Polishing Pad Research Articles

In situ monitoring and controlling surface shape of the polishing pad in continuous polishing

High-power laser devices have stringent requirements for the surface accuracy of optical elements. Continuous polishing is an effective technique for polishing high-precision optical elements. To overcome the problem of poor real-time capability and low accuracy in traditional surface shape monitoring and controlling methods used in continuous polishing, an online monitoring device is developed to monitor the surface shape of the polishing pad. The experimental results of the online measurement are highly consistent with the offline results obtained using an interferometer. The correctness and feasibility of the online monitoring scheme are well validated. Based on the online monitoring device for the surface shape of the polishing pad, we propose a method of automatic control for the surface shape of the polishing pad. This method maintains the flatness of the polishing pad to 0.05λ (λ = 632.8 nm), peak to valley, as measured on a 100-mm monitoring element through computer control.

Development of Non-foaming Polishing Pads Using Polyamide-based Epoxy Resin

Development of Non-foaming Polishing Pads Using Polyamide-based Epoxy Resin

Development of Particle-containing Epoxy-resin Polishing Pads

The process of polishing glassware is critically important in the production of flat-panel displays, lenses and cover glass. This study focused on the development of a new particle-containing epoxy-resin polishing pad. The addition of polymer particles to an epoxy-resin polishing pad improves the polishing performance by retaining and increasing the invasive ability of the abrasives. The fine surface asperity of the particle-containing polishing pad is improved as the polishing process advances since the wear rate between the embedded polymer particles and the epoxy-resin matrix differ. Polymer particles embedded within the epoxy-resin matrix fixate abrasives on the polishing pad. The new particle-containing polishing pad has a greater material removal rate as compared to the traditional polishing pad. The hydrophilicity, hardness, and size of the polymer particles employed within a particle-containing epoxy-resin polishing pad can significantly improve polishing performance and efficiency over that typically experienced with traditional polishing approaches.

Comprehensive study to evaluate the lifespan of flexible polishing pads by 3D surface characterization technique

The topography of a polishing pad plays a significant role to maintain the effectiveness of the finishing process and to preserve the work surface integrity. 3D surface characterization is an efficient tool to reveal the micro-geometry of the pad. A sequential finishing operation of WC-Co coating is performed by shape adaptive grinding (SAG), and chemical assisted SAG (CA-SAG) using zirconia–alumina polishing pads with mean particle sizes of 125 µm, 80 µm and 60 µm. Coherence correlation interferometry (CCI) is employed to investigate the topography of the polishing pads and to assess the microscopic wear and the lifespan of the pads. A new criterion for selecting the optimum sampling interval is proposed to ascertain the peak density precisely. A comprehensive study is undertaken to quantify and analyse the abrasive wear of the polishing pads after both SAG and CA-SAG by employing 13 advanced 3D surface texture parameters. The density and sharpness of the abrasive particles, the coarseness of the polishing pad, the area and volume of the individual motifs and the bearing and fluid retention properties of the pads are characterized. In the case of CA-SAG, the chemical reagent attacks the backing material of the pads and reduces its effective lifespan as compared to SAG.

Analysis of material removal rate and stability in lap-magnetorheological finishing

A magnetorheological finishing (MRF) method, which is named lap-MRF, is proposed in this paper. A lap, instead of a large polishing wheel, is used to expand the polishing area, which significantly improves the material removal rate. Lap-MRF uses the flexible magnetorheological fluid (MR fluid) as a polishing pad to match the surface well. Moreover, the MR fluid in the polishing zone can be renewed continuously to ensure the stability of the material removal rate. The principle of Lap-MRF and the theoretical model of the material removal rate are presented. The effects of the spindle speed and the working gap distance on the polishing normal pressure and the material removal rate are analyzed. Finally, a series of polishing experiments and simulations are carried out. The volume removal rate for K9 is up to 0.76 mm3 / min and the comprehensive material removal stability is 6.7%. Using MATLAB simulation process method, the convergence efficiency for a ϕ1000 mm mirror is 98.5%. The results verify the validity of the proposed method.

Electrochemical Characterization of Ruthenium Using Potassium Bromate As Oxidizer for Titania Based CMP Slurry

Introduction: Chemical mechanical planarization (CMP) uses chemical and mechanical action for removing the surface topography. It is widely used in integrated chip fabication. Due to the miniaturization of semiconductor chips, focus on the use of ruthenium (Ru) as barrier layer has increased as it allows direct electrodeposition of copper (Cu). The present work involved study of different parameters such as concentration and pH on Ru removal rate (RR) using a slurry consisting of titania as abrasive and potassium bromate (KBrO3) as oxidizer. Electrochemical characterization of Ru was carried out in KBrO3 solutions to investigate the dissolution phenomena. The corrosion current (I corr) values of Ru were obtained from the extrapolation of Tafel curves. An electrical equivalent circuit (EEC) was proposed to model the electrochemical impedance spectroscopy (EIS) results. Methods: A bench top polisher was used to perform the CMP experiments. A pressure of 3.5 psi was applied to the Ru disc and the platen speed was maintained at 150 rpm for all the CMP runs. The specimen holder speed was kept at 250 rpm. For studying the effect of pH on Ru RR, 1 wt% concentration of oxidizer and abrasive was used. For studies on the effect of concentration of abrasives, 1 wt% concentration of oxidizer was used while maintaining the pH at 2. Similarly, the effect of oxidizer concentation was carried out at pH 2, maintaining abrasive concentration at 1 wt%. Slurry pH was adjusted using HNO3 or KOH. Electrochemical studies were performed to understand the chemical dissolution of Ru. All the electrochemical runs were conducted using 1 wt% oxidizer concentration. Three electrode configuration with platinum counter and Ag/AgCl reference electrodes were used for the electrochemical studies. A scan rate of 1 mV/s was used for potentiodynamic polarization studies and the EIS runs were performed at OCP between the frequency range 100 kHz and 0.01 Hz. Results: The effect of pH on Ru RR reveals that the Ru RR is maximum at pH 2, decreases at pH 3 and increases till pH 7 and decreases gradually in the alkaline region. The effect of abrasive loading on Ru RR in presence of 1 wt% KBrO3 at pH 2 shows that the removal rate of Ru increases significantly till abrasive loading of 3 wt% and saturates after that. The effect of oxidizer concentration on Ru RR in presence of 1 wt% titania at pH 2 shows that the Ru RR increases with increase in oxidizer concentration of the slurry due to the formation of oxide layer on the surface which is removed with the help of polishing pad and/or the abrasive particles. The potentiodynamic polarization curves of Ru (as shown in Fig. 1) at various pH values in presence of 1 wt% KBrO3 were studied. I corr value of ruthenium in KBrO3 solution at various pH follows a trend similar to the CMP RR. Fig. 1 shows the Nyquist plot of Ru at various pH values in presence of 1 wt% KBrO3. The Nyquist plots of Ru exhibits capacitive loop at high frequency with depressed semicircle. Discussion: It has been reported that the isoelectric point of ruthenium oxide ranges from 4 to 6 and titanium (IV) oxide ranges from 5 to 6 [1-3]. Therefore, Ru and titania particles act as positively charged at low pH [4]. KBrO3 dissociates to form K+ and BrO3 - ions. Bromate ions surround the titania particles. Thus the particle charge is negative in the presence of KBrO3. Due to the opposite charge between the abrasive particle and the ruthenium surface, there exists a strong electrostatic interaction, which causes higher removal rate at lower pH.

Effect of Pad Type on Passivation Film Formation Relevant to Copper Chemical Mechanical Planarization

Copper (Cu) chemical mechanical planarization (CMP) is an extremely critical step in the manufacturing of ultra-large-scale integrated (ULSI) semiconductor devices. By optimizing the synergistic relationship between a chemical dispersion, referred to as a slurry, and mechanical parameters, global planarization is able to be achieved utilizing CMP. Traditional slurries for Cu CMP promote Cu oxidation, promoting the creation of a passivation film which readily able to be removed by the same mechanical process. However, the efficiency of film removability is strongly correlated to the molecular structure of the passivating agent and also the composition of the polyurethane polishing pad. This work aims to mechanistically understand the relationship between molecular structure of the passivating agent and the pad type on the modulation of the passivation film formed. The film formation kinetics and characteristics were studied through various electrochemical techniques and surface spectroscopy. Results have indicated that the film is directly correlated to the molecular structure of the passivating agent, and the ease of removing the film is strongly contingent on the type of polyurethane pad implemented in the CMP polishing process.

Study on high efficient sapphire wafer processing by coupling SG-mechanical polishing and GLA-CMP

Abstract A novel surface finish process sequence has been developed with a sequential process employing sol-gel (SG) semi-fixed abrasive polishing tool and gas-liquid assisted chemical mechanical polishing (GLA-CMP) instead of general copper-resin lap or plate (CP) and chemical mechanical polishing (CMP) to enhance the surface finishing efficiency for sapphire wafer. The surface and subsurface quality of sapphire wafer after the SG and GLA-CMP process have been compared with those by CP and CMP, respectively. Results show that the SG polishing can offer a better surface quality in terms of both surface roughness and sub-surface damage for the next fine polishing step. Based on the contact mechanics models, yielding effects of the SG polishing pad are found to be effective to scratch mitigation. This trend is consistent with experimental results. Furthermore, oxygen is applied as catalyst to improve the removal material rate (MRR) of sapphire by GLA-CMP. It is found that oxygen concentration can improve MRR of sapphire polishing. Among four combinations of CP, SG, CMP, and GLA-CMP, the machining by coupling SG and GLA-CMP shows the maximum MRR approximately as high as 77.6 nm/min, more than 10.23% larger than that of CP-machined wafer and traditional CMP. Ultra-smooth wafer surface with damage-free can be achieved by this new process sequence and the sapphire wafer with qualified surface can be obtained within 50 min by GLA-CMP, which is 90 min shorter than the original 140 min polished by the conventional CMP method. Compared to the conventional surface finish process sequence, the proposed sequence shows superior processing efficiency and quality for sapphire wafers.

Characteristics and Mechanism of Catalyst-Referred Etching Method: Application to 4H-SiC

A novel abrasive-free planarization method named catalyst-referred etching (CARE) was developed. A polishing pad is coated with a catalytic material to promote chemical etching of the work substrate. During processing, the topmost areas of the work substrate, which are in contact with the catalyst surface, are selectively etched off. Atomically highly ordered surfaces are obtained for many types of work substrates. In this paper, the removal characteristics and mechanism of CARE for single crystalline 4H-SiC are reviewed.

Surface damage of single-crystal diamond (100) processed based on a sol-gel polishing tool

A semi-fixed abrasive polishing tool fabricated by sol-gel (SG) technique used diamond abrasives for mechanical polishing (MP), diamond and SiC abrasives for mechanical chemical polishing (MCP), and diamond abrasives and chemical reagent of KNO3 for chemical mechanical polishing (CMP). Then, the surface damage of 100-oriented single-crystal diamond (SCD) was investigated by comparing three different polishing methods. The surface quality of SCD specimen was observed with an optical profiler and scanning electron microscopy, and subsurface damage was detected by transmission electron microscopy (TEM) after processing. Moreover, products and wear debris of diamond after MCP were investigated using Raman spectroscopy and high-resolution TEM. The results show that surface damage is reduced in SCD polished by the SG polishing pad. Subsurface damage with the nanoscale ranges from 2.0 nm to 3.3 nm. No significant difference in subsurface damage was observed between the hard and soft directions when the SG polishing pad was used. In addition, the polishing rate of MCP was 25.5 nm/min, which was higher than that of other approaches owing to the combination of mechanical force and chemical reaction. Subsurface damage in the soft direction induced by MCP includes amorphization, dislocation, and lattice distortion, which is 3.3 nm deeper than that in the hard direction with thickness of 2.3 nm.

Material removal mechanism of two-dimensional ultrasonic vibration assisted polishing Inconel718 nickel-based alloy

In this paper, a two-dimensional ultrasonic-assisted polishing Inconel718 nickel-based alloy has been investigated. This polishing technique combines the functions of ultrasonic machining and conventional mechanical polishing, which improves the material removal rate (MRR) of the Inconel718 nickel-based alloy by nearly two times (from 220 nm/min to 415 nm/min), and the surface roughness and average standard deviation of the roughness values are significantly reduced. The MRR model of two-dimensional ultrasonic-assisted polishing Inconel718 nickel-based alloy was established by analyzing the mechanism of material removal and the movement of abrasive grains, including the polishing pad material and properties, abrasive particle size and ultrasonic vibration frequency and amplitude and other related polishing process parameters. The experimental results show that the MRR prediction model of ultrasonic-assisted polishing material has a good consistency with the experimental results. The model can be used to predict and guide the two-dimensional ultrasonic-assisted polishing process of Inconel718.

A novel Lap-MRF method for large aperture mirrors

A novel magnetorheological finishing (MRF) method, which is named Lap-MRF, is proposed in this paper. The magnetorheological fluid (MR fluid) in the polishing zones can be renewed continuously so that the determinacy is ensured. A lap, instead of a large polishing wheel, is used to expand the polishing area, which improves the material removal rate largely. Lap-MRF uses flexible MR fluid as polishing pad to match the surface well. Moreover, the polishing pad executes planetary motion so as to obtain smooth surface. In this paper, the principle of Lap-MRF and the theoretical model of material removal rate are presented. Using the finite element analysis method, the permanent magnet unit is simulated and a multi-parameter optimization is conducted to improve the performance of Lap-MRF. Finally, a series of polishing experiments and simulation process are carried out. For K9 sample, the volume removal rate is up to 0.76 mm3/min and its relative change rate is less than 5.5%. For silicon modification layer sample, the surface roughness is improved to 0.788 nm RMS (root mean square) from 1.610 nm RMS. There is no deep pit and the polishing ripple is not apparent on the surface. For Φ1000 mm flat mirror, the convergence efficiency of simulation process is up to 97.2%. These results verify the validity of the proposed method, which makes Lap-MRF to be a promising finishing technology for large aperture mirrors.

Monitoring the Physicochemical Degradation of Polishing Pad Soaked in Hydrogen Peroxide during Chemical Mechanical Polishing

The porous polyurethane polishing pads are extensively used in the chemical mechanical polishing. The pad property is very important and influences the polishing effectiveness and the wafer surface quality. Hence, in the present work, the physicochemical degradation of unused polyurethane polishing pads during metal chemical mechanical polishing (CMP) in the presence of hydrogen peroxide (H2O2) was studied. It was found that the polishing pads were reacted chemically with H2O2 resulting in degradation of the polymer chain network of polishing pad and reduction in the pad elastic modulus. Pad polymer network chain scission was observed during FT-IR evaluation confirming the degradation of the pad. CMP experiments with the H2O2 soaked pads resulted in change in material removal rate (MRR) and the within-wafer non-uniformity (WIWNU). Further Pad elastic modulus estimated by colorimetric evaluation and CIE Lab color coordinates.

Study on Pad Performance Deterioration in Chemical Mechanical Polishing (CMP) of Fused Silica

Polishing pad is considered one of the most important factors in chemical mechanical polishing (CMP) toward the material surface fabrication. Here, based on the ultra-smooth surface polishing of fused silica, the variation and deterioration of the pad performance are studied. The variations of the removal rate and polished surface quality of fused silica with the used time of the pad are investigated. Meanwhile, the variations of the pad performance during CMP process are analyzed. Scanning electronic microscope (SEM) is used to observe the physical morphology change of the pad. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) is used to evaluate the chemical change of the pad. And the surface roughness and hardness of the new and the used pad are characterized. The results indicate that with the prolonging of the usage time of the pad, the thickness of the pad becomes reduced and the surface of the pad becomes roughened, resulting in the decrease of removal rate of fused silica and the roughening of the polished surface. The mechanism of the pad performance deterioration is discussed. In addition, the effect of the downward pressure in CMP on the pad performance deterioration is presented.

Development of new polishing pad with a semispherical shape formed by materials with different wear rates

Development of new polishing pad with a semispherical shape formed by materials with different wear rates

Development of epoxy resin polishing pads with the addition of polymer particles

Development of epoxy resin polishing pads with the addition of polymer particles

Ultrasonic vibration-assisted chemical mechanical polishing of sapphire substrate using suede-type polishing pad

Ultrasonic vibration-assisted chemical mechanical polishing of sapphire substrate using suede-type polishing pad

An Oxide Chemical Mechanical Planarization Model for HKMG Structures

In order to predict the surface topography, a chip-scale oxide chemical mechanical planarization (CMP) model is proposed in poly opening polishing processing of high-k metal gate (HKMG) structures. A geometrical chemical vapor deposition model is first constructed to describe the influence of design pattern effects on the initial surface profiles of dielectric oxides. Based on contact mechanics, the global pressure distribution is then computed to incorporate the long-range features of design structures and polishing pad deformation. The global pressure is further combined with local pattern effects to construct a feature-scale material removal rate model, which can be utilized for surface topography simulation of design chips. The predicted results of the proposed CMP model are consistent with the experimental data collected from the test patterns of HKMG CMP process. Consequently, the oxide CMP model has good potentials of predicting the surface planarity of polishing wafers and optimizing some design rules for HKMG design layouts.

Experimental Investigations on the Polishing Forces Characteristics of Dynamic Magnetic Field Magnetorheological Effect Polishing Pad

Experimental Investigations on the Polishing Forces Characteristics of Dynamic Magnetic Field Magnetorheological Effect Polishing Pad

研磨パッド・アスペリティ内のミクロなスラリー循環流れ

Chemical mechanical polishing (CMP) is used in a wide range of processes in semiconductor production. However, the polishing mechanism of CMP is not completely understood. The behavior of the abrasive particles and chemical species in the slurry is believed to play a critical role in the polishing mechanism. Therefore, in this study, we observed the slurry flow occurring in the polishing pad asperities experimentally. Because in situ observation of the slurry flow is exceptionally difficult, an enlarged visualization model of the pad asperities was made, based on the scaling laws of fluid dynamics. A refractive index matching technique and a particle suspension method were applied to visualize the scaled-up slurry flow. As a result, the circulation flows in the vertical direction to the wafer surface have been observed at the openings of the pad pores, and at the valleys of the undulations formed by the pad conditioning. The size of the biggest circulation flow observed in this study is approximately 200 μm. This result suggests that, similar to the pad pores, the valleys of undulations of the pad have the function of aiding the slurry transport to the entire wafer surface.