Short- and long-term plasma phenomena in a HiPIMS discharge
Short- and long-term plasma phenomena in a HiPIMS discharge
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DOI：
10.1088/0963-0252/19/2/025010
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发表时间：
2010-04
影响因子：
3.8
通讯作者：
P. Poolcharuansin;J. Bradley
中科院分区：
文献类型：
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作者：
P. Poolcharuansin;J. Bradley
利用时间分辨朗缪尔探针研究了高功率脉冲磁控溅射（HiPIMS）放电中不同放电条件下等离子体参数的时间演化规律。磁控管在0.5至1.6 Pa的氩气中使用钛靶操作，峰值靶功率密度高达1000 W cm-2。脉冲宽度和重复频率分别保持恒定在100 µs和100 Hz。使用OML分析以及Druyvesteyn公式，获得了整个脉冲周期（0-9 ms）的电子密度，有效温度和能量分布函数，包括前10 µs的详细研究，其时间分辨率优于0.5 µs。在电压脉冲的初始阶段（t = 1-4 µs），观察到三组不同的电子（与麦克斯韦电子无法区分），即有效温度分别为70-100 eV，5-7 eV和0.8-1 eV的“超热”，“热”和“冷”群体。4 µs后，这些基团在能量上变得无法区分，形成一个单一的分布，电子温度在其余的脉冲开启时间内从5 eV衰减到3 eV。在脉冲的初始阶段，“超热”电子群的存在将探针浮置电位推到非常负的值（比−95 V深得多）。在非工作时间，电子密度以两倍的特征时间衰减，揭示了最初的短期（30-40 µs）和最终的长期（3-4 ms）衰减速率。这些长的衰减时间导致在截止时间结束时相对高密度的残余等离子体（2 × 109 cm−3），其用于播种下一个电压脉冲。电子温度和等离子体电势在关断时间内也表现出两倍的衰减，但通常会有更快的衰减，特别是在关断时间结束前的长期衰减（100-500 µs）。等离子体电位的时间演化表明，在相当长的导通时间内，等离子体电位保持为负（低至−12 V），仅在t ≤ 60 µs后变为正，这对应于最大等离子体密度的时间（典型值为2 × 1012 cm−3）。在放电的初始阶段的超热电子的产生，认为通过一个简单的磁化电子反弹模型的扩展鞘的发展。
Using a time-resolved Langmuir probe the temporal evolution of the bulk plasma parameters in a high-power impulse magnetron sputtering (HiPIMS) discharge was investigated for a number of different discharge conditions. The magnetron was operated in argon between 0.5 and 1.6 Pa with a titanium target and with peak target power densities up to 1000 W cm−2. The pulse width and repetition rate were held constant at 100 µs and 100 Hz, respectively. Using an OML analysis as well as a Druyvesteyn formulation, the electron densities, effective temperatures and energy distribution functions were obtained throughout the pulse period (0–9 ms), including a detailed study of the first 10 µs, which was achieved with a temporal resolution better than 0.5 µs. In the initial phase of the voltage pulse (t ∼ 1–4 µs), three distinct groups of electrons (indistinguishable from Maxwellian electrons) were observed, namely ‘super-thermal’, ‘hot’ and ‘cold’ populations with effective temperatures of 70–100 eV, 5–7 eV and 0.8–1 eV, respectively. After 4 µs these groups become energetically indistinguishable from each other to form a single distribution with an electron temperature that decays from about 5 to 3 eV during the rest of the pulse on-time. The presence of the ‘super-thermal’ electron group pushes the probe floating potential to a very negative value (significantly deeper than −95 V) during the initial period of the pulse. In the off-time, the electron density decays with two-fold characteristic times, revealing initially short-term (30–40 µs) and ultimately long-term (3–4 ms) decay rates. These long decay times lead to a relative high density remnant plasma (2 × 109 cm−3) at the end of the off-time, which serves to seed the next voltage pulse. The electron temperature and plasma potential also exhibit two-fold decay in the off-time, but with typically somewhat faster decays, particularly for the long-term decay (100–500 µs) up to the end of the off-time. The time evolution of the plasma potential shows that for a considerable fraction of the on-time the plasma potential remains negative (down to −12 V) only becoming positive after t ∼ 60 µs which corresponds to a time of maximum plasma density (typical values of 2 × 1012 cm−3). The generation of super-thermal electrons in the initial phase of the discharge is argued through the development of a simple magnetized-electron bounce model of the expanding sheath.