GOALI: Diamond Coated Carbon Fiber Wire Sawing of Silicon Ingots

用金刚石涂层线锯将硅锭切割成单独的硅片占太阳能电池生产成本的11%。这一成本主要与硅粉的产生有关，硅粉是一种废物流，需要能源密集型的回收策略。更细的线材可以在线材锯切过程中产生最小的粉末。然而，较细的钢丝（直径小于100微米）在有效切割硅所需的应力下容易断裂。这项学术与工业联络资助机会（GOALI）奖支持对直径小于100微米的碳纤维丝在金刚石涂层线锯硅锭成晶圆中的使用进行科学研究。该项目的研究结果将减少硅的浪费，从而降低硅基太阳能电池的每瓦成本。第一个研究目标是建立锯切条件（如线速度和法向力）与涂层在碳纤维线材上的单个金刚石颗粒的化学和结构变化之间的关系。观察到的金刚石颗粒的变化是软化（即石墨化）、解理、钝化或从碳纤维丝上完全去除。实现这一目标的方法是使用微拉曼光谱测量金刚石颗粒、碳纤维丝和生成的硅粉锯切后的化学和结构变化。该技术可以在微米尺度的空间分辨率上绘制金刚石颗粒、碳纤维丝和硅粉的化学和结构变化。将使用一台工业锯床和15厘米× 15厘米方形截面的单晶硅锭进行锯切实验。钢丝速度可达25米/秒，法向力可达15牛。第二个研究目的是了解金刚石颗粒和碳纤维磨损对锯切速率的影响。实现这一目标的方法是在现场测量金刚石涂层碳纤维丝在锯切时的弯曲程度。这允许估计线张力和摩擦的力量，在锯切过程中，由线内部的硅切口。随着磨损的进行，金属丝弯曲增大，摩擦力也增大。锯速率将被测量为硅锭压在金属丝上时的垂直速度。碳纤维丝直径（从60µm到100µm）和金刚石尺寸（从6µm到20µm）等参数将有所不同。

Diamond coated wire sawing of silicon ingots into individual wafers accounts for 11 percent of solar cell production costs. This cost is primarily associated with generation of silicon powder which is a waste stream and requires energy intensive recycling strategies. Thinner wires can lead to minimal powder generation during wire sawing. However, thinner steel wires (smaller than 100 microns in diameter) break easily under the stress required for efficient cutting of silicon. This Grant Opportunity for Academic Liaison with Industry (GOALI) award supports scientific investigations on the use of carbon fiber wires smaller than 100 microns in diameter in diamond coated wire sawing of silicon ingots into wafers. Research results from this project will lead to reduced wastage of silicon and, therefore, reduced dollar-per-watt of silicon based solar cells. The first research objective is to establish relationships between sawing conditions (such as wire velocity and normal force) and the chemical and structural changes of individual diamond particles coated on a carbon fiber wire. The changes observed in the diamond particles are softening (i.e., graphitization), cleavage, blunting, or complete removal from the carbon fiber wire. The approach to achieve this objective is to measure chemical and structural changes after sawing in diamond particles, carbon fiber wire, and generated silicon powder using micro-Raman spectroscopy. This technique can map chemical and structural changes in the diamond particles, carbon fiber wire and the silicon powder with micron scale spatial resolution. An industrial sawing machine, and single crystalline silicon ingots with a 15 cm x 15 cm square cross-section, will be used for sawing experiments. Wire velocities of up to 25 m/s and a normal force of up to 15 N will be used. The second research objective is to understand the effects of wear of diamond particles and carbon fiber on sawing rate. The approach to achieve this objective is to measure, in situ, wire bowing of the diamond coated carbon fiber wire as it performs sawing. This allows estimation of wire tension and frictional forces experienced by the wire inside the silicon kerf during sawing. As wear proceeds, wire bowing increases and so do frictional forces. Sawing rate will be measured as the vertical velocity of the silicon ingot as it presses down on the wire. Parameters such as carbon fiber wire diameter (from 60 µm to 100 µm) and diamond size (from 6 µm to 20 µm) will be varied.