Printability study with polarisation capable AIMS™ to investigate polarisation effects
Axel Zibold, Ulrich Stroessner, Norbert Rosenkranz, Rainer Schmid,
Wolfgang Harnisch
Immersion lithography offers the semiconductor industry the chance to extend the current ArF processes further down to smaller nodes before switching to shorter wavelength. The move to immersion requires increased attention to the photomask along with new effects influencing the aerial image formation as numerical apertures (NA) of scanners move up to at least 0.93 and even higher for hyper NA. Feature sizes on the photomask become comparable or even smaller than the wavelength and hence act more like wire grid polarisers which lead to polarisation effects. In addition polarisation effects from imaging or vector effects will occur. These effects result in a loss of contrast for the p-type (TM) polarised light contribution whereas s-type (TE) contributions are imaged without contrast loss. To optimize the printing process it matters for scanners to work especially with s-type polarisation and understand the polarisation changes induced by the photomask.
As of today AIMS™ fab tools are in operation in all major mask shops worldwide. The novel AIMS™ fab 193i tool with NA up to 0.93 is the latest aerial image measurement system for ArF-lithography emulation down to the 65nm node. Common adjustments are numerical aperture, illumination type and partial illumination coherence to match the conditions in 193nm dry or immersion scanners. In addition to the non-polarised illumination, the AIMS™ fab 193i allows to select linear x and y polarised illumination for different illumination settings and types, e.g. off-axis dipole illumination. In this paper polarisation effects of different photomask features are explored. MoSiON embedded phase shift masks and binary masks have been investigated at different high NA close to 1 and for different half-pitches between 500nm and 260nm for reticle polarisation effects and vector effects. It is shown that it is important for mask inspection and evaluation that the mask is observed with the right polarisation.
An outlook will be given on first measurement results obtained on an alpha tool of a new AIMS™ system addressing hyper NA aerial imaging. Key features are increased numerical apertures up to 1.4 (4x scanner), scanner equivalent polarisation settings and vector effect emulation, as well as other tool improvements. |