Hydrogen-free SiCN Films Obtained by Electron Cyclotron Resonance Plasma

Abstract

Electron cyclotron resonance plasma enhanced chemical vapor deposition of hydrogen-free SiCN films has been studied. Infrared and Raman spectroscopies were used for chemical characterization of deposited films, showing Si-N, Si-C, Si-Si, and C-N bonds in composition. Optical responses of the films between 1.5 and 4.5 eV were obtained by spectroscopic ellipsometry. Cathodoluminescence of the films shows mainly a broad band of emission at around 2.3 eV together with overlapped contributions at higher energies depending on the composition. Surface morphology and roughness has been investigated by atomic force microscopy. 18 The optical properties of SiCN suggest the behavior as a wide-bandgap semiconductor in the case of the crystalline phase, with potential applications for blue or ultraviolet optoelectronic devices.6,15 The variety of silicon carbonitride compositions obtained with any of these techniques allows one to think of these materials as tunable bandgap ones for applications in flat panel displays. Furthermore, SiCN nanorods exhibit promising characteristics as field emitters. 9,19More recently, with the introduction of new synthesis methods, other innovative applications have been described for this family of compounds, such as its feasibility in the fabrication of microelectrical mechanical systems ͑MEMS͒ working in high-temperature environments. 20,21 With the continuous shrinking size in integrated circuits technology there is a continuous effort in the search for materials with low dielectric constant for metal layer isolation. Further, due to its low dielectric constant, hydrogenated silicon carbonitrides prevent Cu diffusion in between the metallization layers. 22 The hydrogen incorporation in amorphous SiCN films results in a degradation of the mechanical properties of these films. 8In this work, we report the synthesis of amorphous hydrogen-free SiCN films by electron cyclotron resonance plasma at 850°C. Their composition and bonding structure have been studied by Fourier transform infrared ͑FTIR͒ and Raman spectroscopy. The surface morphology has also been studied by atomic force microscopy. The dielectric constant for different layer compositions has been obtained by spectroscopic ellipsometry and their potential optoelectronic applications explored by cathodoluminescence measurements. ExperimentalSiCN films were deposited on float zone ͑FZ͒ silicon wafers, polished on both sides, at 850°C in an electron cyclotron resonance plasma ͑ECR͒ reactor. The substrate holder was radiatively heated with a tungsten filament lamp and the temperature, 850°C, monitored with a pyrometer across a quartz window. The base pressure of the system was 10 −7 Torr. Low oxygen content FZ silicon wafers with a resistivity higher than 100 ⍀ cm were used as substrates. Before deposition, silicon substrates were chemically etched with a HF buffer solution. Gas mixtures of Ar, CH 4 , N 2 , and SiH 4 were employed in the deposition processes; the precursor gas flows were controlled by mass flow meters in such a way that a...