中温制备多晶硅薄膜及相关理论问题的探讨

【作者】 靳瑞敏；

【导师】 卢景霄；

【作者基本信息】 郑州大学 ， 凝聚态物理学， 2006， 博士

【摘要】 太阳能电池在缓解能源危机和解决环境污染方面有其重要的研究和应用价值。我国当前经济处在高速发展期，能源供需矛盾突出，同时又是太阳能资源比较丰富的国家，发展太阳能电池有迫切的需求和巨大的市场潜力。太阳能电池的发展方向在于降低成本和提高效率。本文首先分析了各种太阳能电池的价格、材料二次污染、电池效率等因素，从影响太阳能电池民用化的成本和稳定性方面考虑，认为多晶硅薄膜集晶体硅和非晶硅薄膜材料优点于一身，与现有的太阳能电池生产技术具有兼容性，有可能成为制作太阳能电池的廉价优质材料，在将来极具潜力。根据处理温度不同，我们进一步把制备多晶硅薄膜电池分为高温、中温和低温路线。考虑到以玻璃材料为电池衬底，它在透光性、软化点、廉价、美观、可以与建筑一体化等优点，我们选择中温线路作为制备多晶硅薄膜电池的研究方向。制备大晶粒多晶硅薄膜是提高多晶硅薄膜电池效率的关键，本文将重点研究中温制备大晶粒多晶硅薄膜。本文研究用常规高温炉中温制备多晶硅薄膜材料的工艺参数。在550℃-1000℃温区选择不同的晶化温度和时间，发现在中温炉子退火制备多晶硅薄膜的过程中，退火温度与退火时间是相互关联的。对于同样的晶化效果，退火温度高，在较少的时间内晶化；退火温度低，在较长的时间内完成晶化。本文发现在中温炉子退火制备多晶硅薄膜的过程中，出现一系列的晶化效果好的极值点，比如940℃下退火1h，850℃下退火3h等。多晶硅薄膜的晶化效果也与不同条件下沉积的非晶硅薄膜有关。对中温光退火制备多晶硅薄膜的研究表明，退火温度与退火时间是相互关联的，同样存在一系列的晶化效果好的极值点，比如850℃下退火5分钟，750℃下退火8分钟等。并且发现700℃和750℃之间存在一个开始晶化温度点。当退火温度低于这个温度时，非晶硅薄膜晶化比较困难；而当退火温度高于这个温度时，非晶硅薄膜则很容易发生晶化。本文对比了常规高温炉和光退火两种方法，发现光退火后获得的多晶硅薄膜晶粒分布比较均匀，常规炉子退火后的薄膜晶粒分布不均匀。用两种方法都可以达到一定的晶化效果，都可以获得的相同晶粒大小的多晶硅薄膜，但光退火比常规退火的时间大大缩短。我们研究沉积温度对制备大晶粒多晶硅薄膜的影响，用PECVD法在30℃、350℃和450℃沉积的非晶硅薄膜，在相同条件下退火，350℃附近沉积的非晶硅薄膜的结晶颗粒比较低温度30℃沉积的大。这一点与以前认为，“非晶硅薄膜的沉积温度越低，晶化后所得的多晶硅薄膜材料的晶粒就越大”的结论不一致。本文研究PECVD沉积非晶硅薄膜的衰变，观察到在自然条件下会发生衰变，因此，中温光退火制备多晶硅薄膜的过程中，应减少中间停留的时间，尽快进入下一步工艺。本文研究了多晶硅薄膜与玻璃衬底的结合问题。发现硅薄膜与玻璃衬底有明显的分离现象，研究选择合适软化点的玻璃衬底，使玻璃的软化点温度与最高退火温度点匹配，可以避免处理过程中玻璃与硅膜相分离。在此基础上总结中温制备大晶硅薄膜的较好技术路线和工艺参数。首先用PECVD法在玻璃衬底和一定温度情况下沉积，然后用光退火制备的多晶硅薄膜。具体沉积工艺参数：真空度5.6×10^-4pa，沉积室中电极间距2cm，工作气压133.3Pa，氢稀释比98％、衬底温度350℃、射频功率60W；退火条件：850℃下光退火5分钟。最后，本文发现在PECVD沉积硅膜和进行固相晶化过程中，晶粒大小等状态在一定范围内随着退火温度、时间的变化，出现极值点现象。本文对这种现象进行了分析，认为这与微观量子现象有紧密的联系，根据这一想法，提出等能量驱动原理，并计算了光退火制备多晶硅薄膜的过程，与实验结果一致。更多还原

【Abstract】 The wide use of solar cell exhibits important role to solve the resource crisis and environmental crisis. There exists a huge contradiction between the production and needs in the high developing period of our country. The rich Solar energy and huge market give a very good opportunity to solar cell.The development of solar cells is showing a tendency to improve efficiency and reduce cost. The material price, pollution and cell efficiency were analyzed. Polycrystalline silicon thin film possesses the excellences of both crystalline silicon and amorphous thin film silicon. It not only is compatible with the existing solar cell technology but also promise cheap and excellent material for solar cell. The fabricating procession was divided into three kinds: low temperature, middle temperature and high temperatures according to the process temperature. Because the glass material has good transmission, suitable soft point, cheap, aesthetic and integrated with building easily, middle temperature procession was considered a suitable direction. Fabricating polycrystalline silicon thin films with large grain size is the key technique to increase cell efficiency. To achieve this aim, polycrystalline silicon thin films at middle temperature were focused in this thesis.A better parameters to fabricating polycrystalline silicon thin films at middle temperature by conventional furnace annealing were studied. Different annealing temperature and time were found to be connected in 550°C-1000°C. The high annealing temperature was corresponding short time, the low annealing temperature was corresponding long time in the procession of getting the same crystalline effect. It was found that there existed a series of critical point in the procession, for example, annealed at 940℃for 1h, annealed at 850℃for 3h, et. al. The crystalline effect was dependent on the deposit condition too.The performance of annealing procession by rapid thermal annealing was investigated, annealing temperature and time were connected too. There existed a series of critical point in the procession, for example, annealed at 850℃for 5 min, annealed at 750℃for 8min, et. al. and there exists a start crystalline temperature point between 700℃and 750℃, it is difficult to be crystallized beyond the temperature, however, it is easy to be crystallized above the temperature.It was found that the poly-silicon thin film fabricated by FA were roughness and requires very long annealing times compared with RTA. The similar size of poly-silicon thin film so is obtain; the thin film made by pulsed rapid thermal method is smoothly and perfect structure. The effect of deposit temperature was investigated. The amorphous silicon thin film deposited at 30℃, 350℃and 450℃, annealed at same condition, it was found that the poly-silicon deposited at 350℃had bigger grain size that those at other temperatures. This was not coincident with the old idea: the lower depositing temperature, the bigger grain size of the poly-silicon.The decay of amorphous silicon deposited by PECVD was studied. The decay was found in nature, so the delay in the procession should be avoided. The match of polycrystalline silicon thin films and glass substrate was studied too. It was found that there was separation between silicon thin films and glass substrate, and choose glass with suitable soft point could avoid the separation phenomena.Draw a conclusion, a better parameters was found in fabrication of polycrystalline silicon thin film on glass at middle temperature: amorphous silicon film to be annealed were deposited at a certain temperature on glass substrate and fused quartz by plasma enhanced chemical vapor deposition （PECVD） method, using SiH₄, H₂ mixture. The gas flow ratios was 2%, the chamber pressure 1 Torr, substrate temperatures 350℃and the radio-frequency power 50W. Then the a-Si thin films are crystallized in a rapid thermal processor, the time-temperature budget of the process is 850℃-5min.Finally, it was found that the critical point phenomena was shown between polycrystalline silicon size and the annealing temperature and time in the solid phase crystallize procession. The phenomena was investigated at the angle of the micro quantum state, according to which the principle of equal energy driving was put up and the rapid thermal procession was calculated, the result was corresponding to the experiment.更多还原