Influence of deposition conditions on the composition of tantalum coatings

In this paper, tantalum coatings obtained by the chemical vapour deposition in reactors with “hot” and “cold” walls were analyzed. Holder with a sample was put into the tube-shaped screen to limit the interaction zone in the reaction chamber. Screens from different materials were used: one from the quartz glass and the other one from the stainless steel. Induction heating was used to heat the substrates in the reactor. The inductor coil was located on the outside surface of the screen. In the case of quartz glass screen, only the holder with the sample was heated which corresponds to the reactor with the “cold” walls. When the screen made from stainless steel was used, the heat transfer from the screen walls to the sample occurred and this corresponded to the “hot” wall reactor scenario. Tantalum coatings were produced on tungsten substrates by the reduction of tantalum bromide with cadmium vapour. It was found out that the formation of reverse flows containing products of chemical reaction and the non-reacting reagents during deposition of coatings was possible due to the effect of ejection. As a result, in a reactor with “hot” walls, part of the reagents interacted with the surface of the stainless steel screen, which led to the formation of Fe2Br4 and CrBr2, and the subsequent reduction of not only tantalum bromide, but also iron bromide on the substrate. Thus, the tantalum coating was formed on the sample during the deposition in the reactor with “cold” walls, and the coating consisting of a mixture of Ta + Fe2Ta was formed using a reactor with “hot” walls.