Positive and Negative Photo resist

There are two types of photo resist: positive and negative. For positive resists, the resist is exposed with UV light where the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer. The exposed resist is then washed away by the developer solution, leaving windows of the bare underlying material. In other words, "whatever shows, goes." The mask, thus, having an exact copy of the pattern which is to remain on the wafer.