Static Etch Rate Research Articles

The Effect of Electrolytes on Polshing Behavior in Cu ECMP

The purpose of this study is to characterize various electrolytes on electrochemical mechanical planarization (ECMP). The ECMP system was modified from conventional CMP system to measure the potentiodynamic curve and removal rate of Cu. The potentiodynamic curves were measured in static and dynamic states in investigated electrolytes using a potentiostat for the evaluation of the polishing behavior on ECMP. KOH (alkaline) and NaNO (salt) were selected as electrolytes which have high conductivity. In static and dynamic states, the corrosion potential decreased and the corrosion current increased as a function of the electrolyte concentration. But, the electrochemical reaction was prevented by mechanical polishing effect in the dynamic state. The static etch and removal rate were measured as functions of concentration and applied voltage. When NaNO was used, the dissolution was much faster than that of KOH. It was concluded that the removal rate was strongly depended on electrochemical dissolution. The removal rate increased up to 350 nm/min in NaNO based electrolyte.

Copper CMP with Composite Polymer Core - Silica Shell Abrasives: A Defectivity Study

ABSTRACTThe results of copper Chemical Mechanical Planarization (CMP) experiments with a model slurry chemistry based on the combination of Glycine-water-Benzotriazole (Gly-H2O2-BTA), and different types of composite A (silane coupling agents between the polymer core and the silica shell) and B (electrostatic attraction between the polymer core and the silica shell) abrasives, are presented. While the presence of BTA allows a ten-fold reduction in the static etch rate from 95 nm/min. to 10 nm/min., combining oxidizer and complexing agent leads to removal rates higher than 400 nm/min. Different surface morphology and RMS roughness are observed after polishing with composite abrasives and different peroxide concentrations. Oxidizer concentrations as low as 0.1 vol.% lead to high non-uniformity and defectivity values. In particular, composite B performs better than pure colloidal/fumed silica during copper CMP using the IC-1000 pad, giving comparable Material Removal Rate (MRR), but a better surface finish due to the contribution of the elasticity of the polymer in gently transferring the applied load to the wafer surface. Cu CMP with pure polymer particles is a promising alternative to the hard inorganic material especially if combined with suitable surfactants that act from both particle stabilization and friction reduction / lubrication improvement perspectives.The use of the medium/high-hardness pad IC-1000 is compared to the use of a soft Politex pad. In the former case, differences in terms of MRR, MRS roughness, and total defects are observed between the composite abrasives A and B; in the latter case, the behaviour of the two composites is similar. In the case of a soft pad in combination with composite abrasives, there is a remarkable improvement in the defectivity without any loss in MRR.As revealed by SEM inspection of the composite particles collected in the slurry drain after CMP, for all the composites, the silica shell coverage is not disrupted by the shear forces and chemistry during the 1 min. polishing. Consequently, the stability and agglomeration properties of the particles in the complex Cu CMP chemistry can be helpful in explaining the experimental results in terms of MRR and surface finishing.

Chemical mechanical planarization of copper in alkaline slurry with uric acid as inhibitor

Chemical mechanical planarization of copper disks in hydrogen peroxide and l-arginine based alkaline slurry was investigated. Various commonly proposed inhibitors were screened by static etch rate experiments and only BTA and uric acid were found to be effective in the alkaline pH range, while potassium sorbate was moderately effective. The combination of arginine, hydrogen peroxide and uric acid leads to a more robust polish rate than can be achieved with glycine, hydrogen peroxide and BTA based slurries. The dissolution in presence of uric acid was further studied by potentiodynamic and cyclic polarization experiments which indicate formation of a passivation layer on the copper surface. Silicon dioxide wafers were polished to determine the Cu/silicon dioxide polish rate selectivity in alkaline pH range and a high selectivity (>100) was observed. These results indicate that it is possible to conduct a robust copper CMP with alkaline slurries while maintaining an excellent Cu/silicon dioxide polish rate selectivity.

A Liposome-Containing Slurry for Tungsten Chemical Mechanical Polishing

Chemical mechanical planarization (CMP) has become an essential process in the manufacturing of advanced semiconductor devices found in cell phones, computers, and other everyday electronics. The three major applications of CMP involve the planarization of structures and films made of copper, tungsten, and silicon dioxide at wafer level. While CMP of silicon dioxide or interlayer dielectric materials represents the earliest application of CMP and copper CMP has become an enabling and fast-growing segment of CMP, tungsten CMP remains steady in production volume and growth. The yield of a CMP process is heavily dependant upon the performance of its corresponding slurry, a stable colloidal aqueous dispersion of abrasive particles and various chemical additives. It is generally true that, other than the dispersed abrasive particles, all other chemical additives are homogenously dissolved in a single aqueous phase. In this paper, we report the design and performance of a liposome-containing slurry for tungsten CMP. More specifically, in addition to the abrasive particles and other chemical additives commonly found in a metal CMP slurry, this new slurry contains a model catalyst that is encapsulated inside of liposome. The caged catalyst does not interact with the oxidizer outside until the polish. The purpose of encapsulating a catalyst is to increase the pot lifetime of the slurry and reduce the static etch caused by the reaction between the catalyst and the oxidizer if they are exposed to each other directly. In this study, we demonstrated that, by caging the catalyst, the static etch rate is significantly reduced and the pot lifetime is significantly increased. The material removal rate remains high. In this paper, the basic design of such slurry is first introduced. The evidence for the encapsulation of a representative catalyst is presented. The performance of such slurry on the polish of blanket and patterned wafers is discussed.

Effects of Additives in KOH Based Electrolytes on Cu ECMP

ABSTRACTThe purpose of this study was to characterize KOH based electrolytes and effects of additives on electro-chemical mechanical planarization. The electrochemical mechanical polisher was made to measure the potentiodynamic curve and removal rate of Cu. The potentiodynamic curves were measured in static and dynamic states in investigated electrolytes using a potentiostat. Cu disk of 2 inch was used as a working electrode and Pt electroplated platen was used as a counter electrode. KOH was used as the electrolyte. H2O2 and citric acid were used as additives for the ECMP of Cu. In static and dynamic potentiodynamic measurements, the corrosion potential decreased and corrosion current increased as a function of KOH concentration. In dynamic state, different potentiodynamic curve was obtained when compared to the static state. The current density did not decrease in passivation region by mechanical polishing effect. The static etch and removal rate were measured as function of KOH concentration and applied voltage. In ECMP system, polishing was performed at 30 rpm and 1 psi. The removal rate was about 60 nm/min at 0.3 V when 5 wt% KOH was used. Also, the effect of additive was investigated in KOH based electrolyte on removal rates. As a result, The removal rate was increased to 350 nm/min when 5wt% KOH, 5vol% H2O2, 0.3 M citric acid were used.

Development and Optimization of Slurry for Ru CMP

ABSTRACTIn this study, Ruthenium (Ru) chemical mechanical planarization (CMP) slurry was studied and developed to apply it for the formation of Ru bottom electrode in DRAM capacitor. An acidic chemical was chosen as both oxidant and etchant. The effects of the chemical on polishing and etching behavior were investigated as functions of chemical concentration and pHs. The static etch rate of Ru increased with increase of chosen chemical concentration. Also, thin Ru oxide was generated in chemical solution. The highest etching and removal rate were obtained in slurry of pH 6. Ru over etching was generated due to the high etch rate of Ru, and then good planarity was not obtained. However, because Ru over etching was prevented due to low etch rate of Ru, the plarnarity and isolation of each capacitor in slurry of pH 9 was acquired successfully.

Research on Effects of Slurry Additives in Cu CMP for ULSI Manufacturing

In this paper, in order to analyze the oxidation, dissolution and corrosive inhibition effects of additives in the slurry for copper Chemical-mechanical polishing(CMP), the slurry(pH5) with the peroxide as an oxidant, the citric acid as a complexing agent and the benzotriazole(BTA) as an inhibitor is studied. The static etching rate and polishing rate of the Cu-H2O2-Citric acid-BTA slurry are measured. The electrochemical behavior involved in the dissolution and corrosive inhibition of copper in the solutions containing additives is investigated by the electrochemical impedance spectroscopy (EIS) studies. The surface roughness is measured using ZYGO 3-D surface profiler. It is observed that when the slurry is with only 5wt% peroxide existing, copper is stable and slight etching rate on the copper is produced, and the etching rate is only 8.7nm/min. When 0.6wt% citric acid presents after adding 5wt% hydrogen peroxide, the etching rate will increase by 5.3 times, with a blue complexing product emerging. When the inhibitor BTA is added, the corrosion will be effectively restrained. From the EIS results, the impedance of copper in 5wt% peroxide solution which is in passivation can be greatly decreased by adding the citric acid as a complexing reagent. And the impedance of copper in the solution containing peroxide and citric acid can be increased by the addition of BTA. The surface roughness of the wafer polished with the slurry of 5wt% peroxide+0.6wt% citric acid+0.12wt% BTA slurry is Ra 4.7 Å.

The Role of Arginine as a Complexing Agent in Copper CMP

AbstractChemical mechanical polishing (CMP) of copper was investigated in hydrogen peroxide and arginine slurries. Arginine was found to be a complexing agent for the copper in peroxide based slurries, in the alkaline region. The copper polish rate was measured in a Struers LaboPol-5 and LaboForce-3 CMP polishing tool. Static etch rate experiments of copper discs (25.4 mm Dia × 10 mm) were carried in 200 ml beakers with different combinations of hydrogen peroxide and arginine concentrations. Peroxide concentration was varied from 0 to 10 vol%, while the arginine concentration was varied from 0 to 1 wt% for both static etch and polish rate experiments. Fumed silica used as the abrasive medium for polishing.The electrochemical processes involved in oxidative dissolution of copper were investigated by the Tafel corrosion plots and OCP measurements, using the Princeton Applied Research potentiostat. Three electrode corrosion flat cell was used for the electrochemical measurements. Corrosion current density and open circuit potentials (OCP) were used to elucidate the oxidative behavior of peroxide and the complexing role of arginine. Surface characteristics of the polished copper surface were analyzed with the Digital Instruments NanoScope AFM. Polishing with these chemicals resulted in smooth finish.These results indicated that the arginine curtails the formation of oxidative layer on the copper surface and the removal rate was increased by forming complex with the copper.

Characterization of copper chemical mechanical polishing (CMP) in nitric acid–hydrazine based slurry for microelectronic fabrication

Chemical mechanical polishing of copper in nitric acid based slurry, with hydrazine as inhibitor was investigated. The polish rate and static etch rate decreased with the addition of hydrazine. Electrochemical corrosion studies confirm the inhibiting effect of hydrazine. The roughness of the polished copper surface improved with the addition of hydrazine.

Corrosion Inhibiting Effect on Copper Chemical Mechanical Planarization (CMP) in Fe(NO3)3 Based Slurries

The slurry of Copper chemical mechanical planarization for ultra large-scale integrate circuit (ULSI) usually contains oxidizer, etchant, complexing reagent and corrosive inhibitor. In planarization process, the corrosive inhibitor has an important effect on the planarization. Only if the concave surface of the wafer is properly protected from corrosion by the inhibitor, the process can obtain perfect surface planarity. In this paper, with Fe(NO3)3 as an oxidant and several corrosive inhibitors selected, the corrosive efficiency of slurries are investigated. The static etching rate and the polishing material removal rate of wafer are obtained. The electrochemical behavior of the slurry is investigated by the potentiodynamic polarization studies. And the inhibitive efficiency of the related corrosive inhibitors is calculated from the polarization data. X-ray diffraction is applied to analyze the composition modification of the copper surface. Atom force microscopy is applied to measure the surface topography of corrosive copper wafer and the value of surface roughness is measured by ZYGO surface analysis system. The result shows that the benzotriazole (BTA) is a perfect corrosive inhibitor. With addition of 0.1wt% BTA into 1.5wt% Fe(NO3)3 solution, the inhibitive efficiency can reach 99.1%. The polishing test shows that if only 1.5wt% Fe(NO3)3 is added as an oxidizer without any other additive, the surface roughness of the polished wafer is 26.9Å, while with 0.1wt%BTA added in the meantime, 5.2 Å of surface roughness can be obtained.

Mechanism of Copper Removal during CMP in Acidic H 2 O 2 Slurry

Chemical mechanical polishing of copper was performed using as oxidizer and alumina particles as abrasives. Electrochemical techniques were used to investigate the dissolution/passivation behavior of high-purity Cu disk under static and dynamic conditions at pH 4 with varying concentrations. Changes in the surface chemistry of the statically etched Cu disk were investigated using X-ray photoelectron spectroscopy. The Cu removal rate reached a maximum at 1% concentration and decreased with a further increase in concentration. The static etch rate showed the same trend. The etched surface morphology indicates that the removal of copper is primarily the result of electrochemical dissolution of copper at low concentrations. However, at increased concentrations, the copper oxidation rate increases, resulting in a change in the Cu removal mechanism to mechanical abrasion of the oxidized surface. © 2004 The Electrochemical Society. All rights reserved.

Challenges and Rewards of Low-Abrasive Copper CMP: Evaluation and Integration for Single-Damascene Cu/Low-k Interconnects for the 90nm Node

AbstractLow-abrasive content slurries for copper (Cu) chemical-mechanical planarization (CMP) have been developed to achieve removal rate and removal uniformity comparable to conventional slurries. They can improve post-CMP defectivity, improve topography and allow operation at lower polish pressures that are more compatible with the low-dielectric constant (low-k) materials required for current and future high-performance interconnects. Integration of these slurries into a yielding product with 9-level Cu/low-k metallization requires fundamental learning and process characterization. This paper discusses the some of the challenges encountered during development, integration, and qualification of a low-abrasive Cu CMP process for Texas Instruments (TI) Incorporated's 90 nm technology node with copper/organosilicate interconnect. As abrasive content is reduced, the slurry chemistry must play a larger role in CMP removal. A more aggressive reactive chemical formulation requires an effective inhibitive component to keep Cu static etch rate low. As a result, wafer-scale process and consumable interactions, die-scale planarization efficiency, and feature-scale removal rates each become more sensitive to process changes. Pressure and temperature have larger effects on removal rate/profile than conventional slurries, and complete clearing of Cu puddled over underlying topography becomes more difficult. Successful integration of these slurries, however, can achieve excellent results in dishing and erosion topography, Cu thickness uniformity, and Cu loss in small features such as vias and landing pads. Low-abrasive content solutions are also more stable and easy to handle in slurry distribution vessels and lines, have lower scratch and residue defectivity, and have greatly extended margin for overpolish. As lowabrasive content Cu slurry options continue to evolve to become manufacturable solutions, their benefits far outweigh the costs and challenges encountered in their successful integration.

Electrochemical characterization of copper chemical mechanical polishing

Chemical mechanical polishing (CMP) of copper was performed using H 2O 2 as oxidizer and alumina particles as abrasives. The interaction between the Cu surface and the slurry was investigated by potentiodynamic measurements taken during the polishing process as well as under static conditions. The Cu removal rate reached a maximum at 1% H 2O 2 concentration, and decreased with a further increase in H 2O 2 concentration. The static etch rate showed the same trend. Atomic force microscopic measurements were performed on both the etched surface and polished surface. It was shown that the surface roughness of the polished surface increased as the H 2O 2 concentration increased. This can be explained by changes in the structure of the passivating layer and the dominating role of the dynamic repassivation during polishing.

Slurries for Copper Damascene Patterning: Similarities and Differences

AbstractTwo first-step copper damascene slurries and one commercial second-step slurry are characterized in terms of their intrinsic properties and CMP performance. A prototype first-step slurry with high static etch rate (∼150 nm/min) yielded higher dishing in the copper lines (∼200 nm in 100 μm lines) compared to a commercial first-step slurry with negligible static etch rate. In both the cases, dishing in copper lines is observed to be a strong function of line width and radial position on the wafer. High static etch rate of the prototype slurry is believed to be responsible for the high dishing. Non-selective second-step polishing removes the liner layer while maintaining planarity.

Effect of Copper Film Surface Properties on CMP Removal Rate

SummaryIt has been observed that CMP removal rate of copper varies for films from different sources. While the film hardness and static wet etch rate in the absence of inhibitors are similar for various films, the static etch rate in the presence of inhibitors is significantly different. Analysis by AFM, XPS, and ion beam sputtering showed the film roughness and surface composition were different for different Cu films within 160 angstroms of the surface. Thus the different in Cu CMP removal rates can be explained by a synergetic effect of copper film roughness (grain size), surface composition, and effective adsorption of inhibitors. This explanation suggests that if polishing is initiated by an aggressive polishing step, removal rate of the remaining bulk copper films become more consistent. Based on these findings, the polishing slurry and process were further optimized.