Wright etch

The Wright Etch is a preferential etch for revealing defects in (100) and (111) oriented, p- and n-type silicon. It was developed by Margaret Wright Jenkins in 1976 while working in research and development at Motorola Inc. It was published in 1977. This etchant reveals clearly defined oxidation-induced stacking faults, dislocations, swirls and striations with minimum surface roughness or extraneous pitting. These defects are known causes of shorts and current leakage in finished semiconductor devices (such as transistors) should they fall across isolated junctions. A relatively slow etch rate (~1 micron per minute) at room temperature provides etch control. The long shelf life of this etchant allows the solution to be stored in large quantities.

The composition of the Wright etch is as follows:

60 ml conc. HF (hydrofluoric acid)

30 ml conc. HNO3 (nitric acid)

30 ml of 5 molal CrO3 (mix 1 gram of chromium trioxide per 2 ml of water)

2 grams Cu (NO3)2 . 3H2O (copper nitrate)

60 ml conc. CH3COOH (acetic acid)

60 ml H2O (deionized water)

In mixing the solution, the best results are obtained by first dissolving the copper nitrate in the given amount of water; otherwise the order of mixing is not critical.

The Wright etch consistently produces well-defined etch figures of common defects on silicon surfaces. This etch process is a quick and reliable method of determining the integrity of starting materials or to reveal defects induced at any point during silicon wafer processing. It has been demonstrated that Wright etch is superior in revealing stacking faults and dislocation etch figures when compared with those revealed by Sirtl and Secco etchings