# Exposure

The exposure modeling depends on the treatment of the changes in the optical properties of resist with depth and time based on *I _{sw} (у; t)* and photochemical changes. The positive photoresist normally contain a base resin, a solvent, a photoactive compound (PAC), and a reaction product. PAC reduces the development rate of the resist and is hence called as inhibitor. Three parameters: (A) exposure dependent absorption, (B) exposure independent absorption (by resist) and (C) representing rate of exposure or PAC destruction define exposure.

# Development

The final relative inhibitor (PAC) concentration *m(x, y)* after an exposure gives the exposure state. The development process is modeled as a surface controlled etching reaction, that is determined by the local value of m. If *R(x, y)* is the development rate at a point *P(x, y),* the position of *P* at a time *t+At* is given by

**
**

where и is the surface normal unit vector. *R(x, y)* is the development rate in ^m/minute calculated from one of the known models.