=================================================================
TITLE: Resolution Enhancement for Optical Lithography
Optical lithography distortions that occur in the manufacture of
integrated circuits are being addressed by multiple techniques.
Since the early 1970's, optical proximity correction or OPC has
been used to produce smaller features in an IC using a given
equipment set. OPC applies systematic changes to photomask
geometries to compensate for nonlinear distortions caused
by optical diffraction and resist process effects.
Specifically, these distortions include line-width variations
dependent on pattern density which affect a device's speed of
operation and line-end shortening which can break
connections to contacts. Causes include reticle pattern
fidelity, optical proximity effects, and diffusion and loading
effects during resist and etch processing. A mask
incorporating OPC is thus a system that negates
undesirable distortion effects during pattern transfer.
OPC works by making small changes to the IC layout that
anticipate the distortions. To compensate for line-end
shortening, the line is extended using a hammerhead shape that
results in a line in the resist that is much closer to the
original intended layout. To compensate for corner rounding,
serif shapes are added to (or subtracted from) corners to produce
corners in the silicon that are closer to the ideal layout.
Determining the optimal type, size, and symmetry (or lack
thereof) is very complex and depends on neighboring geometries
and process parameters. A sophisticated computer program is
necessary to properly implement OPC.
Proper OPC provides for an enhanced process window for both dense
and isolated lines. It provides wider process latitude for an
existing process or creates a process window for a new, smaller
feature process. OPC enables significant savings through
extending the lifetime of existing lithography equipment. OPC
offers basic corrections and a useful amount of yield
improvement.
For additional information, access: OPC
=================================================================
FILENUMBER: 1145
BEGIN_KEYWORDS
Resolution Enhancement Optical Lithography OPC
END_KEYWORDS
DATE: November 2003
TITLE: Resolution Enhancement for Optical Lithography
Return to MSN Home Page