Electrochemical etching of patterned n-type silicon in hydrofluoric acid (HF) solution has been employed as a useful
micromachining technique. In this paper, 4 um pitch regular wall array structures with high aspect ratio (larger than 20)
were fabricated in n-typed silicon with back side illuminating. Differing from common hole array's fabrication,
undesired formation of separated pores along the trench bottom becomes a serious problem in the wall array's
fabrication. By adjusting the etching current density, we have successfully suppressed this phenomenon. A theoretical
analysis of the formation mechanism of wall array will also be discussed in this paper.