Electrical and structural properties of NiCr thin film resistors reactively sputtered in O2

NiCr thin film resistors have been reactively sputtered using a d.c. diode system in which the anode is formed by a carousel. The substrates are mounted on this carousel and can be rotated through the discharge. For films deposited onto a stationary carousel (the substrates permanently fixed in the discharge), film resistivities range from 150 to 300 μΩ as the oxygen partial pressure is increased from the base pressure to 3 × 10^-5 torr. The TCR values range from 150 to 300 ppm/°C. For carousel rotation at 20 rev/min the corresponding resistivities may be increased by a factor as large as 20 without greatly affecting the TCR. Microprobe analysis indicates that the Ni/Cr concentration ratio is independent of the deposition conditions, but that for a given oxygen partial pressure the film density is less for films deposited onto a rotating carousel than for films deposited onto a stationary carousel. Transmission electron microscopy indicates that the crystallographic structure consists of a metallic phase and an oxide phase which do not change with carousel rotation, but that films deposited onto a stationary carousel have an island structure while those deposited onto a rotating carousel have a worm-like structure. The structural features of films deposited onto a rotating carousel may be due to oblique incidence effects. Measurements of film resistance at low temperatures indicate that conduction in the film may be considered to consist of a metallic conduction mechanism of positive TCR acting in conjunction with an oxide conduction mechanism of negative TCR, with the relative contribution of each mechanism being a function of the physical microstructure of the films. Heat treatment of films deposited onto a rotating carousel produces an increase in resistance which is attributed to oxidation of the film surface, while heat treatment of films deposited onto a stationary carousel produces a resistance decrease which is attributed to thermal annealing effects dominating surface oxidation effects.