MEMS Device

Micro-Electro-Mechanical Systems (MEMS), also known as microsystems technology or micromechanical devices, refer to micro-scale mechanical and electro-mechanical elements (devices and structures) constructed using microfabrication techniques. The typical component of MEMS is an integrated circuit chip that processes data (such as a microprocessor), as well as several components that interact with the surroundings. In short, MEMS is an umbrella term for various microfabrication designs, methods, and mechanisms. MEMS devices are made up of components ranging in size from 0.001 to 0.1 mm, and their critical physical dimensions generally range from 20 micrometers to a millimeter. The fabrication of MEMS requires photolithography and photoresist to realize component patterning.

How photoresist is involved in MEMS manufacturing?

MEMS have several layers composed of thin films of metal, bulk silicon, silicon dioxide or nitride, or polysilicon to build devices. Each layer is a different component and requires a different pattern. Photolithography is the process used to define and transfer patterns to the respective layer of the MEMS device, while photoresist serves as the key material that enables patterning of each layer of the MEMS device. Photoresist works as a photosensitive layer, transferring the pattern of a mask to an underlying layer through photolithography to construct MEMS devices. A few key steps in the fabrication of MEMS devices using photoresists are described below ^[1].

• Coating

Photoresist is coated thickly and evenly on the clean surface of the wafer. In order to enhance the adhension of the photoresist to the wafer's surface, hexamethyldiazane (HMDS) is used as an intermediate chemical that is applied to the wafer prior to photoresist coating to provide a hydrophobic surface.

• Soft baking

Most photoresists require a soft bake to bake off the remaining solvent after coating to the desired thickness. Soft baking removes the residue solvent from the photoresist to make it more solid.

• Alignment

Alignment is one of the most critical steps in the entire MEMS fabrication process. The photoresist layer on the substrate must be aligned with the photomask to achieve complete replication of the pattern. Considering the tiny size of MEMS devices, a misalignment of even one micrometer can destroy the entire device.

• Exposure

The photoresist layer is exposed when UV light from a source travels through the photomask to the photoresist. Exposed areas of positive photoresist undergo a photochemical reaction to change their solubility, which is just the opposite of negative photoresists.

• Development

Exposed areas of positive photoresist or unexposed areas of negative photoresist are dissolved during the development process. This results in the pattern on the photoresist being transferred to the metal layer of the MEMS, ultimately obtaining a MEMS device with the desired structure.

Please kindly note that our products and services are for research use only.