nitride removal rates for all slurries markedly decreased and very quickly saturated at a lower surfactant pH. Moreover, with an increase in the surfactant concentration from 0.1 to 0.3 wt %, the slurries whose surfactants had a medium or the lowest molecular weight maintained higher nitride removal rates than did the slurry whose surfactant had the highest molecular weight.

Colloidal Silica based High Selectivity Shallow Trench Isolation (STI) Chemical Mechanical Polishing (CMP) Slurry

AbstractAmong various properties of chemical mechanical polishing (CMP) slurry, selectivity plays a key role in global planarization of high density and small pattern size shallow trench isolation (STI) process. Lack of adequate selectivity can lead to defects such as dishing and erosion. To improve the selectivity of STI CMP process, CMP characteristics of silica and silicon nitride wafer were investigated using colloidal silica slurry as a function of slurry pH. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added to increase the selectivity of the slurry. As a result, selectivity increased from 3 to 25. It was concluded that selective passivation layer formed on silicon nitride wafer surface at acidic slurry pH range was responsible for the observed selectivity increase. Adsorption characteristics of SDS on silica and silicon nitride were measured as a function of slurry pH and concentration of SDS. As indicated by zeta potential behavior under acidic pH conditions, SDS adsorption on silicon nitride was significantly higher han silica due to the electrostatic forces. Significantly higher SDS coating on silicone nitride seems to have resulted in lubrication layer leading to increased polishing selectivity.

Determination of process margin and global planarization characteristics in the direct STI-CMP process

The direct shallow trench isolation–chemical mechanical polishing (STI–CMP) process without conventional reverse moat etch step was studied in order to compare the global planarization procedure in the each region with different pattern size. Because the removal rates of each region were different in the STI–CMP process, the determination of process margin is very important parameter in the viewpoint of exact control for polishing thickness. Therefore, the process margins (upper and lower limits), which can minimize the dishing effects in the large field area, were investigated through the analysis of global planarization. As a result, we could perfectly remove the silicon oxide on the silicon nitride layer in the moat region. This means that it was possible to achieve a global planarization without the complicated reverse moat process.

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.

Correlation analysis between pattern and non-pattern wafer for characterization of shallow trench isolation–chemical–mechanical polishing (STI–CMP) process

This study is about control of oxide removal amounts on the shallow trench isolation (STI) patterned wafers using removal rate and thickness of blanket (non-patterned) wafers. At first, the removal properties of plasma enhanced tetra-ethyl ortho-silicate (PETEOS) blanket wafers was investigated, and then it was compared with the removal properties and the planarization (step height) as a function of polishing time of the specific STI patterned wafers. We found that there is a relationship between the amount of oxide removal by blanket and patterned wafers. We analyzed this relationship, and the post-CMP thickness of patterned wafers could be controlled by removal rate and removal target thickness of blanket wafers. As the result of correlation analysis, we confirmed that there was the strong correlation between patterned and blanket wafers (correlation factor: 0.7109). So, we could confirm the repeatability as applying to STI CMP process from the linear formula obtained.