Selective etching is used to remove specific materials from a substrate, such as GaAs, while leaving other materials intact, such as Al0.3Ga0.7As. This process is commonly used in semiconductor device fabrication to create precise patterns or structures on a substrate.
Selective etching works by using a chemical solution or plasma that can selectively dissolve or etch certain materials while leaving others untouched. The selectivity of the etching process is determined by the chemical properties of the etchant and the materials being etched.
Selective etching allows for precise control over the patterns and structures created on a substrate. This is important in semiconductor device fabrication as it can improve device performance and yield. It also allows for the creation of complex devices with multiple layers of different materials.
Al0.3Ga0.7As serves as a mask or protective layer during the etching process. It is resistant to the etchant being used, so it protects the underlying GaAs from being etched away. This allows for the selective removal of only the GaAs material.
Some common etchants for this process include hydrofluoric acid (HF) and citric acid (C6H8O7). These etchants have a high selectivity for GaAs over Al0.3Ga0.7As and can be controlled to achieve precise etching depths. Other etchants, such as potassium hydroxide (KOH) and sulfuric acid (H2SO4), can also be used for selective etching depending on the specific materials and desired results.