毫米级空气轴承的结构与MEMS制造工艺研究

Characterization and Fabrication of Micro Air Bearing with Micro Channels Via MEMS Technique

为了研究应用于微型推进系统的微型空气轴承(Micro Air Bearing,MAB)的结构形式及微机电系统(Micro-Electro-Mechanical System,MEMS)制造工艺,在保证性能需求的前提下,充分考虑轴承结构与MEMS工艺尤其是多层硅直接键合技术(Silicon Direct Bonding,SDB)的兼容性,提出了总厚度为1.5mm的新型结构形式并制定了完整的制造工艺流程;针对微型空气轴承制造的3B(Bearing,Blade,Bonding)挑战,采用变量实验的方法,研究了刻蚀参数对于轴承结构精度的影响规律,轴承侧壁垂直度达到89°,侧壁粗糙度小于10nm,消除了腐蚀扩散等常见的MEMS工艺缺陷,提高了叶片结构的完整性和均匀性,获得了多层硅直接键合的最优工艺参数,通过MATLAB图像处理程序定量分析三层直接键合率达到85%,优于之前报道的结果。研究结果说明,MEMS制造工艺能够用于微型空气轴承的制造,但在结构设计中必须考虑工艺兼容性,刻蚀的偏压功率和腔体压力对于径向轴承的侧壁垂直度和粗糙度具有重要影响,在刻蚀叶片时必须调整刻蚀保护循环比来保证其结构的完整性和均匀性,减少键合层数和应力累积水平对于多层硅直接键合率的提升具有重要作用。

In order to study the structure and Micro-Electro-Mechanical System （MEMS） manufacturing process of micro air bearing （MAB） applied to micro propulsion system, on the premise of ensuring performance requirements, the compatibility of the structure with the MEMS process, especially the silicon direct bonding technique （SDB） of muhilayer, is fully considered and an innovative structure with a total thickness of 1.Smm is proposed, the manufacturing process of which is also developed. Many new approaches are proposed to overcome the 3B （Bearing, Blade, Bonding） challenges for MEMS manufacturing of micro air bearing. The influence of the etching parameters on structural accuracy of bearings is investigated by means of variable experiment, the verticality of bearing side wall exceeded 89~with its roughness less than 10nm. The common defect of wet etch diffu- sion is eliminated, in addition, the integrity and uniformity of the blade structure are improved. The optimum pro- cess parameters for SDB of muhilayer are obtained and the SDB bonding rate of three layers reached 85% through the quantitative analysis of MATLAB image processing program, which is better than previously reported results. The results show that the MEMS process can he used in the manufacture of micro air bearing, but the process compatibility must be cautiously considered in the structural design process. The bias power and chamber pres- sure have important influence on the verticality and roughness of the side wall of journal bearing. Besides, the etching to protection cycle must be adjusted to ensure the integrity and uniformity of the structure when etching the blades. The reduction of bonding layers and stress accumulation of silicon wafer plays an important role in im- proving the SDB bonding rate of multilayer.