In semiconductor wafer fabrication, etching refers to the process of removing unwanted material from wafer surface through a subtractive process. Metal etching is most commonly used in the patterning of metal films for interconnects by establishing specific connection and conduction paths and can be classified by dry etching, de-plating and dissolution of the layers on various substrates such as silicon, SiO2, Si3N4, GaAs, germanium, and sapphire. Dry etching is used to produce very precise etching of vertical channels or vias forming the device features or lines which make up the conductive path because it is anisotropic or etching in one direction. Dry etching is achieved by using chemical gases and plasma in a process chamber so dry etching tools are very large, complex and expensive to purchase and operate. De-plating is a process of electro-chemically removing metal material from the surface of the wafer to an anode by creating a difference in electrical potential between the surface to be etched/de-plated (typically cathode) and the “target” or anode where the material is to be collected. De-plating in single wafer tools has also replaced immersion processing due to the better uniformity it provides. However, De-plating single wafer tools are also very large and expensive to operate and have low throughput (wafers per hour). Dissolution/Immersion is the used of recirculated chemical baths to perform the etching process. In an immersion bath chemical is used to dissolve the metal layer that is unprotected by the mask. Immersion metal etch process has been on the decline because of its isotropic etching property and poor etch uniformity caused by non-uniform chemical flow around wafers in the tank. For the most of etch processes lateral etching is undesired because it occurs on the walls of the features and makes them thinner or misshapen. As a result, most of critical etching steps are performed by dry etching systems. However, if etch uniformity is precise, immersion etching can be used for less critical features in place of complex dry etching and de-plating.
Crack-based strain sensor with diverse metal films by inserting an inter-layer
