Oxidation resistance of Ru-capped EUV multilayers

Abstract

Differently prepared Ru-capping layers, deposited on Mo/Si EUV multilayers, have been characterized using a suite of metrologies to establish their baseline structural, optical, and surface properties in as-deposited state. Same capping layer structures were tested for their thermal stability and oxidation resistance. Post-mortem characterization identified changes due to accelerated tests. The best performing Ru-capping layer structure was studied in detail with transmission electron microscopy to identify the grain microstructure and texture. This information is essential for modeling and performance optimization of EUVL multilayers.

Oxidation and Reduction of Ultrathin Nanocrystalline Ru Films on Silicon: Model System for Ru-Capped Extreme Ultraviolet Lithography Optics

“…This finding is consistent with a recent transmission electron microscopy (TEM) study of a 2.3 nm thick Ru capping layer. 11 Using the Scherrer formula, the vertical grain size can be estimated from the fwhm of the Ru(0002) Bragg reflection. We deduce grain dimensions of 2.2, 4.8, and 7.1 nm along the surface normal, respectively, which correlate nicely with the Ru film thicknesses determined by XRR.…”

Growth of Atomic Layer Deposited Ruthenium and Its Optical Properties at Short Wavelengths Using Ru(EtCp)2 and Oxygen

“…Ultrathin metal films are essential for numerous applications, especially in microelectronics [1], heterogeneous catalysis [2], soft X-ray optics, and sensing. Ruthenium, as a relatively low-cost noble metal, is an attractive material when high oxidation resistance is needed [3]. Smooth and high-density Ru thin films are a preferred solution, for example, as electrodes for dynamic random access memories (DRAM) [4][5][6][7], metal-oxide-semiconductor field-effect transistors (MOSFET) [8], metal-insulator-metal capacitors [9,10], and grazing-incidence soft X-ray mirrors [11].…”

Time-frequency analysis assisted determination of ruthenium optical constants in the sub-EUV spectral range 8 nm – 23.75 nm

“…𝜎 𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 is the evaluated error of the measurement from the experimental setup, the two parameters a and b are supposed to compensate the effects of the model's deficiencies in describing the sample's real structure and the possible underestimation of the experimental error in our measurements, since it is very difficult to ascertain the effect of all the measurement's uncertainties on the measurands in such a complicated setting, these parameters are included in the parameters array p and to be sampled in the MCMC-based evaluation. In (5) we assume that the modelling error is normally distributed and has the same properties as the known measurement error.…”

“…Due to its high chemical stability and oxidation resistance, high reflectivity in the EUV spectral range and high etch selectivity to the materials of mask absorber layers (e.g. : TaN), Ru thin films are used as capping layers of the Mo/Si multi-layer mirrors of the masks, extending the lifetime of the deposited multi-layer mirror (MLM) reflector and protecting it during pattern repair and cleaning processes [4,5]. In addition to the outstanding performance of Ru capping layers in EUVL masks, Ru has been used and investigated to enhance the performance of other key EUVL components as it can be used for example in the coating of the inner reflective surface of the EUV grazing-incidence collectors and due to its high thermal emissivity Ru coated pellicles are reported to have better performance characteristics [4].…”