The S.M. George research group is well equipped to study surface chemistry, thin film growth and etching and thin film properties. Many of these studies are focused on atomic layer deposition (ALD), atomic layer etching (ALE) and molecular layer deposition (MLD). Thin film growth and etching investigations using ALD, ALE and MLD are conducted in a variety of home-built reactors.
The research group also has equipment for analysis of surface chemistry and thin film growth and etching. Some of this analysis is performed in situ during film growth and etching. Other ex situ studies are conducted after removing the samples from the reactors. All of the techniques and equipment described below are available within the research group.
1. Reactors for ALD, ALE and MLD
The reactors in the group currently include:
5 Hot wall viscous flow reactors equipped with an in situ quartz crystal microbalance (QCM) to monitor film growth and etching. One of these reactors can accommodate 8” wafers.
1 Hot wall viscous flow reactor equipped for in situ Fourier transform infrared (FTIR) investigations of film growth and etching.
1 Hot wall viscous flow reactors for routine growth and etching without in situ probing techniques. One of these reactors can accommodate 6” wafers.
1 Plasma ALD reactor equipped with an in situ spectroscopic ellipsometer.
2 Hot wall rotary reactors for coating or etching particles using ALD/MLD or ALE.
1 Hot wall open-ended rotary reactor equipped with a plasma source for coating or etching particles.
1 UHV ALD reactor equipped with an electron gun for electron-stimulated desorption to promote ALD growth at low temperature.
1 Spatial ALD reactor equipped with a plasma electron source for electron-stimulated desorption to promote ALD growth on flat 6” substrates at low temperature.
2 Rotating cylinder spatial ALD/MLD reactors for depositing on flexible substrates and extendable to roll-to-roll processing.
2. Quartz Crystal Microbalance
In situ quartz crystal microbalance (QCM) measurements are employed to monitor ALD, ALE and MLD in viscous flow reactors. The QCMs from Inficon/Maxtek have exceptional mass sensitivity and the mass changes for each reaction are able to unravel the stoichiometry of the surface reactions. The growth/etching of the film is also determined by the linear mass increase/decrease versus the AB reaction cycles. In situ QCM measurements are utilized in five hot wall viscous flow reactors.
3. FTIR Spectroscopy
Surface species are monitored during ALD, ALE or MLD using a vacuum chamber designed for in situ Fourier Transform Infrared (FTIR) spectroscopy studies. These investigations employ a Nicolet 6700 FTIR spectrometer. 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 absorbance of the material either grows during ALD/MLD or is lost during ALE.
4. Quadrupole Mass Spectrometry
Quadrupole mass spectrometry (QMS) is utilized to monitor reactants and products in the viscous flow reactors for ALD, ALE and MLD. When employed to sample reactor pressures of 1-10 Torr, the mass spectrometer is differentially-pumped using a turbomolecular pump. Quadrupole mass spectrometers from Stanford Research Systems with an upper mass limit of 200 amu are utilized on two viscous flow reactors. QMS is also used for residual gas analysis in the high vacuum chambers. Mass spectrometers are located on the PHI 5600 XPS spectrometer and the UHV ALD reactor equipped with an electron gun for electron-stimulated desorption.
5. X-Ray Photoelectron Spectroscopy
The composition and chemical state information of thin films is obtained using a PHI 5600 X-ray photoelectron spectroscopy (XPS) system. This PHI 5600 XPS system has both a standard X-ray source and a monochromatic x-ray source. The monochromatic x-ray source is needed for analyzing organic and polymeric samples. The PHI 5600 is also equipped with a sputter gun for depth-profiling the samples. The angle of the sample can also be adjusted to obtain depth-profile information.
6. X-ray Diffraction and X-ray Reflectivity
The research group utilizes a Bede D1 X-ray diffractometer (XRD) that is optimized for X-ray reflectivity (XRR) of thin films and nanolaminates. XRD is important for structural characterization and crystalline alignment. XRR is very useful to evaluate film thickness, film density and interfacial roughness. XRR is especially valuable in characterizing superlattices and nanolaminates.
7. Spectroscopic Ellipsometry
Film thickness and film refractive indices can be measured using spectroscopic ellipsometry. The group uses two M-2000 spectroscopic ellipsometers from the J.A. Woollam Company. One of the spectroscopic ellipsometers is configured for variable incident angle measurements. This spectroscopic ellipsometer can also employ focusing optics to obtain spot sizes of 300 mm. The other spectroscopic ellipsometer can be mounted on our plasma ALD reactor to monitor nucleation and growth during plasma ALD.
8. Surface Profilometry
The ALD or MLD film growth or ALE film removal can be determined using ex situ surface profilometry. The profilometer obtains the film thickness by measuring the step height between the deposited/etched film and an area that was masked using tape or photoresist. The research group uses a Dektak 3 surface profilometer.
9. Electrical Characterization
The current-voltage (IV) and capacitance-voltage (CV) properties of insulating films can be characterized using a Hg-probe from the Materials Development Corporation (MDC). This Hg-probe has been used to study the Fowler-Nordheim tunneling behavior of Al2O3 ALD films that may have application for high k capacitors and gates.
10. Thin Film Resistivity
Thin film conductivity can be measured using an ex situ 4-point probe from Signatone. In addition, an in situ 4-point probe has been developed to measure film conductivity during ALD. This 4-point probe can monitor ALD growth during the sequential reactant exposures.
11. Gas Leak Detection Station
The research group maintains a gas leak detection station to evaluate the vacuum quality of the reactors and vacuum chambers. The gas leaks are detected using a quadrupole mass spectrometer that is differentially-pumped by a turbomolecular pump. This gas leak detection station is portable and can easily be moved throughout the laboratory.
12. Physical Vapor Deposition Chamber
Many different films can be deposited using physical vapor deposition (PVD) techniques. The custom PVD chamber from Kurt Lesker can perform either magnetron sputtering or thermal evaporation. This PVD chamber has a sample load lock for easy sample entry. In addition, the PVD chamber is equipped with a rotating sample stage and a QCM film thickness monitor.
13. Glove Box
The research group has a glove box from Vacuum Atmospheres that is attached to the PVD chamber. This glove box allows oxygen-sensitive films to be removed from the PVD chamber without air exposure. A hot wall ALD reactor is also attached to the glove box and allows the oxygen-sensitive films to be transferred directly into the ALD reactor without air exposure.
14. Environmental Test Chamber
The research group maintains an environmental test chamber from Espec that can control temperature and H2O relative humidity. This environmental test chamber is used to maintain the conditions during measurement of water vapor transmission rates (WVTRs).
15. Electrochemical Analysis of Energy Storage Materials
The group has a potentiostat/galvanostat/EIS analyzer (BioLogic SP-300) for electrochemical analysis of Li ion battery and pseudocapacitance material. In addition, the group recently obtained an Arbin Instruments MSTAT4 for repetitive charge/discharge analysis of Li ion battery material.
16. Spin Coater for Polymer Film Fabrication
Polymer films are prepared using a spin coater that can deposit polymer films on silicon wafers or QCM sensors. The research group has a dedicated spin coater from Laurell that has facilitated our research on polymers.