Fabrication of Ferroelectric Thin Films on Large Size Wafers at High Growth Rate by Metal Organic Chemical Vapor Deposition and Their Application to Memory

采用金属有机化学气相沉积（MOCVD）技术在大尺寸硅片上高速制备了Pb(Zr, Ti)O3 （PZT）铁电薄膜，并对其在FeRAM等存储器件中的应用性能进行了评价。在6-8英寸晶圆上形成了成分分布为+- 1.1%、厚度分布为+-1.2%的均匀PZT薄膜。生长速率为4 ~ 15 nm/min。这对于批量生产和源输送系统的改进是不够的。我们发现薄Ir底电极（23 nm）对PZT薄膜铁电性能的改善作用不大，尽管相对厚的Ir底电极显著改善了PZT薄膜的铁电性能。PZT薄膜与Ir电极界面处形成的Pb-Ir非晶层抑制了Pb原子向电极的扩散。IrO_2/Ir/PZT/Ir/IrO_2电容器具有无疲劳性能。我们还发现在MOCVD中使用的金属有机源的纯度对PZT薄膜的电学性能有一定的影响。高纯度源（99.9999%）制备的PZT薄膜的疲劳性能、漏电流和击穿电压均优于低纯度源（99.995%）制备的PZT薄膜。我们通过改变底部Ir电极的晶粒尺寸，成功地控制了相同厚度PZT薄膜的晶粒尺寸。从150 nm左右开始，PZT薄膜的剩余极化随晶粒尺寸的减小而减小。薄膜中的一些缺陷及其在界面或边界处的夹持产生空间电荷分布。我们得出结论，这种空间电荷分布引起了磁滞环的位移和畴钉住。

Pb-based ferroelectric thin films such as Pb(Zr, Ti)O3 (PZT) were fabricated on large size silicon wafers at high growth rate by metalorganic chemical vapor deposition (MOCVD) and their properties were evaluated for the applications to memory devices such as FeRAM.Homogeneous PZT thin films with a composition distribution of +- 1.1% and a thickness distribution of +-1.2% were formed on 6-8 inch wafers. However growth rate was 4-15 nm/min. It is not enough for mass production and improvement of source delivery system. We have found that thin Ir bottom electrodes (23 nm) had little effect on improvement of ferroelectric properties of PZT thin films although relatively thick Ir bottom electrodes significantly improved the properties. It seems that Pb-Ir amorphous layer formed at the interface between the PZT films and the Ir electrodes suppress the diffusion of Pb atoms into the electrodes. IrO_2/Ir/PZT/Ir/IrO_2 capacitor exhibited fatigue-free properties. We have also found that purity of metalorganic sources using in MOCVD had some effect on the electrical properties of PZT thin films. PZT thin films fabricated by using high purity sources (99.9999%) were better in fatigue properties, leakage current and breakdown voltage than those fabricated by using low purity ones (99.995%). We have succeeded in the control of grain size of PZT thin films with same thickness by changing the grain size of bottom Ir electrodes. It is found that remanent polarization of the PZT thin films begin to decrease with decreasing of grain size from about 150 nm. Some defects in the films and their entrapment at the interface or boundary generate space charge distribution. We have concluded that this space charge distribution cause the shift of hysteresis loops and domain pinning.