添加剂在单晶硅湿法刻蚀中的作用及刻蚀形貌控制研究

The traditional character of silicon wet etching is changed when the etchant TMAH mixes with the additive, eg. surfactant or IPA. This etching technology benefits from the CMOS-compatibility, easy of operation and great potential applications in the fabrication of integrated micro devices. In this work, the effect of the additive in an etchant will be studied. Based on the adsorption of additives on hydrophobic single-crystalline silicon surfaces, relation between adsorption density and silicon planes will be defined. The characterization of orientation dependence of etch rates and etched morphologies at difference temperatures will be carried out. The influence of additive in an etchant is analyzed and the mechanism of etching with additive will be modelled. Then newly wet etching character with two additives together will be obtained, following by the analysis of competiton of additive adsorption. Next, taking the MEMS inertial mass fabrication as an example, the reason of the etched-profile change during MEMS structure etching will be discussed. Then the methods of controlling the etched-profile in the additive-modified TMAH solutions are studied. In a word, this work will correctly discover the effect of the additive during single -crystalline silicon wet etching and MEMS fabrication, with which the micro structures will be fabricated efficiently according to the desired application. Therefore it will provide the necessary scientific basis for the development of MEMS devices and systems with high-quality and integration.

添加剂（如表面活性剂或异丙醇）修饰的TMAH溶液改变了对单晶硅的传统湿法刻蚀特性，具有与CMOS工艺兼容，操作简单的优点，在集成化微型器件的工艺开发中有重要应用前景。本项目基于添加剂在疏水性单晶硅材料表面的吸附性研究基础，针对实际微型器件结构的多样性，构建在不同外界条件下添加剂分子层与单晶硅晶面之间的定量吸附关系模型，研究添加剂的吸附密度与单晶硅刻蚀速率和刻蚀表面粗造度的相关性，分析一种添加剂修饰和两种添加剂共同修饰的TMAH湿法刻蚀溶液对硅表面刻蚀特性的影响及原因；进一步地，以MEMS惯性质量块的形成为依据，探讨MEMS结构刻蚀过程中刻蚀形貌发生变化的原因，研究在添加剂修饰的TMAH溶液中刻蚀形貌的控制方法。本项目可以正确揭示添加剂在单晶硅湿法刻蚀工艺中的作用，并在此指导下依据初始设计准确实现针对具体应用的微结构加工，为高性能集成化微机电系统的研制提供相关科学依据。

在MEMS(Microelectromechanical Systems)工艺中，单晶硅各向异性湿法刻蚀技术在制作MEMS器件的过程中发挥了重要的作用，添加剂修饰的单晶硅TMAH湿法刻蚀技术具有无毒、刻蚀精度易控制、与CMOS兼容的优点，在集成化微器件的工艺开发中具有广泛的应用前景。首先，我们研究了添加剂在单晶硅表面的物理化学性质，明确了添加剂分子在单晶硅表面的吸附过程；基于界面分析手段，通过理论与实验相结合的方法，建立了不同外界条件下添加剂分子层与单晶硅晶面之间的定量吸附关系模型；研究了添加剂的吸附密度与单晶硅刻蚀特性的相关性，分析了一种和两种添加剂共同修饰的TMAH湿法刻蚀溶液对硅表面刻蚀特性的影响及原因；以摆式微加速度计的制作为对象，探讨了MEMS结构形成过程中刻蚀形貌发生变化的原因，获得了添加剂修饰的TMAH溶液中刻蚀形貌控制方法，制作出了性能良好的全硅结构摆式电容微加速度计。研究成果对单晶硅各向异性湿法刻蚀技术在MEMS器件形成中的应用提供了一定的理论与实验依据。