Due to their technological importance, native films on III-V semiconductors have been studied intensively. 1 Investigations of thermal or anodic oxides on GaAs have been performed for a number of years. [2][3][4] Many inherent problems in these two oxidation methods need to be overcome as they are applied to GaAs metal oxide semiconductor (MOS) technologies. In the case of anodic oxidation, a high electric field (ϳ5 MV/cm) in oxide films cause Ga and As atoms to diffuse through the oxide layer to the surface where they are oxidized. 5 It has also been reported that growth of anodic oxides are initiated by the reactions on the oxide surface. 6 Therefore, anodic oxidation is sensitive to contamination of the GaAs surface. As compared to the anodic method, the advantage of thermal oxidation is that it generates a fresh interface with surface contamination ending up at the oxide surface, since thermal oxidation takes place at the interface by in-diffusion of oxygen. 7 However, oxidation of GaAs proceeds very slowly below 450ЊC (<50 Å/h). 8 In addition, because the oxidation temperature exceeds the volatile temperature of As 2 O 3 , thermal oxides are composed of mostly Ga 2 O 3 . These results lead to loss of stoichiometry both in the oxide films and at the interface. At higher temperatures (>530ЊC), the films tend to crystallize and become porous, and even incongruent evaporation from substrates possibly occurs. Extensive efforts have been made to overcome this problem, such as high-pressure, 2,9 photoassisted, 10 plasma-enhanced, 11 or steam oxidation 12 methods. Among the above techniques, the required systems are complex, or the temperatures are still high.Recently, a new liquid-phase chemical-enhanced oxidation (LPCEO) technique has been proposed. 13 Neither photoenergy nor plasma source is needed. As compared to the anodic method, oxide films of GaAs can be grown near room temperature (40-70ЊC) without the assistance of electric potential. Featureless and uniform oxide films can be grown at a relatively high oxidation rate (ϳ1000 Å within an hour). In addition, good insulating and thermally stable LPCEO oxide films have been demonstrated, 14 and device applications to GaAs metal-oxide semiconductor field effect transistors (MOSFETs) have also been realized. 15 Interesting properties of the oxide growth kinetics of the LPCEO technique have been found, such as an optimum pH window for oxide growth, increase of oxide refractive index, a relatively high oxidation rate at low temperature, and etchback of oxide thickness. The experimental results indicate that the pH value of oxidation solution seems to be the dominant factor in oxide growth. In this work, the mechanisms of the Ga-containing cations as well as the role of the pH value in the LPCEO technique are investigated.Experimental Figure 1a illustrates the oxidation system which is very low cost and mainly consists of a temperature regulator and a pH meter. The flowchart of the procedure is shown in Fig. 1b. The LPCEO procedure is started with the preparation o...

A new chemical enhanced oxidation method for gallium arsenide (GaAs) in liquid phase near room temperature (40 • C-70 • C) is proposed and investigated. Featureless oxide layers with good uniformity and reliability can be grown efficiently on GaAs without any extra energy source. A relatively high oxidation rate ( 1000Å/h), about 50 times higher than that obtained during oxidation in boiling water has been realized. Based on the results of X-ray photoelectron spectroscopy (XPS), excellent chemical stability after thermal annealing as well as good chemical stoichiometry have been realized. The oxide was determined to be composed of Ga 2 O 3 and As 2 O 3 .

The initial stage of GaAs oxidation by a near-room-temperature liquid phase chemical-enhanced technique has been studied. Based on the experimental results of X-ray photoelectron spectroscopy, a complete model illustrating the chemical composition of the grown oxide film has been established. To clarify the kinetics of oxide growth in a liquid solution in more detail, we have also performed selective oxidation and surface profile measurements. Unusual features of the oxide growth kinetics have been observed by investigating the physical structure of oxide at the edge of mask in the selective oxidation.

Selective oxidation on GaAs operated at near room temperature, by a liquid phase chemically enhanced method using photoresist as a mask, is proposed and demonstrated. Because of the low temperature and electroless features of the oxidation method, the process is simple, economic and reliable. Good electrical insulating properties comparable with those of thermal oxide have been obtained. According to the results of X-ray photoelectron spectroscopy, the chemistry of the oxide surface is stable after thermal annealing. The thermal stability shows the potential for device fabrication.

No abstract