PMMA resists can also be patterned using UV-lithography, but only at exposure wavelengths of 200 – 270 nm (deep UV light). Typically used is the wavelength-range of the lowest line of high-pressure mercury lamps at 254 nm.
In certain applications it is desirable to keep the original properties of a polymer unchanged, e.g. without addition of light-sensitive components like for example for a use as moisture sensor.
With the development of photoresists for an exposure in the wavelength range of 500 to 1100 nm using laser light, new procedures became possible. Lithographic processes at an exposure wavelength greater than 480 nm are not possible with standard photoresists.
Hydrofluoric acid etchings, even those in highly concentrated acids (48%), are technologically used despite the high risk involved with HF applications.