Niobium nitride films formed by rapid thermal processing (RTP): a study of depth profiles and interface reactions by complementary analytical techniques

Abstract

The nitridation of niobium films approximately 250 and 650 nm thick by rapid thermal processing (RTP) at 800 degrees C in molecular nitrogen or ammonia was investigated. The niobium films were deposited by electron beam evaporation on silicon substrates covered by a 100 or 300 nm thick thermally grown SiO(2) layer. In these investigations the reactivity of ammonia and molecular nitrogen was compared with regard to nitride formation and reaction with the SiO(2) substrate layer. The phases formed were characterized by X-ray diffraction (XRD). Depth profiles of the elements in the films were recorded by use of secondary neutral mass spectrometry (SNMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy-filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride, and oxide phases. The results provide clear evidence of the expected higher reactivity of ammonia in nitride formation and reaction with the SiO(2) substrate layer. Outdiffusion of oxygen into the niobium film and indiffusion of nitrogen from the surface of the film result in the formation of oxynitride in a zone adjacent to the Nb/SiO(2) interface. SNMS profiles of nitrogen reveal a distinct tail which is attributed to enhanced diffusion of nitrogen along grain boundaries.

Annealing of evaporated and sputtered niobium films in oxygen and nitrogen rich atmospheres by Rapid Thermal Processing (RTP)

“…The oxide zone itself is homogenous, implying that crystallites were oxidized completely before diffusion through the film continued. The high concentration of nitrogen in the bulk of the Nb film is in disagreement with former investigations [18,19], detecting a decreasing nitrogen concentration from surface to deeper film regions. The here observed nitrogen concentration profile may be a result of relatively broad grain boundaries, allowing nitrogen fast permeation of the film.…”

“…It is not possible to detect a distinct boundary between Nb 2 N and Nb 4 N 3 , but probably there is a phase mixture consisting of Nb 2 N and Nb 4 N 3 , with an increasing amount of Nb 4 N 3 towards zone 2. The high concentration of carbon in the surface region may be explained by residual oxygen in the applied nitrogen, oxidizing the graphite susceptor and therefore enabling CO to permeate the film [18]. Zone 2 (900-1180 s): This region of the film consists of Nb and O with ratios of about 33 at% and 60 at%, which corresponds well to the composition of NbO 2 as identified by XRD.…”

The effect of heat treatment on structural and electronic properties of niobium nitride prepared by a thermal diffusion method

“…Nitriding of bulk Nb substrates can be achieved by the so-called reactive diffusion method [15,19] or combustion synthesis [20]. NbN x thin films were also produced using rapid thermal processing by heating of Nb thin films deposited on Si in molecular nitrogen or ammonia [21,22]. In general, these methods depend on adsorption of nitrogen or ammonia gas at the surface of the Nb substrate that is heated at high temperatures, then it diffuses into Nb and forms NbN x .…”

Properties of niobium oxide films deposited by pulsed DC reactive magnetron sputtering

“…Various chemical and physical preparation of niobium oxides film like sol-gel processes [5], thermal evaporation [6] and magnetron sputtering [7]has been reported.…”