Challenges in atomic layer deposition of carbon-containing silicon-based dielectrics

Abstract

The authors have designed experiments to test three different approaches for the incorporation of carbon atoms into amorphous SiNx or SiO2 films grown using atomic layer deposition (ALD). In each approach, the surface reactions of the precursors were monitored in situ using attenuated total reflection Fourier transform infrared spectroscopy. In the first approach, for depositing carbon-containing SiNx films using ALD, carbon was introduced into the process through a silicon precursor, SiCl2(CH3)2, followed by NH3 plasma exposure. While our infrared data show that SiCl2(CH3)2 reacts with an –NHx (x = 1, 2) terminated surface created after NH3 plasma exposure, –CH3 groups are eliminated in the precursor adsorption step leading to no significant carbon in the films. In the second approach, the authors hypothesized a three-step ALD process, which would involve Si-, C-, and N-containing precursors, and tested the reactivity of two carbon-containing precursors, CH3I and Al(CH3)3, with H- and Cl-terminated silicon surfaces, respectively. The authors show that both precursors readily react with the silicon surfaces, but neither one provides the appropriate surface termination. CH3I reacts with surface –SiHx (x = 1, 2, 3) to create surface –SiIx (x = 1, 2, 3) species with CH3 as the leaving groups. While Al(CH3)3 reacts with the Cl-terminated Si surface to form a surface –SiCH3 group, residual aluminum remains on the surface as –Al(CH3)x (x = 1, 2) groups that are not completely removed as volatile Al(CH3)xCl3−x (x = 1, 2). Finally, in the third approach for ALD of carbon-containing SiO2 films, the authors used Si2Cl6 with CO and CO/O2 plasmas. A pure CO plasma led to amorphous carbon growth, and a CO plasma diluted with of O2 led to no detectable carbon incorporation in the SiO2 film.