Photomask Integrity / Cleaning

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Efficient ozone, sulfate and ammonium free resist stripping process

Conventional resist strip processes employ a variety of steps geared towards highly effective removal of organic and inorganic contamination from the mask surface. For proper wetting of the photomask surface with cleaning chemicals, higher surface energy is desired. A photomask surface is needed to be in hydrophilic state prior to the application of wet chemistries. Hydrophilic surfaces promote better liquid distribution and uniform chemical effects across the surface; as part of the POR cleaning process flow a 172nm excimer VUV step was used to achieve a low water contact-angle on the surface.


Extending the Ruthenium Capping Layer Life Time of Extreme Ultra-Violet Lithography Photomasks in Physical Force Cleaning

Extreme Ultra-Violet Lithography (EUVL) is currently considered one of the most promising Next Generation Lithography (NGL) choices to extend shrinkage of transistor sizes. This is also reflected in the International Technology Roadmap for Semiconductors (ITRS).EUVL works at an exposure wavelength of 13.5 nm, which is electromagnetic radiation absorbed at a high rate by nearly any solid material. Therefore, photomasks must be of reflective nature. This is accomplished by a Multi-layer structure deposited on top of a low-thermo expansion quartz substrate (LTEM substrate).


MegaSonic Cleaning: Possible solutions for 22nm node and beyond

MegaSonic energy transfer to the photomask surface is indirectly controlled by process parameters that provide an effective handle to physical force distribution on the photomask surface. A better understanding on the influence of these parameters on the physical force distribution and their effect on pattern damage of fragile mask features can help in optimizing MegaSonic energy transfer as well as assist in extending this cleaning technology beyond 22nm node. In this paper we have specifically studied the effect of higher MegaSonic frequencies (3 & 4 MHz) and media gasification on pattern damage; effect of cleaning chemistry, media volume flow rate, process time and nozzle distance to the mask surface during the dispense is also discussed. MegaSonic energy characterization is performed by measuring the acoustic energy as well as cavitation created by MegaSonic energy through Sonoluminescence measurements.


Investigating the intrinsic cleanliness of automated handling designed for EUV mask pod-in-pod systems

Extreme Ultraviolet Lithography (EUVL) is the most promising solution for technology nodes 16nm (hp) and below. However, several unique EUV mask challenges must be resolved for a successful launch of the technology into the market. Uncontrolled introduction of particles and/or contamination into the EUV scanner significantly increases the risk for device yield loss and potentially scanner down-time. With the absence of a pellicle to protect the surface of the EUV mask, a zero particle adder regime between final clean and the point-of-exposure is critical for the active areas of the mask. A Dual Pod concept for handling EUV masks had been proposed by the industry as means to minimize the risk of mask contamination during transport and storage. SÜSS MicroTec introduces MaskTrackPro InSync as a fully automated solution for the handling of EUV masks in and out of this Dual Pod System and therefore constitutes an interface between various tools inside the Fab. The intrinsic cleanliness of each individual handling and storage step of the inner shell (EIP) of this Dual Pod and the EUV mask inside the InSync Tool has been investigated to confirm the capability for minimizing the risk of crosscontamination. An Entegris Dual Pod EUV-1000A-A110 has been used for the qualification. The particle detection for the qualification procedure was executed with the TNO’s RapidNano Particle Scanner, qualified for particle sizes down to 50nm (PSL equivalent).
It has been shown that the target specification of < 2 particles @ 60nm per 25 cycles has been achieved. In case where
added particles were measured, the EIP has been identified as a potential root