Detection of Discontinuities in Passivating Layers on Silicon by NaOH Anisotropic Etch

Discontinuities in glasses deposited on silicon substrates are readily detected by a silicon-preferential etch that uses single component alkali solutions. The etchants can be applied to thermally gown oxide films, pyrolytically-deposited passivating layers or sputtered quartz. The character of the discontinuities in these films is shown and the size can be estimated (although both observations are subject to the limitations of the optical tools used for observation or micrography). When applied in the temperature range below +70°C, the etchant attacks the oxides insignificantly and the concentration, as well as the temperature, is chosen for convenience. Above +70°C the passivating layers, particularly thermal SiO
2
, are etched at higher rates, and the etching effects must be taken into account if the oxide thickness is less than 1000 Å. The etchants are applicable to intrinsic as well as extrinsic silicon up to a doping level of 10
²⁰
cm
⁻³
.