Lithography Glossary

Written by Chris Mack
Brought to you by the creators of PROLITH

Latent Image
The reproduction of the aerial image in resist as a spatial variation of chemical species (for example, the variation of photoactive compound concentration).

Example: The latent image was visible to the naked eye due to the change in the resist optical properties with exposure.

LER
see Line Edge Roughness

LES
see Line End Shortening

Levenson PSM
see Alternating PSM

Lifting, Resist
The separation of the resist pattern from the substrate, either partially or completely, due to a loss of adhesion.

Example: Resist lifting could not be avoided without the use of an adhesion promoter.

Lift-Off Process
A lithographic process by which the pattern transfer takes place by coating a material over a patterned resist layer, then dissolving the resist to "lift off" the material that is on top of the resist.

Example: The lift-off process allowed the patterning of the metal without the use of an etch step.

Line Edge Roughness (LER)
The deviation of a feature edge (as viewed top down) from a smooth, ideal shape. That is, the edge deviations of a feature that occur on a dimensional scale much smaller than the resolution limit of the imaging tool that was used to print the feature.

Example: One simple measure of line edge roughness is the RMS deviation of an edge from a best fit straight line.

Line End Shortening (LES)
The reduction of the length of a line (where a line is defined here as any rectangular feature whose length is significantly greater than its width) as measured only at one end. Thus, the line end shortening is characterized as the difference between the actual position of the end of a line and the intended (designed) position.

Example: The amount of line end shortening for the feature increased sharply when out of focus.

Linewidth
see Critical Dimension

Lithographer
1. A practitioner of lithography.
2. A harmless drudge.

Example: The overworked and under appreciated lithographer paused for a moment and daydreamed, "Will Moore's Law ever end?"

Lithography
A method of producing three-dimensional relief patterns on a substrate (from the Greek lithos, meaning stone, and graphia, meaning to write).

Example: Although lithography is a centuries-old patterning technique, the small features used in integrated circuits make semiconductor lithography very challenging.

LSI
Large Scale Integration, an integrated circuit made of hundreds to thousands of transistors.

Example: As integrated circuits entered the LSI era, contact and proximity printing gave way to projection lithography.