Copper Chemical Mechanical Polishing Research Articles

Rational utilization of the size and electronic effect of inhibitors enabling high polishing rate with minimum corrosion in copper chemical mechanical polishing

Chemical mechanical polishing (CMP) relies on corrosion to remove excess materials, while also on corrosion inhibitors to ensure post-polished surface quality. The robust adsorption of inhibitors onto metal surfaces typically improves inhibition effectiveness but significantly reduces the polishing rate. In this study, we propose and validate a novel strategy that focuses on the utilization of large-sized physisorption-type inhibitors to address this inherent conflict. By incorporating disproportionated rosin (DR) as the inhibitor, the developed slurry facilely obtained a balance between polishing efficiency and quality for copper CMP. The inhibition mechanism of DR was elucidated through electrochemical characterization, adsorption isotherms, and reactive forcefield molecular dynamics (ReaxFF MD) simulations. The weak physisorption of the inhibitors facilitated their easy removal, resulting in minimal impact on the polishing rate. Additionally, the large-size structure of DR effectively hindered corrosive substances from reaching concave areas not under external force, thereby demonstrating superior inhibition efficacy. The adsorption mode of DR on copper was simultaneously determined through adsorption isotherms and ReaxFF MD simulations, marking the first instance of linking classic adsorption theory with MD simulations. The advantage of the ReaxFF MD simulations over classic MD simulations and density-functional-theory calculations for the metal-inhibitor adsorption systems was also discussed and demonstrated.

A quick diagnostic method for corrosion-inhibition balance and a green slurry for copper chemical mechanical polishing

In this paper, a green inhibitor, adenine, is introduced into the Cu-CMP slurry to prevent the toxic ingestion in the CMP process. Moreover, in order to effectively optimize and control the copper chemical mechanical polishing based on the corrosion-inhibition balance, an expression is proposed to diagnostic the balance quickly via the least square fitting of the experimental data. Based on the corrosion-inhibition balance optimization, a pH-neutral slurry (pH = 6.8 ∼ 7.2) incorporating adenine with a high material removal rate (MRR > 600 nm/min), a low surface roughness (Ra < 1 nm) as well as low surface defects (no micro-scratches, number of surface corrosion pits ≤ 0.02 counts·μm−2, particle residues ≤ 0.98 counts·μm−2) is achieved. This newly developed slurry and the diagnostic method for the corrosion-inhibition balance should be promising for designing the green slurry for Cu-CMP.

Green chemical mechanical polishing of copper with 2,5-dihydroxy-1,4-dithianeas as the inhibitor: Experimental and theoretical studies

It is a great challenge to develop green chemical mechanical polishing (CMP) technique owing to the limited inhibitory performance of green inhibitors. In this study, 2,5-dihydroxy-1,4-dithiane (DHD) was found and utilized as a superior inhibitor in CMP slurry, which realized nanometer-scale smoothness for copper surface. The strong inhibition effect of DHD, in both static and dynamic situations, was demonstrated by microscopic observations and electrochemical characterizations. The effectiveness of DHD was achieved mainly through its chemisorption onto copper surface, determined by Langmuir adsorption isotherm. X-ray photoelectron spectroscopy and density-functional-theory calculations proved that the chemisorption occurred between the S atom of DHD and Cu. Overall, DHD as an efficient and eco-friendly inhibitor with low-cost exhibits immense potential for applications in chip fabrication, particularly at a low technology node.

First-principles insight into the pH-dependency of the corrosion inhibition ability of benzotriazole and 1,2,4-triazole for copper in chemical mechanical polishing slurry

A comprehensive set of first-principles calculations was conducted to elucidate the disparity and pH-dependency of the corrosion inhibition performance of benzotriazole and 1,2,4-triazole in copper chemical mechanical polishing (CMP) slurry. Unlike previous calculations adopted the simplified and rigid model with neutral molecules adsorbed on metallic copper surface, the models, including Cu and Cu2O surfaces covered with O or -OH species, as well as neutral and deprotonated forms of inhibitor molecules, were constructed to simulate the adsorption interface based on the experimental results. The calculated adsorption energy successfully explained the pH-dependency of the inhibition ability of the two inhibitors.

Micro-scratches generation mechanism by copper oxides adhered on silica abrasive in copper chemical mechanical polishing

Chemical mechanical polishing (CMP) may introduce micro-scratches on the copper surface, posing a substantial challenge for developing advanced technology nodes. This study used macroscopic CMP and microscopic atomic force microscopy to investigate the micro-scratches generation mechanism in copper CMP from the perspective of abrasive particles. In the near-neutral slurry containing a low concentration of H2O2, copper can be oxidized to cuprous oxide and/or cupric oxide, forming a fragile oxide layer that can be removed by silica abrasive particles. The removed copper oxides can be adhered on the silica abrasive particles through electrostatic attraction, modifying the surface state. The adhered copper oxides possess irregularities and high hardness, likely inducing high contact stress locally and resulting in micro-scratches on the copper surface.

Corrosion inhibition mechanisms of triazole derivatives on copper chemical mechanical polishing: Combined experiment and DFT study

The impact of triazole derivative groups on corrosion inhibition performance of copper (Cu) film is studied by using 3-amino-1,2,4-triazole-5-carboxylicacid (ATA-O), 1H-1,2,4-triazole-3,5-diamine (ATA-N) and 3-amino-5-mercapto-1,2,4-triazole (ATA-S) as environment-friendly inhibitors. Electrochemical analysis showed that anti-corrosion passivation layer is formed on Cu surface after adding inhibitors with high inhibition efficiency of 54 %, 87 % and 98 % respectively, and improve the surface quality which is verified by atomic force microscope (AFM) and scanning electron microscopy (SEM) tests. Such results are consisted with static etch experiments. The mechanism of corrosion inhibition was revealed by theoretical calculation, which prove that the lone electron pair in empty orbitals of the O, N, S atoms on inhibitors hybridize with the Cu-d orbital to form covalent bonds and enhance the adsorption passivation action. Such study dissects the reasons for the potent inhibitory effect of triazole derivatives at the atomic level, and provides new method for efficient selection of inhibitors.

Surface Interaction Effect and Mechanism of Methionine Derivatives as Novel Inhibitors for Alkaline Copper CMP: Insights from Molecular Simulation and Experimental Analysis

To prevent excessive corrosion caused by the slurry in the copper (Cu) chemical mechanical polishing (CMP) process, a corrosion inhibitor is normally required. In this study, the methionine (Met) derivative FMOC-L-Methionine (Fmoc-Met-OH) was explored as a corrosion inhibitor for Cu film CMP in weak alkaline conditions (pH = 8.5). A comprehensive evaluation was conducted to confirm the efficiency of Fmoc-Met-OH as a corrosion inhibitor, combining experiments and theoretical calculations. The results showed that Fmoc-Met-OH could effectively inhibit the corrosion of Cu, with a high inhibition efficiency (IE) of 78.26% while maintaining a high removal rate (RR) of 5703 Å min−1, a low static etch rate (SER) of 676 Å min−1, and a low surface root mean square deviation (Sq) of 1.41 nm. Simultaneously, the results of X-ray photoelectron spectroscopy (XPS) tests and electrochemical analysis confirm that Fmoc-Met-OH molecules can form a dense and ordered adsorption film on the Cu surface. According to the density functional theory (DFT) calculations and molecular dynamics (MD) simulation, it was verified that Fmoc-Met-OH exhibited strong chemical adsorption on Cu substrates, as evidenced by the high binding energy (E Binding) value, low energy gap (ΔE), and radial distribution function (RDF) analysis. The findings provided theoretical evidence of the better inhibition effectiveness of Fmoc-Met-OH at a molecular or atomic level.

Nanoscale friction behavior and deformation during copper chemical mechanical polishing process.

The mechanical characteristics and deformation behavior of Cu material under the nanoscratching through a diamond tooltip on the workpiece are studied using molecular dynamics (MD) simulation. Effects of scratching velocity, scratching depth, workpiece temperature, and grain size on the total force, shear strain, pile-up, shear stress, workpiece temperature, and phase transformation are investigated. The results reveal that increasing the scratching velocity leads to higher oscillation in total force, greater shear strain and shear stress, higher pile-up on the workpiece surface, and higher workpiece temperatures. The effect of the scratching velocity on phase transformation shows that most of the dislocation is a transformation structure from the FCC structure to the HCP, BCC, and other structures in all workpieces during the nanoscratching process. In addition, with increasing the scratching depth, material pile-up becomes more prominent, consequently elevating the contact area between the diamond tooltip and the workpiece, which simultaneously leads to an increase in total force, shear strain, pile-up, shear stress, and workpiece temperature. The MD simulation results revealed that the subsurface region of nanoscratched Cu single-crystal experiences the formation of stacking faults, vacancy defects, and cluster vacancies. In studying the effect of workpiece temperature, the results show that higher temperatures lead to the decline of scratching force, high plastic deformation, increased shear strain and stress, lower pile-up height, and high transition from the FCC structure to both other and BCC structures. For polycrystalline structures, the force curves occur in the oscillation state in all cases of different grain sizes because of the dislocation deformation during the cutting process. The maximum force decreases with diminishing grain size, attributed to the inverse Hall-Petch relation. As the grain size increases, leading to a decrease in the shear strain, stress, and an uneven pile up; also, the HCP structure rises with decreasing grain boundary and the partial dislocation and stacking fault mobilize inside grains. By using molecular dynamics (MD) simulation based on the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software, all molecular interactions were described by the Lennard-Jones (LJ) and embedded atom method (EAM) potentials. In order to mitigate the effects of temperature fluctuations, the system employs an isothermal and isobaric (NPT) ensemble for precise temperature control. The temperature was set as 300 K and the time step was 1 fs (femtosecond).

Monodispersion of SiO2/CeO2 Binary Nano-Abrasives with Adjustable Size in Chemical Mechanical Polishing Performance of Copper

Chemical mechanical polishing (CMP) is an efficient methodology to achieve atomic-level roughness and global planarization. The selection and structural design of the abrasive particles in the polishing slurries play an essential role in the CMP process. In this work, silica (SiO2) microspheres with adjustable size and structure were prepared by a modified Stöber template approach, and ceria (CeO2) nano-shell layers were coated via in situ chemical precipitation on the core surfaces forming core/shell composite particles. The SiO2/CeO2 composites were characterized by XRD, SEM, TEM, XPS, and BET. The polishing performance of SiO2/CeO2 abrasives in copper (Cu) CMP was investigated by AFM. The small-sized (ca. 98 nm), large-sized (ca. 296 nm), and mesoporous (ca. 277 nm) composite abrasives were named as SiO2/CeO2-1, SiO2/CeO2-2, and mSiO2/CeO2, respectively. The best average surface roughness (Ra) and root-mean-square roughness (Rq) were obtained using SiO2/CeO2-1 abrasives, which decreased from 1.485 and 1.832 to 0.363 and 0.511 nm, respectively. The material removal rate (MRR) of the composite abrasives was improved to 279 nm min−1 by SiO2/CeO2-2 abrasives. The mSiO2/CeO2 composites were not manifested with evident superiority in terms of polishing characterization, which was attributed to the coating of CeO2 nanolayers. Finally, the material removal of Cu-CMP mechanisms was discussed.

Polyacrylic Acid as a Lubricant and a Complement to 1,2,4-Triazole for Copper Chemical Mechanical Polishing

Polyacrylic Acid as a Lubricant and a Complement to 1,2,4-Triazole for Copper Chemical Mechanical Polishing

Competitive effect between corrosion inhibitors in copper chemical mechanical polishing

Corrosion inhibitors are critical to realizing local and global planarization in copper chemical mechanical polishing (CMP). It is necessary to explore the interaction between components of composite corrosion inhibitors. This study reported a type of composite corrosion inhibitors of 1,2,4-triazole (TAZ) and 5-methyl-benzotriazole (5-MBTA) having a competitive effect between TAZ and 5-MBTA, different from the conventional synergistic effect. It is revealed that after adding either TAZ or 5-MBTA or their combination, the copper surface quality can be improved, while the copper material removal rate (MRR) ranks: TAZ > TAZ + 5-MBTA > 5-MBTA. For the competitive effect, TAZ and 5-MBTA can be co-adsorbed on the copper surface. Meanwhile, the electrochemical results indicate that the corrosion inhibition effect can rank: 5-MBTA > TAZ + 5-MBTA > TAZ, implying that TAZ and 5-MBTA may compete for the adsorption sites. The competitive effect may root in the different molecular structures, presumably the benzene ring. According to the corrosion wear mechanism of copper CMP, the stronger the corrosion inhibition effect, the lower the MRR. Therefore, the MRR of the composite corrosion inhibitors is between TAZ and 5-MBTA. The finding provides an enhanced understanding of composite corrosion inhibitors in the copper CMP.

The mechanical effect of soft pad on copper chemical mechanical polishing

Smaller transistor size challenges traditional chemical mechanical polishing (CMP) in semiconductor fabrication. Novel consumables and in-depth mechanism research can support defect mitigation and improve yield. This study focused on soft pad polishing of copper film from the perspective of mechanical effects. To reduce the defects, a soft pad is replacing the hard pad in the barrier layer polishing and over-polishing steps of copper CMP. When the contact behavior of pad asperity and wafer was in the elastic-plastic regime, the exponential influence factors of pressure, abrasive concentration, and sliding velocity on the material removal rate (MRR) were around 0.64, 0.22, and 0.64, respectively. Stick-slip friction with squeal noise scratched the copper film at the beginning and end of the CMP process. The pad conditioning removed polishing residues but deflected the pad asperity. Proper conditioning frequency is necessary to optimize the polishing process.

Application of an optimized alkaline cleaning solution for inhibitor removal during the post-CMP process: Performance evaluation and mechanism analysis

With the continuous miniaturization of the feature size of semiconductor integrated circuits, the development of chemical mechanical polishing (CMP) technology for copper interconnection has been promoted, and at the same time, more stringent requirements and challenges have been put forward for post-CMP cleaning technology. Benzotriazole (BTA), which has been used as an inhibitor to decrease metal corrosion especially in copper CMP process, is the main object to be removed after the CMP process due to its highly hydrophobic nature. However, the current post-CMP cleaning method cannot achieve an effective balance between high removal efficiency of BTA and excellent surface quality after CMP cleaning. Therefore, a novel and efficient alkaline cleaning solution for post-CMP cleaning of copper is proposed, which is based on tetraethylammonium hydroxide (TEAOH), l-glutamate (Glu) and polyvinylpyrrolidone (PVP). The cleaning effect of copper surface was characterized by contact angle measurement, electrochemical system, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The ion exchange of TEAOH and Glu promotes desorption of BTA molecules from the copper surface. The presence of PVP plays a key role in improving the surface quality after cleaning. This cleaning solution was proved to be effective for BTA removal and achieving a nearly defect-free clean surface.

Effect of radial grooves pads on copper chemical mechanical polishing

In this study, the effect of radial grooves (RG) pads employed in the copper chemical mechanical polishing/planarization (CMP) process was investigated, to improve the copper CMP performance. To this end, four types of pads were selected according to the number of RGs; the numbers of RGs were 0, 8, 16, and 32. The amount of slurry inflow/outflow was calculated for the selected number of RGs over the same duration, and the change in the slurry inflow/outflow according to the rotational speed of the head/platen was determined using a numerical method. The simulation results thus obtained demonstrated the differences in the amount of slurry inflow/outflow according to the number of RGs and the rotational speed of head/platen. At 90 rpm, the new slurry mass fractions of the circular groove (CG) pad and the RG-32 pad were 0.52754 and 0.67606, respectively, and the new slurry mass fraction of the RG-32 pad increased by about 22% compared to the result of the CG pad. Subsequently, the CMP process was performed using four types of pads at different head/platen rotational speed, and Cu removal rates were compared. According to the CMP evaluation results, the Cu removal rates improved with an increase in the number of RGs. At 90 rpm, the Cu wafer removal rates of the CG pad and the RG-32 pad were 4051.3 Å/min and 5047.2 Å/min, respectively, and when the RG-32 pad was used, the Cu wafer removal rate was increased by about 24.6%. Furthermore, the roughness of the Cu wafers was improved by increasing the number of RGs. Therefore, supplying new slurry and releasing the old slurry can affect the performance Cu CMP process.

Effect of brush cleaning on defect generation in post copper CMP

Chemical Mechanical Polishing (CMP) has been utilized for surface topography control and planarization since it was introduced in semiconductor fabrication. However, the concept of CMP now encompasses defect control process. Post CMP in-situ cleaning has employed brush scrubber and brush scrubber is considered as highly effective method for particle removal. CMP-induced defects are well defined and easy to identify such as scratches, slurry abrasive particles, metal residue, corrosion and organic residues. Most of them are yield-detracting defects. In this paper, defect generation during the copper (Cu) CMP in-situ cleaning process is explored and the investigation focus is cross contamination by the brush cleaning process. Experiments were conducted with blanket oxide wafers and Cu pattern wafers. Brush gap, brush life, and brush cleaning time were variables for the experiments. After brush cleaning experiment, wafer surface charge characterization was performed by mercury probe method. The experiment results in this paper underscore surface charge variation during the brush cleaning process playing a critical role in defect generation. This is a new finding as to how brush cross contamination occurs during brush cleaning, and results in this paper will provide insights on defect reduction strategy in CMP process development.

Analytical Modelling of Material Removal in Copper Chemical Mechanical Polishing Incorporating the Scratch Hardness of the Passivated Layer on Copper Thin Film Wafer

Chemical mechanical polishing (CMP) is the most crucial process for semiconductor fabrication and the scale of its application is broadening year by year. And understanding the varied mechanical interaction at pad-wafer contact as well as chemical alteration of the wafer surface is essential to comprehend the mechanism of material removal in the CMP process. In this study, an analytical material removal model is established as a function of polishing pad properties and scratch hardness of copper thin film wafer in CMP slurry environment. The model incorporates both, the mechanical material wear of chemically altered surface and, the chemical dissolution of copper based on corrosion theory. The contact between the polishing pad, wafer and abrasive is analysed and, in addition, the effect of the polishing pad and wafer properties on material removal is simulated. The model predicted MRR is compared to the copper CMP experiment MRR. This study establishes a strong correlation between the experimentally measured polishing pad and wafer properties and the material removal within the nanoscale contact model assumptions. The model provides a theoretical and experimental framework for optimizing the CMP process parameters, which can be employed to develop a simulator to analyze the advanced node copper CMP process

Organic additives based alkaline alumina slurry for selective removal of barrier layer metals

In the present work, tantalum (Ta) and copper (Cu) chemical mechanical polishing (CMP) has been carried out using a polishing slurry containing 2 wt% alumina (abrasive), 1 wt% potassium carbonate (oxidizer), and 0.25 wt% each urea and citric acid (additives). The Cu removal rate (RR) decreases with an increase in pH and is found to be minimum at pH 11 while Ta RR increases till neutral pH and then decreases till pH 11 having maximum RR at pH 7. Ta to Cu removal rate selectivity of 1:1.02 is attained at pH 11. Other parameters such as the effect of additives concentration, applied pressure, and platen rotational speed are also studied and results are reported to get a clear scenario. Surface charge analysis reveals that with change in pH, zeta potential alters and 30mV zeta potential is found at pH 11 which confirms the stability of the formulated slurry. To comprehend the removal mechanism of the metals, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) are employed. The same trend is encountered for both corrosion current density (Icorr) and film resistance (Rfilm)values resulting from Tafel and EIS. Based on the research conducted a plausible material removal mechanism is suggested.

An optimized passivation mechanism at the copper film recess for achieving efficient planarization of copper chemical mechanical polishing

This article proposed an improvement plan for the slurry to reduce the dishing caused during copper chemical mechanical polishing (CMP) of the interconnect structure. According to the difference in the pressure between the concave and convex parts of the copper film in the high-hardness polishing pad, polishing slurries were designed with a distinct difference in the polishing removal rate under high and low platen pressures to improve their planarization efficiency. 2 wt% GLY (glycine) and 1 wt% H2O2 can provide a chemical dissolution effect, adding 0.1% TAZ (1,2,4-triazole) to slow down the corrosion mainly for the recession, by adjusting the slurry pH to 7. The polishing results showed that the slurry had a high copper removal rate (6772 Å/min) at high pressure (3.0 psi) and a much lower removal rate (3273 Å/min) at low pressure (1.2 psi). The pattern wafer polished with this slurry obtained relatively low dishing. The other comparison groups showed slight differences in copper removal rate at high and low pressure and a deeper dishing of the polished pattern wafer. In this paper, based on the analysis of static dissolution experiments, electrochemical experiments, and XPS experiments of copper films in different slurries, the chemical reaction mechanism of copper films in the solution system of GLY and H2O2 was studied at different pH values. In addition, the inhibition mechanism of TAZ on the copper surface at different slurry pH values was proposed, including the properties of the TAZ molecule adsorption film on the copper surface, the uniformity of the surface coverage, and the thickness of the passivation layer. The results can reflect the polishing results to a certain extent despite some deviations, but it can also be used as a more reasonable argument to explain the optimization scheme of the slurry proposed in this article.

Investigation of thermal effects in copper chemical mechanical polishing

With the demand for manufacturing large (e.g., 450 mm) wafers, problems arise due to temperature increases associated with the chemical mechanical polishing (CMP) process. Various methods have been employed to stabilize the in-situ polishing temperature. The use of a high-temperature slurry can improve the removal rate, but a degradation in surface morphology occurs during the copper CMP procedure. To explain this mechanism, the effects of temperature on the slurry, CMP pad, and copper wafer were separately investigated. A temperature of approximately 40 °C was demonstrated to be a suitable choice when considering polishing efficiency and quality, thereby facilitating the rapid production of semiconductors. Particle aggregation was also observed with a rise in temperature. The work presented here may allow for a reduction in defects during low-hardness material polishing.

Influence of chemical mechanical polishing of copper on the inherently selective atomic layer deposition of zirconia

Copper is a highly used material for making interconnects in complementary metal-oxide-semiconductor devices in today's semiconductor industry. In this process, chemical mechanical polishing (CMP) is performed on silicon (Si) wafers patterned with electroplated (EP) copper (Cu) whereby further processing by selective atomic layer deposition (SALD) of zirconia on Si only is highly desirable. Although there have been previous studies of the selectivity on Si over Cu, inherent selectivity of an ALD process on post-CMP Cu was not discussed. CMP can modify the Cu surface and leave residual contaminants which can influence the selectivity of deposition. To understand the impact of CMP treated Cu surface on SALD, this study, first, examines the chemical surfaces of three forms of Cu: electron-beam deposited, EP, and post-CMP Cu and then evaluates the selectivity of the ALD process by altering process parameters. X-ray photoelectron spectroscopic surface analysis and atomic force microscopy reveal post-CMP Cu having a slightly different chemical composition and lower surface roughness than EP Cu. SALD of zirconia was performed using ethanol both as the pre-deposition surface treatment agent and the oxygen source for the zirconium precursor used - tris(dimethylamino)cyclopentadienyl zirconium under variable process parameters. Since CMP of Cu is a necessary component of semiconductor manufacturing, assessing selectivity of this process on this form of Cu was necessary. In this study, we show a ∼2 nm ZrO2 layer on Si via ALD was possible with no deposition on post-CMP Cu under a less robust process window than that observed for other forms of Cu.