微剪切应力传感器的加工工艺

提出了一种感测单元不直接接触流场的微剪切应力传感器结构，详细阐述了其感测单元MEMS制作工艺。采用热氧化硅掩膜方法解决了硅深刻蚀的选择比问题；优化后的硅深刻蚀工艺参数：刻蚀功率1600 W、低频(LF)功率100 W，SF6流量360 cm3/min，C4F8流量300 cm3/min，O2流量300 cm3/min。采用Cr/Au掩膜，30 ℃恒温低浓度HF溶液解决了玻璃浅槽腐蚀深度控制问题；喷淋腐蚀和基片旋转等措施提高了玻璃浅槽腐蚀表面质量。采用上述MEMS工艺制作了微剪切应力传感器样品，样品测试结果表明：弹性悬梁长度和宽度误差均在2 m以内、玻璃浅槽深度误差在0.03 m以内、静态电容误差在0.2 pF以内，满足了设计要求。

Fabrication process of micro shear stress sensors

The research and testing technique of friction sensor is an important support for hypersonic aircraft. Compared with the conventional skin friction sensor, the micro shear stress sensor has the advantages of small size, high sensitivity, good stability, and good dynamic response. The micro shear stress sensor can be integrated with other flow field sensors whose process is compatible with that of the micro shear stress sensor to achieve multi-physical measurement of the flow field; and the micro-friction balance sensor array enables large area and accurate measurement for the near-wall flow. A micro shear stress sensor structure is proposed, whose sensing element does not directly contact with the flow field. The MEMS fabrication process of the sensing element is described in detail. The thermal silicon oxide is used as the mask to solve the selection ratio problem of silicon deep reactive ion etching(DRIE). The optimized process parameters of DRIE are etching power 1600 W/LF power 100 W, SF6 flux 360 cm3/min, C4F8 flux 300 cm3/min, O2 flux 300 cm3/min. With Cr/Au mask, etching depth of glass shallow groove can be controlled at 30 ℃ and low concentration HF solution; spray etching and wafer rotating improve the corrosion surface quality of glass shallow groove. The micro shear stress sensor samples were fabricated by the above MEMS process, and results show that the error of the length and width of the elastic cantilever is within 2 m, the depth error of the shallow groove is less than 0.03 m, and the static capacitance error is within 0.2 pF, which satisfy the design requirements.