THE CONSTRUCTION OF A CVD PROCESS WITH MATERIAL RECYCLE TO PRODUCE EFFICIENT SOLAR CELLS AT LOW-COST.

我们试图建立低成本、高效率的CVD沉积多晶硅工艺，以形成太阳能电池的电子发电层。1996年，我们研制了一套沉积硅薄膜的设备，以了解作为原料的氯硅烷的沉积和刻蚀特性，并从反应堆出口获得气体信息。该装置为热壁常压CVD系统，由原料气供应系统、反应炉、气相色谱和出口气体处理系统组成。以三氯硅烷(SiHCl_3)和四氯硅烷(SiCl4)为原料，氢气为载气。我们进行了沉积实验，然后从管式反应器的生长速率分布中确定了速率常数，并计算了反应器中的转化率。此外，我们还利用气相色谱对反应气体进行了分析，从反应器入口和出口气体组成的差异来了解氯硅烷的质量平衡，从而获得气相反应的信息。1997年，我们从热力学上估计了平衡状态。通过计算结果与实验结果的比较，证明了以氯硅烷为原料的CVD反应反映了平衡状态。因此，可以通过操作平衡态来控制硅的沉积和刻蚀。因此，根据Si/H/Cl体系的这些特点，我们提出了利用刻蚀反应来再生和回收原料气体的太阳能电池的新工艺。

We have tried to establish low-costly and high-efficient CVD process of depositing poly-silicon for the formation of electronic power generation layr of the solar cell, by constructing the recycling methods of raw gases.In 1996, we made an equipment to deposit silicon thin films for the purposeof understanding characteristics of deposition and etching of chlorosilane as raw gases and obtaining information of the gases from the reactor outlet. The equipment is a hot-wall atmospheric pressure CVD system which consists of supplying system of raw gases, reactor furnace, gas chromatography and disposing system of outlet gases. We used trichlorosilane (SiHCl_3) and tetrachlorosilane (SiCl_4) as raw gases, and hydrogen as carrier gas. We operated depositing experiments, and then detremined rate constants from the growth rate profile of the tubular reactor and calculated the conversion in the reactor. Also, we analyzed reactant gases by gas chromatography to understand the mass balance of chlorosilane from the difference of gas composition between inlet and outlet of the reactor, so that we obtained information of gas-phase reactions.In 1997, we estimated equilibrium states thermodynamically. From the comparison between the estimation and the experimental results, we proved that the CVD reactions using chlorosilane as raw gases reflect the equilibrium state. Therefore, it is possible to control deposition and etching of silicon by operating equilibrium state. Consequently, we suggested newly process for producing solar cell that we can reproduce and recycle raw gases using etching reactions on the basis of these characteristics of Si/H/Cl system.