Lowering the temperature of CNT synthesis before any attempts of integration is a technical challenge. The improvement of CNT carpet growth on Ni/TiN/SiO2/Si by previously reducing the size of Ni particles using H-2 plasma prior to be exposed to H-2:C2H4 plasma is studied. Different techniques, SEM, in situ Raman, NEXAFS, XPS and TEM were combined to investigate the growth rate and the quality of CNT films. An original use of in situ Raman spectroscopy allowed us to determine the increase of sample surface temperature in contact with H-2 plasma through Si anharmonicity. Finally it was possible to grow CNT carpets by PECVD with a process temperature of 480 degrees C.