Low temperature deposition of Al_2O_3 insulating thin films by photo-CVD

以三异丙醇铝（ATI）为原料，采用光气相沉积法制备了Al_2O_3薄膜，并对其性能进行了表征。1. 在N_2+O_2或N_2+H_2气氛下，沉积速率比在N_2气氛下（无UV）有所提高。在N_2+O_2和N_2+H_2气氛下，沉积活化能分别为1.5 kcal/mol和3.5 kcal/mol。这些数值与N_2气氛下分解沉积的18 ~ 20 kcal/mol相比较小，说明ATI与O_2或H_2的反应有助于Al_2O_3的沉积。从O_2流速对沉积速率的依赖关系可以看出，ATI和O_2分子的Langmuir-Hinshelwood机制沉积和ATI的热分解沉积都有发生。在N_2+O_2气氛下，低压汞灯紫外照射下，基底温度低于300℃时，沉积速率显著提高，沉积反应活化能低至1.5 kcal/mol。在60 ~ 300 sccm的O_2流量范围内，沉积速率基本不变。来自汞灯的185 nm光被发现是导致沉积速率增加的主要原因。2. 所沉积的Al_2O_3薄膜主要以介电损耗因子tan为表征指标。在260℃的n2 +O_2气氛下，光气相沉积法制备的样品比在n2或n2 +O_2气氛下热气相沉积法制备的样品的tan值更小，即光气相沉积法制备的薄膜质量得到了较大的改善。在O_2流速为20 ~ 300 sccm，衬底温度为280 ~ 340℃的条件下，tan的值基本不变，在衬底温度为280℃时，tan的典型值为2.5%。由此可见，在N_2+O_2气氛下，在低于300℃的衬底温度下，以较高的沉积速率获得了高质量的Al_2O_3薄膜。

Al_2O_3 thin films were deposited by photo-CVD using Aluminum- triisopropoxide(ATI) as a source material, and their properties were characterized. 1. The deposition rate increased under N_2+O_2 or N_2+H_2 atmosphere compared with that under N_2 atmosphere (without UV). The activation energy of deposition was 1.5 kcal/mol and 3.5 kcal/mol for N_2+O_2 and N_2+H_2 atmosphere, respectively. These values are small compared with the value of 18-20 kcal/mol for the decomposition deposition under the N_2 atmosphere, which shows that reactions of ATI with O_2 or H_2 help Al_2O_3 deposition. It turned out from the O_2 flow rate dependence of the deposition rate that the deposition due to the Langmuir-Hinshelwood mechanism of ATI and O_2 molecules occurred as well as the deposition due to the thermal decomposition of ATI.With UV irradiation of low-pressure Hg lamps under N_2+O_2 atmosphere, the deposition rate increased largely at low substrate temperatures less than 300 C, and the activation energy of the deposition reaction was as small as 1.5 kcal/mol. The deposition rates were almost constant in the O_2 flow rate range of 60 - 300 sccm. The 185 nm light from the Hg lamps was found to be strongly responsible for the increase in the deposition rate. 2. The Al_2O_3 films deposited were characterized mainly by the dielectric loss factor tan at, 100 Hz. The samples prepared by photo-CVD under N_2+O_2 atmosphere at 260 C showed smaller tan values compared with those of the samples prepared by thermal CVD under N_2 or N_2+O_2 atmosphere, that is, the film quality was improved largely by photo-CVD. The values of tan were almost constant under the conditions of the O_2 flow rate of 20 - 300 sccm and the substrate temperature of 280 - 340 C. The typical value of tan was 2.5 % at the substrate temperature of 280 C.In conclusion, Al_2O_3 films with high quality were obtained at high deposition rates at low substrate temperatures less than 300 C by photo-CVD under N_2+O_2 atmosphere.