Deep reactive-ion silicon carbide etching

Method produces smoother, straighter, and more symmetrical single-crystal silicon carbide materials for micro-electromechanical systems and microelectronics manufacturing

Materials Electronics

Navy scientists, including Gene Imhoff, a research physicist at Naval Research Laboratory, have developed a new method and structure for on-axis etching of silicon carbide (SiC) materials for MEMS components. The patented technology is available via license agreement to companies that would make, use, or sell it commercially.

Etched hexagonal single-crystal materials are used in microelectromechanical systems (MEMS) and components such as beams, membranes, cantilevers, bridges, and field-effect transistor devices. Existing methods for etching SiC materials focus on etching off-axis (particularly 4° off-axis), and thus suffer from poor etch symmetry and straightness, unsatisfactory sidewall straightness and smoothness, and unfortunately high levels of sidewall wander.

This is a SEM image of a gyroscope fabricated by bonding two SiC substrates together using a 5-micron thick SiO2 layer between the two. One of the substrates was thinned to 40 microns. The gyroscope pattern was etched into the 40-micron thick on-axis hexagonal SiC using the deep SiC etch technique.

The Navy researchers developed a new method for deep reactive-ion etching (RIE) in which SiC materials are etched on-axis or near on-axis. This process addresses the undesirable side effects of the previous off-axis etching process.

One example of the new process consists of applying an etch mask to a hexagonal, single-crystal SiC material that is oriented approximately on-axis with respect to a c-axis of the SiC crystal. The RIE process is then conducted no more than 2.4° off the c-axis of the SiC material to produce etch features with improved symmetry.

The resulting etched hexagonal SiC material’s etch features have a width of fewer than 8 μm and an aspect ratio (trench depth: trench width) greater than 25. The method also includes etching of other SiC materials such as bulk substrate materials, SiC material layers bonded to a silicon oxide layer, suspended SiC material layers, or a SiC material layer anodically bonded to a glass layer.

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