The process of etching a material can be done by two methods, wet (chemical) or dry (plasma) etching. The mask will act as a guide to the process that is used to create the pattern.
Opposite of wet etching is dry etching, a process that uses plasma as a means to imprint a pattern on a surface. No specific materials are needed to act as an etching mask. Even tape can be used to mark patterns. Leaving out the need for dangerous chemicals and unnecessary risk that can be easily avoided by using the dry etching process.