SURFACE SELF-DIFFUSION ON SI FROM THE EVOLUTION OF PERIODIC ATOMIC STEP ARRAYS

The development, during annealing, of periodic atomic step arrays associated with etched grating structures on Si(001) has been monitored by optical methods and by STM. The grating amplitudes decay exponentially with time in the temperature range from 800 to 1100 degrees C with characteristic decay constants that scale approximately as the inverse fourth power of the grating period; this indicates the dominance of surface diffusion as the mass transport mechanism. The activation energy for Si surface self diffusion is found to be similar to 2.3 eV. Various detailed atomic mechanisms of diffusion are possible; comparing with other relevant data and calculations, our experimental value is consistent with an adatom transfer process. The details of the atomic step morphologies as determined by STM for these grating structures are described. The interactions of the atomic steps during decay are related to the curvature dependent driving forces for mass transfer.