On-line monitoring of solar cell module production by ellipsometry technique

Non-destructive analysing tools are needed at all s tages of thin film photovoltaic (PV) development, a nd on production lines. In thin film PV, layer thicknesse s, micro-structure, composition, layer optical prop erties, and their uniformity (because each elementary cell is c onnected electrically in series within a big panel) serve as an important starting point in the evaluation of the p erformance of the cell or module. An important focu s is to express the dielectric functions of each component material in terms of a handful of wavelength indepe ndent parameters whose variation can cover all process va riants of that material. With the resulting databas e, spectroscopic ellipsometry coupled with multilayer analysis can be developed for on-line point-by-poin t mapping and on-line line-by-line imaging. This work tries to review the investigations of dif ferent types of PV-layers (anti-reflective coating, transparent-conductive oxide (TCO), multi-diode-str ucture, absorber and window layers) showing the exi sting dielectric function databases for the thin film com ponents of CdTe, CIGS, thin Si, and TCO layers. Off-line point-by-point mapping can be effective fo r characterization of non-uniformities in full scal e PV panels in developing labs but it is slow in the on- line mode when only 15 points can be obtained (with in 1 min) as a 120 cm long panel moves by the mapping station . In the last years [M. Fried et al, Thin Solid Films 519 , 2730 (2011)], instrumentation was developed that pr ovides a line image of spectroscopic ellipsometry ( wl=350- 1000 nm) data. Upto now a single 30 point line imag e can be collected in 10 s over a 15 cm width of PV material. This year we are building a 30 and a 60 c m width expanded beam ellipsometer the speed of whi ch will be increased by 10X. Then 1800 points can be mapped in a 1 min traverse of a 60*120 cm PV panel or fle xible roll-to-roll substrate

Optikai modellek fejlesztése sokösszetevős anyagrendszerek ellipszometriai vizsgálatához = Optical model development for ellipsometric study of many-compound materials

A kutatás célja volt a korábban alkalmazott optikai modelljeink továbbfejlesztése oly módon, hogy a mikroelektronika új anyagai (pl. magas dielektromos állandójú anyagok, napelem készítéséhez alkalmas félvezetők) és struktúrái is jól vizsgálhatók legyenek az ellipszometria módszerével. Vizsgáltunk magas dielektromos állandójú anyagokat (BaxSr1-xTiO3 vagy SrBi2Ta2O9) az Adachi modellel, amely a Cauchy modellnél kevesebb paramétert tartalmaz és a direkt átmenet hatását is figyelembe veszi, így szélesebb spektrális tartományban bizonyult használhatóbbnak. Ezenkívül bizonyos paraméterei összekapcsolhatóak a szemcsemérettel. A továbbfejlesztett modellek alkalmazásával újtípusú napelemekhez alkalmazható anyagokat is vizsgáltunk pl. CIS (CuInSe2) ill. CIGS (CuInxGa1-xSe2) és ZnO. Folytattuk a félvezetőkben ionimplantációval létrehozott nanokristályok vizsgálatát, elsősorban Si, CdTe, SiC és Ge anyagokra. Si-ban az Adachi-féle ?Model Dielectric Function?-t, CdTe-ban az Aspnes féle magasabb derivált módszert, SiC és Ge anyagokban pedig kezdeti lépésként egyszerűbb (pl. Tauc-Lorentz oszcillátor) modelleket használtunk. Az eredményeket 24 publikációban (konferenciákon és folyóiratcikkekben) jelentettük meg. A cikkek kumulált impakt faktora 24 felett van. | The aim of this research was to enhance the earlier applied optical models for the investigation of new materials and structures of microelectronics (for example high-k materials, semiconductors for solar cells) by ellipsometry. We established correlation between the parameters of the dispersion relation and the microscopical structural properties of the materials studied making possible in-situ, real-time qualification. We studied the complex refractive index of coumpound materials such as BaxSr1-xTiO3 and SrBi2Ta2O9. We determined parameters which can be coupled with microscopical structural properties (such as band gap or grain size or different phases) using the Adachi model which contains less parameters than the Cauchy model and usable in a wider spectral range. We used the enhanced optical models to study new type of solar-cell materials such as CIS (CuInSe2) or CIGS (CuInxGa1-xSe2) and ZnO. We continued the investigation of semiconducting nanocrystals created by ion implantation, mainly Si, CdTe, SiC and Ge. We used the ?Model Dielectric Function? of Adachi for Si, the higher derivative method of Aspnes for CdTe and the Tauc-Lorentz oscillator model for SiC and Ge. We published the results in 24 (conference and per reviewed) publications with higher than 24 cumulative impact factor

Optikai modellek fejlesztése sokösszetevős anyagrendszerek ellipszometriai vizsgálatához = Optical model development for ellipsometric study of many-compound materials

Az ellipszometria olyan optikai módszer, amely felületközeli, roncsolásmentes, in situ vizsgálatokat tesz lehetővé. A technológiába bekerülő összetett rétegek törésmutatója általában nem ismert, vagy éppen az a meghatározandó mennyiség. Ebben az esetben a törésmutatót diszperziós formulákkal, vagy az ún. effektív közeg közelítéssel (vagy egyszerre mindkettővel) határozhatjuk meg. Van lehetőség olyan paraméterek meghatározására is, amelyek egy-egy mikroszkópikus szerkezeti tulajdonsággal (pl. sávszélesség ill. szemcseméret, különböző fázisok) kapcsolatba hozhatók. Ebben a munkában az egy- és polikristályos CdTe (amely egy igéretes fotovoltaikus anyag) ion implantációval keltett hibasűrűségének az optikai tulajdonságaira való hatását vizsgáltuk. A CdTe optikai tulajdonságainak kritikus pont struktúráinak szélességét a kontrollált roncsoltság függvényében határoztuk meg. Az effektív roncsoltság mint egyetlen paraméter szerinti parametrizációt kerestük, amely elegendő az összes minta és a kritikus pontok szélességének szimultán leírásához. Ez a parametrizáció szolgálhat adatbázisul a különböző feltételek között leválasztott CdTe filmek optikai tulajdonságainak fitteléséhez. Ezen az úton nyílik lehetőség a CdTe gyártásközi, valósidejű ellenőrzésére. | Ellipsometry is an optical method which makes possible near-surface, non-destructive, in-situ studies. However, the refractive index of the coumpound materials in the technology is usually unknown or just the only question. In this case, the refractive index can be determined using dispersion formula or the so called effective medium approximation, or both. There is a possibility to determine parameters which can be coupled with microscopical structural properties (such as band gap or grain size or different phases). In this project, we studied the effects of defect density caused by ion implantation on the optical properties of single and polycrystalline CdTe, which is a promising photovoltaic material. The widths of the critical point structures in the optical properties of CdTe were determined as a function of the controlled defect density. We seeked a parameterization of the optical properties with a single parameter – an effective defect density -- that is sufficient to modify all critical point widths simultaneously and describe the optical properties for the full set of samples. This parameterization can serve as a database to fit the optical properties of CdTe films during different growth conditions. In this way, it will be possible to use real time optical measurements of CdTe during its fabrication and processing

Bloch surface waves biosensing in the ultraviolet wavelength range – Bragg structure design for investigating protein adsorption by in situ Kretschmann-Raether ellipsometry

We designed a Bragg mirror structure with an SiO2 top layer to create a resonance in the ultraviolet wavelength range, near the absorption peak position of various proteins. We demonstrate that the wavelength of enhanced sensitivity can be adjusted by proper design of the 1D photonic structure. The possibility to design the wavelength of enhanced sensitivity supports measurements of better selectivity, optimized for the absorption of the target material. Since the width of the resonant peak in the reflectance spectra can be sharper than those of plasmonics, and they can be positioned at more favourable regions of the instrument and material (e.g., in terms of intensity or selectivity), the sensitivity can exceed those of plasmon-enhanced measurements. In this study we demonstrate the main features of the concept at the example of in situ spectroscopic ellipsometry of fibrinogen adsorption in the Kretschmann-Raether configuration. We realized a resonant peak with a full width at half maximum of 3 nm near the wavelength of 280 nm, which coincides with the absorption maximum of fibrinogen. The influence of depolarization and surface roughness on the measurements, and the potential for improving the current experimental detection limit of 45 pg/mm2 is also discussed

Characterization of in-depth cavity distribution after thermal annealing of helium-implanted silicon and gallium nitride

Single-crystalline silicon wafers covered with sacrificial oxide layer and epitaxially grown gallium nitride layers were implanted with high-fluence helium ions (2-6 × 1016 cm- 2) at energies of 20-30 keV. Thermal annealings at 650-1000 °C, 1 h were performed on the Si samples and rapid thermal annealings at 600-1000 °C, 120 s under N2 were performed on the GaN samples. The as-implanted samples and the near-surface cavity distributions of the annealed samples were investigated with variable angle spectroscopic ellipsometry. In-depth defect profiles and cavity profiles can be best described with multiple independent effective medium sublayers of varying ratio of single-crystal/void. The number of sublayers was chosen to maximize the fit quality without a high parameter cross-correlation. The dependence of the implantation fluence, oxide layer thickness and annealing temperature on the cavity distribution was separately investigated. The ellipsometric fitted distributions were compared and cross-checked with analyses of transmission electron micrographs where the average surface cavity was determined sublayer by sublayer. The in-depth profiles were also compared with simulations of He and vacancy distributions