QUANTUM-CHEMICAL STUDY ON THE OXIDATION PROCESS OF A HYDROGEN-TERMINATED SI SURFACE

The initial oxidation process of a hydrogen terminated Si surface was investigated by molecular orbital calculations using the cluster model s representing H-Si(100)-2 x 1 and H-Si(111)-1 x 1. Ab initio calculat ions using small cluster models revealed that as a Si atom is coordina ted by more oxygen atoms, it increases the affinity toward another oxy gen. Furthermore, the insertion of up to five oxygen atoms into Si-Si bonds of large models were traced by the semiempirical AM1 method, who se reliability was proven by comparison with ab initio results. The st ructural relaxation was suggested to be as important as the electronic effect on the stability of oxides, and on the HSi(111)-1 x 1 surface- oxidation was predicted to proceed to the second layer before its comp letion on the first layer to avoid a large strain which otherwise woul d be caused. It was also revealed that on the H-Si(100)-2 x 1 surface, the growth of the oxide island and the nucleation of oxide at a dista nt site have almost the same probabilities. In contrast, the lateral g rowth of the oxide island is preferred to the formation of an isolated oxide nuclei on the H-Si(111)-1 x 1 surface. These differences derive from the different Si-Si bond topology on each surface. (C) 1998 Amer ican Institute of Physics.