Equipment and Techniques
The research group is well equipped to study surface chemistry, thin film growth and thin film properties. All of the techniques and equipment described below are available within the research group.
1. FTIR Spectroscopy
We monitor the surface species during ALD using vacuum chambers designed for in situ Fourier Transform Infrared (FTIR) spectroscopy studies. High surface area particles provide sufficient surface sensitivity for transmission FTIR experiments. Vibrational spectroscopy reveals the gain and loss of surface species during the two surface half-reactions. The vibrational spectrum of the deposited material also grows with AB reaction cycles. We have recently studied Al2O3 and SiO2 ALD on BN particles [1,2], BN ALD on ZrO2 particles , Al2O3 ALD on low density polyethylene particles and SiO2 ALD on BaTiO3 particles.
2. Quartz Crystal Microbalance
To monitor ALD growth in our viscous flow reactors, we employ in situ quartz crystal microbalance (QCM) measurements [4,5]. The QCM has exceptional mass sensitivity and the mass changes for each half-reaction are able to unravel the stoichiometry of the surface reactions. The growth of the film is also determined by the linear mass increase versus the AB reaction cycles.
3. Surface Profilometry
The ALD film growth can be determined using ex situ surface profilometry. The profilometer obtains the film thickness by measuring the step height between the deposited film and an area that was masked using tape or photoresist. The research group uses a Dektak 3 surface profilometer.
4. Auger Electron Spectroscopy
Film nucleation and growth mechanisms during ALD are evaluated in an ultrahigh vacuum chamber equipped for Auger electron spectroscopy (AES) studies . AES is very sensitive to the surface and near surface region and yields elemental composition to a precision of ~1%. AES studies have illustrated the importance of film nucleation during the initial stages of
W ALD on oxide surfaces .
5. Spectroscopic Ellipsometry
Film thickness and film refractive indices can be measured using spectroscopic ellipsometry [7,8]. These spectroscopic ellipsometry measurements are also useful to study interfacial layers such as the interfacial SiO2 layer between high k dielectrics and silicon substrates. The group uses a spectroscopic ellipsometer that employs 44 wavelengths from the J.A. Woolam Company.
6. Atomic Force Microscopy
The film topography and surface roughness can be obtained using and ex situ atomic force microscope (AFM) . The group has a AutoProbe CP scanning probe microscope from Thermomicroscopes. This scanning probe microscope is equipped for AFM, conducting-AFM, and scanning thermal microscopy.
7. Electrical Characterization
The current-voltage (IV) and capacitance-voltage (CV) properties of insulating films can be characterized using a Hg-probe. This Hg probe has been used recently to study the Fowler-Nordheim tunneling behavior of Al2O3 ALD films that may have application for high k capacitors and gates .
8. Thin Film Resistivity
Thin film conductivity can also be measured using an ex situ 4-point probe. In addition, we have recently developed a new in situ 4-point probe to measure film conductivity during ALD . This new 4-point probe can monitor ALD growth during the sequential reactant exposures. In addition,
this in situ probe is being used to understand and optimize metal oxide semiconductor gas sensors.
9. X-ray Diffraction
The research group also recently installed a new x-ray diffraction instrument in fall 2002. This apparatus is optimized for x-ray reflectivity (XRR) and x-ray diffraction (XRD) of thin films and nanolaminates. XRR is very useful to evaluate film thickness, film density, interfacial roughness.
XRR is especially valuable in characterizing superlattices . XRD is important for structural characterization and crystalline alignment.
10. Spin Coaters for Polymer Film Fabrication
Polymers films are prepared using a spin coater that can deposit polymer films on Si(100) wafer or QCM sensors. The research group has a dedicated spin coater that has facilitated our new project on ALD on polymers .
J.D. Ferguson, A.W. Weimer and S.M. George, "Atomic Layer Deposition of Ultrathin and Conformal Al2O3 Films on BN Particles", Thin Solid Films 371, 95-104 (2000).
J.D. Ferguson, A.W. Weimer and S.M. George, "Atomic Layer Deposition of SiO2 Films on BN Particles Using Sequential Surface Reactions", Chem. Mater. 12, 3472-3480 (2000).
J.D. Ferguson, A.W. Weimer and S.M. George, "Atomic Layer Deposition of Boron Nitride Using Sequential Exposures of BCl3 and NH3", Thin Solid Films 413, 16-24 (2002).
J.W. Elam, M.D. Groner and S.M. George, "Viscous Flow Reactor with Quartz Crystal Microbalance for Thin Film Growth by Atomic Layer Deposition", Rev. Sci. Instrum. 73, 2981-2987 (2002).
J.W. Elam and S.M. George, "Growth of ZnO/Al2O3 Films Deposited Using Atomic Layer Deposition Techniques", Chem. Mater. 15, 1020- 1028 (2003).
J.W. Elam, C.E. Nelson, R.K. Grubbs and S.M. George, "Nucleation and Growth During Tungsten Atomic Layer Deposition on SiO2 Surfaces", Thin Solid Films 386, 41-52 (2001).
J.W. Klaus, A.W. Ott, J.M. Johnson and S.M. George, "Atomic Layer Controlled Growth of SiO2 Films Using Binary Reaction Sequence Chemistry", Appl. Phys. Lett. 70, 1092-1094 (1997).
J.W. Klaus, S.J. Ferro and S.M. George, "Atomic Layer Deposition of Tungsten Using Sequential Surface Chemistry with a Sacrificial Stripping Reaction", Thin Solid Films 360, 145-153 (2000).
J.W. Elam, Z.A. Sechrist and S.M. George, "ZnO/Al2O3 Nanolaminates Fabricated by Atomic Layer Deposition: Growth and Surface Roughness Measurements", Thin Solid Films 414, 43-55 (2002).
M.D. Groner, J.W. Elam, F.H. Fabreguette and S.M. George, "Electrical Characterization of Thin Al2O3 Films Grown by Atomic Layer Deposition on Silicon and Various Metal Substrates", Thin Solid Films 413, 186- 197 (2002).
M. Schuisky, J.W. Elam and S.M. George, "In situ Resistivity Measurements during the Atomic Layer Deposition of ZnO and W Thin Films", Appl. Phys. Lett. 81, 180-183 (2002).
J.M. Jensen, A.B. Oelkers, R. Toivola, D.C. Johnson, J.W. Elam and S.M. George, "X-ray Reflectivity Characterization of ZnO/Al2O3 Multilayers Prepared Using Atomic Layer Deposition", Chem. Mater. 14, 2276-2282 (2002).
J.W. Elam, C.A. Wilson, M. Schuisky, Z.A. Sechrist and S.M. George, "Improved Nucleation of TiN ALD Films on SiLK Low-k Polymer Dielectric Using an Al2O3 Adhesion Layer", J. Vac. Sci. Technol. B 21, 1099-1107 (2003).
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