Masking effect of copper during anisotropic etching of silicon in bufferedhydrofluoric acid solutions

The etching characteristics of silicon samples of (100) orientation in buff ered hydrofluoric acid (BHF) solutions containing different levels of disso lved copper were studied systematically using atomic force microscopy, tota l reflection x-ray fluorescence, inductively coupled plasma mass spectrosco py and transmission electron microscopy techniques. It was found that the p resence of trace amounts of copper ions in BHF solutions can cause not only metallic contamination but also very severe surface roughness. Copper depo sits onto the silicon surfaces in the form of submonoatomic layer clusters which act as masks during silicon anisotropic etching in BHF solutions. Sur face roughness as high as 12 nm was generated in 30 min of etching in buffe red hydrofluoric acid solution containing 100 ppb Cu2+. Cross-sectional TEM micrographs showed that silicon was etched anisotropically in BHF solution s containing Cu2+ ions. Etching rates as high as 1.0 nm/min were obtained o n the (100) planes of p-type silicon in the presence of a 100 ppb Cu2+. The size of the etching structures depends on the Cu2+ concentration in soluti on and the etching time. (C) 1999 American Institute of Physics. [S0021-897 9(99)01803-4].