Chemical Mechanical Planarization Research Articles

CMP에서 디바이스 패턴의 실 접촉 면적 측정을 통한 평탄화 규명

Chemical Mechanical Planarization (CMP) is an essential process for device integration and planarization in a semiconductor manufacturing process. The most critical function in the CMP process, is to predict and cover the geometrical characteristics of various sizes and densities, of patterned wafers for local and global planarization. To achieve the wafer-level and die-level planarization, it is necessary to understand the contact mechanism between the CMP pads and the macro-scale patterns. In the macro-scale pattern, pad deformation is divided into two layers: an asperity layer and a bulk pad layer. Through bulk pad deformation, asperity contact distribution within the pattern is predicted. In this paper, the distribution of asperity contact according to the pattern geometrical characteristics was analyzed, through large-area real contact area (RCA) measurement. Bulk pad deformation was predicted by analyzing RCA distribution according to pattern geometry such as pattern size and density, pattern shape and step height according to the polishing time, and applied pressure. Additionally, through the distribution of the contact area and the number of contact points, the rounding phenomenon and planarization characteristics in the pattern CMP were predicted.

Study of synergy of monoethanolamine and urea on copper corrosion inhibition in alkaline solution

• Cu corrosion in TMAH-containing solution is investigated. • MEA and urea are used as corrosion inhibitors to retard the Cu corrosion. • The synergy of MEA and urea on Cu corrosion inhibition is concentration ratio dependent. • Cu corrosion becomes more serious at low concentration ratio of MEA to urea. • Cu corrosion is effectively retarded at high concentration ratio of MEA to urea. Tetramethylammonium hydroxide (TMAH) is an important constituent used in the post cleaning process of chemical mechanical planarization and lithography; however, its corrosive property causes damage to the Cu metallization. Addition of corrosion inhibitor in the cleaning solution is a promising method to protect Cu. In this study, two corrosion inhibitors, monoethanolamine (MEA) and urea, are used to investigate their synergy on the Cu corrosion protection. Electrochemical and four-point probe methods are adopted to analyze the corrosion behaviors of Cu. Microstructural characterizations of Cu are performed using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. X-ray photoelectron spectroscopy is used to realize the adsorption behaviors of inhibitors on the Cu surface. The results of corrosion current ( I corr ) and charge transfer resistance ( R ct ) indicate that addition of MEA and urea at an identical concentration does not produce a typical synergistic effect on the Cu corrosion protection due to mutual interference of two inhibitors. An increase of the MEA concentration overcomes the mutual interference, giving rise to a reduction of I corr and an increase of R ct . The effective retardation of the Cu corrosion is attributed to the sufficiency of inhibitors which can construct a dense protection layer on the Cu surface.

Coupling Supramolecular Assemblies and Reactive Oxygen Species (ROS) with Megasonic Action for Applications in Shallow Trench Isolation (STI) Post-Chemical Mechanical Planarization (p-CMP) Cleaning.

Due to the continued miniaturization of semiconductor devices, slurry formulations utilized in the chemical mechanical planarization (CMP) process have become increasingly complex to meet stringent manufacturing specifications. Traditionally, in shallow trench isolation (STI), CMP, a contact cleaning method involving a poly(vinyl alcohol) (PVA) brush, is used to effectively transfer cleaning chemistry to the oxide substrate. This PVA brush can cause nonuniform cleaning chemistry transport, increased interfacial shear force, and cleaning-induced defectivity from brush loading. Previous work with traditional cleaning processes has shown that using “soft” supramolecular cleaning chemistries has dramatically improved cleaning efficacy while also minimizing the number of induced p-CMP defects. To minimize these effects, noncontact cleaning via the implementation of megasonic action has gained attention. This work employs “soft” cleaning chemistries with Cu2+–amino acid complexes, which can catalyze the formation of critical reactive oxygen species (ROS), and evaluates the p-CMP performance under megasonic action. Results from a second-order kinetic model indicate that megasonic conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low shear stress conditions.

Design of “Low Stress” Post-CMP Cleaning Processes for Advanced Technology Nodes

As integrated circuit and logic device feature sizes approach the 3-nm node, limiting induced defectivity during Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) is of utmost importance. The CMP process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method involving a poly-vinyl alcohol (PVA) brush is used to transfer cleaning chemistry to the substrate of interest as well as provide the necessary mechanical energy for defect removal. While this process is effective in contaminant removal its reliance on shear forces can induce secondary defect modes, such as scratching. To minimize the aforementioned induced defectivity during contact p-CMP processes, the implementation of non-contact modalities has become of the utmost importance. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials such as SiC, GaN, carbon-doped oxides, and metals. More specifically, “OVER”-cutting and “soft” cleaning processes that balance the modulation of surface reaction kinetics (chemical and adsorption) with advanced low shear force environment will be evaluated. For example, employing supramolecular cleaning chemistries coupled with reactive oxygen species (ROS) generating complexes under megasonic action were evaluated for effective SiC cleaning. Results from a second order kinetic model indicate that processing conditions (i.e., time and power), “soft” cleaning chemistry structure (i.e., shape and charge), and the generation of ROS all play a critical role in cleaning efficacy under low stress conditions in the megasonic field. Utilizing a suite of dynamic analytical techniques (i.e., atomic force microscopy, quartz crystal microbalance, contact angle, zeta potential, and electrochemical analysis, shear force analysis) a correlation between interfacial reaction mechanisms and effective p-CMP cleaning will be presented.

Utilization of an α,β-Unsaturated Carboxylic Acid to Employ an “over Cutting” Mechanism for Defect Mitigation during Cu Post-Chemical Mechanical Planarization (p-CMP) Cleaning

As features on integrated circuits (IC) continue to shrink, the implementation of chemical mechanical planarization (CMP) is a critical processing step to reduce surface topography in an effort to continue to extend Moore’s law. Specifically, Cu CMP utilizes complex slurry formulations containing an abrasive nanoparticle (SiO2) and additives (i.e., corrosion inhibitors, oxidizers, and complexing agents) to achieve angstrom level uniformity. However, one drawback to this process is the generation of detrimental surface defects that result from residual contamination (i.e., organic residues, abrasive particles, pad remnants, etc.) that are reliant on post-CMP (p-CMP) cleaning methods. Current Cu p-CMP cleaning methods implement the use of an industry standard polymer brush coupled with cleaning chemistries to remove residual contamination. It has been well established that shear and compressive forces coupled with surface active cleaning chemistries have proven to be efficient albeit with the potential for secondary defect induction (i.e., pitting, etching, scratching). Additionally, current cleaning formulations rely on additives that promote aggressive redox conditions to remove residues through an undercutting mechanism, which leads to the propagation of the aforementioned defect modes. This work focuses on the investigation of “soft” cleaning chemistries via the implementation of a structurally unique additive to create a synergy at the liquid-brush-wafer interface. More specifically, the implementation of an -unsaturated carboxylic acid (i.e., itaconic acid) has shown the capability of chemically activating an organic residue mosaic (i.e., BTA/nanoparticle) resulting in effective removal through an “overcutting” mechanism to significantly alter mechanical processing conditions. Through the implementation of corrosion studies utilizing a rotating disk electrode, the addition of itaconic acid has shown a reduction in icorr value and a shift in the passivation characteristics of the system. Open circuit potential (OCP) vs. time measurements indicates that the recovery of the passivation film is more effective in the itaconic acid formulation. A time resolved contact angle technique showed that itaconic acid had a significantly faster diffusion rate on a Cu surface coated with an exaggerated residue film indicating an enhanced surface adsorption. Furthermore, there is clear evidence that under brush conditions the presence of itaconic acid significantly enhances the removal of organic residues at the surface of a Cu substrate without the expense of effective nanoparticle removal.

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.

A nanoclustered ceria abrasives with low crystallinity and high Ce3+/Ce4+ ratio for scratch reduction and high oxide removal rates in the chemical mechanical planarization

A nanoclustered ceria abrasives with low crystallinity and high Ce3+/Ce4+ ratio for scratch reduction and high oxide removal rates in the chemical mechanical planarization

Theoretical validation of inhibition mechanisms of benzotriazole with copper and cobalt for CMP and post-CMP cleaning applications

Corrosion inhibitors are essential additives for metal CMP (chemical mechanical planarization) slurries and post-metal CMP cleaning solutions. They effectively address corrosion issues by forming complexes with the metal surfaces, but they sometimes cause organic defects. Hence understanding the interactions between the corrosion inhibitor and metal surface is important. In this study, the formation and stability of the Cu/Co-benzotriazole (BTA) complex on Cu and Co surfaces were experimentally investigated, and the experimental results were theoretically explained through computational calculations. The characteristics of the Cu/Co-BTA complex layer on Cu and Co surfaces were analyzed using sequential EIS, AFM, and contact angle measurements. A Cu/Co-BTA complex layer was formed when the Cu and Co surfaces were exposed to the BTA solution. After a de-ionized (DI) water rinse, the Cu-BTA complex on the Cu surface remained a stable film, whereas the Co-BTA complex layer on the Co surface was removed. Computational calculations provided BTA binding energies, d-band center, and electron charge transfer between BTA and metal surfaces. The BTA binding energy and electron charge transfer to the Co(001) surface were lower than that of Cu(111), which supports the removal of the Co-BTA complex by a DI water rinse in the experimental results.

Surface action mechanism and design considerations for the mechanical integrity of cu/low K BEOL interconnect during chemical mechanical polishing process

Chemical mechanical planarization (CMP) is a high-precision and complex manufacturing process during which materials are removed with chemical and mechanical actions to achieve highly planar surfaces. However, mechanical failures in interlayer dielectrics (ILD) and adjacent interfaces during Cu CMP processes have already raised serious reliability concerns. An appropriate polishing process is quite necessary to ensure that the structure could bear repeated mechanical and thermal stresses. In this work, we established a Cu CMP finite element model and proposed a surface softer layer removal method, which focused on the reliability of Cu/low K interconnect for 7-nm process technology and beyond. Meanwhile, effects of the polishing down pressure, the coefficient of friction and copper thickness were also investigated comprehensively. The simulation results found that the probability of interface delamination in the low K layer was raised when the polishing down pressure and COF increased, as well as Cu thickness decreased. The maximum peeling stress (MPS) showed a little variation as the COF, Cu thickness and vertical pressure increased. The maximum shear stress (MSS) changed slightly along with the COF and Cu thickness but could be significantly impacted by the vertical pressure. Furthermore, the potential of improving BEOL interconnect reliability through structure and process optimization was explored when the technology continued with dimensional scaling and introduction of porous dielectrics materials.

Effect of ionic strength on amorphous carbon during chemical mechanical planarization

A hard mask is an essential to prevent pattern collapse resulting from leaning, wiggling, or other defects. It is critical to achieve high removal rates of hard masks. The process of amorphous carbon chemical mechanical planarization (CMP) forms OH radicals on the surface by an oxidation and breaks bonds in the weakest area. Electrolytes with different ionic strengths were added, to facilitate the formation of OH radicals. When electrolytes were added, the removal rates increased by approximately 2.3 times over those without any additives. The increase in surface roughness is another significant factor. The roughness increased in all cases. In particular, a mixed slurry achieved the best results, with a mean surface roughness value of 0.147 nm for a scanning area of 5 × 5 μm2. Thus, the ionic strength of the electrolyte is critical in the CMP of amorphous carbon.

Design of “Low Stress” Post-CMP Cleaning Processes for Advanced Technology Nodes

The Chemical Mechanical Planarization (CMP) process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Traditionally, a contact cleaning method involving a poly-vinyl alcohol (PVA) brush is used to transfer cleaning chemistry to the substrate of interest as well as provide the necessary mechanical energy for defect removal. While this process is effective in contaminant removal its reliance on shear forces can induce secondary defect modes, such as scratching. To minimize the aforementioned induced defectivity during contact p-CMP processes, the implementation of non-contact modalities has become of the utmost importance. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials such as SiC, carbon-doped oxides, and metals. “Soft” cleaning chemistry structure (i.e., shape and charge), and processes play a critical role in cleaning efficacy under low stress conditions.

Revealing the mechanisms for inactive rolling and wear behaviour on chemical mechanical planarization

The paper examines the influences of abrasive conditions, silica thickness, and motion parameters on the polishing process of a silicon substrate covered by a thin silica film. The silica film minimizes the direct collision of the abrasive on the silicon substrate. During the polishing process, the adhesion phenomenon plays the main role in atomic removal. Notably, the abrasive sliding motion can generate an inactive rolling motion. The inactive rolling motion can be used to explain the stick-slip motion by showing the system of periodic high-strain marks. In rolling, the deformation behaviors of the workpiece rely on the correspondence between the rolling and the moving speeds. In the fixed diamond abrasive (FDA) cases, the atomic sticking rate is lower but the workpiece deformation is higher than the loose diamond abrasive (LDA) cases. Besides, the FDA cannot create the inactive rolling motion and the stick-slip motion as the LDA. In general, the paper points out the existence of the inactive rolling motion and its role in the atomic removal process through the stick-slip motion phenomenon at the nanoscale, the advantage of this type of motion in a conventional chemical mechanical polishing (CMP) process, and the padding role of the silica layer.

Palladium Chemical Mechanical Planarization in Packaging and Barrier Level Integration

Palladium (Pd) is a chemically inert material known for its ability to improve processing cost and reliability for the packaging level microelectronics integration. In addition, it is used as a sacrificial layer for copper (Cu) integration as a barrier material to protect the copper from oxidation. Successful implementation of Pd requires chemical mechanical planarization (CMP) process in both applications, where selectivity is desired between the Cu, tantalum nitride (TaN), and nitride (Ni) films against Pd. This paper focuses on removal rate selectivity tuning for Pd thin films in a commercial silica-based Cu-CMP slurry compared to a baseline silica slurry as a function of the slurry temperature. Detailed analyses of the integrated materials are presented, investigating the effect of temperature on surface wettability and CMP selectivity. Pd passivation is also presented by electrochemical analysis in the presence of an oxidizer for the selected polishing slurries. It is observed that lowering the slurry temperature promotes palladium CMP removal rate selectivity against Ni, Cu, and TaN by modifying slurry viscosity and wafer surface wettability with no detrimental effect observed on the surface defectivity.

875-MW/cm² Low-Resistance NO₂ p-Type Doped Chemical Mechanical Planarized Diamond MOSFETs

In this study, an Al₂O₃ passivated, NO₂ p-type doped diamond metal&#x2013;oxide&#x2013;semiconductor field-effect transistor (MOSFET) was fabricated on a chemical mechanical planarized high-quality heteroepitaxial diamond (Kenzan diamond^&#x00AE;) substrate. This MOSFET exhibited a low specific ON-resistance of 7.54 <inline-formula> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula>cm² and a high OFF-state breakdown voltage of &#x2212;2568 V. The chemical mechanical planarization (CMP) was performed for 200 h on the diamond surface which effectively removed the subsurface damages resulting in a low resistive diamond surface. Thus, the MOSFET showed a high drain current density of &#x2212;0.68 A/mm and a maximum available power density (Baliga&#x2019;s figure-of-merit) of 874.6 MW/cm²&#x2014;the highest reported value for diamond devices.

Effect of Skin Layer on Brush Loading, Cross-Contamination, and Cleaning Performance during Post-CMP Cleaning

The use of polyvinyl acetal (PVA) brushes is one of the most effective and prominent techniques applied for the removal of chemical mechanical planarization (CMP) contaminants. However, the brush can be a source of defects by entrapping the abrasives inside its porous structure during brush scrubbing. In this study, the effect of brush top skin layer was extensively studied on contamination, cross-contamination, and cleaning performance by comparing brushes with and without skin layer. The presence of a dense top skin layer resulted in larger contact areas and high ceria particle adsorption on the skin layer. This leads to higher cross-contamination of the wafers during scrubbing along with high cleaning performances. Conversely, the brushes without skin layer showed lower contamination and negligible cross-contamination with a reduced cleaning performance (removal of ceria particles from oxide surface). Therefore, the role of the brush skin layer is significant and needs to be considered while designing a post-CMP cleaning process.

Controlling Galvanic Corrosion with Oxalic Acid and Imidazole for Chemical Mechanical Planarization of Cobalt-Copper Interface

The work focuses on the investigation of Co/Cu removal rate (RR) selectivity and reduction of galvanic corrosion associated with Co and Cu by using oxalic acid (weak acid) as the complexing agent and imidazole as an inhibitor in hydrogen peroxide (H2O2) and fumed silica-based slurry. The results obtained from dissolution study, polishing experiments and potentiodynamic polarization measurements revealed that the proposed chemistry can achieve a desirable Co/Cu RR selectivity and a significant decrease in corrosion potential of Co and Cu (pH 9) to be used in the semiconductor industry. The corrosion potential difference (CuEcorr - CoEcorr) was reduced to 12 mV by using 0.1 wt% H2O2 + 0.02 M oxalic acid + 5 ppm imidazole solution at pH 9. Meanwhile, a removal rate of ∼147 nm min−1 for Co and ∼140 nm min−1 for Cu was achieved using the same composition in a fumed silica slurry which resulted in Co/Cu selectivity ratio of 1.05:1, which is acceptable for cobalt barrier and copper interconnect CMP. Based on FTIR and UV spectra, the dissolution mechanism in the proposed chemistry is also discussed.

Fe-substituted silica via lattice dissolution–reprecipitation replacement for tungsten chemical mechanical planarization

Chemical mechanical planarization (CMP) is indispensable for processing of integrated circuit semiconductor devices to attain globally planarized surfaces. One of the critical consumables in the CMP process is a slurry containing abrasives like colloidal silica (SiO2). However, there is a limit to the use of CMP slurries containing SiO2 under acidic conditions due to deterioration of colloidal stability, resulting in defects on the planarized surfaces. Herein, we developed an Fe-substituted SiO2 consisting of single-atom Fe(III), enabling improved colloidal stability over universal pH regions for low-defect tungsten CMP applications. The facile and unique single-atom modification process is proposed by controlling the lattice dissolution–reprecipitation replacement of Fe3+ and Si4+ ions. The physicochemical states of Fe atoms in the surficial lattice of Fe-substituted SiO2 were confirmed through Raman spectroscopy, electron microscopy, x-ray absorption spectroscopy, and energy-dispersive x-ray spectroscopy. Consequently, enhanced performance in W CMP was achieved using Fe-substituted SiO2. Regarding defect performance, defects were reduced from 11 scratches to 0 and 94 other defects to only 7. Additionally, the removal rate increased from 67 to 122 Å/min, and the surface topography improved from 6.6 to 2.9 nm.

Surface Transformation of Spin-on-Carbon Film via Forming Carbon Iron Complex for Remarkably Enhanced Polishing Rate.

To scale down semiconductor devices to a size less than the design rule of 10 nm, lithography using a carbon polymer hard-mask was applied, e.g., spin-on-carbon (SOC) film. Spin coating of the SOC film produces a high surface topography induced by pattern density, requiring chemical–mechanical planarization (CMP) for removing such high surface topography. To achieve a relatively high polishing rate of the SOC film surface, the CMP principally requires a carbon–carbon (C-C) bond breakage on the SOC film surface. A new design of CMP slurry evidently accomplished C-C bond breakage via transformation from a hard surface with strong C-C covalent bonds into a soft surface with a metal carbon complex (i.e., C=Fe=C bonds) during CMP, resulting in a remarkable increase in the rate of the SOC film surface transformation with an increase in ferric catalyst concentration. However, this surface transformation on the SOC film surface resulted in a noticeable increase in the absorption degree (i.e., hydrophilicity) of the SOC film CMP slurry on the polished SOC film surface during CMP. The polishing rate of the SOC film surface decreased notably with increasing ferric catalyst concentration. Therefore, the maximum polishing rate of the SOC film surface (i.e., 272.3 nm/min) could be achieved with a specific ferric catalyst concentration (0.05 wt%), which was around seven times higher than the me-chanical-only CMP.

Role of Potassium Tolyltriazole as an Inhibitor in H2O2-Based Slurry on Cu/Ru Patterned Wafer CMP

In the process of chemical mechanical planarization (CMP) during copper interconnection fabrication, the inhibitor in the copper slurry plays an important role in obtaining a good planar surface after CMP. In this paper, a kind of corrosion inhibitor TTAK was introduced in H2O2-based alkaline slurry. The experimental results show that the addition of TTAK can effectively reduce the removal rate (RR) and static corrosion rate (SER) of copper. With the increase of TTAK concentration, the passivation effect is enhanced. The passivation mechanism of TTAK was characterized by electrochemistry and X-ray photoelectron spectroscopy (XPS). The results show that in the H2O2-Gly system (alkaline), TTAK can reduce the corrosion rate and removal rate of copper by absorbing on copper surface to form passivation film. On the contrary, it has no significant influence on Ru. In addition, the dishing and erosion of Ru/Cu structure based patterned wafers were further tested. The experimental results show that the introduction of TTAK can effectively reduce the dishing and erosion depth of different line width and spacing.

Model-Based Optimization of CMP Process Parameters for Uniform Material Removal Selectivity in Cu/Barrier Planarization

Chemical mechanical planarization is a process of achieving planar surfaces in the semiconductor manufacturing industry. The planarization of a surface is achieved by material removal from the wafer surface. The material removal depends on material properties and the process input parameters. Several studies have investigated the role of slurry chemistry to achieve a certain material removal selectivity of different materials on a patterned wafer. Here we propose a methodology of achieving planar patterned surface of Cu/Mn/MnN system using a model-based optimization for mechanical process parameters. The parameters include applied force, slurry solid concentration, and abrasive particle size. The methodology has been developed via optimization using a genetic algorithm. The proposed methodology suggests that a lower downforce is the key parameter to achieve the desired material removal selectivity and planarity. The first part of the study suggests a low material removal rate (MRR) to achieve a lower standard deviation in MRR. The second part investigates the standard deviation in the thickness removed in the average time needed to remove a known thickness of the materials under consideration. It has been found that the application of lower downforce can also minimize the standard deviation in the thickness removed and a planar patterned surface can be achieved.