Growth of epitaxial TiN films deposited on MgO(100) by reactive magnetron sputtering: The role of low-energy ion irradiation during deposition

Abstract

Plan-view and cross-sectional transmission electron microscopy have been used to investigate the role of low-energy ion irradiation in controlling the defect structure of epitaxial TiN(100). The films were deposited by reactive magnetron sputter deposition onto MgO(100) substrates at film growth temperatures T s between 550 and 850°C (0.26 to 0.35 of the melting point of TiN in K) and negative substrate biases V s between 0 and 500 V. Sputtering was carried out in pure N 2 atmospheres, the energy per N ion incident at the film surface was ∼ eV s 2 (N 2 + was the predominant ionic species), the incident ion to thermal-atom flux ratio for films grown with V s ≥100 V was ∼1.3, and the deposition rate was ∼1 monolayer s -1 (1.3 μm h −1). The primary defects observed in the films were dislocation loops on {111} planes. The number density n d of these loops decreased with increasing T s (e.g., for V s =0, n d ranged from 5×10 12 cm −2 at 550°C to 1.5×10 10 cm −2 at 850°C). However, n d also decreased rapidly with increasing V s at constant T s until a minimum defect density was attained at V s ∗(T s) after which n d incre ased again. Films grown at T s ≥750° C and V s=V s ∗ ≅ 300 V were essentially free of dislocation loops. On the other hand, films grown with T s <650° C and V s ≥400 V (i.e., V s > V s ∗ ) exhibited very high dislocation loop densities, ≥5×10 12 cm −2, together with the preci itation of N 2 gas bubbles. The net effect of ion irradiation on film microstructure depended upon a competition between the defect annihilation rate due to enhanced adatom mobilities during deposition and the collisionally-induced defect formation rate. The residual defect density was thus a function of both T s and V s . Under the proper growth conditions, ion irradiation led to a reduction in dislocation loop densities by more than 5 orders of magnitude. Cross-sectional micrographs of multilayer films grown as a function of V s at constant T s showed that n d increased or decreased (depending upon the direction of the change in V s ) abruptly and reversibly.