Structure control of sputter deposited noble metal thin films using surfactant

期望具有非常光滑的表面形态和高晶体取向的贵金属薄膜用作DRAM（动态随机存取存储器）和铁电存储器（FeRAM）的电容器电极，以及用作自旋阀膜，其应用于磁记录装置。为了改善贵金属薄膜的表面形貌和晶体取向，引入少量的活性气体作为表面活性剂，采用射频磁控溅射法制备了Ru薄膜，并将其用作DRAM和FeRAM的电容电极。研究了衬底温度、沉积速率和溅射气体（Ar+O_2）组成对Ru薄膜表面形貌和晶体取向的影响。在衬底温度为500℃、沉积速率小于10 nn/min、溅射的最佳工艺条件下，得到了表面粗糙度约为1 nm、XRD摇摆曲线宽度为1.2°的平整、高度c轴取向的Ru薄膜 ...更多信息 气体流量比O_2/（Ar+O_2）为百分之几。O_2气体作为表面活性剂，降低了Ru C面的表面自由能，进而抑制Ru原子的聚集，改善了Ru膜的表面形貌。其次，研究了介质膜沉积条件对Ru膜表面粗糙度的影响，这对Ru膜在DRAM电容器中的应用具有重要意义。在不同衬底温度下，在Ru膜上溅射沉积Ta_2O_5薄膜。结果表明，当沉积温度低于400℃时，Ta_2O_5/Ru多层膜的表面和界面保持平整，而当沉积温度为500℃时，多层膜的表面和界面变得粗糙。研究发现，Ru膜的氧化和RuO_2的形成是导致表面和界面粗糙的主要原因。为了避免Ru膜的氧化和保持光滑的表面形貌，介质膜的沉积温度应低于400℃。少

Noble metal thin films with very smooth surface morphology and high crystal orientation are desired for use as capacitor electrodes of DRAM (Dynamic Random Access Memory) and Ferroelectric memory (FeRAM), and as spin valve films, which are applied for magnetic recording devices. We aimed to improve the surface morphology and crystal orientation of noble metal thin films by introducing a small amount of active gas which act as a surfactant.Ru thin films, which are used as capacitor electrodes of DRAM and FeRAM were deposited by RF magnetron sputtering system. Effects of substrate temperature, deposition rate and composition of sputtering gas (Ar+O_2) on surface morphology and crystal orientation of Ru thin films were studied. Very flat and highly c-axis single oriented Ru films with surface roughness of about 1nm and XRD rocking curve width of 1.2° were obtained under optimum deposition conditions, which are substrate temperature of 500℃, deposition rate below 10 nn/min, and sputtering … More gas flow ratio, O_2/(Ar+O_2) of several %. It is thought that O_2 gas acts as a surfactant and decrease the surface free energy of Ru c-plane and furthermore, O_2 gas is expected to inhibit aggregation of Ru atoms and improve surface morphology.Next, effects of deposition conditions of dielectric films on the surface roughness of Ru films were studied, because it is very important for the application of Ru films to DRAM capacitors. Ta_2O_5 films were sputter deposited under various substrate temperatures on Ru films. It was found that the surface and interface of Ta_2O_5/Ru multilayer remain flat if the Ta_2O_5 films were deposited below 400℃, however, those of the multilayers become rough at a deposition temperature of 500℃. The reason for the surface and interface roughness was found to be the oxidation of Ru films and the formation of RuO_2. It is clarified that deposition temperature of dielectric films should be lower than 400℃ to avoid the oxidation of the Ru film and maintain smooth surface morphology. Less