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在开管扩散炉中,氮气通常作为杂质的携带气体。在扩散温度下,氮气在硅片上流过,产生一个极薄的表面膜,这一表面膜起着强烈的扩散阻挡层的作用。即使在闭管扩散系统中,由于残存气氛,在硅片表面也形成类似的阻挡层。这些扩散阻挡层使磷杂质分布发生扭曲。本文讨论了这种扭曲的位置及其对各种扩散参数如时间、温度及携带气体中杂质浓度的依赖关系。如果用氩气或其它惰性气体避免薄膜阻挡层的形成,则扭曲消失。提出了一个数学模型来解释这种分布的扭曲特性。
In an open tube diffusion furnace, nitrogen is commonly used as a carrier gas for impurities. At the diffusion temperature, nitrogen flows over the silicon wafer to create an extremely thin surface film that acts as a strong diffusion barrier. Even in closed-tube diffusion systems, a similar barrier is formed on the surface of the wafer due to the residual atmosphere. These diffusion barriers distort the phosphorus impurity distribution. This article discusses the location of this distortion and its dependence on various diffusion parameters such as time, temperature and impurity concentration in the carrier gas. If argon or other inert gas is used to avoid the formation of a thin film barrier, the distortion disappears. A mathematical model is proposed to explain the distortions of this distribution.