scattering study of phase separation at initially mixed HfO 2 -SiO

Transcription

1 ERC TeleSeminar In situ low-angle x-ray x scattering study of phase separation at initially mixed HfO -SiO thin film interfaces Paul C. McIntyre Jeong-hee Ha Department of Materials Science and Engineering, Stanford CA Funding: Semiconductor Research Corporation Task Stanford Initiative in Nanoscale Materials and Processes March 10, 005

2 Motivation Zr(Hf)-Si-O Si SiO Zr(Hf)O Si Subsequent high temperature thermal processing causes phase separation G.Lucovsky et al, Appl.Phys.Lett. 77, 91 (000) Metal oxide/sio interface structure uncertain due to deposition-induced mixing and thermal instability Loss of desired dielectric and electrical properties Need to investigate effects of phase separation upon thermal process Need to understand abruptness and stability of metal oxide/sio interfaces

3 Phase separation of Hf-silicate films forms HfO /SiO interfaces Initially intermixed HfO -SiO alloy experiences a driving force for phase separation upon annealing Form regions of crystalline HfO and amorphous SiO Temperature ( o C) o C ~1687 o C ZrO (tet) + Liquid miscibility gap spinodal 900 ºC ºC 430 o C Two Liquids Liquid Lucovsky et.al ZrO Mole Fraction SiO H. Kim et al., J. Appl. Phys. (00). S. Stemmer et al., Jpn. J. Appl. Phys. (003). Lucovsky et al., Appl. Phys. Lett. (000). Image courtesy of S. Stemmer

4 Growth of Metal Oxide Dielectrics : UV-Ozone Oxidation O UV lamp thin metal film (Hf, Zr) on a Si or Ge substrate UV light supplies atomic oxygen and ozone to surface through the following reactions: O + hν O O + O O 3 atomic oxygen O O 3 + hν O + O molecular O Benefits Low temperature Low contamination Simplicity Can modify substrate surface passivation S. Ramanathan et al., Appl. Phys. Lett. (001)

5 Multilayer test structure for HfO /SiO interfaces (1.4nm SiO / 4nm HfO ) 4 Si (100) substrate Grown by UVO oxidation structure on top of HfO -SiO multilayer sample under study : (by UV-Ozone Oxidation) Courtesy of David Chi Growth conditions - Hf, Si sputtered in mtorr Ar pressure (~0. Å/sec) with base pressure 5E-9 Torr - Oxidized for 1 hr at 600 Torr O pressure in UV light * Advantage of using multilayers : - Deliberate exaggeration of particular interface effects - Separation of interface effects on electrical properties by comparing multi- and single layers

6 X-ray diffraction: probe of local electron density The scattered amplitude of the x-ray diffraction from the given system is just proportional to the Fourier transform of the local electron density : ε c = E0r R iq r [ i( wt kr) ] e ρ ( r dv e exp ) c I ( ) so that iq r e ρ ( r) dv ρ c (r) c E 0 r e : electric field magnitude : electron radius R : distance from the sample to the detector q : scattering vector : spatial electron density distribution So, we can deduce information about changes in the electron density distribution (e.g. a composition profile) by observing XRD data.

7 Multilayer structure and its XRD pattern Electron density distribution in the multilayer sample can be modeled as a square wave. The scattered amplitude is proportional to the Fourier series of the square wave given. The weighting of the n=1 (first order) harmonic wave reflects the degree of the interdiffusion. As-deposited After phase separation Relative concentration profile in HfO /SiO multilayer structure ~ D = L 8 π d dt ln I I ( t ) ( 0 ) : effective interdiffusivity L : bilayer period I : the first-order low-angle x-ray modulation peak

8 In-situ Low-angle XRD Studies Intensity (A.U.) theta Low angle XRD data Intensity (A.U.) E-3 1E-4 1E-5 Total reflectivity peak intensity for (SiO /HfO ) 4 1 n=1 n= theta n= n= multilayer structure HfO -SiO multilayer sample under study : (by UV-Ozone Oxidation) Courtesy of David Chi The scattered intensity for N layers is given by: N 1 iq R sin ( Nq n I ( fn( q) e ) = f ( q) sin ( q z n= 0 zl Measured data agree well with the simulated result : Intensity (A.U.) Intensity (A.U.) E-3 1E-4 1E-5 1E-6 n=1 n=1 L / ) / ) 1E Theta n= n= Theta

9 (HfO /SiO )*4 structure, N anneal Intensity (counts/sec) n= o C As-deposited minutes The intensity of n = 1 satellite peak increases as annealing proceeds Evidence of phase separation at the initially-intermixed as-deposited HfO /SiO interfaces Theta In-situ low-angle XRD

10 (HfO /SiO )*4 structure, N anneal (HfO /SiO )*4 structure, N anneal ~ D = L 8π d dt ln I ( t ) I ( 0 ) ln(i/i o ) o C Temperature ( ) Interdiffusivity(m /sec) * * * *10-4 Time (sec) In-situ low-angle XRD

11 Activation energy for the phase separation The activation energy H for phase separation can be obtained from the Arrhenius rate law : logd L (m /sec) D e = D o exp( H k T B ) The obtained H for the phase separation is.06 ± 0.15 ev /T(K -1 ) In-situ low-angle XRD

12 Summary Accomplishments Used multilayer x-ray scattering to probe the kinetics of phase separation at as-deposited mixed HfO /SiO interfaces Obtained the activation energy of.06 ± 0.15 ev for phase separation in HfO /SiO interface system Determined temperature range for phase separation at initially-intermixed HfO /SiO interface: T > 650 C