Mechanical Stress in SiO2 Films Obtained by Remote Plasma‐Enhanced Chemical Vapor Deposition

Abstract

Using a single laser beam reflection technique, the authors have examined mechanical stress in thin films obtained by a remote plasma‐enhanced chemical vapor deposition technique. The films were deposited in the 200–600°C temperature range, at a total pressure of 8 mTorr, at 30 or 300 W rf power, using a remote oxygen‐plasma silane reaction. All investigated films were found to be in compressive stress at room temperature. Total stress ranged from (compressive), and the calculated intrinsic stress component ranged from (compressive). The total compressive stress value was found to be an increasing function of the deposition temperature, due to the increase in the value of the thermal stress component. Total and intrinsic stresses were found to be also dependent on film thickness, thinner films exhibiting higher stress. films deposited using higher rf power (300 W) were found to exhibit a ∼20% greater compressive stress than films deposited at the lower power (30 W) level. Post‐deposition heat‐treatments of the films were conducted to examine stress relief. Both “high” and “low power” oxides showed a partial stress relief after low temperature (300–400°C) inert gas annealing, for anneal times of the order of 100 h. It was found that the stress in “low power” oxides increased to the pre‐anneal value when the samples were subsequently re‐exposed to a room temperature ambient atmosphere at 35% relative humidity. On the other hand, “high power” oxides did not show any instability when re‐exposed to the air. The instability in “low power” oxides was not observed if the films were first annealed at 1000°C for 15 min in oxygen.