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) surface s have been studied in the temperature range 300-760 K by scanning tun neling microscopy. In the entire temperature range the interaction of Si2H6 with Si(111)-(7 x 7) is dissociative. At room temperature it lea ds to continuous reactions of adatom dangling bonds with hydrogen atom s, which are released in the decomposition process. Protruding surface species observed after prolonged Si2H6 exposition are assigned to dep osited SiHx fragments. After exposures to 120 L at temperatures betwee n 400 and 690 It a variety of surface structures, such as SixHy cluste rs, hydrogen terminated adatoms and disordered regions, are observed. At 730-760 K growth leads to the formation of triangular islands witho ut stacking faults and by incorporation of Si at steps with the grown areas exhibiting a defective adatom structure. Re-annealing to 800 K r estores the DAS structure and allows the amount of silicon deposited t o be determined. The initial sticking coefficient for dissociative Si2 H6 adsorption at 300 K is determined as S-0 = 8.5 x 10(-5). Silicon de position proceeds via an activated adsorption process. The value of th e 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 tow ard an additional reaction channel at temperatures above 650 K. (C) 19 98 Elsevier Science B.V. All rights reserved.