Profile Evolution of High Aspect Ratio Silicon Carbide Trenches by Inductive Coupled Plasma Etching

Abstract

Micromachining silicon carbide (SiC) is challenging due to its durable nature. However, plasma and laser etch processes have been utilized to realize deep and high aspect ratio (HAR) features in SiC substrates and films. HAR topologies in SiC can improve SiC-based MEMS transducers (reduced electrostatic gaps) and enable embedded substrate cooling features. Our process used inductive coupled plasma (ICP) etching with sulfur hexafluoride (SF 6 ) and oxygen (O 2 ) and an electroplated Ni hard mask. We examine the formation of SiC trenches by observing aspect-ratio-dependent and time-dependent etch rate and topography in 4H-SiC substrates. In addition, we studied the effect of ICP etch parameters, such as RF bias power (25-100 W), pressure (5-15 mTorr), and O 2 flow fraction (10%-40%), on etch rate and topography. Our process resulted in SiC etch rates between 0.27 and 0.75 μm/min with aspect-ratio-dependent and depth-dependent characteristics. We observed trench profiles that evolve from square (low AR) to “W” (medium AR) and converged “V” (HAR) shapes. Finally, we report the highest aspect ratio (18.5:1) trench achieved to date in 4H-SiC via ICP etching, which supports many SiC-based MEMS applications.