Abstract
AbstractTo improve the controllability of threshold voltage of FETs for high‐performance GaAs ICs, it is necessary to establish a processing method of fabricating a surface‐protective SiO2 layer without changing the thin active‐layer thickness.In this paper, a new method is proposed for evaluating the thickness of a removed GaAs active layer. This technique involves sheet resistance measurement of FET devices after surface treatment. Using this method, about a 5‐nm thick GaAs layer was found to be removed by the HF etching process for an SiO2 film deposited by thermal CVD. This phenomenon is due to the formation of an intermediate layer between SiO2 and GaAs interfaces. This intermediate layer consists of GaAs oxides and excess As.Spectroscopic ellipsometry has been applied to evaluate the thickness of the intermediate layer. Using this method, it was found that no intermediate layer is formed in the case of SiO2 films fabricated by photo‐CVD, which is advantageous for low‐temperature processing. Furthermore, no removal of the GaAs active layer was found after HF etching of the SiO2 films. SiO2 films made by the photo‐CVD method are most suitable as protective layers for thin GaAs active layers of GaAs ICs.
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