Adsorption of disilane on Si(111)-(7x7) and initial stages of CVD growth

Adsorption and reaction of disilane (Si2H6) on Si(111)-(7 x 7) surfaces have been studied in the temperature range 300-760 K by scanning tunneling microscopy. In the entire temperature range the interaction of Si2H6 with Si(111)-(7 x 7) is dissociative. At room temperature it leads to continuous reactions of adatom dangling bonds with hydrogen atoms, which are released in the decomposition process. Protruding surface species observed after prolonged Si2H6 exposition are assigned to deposited SiHx fragments. After exposures to 120 L at temperatures between 400 and 690 It a variety of surface structures, such as SixHy clusters, hydrogen terminated adatoms and disordered regions, are observed. At 730-760 K growth leads to the formation of triangular islands without stacking faults and by incorporation of Si at steps with the grown areas exhibiting a defective adatom structure. Re-annealing to 800 K restores the DAS structure and allows the amount of silicon deposited to be determined. The initial sticking coefficient for dissociative Si2H6 adsorption at 300 K is determined as S-0 = 8.5 x 10(-5). Silicon deposition proceeds via an activated adsorption process. The value of the activation energy is determined as approximate to 0.1 eV between 300 K and 650 K, while it is 1.1 eV between 650 K and 760 K, pointing toward an additional reaction channel at temperatures above 650 K. (C) 1998 Elsevier Science B.V. All rights reserved.