J. Eur. Opt. Society-Rapid Publ. 22, 51( 2026) 507
Figure 11.( A) Progress of calculated IF mean and the slope, which is used to experimentally obtain the SSD depth after PJE given for Sample # 3.( B – D) Surface topography maps presented for selected positions noted( A).
glass surfaces. The polishing process is intended to eliminate SSD since the extent of polishing removal exceeds the estimated damage depth from the knowledge of the manufacturing process. Despite precise lateral alignment of the samples after each PJE step in order to always measure the same area, a slight shift could not be avoided. Therefore, the measurement area had to be reduced as well in order to investigate the progress of the IF values for the same measurement area.
Although the initial surface shows no damage as can be seen in Figure 12A, visible defects appear after the first etching steps. These defects further develop as the etching process continues as shown in Figures 12B and 12C, reaching the maximum damage depth presented in Figure 12D. Once the maximum has been reached, uniform etching occurs in all directions as indicated by Figure 12E, causing the defect to further expand laterally. The progress of the defect in the center of the image is extracted as cross section profiles shown in Figure 12F. Since ring shaped measurement artifacts occur in the measurement, the cross sections have been fitted by a Gaussian function and shifted to zero level for better comparability. The transition from anisotropic to isotropic etch behavior after the complete removal of SSD is evident. Starting at the 8 th etching step( PJE # 8), isotropic removal is dominant, resulting in a significant widening of defects, while further progress in depth is no longer significant.
The simultaneous surface contact with multiple abrasive grains during the grinding process results in a random distribution of defects. Nevertheless, the method for determining SSD depths can be adapted as shown in the previous examples. The calculation of IF results in the graph shown in Figure 13. Compared to the progress of the slope values S VV, both graphs show a maximum for the same etching depth.
Since the anisotropic removal does mainly occur at a prominent defect, as shown in previous examples, the median value of IF was used to obtain a more reliable result. From a statistical point of view, the median offers greater robustness when dealing with outliers. In addition, the larger number of defects obtain various influences on the etching result of the respective process step. The proportion of anisotropic removal is individually dependent on depth. To some extent, the defects influence each other that small defects which are close to each other can combine to form a larger defect. The impact to the increase of VV is not equal over the whole measurement area. To overcome this inhomogeneity, the IF med is compared to the slope value.
According to equation( 5) the SSD depth of the isolated defect in measurement Sample # 4 yields a value of 6.37 lm. For the overall sample, where 25 measurements after each process step have been taken into account, the SSD depth was calculated to be 8.8 lm. The example shows that the method can also be applied to determine rather shallow SSD depths. The vertical resolution of the method is approximately 1 lm and mainly depends on the etching steps chosen to identify the maximum of slope( S VV) orIF value.
The OCT measurement provided by the University of Applied Sciences in Jena yields 9.5 lm, which shows a good agreement. Furthermore, it demonstrates that the