Surface Roughness of Z-Cut Quartz Etched by Ammonium Bifluoride and Ammonium Bifluoride Mixed with Isopropyl Alcohol Solutions

Zhaoyun Zhang,Wei Xu,Wei Su,Zhuang Xiong,Bin Tang

doi:10.3390/mi8040122

Abstract

It is meaningful to study the surface morphology of monocrystalline material, but there are few studies on the surface roughness of quartz. So, surface roughness of Z-cut quartz etched by pure ammonium bifluoride and ammonium bifluoride mixed with isopropyl alcohol (IPA) solution was investigated for the first time in this paper. Firstly, when etching in pure ammonium bifluoride solutions, the surface roughness change with etching time, etching temperature, and solution concentration were studied. Then, the surface roughness improvement given by isopropyl alcohol solution was analyzed carefully. The experimental results indicated that: the surface roughness of Z-cut quartz (0001) plane increased with etching time, but decreased with etching temperature and solution concentration; the adding of isopropyl alcohol in ammonium bifluoride solution could decrease the roughness and improve the surface quality. This is the first systemic research of the evolution of quartz surface roughness when etching in ammonium bifluoride solution, and will benefit the future design and manufacture of quartz MEMS devices.

Highlights

There are two reasons for the longstanding lack of interest in quartz
Quartz has excellent properties, such as outstanding piezoelectric properties, low temperature coefficient, offers good electric insulation, and allows optical transmission in the wavelength range of UV light. These features have favored the utilization of quartz as a substrate for the fabrication of several types of MEMS, such as resonators [1], tuning-fork probes [2] or microlenses [3], in the field of vibrating inertial sensors—i.e., vibrating beam accelerometer (VBA) [4,5,6,7] and Coriolis vibrating gyro (CVG) [7,8,9,10,11], based on a resonator as sensitive element
Hedlund et al [16] studied the etching properties of Z-cut quartz in hydrofluoride-based etchants; the side-wall slopes varied with different orientation, etchants, and temperatures, the anisotropy and etching rate increased with HF concentration, and the transition between various planes can be described by an interaction of adjacent natural crystal planes

Summary

Introduction

There are two reasons for the longstanding lack of interest in quartz. One essential reason is that the amount of knowledge and manufacturing equipment for quartz is neither as extensive, nor as widespread, as for semiconducting materials such as Si and GaAs. Quartz has excellent properties, such as outstanding piezoelectric properties, low temperature coefficient, offers good electric insulation, and allows optical transmission in the wavelength range of UV light. Et al [19] studied the sidewall arris flatting process in quartz fabrication etching in hydrofluoride-based etchants These studies were mainly focused on the etching properties, such as etched profiles and etching rate in different etchants, such as HF, HF+NH4F, NH4HF2. The surface roughening and the methods to improve the surface quality have not been studied

Methods

Results

Conclusion