Bond strain, chemical induction, and OH incorporation in low-temperature (350-100°C) plasma deposited silicon dioxide films

New device concepts are being considered with very demanding requirements for low-temperature processing. In this article, infrared transmission and ellipsometry is used to compare silicon oxide films formed by plasma chemical vapor deposition using SiH4 N2O, and either He or H-2 dilution, gas between 350 and 100 degrees C. The Si-O asymmetric stretching mode is affected by bond strain and chemical induction, and monitoring the Si-O peak position gives insight into the effect of process conditions on local bond structure. Hydrogen is expected to affect surface processes during growth, for instance, to enable the removal of surface SiOH bonds through H-mediated abstraction, leading to improved bonding structure at low temperature. We find that exposing the surface to hydrogen atoms during grow ih helps eliminate isolated SiOH bonds, leading to Si-Si bond formation. However, an increase in associated SiOH bonding groups, stabilized by hydrogen bonding, is also observed. The density of associated SiOH groups is larger at low temperature where the rate of water desorption is reduced, suggesting that the associated OH is formed by physisorbed water produced during OH removal. Films deposited with hydrogen dilution show somewhat improved electrical performance at <200 degrees C, but further work is required to produce high quality films at very low temperatures. (C) 2000 American Vacuum Society.