Novel Process to Create Structured Membrane Films for Micromachining Applications

The technology is an innovative process for creating metal-patterned, structured membranes for micromachining applications. The method uses potassium hydroxide to remove silicon, in combination with XHRiC. Hafnium metal is first patterned onto a silicon nitride wafer, which serves as the starting substrate. XHRiC is then applied to the wafer, followed by patterning with photoresist and etching using O2 plasma to define cut slots in the membrane. The photoresist is then removed. Next, the wafer is bonded to a Pyrex carrier wafer with wax, and the backside of the silicon nitride is patterned and reactive-ion etched. The wafer is then placed in hot potassium hydroxide for 16 hours to remove the silicon layer, creating a silicon nitride membrane. The wafer is subsequently placed in acetone to dissolve the wax. The wafer is resecured to the Pyrex carrier wafer, and the topside of the silicon nitride membrane is subjected to reactive-ion etching. Finally, the XHRiC layer is removed using O2 plasma, and the Pyrex handle wafer is released, resulting in a metal-patterned silicon nitride membrane with cut slots. This novel process supports the creation of structured membranes with a wide range of applications in MEMS fabrication. The use of XHRiC as a patterned hard mask and/or etch protection material enables its application in various MEMS devices. The process can be used to fabricate cut membranes, micro/nano structures, and ultra-thin films for device applications, making it an excellent candidate for MEMS foundry companies and accelerometer manufacturers. It has reached a Technology Readiness Level (TRL) 5 (component validation in a relevant environment) and is now available for patent licensing. Conventional micromachining and etching techniques used in microelectromechanical (MEMS) devices have several disadvantages such as the use of etch stop materials, the use of hazardous gases and specialized equipment, and localized heating effects. As a result, devices or membranes may be damaged or unnecessary redeposition of materials may be required. While wet etching is often employed to mitigate these issues, it presents its own challenges, such as the need to protect MEMS devices during the process and the risk of structural damage when forming openings in membranes. To address these limitations, a new process for protecting membranes during wet etching is needed. Researchers at NASA’s Goddard Space Flight Center have developed an innovative method for creating structured membrane films, enabling the micromachining of ultra-thin membranes and micro/nano-scale structures. This invention utilizes XHRiC in combination with a potassium hydroxide etch to produce an ultra-thin silicon nitride membrane with metal leads and precise membrane cuts.