In silicon epitaxy technology, residual O/H2O contamination requires thermal reduction using hydrogen pre-bakes to achieve atomically clean Si surfaces. This H2 pre-bake leads to unwanted increase of thermal budget. The higher the level of interfacial O, the longer the pre-bake period and the higher the temperature have to be for removal of these contaminants. Moisture contamination from the pre-epi chamber etch (immediately before the wafer is loaded), with it's use of high flows of HCl, is identified as a major contributor to the area density of the interfacial O. Stringent control of moisture impurity in the HCl is required to reduce thermal budget. Ultra low temperature technology to desiccate HCl is used to achieve single digit ppb moisture resulting in lower temperature hydrogen pre-bakes than achieved with standard solid media-type HCl purification.
