SOI埋氧层应力对高灵敏微悬臂梁制作的影响机理研究

Based on the thermo-mechanical noise theory, a long, narrow and thin microcantilever with a high quality factor (Q factor) will be a perfect ultra-sensitive force detector .The spring constant of the ultra-sensitve microcantileve is 1000 times smaller than that of the typical cantilever in atomic force microscopy (AFM). Thus, it is fragile and easily to break during the fabrication. The buried oxide (BOX) layer is found to crack at the end of the bulk etching due to the large internal compressive stress formed during the thermal oxidation. It leads to the breaking of the Si cantilevers on the BOX. After confirming the source of the internal compressive stress, we prepare to build the theory model, to analyse the reason of the BOX breaking. Based on the research, two kinds of solutions are proposed to make sure of the success of the cantilevers fabrication. The first solution is to pattern the BOX layer, to realease the internal compressive stress, which is making the BOX layer break at the pointed place. Thus, it will avoid the breaking of the silicon cantilevers. The second solution is to sputter a film with internal tensile stress, such as silicon nitride film with PECVD, to restrict the deformation of the BOX layer, and reinforce the structure. As the development of the SOI technology, more and more micro-sensors would fabricated based on SOI wafer. This work is researching the discipline between the BOX stress and the fabricaiton of the silicon cantilevers, however, is meaningful to the entire fabrication of micro-sensors based on SOI wafer.

基于热噪声原理，更长、更薄、更窄的高品质因数(Q值)微悬臂梁，是高灵敏力探测器。由于尺寸特性，高灵敏微悬臂梁与普通悬臂梁相比，刚度低三个数量级，使得加工时容易造成损坏。在制作高灵敏微悬臂梁实验中，我们发现SOI埋氧层薄膜会发生破裂，从而导致微悬臂梁随之折断，使得加工失败。经分析，埋氧层破裂源于薄膜内部存在压应力。针对该问题：我们首先明确内应力来源；其次对埋氧层薄膜进行力学建模，分析破裂机理。在此基础之上，提出两种解决方案：埋氧层图形化释放内应力；表面覆盖拉应力薄膜约束埋氧层。其中，前者是令埋氧层在指定位置破裂，后者是加固整体结构防止破裂，最终实现微悬臂梁高产率加工。随着SOI技术发展，基于SOI制作薄结构传感器的场合越来越多。本课题以高灵敏微悬臂梁传感器为代表，系统研究SOI埋氧层应力对传感器制作的影响机理，得出的影响规律对整个基于SOI的微传感器制作领域均具有实际意义。

经分析，埋氧层破裂源于薄膜内部存在压应力。针对该问题：我们首先明确内应力来源；其次对埋氧层薄膜进行力学建模，分析破裂机理。在此基础之上，提出两种解决方案：埋氧层图形化释放内应力；表面覆盖拉应力薄膜约束埋氧层。其中，前者是令埋氧层在指定位置破裂，后者是加固整体结构防止破裂，最终实现微悬臂梁高产率加工。随着SOI技术发展，基于SOI制作薄结构传感器的场合越来越多。本课题以高灵敏微悬臂梁传感器为代表，系统研究SOI埋氧层应力对传感器制作的影响机理，得出的影响规律对整个基于SOI的微传感器制作领域均具有实际意义。发表论文4篇，申请发明专利3项，培养硕士研究生一名。