Copper Chemical Mechanical Planarization Research Articles

Mechanisms of Chemically Promoted Material Removal Examined for Molybdenum and Copper CMP in Weakly Alkaline Citrate-Based Slurries

Chemical mechanical planarization (CMP) of metal components is an essential step in the fabrication of integrated circuits. Metal CMP is a complex process where strategically activated (electro)chemical reactions serve to structurally weaken the surface layers of the material being processed, and the resulting overburdens are removed under low-force abrasion. Understanding the tribo-electrochemical mechanisms of this process is crucial to successfully designing the consumable materials for advanced CMP slurries that are needed for the new technology nodes. Using a model CMP system involving copper (wiring material in interconnect structures) and molybdenum (a new diffusion barrier material for copper), the present work illustrates a tribo-electroanalytical scheme for studying various mechanistic details of metal CMP. Electroanalytical probes are employed both in the absence and in the presence of surface polishing to quantify the interplay between mechanical abrasion and chemical surface modification. Weakly alkaline slurry formulations are tested with variable concentrations of silica abrasives and a complexing agent, citric acid. The results serve to examine the link between material removal and tribo-corrosion and to identify the functions of the active slurry additives in governing the rates and selectivity of material removal for CMP.

Molecular Interactions in Copper Chemical Mechanical Planarization: A Phenomenological Study

In this study, the molecular interactions occurring during Chemical Mechanical planarization of Copper in Ferric nitrate–Alumina–Benzotriazole system is investigated. This system is characterized by sudden and dramatic transitions in removal rates when experimental parameters such as downforce and concentrations of the slurry components (Benzotriazole, abrasive, oxidizer) are varied. This behavior is interpreted in terms of the three surface kinetic processes viz. Cu dissolution, film formation and film removal by abrasion, that determine the overall removal rate. A phenomenological model incorporating Frumkin isotherm for the adsorption of Benzotriazole molecules and Langmuir isotherm for the adsorption of surfactants/ions is proposed. Mathematical equations relating the rates of film formation, film removal and metal dissolution to the overall removal rates are derived. The model is validated by comparing the model predictions with experimental data. The non-linear equations describing the sudden transitions are shown to exhibit a cusp catastrophe when the interaction parameter exceeds a certain value.

Investigation of the Two-Way Injection Slurry-Supply Method for the Cu CMP Process

The effect of the two-way injection method during a copper chemical mechanical planarization (CMP) process was investigated. The two-way slurry-injection method has the advantage of not only preventing the degradation of the slurry, but also shortening the process time because the mixing process of the slurry and H2O2 is not required. Compared to the conventional method, the two-way injection method has an equivalent level of less than 9% in material removal rate. In particular, when injecting near the center of the pad, the influence according to the positions and flow rates of the two nozzles is also insignificant, so it deserves to be studied as a slurry-supply method.

Study on enhancement and mechanism of K2SO4 in CMP slurries for copper film polishing removal effect

The efficient copper removal of the in the multi-layer copper interconnect copper film chemical mechanical planarization (CMP) process is one of the important indicators for high production efficiency of integrated circuit process. The chemical corrosiveness of polishing slurries to copper is the key factor affecting the copper removal rate. Since the copper polishing slurries are relied too much on the synergistic effect of complexing agent and oxidant for the copper chemical dissolution to achieve efficient removal of copper film, the planarization and corrosion of copper CMP cannot be well improved. In this paper, it was found that adding potassium sulfate (K2SO4) in polishing slurries can improve the copper removal effect of CMP. In this paper, the mechanism of the effect enhancement of K2SO4 was explored with series of characterization experiments. Firstly, the influence of K2SO4 on the increase of electrochemical corrosion degree of copper electrode was studied by electrochemical method. Secondly, based on X-ray photoelectron spectroscopy (XPS) and laser scanning confocal microscope (LSCM), it was determined that the copper surface oxide formation increased after electrochemical corrosion caused by K2SO4. Finally, the efficiency of copper polishing removal of K2SO4 in polishing slurries was verified by CMP experiments, and the dynamic oxidation enhancement mechanism of K2SO4 in polishing slurries for CMP copper removal was analyzed.

On the Evaluation of Thermodynamic Properties for Copper in Sodium Carbonate and Potassium Carbonate

This study investigates sodium carbonate and potassium carbonate as oxidizers for copper (Cu) chemical mechanical planarization (CMP). The dissolution study was conducted to estimate etch rate (ER) in the entire odd pH range for both the suggested oxidizers. The etch rate decreases as the pH increases from acidic to alkaline region. The effect of change in temperature of the working solution on Cu dissolution is also investigated. Based on the experiment conducted and the values obtained, the enthalpy (ΔHact) and entropy (ΔSact) of both the system were calculated. The contact angle was measured to further examine the surficial synergy between the oxidizers and the exposed Cu surface.

(Invited) Towards Metrology to Enable Standardizing CMP Consumables

In the semiconductor industry, there is a need to establish fundamental, mechanism-based, correlation(s) between process conditions, consumables (e.g., pads and slurries), and observed process performance in Chemical-Mechanical Polishing (CMP) [1-5]. Such understanding can lead to the creation of industry-wide standards that can help reduced cost of ownership. Along these lines, the Chemical Mechanical Planarization Consumables (CMP-C) Task Force under Liquid Chemicals Global Technical Committee within the SEMI Standards Program has been actively developing a guide (SEMI C100) for reporting CMP pad hardness [6], and pad density.In this paper, we revisit our decades old, but still relevant, quest for suitable mechanism-based metrology for CMP-pad. While we focus on polyurethane-based CMP pads, we will touch on alternative pad materials. [10-11]. Using both static and dynamic the dynamic mechanical analysis (DMA) [7-8] and the FTIR [9] we monitored changes in pad polymer properties under various chemical and mechanical stresses. Pad sample were analyzed: prior to use (fresh); after a 24-hr soak in silica-containing oxide slurry (basic); and after oxide polishing (used). Upon comparison it was observed that a characteristic transition feature due to water is present at sub-ambient temperatures in both the slurry soaked and used pads. Exposure of as-received pads to basic oxide slurry results in a broad, high temperature transition thought to be the result of chemical-induced disruption of macrostructural units. Polishing (load-enhanced chemical exposure) introduces further changes to the polymer network represented by an apparent degradation of the pad polymer.References1) P. B. Zantye, et al, 'Chemical mechanical planarization for microelectronics applications, Materials Science and Engineering: R: Reports, 2004, 45, 3–6, doi: 10.1016/j.mser.2004.06.002.2) Zantye, Parshuram B., "Processing, Reliability and Integration Issues In Chemical Mechanical Planarization" (2005). Graduate Theses and Dissertations, https://scholarcommons.usf.edu/etd/9283) S. Deshpande et al, “The Electrochemical Society, find out more Chemical Mechanical Planarization of Copper: Role of Oxidants and Inhibitors”, 2004 J. Electrochem. Soc. 151 G7884) Y. S. Obeng et al., "Impact of CMP consumables on copper metallization reliability," in IEEE Transactions on Semiconductor Manufacturing, vol. 18, no. 4, pp. 688-694, Nov. 2005, doi: 10.1109/TSM.2005.858457.5) Obeng, Yaw S., et al. "Characterization of ‘In-Process’ Degradation of Polyurethane CMP Pads." Chemical Mechanical Planarization V 2002 (2002): 1.6) SEMI C100 - Guide for Reporting Chemical Mechanical Planarization (CMP) Polishing Pads Hardness Used, published by SEMI Standards (https://store-us.semi.org/products/c10000-semi-c100-guide-for-reporting-chemical-mechanical-planarization-cmp-polishing-pads-hardness-used-in-semiconductor-manufacturing, accessed December 15, 2020)7) Li et al, “Dynamic Mechanical Analysis (DMA) of CMP pad materials”, MRS Proceedings, January 2000, Cambridge University Press, DOI: 10.1557/proc-613-e7.3.18) H. Lu et al, "Applicability of dynamic mechanical analysis for CMP polyurethane pad studies” Materials Characterization, 2002, 49, 2, 177-186, DOI: 10.1016/S1044-5803(03)00004-4.9) H Lu, et al., "Quantitative analysis of physical and chemical changes in CMP polyurethane pad surfaces, Materials Characterization", 2002,49, 1, 35-44, DOI: 10.1016/S1044-5803(02)00285-1.10) S. Deshpande, et al. “Surface-modified polymeric pads for enhanced performance during chemical mechanical planarization”, Thin Solid Films, 2005, 483, 1–2, 261-269, DOI: 10.1016/j.tsf.2004.12.063.11) Zantye, P., et al., “Metrology of Psiloquest's Application Specific Pads (ASP) for CMP Applications”. MRS Proceedings, (2004). 816, K5.6. doi:10.1557/PROC-816-K5.6

Development of a Stimuli-Responsive Supramolecular Brush for Enhanced Post-CMP Cleaning

With the miniaturization of device features, slurry chemistries have become increasingly complex and therefore require enhancement of current cleaning processes. Copper (Cu) chemical mechanical planarization (CMP), a critical process step in the fabrication of high-performance microprocessors, utilizes nanoparticle abrasives (i.e. SiO2) and functional chemistry (i.e. complexing agents, inhibitors, and pH adjusters) during the polishing process which can lead to contaminants on the wafer surface. Currently, post-CMP cleaning processes use a standard polyvinyl alcohol (PVA) brush coupled with functional cleaning chemistry to remove these contaminants, including organic residue, particle contaminants, and excess ions. With stringent contaminant-free demands, it is crucial to develop cleaning consumable sets to meet these demands. This work focuses on the functionalization of PVA with supramolecular moieties to enhance the removal of nanoparticle and organic residue. Results have shown that the addition of supramolecular complexes to the PVA brush enhanced particle removal through hydrophobic/hydrophilic interactions at the brush/wafer interface. Additionally, this functionalized PVA brush shows increased adsorption of metal ions (specifically Cu2+) via inclusion complexes. Initial results have also shown that PVA containing pore forming additives have a photochemical response in which when irradiated with specific wavelengths of light the brush can be turned “on” or “off” based on chemical interactions at the brush/wafer interface.

A Neural Network-Based Approach to Material Removal Rate Prediction for Copper Chemical Mechanical Planarization

In modern integrated circuits, chemical mechanical planarization (CMP) has emerged as one of the most important solutions for surface global planarization. The surface uniformity and quality control are greatly dependent on the material removal rate (MRR) of the polished wafers. The construction of accurate physical CMP models to predict MRR is a great challenge due to the complexity of the coupling interplay of mechanical, chemical and design pattern effects in the CMP process. In this work, CMP experiments are designed and performed under different process conditions to obtain the removal rates and a data-driven neural network-based approach is developed to predict the MRR and reveal the relationship between the removal rate and polishing parameters for copper CMP. It is shown that the predicted results of the removal rates are consistent with the experimental data with an optimized network structure. The investigation of the neural networks (NNs) to model the MRR indicates that the NN-based method can provide a general way of capturing the removal rate profiles regardless of the complexity of the polishing mechanism. Therefore, the present CMP model has good potentials of assisting in achieving the surface uniformity control of the copper wafer in semiconductor manufacturing.

Development of endpoint detection using optical transmittance and magnetic permeability based on skin effect in chemical mechanical planarization

For copper chemical mechanical planarization, a novel polishing endpoint detection was developed by combining light reflectance and eddy current with the skin effect. The two endpoint detection techniques are similar in principle, as both involve the penetration of electromagnetic waves into the copper film. In the former method, RSA (Ratio of Spectral Area) using white light is used to determine differences in reflectance by the range of wavelength. The endpoint detection by the RSA is robust and stable during polishing. The latter employs the original mechanism of eddy current utilizing skin effect. The eddy current system can detect accurate film thickness corresponding to skin depth since a local maximum of eddy current appears just before polishing endpoint. The results revealed that the point at which the local maximum of eddy current emerged was the starting point of light transmission to the copper film. It was demonstrated that the two endpoint systems match well each other and it is possible to accurately detect the polishing endpoint based on the remaining film thickness through mutual confirmation of the two methods.

Correlating Removal Rate to Directivity in Copper Chemical Mechanical Planarization

The relationship between directivity (Δ) and removal rate (RR) during copper chemical mechanical planarization (CMP) was investigated. We measured the high-frequency shear and normal forces generated by stick-slip (which has been routinely used to explain micro- and nano-scale interactions that lead to material removal), and found there to be a strong correlation between Δ (defined as the ratio of variances in shear force to those of normal force) and copper RR so long as the tribological mechanism remained constant. In cases where the tribological mechanism changed from “boundary lubrication” (BL) to “mixed lubrication” (ML), the slope of the straight-line correlation between Δ and RR was maintained, albeit it was shifted significantly lower. This was due to the ML regime consisting of hydrostatic or buoyant forces supporting the wafer, which led to less variability in frictional forces or less stick-slip events. Additionally, it was found that Δ and RR increased with sliding velocity while in BL due to an increase in stick-slip events. Conversely, Δ and RR decreased at lower sliding velocities while in ML due to an increase in hydrostatic or buoyant force supporting the wafer.

Integrated electrochemical analysis of polyvinyl pyrrolidone (PVP) as the inhibitor for copper chemical mechanical planarization (Cu-CMP)

Copper chemical mechanical planarization (Cu-CMP) is an essential procedure for the fabrication of integrated circuits (IC). The corrosion inhibitors in the Cu-CMP slurry could balance the over etching from the corrosion reagents to facilitate the global planarization of the copper layers. However, the normally used Cu-CMP inhibitor 1-benzotriazole (BTA) was toxic for the long time usage. In this paper, the biocompatible polyvinyl pyrrolidone (PVP) was proposed to substitute the BTA in the Cu-CMP. With an integrated electrochemical test, including the Tafel polarization, electrochemical impedance spectra (EIS), and the electrochemical noise (EN), it was found that the PVP could possess a good inhibition effect comparable to BTA, which opened up a promising way for the design of biocompatible inhibitors in the Cu-CMP.

Effect of Pad Type on Passivation Film Formation Relevant to Copper Chemical Mechanical Planarization

Copper (Cu) chemical mechanical planarization (CMP) is an extremely critical step in the manufacturing of ultra-large-scale integrated (ULSI) semiconductor devices. By optimizing the synergistic relationship between a chemical dispersion, referred to as a slurry, and mechanical parameters, global planarization is able to be achieved utilizing CMP. Traditional slurries for Cu CMP promote Cu oxidation, promoting the creation of a passivation film which readily able to be removed by the same mechanical process. However, the efficiency of film removability is strongly correlated to the molecular structure of the passivating agent and also the composition of the polyurethane polishing pad. This work aims to mechanistically understand the relationship between molecular structure of the passivating agent and the pad type on the modulation of the passivation film formed. The film formation kinetics and characteristics were studied through various electrochemical techniques and surface spectroscopy. Results have indicated that the film is directly correlated to the molecular structure of the passivating agent, and the ease of removing the film is strongly contingent on the type of polyurethane pad implemented in the CMP polishing process.

Synthetic Design of a Supramolecular Complexing Agent for Advanced Cu Chemical Mechanical Planarization Applications

As the complexity of three-dimensional large-scale integration (3D-LSI) circuits increases, copper (Cu) Chemical Mechanical planarization (CMP) has emerged as a critical step in the fabrication of semiconductor wafers attaining global planarization. Through-silicon Via (TSV) CMP incorporates elimination of deposited excess trench overburden above a silicon wafer at a high removal rate, thus allowing additional layers to be added for substantial 3D-LSI circuit architecture. Enhancing the planarity of the substrate as a result of undesired topography removal is controlled through optimization of slurry composition. In traditional slurries, a synergistic chemical interaction between a corrosion inhibitor and a complexing agent removes irregularities from the surface while at high downforce. To optimize slurry interaction and promote film formation at the interface, a suite of additives incorporating both properties of the slurry are being developed. More specifically, the functionalization of a supramolecular structure enables removal rate to rely heavily on surface chemistry due to its polymeric nature while simultaneously preserving surface uniformity. The introduction of substituents with high-binding affinity for Cu into the slurry such as heterocyclic pyridines, amino, and carboxyl groups directly correlate to a higher removal rate. Preliminary results have shown a correlation between the molecular structure of the complexing and inhibiting agents and their effect on film formation. Adding a system that integrates simultaneous chelation and passivation to the slurry via the supramolecular complex will directly impact the planarity and therefore alter the removal mechanism. This work employs electrochemical surface analysis such as open-circuit potential (OCP) to monitor film formation kinetics and results have shown a direct correlation to CMP parameters.

Real-Time Shear and Normal Force Trends in Copper Chemical Mechanical Planarization with Different Conditioning Discs

The effect of two different commercially-available CVD-coated diamond conditioning discs on copper CMP was investigated tribologically and kinetically with the intent of correlating pad surface micro-texture to polish performance. Data analyses were particularly focused on in-situ shear and normal force measurements taken during polishing at several pressures (P) and sliding velocities (V), including Fast Fourier Transform (FFT) analysis of the data. One of the two discs consistently resulted in greater variances of shear force with increasing P and V indicative of increased pad-slurry-wafer stick-slip events. This trend correlated to higher values of coefficient of friction (COF) and removal rate (RR). By dividing the shear force variance by the normal force variance, a new parameter, termed directivity, was used to further emphasize the improved performance of the above-mentioned disc. Lastly, the tribological and kinetic data, combined with data regarding the pad's micro-texture and its extent of contact with the wafer, showed that at all values of P and V, higher values of directivity correlated to more contacting pad asperities, a greater asperity density and a thinner micro hydrodynamic lubrication layer, thus highlighting the potential importance of directivity in future studies.

Role of the Adhesion Force during Copper Chemical Mechanical Planarization

The adhesion force between slurry particles and the wafer surface has a significant effect on the material removal and ultra-smooth surface formation during the chemical mechanical polishing/planarization (CMP) process. Based on zeta potentials measurements, we calculate the value of adhesion force, which cannot be ignored compared with the Hertz contact force for small sized abrasive particles at low polishing pressures. More over, the impacts of slurry (particle size and pH value) and wafer surface roughness on the adhesion force are evaluated. Theoretical analyses manifest that the adhesion force mainly originates from the van der Waals force and electrical double-layer force, which increases with the increase of the particle size and slurry pH, while decreases with the increase of the wafer surface roughness. The relationships between the adhesion force and scratch depth indicate that scratching would be avoided while enhancing the adhesion force during CMP. These findings would provide some inspirations to understand the CMP technology in depth, and they are also beneficial to engineering super-smooth and super-lubricant surfaces with nano-scaled roughness.

Real-Time Shear and Normal Force Trends in Tungsten Chemical Mechanical Planarization with Different Conditioning Discs

In-situ conditioning is known to increase material removal rate (RR) during chemical mechanical planarization (CMP), because it roughens the pad surface that is in contact with the wafer. Previous studies have shown that the conditioning disc changes the pad surface micro-texture and affects the thermal, kinetic and tribological attributes of the CMP process. This study focuses on two different diamond discs for in-situ conditioning during tungsten CMP, and shows how real-time force data improves our understanding of the effects from using one disc versus the other. Shear and normal forces were analyzed through spectral analysis, variance and force scatter plots. Frequency signatures that appear regardless of the type of disc used were likely attributed to vibrations of the polisher and the harmonics of these vibrations. A new parameter, directivity (Δ), was employed, which highlighted the significant differences in shear force variance between the two discs. Above all, this study confirmed that high Δ correlated with high RR. Compared to a related study on copper CMP with these discs, the trends between Δ and RR seemed to continue to hold.

Effect of Chelating Agent and Ammonium Dodecyl Sulfate on the Interfacial Behavior of Copper CMP for GLSI

Multi-layered copper wiring chemical mechanical planarization (CMP) of Giant Large Scale Integrated circuit (GLSI) is one of the key processes for the improvement of microelectronic technique. During copper interconnection CMP, high removal rate (RR) and lower surface roughness for copper film are required. Slurry is one of the key factors to achieve highly effective planarization for copper film, and is also one of the research hotspots. In this work CMP and electrochemical behavior of copper with the synergistic effect of chelating agent and Ammonium Dodecyl Sulfate (ADS) using a new type alkalescent slurry was investigated. The slurry was composed of colloidal silica, FAOII chelating agent, surfactant (ADS) and hydrogen peroxide. The Potentiodynamic polarization plots revealed that FAOII chelating agent had strong chelating ability to improve copper removal rate, which was verified by polishing experiments. When FAOII concentration increasing from 0 to 5wt%, copper RR dramatically increased from 377Å/min to 5523Å/min. [CuR(NH2)2]2 + as one of the key generated products relating to RR improvement was verified by XPS. Meanwhile, with the addition of ADS, the static etch rate decreased from 1080Å/min to 442Å/min, and the surface roughness decreased from 4.81nm to 2.69nm, which indicated that ADS acted as a surfactant and an inhibitor simultaneously. From the result it can be seen that high and controllable removal rate and low surface roughness can be achieved by adjusting the concentration of FAOII chelating agent and anionic surfactant ADS. Slurry is stabilized till 48 hours. Such simple and component adjustable alkalescent slurry has certain guiding significance to practical production.

Effect of Complexing Agent Choices on Dishing Control Level and the Shelf Life in Copper CMP Slurry

There has been lot of work going on reducing dishing without benzotriazole (BTA) because it can lead to organic debris and other defects during the chemical mechanical planarization (CMP) although being an effective dissolution inhibitor on dishing elimination. Slurry destabilization problems also have to be closely monitored because it can cause surface defects and changes in the material removal due to particle agglomeration and the chemical degradation. In this study, FA/O chelating agent, a unique alkaline organic macromolecule, yielded a lower dishing level under the condition of no BTA compared with glycine, which allows for a substantial reduction in the use of BTA. The dissolution rate, polish rate and changes in the in-situ open circuit potential (OCP) were performed to elucidate the planarization mechanism and how the use of carcinogenic BTA can be reduced. It was also observed that the FA/O based slurry had a shelf life of no more than 7 days and the root cause was the oxidation reduction reaction between FA/O chelating agent and H2O2 rather than the self-decomposition of the hydrogen peroxide.

Signal processing and analysis for copper layer thickness measurement within a large variation range in the CMP process.

In the copper (Cu) chemical mechanical planarization (CMP) process, accurate determination of a process reaching the end point is of great importance. Based on the eddy current technology, the in situ thickness measurement of the Cu layer is feasible. Previous research studies focus on the application of the eddy current method to the metal layer thickness measurement or endpoint detection. In this paper, an in situ measurement system, which is independently developed by using the eddy current method, is applied to the actual Cu CMP process. A series of experiments are done for further analyzing the dynamic response characteristic of the output signal within different thickness variation ranges. In this study, the voltage difference of the output signal is used to represent the thickness of the Cu layer, and we can extract the voltage difference variations from the output signal fast by using the proposed data processing algorithm. The results show that the voltage difference decreases as thickness decreases in the conventional measurement range and the sensitivity increases at the same time. However, it is also found that there exists a thickness threshold, and the correlation is negative, when the thickness is more than the threshold. Furthermore, it is possible that the in situ measurement system can be used within a larger Cu layer thickness variation range by creating two calibration tables.

Influence of slurry components on copper CMP performance in alkaline slurry

In this work, we have designed copper chemical mechanical planarization (CMP) experiments to investigate the effect of slurry components on the planarization performance of copper wafer in the presence of two different surfactants including ammonium dodecyl sulfate (ADS) and fatty alcohol polyoxyethylene ether (AEO). Copper CMP was performed at pH10.5 using hydrogen peroxide (H2O2), silica, benzotriazole (BTA), and FA/O II (a unique alkaline macromolecular organic chelating agent with high activation energy) as an oxidizer, an abrasive, a corrosion inhibitor and a complexing agent, respectively. As hydrogen peroxide is added in the copper slurry, the material removal rate (MRR) increases rapidly and then decreases slowly as a function of the concentration of H2O2. The within-wafer non-uniformity (WIWNU) declines and the surface roughness decreases first and then ascends with the increase of the H2O2 concentration. The addition of BTA has a large effect on the MRR, WIWNU and copper surface roughness. The MRR decreases to approach a minimum as a function of the BTA concentration. While the copper surface WIWNU fluctuates and the surface roughness increases with increasing the amount of BTA. As FA/O II is chosen to be a complexing agent, the MRR increases prominently and the WIWNU decreases with the increase of the FA/O II concentration. The surface roughness also decreases indicating that the addition of FA/O II can effectively improve the surface planarization performance in the present copper CMP experiments. The mechanism of the corresponding experimental results is also elucidated and discussed. All the results show that the copper surface planarization performance could be strictly controlled by proper configuration of the slurry components and an optimal choice of the concentrations of the constituents can obtain a high removal rate, low WIWNU and small surface roughness of the copper wafer in alkaline slurries.