Structuring up to a Defined Depth

Effects of Different Energy Densities and Structure Dimensions 

With increasing energy density of the UV light the thickness of the partially crystallised material increases and, therefore, the depth of the structures i.e. the higher the number of photons, the larger the probability that photons interact with Ce + ions deeper in the bulk material. Extending the exposure time has the same effect. 

Thus the rate of etching decreases continuously with increasing depth of the structures to be created. In this case the etch process does not stop abruptly at a given depth, and distinguishes consequently from the etch stop during the anisotropic etching of silicon at the (lll)-layer. 

The depth of geometrical structures is also influenced by diffraction effects and the quality of the beam used for UV exposure. This is especially important for small structures, Fig. 9.23. The influence of the nominal diameter of the geometrical structures on their depth increases additionally because diffraction effects increase. In the range of energy densities D = 0.4-3 J cm ) investigated it was impossible to fabricate structures with nominal diameters smaller than 10 pm and a depth exceeding 500 pm. 

The wall inclination of the fabricated geometrical structures depends strongly on the kind of glass and the process conditions used as well as the thickness of the substrate. 

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