Inductively coupled plasma etching of bulk tungsten for MEMS applications

Abstract

As a promising material for bulk micromachining for MEMS applications, tungsten can be used as microneedles for medicine injection and tools for micro-inject molding, ultrasonic machining, and electrical discharge machining. However, it is difficult to fabricate microstructures with high aspect ratios and small feature sizes due to the excellent material of tungsten properties, such as chemical stability, high hardness, and high melting point. Here, an inductively coupled plasma (ICP) deep etching process is developed for bulk tungsten, and its process parameters are studied. After optimizing the process parameters, three recipes were developed for different MEMS applications. A patterned tungsten structure with a depth of more than 300 µm was etched by tungsten (W) ICP deep etching (WIDE) at an etch rate of 2.73 µm/min and etch selectivity of 35. The WIDE process produced a tungsten microstructure with a high aspect ratio (> 20), a small feature size (< 3 µm), and a surface roughness of Ra 30 nm. To demonstrate the potential application prospect of deep etching bulk of tungsten, tungsten microneedles with a positive sidewall angle and several non-silicon substrates for MEMS applications were achieved based on the WIDE process. • Bulk tungsten ICP deep etching process development based SF 6 +O 2 +C 4 F 8 . • Effect of process parameters on ER, ES, DUR, roughness, sidewall angle. • μ-structures with > 300 µm deep, > 20 AR, and Ra 30 nm roughness. • Die steel, glass, and polymer μ-structures machined by etched tungsten. • Metal-based and non-silicon-based MEMS application prospect.