J. Eur. Opt. Society-Rapid Publ. 22, 51( 2026) 503
Figure 5. Comparison of measurement( A, B, E, F) to calculated isotropic etched surfaces( C, G) and the resulting map visualizing the isotropic factor IF( D, H). The example A – D shows nearly isotopically etched result, whereas E – H depict significant discrepancy from isotropy.
evident. Comparing the areal representations of the IF in Figures 5D and 5H the IF of the isotropic example in Figure 5D is almost 1, only a slight variation is apparent. Hence, it can be concluded that no SSD was present anymore on this sample. However, a different situation is observed in Figure 5H. In the center and at the periphery of the areal map isotropic etching prevails( IF 1, dark blue color) while the red-colored ring clearly indicates an increased value of IF 1.8... 1.9.
The isotropic factor IF was calculated for Sample # 1. The mean value together with its standard deviation is shown in Figure 6 as a function of the etching depth. The presence of error bars indicates locally varying IF, since the region surrounding the indentation exhibits values of IF 1, and the distorted areas yield higher values. The large deviation at an etching depth of 1.5 lm is due to preferential etch attack of the elevated area in the center of the initial indentation( see Fig. 4), which consists of distorted material at the surface with cracks and local stress. The slope S VV is included for comparison. The error bars for the S VV values result from the propagation of uncertainty based on the estimation of measurement uncertainties for the parameters d and VV, which are used to calculate the slope according to equation( 4). It is obvious that the maximum of both parameters – IF mean and S VV – occur at the same etching depth. That indicates that the process step where the comparatively largest increase in VV occurs also corresponds to the highest level of anisotropic etching. This is obvious, since the increase of VV is caused by the deviation from isotropic etching. Therefore, the etching depth where the IF max is recognized is used to calculate the SSD depth applying equation( 5), yielding a value of SSD = 35.3 lm.