Multi-scale Modeling for Scale-up and Control of a New Solar Cell Wafering Process

本项目旨在为用高纯度多晶硅生产晶体硅晶圆的连续工艺发展科学基础。在这个过程中，硅被漂浮在一个两层的熔融衬底上，形成一个非常薄（小于0.3毫米）的硅片，它固化后可以生产适合太阳能电池的晶体硅晶片。与昂贵的线锯工艺相比，生产成本较低，因为该工艺是连续的，不会造成硅的损失。智力优势：在这项研究中，pi将研究熔融基板上冻结锋的稳定和控制。这种类型的系统可能表现出Mullins-Sekerka不稳定性，需要主动控制来稳定过程。他们将开发多尺度过程模型，能够代表冻结锋中存在的不稳定性。这些模型将使用实验数据与物理系统相匹配。将开发控制方法，以稳定冻结锋使用基于热力学的方法为基础的被动控制。重点是将这些方法应用于制造太阳能电池的硅。将测试一些新的测量技术来解决硅凝固问题，并确定工艺设计、放大和控制所需的工艺参数。在微尺度实验中，将一层薄薄的熔融硅缓慢地浇筑在高密度液体上，作为衬底。衬底的物理性质将被调整，以便熔融硅可以持续冷却并以单晶/多晶硅的连续片状形式取出。他们将表明，使用熔融（液体）衬底形成三液-液层可以防止当前连续、水平晶圆过程中存在的晶体缺陷、位错和晶界。他们也将证明有限的净化是可以体验的。同时目标是建立多尺度数学模型，以比较熔融硅在液体衬底上运动和流动的微尺度实验结果。模型预测将与宏观尺度实验进行比较。广泛影响：由于生产高纯度硅和硅晶片的高成本，太阳能到目前为止还没有充分发挥其潜力。在流化床反应器中制备高纯度多晶硅的廉价工艺方面取得了重大进展。然而，在寻找昂贵的带锯晶圆工艺的替代品方面，进展非常有限。这里描述的想法可能有助于解决这个问题。这种三层工艺从彻底改变玻璃工业的皮尔金顿玻璃工艺中汲取灵感。初步实验表明，用类似的方法生产小规模硅片是可行的。预计这项研究最重要的广泛影响将出现在替代能源领域。该研究还有望为多尺度模拟和凝固锋的稳定与控制提供新的方法。这些问题出现在许多应用领域，包括油漆的干燥，薄膜加工和涂层。

0932556YdstieThis project aims to develop scientific foundations for a continuous process to produce crystalline Silicon wafers from high purity poly-Silicon. In this process Silicon is floated over a two-layered molten substrate to form a very thin (less than 0.3 mm) Silicon sheet, which solidifies to produce crystalline Silicon wafers suitable for solar cells. The production cost will be low relative to expensive wire saw processes since this process is continuous and does not incur Silicon loss. Intellectual Merit: In this research the PIs will study the stabilization and control of a freezing front on a molten substrate. Systems of this type may exhibit Mullins-Sekerka instability and active control is needed to stabilize the process. They will develop multi-scale process models capable of representing the instabilities present in the freezing front. The models will be matched to a physical system using experimental data. Control methods will be developed to stabilize the freezing front using a thermodynamics based approach to passivity based control. The focus is on the application of the methods to Silicon for making solar cells. A number of new measurement techniques will be tested for the Silicon solidification problem and process parameters needed for process design, scale-up and control will be determined. A thin layer of molten Silicon will be slowly poured on a high-density liquid used as a substrate in micro scale experiments. The physical properties of the substrate will be tuned so that the molten Silicon can be continually cooled and withdrawn in the form a continuous sheet of single-/multi-crystalline Silicon. They will show that the use of molten (liquid) substrate forming three liquid-liquid layer prevents the crystal imperfections, dislocations and grain boundaries present in current continuous, horizontal wafering processes. They will also demonstrate that limited purification can be experienced. The simultaneous goal is to develop multi-scale mathematical models to compare the micro-scale experimental results on movement and flow of the molten Silicon over the liquid substrate. Model predictions will be compared with macro-scale experiments. Broad Impact: Solar energy has so far not measured up to its potential due to the high cost of producing high purity Silicon and Silicon wafers. Significant progress has been made in developing cheaper processes for making high purity poly-silicon in fluid bed reactors. Very limited progress has been made in finding alternatives to the expensive band-saw process for wafering, however. The ideas described here may contribute towards solving this problem. This three layer process draws inspiration from the Pilkington glass process which revolutionized the glass industry. Preliminary experiments show that it is feasible to produce silicon wafers in small scale using a similar idea. The most important broader impacts of this research are expected to be found in the area of alternative energy. It is also expected that the research will lead to new methods for multi-scale modeling and stabilization and control of solidification fronts. These problems turn up in a number of application areas, including the drying of paints, film processing and coating.