Surface Reaction Processes of Fluorocarbon Molecule and Fundamental Research on New Etching Process

氟碳等离子体SiO_2/Si选择性蚀刻是半导体制造的基本工艺之一。到目前为止，认为氟碳分子对表面反应没有贡献。然而，由于最近对新型氟碳气体的研究和开发，现在在蚀刻过程中使用C_5F_8或其他氟碳气体。C_5F_8具有相当复杂的分子结构，如分子结构中存在双键。我们开始研究碳氟化合物分子对蚀刻表面反应的贡献，这是由于新开发的分子具有有趣的化学结构。首先，我们考察了C_5F_8在SiO_2表面损伤和钝化情况下的表面反应性，发现C_5F_8仅在Ar^+轰击损伤SiO_2表面时才具有反应性。这可能是由于C_5F_8分子的表面悬空键与双键反应所致。其次，将Ar +和C_5F_8同时定向到SiO_2表面，发现C_5F_8与其他氟碳分子如CF_4或C_4F_8相比具有很高的蚀刻反应性，其蚀刻收率几乎是物理溅射SiO_2的3倍。此外，在较高的C_5F_8/Ar^+通量比下，SiO_2也出现了“蚀停”现象。通过XPS测量，证实了较厚的氟碳层影响了蚀刻收率的降低。第三，通过比较不同Ar^+能量下SiO_2和Si的蚀刻产率，发现了Ar^+/C_5F_8共入射的SiO_2/Si选择性蚀刻的能力。最后，根据研究得到的蚀刻产率，评价了C_5F_8分子对实际半导体制造过程中蚀刻速率的贡献。结果表明，C_5F_8对腐蚀速率的最大贡献为~ 30%。

SiO_2/Si selective etching by fluorocarbon plasma is one of fundamental processes for semiconductor fabrication. So far, it is considered that the fluorocarbon molecules do not contribute on the surface reactions. However, C_5F_8 or other fluorocarbon gases are now in use in the etching process due to recent research and development on new fluorocarbon gases. C_5F_8 has rather complicated molecular structure such as double bond in the molecular structure. We have started the study of fluorocarbon molecule contribution to the etching surface reactions, motivated by such interesting chemical structure of newly developed molecules.Firstly, we investigated the surface reactivity of C_5F_8 in the cases of damaged and passivated SiO_2 surfaces, and it was found that the C_5F_8 can be reactive only in the case of damaged SiO_2 surface by Ar^+ bombardment. This is presumably due to the reaction of surface dangling bond with the double bond in the C_5F_8 molecule. Secondly, we Ar^+ and C_5F_8 were simultaneously directed to the SiO_2 surface, and it was found that the C_5F_8 has very high etching reactivity compared with other fluorocarbon molecules such as CF_4, or C_4F_8, and that the etching yield was almost three times higher than that of physical sputtering of SiO_2. Furthermore, "etch stop" of SiO_2 was also found in the case of higher C_5F_8/Ar^+ flux ratios. From the XPS measurement, it was confirmed that the thick fluorocarbon layer influenced the decrease in the etching yield. Thirdly, ability of SiO_2/Si selective etching by Ar^+/C_5F_8 co-incidence was found by comparing the etching yields for SiO_2 and Si at various Ar^+ energies. Finally, contribution of C_5F_8 molecule to the etching rate in real semiconductor fabrication process was evaluated based on the etching yields obtained by our research. It was found that the maximum contribution of C_5F_8 to the etching rate is 〜 30%.