Purified steam for industrial thermal oxidation processes

Silicon surfaces are very effectively passivated by silicon thermal oxides. Silicon thermal oxides are grown in a dry oxygen atmosphere or in steam, whereas the thermal oxide growth rate is about one order of magnitude higher for a steam ambient. This considerably reduces the process time and cost. State of the art pyrox systems generate steam by pyrolysis of hydrogen and oxygen gas. A new approach is the purification of vaporized deionized water. In this work, we present a direct comparison of both systems. Additionally both systems are connected to the same quartz oxidation tube. The higher steam saturation of the steam purifying device results in a 20% higher growth rate. Nevertheless, on low resistivity p-type substrates, after a forming gas anneal an excellent surface recombination velocity of around 25 cm/s is found for thermal oxides grown with each of the systems. Moreover, 110 μm thick thermal oxide rear surface passivated silicon solar cells show similar efficiencies of 18%, irrespective of the applied steam generation technology.