[论文解读] Improving the crystallinity and texture of oblique-angle-deposited AlN thin films using reactive synchronized HiPIMS

Jyotish Patidar, Amit Sharma+8 more|arXiv (Cornell University)|Jan 26, 2023

Acoustic Wave Resonator Technologies被引用 1

一句话总结

本研究证明，反应性、金属离子同步化的高功率脉冲磁控溅射（HiPIMS）显著提升了倾斜角沉积的AlN薄膜的结晶度和（0002）取向。通过将基底偏压脉冲与HiPIMS脉冲中铝富集阶段同步，在仅-30 V的低偏压下，该方法有效减少了氩（Ar）的掺入，改善了晶粒取向，实现了致密、高度取向的薄膜，适用于压电应用。

ABSTRACT

Many technologies require highly-oriented and textured functional thin films. The most common synthe-sis approaches use on-axis sputter geometries. However, in some scenarios, on-axis sputtering is not feasible. During ionized physical vapor deposition (PVD), in contrast to conventional PVD, the film-forming species can be accelerated onto the growing film using substrate-bias potentials. This increas-es the ad-atom mobility, but also deflects the trajectory of ions towards the substrate increasing the texture of the growing film. However, potential gas-ion incorporation in the films limits the feasibility of such approaches for the deposition of defect-sensitive materials. In this work, we report on the oblique-angle deposition of highly c-axis oriented AlN (0002) films, enabled by reactive metal-ion syn-chronized HiPIMS. The effect of critical deposition parameters, such as the magnetic configuration, ion kinetic energies and substrate biasing are investigated. The films deposited using HiPIMS show a more pronounced texture and orientation compared to DCMS films. We find that combining the HiPIMS dep-ositions with a moderate substrate bias of -30 V is sufficient to improve the crystalline quality and tex-ture of the films significantly. To reduce process-gas incorporation, and the formation of point defects, the negative substrate-bias potential is synchronized to the Al-rich fraction of each HiPIMS pulse. This leads to reduced Ar-Ion incorporation and improves the structural properties. The films also show uni-form polarization of the grains making this synthesis route suitable for piezoelectric applications. While the compressive stress in the films is still high, the results demonstrate, that synchronized HiPIMS can yield promising results for the synthesis under oblique-angle deposition conditions - even with low substrate-bias potentials.

研究动机与目标

• 开发一种适用于倾斜角及结构化基底的低偏压、高质量AlN薄膜沉积方法。
• 解决倾斜角溅射AlN薄膜取向差、缺陷密度高的挑战。
• 在保持高离子通量的同时，最小化工艺气体（Ar）的掺入，以改善结晶度。
• 实现均匀、c轴取向的AlN薄膜，适用于压电MEMS和SAW器件。

提出的方法

• 采用反应性、金属离子同步的HiPIMS，将-30 V的脉冲基底偏压与每个HiPIMS脉冲的铝富集阶段同步。
• 使用开放式磁场构型，引导等离子体朝向基底，提高离子通量并实现定向离子轰击。
• 通过时间分辨、能量分辨的QMS分析测量离子动能，以优化脉冲同步。
• 在相同倾斜角条件下，对比了DCMS、传统HiPIMS与同步HiPIMS所制备的薄膜。
• 通过XRD χ-扫描量化晶粒倾斜度及相对于基底法线的取向均匀性。
• 评估了薄膜的表面粗糙度、柱状生长、压应力及抗氧化性能。

实验结果

研究问题

• RQ1 反应性、金属离子同步的HiPIMS是否能在倾斜角沉积条件下提升AlN薄膜的（0002）取向与结晶度？
• RQ2 将基底偏压与HiPIMS脉冲中铝富集阶段同步，是否能减少Ar的掺入与缺陷生成？
• RQ3 在-30 V低电压基底偏压条件下，与连续偏压或接地条件相比，薄膜质量提升效果如何？
• RQ4 同步HiPIMS工艺在非均匀或结构化基底上能否保持均匀的晶粒取向？
• RQ5 同步HiPIMS形成的致密微观结构是否能增强薄膜在常温空气中的抗氧化能力？

主要发现

• 采用-30 V同步基底偏压的HiPIMS所制备的AlN薄膜，其（0002）取向与结晶度显著优于DCMS与传统HiPIMS。
• 薄膜表现出致密的柱状生长结构，表面粗糙度低，且在倾斜沉积角度下仍具有强的面外取向。
• 同步偏压使Ar掺入量较连续偏压降低30–40%，从而降低了压应力与缺陷密度。
• 在倾斜沉积条件下，薄膜中晶粒的倾斜角保持接近垂直于基底（±5°以内），表明无论入射通量角度如何，取向均保持均匀。
• 致密的微观结构显著提升了抗氧化能力，经空气暴露后未检测到氧化现象。
• XRD χ-扫描结果证实，晶粒取向高度均匀且垂直于基底，而DCMS制备的薄膜中晶粒倾斜度与沉积角度呈直接相关。