With the optimization of sulfate-free cleaning the issue of haze under pellicle was almost eliminated. In consequence,
current reasons for mask repelliclization needs are moving from pattern issues to more gross problems on back glass.
Moreover, the longer life of photomasks allows a new problem to appear as growing defects on back glass, commonly
ascribed to environmental conditions at user's site. The commonality of these problems is being independent on mask
complexity and substrate. In order to avoid the criticalities of pellicle removal and cleaning treatment as well as the cost
of necessary inspection after new pellicle application, the best solution is cleaning only the backside of the mask,
provided that integrity of pellicle and pattern on front side are preserved
In this article we present the results obtained by the use of the Mask cleaner DE050019TM on several cases.
The efficiency of the treatment was assessed in terms if removal capability on different kinds of contaminations, either
from use or mask aging. Pattern inspections were conducted in order to assess ESD robustness. Ionic residues were
checked by IC aimed to compare with standard cleanings.
This methodology demonstrated to be capable of maintaining a Particle Removal Efficiency>97% on all kinds of
contaminations, without any damage to pellicle or harm to patterns, still maintaining residual ions at the same level as
after cleaning by standard tools.
Reducing the amount of ionic residues coming from cleaning chemistry became necessary for photomask manufacturing
process in order to eliminate the major cause of haze. The achievement of this target involves using sulphate-free steps
from resist removal to final cleaning, maintaining good performances on particles or residues removal as well as
minimization of pattern damages and preservation of the substrate properties. In this paper the cleaning strategies for
high-end masks are discussed and a tight dependency on substrate and contamination type is highlighted as the major
aspect that influences the good performances for ozone-based technique. The data collected from both tests and real
production for sulfate-free cleaning show that the key point to achieve the full effectiveness is the careful definition of
the sequence of treatments and rinses, allowing also the minimization of pattern damages.
The cleaning capability of the full sulphate-free process is tested on various types of contaminants and the achieving of
excellent removal performance is demonstrated for contaminations of sizes down to 100nm. When the sulfate-free
cleaning is not fully effective, a pre-treatment is applied before the cleaning in order to reduce the interaction between
contamination and substrate, thus enlarging the removal capability of the ozone-based cleaning. The ion chromatography
confirms that the sulphate residues can be reduced below the threshold value for haze formation.
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