Structural, optical, and electrical properties of WOx(Ny) films deposited by reactive dual magnetron sputtering

Abstract

Thin films of tungsten oxynitrides were prepared by dual magnetron sputtering of tungsten using argon/oxygen/nitrogen gas mixtures with various nitrogen/oxygen ratios.The presence of even relatively small amounts of oxygen led to close-to-stoichiometric WO 3 , with little incorporation of nitrogen, therefore the films were labeled as WO x (N y ). Oxygen had a great effect not only on the composition but on the structure of WO x (N y ) films, as shown by Rutherford backscattering and x-ray diffraction, respectively. Significant incorporation of nitrogen occurred only when the nitrogen partial pressure exceeded 89% of the total reactive gas pressure. Sharp changes in the stoichiometry, deposition rate, room temperature resistivity, electrical activation energy and optical band gap were observed when the nitrogen/oxygen ratio was high. The deposition rate increased from 0.31 to 0.89 nm/s, LBNL-59900 1 the room temperature resistivity decreased from 1.65 × 10 8 to 1.82 × 10 -2 Ωcm, the electrical activation energy decreased from 0.97 to 0.067 eV, and the optical band gap decreased from 3.19 to 2.94 eV upon nitrogen incorporation into the films. WO x (N y ) films were highly transparent as long as the nitrogen incorporation was low, and were brownish (absorbing) and partially reflecting as nitrogen incorporation became significant.

Combining reactive sputtering and rapid thermal processing for synthesis and discovery of metal oxynitrides

“…The XRD pattern for thin films deposited at 0.040 O 2 PP shows the presence of a broad amorphous peak centered around the expected value for the (1, 11, 0) peak of Ta 2 O 5 . A similar observation of low crystallinity for refractory oxide phases was observed during reactive sputter deposition of tungsten 20 and titanium oxynitrides. 27 The observation of poorly crystalline or amorphous thin films for the N/O stoichiometries of interest is in agreement with previous reports, and as described by Cristea et al, 23 sputter deposited TaO x N y with p O 2 þ p N 2 > 0:15 Pa encourages the formation of amorphous phases, which highlights the need for an independent thermal processing step to achieve amorphous to crystalline transitions in oxynitride systems.…”

“…For N 2 PPs sufficient to introduce significant nitrogen into the films, N/O stoichiometry varies nonlinearly as a function of the ratio of N 2 and O 2 gas flow rates, highlighting the importance of careful control and calibration of the reaction gas atmosphere. 20,21,[25][26][27][28][29] Using a variable leak valve to control O 2 PP, we demonstrate the ability to carefully control O 2 PPs and fine-tune oxynitride chemistries. We further discuss a heuristic approach to rapidly obtain the optimal O 2 PP for depositing oxynitride films.…”

“…20,21,23,25,27 While oxynitride phases have been observed in the as-deposited films in some cases, 26,30,31 several factors such as total pressure, power, and substrate temperature during sputtering are likely to simultaneously control both the composition and crystal structure of the as-deposited oxynitride chemistries. To decouple the temperature-dependent reactivity of the growing film in sputter atmosphere and thermally activated crystallization, we demonstrate RTP as postdeposition, iso-compositional crystallization process that provides access to high-temperature phases without compromising anion stoichiometry.…”

Physical characterization of sputter-deposited amorphous tungsten oxynitride thin films

“…Several of the early studies have contributed extensively towards the understanding of W-N system, especially the knowledge of fundamental relationship between different parameters, such as deposition conditions and their effect on the internal stress, microstructure, and elemental concentration [18][19][20][21][22][23][24][25][26][27][28][29][30][31]. Similarly, tungsten oxides have been studied for a wide variety of electrical, optical, and energy related applications [1][2][3][4][5][6][7][8][9][10][11][12] to longer wavelengths, and concluded that the conductivity of said films is lowered with increased nitrogen content [33]. While earlier efforts were focused on either thicker coatings …”

“…Tungsten oxide (WO 3 ) is a widely studied "chromogenic" material with interesting structural, electronic, and optical properties for utilization in many scientific and technological applications [1][2][3][4][5][6][7][8][9][10]. Among metal oxide semiconductors, WO 3 has become a focal point of interest where nanostructured and low-dimensional forms of WO 3 are beneficial for technological development.…”