Wet photomask cleaning relies on megasonic agitation to enhance the process, but there are many
challenges to reliably maximize particle removal efficiency (PRE) and minimize damage. With the shift to
pellicle-free EUV masks, photomask processes are more vulnerable to contamination, increasing the urgency
to improve the cleaning process. This difficulty is largely due to the unavailability of appropriate
measurement of the acoustic field. Typically all that is known about the acoustic output is the driving
frequency and the electric power delivered to a transducer, both global parameters that tell little about the
field distribution over the substrate, the actual amplitude of the sound at the substrate, or the levels of
cavitation (stable and transient) present at the substrate.
One of the main challenges in photomask cleaning is balancing particle removal efficiency (PRE) with pattern
damage control. To overcome this challenge, a high frequency megasonic cleaning strategy is implemented.
Apart from megasonic frequency and power, photomask surface conditioning also influences cleaning
performance. With improved wettability, cleanliness is enhanced while pattern damage risk is simultaneously
reduced. Therefore, a particle removal process based on higher megasonic frequencies, combined with proper
surface pre-treatment, provides improved cleanliness without the unintended side effects of pattern damage, thus
supporting the extension of megasonic cleaning technology into 10nm half pitch (hp) device node and beyond.
In the absence of pellicle a EUVL reticle is expected to withstand up to 100x cleaning cycles. Surface damage upon wet and dry cleaning methods has been investigated and reported in recent years.  Thermal stress, direct photochemical oxidation and underlying Silicon layer oxidation are reported as the most relevant root-causes for metal damage and peeling off. [2,3] An investigation of final clean performance is here reported as a function of operating pH; the results show increased Ruthenium durability in moderately alkaline environment. The electrochemical rationale and the dependency of the reducing strength of the media with the pH will be presented as possible explanations for reduced damage.
ALTA4700 DUV laser pattern generator employs chemical amplified resist to get better resolution. The capability of
ALTA4700 for 130nm technology node mask production is obviously. Further improvement on ALTA4700 was
performed to meet the state-of-the-art mask requirement. System optimization eliminates unusual critical dimension (CD)
points and then reduces the range of uniformity. Appropriate post-exposure baking (PEB) temperature gets larger mask
printing window and better CD linearity. ALTA4700 incorporate NTAR7 blank with particular dry etch recipe, the mask
CD uniformity reduced from 25 to 15nm (range). Good Cr layer profile also obtains.
Photomask plays a key role in optical lithography. Laser pattern generators are widely used for photomask manufacturing
due to their high throughput. However, corner rounding and line-end shortening degrade pattern fidelity resulting in
distorted pattern image s on wafer. ALTA 4700 incorporates a new 0.9 NA, 42X reduction lens that significantly
improves resolution and pattern accuracy performance.
In this study, three critical line/space 130nm technology device patterns are printed by ALTA4700 laser pattern generator.
Input data for these layers was based on existing OPC model generated for e-beam pattern generator. ALTA4700 printed
masks have the same aerial image performance compare with e-beam pattern generator.