## 4 Results and Discussion
### Shape Evolution of DEE Process Conditions
This is because the side etches proceeded even after the copper layer was removed due to an excessive etching time in the etching step. If the DEE process is repeated under the condition of having an excessive etching time, a very big taper angle is generated, and the shape of the vertical wall becomes irregular. Therefore, in order to minimize irregular shape of the side wall in the DEE process, an appropriate etching time condition per cycle of the DEE process is required. [PERSON] et al. confirmed that an excessive taper angle occurs when the etching time exceeds 10 s in selective electrochemical etching using a copper layer formed at 2 V with a 60 s condition [13]. In the DEE process, in order to minimize the taper in one cycle, an etching time of fewer than 10 s should be selected. Figure 5: SEM image of taper angle after repeating DEE process 10 times at excessive etching time (etching voltage: 10 V, etching time: 10 s): (**a**) square pattern; (**b**) magnified image of the square dotted line area in (**a**). Figure 6: Surface profile of the cross-section of line AA’ in Figure 5a. Figure 7a is a picture of one cycle of the DEE process completed by performing electrochemical etching after laser patterning of the deposited layer. Figure 7b-e is the results of performing the DEE process five times, 10 times, 15 times, and 20 times, respectively. Electrodeposition conditions are 2 V and 60 s, and laser patterning conditions are shown in Table 2. Figure 7c is an optical image when the number of repeated cycles in the DEE process is 10 times, and the etching depth at this time is about 37 \(\upmu\)m. Figure 7e is an optical image when the number of repeated cycles in the DEE process is 20 times, and the etching depth at this time is about 81.6 \(\upmu\)m. As shown in Figure 8, as the number of repeated cycles increases in the DEE process, the etching depth increases. As shown in Figure 8, as the number of repeated cycles increases up to five, it can be seen that the average depth of 20 \(\upmu\)m per cycle has been processed. This is for the experiment repeated 20 times and can be said to show reproducibility with an average etching depth of 4.08 \(\upmu\)m per cycle. Figure 7: Shape change according to the number of repeated cycles of the DEE process cycle (etching voltage: 10 V, etching time: 7 s): (**a**) once; (**b**) five times; (**c**) 10 times; (**d**) 15 times; and (**e**) 20 times. Figure 10 shows the microsquare groove structure fabricated through the DEE process. This microsquare groove structure was obtained by repeating the DEE process cycle 56 times. As a result of measuring the surface profile, it was confirmed that a structural pattern with an etching depth of 220 \(\upmu\)m and pitch spacing of 200 \(\upmu\)m was successfully fabricated. In addition, the average etching depth per cycle was measured as 3.92 \(\upmu\)m. By performing the DEE process on a one-hundred-\(\upmu\)m-thick stainless steel specimen, a through-rectangular pattern was successfully fabricated, as shown in Figure 11. Perforated areas from some bottom surfaces were first observed when the number of repeated cycles of the DEE process exceeded 20. As a result of repeating the DEE process cycle up to 27 times in order to reduce the remaining nonpenetrating portion, it can be seen that the remaining nonpenetrated area was reduced, as shown in Figure 11. These results mean not only the blind shape but also the through shape pattern could be implemented through the DEE process. Figure 9: Variation of the etching depth and width (L2) according to repeated cycles of the DEE process: (a) etching depth and (b) width (L2).