Twin formation during the atomic deposition of copper

Vapor deposited copper films with [111] growth texture usually contain twin plates stacked normal to the growth direction. However, twins are rarely s een when growth occurs in other principle crystallographic directions. Atom istic modeling indicated that during [111] growth, adatoms occupied either parent or twin surface lattice sites with almost equal probability, resulti ng in a high nucleation density of twin domains. During growth on either {1 10} or {100} surfaces, adatoms were only able to occupy parent lattice site s, and no twin nucleation occurred. A phase field method was used to model the twin domain evolution during [111] growth as a function of deposition r ate and temperature. Simulation results indicated that twin domains evolved by rapid lateral expansion with very little vertical thickening. The later al expansion was found to be fast compared with the deposition rate, and as a result twin domains usually grew to occupy the entire width of a growth column, in good agreement with experimental observations. The model indicat ed that the twin structures formed during the [111] growth of copper are no t directly controllable by either the processing temperature or the deposit ion rate. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd . All rights reserved.