Zhu Ji Jin

Electroforming of Copper/ZrB2 Composites Coatings and Its Performance as Electro-Discharge Machining Electrodes

Copper electroforming, together with rapid prototyping (RP) technology, provides a method for manufacturing EDM electrodes rapidly. However, the use of conventional electroformed copper electrodes is restricted because of the high electrode wear rate in EDM processes. This paper presents a study on the electroforming technique of copper/zirconium diboride (ZrB2) composite coating and its performance as an EDM electrode. Cu-ZrB2 composite coating is electroformed from a copper nitrate bath containing micro-sized ZrB2 particles in such a way that by varying the process parameters, ZrB2 particles approximate to 20 Vol.% are incorporated in the coatings. Analyses by optical microscopy and scanning electron microscopy reveal that ZrB2 particles are uniformly dispersed in the copper matrix and the grains of the coating are refined due to the incorporation of ZrB2 particles. The electroformed coatings deposited on copper substrates with approximately 1mm thickness are used as electrodes. EDM experiment shows that performance such as the spark-resistance of the new electrodes is improved compared with that of conventional electroformed copper electrodes because the incorporation of refractory particles in the copper matrix as well as the refinement of the grains of the coating, and the. Cu-ZrB2 composites show good performance in finish machining condition.

Modeling and Analyzing on Nonuniformity of Material Removal in Chemical Mechanical Polishing of Silicon Wafer

Chemical mechanical polishing (CMP) has already become a mainstream technology in global planarization of wafer, but the mechanism of nonuniform material removal has not been revealed. In this paper, the calculation of particle movement tracks on wafer surface was conducted by the motion relationship between the wafer and the polishing pad on a large-sized single head CMP machine. Based on the distribution of particle tracks on wafer surface, the model for the within-wafer-nonuniformity (WIWNU) of material removal was put forward. By the calculation and analysis, the relationship between the motion variables of the CMP machine and the WIWNU of material removal on wafer surface had been derived. This model can be used not only for predicting the WIWNU, but also for providing theoretical guide to the design of CMP equipment, selecting the motion variables of CMP and further understanding the material removal mechanism in wafer CMP.

Investigation on Material Removal Rate in Rotation Grinding for Large-Scale Silicon Wafer

In this paper, the formula of material removal rate (MRR) in wafer rotation grinding process is deduced based on kinematics. The main effect on MRR of the grit size and the process parameters, including the rotational speed of the cup grinding wheel, the down feed rate of the grinding wheel spindle and the rotational speed of the chuck table, is both theoretically and experimentally investigated. The influence on MRR of the cup wheel grinding status, the geometric dimension of the cup-grinding wheel, the rigidity of the grinding machine and the coolant is also analyzed. The investigating results show that, the increase of the grit size and the down feed rate of the cup grinding wheel results in great increase of the MRR; the MRR increases as the rotational speed of the cup wheel increases whereas the MRR reduces and the ground surface becomes bad due to size effect if the rotational speed of the cup wheel is overlarge; in normal grinding, the MRR decreases as the rotational speed of the chuck table increases. The results provide a theoretical basis to improve grinding efficiency, reduce grinding cost and select the proper parameters of grinding process.

Study on Grinding Performance of Soft Abrasive Wheel for Silicon Wafer

With the development of IC manufacturing technology, the machining precision and surface quality of silicon wafer are proposed much higher, but now the planarization techniques of silicon wafer using free abrasive and bonded abrasive have the disadvantage of poor profile accuracy, environmental pollution, deep damage layer, etc. A soft abrasive wheel combining chemical and medical effect was developed in this paper, it could get super smooth, low damage wafer surface by utilizing mechanical friction of abrasives and chemical reaction among abrasives, additives, silicon. A comparison experiment between #3000 soft abrasive wheel and #3000 diamond abrasive wheel was given to study on the grinding performance of soft abrasive wheel. The results showed that: wafer surface roughness ground by soft abrasive wheel was sub-nanometer and its sub-surface damage was only 0.01µm amorphous layer, which were much better than silicon wafer ground by diamond abrasive wheel, but material removal rate and grinding ratio of soft abrasive wheel were lower than diamond wheel. The wafer surface ground by soft abrasive wheel included Ce4+, Ce3+, Si4+, Ca2+ and Si, which indicated that the chemical reaction really occurred during grinding process.

An Experimental Study of the Polishing Process for MgO Single Crystal Substrate

In order to obtain ultra-smooth and damage free substrate surfaces for MgO single-crystal substrate with high polishing efficiency, an experimental investigation based on systemically designed polishing experiments are presented and discussed. Considering the structural characteristics and chemical properties of the MgO single crystal, the experiments use a polishing slurry containing SiO2 abrasives so that the process is performed under a combination of mechanical and chemical actions. The effects of the polishing process parameters, such as polishing pressure, rotational speed of polishing plate, and the flow rate and concentration of the polishing slurry, on the surface roughness and material removal rate (MRR) are analyzed. Finally, a recommendation is made for selecting the appropriate polishing parameters for MgO single crystal substrate, based on which a surface roughness of 0.3nm can be achieved on the MgO substrate in 20min of polishing time.

Study on the Surface and Subsurface Integrity of Ground Monocrystalline Silicon Wafers

Wafer rotation grinding, as an important processing technology, is widely used in manufacturing and back thinning of the silicon wafer. However, the surface/subsurface integrity of the ground wafer, which has important influences on the surface quality and the output of the wafer in subsequent process, is becoming an attention-catching problem. This study is aimed at experimental investigation of the surface/subsurface integrity in wafer rotation grinding. The surface roughness, the subsurface crack configurations, the subsurface damage depth (SSD) and the phase transformations are evaluated by corresponding methods. The results show that the integrity of the ground wafer has a close relationship with the grit size of the grinding wheel. The surface roughness and the SSD increase with increasing of the grit size. The subsurface crack configurations of (100) silicon wafers are complicated. The material removal mechanism is different under different grinding conditions. Ductile grinding is accompanied by the phase transformations of diamond structure silicon (Si-I). The amorphous silicon (α-Si), the Si-XII phase (r8-rhombohedral structure) and the Si-III phase (bc8-body-centered cubic structure) exist on the near surface region of the wafer ground by #600 and #2000 grinding wheels.

Study on Two Kinds of Grinding Wheels for Dynamic Friction Polishing of CVD Diamond Film

This paper investigates two kinds of grinding wheels prepared by the combination of mechanical alloy and hot-press sintering (MA-HPS). Scanning electro microscopy, Optical microscope, Talysurf surface profiler, X-Ray diffraction and Raman spectroscopy were used to characterize two kinds of grinding wheels and identify the removal mechanism. It was found that FeNiCr matrix-TiC (FMT) grinding wheel yielded higher removal rate than TiAl abrasiveless carbophile (TAC) grinding wheel, which conversely owned good polishing quality; diamond was removed by transformation diamond to non-diamond carbons and then removed by mechanically or diffusion to grinding wheel during polishing process with FMT grinding wheel. While TAC grinding wheel polishing CVD diamond film mainly depended on the reaction between diamond carbon and titanium.

The High-Efficient Low-Cost Wheel-Grinding Technology for CVD Diamond Films

CVD diamond films have been used in many high-tech fields with the industrial and scientific developments, while the lagging of the polishing technology for the CVD diamond films has limited their widely applications. This paper presents a high-efficient low-cost wheel-grinding technology for CVD diamond polishing, and the two key techniques of this technology are introduced in detail based on thermo-chemical polishing technology. Furthermore, wheel grinding technology exhibits a promising perspective for the widely application in the diamond films.

An Advanced Support Method of Aircraft Skin Mirror Milling - Fluid Lubricating Support

A new support method used in aircraft skin mirror milling, liquid lubricating support, is proposed in order to solve the problems of scratching aircraft skin surface caused by rolling support or sliding support. The thickness and stiffness of liquid film between skin and support head are obtained with different feed pressure. The effects of thickness and stiffness of liquid film on surface quality and dimensional uniformity of workpiece are analyzed. The surface roughness is better under the condition of liquid film. With better film stiffness, dimensional uniformity is better, and actual axial cutting depth is closer to nominal axial cutting depth.

Friction-Based In Situ Endpoint Detection of Copper CMP Process

Chemical mechanical polishing (CMP) has been extensively used in the integrate circuit (IC) manufacturing industry as a widely accepted global planarization technology, accurate in situ endpoint detection of CMP process can reduce the product variance, significantly improve yield and throughput. A CMP in situ endpoint detection system, which measured the friction and downforce during CMP process using a specially designed three-axis strain gauge force sensor, was developed. The frictional transition from copper (Cu) to tantalum (Ta) barrier as well as Ta barrier to silicon dioxide (SiO2) dielectric was detected during CMP process. The experimental results showed that the change of friction could be detected when the polished material changed. The developed CMP in situ endpoint detection system is feasible for 300 mm and 450 mm copper CMP process.