Rapid atomic layer etching of Al2O3 using sequential exposures of hydrogen fluoride and trimethylaluminum with no purging
Rapid atomic layer etching of Al2O3 using sequential exposures of hydrogen fluoride and trimethylaluminum with no purging
复制标题
使用氟化氢和三甲基铝连续暴露进行 Al2O3 快速原子层蚀刻，无需吹扫
DOI：
10.1116/1.5043488
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发表时间：
2018
影响因子：
2.9
通讯作者：
S. George
中科院分区：
文献类型：
--
作者：
David R. Zywotko;J. Faguet;S. George
使用氟化氢 (HF) 和三甲基铝 (TMA) 作为反应物的连续、自限制暴露且无需吹扫，证明了 Al2O3 原子层蚀刻 (ALE) 速率随时间的显着增加。在 Al2O3 ALE 期间，不需要进行正常的吹扫以防止化学气相蚀刻或化学气相沉积 (CVD)。使用各种技术在 250 至 325°C 的温度范围内对这种免吹扫快速原子层蚀刻 (R-ALE) 进行了研究。原位石英晶体微天平 (QCM) 测量在 300°C 下监测 Al2O3 R-ALE。 Al2O3 R-ALE 工艺产生与 R-ALE 循环次数的线性蚀刻。每次 HF 暴露都会氟化 Al2O3 基材以产生 AlF3 表面层。随后每个剂量的 TMA 都会与 AlF3 表面层发生配体交换金属转移反应，产生挥发性产物。使用 HF = 320 mTorr 和 TMA = 160 mTorr 的反应物分压，氟化和配体交换反应产生了 -32.1 ng/（cm2 循环）的每个循环质量变化（MCPC），使用 HF 和 TMA 连续暴露 1 s，无需吹扫。该 MCPC 相当于 0.99 A/周期或 0.49 A/s 的厚度损失。使用相同的反应物暴露和 30 秒的吹扫时间进行的比较实验产生了几乎相同的 MCPC 值。这些结果表明，Al2O3 R-ALE 的蚀刻速率比普通 Al2O3 ALE 的蚀刻速率快得多，因为循环时间更短且无需净化。对于 Al2O3 R-ALE 和 Al2O3 ALE，在较低反应物压力下也观察到较小的 MCPC 值。 QCM 研究表明 Al2O3 R-ALE 过程相对于反应物暴露具有自限性。非原位光谱椭偏仪和 X 射线反射率 (XRR) 测量揭示了与温度相关的蚀刻速率，从 270°C 时的 0.02 A/周期到 325°C 时的 1.12 A/周期。在较低温度下，AlF3 生长是主要机制，在 250°C 下 AlF3 原子层沉积 (ALD) 生长速率为 0.33A/循环。 AlF3 生长和 Al2O3 蚀刻之间的转变温度发生在~270°C。 XRR 扫描表明，Al2O3 R-ALE 在 ≥270°C 的温度下使 Al2O3 ALD 薄膜变得平滑。此外，还使用图案化晶圆来比较高深宽比结构中的 Al2O3 R-ALE 和普通 Al2O3 ALE。扫描电子显微镜图像显示，两种工艺的蚀刻都是均匀的，并且在高深宽比结构和平坦晶圆上每个周期产生的蚀刻速率相当。 HF 和 TMA 前体也有意重叠，以探索两种前体同时存在时的行为。与 ALD 类似，前体重叠产生 CVD，Al2O3 ALE 期间前体重叠导致 AlF3 CVD。然而，在前体重叠期间发生的任何 AlF3 CVD 生长都会在随后的 TMA 曝光期间通过自发 AlF3 蚀刻去除。这种自发的 AlF3 蚀刻解释了为什么在 R-ALE 过程中不需要净化。 R-ALE 代表了热 ALE 领域的一项重要进步，它产生的快速蚀刻速度将促进许多 ALE 应用。通过使用氟化氢 (HF) 和三甲基铝 (TMA) 作为反应物的连续、自限性暴露而无需吹扫，证明了 Al2O3 原子层蚀刻 (ALE) 速率随时间的显着增加。在 Al2O3 ALE 期间，不需要进行正常的吹扫以防止化学气相蚀刻或化学气相沉积 (CVD)。使用各种技术在 250 至 325°C 的温度范围内对这种免吹扫快速原子层蚀刻 (R-ALE) 进行了研究。原位石英晶体微天平 (QCM) 测量在 300°C 下监测 Al2O3 R-ALE。 Al2O3 R-ALE 工艺产生与 R-ALE 循环次数的线性蚀刻。每次 HF 暴露都会氟化 Al2O3 基材以产生 AlF3 表面层。随后每个剂量的 TMA 都会与 AlF3 表面层发生配体交换金属转移反应，产生挥发性产物。使用 HF = 320 mTorr 和 TMA = 160 mTorr 的反应物分压，氟化和配体交换反应产生了质量变化……
A dramatic increase in the Al2O3 atomic layer etching (ALE) rate versus time was demonstrated using sequential, self-limiting exposures of hydrogen fluoride (HF) and trimethylaluminum (TMA) as the reactants with no purging. The normal purging expected to be required to prevent chemical vapor etching or chemical vapor deposition (CVD) is not necessary during the Al2O3 ALE. This purgeless, rapid atomic layer etching (R-ALE) was studied from 250 to 325 °C using various techniques. In situ quartz crystal microbalance (QCM) measurements monitored Al2O3 R-ALE at 300 °C. The Al2O3 R-ALE process produced linear etching versus number of R-ALE cycles. Each HF exposure fluorinates the Al2O3 substrate to produce an AlF3 surface layer. Each subsequent dose of TMA then undergoes a ligand-exchange transmetalation reaction with the AlF3 surface layer to yield volatile products. Using reactant partial pressures of HF = 320 mTorr and TMA = 160 mTorr, the fluorination and ligand-exchange reactions produced a mass change per cycle (MCPC) of −32.1 ng/(cm2 cycle) using sequential, 1 s exposures for both HF and TMA with no purging. This MCPC equates to a thickness loss of 0.99 A/cycle or 0.49 A/s. Comparison experiments using the same reactant exposures and purge times of 30 s yielded nearly identical MCPC values. These results indicate that the etch rates for Al2O3 R-ALE are much faster than for normal Al2O3 ALE because of shorter cycle times with no purging. Smaller MCPC values were also observed at lower reactant pressures for both Al2O3 R-ALE and Al2O3 ALE. The QCM studies showed that the Al2O3 R-ALE process was self-limiting versus reactant exposure. Ex situ spectroscopic ellipsometry and x-ray reflectivity (XRR) measurements revealed temperature-dependent etch rates from 0.02 A/cycle at 270 °C to 1.12 A/cycle at 325 °C. At lower temperatures, AlF3 growth was the dominant mechanism and led to an AlF3 atomic layer deposition (ALD) growth rate of 0.33 A/cycle at 250 °C. The transition temperature between AlF3 growth and Al2O3 etching occurred at ∼270 °C. XRR scans showed that the Al2O3 ALD films were smoothed by Al2O3 R-ALE at temperatures ≥270 °C. Additionally, patterned wafers were used to compare Al2O3 R-ALE and normal Al2O3 ALE in high aspect ratio structures. Scanning electron microscope images revealed that the etching was uniform for both processes and yielded comparable etch rates per cycle in the high aspect ratio structures and on flat wafers. The HF and TMA precursors were also intentionally overlapped to explore the behavior when both precursors were present at the same time. Similar to ALD, where precursor overlap produces CVD, precursor overlap during Al2O3 ALE leads to AlF3 CVD. However, any AlF3 CVD growth that occurs during precursor overlap is removed by spontaneous AlF3 etching during the subsequent TMA exposure. This spontaneous AlF3 etching explains why no purging is necessary during R-ALE. R-ALE represents an important advancement in the field of thermal ALE by producing rapid etching speeds that will facilitate many ALE applications.A dramatic increase in the Al2O3 atomic layer etching (ALE) rate versus time was demonstrated using sequential, self-limiting exposures of hydrogen fluoride (HF) and trimethylaluminum (TMA) as the reactants with no purging. The normal purging expected to be required to prevent chemical vapor etching or chemical vapor deposition (CVD) is not necessary during the Al2O3 ALE. This purgeless, rapid atomic layer etching (R-ALE) was studied from 250 to 325 °C using various techniques. In situ quartz crystal microbalance (QCM) measurements monitored Al2O3 R-ALE at 300 °C. The Al2O3 R-ALE process produced linear etching versus number of R-ALE cycles. Each HF exposure fluorinates the Al2O3 substrate to produce an AlF3 surface layer. Each subsequent dose of TMA then undergoes a ligand-exchange transmetalation reaction with the AlF3 surface layer to yield volatile products. Using reactant partial pressures of HF = 320 mTorr and TMA = 160 mTorr, the fluorination and ligand-exchange reactions produced a mass change per...