Papers by Author: Pei Lum Tso

Abstract: In this thesis, an 8-link mechanism was design to simulate a real horse running leg. The 8-link type has been decided first, than the solution plane method has been used to the linkage synthesis. A computer software has been developed to solve the given loop equations. This software can give the profile of the mechanism and the information of the link length and the moving curve of the decided touch-ground point quickly. Several 8-link mechanisms were presented according to the designers choice. The results show that this method as well as software is able to develop complicate 8-link mechanism freely and correctly.

Abstract: The technology of ultrasonic assisted machining has been successfully used in many machining processes recently. Conditioning in the CMP not only can extending the life of the polishing pad but also improve process stability. In this paper we develop a brand new conditioning process with ultrasonic assisted conditioning UAC head for chemical mechanical polishing CMP process. The slurry came from inside the polishing spindle and had an independent cyclic system. As a result, this UAC device can remove polishing debris 4-6 times faster than conventional conditioning process. This conditioning process may even use water instead of slurry to reduce the cost of consumables of CMP. Key word: Chemical mechanical polishing CMP, Ultrasonic assisted conditioning UAC, Polishing Pad

Abstract: The purpose of this paper is to develop a tool radius compensation method for a 5-axis horizontal machine center with a tilting rotary table. The generalized expression is presented first to determine the cutting contact location for any type of milling tools. The spindle orientation solved from a closed form of the inverse kinematics is applied for generating the postprocessor, and a compensating procedure is implemented to verify the offset path.

Abstract: Due to the continual improvement of CMP technologies, and the need for polishing delicate wafers at high speed, graphite impregnated pads (GiP) dressed by brazed organic dia mond disks (BODD) can double the throughput of wafer-pass at the reduced cost of ownership (CoO). The increased polishing rate is due to the act of nano graphite particles that absorb slurry. The nano graphite particles coated with chemical and abrasive can achieve high removal rate without causing scratches on the wafer. In addition, nano graphite particles do not stick to wafer surfaces, so they can be cleaned easily. BODD can uniquely dress GiP to create slurry channels so the pore free pad is not bottlenecked by slurry supply. This paper also demonstrated the low stress polishing by applying ultrasound during the CMP process.

Abstract: Chemical Mechanical Polishing(CMP) is currently the most effective planarization method used in the semiconductor industry. Because of the continuous improvement of the wafer size and line width, the CMP process must be promoted and improved. Many studies have been undertaken to try and achieve both a high material remval rate (MRR) while maintaing a high surface quality of silicon wafer, however up until this point it appears that the two objectives are mutually exclusive. In this paper, an innovative method which integrated ultrasonic vibration assisted machining and CMP (UCMP) has been developed. With the use of ultrasonic vibration, the CMP efficiency and the quality of ploished suface improves considerably as shown in this paper. The basic principle effects of ultrasonic vibration are further illustrated and the experiments had been done to demostrate the proper procedure. The results showed that UCMP achieves a higher material removal rate (MRR) and better surface quality at the same time.

Abstract: Current polishing pads cannot polish a workpiece without using slurry with free abrasive. The new slurry is required to be continually poured into the working area, so more than half of the slurry may be lost from the table without contacting the wafer surface; this leads to economic and environmental problems. In the current work, the fixed abrasive pad was used, where nano-sized diamond abrasives were embedded in the polishing pad; distilled water, rather than slurry, was used. The effect of various fixed abrasive pad designs on polishing characteristics during silicon wafer polishing was investigated. Moreover, the primary function of fixed abrasive was to remove the rough parts of silicon wafer as they were being polished. Consequently, it needed to disperse the nano-sized abrasives into the pad material with high hardness value; this way, working abrasives are not pressed into the pad material. Furthermore, with the use of a pad conditioner, the interior working abrasives were exposed to the pad surface. As a result, the best outcome of using the fixed abrasive pad with a nano-sized diamond was a surface roughness of Ra 0.47 nm.

Abstract: Chemical vapor deposition (CVD) diamond thin films are widely used in modern industries. However, due to the nature of polycrystalline, thin films are required to be polished in the final process to increase its surface quality. Thermal-chemical polishing is known for its less processing time and low cost. In this paper, the experiments are carried out to observe the effect of processing conditions such as temperature, rotational speed, polishing pressure, and substrate material on the surface roughness and on the material removal rate of the chemical vapor deposition diamond (CVDD). At the same time, the processing mechanism for this thermal-chemical polishing is investigated, and a polishing model is built for comparison with the experiment results. The results show that the material removal rate is affected mainly by the diffusing rate in the Fe-C polishing system. By using the model, the approximate value of material removal rate can be calculated according to the polishing temperature.

Abstract: Sintered polycrystalline diamond (PCD) compacts are normally used for cutting tools, drill bits and wire dies. A novel application of PCD has been developed to use its entire surface carved to create different patterns which are triangle or square shape loaded with leveled millers that can shave brittle materials in ductile mode. Due to numerous cutting edges formed on the same level of PCD tools, which can be used to thin the wafer surface to achieve both flatness and smoothness of the industrial requirements. SEM has been used to observe the surface and subsurface of the thinned wafer surface. The critical depth of cut between ductile and brittle cutting mode is close to 2 µm in this thinning operation. The damaged layers of machined surface have been observed and studied in this paper.

Abstract: A mechanical polishing process was used to reduce surface roughness through mechanical fracturing and removal of the substrate’s roughened regions. It was thus necessary to understand the effect of grain size and morphology on the material removal mechanisms of silicon wafers by stepwise polishing using a fixed abrasive pad. A hybrid process combining the optimized silicon polishing recipe for rapid roughness reduction with a micro-sized diamond, and then polishing using a nano-sized diamond to produce a final finished surface, may be the optimum approach. The best result using the hybrid polishing process was the surface roughness (Ra) value of 3.32 nm.

Abstract: The primary consumables in chemical mechanical polishing (CMP) are the polishing pad and the slurry. The polishing pad significantly influences the stability of the polishing process and the cost of consumables (CoC). During the polishing process, a diamond dresser must be frequently employed to remove the debris to prevent accumulation, a process known as pad conditioning. In this paper, we investigated the physical properties of the CMP pad such as compressibility, thickness, and surface roughness. The difference between new and used pads has been studied. Conclusively, conditioning via a diamond dresser will extend pad life and reduce CoC.