Specific Process Knowledge/Lithography/Resist/UVresist: Difference between revisions

During exposure of the resist, the photoinitiator, or photo-active component, reacts with the exposure light, and starts the reaction that makes the resist develop in the developer. In a positive resist, it makes the resist become soluble in the developer. In a negative resist, usually assisted by thermal energy in the post-exposure bake, it makes the resist insoluble in the developer. The amount of light required to fully develop the resist in the development process, is the exposure dose.

The resist sensitivity is a measure of how efficiently it reacts to the exposure light. Spectral sensitivity is the sensitivity of the resist as a function of wavelength. It is usually given simply as the range from the wavelength below which absorption in the resist material makes lithography impractical to the wavelength at which the photoinitiator is no longer efficiently activated. The spectral sensitivity is listed in the [[Specific_Process_Knowledge/Lithography/UVLithography#Resist_Overview|Resist Overview]]. Within this range, the optical absorption is commonly used as a measure of sensitivity. A high absorption coefficient signifies a high sensitivity, as the light is absorbed by the photoinitiator. Because of spectral sensitivity, the optimal dose of a given resist type and thickness is also a function of the spectral distribution of the exposure light, i.e. the equipment used for the exposure, see tables below. Using a combination of experience, calculation, and assumption, one may be able to estimate the dose for one equipment from the known dose on another equipment.

Due to reflection and refraction at the interface between the resist and the substrate, the optimal dose may also be a function of the type of substrate used. Unless otherwise stated, the exposure doses given here are for standard silicon wafers.