Polishing Pressure Research Articles

Influence of Lapping Parameters on 6H-SiC Crystal Substrate (0001) C Surface Based on Diamond Particle

The SiC crystal substrate has been widely used in the area of microelectronics, photonics and new materials, such as semiconductor lighting, integrated circuits, and so on. In this paper, the influences of the lapping parameters, such as the rotational velocity of the lapping platen and the carrier and the polishing pressure on the material removal rate (MRR) and surface roughness Ra of SiC crystal substrate (0001) C surface based on the diamond particle in lapping. This study results will provide the reference for developing the abrasive paste, optimizing the process parameters and researching the material removal mechanism in lapping of SiC crystal substrate.

Noncontact Figuring of Millimeter-Thick Elliptical Mirror Substrate by Numerically Controlled Local Wet Etching

Aspherical supermirrors are some of the most useful neutron-focusing optics. We aim to develop multiple aspherical supermirror devices using high-precision figured aspherical focusing supermirrors to focus neutron beams with high intensities, because multiple mirrors collect a very large beam divergence. Thin mirrors with millimetre thickness are required to minimize the absorption loss of incident neutron beams since the thickness of a mirror shadows the reflective area of other mirrors. However, it is difficult to fabricate thin mirror substrates with a form accuracy at the sub-micrometre level by conventional machining. Conventional machining deforms a substrate by machining force and spring back after machining causes figure error. Furthermore the deposition of supermirrors deforms the mirror substrate by film stress. Thus, we developed a new process of fabricating a precise millimetre-thick elliptical supermirror. This process consists of non-contact figuring by the numerically controlled local wet etching technique, the minimization of surface roughness without degrading form accuracy by low-pressure polishing with a polishing pressure less than about 7 kPa (1psi), and the ion beam sputter deposition of NiC/Ti multilayers on both sides of the mirror substrate to compensate for film stress. In this paper, we report on the fabrication results of aplano-elliptical mirror substrate with a thickness of 1 mm.

Laboratory evaluation of aggregate polishing as a function of load and velocity. Application to the prediction of damages on skid resistance of road surfaces due to trucks and passenger cars

Skid resistance of road surfaces depends mostly on pavement texture. This texture is usually divided to two components: microtexture and macrotexture. Microtexture refers to the small-scale texture of the road aggregate component while macrotexture refers to the large-scale texture of the road as a whole due to the aggregate particle arrangement. Both components contribute to the generation of friction between tyre and road. However, due to traffic, the first-cited component is continuously polished over the road's life. Maintaining that microtexture depends greatly on the aggregates used in the wearing course, the traffic level and the vehicle velocities. This work tries to quantify the influence of these three parameters on skid resistance degradation. Different specimens fabricated from different types of aggregates are submitted to different polishing pressure levels and velocities. From experimental results, an updated version of an existing model of skid resistance evolution is thereby proposed and validated. As a possible application of the new model, a prediction of damages induced by truck and passenger car traffic on skid resistance is proposed.

Study on Material Removal Rate of CMP 6H-SiC Crystal Substrate (0001) C Surface Based on Abrasive Alumina (Al<sub>2</sub>O<sub>3</sub>)

SiC crystal substrate has been widely used in the area of microelectronics, photonics and new materials, such as semiconductor lighting, integrated circuits, and so on. In this paper, the influences of the polishing slurry composition, such as the pH value, the abrasive size and its concentration, the dispersant and the oxidants, the rotational speed of the polishing platen and the workpiece and the polishing pressure on the material removal rate (MRR) of SiC crystal substrate (0001) C surface based on the alumina abrasive in chemical mechanical polishing (CMP). This study results will provide the reference for developing the slurry, optimizing the process parameters and researching the material removal mechanism in CMP of SiC crystal substrate.

An Analytical Model for Contact Height and Contact Pressure in Chemical Mechanical Polishing (CMP) for Different Pattern Structure

Pattern structures have a great effect on CMP. Predicting the evolution of pattern structures in CMP is important in pattern design and in polishing parameters determination. Determining the contact pressure between the wafer and the pad in CMP and the contact height at which the pad will be in continuous contact with the profile on the wafer is essential for the pattern evolution calculation. An analytical model for calculating the contact pressure and the contact height for different pattern structure is proposed in the paper. The evolutions of pattern structure with different pattern densities are simulated and compared with the experimental data.

Application of Real-Time Cu Thickness Profile Control in Cu CMP

In this paper, a real-time profile control (RTPC) system in Cu CMP is introduced. The system mainly contains two parts: 1). Real-time metal thickness monitoring based on electromagnetic induction of eddy current in conductive metal layer; 2). Real-time new polishing pressure computing and adjusting for desired metal thickness profile. The RTPC system has been applied in bulk Cu removal step of Cu CMP. The result showed that the Cu thickness profile after bulk Cu removal was flatter and its WIW uniformity was improved by greater than 35% while WTW uniformity could be improved by greater than 65%.

Synthesis of Monodispersed CeO<sub>2</sub> Nanoparticles Induced by Microwave Irradiation in Alcohol/Water Mixed Solvent and their Application in CMP

CeO2nanoparticles were synthesized by homogeneous precipitation in mixed solvent of alcohol and deionized water under microwave radiation using Ce(NO3)3•6H2O and HMT as starting materials. The structure and morphology of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and BET-N2. The oxide chemical mechanical polishing (CMP) behavior of the as-papered CeO2abrasives was investigated by atomic force microscope (AFM). The results indicated that the obtained CeO2particles were monodispersed with an average diameter of ca. 10 nm. There was a quite good consistency in the particle sizes from TEM and BET analyses. Polishing tests showed that the as-prepared ceria abrasives exhibited a good oxide CMP performance, which might attribute to the uniform size and shape of the as-prepared CeO2particles. In addition, the polishing pressure had an obvious influence on the surface topography, profilogram and roughness.

Research on the Precession Angle (PA) Adopted in Polishing Large Aspheric Mirror

This paper focus on the relationship between PA and the distribution of polishing pressure, on the basis of the theory that the distribution of polishing pressure is a Modified Gaussian Function and has highly symmetry. Through the simulation experiments, the optimum PA has been determined. And it’s further validated that this optimum PA fits for polishing large aspheric mirror under the conditions with both different internal pressure and bonnet decrement by a series of simulation experiment. It’s also found that PA makes little difference to the size of the contact area and the bonnet decrement has greater influence to the size of the contact area than the internal pressure.

Effects of the Polishing Variables on the Wafer-Pad Interfacial Fluid Pressure in Chemical Mechanical Polishing of 12-Inch Wafer

In this paper, an in-situ interfacial fluid pressure measurement system had been developed for 12″ CMP equipment. Using this system, the interfacial fluid behavior is studied during the polishing process of 12-inch silicon wafer. The effects of the basic polishing variables, including the slurry injection position, the down force, the rotational speed, and the slurry flow rate, on the fluid pressure are investigated systematically. The results suggest that all of these polishing variables have obvious effects on the fluid pressure: the slurry injection position with suitable center distance between the pad and angular distance to the wafer leading edge is good for uniform slurry dispersion and the fluid pressure building; the increasing down force can increase the ratio of the positive pressure and the average fluid pressure significantly; the fluid pressure increases with the rotational speed till a critical speed and then decreases; the fluid pressure increases with the slurry flow rate slightly, the slurry injection position with larger center distance has lower critical speed and has greater dependence on the slurry flow rate due to the lower slurry utilization efficiency caused by larger centrifugal spraying effect.

Buffing performance analysis of viscoelastic polymer with sensor-less polishing pressure control

Buffing performance analysis of viscoelastic polymer with sensor-less polishing pressure control

Effects of Curvature on Material Removal in NC Polishing of Aspheric Part

The objective of this paper is to investigate the effect of radius of curvature on the material removal in the NC polishing of aspheric part. The models of polishing pressure and material removal rates were established based on Preston equation and Hertz theory. The material removal rates was analyzed. Experiments were carried out. Results showed that the material removal rate varies with the variations of the curvature under a constant polishing force and velocity, and the part can not be polished uniformly.

Analysis on Contact Forms of Interface in Wafer CMP Based on Lubricating Behavior

Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. In this paper, the distinguish method of lubricating behavior in wafer CMP had been analyzed in theory firstly. Then, the tests of wafer 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 wafer 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 wafer surface constantly. The contact form between the Wafer and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP. Keywords: Chemical mechanical polishing, material removal mechanism, lubrication form, boundary lubrication.

Wafer back pressure control and optimization in the CMP process

Chemical mechanical polishing (CMP) is the most effective wafer global planarization technology. The CMP polishing head is one of the most important components, and zone back pressure control technology is used to design a new generation of polishing head. The quality of polishing not only depends on slurry, but also depends on the precise control of polishing pressures. During the CMP polishing process, the set pressure of each chamber is usually not the same and the presence of a flexible elastic diaphragm causes coupling effects. Because of the coupling effects, the identification of multi-chambers and pressure controls becomes complicated. To solve the coupling problem, this paper presents a new method of multi-chamber decoupled control, and then system identification and control parameter tuning are carried out based on the method. Finally, experiments of multi-chambers inflated at the same time are performed. The experimental results show that the presented decoupling control method is feasible and correct.

Optimization of the chemical mechanical polishing process for optical silicon substrates

Chemical mechanical polishing (CMP) experiments are performed to study the effects of four key process factors on the flatness and surface finish of the polished optical silicon substrates and on the material removal rate (MRR). The experimental results and analyses reveal that the pad rotational speed and polish pressure have significant effects on the MRR, the interaction of the polish head rotational speed and slurry supply velocity and the interaction of the polish pressure and polish head rotational speed have significant effects on the flatness, and the pad rotational speed has a significant effect on the surface roughness Rt of the optical silicon substrates polished. The optimal combination of the four factors investigated is a polish pressure of 9,800 Pa, a pad rotational speed of 20 rpm, a polish head rotational speed of 20 rpm, and a slurry supply velocity of 100 ml/min. A confirmation CMP experiment has been carried out using the optimal process parameter setting obtained from the design of experiments analyses. The goal to attain optical silicon substrates with nanometric surface roughness and micrometric flatness by an optimized CMP process with a high MRR simultaneously so as to reduce the polishing time to only 15 min from over 8 h has been achieved.

Effects of High Dielectric Constant Abrasives on ECMP

ECMP (Electro-Chemical Mechanical Polishing) presents high removal rate, low polishing pressure and good polished surface because the action of electrochemistry accelerates copper dissolution. It is considered to be a most promising novel Cu planarization process to replace traditional CMP (Chemical Mechanical Polishing). However, the micro asperity heights of coarse surface are often too small compared to the distance between anode and cathode, so the asperities are difficult to be selectively removed. In this paper, high dielectric constant abrasives were used in ECMP to solve this problem. High dielectric constant abrasives can improve the distribution of electric field, amplify the gradient of electric field and enhance the ability of selective removal. Based on the results of experiments, rutile TiO2, as one of high dielectric constant abrasives, is better than SiO2 and anatase TiO2 in ECMP process. The material removal rate of electrolyte containing rutile TiO2 is 0.078mg/min, and the surface roughness is Ra18.2nm.

Experimental Research of the Elastic Abrasive Tool Used for Finishing Mould Surface

A compliant abrasive tool is investigated in this paper. By the polishing experiment of this abrasive tool, the technique of polishing the large mould free-form surface is acquired. The polishing experiments about the elastic abrasive tool are carried out, which indicates that the abrasive tool has the advantages of the high efficiency, the elasticity and compliant performance. The relation of the deflection and polishing force is investigated and it is concluded that they is approximately linearity. The effect of polishing pressure on the surface roughness is researched by experiment. Polishing quality for the edge of abrasive tool was investigated and presented. These experiment results provide significant foundation for planning polishing path and controlling process parameters to achieve good surface roughness and high efficiency in the next research.

A statistical model for material removal prediction in polishing

This paper develops analytically a statistical model for predicting the material removal in mechanical polishing of material surfaces (MS). The model was based on the statistical theory and the abrasive–MS contact mechanisms. The pad-MS and pad-abrasive-MS interactions in polishing were characterised by contact mechanics. Two types of active abrasive particles in the polishing system were considered, i.e., Type I – the particles that can slide and rotate between the pad and MS, and Type II – those embedded in the pad without a rigid body motion. Accordingly, the material removal is considered to be the sum of the contributions from the two types of abrasive interactions. It was found that the mechanical properties and microstructure of the polishing pad and polishing conditions have a significant effect on the material removal rate, such as the porosity and elastic modulus of the pad, polishing pressure, volume concentration of abrasives, particle size, pad asperity radius and pad roughness. It was also found that different types of active particles contribute quite differently to the material removal. When the mean particle radius is small, the material removal is mainly due to the Type II particles, but when the mean particle radius becomes large, the Type I particles remove more materials. The model predictions are well aligned with experimental results available in the literature and can be used for the material removal prediction in chemo-mechanical polishing if a proper treatment of the chemical effect is introduced.

Effect of mechanical anisotropy on material removal rate and surface quality during polishing CdZnTe wafers

The mechanical characters of CdZnTe crystal were investigated by nanoscratch tests, and the effects of mechanical anisotropy on the material removal rate and surface quality were studied by polishing tests. There is a peak of frictional coefficient at the early stage of scratch, and increasing the vertical force will result in the increase of peak value correspondingly. The fluctuation phenomenon of frictional coefficient is generated at high vertical force. The lateral forces show the apparent twofold and threefold symmetries on (110) and (111) planes, respectively. To obtain high surface quality, low polishing pressure and hard direction (〈 \(\bar 1\)10 〉 directions on (110) plane and 〈 11\(\bar 2\) 〉 directions on (111) plane) should be selected, and to achieve high material removal rate, high polishing pressure and soft direction (〈 001 〉 directions on (110) plane and 〈 \(\bar 1\)2\(\bar 1\) 〉 directions on (111) plane) should be selected.

Buffing Performance Analysis of Viscoelastic Polymer with Sensor-Less Polishing Pressure Control

Viscoelastic polymer with high scratch resistance has been developed for coating material of product. Due to some particular characteristics such as viscoelasticity, it is difficult to finish the polymer coated surface. In the present circumstances, its polishing process is carried out by the trained technician and depends on the skill like adjustment of the polishing pressure according to the situation. To realize automation of the polishing, high-precision and highly-responsive force control is required firstly. Typically force control is done with force sensor. However when external sensor is used, there are some problems such as high-cost, reduction of machine stiffness and thermal drift. The thermal drift which is caused by polishing heat prohibits accurate measuring of force. The purpose of this research is to develop the polishing pressure control method without any additional sensor. In addition, applying the control method to buffing machine, buffing performance of viscoelastic polymer is experimentally analyzed.

Tribological Aspects of Chemical Mechanical Polishing Diamond Surfaces

Mechanical energy may initiate and accelerate chemical reaction in chemical mechanical polishing (CMP). To study the effect of mechanical energy on the chemical reactions, a special friction measuring system was designed in this paper. The system could measure the local friction to reduce the error caused by resultant force. The effects of rotational speed, polishing pressure and the concentration of oxidant on friction and material removal rate were investigated. The results showed that the system could accurately measure the friction of small area diamond film in CMP process. The frictional system was in a mixed lubrication state since the value of the friction coefficient located in the range of 0.060~0.065.