GOALI: Diamond Coated Carbon Fiber Wire Sawing of Silicon Ingots

将硅锭切割成单个晶片的金刚石涂层线锯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，这是一种废流，需要能源密集型回收策略。较细的钢丝可导致在钢丝锯切过程中产生的粉末最少。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很容易断裂。GOALI学术联络机会奖支持使用直径小于100微米的碳纤维线将硅锭切割成晶片的科学研究。该项目的研究成果将减少硅的浪费，从而降低硅基太阳能电池的每瓦特成本。第一个研究目标是建立锯切条件(如钢丝速度和法向力)与涂覆在碳纤维线上的单个金刚石颗粒的化学和结构变化之间的关系。在金刚石颗粒中观察到的变化是软化(即石墨化)、解理、钝化或完全从碳纤维线上移除。实现这一目标的方法是使用显微拉曼光谱测量金刚石颗粒、碳纤维线和生成的硅粉在锯切后的化学和结构变化。这项技术能够以微米级的空间分辨率绘制出金刚石颗粒、碳纤维线和硅粉中的化学和结构变化。将使用工业锯床和横截面为15厘米×15厘米的单晶硅锭进行锯切实验。将使用高达25m/S的线速和高达15N的法向力。第二个研究目标是了解金刚石颗粒和碳纤维的磨损对锯切速度的影响。实现这一目标的方法是在现场测量金刚石涂层碳纤维线在锯切时的钢丝弯曲。这使得可以估计锯切过程中硅缝内的钢丝所经历的钢丝张力和摩擦力。随着磨损的进行，钢丝弯曲增加，摩擦力也增加。锯切速度将被测量为硅锭向下压在钢丝上时的垂直速度。碳纤维丝直径(从60微米到100微米)和钻石尺寸(从6微米到20微米)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.