Low thermal budget surface preparation of Si and SiGe

Abstract

Using a two-step cleaning, we have investigated the low thermal budget surface preparation of Si and Si 1− x Ge x ( x=0.2–0.33). It consists of an ex situ “HF-last” wet-cleaning and an in situ low thermal budget H 2 bake in a reduced pressure–chemical vapor deposition reactor. Using secondary ion mass spectrometry, we have evaluated the effects of different H 2 bake temperatures (in between 750 and 850 °C for 2 min) on the removal efficiency of C, O and F atoms still present on the surface of Si and SiGe virtual substrates after the “HF-last” wet-cleaning. We have then examined the impact of the (wet-cleaning+H 2 bake) combination on the surface cross-hatch of SiGe as-grown virtual substrates, focusing on the analysis, notably by atomic force microscopy, of the surface topography before and after the miscellaneous thermal treatments. In situ hydrogen baking steps in between 775 and 850 °C do not modify the surface morphology and roughness. An easy and rapid optical characterization method, i.e. the optical interferometry, is presented as well to monitor in line the morphological changes induced by such processing steps as chemical mechanical polishing, wet-cleaning, H 2 bake, etc. Despite the lower resolution of the optical profilometer, the surface roughness values coming from it have been correctly correlated with those obtained from AFM. An optimized “HF-last” wet-cleaning using a diluted chemistry in conjunction with a H 2 bake at 800 °C for 2 min (775 °C, 2′) is a good compromise for SiGe (Si) surface preparation.