Vacuum ultraviolet (VUV) enhanced atomic layer etching (ALE) of thin (∼8 nm) Ru films is demonstrated. Oxidation half-cycles of 2–5 min VUV/O₂ co-exposure are used to oxidize near-surface Ru to RuO₂ at 1 Torr O₂ and 100–150 °C. In situ x-ray photoelectron spectroscopy measurements indicate that RuO₂ formation saturates after ∼5 min of VUV/O₂ exposure at 100 and 150 °C. The depth of Ru oxidation is limited by the rate of oxidation and can be controlled with substrate temperature and exposure time. Etching half-cycles are performed by exposing the oxidized Ru film to HCOOH vapor at 0.50 Torr for 30 s isothermally, which results in the removal of the oxidized Ru layer. The amount of Ru removed per ALE cycle is determined by comparing ex situ x-ray reflectivity (XRR) measurements of the film before and after etching. When using 2 min VUV/O₂ co-exposure, approximately 0.8 and 0.9 Å of Ru is etched per cycle at 100 and 150 °C, respectively. XRR and atomic force microscopy measurements indicate that the as-deposited and sputtered Ru film surface becomes smoother as ALE is performed. The etch rate decreases with ALE cycles and corresponds to a slowing oxidation rate, which is likely associated with the decrease in surface roughness. Density functional theory is used to study the adsorption of oxidants in a model Ru system, and nudged elastic band (NEB) calculations describe O diffusion into the Ru substrate by following an O “probe” atom as it moves between Ru(002) atomic planes with 0.50 monolayer (ML) O on the surface. NEB results reveal an approximate energetic barrier to diffusion, E_a, of 5.10 eV for O to move through the second and third atomic Ru layers when O, which can form an RuO_x species, is subsurface. This E_a is in excess of the energetic gain of 4.23 eV in adsorbing an O atom to Ru(002) with 0.50 ML O. The difference in E_a and the adsorption energy likely contributes to the self-limiting nature of the oxidation and explains the observation that VUV/O₂ co-exposure time must be increased to allow additional time for O diffusing into the subsurface as it overcomes the barrier to subsurface O diffusion. The self-limiting oxidation of Ru arising from VUV/O₂ at low temperatures, in turn, enables an ALE process for Ru.

中文翻译：

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真空紫外线增强钌膜原子层刻蚀

证明了Ru（〜8 nm）薄膜的真空紫外（VUV）增强原子层蚀刻（ALE）。在1 Torr O ₂和100–150°C下，使用2-5分钟的VUV / O ₂共暴露氧化半周期将近表面Ru氧化为RuO ₂。原位X射线光电子能谱测量表明，VUV / O ₂约5分钟后RuO ₂形成饱和暴露在100和150°C下。Ru氧化的深度受氧化速率的限制，可以通过基板温度和曝光时间进行控制。通过将氧化后的Ru膜在0.50 Torr的HCOOH蒸气中等温暴露30 s，进行蚀刻半循环，从而去除了氧化后的Ru层。每ALE周期除去钌的量是通过比较确定易地前和蚀刻后的膜的X射线反射率（XRR）测量。使用2分钟VUV / O _2时共暴露时，在100和150°C下每个循环分别蚀刻约0.8和0.9Å的Ru。XRR和原子力显微镜测量表明，随着ALE的进行，沉积和溅射的Ru膜表面变得更光滑。刻蚀速率随着ALE循环而降低，并且对应于缓慢的氧化速率，这很可能与表面粗糙度的降低有关。密度泛函理论用于研究模型Ru系统中氧化剂的吸附，微动弹性带（NEB）计算通过跟随O“探针”原子在Ru（002）原子面之间移动来跟踪O扩散到Ru基体中的过程。表面上具有0.50单层（ML）O的表面。NEB结果显示大约能垒扩散，E_一当能形成RuO _x的O位于表面以下时，O的5.10 eV可以穿过第二和第三原子Ru层。此电子_一个是在过量的4.23电子伏特的能量增益的与0.50 ML O.吸附O原子与Ru（002）在E中的差_一个且可能有助于吸附能量到氧化的自限制性质，并解释观察到，必须增加VUV / O ₂共同暴露时间，以便为O扩散到地下提供更多的时间，因为它克服了地下O扩散的障碍。反过来，在低温下由VUV / O ₂引起的Ru的自限氧化作用使得ALE可以进行ALE处理。