Thermal stability of diamondlike carbon buried layer fabricated by plasma immersion ion implantation and deposition in silicon on insulator

Diamondlike carbon (DLC) as a potential low-cost substitute for diamond has been extended to microelectronics and we have demonstrated the fabrication of silicon on diamond (SOD) as a silicon-on-insulator structure using plasma immersion ion implantation and deposition in conjunction with layer transfer and wafer bonding. The thermal stability of our SOD structure was found to be better than that expected for conventional DLC films. In the work reported here, we investigate the mechanism of the enhanced thermal stability. We compare the thermal stability of exposed and buried DLC films using Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). Our Raman analysis indicates that the obvious separation of the D and G peaks indicative of nanocrystalline graphite emerges at 500°C in the exposed DLC film. In contrast, the separation appears in the buried DLC film only at annealing temperatures above 800°C. Analysis of the XPS C1s core-level spectra shows that the (sp3+C–H) carbon content of the unprotected DLC film decreases rapidly between 300–700°C indicating the rapid transformation of sp3-bonded carbon to sp2-bonded carbon combined with hydrogen evolution. In comparison, the decrease in the (sp3+C–H) carbon content of the buried DLC film is slower below 800°C. Elastic recoil detection results show that this superior thermal stability is due to the slower hydrogen out diffusion from the buried DLC film thereby impeding the graphitization process. We propose that the SiO2 overlayer retards the graphitization process during annealing by shifting the chemical equilibrium.