Lithography Glossary

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

T-Top, Resist Profile
The T-shape of a resist profile caused by the formation of a low-solubility region at the top of a positive chemically amplified resist. This is usually caused by acid loss at the top of the resist due to atmospheric base contamination or acid evaporation.

Example: The initial formation of a resist T-top determines the maximum permissible post-exposure delay.

Tangential Lines
Line patterns oriented perpendicular to the radial direction from the optical axis (i.e., the center) of an imaging system.

Example: The difference in best focus between tangential lines and saggital lines is called astigmatism.

TARC
see Top Antireflective Coating

TIS
see Tool Induced Shift

Tool Induced Shift (TIS)
The difference in overlay measurements that result when the wafer is rotated by 180?and remeasured in the same overlay measurement tool.

Example: While tool induced shift can be easily measured and calibrated out of overlay measurements, variations in the TIS are more problematic.

Top Antireflective Coating (TARC)
A thin film coated on top of the photoresist used to reduce reflections from the air-resist interface and thus reduce swing curves.

Example: By optimizing the refractive index and the thickness of the top antireflective coating, the swing ratio was minimized.

Top Surface Imaging
A resist imaging method whereby the chemical changes of exposure take place only in a very thin layer at the top of the resist.

Example: The high absorption of polymers to EUV wavelength light means that top surface imaging may be required.