Fabrication of high aspect ratio tungsten nanostructures on ultrathin c-Si membranes for extreme UV applications

Abstract

In this work, we demonstrate a full process for fabricating high aspect ratio diffraction optics for extreme ultraviolet lithography. The transmissive optics consists in nanometer scale tungsten patterns standing on flat, ultrathin (100 nm) and highly transparent (>85% at 13.5 nm) silicon membranes (diameter of 1 mm). These tungsten patterns were achieved using an innovative pseudo-Bosch etching process based on an inductively coupled plasma ignited in a mixture of SF6 and C4F8. Circular ultra-thin Si membranes were fabricated through a state-of-the-art method using direct-bonding with thermal difference. The silicon membranes were sputter-coated with a few hundred nanometers (100-300 nm) of stress-controlled tungsten and a very thin layer of chromium. Nanoscale features were written in a thin resist layer by electron beam lithography and transferred onto tungsten by plasma etching of both the chromium hard mask and the tungsten layer. This etching process results in highly anisotropic tungsten features at room temperature. The homogeneity and the aspect ratio of the advanced pattern transfer on the membranes were characterized with scanning electron microscopy after focus ion beam milling. An aspect ratio of about 6 for 35 nm size pattern is successfully obtained on a 1 mm diameter 100 nm thick Si membrane. The whole fabrication process is fully compatible with standard industrial semiconductor technology.

Meso scale component manufacturing: a comparative analysis of non-lithography and lithography-based processes

“…However, the obtained reflectivity is around 60%-70% at these wavelengths. Table 5(e) shows dense patterns of tilted cross-section SEM images after Cr and W etching by EUV lithography [86].…”

Heterostructure based demultiplexer using solid–solid phononic crystal ring resonators

“…The lattice constant is a = 550 nm, and the inclusions radii are r 1 = 158 nm, r 2 = 168 nm, and r 3 = 178 nm. Such PnC configurations in the GHz range applications are practically realized by different methods such as the focused ion beam (FIB) in many works [39][40][41][42]. Using the finite element method (FEM), the dispersion curves of PnCs are simulated and illustrated for three different radii in figure 3.…”

Laser ablation of high-aspect-ratio hole arrays in tungsten for X-ray applications

“…Patterning directly on a tungsten substrate allows for reducing the number of fabrication steps. The fabrication of tungsten gratings for X-ray optical elements using reactive ion etching has previously been reported [12,13]. However, this technique is, to our knowledge, limited to aspect ratios lower than 10 in tungsten thin films.…”