Using a slit doser to probe gas dynamics during Al2O3 atomic layer deposition and to fabricate laterally graded Al2O3 layers

A special slit doser is used to form near unit steps in the spatial profile of an Al₂O₃ ALD film thickness. The unit step is formed as the Al₂O₃ ALD occurs mainly downstream from the slit doser because the trimethylaluminum and H₂O reactants are entrained in a viscous flow carrier gas. Spectroscopic ellipsometry measurements yielded thickness profiles of Al₂O₃ ALD on samples placed at different locations relative to the exit of the slit doser and the ALD growth zone. The effects of carrier gas flow rate, reactor pressure, and reactant dose and purge times on the Al₂O₃ ALD film profile provided details about the gas dynamics around the slit doser. Experimental indications of gas turbulence were observed at the exit of the slit doser. Lateral gradients in the Al₂O₃ ALD film thickness were also formed by linear translation of the sample relative to the slit doser during ALD. Lateral gradients of various desired pitches ranging from 119 Å/in to 444 Å/in were achieved as a result of accurate control of the Al₂O₃ ALD film thickness and small sample translation steps relative to the slit doser.     

Simple method for coating Si (1 0 0) surfaces with ferritin monolayers—Iron oxide quantum dots

With the goal to develop iron oxide quantum dots we developed a simple method to spread horse spleen ferritin monolayers on a Si (1 0 0) surface. Application of atomic force microscopy and spectroscopic ellipsometry showed the existence of regions with dense ferritin monolayers. Application of transmission electron microscopy identified the core of the spread ferritin as FeO nanocrystals.     

Substrate treatment and drying conditions effect on the properties of roll-to-roll gravure printed PEDOT:PSS thin films

The optical, structural and electrical properties of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) thin films printed by roll-to-roll gravure have been investigated. Corona treatment has been applied to enhance the adhesion of PEDOT:PSS on PolyEthylene Terephthalate (PET) web. It has been found that there was a stronger in-depth surface modification of PET with the increase of corona efficiency; however, the adhesion of PEDOT:PSS was not actually affected. Also, Spectroscopic Ellipsometry and Atomic Force Microscopy have been used to extract information on the mechanisms that define PEDOT:PSS properties. The increase of the drying temperature of the PEDOT:PSS films has been found to reduce the remaining water inside the films and lead to the decrease of the PEDOT:PSS particles size.     

Determination of the Dill parameters of thick positive resist for use in modeling applications

The determination of Dill parameters of thick resist is very important to improve simulation models of resist exposure and real world processes. A new extraction technique of Dill parameters based on spectroscopic ellipsometry in combination with an advanced resist exposure model is proposed for thick resist analysis. The complex refractive index of the resist is related to the relative concentration of the photoactive compound in the resist in order to describe the vertical distribution of the refractive index and the extinction coefficient. Moreover, Dill parameters are extracted by directly fitting the bleaching curves to the measured ellipsometry data. The new approach was investigated experimentally by spectroscopic ellipsometry measurements on AZ5214E resist with two moderate layer thickness values in order to verify the accuracy of the new method. Dill parameters were extracted by using this new technique and by applying resist samples subjected to different exposure doses. Possible reasons for the variation of Dill parameters depending on resist thickness are explained. Furthermore, advantages, limitations and potential improvements of the model are discussed. Finally, the impact of Dill parameter variation on image formation in the resist is demonstrated by applying the spectroscopic ellipsometer analysis results as input parameters to the lithography simulator Dr.LiTHO.     

Micelle-assisted bilayer formation of cetyltrimethylammonium bromide thin films studied with combinatorial spectroscopic ellipsometry and quartz crystal microbalance techniques

We report on a combinatorial approach to study the formation of ultra-thin organic films using in-situ spectroscopic ellipsometry and quartz crystal microbalance methods. In contrast to the quartz crystal microbalance, which is sensitive to the total mass attached to the surface, including coupled and entrapped solvent, spectroscopic ellipsometry only measures the amount of adsorbent on the surface. By using these two techniques in tandem, we define and determine the solvent fraction of cetyltrimethylammonium bromide thin films adsorbed onto a gold-coated quartz crystal. Cetyltrimethylammonium bromide thin films grown from aqueous solutions above the critical micelle concentration reveal critical phases in thickness and porosity evolution. We relate these effects to the mechanisms of formation and removal and the structure of cetyltrimethylammonium bromide films, which we determine to have systemic defects due to the presence of micelles.     

Application of ellipsometry techniques to biological materials

Ellipsometry is well-suited for bioadsorption studies and numerous reports, mainly using null ellipsometry, are found on this subject whereas investigations addressing structural properties of thin biolayers are few. Here two examples based on the use of spectroscopic ellipsometry (SE) on the latter are briefly discussed. In the first example, time evolution of thickness, spectral refractive index and surface mass density of a fibrinogen matrix forming on a silicon substrate are investigated with SE and a structural model of the protein matrix is discussed. In the second example a model dielectric function concept for protein monolayers is presented. The model allows parameterization of the optical properties which facilitates monitoring of temperature induced degradation of a protein layer. More recently, photonic structures in beetles have been studied with SE. It is shown here that full Mueller-matrix SE can resolve very complex nanostructures in scarab beetles, more specifically chiral structures causing reflected light to become circularly polarized.     

Internal reflection ellipsometry for real-time monitoring of polyelectrolyte multilayer growth onto tantalum pentoxide

Internal reflection ellipsometry was used for detection of the consecutive coating of two polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA), onto a tantalum pentoxide (Ta₂O₅) substrate until the 10th bilayer. The UV patterned PAH-PAA-multilayer was characterized in air via ellipsometry and atomic force microscopy. Suited optical models enabled the determination of the layer thicknesses in wet and dry states. Linear multilayer formation could be proved by Attenuated Total Reflection — Fourier Transformed Infrared Spectroscopy measurements following the increase of the ν(C=O) band depending on the adsorption of the PAA. Streaming potential measurements after each layer deposition step indicated a change in surface charge after each layer deposition due to the consecutive coating of PAH and PAA. In this article the internal reflection ellipsometry is shown to be a convenient possibility to analyze the modification of a thin transparent Ta₂O₅ substrate.     

Real time spectroscopic ellipsometry of Ag/ZnO and Al/ZnO interfaces for back-reflectors in thin film Si:H photovoltaics

Real time spectroscopic ellipsometry (RTSE) has been applied to analyze the optical characteristics of Ag/ZnO and Al/ZnO interfaces used in back-reflector (BR) structures for thin film silicon photovoltaics. The structures explored here are relevant to the substrate/BR/Si:H(n-i-p) solar cell configuration and consist of opaque Ag or Al films having controllable thicknesses of microscopic surface roughness, followed by a ZnO layer up to ~ 3000 Å thick. The thicknesses of the final surface roughness layers on both Ag and Al have been varied by adjusting magnetron sputtering conditions in order to study the effects of metal film roughness on interface formation and interface optical properties. The primary interface loss mechanisms in reflection are found to be dissipation via absorption through localized plasmon modes for Ag/ZnO and through intraband and interband transitions intrinsic to metallic Al for Al/ZnO.     

Spectroscopic ellipsometry characterization of high-k gate stacks with Vt shift layers

We have used spectroscopic ellipsometry (SE) to measure layer thicknesses of HfO₂/La₂O₃ and La₂O₃/HfO₂ stacks on SiO₂/p-Si. Two approaches to extract layer thicknesses from a single SE measurement were shown to be inaccurate, possibly due to similarities in the optical dispersions of HfO₂ and La₂O₃. The approach where SE data was collected after deposition of each layer and only the thickness of the top layer was determined by modeling was found to be capable of accurately measuring the thickness of each layer. These conclusions are supported by angle resolved X-ray photoelectron spectroscopy (ARXPS), X-ray reflectivity (XRR) and Rutherford backscattering spectroscopy (RBS) measurements.     

Temperature dependent model dielectric function of highly disordered Ga0.52In0.48P

We report on the temperature dependence of the dielectric function of Ga_0.52In_0.48P from room temperature to 500°C, and for photon energies from 0.75 eV to 5 eV. The undoped, highly disordered Ga_0.52In_0.48P thin film was grown by metal-organic vapor phase epitaxy lattice matched onto a (001) GaAs substrate. The dielectric function of Ga_0.52In_0.48P was measured by in-situ spectroscopic ellipsometry, and analyzed using Adachi's composite critical point model. We provide a second-order temperature expansion parameter set for calculation of the Ga_0.52In_0.48P dielectric function and its temperature dependence, and which may become useful for in situ growth control or optoelectronic device performance evaluation at elevated temperatures. We discuss the temperature-induced shift of critical point transition energy parameters.