Final answer:
The correct answer is that all the provided statements regarding etching methods are true. An anisotropic etch is directional, dry etching often uses plasma and etches in one direction, an isotropic etch occurs uniformly in all directions, and wet etching uses liquid chemicals and typically etches in all directions.
Step-by-step explanation:
The question pertains to the comparison between different methods of etching, which is a critical process in semiconductor device fabrication. Among the given options, the following statements are true:
- An anisotropic etch is one which etches mostly in only one direction, usually vertically down into the substrate to create well-defined patterns with high resolution.
- Dry etching uses a plasma to remove material and is typically anisotropic, allowing for precise control over the etch profile.
- Isotropic etching etches uniformly in all directions, often leading to undercuts beneath the mask edges due to the horizontal as well as vertical removal of the material.
- Wet etching uses liquid chemicals to remove material and is commonly isotropic, although there are instances where it can be somewhat anisotropic depending on the etchant and material system.
Option (b) 'All of these' is the correct answer since it encompasses all the correct individual statements regarding etching methods.