Minimizing the Carbon Content of Thin Ruthenium Films by MOCVD Precursor Complex Design and Process Control

[(Benzene)(1,3-cyclohexadiene)Ru] was investigated as a designed metal-organic (MO) CVD precursor where the inherent structural and chemical features of the ligands help the formation of pure ruthenium films. The investigations have been performed with Si wafers as the substrate at a total gas pressure of 50 mbar, substrate temperature range of 200–450 °C, and helium carrier gas velocity of 1.5 to 16.5 cm s–1. The main focus was on the evaluation of the process parameters that promote the purity of the deposited ruthenium films without the help of a reactive gas component. The composition of the MOCVD exhaust gas was analyzed by gas chromatography (GC), and the deposited ruthenium films characterized by elastic recoil detection analyses (ERDA) to relate the carbon content of the films with the follow-up chemistry of the ligands. The primary process of highly effective dehydrogenation of the 1,3-cyclohexadiene ligand at the freshly formed ruthenium surface to form benzene was built in by the choice of the ligand. Further, but much less effective, was the dehydrogenation of benzene, which is presumed to be the main process for carbon contamination. Ruthenium films with only 3 mol.-% carbon content were deposited at a substrate temperature of 300 °C and a carrier gas velocity of 12.8 cm s–1. In all cases the deposited films consist of polycrystalline metallic ruthenium with a low surface roughness.