A photoresist is a light-sensitive material that is photographically exposed and processed before transferring a pattern onto an object via sandblasting. It is used for processes like photolithography and can be used to form patterned coating on a given surface for photoengraving. Photoresists are a major part of many industries, including the semiconductor industry.
Photoresists can be classified into two different groups. They are either seen as positive resists or negative resists. The first type, a positive resist, is a photoresist in which the light exposed part of the photoresist becomes soluble to the developer or the photoresist. The part of the photoresist unexposed to the light is still insoluble to the developer. It is fairly expensive but can be very small, with a minimum size of .5 micrometers. It also has good step coverage and has an aqueous developer base.
The second type of photoresist is called a negative resist. In a sense, the process that a negative resist undergoes is somewhat the polar opposite of that which a positive resist experience. In contrast to a positive resist, the piece of the negative resist that is exposed to the light becomes insoluble to the developer. The unexposed part of the photoresist is then dissolved by the developer of the photoresist. Though it has a lower step coverage than positive resist, it costs less, has an excellent adhesion to silicon, and has a great wet chemical resistance.
Photoresists have the ability to also be exposed to electron beams and can produce the same results as when it is exposed to light. The biggest difference between exposure to light and exposure to an electron beam is that when the photons are absorbed, the electrons deposit their energy and then scatter within the photoresist all at the same time, rather than the less excitement that occurs with a normal light. The high energy causes lots of movement, but the result is still basically similar to that produced by light exposure.