离子束刻蚀技术在SAW滤波器频率修整上的应用

Application of Ion Beam Etching Technique in SAW Filter Frequency Trimming

随着声表面波(SAW)滤波器的应用向高频、窄带方向延伸,在制造过程中准确地控制其中心频率及一致性变得越来越困难,需要对SAW滤波器的频率进行微调。重点介绍了一种在SAW滤波器上可实现目标频率修整的离子束刻蚀修频工艺,通过实验发现刻蚀厚度不同对滤波器表面的影响程度不同,一次离子束刻蚀厚度为50 nm时,铝膜表面出现微结构变化。分析了对晶圆、器件进行离子刻蚀工艺引起热损伤的机理,表征了不同刻蚀厚度对SAW滤波器粘接芯片的剪切力和硅铝丝键合力的影响。根据实验现象及结果提出了分梯度多次刻蚀的优化方案,给出了不同刻蚀厚度的刻蚀精度,对实验结果进行拟合,得到中心频率与刻蚀厚度的关系方程,从频率、插入损耗和通带方面分析了离子束刻蚀工艺对SAW滤波器电学性能的影响。经离子束刻蚀修频后,滤波器中心频率提高2 MHz,中心频率标准差由0.4 MHz减少为0.15 MHz,中心频率的均一性由0.29%改善至0.11%,频率一致性变好。

As application of surface acoustic wave(SAW)filters extends to the direction of high frequency and narrow band,it becomes more and more difficult to accurately control the center frequency and consistency of SAW filters during manufacturing process,which requires finetuning the frequencies of SAW filters.An ion beam etching frequency trimming technology to achieve target frequency trimming on SAW filters was introduced.Through experiments,it is found that different etching thicknesses have different influences on the filter surface.The microstructure of aluminum film surface is changed when the etching thickness is 50 nm in a single ion beam etching.The mechanism of thermal damage caused by ion etching technology on wafers and devices was analyzed,and the influences of different etching thicknesses on the chip shear force and Si-Al wire bonding force of SAW filters were characterized.According to the experimental phenomena and results,the optimal solution of multiple etching in gradient was proposed.The etching accuracy of different etching thicknesses was given.The relation equation between center frequency and etching thickness was obtained by fitting the experimental results.The effect of ion beam etching technology on the electrical properties of SAW filters was analyzed from the aspects of frequency,insertion loss and passband.After frequency trimming by ion beam etching,the center frequency of the filter increases 2 MHz,the center frequency standard deviation decreases from 0.4 MHz to 0.15 MHz,the center frequency uniformity improves from 0.29%to 0.11%,and the frequency consistency becomes better.