Deep reactive-ion etching

Reactive-ion etching

Nanotechnology

Microelectromechanical systems

Etching (microfabrication)

Visual arts

Trench

Wafer

Materials science

Masking (illustration)

Layer (electronics)

Silicon

Aspect ratio (aeronautics)

Passivation

Optoelectronics

Journal of Microelectromechanical Systems

This paper reports an advanced deep reactive ion etching (DRIE) process for realizing ultra-deep ( 500-μm) and ultra-high aspect-ratio (UHAR) silicon structures (AR 40 for 1-mm through-trench etch, AR ≈ 80 for 500-μm through-trench etch, and AR 20 for 500-μm through-hole etch), with straight sidewalls across a wide range of feature sizes. The challenges of making such structures are overcome by continuously ramping critical parameters of the Bosch DRIE process throughout the process, including the 380-kHz bias power during etch step, the etch/passivation step duration, and the chamber pressure. The masking material capable of enduring the long DRIE process is also discussed; 10-μm and 25-μm wide trenches are etched to a depth of 750-μm and 1000-μm, respectively, in 1-mm-thick silicon wafers with straight sidewall profiles and flat trench bottoms. Deeper trenches are expected to be etched beyond a 1-mm thick wafer with thicker and/or higher selectivity masking materials. We have also demonstrated etching of circular holes of diameters as small as 25-μm to a depth of 500-μm, and potentially with 10-15 μm diameter holes. This advanced DRIE process offers opportunities for applications ranging from through-silicon via in 3-D CMOS integration to emerging microand meso-scale microelectromechanical system applications that demand ultra-deep and UHAR DRIE.

Ultra Deep Reactive Ion Etching of High Aspect-Ratio and Thick Silicon Using a Ramped-Parameter Process