There is an urgent need to deposit uniform, high-quality, conformal SiN_x thin films at a low-temperature. Conforming to these constraints, we recently developed a plasma enhanced atomic layer deposition (ALD) process with bis(tertiary-butyl-amino)silane (BTBAS) as the silicon precursor. However, deposition of high quality SiN_x thin films at reasonable growth rates occurs only when N₂ plasma is used as the coreactant; strongly reduced growth rates are observed when other coreactants like NH₃ plasma, or N₂–H₂ plasma are used. Experiments reported in this Letter reveal that NH_x- or H- containing plasmas suppress film deposition by terminating reactive surface sites with H and NH_x groups and inhibiting precursor adsorption. To understand the role of these surface groups on precursor adsorption, we carried out first-principles calculations of precursor adsorption on the β-Si₃N₄(0001) surface with different surface terminations. They show that adsorption of the precursor is strong on surfaces with undercoordinated surface sites. In contrast, on surfaces with H, NH₂ groups, or both, steric hindrance leads to weak precursor adsorption. Experimental and first-principles results together show that using an N₂ plasma to generate reactive undercoordinated surface sites allows strong adsorption of the silicon precursor and, hence, is key to successful deposition of silicon nitride by ALD.

中文翻译：

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表面终止在氮化硅原子层沉积中的作用

迫切需要在低温下沉积均匀，高质量，保形的SiN _x薄膜。符合这些限制，我们最近开发了一种以双（叔丁基-氨基）硅烷（BTBAS）为硅前体的等离子体增强原子层沉积（ALD）工艺。然而，只有当使用N ₂等离子体作为共反应剂时，才能以合理的生长速率沉积高质量的SiN _x薄膜。当使用其他互感剂（例如NH ₃血浆或N ₂ -H ₂血浆）时，观察到生长速率大大降低。这封信中报道的实验表明，NH _x-或H-等离子体通过终止具有H和NH _x基团的反应性表面位点并抑制前体吸附来抑制膜沉积。为了理解这些表面基团的前体上吸附的作用，我们在执行前体吸附的第一原理计算β型Si ₃ Ñ ₄（0001）表面具有不同表面端接。他们表明，前体在表面位置不协调的表面上的吸附很强。相反，在具有H，NH ₂基团或两者的表面上，空间位阻会导致前体吸附较弱。实验和第一性原理结果一起表明使用N ₂ 等离子体产生反应性不足的表面位点可以使硅前驱物强力吸附，因此，这是通过ALD成功沉积氮化硅的关键。