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As feature sizes decrease, an investigation of pad unevenness caused by pad conditioning and its influence on chemical mechanical polishing is necessary. We set up a kinematic model to predict the pad wear profile caused by only diamond disk conditioning and verify it. This model shows the influences of different kinematic parameters. To keep the pad surface planar during polishing or only conditioning, we can change the sweep mode and range of the conditioner arm. The kinematic model is suitable for the prediction of the pad wear profile without considering the influence of mechanical parameters. Furthermore, based on the pad wear profile obtained from a real industrial process, we set up a static model to preliminarily investigate the influence of pad unevenness on the pad–wafer contact stress. The pad–wafer contact status in this static model can be approximated as an instantaneous state in a dynamic model. The model shows that the existence of a retaining ring helps to improve the wafer edge profile, and that pad unevenness can cause stress concentration and increase the difficulty in multi-zone pressure control of the polishing head. [ABSTRACT FROM AUTHOR]

As the development of technology nodes proceeds to 7 nm node, chemical mechanical polishing (CMP) slurries for shallow trench isolation (STI) cannot fully meet the technical requirements. Higher goals are put forward for the polished surface qualities and the removal selectivity control. The polishing liquid exhibits issues such as easy agglomeration, removal rate of Si3N4 exceeding 50 Å/min, removal selectivity ratio of SiO2/Si3N4 below 20, increased surface scratches and roughness of SiO2 and Si3N4 after polishing exceeding 1 nm. Here, attention is given to studying the STI CMP process by introducing various ionic surfactants in ceria slurries, aiming to control removal rates, selectivity, as well as surface qualities. The findings of ball milling and settling tests were used as a starting point for choosing the effective surfactants, searching the minimal delamination phenomenon. Then the impact of surfactants on removal rates, selectivity and surface characteristics were next investigated in polishing trials at various pH levels. Depth of scratches on polished wafers and corresponding surface roughness, as well as morphology of ceria abrasive particles were characterized. Action mechanisms of selected ionic surfactants in ceria slurries have been revealed by solid-liquid interface adsorption characterization, thermogravimetric analysis and zeta potential tests. Through research finding the addition of piperazine and 2-methylpiperazine surfactant can reduce the number and depth of scratches on the surfaces of SiO2 and Si3N4 after polishing, and it exhibits better dispersibility in alkaline environment compared to acidic environment. [ABSTRACT FROM AUTHOR]

With the rapid development of high-energy laser system, thick silicon mirror, as an important optical component to reflect laser, is required to have a surface with micron-level flatness, which poses significant challenges to silicon mirror manufacture process. Fine rotation grinding (FRG) is a typical efficient method for silicon mirror manufacture. A geometric model is developed in this paper to research silicon mirror surface figure control mechanism in FRG process. The model demonstrates the relationship between the grinding spindle obliquity and the mirror surface figure. From an application perspective, the relationship between the spindle obliquity and the spindle dial gauge indication is further presented. Based on this model, a MATLAB program is designed to give a series of simulation results for researching spindle adjustment regularity and getting the most ideal spindle obliquity. Besides, several grinding experiments are carried out. The simulation and experiment results are in good agreement, and a silicon mirror surface with the flatness of less than 2 μm is achieved. The proposed grinding geometric model can provide an actual guide for grinding spindle adjustment to control the surface figure of silicon mirror. [ABSTRACT FROM AUTHOR]

Ruthenium is the most promising material for the barrier layer used for the sub 14 nm technology node in integrated circuits manufacturing. Potassium periodate (KIO)-based slurry is used in the chemical mechanical planarization (CMP) process of the barrier layer. However, the electrochemical and corrosion properties of ruthenium have not been investigated in such slurry. In this paper, the electrochemical and corrosion behaviors of ruthenium in KIO solutions were investigated under static conditions but at different pH values by potentiodynamic polarization and electrochemical impedance spectroscopy measurements, combined with surface chemical analysis using auger electron spectroscopy. Moreover, to study wear enhanced corrosion during CMP, tribocorrosion experiments were carried out to monitor the current density changes during and after mechanical scratching. The results show that at pH 6, ruthenium forms a relatively thick and heterogeneous surface film composed of RuO·2HO/RuO, showing a high corrosion resistance and it exhibits a quick repassivation after mechanical scratching. At pH 4, ruthenium shows a passivation behavior with formation of a uniform and conductive oxide like RuO·2HO. It should be noted that there is a possible formation of RuO toxic gas under this condition, which should be avoided in the actual production. However, at pH 11, ruthenium exhibits no considerable passivity and the corrosion proceeds uniformly. [ABSTRACT FROM AUTHOR]

Copper chemical mechanical polishing (CMP) in barrier layer slurries with periodate as oxidant has not been intensively studied. This work presents an investigation into copper tribocorrosion in potassium periodate-based slurries during CMP. The research focused on copper tribocorrosion behavior, the surface chemical and electrochemical reaction products, and the electrochemical mechanism during CMP. The copper surface film was characterized by Raman spectra experiments. Tribocorrosion tests combined with CMP chemical experiments were conducted to study the tribochemical behavior and wear-accelerated corrosion effect. The results show that copper corrosion is more severe in acid solutions than in alkaline conditions. The copper surface is mainly passivated with copper oxides, copper hydroxide, and copper iodide. Small amounts of copper iodate, copper periodate, and iodine could be detected under specific pH conditions. Abrasion could help to get a uniform passivation film on copper surface consisting of copper oxides, copper hydroxide, and copper iodide only. The material loss due to wear-accelerated corrosion during CMP was also investigated. The results show that under weakly alkaline conditions (pH 9 and pH 10), the wear-corrosion effect plays an important role in the total material loss due to corrosion. The wear-accelerated corrosion is mainly caused by the exposure of more cathodic reaction sites to the slurry for participation in the redox reaction and the local galvanic corrosion during the CMP process. The high wear corrosion proportion of the total corrosion (Δ I/ I) could help to obtain a better surface quality and desirable material removal rate during CMP. [ABSTRACT FROM AUTHOR]

Chemical mechanical planarization/polishing (CMP) of copper has emerged as an important component in semiconductor processing. It involves both chemical and mechanical effects, consisting of several steps such as passivation, film dissolution, chemical corrosion, and abrasive abrasion. It is important to understand the individual steps in the removal process. In this paper, investigations were focused on the tribo-chemical behavior of copper in hydrogen peroxide solution at different pH values. The repassivation current and friction coefficient were measured in situ as a function of time. The compositions of unworn and worn surfaces after the tribocorrosion experiments were also analyzed by Raman spectra. The copper exhibited a tendency of repassivation during the potentiostatic tests; furthermore, the repassivation kinetics varied with the surface species and the quantity of passive films formed at different pH values. The results indicate that both relatively high material removal rate and good surface quality may be achieved in the weak acidic solution during CMP. [ABSTRACT FROM AUTHOR]

In this paper, the kinematic analysis and numerical calculation are used to discuss the effect of the kinematic parameters on the final polishing result of typical rotary chemical-mechanical polishing (CMP) equipment. The relative velocity distribution and the sliding distance distribution are calculated based on the kinematic analysis. Especially, the coupling relationships between the kinematic parameters are investigated and discussed. And two parameters of the sliding distance nonuniformity (SDNU) and the sliding distance nonuniformity within concentric circles (SDNU\-cc) are proposed and calculated to evaluate the global uniformity of the sliding distance and to reveal the coupling relationships between the kinematic parameters. The results suggest that the relative velocity distribution and the sliding distance distribution are significantly affected by the coupling effects of the basic motions of CMP system; the SDNU is mainly affected by parameter \alpha, which represents the coupling relationship between the rotary motions of the wafer carrier and the polishing platen; the SDNU\-cc is mainly affected by parameter kT{0}^{\prime}(\alpha kT0), which represents the coupling relationship between the reciprocating motion and the rotary motion of the wafer carrier; \alpha\approx 1 and \alpha kT0>2 are proper for better polishing uniformity in real CMP process. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, the contact stress distribution on the wafer surface in multi-zone CMP is investigated using finite-element analysis based on a 12-in. and four-zone CMP model. Afterwards, a 12-in. and four-zone polishing head with the same size as the numerical model is developed and CMP experiments are carried out to verify the above numerical calculations. The results show that both the contact stress on the wafer surface and the material removal rate of the wafer can be adjusted by varying the applied load at the zones and the retaining ring in multi-zone CMP, the multi-zone MRR model appears to agree well with the experimental data, and the non-uniformity material removal rate of the wafer can be improved in multi-zone CMP. It is expected that this investigation can give some direct assistance to the 12-in. wafer fab. [Copyright &y& Elsevier]

Abstract: The sapphire substrates are polished by traditional chemical mechanical polishing (CMP) and ultrasonic flexural vibration (UFV) assisted CMP (UFV–CMP) respectively with different pressures. UFV–CMP combines the functions of traditional CMP and ultrasonic machining (USM) and has special characteristics, which is that ultrasonic vibrations of the rotating polishing head are in both horizontal and vertical directions. The material removal rates (MRRs) and the polished surface morphology of CMP and UFV–CMP are compared. The MRR of UFV–CMP is two times larger than that of traditional CMP. The surface roughness (root mean square, RMS) of the polished sapphire substrate of UFV–CMP is 0.83Å measured by the atomic force microscopy (AFM), which is much better than 2.12Å obtained using the traditional CMP. And the surface flatness of UFV–CMP is 0.12μm, which is also better than 0.23μm of the traditional CMP. The results show that UFV–CMP is able to improve the MRR and finished surface quality of the sapphire substrates greatly. The material removal and surface polishing mechanisms of sapphire in UFV–CMP are discussed too. [Copyright &y& Elsevier]

Abstract: Scrub, ultrasonic and megasonic are widely used in industry as post-CMP (chemical mechanical polishing/planarization) cleaning procedure. In this paper experiments and results are described to analyze the particle contaminations of hard disk substrate after each process of post-CMP cleaning. A scatter spot method has been exploited to detect the location and characteristics of the particles. SEM with EDX is used to observe and analyze the particles’ shape and size as well as the elements. The results indicate that brush scrub process can remove 99% contaminations after CMP but not that efficient for submicron particle. Megasonic is a refined method for cleaning nano-particles. However, contaminations like metallic particles and bacteria from the equipment may cause pollution. The abrasive particles embedded in the plating pits cannot be removed by mechanical force. Pollution in the dryer is also discussed. [Copyright &y& Elsevier]

Chemical mechanical polishing (CMP) process is commonly regarded as the best method for achieving global planarization in the field of surface finishing with ultra-precision. The development of investigation on material removal mechanisms for different materials used in computer hard disk and ultra-large scale integration fabrication are reviewed here. The mechanisms underlying the interaction between the abrasive particles and polished surfaces during CMP are addressed, and some ways to investigate the polishing mechanisms are presented. [ABSTRACT FROM AUTHOR]

Abstract: A 3D lubrication model between a soft porous brush and rigid flat surface in the post-CMP (chemical mechanical polishing) cleaning process for wafer or hard-disc surface is set up in this article. The mesh porous structure of the brush and the kinematic relations between the brush and the surface are taken into account. The flow governing equations for cleaning process are deduced with Newtonian fluids between the brush nodule and the substrate. The distributions of fluid pressure and hydrodynamic removal moment are calculated. The simulation results show that the fluid pressure has negative regions in inlet area. The removal force is depended on system parameter, location, time and particle size. The load and hydrodynamic moment increase with the increase of brush velocity and deflection of brush nodule, which is effective for cleaning. A low wafer rotation speed is recommended to keep the cleaning uniformity. The removal moment is increasing during the cleaning process. The hydrodynamic drag force decreases rapidly with decreasing of particle size. The models are coincident with the actual process and can be used as reference for designing a higher level cleaning process and the analysis of the formation of particle defect. [Copyright &y& Elsevier]

ReaxFF reactive molecular dynamics simulations are employed to study the process of the silica abrasive particle sliding on the Si (1 0 0) substrate in the aqueous H 2 O 2 in order to clarify the atomistic mechanisms of the Si chemical mechanical polishing (CMP) process. Our results reveal that the mechanical sliding effects induced chemical reactions at the abrasive particle and Si substrate interface dominate the CMP process and lead to the removal of Si atoms. Before the abrasive particle and Si substrate surface interact mechanically, aqueous H 2 O 2 can make the Si substrate more oxidized. Once they contact with each other, they are connected by the interfacial Si O Si bridge bonds due to the chemical reactions at the interface. Under the mechanical sliding effects, the Si Si and Si O bonds on the Si substrate can be mechanically strained to be broken, leading to the removal of Si atoms from the Si substrate. Compared with the CMP process in pure H 2 O, the CMP process in the aqueous H 2 O 2 leads to more oxidized substrate and the removal of more Si atoms, demonstrating the significant role of H 2 O 2 as an oxidizer. Besides, the friction force is higher than that in the pure H 2 O case due to the stronger interfacial covalent bonds formation and breaking. Our results may shed light on the removal mechanism of Si atoms in the CMP process at the atomic level and provide an effective method to help design the components of the CMP slurry. [ABSTRACT FROM AUTHOR]

In this study, a specially designed carrier with a one-zone pneumatic loading system that uses a thick copper disk as the workpiece was developed. Comparative studies of the fluid pressure and workpiece orientation between the disk and wafer carriers during chemical mechanical polishing were conducted. The results reveal that the copper disk leans down toward the leading edge and produces a negative-dominated (approximately 70%) fluid pressure, which differs from the multi-zone carrier but agrees with other studies in which the fluid pressure is measured from the disk side. Different balancing statuses and wedged gaps are formed in these two structures. [ABSTRACT FROM AUTHOR]

Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing (CMP) of GaN were deeply investigated in this paper. Working as an ideal homogeneous substrate material in LED industry, GaN ought to be equipped with a smooth and flat surface. Taking the strong chemical stability of GaN into account, photocatalytic oxidation technology was adopted in GaN CMP process to realize efficient removal. It was found that, because of the improved reaction rate of photocatalytic oxidation, GaN material removal rate (MRR) increases by a certain extent with catalyst concentration increasing. Cross single line analysis on the surface after polishing by Phase Shift MicroXAM-3D was carried out to prove the better removal effect with higher catalyst concentration. Ultraviolet intensity field in H 2 O 2 -SiO 2 -based polishing system was established and simulated, revealing the variation trend of ultraviolet intensity around the outlet of the slurry. It could be concluded that, owing to the higher planarization efficiency and lower energy damage, the UV lamp of 125 W is the most appropriate lamp in this system. Based on the analysis, defects removal model of this work was proposed to describe the effects of higher catalyst concentration and higher power of UV lamp. [ABSTRACT FROM AUTHOR]

When the feature size of integrated circuit continues to shrink below 14 nm, ruthenium (Ru) has become one of the most promising candidates for the application of novel barrier layer. To reveal the material removal mechanism of Ru during chemical mechanical polishing (CMP), surface characteristics of Ru in KIO 4 -based slurry were investigated. The corrosion behavior of ruthenium was measured by the surface chemistry and morphology analysis. Then the mechanical properties of the passivated/corroded surface were evaluated by AES and tribocorrosion experiments. CMP experiments were carried out to make clear the effects of surface property during polishing. It was found that the Ru surface chemistry and mechanical properties vary obviously as a function of slurry pH. In neutral slurries, the Ru surface is covered with RuO 2 ·2H 2 O/RuO 3 inhomogeneous passivation films, with the highest material removal rate obtained during the CMP process. It could be concluded that the material removal mechanism largely depends on the slurry pH values. In near neutral slurries, Ru is passivated with thick and heterogeneous oxides film, which proves the easiest to be mechanically removed during polishing. The weak alkaline slurry is preferred in order to achieve desirable polishing rate as well as avoid the formation of toxic RuO 4 . [ABSTRACT FROM AUTHOR]

Silicon wafers are commonly thinned employing an ultra-precision grinding machine based on a workpiece self-rotational principle. The diamond grains, stochastically located on the grinding wheel surface, remove the workpiece material and generate a difference in the size and shape of undeformed chips. However, an in-depth understanding of the grain-workpiece interaction randomness in wafer thinning process and its link with surface roughness has not been revealed yet. In this paper, a new index, i.e., undeformed chip width, is first proposed to analyze and describe the stochastic characteristics in material removal process as well as predict the surface roughness of ground wafer. The grinding wheel morphology is constructed by the random operation for grain size and position. Then, a 2D topography generation model is established to calculate the undeformed chip width. The non-uniform distribution characteristics of undeformed chip width under different grinding conditions are further analyzed. Finally, the relation between undeformed chip width and surface roughness of ground wafer is presented. The correctness of developed models is verified using a series of grinding experiments. • A ground wafer undeformed chip modeling framework from a micro scale is proposed. • A wheel morphology is reconstructed by random operation for grain size and position. • An undeformed chip width is defined to describe random properties in material removal. • A regression model of surface roughness in wafer self-rotational grinding is derived. [ABSTRACT FROM AUTHOR]

Although there are substantial studies on chemical mechanical polishing (CMP) processes of ruthenium (Ru) as a barrier layer in periodate-based slurries, little is known about the passivation mechanism of inhibitors and the galvanic corrosion mechanism of Cu. In this study, the synergetic effect of benzotriazole (BTA) and potassium molybdate (K 2 MoO 4 ) on the polishing performance of Ru and Cu in KIO 4 -based slurry was investigated. The galvanic corrosion of Cu in a Cu–Ru coupled system was studied from a completely different perspective. X-ray photoelectron spectroscopy combined with other measurements was used to reveal the synergetic passivation mechanism of BTA and K 2 MoO 4 . The results show that the galvanic corrosion of Cu is strongly mitigated in the presence of both BTA and K 2 MoO 4 . Based on the data, it was regarded that the adsorbed MoO 4 2− not only modified the surface structure of Ru and Cu, but also supported the adsorption of BTA passivation film. Also, it was found that insoluble salts were deposited into the gaps of the passivation film, which improved the compactness of the molybdate-BTA film. The CMP tests showed that the selectivity of the material removal rate of Cu to Ru can be evidently improved in the presence of BTA and K 2 MoO 4 . The increase of oxidizer content and the reduction of polishing down force could help to further decrease the MRR selectivity between Cu and Ru. [ABSTRACT FROM AUTHOR]

Abstract: A novel in-situ wafer bending/orientation measurement system, cooperated with our previous developed fluid pressure mapping system, was developed for 12-inch chemical mechanical polishing (CMP) equipment. Wafer bending and wafer orientation are studied for copper wafer sliding against the IC1000 pad. The results reveal a micron level wafer bending, and a slight wafer pitch angle of 10−5 degree. Both the wafer pitch angle and interfacial fluid pressure increase with the speed till a critical speed and then decrease. The convergent-dominated wedged gap caused by the convexly bended, trailing edge pitched wafer gives a reasonable explanation to the positive-dominated fluid pressure. [Copyright &y& Elsevier]

Using atomic force microscopy and scanning electron microscopy, the mechanical removal mechanism of silicon with different exposure surfaces of cerium oxide (CeO 2) is studied. It is discovered that the main type of mechanical wear between Si and CeO 2 is adhesive wear. The silicon removal rate relationship is RR 1 1 RR means removal rate of silicon by CeO 2. (CeO 2 (111))> RR(CeO 2 (100))> RR(CeO 2 (110)). Additionally, the relationship of the friction force remains constant: F 2 2 F means friction force between silicon and CeO 2. (CeO 2 (111)) > F(CeO 2 (110)) > F(CeO 2 (100)). This is consistent with the ceria wear rate relationship of WR 3 3 WR means wear rate of CeO 2. (CeO 2 (111)) > WR(CeO 2 (110)) > WR(CeO 2 (100)). This paper provides a deeper insight into the mechanical material removal mechanism during chemical mechanical polishing processes; thus, providing a reference for CeO 2 particle orientation control. Image 1 • Si mechanical removal mechanism was studied using different exposure surfaces of CeO 2. • Adhesive wear is the main wear type between Si and CeO 2. • The friction relationship between Si and CeO 2 remains constant. • CeO 2 (111) is found to have the strongest Si removal capacity. • CeO 2 (110) has the weakest Si removal capacity, related to its highest surface energy. [ABSTRACT FROM AUTHOR]

• Surface doping of CeO 2 as CMP abrasives was done using La, Nd and Yb. • O vacancy formation energy and Ce3+ content was calculated by DFT and XPS. • Ce3+ content of CeO 2 is largely improved after doping. • Doped CeO 2 as CMP abrasive improves the polishing rate of SiO 2 and surface quality. Ce3+ in CeO 2 , rather than Ce4+, is believed to provide assistance to the breaking up of Si O bond during chemical mechanical polishing (CMP) of silica. In the paper, lanthanide metals (La, Nd and Yb) doped CeO 2 nanoparticles were synthesized by modified incipient impregnation method in order to improve the content of Ce3+ in CeO 2 as polishing. X-ray photoelectron spectroscopy (XPS) experiments and density function theory (DFT) calculation demonstrate this approach could achieve surface doping of CeO 2 nanoparticles, and facilitates the formation of oxygen vacancy and Ce3+ content. CMP experiments show that the polishing rate and the surface quality of silica wafer are obviously improved by using the doped CeO 2 as abrasive particles. Especially for Nd/CeO 2 , content of Ce3+ increases from 0.146 to 0.235, the polishing rate of silica is accelerated by 29.6% in alkaline slurries, and a better surface quality (Sa = 9.6 Å) is obtained. [ABSTRACT FROM AUTHOR]