Preparation of Ta Solid Solution Anodized Capacitor and Evaluation of its Reliability

尽管HfO_2和ZrO_2膜作为Si-LSI MOS器件中的高介电常数材料近年来备受关注，但对Hf和Zr氧化膜的电学性质的研究还很少。在此基础上，我们对Hf膜和Zr膜的电容器特性和阳极氧化电容器的漏电流特性进行了初步的研究，并与Ta膜进行了比较。结果表明，Hf和Zr两种阳极氧化膜的电容器性能均优于Ta阳极氧化膜，因为即使在阳极氧化厚度变薄的情况下也能获得低损耗和高介电常数的电容器。此外，我们还发现Hf阳极氧化膜的导电机制是由于肖特基效应，而锆阳极氧化膜的导电机制是由于Poole-Frenkel导电。其次，从氧化层厚度的降低效应和耐热性能的角度考察了Ta-Zr合金固溶体阳极氧化膜的电容器性能和漏电流特性。结果表明，在氧化层厚度很薄的情况下，使用这种钽锆阳极氧化电容器可以实现高介电常数和高耐热性能的低损耗电容器。我们推测，高可靠性能的原因可能归因于Ta与Zr的合金化作用和导电机制从Poole-Frenkel转变为肖特基导电。

Electrical properties of anodic oxide films of Hf and Zr have not yet been investigated sufficiently, although HfO_2 and ZrO_2 films are recently attracted much attention as high -k materials in Si-LSI MOS devices. Then, we investigated fundamentally the capacitor properties and the leakage current properties of anodized capacitors of Hf and Zr films and compared with that of Ta anodized capacitor. As a result, it is revealed that the capacitor properties of both Hf and Zr anodized films are superior to that of Ta anodized film, because capacitors with low - loss properties and high permittivity are obtained, even if anodized thickness becomes very thin. In addition, we found that the electrical conduction mechanisms of Hf anodized film was due to the Schottky effect, while that of Zr anodized film was due to the Poole-Frenkel conduction. Furthermore, it is confirmed that the thermal stability of Hf anodized capacitor is superior to that of Zr anodized capacitor.Next, we examined the capacitor properties and the leakage current properties of anodized film of Ta - Zr alloy as a solid solution, from the viewpoints of reduction effect of oxide thickness and heat - proof properties. As a result, it is concluded that the low - loss capacitor with high permittivity and high heat-proof properties can be realized, using this Ta -Zr anodized capacitor, in spite of very thin oxide thickness state. We speculated that the reason of the high reliable properties may be ascribed to the alloying effect of Ta with Zr and the change of conduction mechanism from Poole-Frenkel to Schottky conduction.