Solid State Phenomena Vol. 314

Abstract: In chemical mechanical planarization (CMP) processes, ceria is generally used as the abrasive . After the CMP process, many ceria particles adhere to the wafer surface and must be removed prior to subsequent processing. In this study, the effect of varied viscosity was investigated during the buffing CMP process for ceria particle removal. After contaminating the wafer surface with ceria slurry, the ceria particles were removed through the buffing CMP process. The wafer surface was analyzed through inductively coupled plasma mass spectrometry (ICP-MS) to confirm cleaning efficiency. The ICP-MS data showed that, as buffing CMP solution viscosity increased, cleaning efficiency improved. These results suggest that increasing the viscosity of the buffing CMP solution improves its effectiveness in removing ceria particles.

Abstract: It is very difficult to remove extremely small particles from the surface of the wafer. Here, we proposed a new cleaning strategy using brush scrubbing, namely, nodule deformation induced fluid flow. Liquid absorption and desorption due to brush deformation enhance the mixing of liquids containing small particles. In this study, we developed a setup that reproduced the actual movement of PVA roller brushes on a rotating wafer and observed the contact surface of the brush nodule. We modeled the brush nodule deformation for each rotating condition. As a result, three types of nodule deformation were observed. In most cases, the nodule side face, rather than the bottom face was mainly in contact with the wafer surface. Moreover, we compared two types of roller brushes, normal cylindrical nodules, and edge treated nodules and found that the deformation can be significantly changed by chamfering nodule edge.

Abstract: Brush scrubbing is a well-known post CMP cleaning process. Interaction between PVA brush and the particles removed during the process must be considered while designing a cleaning process. In this work, the effect of cleaning solution pH was investigated in terms of particle removal from the wafer and subsequent loading to the PVA brush nodule. Higher cleaning of particles from wafer was observed for pH 2 and 12 cleaning solutions and poor cleaning for pH 7 cleaning solution. In contrast, the brushes were loaded heavily for pH 7 compared to pH 2 and 12. Higher electrostatic attraction between oppositely charged PVA and ceria surfaces provided higher ceria particles loading to PVA brush in acidic and neutral cleaning solutions. This particle loading to PVA brush can further effect cleaning efficiency as well as cross-contamination.

Abstract: We have shown how different micellar (SDBS) vs. polyelectrolytic (PSSA) supramolecular assemblies in post-CMP cleaning solutions differ in their tribological performance when used in a novel PVA scrubber for 300-mm silicon dioxide wafer cleaning. Significant differences in real-time shear force and coefficient of friction data from the wafer-solution-brush interface (both in time domain as well as frequency domain) have been attributed to differences in each supramolecule’s chemical functionality and structure, which in turn, have been correlated to wafer-level defects. The work has underscored the importance of measuring the tribological attributes of post-CMP cleaning processes in an effort to improve cleaning performance.

Abstract: A systematic study of the adsorption of benzotriazole on Co surface and its removal in aqueous solutions was carried out for post-CMP cleaning application. Static etch rate (SER) measurements and electrochemical impedance spectroscopy (EIS) were employed. The experimental results show that BTA adsorbed well on Co surface when it exposed to BTA solution at neutral and alkaline pH. BTA did not adsorb due to active Co dissolution at acidic pH. The effect of dissolved oxygen (DO) concentration in de-ionized (DI) water on the removal of Co-BTA complex layer was investigated. At DI water rinse process after BTA treatment, Co-BTA layer was maintained on Co surface when DO concentration of DI water was low. Interestingly, BTA was removed by DI water with high DO concentration.

Abstract: Particle removal from BEOL low-k structures is studied using a novel particle removal technique, called Nanolift which removes particles from the substrate by forming a thin polymer film on the surface and removing the polymer film together with the particles. It was confirmed that Nanolift is capable to remove TiF_x particles successfully which are generated during the low-k dry etch process for dual damascene structure formation for BEOL interconnect fabrication. Pattern collapse of the fragile low-k structure was confirmed to be prevented by Nanolift in comparison with conventional dual fluid spray cleaning method. FTIR results show that Nanolift leaves no residual polymer remain in low-k films and K-value shift by the Nanolift process was negligible and comparable with the conventional formulated chemistry cleaning process. From these results, Nanolift can be concluded as a suitable cleaning process for advanced BEOL fabrication process.

Abstract: The use of various H₂O₂ based chemistries for TiW etch was studied on single wafer and wet bench tools. The focus of the investigation was put on the different behaviors of these chemicals on blanket and patterned wafers. The results of the etch rate tests showed much higher values on the wafers where copper was exposed, leading to the hypothesis that the etch rate on TiW should be driven by the catalysis effect of the transition metal on the H₂O₂ decomposition reaction. Additional optical inspections, ToF SIMS, SEM and TEM analyses were carried out to confirm this hypothesis and find the best conditions in terms of morphology for RDL applications. Finally, the collected data were also used to evaluate the process cycle time and cost of ownership.

Abstract: During silicide formation, unreacted NiPt metals is traditionally removed either by aqua regia (ESH concern) or SPM. This latter can easily degrade the device yield in HKMG (High K Metal Gate) nodes if the metal gates (usually TiN based) aren’t perfectly encapsulated. First some new characterizations are presented to better understand the NiPt metal alloy removal, then a new solution is given to be able to remove this alloy without degrading HKMG materials.

Abstract: In this work the wet etching of molybdenum thin films was investigated for applications requiring controlled recess without roughening or pattern loading. First, continuous etching of Mo in alkaline and oxidative peroxide solutions was studied. Then, additives like glycine and diethylenetriamine were used and their effect on etch rate and roughness was assessed. Finally, we evaluated if the requirements for a stepwise etching approach for Mo recess using peroxide or ozonated water as the oxidizing step and ammonia as the oxide dissolution agent were met.

Abstract: Different types of ALD Ru films, including as-deposited, annealed Ru, without and with a subsequent CMP step, were used for wet etching study. With respect to the as-deposited Ru, the etching rate of the annealed Ru film in metal-free chemical mixtures (pH = 7-9) was found to decrease substantially. X-ray photoelectron spectroscopy characterization indicated that this behavior could be explained by the presence of the formation of RuOx (x = 2,3) caused by the anneal. A short CMP step applied to the annealed Ru wafer removed the surface RuOx, at least partially, resulting in a significant increase of the etching rate. The change in surface roughness was quantified using atomic force microscopy.