Papers by Keyword: Silicon Wafer

Abstract: As advancing technologies increase the demand for yield and planarity in integrated circuits, wafers have become larger and their specifications more stringent. Flatness, thickness variation and nanotopography have emerged as important concerns in the wafering process. Double side polishing has been adopted as a solution to these problems. This paper focuses on the material removal characteristics and wafer profile variation during Si double side polishing. A polishing experiment to investigate Si removal characteristics according to process parameters was carried out in a single head rotary polisher equipped with a monitoring system for friction force. It was found that the material removal rate is related to friction energy rate, and the polishing state was transited and divided into three conditions according to pressure. On the basis of the experimental results, the wafer profile variation in double side polishing was modelled and simulated according to pressure. The friction energy was calculated to find the material removal amount across the wafer. With the conversion of calculated friction energy to the material removal amount, wafer profile variation was simulated. As a result, the wafer profile variation and its range were increased with a pressure increase, and originated from the position near the wafer edge.

Abstract: In this paper, we created some microstructures on the surface of silicon by irradiating a silicon wafer for soalr cell with trains of short pulses in the presence of an ambient gas.The laser pulse produced by TEA CO2 laser is high power and shorter than a microsecond in duration. We found that the morphology of the structures is highly dependent on the species of ambient gas and the number of laser pulses used. I note that surfaces covered with these microstructures have striking optical properties: structures absorb approximately 90% of incident light with wavelengths between 250 nm and 0.85μm.The remarkable and potentially useful optical properties of the structures should be beneficial in increasing the efficiency of crystalline silicon soalr cell.

Abstract: In this paper, in order to avoid aggregate of nanodiamonds and reduce the damage problem caused by the hard abrasives during polishing, a kind of ultra-fine nanodiamond abrasive polishing pad was fabricated by means of sol-gel technology. The polishing pad was then used to polish silicon wafer on a nano-polishing machine. The surface morphologies and roughness were measured by both optical microscope and atomic force microscope (AFM). It is found that it was easy to machine the silicon wafer to mirror surface after polishing with the nanodiamond pad. And the surface roughness of the silicon wafer was reduced to 0.402 nm.

Abstract: This paper reports a micro-pulsating heat pipe (micro-PHP) fabricated in a silicon wafer that consists of trapezoidal microchannels with a hydraulic diameter of 394μm for electronic cooling applications. Electronic liquid FC-72 was used as the working fluid. To evaluate the maximum temperature reduction of the evaporator wall, experimental results of the vertical and horizontal-located micro-PHP at filling ratios ranging from 47% to 62% were compared with those measured from the empty micro-PHP (0% filling ratio). Results show that incorporating a micro-PHP as an integral part of silicon wafer could significantly decrease the maximum wafer temperatures and reduce the intensity of localized hot spots. At a power input of 6.0W, reductions in the evaporator wall temperature of about 32.3°C and 24.4°Cwere obtained for the micro-PHP at vertical and horizontal orientations, respectively. In addition, a CCD camera was employed to record the fluid movement inside microchannels and affirmed the existence of nucleation boiling and bulk circulation flow in the micro-PHP.

Abstract: In this study, the design of the mechanism of a recycling system using composite electrochemical and chemical machining for removing the surface layers from silicon wafers of solar cells is studied. The reason for constructing a new engineering technology and developing a clean production approach to perform the removal of surface thin film layers from silicon wafers is to develop a mass production system for recycling defective or discarded silicon wafers of solar cells that can reduce pollution. The goal of the development is to replace the current approach, which uses strong acid and grinding and may cause damage to the physical structure of silicon wafers and cause pollution to the environment, to efficiently meet the requirements of industry for low cost. It can not only perform highly efficient recycling of silicon wafers from discarded solar cells to facilitate the following remelting and crystal pulling process, but can also recycle defective silicon wafers during the fabrication process of solar cells for rework. A small gap width between cathode and workpiece, higher temperature, higher concentration, or higher flow rate of machining fluid corresponds to a higher removal rate for Si3N4 layer and epoxy film. Pulsed direct current can improve the effect of dregs discharge and is advantageous to associate with the fast feed rate of workpiece, but raises the current rating. A higher feed rate of silicon wafers of solar cells combine with enough electric power produces fast machining performance. The electrochemical and chemical machining just needs quite short time to make the Si3N4 layer and epoxy film remove easily and cleanly. An effective and low-cost recycle process for silicon wafers of solar cells is presented.

Abstract: Demand for diminishing edge roll off of workpiece has rapidly increased, especially in polishing silicon wafers and glass disks. However, the conventional polishing technologies cannot meet the demand. To address this problem, the influence of carrier film properties and that of polishing pad properties on the stress distribution near the workpiece edge were investigated using finite element methods. Based on the analytical results, double-layered polishing pads having an extra-fine fiber thin layer and a hard polymer layer were developed. Polishing experiments on silicon wafers and glass plates showed that the developed polishing pads achieved high finishing efficiency and extremely flat surface near the edge.

Abstract: The behavior of the oxygen-containing precipitate in silicon wafer on different stages of the getter formation process is considered from the mechanical point of view. The precipitate is modeled as a spheroidal inclusion undergoing inelastic eigenstrains in an anisotropic silicon matrix. The stress-strain state in the precipitate and matrix is calculated within the framework of the model. An energetic criterion of breaking the spherical shape by the coherent precipitates is obtained and analyzed. Criteria of the formation and onset of motion of the dislocation loops in the vicinity of the precipitate are also proposed. The obtained results are compared with the available experimental data.

Abstract: Experiment on ablation of silicon wafer on different crystallographic facet planes by single laser pulse irradiation was carried out with a femtosecond pulsed laser operating at a wavelength of 780 nm and a pulse width of 160 fs. The quality and morphology of the laser ablated silicon surface were evaluated by atomic force microscopy. The ablation threshold fluences on different crystallographic facet planes were obtained through the relationship between the squared diameter of the craters and pulse energy. The effects of different crystallographic facet planes of silicon wafer on the process of femtosecond laser ablation of silicon wafer were studied.

Abstract: The surface roughness and surface morphology of silicon wafers polished by three different polishing methods were analyzed in this paper. A polishing pad was prepared by means of sol-gel technology as semi-fixed abrasive tool. An electroplated polishing pad was chosen as fixed abrasive tool. And a polishing cloth was chosen as free abrasive tool. The results showed that the surface of silicon wafer polished by the sol-gel polishing pad was superior to the other two. It was easy to get mirror effect with few scratches while the free abrasive and fixed abrasive got lots of scratches on 23silicon wafers. The surface roughness of silicon wafer polished by the sol-gel polishing pad reached 1.41nm measured by atomic force microscope (AFM).

Abstract: Back grinding is the key working procedure in the silicon wafer manufacturing process. Ground silicon wafers ought to have low subsurface damage layer thickness (SSD ) and surface roughness value. It requires that the wheel should have high self-sharpening ability and consistent performance. In this paper, the research on pore-forming agent in order to improve the wheel’s self-sharpening ability of the resin-bond diamond grinding was conducted. The research includes the pore-forming mechanism of various pore-forming agent, the influence of pore-forming agent’s type and the effect on the bond’s strength, the influence of pore-forming agent on the grinding performance of the wheel. Moreover, it examines the improved grinding wheel’s grinding effect by grinding tests.