Novel Growth and Wafer-Scale Integration of Q-Carbon Thin Films

We report the single-step, wafer-scale growth of highly uniform quenched-in carbon (Q-carbon) thin films of two different thicknesses (10 nm and 20 nm) via the plasma-enhanced chemical vapor deposition (PECVD) process. A mixture of 25 SCCM hydrogen and 2 SCCM methane were used as precursor gases for the formation of Q-carbon layers. Through this method, we show that the amorphous carbon layers can be effectively converted into Q-carbon by bombarding the surface with 250 eV Ar⁺ ions via negative biasing. The surface topography, structure, morphology, chemical composition, and bonding characteristics in the as-deposited thin films were thoroughly investigated by AFM, Raman, XPS, TEM-EDS, and EELS studies. High-resolution TEM imaging and AFM analysis reveal the formation of highly uniform Q-carbon thin films with negligible surface roughness. EELS, XPS, and Raman analysis consistently indicate higher sp³ content (> 75%) in films, a characteristic feature of Q-carbon structures. Further, sp³ content was shown to decrease with the increase in the thickness of the film as the conversion of amorphous carbon into Q-carbon is incomplete in films thicker than 10 nm. We propose a detailed mechanism to describe the formation of Q-carbon thin films via the low-energy ion bombardment in the PECVD process. The energy of these ions is just adequate to generate a Frenkel pair, that facilitates the conversion of three-fold coordinated sp² carbon units in the as-deposited carbon layer to five-hold sp³-bonded tetrahedral carbon units in Q-carbon but does not induce damage to the formed structure. This enhances the sp³ content and the atomic number density due to the random packing of tetrahedral units in the Q-carbon structure, providing easy nucleation sites for diamond growth. If the underlying substrate facilitates the epitaxial growth of diamond films via domain matching epitaxy, the wafer scale integration of Q-carbon opens up new avenues in the development of diamond-based novel devices and systems.