Figure 4.

High-aspect-ratio local macropore etching in low-doped n-type silicon. Macropores of 15.5 μm in diameter with 30-μm pitch were etched into HF (2.4 wt.%)-CTAC (120 ppm) for 4 h. The electrochemical etching was performed under potentiostatic control (3.25 V/CE) and 130-W backside illumination. (a) Middle of the macropore array region. (b) Border of the macropore array region.