Any cleaning technology for state-of-the-art photo masks requires that pattern damage does not occur and optical
characteristics do not change. Particularly with EUV masks, an important challenge is to suppress/prevent changes
to the optical characteristics of ruthenium (Ru) film that generates when resist is removed (separated).
This report illustrates a model explaining why optical characteristics change when conventional resist removal
(separation) technologies are used on EUV mask. It also proposes a new resist removal technology that allows resist
to be removed without any optical damage to Ru films.
The recent trend towards the shrinkage of semiconductor devices is sparking the miniaturization of photomask patterns.
In turn, this has resulted in a demand for photomask cleaning technology that can eliminate contamination without
causing damage, such as mask pattern collapsing and degradation of photomask optical properties. A two-fluid cleaning
technology that can remove contamination without causing pattern collapsing has been gaining attention as a recent
physical cleaning technology. It is now known that the advanced technology photomask cleaning is possible by
controlling the diameter and the flow velocity of the liquid droplets discharged from the nozzle with two-fluid cleaning.
However, it becomes impossible to explain damage only by the diameter of liquid droplets and flow velocity. In order to
achieve a further improvement of the two-fluid cleaning technology, it is necessary to understand the mechanism of the
damage accurately. We pay attention the study on a new parameter of damage and particle removal. The new parameter
is liquid film thickness. We can rigorously describe the relation between damage and particle removal in terms of liquid
droplet diameter, flow velocity and liquid film thickness by this study.
Along with the increased miniaturization of electronic devices, two-fluid cleaning technology is
garnering the spotlight as a solution for the manufacturing process of Photomask. This is because it is
now known that implementing energy control of the particles that are sprayed on the substrate allows
cleaning of miniature patterns. However, it is not yet clear just how miniature of a pattern is cleanable
with two-fluid cleaning technology. This study discusses mechanisms to miniaturize the droplets created
by a two-fluid nozzle. In addition, this study also considers the impact of droplet size on pattern damage
to the Photomask and speaks on the potential for applying two-fluid cleaning technology in the future.
Damage to minute features of 45nm-node device masks occurred during megasonic cleaning.
Since we were obliged to weaken the mechanical effect of megasonics in order to prevent the collapse of minute
features, we could not obtain acceptable cleaning results.
In order to manage the minute features, there is a need to develop a new mechanical cleaning method that
causes less damage, but does not compromise the ability to remove particles. Cleaning using a two-fluid nozzle
is a promising candidate. We investigated the two-fluid nozzle and compared it with megasonic cleaning, and
we confirmed that the two-fluid nozzle achieved acceptable cleaning results without damaging 45nm-node
device masks. Furthermore, for 32nm-node device masks, we have improved the two-fluid nozzle in terms of
the cleaning energy distribution.