Comprehensive Stoichiometric Studies on the Reaction of Silicon in HF/HNO3 and HF/HNO3/H2SiF6 Mixtures

The stoichiometry of the wet chemical etching of silicon in concentrated binary and ternary mixtures of HF, HNO3 and H2SiF6 was comprehensively investigated. A complete quantification of both dissolved and...

Microfabrication of Alkali Vapor MEMS Cells for chip-scale atomic clock

The technology of MEMS atomic cells containing rubidium or caesium vapors in an atmosphere of neon buffer gas has been developed. Two-chamber silicon cells containing an optical cavity, shallow filtration channels and a technical container for a solid-state alkali source have been implemented in a single-step process of anisotropic wet chemical etching. To prevent significant undercutting of the filtration channels during etching of the through silicon cavities, the shapes of the compensating elements at the convex corners of the silicon nitride mask have been calculated and the composition of the silicon etchant has been experimentally found. The sealing of the cells has been carried out by silicon-glass anodic bonding at a temperature of 250 °C. For this purpose the LK5 glass which has an increased ionic conductivity in comparison with the conventional glass Borofloat 33 was used. The best microfabricated cells allowed us to obtain estimates of the relative instability of the coherent population trapping resonance frequency at the level of 5 · 10-11 at 1 s.

Dry Phosphorus silicate glass etching and surface conditioning and cleaning for multi-crystalline silicon solar cell processing

As an alternative to the wet chemical etching method, dry chemical etching processes for Phosphorus silicate glass [PSG} layer rel11ova] using Tri?uormethane/Sulfur Hexafluoride (CHF3/ SF6) gas mixture in commercial silicon-nitride plasma enhanced chemical vapour deposition (SiN-PECVD) system is applied. The dependence of the solar cell performance on the etching temperature is investigated and optimized. It is found that the SiN-PECVD system temperature variation has a signi?cant impact on the whole solar cell characteristics. A dry plasma cleaning treatment of the Si wafer surface after the PSG removal step is also investigated and developed. The cleaning step is used to remove the polymer ?lm which is formed during the PSG etching using both oxygen and hydrogen gases. By applying an additional cleaning step, the polymer ?lm deposited on the silicon wafer surface after PSG etching is eliminated. The effect of different plasma cleaning conditions on solar cell performance is investigated. After optimization of the plasma operating conditions, the performance of the solar cell is improved and the overall gain in ef?ciency of 0.6 % absolute is yielded compared to a cell without any further cleaning step. On the other hand, the best solar cell characteristics can reach values close to that achieved by the conventional wet chemical etching processes demonstrating the effectiveness of the additional O2/H2 post cleaning treatment.