Approach to control deposition of ultra thin films from metal organic precursors: Ru deposition

Atomic layer deposition (ALD) processes have attracted attention during the past decade as a method allowing one to obtain high-quality thin films of various materials including metal oxides, metal nitrides and pure metals. Here we investigated a novel pulse method for the deposition of ultra thin films; the characteristics of which are close to those of ALD technology. In our process, the step of the reactor purging after supplying a dose of precursor vapor is excluded. Instead, the precursor vapor pulse is directly followed by a reagent gas to react with precursor adsorbed onto the substrate resulting in film deposition. The selection of time between pulses is defined by the lifetime of adsorbed molecules on the substrate surface and by the kinetic parameters of decomposition. We demonstrated this technique for ruthenium deposition using ruthenium tris-acetylacetonate with hydrogen as reagent gas. In addition, we studied the chemical behavior of this ruthenium precursor under different conditions by using high-temperature mass spectrometry. Thus we were able to investigate its thermal stability at elevated temperatures, its vapor pressure and its interaction with hydrogen under ALD type conditions for ruthenium film growth. For the latter we monitored the gas phase of the reactor at various points during the process cycles. From these studies we were able to optimize our process to grow homogeneous ruthenium films several nanometers thick on SiO2/Si surfaces at growth rates of 0.02–0.07 Å per cycle from 300 to 370 °C. Ruthenium films were grown between 5 to 25 nm and were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES).