外延硅片表面时间雾的形成及其机理EI北大核心CSCD

外延片生产中有时会遇到外延硅片在洁净室中暴露--段时间后产生雾状宏观缺陷(即所谓的时间雾)的不利情形,然而关于外延硅片表面时间雾的成因目前尚不清楚。通过探究常压化学气相外延工艺生长的外延硅片表面时间雾的形成条件,发现外延硅片取出之前生长腔和传递腔之间的压力差是时间雾形成与否的关键因素。分析认为:取片之前,当生长腔相对传递腔为正压时,外延尾气的返流使得外延硅片表面吸附了尾气中的SiCl_(2)及其团簇(SiCl_(2))_(n),进一步吸附空气中的水分并与之发生化学反应,这是时间雾形成的内因。采用扫描电子显微镜(SEM)、X光能量色散谱(EDS)和全反射X光荧光光谱(TXRF)等手段,对时间雾相关的颗粒形貌和组分进行表征。结果表明:时间雾相关的颗粒呈现为规则多面体和球形两种典型形貌,前者与NH_(4)Cl小晶体有关,而后者与有机物有关。分析认为:洁净室空气中的含NH_(4)^(+)无机组分以及异丙醇(IPA)等有机组分是形成时间雾的外因。生产中避免外延硅片表面时间雾的根本措施在于,在外延炉腔中取片之前必须避免外延工艺的尾气不会返流至生长腔。

Formation of Time-dependent Haze on the Surface of Epitaxial Silicon Wafers and Its Mechanism

During the production of epitaxial silicon wafers, it sometimes suffers from the undesirable case that the haze-like macro-defects, namely, time-dependent haze (TDH), appear on the epitaxial silicon wafers which are exposed to the clean-room for a period of time. Unfortunately, the causes for the formation of TDH have not essentially been known so far. The formation conditions of TDH are investigated for the epitaxial silicon wafers grown by chemical vapor deposition under atmospheric pressure. It is found that the pressure difference between the process and transfer chamber, which occurs prior to unloading the epitaxial silicon wafer, is the key factor for the formation of TDH. It is pointed out that the exhaust will reflow into the process chamber if the pressure of process chamber is larger than that of transfer chamber prior to the unloading procedure, thus making the epitaxial silicon wafer absorb the SiCl₂ and (SiCl₂)_n species, which further react with the moisture in the air of clean-room. This is the root cause for the formation of TDH. By means of scanning electron microscopy, X-ray energy dispersion spectroscopy and total reflection X-ray fluorescence, the morphologies and compositions of the TDH-related particles have been characterized. It is indicated that the TDH-related particles are manifested with two kinds of morphologies of polyhedron and sphere. The polyhedron-like particles are supposed to be associated with small NH₄Cl crystals, while the sphere-like particles are believed to be related to the organics. It is further pointed out that the inorganic components containing NH₄ ⁺ and the organic components such as isopropanol (IPA) in the air of cleaning room are the external causes of the formation of TDH. In brief, the fundamental countermeasure for avoiding the formation of TDH on the epitaxial silicon wafers is to disable the backflow of exhaust gas into the epitaxial chamber prior to unloading the epitaxial silicon wafers.