MICROSTRUCTURE AND ELECTRICAL-RESISTIVITY OF TIN FILMS DEPOSITED ON HEATED AND NEGATIVELY BIASED SILICON SUBSTRATES

Titanium nitride films were prepared by d.c. diode sputtering of a titanium target in a gas mixture of argon and nitrogen. The properties of the films were investigated by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, X-ray microanalysis, scanning electron microscopy and electrical resistivity measurements. When the temperature of the substrate is low (T-s approximate to 150 degrees C), many oxygen atoms from the residual gases are incorporated in the films when they are not biased (O:Ti approximate to 0.5 at V-b = 0 V); some argon ions are incorporated when the bias voltage applied to the substrate is negative enough (Ar:Ti approximate to 0.03 at V-b = -200 V). Oxygen release is achieved either with negative substrate bias (V-b approximate to -60 V) or with substrate heating during the deposition (T-s approximate to 900 degrees C); the atomic argon-to-titanium ratio decreases as the substrate temperature is increased. A relationship between the resistivity and the oxygen-to-titanium ratio is given. The microstructure depends on both V-b and T-s. When the bias voltage is made more and more negative, the film density is increased and the formation of a columnar structure is inhibited; on the other hand, an increase in temperature modifies the grain shape and size. Generally these variations in the sputtering conditions lead to a decrease in resistivity, but in some cases two kinds of grains coexist and the resistivity is increased (this is the case with values of V-b and T-s near -60 V and 500 degrees C respectively).