Multi-wire Sawing Research Articles

Design and Test of a Rapid Thermal Annealing Furnace for Improving Surface Properties of Silicon Brick in Multi-Wire Sawing Process

Multi-wire sawing process with free abrasive slurry or called multi-wire slurry wire sawing (MW-SWS) process has been popularly adopted in slicing of silicon substrates for solar cell application. However, the chipping or edge cracking of thin thickness as 200 μm of such silicon substrates need to be improved in current mass production. The potential subsurface cracks induced by previous edge grinding or brush polishing of silicon brick may be the main cause. This paper is to develop a rapid thermal annealing (RTA) process for thermal annealing of the surface quality of silicon brick before MR-SWS. In this study, a RTA furnace is designed and used to improve the material property of surface of silicon brick. A quartz crucible is used as heating source with the maximum heated specimen size of 156×156×100 mm (W×H×L). The bulk silicon brick used in this study is selected with a size of 20×10×20 mm (W×H×L) and supplied by the Sino-American Silicon Ltd. (SAS) in Hsinchu, Taiwan. The nitrogen gas is also injected as a protective gas for target heating temperature around 550°C with rapid heating rate of 50°C per second. The micro-Vickers (Akashi MVK-H1) and SEM (JSM-6500F, JOEL) instruments have been used to observe the improvement of rectified material properties of bulk silicon substrate. Experiments of silicon wafers have been first performed for obtaining the recipe of RTA testing and then adjusting for silicon brick testing. Results have been verified by the lower surface hardness and larger crystal grain size after RTA treatment. Furthermore, such treated silicon brick can be further adopted for MW-SWS process to identify the effects of reducing chipping or edge cracking of silicon substrates for solar cell application.

High-Speed Slicing of SiC Ingot by High-Speed Multi Wire Saw

Development of high efficient and high accuracy slice processing technology is required for realizing the high quality and low cost large SiC wafer. Our target of high speed slicing is slicing a 6 inch SiC single crystal ingot in about 9 hours. This slicing speed is about 10 times higher than the loose abrasive slurry sawing and about 4 times higher than the current technology of diamond wire sawing. The slicing speed and the slicing accuracy are in the relationship of trade-off. Therefore, in this research, we have studied the high speed slicing technique of 3 inch and 4 inch SiC single crystal ingot aiming at reduction of sliced wafers SORI. Moreover, we have extracted subjects to scale-up for the high speed slicing of the 6 inch SiC single crystal ingot.

Clay Ceramic Incorporated with Granite Waste Obtained from Diamond Multi-Wire Sawing Technology

The technology of subdividing stone blocks by diamond multi-wire sawing has recently been used by the ornamental stone industrial sector in the state of Espirito Santo, southeast of Brazil. The waste generated by this sawing procedure is iron free and relatively clean as compared to other stone processing operations. In principle, the diamond multi-wire sawn waste could be a viable alternative of incorporation into clays ceramics. The possibility of incorporating up to 40 wt% of a granite waste generated from diamond multi-wire sawing into clay ceramics, fabricated in the neighbor state of Rio de Janeiro, was investigated in this work. The incorporated ceramics were fired at 750, 950 and 1050oC. The apparent density, liner shrinkage and flexural strength were evaluated. The results indicated that the incorporation of the waste improved the ceramic properties, particularly at 1050oC.

Properties of High Temperature Sintered Clay Ceramic Added with Multi-Wire Sawn Granite Waste

Brazil is currently one of the world leading producers and exporters of ornamental stones. The increasing production also generates a proportionally huge amount of wastes. Depending on stones such as granite, these wastes may be composed of relatively high content of alkaline oxides. This is a low melting point flux with advantage for a potential addition of the waste into common clay ceramic. Thus, the present work investigated the addition of a granite waste, generated during the sawing stage using the multi-wire technology, into clayey ceramics fired at 1200oC. This ceramic added with up to 30 wt% waste were evaluated in terms of linear shrinkage, water absorption and flexural strength. It was found that the waste fluxing compounds promoted a reduction in water absorption and increase in strength that are associated with an improved clayey ceramic.

Fracture Analysis and Distribution of Surface Cracks in Multicrystalline Silicon Wafers

Solar silicon wafers are mainly produced through multiwire sawing. The sawing process induces micro cracks on the wafer surface, which are responsible for brittle fracture. Hence, it is important to scrutinize the crack geometries most commonly generated in silicon wafer sawing or handling process and link the surface crack to the fracture of wafers. The fracture of a large number of multicrystalline silicon wafers has been investigated by means of 4-point bending and twisting tests and a failure probability function is presented. By neglecting the material property variation and assuming that one surface crack is dominating the wafer breakage, 3D finite element models with various crack sizes (depth, length, and orientation) have been analyzed to identify the distribution of surface crack geometries by fitting the failure probability from the experiments. With respect to the 63% probability, the existing surface cracks in the wafers studied appear to have depth and length ratios less than 0.042 and 0.19, respectively. Furthermore, it has been shown that the surface cracks with depth in the range from 10 to 20 μm, length up to 10 mm and angles in the range of 30 deg–60 deg, can be considered as the most common crack geometries in wafers we tested. Finally, it has been found that the mechanical strength of the wafers tested parallel to the sawing direction is approximately 15 MPa smaller than those tested perpendicular to the sawing direction.

Loss of wire tension in the wire web during the slurry based multi wire sawing process

In the multi wire sawing process the wire tension is an important parameter for reliability and wafer quality. Changes of wire quality and wire tension from one end of a wire web in a multi wire saw to the other are investigated by several methods: wire tension measurements in the wire saw, wire elongation during an industrial process and material testing of representative wires. Two mechanisms for the loss of wire tension are identified. Firstly, the decrease of wire diameter due to abrasion causes a slow loss of wire tension along the whole wire web. Secondly, plastic deformation of the wire due to random overloading leads to a fast decrease of the wire tension within the first few centimeters of the wire web. Both effects are confirmed by modeling and calculations.

Multi-wire sawing of sapphire crystals with reciprocating motion of electroplated diamond wires

This study examined the multi-wire sawing of C-plane sapphire ingots using diamond wires. Feeding new wire during the reciprocating motion of the wire was found to vary the cutting force, wafer shape, and roughness as a result of the break-in effect. The break-in and wire wear seemed to cause a gradual change in the cutting performance along the ingot position. The cutting force results indicated that an inappropriate supply of wire yielded an unbalanced force between the front and back sides of the ingot, which was caused by a difference in the cutting depth along the ingot. The results showed that controlling the wire consumption resulted in an average flatness of 16μm, with a maximum value of 26μm.

S133012 Siのエッチング援用スライスにおける切断特性の向上([S133]先進砥粒加工技術)

Si wafers for solar cells are fabricated by slicing ingot using mechanical slicing method such as multi-wire sawing. Recently, the slicing method for achieving low kerf loss and thin wafer without generating subsurface damage is strongly required because of the increasing demand of low-cost Si wafers. The etching-assisted slicing method is abrasive free machining process employing chemical etching of Si. The method can achieve a lower kerf loss than the mechanical slicing and damage-free Si surface. In this paper, the removal characteristics of Si ingot are discussed under the different slicing conditions.

Heat Transfer During Multiwire Sawing of Silicon Wafers

During sawing of silicon wafers for the photovoltaic industry, the variations in temperature will influence the process performance and surface quality of the wafers. To investigate the significance of this effect, the temperature field and heat transfer have been studied experimentally and computationally. Among others, it is found that the temperature typically can increase from 30 °C at the inlet to 65 °C at the outlet of the sawing channel. It is also shown that viscous dissipation is by far the most significant heating source in the process.

マルチワイヤソーによる金属間化合物のスライシングに関する研究:Fe-Al系金属間化合物のスライシング特性

マルチワイヤソーによる金属間化合物のスライシングに関する研究:Fe-Al系金属間化合物のスライシング特性

Effect of slurry parameters on material removal rate in multi-wire sawing of silicon wafers: a tribological approach

The main goals for the silicon wafering industry are to improve the surface quality of wafers by reducing the total thickness variation and subsurface defects and to increase the production by reducing the wafer thickness. To attain these goals, it is important to understand the material removal mechanisms involved in the process, which at the moment are little understood and explored. In this study, the effect of slurry parameters on the wear rate and surface roughness of solar grade silicon have been investigated using a tribological approach. A reciprocating pin-on-plate tribometer has been used to simulate the abrasion process occurring in a slurry-based multi-wire silicon saw. The tribological system consisted of silicon, SiC slurry, and stainless steel counterpart. The results showed that a narrow size distribution of the SiC particles in the slurry increases the wear rate and improves the surface quality. The shape factors of the SiC particles in the slurry were also investigated and revealed that particles with lower degree circularity and higher aspect ratio led to lower roughness.

Machining processes for sapphire wafers: a literature review

Sapphire wafers are widely used as the substrates for fabricating GaN light-emitting diodes (LEDs). The quality of LEDs depends directly on the quality of the sapphire wafers. A series of machining processes is required to turn sapphire barstock into wafers with the desired geometry and surface quality. This paper reviews the literature on various machining processes for sapphire wafers: slicing (including outer diameter cut-off grinding, inner diameter cut-off grinding, loose abrasive multi-wire sawing, fixed abrasive slicing, and fixed abrasive multi-wire sawing), flattening (including lapping and grinding), and surface finishing (including mechanical polishing and chemical mechanical polishing). New machining technologies are also introduced.

Design and Simulation of Cutting Optimization and Controller for the Diamond Multi-Wire Sawing System

The purpose of this paper is to investigate the effect of ablation parameters on the ablation characteristics for the fixed diamond multi-wire sawing by using Taguchi method. Meanwhile, using the optimal ablation parameters, we accomplish the cutting dynamic analysis and controller design of the diamond multi-wire sawing system. In this paper, we apply the Chemical Mechanical Polishing (CMP) theorem to derive the ingot profile and cutting rate equations of the diamond multi-wire sawing system. The characteristics discussed in this paper include ingot profile variance, cutting rate. The ablation parameters are tension force, wire velocity, cutting force, width of the kerf. The orthogonal array, signal-to-noise (S/N) ratio and analysis of variance (ANOVA) are employed to analyze the effect of these ablation parameters. In the meantime, we use the optimal ablation parameters to accomplish the controller design of the diamond multi-wire sawing system, include diamond high-speed control of the main roller in the cutting system, cutting rate control and the moving wire bow angle holding.

Improvement in Ovality of Pipeline Steel X80 with Weld Power under Multi-Wire SAW Welding Process

Pipeline steel X80 is a kind of advanced high grade steel and commonly used in long-distance transportation of oil and gas. Ovality of the pipe plays key role in improving its crushing strength. In this paper, a simulation method is proposed to improve the performance of ovality of X80 Pipeline Steel. First, a 3D thermo-mechanical coupled finite element model of the multi-wire SAW welding processes is built using MSC.MARC, upon which parameters of double ellipsoid heat source model is determined. Then, the relationship between weld power and ovality is studied under difference process inputs and a satisfactory weld power is found to decrease the ovality of the pipeline steel. Finally, validation and prediction of deformation and ovality of the pipeline is carried out via plate welding experiments.

Development of Control System in the Multi-wire Saw with Rocking Mechanism

In traditional multi-wire saw have function of manual winding only and the limitations of LED base material uneven force,the rocking mechanism is proposed to substitute for the original fixed structure,automatic winding function is increased,the quality and efficiency of slice and utilization rate of the diamond wire are improved.The mechanical structure and working principle are analysed after machine structure is improved.Two difficult problems which are automatic winding and multi-motor high-speed synchronization are mainly studied.Combining the advantages of fuzzy control and iterative learning control,a fuzzy iterative learning control strategy of Multi-wire saw with rocking mechanism is given.This strategy overcomes the steady-state error of single fuzzy control and get better control effect.The automatic winding error control scheme is designed,when diamond wire do not embed into the slot and around the slot wall,the control scheme can act quickly to make the diamond wire into the slot.Experimental results show that the system automatic winding performs fast speed,high precision and synchronous control performance is good.

Tension Control of Wire-traveling System for Multi-wire Saw

With rapid development of integrate circuit and photovoltaic industry,silicon material processing technology is becoming more and more appreciated.Especially slicing is a key procedure in silicon material processing.Overall structure of wire-traveling system for multi-wire saw is introduced and its working principle is explained.The kinematics equation of tension control structure for pay-off system is established.The reasons for tension fluctuation are analyzed,and corresponding solution is proposed.After a hardware platform of tension control system is built,indirect tension control is carried out through multi-motor synchronization control.A multi-motor synchronization control method is proposed on the basis of adjacent axis error through definition of tracking error and synchronization error.The integral sliding mode surface is defined for designing control torque,and multi-motor synchronization motion is guaranteed,tension fluctuation is reduced and tension stability is ensured.Experimental results show that the proposed tension control method is very effective.This tension control system has the merits of small tension fluctuation range,high-precision control and convenient adjustment.

Design of Multi-Wire Saw Winding System

On the basis of the analysis of winding drive system’s technological requirements of multi-wire cutting system and the characteristics of torque motor, the article proposes a scheme of wrap wheel with torque motor control to overcome the deficiency of the general control motor driven wrap wheel. In determination process of winding system parameter, it provides the selective calculation methods and the control strategy of the torque motor. According to processing materials, we get tension values, and then calculate the output torque, and choose a suitable torque motor and determine the control strategy. Then the design process of winding drive system finishes. Adopting the torque motor as wrap wheel control motor can make wrap device to meet the system requirements. Meanwhile it can simplify the structure of wrap device, and make the cutting-process runs smoothly.

Surface Texture Analysis of Fixed and Free Abrasive Machining of Silicon Substrates for Solar Cells

Multi-wire sawing process has been widely used for wafer slicing of silicon substrates for solar cells. Usually there are two different kinds of wire saw in multi-wire sawing process including free abrasive wire sawing with SiC grits and fixed abrasive wire sawing with diamond wire. For free abrasive wire sawing process, the material removal mechanism can be considered as lapping and the fixed abrasive wire sawing can be considered as grinding. This paper is to investigate the characteristics of the surface texture of silicon substrate fabricated by these two wire sawing process. Experimental results have been observed by white light interferometry and SEM. Some different properties of both processes have compared been with variant characteristics including 2-D and 3-D surface roughness parameters. Results of this paper can be further used to evaluate the feasibility of wire sawing process of silicon substrates for solar cells.

Dynamic Analysis of Wafer Slicing by Using Multi Wire Saw

Multi wire saw is the important basis of integrate circuit, optoelectronic, photovoltaic industry, and it becomes a promising technology for semiconductor wafer production because of its advantage of slicing large ingot into thin wafers with high efficiency and good quality. In the process of moving, the inevitable wiresaw vibration is directly related to the whole process with both benefit and harm. This paper analyses the wire vibration behavior in cutting area, the dynamic model is built by modeling the interaction between the dynamics of wire and hydrodynamic characteristics of slurry flow, available modal analysis provides closed form expressions for the steady state response, obtain the vibration of wire subject to different process parameters on wire saw manufacturing process.

Chip Size Estimation for Effective Blending Ratio of Slurries in Wire Sawing of Silicon Wafers for Solar Cells

Multi-wire sawing process with slurry has been popularly adopted for wafer slicing of silicon substrates for solar cells. This paper is to investigate the chip size estimation for effective blending ratio of mixing slurry of wire sawing. Different combination of slurry has been studied with microscopic pictures of abrasive grits by SEM and distribution of particle size of slurry. The chip size can be estimated by the developed method and then the TTV of sliced substrates is used to evaluate the blending ratio of slurry for cost efficiency of wire sawing. Experimental results indicate that the slurry with certain ratio of reborn grits increases the TTV value of sliced substrates. As the weight percentage of silicon chips is above 6 % for the blending ratio of 50% reborn abrasive grits after sawing run 2, the slurry is suggested to be changed to new slurry for wire sawing. Under this developed rule, the average TTV can be maintained under 0.016 mm for nominal thickness of 200 m silicon substrates. Results of this paper can be used to estimate the feasible blending ratio for maintaining the TTV under the desired specifications of silicon substrates for cost efficiency.