The laser bandwidth and the wavelength stability are among the important factors contributing to the CD Uniformity
budget for a 45 nm and 32nm technology node NV Memory. Longitudinal chromatic aberrations are also minimized by
lens designers to reduce the contrast loss among different patterns. In this work, the residual effect of laser bandwidth
and wavelength stability are investigated and quantified for a critical DOF layer. Besides the typical CD implications we
evaluate the "image placement error" (IPE) affecting specific asymmetric patterns in the device layout. We show that
the IPE of asymmetric device patterns can be sensitive to laser bandwidth, potentially resulting in nanometer-level errors
in overlay. These effects are compared to the relative impact of other parameters that define the contrast of the
lithography image for the 45nm node. We extend the discussion of the contributions to IPE and their relative importance
in the 32 nm double-patterning overlay budget.
CD uniformity budget for a 45-nm NV memory device requires the analysis and compensation of each single contributor
factor. A dedicated simulation tool "CDU Predictor" helps to quantify the impact of main scanner and process factors
for a comprehensive study of the CD Uniformity for an ideal flat wafer. However this analysis could under estimate the
real CD distribution on a real production wafer if artefacts induced by thin-film effects and underling device topography
significantly increase the contribution of the optical leveling-device to the total focus-error and hence spread the CD
distribution for processes with low DOF. Such artefacts can be eliminated by application of an offset-map obtained by
probing the mechanical top-surface of the resist-stack with an AirGauge (AirGaugeImprovedLEvelling, AGILE). The
systematic variation of CD across the wafer, no matter whether due to fingerprints of the reticle, the device-topography,
the track-process or the exposure-tool, can be mapped into dose-corrections for compensation (DoseMapper). We discuss
an experimental case with a combination of both tools for an effective CD Uniformity optimization.
Aggressive pitch requirements for line/space pattern devices require the usage of extreme off-axis illumination schemes
to enhance the resolution of the exposure tools. These illumination schemes stress the quality of the optics because of the
anisotropy of the optical paths through the lens. Moreover, the marginalities on the patterning are dramatically enhanced
if two or more illumination modes are requested in the lithography process.
The effects on overlay between double exposure layers exposed with different illumination settings, with one being an
extreme illumination setting, will be discussed and two approaches will be addressed to compensate the resulting overlay
The first approach optimizes the lens setup by means of a dedicated scanner option to minimize the lens effects on
overlay and reduce the distortion for each layer: in this case the simulation time and the impact on other imaging
parameters will be carefully evaluated.
The second methodology corrects the induced misalignment by a high order modelling compensation. This approach
requests the insertion of a suitable set of overlay measurement targets into the product frame to appropriately fit the
distortion matching of the two layers.
Double patterning is the best technique which allows 193nm immersion lithography to anticipate the 32 nm node, before
EUV lithography. The final device pattern is formed by two independent patterning steps where the dense pitch is
doubled. This allows printing each patterning step with higher k1 imaging factor.
In this paper we present the overlay and CD budget applied to a double patterning (DP) technique for the definition of a
32nm technology node device, using an immersion scanner tool. A balance among different factors which affects the
final CD of the device is necessary to optimize the imaging and the alignment performances of the exposure tool. A
preliminary activity is also necessary to choose the most suitable mask splitting strategy. Adopting a single mask, which
is exposed twice with the appropriate shift - the final pitch - , makes the overlay between the two exposures less critical
than splitting the complementary layouts on two different masks. Finally, the CD uniformity of the pooled distributions
from the two exposures is evaluated in order to define the requested tool performances in terms of overlay, CD control