FUNDAMENTAL SELECTIVE ETCHING CHARACTERISTICS OF HF+H2O2+H2O MIXTURES FOR GAAS

Selective etching characteristics of HF+ H2O2 + H2O mixtures have been investigated for GaAs (111)A, (111BAR), (001), and (110) surfaces. Mixtures with excess H2O2 have shown excellent selective etching characteristics controlled by the H2O and H2O2 contents for extensive practical applications. The lowest etching rate in directions other than [111]A has been achieved with the present mixture system. Etching profiles strongly reflecting crystallographic anisotropy have been produced for low H2O and high H2O2 concentrations, while those for high H2O and low H2O2 concentrations have shown similar isotropic features irrespective of the substrate orientation. A continuous and extensive control of the intersection angle between the side wall and the substrate surface has been achieved successfully on all substrates. The etching profile and its dependence on the mixture composition for the four substrates have been discussed in detail in connection with the degree of anisotropy of the etching rate and the contrast that the (111)A plane sharply intersects with other planes while the (111BAR)B plane has a round intersection comer. The etching characteristics of the mixture have been discussed based on the special chemical properties of HF and H2O and compared with those of other mixture systems.