A pellicle is employed to protect a photomask from particle contamination. The pellicle is positioned at a distance from the photomask pattern such that particle contaminants are out of focus. To extend the lifetime of a photomask, the pellicle must be replaced when it becomes heavily contaminated or damaged. The replacement process generally consists of the following three steps, 1) removal of the existing pellicle, 2) cleaning of the photomask, and 3) installation of a new pellicle. The cleaning step is primarily required for the removal of pellicle-glue residue unintentionally left behind during the pellicle removal process. This cleaning step has traditionally employed aggressive chemistries, such as a long process cycle, utilizing a Sulfuric Acid and Hydrogen Peroxide mix (SPM). The major drawback from this approach is that it inadvertently exposes the photomask pattern to aggressive chemistries, risking CD shift, damage to sub-resolution assist features (SRAFs), and accelerated haze growth, thus, ultimately reducing a masks lifetime . To overcome these shortcomings, this paper presents a localized approach for removal of pellicle-glue residue, which does not require long SPM cycles for post-clean.
Megasonic cleaning remains the industry’s workhorse technology for particle removal on advanced 193i and extreme ultraviolet (EUV) photomasks. Several megasonic cleaning technologies and chemistries have been proposed and implemented over the years in diverse production environments. The operational range of these process technologies, over a wide array of applications, is ultimately defined by measurable capability limits. As geometries continue to scale-down and new materials are introduced, existing cleaning technologies will naturally fade out of range and new capability is ultimately required. This paper presents a novel fundamental approach for expanding cleaning capability by use of high-frequency megasonics and tenside-based additives (BASF SELECTIPUR C-series). To this end, a sonoluminescence-based experimental test bench was configured to characterize and study the effects of various process parameters on cleaning performance, with a particular emphasis on cavitation-induced damage and enhancement of particle removal capabilities. The results from the fundamental studies provide a path forward towards delivering new cleaning capability by enabling high-frequency megasonic systems and tenside-based additives.
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.
Tip-enhanced Raman spectroscopy (TERS), with nanometer spatial resolution, has the capability to monitor chemical composition, strain, and activated dopants and is a promising metrology tool to aid the semiconductor R&D processes. This paper addresses the major challenges which limit the application of TERS from routine measurement: the lack of comparability, reproducibility, calibration, and standardization. To address these issues, we have developed a robust test structure and the ability to generate high-quality tips using a high volume manufacturing (HVM) approach. The qualifying data will be presented.
Particle contamination in ultra-pure water (UPW) and chemicals will eventually end up on the surface of a wafer and may result in killer defects. To improve the semiconductor processing yield in sub-10 nm half pitch nodes, it is necessary to control particle defectivity. In a systematic study of all major techniques for particle detection, counting, and sizing in solutions, we have shown that there is a gap in the required particle metrology which needs to be addressed by the industry. To reduce particles in solutions and improve filter retention for sub-10 nm particles with very low densities (<10 particles/mL), liquid particle counters that are able to detect small particles at low densities are required. Non-volatile residues in chemicals and UPW can result in nanoparticles. Measuring absolute non-volatile residues in UPW with concentrations in the ppb range is a challenge. However, by using energy-dispersive spectroscopy (EDS) analysis through transmission electron microscopy (TEM) of non-volatile residues we found silica both in dissolved and colloidal particle form which is present in one of the cleanest UPW that we tested. A particle capture/release technique was developed at SEMATECH which is able to collect particles from UPW and release them in a controlled manner.
Using this system we showed sub-10 nm particles are present in UPW. In addition to colloidal silica, agglomerated carbon containing particles were also found in UPW.