Reliability assessment of the complete 3D etch rate distribution of Si in anisotropic etchants based on vertically micromachined wagon wheel samples

As a sequel to part I (Gosálvez et al J. Micromech. Microeng. 12 125007), the present paper is part II of a series of two papers dedicated to the presentation of a novel, large-throughput, experimental procedure to determine the complete three-dimensional orientation dependence of the etch rate of silicon by using vertically micromachined wagon wheel samples. While the first part provides the experimental details and compares the results to realistic simulations, the present paper focuses on characterizing the reliability of the obtained etch rates. For this purpose, the shape of the etched structures is analyzed and corresponding formulas are derived, enabling the estimation of an upper bound to the measured etch rates. It is shown that the measured etch rates remain below this limit, strongly indicating that the observed wedge retraction values are consistent with the assumed geometrical shape of the wedges. An exception to this rule are the etch rates of {1 1 0} obtained from (1 1 0)-oriented wafers, which are systematically larger. This deviation is explained by a kinetic acceleration process due to the small size of the step-flow structures that are formed on the affected wagon wheel spokes. The comparison to previous experiments indicates that the proposed method provides similar or even more accurate etch rates for some of the etchants with a more affordable and less labor-intensive approach.