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Glossary of Lithography Terms - H


H-D Curve The standard form of the H-D or contrast curve is a plot of the relative thickness of resist remaining after exposure and development of a large clear area as a function of log-exposure energy. The theoretical H-D curve is a plot of log-development rate versus log-exposure energy. (H-D stands for Hurter-Driffield, the two scientists who first used a related curve in 1890.) Also called the photoresist contrast curve or characteristic curve.

Example: The H-D curve was measured by exposing one wafer with a series of open-frame exposures of increasing energy.


H-Line A line of the mercury spectrum corresponding to a wavelength of about 405 nm.

Example: The h-line of the mercury spectrum was essentially skipped as the industry moved from g-line directly to i-line steppers.


H-V Bias The difference in linewidth between horizontally and vertically oriented resist features that, other than orientation, should be identical.

Example: The variation of H-V bias with focus was an indication of astigmatism in the stepper lens.


Hard Bake The process of heating the wafer after development of the resist in order to harden the resist patterns in preparation for subsequent pattern transfer. Also called postbake and post-develop bake.

Example: The hard bake step was necessary to ensure good etch resistance of the photoresist during plasma etching.


Hurter-Driffield Curve see H-D Curve


Huygens’ Principle The idea that any wavefront can be decomposed into an array of spherically radiating point sources. The propagation of the wavefront can be calculated as the sum of the propagating point source spherical waves.

Example: Huygens’ Principle, when coupled with the concept of interference, can be used to derive a simple scalar diffraction theory.


Hyper-NA A euphemistic term to describe numerical apertures greater than 1.0.

Example: Immersion lithography enables the design and manufacture of hyper-NA lenses.