Ruthenium (Ru) film used as capping layer in extreme ultraviolet (EUV) mask peeled off after annealing and in-situ UV (IUV) cleaning. We investigated Ru peeling and found out that the mechanical stress caused by the formation of Si oxide due to the penetration of oxygen atoms from ambient or cleaning media to top-Si of ML is the root cause for the problem. To support our experimental results, we developed a numerical model of finite element method (FEM) using commercial software (ABAQUS™) to calculate the stress and displacement forced on the capping layer. By using this model, we could observe that the displacement agrees well with the actual results measured from the transmission electron microscopy (TEM) image. Using the ion beam deposition (IBD) tool at SEMATECH, we developed four new types of alternative capping materials (RuA, RuB, B4C, B4C-buffered Ru). The durability of each new alternative capping layer observed by experiment was better than that of conventional Ru. The stress and displacement calculated from each new alternative capping layer, using modeling, also agreed well with the experimental results. A new EUV mask structure is proposed, inserting a layer of B4C (B4C-buffered Ru) at the interface between the capping layer (Ru) and the top-Si layer. The modeling results showed that the maximum displacement and bending stress observed from the B4C-buffered Ru are significantly lower than that of single capping layer cases. The durability investigated from the experiment also showed that the B4C-buffered structure is at least 3X stronger than that of conventional Ru.
In EUV Lithography, an absence of promising candidate of EUV pellicle demands new requirements of EUV mask cleaning which satisfy the cleaning durability and removal efficiency of the various contaminations from accumulated EUV exposure. It is known that the cleaning with UV radiation is effective method of variety of contaminants from surface, while it reduces durability of Ru capping layer. To meet the expectation of EUV mask lifetime, it is essential to understand the mechanism of Ru damage. In this paper, we investigate dominant source of Ru damage using cleaning method with UV radiation. Based on the mechanism, we investigate several candidates of capping to increase the tolerance from the cycled UV cleaning. In addition, we study durability difference depending on the deposition method of Ru capping. From these studies, it enables to suggest proper capping material, stack and cleaning process.
In EUVL, major impacts on determining critical dimension (CD) are resist process, scanner finger print, and mask characteristics. Especially, reflective optics and its oblique incidence of light bring a number of restrictions in mask aspect. In this paper, we will present one of the main contributors for wafer CD performance, such as center wavelength (CW) of multilayer (ML) in EUVL mask. We evaluate wafer CDs in 27.5nmHP L/S, 30nmHP L/S, and 30nmHP contact patterns with NXE3100 by using masks with purposely off-targeted CW ranging from 13.4 to 13.7nm. Based on the results from the exposure experiments, we verify that the CW specification for NXE3100 is regarded as 13.53 ± 0.015nm at CWU=0.03nm to satisfy the wafer CD requirements. According to verified simulations, however, we suggest a new CW specification for NXE3300 with higher values considering wide illumination cone angle from larger numerical aperture (0.33NA). Moreover, simulations in different exposure conditions of NXE3300 with various patterns below 20nm node show that customized CW specification might be required depending on target layers and illumination conditions. We note that it is also important to adjust CW and CWU in final mask product considering realistic difficulties of fabrcation, resulting in universal CW specification.
Reduced design rules demand higher sensitivity of inspection, and thus small defects which did not affect printability
before require repair now. The trend is expected to be similar in extreme ultraviolet lithography (EUVL) which is a
promising candidate for sub 32 nm node devices due to high printing resolution. The appropriate repair tool for the small
defects is a nanomachining system. An area which remains to be studied is the nano-machining system performance
regarding repair of the defects without causing multilayer damage. Currently, nanomachining Z-depth controllability is 3
nm while the Ru-capping layer is 2.5 nm thick in a Buffer-less Ru-capped EUV mask. For this report, new repair
processes are studied in conjunction with the machining behavior of the different EUVL mask layers. Repair applications
to achieve the Edge Placement(EP) and Z-depth controllability for an optimal printability process window are discussed.
Repair feasibility was determined using a EUV micro exposure tool (MET) and Actinic Imaging Tool (AIT) to evaluate
repairs the 30 nm and 40 nm nodes. Finally, we will report the process margin of the repair through Slitho-EUVTM
simulation by controlling side wall angle, Z-depth, and EP (Edge Placement) on the base of 3-dimensional experimental
Nano-machining repair tool plays an important role in the current 65 nm node photomask repair. It
removes defects mechanically with nanometer sized diamond tip with high accuracy and low damage using
high accuracy AFM data. The repair performance of nano-machining repair system largely depends on the
diamond tip whose aspect ratio decides the minimum reparable feature size. As the device shrinks to 45 nm
or 32 nm node, higher aspect ratio tip with weak structure is required. It is contradiction to the fact that
more accurate edge placement and better repair slope is required in smaller node repair, because deflection
or tip wear effect could happen in high aspect ratio tip. In this article, deflection and wear effect were
investigated in single layer repair recipe using SEM and AIMSTM. Multilayer recipe which complements
weak structure was estimated carefully, and some limits were discussed. Finally some requirements of
nano-machining repair system for 45 nm node were presented.