High aspect ratio anisotropic silicon etching for x-ray phase contrast imaging grating fabrication

Lab based x-ray phase contrast imaging (XPCI) systems have historically focused on medical applications, but there is growing interest in material science applications for non-destructive analysis of low density materials. Extending this imaging technique to higher density materials or larger samples requires higher aspect ratio gratings, to allow the use of a higher energy x-ray source. In this work, we demonstrate the use of anisotropic silicon (Si) etching in potassium hydroxide (KOH), to achieve extremely high aspect ratio gratings. This method has been shown to be effective in fabricating deep, uniform gratings by taking advantage of the etch selectivity of differing crystalline planes of silicon. Our work has demonstrated a method for determining Si crystalline plane directions, specific to (110) Si wafers, enabling high alignment accuracy of the etch mask to these crystalline planes.