Thickness measurements of thin anodic oxides on GaAs using atomic force microscopy, profilometry, and secondary ion mass spectrometry

Techniques to determine the thickness of thin (30–200 Å) anodic oxide films on p-GaAs (100) are reported. The layers were grown potentiostatically in 0.3 M NH4H2PO4 (pH 4.4) solution. By lithographic techniques, several series of squares were etched into the oxide and the step height was measured using both atomic force microscopy (AFM) and a stylus surface profiler (Dektak). Secondary ion mass spectrometry (SIMS) profiles of samples prior to and after the photolithographic treatment show that neither the thickness nor composition of the layers are affected by the treatment. The thickness values obtained in the investigated range show standard deviations better than ±9 Å (AFM) and ±22 Å (Dektak) and correlate well in a linear relation to SIMS sputter times to the interface.