Fluorocarbon based atomic layer etching of Si3N4 and etching selectivity of SiO2 over Si3N4
Fluorocarbon based atomic layer etching of Si3N4 and etching selectivity of SiO2 over Si3N4
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DOI：
10.1116/1.4954961
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发表时间：
2016-07-01
影响因子：
2.9
通讯作者：
Oehrlein, Gottlieb S.
中科院分区：
文献类型：
--
作者：
Li, Chen;Metzler, Dominik;Oehrlein, Gottlieb S.
埃级等离子体蚀刻精度是亚10 nm关键尺寸特征的半导体制造所需要的。原子层蚀刻（ALE）通过一系列自限循环实现，可以通过限制表面可用的化学反应物的量来精确地控制蚀刻深度。最近，SiO2 ALE已经通过在材料表面上使用受控的FC前体流和随后的低能量Ar+离子轰击以循环方式沉积薄（几埃）反应性氟碳（FC）层来实现。低能离子轰击用于从表面去除FC层沿着有限量的SiO2。在本文中，作者描述了使用这种循环ALE方法的Si 3 N4和SiO2层的一个到几个埃的控制蚀刻。Si 3 N4蚀刻和蚀刻选择性SiO2 Si 3 N4的研究和评估方面的依赖于最大离子能量，蚀刻步长（ESL），FC表面覆盖，和前体的选择。通过X射线光电子能谱（XPS）研究了ALE过程中真空转移后Si 3 N4的表面化学。由于Si 3 N4具有比SiO2更低的物理溅射能量阈值，因此对于相对高的离子能量，在每个循环结束时去除化学蚀刻剂之后可以发生Si 3 N4物理溅射。对于这些FC耗尽条件，观察到Si 3 N4对SiO2 ALE蚀刻选择性。通过优化ALE工艺参数，例如，低离子能量、短ESL和/或每循环高FC膜沉积，对于FC累积条件，可以实现高选择性的SiO2到Si 3 N4蚀刻，其中FC可以选择性地累积在Si 3 N4表面上。这种高度选择性的蚀刻是通过与SiO2相比Si 3 N4的较低碳消耗来解释的。C4 F8和CHF 3的比较仅显示出对于FC耗尽条件的蚀刻选择性的差异。对于FC积累条件，前体化学对蚀刻选择性的影响很弱。表面化学分析表明，在FC耗尽条件下，在单个ALE循环过程中发生表面氧化和FC还原。富氟碳层观察到的ALE过程后，FC积累发生在Si 3 N4表面上。角分辨XPS厚度计算在所有情况下证实了椭圆偏振测量的结果。(C)2016年美国真空学会。
Angstrom-level plasma etching precision is required for semiconductor manufacturing of sub-10 nm critical dimension features. Atomic layer etching (ALE), achieved by a series of self-limited cycles, can precisely control etching depths by limiting the amount of chemical reactant available at the surface. Recently, SiO2 ALE has been achieved by deposition of a thin (several Angstroms) reactive fluorocarbon (FC) layer on the material surface using controlled FC precursor flow and subsequent low energy Ar+ ion bombardment in a cyclic fashion. Low energy ion bombardment is used to remove the FC layer along with a limited amount of SiO2 from the surface. In the present article, the authors describe controlled etching of Si3N4 and SiO2 layers of one to several Angstroms using this cyclic ALE approach. Si3N4 etching and etching selectivity of SiO2 over Si3N4 were studied and evaluated with regard to the dependence on maximum ion energy, etching step length (ESL), FC surface coverage, and precursor selection. Surface chemistries of Si3N4 were investigated by x-ray photoelectron spectroscopy (XPS) after vacuum transfer at each stage of the ALE process. Since Si3N4 has a lower physical sputtering energy threshold than SiO2, Si3N4 physical sputtering can take place after removal of chemical etchant at the end of each cycle for relatively high ion energies. Si3N4 to SiO2 ALE etching selectivity was observed for these FC depleted conditions. By optimization of the ALE process parameters, e.g., low ion energies, short ESLs, and/or high FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for FC accumulation conditions, where FC can be selectively accumulated on Si3N4 surfaces. This highly selective etching is explained by a lower carbon consumption of Si3N4 as compared to SiO2. The comparison of C4F8 and CHF3 only showed a difference in etching selectivity for FC depleted conditions. For FC accumulation conditions, precursor chemistry has a weak impact on etching selectivity. Surface chemistry analysis shows that surface fluorination and FC reduction take place during a single ALE cycle for FC depleted conditions. A fluorine rich carbon layer was observed on the Si3N4 surface after ALE processes for which FC accumulation takes place. The angle resolved-XPS thickness calculations confirmed the results of the ellipsometry measurements in all cases. (C) 2016 American Vacuum Society.