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Postdeposition annealing effect on the reliability of atomic-layer-deposited Al2O3films on GaN
Journal of Vacuum Science & Technology B ( IF 1.4 ) Pub Date : 2020-10-09 , DOI: 10.1116/6.0000531
Kiyotaka Horikawa 1 , Satoshi Okubo 1 , Hiroshi Kawarada 1, 2, 3 , Atsushi Hiraiwa 3, 4
Affiliation  

Atomic-layer-deposited (ALD) Al2O3 is a promising gate insulation material for wide-bandgap semiconductor devices of increasing importance for high-speed and high-power switching operation. This study comprehensively reports on postdeposition annealing (PDA) effects on the reliability of ALD-Al2O3/GaN metal-insulator-semiconductor capacitors. High-temperature (450 °C) ALD for the Al2O3 growth was effective for reducing the bias instability (BI) of the capacitors and for suppressing the blisters caused by PDA in the Al2O3 films. The BI of the high-temperature Al2O3 capacitors was reduced more remarkably by PDA at high temperatures. The conduction current in the capacitors was also reduced by PDA at 800 °C and higher by 2 orders of magnitude. The high-temperature PDA, however, caused a positive flat-band voltage shift and increased the distribution of times to breakdown of the capacitors and the interface-state density from 1 × 1011 to 3 × 1012 cm−2 eV−1, causing the large frequency dispersion of CV characteristics. This increase in the interface-state density was found to be the major cause of the aforementioned flat-band voltage shift by PDA, whereas the stress-induced flat-band voltage shift was mostly due to the negative Al2O3 charging. In agreement with the literature, transmission electron microscope observations demonstrated the crystallization of Al2O3 films by annealing at 800 °C and higher, ascribing the increased distribution of times to breakdown to some crystalline defects in the Al2O3 films. Hence, the best PDA effect was achieved at 700 °C, reducing BI by half in 200 °C operation. For this PDA, the breakdown lifetimes of capacitors were confirmed to be the same, if not longer, as those of unannealed samples even at an elevated temperature of 200 °C, achieving 300 years at the rating of 3 MV/cm, well over the reliability target of 20 years. To put the ALD-Al2O3/GaN capacitors into practical use, PDA possibly needs to be performed before contact formation and their BI should preferably be further improved, simultaneously carrying out its long-term projections.

中文翻译:

沉积后退火对GaN上原子层沉积Al2O3薄膜可靠性的影响

原子层沉积(ALD)Al 2 O 3是一种有前途的栅极绝缘材料,用于宽带隙半导体器件,对高速和大功率开关操作越来越重要。这项研究全面报道了沉积后退火(PDA)对ALD-Al 2 O 3 / GaN金属-绝缘体-半导体电容器可靠性的影响。Al 2 O 3生长的高温(450°C)ALD有效降低了电容器的偏压不稳定性(BI),并抑制了PDA引起的Al 2 O 3膜起泡。高温Al 2 O 3的BI在高温下,PDA可显着减少电容器的使用。PDA在800°C时,电容器中的传导电流也降低了,并提高了2个数量级。但是,高温PDA会引起正的平带电压偏移,并使电容器击穿的时间分布和界面态密度从1×10 11增加到3×10 12 cm -2  eV -1,导致CV特性的大频率色散。发现界面态密度的这种增加是上述PDA引起的平带电压偏移的主要原因,而应力引起的平带电压偏移主要是由于负的Al 2引起的。O 3充电。与文献一致的是,透射电子显微镜的观察结果表明,通过在800°C和更高的温度下退火,Al 2 O 3膜发生了结晶,这归因于分解到Al 2 O 3膜中某些晶体缺陷的时间增加了。因此,在700°C时可获得最佳的PDA效果,在200°C的操作中将BI降低了一半。对于这种PDA,即使在200°C的高温下,也可以确定电容器的击穿寿命与未退火样品的击穿寿命相同,甚至更长,在3 MV / cm的额定值下可以达到300年,远超过可靠性目标为20年。放入ALD-Al 2 O 3在/ GaN电容器投入实际使用时,可能需要在接触形成之前执行PDA,并且最好进一步改善其BI,同时执行其长期预测。
更新日期:2020-12-04
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