Resolution Enhancement Techniques (RET), or low k1 imaging, has been deployed successfully to extend the resolution limits of optical lithography significantly below half-λ for today's poly gate mask in the state-of-the-art manufacturing processes. However, achieving satisfactory contact hole patterning through the full pitch range required for the 90nm and 65nm technology nodes has greatly challenged the leading process development effort. Currently, attenuated PSM's with transmission between 5% and 9% are used to enhance the resolution of dark field contact hole patterns. Using conventional illumination with a low sigma, which is the common method employed for att-PSM, limits the minimum pitch that can be resolved on the wafer. By using off-axis illumination (OAI) it is possible to image smaller pitches. However, the same attributes that enhance imaging for dense patterns severely degrade the imaging of isolated patterns. Using Chromeless Phase Lithography (CPL), sub-wavelength isolated contact patterns can be imaged using strong off-axis illumination, such as Quasar, dipole and double dipole, etc. By applying modeled sub-resolution and non-printing features, we found it is possible to achieve very high-resolution contact imaging with exceptional process latitude. Both phase shifted and non-phase shifted patterns can be much larger than sub-resolution assist features (or anti-Scattering Bars) used on dark field binary reticles (~three times larger), making the reticle pattern easier to manufacture. Using this method, sub-wavelength bright patterns on a dark field can be imaged through the full pitch range. We have shown that it is feasible to push the contact resolution limit to 0.33 k1 or smaller.