(A) study on the atomic layer deposition of Ir and $IrO_2$ thin films

Abstract

Recently, high-k dielectrics are widely used for dynamic random access memory (DRAM) capacitor to guarantee storage capacitance. To integrate high-k dielectrics, high temperature process in oxygen ambient is required for deposition or crystallization of the high-k dielectrics. And thus electrode materials should remain conductively after exposure of highly oxidizing conditions. Ir and $IrO_2$ are one of the most promising candidates for DRAM capacitor electrode because of their low resistivity, oxygen barrier property and thermal stability. In this study, atomic layer deposition (ALD) of Ir and $IrO_2$ thin films was investigated for the first time using (ethylcyclopentadienyl)(1,5-cyclooctadien)iridium [Ir(EtCp)(COD)] as a metal precursor and oxygen as a reactant gas at a temperature range from 210 to $290^\circ C$. And this is the first result of $IrO_2$ deposition using ALD all over the world. Control of Ir and $IrO_2$ is achieved successfully by control of $O_2/(Ar+O_2)$ ratio, deposition pressure, and deposition temperature. The dominant factor for transition of Ir and $IrO_2$ is oxygen partial pressure during oxygen injection pulse. Above the critical oxygen partial pressure, deposition rate and resistivity of deposited films were increased due to formation of $IrO_2$ film. High oxygen partial pressure can be obtained by increment of $O_2/(Ar+O_2)$ ratio and increment of deposition pressure. And thus $IrO_2$ films can be obtained by increasing $O_2/(Ar+O_2)$ ratio at the same deposition pressure or can be obtained by increasing deposition pressure at the same $O_2/(Ar+O_2)$ ratio. As the deposition temperature is increased, the critical oxygen partial pressure for transition of Ir and $IrO_2$ is also increased. Thermodynamical calculation was performed to explain this phenomenon. Ir film having resistivity of about 9 $μΩ \cdot cm$ was deposited with saturated deposition rate of 0.145 nm/cycle and digital thickness control. $IrO_2$ films with 120 $...