Influence of hydrogen content and network connectivity on the coefficient of thermal expansion and thermal stability for a-SiC:H thin films

• Influence of hydrogen content on a-SiC:H thermal expansion coefficient (CTE)
• Observation of singularity in a-SiC:H CTE predicted by constraint theory
• Observation of inverse bond percolation/connectivity effect on a-SiC:H CTE
• Investigation of a-SiC:H thermal stability as a function of hydrogen content
• Correlation between a-SiC:H thermal stability and average bond coordination

Thin films of a-SiC:H are of interest for numerous applications in optoelectronic, nanoelectronic, and nanoelectromechanical devices due to a large optical band gap and excellent chemical inertness. In many cases, a low coefficient of thermal expansion (CTE) and high temperature stability are also desired. In this regard, we report an investigation of the influence of hydrogen content and average bond coordination (〈r〉) on the thermal stability and CTE of a-SiC:H thin films deposited by plasma enhanced chemical vapor deposition. The a-SiC:H hydrogen content determined by combined nuclear reaction analysis and Rutherford backscattering measurements (NRA–RBS) was skewed from 25 to 60% resulting in films with 〈r〉 ranging from 2.0 up to 3.2. We show that increased hydrogen content is accompanied by changes in the thermal stability and CTE for the a-SiC:H films. The most dramatic changes were observed to occur for films with hydrogen content > 45% where 〈r〉 is near the critical coordination number (〈r〉c) that delineates over and under constrained materials. For a-SiC:H films above 〈r〉c, relatively little change was observed in CTE with 〈r〉. However for films near or below 〈r〉c, CTE was observed to increase with decreasing 〈r〉 and significant hydrogen loss was observed after the annealing measurements.