A Wet Bench is used for all the chemical handling and etching of the materials. After the photoresist has been processed, then the pattern can be transferred into the thin film. This requires specific combinations of chemicals to etch specific materials. The photoresist shield specific parts of the wafer allowing the chemical to etch the exposed parts of the wafer. After the etching is complete the photoresist is stripped off.
In etching, a liquid (“wet”) or plasma (“dry”) chemical agent removes the uppermost layer of the substrate in the areas that are not protected by photoresist. In semiconductor fabrication, dry etching techniques are generally used, as they can be made anisotropic, in order to avoid significant undercutting of the photoresist pattern. This is essential when the width of the features to be defined is similar to or less than the thickness of the material being etched (ie when the aspect ratio approaches unity). Wet etch processes are generally isotropic in nature, which is often indispensable for microelectromechanical systems, where suspended structures must be “released” from the underlying layer.
The development of low-defectivity anisotropic dry-etch process has enabled the ever-smaller features defined photolithographically in the resist to be transferred to the substrate material.