Research On The Influence Mechanism And Application Of Additives On The Wet Etching Characteristics Of Quartz Single Crystals

Quartz is an important material in MEMS.Because of its excellent properties such as excellent mechanical elasticity,low temperature coefficient,high quality factor and chemical stability,quartz MEMS has been used in various industries,especially in the field of inertial sensors.For example,quartz Coriolis Vibrating Gyro(CVG)and quartz Vibrating Beam Accelerometer(VBA)have been widely used in aviation,aerospace,navigation,missile control and so on.In the case of the micromachining of quartz-based MEMS,wet etching is one of the most widely used methods,benefitting from similar features as silicon etching:low cost,the creation of flat surfaces and the possibility of batch processing.There are two main problems in the wet etching.One is that the etched surface appears some hillocks,and the hillocks cause a roughness surface.The other is that it is difficult to process a ideal rectangular cross section,and the etching cross section morphology will change with the crystal direction,the direction angle,the size of opening hole and the etching depth.At present,the study on the etching characteristics of quartz is not sufficient.The mechanism of the hillocks appearing on the etched surface has not yet been analyzed and there are no effective methods to reduce the surface roughness.And there is no sufficient understanding of the evolution law of the lateral etching cross section morphology.So it is necessary to further study the wet etching characteristics of quartz and find out the formation mechanism of the hillocks and the ways to reduce the surface roughness,fully understand the evolution rule of the section morphology.Some additives have been reported to be able to reduce the undercut and improve the roughness of etched surface in silicon wet etching.But in the wet etching of quartz,the mothod of adding additives in the etchant to change the etching properties of the quartz have not been reported.Therefore,on the basis of further research on the characteristics of wet etching of quartz,the study of the influence mechanism of additives on the etching characteristics of quartz and the use of additives to regulate the characteristics of quartz wet etching,will be more effective to improve the performance of MEMS and accelerate the development of new devices.It has important academic significance and application value.And obtain economic benefits and social benefits.In this paper,in view of the etching surface and side etching morphology of quartz single crystal,the wet etching characteristics of quartz have been further studied.On this basis,the influence of additives on the wet etching characteristics of quartz crystal is explored,and the related achievements are applied to a new quartz pendulum micro accelerometer.The main contents are as follows:1.The etching characteristics of quartz in pure ammonium bifluoride solution are further studied.On the basis of the study of the wet etching mechanism of quartz,the etching characteristics of quartz crystal in ammonium bifluoride solution are further studied.The alteration of etching rate,etching surface roughness and lateral etching morphology with etching conditions is studied.The formation mechanism and the formation process of the hillocks apearing on the(0001)plane is studied and the evolution law of sidewall etched profile is discussed.2.The adsorption mechanism of additive molecules on the surface of quartz is studied,and the adsorption model is established.The surface properties of quartz and the properties of solid liquid interface are fist studied.Based on this and the adsorption isotherm of surfactant DPC on quartz surface,the adsorption mechanism of surfactant on quartz surface was deeply analyzed.On this basis,the adsorption model of additives on quartz surface was established.3.The properties of additive-modified wet etching of quartz are studied.First,the influence of single additive on the etching rate and the etching surface roughness of quartz crystal is studied,and the influence mechanism is analyzed.Then the influence of two type of additives on the surface roughness of quartz crystal is studied,and the influence mechanism is analyzed.Through the above research,we have effectively revealed the mechanism of additive-modified wet etching of quartz4.A quartz pendulum micro accelerometer based on wet etching technology is developed.Based on the above results,the quartz wet etching technology is applied to the fabrication of quartz pendulum micro accelerometer.The structure of the quartz pendulum micro accelerometer is designed.The key process steps are discussed.The quartz pendulum micro accelerometer with high quality is made by optimizing the etching conditions.Through testing,the sidewall of the quartz pendulum micro accelerometer mass is steep,the whole stucture has a good symmetry,and the surface roughness of the cantilever beam is reduced by about 50%.The performance of the accelerometer is preliminarily tested and the accelerometer has a good performance.