沉积温度对电子束蒸发HfO_2薄膜残余应力的影响

Influences of Deposition Temperature on Residual Stress of HfO_2 Films Prepared by Electron Beam Evaporation

采用电子束蒸发沉积方法在BK7玻璃基底和熔融石英基底上沉积了HfO2薄膜,研究了不同沉积温度下的应力变化规律。利用ZYGO干涉仪测量了基片镀膜前后曲率半径的变化,计算了薄膜应力。结果发现在所考察的实验条件下HfO2薄膜的残余应力均为张应力,应力值随沉积温度的升高先增大后减小。两种基底上薄膜的残余应力的主要产生机制不同。对于BK7玻璃基底HfO2薄膜的残余应力起决定作用的是内应力,熔融石英基底上HfO2薄膜的残余应力在较低沉积温度下制备的薄膜起决定作用的是热应力,在沉积温度进一步升高后内应力开始起决定作用。通过对样品的X射线衍射(XRD)测试,发现在所考察的温度范围内,HfO2薄膜的结构发生了晶态转换,这一结构转变与薄膜残余应力的变化相对应。两种基底上薄膜微结构的演变及基底性能差异是两种基底上薄膜应力不同的主要原因。

HfO2 films were prepared by electron beam evaporation on BK7 glass and fused silica substrates. The residual stress was measured by viewing the substrate deflection using ZYGO interferometer. The results show that the residual stresses of HfO2 films on both substrates are tensile and increase with the increase of deposition temperature firstly, then decrease. The main origin mechanisms of residual stress are different. For films on BK7 glass substrate, the intrinsic stress is the determinate factor. While for films on fused silica substrate, the evolution of the residual stress is mainly due to the thermal stress in lower temperature. The microstructure of the HfO2 films was inspected by X-ray diffraction （XRD）. It is found that the microstructure of the films transmitted from amorphous to polycrystalline, which is corresponding to the variation of the residual stress. The differences of the film residual stress for two substrates may be due to the evolution of the microstructure as the increasing of the deposition temperature and differences of properties between two kinds substrates.