The POCl₃ diffusion is the main technology to form the p-n junction of industrial silicon solar cells. However, the diffusion mechanism of phosphorus (P) into the silicon wafer is not fully understood. In this article, we study the P diffusion mechanism during drive-in by systematically varying the drive-in time in the oxygen (O₂) atmosphere and subsequently in nitrogen (N₂). When increasing the drive-in time in O₂ from 0 to 120 min, the sheet resistance R_sheet stays constant at 485±30 Ω/sq. Hence, we demonstrate for the first time that the phosphorus diffusion can be completely suppressed in the O₂ atmosphere. When adding a drive-in in the N₂ atmosphere directly after the drive-in in O₂, we find that the SiO₂ thickness d_SiO2,O2 changes from initially 2 to 10 nm after O₂ drive-in to an equilibrium SiO₂ thickness d_SiO2,eq of 4.7 nm after N₂ drive-in. We prove for the first time that if d_SiO2,O2 > d_SiO2,eq, no P diffuses into the silicon wafer even in the N₂ atmosphere. Only if d_SiO2,O2 < d_SiO2,eq, phosphorus diffuses into the silicon wafer in the N₂ atmosphere. We propose a detailed chemical model to explain our experimental results, which assumes that the diffusion of Si from the wafer through the SiO₂ interface toward the PSG plays a key role. In this model, P can only diffuse into the Si wafer if P₂O₅ in the PSG is reduced by the Si from the wafer to P and SiO₂.

中文翻译：

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在 POCl$_{3}$ 扩散过程中磷扩散到硅晶片中的详细化学模型

POCl ₃扩散是形成工业硅太阳能电池pn结的主要技术。然而，磷 (P) 扩散到硅晶片的机制尚不完全清楚。在本文中，我们通过系统地改变氧气 (O ₂ ) 气氛和随后的氮气 (N ₂ )中的推进时间来研究推进过程中的 P 扩散机制。当 O _{2 中}的驱动时间从 0 分钟增加到 120 分钟时，薄层电阻电阻_片保持恒定在 485±30 Ω/sq。因此，我们首次证明了在 O ₂气氛中可以完全抑制磷扩散。在 O ₂驱入之后直接在N ₂气氛中添加驱入时，我们发现 SiO ₂厚度d_SiO2,O2在 O ₂驱入到平衡 SiO ₂厚度后从最初的 2 nm 变为 10 nmdN ₂驱入后的_SiO2,eq为 4.7 nm 。我们第一次证明如果d_SiO2,O2 >d即使在 N ₂气氛中，_{SiO2,eq 也}没有 P 扩散到硅晶片中。除非d_SiO2,O2 <d_SiO2,eq、磷在 N ₂气氛中扩散到硅晶片中。我们提出了一个详细的化学模型来解释我们的实验结果，该模型假设 Si 从晶片通过 SiO ₂界面向 PSG的扩散起着关键作用。在该模型中，如果PSG 中的P ₂ O ₅被硅从晶片还原为 P 和 SiO ₂，则 P 只能扩散到 Si 晶片中。