Spectral data of refractive index and extinction coefficient for thin films of titanium group metals used for fabrication of optical microstructures

In this data paper we share the information on refractive index and extinction coefficient of metallic films of the titanium group (Ti, Zr, Hf), measured by ellipsometry in the wavelength range of 300–1100 nm. The presented data can be used to indirectly measure the thickness of metal films when they are sputtered onto a substrate, using the measured data on transmission and reflection coefficients depending on the wavelength of the probe beam, as well as to calculate the energy characteristics of diffraction gratings, formed on the surface of these films, under rigorous electromagnetic theory. The data were used in the research article “Increasing the spatial resolution of direct laser writing of diffractive structures on thin films of titanium group metals” [1].

In this data paper we share the information on refractive index and extinction coefficient of metallic films of the titanium group (Ti, Zr, Hf), measured by ellipsometry in the wavelength range of 300 e1100 nm. The presented data can be used to indirectly measure the thickness of metal films when they are sputtered onto a substrate, using the measured data on transmission and reflection coefficients depending on the wavelength of the probe beam, as well as to calculate the energy characteristics of diffraction gratings, formed on the surface of these films, under rigorous electromagnetic theory. The data were used in the research article "Increasing the spatial resolution of direct laser writing of diffractive structures on thin films of titanium group metals" [1].
© 2019 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons. org/licenses/by/4.0/).

Data
Here we show measured data of spectral dependence of refractive index ( Fig. 1) and extinction coefficient ( Fig. 2) for thin films of Hf, Ti, and Zr. The zirconium film has minimal values of extinction coefficient and refractive index in spectral range of 350e1100 nm.

Experimental design, materials, and methods
The data were obtained by the method of spectral ellipsometry using the device "ELLIPS-1991", which uses the original static dual-channel scheme developed and patented in the ISP SB RAS [2]. As a light source, this device uses a 75 W xenon arc lamp, and the spectral measurement range is 300e1100 nm with a resolution of 2 nm. The probe beam diameter onto sample surface has a size of 1 mm. The refractive indices n and the extinction coefficients k of the metal films were calculated from the measured ellipsometric spectrums using the software of this ellipsometer.
The measurements were made on Ti and Zr films with 1% transmission and Hf film with 0.13% transmission measured at 650 nm wavelength. The studied thin metal films were deposited onto fused silica substrates by a vacuum magnetron sputtering technique. At that, targets of Ti, Zr and Hf with the purity of the materials of not less than 99.9% were used. The metal films were sputtered onto the hot surface of the substrate. The cleaned substrate was placed in a vacuum chamber and heated for 30 minutes in a vacuum of 10 À1 mmHg at 200 о С. After warming up, the chamber was pumped out to a pressure of 5 Â 10 À5 mmHg. The substrate was located at a distance of 25 mm from the surface of the magnetron target (Kurt j. Lesker TORUS TM3 -3") above its center. The power supply time mode of the magnetrons was low-frequency voltage pulses with a Specifications Value of the Data The data can be used to calculate reflection and transmission of the light illuminated diffractive micro/nano-structures formed on the surface of the Ti, Zr or Hf films when using rigorous electromagnetic theory. Optical parameters of the metal films are very important at fabrication of micro/nanostructures on their surface. This data can be used for fast estimation of the thickness of metal films when they are sputtered onto the substrate as shown in Ref. [1]. The spectral dependences of refractive index and extinction coefficient for hafnium in 300e1100 nm wavelength range were obtained for the first time by our knowledge.
duty cycle of 10, following with the frequency of 20e30 kHz. Using the frequency selection, the average discharge current was selected (I ¼ 0.3 A). The magnetron discharge was stabilized by voltage (U ¼ 1 kV) to maximize the energy of the sputtered particles. Argon was used as a buffer gas. Its pressure during the sputtering was 10 À3 mmHg, to achieve free (hammerless with the atoms of the buffer gas) deposition of sputtered particles on the surface of the substrate. The buffer gas was supplied directly to the target of the magnetron. The characteristic sputtering rate was about 4 nm/s. Using the Ntegra by NT-MDT atomic-force microscope (AFM), images of the surfaces of the investigated metal films were obtained (Fig. 3aef). The obtained AFM-images show that the most homogeneous is the hafnium film sample. The Zr film has a microcrystalline structure. Diagonal fringes on the images of areas 5х5 mm are explained by surface imperfections of fused silica microscope slides with 1-mm thickness used as substrates for the film sputtering.