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Sulfuric Peroxide Mixture (SPM, H2SO4 + H2O2) has been widely used in semiconductor manufacturing processes due to its high reactivity and attractive price. However, SPM releases SO42- ions that can be high impact on the environmental contaminations. Therefore, the SPM process requires a high cost wastewater treatment. So, the development of alternative chemicals has been becoming an important task in the semiconductor manufacturing process. In this paper, we evaluated the feasibility of replacing SPM with dissolved ozone water (DIO3) in the wafer cleaning process, and confirmed that the Particle removal efficiency (PRE) was improved around 68% by mixing with diluted hydrofluoric acid (DHF). And, the PRE was also increased when the concentration of ozone in dissolved ozone water increased. Additionally the PRE was improved up to 98% by combining physical cleaning after O3 process.

Ce3+ ions in ceria nanoparticles (NPs) play a role as reactive sites in the adsorption of silicate anions. However, the limited concentration of Ce3+ ions in ceria NPs remains a major challenge in this regard. Herein, we report a simple strategy to synthesize Ce3+-enriched core–shell ceria NPs for enhanced adsorption of silicate anions. To increase the overall Ce3+ concentration, a shell layer is composed of Ce3+-rich ultrasmall ceria NPs approximately 5 nm in size. The Ce3+ concentration of such core–shell ceria NPs is increased by 12.7–17.1% relative to that of the pristine ceria NPs, resulting in increased adsorption of silicate anions. The Freundlich model fits the observed adsorption isotherm well and the constants of adsorption capacity (KF) and adsorption intensity (1/ n) indicate higher adsorption affinity of the core–shell ceria NPs for silicate anions. We attribute these improvements to the increased Ce3+ concentration contributed by the ultrasmall ceria coating. This strategy can be used for enhancing the reactivity of ceria materials.

In this study, a response surface methodology (RSM) coupled with a face center cube design (FCD) was used to optimize the three principal components (i.e., Fe(NO3)3, H2O2, and SiO2 abrasives) in polishing slurries for a W barrier chemical mechanical planarization (CMP) process. The experimental ranges of the three components were 10–50 ppm of Fe(NO3)3, 0.3–0.9 wt% of H2O2, and 1–5 wt% of SiO2 abrasives. Based on the experimental data from the FCD, the second-order models for the material removal rate (MRR) of the W and Oxide films were fitted; these were determined to be statistically valid and reliable. We have achieved the optimal conditions for the three components where the MRR is maximized and the selectivity between the W and Oxide MRRs is ~1. The predicted MRR and selectivity at the optimal conditions were well correlated with the results of a confirmation run, which was conducted by using the W barrier CMP process with W-patterned wafers. In addition, we employed a particular RSM called dual-response optimization in order to investigate the tradeoff between the MRR and selectivity. Based on the tradeoff information, process engineers can conduct the optimization of the three components more flexibly. Keywords: Chemical mechanical planarization, Optimization, Response surface methodology, Slurries, Semiconductor manufacturing process

In this study, we have investigated the role of the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surfaces for silicate adsorption. In aqueous medium, the Ce3+ sites lead to the formation of −OH groups at the CeO2 surface through H2O dissociation. Silicate ions can adsorb onto the CeO2 surface through interaction with the −OH groups (−Ce−OH− + −Si−O− ↔ −Ce−O−Si− + OH−). As the Ce3+ concentration increased from 19.3 to 27.6%, the surface density of −OH group increased from 0.34 to 0.72 OH/nm2. To evaluate the adsorption behaviors of silicate ions onto CeO2 NPs, we carried out an adsorption isothermal analysis, and the adsorption isotherm data followed the Freundlich model. The Freundlich constant for the relative adsorption capacity (KF) and adsorption intensity (1/n) indicated that CeO2 NPs with high Ce3+ concentration show higher adsorption affinity with silicate ions. As a result, we have demonstrated that the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surface can have a significant influence on the silicate adsorption.

Although poly(acrylic acid) (PAA) has been used as a passivation agent for high polish rate selectivity between SiO 2 and Si 3 N 4 in STI CMP, it causes severe dishing during the over-polishing step. Here, we fabricated interpolymer complexes of PAA and poly(ethylene glycol) (PEG) as passivation agent for low dishing as well as high selectivity. PAA and PEG form a cross-linked network structure through H-bonding, which is called an “interpolymer complex”. During the over-polishing step, the cross-linked network structure of the PAA-PEG interpolymer complex prevents abrasives from polishing SiO 2 in the trenches, resulting in a significant decrease in dishing. These results provide researchers with a new approach toward passivation agents to provide low dishing in STI CMP.

In the semiconductor process, chemical mechanical polishing/planarization (CMP) is inevitable in copper (Cu) interconnect forming. Cu damascene scheme is achieved by help of CMP to form highly ordered metal lines. As the CMP process uses a set of partial polishing steps to complete a damascene structure, slurries of each partial step is designed to have different performances to that of other steps. Among the steps, final partial step, so called, barrier metal (BM) CMP is a critical step because it determines the superior flat finish. In the BM CMP, a structure consists of heterogeneous materials such as Cu, dielectric oxide, and BM should be polished at once. Thus, abrasive suspended in the BM slurry should be optimized to achieve the superior flat finish. In the present study, 3 kinds of BM slurry were utilized. Abrasive of those slurries are made of colloidal silica in the size of 30 nm to 60 nm. The abrasive surfaces, however, are differently modified to have suitable performance for various polishing environments. The modification involves shape of abrasive, chemical additive to increase suspension stability, coating with polymers, and operation pH. Their effects on the CMP performance not only for blanket wafers but also for pattern wafers having 2x nm pitch were observed experimentally. The results indicated that not only polishing performance but also defect occurrence, which is important in mass fabrication, should be considered equally. Finally, strategy for reducing defect occurrence while maintaining Cu damascene performance will be discussed.

We have investigated the synergistic effect with mixing of three different-sized SiO2 abrasives (30 nm-SiO2, 70 nm-SiO2 and 200 nm-SiO2) and the corresponding W chemical mechanical planarization (CMP) performances. W removal rate significantly increased when the different-sized SiO2 abrasives were mixed, which is attributed to the increase in the total contact area between the abrasives and the W film. Based on the statistical model, we obtained the optimal mixing ratio (30 nm, 70 nm, 200 nm) = (0.49, 0.23, 0.28) for the highest W removal rate. These results, investigated in this study, show that the removal rate of W film can be improved via simple mixing process.

The adhesion force between ceria and polyurethane (PU) pad was controlled to remove the step height from cell region to peripheral region during Shallow Trench Isolation Chemical Mechanical Planarization (STI-CMP) for NAND flash. Picolinic acid was found to be adsorbed on ceria particles at pH 4.5 following a Langmuir isotherm with the maximum adsorbed amount of 0.36 mg/m2. The ceria suspension with full surface coverage of picolinic acid showed a threefold increase in the number of adhered ceria particles on the PU pad over non-coated ceria particles. It was shown that the coverage percent of picolinic acid on ceria corresponds well with the amount percent of adsorbed ceria on PU pad. The change in adsorbed particles was directly reflected in the CMP polishing process where significant improvements were achieved. Particularly, convex areas on the chip experienced higher friction force from the attached abrasives on the PU pad than concave areas. As a result, the convex areas have increased removal rate of step height compared to the ceria suspension without picolinic acid. The changing profiles of convex areas are reported during the step height reduction as a function of polishing time.

We investigated the effect of poly (ethyleneimine) (PEI)-modified silica abrasive on the removal rate and the degree of dishing during Cu chemical mechanical planarization (CMP). The PEI-modified silica abrasive was prepared by mutually attractive electrostatic forces between PEI and silica abrasive. The physico-chemical behaviors between PEI and the silica abrasive were evaluated by total organic carbon (TOC), force-separation measurements using atomic force microscopy (AFM) with molecular weight of PEI, which was found to adsorb on silica at pH 7.0 following a Langmuir isotherm. The maximum adsorbed amounts of low and high molecular weight PEI were 0.195mg/m^2 and 0.228mg/m^2, respectively. AFM results showed the repulsive force of the adsorbed PEI layers on the silica surface and the adsorption thickness of PEI on silica vary with the molecular weight of PEI. A twofold change was observed in the AFM analysis. First, the increased areal density of adsorbed PEI caused a higher zeta-potential and longer reaching repulsive force. Second, the adsorption thickness was also significantly enlarged. High molecular weight showed increased adsorption thickness under similar conditions compared to low molecular weight of PEI. These changes of silica abrasive such as electrostatic forces and steric interaction vary with molecular weight of PEI reduced the dishing of Cu pattern film from 50 to 20nm.

We have investigated the surface chemistry of SiO 2 nanoparticles (NPs) with different sizes and their corresponding interactions with a flat substrate of surface curvature ∼0. As the size of the NPs increases, the SiO 2 surface is increasingly covered with H-bonded silanol groups, thereby increasing the ζ-potential and shifting the isoelectric point higher in pH. Interactions between the SiO 2 NPs and the flat SiO 2 surface were analyzed in situ using quartz crystal microbalance with dissipation (QCM-D) method, and the results were interpreted based on an extended Derjaguin–Landau–Verwey–Overbeek theory. At very low ionic strength (1 mM NaCl), there was no particle adsorption onto the surface due to the highly repulsive energy barriers to this interaction. On the other hand, QCM-D results showed that the significant adsorption of SiO 2 NPs onto a flat SiO 2 surface occurred under conditions of high ionic strength (100 mM NaCl). Interestingly, the adsorption behaviors of three different-sized SiO 2 NPs on the surface varied considerably with size. SiO 2 NPs with small size have high adsorption affinity with the flat SiO 2 surface due to an extremely low energy barrier for the interactions, whereas relatively large SiO 2 NPs have very weak adsorption affinity with the flat surface due to the repulsive energy barrier formed by the increase in the electrostatic and hydration repulsion energy.

Rectangular ceria particles were synthesized using the flash creation method. The influence of the morphology of ceria particles and the surfactant concentration on the removal rate was systematically investigated. These ceria slurries with polymeric surfactant molecules as the passivation agents of Si3N4 film, shows an exceptional non-Prestonian behaviors. The non-Prestonian behavior can be attributed to the increase in the contact area of the ceria particles with the SiO2 film, which is dominated by the morphology of the ceria particles. Force measurements using an atomic force microscope (AFM) at different concentrations of polymeric surfactant molecules was used to identify the interactions between the polymeric molecules and the oxide film and analyze the non-Prestonian behavior of ceria slurry having rectangular abrasives.

Localized galvanic corrosion at the tungsten (W) and titanium nitride (TiN) interface causes fatal defects (e.g., corrosion and pitting issues) in chemical mechanical planarization (CMP) process. In this study, we control the corrosion potential difference between W and TiN via mixing of two corrosion inhibitors in order to decrease those defects. The roles of corrosion inhibitors in CMP slurry are analyzed by open circuit potential (OCP) measurements, linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Through these electrochemical approaches, we found that two mixed inhibitor system can decrease the galvanic potential and current density. CMP result with W/TiN patterned structure wafer shows that mixed inhibitor system prevents galvanic corrosion at the W/TiN interface during CMP, leading to decreasing the defects. We believe that the results investigated in this study will provide researchers with the importance of electrochemical approaches in W CMP.

A chemical mechanical planarization (CMP) of copper (Cu) damascene structure is prone to defect formation due to variety of chemical agents in slurry and chemical complex formation. In post CMP cleaning process, which should remove such defects, a mechanical scrubbing of wafer by porous and elastic brushes are eligibly used. Although, chemical effects are the main mechanism of defect detachment and dissolution during cleaning process, mechanical effects also play key role by transportation of chemical agent and discharge of reacted species. The most relevant defect caused by mechanical effect is ring shaped scratch due to exceeding contact pressure. In this study, however, we focused on ring shaped residue after post Cu CMP cleaning which is not caused by direct solid contact. To investigate root cause, analysis are carried out such as chemical composition of residue, surface charge map on a wafer, kinematic analysis on brush and wafer motion, and fluid dynamic simulation on chemical motion. In conclusion, it is revealed that both chemical and mechanical effects are interacted to form ring shaped residue. Elimination of defects by chemical effect is suppressed by mechanical motion of brush and chemical fluid. Figure 1

Ceria has been widely used as an abrasive for polishing SiO2 film due to the high removal rate of SiO2 during Shallow Trench Isolation (STI) CMP.1 As the scale of transistor has been reduced, the number of maximum acceptable defects was decreased. Recently, numerous researchers have studied prevention of defect formation on the SiO2 film by using solution-grown ceria with spherical shape. Although solution-grown ceria is spherical shape and smaller particle size, it leads to unexpected results such as removal rate of SiO2 and higher defects compared to solid-state ceria with irregular shape. Recently, the study of surface chemistry appears to be more important than morphology, as ceria reacts with the SiO2film to remove it. Here, the effect of the surface chemistry of solution-grown ceria on the CMP performance was investigated. Nitrate- and hydroxyl-functionalized ceria nanoparticles were prepared by ion-exchange method. Figure 1(a) shows the adsorption behavior of silicate ions on nitrate- and hydroxyl-ceria particles at pH 7.0. The presence of surface nitrate group induces high affinity between ceria particles and silicate ions at pH 7. Figure 1 (b) shows the effect of nitrate group on the surface on the CMP performance. Nitrate-ceria particles increase the removal rate of SiO2film, which correlates well with the adsorption behavior of silicate ions on the ceria particles. To interpret the adsorption behavior of nitrate- and hydroxyl-functionalized ceria particles, the adsorption reaction at the molecular level through quantum mechanical calculation was investigated.2 As the second step, the hydroxyl-ceria adsorption on the H-terminated SiO2 surface is water generating reaction (Figure 2e). The binding energies of the both cases are -2.865 and -3.813 eV, respectively. On the other hand, only one step adsorption was considered for the nitrate-ceria without generating water molecule (Figure 2f). The binding energy of this nitrate ceria on the SiO2surface is much higher than that of the hydroxyl-ceria as -4.383 eV. In this study, we revealed that surface functional groups such as hydroxyl and nitrate groups have a significant influence on the characteristics of CMP. The adsorption behavior based on surface chemistry is important for understanding of reaction between ceria and SiO2. Acknowledgement This work was supported by the Global Research Laboratory (GRL) Program (K20704000003TA050000310) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (Information and Communication Technologies) and Future Planning, and the International Cooperation program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government of Ministry of Trade, Industry & Energy (2011T100100369) Reference [1] Cook, L. M.“Chemical Processes in Glass Polishing.” Journal of Non-Crystalline Solids, 120, (1-3), 152-171, (1990) [2] Perdew, J. P. et al. “Accurate and Simple Analytic Representation of the Electron-Gas Correlation-Energy” Physical Review B, 45, (23), 13244-13249, (1992)

Shallow trench isolation (STI) process has been a crucial technology to isolate the transistors in ultra large scale integration (ULSI) device [1]. In STI process, step height of dielectric material is inevitably formed after gap-filling process due to the different pattern density. Chemical mechanical planarization (CMP) process has been employed to remove the step height. Remaining step height would cause defects such as dishing and erosion, therefore the reduction of step height can be considered as one of the critical issues in STI-CMP process. Several groups have studied about the step height reduction using ceria due to its high removal rate of SiO2 [2]. Lim et al. reported that the effect of particle size on step height reduction. They showed that the large particle size could improve the step height reduction by its high removal rate. Recently, the needs of small particle have been increased because the defect control has been more important as the design rule is getting narrow. Therefore, it is inevitable to develop new methodology to enhance the step height reduction. Here, we used different amino acid to modify the surface of ceria and enhance the interaction between the ceria slurry and SiO2. We investigated the effect of ceria slurries prepared with L-serine, proline, glutamine and amino butyric on step height reduction. We calculated the interaction forces between ceria with different amino acids and SiO2 film by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The result shows that ceria slurry with L-serine or proline has higher attractive interaction forces with SiO2 than the slurry with glutamine or amino butyric acid (Fig. 1). The results of SiO2 pattern as different pattern density and line width show that the ceria slurry with L-serine or proline produces higher step height reduction than the slurry with glutamine or amino butyric (Fig. 2). As a result, we found that the high interaction forces between ceria slurry and SiO2 contribute to high step height reduction and it is stronger in case of the slurry with L-serine or proline than the slurry with glutamine and amino butyric acid.

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