ArF lithography options for 100nm technologies

As ArF resists mature, lithographers are pushing the imaging limits as far as possible. As shown earlier(1), ArF lithography is getting ready for the 130nm technology node and currently even the 100nm node printability with ArF is being studied. Since high numerical aperture (NA) ArF scanners are not yet available in volume, strong enhancement techniques will be required to meet these challenging targets at lower NA (0.63NA). In this paper we give an overview of the status of 193nm lithography towards 100nm patterning of memory and logic front-end features, and explore the various enhancement techniques needed. One of the options is off-axis illumination in combination with either a binary or attenuated phase-shift mask. With the use of annular, quadrupole and even dipole illumination, process latitudes of dense and semi-dense features clearly improve as compared to conventional illumination(1, 2.) The main drawback here is the limited depth-of-focus for the isolated lines. A possible solution to this problem is the application of assisting features that makes the diffraction pattern of the isolated lines look more like dense lines. Another proven technique is the alternating phase-shift mask (altPSM) which is known to improve the process latitudes of semi-dense to isolated lines as compared to a binary mask. Design complexity and mask manufacturability are well known problems with altPSM. But issues as image misplacement and the sensitivity to lens aberrations at high coherent light are lesser-known drawbacks for this technique. In this paper we give an indication towards the preferred strategy when 100nm node critical front-end layers of various technologies need to be printed in 193nm. We look at the status of 193nm lithography using the most favourable enhancement techniques, indicating the possible drawbacks. We also indicate where high NA scanners may overcome the restrictions of lower NA lenses.