Aspect ratio dependent etching in advanced deep reactive ion etching of quartz

Quartz due to its piezoelectricity and its good temperature stability is one of the most used materials in devices for time-frequency applications. Quartz resonators are generally obtained by chemical etching or chemical mechanical polishing but these two methods do not allow the shrinking of the dimensions of the devices and limit reachable geometry: in particular structures with high aspect ratios or vertical flanks are not feasible. The development of the deep reactive ion etching (DRIE) of quartz over the last fifteen years allowed the manufacture of the first quartz resonators with structures not realizable by the conventional methods However, the DRIE technology on quartz is not as mature as that on silicon and undesired effects such as the aspect ratio dependent etching (ARDE) which consists in a decrease of the etching rate as the width of the features shrinks or micro-loading which involves decreasing of the etching rate as the density of features rises have not been widely studied. In this paper, experimental data reveal the phenomenon known as ARDE. The effect of key experimental parameters on ARDE has been studied and a simple model is used to analyse this phenomenon.