Highly selective dry etching of GaP in the presence of Al_xGa_1–xP with a SiCl₄/SF₆ plasma

We present an inductively coupled-plasma reactive-ion etching process that simultaneously provides both a high etch rate and unprecedented selectivity for gallium phosphide (GaP) in the presence of aluminum gallium phosphide (Al_xGa_1–xP). Utilizing mixtures of silicon tetrachloride (SiCl₄) and sulfur hexafluoride (SF₆), selectivities exceeding 2700:1 are achieved at GaP etch rates above 3000 nm min⁻¹. A design of experiments has been employed to investigate the influence of the inductively coupled-plasma power, the chamber pressure, the DC bias and the ratio of SiCl₄ to SF₆. The process enables the use of thin Al_xGa_1–xP stop layers even at aluminum contents of a few percent. (paper)