In this study, the interfacial and electrokinetic phenomena of mixtures of isopropyl alcohol ͑IPA͒ and deionized ͑DI͒ water in relation to semiconductor wafer drying is investigated. The dielectric constant of an IPA solution linearly decreased from 78 to 18 with the addition of IPA to DI water. The viscosity of IPA solutions increased as the volume percentage of IPA in DI water increased. The zeta potentials of silica particles and silicon wafers were also measured in IPA solutions. The zeta potential approached neutral values as the volume ratio of IPA in DI water increased. A surface tension decrease from 72 to 23 dynes/cm was measured when the IPA concentration increased to 30 vol %. The surface excess of IPA at the air-liquid interface reached a maximum at around 20 vol % IPA. The adhesion forces of silica particles on silicon wafers were measured using atomic force microscopy in IPA solutions. The adhesion force increased as the volume percent of IPA in water increased. Lower particulate contamination was observed when the wafers were immersed and withdrawn from solutions containing less than 25 vol % IPA.
The adhesion force of silica particles to Cu films and the role of additives on adhesion and removal of particles have been theoretically and experimentally investigated in citric-acid-based post-Cu chemical mechanical planarization ͑CMP͒ cleaning solutions. The zeta potential of silica and Cu slightly increases when citric acid is added due to the adsorption of citrates. Citric acid is adsorbed on silica and Cu surfaces, resulting in more negative charges on these surfaces. The adhesion force of silica particles on Cu decreases as the citric acid concentration increases due to more repulsive electrostatic interaction between surfaces. The addition of benzotriazole in the cleaning solution initially decreases adhesion then increases it at high concentrations due to the change in zeta potentials. The addition of tetramethylammonium hydroxide to citric acid increases the particle adhesion force. However, the addition of NH 4 OH results in the lowest adhesion forces. The highest particle removal efficiency is observed when using cleaning solutions that yield the lowest adhesion force.Cu has been widely accepted as an interconnection material in deep submicrometer multilevel device applications because of its lower resistance, superior resistance to electromigration, and the reduction of resistance-capacitance ͑RC͒ time delay compared with aluminum. 1 The Cu interconnection is made possible by novel damascene chemical mechanical planarization ͑CMP͒. During Cu CMP, wafer surfaces are exposed to at least two different slurry solutions. After polishing, the removal of abrasive particles and trace metals left on the wafer surfaces becomes as important as the polishing process itself in order to maintain device yield. 2 Since the CMP process leaves these contaminants on the wafer surface, post-Cu CMP cleaning is a necessary step to eliminate or reduce them before the next process step. Earlier studies reported on the effect of pH on removal and adhesion of silica particles in slurry solutions, 3 however, very little has been reported on the effects of additives in cleaning solutions on removal and adhesion of particles of interest to post-Cu CMP cleaning.The objective of this study is to investigate the effects of additives in citric acid-based Cu cleaning solutions on the adhesion and removal of silica particles on Cu surfaces. Since the smallest possible adhesion force between abrasive particles and wafer surfaces is highly desirable for reducing particulate contamination, the adhesion force of silica particles on Cu was studied in post-Cu CMP cleaning solutions with different additives. The interaction forces between particles and wafer surfaces during post-Cu CMP cleaning were calculated based on the Derjaguin-Landau-Verwey-Overbeek ͑DLVO͒ theory. 4 The adhesion forces between the particles and surfaces were also experimentally measured using an atomic force microscopy ͑AFM͒. The level of particulate contamination on Cu surfaces was measured by field emission scanning electron microscopy ͑FESEM͒ before and after clean...
The removal of nanoparticles is becoming increasingly challenging as the minimum linewidth continues to decrease in semiconductor manufacturing. In this paper, the removal of nanoparticles from flat substrates using acoustic streaming is investigated. Bare silicon wafers and masks with a 4 nm silicon cap layer are cleaned. The silicon-cap films are used in extreme ultraviolet masks to protect Mo-Si reflective multilayers. The removal of 63 nm polystyrene latex ͑PSL͒ particles from these substrates is conducted using single-wafer megasonic cleaning. The results show higher than 99% removal of PSL nanoparticles. The results also show that dilute SC1 provides faster removal of particles, which is also verified by the analytical analysis. Particle removal from the 4 nm Si-cap substrate is slightly more difficult as compared to bare silicon wafers. The experimental results show that the removal of nanoparticles takes a relatively long removal time. Numerical simulations showed that the long time is due to particle oscillatory motion and redeposition, and that this phenomenon is not observed in the removal of sub-m or larger size particles. Fabrication of micro-and nanoelectronics requires nanoscale particle and other contaminant removal from wafers and associated thin films. These undesired particles on the wafer surface influence the device yield and reliability. These particles could result from chemical vapor deposition, physical vapor deposition, etching processes, and many other fabrication processes. The FEOL ͑front end of the line͒ critical particle size is expected to decrease to 9 nm by the year 2018.1 The smaller the particles, the harder it is to overcome the adhesion force between the particle and the substrate. The adhesion force consists of the van der Waals and the electrostatic double-layer forces. High-frequency sonic energy in liquids ͑megasonic cleaning͒ has proven to be an effective method for particle removal. Although megasonic cleaning is widely used in the semiconductor industry, the fundamental physical processes are not thoroughly understood. Olaf 2 made early observations of sonic cleaning of glass surfaces in the range from 15 kHz to 2.5 MHz. McQueen 3 recognized the importance of acoustic streaming and the thin boundary layer thickness in small particles removal from surfaces. Busnaina and Kaskoush 4 found that increasing the frequency above 300 kHz could eliminate the surface damages on wafer surfaces during wafer cleanings. Gale and Busnaina 5 studied the mechanisms of particle removal in megasonic and ultrasonic cleaning, including the effects of frequency, temperature, and power density.Acoustic streaming is considered to be the key cleaning mechanism in the removal of sub-m particles.6-8 According to Olim, 9 theoretically it is not possible to remove particles below 100 nm using megasonic cleaning. But, in practice, particle sizes down to and less than 100 nm have been effectively removed using megasonics. The underestimation of Olim's model is because the viscous drag force and the ...
In this study, sodium periodate (NaInormalO4) was chosen as both oxidant and etchant on ruthenium (Ru) chemical mechanical planarization (CMP) slurry for the formation of Ru bottom electrodes in dynamic random access memory capacitors. The effect of NaInormalO4 on etching and polishing behavior was investigated as a function of slurry pH. Below pH 7.5, the high static etch rate was measured due to the dissolution of soluble RunormalO4 . Above pH 7.5, the static etch rate decreased due to the formation of insoluble RunormalO2⋅2normalH2O and the depletion of periodate ions. The highest etching of 20nm∕min was obtained at pH 6. In a slurry of 0.1M NaInormalO4 and 2wt% alumina particles at pH 6, the removal rate of Ru was about 130nm∕min . Even though the highest removal rate was obtained at pH 6, Ru overetching occurred on Ru-patterned wafers due to the high static etch rate of Ru. A selectivity of Ru to oxide of about 23:1 was achieved at pH 8–9. In slurry of pH 9, the planarity and isolation of each capacitor were reached successfully because Ru overetching was prevented due to a low etch rate of Ru.
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