AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS-ThP

Paper SS-ThP18
Vacancy Creation as the Rate Limiting Step in Halogen Etching of Si(100)-2x1

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Surface Science Division Poster Session
Presenter: K. Nakayama, University of Minnesota
Authors: K. Nakayama, University of Minnesota
C.M. Aldao, Universidad Nacional de Mar del Plata-CONICET, Argentina
J.H. Weaver, University of Minnesota
Correspondent: Click to Email
We have studied the etching on Si(100)-2x1 using scanning tunneling microscopy. Surfaces exposed to Cl@sub 2@ or Br@sub 2@ are etched at elevated temperature via the thermal activation reaction 2SiX(a) <--> SiX@sub 2@(a) + Si(a), where SiX@sub 2@(a) is a volatile molecule, Si(a) is a bystander Si atom, and X = Cl or Br. Formation of SiX@sub 2@(a) breaks the dimer @sigma@-bond and leaves the destabilized bystander with two dangling bonds. Conventional wisdom would indicate that SiX@sub 2@ desorption is the rate-limiting step. Instead, we show that the rate limiting step occurs when the bystander breaks away and moves onto the terrace. Thus, the de-excitation pathway to 2SiX(a) is eliminated. This increases the overall probability for SiX@sub 2@ desorption. We show that the rate of etching increases with halogen concentration until ~0.8 ML. It is reduced at higher coverage as the adsorbates block the escape of the bystander onto the terrace. We discuss the consequences and examine the post-etch surface morphology.