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electronic computer-aided design (ECAD)

The second type of Reticle Enhancement involves actually improving the manufacturability or resolution of the process. Examples of this include:

RET TechniqueManufacturability Improvement
Scattering BarsSub resolution assist features that improves the depth of focus of isolated features.
Phase-shift MaskEtching quartz from certain areas of the mask (alt-PSM) or replacing Chrome with phase shifting Molybdenum Silicide layer (attenuated embedded PSM) to improve CD control and increase resolution
Double or Multiple PatterningInvolves decomposing the design across multiple masks to allow the printing of tighter pitches.

For each of these manufacturability improvement techniques there are certain layouts that either cannot be improved or cause issues in printing. These are classed as non-compliant layouts. These are avoided either at the design stage – using, for instance, Radically Restrictive Design Rules and/or creating addition DRC checks if appropriate. Both the lithographic compensations and manufacturability improvements are usually grouped under the heading resolution enhancement techniques (RET). Such techniques have been used since the 180nm node and have become more aggressively used as minimum feature size as dropped significantly below that of the imaging wavelength, currently limited to 193 nm.

This is closely related to, and a part of, the more general category of design for manufacturability (IC) or DFM.

After RET, the next step in an EDA flow is usually mask data preparation.