EUV Lithography Process Research Articles

Pinpoint Particle Removal for EUV Pellicle Productivity Enhancement

The EUV lithography process is increasingly employed in the advanced semiconductor process, and high-NA EUV equipment is being developed for high-volume manufacturing. Therefore, particle contamination control for EUV masks is a key success factor for the yield increase of the EUV lithography process in the future and for this, the needs of EUV pellicle will increase. Although materials for the EUV pellicle membrane are still under development, unlike ArF pellicles, its fabrication is complicated and difficult, resulting in low production yield and high production costs. To reduce EUV pellicle operating costs, it is possible to consider ways to reduce production costs by enhancing the yield of EUV pellicle or reusing particle contaminated EUV pellicle by particle removal. Both methods require damage-free particle removal technology of EUV pellicle. Pinpoint particle removal technology, a cleaning technology that satisfies these requirements, was developed, and particles bigger than 5 μm could be removed in a cleanroom environment without damaging fragile EUV pellicle. The possibility of the damage-free EUV pellicle cleaning process was verified through the process window evaluation of Pinpoint cleaning technology.

Screening of 193i and EUV lithography process options for STT-MRAM orthogonal array MTJ pillars

Spin-transfer torque magnetic random-access memory (STT-MRAM) is considered as the most promising candidate to replace the complementary metal-oxide-semiconductor (CMOS) based memories that are dominating the market in the last few decades. What makes STT-MRAM superior to other memories is the high read and write speeds, non-volatility, good cycling endurance and near-zero leakage. Moreover, with the perpendicular device topology and the single transistor cell configuration, it becomes a very promising candidate for further device scaling which is essential to increase the memory densities. This paper focuses on the experiments performed using different lithography approaches in order to explore the smallest printable pitches for orthogonal array magnetic tunnel junction (MTJ) pillars, which are the main components of the STT-MRAM. Considering the high impact of the MTJ patterning process on the robustness of the memory device, several post-litho performance parameters such as wafer critical dimension uniformity (WCDU), local critical dimension uniformity (LCDU) and pillar circularity have also been measured and compared.

Removal of CrN Contamination from EUV Mask Backside Using Dry Cleaning

For EUV lithography, a reflective mask is essential because of use of the strong energy, wavelength of 13.5 nm. The EUV mask consists of multi-layered, multi-material structure and is susceptible to various contaminants. Since EUV lithography process should be used in a high vacuum environment, an electrostatic chuck (ESC) is used to fix or hold the EUV mask using electrostatic force. In general, in order to use ESC chuck, it needs a thin conductive layer (CrN layer) on the backside. However, the contact points of the electrostatic pin chuck can make exfoliation of conductive CrN layer producing CrN particles. If these particles are present on the backside of the mask, CD or DOF may be affected during EUV exposure. The 1 μm particle can leads to a gap radius of 42mm [4]. Moreover, these backside particles may travel to the front side. Therefore, backside cleaning should be performed to remove particles from the mask backside surface.

Prediction of resolution using wet-develop type single layer and dry-development process for EUV lithography

This paper predicts the resolution of EUV lithography by using wet and dry developable resist process. We demonstrated that there is a possibility of the wet-develop type single layer resist whose type is positive-tone or negative-tone CA resist. The resist-film thickness is 200–400 nm. An exposure light (13.5 nm) reached at the bottom of resist film and the resists were reacted sufficiently by chemically amplification. We also showed that the EUV lithography process (13.5 nm, NA = 0.1) with the dry development prossess has the capability to resolve 50 nm L/S pattern. We can confirm that the space pattern of 50 nm can be resolved by dry-development.