Structured wire: From single wire experiments to multi-crystalline silicon wafer mass production

Residual stresses in multi-crystalline silicon photovoltaic wafers due to casting and wire sawing

In the industrial production of multicrystalline silicon (mc-Si) wafers used for solar cells, linear wire-sawing defects are sometimes generated on the surfaces of mc-Si wafers. The presence of such wire-sawing defects makes the mc-Si wafers unsuitable for the fabrication of solar cells. In this work, we first studied the nature of the linear wire-sawing defects on the mc-Si wafers, and then investigated how these wire-sawing defects were generated during the wire-sawing process. It has been found that the linear wire-sawing defects are sawing ridges and ditches on the wafer surfaces, and direct evidence has suggested that they are generated due to the presence of SiC particles embedded within mc-Si. The SiC particles form an obstacle to the movement of the sawing wire during the wire-sawing process, and the sawing wire tends to climb over the SiC obstacle, resulting in the generation of the wire-sawing defects. A model for the generation of the wire-sawing defects has been proposed. This work will be of much practical interest to the commercial mc-Si wafer production communities for solar cells.

The silicon slicing efficiency and quality of silicon wafer seriously affect the cost of solar power generation and the development of photovoltaic energy industry. This paper proposed an improved cooling and lubrication method using a water tank bath for diamond wire sawing. Compared with the traditional jet sawing with array nozzles, it can be found that the surface roughness is better, no matter the average roughness value, the skewness coefficient, or the kurtosis coefficient, especially in high production efficiency processing. Similar conclusions can also be obtained from the comparative analysis of surface profile distribution and SEM micrographs. This is because the bath sawing can make full use of the cooling and lubricating capability of the cutting fluid, so that the diamond wire can achieve better fluid-carrying effect with the same directionality as the sawing direction into the cutting zone. Furthermore, the service life of diamond wire in bath sawing is longer and wire consumption is lower.

Finite element analysis for grinding and lapping of wire-sawn silicon wafers

A practical challenge in slicing of low-cost multi-crystalline silicon (mc-Si) wafers by the fixed abrasive diamond wire sawing process is increased wire consumption due to greater wear of the diamond compared to slicing of the more expensive mono-crystalline silicon (mono-Si) wafers. In this paper, we present the results of scribing of mc-Si and mono-Si materials with two conical tip diamond indenters of the same geometry to understand the possible reasons for increased diamond wear in cutting of multi-crystalline silicon. Specifically, the scribing forces and the diamond indenter wear produced in scribing of the two silicon materials are analyzed. The results show that the forces generated in scribing of mc-Si are higher than in scribing of mono-Si. The higher forces in scribing of mc-Si are consistent with the corresponding higher tip radius of curvature (due to wear) of the diamond indenter compared to the tip radius produced in scribing of mono-Si. Scanning electron microscopy and confocal microscopy of the diamond indenters show that wear is primarily due to physical micro-fracture and blunting of the diamond. Raman spectroscopy shows evidence of stress-induced phase transformation of the diamond and the formation of compressive residual stress in the diamond. Plausible physical reasons, including the role of material inhomogeneity in mc-Si, for the wear of diamond during scribing are given.

Multi-wire saw becomes the dominant method in slicing the hard brittle material into wafers. In this process, saw wire is the critical consumable and the dominant component of the wafer’s slicing cost. However, unreasonable process parameters lead to the fact that the saw wire was not fully used. This enormously increases the wire cost. For this reason, the constant wire wear loss model is presented by taking the free abrasive wire sawing as an example. This model takes the various cutting conditions into account and ensures the whole wire wear loss to reach the preset reasonable value. Firstly, a hypothesis that there is a mapping relation between the wire wear loss and the wire slicing area during the wire lifetime is built. According to this hypothesis, the wire allowed wear loss can be transformed into wire allowed slicing area. Secondly, the calculation method is deduced based on the model. The function relation is obtained between the wire feedback ratio and the actual slicing conditions under the constraint condition of the preset wire wear allowed loss. This rational feedback ratio of wire is obtained based on the actual process parameters. Thirdly, experiments are carried out. The results indicate that the relation between wire wear loss and wire slicing area is linear under the condition of the experiments and the wire consumption is reduced obviously. Meanwhile, wafers’ quality meets the requirements. This method can effectively save saw wire cost, referring to slicing other hard brittle materials by multi-wire saw.

Sawing force modeling and analysis for diamond wire sawing PV monocrystalline silicon considering abrasive wear

An experimental investigation on energy-effective additive manufacturing of aluminum parts via process parameter selection

Experimental study has been carried out to look for the effect of varying parameters such as diameter, the rate of rise of current, and coating on the behavior of copper wire explosion in the air with an aim to, especially, observe the effect of parameters which has significance in confinement of exploded wire plasmas by inhibiting its expansion. Single-wire experiments are performed on a capacitor of 2-μF charged to voltages in the range of 11-40 kV. Effects of parameters such as dielectric coating and change in diameter (58-233 μm) of coated wires on specific energy deposition are experimentally observed at varying rates of rise of current (peak current 28-104 kA in a quarter period of 1.1 μs). Current in the circuit and the voltage across the load are measured using Rogowsky coil and voltage divider, respectively. The results indicate that the specific energy deposition can be enhanced by optimizing radial dimensions of wire, charging voltage, and surface coating. Analysis of results also suggests that the action integral is affected by the diameter of the wire and the rate of rise of currents as reported by some theoretical works so far.

Wire sawing is widely used for wafer cutting in the photovoltaic and microelectronics industries. The quality of cutting wafers is affected by the wire bow deflection. In this study, wire bow deflections in a crystal sawing process were systematically measured with a high-speed camera. A simulation model of wire bow deflection was established using the Adams software on the basis of experimental conditions. It is shown that the curve of the wire bow deflection was a quadratic curve. Wire bow deflection was obviously affected by the wire tension force and the feeding speed. However, wire speed had little effect on the wire bow deflection. The experimental and the simulation results of wire bow deflection were similar for different process parameters. The force ratio played a key role in influencing the wire bow deflection.

The currently dominant method in the production of wafers is to use slurry wire-saw slicing. This paper reports a new wire-saw slicing technology, namely, semifixed abrasive wire-saw slicing. The traditional smooth wire is replaced by a patterned wire with a textured surface that can help the wire carrying the abrasives. It aims to improve the number of transient fixed abrasives in the machining process. Transient fixed abrasives can produce “scratch-indenting” processes that are similar to fixed-abrasive wire slicing thereby improving the efficiency of the wire-saw cutting. This study focuses on the behavioral mechanics of the abrasive grits in the slurry during the slicing process. The dynamic images of the movement of abrasive grits in the slicing process are obtained by a high-speed camera. At the microlevel, using statistical methods, the behavioral mechanics of the abrasive grits are investigated by changing the slicing parameters. The results contribute toward a more intuitive and profound understanding of the principle of free-abrasive wire sawing.

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.

Surface damage and metal-catalyzed chemical etching investigation of multicrystalline silicon by diamond wire sawing

Grain (Oryza sativa L) drying process is generally still done traditionally by direct sunlight. The drying process has several disadvantages such as it can only be done when sunlight is available, a longer drying time, a large area, requirement. An alternative that could be done to dry the grain in addition to using traditional drying was to use a grain dryer machines with do Wargi Mekar Farmer at Kerawang. There are several fuels that are used as heat sources for rice drying machines, one of them is firewood. This study aimed to measure the actual capacity of the wood-fired grain dryer, and also to analyzed the efficiency of drying and specific energy consumption to dry the grain. The research method used is descriptive analysis research method, namely data collection, data processing and data analysis. Research resulted that grain drying using a grain dryer as much as 761 kg.hr-1 . The yield of dry grain is 89.77%, and the value of weight loss is 10.33%. The moisture content of the material after drying is 13.06% wet basis. The drying efficiency in the process was 17.19% and the specific energy consumption was 15,318.24 KJ / Kg water vapor. Keywords: efficiency energy, grain drying, specific energy consumption

Recycling of silicon from waste PV diamond wire sawing silicon powders: A strategy of Na2CO3-assisted pressure-less sintering and acid leaching