AVS 52nd International Symposium
    Thin Films Tuesday Sessions
       Session TF-TuA

Paper TF-TuA5
Quartz Crystal Microbalance Measurements of W ALD Nucleation on Al@sub 2@O@sub 3@

Tuesday, November 1, 2005, 3:20 pm, Room 306

Session: Atomic Layer Deposition - Metals
Presenter: R.A. Wind, University of Colorado
Authors: R.A. Wind, University of Colorado
F.H. Fabreguette, University of Colorado
S.M. George, University of Colorado
Correspondent: Click to Email
Nucleation phenomena can critically affect the growth of nanolaminates using atomic layer deposition (ALD). A good example is W/Al@sub 2@O@sub 3@ nanolaminates where the nucleation of W ALD on Al@sub 2@O@sub 3@ limits the minimum thickness of a continuous and ultrasmooth W nanolayer to ~25 Å. Quartz crystal microbalance (QCM) studies can measure the mass gain per cycle (MGPC) during ALD with a precision of ~0.4 ng/cm@super 2@. QCM investigations of W ALD nucleation on Al@sub 2@O@sub 3@ reveal complex behavior. During optimum nucleation conditions, WF@sub 6@ exposures lead to mass gain but Si@sub 2@H@sub 6@ exposures produce no measurable mass gain for the first 2 cycles. After 3 cycles, the MGPC for both reactants increases and reaches a maximum after 8 cycles for WF@sub 6@ and after 12 cycles for Si@sub 2@H@sub 6@. The total MGPC exhibits a "ringing" behavior and a second maximum is observed before reaching the steady state growth rate. For different reactant exposures, the positions of the first and second maxima in the MGPC shift to a longer number of cycles. Modeling of these QCM results is in agreement with three-dimensional W island growth that produces a maximum in the MGPC. This maximum corresponds to the largest W surface area prior to the coalescence of the W islands. The existence of these W islands is confirmed by atomic force microscope (AFM) measurements. The changing ratio of the WF@sub 6@ and Si@sub 2@H@sub 6@ MGPCs is consistent with distinct growth regimes. These different ratios suggest that the relative density of reactive surface sites evolves as W islands are created, grow, and coalesce prior to forming a continuous W film.