In the front end manufacture of CMOS semi-conductor devices, a passivation film such as SiN is formed on the gate electrode of each MOS transistor. This SiN film deposited on top and on side surface of the gate electrodes (such as polycrystalline silicon or metallic layers) in order to increase the breakdown voltage of each transistor.
Attempts have been made to reduce the temperature deposition of such SiN, to reach a temperature which is not higher than 400° C.
However, SiN films deposited at temperatures below 400° C. have usually poorer film qualities. In order to overcome this issue, it has been proposed to use SiO2 films to reinforce SiN film properties (“dual spacer”) and thereby make effective electrical barrier layers to improve significantly the device performances. Also, SiO2 films are used as STI (shallow trench insulation), inter layer dielectric (ILD) layers, passivation layers, etch-stop layers and attempts are made to find a deposition process of these SiO2 layers at low temperature, i.e. below 400° C. In the specific case of dual spacer applications, the deposition of a very (20-50 A thick) thin films performed at low deposition temperatures (300° C. at the most), should not lead to the oxidation of the metal electrode and should be perfectly uniform all along the gate, and an atomic layer deposition process is the most suitable such a requirement. As far as the STI applications are concerned, conformal films should be deposited with high deposition rate (several hundred A per minute) below 500° C.
Deposition of silicon oxide films made from silane and oxygen at low temperature using a PECVD reactor have failed up to now for these applications, due to the incorporation of Si—H bonds into the SiOx film thereby obtained, which may originate with the presence of hydrogen in the silane gas introduced as a precursor gas. This Si—H bonds then probably readily react with an oxygen source in the environment to produce the Si—Ohio bond.
The presence of such Si—OH bonds increases the risk of having transistors with an increased leakage current, and therefore a reduced breakdown voltage of the related transistors.
The inventors believe that the presence of a large number of hydrogen atoms bonded to the silicon atom in the Si precursor and of oxygen or oxygen containing gas to generate the SiO2 film, probably also generates moisture (H2O) formation which then reacts with Si to make SiOH.
The inventors also believe that the silicon containing compound shall have preferably a high purity regarding hydrogen containing residues to limit H2O generation, preferably it shall contain less than 100 ppm of H2 or H containing compounds.