D. Daineka

Optical thin films deposition by MDECR-PECVD

We designed and built Matrix Distributed ECR (MDECR) PECVD reactor dedicated for dielectric filters deposition and equipped it with multiple sensors for process control. Planar matrix geometry of plasma source is based on electron cyclotron resonance effect at 2.45 GHz microwave frequency and provides scalability of the deposition on large area substrates. High (up to 5 nm/sec) deposition rate obtained due to high dissociation efficiency and careful design of the gas injection system. Optical emission spectroscopy, quadrupole mass-spectrometry and spectroscopic and multi-channel kinetic ellipsometry are installed for in-situ studies and control of the film deposition. We performed studies of the nature of high-density plasma discharge in silane, oxygen and nitrogen mixture and correlated its properties with optical and physical properties of deposited materials. To demonstrate the capabilities, a wide band gradient index antireflection coating on glass was realized by deposition of SiOxNy alloy thin films. The predefined variation of an index in a profile is obtained by changing the flows of precursors. Real-time control is performed with multi-channel kinetic ellipsometry.

Parameter extraction method for universal amorphous silicon thin-film transistors simulation program with integrated circuit emphasis model

The universal simulation program with integrated circuit emphasis (SPICE) model for hydrogenated amorphous silicon thin-film transistor is largely used in circuit simulation. This model has more than 10 parameters to be extracted through experimental data, and the optimal method to determine them is still open to discussion. In this study, the authors propose a new method for the extraction of the main above-threshold regime parameters. This method can be used regardless of the resistance value between the channel and the source-drain. The parameters extracted with this method are less sensitive on experimental data selection than the ones obtained through conventional methods. In addition, these parameters successfully describe the experimental data.

Crystalline silicon solar cells with doped epitaxial silicon films obtained at low-temperature by PECVD

In spite of dramatic improvements in thin film technologies, crystalline silicon (c-Si) solar cells are still leading the photovoltaic market thanks to continuous progress. In this field, one innovative way is the development of thin silicon epitaxial films (epi-Si) on (100) c-Si wafers to fabricate the emitter and/or back surface field of solar cells. Among the possible techniques, we used radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) for it is a low thermal budget, scalable, wide-spread process in photovoltaics and it is well-suited to make solar cells on thin c-Si wafers (< 150 µm) without too much stress induced.

Effect of Dopants on the Dynamic of Powder Formation and the Properties of Polymorphous Silicon Thin Films

Polymorphous silicon (pm-Si:H) is a nanostructured material produced by the dissociation of silane-hydrogen mixtures under plasma conditions where silicon radicals, clusters and agglomerates contribute to the growth. The dynamics of power formation in a capacitively coupled radio-frequency (RF) discharge has been studied as a function of dopant gas concentration through the analysis of the evolution of the second harmonic of RF current. The intrinsic and doped films were characterized by spectroscopic ellipsometry, dark conductivity and Raman spectroscopy measurements. We have demonstrated the possibility of obtaining doped pm-Si:H films with transport properties comparable to those of standard amorphous silicon using trimethylboron or phosphine. We have found that the addition of trimethylboron reduces cluster and agglomerate concentration while phosphine has no prominent effect on particle formation. The best ordered polymorphous films were deposited under conditions where not only 1-2 nm clusters but even larger (~10 nm) agglomerates contribute to the growth. For these conditions the deposition rate reaches 5 A/s for i- and n-type, and 7 A/s for p-type materials. The dark conductivity at room temperature was 10 �2 �10 �3 � �1 cm �1 and 10 �6 � �1 cm �1 for the n- and p-type films, respectively.