LOW-TEMPERATURE SILICON DIRECT BONDING FOR APPLICATION IN MICROMECHANICS - BONDING ENERGIES FOR DIFFERENT COMBINATIONS OF OXIDES

Plain or structured hydrophillic silicon wafers covered with native ox ide or with thermally grown oxide layers have been directly bonded at room temperature; afterwards, the samples were annealed at 100 degrees C to 400 degrees C. There is a significant difference in the observed bonding energy depending on the wafer pairing chosen. If one or both wafers are covered with a native oxide layer, high bonding strengths a re reached even at low temperatures. This can be explained by the diff erent diffusion behaviour of water molecules through a thick thermal o xide layer on one hand, and through a thin native oxide layer on the o ther hand. Two different methods for the activation of the wafer surfa ces just prior to bonding are described. (C) 1998 Elsevier Science S.A . All rights reserved.