Polishing Slurry Research Articles

Enhancing dispersion stability and recyclability of ceria slurry with polyacrylic acid for improved glass polishing performance

This study aimed to enhance both the dispersion stability and recyclability of micron-sized ceria slurry in glass polishing by incorporating polyacrylic acid (PAA). PAA with a molecular weight of 240 k was very effective as a dispersant for ceria slurry due to its unique surface adsorption and its characteristics as an anionic polyelectrolyte. Using a 240 k-PAA concentration of 1.0 wt% led to significant improvements in polishing performances, as demonstrated by consistent glass removal rates across recycling cycles. Additionally, the study investigated the physico-chemical properties of polishing slurries, such as specific gravity, particle size, zeta potential, and pH. These properties were effectively maintained with the use of PAA as the dispersant, particularly when KOH was used as a pH adjuster. A 100 µm bag-type filtration system was also introduced for handling the micron-sized ceria slurry, highlighting its practical benefits in slurry management. In conclusion, employing 240 k-PAA as a dispersant in micron-sized ceria slurries for Gorilla glass polishing not only maintains quality and stability across recycling cycles but also provides notable economic advantages by enabling the recycling of the slurry.

Controlled Synthesis of Triangular Submicron-Sized CeO2 and Its Polishing Performance.

CeO2 is widely used in the field of chemical-mechanical polishing for integrated circuits. Morphology, particle size, crystallinity, and Ce3+ concentration are crucial factors that affect polishing performance. In this study, we successfully synthesized two novel triangular CeO2 abrasives with similar particle sizes (600 nm) but different morphologies and Ce3+ concentrations using a microwave-assisted hydrothermal method with high-concentration raw materials, and no surfactants or template agents were added. It is generally believed that CeO2 with a higher Ce3+ concentration leads to better polishing performance. However, the results of polishing indicate that CeO2 synthesized at 200 °C, despite its lower Ce3+ concentration, demonstrates outstanding polishing performance, achieving a polishing rate of 324 nm/min, and the Sa of Si wafers decreased by 3.6% after polishing. This suggests that, under similar particle size conditions, the morphology of CeO2 plays a dominant role in the mechanical effects during the polishing process. Additionally, compared to commercial polishing slurries, the synthesized samples demonstrated better polishing performance. This indicates that, in CMP, the pursuit of smaller spherical abrasives may not be necessary. Instead, the appropriate shape and particle size can better balance the material removal rate and surface roughness.

Material removal rate model for chemical–mechanical polishing of single-crystal SiC substrates using agglomerated diamond abrasive

Material removal mechanisms are essential for the selection of polishing slurries and parameter optimization of chemical–mechanical polishing (CMP) processes. This study established a material removal rate (MRR) model for CMP of single-crystal SiC substrates using a fixed agglomerated diamond (AD) abrasive pad (FADAP). The distribution of the polishing pressure between the AD abrasive and FADAP matrix was examined, and the influence of the abrasive and polishing parameters on the MRR was revealed. Furthermore, single-factor experiments were conducted to validate the rationality of the MRR model. The experiments demonstrated that when the thickness of the surface-affected layer of the single-crystal SiC substrate in the MRR model was set to 5 nm, the error between the calculated and experimental values of the model could be controlled to within 20%. This result experimentally verified the validity of the MRR model and its associated assumptions. Moreover, the MRR of the CMP process of a single-crystal SiC substrate reached 36.26 μm/h with a polishing pressure of 27.6 kPa and an AD abrasive primary particle size range of 7–10 μm. Therefore, the feasibility of efficiently processing single-crystal SiC substrates using an FADAP was theoretically confirmed.

A Systematic Study of the Factors Affecting the Surface Quality of Chemically Vapor-Deposited Diamond during Chemical and Mechanical Polishing.

Diamond surfaces must be of high quality for potential use in semiconductors, optical windows, and heat conductivity applications. However, due to the material's exceptional hardness and chemical stability, it can be difficult to obtain a smooth surface on diamond. This study examines the parameters that can potentially influence the surface quality of chemically vapor-deposited (CVD) diamonds during the chemical and mechanical polishing (CMP) process. Analysis and experimental findings show that the surface quality of polished CVD diamonds is significantly influenced by the crystal structure and the growth quality of the diamond. In particular, when the surface roughness is below Ra 20 nm, the pores and grain boundaries on CVD diamond obstruct surface roughness reduction during mechanical polishing. To obtain a smooth polished surface, careful consideration of the size of diamond abrasives and polishing methods is also a prerequisite. Chemical mechanical polishing is a novel method to achieve a surface quality with roughness below Ra 3 nm, as in this method, the anisotropy of the CVD diamond allows the uneven steps to be efficiently erased. However, the chemical actions of polishing slurry should be controlled to prevent the formation of chemical etching pits.

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

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

Experimental Strategies for Studying Tribo-Electrochemical Aspects of Chemical–Mechanical Planarization

Chemical–mechanical planarization (CMP) is used to smoothen the topographies of a rough surface by combining several functions of tribology (friction, lubrication), chemistry, and electrochemistry (corrosion, wear, tribo-corrosion). The surface layer of interest is structurally weakened by the chemical and/or electrochemical reactions of selected additives in a polishing slurry, and the modified surface is flattened by the abrasion of a polishing pad with or without abrasive particles. The chemically active CMP slurry also serves as a lubricant for polishing and enables planarization at a microscopic level while avoiding the formation of defects at the processed surface. Applications of CMP are wide-ranging in various material-processing technologies and, specifically, it is a critical manufacturing step of integrated circuits. The CMP of metals is a significant part of this processing scheme and is associated with highly complex tribo-electrochemical mechanisms that are now additionally challenging due to various new requirements of the advanced technology nodes. The present review examines the current statuses of experimental strategies for collecting important mechanistic details of metal CMP that are necessary to design and assess CMP consumables. Both traditional and underexplored experimental techniques are discussed with illustrative results, including many previously unpublished findings for certain CMP systems of current interest.

Development of core–shell SiO2@A-TiO2 abrasives and novel photocatalytic chemical machinal polishing for atomic surface of fused silica

It is extremely hard to achieve atomic surface on fused silica with a high material removal rate (MRR). Furthermore, in traditional chemical mechanical polishing (CMP), toxic and corrosive slurries are widely employed. To address these challenges, core–shell SiO2@A-TiO2 abrasives were prepared, and novel photocatalytic CMP was developed. The developed CMP slurry consists of sodium carbonate, hydrogen peroxide, sodium carboxymethylcellulose and deionized water. After CMP, atomic surface with surface roughness Sa of 0.181 nm was achieved at a scanning area of 50 × 50 μm2 and a high MRR of 10.727 μm/h. X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared were used to elucidate the photocatalytic CMP mechanisms. The developed SiO2@A-TiO2 abrasives could generate electrons and holes irradiated by simulated solar light, producing free radicals (OH–). As a result, OH– combined with Si atoms on the surface of fused silica, forming Si-OH-Si bonds. This constructed interlinkage of slurry and surface of fused silica via SiO2@A-TiO2 abrasives improved synergistic effect between chemical and mechanical functions. The developed core–shell abrasives and photocatalytic CMP suggest new findings to achieve atomic surface for a hard-brittle solid with a high MRR.

Atomic surface achieved through a novel cross-scale model from macroscale to nanoscale.

Chemical mechanical polishing (CMP) is widely used to achieve an atomic surface globally, yet its cross-scale polishing mechanisms are elusive. Moreover, traditional CMP normally employs toxic and corrosive slurries, resulting in potential pollution to the environment. To overcome these challenges, a novel cross-scale model from the millimeter to nanometer scale is proposed, which was confirmed by a newly developed green CMP process. The developed CMP slurry consisted of hydrogen peroxide, sodium carbonate, sodium hydroxycellulose, and silica. Prior to CMP, fused silica was polished by a ceria slurry. After CMP, the surface roughness (Sa) was 0.126 nm, the material-removal rate was 88.3 nm min-1, and the thickness of the damaged layer was 8.8 nm. The proposed model was built by fibers, through integrating Eulerian and Lagrangian models and reactive force field-molecular dynamics. The results predicted by the model were in good agreement with those of CMP experimentally. A model for large-sized fibers revealed that a direct contact area of 11.12% was obtained for a non-woven polishing pad during the CMP experiments. Another model constructed via combining Eulerian and Lagrangian functions showed that the stress at the intersections of the fibers varied mainly from 0.1 to 0.01 MPa and was higher than the stress at other parts. An increase in viscosity led to a decrease in the areas with low stress, demonstrating that viscosity enhanced the stress and facilitated the removal of material. At the microscale and nanoscale, the stress of the abrasive surface exposed to the workpiece changed from 2.21 to 6.43 GPa. Stress at the interface contributed to the formation of bridging bonds, further promoting the removal of material. With increasing the compressive stress, the material-removal form was transformed from a single atom to molecular chains. The proposed model and developed green CMP offer new insights to understand the cross-scale polishing mechanism, as well as for designing and manufacturing novel polishing slurries, pads, and setups.

Additive manufactured cerium oxide foils, used as pads for polishing processes of brittle-hard materials

A new concept for polishing pads for flat and spherical surfaces is introduced which comprises additive manufactured polishing pads made of cerium oxide. By using additive manufacturing technologies, polishing processes with polishing slurry can be substituted with tools containing bonded grain. The bonded polishing pads can be fabricated using rolling processes. The pad geometries can be adjusted by using laser cutting. Furthermore, surface modifications of the pad can be applied with laser processes to favour quality and economic factors of the polishing procedure. First results from the experimental setup are showing, that lapped surfaces with a roughness Rq of ~ 500 nm can be improved to approx. Rq = 30 nm roughness by polishing with bonded grain cerium oxide foils. Further approaches for future investigations and applications are proposed.

Using Acoustic Emissions for an in-situ evaluation of the polishing process and its parameters

Mechanical chemical glass polishing is a complex process with mechanical and chemical interactions. While we have used Acoustic Emissions (AEs) already for basic measurements, we have researched the process and its parameters e.g., the density of the polishing slurry or the glass type for further investigation. We also have carried out crack tests on samples to investigate the crack mechanism. We suggest the further investigation of AEs to improve the above mentioned process and to prepare a transfer of this approach for further processes.

The influence of CeO2 abrasive size on the performance of photocatalytic assisted chemical-mechanical polishing by Y/Pr co-doping strategy

The synergistic effect of photochemical oxidation activity and tribochemical ability of CeO2 material is a necessary prerequisite for the formation of photocatalytic assisted chemical-mechanical polishing (PCMP) abrasive system. However, it is precisely due to the large band gap (∼ 3.2 eV) of CeO2 and the high recombination rate of photogenerated carriers that the improvement of the photocatalytic oxidation activity of traditional CeO2 photocatalysts is greatly limited, thus preventing the further wide application of cerium-based abrasives in PCMP. Based on this, a series of Ce1–2xYxPrxO2 abrasives were synthesized by molten salt method to improve the performance of cerium oxide based polishing paste with PCMP. The physicochemical properties of Ce1–2xYxPrxO2 samples were analyzed by a series of characterization methods. The results show that Ce1–2xYxPrxO2 abrasive has a normal octahedral shape with a particle size of 190 ∼ 260 nm. With the increase of doping amount, the particle size of abrasive decreases gradually, but the photocatalytic activity increases. Compared with undoped CeO2 abrasives, the removal rate (RR = 932.42 nm/min) of quartz glass by Ce1–2xYxPrxO2 abrasive was increased by about 87.10%. At the same time, the surface quality has been significantly improved. A smooth, flawless and low roughness surface was obtained. The improvement in surface quality can be demonstrated by reducing surface roughness (Ra). The Ra of quartz glass decreased to 0.36 nm after Y3+/Pr3+ co-doped CeO2 abrasive by PCMP (the original Ra of glass was 1.08 nm). It was considered that the size of the abrasive had a close relationship with the surface quality and the RR of the polished glass. Meanwhile, characteristic co-doping strategy was conducive to increase the Ce3+ and oxygen vacancy concentration of CeO2 particles, which optimized the separation efficiency of the photogenic carrier of the photocatalyst. This further promoted the generation of oxidizing active substances in the polishing slurry, and therefore expediting the formation and removal of the chemical reaction soft layer. The removal mechanism of Ce1–2xYxPrxO2 abrasives in PCMP process was discussed.

Experimental Study on Chemical-Mechanical Synergistic Preparation for Cemented Carbide Insert Cutting Edge.

Typical edge defects in the edge region of a new cemented carbide insert without edge preparation include burrs, poor surface quality, micro-breakages, and irregularities along the edge. To address the problems in new cemented carbide inserts without edge preparations, a chemical-mechanical synergistic preparation (CMSP) method for the cemented carbide insert cutting edge was proposed. Firstly, the CMSP device for the insert cutting edge was constructed. Then, the polishing slurry of the CMSP for the insert cutting edge was optimized using the Taguchi method combined with a grey relation analysis and fuzzy inference. Finally, orthogonal experiments, the Taguchi method, and analysis of variance (ANOVA) were used to investigate the effect of the polishing plate's rotational speed, swing angle, and input frequency of the controller on the edge preparation process, and the parameters were optimized. The results showed that the best parameter combination for the polishing slurry for the cemented carbide inserts was the mass concentration of the abrasive particle of 10 wt%, the mass concentration of the oxidant of 10 wt%, the mass concentration of the dispersant of 2 wt%, and the pH of 8. The CMSP process parameter combination for the linear edge had the polishing plate's rotational speed of 90 rpm, the swing angle of 6°, and the input frequency of the controller of 5000 Hz. The optimum CMSP process parameter combination for the circular edge had the polishing plate's rotational speed of 90 rpm, the swing angle of 6°, and the input frequency of the controller of 7000 Hz. The polishing plate's rotational speed had the most significant impact on the edge preparation process, followed by the swing angle, and the effect of the input frequency of the controller was the smallest. This study demonstrated that CMSP is a potential way to treat the cemented carbide insert cutting edge in a tool enterprise.

Improvement of dispersion stability and polishing performance of chemical mechanical polishing slurry for cemented carbide inserts

Aiming at defects such as small pits and scratches on the surface caused by the aggregation of alumina particles during the chemical mechanical polishing (CMP) process of the cemented carbide inserts, the effect of the dispersant types, pH and dispersant concentration on the dispersion stability of the alumina suspension is investigated. It is found that sodium dodecyl sulfate (SDS) is the best dispersant of the six different dispersants, and the suspension has good dispersion stability when the pH value is 11 and the SDS concentration is 3 wt%. Furthermore, based on the DLVO theory, SDS is verified to improve suspension stability at the micro-scale. Finally, the insert CMP experiments are carried out using the polishing slurry with SDS and without dispersant. CMP experiments show that using the polishing slurry with SDS to polish the insert can achieve a better material removal rate (MRR) and lower surface roughness.

Nanomaterials and Equipment for Chemical–Mechanical Polishing of Single-Crystal Sapphire Wafers

Single-crystal sapphire (α-Al2O3) has been widely used in semiconductor, optics, communication, national defense, and other fields. Before application, an ultra-smooth surface which is scratch free and subsurface damage free is essential. Furthermore, the sapphire has unique qualities such as significant rigidity and chemical stability, which make it extremely arduous to process. Chemical mechanical polishing (CMP) is recognized as the final process to reduce the roughness and eliminate surface defects of a sapphire surface. In this review, the materials and equipment used for the chemical polishing of a sapphire wafer are summarized, and the surface nanoscale changes of sapphire wafer are reviewed from the angles of regulating polishing-process parameters, composition of polishing slurry including that which is nano-abrasive, a pH regulator, a complexing agent, and other additives, as well as hybrid CMP technologies. The outlook and future applications are also summarized.

The Role of Alanine in the Chemical Mechanical Polishing of Aluminum

With the evolution of integrated circuits, the transition from polycrystalline silicon to aluminum as the gate electrode has become prevalent due to its inherent advantages. This study considers the impacts of pH, H2O2 and alanine on the aluminum removal rate and surface roughness during chemical mechanical polishing (CMP) with abrasive colloidal silica. Alanine was incorporated as a complexing agent in the polishing slurry in an acidic environment. The mechanistic role of alanine in the aluminum CMP process was investigated with various techniques, including electrochemical tests, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy (UV–vis). Additionally, density functional theory (DFT) calculations were used to examine the quantum chemical parameters of alanine and elucidate the complexation mechanism. The experimental results indicated that at an alanine concentration of 1.5 wt%, the Al removal rate was 2124.07 Å min−1 with a surface roughness of 1.33 nm. The interactions between alanine and the aluminum ions (Al3+) yielded soluble Al-alanine complexes, which facilitated corrosion on the Al and enhanced the removal rate.

ReaxFF molecular dynamics simulation and experimental validation about chemical reactions of water and alcohols on SiC surface

The high chemical inertness of silicon carbide (SiC) makes it difficult for surface chemical reactions to occur. Surface oxidation reactions are crucial for improving the processing efficiency and surface quality of SiC wafers. Extensive research has been conducted on conventional aqueous polishing slurries, while investigations on non-aqueous solvent-based polishing slurries have emerged as alternative options for enhancing SiC surface processing, as evidenced by recent scholarly reports. However, the surface chemical reaction mechanism of silicon carbide in either water or other hydroxyl groups containing solvents remains still unclear and is not well understood. In this work, ReaxFF molecular dynamics simulation was used to study the dynamic reaction processes between solvents and 6H SiC (001) surfaces. The oxidation of SiC surface in water and alcohol solvent is found to go through three stages: in the first stage, the solvent molecules move towards the SiC surface and react with the uncoordinated Si atoms and C atoms on the surface; in the second stage, the solvent molecules adsorbed on the surface of SiC reduces the Si–C bonding energy and promotes the breaking of Si–C bonds; in the third final stage, the migration of OH and H on the SiC surface induces the formation of Si–O–Si bonds, which promotes the continuous oxidation of the SiC surface. The order of simulated chemical reactivity between solvent and silicon carbide surface is consistent with experimental polishing removal rates. The reaction mechanism of solvent on silicon carbide surface was proposed by combining ReaxFF simulation results with polishing experiments, AFM, and XPS data analysis, shedding new insights on better understanding the mechanism of SiC chemical mechanical polishing.

Insight into Polishing Slurry and Material Removal Mechanism of Photoassisted Chemical Mechanical Polishing of YAG Crystals.

Yttrium aluminum garnet (YAG) crystals are an important gain medium in thin-sheet solid-state lasers, and their processing quality directly affects the performance of solid-state lasers. But it is difficult to achieve high efficiency and high quality of YAG crystals by traditional chemical mechanical polishing (CMP). In this study, we developed a new polishing slurry for photoassisted chemical mechanical polishing (PCMP) of YAG crystals. The polishing slurry is composed of peroxymonosulfate (PMS), manganese ferrite (MnFe2O4), alumina (Al2O3) abrasives, and deionized water. PCMP is conducted in an ultraviolet (UV) light environment. When employing this polishing slurry for PCMP processing of YAG crystals, the material removal rate (MRR) achieved 250 nm/min and the surface roughness achieved 0.35 nm Sa. The experiments verified that both UV light and MnFe2O4 can effectively activate PMS to produce active free radicals and further enhance the chemical action of the polishing slurry. X-ray photoelectron spectroscopy (XPS) analysis results indicated that active radicals reacted with the surface structure of the crystal and removed the aluminum-oxygen octahedron in large quantities from it. The structural defects reduced the surface hardness of the crystal, which means that active free radicals can modify the crystal surface materials.

Electrochemical corrosion behavior and theoretical simulation of cobalt in chemical mechanical polishing process

The chemical mechanical polishing (CMP) process for cobalt (Co) interconnects is essential for the fabrication of integrated circuits with feature sizes below 10 nm. However, achieving high removal rates coupled with low dissolution rates remains a significant challenge. In this work, we have developed a dual-functional polishing slurry, which integrates ethylenediamine tetramethylphosphonic acid (EDTMPA) as a complexing agent, and octahydroxamic acid (OHA) as a corrosion inhibitor. The novel slurry-derived Co CMP meets ideal situation, delivering a removal rate (RR) of 246 nm/min, a dissolution rate (DR) of 0.8 nm/min, and a root mean square (RMS) roughness (Sq) of 2.31 nm. Experimental data and theoretical calculations reveal that the improved CMP performance results from the effective complexation of EDTMPA with Co ions. Furthermore, the adsorption of OHA as a corrosion inhibitor on the Co surface effectively counteracts the corrosion induced by EDTMPA. The development of this novel polishing slurry presents a strategy that harmoniously combines reduced process time with enhanced surface quality, holding the potential to significantly influence the CMP field.

Environmentally Friendly Amino Acid-Based Polishing Slurry with Reduced Galvanic Corrosion at Copper/Cobalt Interface for Advanced Cu Interconnect Applications

Chemical mechanical planarization (CMP) is an integral part in semiconductor processing including the back-end-of-line (BEOL) step. A goal of CMP is to uniformly polish the metal interconnects and the liner/barrier materials while minimizing CMP-related defects such as pitting, dissolution, and galvanic corrosion. A variety of azoles are used as corrosion inhibitors such as benzotriazole (BTA) to prevent corrosion defects during polishing. [1,2] These azoles work together with particles in the slurries to polish the overplated metal forming the interconnects. However, azoles are very poorly biodegradable during wastewater treatment and highly toxic to the nitrification process, which requires expensive wastewater treatment challenges.[3,4] Also, it is known that the use of BTA leads to contamination of Cu films by forming undesirable hydrophobic organic residues (e.g., BTA and Cu-BTA complexes),[5] making their removal very difficult during cleaning. To address these challenges aliphatic amino acids were examined as potential corrosion inhibitors to replace problematic azoles in CMP slurries.Three amino acids were considered in a model CMP slurry. These three were chosen for their unique functional groups: methionine, containing a sulfur group, glutamic acid, having an extra carboxylic acid group, and leucine, having a branched hydrocarbon chain. A representative polishing slurry with 35 nm colloidal silica abrasives, 1 wt% hydrogen peroxide as an oxidizer, 0.5wt% arginine as a complexing agent, at pH 8 was used. Three experimental aims were considered (1) corrosion characterization of the three amino acid and BTA electrolytes with linear sweep voltammetry; (2) comparison of the Co and Cu metal removal rate (MRR) in polishing experiments with a proto-type CMP polisher with 8” wafers, and (3) oxidation of the amino acids and BTA in a Fenton assisted electrooxidation reaction. Methionine was most effective in controlling the galvanic corrosion of the Cu-Co couple. The Co and Cu MRR decreased in the presence of three amino acids and showed comparable removal selectivity. The forced degradation of the amino acids under the Fenton-assisted electrooxidation confirmed that they were more readily degraded compared to BTA. Acknowledgments: This work was supported by the Semiconductor Research Corporation grant (Task 3100.001) under the Global Research Collaboration program. References Seo, J., A review on chemical and mechanical phenomena at the wafer interface during chemical mechanical planarization. Journal of Materials Research 2021, 1-23.C. Peethala, H. P. Amanapu, U. Lagudu, and S.V. Babu, J. Electrochem. Soc, 159(6), H582-H588, 2012.D.E. Speed, Chapter 11, Advances in chemical mechanical planarization (CMP) 2nd edition, Babu, S. V., Ed. 2021.G. Li et al. / Chemosphere 241 (2020) 1249932.Seo, J.; Vegi, S. S. R. K. H.; Babu, S.V. ECS Journal of Solid State Science and Technology 2019, 8 (8), P379–P387.

Analysis of cavitation and shear in bellows pump: transient CFD modelling and high-speed visualization

Pneumatic drive bellows pumps (PDBPs) are a crucial fluid control component in the semiconductor industry. However, when dealing with specific chemical mechanical polishing (CMP) slurries, agglomeration of particles can occur, leading to scratches, particle residues, pits, and other defects on the wafer surface. The leading cause of agglomeration has been proposed to be cavitation and excessive shear in PDBPs. A high-fidelity multiphase computational fluid dynamics (CFD) model, which fully resolves the response of check valves under hydrodynamic and other external loads, was established to evaluate cavitation behaviour and shear distribution in PDBPs. Moreover, a test rig was built to visualize cavitating flow patterns in PDBPs and verify the accuracy of the CFD model. Among different cavitation regions captured by high-speed visualization, the region near the inner leading edge of the end-ring of the inlet valve is dominant, with high intensity, long duration, and complex morphology evolution. Detailed initiation and development process of cavities in the dominant region are analysed numerically. The shear rate in different domains of PDBPs is estimated, and the inlet valve domain stands out from the other. The strongest shear rate is observed near the leading edge of the end-ring. Furthermore, an analysis of the relationship between cavitation and shear indicates that the high-intensity vortices generated owing to strong shear account for the inception of cavitation. This study contributes to understanding inner flow details in PDBPs and provides a guideline for further optimization of similar pumps.