CHROMIUM-FREE ETCH FOR REVEALING AND DISTINGUISHING METAL CONTAMINATION DEFECTS IN SILICON

A new preferential etch has been developed which is free of chromium o xide. It is based on various combinations of nitric acid, hydrofluoric acid, and acetic acid. The optimum composition for an etch to reveal haze of all haze-forming metals (Co, Ni, Cu, Rh, Pd) can be determined from a given equation. With the aid of this equation the proportion o f acetic acid is calculated as a function of the preselected proportio n of nitric acid to hydrofluoric acid. For the first time haze due to nickel can be distinguished from haze due to copper by etching the sam ple with solutions of different composition. The new etch is highly se nsitive to impurity metals precipitated at the surfaces of silicon sam ples (haze, shallow etch pits) but it reveals also all other lattice d efects (slips, dislocations, epitaxial and oxidation-induced stacking faults). The etch works independently of the water orientation.