PRECISE MASK ALIGNMENT TO THE CRYSTALLOGRAPHIC ORIENTATION OF SILICON-WAFERS USING WET ANISOTROPIC ETCHING

A design tool for fast and precise determination of the crystallograph ic orientation in (001) and (011) silicon wafers using anisotropic wet etching is introduced. The design takes advantage of the symmetric un der-etching behaviour around, but not at (!), the (110)-directions. Th e pattern needs to be etched only for a short time, and after a very q uick optical inspection it can be used for aligning subsequent masks, using the same masking layer, more or less automatically. Two effects were investigated in a number of common anisotropic etchants: KOH, KOH with isopropyl alcohol (KOH/IPA), ethylenediamine based solutions (ED P), and tetramethyl ammonium hydroxide (TMAH). The precision of the me thod was found in most cases to be better than +/-0.05 degrees.