In recent years, photomask resist strip and cleaning technology development was substantially driven by the industry's
need to prevent surface haze formation through the elimination of sulfuric acid from these processes. As a result, ozone
water was introduced to the resist strip and cleaning processes as a promising alternative to a Sulfuric - Peroxide
Mixture (SPM). However, with the introduction of 193i double patterning, EUVL (Extreme Ultraviolet Lithography) and
NanoImprint Lithography (NIL) the demand on CD-linewidth control and surface layer integrity is significantly
expanded and the use of ozone water is questionable. Ozone water has been found to cause significant damage to metal
based mask surface layers, leading to significant changes in optical properties and CD-linewidth shift.
In this paper HamaTech APE demonstrates the use of an alternative acid-free resist strip and cleaning process, which not
only overcomes the named drawbacks of conventional ozone water use, but reduces resist strip time by 50% to 75%. The
surface materials investigated during this study are; chrome absorber layers on binary masks, MoSi based shifters,
chrome hard mask layers on EPSM, and ruthenium capping layers on EUV masks. Surface material integrity and CD-stability
results using this new, acid-free approach are presented in the following pages.
The use of MegaSonic energy is widely accepted in photomask cleaning. For the advanced technology nodes, beyond
65nm, the problem of damaged sub resolution assist features (SRAF) becomes highly prevalent. Such feature damages
are often related to the application of MegaSonic energy.
We investigated the influence of common cleaning media and MegaSonic parameters for damaging SRAF patterns. A
special option of our cleaning tool was utilized to test a large number of different settings with low resources for test
mask and defect inspections. In this paper we will present the results of our investigations and present conditions for
MegaSonic cleaning which will enable the wide use of this technology beyond the 45nm technology node.
Today, haze and crystal growth on the reticle surface are still a primary concern of the microlithography industry. The crystals limit the reticle usage as they result in printable defects on the wafers. Numerous studies have been presented so far. The general belief is that different root causes can lead to crystal growth and haze formation, among them the contaminants on the mask surface from the clean processes.
In this paper we are investigating the potential of sulfate free clean processes based on ozonated and hydrogen water for the next generation of photomasks. Key parameters such as cleaning efficiency, as well as the impact of the chemistry on the mask optical properties will be presented. The potential of the chemistry will be discussed and compared to the standard cleaning processes.
Contaminants and residues on the mask surface are still a concern to the Microlithography industry as they influence the reticle printing properties. It is conceivable that this effect will worsen as the industry moves toward smaller nodes for the next generation lithography, i.e. 193nm immersion and/or EUV.
The AUV5500 (advanced UV-cleaning and inspection) tool provides the possibility to investigate the effect of mask contaminants from transmission and reflection measurements in the spectral range 145nm to 270nm, and to clean the mask surface as well. In this paper, we are investigating the change of optical properties with organic contaminants on mask features and the ability to clean the surface to its original optical properties. At first we discuss the behavior of the 193nm illumination of the features on the mask properties. Then, with the help of a controlled contamination method to pollute the surface, we investigate the influence of the contaminant on the features on the photomask optical properties. The impact of the contaminant on AIMS data will be discussed as well.
Today, the industry is suffering from the consequences of residue and contaminants on the mask surface as they significantly affect the printing quality of the reticle. Thus a good control of the mask cleanliness via its optical properties is becoming essential to minimize this impact. The AUV5500 is specifically addressing organic contaminants. The principle of the tool set-up, its process functionality is presented. Preliminary data on the impact of organic contaminants on binary and embedded phase shift masks optical properties and the tool cleaning capability are analyzed and discussed.