Modification of niobium film stress by low-energy ion bombardment during deposition

Abstract

The effect of ion bombardment on film stress was studied by evaporating Nb thin films in the presence of a controlled ion beam from a Kaufman ion source. Films were deposited at 4 Å/s by electron-beam evaporation with ion bombardment over the energy range 100–800 eV, at ion current densities of 0.001 to 1.1 mA/cm2. Film stress was measured by an x-ray bending-beam technique on Si substrates. Stress values were found to depend strongly on both ion flux and sample temperature. For films deposited at 400 °C, film stress is tensile in the absence of ion bombardment. Increasing argon ion flux causes a change toward compressive stress, in some cases passing through zero. For films deposited at room temperature, film stress is compressive in the absence of ion bombardment, due to incorporation of oxygen. Argon ion bombardment causes a change toward tensile stress, correlating with an improvement in film purity by preferential resputtering of oxygen. With 100 eV argon ions, an ion-to-atom ratio of only 3–10 % is sufficient to cause reversal of the sign of film stress in most cases. Results are interpreted as a combination of cleaning by resputtering and annealing or compacting the film microstructure. In addition, nitrogen ion bombardment is shown to produce superconducting NbN films with a superconducting transition temperature up to 14.5 K.

Tuning Material Properties of Oxides and Nitrides by Substrate Biasing during Plasma-Enhanced Atomic Layer Deposition on Planar and 3D Substrate Topographies

“…No inert argon gas or detectable carbon impurities were incorporated in this film (Table ). For deposition involving highly reactive materials such as Ti, Hf, Nb, etc., the partial pressure of the vacuum species (e.g., background water, oxygen) can influence the amount of impurity incorporation (e.g., up to tens of an atomic percent of oxygen) in the deposited film. ,,, Assuming a partial pressure of ∼10 –8 Torr for background impurities (for the base pressure of ∼10 –6 Torr in the FlexAL system) corresponds to an impingement rate of about ∼0.5 impurity atoms per nm 2 /s on the growing film surface. , A plasma exposure time of 10 s can therefore, lead to the incorporation of ∼0.5 impurity at./nm 2 in the film (assuming a sticking coefficient of 1) which is of the same order as the GPC [O] value obtained for the TiN x film grown without biasing. Another reason for the significant [O] content could be due to oxidation of the film upon exposure to the environment.…”

Effect of magnetron sputtering parameters and stress state of W film precursors on WSe2 layer texture by rapid selenization

“…The substrate bias voltage can increase the compressive stress or decrease the tensile stress192021. When the substrate is applied with a bias voltage, an electric field is formed between the substrate and the anode.…”

Mechanical Stress in Optical Coatings

“…The effects on the mechanical properties due to ion bombardment of the growing film are mainly depending on the kind, the amount and the energies of the involved ions, atoms and molecules. First descriptions concerning the development of compressive stress as consequence of an ion peening effect were carried out by d'Heurle (d'Heurle 1970) and later from different research groups starting in 1980 (Hoffman and Gaertner 1980;Cuomo et al 1982;Huang et al 1985;Windischmann 1987;d'Heurle and Harper 1989;Volkert 1991). Some calculations and computer simulations concerning the densification of the films due to ion bombardment and the effect on the microstructure of the films were carried out by Miiller (Miiller 1986.…”