Etching methods that use chemical resistant photosensitive film are called Photo Etching, or Photo Engraving.

The photo etching is a process of obtaining intended patterns by: depositing a film of photo-resistive material on a metal work piece > light expose a pattern on the film using a separately created photo-mask template, causing the exposed portion developer solution insoluble > dissolve the unexposed portion by immersing in developer solution, leaving the final pattern intact. (There are types of photo-resist material that exposed nature is opposite.)

This method is also used for chemical blanking as well as chemical milling. In either case, pre/post processes are the same. Typical photo etching process is shown in [Fig.1].

To perform a micro-fabrication process with etching requires a creation of a Photo-Mask. This is an important process step since the final product quality is largely affected by the accuracy and quality of the photo-mask. Typically, the photo-masks are produced by photographic processes where enlarged original design drawings are reduced into film or dry-plates of the actual work sizes. The process of making the enlarged original drawings is called "Artwork", and making of the working size photo masks is called "Camera work".

For economical and handling purposes, multiples of small parts are made on the same photo mask original. By doing so, many small parts can be produced from a single metal piece at once.

There are two types of photo-resists, Negative resist and Positive resist. The negative resist is a type where exposed portion becomes insoluble to developer solution, and the positive type becomes soluble where exposed. To crate photo-resist patterns on work pieces, a negative image photo mask for the negative resist, positive image photo mask for the positive resist are used. Typically, the negative resist is used. After the exposure and develop processes are completed, the work can be processed for chemical blanking.