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 Lower particulate contamination was observed when the wafers were immersed and withdrawn from solutions containing less than 25 vol % IPA.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...
This study investigated the wettability effect of polysilicon on the polishing performance and organic defect contamination during polysilicon chemical mechanical polishing ͑CMP͒. Contact angle measurement was utilized to understand the nature of polysilicon surfaces. An oxidizer, H 2 O 2 , was added to the silica slurry to modify a hydrophobic polysilicon surface to a hydrophilic surface during polishing. The adhesion force was measured between a polymeric pad particle and a poly-Si wafer surface in KOH solution ͑pH 11͒ as a function of H 2 O 2 concentration. The adhesion force of the polymeric pad particle on the polysilicon decreased from 14 to 8 nN as the peroxide concentration increased to 10 vol %, at which the surface became hydrophilic. The hydrophilization of the polysilicon surface during polishing drastically reduced the organic contamination on the polysilicon wafers after polishing. The removal rate, frictional force, and pad temperature during CMP, with and without oxidizing the surface, were measured. They all decreased with the increasing concentrations of the oxidizer. The decrease was attributed to the formation of the lubrication layer of the oxide surface due to the oxidation of polysilicon.Dynamic random access memory ͑DRAM͒ process technology has become a leading semiconductor technology, with the highest production volume among very large scale integration ͑VLSI͒ semiconductor products. The density of DRAM quadrupled approximately every three years by virtue of advances in DRAM technology. 1 Because of the decrease in device feature size, the chemical mechanical polishing ͑CMP͒ process has become a necessary processing step for planarizing the surfaces during the DRAM process. 2 Poly-Si CMP is implemented to reduce the step height of a gate poly-Si in the construction of a recess channel array transistor and Fin Field Effect Transistor ͑FinFET͒ three-dimensional structures. 3 Although the CMP process is performed effectually, there are several problems that need to be overcome, such as local dishing/erosion, scratches, and abrasive and organic particle contamination. 4 After the CMP process, the wafer surface might be contaminated by the abrasive particles and polymeric residues from the pad, the retainer ring, and other consumables. The removal of organic residues from the wafer surfaces is a great challenge for the next processing step. The surface of poly-Si is hydrophobic in nature. Hence, it attracts hydrophobic organic residues, mostly pad debris, during the CMP process. These organic defects are difficult to be removed by general post-CMP cleaning methods. 5-7 Because there is much concern about organic contamination on polished polysilicon surfaces after polishing, understanding the interaction between the organic residues and the polysilicon surface is required.Therefore, this study investigated the organic contamination mechanism of polymeric residues on polished polysilicon surfaces. H 2 O 2 , as an oxidizer, was added to the silica slurry to modify the wettability of the polysil...
The effect of frictional and adhesion forces attributed to slurry particles on the quality of copper surfaces was experimentally investigated during copper chemical mechanical planarization process. The highest frictional force of 9 Kgf and adhesion force of 5.83 nN were observed in a deionized water-based alumina slurry. On the other hand, the smallest frictional force of 4 Kgf and adhesion force of 0.38 nN were measured in an alumina slurry containing citric acid. However, frictional ͑6 Kgf͒ and adhesion ͑1 nN͒ forces of silica particles in the slurry were not significantly changed regardless of the addition of citric acid. These differences were explained by the strong adsorption of citric ions on alumina but not on silica, which was verified by the charge reversal of alumina in zeta potential measurements. Higher particle adhesion forces resulted in higher friction. A higher magnitude of particle contamination and scratches was observed on polished copper surface in slurry condition with higher adhesion and friction forces. Copper has been widely used as an interconnection material in submicrometer multilevel device fabrication because of its many benefits including lower resistivity ͑1.7 ⍀ cm͒, superior resistance to electromigration, and the reduction of resistance-capacitance ͑RC͒ time delay when compared with aluminum ͑2.66 ⍀ cm͒. The formation of the copper interconnection is only possible by a novel damascene chemical mechanical planarization ͑CMP͒ process. During copper CMP, wafer surfaces are usually exposed to at least two different slurry solutions. Despite that the CMP process is well recognized as a powerful method for global planarization, several issues remain, such as local erosion, dishing, scratches, and abrasive particle contamination after the CMP process. After polishing, the residue of abrasive particles and scratches that remain on the wafer surfaces become a great challenge. 2Any adhesion forces between two surfaces will induce the increase of contact area and generally contributes to the overall frictional force.3 Adhesion force might act as an additional normal load and increase the frictional force. The frictional force could also increase the contamination on the surface. 4,5 Past research has focused on the relation between the adhesion force and frictional behavior on microelectromechanical system ͑MEMS͒ structures and thin films. [6][7][8] We have studied the effect of the pH on the removal and adhesion of silica particles in slurry solutions. 9,10 No study has yet reported, however, on the effect of the adhesion force of slurry particles on the frictional behavior and the defects such as scratches and particles in the copper CMP process.The objective of this research was to see the relationship among friction force, removal rates, adhesion forces, and defects such as scratches and particle contaminations in copper polishing. Because low adhesion forces and the minimal friction between abrasive particles and wafer surfaces are required for reducing particle contamination and scr...
In this study, the effect of BTA on polishing behavior was investigated as functions of H2O2, slurry pH and abrasive particles. The addition of BTA effectively prevented Cu from etching by forming the passivation layer of Cu-BTA regardless of pH and H2O2 concentration in slurry. A thinner passivation layer was grown on Cu in BTA added slurry solutions with a higher contact angle of 60°. The dynamic etch rate, the removal rate with abrasive free slurry, also decreased when BTA was added in slurry at pH 2, 4 and 6. The removal rate of Cu was strongly dependent on types of abrasive particles in slurry. The larger hardness of slurry abrasive particles, the higher removal rates of Cu. The reduction of removal rates in BTA added slurry was determined by the competition between chemical dissolution rate and mechanical abrasion rate.
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