Advanced 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.

Restricted hydrolysis reaction of Si3N4 via nonionic polymer adsorption in advanced shallow trench isolation chemical mechanical planarization

The adoption of ultra-fine nanoparticles as an abrasive has garnered notable attention in shallow trench isolation (STI) chemical mechanical planarization (CMP) due to its potential in scratch reduction. However, the poor removal rate, attributed to the physicochemical interaction between abrasive and conventional organic passivation agent, limits the introduction of ultra-fine nanoparticles. Here, a nonionic polymer polyvinyl alcohol (PVA), without particle interaction, is proposed as a novel passivation agent to restrict the hydrolysis reaction of Si3N4 film in the advanced STI CMP process. The selective adsorption of PVA onto the Si3N4 film lowers its removal rate by suppressing the hydrolysis reaction via hydrogen bonding while the removal rate of SiO2 film remains constant. Moreover, the uniformity of SiO2 removal is improved due to the enhanced fluidity of slurry, resulting from increased wettability between pad and slurry. As a result, the removal selectivity between both films has been improved to 113.4:1 and the in-wafer-uniformity (IWU) of SiO2 film is supplemented by 96.8 % simultaneously.

Single Particle Inductively Coupled Plasma Mass Spectrometry Study of Ceria Nanoparticle Size Distribution from 300mm Wafer Oxide CMP with Microreplicated Pads

This work describes the use of Single Particle Inductively Coupled Plasma Mass Spectrometry (spICP-MS) to measure ceria particle number concentrations and compare changes in size distributions to silicon dioxide wafer removal rates from different chemical mechanical planarization (CMP) processes. Particle number concentrations were measured for the 21 to 559 nm size range at 1nm size resolution. Changes in the ceria particle size distribution after CMP included a decrease in large (>130 nm) particles, an increase in small (<40 nm) particles, an increase in the total number of particles, and a decrease in median particle size. The decrease in median size was as high as 7% and influenced by slurry flow rate, wafer pressure and pad type. A novel microreplicated CMP pad was used which requires no pad conditioning to ensure consistent pad surface features, and the effect of different pad types on removal rate and particle size was isolated. A decrease in the median particle size correlated with higher silicon dioxide removal rates (R2=0.96) for a series of pad types with unique combinations of chemistry and surface features. This new combination of nano particle metrology and control of pad surface features is an improved tool set for modeling advanced CMP processes.

(Invited) Controlling Nano-Scale Chemically Modified Thin Films for Chemical Mechanical Planarization

This is a review paper on the effect of chemicals modified thin films on CMP process development. As the microelectronics manufacturing faces the challenges related to the Beyond Moore’s Scale adaptation, Chemical Mechanical Planarization (CMP) process control becomes much more critical yet difficult simultaneously. The need for planarizing larger scale wafers at an atomic scale precision with superior removal rate selectivity and zero defect focus demands a nano-scale control on the process performance. This study reviews the atomic scale chemical and mechanical interactions on CMP as it applies to traditional as well as the next generation materials in microelectronics manufacturing. Once the behavior of the wafer surface is understood at an atomic level, the process control metrics can be tuned accordingly.In an attempt to come up with the design criteria for the slurry chemistry, chemically modified layer formation is evaluated on conducting, semiconducting and insulating materials as a function of evaluating the nano-scale surface topography and change in surface energy. Metallic films are studied in terms of their corrosion and passivation behavior through macro-scale electrochemical evaluations as well as the surface sensitive characterization techniques such as XRR, XRD and FTIR [1, 2]. In addition, a modeling approach is introduced through Cahn Hilliard Equation (CHE) approximation to the surface energy minimization on the metal-oxide formation by nucleation [3]. Furthermore, removal rate selectivity properties of the semiconductor materials are discussed on conventional and III-V semiconductors and insulators as a function of chemically modified film alteration [4-5]. Some high-end applications such as (i) tungsten T-gate transistors, (ii) new liner/barrier materials [6], (iii) germanium based high-speed, shallow trench isolation transistors and (iv) high-power transistors and LED applications where III/V semiconductors are deliberated. As a new challenge, 3-D implementations of the CMP process, where the chemically modified nano-films impact the materials performance are also introduced. Ozdemir, Basim, G.B. "Effect of Chemical Mechanical Polishing on Surface Nature of Titanium Implants FT-IR and Wettability Data of Titanium Implants Surface After Chemical Mechanical Polishing Implementation," Data, in Brief, 10, P 20-25, 2017. Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents," ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104, 2015. Karagoz, A., Sengul, , Basim, G.B., “A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications," 225th ECS Meeting – Orlando, Florida, USA, May 11-15, 2014, ECS Transactions, 61 (17) 15-20 (2014). Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1-P8, 2015. Ozbek, S., Akbar, W., Basim, G.B. “ Optimized Process Design for GaN Chemical Mechanical Planarization” ECS Journal of Solid State Science and Technology, Special Issue on GaN-Based Electronics for Power, RF, and Rad-Hard Applications , 6-11, P S3084-S3092, 2017. Yagan, R., Basim, G.B., “A Fundamental Approach to Electrochemical Analyses on Chemically Modified Thin Films for Barrier CMP Optimization," ECS J. Solid State Sci. Technol. 8-5, P3118-P3127, 2019.

Single Particle Inductively Coupled Plasma Mass Spectrometry Study of Ceria Nanoparticle Size Distribution from Oxide CMP with Microreplicated Pads

This work describes the use of Single Particle Inductively Coupled Plasma Mass Spectrometry (spICP-MS) to measure ceria particle number concentrations and compare changes in size distributions to silicon dioxide wafer removal rates from different chemical mechanical planarization (CMP) processes. Particle number concentrations were measured for the 21 to 559 nm size range at 1 nm size resolution. Changes in the ceria particle size distribution after CMP included a decrease in large (>130 nm) particles, an increase in small (<40 nm) particles, an increase in the total number of particles, and a decrease in median particle size. The decrease in median size was as high as 7% and influenced by flow rate, pressure and pad type. A novel microreplicated CMP pad was used which requires no pad conditioning to ensure consistent pad surface features, and the effect of different pad types on removal rate and particle size was isolated. A decrease in the median particle size correlated with higher silicon dioxide removal rates (R2 = 0.96) for a series of pad types with unique combinations of chemistry and surface features. This new combination of nano particle metrology and control of pad surface features is an innovative tool set for modeling advanced CMP processes.

Advanced chemical–mechanical planarization for 4H-SiC substrate by water-soluble inclusion complexes of fullerene

This study investigated the behavior of water-soluble inclusion complexes (fullerene/β-cyclodextrin, C60/β-CD) as solid-state reacted abrasive particles for chemical–mechanical planarization (CMP) of 4H-SiC substrates. The size of C60/β-CD was measured by dynamic light scattering. The material removal rate with the aid of C60/β-CD was increased by 49%. Also, the indentation hardness and wettability were examined for the transition area by mechanochemical reaction. According to the decreasing hardness and contact angle, an adlayer consisting of C60/β-CD was indented by a Berkovich indenter against the substrate. Thus, the removal mechanism of advanced CMP among SiC substrates, C60/β-CD, and SiO2 abrasives is theoretically proposed.

(Invited) A Review on the Role of Slurry Chemistry on Chemically Modified Thin Film Formation for CMP Applications

Chemical Mechanical Planarization (CMP) process is currently facing the challenge of planarizing larger scale wafers at an atomic scale precision with superior removal rate selectivity and zero defect focus. While the horizontal dimensions of the processed wafers (x-axis and y-axis as the wafer diameter) extend up to 300 mm, the z-axis has to be planarized to a margin of a couple of hundred nanometers. This requirement highlights the need for fundamental understanding on the surface chemistry of the layers being exposed to the planarization process in terms of their interactions with the CMP slurry chemistry. Once the behavior of the wafer surface is understood at an atomic level, the process control metrics can be tuned accordingly. This paper reviews the role of slurry chemistry in effectively modifying the top surface films of the various materials including conductors, semiconductors and insulators exposed to CMP operations in semiconductor manufacturing. Metallic films are studied in terms of their corrosion and passivation behavior [1, 2] as well as through a modeling of the energy minimization through a Cahn Hilliard Equation (CHE) approach [3]. Furthermore, formation and selectivity properties of the semiconductor materials including conventional and III-V semiconductors and insulators were investigated [4-5]. Some high-end applications where the nano-scale chemically modified films critical are: Metal CMP applications of the tungsten T-gate transistors, new barrier materials, germanium based high-speed shallow trench isolation transistors and high-power transistors and LED applications where III/V semiconductors, such as GaN, are used. Ozdemir, Basim, G.B. “Effect of Chemical Mechanical Polishing on Surface Nature of Titanium Implants FT-IR and Wettability Data of Titanium Implants Surface After Chemical Mechanical Polishing Implementation”, Data in Brief, 10, P 20-25, 2017. Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents”, ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104, 2015. Karagoz, A., Sengul, , Basim, G.B., “A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications”, 225th ECS Meeting – Orlando, Florida, USA, May 11-15, 2014, ECS Transactions, 61 (17) 15-20 (2014). Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1-P8, 2015. Ozbek, S., Akbar, W., Basim, G.B. “ Optimized Process Design for GaN Chemical Mechanical Planarization” ECS Journal of Solid State Science and Technology, Special Issue on GaN-Based Electronics for Power, RF, and Rad-Hard Applications, 6-11, P S3084-S3092, 2017.

Recurrent feature-incorporated convolutional neural network for virtual metrology of the chemical mechanical planarization process

In semiconductor manufacturing, the chemical mechanical planarization (CMP) process produces higher thickness variability in the edge area of the wafer than that in the center area due to the characteristics of the polishing operation. To address this problem, advanced CMP equipment includes a function that controls the removal rate of each area. However, to take full advantage of this capability, effective advanced process control systems must be implemented with a virtual metrology (VM) model. However, the prediction performance of the VM model often deteriorates due to process drift. Here, we present a deep learning-based VM model that demonstrates high performance in the presence of nonlinear process drift. The proposed model combines a recurrent neural network and a convolutional neural network to extract time-dependent and time-independent features. A two-stage model training method is proposed that alternately updates the weights of each network to improve prediction performance. In the experiments using on-site CMP process data, the performance of the deep learning models exceeded that of standard machine learning models. The proposed model showed an 8.48% decrease in process variability relative to the best-performing machine learning model, which was elastic nets.

Next generation barrier CMP slurry with novel weakly alkaline chelating agent

To strengthen the device performance with the pattern wafer by enhancing the Cu polishing rate and improve the surface roughness with the Cu lines, a new weakly alkaline chelating agent with a barrier slurry is developed to meet the process demand of the advanced barrier chemical mechanical planarization (CMP). This new chelating agent has a stronger chelating ability and a lower pH value than the previous generation-FA/O I chelating agent researched before. Without an unstable oxidant agent added in the polishing slurry, it is difficult to enhance the copper polishing rate during the barrier CMP. The stronger chelating ability of the new chelating agent could increase the copper polishing rate along with controlling the Cu/Ta/TEOS removal rate selectivity to meet the requirements of the IC fabrication process. Thus it has solved the problem of excessive roughness due to the lower polishing rate, avoiding reducing the device performance with the pattern wafer. The new chelating agent with its lower pH value could make it possible to protect the low-k dielectric under the barrier layer from structurally breaking. The CMP experiment was performed on the 12 inch MIT 854 pattern wafers with the barrier slurry containing the new weakly alkaline chelating agent. By the DOE optimization, the results indicate that as the new chelating agent concentration in the slurry was up to 2.5 mL/L, the copper polishing rate is about 31.082 nm/min. Meanwhile, the wafer surface has a rather low roughness value of 0.693 nm (10 × 10 μm), the correction ability with the above slurry is adapted to the next generation barrier CMP and the k value of the low-k dielectric seems to have no k-shift. All the results presented show that the new weakly alkaline chelating agent with its superior performance can be used for the advanced barrier CMP.

Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents

New developments and device performance requirements in microelectronics industry add to the challenges in chemical mechanical planarization (CMP) process. One of the recently introduced materials to semiconductor manufacturing is germanium which enables improved device performance through better channel mobility in shallow trench isolation (STI) applications for advanced circuits. This paper focuses on controlling germanium/silica selectivity for advanced STI CMP applications through slurry modification by surface active agents. Surface adsorption characteristics of cationic and anionic surfactants on germanium and silica wafers are analyzed in order to control selectivity as well as the defectivity performance of the CMP applications. The effects of surfactant charge and concentration (up to self-assembly) are studied in terms of slurry stability, material removal rates and surface defectivity. Surface charge manipulation by the surfactant adsorption on the germanium surface is presented as the main criteria on the selection of the proper surfactant/oxidizer systems for CMP. The outlined correlations are systematically presented to highlight slurry modification criteria for the desired selectivity results. Consequently, the paper evaluates the slurry selectivity control and improvement criteria for the new materials introduced to microelectronics applications with CMP requirement by evaluating the germanium silica system as a model application.

Tribo-Electrochemical Characterization of Ru, Ta and Cu CMP Systems Using Percarbonate Based Solutions

Defect-control is a critical requirement for chemical mechanical planarization (CMP) of the ultrathin diffusion barriers considered for the new Cu-interconnects. The challenging task of developing advanced CMP slurries for such systems can be aided by electrochemical evaluations of model CMP schemes under tribological conditions. The present work uses this strategy to characterize an alkaline slurry formulation aimed at minimizing galvanic corrosion in the CMP systems involving Ru, Ta (barrier metals) and Cu (wiring metal). This slurry is based on percarbonate and guanidine additives, and the test metals are polycrystalline disc samples. A particular goal of this study is to explore the essential analytical aspects of evaluating CMP systems in the tribo-electrochemical approach. The CMP specific surface reactions are characterized by potentiodynamic polarization and open circuit voltage measurements, performed both in the presence and in the absence of polishing, and by employing abrasive free as well as abrasive (colloidal SiO2) added solutions. The findings of these experiments are further checked by using impedance spectroscopy. The electrochemical mixed potential steps of the CMP promoting reactions are analyzed, and the removable surface species formed by these reactions are discussed.

Investigation of Mechanical Effects on Advanced Copper CMP

Chemical mechanical planarization (CMP) of copper is a critical step in advanced IC interconnects technology. The key performance metrics of a Cu CMP are the removal rate, removal rate profile, dishing and erosion, process window, and defectivity. Many researchers have studied the mechanisms of Cu CMP. The present investigations will mainly focus on the mechanical effects on advanced Cu CMP at low down forces. The two main mechanical factors, intrinsic properties of abrasives and polishing process conditions, were evaluated. It was found that the abrasive properties such as mean size, surface area, solid concentration and process conditions such as polishing down force and rotation speed have strong impacts on Cu CMP performance.