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Low Thermal Budget Surface Preparation for Selective Epitaxy. A Study on Process Robustness

The robustness of a low thermal budget surface preparation method for selective silicon epitaxial growth has been investigated. After the HF dip, the stability of hydrogen passivation on Si(100) in deionized water and air has been studied. No significant increase was observed in oxygen and carbon coverage for deionized water rinse times varying from 10 to 1000 s. On wafers exposed to air for up to 10,000 s, carbon coverage on Si(100) stayed at the same level, whereas the oxygen coverage increased steadily. An in situ clean at 800°C for 10 s reduced the interfacial oxygen below the secondary ion mass spectroscopy detection levels on wafers that had been contaminated by exposure to air for up to 1000 s. In situ cleaning was studied in ambients with different partial pressures of intentionally introduced oxygen and nitrogen backgrounds. Oxygen was removed from Si(100) during the in situ clean for nitrogen partial pressures up to I X 10 -6 Torr. When the oxygen partial pressure is sufficiently high (I X 10 -6 Torr), oxide removal was not complete after in situ cleaning. There was no observable increase in the surface roughness for samples annealed in oxygen partial pressure up to I × 10 -5 Torr. Hydrogen passivation was removed from the substrates and the surfaces were exposed to vacuum at room temperature for different times. After 10,000 s, the oxygen coverage was less than 2% of a monolayer. The carbon contamination on the surface was instantaneous and no additional carbon accumulation on the surface was observed up to 10,000 s. There was no apparent increase in the defect density for these wait times.