Substrate Chemical Mechanical Polishing Research Articles

Effect of EDTA-modified alumina composite abrasive on the CMP performance of sapphire substrate

Sapphire is one of the most widely used substrate materials for semiconductor lighting. With the improvement of chemical mechanical polishing (CMP) processing technology for sapphire substrate, mass production, and cost control requires faster polishing efficiency and better surface quality. In CMP, alumina abrasive is widely used for its high polishing rate, but it also has the disadvantages of easy agglomeration and poor polishing quality. Therefore, ethylenediamine tetraacetic acid (EDTA)-grafted alumina composite abrasives were produced by a two-step process for the sapphire substrate CMP. As demonstrated by time of flight secondary ion mass spectrometry and fourier transform infrared spectroscopy, EDTA has been successfully grafted onto the surface of alumina particles. As shown by the scanning electron microscope, particle size distribution, and zeta potential analyses, the modified alumina composite abrasives exhibit superior dispersion properties than pure alumina particles. CMP experiment results show that the material removal rate (MRR) of the alumina composite abrasives can reach up to 2.6 μm/h, and the surface roughness (Sa) of the sapphire substrate can be reduced to 0.89 nm, which is 53 % higher and 66 % lower than pure alumina, respectively. According to X-ray photoelectron spectroscopy, the chemical etch of modified abrasive particles was strengthened, and the complex reaction occurred throughout the CMP process to generate the C–O–Al structural compound. Meanwhile, the friction coefficient test and contact angle test were combined to create the contact wear model. It shows that the addition of EDTA expands the contact area between the composite abrasives and the surface of substrates, improving the mechanical interaction during CMP. The chemical reaction and mechanical action combine and promote each other to enhance the CMP performance.

Engineered Ceria Slurries for Electronic Glass Substrate CMP Application

Glass substrates have gradually gained more attention as the media platters in hard disk drives (HDD) used in laptops, data centers, and cloud storage due to its advantageous properties. Particularly, advanced technologies like Heat Assisted Magnetic Recording (HAMR) in HDD and Through-Glass-Via (TGV) in 3D packaging applications all require the use of glass substrates with precisely controlled surface properties. Glass substrate’s advantages include lower weight, improved flatness, less flutter at high RPM’s and lower thermal expansion as compared to aluminum / NiP substrates. This lower expansion when exposed to heat makes it ideal for HAMR technology, which will be the key to creating hard disk drives with growing storage capacity. Chemical mechanical polishing (CMP) is a method to eliminate surface defects induced by grinding & lapping to meet final requirements of HAMR or TGV for glass substrates with surface finishes down to a few angstrom level or less. Key performance targets include removal rate, surface roughness, TTV, FSW, ceria residue / particle content (cleanability) on glass disks as well as recyclability. In this study, slurries for CMP are investigated utilizing engineered ultra-pure ceria particles which are known to have high material removal rate (MRR) on glass substrates. Various particle sizes, morphology, and chemical additives were evaluated. Results of systematic CMP tests including MRR, surface roughness, recyclability, and most importantly, ease of ceria residue removal from the glass substrate will be reported. Morphology of ceria particles was found to play a critical role in MRR. An optimized combination of ceria morphology and additive chemistries enables high MRR together with improved Ceria residue / cleanability performance. Figure 1

Effect of Sr(OH)2 as a pH Regulator on Different Plane Sapphire Substrate Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) process is widely used on GLSI multilayer metallization planarization which requires the highest precision atomic surface. In order to improve the removal rate and surface quality of sapphire substrate, CMP method was used and a novel pH regulator Sr(OH)2 was investigated. According to c/a/r-plane sapphire CMP experimental results good surface quality and higher material removal rate (MRR) were obtained by using the Sr(OH)2 solution as pH regulator comparing with traditional KOH as pH regulator. Meanwhile, it indicated Sr(OH)2 cannot only replace the traditional pH regulators, but also not introduce other metal ions contamination for sapphire CMP. According to the chemical thermodynamics basic principles, the trend and products of chemical reaction between sapphire and traditional water-based SiO2 slurry and between sapphire and Sr(OH)2 was analyzed by using HSC software. In addition, the action mechanism of Sr(OH)2 on sapphire substrate CMP was investigated. According to the results of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), it was found there were solid-chemical reactions between Sr(OH)2 and sapphire and Al2Si2O7·2H2O, Al2SiO5, SrAl2Si2O8 and SrAl2O4 were generated on the sapphire surface, which improved chemical action effectively and material removal rate. This CMP method of improving chemical action has important significance to actual production.

Preparation of MgO doped colloidal SiO2 abrasive and their chemical mechanical polishing performance on c-, r- and a-plane sapphire substrate

Chemical mechanical polishing (CMP) has been proved to be one of the most important methods to achieve atomic ultra-smooth surface, and it becomes widely used as global planarization techniques. There are some influence factors for CMP processing quality, and abrasive in the slurry is one of the key ones. In order to improve the removal rate and surface quality of sapphire substrate, a new-type MgO doped colloidal silica abrasive was studied Based on the basic principle of chemical thermodynamics, the HSC software was used to analyze the tendency of reactions between MgO doped colloidal silica abrasive and sapphire and between H2O and sapphire to generate solid solutions, compounds and hydrates on the sapphire surface. From the CMP experiment results of a-, r- and c-plane sapphire, it indicated that higher material removal rate (MRR) and lower surface roughness (Sq) were obtained with the slurry containing MgO doped colloidal SiO2 abrasive instead of containing pure SiO2 abrasive under the same conditions. In addition, the action mechanism of MgO doped colloidal SiO2 abrasive on sapphire substrate CMP was studied. From the analyzing result of X-ray photoelectron spectroscopy (XPS), it deduced solid-chemical reaction between sapphire surface and MgO doped colloidal silica abrasive was occurred and Al2Si2O7·2H2O, MgAl2O4 and Al2SiO5 were generated, which can promote chemical effects during CMP and lead to the increase of MRR. Such results have certain guiding significance to practical production.

Research on R-Plane Sapphire Substrate CMP Removal Rate Based on a New-Type Alkaline Slurry

Chemical mechanical polishing (CMP) is widely used as one of the most effective methods to achieve atomic-scale smooth surface. In order to investigate the mechanism of sapphire (α-Al2O3) substrate CMP, the X-ray photo-emission spectroscopy (XPS) was applied to analyze the chemical state of elements. From XPS analysis it was demonstrated that AlO(OH) whose hardness was lower than α-Al2O3, existed only in c-plane sapphire after c- and r-plane polishing, so it's difficult to get high removal rate for r-plane CMP. But GaN epitaxial film grown on the r-plane sapphire substrate is semi-polar, and the luminous efficiency of the thin film is significantly improved. In order to improve r-plane sapphire substrate processing efficiency and accuracy, effects of pH regulator, KNO3 concentration and surfactant concentration on r-plane sapphire CMP were studied. Higher removal rate of r-plane was obtained when KNO3 concentration was 0.1 wt%, which was attributed to the particle size increase and new chemical reaction. But the removal rate decreased slightly due to the broadening of particle size distribution scope at higher ionic strengths. Anionic surfactant could improve removal rate and surface quality due to its good dispersion and stability to prevent nano-SiO2 sol agglomeration. For r-plane sapphire, removal rate and surface roughness Sq can reach 1.43 um/h and 0.173 nm respectively, which provides guiding significance for the development of industrial sapphire ultra precise processing.

Effect of a pH Regulator on Sapphire Substrate CMP

Chemical mechanical polishing (CMP) is one of the most important methods for solid surface ultra-precision machining, and the pH value of slurry is one of the key factors influencing the material removal rate and surface roughness during CMP process. The macromolecular chelating agent and KOH were mixed as a novel pH regulator in this study. The influence of the novel pH regulator on c-plane and r-plane sapphire material removal rate and surface roughness were also investigated. As the mixed ratio of macromolecular chelating agent and KOH is 1:20 and 1:10 for c-plane and r-plane sapphire respectively with the pH value of 10, the higher removal rate and lower surface roughness were gotten. Due to anisotropic atomic structure and hydrate layer formed on c-plane surface the material removal rates were 3.23 μm/h and 0.607 μm/h for c-plane and r-plane sapphire respectively, and the surface roughness were 0.226 nm and 0.309 nm. Through observing the change of pH value, the mean particle size and zeta potential with aging time, it was found the slurry with a novel pH regulator has a better stability.

Effects of non-spherical colloidal silica slurry on Al-NiP hard disk substrate CMP application

Spherical and non-spherical colloidal silica size and shape were characterized and its effects on aluminum alloy nickel plated (Al-NiP) hard disk substrate during chemical mechanical polishing (CMP) was investigated. Non-spherical colloidal silica slurry shows significantly higher material removal rate (MRR) with higher coefficient of friction (CoF) when compared to spherical colloidal silica of similar size. CMP evaluations on non-spherical colloidal silica slurry particle size distribution (PSD) reveal that MRR can be further increased by using wider PSD. Conventional slurry for Al-NiP hard disk substrates which use alumina–silica composite slurry induces embedded alumina thermal asperities (TA) defects which can cause reliability failure at product level. CMP comparison between conventional alumina–silica slurry and non-spherical colloidal silica slurry shows substrates polished by using non-spherical colloidal silica slurry have no embedded TA defects, lower surface roughness and lower surface defects.

Probing the Film Formation Mechanisms at the Slurry/Substrate Interface Relevant to the Chemical Mechanical Planarization Process

Chemical Mechanical polishing (CMP) has emerged as a critical technology for achieving global planarization of substrates used in advanced technologies such as integrated circuits and data storage media. CMP has been described as a kinetic/thermodynamic balance between the formation of a chemically modified layer and its subsequent abrasion via nanoparticles. While the nanoparticle in the slurry plays a key role it has been proposed that the chemically modified surface layer is the key activation barrier to achieving desired removal and surface quality. Therefore it is necessary to optimize and balance the rates of chemical modification and mechanical abrasion in the system, which is dependent on the nature of the complexing/passivation chemistry in the slurry. This presentation will provide insight into the key reaction mechanisms that occur at the slurry/substrate interface relevant to integrated circuit (copper) and data storage substrate (nickel phosphorous) CMP processes. This worked explored the use of electrochemical techniques (static/dynamic open circuit potential (OCP) and Tafel analysis) to probe the impact of organic additives on the surface redox and film forming mechanisms. More specifically, through monitoring the OCP (under both abrasive and non-abrasive conditions) versus time the film removal rate and subsequent passivation film formation kinetics can be determined as a function of slurry additives (complexing agents). These results can be correlated to macroscopic performance metrics such as static/dynamic etch rates and overall polishing rates. Additionally, the surface quality will be measured using atomic force microscopy (AFM) and a correlation between surface roughness and the film formation kinetics will be presented.

A Chemism Analysis of Alkali in the Chemical Mechnical Polishing Process of SiC Substrate

In this study, according to physic-chemical characteristic of the SiC crystals, we analyzed and researched the role of pH modifier in SiC crystal substrate chemical mechanical polishing and the surface after polishing. We used different polish agents which was made up with inorganic and organic bases to experiment, and then analyzed the results. The parameters of the polishing specimen, such as the removal rate of material, surface scanning and the roughness, were analyzed and used to determine the different pH modifiers played different roles in the stability of polish agents and surface quality of the specimen.

Preparation of porous alumina abrasives and their chemical mechanical polishing behavior

Porous alumina abrasives with different pore sizes were prepared using hydrothermal synthesis method by different hydrothermal temperatures. The pore structure, pore size and pore volume of the products were characterized by transmission electron microscopy and nitrogen adsorption desorption isotherm measurement. The chemical mechanical polishing (CMP) performances of porous alumina abrasives in hard disk substrate CMP were investigated. The results show that, the polished surface average roughness (Ra) decreases when the pore diameter of porous alumina abrasive increases. By comparison with solid alumina abrasive, the prepared porous alumina abrasives give lower Ra, and the porous alumina abrasive with 8.61nm pore diameter has higher material removal rate under the same polishing conditions.

Study on Lubricating Behavior in Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the metal and hard-brittle crystal substrate manufacturing process. In this paper, the distinguish method of lubricating behavior in CMP had been analyzed in theory firstly. Then, the tests of CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on hard-brittle crystal substrate surface constantly. The contact form between the workpiece and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in hard-brittle crystal substrate CMP.

Investigation on Slurry Flow and Temperature in Polishing Process of Quartz Glass Substrate

A fluorescent agent was used instead of slurry to visualize the flow of slurry, the polishing liquid solution supplied in Chemical Mechanical Polishing (CMP). Under ultraviolet irradiation, the fluorescent agent emits light, which performs the flow of the slurry under the quartz glass, which is applied as a photomask substrate in Flat-Panel Display (FPD) manufacturing. The emitted light was observed with a digital camera. Compared to a round shape of quartz glass substrate, a large amount of fluorescent agent supplied was taken away by the straight edges of the quadrilateral geometry of the substrate and moved to the outer edge of a polishing pad placed on a platen. The fluorescent agent that was taken away by the quadrilateral geometry also remained as several uneven spiral patterns on the polishing pad when the revolution speeds both of the quadrilateral substrate and the platen, which are practically set at same or almost revolution speed, were not sufficient. Next, when the quadrilateral substrate rotated at high revolution speed (60 min-1), the fluorescent agent flowed most evenly and spread throughout the entire substrate area in the shortest time. Finally, a combination of thermocouples and a wireless signal transmission system is introduced to investigate the temperature in glass substrate CMP process.

Preparation of Silica-Based Alkaline Slurry and its Application on Chemical Mechanical Polishing of Hard Disk Substrates

Chemical mechanical polishing (CMP) is the effective technology which obtains high accuracy surface of hard disk substrate with nickel-phosphorus (Ni-P) coating. The slurry is significant factor in hard disk substrate CMP. Colloidal silica-based alkaline slurry was prepared based on negative pressure vortex method. The effects of slurry parameters such as abrasive concentration, organic alkali concentration and oxidant concentration on material removal rate and surface characteristics were investigated. The experimental result indicated that the abrasive concentration was 20wt%, the slurry pH value was 11.2, the oxidant concentration was 15ml/L, improved surface roughness and polishing efficiency of hard disk substrates, a smooth surface was obtained and micro scratches could hardly be observed.

Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.

Polishing properties of porous silica abrasive on hard disk substrate CMP

Chemical mechanical polishing (CMP) is the only technology to provide global planarisation of topography with a low post-planarisation slope. Abrasive is one of the key influencing factors on the surface quality during the CMP. Traditional silica abrasive is easy to cause polishing scratches since it is compact solid particle. In this work the polishing properties of porous silica abrasive in hard disk substrate CMP were investigated. The results show that the polishing down force and rotating speed have a strong influence on the material removal rate and average surface roughness of the hard disk substrate. After polishing with the slurry containing the porous silica abrasive, a smooth hard disk substrate surface was obtained.

Preparation and Polishing Properties of Spherical Porous Silica Abrasive

Problem statement: Abrasive is one of key influencing factors on the polished surface quality in Chemical Mechanical Polishing (CMP). Solid abrasives in CMP slurries are easy to cause polishing scratches. It is well known that reducing the hardness of abrasives would improve the polished surface quality. Therefore, the change in structure or shape of the abrasives means a change in polished surface quality. The aim of this research paper is to find the differences of CMP performances on hard disk between solid silica abrasives and porous silica abrasives. Approach: A kind of spherical porous silica abrasive was prepared and its CMP performances on hard disk had been investigated. The influences of polishing parameters including polishing time, down force and rotation speed on Material Removal Rate (MRR) and average roughness (Ra) were studied in hard disk substrate CMP with these prepared spherical porous SBA-15 abrasives and solid silica abrasives. Results: After polished in slurry containing solid SiO2, the surface became smooth and Ra decreased from 8.234-1.159 nm. However some small scratches still existed there. When polished with slurry containing spherical porous SBA-15 under the same polishing conditions, the surface became smoother, the scratches could hardly be observed and Ra decreased from 8.409-0.539 nm. Conclusion: Compared with solid silica abrasive, the prepared spherical porous silica abrasive has better hard disk substrates CMP performance under the same polishing conditions.

Three steps chemical mechanical polishing technology of digital compact disc glass substrate

In order to get ultra-smooth glass substrate of digital compact disc(CD),2μm and 0.3μm cerium dioxide slurries as well as 50 nm silica slurry are prepared respectively,and three steps chemical-mechanical polishing(CMP)of sodium-calcium glass substrate in the three slurries has been studied.Results show that during the first step polishing with 2μm cerium di- oxide slurry,a high material removal rate is reached and the average roughness Ra value of the polished surfaces can be decreased from previous 537.9 nm to 1.63 nm.In the second step CMP with 0.3μm cerium dioxide slurry,the R_a value can be decreased to 0.73 nm.By using 50 nm silica slurry in the final CMP,the R_a value of the glass substrate surfaces can be further reduced to 0.44 nm,which is the lowest value reported to date for CD glass substrate polishing.Atom force micros- copy(AFM)analysis shows that the polished surfaces are ul- tra-smooth without micro-defects.Based on the analyses of the mechanical and chemical effects during the glass substrate CMP,the CMP mechanism is deduced preliminarily.