Chemical Mechanical Polishing Experiments Research Articles

The synergistic inhibitory effect and density functional theory study of 2,2’-[[(Methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol and potassium oleate on copper in H2O2 based alkaline slurries

Copper (Cu), during the chemical mechanical polishing (CMP) of barrier layer, was associated with several challenges, one of which is to screen slurries required to address the corrosion of Cu. A large number of CMP studies have proved the effectiveness of inhibitors on Cu, but the passivation mechanism is not clear from the perspective of atoms, which needs further confirmation by computational chemistry. In this study, 2,2’-[[(Methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol (TT-LYK) and potassium oleate (PO) as inhibitors for Cu were widely investigated by experimental and density functional theory (DFT) methods. The CMP experiments and potentiodynamic polarization data showed that both of them were mixed - type corrosion inhibitors with significant corrosion inhibition ability on Cu. Besides, the combination of TT-LYK and PO exhibited excellent performance in suppressing the Cu corrosion, which were well prove by the surface morphology, single frequency electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) measurements. In addition, DFT calculation show that TT-LYK and PO were adsorbed on the Cu surface by the Cu-N bonds and Cu-O bonds at the bridge site, respectively, thereby obtaining the most stable configuration. This work is conducive to elucidate the role of corrosion inhibitors from a micro level.

Corrosion control of copper wiring by barrier CMP slurry containing azole inhibitor: Combination of simulation and experiment

In the chemical mechanical polishing (CMP) process of barrier layer of multilayer copper wiring in integrated circuits, it is necessary to add appropriate corrosion inhibitor into the polishing slurry to protect copper from corrosion, reduce the height difference with the barrier material and achieve high planarization. There are few literatures about the behavior of inhibitors on metal surface in CMP studied by computational chemistry. In this study, density functional calculation and Monte Carlo simulation combined with electrochemical and CMP experiments were used to investigate the adsorption and corrosion inhibition of azole inhibitors (BTA, TAZ and TT-LYK) on copper wiring in barrier layer in glycine/hydrogen peroxide reference solution system. The results show that all the azole inhibitors in the reference solution system have obvious corrosion inhibition on copper surface, and the inhibition effect of azole inhibitors was positively correlated with the increase of concentration. In particular, TT-LYK has a stronger corrosion inhibition effect, which was verified by electrochemical and CMP measurements, MD results support there are more adsorption sites between TT-LYK and copper surface. In addition, the stability of the solution containing TT-LYK and the state of copper surface evaluated by SEM after TT-LYK treatment are better. The combination of molecular dynamics methods and experiments approach may well be able to study corrosion inhibitors at the micro level and foretell better molecular structures which is more suitable to improve the efficiency of wiring corrosion inhibition.

RE (La, Nd and Yb) doped CeO2 abrasive particles for chemical mechanical polishing of dielectric materials: Experimental and computational analysis

Ce3+ in CeO2, rather than Ce4+, is believed to provide assistance to the breaking up of SiO bond during chemical mechanical polishing (CMP) of silica. In the paper, lanthanide metals (La, Nd and Yb) doped CeO2 nanoparticles were synthesized by modified incipient impregnation method in order to improve the content of Ce3+ in CeO2 as polishing. X-ray photoelectron spectroscopy (XPS) experiments and density function theory (DFT) calculation demonstrate this approach could achieve surface doping of CeO2 nanoparticles, and facilitates the formation of oxygen vacancy and Ce3+ content. CMP experiments show that the polishing rate and the surface quality of silica wafer are obviously improved by using the doped CeO2 as abrasive particles. Especially for Nd/CeO2, content of Ce3+ increases from 0.146 to 0.235, the polishing rate of silica is accelerated by 29.6% in alkaline slurries, and a better surface quality (Sa = 9.6 Å) is obtained.

Effect of Chloride Ions on the Chemical Mechanical Planarization Efficiency of Sapphire Substrate

Sapphire is widely used in solid lasers, semiconductor chip substrates, light emitting diodes substrates and other high-tech fields for its excellent mechanical and optical properties. At the same time, the chemical mechanical polishing(CMP) performance and quality need to be improved for different crystal plane sapphire substrate. In this paper, in order to improve the removal rate NaCl was used as an additive in sapphire slurry. From the CMP experiment results of a- and c-plane sapphire, it was found that higher material removal rate (MRR) and lower surface roughness (Sq) were obtained by adding NaCl with the concentration of 0.2wt% in sapphire slurry. In order to reveal the action mechanism of NaCl, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) measure methods were used. From the SEM measure results it can be seen that there were microscopic corrosion pits on substrate surface, which indicates that chemical reaction took place between NaCl and substrate material. From XPS measure results it was verified that sodium tetrachloroaluminate (NaAlCl4) was formed during CMP. However, during the experiment, it was found there was a very small amount of silica sol crystalline particles after NaCl was added to the slurry. After analyzing the formation mechanism of crystalline particles, KCl was selected to replace NaCl. The same polishing effect was obtained and there were no crystalline particles found in the slurry tank. From the results it is found chloride ions played an important role in improving the removal rate and surface roughness of sapphire substrate.

Effect of chemical action on the chemical mechanical polishing of β-Ga2O3(100) substrate

Chemical mechanical polishing (CMP) is an essential processing step to realize ultra-precision machining of the fragile material Ga2O3 crystal and obtain ultra-smooth and undamaged crystal surface. The chemical auxiliary polishing mechanism of Ga2O3 in the CMP process was studied considering that the chemical action directly affects the CMP result. First, H3PO4 and NaOH were used to regulate the pH of slurry. This slurry was then applied to the CMP experiment of Ga2O3, and the corrosion test of Ga2O3 was implemented in H3PO4 and NaOH solutions. Second, the influence of the slurry with different acids or bases on the polishing result was analyzed. Finally, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the influence of the corrosive action on the chemical structure of the crystal surface. Results showed that the slurry prepared by H3PO4 was more suitable for the CMP of Ga2O3 than that prepared by NaOH. The polishing efficiency was enhanced by approximately 20% and the surface quality was improved, with surface roughness of 0.21 nm. This study provides a reference for preparing the slurry of Ga2O3.

Preparation of MgO doped colloidal SiO2 abrasive and their chemical mechanical polishing performance on c-, r- and a-plane sapphire substrate

Chemical mechanical polishing (CMP) has been proved to be one of the most important methods to achieve atomic ultra-smooth surface, and it becomes widely used as global planarization techniques. There are some influence factors for CMP processing quality, and abrasive in the slurry is one of the key ones. In order to improve the removal rate and surface quality of sapphire substrate, a new-type MgO doped colloidal silica abrasive was studied Based on the basic principle of chemical thermodynamics, the HSC software was used to analyze the tendency of reactions between MgO doped colloidal silica abrasive and sapphire and between H2O and sapphire to generate solid solutions, compounds and hydrates on the sapphire surface. From the CMP experiment results of a-, r- and c-plane sapphire, it indicated that higher material removal rate (MRR) and lower surface roughness (Sq) were obtained with the slurry containing MgO doped colloidal SiO2 abrasive instead of containing pure SiO2 abrasive under the same conditions. In addition, the action mechanism of MgO doped colloidal SiO2 abrasive on sapphire substrate CMP was studied. From the analyzing result of X-ray photoelectron spectroscopy (XPS), it deduced solid-chemical reaction between sapphire surface and MgO doped colloidal silica abrasive was occurred and Al2Si2O7·2H2O, MgAl2O4 and Al2SiO5 were generated, which can promote chemical effects during CMP and lead to the increase of MRR. Such results have certain guiding significance to practical production.

Monitoring the Physicochemical Degradation of Polishing Pad Soaked in Hydrogen Peroxide during Chemical Mechanical Polishing

The porous polyurethane polishing pads are extensively used in the chemical mechanical polishing. The pad property is very important and influences the polishing effectiveness and the wafer surface quality. Hence, in the present work, the physicochemical degradation of unused polyurethane polishing pads during metal chemical mechanical polishing (CMP) in the presence of hydrogen peroxide (H2O2) was studied. It was found that the polishing pads were reacted chemically with H2O2 resulting in degradation of the polymer chain network of polishing pad and reduction in the pad elastic modulus. Pad polymer network chain scission was observed during FT-IR evaluation confirming the degradation of the pad. CMP experiments with the H2O2 soaked pads resulted in change in material removal rate (MRR) and the within-wafer non-uniformity (WIWNU). Further Pad elastic modulus estimated by colorimetric evaluation and CIE Lab color coordinates.

Germanium electrochemical study and its CMP application

When the feature size of ultra-large scale integrated(ULSI) circuit shrinks to sub–10nm, germanium(Ge) as a novel material with high hole mobility is needed for further development. Chemical mechanical polishing(CMP) is an important process for the integration of channel materials into silicon wafer. In this paper, starting with electrochemical studies of Ge, different types and concentrations of oxidants for Ge corrosion were investigated; then the effect of NaCl and Dodecylamine for Ge activation and inhibition were studied. After that, corresponding CMP experiments were conducted, which confirmed the results of electrochemical experiments. Moreover the polish selectivity of Ge/SiO2 in H2O2-based slurry was also investigated. Atomic force microscope(AFM) was used to test the surface morphology of wafers after polish. Finally the slurry with 5wt% SiO2 abrasive and 1 vol.% H2O2 at pH 9 were chosen to polish Ge/SiO2 wafers, and it has a high polish selectivity of Ge to SiO2 while high Ge removal rate and good quality surface were obtained.

Establishing a theoretical model for abrasive removal depth of silicon wafer chemical mechanical polishing by integrating a polishing times analytical model and specific down force energy theory

This study uses the polishing pad with cross pattern, and it is supposed that the contact area between polishing pad surface of cross pattern and wafer is Gaussian distribution to establish and analyze an innovative abrasive removal depth theoretical model of chemical mechanical polishing (CMP) silicon wafer. In this model, it uses the binary image pixel division to calculate polishing times and it derives the contact force of each abrasive particle and uses the specific down force energy (SDFE) theoretical equation to calculate the abrasive removal depth on each abrasive particle after down force being applied. This study carries out CMP silicon wafer experiment as well as atomic force microscopy (AFM) measurement experiment of SDFE of silicon wafer. The abrasive removal depth of silicon wafer acquired from simulation analysis is compared with the abrasive removal depth of silicon wafer obtained from CMP experiment of silicon wafer, and the difference in between will also be analyzed. It shows that the difference between the results of simulation and experiment is in the acceptable range.

Effects of KIO4 concentration and pH values of the solution relevant for chemical mechanical polishing of ruthenium

Ruthenium (Ru), as one of the most promising barrier layer applied for the 14nm node and below technology in the integrated circuits manufacturing, the effects of the polishing variables on the chemical mechanical polishing (CMP) process are not intensively investigated. Corrosion investigation methods combined with CMP experiments were utilized to comprehensively reveal the polishing mechanism affected by the potassium periodate (KIO4) concentration and the slurry pH values. The results of both the static and in-situ corrosion investigation show that the static corrosion rate of Ru is the lowest when the slurry is weak alkaline, but it is the most obviously enhanced by the polishing process under this condition. Considering the different oxidant concentration, the corrosion of Ru distinctively accelerates, and turns to be more like a diffusion-limited mass transfer controlled process when the KIO4 concentration increases. Because the corrosion plays a significant role in the whole CMP process, with a full accounting of other variables, the polishing process of Ru is preferred to be carried out under low down pressure in weak alkaline slurries. Under this condition, the mechanical-enhanced chemical effect is predominating, which is helpful to obtain a good surface quality, and a high material removal rate.

Development of green CMP by slurry reduction through controlling platen coolant temperature

Chemical mechanical polishing (CMP) is currently replacing a conventional chemical etching or mechanical polishing to remove overburdened copper deposit in printed circuit board (PCB) manufacturing process owing to its ability to realize a global planarization. In order to stabilize the CMP as one of the PCB manufacturing processes, the CMP machine has been investigated. This paper introduces a newly developed Oscar-type CMP machine and copper CMP process to polish rectangular PCB with a size up to 510 mm by 510 mm, especially focused on the effect of platen coolant temperature on removal rate and removal uniformity during copper CMP to reduce the amount of slurry consumed. The CMP experiments are implemented under the coolant temperatures of 10, 15, 20, 25 and 30°C, and the slurry flow of 600, 800, 1000 and 1200 mL/min. The experimental results show that the removal rate goes up with an increase in the platen coolant temperature during polishing at a fixed slurry flow rate, and the removal rate goes down at any fixed the platen coolant temperature when the slurry flow rate increases. It means that the reduction of thermochemical reaction rate in the chemical mechanical removal, resulting from cooling down of the copper surface when the.

Core–shell structured polystyrene coated silica composite abrasives with homogeneous shells: The effects of polishing pressure and particle size on oxide-CMP

To improve the structural stability of the core–shell organic–inorganic composite abrasives during chemical mechanical polishing (CMP) processes, the polystyrene (PS) coated silica composites with homogeneous shells (amorphous silica networks, 15–20nm in thickness) were synthesized via the sol–gel process of tetraethoxysilane at acidic aqueous condition in the presence of PS colloids (210–540nm). Transmission electron microscopy and scanning electron microscopy were applied to characterize the as-synthesized samples. The effects of particle sizes and polishing pressures on oxide CMP performance were explored by atomic force microscopy. The results indicated that the obtained composite abrasives exhibited excellent polishing performance and structural stability during polishing processes. With the increase of the polishing pressures (13.8–41.4kPa), the layer removal rate (RR) increased correspondingly, while the root-mean-square (RMS) roughness of polished substrates decreased firstly and then increased. Moreover, the RR and RMS for the composite abrasives increased with the increase of PS core sizes. At a given polishing pressure of 27.6kPa, the highest RR (82.5±7nm/min) was obtained for the PS coated silica composites with largest cores (ca. 540nm), while the lowest RMS roughness (0.189±0.02nm) was observed for the composites with smallest cores (ca. 210nm). Furthermore, the polishing results in our CMP experiments were rationalized according to the indentation-based material removal mechanism (Chen et al. Appl Surf Sci 2012; 258:8469–74).

A Full Wafer-Scale PAML Modeling Approach for Predicting CMP

Chemical mechanical polishing (CMP) is a complex, multi-scale problem with several order of physics. As it is a subtractive manufacturing process, it involves cutting tool–workpiece interaction. The cutting tool in CMP are nanoscale abrasives trapped in the contact between the workpiece (wafer) and a soft, rotating pad. These abrasives are suspended in a liquid medium and transported across the interface to provide even material removal. The current model presents an expansive wafer-scale framework that not only accounts for the solid–solid contact mechanics and wear, but also utilizes the mechanics of the slurry through fluid and particle dynamics. Results from this work include the temporal evolution of hydrodynamic fluid pressure, contact stress and material removal at the die and wafer scales. Comparisons with published CMP experiments have been made, and the results are favorable. Parametric studies have been conducted to predict the influence of different polishing parameters on the material removal rate. With this new framework, the entire wafer–pad interface can be studied under the influence of the four major physical interactions (contact mechanics, fluid mechanics, particle mechanics, wear). The result is a significantly faster multi-physical model that can simulate realistic CMP conditions without sacrificing accuracy.

Surface characteristics of ruthenium in periodate-based slurry during chemical mechanical polishing

When the feature size of integrated circuit continues to shrink below 14nm, ruthenium (Ru) has become one of the most promising candidates for the application of novel barrier layer. To reveal the material removal mechanism of Ru during chemical mechanical polishing (CMP), surface characteristics of Ru in KIO4-based slurry were investigated. The corrosion behavior of ruthenium was measured by the surface chemistry and morphology analysis. Then the mechanical properties of the passivated/corroded surface were evaluated by AES and tribocorrosion experiments. CMP experiments were carried out to make clear the effects of surface property during polishing. It was found that the Ru surface chemistry and mechanical properties vary obviously as a function of slurry pH. In neutral slurries, the Ru surface is covered with RuO2·2H2O/RuO3 inhomogeneous passivation films, with the highest material removal rate obtained during the CMP process. It could be concluded that the material removal mechanism largely depends on the slurry pH values. In near neutral slurries, Ru is passivated with thick and heterogeneous oxides film, which proves the easiest to be mechanically removed during polishing. The weak alkaline slurry is preferred in order to achieve desirable polishing rate as well as avoid the formation of toxic RuO4.

Core/Shell Structured Solid-Silica/Mesoporous-Silica Microspheres as Novel Abrasives for Chemical Mechanical Polishing

The allotropic silica microsphere as a novel abrasive, which consisted of a solid-silica ( S SiO2) core and a mesoporous-silica shell ( M SiO2), was introduced into chemical mechanical polishing (CMP) process. The shell thickness of the core/shell structured S SiO2/ M SiO2 microspheres was tailored by adjusting the amount of cetyltrimethylammonium bromide (mesoporous template) and tetraethylorthosilicate (silica source). The obtained S SiO2/ M SiO2 samples were structurally confirmed by small-angle X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy and nitrogen adsorption–desorption technique. The results of oxide CMP experiments revealed that the S SiO2/ M SiO2 abrasives exhibited higher material removal rate (=269 nm/min), lower root-mean-square (=0.203 nm) surface roughness as well as lower topographical variations than those of conventional solid-silica abrasives (137 nm/min, 0.343 nm). The enhanced CMP performance might be attributed to the optimization of the real contact environments between abrasives and substrates based on the synergetic aspects of chemical corrosion and mechanical abrasion. These results suggested that the core/shell structured S SiO2/ M SiO2 abrasives presented an important potential application in efficient and damage-free polishing. This work will provide experimental and theoretical basis for the design and application of porous abrasives or core/shell structured composites with porous shells in CMP.

Material removal mechanism of copper chemical mechanical polishing in a periodate-based slurry

The material removal mechanism of copper in a periodate-based slurry during barrier layer chemical mechanical polishing (CMP) has not been intensively investigated. This paper presents a study of the copper surface film chemistry and mechanics in a periodate-based slurry. On this basis, the controlling factor of the copper CMP material removal mechanism is proposed. The results show that the chemical and electrochemical reaction products on the copper surface are complex and vary considerably as a function of the solution pH. Under acidic conditions (pH 4) the copper surface underwent strong chemical dissolution while the corrosion was mild and uniform under alkaline conditions (pH 11). The corrosion effect was the lowest in near neutral solutions because the surface was covered with non-uniform Cu(IO3)2·H2O/Cu-periodate/copper oxides films, which had better passivation effect. The surface film thickness and mechanical removal properties were studied by AES and AFM nano-scratch tests. Based on the combined surface film analysis and CMP experiment results, it can be concluded that the controlling factor during copper CMP in a periodate-based slurry is the chemical-enhanced mechanical removal of the surface films. The periodate-based slurry should be modified by the addition of corrosion inhibitors and complexing agents to achieve a good copper surface quality with moderate chemical dissolution.

Research on influences of contact force in chemical mechanical polishing (CMP) process

A series of simulations of chemical mechanical polishing (CMP) were conducted to investigate the contact force between abrasive particles and specimens by using the finite element method (FEM). In this paper, a micro-contact model, which only involves the mechanical interactions, was set up to simulate the polishing process by changing the processing parameters, including the downward pressure, abrasive size, and polishing speed. Simulation results show that the contact force becomes larger when the downward pressure increases. In addition, when the downward pressure and abrasive size increase, the fluctuation of the contact force becomes large, whereas it declines with decreases in the polishing speed. In addition, corresponding CMP experiments were done to investigate the material removal rate (MRR) and polished average roughness (Ra) under different simulation conditions. Through the establishment of the contact force properties in the simulation and the MRR and Ra in the CMP experiment, qualitative research has been done on the relationship between the contact force in the simulation and experimental results. Experimental results indicate that the MRR and surface roughness are influenced by the contact force. A high MRR can be obtained by a large contact force and dramatic fluctuations can lead to poor surface-finish quality. The investigation contributes to obtaining higher polishing efficiency and lower surface roughness through optimization of the polishing parameters.

Effect of contact angle between retaining ring and polishing pad on material removal uniformity in CMP process

This paper presents the effect of the contact angle between the retaining ring and the polishing pad in chemical mechanical polishing (CMP) on the profile of the material removal rate (MRR) around the wafer edge and on the within-wafer nonuniformity (WIWNU). This study demonstrates that the mechanical interaction among the polishing pad, wafer, and retaining ring influences the ability to achieve planarization from the CMP process. In particular, the purpose of this study is to understand the effect of the contact conditions between the retaining ring and the pad on the CMP process. In order to verify the mechanical aspects of the MRR near the wafer edge, retaining rings with different contact angles were prepared. Finite element analysis (FEA) verified the effect of the contact angle between the retaining ring and the polishing pad on the stress distribution around the edge of the wafer. The results of the analysis were corroborated by conducting CMP experiments with 200-mm blanket oxide wafers. As expected, the FEA results were in good agreement with the MRR profile around the edge area. Through simulations and experiments, we concluded that the contact angle is an important factor to achieve a flatter edge profile and the material removal profile around the edge of the wafer was optimum at a 0o contact angle. In particular the WIWNU was below 4% when a flat retaining ring was used. The results of this study make it possible to improve the yield of chip production by ensuring the retaining ring maintains perfect flatness without making any special design changes to the CMP equipment.

Effects of chemical slurries on fixed abrasive chemical-mechanical polishing of optical silicon substrates

Chemical mechanical polishing (CMP) with fixed abrasive pad is an alternative machining method to loose abrasive lapping and partial polishing with traditional pad in the fabrication of optical silicon substrates. However, the effects of chemical slurry on the fixed abrasive polishing performance are not fully understood. In this work, a serial of CMP experiments with a fixed abrasive pad were carried out for optical silicon substrates using seven different chemical slurries i.e. de-ionized water, alkaline lubricant, colloidal silica, hydrogen peroxide (H2O2) and potassium hydroxide (KOH). The polishing performances of these slurries were evaluated and compared in terms of material removal rate (MRR), surface roughness and flatness of the polished silicon substrates. The polishing characteristics were also discussed to reveal material removal mechanism and silicon surface generation under different chemical environments.

Chemical Mechanical Polishing of Glass Disk Substrates: Preliminary Experimental Investigation

Glass disk substrates are used in a wide range of portable devices because of their relatively high resistance to heat and shocks compared with aluminum substrates. Chemical mechanical polishing (CMP) is an available method to eliminate residual surface defects induced by grinding/lapping to meet final product requirements. In this work, CMP experiments with a low-cost fabric cloth pad were performed to study the effects of four key process factors on the material removal rate (MRR), flatness, and surface finish of polished glass disk substrates, and to explore the feasibility to achieve high machining efficiency, sub-nanometric surface roughness, and micrometric flatness of polished glass disk substrates simultaneously under optimized CMP conditions. The experimental results and analyses reveal that the interaction of pad rotational speed and polish head rotational speed had significant effect on the roughness (Ra), down force, and the interaction of down force and pad rotational speed had significant effects on the flatness, and down force and pad rotational speed had significant effects on the MRR. After compromise and prioritization analyses are performed, a combination of the four variables, which is the combination of 50 g/cm2 for down force, 40 rpm for pad rotational speed, 20 rpm for polish head rotational speed, and 100 ml/min for slurry supply velocity, is obtained to achieve high machining efficiency, sub-nanometric surface roughness and micrometric flatness of polished glass disk substrates simultaneously.