CHEMISTRY AT SILICON CRYSTALLINE SURFACES

The chemistry at silicon crystalline surfaces often results in seeming ly extravagant terminations: fluorine termination after gaseous HF att ack, hydrogen termination after etching with HF solutions or with KOH solution at pH similar or equal to 11.5, and oxygen termination after H2O rinsing. The physico-chemical factors producing the observed termi nations after different attacks are discussed. It is concluded that th e termination resulting after HF attack, either in gas phase or in wat er solution, is controlled by thermodynamic rather than kinetics facto rs, while hydrogen termination resulting after alkaline attack at pH s imilar or equal to 11.5 is mainly controlled by kinetic factors. The s urface structures resulting on (111) and (100) silicon after HF etchin g or water rinsing are somewhat different, but can be understood in th e frame of two unifying concepts: nucleophilic attack of weak Si-Si ba ckbonds, and instability of isolated mono- and di-silanol groups.