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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 results when the wafer is rotated by 180º 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.