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Polyvinyl acetal (PVA) brush cleaning is one of the most important processes in the post chemical mechanical planarization (CMP)cleaning process. However, PVA brush could be severely contaminated due to strong direct contact with a large amount of abrasiveparticles during the long-time post CMP cleaning, and the particles on the brush can be easily...
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... ability of particles as shown in Figs. 6.1 respectively. Generally the particle removal efficiency depends on the pH region of cleaning solution due to zeta-potential between particles and adsorbed substrate. 14,[19][20][21][22] The zeta-potential of silica particles and PVA brush in pH 11 solution are −53 mV and −24 mV, respectively, as shown in Fig. 7. The zeta-potential of silica particle and PVA brush were strongly electrostatic repulsive in the alkaline region. 14,23 Thus, silica particles and a PVA brush will have strong repulsive force allowing particles to be easily dislodged from the brush surface. The contaminated abrasive particles on a PVA brush after flow-through using pH ...
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Polyvinyl acetal (PVA) brush cleaning is a widely accepted and efficient process for removing contaminants of the chemical mechanical planarization process during semiconductor processing. However, contaminants can adhere to the PVA brush, due to its highly hydrophilic and porous nature, and deteriorates its performance. This contamination is a ser...
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 lay...
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... Calcined ceria particles (mean size 100 nm, US Research Nanomaterials Inc., USA) were used as abrasives throughout the study. Lab-scale noduletype brush scrubber (CSY, Korea) was used to evaluate the brush scrubbing effect during the post-CMP cleaning as represented by a schematic in Fig. 1. 21 The chemicals HNO 3 (60%, Samchun Chemicals, Korea) and KOH (85%-87%, Daejung Chemical & Metals, Korea) were used to adjust the pH of ceria slurries. ...
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.
... Among several types of post-CMP cleaning processes, polyvinyl acetal (PVA) brush cleaning has been the most effective method for contaminant removal due to the physical force imposed by direct contact between the brush and wafer surface that also provides low cost of ownership (COO). [6][7][8] The contact elastic force, hydrodynamic drag force, and friction between brush and particles are the dominant removal forces during brush scrubbing. In the boundary lubrication regime, particles can be removed by both rolling and lifting, mainly due to van der Waals forces. ...
... 9,12,29,30 However, the oxide surface showed a negative surface charge over the entire pH range except at highly acidic pH (IEP of silica ∼2), where it has a slightly positive potential. 7 Hence, at lower pH (∼ pH 2), ceria and oxide display electrostatic repulsive forces due to similar positive charges. 31,32 In addition, slight dissolution of CeO 2 in HNO 3 was reported previously. ...
... Zeta potential results presented in Fig. 4 show a negative zeta potential for PVA over the entire pH range, whereas ceria shows positive charge at lower pH conditions, slightly positive at neutral pH, and negative charges at alkaline conditions. 7,9,12 Surface charges indicate a strong electrostatic attraction between ceria and PVA at acidic and neutral pH due to opposite surface charges; therefore, particles detached from the oxide wafer were loaded directly onto the brush surface. Similarly, the strong electrostatic repulsion between ceria and PVA at pH 12 resulted in negligible ceria loading to the top surface of the brush. ...
Polyvinyl acetal (PVA) brush cleaning is a widely accepted and efficient process for removing contaminants of the chemical mechanical planarization process during semiconductor processing. However, contaminants can adhere to the PVA brush, due to its highly hydrophilic and porous nature, and deteriorates its performance. This contamination is a serious problem, especially for processing devices smaller than 10 nm. Here, the effect of cleaning solution pH was investigated for ceria removal from oxide wafers and subsequent transfer to the PVA brush during scrubbing. A cleaning solution of pH 7 resulted in lower ceria removal efficiency compared to pH 2 and 12. The pH 2 and 7 cleaning conditions resulted in high brush loading compared to the pH 12 condition. High brush contamination at pH 7 resulted in higher cross contamination, whereas very low cross-contamination was observed at pH 2 and 12. The effect of ultrasonication and scrubbing on improvement of brush performance and lifetime was evaluated. Scrubbing in the presence of NH4OH efficiently removed all ceria particles from contaminated brushes. Because the bonding between brush and ceria particles is strong, only a robust physical force combined with a high chemical action can remove ceria particles loaded onto a PVA brush.
... Brush scrubbing continues to be widely used in advanced-node post-CMP cleaning applications to remove contaminants (e.g., trace metals, organic slurry residues, polishing pad debris, and abrasive particles) from the wafer surface. 17,18 It has been reported that abrasive particle removal mainly results from direct contact between a soft polyvinyl alcohol (PVA) brush and the wafer surface in which asperities atop nodules engulf the particles while the rotating motion of the brush and the wafer, as well as the cleaning fluid at the surface, dislodge and carry the particles away from the wafer. Among many factors, the effectiveness of brush scrubbing depends on the shear force (SF) present in the brush-solution-wafer interface as well as the kinematics of the PVA brush scrubber. ...
... The physical attributes of the PVA brush such as its compressive stress, apparent density, water uptake ratio, porosity, and average pore size play important roles in the quality of the surface finish of the post-CMP cleaned wafer. 17,19 Furthermore, there have been reports that the selection of formulation chemistry coupled with its effective delivery to wafer surface impacts the overall cleaning efficiency. Current formulations have increased in complexity to meet stringent wafer-level defect requirements and contain organic acids, supra-molecular surfactants, corrosion inhibitors, lubricants, and organic pH adjusters to enhance performance. ...
Results from a series of post-CMP PVA scrubbing marathon runs performed in a high-volume manufacturing fab are scientifically explained via a series of controlled laboratory tests. The major differences in the ingredients within the cleaning solutions, and some of the key physical properties of the brushes are identified and their effects on various critical factors are studied. These include the magnitude of shear forces present in the brush-solution-wafer interface, the water uptake and porosity of the brushes, the diffusivity of a given cleaning solution through the micro-pores and macro-pores of each type of brush, the open-circuit potential in a dynamic process, and the availability of the cleaning fluid between the brush nodules and the wafer surface. Results show a strong inverse correlation between wafer-level defects and shear force. The latter is shown to decrease with solution availability at the brush-wafer interface which in turn is shown to depend on brush porosity and the diffusion rate of the solution through the pores. Our understanding is further strengthened by dynamic electrochemical analysis data where we see a greater interfacial chemical activity (i.e., an increase in corrosion current) as solution availability is increased.
... PVA brush scrubbing is the most commonly used method for post CMP cleaning applications [19,20]. Hence, a contact shear force provided by brush scrubbing was used to study the effect of physical forces in detaching strongly attached nanosize ceria abrasives. ...
Ceria removal during the STI post-CMP cleaning process has recently become a serious concern in the semiconductor industry. Understanding ceria adhesion and its removal mechanism is necessary for designing a suitable post CMP cleaning methodology. Recently, colloidal ceria slurries have been heavily used due to the low defectivity factor. In this work, colloidal ceria adhesion and removal behaviors were studied as a function of particle sizes. It was found that polishing produces more contamination of ceria to oxide surface than dipping conditions and the strength of adhesion is increased with decreasing ceria size due to a higher Ce³⁺ concentration for smaller size particles resulting in more Ce-O-Si bonding. Ceria adhesion is mainly attributed to Ce-O-Si bond formation. Different cleaning methods (megasonic, brush scrubbing, SC1 (standard cleaning solution 1), DHF (diluted hydrofluoric acid) and SPM (sulfuric acid and hydrogen peroxide solution) were employed in removing these ceria particles. It was found that larger particles could be removed effectively with physical force, and smaller particles could be removed using chemicals such as DHF or SPM. Hence, it is concluded that an appropriate cleaning method should be chosen based on the size of the ceria.
... The brush is compressed to the wafer surfaces, and then the particle contaminants are removed by the physical force of the compressed brush. However, the surface and inside the pore structure of PVA brushes are contaminated with the particles, organic residues, and pad debris (Figure 4a), which can be transported to the next wafers and cause cross-contamination of the wafers during the brush scrubbing [56,58]. More cross-contamination is observed on the wafer surfaces when the contact pressure and contact area between the brush and the wafer increase [59]. ...
... Before brush scrubbing, brush soaking treatment and break-in and their optimized process may be useful to reduce the cross-contamination and improve the cleaning efficiency [58]. Also, the ultrasonication method with DIW was very effective in removing the contaminants from the PVA brushes without damage [56]. ...
... (b) Wafer backside signature after CMP and cleaning process. Reproduced with permission from Ref.[56]. Copyright 2019 IOP Publishing. ...
Chemical mechanical planarization (CMP) process has been widely used to planarize a variety of materials including dielectrics, metal, and semiconductors in Si-based semiconductor devices. It is one of the most critical steps to achieve the nanolevel wafer and die scale planarity. However, various contaminants are observed on the wafer surfaces after the CMP process, and they become the most critical yield detractor over many generations of rapidly diminishing feature sizes because they have the most direct impacts on device performance and reliability. This book chapter provides (1) CMP consumables-induced contaminants such as residual particles, surface residues, organic residues, pad debris and metallic impurities, pad contamination, watermark, etc., (2) brush-induced cross-contamination during post CMP cleaning, (3) post-CMP cleaning for removing these contaminants. Fundamental understanding of the formation of various types of CMP contaminants and their characteristics will significantly benefit the development of next-generation CMP slurries and post-CMP cleaning solutions.
... First, adhesive particles on wafer are detached by e.g. a polyvinyl acetal (PVA) Roll Brush. [1][2][3] The detaching process of particles from the wafer has been observed using an evanescent technique. 4,5 The contact conditions between the substrate and the PVA brush has also been investigated. ...
Adhesive particles on polished wafers are detached by e.g. scrubbing, and removed by liquid flow from the wafer. However, the relationship between the characteristic of liquid flow and the removal of detached particles has not yet been examined in detail. Therefore, the re-adhesion of detached particles to wafer surfaces in liquid flow on rotating wafers was experimentally investigated. The number of residue particles on a wafer was counted using a defect inspection tool after de-ionized water (DIW) rinse for particle removal. To discuss the mechanism of particle removal, a model was constructed and compared with experimental results. The model is based on boundary layer theory of fluid dynamics and advection diffusion theory of transport phenomena for particle removal in liquid flow near the wafer surface. The model results confirmed that detached particles in liquid flow moved into the sublayer and re-adhered to the wafer surface by diffusion. Moreover, particles in the sublayer, where the liquid velocity is several hundred um/s, could not be moved from the sublayer and removed from the wafer. It was also found that the number of particles re-adhering to the wafer surface depends on the Sherwood number.
... This superabsorbent polymer (SAP) is commonly used in household cleaning and washing [2]. It is also used as the sponge rollers in the post-CMP process for cleaning electronic components, such as hard disk, silicon wafer, glass panels for TFT-LCD, etc. [3]. The key reaction involved in the manufacturing of conventional porous PVA sponge is hybrid acetalization of highly-hydrolyzed polyvinyl alcohol with formaldehyde using starch as the pore-making agent and sulfuric acid as the catalyst. ...
In order to minimize environmental pollution caused by the wastewater produced in the manufacturing process of conventional poly(vinyl alcohol) (PVA) sponge, applying with the case study, a new method of reusing recycled wastewater is proposed in the present study. This method replaces our previous method in which the wastewater can only be reused once. The acidified starch and the residual partially polymerized PVA make the reused wastewater too viscous to be agitated homogenously. So, instead of recycling all of the wastewater produced, we only reuse part of it and supplement it with fresh reactant solution. With the reactant ingredients determined in the resupplied solution, we find that the present proposed method allows the recycled wastewater to be reused at least twice. In the meantime, the quality of the conventional PVA sponge as a superabsorbent can be maintained very well.
... Figure 1 presents a schematic of the role of adhesion forces on defect generation. Furthermore, PVA brushes are one of the consumables in the actual cleaning process; thus, one must know the timing after finishing the break-in process of the brush 25,26 or the brush's lifetime. 27 Adhesion force is one of the factors that affects the brush's condition. ...
... We believe that there is some possibility of using this adhesion force measurement to monitor the brush condition. In the actual post-CMP cleaning process, a "breaking-in" pretreatment process 25,26 is required to remove impurities from the brush. Additionally, the timing for replacing the brush is determined by the number of wafers to be cleaned. ...
The adhesion force between two materials is a key factor in surface cleaning. In this study, we developed a method for measuring adhesion forces between polyvinyl acetal (PVA) brushes and several test surfaces to understand the brushes’ adhesion characteristics. We utilized both the viscoelastic properties of PVA brushes and a high-response load cell to evaluate the adhesion forces of the compressed brushes on a flat surface. The results of the study showed that the adhesion forces increased with increased contact time and amount of compression. Some materials strongly interacted with the PVA brushes. We also observed that the measured adhesion forces were due to the existence of a skin layer on the brush surface. Moreover, we compared the adhesion forces with torques generated from rotating PVA brushes. However, the results did not correlate with the adhesion forces, which suggests that the force in the quasi-static state differs from that in the sliding condition.
Chemical mechanical planarization (CMP), a commonly employed process for attaining local and global planarization in integrated circuits fabrication, leaves contaminants and defects on the surface polished. Due to the miniaturization of devices, new materials/ processes for the fabrication of IC circuits are considered, introducing new post-CMP issues. As such, understanding of post-CMP cleaning process is critical to choose an appropriate method for the given material. Here, the types of contaminants and defects generated during the post-CMP process and the issues related to it are discussed. The different physical and chemical cleaning methods employed in the post-CMP cleaning process to eradicate these defects are elucidated.In particular, the PVA brushing method, which is currently preferred, is elaborated upon in detail. The various chemistries, including the newly suggested ones in recent years for cleaning different substrates, are summarized. The post-CMP cleaning methods for various materials such as Cu, Al, W, Co, Ru, InGaAs, Ge, and SiO2 are mainly addressed here. This review also provides the direction of progress for the post-CMP cleaning process in terms of evolution of new techniques and chemistries for the next generation of materials.
