EFFECT OF TEMPERATURE ON THE DEPOSITION RATE AND PROPERTIES OF HYDROGENATED AMORPHOUS-CARBON FILMS

Hydrogenated amorphous carbon (a-C:H) films were grown from a hydrocarbon vapor (HCV) by the r.f. (13.56 MHz) self-bias method. The temperature increase of 76.2 mm silicon or quartz wafers during film deposition was maintained over a narrow range (1-20-degrees-C) by clamping the wafers to a temperature-controlled cathode and admitting helium between the back side of the wafer and the cathode. Without wafer clamping and helium back-side cooling, wafer temperatures increased as much as 70-100-degrees-C during deposition, depending on the HCV pressure P and negative d.c. self-bias voltage V(b). Films were deposited over ranges of V(b) (from -0.4 to -1.8 kV), P (from 6.7 to 40-mu-bar) and initial wafer temperature T(i) (from - 10 to 90-degrees-C). At a given P and V(b) (i.e. constant ion energy) the deposition rates of a-C:H increased linearly with decreasing T(i), while the film density, Knoop microhardness H(K) and compressive stress decreased with decreasing T(i). In general, the values of film density, H(K) and stress were significantly lower for the temperature-controlled depositions than for films deposited in earlier work without temperature control, but at the same or even lower ion energy. The hydrogen content [H], optical gap E(T) and surface roughness of the films (measured by scanning force microscopy) increased with decreasing T(i). The effect of lower T(i) on the deposition rate and film properties is consistent with a film structure containing a significant fraction of voids. These voids are postulated to form as a result of the lower mobilities of impacting species on the surface of the growing film which prevents densification of the film and retards sputtering or loss of hydrogen.