Cleaning of Silicon Surfaces by Heating in High Vacuum

Results from experiments with four independent surface-sensitive phenomena agree in demonstrating that an atomically clean surface can be produced on silicon single crystals by heating to 1550°K or above for several minutes in high vacuum. The four phenomena studied are: 1. oxidation and gas adsorption, 2. Auger neutralization of He+ ions, 3. external photoelectric emission, and 4. field electron emission in a Müller microscope. Evidence is given as to the nature of the silicon surface before cleaning, properties of the clean surface, and behavior upon contamination with gases and during subsequent recleaning. The surfaces were found to form a permanent p-type layer several microns deep as a result of the vacuum heating.